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Sample records for plant light-harvesting complex

  1. Density of phonon states in the light-harvesting complex II of green plants

    CERN Document Server

    Pieper, J K; Irrgang, K D; Renger, G

    2002-01-01

    In photosynthetic antenna complexes, the coupling of electronic transitions to low-frequency vibrations of the protein matrix (phonons) plays an essential role in light absorption and ultra-fast excitation energy transfer (EET). The model calculations presented here indicate that inelastic neutron scattering experiments provide invaluable information on the phonon density of states for light-harvesting complex II, which may permit a consistent interpretation of contradictory results from high-resolution optical spectroscopy. (orig.)

  2. The light-harvesting complexes of higher-plant Photosystem I : Lhca1/4 and Lhca2/3 form two red-emitting heterodimers

    NARCIS (Netherlands)

    Wientjes, Emilie; Croce, Roberta

    2011-01-01

    The outer antenna of higher-plant PSI (Photosystem I) is composed of four complexes [Lhc (light-harvesting complex) al-Lhca4] belonging to the light-harvesting protein family. Difficulties in their purification have so far prevented the determination of their properties and most of the knowledge abo

  3. Zeaxanthin Radical Cation Formation in Minor Light-Harvesting Complexes of Higher Plant Antenna

    Energy Technology Data Exchange (ETDEWEB)

    Avenson, Thomas H.; Ahn, Tae Kyu; Zigmantas, Donatas; Niyogi, Krishna K.; Li, Zhirong; Ballottari, Matteo; Bassi, Roberto; Fleming, Graham R.

    2008-01-31

    Previous work on intact thylakoid membranes showed that transient formation of a zeaxanthin radical cation was correlated with regulation of photosynthetic light-harvesting via energy-dependent quenching. A molecular mechanism for such quenching was proposed to involve charge transfer within a chlorophyll-zeaxanthin heterodimer. Using near infrared (880-1100 nm) transient absorption spectroscopy, we demonstrate that carotenoid (mainly zeaxanthin) radical cation generation occurs solely in isolated minor light-harvesting complexes that bind zeaxanthin, consistent with the engagement of charge transfer quenching therein. We estimated that less than 0.5percent of the isolated minor complexes undergo charge transfer quenching in vitro, whereas the fraction of minor complexes estimated to be engaged in charge transfer quenching in isolated thylakoids was more than 80 times higher. We conclude that minor complexes which bind zeaxanthin are sites of charge transfer quenching in vivo and that they can assume Non-quenching and Quenching conformations, the equilibrium LHC(N)<--> LHC(Q) of which is modulated by the transthylakoid pH gradient, the PsbS protein, and protein-protein interactions.

  4. Mechanisms of energy transfer and conversion in plant Light-Harvesting Complex II

    Energy Technology Data Exchange (ETDEWEB)

    Barros, Tiago Ferreira de

    2009-09-24

    The light-harvesting complex of photosystem II (LHC-II) is the major antenna complex in plant photosynthesis. It accounts for roughly 30% of the total protein in plant chloroplasts, which makes it arguably the most abundant membrane protein on Earth, and binds about half of plant chlorophyll (Chl). The complex assembles as a trimer in the thylakoid membrane and binds a total of 54 pigment molecules, including 24 Chl a, 18 Chl b, 6 lutein (Lut), 3 neoxanthin (Neo) and 3 violaxanthin (Vio). LHC-II has five key roles in plant photosynthesis. It: (1) harvests sunlight and transmits excitation energy to the reaction centres of photosystems II and I, (2) regulates the amount of excitation energy reaching each of the two photosystems, (3) has a structural role in the architecture of the photosynthetic supercomplexes, (4) contributes to the tight appression of thylakoid membranes in chloroplast grana, and (5) protects the photosynthetic apparatus from photo damage by non photochemical quenching (NPQ). A major fraction of NPQ is accounted for its energy-dependent component qE. Despite being critical for plant survival and having been studied for decades, the exact details of how excess absorbed light energy is dissipated under qE conditions remain enigmatic. Today it is accepted that qE is regulated by the magnitude of the pH gradient ({delta}pH) across the thylakoid membrane. It is also well documented that the drop in pH in the thylakoid lumen during high-light conditions activates the enzyme violaxanthin de-epoxidase (VDE), which converts the carotenoid Vio into zeaxanthin (Zea) as part of the xanthophyll cycle. Additionally, studies with Arabidopsis mutants revealed that the photosystem II subunit PsbS is necessary for qE. How these physiological responses switch LHC-II from the active, energy transmitting to the quenched, energy-dissipating state, in which the solar energy is not transmitted to the photosystems but instead dissipated as heat, remains unclear and is the

  5. Supercomplexes of plant photosystem I with cytochrome b6f, light-harvesting complex II and NDH

    NARCIS (Netherlands)

    Yadav, K N Sathish; Semchonok, Dmitry A; Nosek, Lukáš; Kouřil, Roman; Fucile, Geoffrey; Boekema, Egbert J; Eichacker, Lutz A

    Photosystem I (PSI) is a pigment-protein complex required for the light-dependent reactions of photosynthesis and participates in light-harvesting and redox-driven chloroplast metabolism. Assembly of PSI into supercomplexes with light harvesting complex (LHC) II, cytochrome b6f (Cytb6f) or NAD(P)H

  6. Elucidation of structure-function relationships in plant major light-harvesting complex (LHC II) by nonlinear spectroscopy.

    Science.gov (United States)

    Lokstein, Heiko; Betke, Alexander; Krikunova, Maria; Teuchner, Klaus; Voigt, Bernd

    2012-03-01

    Conventional linear and time-resolved spectroscopic techniques are often not appropriate to elucidate specific pigment-pigment interactions in light-harvesting pigment-protein complexes (LHCs). Nonlinear (laser-) spectroscopic techniques, including nonlinear polarization spectroscopy in the frequency domain (NLPF) as well as step-wise (resonant) and simultaneous (non-resonant) two-photon excitation spectroscopies may be advantageous in this regard. Nonlinear spectroscopies have been used to elucidate substructure(s) of very complex spectra, including analyses of strong excitonic couplings between chlorophylls and of interactions between (bacterio)chlorophylls and "optically dark" states of carotenoids in LHCs, including the major antenna complex of higher plants, LHC II. This article shortly reviews our previous study and outlines perspectives regarding the application of selected nonlinear laser-spectroscopic techniques to disentangle structure-function relationships in LHCs and other pigment-protein complexes.

  7. Supercomplexes of plant photosystem I with cytochrome b6f, light-harvesting complex II and NDH.

    Science.gov (United States)

    Yadav, K N Sathish; Semchonok, Dmitry A; Nosek, Lukáš; Kouřil, Roman; Fucile, Geoffrey; Boekema, Egbert J; Eichacker, Lutz A

    2017-01-01

    Photosystem I (PSI) is a pigment-protein complex required for the light-dependent reactions of photosynthesis and participates in light-harvesting and redox-driven chloroplast metabolism. Assembly of PSI into supercomplexes with light harvesting complex (LHC) II, cytochrome b6f (Cytb6f) or NAD(P)H dehydrogenase complex (NDH) has been proposed as a means for regulating photosynthesis. However, structural details about the binding positions in plant PSI are lacking. We analyzed large data sets of electron microscopy single particle projections of supercomplexes obtained from the stroma membrane of Arabidopsis thaliana. By single particle analysis, we established the binding position of Cytb6f at the antenna side of PSI. The rectangular-shaped Cytb6f dimer binds at the side where Lhca1 is located. The complex binds with its short side rather than its long side to PSI, which may explain why these supercomplexes are difficult to purify and easily disrupted. Refined analysis of the interaction between PSI and the NDH complex indicates that in total up to 6 copies of PSI can arrange with one NDH complex. Most PSI-NDH supercomplexes appeared to have 1-3 PSI copies associated. Finally, the PSI-LHCII supercomplex was found to bind an additional LHCII trimer at two positions on the LHCI side in Arabidopsis. The organization of PSI, either in a complex with NDH or with Cytb6f, may improve regulation of electron transport by the control of binding partners and distances in small domains. Copyright © 2016 Elsevier B.V. All rights reserved.

  8. Disentangling the low-energy states of the major light-harvesting complex of plants and their role in photoprotection.

    Science.gov (United States)

    Krüger, Tjaart P J; Ilioaia, Cristian; Johnson, Matthew P; Ruban, Alexander V; van Grondelle, Rienk

    2014-07-01

    The ability to dissipate large fractions of their absorbed light energy as heat is a vital photoprotective function of the peripheral light-harvesting pigment-protein complexes in photosystem II of plants. The major component of this process, known as qE, is characterised by the appearance of low-energy (red-shifted) absorption and fluorescence bands. Although the appearance of these red states has been established, the molecular mechanism, their site and particularly their involvement in qE are strongly debated. Here, room-temperature single-molecule fluorescence spectroscopy was used to study the red emission states of the major plant light-harvesting complex (LHCII) in different environments, in particular conditions mimicking qE. It was found that most states correspond to peak emission at around 700nm and are unrelated to energy dissipative states, though their frequency of occurrence increased under conditions that mimicked qE. Longer-wavelength emission appeared to be directly related to energy dissipative states, in particular emission beyond 770nm. The ensemble average of the red emission bands shares many properties with those obtained from previous bulk in vitro and in vivo studies. We propose the existence of at least three excitation energy dissipating mechanisms in LHCII, each of which is associated with a different spectral signature and whose contribution to qE is determined by environmental control of protein conformational disorder. Emission at 700nm is attributed to a conformational change in the Lut 2 domain, which is facilitated by the conformational change associated with the primary quenching mechanism involving Lut 1.

  9. Excitation-energy transfer dynamics of higher plant photosystem I light-harvesting complexes.

    Science.gov (United States)

    Wientjes, Emilie; van Stokkum, Ivo H M; van Amerongen, Herbert; Croce, Roberta

    2011-03-01

    Photosystem I (PSI) plays a major role in the light reactions of photosynthesis. In higher plants, PSI is composed of a core complex and four outer antennas that are assembled as two dimers, Lhca1/4 and Lhca2/3. Time-resolved fluorescence measurements on the isolated dimers show very similar kinetics. The intermonomer transfer processes are resolved using target analysis. They occur at rates similar to those observed in transfer to the PSI core, suggesting competition between the two transfer pathways. It appears that each dimer is adopting various conformations that correspond to different lifetimes and emission spectra. A special feature of the Lhca complexes is the presence of an absorption band at low energy, originating from an excitonic state of a chlorophyll dimer, mixed with a charge-transfer state. These low-energy bands have high oscillator strengths and they are superradiant in both Lhca1/4 and Lhca2/3. This challenges the view that the low-energy charge-transfer state always functions as a quencher in plant Lhc's and it also challenges previous interpretations of PSI kinetics. The very similar properties of the low-energy states of both dimers indicate that the organization of the involved chlorophylls should also be similar, in disagreement with the available structural data.

  10. Light-harvesting antenna complexes in the moss Physcomitrella patens: implications for the evolutionary transition from green algae to land plants.

    Science.gov (United States)

    Iwai, Masakazu; Yokono, Makio

    2017-06-01

    Plants have successfully adapted to a vast range of terrestrial environments during their evolution. To elucidate the evolutionary transition of light-harvesting antenna proteins from green algae to land plants, the moss Physcomitrella patens is ideally placed basally among land plants. Compared to the genomes of green algae and land plants, the P. patens genome codes for more diverse and redundant light-harvesting antenna proteins. It also encodes Lhcb9, which has characteristics not found in other light-harvesting antenna proteins. The unique complement of light-harvesting antenna proteins in P. patens appears to facilitate protein interactions that include those lost in both green algae and land plants with regard to stromal electron transport pathways and photoprotection mechanisms. This review will highlight unique characteristics of the P. patens light-harvesting antenna system and the resulting implications about the evolutionary transition during plant terrestrialization. Copyright © 2017 Elsevier Ltd. All rights reserved.

  11. Density of vibrational States of the light-harvesting complex II of green plants studied by inelastic neutron scattering

    CERN Document Server

    Pieper, J K; Renger, G; Lechner, R E

    2004-01-01

    Results of inelastic neutron scattering (INS) experiments are reported for the solubilized trimeric light-harvesting complex of photosystem II (LHC II) in the temperature range from 5 to 100 K. Two incident neutron wavelengths of 2.0 ( similar to 20 meV) and 5.1 A ( similar to 3.2 meV) corresponding to elastic energy resolutions of DeltaE = 0.920 meV and DeltaE = 0.093 meV, respectively, are employed to study INS spectra of LHC II for both neutron energy loss and gain. Solubilized LHC II and D//2O-containing buffer solution are investigated separately in order to properly subtract the contribution of the solvent. The inelastic part of the scattering function S(Q, omega) derived for the LHC II protein resembles the well-known "Boson-peak" and is characterized by a maximum at about 2.5 meV and a strongly asymmetric line shape with a slight tailing toward higher energy transfers. Analysis of the momentum transfer dependence of S(Q, omega) reveals that both the elastic and inelastic contributions to S(Q, omega) e...

  12. Mechanisms of light harvesting by photosystem II in plants

    CERN Document Server

    Amarnath, Kapil; Schneider, Anna R; Fleming, Graham R

    2015-01-01

    Light harvesting by photosystem II (PSII) in plants is highly efficient and acclimates to rapid changes in the intensity of sunlight. However, the mechanisms of PSII light harvesting have remained experimentally inaccessible. Using a structure-based model of excitation energy flow in 200 nanometer (nm) x 200 nm patches of the grana membrane, where PSII is located, we accurately simulated chlorophyll fluorescence decay data with no free parameters. Excitation movement through the light harvesting antenna is diffusive, but becomes subdiffusive in the presence of charge separation at reaction centers. The influence of membrane morphology on light harvesting efficiency is determined by the excitation diffusion length of 50 nm in the antenna. Our model provides the basis for understanding how nonphotochemical quenching mechanisms affect PSII light harvesting in grana membranes.

  13. The structure and function of bacterial light-harvesting complexes.

    Science.gov (United States)

    Law, Christopher J; Roszak, Aleksander W; Southall, June; Gardiner, Alastair T; Isaacs, Neil W; Cogdell, Richard J

    2004-01-01

    The harvesting of solar radiation by purple photosynthetic bacteria is achieved by circular, integral membrane pigment-protein complexes. There are two main types of light-harvesting complex, termed LH2 and LH1, that function to absorb light energy and to transfer that energy rapidly and efficiently to the photochemical reaction centres where it is trapped. This mini-review describes our present understanding of the structure and function of the purple bacterial light-harvesting complexes.

  14. Light-harvesting superstructures of green plant chloroplasts lacking photosystems.

    Science.gov (United States)

    Belgio, Erica; Ungerer, Petra; Ruban, Alexander V

    2015-10-01

    The light-harvesting antenna of higher plant photosystem II (LHCII) is the major photosynthetic membrane component encoded by an entire family of homologous nuclear genes. On the contrary, the great majority of proteins of photosystems and electron transport components are encoded by the chloroplast genome. In this work, we succeeded in gradually inhibiting the expression of the chloroplast genes that led to the disappearance of the photosystem complexes, mimicking almost total photoinhibition. The treated plants, despite displaying only some early signs of senescence, sustained their metabolism and growth for several weeks. The only major remaining membrane component was LHCII antenna that formed superstructures - stacks of dozens of thylakoids or supergrana. Freeze-fracture electron microscopy revealed specific organization, directly displaying frequently bifurcated membranes with reduced or totally absent photosystem II (PSII) reaction centre complexes. Our findings show that it is possible to accumulate large amounts of light-harvesting membranes, organized into three-dimensional structures, in the absence of reaction centre complexes. This points to the reciprocal role of LHCII and PSII in self-assembly of the three-dimensional matrix of the photosynthetic membrane, dictating its size and flexible adaptation to the light environment. © 2015 John Wiley & Sons Ltd.

  15. Exciton coupling induces vibronic hyperchromism in light-harvesting complexes

    CERN Document Server

    Schulze, Jan; Kühn, Oliver; Pullerits, Tõnu

    2013-01-01

    The recently suggested possibility that weak vibronic transitions can be excitonically enhanced in light-harvesting complexes is studied in detail. A vibronic exciton dimer model which includes ground state vibrations is investigated using multi-configuration time-dependent Hartree method with a parameter set typical to photosynthetic light-harvesting complexes. Absorption spectra are discussed in dependence on the Coulomb coupling, the detuning of site energies, and the number of vibrational mode. Calculations of the fluorescence spectra show that the spectral densities obtained from the low temperature fluorescence line narrowing measurements of light-harvesting systems need to be corrected for the exciton effects. For the J-aggregate configuration, as in most of the light-harvesting complexes, the true spectral density has larger amplitude than what is obtained from the measurement.

  16. Atomistic study of energy funneling in the light-harvesting complex of green sulfur bacteria

    CERN Document Server

    Huh, Joonsuk; Brookes, Jennifer C; Valleau, Stéphanie; Fujita, Takatoshi; Aspuru-Guzik, Alán

    2013-01-01

    Phototrophic organisms such as plants, photosynthetic bacteria and algae use microscopic complexes of pigment molecules to absorb sunlight. Within the light-harvesting complexes, which frequently have multiple functional and structural subunits, the energy is transferred in the form of molecular excitations with very high efficiency. Green sulfur bacteria are considered to be amongst the most efficient light-harvesting organisms. Despite multiple experimental and theoretical studies of these bacteria the physical origin of the efficient and robust energy transfer in their light-harvesting complexes is not well understood. To study excitation dynamics at the systems level we introduce an atomistic model that mimic a complete light-harvesting apparatus of green sulfur bacteria. The model contains about 4000 pigment molecules and comprises a double wall roll for the chlorosome, a baseplate and six Fenna-Matthews-Olson trimer complexes. We show that the fast relaxation within functional subunits combined with the...

  17. Photoprotection in higher plants: the putative quenching site is conserved in all outer light-harvesting complexes of Photosystem II.

    Science.gov (United States)

    Mozzo, Milena; Passarini, Francesca; Bassi, Roberto; van Amerongen, Herbert; Croce, Roberta

    2008-10-01

    In bright sunlight, the amount of energy harvested by plants exceeds the electron transport capacity of Photosystem II in the chloroplasts. The excess energy can lead to severe damage of the photosynthetic apparatus and to avoid this, part of the energy is thermally dissipated via a mechanism called non-photochemical quenching (NPQ). It has been found that LHCII, the major antenna complex of Photosystem II, is involved in this mechanism and it was proposed that its quenching site is formed by the cluster of strongly interacting pigments: chlorophylls 611 and 612 and lutein 620 [A.V. Ruban, R. Berera, C. Ilioaia, I.H.M. van Stokkum, J.T.M. Kennis, A.A. Pascal, H. van Amerongen, B. Robert, P. Horton and R. van Grondelle, Identification of a mechanism of photoprotective energy dissipation in higher plants, Nature 450 (2007) 575-578.]. In the present work we have investigated the interactions between the pigments in this cluster not only for LHCII, but also for the homologous minor antenna complexes CP24, CP26 and CP29. Use was made of wild-type and mutated reconstituted complexes that were analyzed with (low-temperature) absorption and circular-dichroism spectroscopy as well as by biochemical methods. The pigments show strong interactions that lead to highly specific spectroscopic properties that appear to be identical for LHCII, CP26 and CP29. The interactions are similar but not identical for CP24. It is concluded that if the 611/612/620 domain is responsible for the quenching in LHCII, then all these antenna complexes are prepared to act as a quencher. This can explain the finding that none of the Lhcb complexes seems to be strictly required for NPQ while, in the absence of all of them, NPQ is abolished.

  18. Phycobilisomes: light-harvesting pigment complexes

    Energy Technology Data Exchange (ETDEWEB)

    Gantt, E.

    1975-12-01

    Phycobilisomes, as a light-harvesting sytem, appear to be organized for maximum energy transfer, with chlorophyll of the lamellae the final acceptor. Phycobilisomes were first observed by electron microscopy, and the suggestion was made that they are sites of phycobiliproteins. The shape of the phycobilisomes may be determined by the predominant phycobiliproteins present, and their size is quite constant with a diameter of about 40 nm which is about the width of two ribosomes. The algae commit a large part of their resources to phycobilin production. Phycobiliproteins can account for as much as 24% of the dry weight of blue-green algal cells and 40% of the total soluble protein. Most, if not all, of this is contained in phycobilisomes. Energy absorbed by phycobiliproteins can be transferred to chlorophyll with a high degree of efficiency, approaching 80 to 90%. Energy transfer in phycobilisomes is expected to progress from phycoerythrin to phycocyanin to allophycocyanin and eventually to chlorophyll. Evidence obtained from dissociation studies and electron microscopy, has made it possible to suggest a phycobilisome model. For efficient energy transfer, the most logical arrangement of the phycobiliproteins would be to have them in the order of the transfer events. In this arrangement, allophycocyanin would be nearest to the photosynthetic membranes, followed by phycocyanin toward the outside. Phycoerythrin would form the outermost layer. Two of the most crucial problems yet to be investigated involve the nature of the attachment site of the phycobilisome to the membrane and the physical relationship of phycobilisomes to the photosynthetic reaction centers. (CAJ)

  19. Quantum entanglement phenomena in photosynthetic light harvesting complexes

    CERN Document Server

    Whaley, K Birgitta; Ishizaki, Akihito

    2010-01-01

    We review recent theoretical calculations of quantum entanglement in photosynthetic light harvesting complexes. These works establish, for the first time, a manifestation of this characteristically quantum mechanical phenomenon in biologically functional structures. We begin by summarizing calculations on model biomolecular systems that aim to reveal non-trivial characteristics of quantum entanglement in non-equilibrium biological environments. We then discuss and compare several calculations performed recently of excitonic dynamics in the Fenna-Matthews-Olson light harvesting complex and of the entanglement present in this widely studied pigment-protein structure. We point out the commonalities between the derived results and also identify and explain the differences. We also discuss recent work that examines entanglement in the structurally more intricate light harvesting complex II (LHCII). During this overview, we take the opportunity to clarify several subtle issues relating to entanglement in such biomo...

  20. Photoprotection in higher plants : The putative quenching site is conserved in all outer light-harvesting complexes of Photosystem II

    NARCIS (Netherlands)

    Mozzo, Milena; Passarini, Francesca; Bassi, Roberto; van Amerongen, Herbert; Croce, Roberta

    2008-01-01

    In bright sunlight, the amount of energy harvested by plants exceeds the electron transport capacity of Photosystem II in the chloroplasts. The excess energy can lead to severe damage of the photosynthetic apparatus and to avoid this, part of the energy is thermally dissipated via a mechanism called

  1. Quantum coherence, decoherence and entanglement in light harvesting complexes

    Science.gov (United States)

    Plenio, Martin; Caruso, Filippo; Chin, Alex; Datta, Animesh; Huelga, Susana

    2009-03-01

    Transport phenomena in networks allow for information and energy to be exchanged between individual constituents of communication systems, networks or light-harvesting complexes. Environmental noise is generally expected to hinder transport. Here we show that transport of excitations across dissipative quantum networks can be enhanced by dephasing noise. We identify two key processes that underly this phenomenon and provide instructive examples of quantum networks for each. We argue that Nature may be routinely exploiting this effect by showing that exciton transport in light harvesting complexes and other networks benefits from noise and is remarkably robust against static disorder. These results point towards the possibility for designing optimized structures for transport, for example in artificial nano-structures, assisted by noise. Furthermore, we demonstrate that quantum entanglement may be present for short times in light-harvesting complexes. We describe how the presence of such entanglement may be verified without the need for full state tomography and with minimal model assumptions. This work is based on M.B. Plenio & S.F. Huelga, New J. Phys. 10, 113019 (2008) and F. Caruso, A. Chin, A. Datta, S.F. Huelga & M.B. Plenio, in preparation

  2. Ultrafast energy relaxation in single light-harvesting complexes.

    Science.gov (United States)

    Malý, Pavel; Gruber, J Michael; Cogdell, Richard J; Mančal, Tomáš; van Grondelle, Rienk

    2016-03-15

    Energy relaxation in light-harvesting complexes has been extensively studied by various ultrafast spectroscopic techniques, the fastest processes being in the sub-100-fs range. At the same time, much slower dynamics have been observed in individual complexes by single-molecule fluorescence spectroscopy (SMS). In this work, we use a pump-probe-type SMS technique to observe the ultrafast energy relaxation in single light-harvesting complexes LH2 of purple bacteria. After excitation at 800 nm, the measured relaxation time distribution of multiple complexes has a peak at 95 fs and is asymmetric, with a tail at slower relaxation times. When tuning the excitation wavelength, the distribution changes in both its shape and position. The observed behavior agrees with what is to be expected from the LH2 excited states structure. As we show by a Redfield theory calculation of the relaxation times, the distribution shape corresponds to the expected effect of Gaussian disorder of the pigment transition energies. By repeatedly measuring few individual complexes for minutes, we find that complexes sample the relaxation time distribution on a timescale of seconds. Furthermore, by comparing the distribution from a single long-lived complex with the whole ensemble, we demonstrate that, regarding the relaxation times, the ensemble can be considered ergodic. Our findings thus agree with the commonly used notion of an ensemble of identical LH2 complexes experiencing slow random fluctuations.

  3. A light-harvesting siphonaxanthin-chlorophyll a/b-protein complex of marine green alga,Bryopsis corticulans

    Institute of Scientific and Technical Information of China (English)

    CHEN Hui; SHEN Shihua; HE Junfang; LENG Jing; LI Liangbi; KUANG Tingyun

    2004-01-01

    A light-harvesting chlorophyll a/b-protein complex (LHCP) was isolated directly from thylakoid membranes of marine green alga, Bryopsis corticulans, by two consecutive runs of liquid chromatography. The trimeric form of the light-harvesting complex has been obtained by sucrose gradient ultracentrifugation. The result of SDSPAGE shows that the light-harvesting complex is composed of at least five apoproteins in which a protein with apparent molecular weight of about 31 kD was never found in the major light-harvesting complex (LHC Ⅱ) from higher plants.The isolated Bryopsis corticulans light-harvesting complex contains a specific carotenoid, siphonaxanthin, as well as chlorophyll (Chl) a, Chl b, neoxanthin and violaxanthin. Siphonaxanthin which is present in the light-harvesting siphonaxanthin-chlorophyll a/b-protein complex of Bryopsis corticulans is responsible for enhanced absorption in the blue-green region (530 nm). Efficient energy transfer from both siphonaxanthin and Chl b to Chl a in Bryopsis corticulans LHCP, which has similar absorption and fluorescence emission spectra to those of the lutein-chlorophyll a/b-protein of higher plants, proved that molecular arrangement of the light-harvesting pigments was highly ordered in the Bryopsis corticulans LHCP. The siphonaxanthin-chlorophyll a/b-proteins allow enhanced absorption of blue-green light, the predominant light available in deep ocean waters or shaded subtidal marine habitats.

  4. Ultrafast Energy Relaxation in Single Light-Harvesting Complexes

    CERN Document Server

    Malý, Pavel; Cogdell, Richard J; Mančal, Tomáš; van Grondelle, Rienk

    2015-01-01

    Energy relaxation in light-harvesting complexes has been extensively studied by various ultrafast spectroscopic techniques, the fastest processes being in the sub-100 fs range. At the same time much slower dynamics have been observed in individual complexes by single-molecule fluorescence spectroscopy (SMS). In this work we employ a pump-probe type SMS technique to observe the ultrafast energy relaxation in single light-harvesting complexes LH2 of purple bacteria. After excitation at 800 nm, the measured relaxation time distribution of multiple complexes has a peak at 95 fs and is asymmetric, with a tail at slower relaxation times. When tuning the excitation wavelength, the distribution changes in both its shape and position. The observed behaviour agrees with what is to be expected from the LH2 excited states structure. As we show by a Redfield theory calculation of the relaxation times, the distribution shape corresponds to the expected effect of Gaussian disorder of the pigment transition energies. By repe...

  5. Atomistic study of energy funneling in the light-harvesting complex of green sulfur bacteria.

    Science.gov (United States)

    Huh, Joonsuk; Saikin, Semion K; Brookes, Jennifer C; Valleau, Stéphanie; Fujita, Takatoshi; Aspuru-Guzik, Alán

    2014-02-05

    Phototrophic organisms such as plants, photosynthetic bacteria, and algae use microscopic complexes of pigment molecules to absorb sunlight. Within the light-harvesting complexes, which frequently have several functional and structural subunits, the energy is transferred in the form of molecular excitations with very high efficiency. Green sulfur bacteria are considered to be among the most efficient light-harvesting organisms. Despite multiple experimental and theoretical studies of these bacteria, the physical origin of the efficient and robust energy transfer in their light-harvesting complexes is not well understood. To study excitation dynamics at the systems level, we introduce an atomistic model that mimics a complete light-harvesting apparatus of green sulfur bacteria. The model contains approximately 4000 pigment molecules and comprises a double wall roll for the chlorosome, a baseplate, and six Fenna-Matthews-Olson trimer complexes. We show that the fast relaxation within functional subunits combined with the transfer between collective excited states of pigments can result in robust energy funneling to the initial excitation conditions and temperature changes. Moreover, the same mechanism describes the coexistence of multiple time scales of excitation dynamics frequently observed in ultrafast optical experiments. While our findings support the hypothesis of supertransfer, the model reveals energy transport through multiple channels on different length scales.

  6. Bio serves nano: biological light-harvesting complex as energy donor for semiconductor quantum dots.

    Science.gov (United States)

    Werwie, Mara; Xu, Xiangxing; Haase, Mathias; Basché, Thomas; Paulsen, Harald

    2012-04-03

    Light-harvesting complex (LHCII) of the photosynthetic apparatus in plants is attached to type-II core-shell CdTe/CdSe/ZnS nanocrystals (quantum dots, QD) exhibiting an absorption band at 710 nm and carrying a dihydrolipoic acid coating for water solubility. LHCII stays functional upon binding to the QD surface and enhances the light utilization of the QDs significantly, similar to its light-harvesting function in photosynthesis. Electronic excitation energy transfer of about 50% efficiency is shown by donor (LHCII) fluorescence quenching as well as sensitized acceptor (QD) emission and corroborated by time-resolved fluorescence measurements. The energy transfer efficiency is commensurable with the expected efficiency calculated according to Förster theory on the basis of the estimated donor-acceptor separation. Light harvesting is particularly efficient in the red spectral domain where QD absorption is relatively low. Excitation over the entire visible spectrum is further improved by complementing the biological pigments in LHCII with a dye attached to the apoprotein; the dye has been chosen to absorb in the "green gap" of the LHCII absorption spectrum and transfers its excitation energy ultimately to QD. This is the first report of a biological light-harvesting complex serving an inorganic semiconductor nanocrystal. Due to the charge separation between the core and the shell in type-II QDs the presented LHCII-QD hybrid complexes are potentially interesting for sensitized charge-transfer and photovoltaic applications.

  7. Dimerization-assisted energy transport in light-harvesting complexes.

    Science.gov (United States)

    Yang, S; Xu, D Z; Song, Z; Sun, C P

    2010-06-21

    We study the role of the dimer structure of light-harvesting complex II (LH2) in excitation transfer from the LH2 [without a reaction center (RC)] to the LH1 (surrounding the RC) or from the LH2 to another LH2. The excited and unexcited states of a bacteriochlorophyll (BChl) are modeled by a quasispin. In the framework of quantum open system theory, we represent the excitation transfer as the total leakage of the LH2 system and then calculate the transfer efficiency and average transfer time. For different initial states with various quantum superposition properties, we study how the dimerization of the B850 BChl ring can enhance the transfer efficiency and shorten the average transfer time.

  8. Dimerization-assisted energy transport in light-harvesting complexes

    CERN Document Server

    Yang, S; Song, Z; Sun, C P

    2010-01-01

    We study the role of the dimer structure of light-harvesting complex II (LH2) in excitation transfer from the LH2 (without a reaction center (RC)) to the LH1 (surrounding the RC), or from the LH2 to another LH2. The excited and un-excited states of a bacteriochlorophyll (BChl) are modeled by quasi-spin. In the framework of quantum open system theory, we represent the excitation transfer as the total leakage of the LH2 system, and then calculate the transfer efficiency and average transfer time at a low enough temperature. For different initial states with various quantum superposition properties, we study how the dimerization of the B850 BChl ring can enhance the transfer efficiency and shorten the average transfer time.

  9. Silica entrapment for significantly stabilized, energy-conducting light-harvesting complex (LHCII).

    Science.gov (United States)

    Roeder, Sebastian; Hobe, Stephan; Paulsen, Harald

    2014-12-02

    The major light-harvesting chlorophyll a/b complex (LHCII) of the photosynthetic apparatus in green plants consists of a membrane protein and numerous noncovalently bound pigments that make up about one-third of the molecular mass of the pigment-protein complex. Due to this high pigment density, LHCII is potentially interesting as a light-harvesting component in synthetic constructs. However, for such applications its stability needs to be significantly improved. In this work, LHCII was dramatically stabilized by enclosing it within polymerizing colloidal silica. The entrapped LHCII stayed functional at 50 °C for up to 24 h instead of a few minutes in detergent solution and clearly showed energy transfer between complexes. Entrapment yield was enhanced by a polycationic peptide attached to the N terminus. Both the extent of stabilization and the yield of entrapment strongly increased with decreasing diameters of the silica particles.

  10. ARCHITECTURE OF A CHARGE-TRANSFER STATE REGULATING LIGHT HARVESTING IN A PLANT ANTENNA PROTEIN

    Energy Technology Data Exchange (ETDEWEB)

    Fleming, Graham; Ahn, Tae Kyu; Avenson, Thomas J.; Ballottari, Matteo; Cheng, Yuan-Chung; Niyogi, Krishna K.; Bassi, Roberto; Fleming, Graham R.

    2008-04-02

    Energy-dependent quenching of excess absorbed light energy (qE) is a vital mechanism for regulating photosynthetic light harvesting in higher plants. All of the physiological characteristics of qE have been positively correlated with charge-transfer between coupled chlorophyll and zeaxanthin molecules in the light-harvesting antenna of photosystem II (PSII). In this work, we present evidence for charge-transfer quenching in all three of the individual minor antenna complexes of PSII (CP29, CP26, and CP24), and we conclude that charge-transfer quenching in CP29 involves a de-localized state of an excitonically coupled chlorophyll dimer. We propose that reversible conformational changes in CP29 can `tune? the electronic coupling between the chlorophylls in this dimer, thereby modulating the energy of the chlorophylls-zeaxanthin charge-transfer state and switching on and off the charge-transfer quenching during qE.

  11. Architecture of a charge-transfer state regulating light harvesting in a plant antenna protein.

    Science.gov (United States)

    Ahn, Tae Kyu; Avenson, Thomas J; Ballottari, Matteo; Cheng, Yuan-Chung; Niyogi, Krishna K; Bassi, Roberto; Fleming, Graham R

    2008-05-01

    Energy-dependent quenching of excess absorbed light energy (qE) is a vital mechanism for regulating photosynthetic light harvesting in higher plants. All of the physiological characteristics of qE have been positively correlated with charge transfer between coupled chlorophyll and zeaxanthin molecules in the light-harvesting antenna of photosystem II (PSII). We found evidence for charge-transfer quenching in all three of the individual minor antenna complexes of PSII (CP29, CP26, and CP24), and we conclude that charge-transfer quenching in CP29 involves a delocalized state of an excitonically coupled chlorophyll dimer. We propose that reversible conformational changes in CP29 can "tune" the electronic coupling between the chlorophylls in this dimer, thereby modulating the energy of the chlorophyll-zeaxanthin charge-transfer state and switching on and off the charge-transfer quenching during qE.

  12. Single-molecule exploration of photoprotective mechanisms in light-harvesting complexes

    Science.gov (United States)

    Yang, Hsiang-Yu; Schlau-Cohen, Gabriela S.; Gwizdala, Michal; Krüger, Tjaart; Xu, Pengqi; Croce, Roberta; van Grondelle, Rienk; Moerner, W. E.

    2015-03-01

    Plants harvest sunlight by converting light energy to electron flow through the primary events in photosynthesis. One important question is how the light harvesting machinery adapts to fluctuating sunlight intensity. As a result of various regulatory processes, efficient light harvesting and photoprotection are balanced. Some of the biological steps in the photoprotective processes have been extensively studied and physiological regulatory factors have been identified. For example, the effect of lumen pH in changing carotenoid composition has been explored. However, the importance of photophysical dynamics in the initial light-harvesting steps and its relation to photoprotection remain poorly understood. Conformational and excited-state dynamics of multi-chromophore pigment-protein complexes are often difficult to study and limited information can be extracted from ensemble-averaged measurements. To address the problem, we use the Anti-Brownian ELectrokinetic (ABEL) trap to investigate the fluorescence from individual copies of light-harvesting complex II (LHCII), the primary antenna protein in higher plants, in a solution-phase environment. Perturbative surface immobilization or encapsulation schemes are avoided, and therefore the intrinsic dynamics and heterogeneity in the fluorescence of individual proteins are revealed. We perform simultaneous measurements of fluorescence intensity (brightness), excited-state lifetime, and emission spectrum of single trapped proteins. By analyzing the correlated changes between these observables, we identify forms of LHCII with different fluorescence intensities and excited-state lifetimes. The distinct forms may be associated with different energy dissipation mechanisms in the energy transfer chain. Changes of relative populations in response to pH and carotenoid composition are observed, which may extend our understanding of the molecular mechanisms of photoprotection.

  13. Self-assembled nanoscale DNA-porphyrin complex for artificial light harvesting.

    Science.gov (United States)

    Woller, Jakob G; Hannestad, Jonas K; Albinsson, Bo

    2013-02-20

    Mimicking green plants' and bacteria's extraordinary ability to absorb a vast number of photons and harness their energy is a longstanding goal in artificial photosynthesis. Resonance energy transfer among donor dyes has been shown to play a crucial role on the overall transfer of energy in the natural systems. Here, we present artificial, self-assembled, light-harvesting complexes consisting of DNA scaffolds, intercalated YO-PRO-1 (YO) donor dyes and a porphyrin acceptor anchored to a lipid bilayer, conceptually mimicking the natural light-harvesting systems. A model system consisting of 39-mer duplex DNA in a linear wire configuration with the porphyrin attached in the middle of the wire is primarily investigated. Utilizing intercalated donor fluorophores to sensitize the excitation of the porphyrin acceptor, we obtain an effective absorption coefficient 12 times larger than for direct excitation of the porphyrin. On the basis of steady-state and time-resolved emission measurements and Markov chain simulations, we show that YO-to-YO resonance energy transfer substantially contributes to the overall flow of energy to the porphyrin. This increase is explained through energy migration along the wire allowing the excited state energy to transfer to positions closer to the porphyrin. The versatility of DNA as a structural material is demonstrated through the construction of a more complex, hexagonal, light-harvesting scaffold yielding further increase in the effective absorption coefficient. Our results show that, by using DNA as a scaffold, we are able to arrange chromophores on a nanometer scale and in this way facilitate the assembly of efficient light-harvesting systems.

  14. Light harvesting complexes of Chromera velia, photosynthetic relative of apicomplexan parasites

    KAUST Repository

    Tichý, Josef

    2013-06-01

    The structure and composition of the light harvesting complexes from the unicellular alga Chromera velia were studied by means of optical spectroscopy, biochemical and electron microscopy methods. Two different types of antennae systems were identified. One exhibited a molecular weight (18-19 kDa) similar to FCP (fucoxanthin chlorophyll protein) complexes from diatoms, however, single particle analysis and circular dichroism spectroscopy indicated similarity of this structure to the recently characterized XLH antenna of xanthophytes. In light of these data we denote this antenna complex CLH, for "Chromera Light Harvesting" complex. The other system was identified as the photosystem I with bound Light Harvesting Complexes (PSI-LHCr) related to the red algae LHCI antennae. The result of this study is the finding that C. velia, when grown in natural light conditions, possesses light harvesting antennae typically found in two different, evolutionary distant, groups of photosynthetic organisms. © 2013 Elsevier B.V. All rights reserved.

  15. Activity of the promoter of the Lhca3.St.1 gene, encoding the potato apoprotein 2 of the light-harvesting complex of Photosystem I, in transgenic potato and tobacco plants

    NARCIS (Netherlands)

    Nap, Jan; VANSPANJE, M; Dirkse, W.G.; BAARDA, G; Mlynarova, L; Loonen, A.; GRONDHUIS, P; STIEKEMA, WJ

    1993-01-01

    We have isolated cDNA and genomic clones for the potato (Solanum tuberosum) apoprotein 2 of the light harvesting complex of Photosystem 1, designated Lhca3.St.l. The protein shows all characteristics of the family of chlorophyll a/b-binding proteins. Potato Lhca3.1 gene expression occurs predominant

  16. Quantum chemical insights in energy dissipation and carotenoid radical cation formation in light harvesting complexes.

    Science.gov (United States)

    Wormit, Michael; Dreuw, Andreas

    2007-06-21

    Light harvesting complexes (LHCs) have been identified in all photosynthetic organisms. To understand their function in light harvesting and energy dissipation, detailed knowledge about possible excitation energy transfer (EET) and electron transfer (ET) processes in these pigment proteins is of prime importance. This again requires the study of electronically excited states of the involved pigment molecules, in LHCs of chlorophylls and carotenoids. This paper represents a critical review of recent quantum chemical calculations on EET and ET processes between pigment pairs relevant for the major LHCs of green plants (LHC-II) and of purple bacteria (LH2). The theoretical methodology for a meaningful investigation of such processes is described in detail, and benefits and limitations of standard methods are discussed. The current status of excited state calculations on chlorophylls and carotenoids is outlined. It is focused on the possibility of EET and ET in the context of chlorophyll fluorescence quenching in LHC-II and carotenoid radical cation formation in LH2. In the context of non-photochemical quenching of green plants, it is shown that replacement of the carotenoid violaxanthin by zeaxanthin in its binding pocket of LHC-II can not result in efficient quenching. In LH2, our computational results give strong evidence that the S(1) states of the carotenoids are involved in carotenoid cation formation. By comparison of theoretical findings with recent experimental data, a general mechanism for carotenoid radical cation formation is suggested.

  17. Photophysics in single light-harvesting complexes II: from micelle to native nanodisks

    Science.gov (United States)

    Gruber, J. Michael; Scheidelaar, Stefan; van Roon, Henny; Dekker, Jan P.; Killian, J. Antoinette; van Grondelle, Rienk

    2016-02-01

    Most photosynthetic pigment-protein complexes of algae and higher plants are integral membrane proteins and are thus usually isolated in the presence of detergent to provide a hydrophobic interface and prevent aggregation. It was recently shown that the styrene maleic acid (SMA) copolymer can be used instead to solubilize and isolate protein complexes with their native lipid environment into nanodisk particles. We isolated LHCII complexes in SMA and compared their photophysics with trimeric LHCII complexes in β-DM detergent micelles to understand the effect of the native environment on the function of light-harvesting antennae. The triplet state kinetics and the calculated relative absorption cross section of single complexes indicate the successful isolation of trimeric complexes in SMA nanodisks, confirming the trimeric structure as the likely native configuration. The survival time of complexes before they photobleach is increased in SMA compared to detergent which might be explained by a stabilizing effect of the co-purified lipids in nanodisks. We furthermore find an unquenched fluorescence lifetime of 3.5 ns for LHCII in SMA nanodisks which coincides with detergent isolated complexes and notably differs from 2 ns typically found in native thylakoid structures. A large dynamic range of partially quenched complexes both in detergent micelles and lipid nanodisks is demonstrated by correlating the fluorescence lifetime with the intensity and likely reflects the conformational freedom of these complexes. This further supports the hypothesis that fluorescence intermittency is an intrinsic property of LHCII that may be involved in excess energy dissipation in native light-harvesting.

  18. Two mechanisms for dissipation of excess light in monomeric and trimeric light-harvesting complexes

    Energy Technology Data Exchange (ETDEWEB)

    Dall' Osto, Luca [Univ. di Verona, Verona (Italy). Dipartimento di Biotecnologie; Cazzaniga, Stefano [Univ. di Verona, Verona (Italy). Dipartimento di Biotecnologie; Bressan, Mauro [Univ. di Verona, Verona (Italy). Dipartimento di Biotecnologie; Paleček, David [Lund Univ. (Sweden). Dept. of Chemical Physics; Židek, Karel [Lund Univ. (Sweden). Dept. of Chemical Physics; Niyogi, Krishna K. [Univ. of California, Berkeley, CA (United States). Howard Hughes Medical Inst., Dept. of Plant and Microbial Biology; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Molecular Biophysics and Integrated Bioimaging Division; Fleming, Graham R. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Molecular Biophysics and Integrated Bioimaging Division; Univ. of California, Berkeley, CA (United States). Dept. of Chemistry, Graduate Group in Applied Science and Technology; Zigmantas, Donatas [Lund Univ. (Sweden). Dept. of Chemical Physics; Bassi, Roberto [Univ. di Verona, Verona (Italy). Dipartimento di Biotecnologie; Consiglio Nazionale delle Ricerche (CNR), Firenze (Italy). Istituto per la Protezione delle Piante (IPP)

    2017-04-10

    Oxygenic photoautotrophs require mechanisms for rapidly matching the level of chlorophyll excited states from light harvesting with the rate of electron transport from water to carbon dioxide. These photoprotective reactions prevent formation of reactive excited states and photoinhibition. The fastest response to excess illumination is the so-called non-photochemical quenching which, in higher plants, requires the luminal pH sensor PsbS and other yet unidentified components of the photosystem II antenna. Both trimeric light-harvesting complex II (LHCII) and monomeric LHC proteins have been indicated as site(s) of the heat-dissipative reactions. Different mechanisms have been proposed: Energy transfer to a lutein quencher in trimers, formation of a zeaxanthin radical cation in monomers. Here, we report on the construction of a mutant lacking all monomeric LHC proteins but retaining LHCII trimers. Its non-photochemical quenching induction rate was substantially slower with respect to the wild type. A carotenoid radical cation signal was detected in the wild type, although it was lost in the mutant. Here, we conclude that non-photochemical quenching is catalysed by two independent mechanisms, with the fastest activated response catalysed within monomeric LHC proteins depending on both zeaxanthin and lutein and on the formation of a radical cation. Trimeric LHCII was responsible for the slowly activated quenching component whereas inclusion in supercomplexes was not required. Finally, this latter activity does not depend on lutein nor on charge transfer events, whereas zeaxanthin was essential.

  19. Measuring quantum effects in photosynthetic light-harvesting complexes with multipartite entanglement

    Science.gov (United States)

    Smyth, Cathal

    This thesis is a compilation of studies on delocalization measures, entanglement, and the role of quantum coherence in electronic energy transfer (EET) in light-harvesting complexes. The first two chapters after the introduction provide foundational knowledge of quantum information and light-harvesting, respectively. Chapter 2 introduces concepts from quantum information such as purity, bipartite entanglement and criteria for its measurement. The peripheral light-harvesting complex LH2, isolated from the anoxygenic purple bacterium Rhodopseudomonas acidophila, is employed as model system of interest. This light-harvesting complex, along with a description of the process of light-harvesting, the presence of quantum coherence, and the different models used to simulate EET, are described in chapter 3. In combination these two chapters lay the foundation for chapter 4, a critical assessment of the current measures of delocalization employed in EET studies, their relationship, and overall effectiveness. The conclusion is that entanglement based measures are most effective at measuring quantum effects, and that they can be related to more conventional delocalization measures such as the inverse participation ratio (IPR) by taking into account the entropy of the system under study. All the measures within this chapter are known as bipartite measures, and only measure the strength of correlation between two sites. The fifth chapter presents the core of this thesis. Following a brief introduction to the concept of multipartite entanglement, the development of multipartite delocalization measures that give high-resolution information on quantum coherence in light-harvesting complexes is detailed. In contrast to other measures, these analytical measures can detect many body correlations in large systems undergoing decoherence. We determine that, much like the bipartite entanglement based measures of chapter 4, these measures are also a function of system entropy, and have a

  20. Noise-assisted energy transfer in quantum networks and light-harvesting complexes

    CERN Document Server

    Chin, Alex W; Caruso, Filippo; Huelga, Susana F; Plenio, Martin B

    2009-01-01

    We provide physically intuitive mechanisms for the effect of noise on excitation energy transfer (EET) in networks. Using these mechanisms of dephasing-assisted transport (DAT) in a hybrid basis of both excitons and sites, we shed new light on how noise enables energy transfer with efficiencies well above 90% across light harvesting molecules, like the Fenna-Matthew-Olson (FMO) complex. We demonstrate explicitly how noise alters the pathways of energy transfer across the complex, suppressing ineffective pathways and facilitating direct ones to the reaction centre. This understanding opens up a new paradigm of `noise-engineering' by which EET can be optimized in artificial light-harvesting structures.

  1. Regulating the Energy Flow in a Cyanobacterial Light-Harvesting Antenna Complex.

    Science.gov (United States)

    Eisenberg, Ido; Caycedo-Soler, Felipe; Harris, Dvir; Yochelis, Shira; Huelga, Susana F; Plenio, Martin B; Adir, Noam; Keren, Nir; Paltiel, Yossi

    2017-02-16

    Photosynthetic organisms harvest light energy, utilizing the absorption and energy-transfer properties of protein-bound chromophores. Controlling the harvesting efficiency is critical for the optimal function of the photosynthetic apparatus. Here, we show that the cyanobacterial light-harvesting antenna complex may be able to regulate the flow of energy to switch reversibly from efficient energy conversion to photoprotective quenching via a structural change. We isolated cyanobacterial light-harvesting proteins, phycocyanin and allophycocyanin, and measured their optical properties in solution and in an aggregated-desiccated state. The results indicate that energy band structures are changed, generating a switch between the two modes of operation, exciton transfer and quenching, achieved without dedicated carotenoid quenchers. This flexibility can contribute greatly to the large dynamic range of cyanobacterial light-harvesting systems.

  2. Evolution of Green Plants Accompanied Changes in Light-Harvesting Systems.

    Science.gov (United States)

    Kunugi, Motoshi; Satoh, Soichirou; Ihara, Kunio; Shibata, Kensuke; Yamagishi, Yukimasa; Kogame, Kazuhiro; Obokata, Junichi; Takabayashi, Atsushi; Tanaka, Ayumi

    2016-06-01

    Photosynthetic organisms have various pigments enabling them to adapt to various light environments. Green plants are divided into two groups: streptophytes and chlorophytes. Streptophytes include some freshwater green algae and land plants, while chlorophytes comprise the other freshwater green algae and seawater green algae. The environmental conditions driving the divergence of green plants into these two groups and the changes in photosynthetic properties accompanying their evolution remain unknown. Here, we separated the core antennae of PSI and the peripheral antennae [light-harvesting complexes (LHCs)] in green plants by green-native gel electrophoresis and determined their pigment compositions. Freshwater green algae and land plants have high Chl a/b ratios, with most Chl b existing in LHCs. In contrast, seawater green algae have low Chl a/b ratios. In addition, Chl b exists not only in LHCs but also in PSI core antennae in these organisms, a situation beneficial for survival in deep seawater, where blue-green light is the dominant light source. Finally, low-energy Chl (red Chl) of PSI was detected in freshwater green algae and land plants, but not in seawater green algae. We thus conclude that the different level of Chl b accumulation in core antennae and differences in PSI red Chl between freshwater and seawater green algae are evolutionary adaptations of these algae to their habitats, especially to high- or low-light environments.

  3. Ab inito study on triplet excitation energy transfer in photosynthetic light-harvesting complexes.

    Science.gov (United States)

    You, Zhi-Qiang; Hsu, Chao-Ping

    2011-04-28

    We have studied the triplet energy transfer (TET) for photosynthetic light-harvesting complexes, the bacterial light-harvesting complex II (LH2) of Rhodospirillum molischianum and Rhodopseudomonas acidophila, and the peridinin-chlorophyll a protein (PCP) from Amphidinium carterae. The electronic coupling factor was calculated with the recently developed fragment spin difference scheme (You and Hsu, J. Chem. Phys. 2010, 133, 074105), which is a general computational scheme that yields the overall coupling under the Hamiltonian employed. The TET rates were estimated based on the couplings obtained. For all light-harvesting complexes studied, there exist nanosecond triplet energy transfer from the chlorophylls to the carotenoids. This result supports a direct triplet quenching mechanism for the photoprotection function of carotenoids. The TET rates are similar for a broad range of carotenoid triplet state energy, which implies a general and robust TET quenching role for carotenoids in photosynthesis. This result is also consistent with the weak dependence of TET kinetics on the type or the number of π conjugation lengths in the carotenoids and their analogues reported in the literature. We have also explored the possibility of forming triplet excitons in these complexes. In B850 of LH2 or the peridinin cluster in PCP, it is unlikely to have triplet exciton since the energy differences of any two neighboring molecules are likely to be much larger than their TET couplings. Our results provide theoretical limits to the possible photophysics in the light-harvesting complexes.

  4. Strong antenna-enhanced fluorescence of a single light-harvesting complex shows photon antibunching.

    Science.gov (United States)

    Wientjes, Emilie; Renger, Jan; Curto, Alberto G; Cogdell, Richard; van Hulst, Niek F

    2014-06-23

    The nature of the highly efficient energy transfer in photosynthetic light-harvesting complexes is a subject of intense research. Unfortunately, the low fluorescence efficiency and limited photostability hampers the study of individual light-harvesting complexes at ambient conditions. Here we demonstrate an over 500-fold fluorescence enhancement of light-harvesting complex 2 (LH2) at the single-molecule level by coupling to a gold nanoantenna. The resonant antenna produces an excitation enhancement of circa 100 times and a fluorescence lifetime shortening to ~20 ps. The radiative rate enhancement results in a 5.5-fold-improved fluorescence quantum efficiency. Exploiting the unique brightness, we have recorded the first photon antibunching of a single light-harvesting complex under ambient conditions, showing that the 27 bacteriochlorophylls coordinated by LH2 act as a non-classical single-photon emitter. The presented bright antenna-enhanced LH2 emission is a highly promising system to study energy transfer and the role of quantum coherence at the level of single complexes.

  5. Spectroscopy of Single Light-Harvesting Complexes from Purple Photosynthetic Bacteria at 1.2 K

    NARCIS (Netherlands)

    Oijen, A.M. van; Ketelaars, M.; Köhler, J.; Aartsma, T.J.; Schmidt, J.

    1998-01-01

    In this Letter we present the first observation of the fluorescence-excitation spectra of individual light-harvesting complexes (LH2) from purple photosynthetic bacteria at 1.2 K. The spectra reveal the electronic transitions to the individual excitonic states of the assembly of absorbing

  6. Spectroscopy of Single Light-Harvesting Complexes from Purple Photosynthetic Bacteria at 1.2 K

    NARCIS (Netherlands)

    Oijen, A.M. van; Ketelaars, M.; Köhler, J.; Aartsma, T.J.; Schmidt, J.

    1998-01-01

    In this Letter we present the first observation of the fluorescence-excitation spectra of individual light-harvesting complexes (LH2) from purple photosynthetic bacteria at 1.2 K. The spectra reveal the electronic transitions to the individual excitonic states of the assembly of absorbing bacterioch

  7. Stark spectroscopy of the light-harvesting complex II in different oligomerisation states

    NARCIS (Netherlands)

    Palacios, M.A.; Frese, R.N.; Gradinaru, C.C.; Stokkum, van I.H.M.; Premvardhan, L.L.; Horton, P.; Ruban, A.V.; Grondelle, van R.; Amerongen, van H.

    2003-01-01

    The electric field-induced absorption changes (Stark effect) of light-harvesting complex 11 (LHCII) in different oligomerisation states-monomeric, trimeric and aggregated-have been probed at 77 K. All the chlorophyll (Chl) a molecules exhibit electro-optic properties in the Q(y) absorption region ch

  8. Energy transfer from conjugated polymer to bacterial light-harvesting complex

    NARCIS (Netherlands)

    Buczynska, D.; Bujak, L.; Loi, M. A.; Brotosudarmo, T. H. P.; Cogdell, R.; Mackowski, S.; Bujak, Ł.

    2012-01-01

    Energy transfer from a conjugated polymer blend (poly(9,9-dioctylfluorenyl-2,7-diyl):poly (2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylenevinylene) to a light-harvesting complex 2 from purple bacteria has been demonstrated using time-resolved fluorescence spectroscopy. For our hybrid nanostructure, we

  9. Ultrafast fluorescence of photosynthetic crystals and light-harvesting complexes

    NARCIS (Netherlands)

    Oort, van B.F.

    2008-01-01

    This thesis focuses on the study of photosynthetic pigment protein complexes using time resolved fluorescence techniques. Fluorescence spectroscopy often requires attaching fluorescent labels to the proteins under investigation. With photosynthetic proteins this is not necessary, because these

  10. Ultrafast fluorescence of photosynthetic crystals and light-harvesting complexes

    NARCIS (Netherlands)

    Oort, van B.F.

    2008-01-01

    This thesis focuses on the study of photosynthetic pigment protein complexes using time resolved fluorescence techniques. Fluorescence spectroscopy often requires attaching fluorescent labels to the proteins under investigation. With photosynthetic proteins this is not necessary, because these prote

  11. Ultrafast fluorescence of photosynthetic crystals and light-harvesting complexes

    NARCIS (Netherlands)

    Oort, van B.F.

    2008-01-01

    This thesis focuses on the study of photosynthetic pigment protein complexes using time resolved fluorescence techniques. Fluorescence spectroscopy often requires attaching fluorescent labels to the proteins under investigation. With photosynthetic proteins this is not necessary, because these prote

  12. Purple Bacterial Light-harvesting Complexes: From Dreams to Structures.

    Science.gov (United States)

    Cogdell, Richard J; Hashimoto, Hideki; Gardiner, Alastair T

    2004-01-01

    This paper describes the main stages involved in the research efforts designed to try and understand the structure and function of purple bacterial antenna complexes. Wherever possible the work has been illustrated by pictures of the major people who carried it out.

  13. Strong antenna-enhanced fluorescence of a single light-harvesting complex shows photon anti-bunching

    NARCIS (Netherlands)

    Wientjes, E.; Renger, J.; Curto, A.G.; Cogdell, R.; Hulst, van N.F.

    2014-01-01

    The nature of the highly efficient energy transfer in photosynthetic light-harvesting complexes is a subject of intense research. Unfortunately, the low fluorescence efficiency and limited photostability hampers the study of individual light-harvesting complexes at ambient conditions. Here we demons

  14. Bloch-Redfield equations for modeling light-harvesting complexes

    CERN Document Server

    Jeske, Jan; Plenio, Martin B; Huelga, Susana F; Cole, Jared H

    2014-01-01

    We challenge the commonly held view that Bloch-Redfield equations are a less powerful tool than phenomenological Lindblad equations for modeling exciton transport in photosynthetic complexes. This view predominantly originates from the misuse of the secular approximation. We provide a detailed description of how to model both coherent oscillations and several types of noise, giving explicit examples. All issues with non-positivity are overcome by a consistent straightforward physical noise model. Herein also lies the strength of the Bloch-Redfield approach because it facilitates the analysis of noise-effects by linking them back to physical parameters of the noise environment. This includes temporal and spatial correlations and the strength and type of interaction between the noise and the system of interest. Finally we analyze a prototypical dimer system as well as a 7-site Fenna-Matthews-Olson (FMO) complex in regards to spatial correlation length of the noise, noise strength, temperature and their connecti...

  15. Bloch-Redfield equations for modeling light-harvesting complexes.

    Science.gov (United States)

    Jeske, Jan; Ing, David J; Plenio, Martin B; Huelga, Susana F; Cole, Jared H

    2015-02-14

    We challenge the misconception that Bloch-Redfield equations are a less powerful tool than phenomenological Lindblad equations for modeling exciton transport in photosynthetic complexes. This view predominantly originates from an indiscriminate use of the secular approximation. We provide a detailed description of how to model both coherent oscillations and several types of noise, giving explicit examples. All issues with non-positivity are overcome by a consistent straightforward physical noise model. Herein also lies the strength of the Bloch-Redfield approach because it facilitates the analysis of noise-effects by linking them back to physical parameters of the noise environment. This includes temporal and spatial correlations and the strength and type of interaction between the noise and the system of interest. Finally, we analyze a prototypical dimer system as well as a 7-site Fenna-Matthews-Olson complex in regards to spatial correlation length of the noise, noise strength, temperature, and their connection to the transfer time and transfer probability.

  16. Thermal Quantum Correlations in Photosynthetic Light-Harvesting Complexes

    Science.gov (United States)

    Mahdian, M.; Kouhestani, H.

    2015-08-01

    Photosynthesis is one of the ancient biological processes, playing crucial role converting solar energy to cellular usable currency. Environmental factors and external perturbations has forced nature to choose systems with the highest efficiency and performance. Recent theoretical and experimental studies have proved the presence of quantum properties in biological systems. Energy transfer systems like Fenna-Matthews-Olson (FMO) complex shows quantum entanglement between sites of Bacteriophylla molecules in protein environment and presence of decoherence. Complex biological systems implement more truthful mechanisms beside chemical-quantum correlations to assure system's efficiency. In this study we investigate thermal quantum correlations in FMO protein of the photosynthetic apparatus of green sulfur bacteria by quantum discord measure. The results confirmed existence of remarkable quantum correlations of of BChla pigments in room temperature. This results approve involvement of quantum correlation mechanisms for information storage and retention in living organisms that could be useful for further evolutionary studies. Inspired idea of this study is potentially interesting to practice by the same procedure in genetic data transfer mechanisms.

  17. Excitation energy transfer between Light-harvesting complex II and Photosystem I in reconstituted membranes.

    Science.gov (United States)

    Akhtar, Parveen; Lingvay, Mónika; Kiss, Teréz; Deák, Róbert; Bóta, Attila; Ughy, Bettina; Garab, Győző; Lambrev, Petar H

    2016-04-01

    Light-harvesting complex II (LHCII), the major peripheral antenna of Photosystem II in plants, participates in several concerted mechanisms for regulation of the excitation energy and electron fluxes in thylakoid membranes. In part, these include interaction of LHCII with Photosystem I (PSI) enhancing the latter's absorption cross-section - for example in the well-known state 1 - state 2 transitions or as a long-term acclimation to high light. In this work we examined the capability of LHCII to deliver excitations to PSI in reconstituted membranes in vitro. Proteoliposomes with native plant thylakoid membrane lipids and different stoichiometric ratios of LHCII:PSI were reconstituted and studied by steady-state and time-resolved fluorescence spectroscopy. Fluorescence emission from LHCII was strongly decreased in PSI-LHCII membranes due to trapping of excitations by PSI. Kinetic modelling of the time-resolved fluorescence data revealed the existence of separate pools of LHCII distinguished by the time scale of energy transfer. A strongly coupled pool, equivalent to one LHCII trimer per PSI, transferred excitations to PSI with near-unity efficiency on a time scale of less than 10ps but extra LHCIIs also contributed significantly to the effective antenna size of PSI, which could be increased by up to 47% in membranes containing 3 LHCII trimers per PSI. The results demonstrate a remarkable competence of LHCII to increase the absorption cross-section of PSI, given the opportunity that the two types of complexes interact in the membrane.

  18. Modelling excitonic-energy transfer in light-harvesting complexes

    CERN Document Server

    Kramer, Tobias

    2014-01-01

    The theoretical and experimental study of energy transfer in photosynthesis has revealed an interesting transport regime, which lies at the borderline between classical transport dynamics and quantum-mechanical interference effects. Dissipation is caused by the coupling of electronic degrees of freedom to vibrational modes and leads to a directional energy transfer from the antenna complex to the target reaction-center. The dissipative driving is robust and does not rely on fine-tuning of specific vibrational modes. For the parameter regime encountered in the biological systems new theoretical tools are required to directly compare theoretical results with experimental spectroscopy data. The calculations require to utilize massively parallel graphics processor units (GPUs) for efficient and exact computations.

  19. Modelling excitonic-energy transfer in light-harvesting complexes

    Science.gov (United States)

    Kramer, Tobias; Kreisbeck, Christoph

    2014-01-01

    The theoretical and experimental study of energy transfer in photosynthesis has revealed an interesting transport regime, which lies at the borderline between classical transport dynamics and quantum-mechanical interference effects. Dissipation is caused by the coupling of electronic degrees of freedom to vibrational modes and leads to a directional energy transfer from the antenna complex to the target reaction-center. The dissipative driving is robust and does not rely on fine-tuning of specific vibrational modes. For the parameter regime encountered in the biological systems new theoretical tools are required to directly compare theoretical results with experimental spectroscopy data. The calculations require to utilize massively parallel graphics processor units (GPUs) for efficient and exact computations.

  20. Hybrid artificial photosynthetic systems comprising semiconductors as light harvesters and biomimetic complexes as molecular cocatalysts.

    Science.gov (United States)

    Wen, Fuyu; Li, Can

    2013-11-19

    Solar fuel production through artificial photosynthesis may be a key to generating abundant and clean energy, thus addressing the high energy needs of the world's expanding population. As the crucial components of photosynthesis, the artificial photosynthetic system should be composed of a light harvester (e.g., semiconductor or molecular dye), a reduction cocatalyst (e.g., hydrogenase mimic, noble metal), and an oxidation cocatalyst (e.g., photosystem II mimic for oxygen evolution from water oxidation). Solar fuel production catalyzed by an artificial photosynthetic system starts from the absorption of sunlight by the light harvester, where charge separation takes place, followed by a charge transfer to the reduction and oxidation cocatalysts, where redox reaction processes occur. One of the most challenging problems is to develop an artificial photosynthetic solar fuel production system that is both highly efficient and stable. The assembly of cocatalysts on the semiconductor (light harvester) not only can facilitate the charge separation, but also can lower the activation energy or overpotential for the reactions. An efficient light harvester loaded with suitable reduction and oxidation cocatalysts is the key for high efficiency of artificial photosynthetic systems. In this Account, we describe our strategy of hybrid photocatalysts using semiconductors as light harvesters with biomimetic complexes as molecular cocatalysts to construct efficient and stable artificial photosynthetic systems. We chose semiconductor nanoparticles as light harvesters because of their broad spectral absorption and relatively robust properties compared with a natural photosynthesis system. Using biomimetic complexes as cocatalysts can significantly facilitate charge separation via fast charge transfer from the semiconductor to the molecular cocatalysts and also catalyze the chemical reactions of solar fuel production. The hybrid photocatalysts supply us with a platform to study the

  1. Quantum coherent energy transfer over varying pathways in single light-harvesting complexes.

    Science.gov (United States)

    Hildner, Richard; Brinks, Daan; Nieder, Jana B; Cogdell, Richard J; van Hulst, Niek F

    2013-06-21

    The initial steps of photosynthesis comprise the absorption of sunlight by pigment-protein antenna complexes followed by rapid and highly efficient funneling of excitation energy to a reaction center. In these transport processes, signatures of unexpectedly long-lived coherences have emerged in two-dimensional ensemble spectra of various light-harvesting complexes. Here, we demonstrate ultrafast quantum coherent energy transfer within individual antenna complexes of a purple bacterium under physiological conditions. We find that quantum coherences between electronically coupled energy eigenstates persist at least 400 femtoseconds and that distinct energy-transfer pathways that change with time can be identified in each complex. Our data suggest that long-lived quantum coherence renders energy transfer in photosynthetic systems robust in the presence of disorder, which is a prerequisite for efficient light harvesting.

  2. Metal-enhanced fluorescence of chlorophylls in light-harvesting complexes coupled to silver nanowires.

    Science.gov (United States)

    Kowalska, Dorota; Krajnik, Bartosz; Olejnik, Maria; Twardowska, Magdalena; Czechowski, Nikodem; Hofmann, Eckhard; Mackowski, Sebastian

    2013-01-01

    We investigate metal-enhanced fluorescence of peridinin-chlorophyll protein coupled to silver nanowires using optical microscopy combined with spectrally and time-resolved fluorescence techniques. In particular we study two different sample geometries: first, in which the light-harvesting complexes are deposited onto silver nanowires, and second, where solution of both nanostructures are mixed prior deposition on a substrate. The results indicate that for the peridinin-chlorophyll complexes placed in the vicinity of the silver nanowires we observe higher intensities of fluorescence emission as compared to the reference sample, where no nanowires are present. Enhancement factors estimated for the sample where the light-harvesting complexes are mixed together with the silver nanowires prior deposition on a substrate are generally larger in comparison to the other geometry of a hybrid nanostructure. While fluorescence spectra are identical both in terms of overall shape and maximum wavelength for peridinin-chlorophyll-protein complexes both isolated and coupled to metallic nanostructures, we conclude that interaction with plasmon excitations in the latter remains neutral to the functionality of the biological system. Fluorescence transients measured for the PCP complexes coupled to the silver nanowires indicate shortening of the fluorescence lifetime pointing towards modifications of radiative rate due to plasmonic interactions. Our results can be applied for developing ways to plasmonically control the light-harvesting capability of photosynthetic complexes.

  3. A comparison of the three isoforms of the light-harvesting complex II using transient absorption and time-resolved fluorescence measurements

    NARCIS (Netherlands)

    Palacios, M.A.; Standfuss, J.; Vengris, M.; Oort, van B.F.; Stokkum, van I.H.M.; Kuhlbrandt, W.; Amerongen, van H.; Grondelle, van R.

    2006-01-01

    In this article we report the characterization of the energy transfer process in the reconstituted isoforms of the plant light-harvesting complex II. Homotrimers of recombinant Lhcb1 and Lhcb2 and monomers of Lhcb3 were compared to native trimeric complexes. We used low-intensity femtosecond transie

  4. Extension of Light-Harvesting Ability of Photosynthetic Light-Harvesting Complex 2 (LH2) through Ultrafast Energy Transfer from Covalently Attached Artificial Chromophores.

    Science.gov (United States)

    Yoneda, Yusuke; Noji, Tomoyasu; Katayama, Tetsuro; Mizutani, Naoto; Komori, Daisuke; Nango, Mamoru; Miyasaka, Hiroshi; Itoh, Shigeru; Nagasawa, Yutaka; Dewa, Takehisa

    2015-10-14

    Introducing appropriate artificial components into natural biological systems could enrich the original functionality. To expand the available wavelength range of photosynthetic bacterial light-harvesting complex 2 (LH2 from Rhodopseudomonas acidophila 10050), artificial fluorescent dye (Alexa Fluor 647: A647) was covalently attached to N- and C-terminal Lys residues in LH2 α-polypeptides with a molar ratio of A647/LH2 ≃ 9/1. Fluorescence and transient absorption spectroscopies revealed that intracomplex energy transfer from A647 to intrinsic chromophores of LH2 (B850) occurs in a multiexponential manner, with time constants varying from 440 fs to 23 ps through direct and B800-mediated indirect pathways. Kinetic analyses suggested that B800 chromophores mediate faster energy transfer, and the mechanism was interpretable in terms of Förster theory. This study demonstrates that a simple attachment of external chromophores with a flexible linkage can enhance the light harvesting activity of LH2 without affecting inherent functions of energy transfer, and can achieve energy transfer in the subpicosecond range. Addition of external chromophores, thus, represents a useful methodology for construction of advanced hybrid light-harvesting systems that afford solar energy in the broad spectrum.

  5. Taxonomic distribution and origins of the extended LHC (light-harvesting complex antenna protein superfamily

    Directory of Open Access Journals (Sweden)

    Brinkmann Henner

    2010-07-01

    Full Text Available Abstract Background The extended light-harvesting complex (LHC protein superfamily is a centerpiece of eukaryotic photosynthesis, comprising the LHC family and several families involved in photoprotection, like the LHC-like and the photosystem II subunit S (PSBS. The evolution of this complex superfamily has long remained elusive, partially due to previously missing families. Results In this study we present a meticulous search for LHC-like sequences in public genome and expressed sequence tag databases covering twelve representative photosynthetic eukaryotes from the three primary lineages of plants (Plantae: glaucophytes, red algae and green plants (Viridiplantae. By introducing a coherent classification of the different protein families based on both, hidden Markov model analyses and structural predictions, numerous new LHC-like sequences were identified and several new families were described, including the red lineage chlorophyll a/b-binding-like protein (RedCAP family from red algae and diatoms. The test of alternative topologies of sequences of the highly conserved chlorophyll-binding core structure of LHC and PSBS proteins significantly supports the independent origins of LHC and PSBS families via two unrelated internal gene duplication events. This result was confirmed by the application of cluster likelihood mapping. Conclusions The independent evolution of LHC and PSBS families is supported by strong phylogenetic evidence. In addition, a possible origin of LHC and PSBS families from different homologous members of the stress-enhanced protein subfamily, a diverse and anciently paralogous group of two-helix proteins, seems likely. The new hypothesis for the evolution of the extended LHC protein superfamily proposed here is in agreement with the character evolution analysis that incorporates the distribution of families and subfamilies across taxonomic lineages. Intriguingly, stress-enhanced proteins, which are universally found in the

  6. A Hidden State in Light-Harvesting Complex II Revealed By Multipulse Spectroscopy

    OpenAIRE

    Oort, Bart van; van Grondelle, Rienk; van Stokkum, Ivo H. M.

    2015-01-01

    Light-harvesting complex II (LHCII) is pivotal both for collecting solar radiation for photosynthesis, and for protection against photodamage under high light intensities (via a process called nonphotochemical quenching, NPQ). Aggregation of LHCII is associated with fluorescence quenching, and is used as an in vitro model system of NPQ. However, there is no agreement on the nature of the quencher and on the validity of aggregation as a model system. Here, we use ultrafast multipulse spectrosc...

  7. Dark excited states of carotenoid in light harvesting complex probing with femtosecond stimulated Raman spectroscopy

    Directory of Open Access Journals (Sweden)

    Sakai S.

    2013-03-01

    Full Text Available Vibrational dynamics of dark excited states in carotenoids have been investigated using tunable Raman pump pulses. The S1 state has same vibrational dynamics in light-harvesting complex (LH1 and solution. The S* state in LH1 has similar vibrational modes with the triplet state of carotenoid. However, the so-called S* state in solution does not have the modes and is concluded to be different from the S* state in LH1.

  8. Light-Induced Infrared Difference Spectroscopy in the Investigation of Light Harvesting Complexes

    Directory of Open Access Journals (Sweden)

    Alberto Mezzetti

    2015-07-01

    Full Text Available Light-induced infrared difference spectroscopy (IR-DS has been used, especially in the last decade, to investigate early photophysics, energy transfer and photoprotection mechanisms in isolated and membrane-bound light harvesting complexes (LHCs. The technique has the definite advantage to give information on how the pigments and the other constituents of the biological system (proteins, membranes, etc. evolve during a given photoreaction. Different static and time-resolved approaches have been used. Compared to the application of IR-DS to photosynthetic Reaction Centers (RCs, however, IR-DS applied to LHCs is still in an almost pioneering age: very often sophisticated techniques (step-scan FTIR, ultrafast IR or data analysis strategies (global analysis, target analysis, multivariate curve resolution are needed. In addition, band assignment is usually more complicated than in RCs. The results obtained on the studied systems (chromatophores and RC-LHC supercomplexes from purple bacteria; Peridinin-Chlorophyll-a-Proteins from dinoflagellates; isolated LHCII from plants; thylakoids; Orange Carotenoid Protein from cyanobacteria are summarized. A description of the different IR-DS techniques used is also provided, and the most stimulating perspectives are also described. Especially if used synergically with other biophysical techniques, light-induced IR-DS represents an important tool in the investigation of photophysical/photochemical reactions in LHCs and LHC-containing systems.

  9. Fluorescence enhancement of light-harvesting complex 2 from purple bacteria coupled to spherical gold nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Bujak, Ł. [Nicolaus Copernicus Univ., Torun (Poland). Inst. of Physics; Czechowski, N. [Nicolaus Copernicus Univ., Torun (Poland). Inst. of Physics; Piatkowski, D. [Nicolaus Copernicus Univ., Torun (Poland). Inst. of Physics; Litvin, R. [Nicolaus Copernicus Univ., Torun (Poland). Inst. of Physics; Mackowski, S. [Nicolaus Copernicus Univ., Torun (Poland). Inst. of Physics; Brotosudarmo, T. H. P. [Ma Chung Univ., Malang (Indonesia). Ma Chung Research Center for Photosynthetic Pigments; Pichler, S. [Univ. of Glasgow, Scotland (United Kingdom). Inst. of Molecular, Cell and Systems Biology; Cogdell, R. J. [Univ. Linz (Austria). Inst. fur Halbleiter-und Festkorperphysik; Heiss, W. [Univ. Linz (Austria). Inst. fur Halbleiter-und Festkorperphysik

    2011-10-24

    The influence of plasmon excitations in spherical gold nanoparticles on the optical properties of a light-harvesting complex 2 (LH2) from the purple bacteria Rhodopseudomonas palustris has been studied. Systematic analysis is facilitated by controlling the thickness of a silica layer between Au nanoparticles and LH2 complexes. Fluorescence of LH2 complexes features substantial increase when these complexes are separated by 12 nm from the gold nanoparticles. At shorter distances, non-radiative quenching leads to a decrease of fluorescence emission. The enhancement of fluorescence originates predominantly from an increase of absorption of pigments comprising the LH2 complex.

  10. Dark States in the Light-Harvesting complex 2 Revealed by Two-dimensional Electronic Spectroscopy

    Science.gov (United States)

    Ferretti, Marco; Hendrikx, Ruud; Romero, Elisabet; Southall, June; Cogdell, Richard J.; Novoderezhkin, Vladimir I.; Scholes, Gregory D.; van Grondelle, Rienk

    2016-02-01

    Energy transfer and trapping in the light harvesting antennae of purple photosynthetic bacteria is an ultrafast process, which occurs with a quantum efficiency close to unity. However the mechanisms behind this process have not yet been fully understood. Recently it was proposed that low-lying energy dark states, such as charge transfer states and polaron pairs, play an important role in the dynamics and directionality of energy transfer. However, it is difficult to directly detect those states because of their small transition dipole moment and overlap with the B850/B870 exciton bands. Here we present a new experimental approach, which combines the selectivity of two-dimensional electronic spectroscopy with the availability of genetically modified light harvesting complexes, to reveal the presence of those dark states in both the genetically modified and the wild-type light harvesting 2 complexes of Rhodopseudomonas palustris. We suggest that Nature has used the unavoidable charge transfer processes that occur when LH pigments are concentrated to enhance and direct the flow of energy.

  11. Dark States in the Light-Harvesting complex 2 Revealed by Two-dimensional Electronic Spectroscopy.

    Science.gov (United States)

    Ferretti, Marco; Hendrikx, Ruud; Romero, Elisabet; Southall, June; Cogdell, Richard J; Novoderezhkin, Vladimir I; Scholes, Gregory D; van Grondelle, Rienk

    2016-02-09

    Energy transfer and trapping in the light harvesting antennae of purple photosynthetic bacteria is an ultrafast process, which occurs with a quantum efficiency close to unity. However the mechanisms behind this process have not yet been fully understood. Recently it was proposed that low-lying energy dark states, such as charge transfer states and polaron pairs, play an important role in the dynamics and directionality of energy transfer. However, it is difficult to directly detect those states because of their small transition dipole moment and overlap with the B850/B870 exciton bands. Here we present a new experimental approach, which combines the selectivity of two-dimensional electronic spectroscopy with the availability of genetically modified light harvesting complexes, to reveal the presence of those dark states in both the genetically modified and the wild-type light harvesting 2 complexes of Rhodopseudomonas palustris. We suggest that Nature has used the unavoidable charge transfer processes that occur when LH pigments are concentrated to enhance and direct the flow of energy.

  12. Solid-state NMR applied to photosynthetic light-harvesting complexes.

    Science.gov (United States)

    Pandit, Anjali; de Groot, Huub J M

    2012-03-01

    This short review describes how solid-state NMR has provided a mechanistic and electronic picture of pigment-protein and pigment-pigment interactions in photosynthetic antenna complexes. NMR results on purple bacterial antenna complexes show how the packing of the protein and the pigments inside the light-harvesting oligomers induces mutual conformational stress. The protein scaffold produces deformation and electrostatic polarization of the BChl macrocycles and leads to a partial electronic charge transfer between the BChls and their coordinating histidines, which can tune the light-harvesting function. In chlorosome antennae assemblies, the NMR template structure reveals how the chromophores can direct their self-assembly into higher macrostructures which, in turn, tune the light-harvesting properties of the individual molecules by controlling their disorder, structural deformation, and electronic polarization without the need for a protein scaffold. These results pave the way for addressing the next challenge, which is to resolve the functional conformational dynamics of the lhc antennae of oxygenic species that allows them to switch between light-emitting and light-energy dissipating states.

  13. Protein dynamics tunes excited state positions in light-harvesting complex II.

    Science.gov (United States)

    Vrandecic, Kamarniso; Rätsep, Margus; Wilk, Laura; Rusevich, Leonid; Golub, Maksym; Reppert, Mike; Irrgang, Klaus-Dieter; Kühlbrandt, Werner; Pieper, Jörg

    2015-03-12

    Light harvesting and excitation energy transfer in photosynthesis are relatively well understood at cryogenic temperatures up to ∼100 K, where crystal structures of several photosynthetic complexes including the major antenna complex of green plants (LHC II) are available at nearly atomic resolution. The situation is much more complex at higher or even physiological temperatures, because the spectroscopic properties of antenna complexes typically undergo drastic changes above ∼100 K. We have addressed this problem using a combination of quasielastic neutron scattering (QENS) and optical spectroscopy on native LHC II and mutant samples lacking the Chl 2/Chl a 612 pigment molecule. Absorption difference spectra of the Chl 2/Chl a 612 mutant of LHC II reveal pronounced changes of spectral position and their widths above temperatures as low as ∼80 K. The complementary QENS data indicate an onset of conformational protein motions at about the same temperature. This finding suggests that excited state positions in LHC II are affected by protein dynamics on the picosecond time scale. In more detail, this means that at cryogenic temperatures the antenna complex is trapped in certain protein conformations. At higher temperature, however, a variety of conformational substates with different spectral position may be thermally accessible. At the same time, an analysis of the widths of the absorption difference spectra of Chl 2/Chl a 612 reveals three different reorganization energies or Huang-Rhys factors in different temperature ranges, respectively. These findings imply that (dynamic) pigment-protein interactions fine-tune electronic energy levels and electron-phonon coupling of LHC II for efficient excitation energy transfer at physiological temperatures.

  14. Light-harvesting Complexes (LHCs) Cluster Spontaneously in Membrane Environment Leading to Shortening of Their Excited State Lifetimes.

    Science.gov (United States)

    Natali, Alberto; Gruber, J Michael; Dietzel, Lars; Stuart, Marc C A; van Grondelle, Rienk; Croce, Roberta

    2016-08-05

    The light reactions of photosynthesis, which include light-harvesting and charge separation, take place in the amphiphilic environment of the thylakoid membrane. The light-harvesting complex II (LHCII) is the main responsible for light absorption in plants and green algae and is involved in photoprotective mechanisms that regulate the amount of excited states in the membrane. The dual function of LHCII has been extensively studied in detergent micelles, but recent results have indicated that the properties of this complex differ in a lipid environment. In this work we checked these suggestions by studying LHCII in liposomes. By combining bulk and single molecule measurements, we monitored the fluorescence characteristics of liposomes containing single complexes up to densely packed proteoliposomes. We show that the natural lipid environment per se does not alter the properties of LHCII, which for single complexes remain very similar to that in detergent. However, we show that LHCII has the strong tendency to cluster in the membrane and that protein interactions and the extent of crowding modulate the lifetimes of the excited state in the membrane. Finally, the presence of LHCII monomers at low concentrations of complexes per liposome is discussed.

  15. Evolution of light-harvesting complex proteins from Chl c-containing algae

    Directory of Open Access Journals (Sweden)

    Puerta M Virginia

    2011-04-01

    Full Text Available Abstract Background Light harvesting complex (LHC proteins function in photosynthesis by binding chlorophyll (Chl and carotenoid molecules that absorb light and transfer the energy to the reaction center Chl of the photosystem. Most research has focused on LHCs of plants and chlorophytes that bind Chl a and b and extensive work on these proteins has uncovered a diversity of biochemical functions, expression patterns and amino acid sequences. We focus here on a less-studied family of LHCs that typically bind Chl a and c, and that are widely distributed in Chl c-containing and other algae. Previous phylogenetic analyses of these proteins suggested that individual algal lineages possess proteins from one or two subfamilies, and that most subfamilies are characteristic of a particular algal lineage, but genome-scale datasets had revealed that some species have multiple different forms of the gene. Such observations also suggested that there might have been an important influence of endosymbiosis in the evolution of LHCs. Results We reconstruct a phylogeny of LHCs from Chl c-containing algae and related lineages using data from recent sequencing projects to give ~10-fold larger taxon sampling than previous studies. The phylogeny indicates that individual taxa possess proteins from multiple LHC subfamilies and that several LHC subfamilies are found in distantly related algal lineages. This phylogenetic pattern implies functional differentiation of the gene families, a hypothesis that is consistent with data on gene expression, carotenoid binding and physical associations with other LHCs. In all probability LHCs have undergone a complex history of evolution of function, gene transfer, and lineage-specific diversification. Conclusion The analysis provides a strikingly different picture of LHC diversity than previous analyses of LHC evolution. Individual algal lineages possess proteins from multiple LHC subfamilies. Evolutionary relationships showed

  16. A Bloch equation approach to intensity dependent optical spectra of light harvesting complex II: excitation dependence of light harvesting complex II pump-probe spectra.

    Science.gov (United States)

    Richter, Marten; Renger, Thomas; Knorr, Andreas

    2008-01-01

    On the basis of the recent progress in the resolution of the structure of the antenna light harvesting complex II (LHC II) of the photosystem II, we propose a microscopically motivated theory to predict excitation intensity-dependent spectra. We show that optical Bloch equations provide the means to include all 2( N ) excited states of an oligomer complex of N coupled two-level systems and analyze the effects of Pauli Blocking and exciton-exciton annihilation on pump-probe spectra. We use LHC Bloch equations for 14 Coulomb coupled two-level systems, which describe the S (0) and S (1) level of every chlorophyll molecule. All parameter introduced into the Hamiltonian are based on microscopic structure and a quantum chemical model. The derived Bloch equations describe not only linear absorption but also the intensity dependence of optical spectra in a regime where the interplay of Pauli Blocking effects as well as exciton-exciton annihilation effects are important. As an example, pump-probe spectra are discussed. The observed saturation of the spectra for high intensities can be viewed as a relaxation channel blockade on short time scales due to Pauli blocking. The theoretical investigation is useful for the interpretation of the experimental data, if the experimental conditions exceed the low intensity pump limit and effects like strong Pauli Blocking and exciton-exciton annihilation need to be considered. These effects become important when multiple excitations are generated by the pump pulse in the complex.

  17. Coherence dynamics in light-harvesting complexes with two-colour spectroscopy

    Directory of Open Access Journals (Sweden)

    Quiney Harry M.

    2013-03-01

    Full Text Available We investigate coherent dynamics in the cryptophyte light-harvesting complex Phycocyanin-645 (PC-645. A two-colour four-wave mixing experiment allows us to isolate a coherence pathway and observe its evolution in the absence of other signals. We measured a decoherence time of 540fs for the coherence [1]. Additionally oscillations in the signal pathway give evidence for the coherent excitation of states outside the bandwidth of the laser pulse. This suggests strong coupling between the excited states and phonon modes [1].

  18. Noise-assisted energy transfer in quantum networks and light-harvesting complexes

    Energy Technology Data Exchange (ETDEWEB)

    Chin, A W; Caruso, F; Huelga, S F; Plenio, M B [Institut fuer Theoretische Physik, Universitaet Ulm, D-89069, Ulm (Germany); Datta, A, E-mail: alex.chin@uni-ulm.d [Institute for Mathematical Sciences, Imperial College London, 53 Exhibition Road, London SW7 2PG (United Kingdom)

    2010-06-15

    We provide physically intuitive mechanisms for the effect of noise on excitation energy transfer (EET) in networks. Using these mechanisms of dephasing-assisted transport (DAT) in a hybrid basis of both excitons and sites, we develop a detailed picture of how noise enables energy transfer with efficiencies well above 90% across the Fenna-Matthew-Olson (FMO) complex, a type of light-harvesting molecule. We demonstrate explicitly how noise alters the pathways of energy transfer across the complex, suppressing ineffective pathways and facilitating direct ones to the reaction centre. We explain that the fundamental mechanisms underpinning DAT are expected to be robust with respect to the considered noise model but show that the specific details of the exciton-phonon coupling, which remain largely unknown in these type of complexes, and in particular the impact of non-Markovian effects, result in variations of dynamical features that should be amenable to experimental verification with current or planned technology. A detailed understanding of DAT in natural compounds could open up a new paradigm of 'noise-engineering' by which EET can be optimized in artificial light-harvesting structures.

  19. Integral Light-Harvesting Complex Expression In Symbiodinium Within The Coral Acropora aspera Under Thermal Stress

    Science.gov (United States)

    Gierz, Sarah L.; Gordon, Benjamin R.; Leggat, William

    2016-04-01

    Coral reef success is largely dependent on the symbiosis between coral hosts and dinoflagellate symbionts belonging to the genus Symbiodinium. Elevated temperatures can result in the expulsion of Symbiodinium or loss of their photosynthetic pigments and is known as coral bleaching. It has been postulated that the expression of light-harvesting protein complexes (LHCs), which bind chlorophylls (chl) and carotenoids, are important in photobleaching. This study explored the effect a sixteen-day thermal stress (increasing daily from 25-34 °C) on integral LHC (chlorophyll a-chlorophyll c2-peridinin protein complex (acpPC)) gene expression in Symbiodinium within the coral Acropora aspera. Thermal stress leads to a decrease in Symbiodinium photosynthetic efficiency by day eight, while symbiont density was significantly lower on day sixteen. Over this time period, the gene expression of five Symbiodinium acpPC genes was quantified. Three acpPC genes exhibited up-regulated expression when corals were exposed to temperatures above 31.5 °C (acpPCSym_1:1, day sixteen; acpPCSym_15, day twelve; and acpPCSym_18, day ten and day sixteen). In contrast, the expression of acpPCSym_5:1 and acpPCSym_10:1 was unchanged throughout the experiment. Interestingly, the three acpPC genes with increased expression cluster together in a phylogenetic analysis of light-harvesting complexes.

  20. Electronic coherence and the kinetics of inter-complex energy transfer in light-harvesting systems.

    Science.gov (United States)

    Huo, Pengfei; Miller, Thomas F

    2015-12-14

    We apply real-time path-integral dynamics simulations to characterize the role of electronic coherence in inter-complex excitation energy transfer (EET) processes. The analysis is performed using a system-bath model that exhibits the essential features of light-harvesting networks, including strong intra-complex electronic coupling and weak inter-complex coupling. Strong intra-complex coupling is known to generate both static and dynamic electron coherences, which delocalize the exciton over multiple chromophores and potentially influence the inter-complex EET dynamics. With numerical results from partial linearized density matrix (PLDM) real-time path-integral calculations, it is found that both static and dynamic coherence are correlated with the rate of inter-complex EET. To distinguish the impact of these two types of intra-complex coherence on the rate of inter-complex EET, we use Multi-Chromophore Förster Resonance Energy Transfer (MC-FRET) theory to map the original parameterization of the system-bath model to an alternative parameterization for which the effects of static coherence are preserved while the effects of dynamic coherence are largely eliminated. It is then shown that both parameterizations of the model (i.e., the original that supports dynamic coherence and the alternative that eliminates it), exhibit nearly identical EET kinetics and population dynamics over a wide range of parameters. These observations are found to hold for cases in which either the EET donor or acceptor is a dimeric complex and for cases in which the dimeric complex is either symmetric or asymmetric. The results from this study suggest that dynamic coherence plays only a minor role in the actual kinetics of inter-complex EET, whereas static coherence largely governs the kinetics of incoherent inter-complex EET in light-harvesting networks.

  1. Solving structure in the CP29 light harvesting complex with polarization-phased 2D electronic spectroscopy

    Science.gov (United States)

    Ginsberg, Naomi S.; Davis, Jeffrey A.; Ballottari, Matteo; Cheng, Yuan-Chung; Bassi, Roberto; Fleming, Graham R.

    2011-01-01

    The CP29 light harvesting complex from green plants is a pigment-protein complex believed to collect, conduct, and quench electronic excitation energy in photosynthesis. We have spectroscopically determined the relative angle between electronic transition dipole moments of its chlorophyll excitation energy transfer pairs in their local protein environments without relying on simulations or an X-ray crystal structure. To do so, we measure a basis set of polarized 2D electronic spectra and isolate their absorptive components on account of the tensor relation between the light polarization sequences used to obtain them. This broadly applicable advance further enhances the acuity of polarized 2D electronic spectroscopy and provides a general means to initiate or feed back on the structural modeling of electronically-coupled chromophores in condensed phase systems, tightening the inferred relations between the spatial and electronic landscapes of ultrafast energy flow. We also discuss the pigment composition of CP29 in the context of light harvesting, energy channeling, and photoprotection within photosystem II. PMID:21321222

  2. Excited state dynamics in photosynthetic reaction center and light harvesting complex 1

    Science.gov (United States)

    Strümpfer, Johan; Schulten, Klaus

    2012-08-01

    Key to efficient harvesting of sunlight in photosynthesis is the first energy conversion process in which electronic excitation establishes a trans-membrane charge gradient. This conversion is accomplished by the photosynthetic reaction center (RC) that is, in case of the purple photosynthetic bacterium Rhodobacter sphaeroides studied here, surrounded by light harvesting complex 1 (LH1). The RC employs six pigment molecules to initiate the conversion: four bacteriochlorophylls and two bacteriopheophytins. The excited states of these pigments interact very strongly and are simultaneously influenced by the surrounding thermal protein environment. Likewise, LH1 employs 32 bacteriochlorophylls influenced in their excited state dynamics by strong interaction between the pigments and by interaction with the protein environment. Modeling the excited state dynamics in the RC as well as in LH1 requires theoretical methods, which account for both pigment-pigment interaction and pigment-environment interaction. In the present study we describe the excitation dynamics within a RC and excitation transfer between light harvesting complex 1 (LH1) and RC, employing the hierarchical equation of motion method. For this purpose a set of model parameters that reproduce RC as well as LH1 spectra and observed oscillatory excitation dynamics in the RC is suggested. We find that the environment has a significant effect on LH1-RC excitation transfer and that excitation transfers incoherently between LH1 and RC.

  3. Realistic and verifiable coherent control of excitonic states in a light harvesting complex

    CERN Document Server

    Hoyer, Stephan; Montangero, Simone; Sarovar, Mohan; Calarco, Tommaso; Plenio, Martin B; Whaley, K Birgitta

    2013-01-01

    We explore the feasibility of coherent control of excitonic dynamics in light harvesting complexes despite the open nature of these quantum systems. We establish feasible targets for phase and phase/amplitude control of the electronically excited state populations in the Fenna-Mathews-Olson (FMO) complex and analyze the robustness of this control. We further present two possible routes to verification of the control target, with simulations for the FMO complex showing that steering of the excited state is experimentally verifiable either by extending excitonic coherence or by producing novel states in a pump-probe setup. Our results provide a first step toward coherent control of these systems in an ultrafast spectroscopy setup.

  4. Quantum dynamics in light-harvesting complexes: Beyond the single-exciton limit

    CERN Document Server

    Cui, B; Yi, X X

    2011-01-01

    Primitive photosynthetic cells appear over three billion years prior to any other more complex life-forms, thus it is reasonable to assume that Nature has designed a photosynthetic mechanism using minimal resources but honed to perfection under the action of evolution. A number of different quantum models have been proposed to understand the high degree of efficient energy transport, most of them are limited to the scenario of single-exciton. Here we present a study on the dynamics in light-harvesting complexes beyond the single exciton limit, and show how this model describes the energy transfer in the Fenna-Matthew-Olson (FMO) complex. We find that the energy transfer efficiency above 90% under realistic conditions is achievable.

  5. Effect of Pulse Shaping on Observing Coherent Energy Transfer in Single Light-Harvesting Complexes.

    Science.gov (United States)

    Song, Kai; Bai, Shuming; Shi, Qiang

    2016-11-17

    Recent experimental and theoretical studies have revealed that quantum coherence plays an important role in the excitation energy transfer in photosynthetic light-harvesting (LH) complexes. Inspired by the recent single-molecule two-color double-pump experiment, we theoretically investigate the effect of pulse shaping on observing coherent energy transfer in the single bacterial LH2 complex. It is found that quantum coherent energy transfer can be observed when the time delay and phase difference between the two laser pulses are controlled independently. However, when the two-color pulses are generated using the pulse-shaping method, how the laser pulses are prepared is crucial to the observation of quantum coherent energy transfer in single photosynthetic complexes.

  6. Disentangling electronic and vibrational coherence in the Phycocyanin-645 light-harvesting complex

    CERN Document Server

    Richards, Gethin H; Curmi, Paul M G; Davis, Jeffrey A

    2013-01-01

    Energy transfer between chromophores in photosynthesis proceeds with near unity quantum efficiency. Understanding the precise mechanisms of these processes is made difficult by the complexity of the electronic structure and interactions with different vibrational modes. Two-dimensional spectroscopy has helped resolve some of the ambiguities and identified quantum effects that may be important for highly efficient energy transfer. Many questions remain, however, including whether the coherences observed are electronic and/or vibrational in nature and what role they play. We utilise a two-colour four-wave mixing experiment with control of the wavelength and polarization to selectively excite specific coherence pathways. For the light-harvesting complex PC645, from cryptophyte algae, we reveal and identify specific contributions from both electronic and vibrational coherences and determine an excited state structure based on two strongly-coupled electronic states and two vibrational modes. Separation of the cohe...

  7. Bio-Photoelectrochemical Solar Cells Incorporating Reaction Center and Reaction Center Plus Light Harvesting Complexes

    Science.gov (United States)

    Yaghoubi, Houman

    onto Au electrodes via surface exposed cysteine residues. This resulted in photocurrent densities as large as ~600 nA cm-2 while still the incident photon to generated electron quantum efficiency was as low as %3 x 10-4. 2- The second approach is to immobilize wild type RCs of Rhodobacter sphaeroides on the surface of a Au underlying electrode using self-assembled monolayers of carboxylic acid terminated oligomers and cytochrome c charge mediating layers, with a preferential orientation from the primary electron donor site. This approach resulted in EQE of up to 0.06%, which showed 200 times efficiency improvement comparing to the first approach. In the third approach, instead of isolated protein complexes, RCs plus light harvesting (LH) complexes were employed for a better photon absorption. Direct attachment of RC-LH1 complexes on Au working electrodes, resulted in 0.21% EQE which showed 3.5 times efficiency improvement over the second approach (700 times higher than the first approach). The main impact of this work is the harnessing of biological RCs for efficient energy harvesting in man-made structures. Specifically, the results in this work will advance the application of RCs in devices for energy harvesting and will enable a better understanding of bio and nanomaterial interfaces, thereby advancing the application of biological materials in electronic devices. At the end, this work offers general guidelines that can serve to improve the performance of bio-hybrid solar cells.

  8. Modeling Electronic-Nuclear Interactions for Excitation Energy Transfer Processes in Light-Harvesting Complexes.

    Science.gov (United States)

    Lee, Mi Kyung; Coker, David F

    2016-08-18

    An accurate approach for computing intermolecular and intrachromophore contributions to spectral densities to describe the electronic-nuclear interactions relevant for modeling excitation energy transfer processes in light harvesting systems is presented. The approach is based on molecular dynamics (MD) calculations of classical correlation functions of long-range contributions to excitation energy fluctuations and a separate harmonic analysis and single-point gradient quantum calculations for electron-intrachromophore vibrational couplings. A simple model is also presented that enables detailed analysis of the shortcomings of standard MD-based excitation energy fluctuation correlation function approaches. The method introduced here avoids these problems, and its reliability is demonstrated in accurate predictions for bacteriochlorophyll molecules in the Fenna-Matthews-Olson pigment-protein complex, where excellent agreement with experimental spectral densities is found. This efficient approach can provide instantaneous spectral densities for treating the influence of fluctuations in environmental dissipation on fast electronic relaxation.

  9. On improving the performance of nonphotochemical quenching in CP29 light-harvesting antenna complex

    Energy Technology Data Exchange (ETDEWEB)

    Berman, Gennady P. [Theoretical Division, T-4, Los Alamos National Laboratory, and the New Mexico Consortium, Los Alamos, NM 87544 (United States); Nesterov, Alexander I., E-mail: nesterov@cencar.udg.mx [Departamento de Física, CUCEI, Universidad de Guadalajara, Av. Revolución 1500, Guadalajara, CP 44420, Jalisco (Mexico); Sayre, Richard T. [Biological Division, B-11, Los Alamos National Laboratory, and the New Mexico Consortium, Los Alamos, NM 87544 (United States); Still, Susanne [Department of Information and Computer Sciences, and Department of Physics and Astronomy, University of Hawaii at Mānoa, 1860 East–West Road, Honolulu, HI 96822 (United States)

    2016-03-22

    We model and simulate the performance of charge-transfer in nonphotochemical quenching (NPQ) in the CP29 light-harvesting antenna-complex associated with photosystem II (PSII). The model consists of five discrete excitonic energy states and two sinks, responsible for the potentially damaging processes and charge-transfer channels, respectively. We demonstrate that by varying (i) the parameters of the chlorophyll-based dimer, (ii) the resonant properties of the protein-solvent environment interaction, and (iii) the energy transfer rates to the sinks, one can significantly improve the performance of the NPQ. Our analysis suggests strategies for improving the performance of the NPQ in response to environmental changes, and may stimulate experimental verification. - Highlights: • Improvement of the efficiency of the charge-transfer nonphotochemical quenching in CP29. • Strategy for restoring the NPQ efficiency when the environment changes. • By changing of energy transfer rates to the sinks, one can significantly improve the performance of the NPQ.

  10. On Improving the Performance of Nonphotochemical Quenching in CP29 Light-Harvesting Antenna Complex

    CERN Document Server

    Berman, Gennady P; Sayre, Richard T; Still, Susanne

    2015-01-01

    We model and simulate the performance of charge-transfer in nonphotochemical quenching (NPQ) in the CP29 light-harvesting antenna-complex associated with photosystem II (PSII). The model consists of five discrete excitonic energy states and two sinks, responsible for the potentially damaging processes and charge-transfer channels, respectively. We demonstrate that by varying (i) the parameters of the chlorophyll-based dimer, (ii) the resonant properties of the protein-solvent environment interaction, and (iii) the energy transfer rates to the sinks, one can significantly improve the performance of the NPQ. Our analysis suggests strategies for improving the performance of the NPQ in response to environmental changes, and may stimulate experimental verification.

  11. Investigation of detergent effects on the solution structure of spinach Light Harvesting Complex II

    Energy Technology Data Exchange (ETDEWEB)

    Cardoso, Mateus B; Smolensky, Dmitriy; Heller, William T; O' Neill, Hugh, E-mail: hellerwt@ornl.gov, E-mail: oneillhm@ornl.gov [Center for Structural Molecular Biology, Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

    2010-11-01

    The properties of spinach light harvesting complex II (LHC II), stabilized in the detergents Triton X-100 (TX100) and n-Octyl-{beta}-D-Glucoside (BOG), were investigated by small-angle neutron scattering (SANS). The LHC II-BOG scattering curve overlaid well with the theoretical scattering curve generated from the crystal structure of LHC II indicating that the protein preparation was in its native functional state. On the other hand, the simulated LHC II curve deviated significantly from the LHC II-TX100 experimental data. Analysis by circular dichroism spectroscopy supported the SANS analysis and showed that LHC II-TX100 is inactivated. This investigation has implications for extracting and stabilizing photosynthetic membrane proteins for the development of biohybrid photoconversion devices.

  12. Photoprotection Mechanism of Light-Harvesting Antenna Complex from Purple Bacteria.

    Science.gov (United States)

    Kosumi, Daisuke; Horibe, Tomoko; Sugisaki, Mitsuru; Cogdell, Richard J; Hashimoto, Hideki

    2016-02-11

    Photosynthetic light-harvesting apparatus efficiently capture sunlight and transfer the energy to reaction centers, while they safely dissipate excess energy to surrounding environments for a protection of their organisms. In this study, we performed pump-probe spectroscopic measurements with a temporal window ranging from femtosecond to submillisecond on the purple bacterial antenna complex LH2 from Rhodobacter sphaeroides 2.4.1 to clarify its photoprotection functions. The observed excited state dynamics in the time range from subnanosecond to microsecond exhibits that the triplet-triplet excitation energy transfer from bacteriochlorophyll a to carotenoid takes place with a time constant of 16.7 ns. Furthermore, ultrafast spectroscopic data suggests that a molecular assembly of bacteriochlorophyll a in LH2 efficiently suppresses a generation of triple bacteriochlorophyll a.

  13. First-Principles Models for Biological Light-Harvesting: Phycobiliprotein Complexes from Cryptophyte Algae.

    Science.gov (United States)

    Lee, Mi Kyung; Bravaya, Ksenia B; Coker, David F

    2017-06-14

    There have been numerous efforts, both experimental and theoretical, that have attempted to parametrize model Hamiltonians to describe excited state energy transfer in photosynthetic light harvesting systems. The Frenkel exciton model, with its set of electronically coupled two level chromophores that are each linearly coupled to dissipative baths of harmonic oscillators, has become the workhorse of this field. The challenges to parametrizing such Hamiltonians have been their uniqueness, and physical interpretation. Here we present a computational approach that uses accurate first-principles electronic structure methods to compute unique model parameters for a collection of local minima that are sampled with molecular dynamics and QM geometry optimization enabling the construction of an ensemble of local models that captures fluctuations as these systems move between local basins of inherent structure. The accuracy, robustness, and reliability of the approach is demonstrated in an application to the phycobiliprotein light harvesting complexes from cryptophyte algae. Our computed Hamiltonian ensemble provides a first-principles description of inhomogeneous broadening processes, and a standard approximate non-Markovian reduced density matrix dynamics description is used to estimate lifetime broadening contributions to the spectral line shape arising from electronic-vibrational coupling. Despite the overbroadening arising from this approximate line shape theory, we demonstrate that our model Hamiltonian ensemble approach is able to provide a reliable fully first-principles method for computation of spectra and can distinguish the influence of different chromophore protonation states in experimental results. A key feature in the dynamics of these systems is the excitation of intrachromophore vibrations upon electronic excitation and energy transfer. We demonstrate that the Hamiltonian ensemble approach provides a reliable first-principles description of these

  14. From Atomistic Modeling to Excitation Transfer and Two-Dimensional Spectra of the FMO Light-Harvesting Complex

    NARCIS (Netherlands)

    Olbrich, Carsten; Jansen, Thomas L. C.; Liebers, Joerg; Aghtar, Mortaza; Struempfer, Johan; Schulten, Klaus; Knoester, Jasper; Kleinekathoefer, Ulrich; Strümpfer, Johan

    2011-01-01

    The experimental observation of long-lived quantum coherences in the Fenna-Matthews-Olson (FMO) light-harvesting complex at low temperatures has challenged general intuition in the field of complex molecular systems and provoked considerable theoretical effort in search of explanations. Here we repo

  15. Spectroscopic studies of two spectral variants of light-harvesting complex 2 (LH2) from the photosynthetic purple sulfur bacterium Allochromatium vinosum

    National Research Council Canada - National Science Library

    Niedzwiedzki, Dariusz M; Bina, David; Picken, Nichola; Honkanen, Suvi; Blankenship, Robert E; Holten, Dewey; Cogdell, Richard J

    2012-01-01

    Two spectral forms of the peripheral light-harvesting complex (LH2) from the purple sulfur photosynthetic bacterium Allochromatium vinosum were purified and their photophysical properties characterized...

  16. Evolution of low-light adapted peripheral light-harvesting complexes in strains of Rhodopseudomonas palustris.

    Science.gov (United States)

    Kotecha, Abhay; Georgiou, Theonie; Papiz, Miroslav Z

    2013-03-01

    Purple bacteria have peripheral light-harvesting (PLH) complexes adapted to high-light (LH2) and low-light (LH3, LH4) growth conditions. The latter two have only been fully characterised in Rhodopseudomonas acidophila 7050 and Rhodopseudomonas palustris CGA009, respectively. It is known that LH4 complexes are expressed under the control of two light sensing bacteriophytochromes (BphPs). Recent genomic sequencing of a number of Rps. palustris strains has provided extensive information on PLH genes. We show that both LH3 and LH4 complexes are present in Rps. palustris and have evolved in the same operon controlled by the two adjacent BphPs. Two rare marker genes indicate that a gene cluster CL2, containing LH2 genes and the BphP RpBphP4, was internally transferred within the genome to form a new operon CL1. In CL1, RpBphP4 underwent gene duplication to RpBphP2 and RpBphP3, which evolved to sense light intensity rather than spectral red/far-red intensity ratio. We show that a second LH2 complex was acquired in CL1 belonging to a different PLH clade and these two PLH complexes co-evolved together into LH3 or LH4 complexes. The near-infrared spectra provide additional support for our conclusions on the evolution of PLH complexes based on genomic data.

  17. Understanding the changes in the circular dichroism of light harvesting complex IIupon varying its pigment composition and organization

    NARCIS (Netherlands)

    Georgakopoulou, S.; Zwan, van der G.; Bassi, R.; Grondelle, van R.; Amerongen, van H.; Croce, R.

    2007-01-01

    In this work we modeled the circular dichroism (CD) spectrum of LHCII, the main light harvesting antenna of photosystem II of higher plants. Excitonic calculations are performed for a monomeric subunit, taken from the crystal structure of trimeric LHCII from spinach. All of the major features of the

  18. Synthesis and Characterization of Plant based Polythiophene Copolymers for Light Harvesting Applications

    Science.gov (United States)

    Kodithuwakku, Udari; Malavi Arachchi, Prashantha; Ratnaweera, Dilru

    Polythiophenes became more attractive in diverse applications due to some of their inherent properties including thermal and environmental stability as well as optical and electronic conductive properties. Commonly thiophene monomers are obtained from byproducts of crude oils. The current study discuss for the first time the synthesis and characterization of light harvesting polythiophenes copolymers from thiophene derivatives extracted from Tagetes species. There were mainly two thiophenes derivatives, 5-(3-buten-1-ynyl)-2, 2-bithienyl and 2, 2', 5, 2''-terthienyl (terthiophene), in the roots of the plant. Chemical oxidative radical polymerization was followed during the synthesis of copolymers with various block compositions of plant based terthiophenes and 3-hexyl terthiophenes. Structural characterization of the synthetic products was done using FTIR, NMR, Uv-vis, XRD and DSC techniques. Polythiophene homopolymers obtained from plant based terthiophenes have limited processability of solar cells due to poor solubility in common organic solvents. A significant solubility improvement was observed with copolymers having minor contributions of 3-hexylthiophenes. Research Grants, University of Sri Jayewardenepura, Sri Lanka.

  19. Quantum transport through complex networks - from light-harvesting proteins to semiconductor devices

    Energy Technology Data Exchange (ETDEWEB)

    Kreisbeck, Christoph

    2012-06-18

    Electron transport through small systems in semiconductor devices plays an essential role for many applications in micro-electronics. One focus of current research lies on establishing conceptually new devices based on ballistic transport in high mobility AlGaAs/AlGa samples. In the ballistic regime, the transport characteristics are determined by coherent interference effects. In order to guide experimentalists to an improved device design, the characterization and understanding of intrinsic device properties is crucial. We develop a time-dependent approach that allows us to simulate experimentally fabricated, complex devicegeometries with an extension of up to a few micrometers. Particularly, we explore the physical origin of unexpected effects that have been detected in recent experiments on transport through Aharonov-Bohm waveguide-interferometers. Such interferometers can be configured as detectors for transfer properties of embedded quantum systems. We demonstrate that a four-terminal waveguide-ring is a suitable setup for measuring the transmission phase of a harmonic quantum dot. Quantum effects are not restricted exclusively to artificial devices but have been found in biological systems as well. Pioneering experiments reveal quantum effects in light-harvesting complexes, the building blocks of photosynthesis. We discuss the Fenna-Matthews-Olson complex, which is a network of coupled bacteriochlorophylls. It acts as an energy wire in the photosynthetic apparatus of green sulfur bacteria. Recent experimental findings suggest that energy transfer takes place in the form of coherent wave-like motion, rather than through classical hopping from one bacteriochlorophyll to the next. However, the question of why and how coherent transfer emerges in light-harvesting complexes is still open. The challenge is to merge seemingly contradictory features that are observed in experiments on two-dimensional spectroscopy into a consistent theory. Here, we provide such a

  20. Efficient estimation of energy transfer efficiency in light-harvesting complexes.

    Science.gov (United States)

    Shabani, A; Mohseni, M; Rabitz, H; Lloyd, S

    2012-07-01

    The fundamental physical mechanisms of energy transfer in photosynthetic complexes is not yet fully understood. In particular, the degree of efficiency or sensitivity of these systems for energy transfer is not known given their realistic with surrounding photonic and phononic environments. One major problem in studying light-harvesting complexes has been the lack of an efficient method for simulation of their dynamics in biological environments. To this end, here we revisit the second order time-convolution (TC2) master equation and examine its reliability beyond extreme Markovian and perturbative limits. In particular, we present a derivation of TC2 without making the usual weak system-bath coupling assumption. Using this equation, we explore the long-time behavior of exciton dynamics of Fenna-Matthews-Olson (FMO) portein complex. Moreover, we introduce a constructive error analysis to estimate the accuracy of TC2 equation in calculating energy transfer efficiency, exhibiting reliable performance for system-bath interactions with weak and intermediate memory and strength. Furthermore, we numerically show that energy transfer efficiency is optimal and robust for the FMO protein complex of green sulfur bacteria with respect to variations in reorganization energy and bath correlation time scales.

  1. Effect of Photo-Oxidation on Energy Transfer in Light Harvesting Complex (LH2) from Rhodobacter Sphaeroides 601

    Institute of Scientific and Technical Information of China (English)

    LIU Kang-Jun; LIU Wei-Min; YAN Yong-Li; DONG Zhi-Wei; LIU Yuan; XU Chun-He; QIAN Shi-Xiong

    2006-01-01

    @@ We study the photo-oxidation of bacteriochlorophylls (BChls) in peripheral light harvesting complexes (LH2) from rhodobacter sphaeroides by using the steady absorption and the femtosecond pump-probe measurement, to realize the detailed dynamics of LH2 in the presence of photo-oxidation.

  2. Studies of Structure and Dynamics of Light Harvesting Complex 1 of R. Sphaeroides by Solid State NMR

    Energy Technology Data Exchange (ETDEWEB)

    McDermott, Ann E [Columbia Univ., New York, NY (United States)

    2014-11-14

    Studies of the structure and dynamics of a light harvesting complex from photosynthetic bacteria are described. Using Nuclear Magnetic Resonance methods, we explored the idea that optical properties are modulated via a conformational switch in the BChl chromophores, in a way that provides benefits for the efficiency of energy conversion.

  3. Singlet Energy Dissipation in the Photosystem II Light-Harvesting Complex Does Not Involve Energy Transfer to Carotenoids

    NARCIS (Netherlands)

    Mueller, Marc G.; Lambrev, Petar; Reus, Michael; Wientjes, Emilie; Croce, Roberta; Holzwarth, Alfred R.; Müller, Marc G.

    2010-01-01

    The energy dissipation mechanism in oligomers of the major light-harvesting complex II (LHC II) from Arabidopsis thaliana mutants npq1 and npq2, zeaxanthin-deficient and zeaxanthin-enriched, respectively, has been studied by femtosecond transient absorption. The kinetics obtained at different excita

  4. Site-specific incorporation of perylene into an N-terminally modified light-harvesting complex II

    NARCIS (Netherlands)

    Peneva, Kalina; Gundlach, Kristina; Herrmann, Andreas; Paulsen, Harald; Muellen, Klaus; Müllen, Klaus

    2010-01-01

    Employing the utility of the native chemical ligation, site-specific attachment of an ultrastable perylene dye to a derivative of the major light-harvesting complex (LHCII) was demonstrated. Biochemical analysis of the conjugate indicated that the structure and function of LHCII remain largely unaff

  5. Classification of novel thiazole compounds for sensitizing Ru-polypyridine complexes for artificial light harvesting

    Energy Technology Data Exchange (ETDEWEB)

    Schaefer, Johann [Institute of Photonic Technology (IPHT) Jena e.V., Albert-Einstein-Strasse 9, 07745 Jena (Germany); Menzel, Roberto; Weiss, Dieter [Institute for Organic Chemistry and Macromolecular Chemistry, Friedrich-Schiller-University Jena, Humboldtstr. 10, 07743 Jena (Germany); Dietzek, Benjamin, E-mail: benjamin.dietzek@uni-jena.d [Institute of Photonic Technology (IPHT) Jena e.V., Albert-Einstein-Strasse 9, 07745 Jena (Germany); Institute for Physical Chemistry and Abbe Center of Photonics, Friedrich-Schiller-University Jena, Helmholtzweg 4, 07743 Jena (Germany); Beckert, Rainer [Institute for Organic Chemistry and Macromolecular Chemistry, Friedrich-Schiller-University Jena, Humboldtstr. 10, 07743 Jena (Germany); Popp, Juergen [Institute of Photonic Technology (IPHT) Jena e.V., Albert-Einstein-Strasse 9, 07745 Jena (Germany); Institute for Physical Chemistry and Abbe Center of Photonics, Friedrich-Schiller-University Jena, Helmholtzweg 4, 07743 Jena (Germany)

    2011-06-15

    A systematic study of the Foerster resonance energy transfer (FRET) efficiency between thiazole dyes and a ruthenium-polypyridine complex is presented. While ruthenium-polypyridines are conventionally used in artificial light harvesting systems as primary electron donors, their application suffers from rather low extinction coefficients in the visible spectral range and an absorption gap between the {pi}{pi}{sup *} transitions of the ligands and the MLCT transitions. In this paper it is shown how thiazoles might help to circumvent theses issues. The absorption and emission spectra of the thiazole can be synthetically adjusted to fall into the absorption gap of the Ru dye and to efficiently overlap with the {sup 1}MLCT absorption of the complex, respectively. Thereby, the thiazoles might serve as antenna structures to funnel energy to the Ru-polypyridine unit, which finally can act as a photoactivated primary electron donor. Systematic investigations of the Foerster radii of representative thiazole Ru-polypyridine dye pairs corroborate this potential quantitatively. - Research highlights: {yields} First systematic study of Foerster radii in thiazole (donor)-Ru-polypyridine (acceptor) pairs. {yields} Large Foerster radii are observed (up to 40 A) comparable to systems optimized for FRET microscopy. {yields} Ru-polypyridine complexes dressed by thiazole-antennas as primary electron donors in artificial photosynthetic systems.

  6. Filling the "green gap" of the major light-harvesting chlorophyll a/b complex by covalent attachment of Rhodamine Red.

    Science.gov (United States)

    Gundlach, Kristina; Werwie, Mara; Wiegand, Sabine; Paulsen, Harald

    2009-12-01

    The major light-harvesting chlorophyll a/b complex (LHCII) greatly enhances the efficiency of photosynthesis in green plants. Recombinant LHCII can be assembled in vitro from its denatured, bacterially expressed apoprotein and plant pigments. This makes it an interesting candidate for biomimetic light-harvesting in photovoltaic applications. Due to its almost 20 pigments bound per apoprotein, LHCII absorbs efficiently in the blue and red spectral domains of visible light but less efficiently in the green domain, the so-called "green gap" in its absorption spectrum. Here we present a hybrid complex of recombinant LHCII with organic dyes that add to LHCII absorption in the green spectral region. One or three Rhodamine Red dye molecules were site-specifically attached to cysteine side chains in the apoprotein and did not interfere with LHCII assembly, function and stability. The dyes transferred their excitation energy virtually completely to the chlorophylls in LHCII, partially filling in the green gap. Thus, organic dyes can be used to increase the absorption cross section and, thus, the light-harvesting efficiency of recombinant LHCII.

  7. Ultrafast excitation relaxation in light-harvesting complex LH2 from Rb.sphaeroides 601

    Institute of Scientific and Technical Information of China (English)

    GUO Lijun; LIU Yuan; LIU Weimin; GUO Junhua; XU Chunhe; QIAN Shixiong

    2004-01-01

    The energy relaxation and kinetic evolution of transient spectra of bacteriochloro- phylls (BChls) in light-harvesting complex LH2 from Rb. Sphaeroides 601 were investigated using femtosecond pump-probe technique. Upon 783 nm excitation, the energy at B800 BChls experiences an intramolecular redistribution with 0.35 ps time constant before transferring to B850 BChls. With tuning the excitation wavelength, the dynamical evolution of excited BChls was clearly observed, which indicates an obvious competition between the ground state bleaching and excited state absorption (ESA) of BChls involved and an isosbestic point near 818 nm, and also demonstrates that from the lower electronic excited state of B800 BChls to the higher excitonic state of B850 BChls is an efficient routine for energy transfer. The excitation energy in higher excitonic states of B850 BChls relaxes rapidly to the next lowest excitonic state by interconversion, delocalization to adjacent molecular, populating the lowest excitonic state and the change of molecular conformation.

  8. Ultrafast excitation relaxation in light-harvesting complex LH2 from Rb. sphaeroides 601

    Institute of Scientific and Technical Information of China (English)

    GUO; Lijun; LIU; Yuan; LIU; Weimin; GUO; Junhua; XU; Chunhe

    2004-01-01

    The energy relaxation and kinetic evolution of transient spectra of bacteriochloro- phylls (BChls) in light-harvesting complex LH2 from Rb. Sphaeroides 601 were investigated using femtosecond pump-probe technique. Upon 783 nm excitation, the energy at B800 BChls experiences an intramolecular redistribution with 0.35 ps time constant before transferring to B850 BChls. With tuning the excitation wavelength, the dynamical evolution of excited BChls was clearly observed, which indicates an obvious competition between the ground state bleaching and excited state absorption (ESA) of BChls involved and an isosbestic point near 818 nm, and also demonstrates that from the lower electronic excited state of B800 BChls to the higher excitonic state of B850 BChls is an efficient routine for energy transfer. The excitation energy in higher excitonic states of B850 BChls relaxes rapidly to the next lowest excitonic state by interconversion, delocalization to adjacent molecular, populating the lowest excitonic state and the change of molecular conformation.

  9. Solvation effect of bacteriochlorophyll excitons in light-harvesting complex LH2.

    Science.gov (United States)

    Urboniene, V; Vrublevskaja, O; Trinkunas, G; Gall, A; Robert, B; Valkunas, L

    2007-09-15

    We have characterized the influence of the protein environment on the spectral properties of the bacteriochlorophyll (Bchl) molecules of the peripheral light-harvesting (or LH2) complex from Rhodobacter sphaeroides. The spectral density functions of the pigments responsible for the 800 and 850 nm electronic transitions were determined from the temperature dependence of the Bchl absorption spectra in different environments (detergent micelles and native membranes). The spectral density function is virtually independent of the hydrophobic support that the protein experiences. The reorganization energy for the B850 Bchls is 220 cm(-1), which is almost twice that of the B800 Bchls, and its Huang-Rhys factor reaches 8.4. Around the transition point temperature, and at higher temperatures, both the static spectral inhomogeneity and the resonance interactions become temperature-dependent. The inhomogeneous distribution function of the transitions exhibits less temperature dependence when LH2 is embedded in membranes, suggesting that the lipid phase protects the protein. However, the temperature dependence of the fluorescence spectra of LH2 cannot be fitted using the same parameters determined from the analysis of the absorption spectra. Correct fitting requires the lowest exciton states to be additionally shifted to the red, suggesting the reorganization of the exciton spectrum.

  10. Optoelectronic energy transfer at novel biohybrid interfaces using light harvesting complexes from Chloroflexus aurantiacus.

    Science.gov (United States)

    Sridharan, Arati; Muthuswamy, Jit; Pizziconi, Vincent B

    2009-06-02

    In nature, nanoscale supramolecular light harvesting complexes initiate the photosynthetic energy collection process at high quantum efficiencies. In this study, the distinctive antenna structure from Chloroflexus aurantiacusthe chlorosomeis assessed for potential exploitation in novel biohybrid optoelectronic devices. Electrochemical characterization of bacterial fragments containing intact chlorosomes with the photosynthetic apparatus show an increase in the charge storage density near the working electrode upon light stimulation and suggest that chlorosomes contribute approximately one-third of the overall photocurrent. Further, isolated chlorosomes (without additional photosynthetic components, e.g., reaction centers, biochemical mediators) produce a photocurrent (approximately 8-10 nA) under light saturation conditions. Correlative experiments indicate that the main chlorosome pigment, bacteriochlorophyll-c, contributes to the photocurrent via an oxidative mechanism. The results reported herein are the first to demonstrate that isolated chlorosomes (lipid-enclosed sacs of pigments) directly transduce light energy in an electrochemical manner, laying an alternative, biomimetic approach for designing photosensitized interfaces in biofuel cells and biomedical devices, such as bioenhanced retinal prosthetics.

  11. A Hidden State in Light-Harvesting Complex II Revealed By Multipulse Spectroscopy.

    Science.gov (United States)

    van Oort, Bart; van Grondelle, Rienk; van Stokkum, Ivo H M

    2015-04-23

    Light-harvesting complex II (LHCII) is pivotal both for collecting solar radiation for photosynthesis, and for protection against photodamage under high light intensities (via a process called nonphotochemical quenching, NPQ). Aggregation of LHCII is associated with fluorescence quenching, and is used as an in vitro model system of NPQ. However, there is no agreement on the nature of the quencher and on the validity of aggregation as a model system. Here, we use ultrafast multipulse spectroscopy to populate a quenched state in unquenched (unaggregated) LHCII. The state shows characteristic features of lutein and chlorophyll, suggesting that it is an excitonically coupled state between these two compounds. This state decays in approximately 10 ps, making it a strong competitor for photodamage and photochemical quenching. It is observed in trimeric and monomeric LHCII, upon re-excitation with pulses of different wavelengths and duration. We propose that this state is always present, but is scarcely populated under low light intensities. Under high light intensities it may become more accessible, e.g. by conformational changes, and then form a quenching channel. The same state may be the cause of fluorescence blinking observed in single-molecule spectroscopy of LHCII trimers, where a small subpopulation is in an energetically higher state where the pathway to the quencher opens up.

  12. Statistical considerations on the formation of circular photosynthetic light-harvesting complexes from Rhodopseudomonas palustris.

    Science.gov (United States)

    Taniguchi, Masahiko; Henry, Sarah; Cogdell, Richard J; Lindsey, Jonathan S

    2014-07-01

    Depending on growth conditions, some species of purple photosynthetic bacteria contain peripheral light-harvesting (LH2) complexes that are heterogeneous owing to the presence of different protomers (containing different αβ-apoproteins). Recent spectroscopic studies of Rhodopseudomonas palustris grown under low-light conditions suggest the presence of a C 3-symmetric LH2 nonamer comprised of two distinct protomers. The software program Cyclaplex, which enables generation and data-mining of virtual libraries of molecular rings formed upon combinatorial reactions, has been used to delineate the possible number and type of distinct nonamers as a function of numbers of distinct protomers. The yield of the C 3-symmetric nonamer from two protomers (A and B in varying ratios) has been studied under the following conditions: (1) statistical, (2) enriched (preclusion of the B-B sequence), and (3) seeded (pre-formation of an A-B-A block). The yield of C 3-symmetric nonamer is at most 0.98 % under statistical conditions versus 5.6 % under enriched conditions, and can be dominant under conditions of pre-seeding with an A-B-A block. In summary, the formation of any one specific nonamer even from only two protomers is unlikely on statistical grounds but must stem from enhanced free energy of formation or a directed assembly process by as-yet unknown factors.

  13. Observation of Electronic Excitation Transfer Through Light Harvesting Complex II Using Two-Dimensional Electronic-Vibrational Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Lewis, NHC; Gruenke, NL; Oliver, TAA; Ballottari, M; Bassi, R; Fleming, GR

    2016-10-05

    Light-harvesting complex II (LHCII) serves a central role in light harvesting for oxygenic photosynthesis and is arguably the most important photosynthetic antenna complex. In this article, we present two-dimensional electronic–vibrational (2DEV) spectra of LHCII isolated from spinach, demonstrating the possibility of using this technique to track the transfer of electronic excitation energy between specific pigments within the complex. We assign the spectral bands via comparison with the 2DEV spectra of the isolated chromophores, chlorophyll a and b, and present evidence that excitation energy between the pigments of the complex are observed in these spectra. Lastly, we analyze the essential components of the 2DEV spectra using singular value decomposition, which makes it possible to reveal the relaxation pathways within this complex.

  14. Characteristics and phylogeny of light-harvesting complex gene encoded proteins from marine red alga Griffithsia japonica

    Institute of Scientific and Technical Information of China (English)

    LIU Chenlin; HUANG Xiaohang; LEE Yookyung; LEE Hongkum; LI Guangyou

    2005-01-01

    Six genes encoding light-harvesting complex (LHC) protein have been characterized in the multicellular red alga Griffithsia japonica EST analysis. Three of them were full sequences while others were partial sequences with 3'-UTRs. The cleavage sites between signal peptide and mature LHC protein were analyzed on these three full sequences. The sequence characteristics, calculated molecular weights and isoelectric point (pI) values and hydrophobieity of the mature proteins were deduced and analyzed. Comparing the LHC sequences of G. japonica with higher plant, Chlorophyta, chromophytes and other red algae, the high conservation of the chlorophyll (Chl) binding site among chromophytes and red algae were revealed. Phylogenetic analysis on LHC proteins from higher plant, green algae, euglena, brown algae, diatom, cryptomonad, Raphidophyte and red algae reveals that (1) there are two distinct groups of Chl a/b and Chl a/c -binding LHC; (2) Chl a binding proteins of red algae share greater similarities with the Chl a/c-binding proteins of the chromophytes and dinoflagellate than with the Chl a/b - binding proteins of the green algae and higher plants; (3) chromophyte' s LHC is supposed to be evolved from red algae LHC.

  15. 9-cis-Neoxanthin in Light Harvesting Complexes of Photosystem II Regulates the Binding of Violaxanthin and Xanthophyll Cycle.

    Science.gov (United States)

    Wang, Ke; Tu, Wenfeng; Liu, Cheng; Rao, Yan; Gao, Zhimin; Yang, Chunhong

    2017-05-01

    The light-harvesting chlorophyll a/b complex of photosystem II (LHCII) is able to switch to multiple functions under different light conditions (i.e. harvesting solar energy for photosynthesis and dissipating excess excitation energy for photoprotection). The role of the different carotenoids bound to LHCII in regulating the structure and function of the complex is a long-lasting question in photosynthesis research. 9-cis-Neoxanthin (Nx) is one of the important carotenoids, which can only be found in the LHCIIs. High-resolution structural analysis of LHCII shows that Nx is located between different monomeric LHCIIs, with one side protruding into the lipid membrane. In this study, the various functional significances of this unique feature of Nx binding in LHCII are studied with the in vitro reconstituted LHCIIs both with and without Nx and the native complexes isolated either from wild-type Arabidopsis (Arabidopsis thaliana) or from its mutant aba4-3 lacking Nx Our results reveal that the binding of Nx affects the binding affinity of violaxanthin (Vx) to LHCII significantly. In the absence of Nx, Vx has a much higher binding affinity to trimeric LHCII. The strong coordination between Nx and Vx at the interfaces of adjacent monomers of LHCII plays an important role both in operating the xanthophyll cycle and in the transient modulation of nonphotochemical quenching. © 2017 American Society of Plant Biologists. All Rights Reserved.

  16. Low light adaptation: energy transfer processes in different types of light harvesting complexes from Rhodopseudomonas palustris.

    Science.gov (United States)

    Moulisová, Vladimíra; Luer, Larry; Hoseinkhani, Sajjad; Brotosudarmo, Tatas H P; Collins, Aaron M; Lanzani, Guglielmo; Blankenship, Robert E; Cogdell, Richard J

    2009-12-01

    Energy transfer processes in photosynthetic light harvesting 2 (LH2) complexes isolated from purple bacterium Rhodopseudomonas palustris grown at different light intensities were studied by ground state and transient absorption spectroscopy. The decomposition of ground state absorption spectra shows contributions from B800 and B850 bacteriochlorophyll (BChl) a rings, the latter component splitting into a low energy and a high energy band in samples grown under low light (LL) conditions. A spectral analysis reveals strong inhomogeneity of the B850 excitons in the LL samples that is well reproduced by an exponential-type distribution. Transient spectra show a bleach of both the low energy and high energy bands, together with the respective blue-shifted exciton-to-biexciton transitions. The different spectral evolutions were analyzed by a global fitting procedure. Energy transfer from B800 to B850 occurs in a mono-exponential process and the rate of this process is only slightly reduced in LL compared to high light samples. In LL samples, spectral relaxation of the B850 exciton follows strongly nonexponential kinetics that can be described by a reduction of the bleach of the high energy excitonic component and a red-shift of the low energetic one. We explain these spectral changes by picosecond exciton relaxation caused by a small coupling parameter of the excitonic splitting of the BChl a molecules to the surrounding bath. The splitting of exciton energy into two excitonic bands in LL complex is most probably caused by heterogenous composition of LH2 apoproteins that gives some of the BChls in the B850 ring B820-like site energies, and causes a disorder in LH2 structure.

  17. Low light adaptation: Energy transfer processes in different types of light harvesting complexes from Rhodopseudomonas palustris

    Energy Technology Data Exchange (ETDEWEB)

    Moulisova, Vladimira; Luer, Larry; Hoseinkhani, Sajjad; Brotosudarmo, Tatas H.P.; Collins, Aaron M.; Lanzani, Guglielmo; Blankenship, R. E.; Cogdell, Richard J

    Energy transfer processes in photosynthetic light harvesting 2 (LH2) complexes isolated from purple bacterium Rhodopseudomonas palustris grown at different light intensities were studied by ground state and transient absorption spectroscopy. The decomposition of ground state absorption spectra shows contributions from B800 and B850 bacteriochlorophyll (BChl) a rings, the latter component splitting into a low energy and a high energy band in samples grown under low light (LL) conditions. A spectral analysis reveals strong inhomogeneity of the B850 excitons in the LL samples that is well reproduced by an exponential-type distribution. Transient spectra show a bleach of both the low energy and high energy bands, together with the respective blue-shifted exciton-to-biexciton transitions. The different spectral evolutions were analyzed by a global fitting procedure. Energy transfer from B800 to B850 occurs in a mono-exponential process and the rate of this process is only slightly reduced in LL compared to high light samples. In LL samples, spectral relaxation of the B850 exciton follows strongly nonexponential kinetics that can be described by a reduction of the bleach of the high energy excitonic component and a red-shift of the low energetic one. We explain these spectral changes by picosecond exciton relaxation caused by a small coupling parameter of the excitonic splitting of the BChl a molecules to the surrounding bath. The splitting of exciton energy into two excitonic bands in LL complex is most probably caused by heterogenous composition of LH2 apoproteins that gives some of the BChls in the B850 ring B820-like site energies, and causes a disorder in LH2 structure.

  18. The three isoforms of the light-harvesting complex II Spectroscopic features, trimer formation, and functional roles

    CERN Document Server

    Standfuss, Jorg

    2004-01-01

    The major light-harvesting complex (LHC-II) of higher plants plays a crucial role in capturing light energy for photosynthesis and in regulating the flow of energy within the photosynthetic apparatus. Native LHC-II isolated from plant tissue consists of three isoforms, Lhcb1, Lhcb2, and Lhcb3, which form homo- and heterotrimers. All three isoforms are highly conserved among different species, suggesting distinct functional roles. We produced the three LHC-II isoforms by heterologous expression of the polypeptide in Escherichia coli and in vitro refolding with purified pigments. Although Lhcb1 and Lhcb2 are very similar in polypeptide sequence and pigment content, Lhcb3 is clearly different because it lacks an N-terminal phosphorylation site and has a higher chlorophyll a/b ratio, suggesting the absence of one chlorophyll b. Low temperature absorption and fluorescence emission spectra of the pure isoforms revealed small but significant differences in pigment organization. The oligomeric state of the pure isofo...

  19. STUDY ON THE STRUCTURAL BASIS OF PERIPHERAL LIGHT HARVESTING COMPLEXES (LH2 IN PURPLE NON-SULPHUR PHOTOSYNTHETIC BACTERIA

    Directory of Open Access Journals (Sweden)

    Tatas H.P. Brotosudarmo

    2010-12-01

    Full Text Available Photosynthesis provides an example of a natural process that has been optimized during evolution to harness solar energy efficiently and safely, and finally to use it to produce a carbon-based fuel. Initially, solar energy is captured by the light harvesting pigment-protein complexes. In purple bacteria these antenna complexes are constructed on a rather simple modular basis. Light absorbed by these antenna complexes is funnelled downhill to reaction centres, where light drives a trans-membrane redox reaction. The light harvesting proteins not only provide the scaffolding that correctly positions the bacteriochlorophyll a and carotenoid pigments for optimal energy transfer but also creates an environment that can modulate the wavelength at which different bacteriochlorophyll molecules absorb light thereby creating the energy funnel. How these proteins can modulate the absorption spectra of the bacteriochlorophylls will be discussed in this review.

  20. The molecular second hyperpolarizability of the light-harvesting chlorophyll a/b pigment-protein complex of photosystem II.

    Science.gov (United States)

    Tokarz, Danielle; Cisek, Richard; Fekl, Ulrich; Barzda, Virginijus

    2013-09-26

    Photosynthetic structures when imaged with nonlinear optical microscopy give rise to high third harmonic generation (THG) signal intensity due to the presence of chlorophylls and xanthophylls which have large second hyperpolarizabilitiy (γ) values. The γ value of trimers of the light-harvesting chlorophyll a/b pigment-protein complex of photosystem II (LHCII) isolated from pea (Pisum sativum) plants was investigated by the THG ratio technique at 1028 nm wavelength and found to have the value (-1600 ± 400) × 10(-41) m(2) V(-2). The large negative γ value of trimeric LHCII is due to the presence of chlorophyll a and chlorophyll b which have large negative γ values, while positive γ values of xanthophylls reduce the magnitude of the THG signal. Variation was observed between the measured γ value of LHCII and the approximated γ value of LHCII obtained by adding individual γ values of chlorophylls and xanthophylls. This difference can be attributed to the differing inter-pigment interactions of oriented chlorophylls and xanthophylls in the pigment-protein complex compared to randomly oriented non-interacting pigments in solution, as well as a differing dielectric environment of the pigments within LHCII versus the surrounding organic solvent.

  1. J-aggregates of amphiphilic cyanine dyes: Self-organization of artificial light harvesting complexes

    Directory of Open Access Journals (Sweden)

    Stefan Kirstein

    2006-01-01

    Full Text Available The simultaneous chemical linkage of cyanine dye chromophores with both hydrophobic and hydrophilic substituents leads to a new type of amphiphilic molecules with the ability of spontaneous self-organization into highly ordered aggregates of various structures and morphologies. These aggregates carry the outstanding optical properties of J-aggregates, namely, efficient exciton coupling and fast exciton energy migration, which are essential for the build up of artificial light harvesting systems. The morphology of the aggregates depends sensitively on the molecular structure of the chemical substituents of the dye chromophore. Accordingly, lamellar ribbon-like structures, vesicles , tubes, and bundles of tubes are found depending on the dyes and the structure can further be altered by addition of surfactants, alcohols, or other additives. Altogether the tubular structure is the most noticeable structural motif of these types of J-aggregates. The optical spectra are characterized in general by a complex exciton spectrum which is composed of several electronic transitions. The spectrum is red-shifted as a total with respect to the monomer absorption and exhibits resonance fluorescence from the lowest energy transition. For the tubular structures, the optical spectra can be related to a structural model. Although the molecules itself are strictly achiral, a pronounced circular dichroism (CD is observed for the tubular aggregates and explained by unequal distribution of left- and right-handed helicity of the tubes. Photo-induced electron transfer (PET reactions from the dye aggregates to electron acceptor molecules lead to superquenching which proves the delocalization of the excitation. This property is used to synthesize metal nanoparticles on the aggregate surface by photo-induced reduction of metal ions.

  2. Energy Transfer among Chlorophylls in Trimeric Light-harvesting Complex Ⅱ of Bryopsis corticulans

    Institute of Scientific and Technical Information of China (English)

    Su-Juan ZHANG; Shui-Cai WANG; Jun-Fang HE; Hui CHEN

    2006-01-01

    A study on energy transfer among chlorophylls (Chls) in the trimeric unit of the major light-harvesting complex Ⅱ (LHC Ⅱ) from Bryopsis corriculan, was carried out using time-correlated single photon counting. In the chlorophyll Q region of LHC Ⅱ, six molecules characterized as Chlb628, Chlb646,Chlb654,657 652 , Chla666 664 , Chla677,680 674, and Chla683 682 were discriminated according to their absorption spectrum and fluorescence emission spectrum. Then, excited by pulsed light of 628 nm, fluorescence kinetics spectra in the chlorophyll Q region were measured. In accordance with the principles of fluorescence kinetics, these kinetics data were analyzed with a multi-exponential model. Time constants on energy transfer were obtained.An overwhelming percentage of energy transfer among chlorophylls undergoes a process longer than 97 picoseconds (ps), which shows that, before transferring energy to another Chl, the excited Chl might convert energy to vibrations of a lower state with different multiplicity (intersystem crossing). Energy transfer at the level of approximately 10 ps was also obtained, which was interpreted as the excited Chls may go through internal conversion before transferring energy to another Chl. Although with a higher standard deviation, time constants at the femtosecond level can not be entirely excluded, which can be attributed to the ultrafast process of direct energy transfer. Owing to the arrangement and direction of the dipole moment of Chls in LHC Ⅱ, the probability of these processes is different. The fluorescence lifetimes of Chlb652 654,657, Chla666 664,Chla674 677,680, and Chla683 682 were determined to be 1.44 ns, 1.43 ns, 636 ps and 713 ps, respectively. The percentages of energy dissipation in the pathway of fluorescence emission were no more than 40% in the trimeric unit of LHC Ⅱ. These results are important for a better understanding of the relationship between the structure and function of LHC Ⅱ.

  3. Subtle spectral effects accompanying the assembly of bacteriochlorophylls into cyclic light harvesting complexes revealed by high-resolution fluorescence spectroscopy

    Science.gov (United States)

    Rätsep, Margus; Pajusalu, Mihkel; Linnanto, Juha Matti; Freiberg, Arvi

    2014-10-01

    We have observed that an assembly of the bacteriochloropyll a molecules into B850 and B875 groups of cyclic bacterial light-harvesting complexes LH2 and LH1, respectively, results an almost total loss of the intra-molecular vibronic structure in the fluorescence spectrum, and simultaneously, an essential enhancement of its phonon sideband due to electron-phonon coupling. While the suppression of the vibronic coupling in delocalized (excitonic) molecular systems is predictable, as also confirmed by our model calculations, a boost of the electron-phonon coupling is rather unexpected. The latter phenomenon is explained by exciton self-trapping, promoted by mixing the molecular exciton states with charge transfer states between the adjacent chromophores in the tightly packed B850 and B875 arrangements. Similar, although less dramatic trends were noted for the light-harvesting complexes containing chlorophyll pigments.

  4. Subtle spectral effects accompanying the assembly of bacteriochlorophylls into cyclic light harvesting complexes revealed by high-resolution fluorescence spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Rätsep, Margus, E-mail: margus.ratsep@ut.ee; Pajusalu, Mihkel, E-mail: mihkel.pajusalu@ut.ee; Linnanto, Juha Matti, E-mail: juha.matti.linnanto@ut.ee [Institute of Physics, University of Tartu, Riia 142, 51014 Tartu (Estonia); Freiberg, Arvi, E-mail: arvi.freiberg@ut.ee [Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia and Institute of Molecular and Cell Biology, University of Tartu, Riia 23, 51010 Tartu (Estonia)

    2014-10-21

    We have observed that an assembly of the bacteriochloropyll a molecules into B850 and B875 groups of cyclic bacterial light-harvesting complexes LH2 and LH1, respectively, results an almost total loss of the intra-molecular vibronic structure in the fluorescence spectrum, and simultaneously, an essential enhancement of its phonon sideband due to electron-phonon coupling. While the suppression of the vibronic coupling in delocalized (excitonic) molecular systems is predictable, as also confirmed by our model calculations, a boost of the electron-phonon coupling is rather unexpected. The latter phenomenon is explained by exciton self-trapping, promoted by mixing the molecular exciton states with charge transfer states between the adjacent chromophores in the tightly packed B850 and B875 arrangements. Similar, although less dramatic trends were noted for the light-harvesting complexes containing chlorophyll pigments.

  5. Thermal Adaptability of the Light-Harvesting Complex 2 from Thermochromatium tepidum: Temperature-Dependent Excitation Transfer Dynamics.

    Science.gov (United States)

    Shi, Ying; Zhao, Ning-Jiu; Wang, Peng; Fu, Li-Min; Yu, Long-Jiang; Zhang, Jian-Ping; Wang-Otomo, Zheng-Yu

    2015-11-25

    The photosynthetic purple bacterium Thermochromatium (Tch.) tepidum is a thermophile that grows at an optimal temperature of ∼50 °C. We have investigated, by means of steady-state and time-resolved optical spectroscopies, the effects of temperature on the near-infrared light absorption and the excitation energy transfer (EET) dynamics of its light-harvesting complex 2 (LH2), for which the mesophilic counterpart of Rhodobacter (Rba.) sphaeroides 2.4.1 (∼30 °C) was examined in comparison. In a limited range around the physiological temperature (10-55 °C), the B800-to-B850 EET process of the Tch. tepidum LH2, but not the Rba. sphaeroides LH2, was found to be characteristically temperature-dependent, mainly because of a temperature-tunable spectral overlap. At 55 °C, the LH2 complex from Tch. tepidum maintained efficient near-infrared light harvesting and B800-to-B850 EET dynamics, whereas this EET process was disrupted in the case of Rba. sphaeroides 2.4.1 owing to the structural distortion of the LH2 complex. Our results reveal a remarkable thermal adaptability of the light-harvesting function of Tch. tepidum, which could enhance our understanding of the survival strategy of this thermophile in response to environmental challenges.

  6. Absence of the Lhcb1 and Lhcb2 proteins of the light-harvesting complex of photosystem II - effects on photosynthesis, grana stacking and fitness.

    Science.gov (United States)

    Andersson, Jenny; Wentworth, Mark; Walters, Robin G; Howard, Caroline A; Ruban, Alexander V; Horton, Peter; Jansson, Stefan

    2003-08-01

    We have constructed Arabidopsis thaliana plants that are virtually devoid of the major light-harvesting complex, LHC II. This was accomplished by introducing the Lhcb2.1 coding region in the antisense orientation into the genome by Agrobacterium-mediated transformation. Lhcb1 and Lhcb2 were absent, while Lhcb3, a protein present in LHC II associated with photosystem (PS) II, was retained. Plants had a pale green appearance and showed reduced chlorophyll content and an elevated chlorophyll a/b ratio. The content of PS II reaction centres was unchanged on a leaf area basis, but there was evidence for increases in the relative levels of other light harvesting proteins, notably CP26, associated with PS II, and Lhca4, associated with PS I. Electron microscopy showed the presence of grana. Photosynthetic rates at saturating irradiance were the same in wild-type and antisense plants, but there was a 10-15% reduction in quantum yield that reflected the decrease in light absorption by the leaf. The antisense plants were not able to perform state transitions, and their capacity for non-photochemical quenching was reduced. There was no difference in growth between wild-type and antisense plants under controlled climate conditions, but the antisense plants performed worse compared to the wild type in the field, with decreases in seed production of up to 70%.

  7. Direct evidence of quantum transport in photosynthetic light-harvesting complexes

    Science.gov (United States)

    Panitchayangkoon, Gitt; Voronine, Dmitri V.; Abramavicius, Darius; Caram, Justin R.; Lewis, Nicholas H. C.; Mukamel, Shaul; Engel, Gregory S.

    2011-01-01

    The photosynthetic light-harvesting apparatus moves energy from absorbed photons to the reaction center with remarkable quantum efficiency. Recently, long-lived quantum coherence has been proposed to influence efficiency and robustness of photosynthetic energy transfer in light-harvesting antennae. The quantum aspect of these dynamics has generated great interest both because of the possibility for efficient long-range energy transfer and because biology is typically considered to operate entirely in the classical regime. Yet, experiments to date show only that coherence persists long enough that it can influence dynamics, but they have not directly shown that coherence does influence energy transfer. Here, we provide experimental evidence that interaction between the bacteriochlorophyll chromophores and the protein environment surrounding them not only prolongs quantum coherence, but also spawns reversible, oscillatory energy transfer among excited states. Using two-dimensional electronic spectroscopy, we observe oscillatory excited-state populations demonstrating that quantum transport of energy occurs in biological systems. The observed population oscillation suggests that these light-harvesting antennae trade energy reversibly between the protein and the chromophores. Resolving design principles evident in this biological antenna could provide inspiration for new solar energy applications. PMID:22167798

  8. Direct evidence of quantum transport in photosynthetic light-harvesting complexes.

    Science.gov (United States)

    Panitchayangkoon, Gitt; Voronine, Dmitri V; Abramavicius, Darius; Caram, Justin R; Lewis, Nicholas H C; Mukamel, Shaul; Engel, Gregory S

    2011-12-27

    The photosynthetic light-harvesting apparatus moves energy from absorbed photons to the reaction center with remarkable quantum efficiency. Recently, long-lived quantum coherence has been proposed to influence efficiency and robustness of photosynthetic energy transfer in light-harvesting antennae. The quantum aspect of these dynamics has generated great interest both because of the possibility for efficient long-range energy transfer and because biology is typically considered to operate entirely in the classical regime. Yet, experiments to date show only that coherence persists long enough that it can influence dynamics, but they have not directly shown that coherence does influence energy transfer. Here, we provide experimental evidence that interaction between the bacteriochlorophyll chromophores and the protein environment surrounding them not only prolongs quantum coherence, but also spawns reversible, oscillatory energy transfer among excited states. Using two-dimensional electronic spectroscopy, we observe oscillatory excited-state populations demonstrating that quantum transport of energy occurs in biological systems. The observed population oscillation suggests that these light-harvesting antennae trade energy reversibly between the protein and the chromophores. Resolving design principles evident in this biological antenna could provide inspiration for new solar energy applications.

  9. Two-dimensional self-organization of the light-harvesting polypeptides/BChl a complex into a thermostable liposomal membrane

    NARCIS (Netherlands)

    Iida, K; Kiriyama, H; Fukai, A; Konings, WN; Nango, M

    2001-01-01

    The detergent-isolated light-harvesting polypeptide (LR)/bacteriochlorophyll alpha (BChl alpha) complex from the photosynthetic bacterium Rhodospirillum rubrum was organized in thermostable liposomal membranes comprising membrane-spanning tetraether lipids from Sulfolobus acidocaldarius to develop a

  10. The study of photo-induced ultrafast dynamics in light-harvesting complex LH2 of purple bacteria

    Institute of Scientific and Technical Information of China (English)

    LIU Wei-min; YAN Yong-li; LIU Kang-jun; XU Chun-he; QIAN Shi-xiong

    2006-01-01

    In this paper,we introduce the photo-induced ultrafast dynamics taking place in the peripheral light harvesting antenna LH2 from purple bacteria Rhodobacter sphaeroides by using absorption,fluorescence emission and ultrafast spectroscopic techniques.Three kinds of LH2 sampies,pH treated LH2 (complete removal of B800 pigments),carotenoid mutated LH2 (GM 309) and electrochemical oxidation treated LH2 were used in comparison with native LH2 to investigate the mechanism of photo-induced ultrafast energy transfer within the LH2 complex.

  11. Purification and characterization of the B808-866 light-harvesting complex from green filamentous bacterium Chloroflexus aurantiacus.

    Science.gov (United States)

    Xin, Yueyong; Lin, Su; Montaño, Gabriel A; Blankenship, Robert E

    2005-11-01

    The integral membrane light-harvesting complex B808-866 from the thermophilic green filamentous bacterium Chloroflexus aurantiacus has been isolated and characterized. Reversed-phase HPLC analysis demonstrated that the number of bacteriochlorophyll (BChl) in the B808-866 antenna complex is 36 +/- 2 per reaction center. The main carotenoid type is gamma-carotene, and the molar ratio of BChl to carotenoid is 3:2. The steady-state absorption and fluorescence spectroscopy of the B808-866 complex are reminiscent of the well-studied LH2 peripheral antenna of purple bacteria, whereas the protein sequence and the circular dichroism spectrum of B808-866 is more similar to the LH1 inner core antenna. The efficiency of excitation transfer from carotenoid to BChl is about 25%. The above results combined with electron microscopy and dynamic light scattering analysis suggest that the B808-866 antenna is more like the LH1, whereas surrounds the reaction center but probably consists of 24 building blocks with a ring diameter of about 20 nm. The above results suggested that there are probably two reaction centers inside the ring of B808-866. The unique properties of this light-harvesting complex may provide insights on the protein-pigment interactions in bacterial photosynthesis.

  12. Modeling of optical spectra of the light-harvesting CP29 antenna complex of photosystem II--part II.

    Science.gov (United States)

    Feng, Ximao; Kell, Adam; Pieper, Jörg; Jankowiak, Ryszard

    2013-06-01

    Until recently, it was believed that the CP29 protein from higher plant photosystem II (PSII) contains 8 chlorophylls (Chl's) per complex (Ahn et al. Science 2008, 320, 794-797; Bassi et al. Proc. Natl. Acad. Sci. U.S.A. 1999, 96, 10056-10061) in contrast to the 13 Chl's revealed by the recent X-ray structure (Pan et al. Nat. Struct. Mol. Biol. 2011, 18, 309-315). This disagreement presents a constraint on the interpretation of the underlying electronic structure of this complex. To shed more light on the interpretation of various experimental optical spectra discussed in the accompanying paper (part I, DOI 10.1021/jp4004328 ), we report here calculated low-temperature (5 K) absorption, fluorescence, hole-burned (HB), and 300 K circular dichroism (CD) spectra for CP29 complexes with a different number of pigments. We focus on excitonic structure and the nature of the low-energy state using modeling based on the X-ray structure of CP29 and Redfield theory. We show that the lowest energy state is mostly contributed to by a612, a611, and a615 Chl's. We suggest that in the previously studied CP29 complexes from spinach (Pieper et al. Photochem. Photobiol.2000, 71, 574-589) two Chl's could have been lost during the preparation/purification procedure, but it is unlikely that the spinach CP29 protein contains only eight Chl's, as suggested by the sequence homology-based study (Bassi et al. Proc. Natl. Acad. Sci. U.S.A.1999, 96, 10056-10061). The likely Chl's missing in wild-type (WT) CP29 complexes studied previously (Pieper et al. Photochem. Photobiol. 2000, 71, 574-589) include a615 and b607. This is why the nonresonant HB spectra shown in that reference were ~1 nm blue-shifted with the low-energy state mostly localized on about one Chl a (i.e., a612) molecule. Pigment composition of CP29 is discussed in the context of light-harvesting and excitation energy transfer.

  13. Two photon absorption energy transfer in the light-harvesting complex of photosystem II (LHC-II) modified with organic boron dye.

    Science.gov (United States)

    Chen, Li; Liu, Cheng; Hu, Rui; Feng, Jiao; Wang, Shuangqing; Li, Shayu; Yang, Chunhong; Yang, Guoqiang

    2014-07-15

    The plant light-harvesting complexes of photosystem II (LHC-II) play important roles in collecting solar energy and transferring the energy to the reaction centers of photosystems I and II. A two photon absorption compound, 4-(bromomethyl)-N-(4-(dimesitylboryl)phenyl)-N-phenylaniline (DMDP-CH2Br), was synthesized and covalently linked to the LHC-II in formation of a LHC-II-dye complex, which still maintained the biological activity of LHC-II system. Under irradiation with femtosecond laser pulses at 754 nm, the LHC-II-dye complex can absorb two photons of the laser light effectively compared with the wild type LHC-II. The absorbed excitation energy is then transferred to chlorophyll a with an obvious fluorescence enhancement. The results may be interesting and give potentials for developing hybrid photosystems.

  14. Synergistic Two-Photon Absorption Enhancement in Photosynthetic Light Harvesting

    Science.gov (United States)

    Chen, Kuo-Mei; Chen, Yu-Wei; Gao, Ting-Fong

    2012-06-01

    The grand scale fixation of solar energies into chemical substances by photosynthetic reactions of light-harvesting organisms provides Earth's other life forms a thriving environment. Scientific explorations in the past decades have unraveled the fundamental photophysical and photochemical processes in photosynthesis. Higher plants, green algae, and light-harvesting bacteria utilize organized pigment-protein complexes to harvest solar power efficiently and the resultant electronic excitations are funneled into a reaction center, where the first charge separation process takes place. Here we show experimental evidences that green algae (Chlorella vulgaris) in vivo display a synergistic two-photon absorption enhancement in their photosynthetic light harvesting. Their absorption coefficients at various wavelengths display dramatic dependence on the photon flux. This newly found phenomenon is attributed to a coherence-electronic-energy-transfer-mediated (CEETRAM) photon absorption process of light-harvesting pigment-protein complexes of green algae. Under the ambient light level, algae and higher plants can utilize this quantum mechanical mechanism to create two entangled electronic excitations adjacently in their light-harvesting networks. Concerted multiple electron transfer reactions in the reaction centers and oxygen evolving complexes can be implemented efficiently by the coherent motion of two entangled excitons from antennae to the charge separation reaction sites. To fabricate nanostructured, synthetic light-harvesting apparatus, the paramount role of the CEETRAM photon absorption mechanism should be seriously considered in the strategic guidelines.

  15. Light-harvesting complex II (LHCII) and its supramolecular organization in Chlamydomonas reinhardtii.

    Science.gov (United States)

    Drop, Bartlomiej; Webber-Birungi, Mariam; Yadav, Sathish K N; Filipowicz-Szymanska, Alicja; Fusetti, Fabrizia; Boekema, Egbert J; Croce, Roberta

    2014-01-01

    LHCII is the most abundant membrane protein on earth. It participates in the first steps of photosynthesis by harvesting sunlight and transferring excitation energy to the core complex. Here we have analyzed the LHCII complex of the green alga Chlamydomonas reinhardtii and its association with the core of Photosystem II (PSII) to form multiprotein complexes. Several PSII supercomplexes with different antenna sizes have been purified, the largest of which contains three LHCII trimers (named S, M and N) per monomeric core. A projection map at a 13Å resolution was obtained allowing the reconstruction of the 3D structure of the supercomplex. The position and orientation of the S trimer are the same as in plants; trimer M is rotated by 45° and the additional trimer (named here as LHCII-N), which is taking the position occupied in plants by CP24, is directly associated with the core. The analysis of supercomplexes with different antenna sizes suggests that LhcbM1, LhcbM2/7 and LhcbM3 are the major components of the trimers in the PSII supercomplex, while LhcbM5 is part of the "extra" LHCII pool not directly associated with the supercomplex. It is also shown that Chlamydomonas LHCII has a slightly lower Chlorophyll a/b ratio than the complex from plants and a blue shifted absorption spectrum. Finally the data indicate that there are at least six LHCII trimers per dimeric core in the thylakoid membranes, meaning that the antenna size of PSII of C. reinhardtii is larger than that of plants.

  16. Optimal and robust energy transport in light-harvesting complexes: (II) A quantum interplay of multichromophoric geometries and environmental interactions

    CERN Document Server

    Mohseni, Masoud; Lloyd, Seth; Rabitz, Herschel

    2011-01-01

    Today, the physical principles for the high efficiency of excitation energy transfer in light-harvesting complexes are still not fully understood. Notably, the degree of robustness of these systems for transporting energy is not known considering their realistic interactions with vibrational and radiative environments within the surrounding solvent and scaffold proteins. In this work, we employ an efficient technique to simulate ultrafast quantum dynamics of such complex excitonic systems in their non-equilibrium environment in the non-perturbative and non-Markovian regimes. We demonstrate that the natural dynamics of the FMO complex leads to optimum and stable energy transport due to a convergence of energy/time scales among important internal and external parameters. In particular, we show that the FMO energy transfer efficiency is optimal and robust with respect to all the relevant parameters of environmental interactions and Frenkel-exciton Hamiltonian including reorganization energy \\lambda, bath frequen...

  17. Singlet-triplet fission of carotenoid excitation in light-harvesting LH2 complexes of purple phototrophic bacteria.

    Science.gov (United States)

    Klenina, I B; Makhneva, Z K; Moskalenko, A A; Gudkov, N D; Bolshakov, M A; Pavlova, E A; Proskuryakov, I I

    2014-03-01

    The current generally accepted structure of light-harvesting LH2 complexes from purple phototrophic bacteria conflicts with the observation of singlet-triplet carotenoid excitation fission in these complexes. In LH2 complexes from the purple bacterium Allochromatium minutissimum, a drop in the efficiency of carotenoid triplet generation is demonstrated, which correlates with the extent of selective photooxidation of bacteriochlorophylls absorbing at ~850 nm. We conclude that singlet-triplet fission of carotenoid excitation proceeds with participation of these excitonically coupled bacteriochlorophylls. In the framework of the proposed mechanism, the contradiction between LH2 structure and photophysical properties of carotenoids is eliminated. The possibility of singlet-triplet excitation fission involving a third mediator molecule was not considered earlier.

  18. Impact of Electronic Fluctuations and Their Description on the Exciton Dynamics in the Light-Harvesting Complex PE545.

    Science.gov (United States)

    Aghtar, Mortaza; Kleinekathöfer, Ulrich; Curutchet, Carles; Mennucci, Benedetta

    2017-02-16

    Temperature-dependent fluctuations of both site energies and electronic couplings are known to affect the excitation energy transfer in light-harvesting complexes. Environment effects on such fluctuations as well as possible spatial correlations among them are investigated here in the PE545 complex from cryptophyte algae using ensemble-averaged wave packet dynamics to extract the exciton dynamics. This strategy directly uses the time-dependent fluctuations of the system Hamiltonian, as described by quantum mechanics/molecular mechanics calculations performed along a classical MD trajectory. Neither the fluctuations in the couplings nor spatial correlations including cross-correlations between site energies and couplings are found to be important in the exciton dynamics of the complex. This finding does not change if a polarizable embedding is used instead of its electrostatic counterpart. The impact of variations in spectral densities and screening of excitonic couplings based on the electrostatic and polarizable embeddings are discussed as well.

  19. Excitonic energy transfer in light-harvesting complexes in purple bacteria

    CERN Document Server

    Ye, Jun; Zhao, Yang; Yu, Yunjin; Lee, Chee Kong; Cao, Jianshu

    2012-01-01

    Two distinct approaches, the Frenkel-Dirac time-dependent variation and the Haken-Strobl model, are adopted to study energy transfer dynamics in single-ring and double-ring light-harvesting systems in purple bacteria. It is found that inclusion of long-range dipolar interactions in the two methods results in significant increases in intra- or inter-ring exciton transfer efficiency. The dependence of exciton transfer efficiency on trapping positions on single rings of LH2 (B850) and LH1 is similar to that in toy models with nearest-neighbor coupling only. However, owing to the symmetry breaking caused by the dimerization of BChls and dipolar couplings, such dependence has been largely suppressed. In the studies of coupled-ring systems, both methods reveal interesting role of dipolar interaction in increasing energy transfer efficiency by introducing multiple intra/inter-ring transfer paths. Importantly, the time scale (~4ps) of inter-ring exciton transfer obtained from polaron dynamics is in good agreement wit...

  20. Unified analysis of ensemble and single-complex optical spectral data from light-harvesting complex-2 chromoproteins for gaining deeper insight into bacterial photosynthesis

    Science.gov (United States)

    Pajusalu, Mihkel; Kunz, Ralf; Rätsep, Margus; Timpmann, Kõu; Köhler, Jürgen; Freiberg, Arvi

    2015-11-01

    Bacterial light-harvesting pigment-protein complexes are very efficient at converting photons into excitons and transferring them to reaction centers, where the energy is stored in a chemical form. Optical properties of the complexes are known to change significantly in time and also vary from one complex to another; therefore, a detailed understanding of the variations on the level of single complexes and how they accumulate into effects that can be seen on the macroscopic scale is required. While experimental and theoretical methods exist to study the spectral properties of light-harvesting complexes on both individual complex and bulk ensemble levels, they have been developed largely independently of each other. To fill this gap, we simultaneously analyze experimental low-temperature single-complex and bulk ensemble optical spectra of the light-harvesting complex-2 (LH2) chromoproteins from the photosynthetic bacterium Rhodopseudomonas acidophila in order to find a unique theoretical model consistent with both experimental situations. The model, which satisfies most of the observations, combines strong exciton-phonon coupling with significant disorder, characteristic of the proteins. We establish a detailed disorder model that, in addition to containing a C2-symmetrical modulation of the site energies, distinguishes between static intercomplex and slow conformational intracomplex disorders. The model evaluations also verify that, despite best efforts, the single-LH2-complex measurements performed so far may be biased toward complexes with higher Huang-Rhys factors.

  1. Synthesis, characterization and light harvesting properties of Sb(III) and Bi(III) ferrocenyl dithiocarbamate complexes.

    Science.gov (United States)

    Chauhan, Ratna; Trivedi, Manoj; Yadav, Reena; Kumar, Abhinav; Amalnerkar, Dinesh P; Gosavi, Suresh W

    2015-11-05

    New Sb(III) and Bi(III) ferrocenyl dithiocarbamate complexes viz. [Sb(FcCH2Bzdtc)3] (Sb) and [Bi(FcCH2Bzdtc)3] (Bi) (Fc=C5H5FeC5H4-; Bz=C6H5CH2-) have been synthesized and characterized by elemental analyses, IR, (1)H and (13)C NMR spectroscopies. The optical, electrochemical and photovoltaic properties of the synthesized complexes were investigated. The light harvesting properties of both of the compounds have been studied using these compounds as photosensitizers in TiO2-based DSSCs. The photovoltaic devices fabricated by Sb and Bi showed a maximum current conversion efficiency of 1.51% and 0.97%, respectively under 1.5 AM illumination (100 mW cm(-2)) and having incident photon to current efficiency (IPCE) of 38% and 31%, respectively. The reason for the higher efficiency of Sb is due its higher dye loading.

  2. Ultrafast time-resolved spectroscopy of the light-harvesting complex 2 (LH2) from the photosynthetic bacterium Thermochromatium tepidum

    Energy Technology Data Exchange (ETDEWEB)

    Niedzwiedzki, Dariusz; Fuciman, Marcel; Kobayashi, Masayuki; Frank, Harry A; Blankenship, R. E.

    2011-10-08

    The light-harvesting complex 2 from the thermophilic purple bacterium Thermochromatium tepidum was purified and studied by steady-state absorption and fluorescence, sub-nanosecond-time-resolved fluorescence and femtosecond time-resolved transient absorption spectroscopy. The measurements were performed at room temperature and at 10 K. The combination of both ultrafast and steady-state optical spectroscopy methods at ambient and cryogenic temperatures allowed the detailed study of carotenoid (Car)-to-bacteriochlorophyll (BChl) as well BChl-to-BChl excitation energy transfer in the complex. The studies show that the dominant Cars rhodopin (N = 11) and spirilloxanthin (N = 13) do not play a significant role as supportive energy donors for BChl a. This is related with their photophysical properties regulated by long π-electron conjugation. On the other hand, such properties favor some of the Cars, particularly spirilloxanthin (N = 13) to play the role of the direct quencher of the excited singlet state of BChl.

  3. The low molecular weight protein PsaI stabilizes the light-harvesting complex II docking site of photosystem I

    DEFF Research Database (Denmark)

    Plöchinger, Magdalena; Torabi, Salar; Rantala, Marjaana

    2016-01-01

    I destabilizes the association of PsaL and PsaH to PSI, both forming the light-harvesting complex (LHC)II docking site of PSI. These alterations at the LHCII binding site surprisingly did not prevent state transition but led to an increased incidence of PSI-LHCII complexes, coinciding with an elevated...... phosphorylation level of the LHCII under normal growth light conditions. Remarkably, LHCII was rapidly phosphorylated in ΔpsaI in darkness even after illumination with far-red light. We found that this dark phosphorylation also occurs in previously described mutants impaired in PSI function or state transition....... A prompt shift of the plastoquinone (PQ) pool into a more reduced redox state in the dark caused an enhanced LHCII phosphorylation in ΔpsaI Since the redox status of the PQ pool is functionally connected to a series of physiological, biochemical, and gene expression reactions, we propose that the shift...

  4. Minimal Model of Quantum Kinetic Clusters for the Energy-Transfer Network of a Light-Harvesting Protein Complex.

    Science.gov (United States)

    Wu, Jianlan; Tang, Zhoufei; Gong, Zhihao; Cao, Jianshu; Mukamel, Shaul

    2015-04-02

    The energy absorbed in a light-harvesting protein complex is often transferred collectively through aggregated chromophore clusters. For population evolution of chromophores, the time-integrated effective rate matrix allows us to construct quantum kinetic clusters quantitatively and determine the reduced cluster-cluster transfer rates systematically, thus defining a minimal model of energy-transfer kinetics. For Fenna-Matthews-Olson (FMO) and light-havrvesting complex II (LCHII) monomers, quantum Markovian kinetics of clusters can accurately reproduce the overall energy-transfer process in the long-time scale. The dominant energy-transfer pathways are identified in the picture of aggregated clusters. The chromophores distributed extensively in various clusters can assist a fast and long-range energy transfer.

  5. Light-harvesting features revealed by the structure of plant Photosystem I

    CERN Document Server

    Ben-Shem, A; Nelson, N; 10.1023/B:PRES.0000036881.23512.42

    2004-01-01

    Oxygenic photosynthesis is driven by two multi-subunit membrane protein complexes, Photosystem I and Photosystem II. In plants and green algae, both complexes are composed of two moieties: a reaction center (RC), where light-induced charge translocation occurs, and a peripheral antenna that absorbs light and funnels its energy to the reaction center. The peripheral antenna of PS I (LHC I) is composed of four gene products (Lhca 1-4) that are unique among the chlorophyll a/b binding proteins in their pronounced long-wavelength absorbance and in their assembly into dimers. The recently determined structure of plant Photosystem I provides the first relatively high- resolution structural model of a super-complex containing a reaction center and its peripheral antenna. We describe some of the structural features responsible for the unique properties of LHC I and discuss the advantages of the particular LHC I dimerization mode over monomeric or trimeric forms. In addition, we delineate some of the interactions betw...

  6. Excitonic energy transfer in light-harvesting complexes in purple bacteria

    Energy Technology Data Exchange (ETDEWEB)

    Ye Jun; Sun Kewei; Zhao Yang; Lee, Chee Kong [School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Yu Yunjin [School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798 (Singapore); College of Physics Science and Technology, Shenzhen University, Guangdong 518060 (China); Cao Jianshu [Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

    2012-06-28

    Two distinct approaches, the Frenkel-Dirac time-dependent variation and the Haken-Strobl model, are adopted to study energy transfer dynamics in single-ring and double-ring light-harvesting (LH) systems in purple bacteria. It is found that the inclusion of long-range dipolar interactions in the two methods results in significant increase in intra- or inter-ring exciton transfer efficiency. The dependence of exciton transfer efficiency on trapping positions on single rings of LH2 (B850) and LH1 is similar to that in toy models with nearest-neighbor coupling only. However, owing to the symmetry breaking caused by the dimerization of BChls and dipolar couplings, such dependence has been largely suppressed. In the studies of coupled-ring systems, both methods reveal an interesting role of dipolar interactions in increasing energy transfer efficiency by introducing multiple intra/inter-ring transfer paths. Importantly, the time scale (4 ps) of inter-ring exciton transfer obtained from polaron dynamics is in good agreement with previous studies. In a double-ring LH2 system, non-nearest neighbor interactions can induce symmetry breaking, which leads to global and local minima of the average trapping time in the presence of a non-zero dephasing rate, suggesting that environment dephasing helps preserve quantum coherent energy transfer when the perfect circular symmetry in the hypothetic system is broken. This study reveals that dipolar coupling between chromophores may play an important role in the high energy transfer efficiency in the LH systems of purple bacteria and many other natural photosynthetic systems.

  7. Efficient light-harvesting using non-carbonyl carotenoids: Energy transfer dynamics in the VCP complex from Nannochloropsis oceanica.

    Science.gov (United States)

    Keşan, Gürkan; Litvín, Radek; Bína, David; Durchan, Milan; Šlouf, Václav; Polívka, Tomáš

    2016-04-01

    Violaxanthin-chlorophyll a protein (VCP) from Nannochloropsis oceanica is a Chl a-only member of the LHC family of light-harvesting proteins. VCP binds carotenoids violaxanthin (Vio), vaucheriaxanthin (Vau), and vaucheriaxanthin-ester (Vau-ester). Here we report on energy transfer pathways in the VCP complex. The overall carotenoid-to-Chla energy transfer has efficiency over 90%. Based on their energy transfer properties, the carotenoids in VCP can be divided into two groups; blue carotenoids with the lowest energy absorption band around 480nm and red carotenoids with absorption extended up to 530nm. Both carotenoid groups transfer energy efficiently from their S2 states, reaching efficiencies of ~70% (blue) and ~60% (red). The S1 pathway, however, is efficient only for the red carotenoid pool for which two S1 routes characterized by 0.33 and 2.4ps time constants were identified. For the blue carotenoids the S1-mediated pathway is represented only by a minor route likely involving a hot S1 state. The relaxed S1 state of blue carotenoids decays to the ground state within 21ps. Presence of a fraction of non-transferring red carotenoids with the S1 lifetime of 13ps indicates some specific carotenoid-protein interaction that must shorten the intrinsic S1 lifetime of Vio and/or Vau whose S1 lifetimes in methanol are 26 and 29ps, respectively. The VCP complex from N. oceanica is the first example of a light-harvesting complex binding only non-carbonyl carotenoids with carotenoid-to-chlorophyll energy transfer efficiency over 90%.

  8. Femtosecond pump probe spectroscopy for the study of energy transfer of light-harvesting complexes from extractions of spinach leaves

    Directory of Open Access Journals (Sweden)

    L. van Rensburg

    2010-01-01

    Full Text Available Measurements of ultrafast transient processes, of temporal durations in the picosecond and femtosecond regime, are made possible by femtosecond pump probe transient absorption spectroscopy. Such an ultrafast pump probe transient absorption setup has been implemented at the CSIR National Laser Centre and has been applied to investigate energy transfer processes in different parts of photosynthetic systems. In this paper we report on our first results obtained with Malachite green as a benchmark. Malachite green was chosen because the lifetime of its excited state is well known. We also present experimental results of the ultrafast energy transfer of light-harvesting complexes in samples prepared from spinach leaves. Various pump wavelengths in the range 600–680 nm were used; the probe was a white light continuum spanning 420–700 nm. The experimental setup is described in detail in this paper. Results obtained with these samples are consistent with those expected and achieved by other researchers in this field.

  9. Effects of excited state mixing on transient absorption spectra in dimers Application to photosynthetic light-harvesting complex II

    CERN Document Server

    Valkunas, L; Trinkunas, G; Müller, M G; Holzwarth, A R

    1999-01-01

    The excited state mixing effect is taken into account considering the difference spectra of dimers. Both the degenerate (homo) dimer as well as the nondegenerate (hetero) dimer are considered. Due to the higher excited state mixing with the two-exciton states in the homodimer, the excited state absorption (or the difference spectrum) can be strongly affected in comparison with the results obtained in the Heitler-London approximation. The difference spectrum of the heterodimer is influenced by two resonance effects (i) mixing of the ground state optical transitions of both monomers in the dimer and (ii) mixing of the excited state absorption of the excited monomer with the ground state optical transition in the nonexcited monomer. These effects have been tested by simulating the difference absorption spectra of the light-harvesting complex of photosystem II (LHC II) experimentally obtained with the 60 fs excitation pulses at zero delay times and various excitation wavelengths. The pairs of coupled chlorophylls...

  10. Insights into the photoprotective switch of the major light-harvesting complex II (LHCII): a preserved core of arginine-glutamate interlocked helices complemented by adjustable loops.

    Science.gov (United States)

    Sunku, Kiran; de Groot, Huub J M; Pandit, Anjali

    2013-07-05

    Light-harvesting antennae of the LHC family form transmembrane three-helix bundles of which two helices are interlocked by conserved arginine-glutamate (Arg-Glu) ion pairs that form ligation sites for chlorophylls. The antenna proteins of photosystem II have an intriguing dual function. In excess light, they can switch their conformation from a light-harvesting into a photoprotective state, in which the excess and harmful excitation energies are safely dissipated as heat. Here we applied magic angle spinning NMR and selective Arg isotope enrichment as a noninvasive method to analyze the Arg structures of the major light-harvesting complex II (LHCII). The conformations of the Arg residues that interlock helix A and B appear to be preserved in the light-harvesting and photoprotective state. Several Arg residues have very downfield-shifted proton NMR responses, indicating that they stabilize the complex by strong hydrogen bonds. For the Arg Cα chemical shifts, differences are observed between LHCII in the active, light-harvesting and in the photoprotective, quenched state. These differences are attributed to a conformational change of the Arg residue in the stromal loop region. We conclude that the interlocked helices of LHCII form a rigid core. Consequently, the LHCII conformational switch does not involve changes in A/B helix tilting but likely involves rearrangements of the loops and helical segments close to the stromal and lumenal ends.

  11. Induction of efficient energy dissipation in the isolated light-harvesting complex of Photosystem II in the absence of protein aggregation.

    Science.gov (United States)

    Ilioaia, Cristian; Johnson, Matthew P; Horton, Peter; Ruban, Alexander V

    2008-10-24

    Under excess illumination, the Photosystem II light-harvesting antenna of higher plants has the ability to switch into an efficient photoprotective mode, allowing safe dissipation of excitation energy into heat. In this study, we show induction of the energy dissipation state, monitored by chlorophyll fluorescence quenching, in the isolated major light-harvesting complex (LHCII) incorporated into a solid gel system. Removal of detergent caused strong fluorescence quenching, which was totally reversible. Singlet-singlet annihilation and gel electrophoresis experiments suggested that the quenched complexes were in the trimeric not aggregated state. Both the formation and recovery of this quenching state were inhibited by a cross-linker, implying involvement of conformational changes. Absorption and CD measurements performed on the samples in the quenched state revealed specific alterations in the spectral bands assigned to the red forms of chlorophyll a, neoxanthin, and lutein 1 molecules. The majority of these alterations were similar to those observed during LHCII aggregation. This suggests that not the aggregation process as such but rather an intrinsic conformational transition in the complex is responsible for establishment of quenching. 77 K fluorescence measurements showed red-shifted chlorophyll a fluorescence in the 690-705 nm region, previously observed in aggregated LHCII. The fact that all spectral changes associated with the dissipative mode observed in the gel were different from those of the partially denatured complex strongly argues against the involvement of protein denaturation in the observed quenching. The implications of these findings for proposed mechanisms of energy dissipation in the Photosystem II antenna are discussed.

  12. Light-harvesting complex 1 stabilizes P+QB- charge separation in reaction centers of Rhodobacter sphaeroides.

    Science.gov (United States)

    Francia, Francesco; Dezi, Manuela; Rebecchi, Alberto; Mallardi, Antonia; Palazzo, Gerardo; Melandri, Bruno Andrea; Venturoli, Giovanni

    2004-11-09

    The kinetics of charge recombination following photoexcitation by a laser pulse have been analyzed in the reaction center-light harvesting complex 1 (RC-LH1) purified from the photosynthetic bacterium Rhodobacter sphaeroides. In RC-LH1 core complexes isolated from photosynthetically grown cells P(+)Q(B)(-) recombines with an average rate constant, k approximately 0.3 s(-1), more than three times smaller than that measured in RC deprived of the LH1 (k approximately 1 s(-1)). A comparable, slowed recombination kinetics is observed in RC-LH1 complexes purified from a pufX-deleted strain. Slowing of the charge recombination kinetics is even more pronounced in RC-LH1 complexes isolated from wild-type semiaerobically grown cells (k approximately 0.2 s(-1)). Since the kinetics of P(+)Q(A)(-) recombination is unaffected by the presence of the antenna, the P(+)Q(B)(-) state appears to be energetically stabilized in core complexes. Determinations of the ubiquinone-10 (UQ(10)) complement associated with the purified RC-LH1 complexes always yield UQ(10)/RC ratios larger than 10. These quinone molecules are functionally coupled to the RC-LH1 complex, as judged from the extent of exogenous cytochrome c(2) rapidly oxidized under continuous light excitation. Analysis of P(+)Q(B)(-) recombination, based on a kinetic model which considers fast quinone equilibrium at the Q(B) binding site, indicates that the slowing down of charge recombination kinetics observed in RC-LH1 complexes cannot be explained solely by a quinone concentration effect and suggests that stabilization of the light-induced charge separation is predominantly due to interaction of the Q(B) site with the LH1 complex. The high UQ(10) complements detected in RC-LH1 core complexes, but not in purified light-harvesting complex 2 and in RC, are proposed to reflect an in vivo heterogeneity in the distribution of the quinone pool within the chromatophore bilayer.

  13. The role of energy losses in photosynthetic light harvesting

    Science.gov (United States)

    Krüger, T. P. J.; van Grondelle, R.

    2017-07-01

    Photosynthesis operates at the bottom of the food chain to convert the energy of light into carbohydrates at a remarkable global rate of about 130 TW. Nonetheless, the overall photosynthetic process has a conversion efficiency of a few percent at best, significantly less than bottom-up photovoltaic cells. The primary photosynthetic steps, consisting of light harvesting and charge separation, are often presented as having near-unity quantum efficiency but this holds only true under ideal conditions. In this review, we discuss the importance of energy loss mechanisms to establish robustness in photosynthetic light harvesting. Thermal energy dissipation of light-harvesting complexes (LHCs) in different environments is investigated and the relationships and contrasts between concentration quenching of high pigment concentrations, photoprotection (non-photochemical quenching), quenching due to protein aggregation, and fluorescence blinking are discussed. The role of charge-transfer states in light harvesting and energy dissipation is highlighted and the importance of controlled protein structural disorder to switch the light-harvesting antennae between effective light harvesters and efficient energy quenchers is underscored. The main LHC of plants, LHCII, is used as a prime example.

  14. Tracking energy transfer between light harvesting complex 2 and 1 in photosynthetic membranes grown under high and low illumination.

    Science.gov (United States)

    Lüer, Larry; Moulisová, Vladimíra; Henry, Sarah; Polli, Dario; Brotosudarmo, Tatas H P; Hoseinkhani, Sajjad; Brida, Daniele; Lanzani, Guglielmo; Cerullo, Giulio; Cogdell, Richard J

    2012-01-31

    Energy transfer (ET) between B850 and B875 molecules in light harvesting complexes LH2 and LH1/RC (reaction center) complexes has been investigated in membranes of Rhodopseudomonas palustris grown under high- and low-light conditions. In these bacteria, illumination intensity during growth strongly affects the type of LH2 complexes synthesized, their optical spectra, and their amount of energetic disorder. We used a specially built femtosecond spectrometer, combining tunable narrowband pump with broadband white-light probe pulses, together with an analytical method based on derivative spectroscopy for disentangling the congested transient absorption spectra of LH1 and LH2 complexes. This procedure allows real-time tracking of the forward (LH2 → LH1) and backward (LH2←LH1) ET processes and unambiguous determination of the corresponding rate constants. In low-light grown samples, we measured lower ET rates in both directions with respect to high-light ones, which is explained by reduced spectral overlap between B850 and B875 due to partial redistribution of oscillator strength into a higher energetic exciton transition. We find that the low-light adaptation in R. palustris leads to a reduced elementary backward ET rate, in accordance with the low probability of two simultaneous excitations reaching the same LH1/RC complex under weak illumination. Our study suggests that backward ET is not just an inevitable consequence of vectorial ET with small energetic offsets, but is in fact actively managed by photosynthetic bacteria.

  15. Spectral heterogeneity and carotenoid-to-bacteriochlorophyll energy transfer in LH2 light-harvesting complexes from Allochromatium vinosum.

    Science.gov (United States)

    Magdaong, Nikki M; LaFountain, Amy M; Hacking, Kirsty; Niedzwiedzki, Dariusz M; Gibson, George N; Cogdell, Richard J; Frank, Harry A

    2016-02-01

    Photosynthetic organisms produce a vast array of spectral forms of antenna pigment-protein complexes to harvest solar energy and also to adapt to growth under the variable environmental conditions of light intensity, temperature, and nutrient availability. This behavior is exemplified by Allochromatium (Alc.) vinosum, a photosynthetic purple sulfur bacterium that produces different types of LH2 light-harvesting complexes in response to variations in growth conditions. In the present work, three different spectral forms of LH2 from Alc. vinosum, B800-820, B800-840, and B800-850, were isolated, purified, and examined using steady-state absorption and fluorescence spectroscopy, and ultrafast time-resolved absorption spectroscopy. The pigment composition of the LH2 complexes was analyzed by high-performance liquid chromatography, and all were found to contain five carotenoids: lycopene, anhydrorhodovibrin, spirilloxanthin, rhodopin, and rhodovibrin. Spectral reconstructions of the absorption and fluorescence excitation spectra based on the pigment composition revealed significantly more spectral heterogeneity in these systems compared to LH2 complexes isolated from other species of purple bacteria. The data also revealed the individual carotenoid-to-bacteriochlorophyll energy transfer efficiencies which were correlated with the kinetic data from the ultrafast transient absorption spectroscopic experiments. This series of LH2 complexes allows a systematic exploration of the factors that determine the spectral properties of the bound pigments and control the rate and efficiency of carotenoid-to-bacteriochlorophyll energy transfer.

  16. Atomistic modeling of two-dimensional electronic spectra and excited-state dynamics for a Light Harvesting 2 complex.

    Science.gov (United States)

    van der Vegte, C P; Prajapati, J D; Kleinekathöfer, U; Knoester, J; Jansen, T L C

    2015-01-29

    The Light Harvesting 2 (LH2) complex is a vital part of the photosystem of purple bacteria. It is responsible for the absorption of light and transport of the resulting excitations to the reaction center in a highly efficient manner. A general description of the chromophores and the interaction with their local environment is crucial to understand this highly efficient energy transport. Here we include this interaction in an atomistic way using mixed quantum-classical (molecular dynamics) simulations of spectra. In particular, we present the first atomistic simulation of nonlinear optical spectra for LH2 and use it to study the energy transport within the complex. We show that the frequency distributions of the pigments strongly depend on their positions with respect to the protein scaffold and dynamics of their local environment. Furthermore, we show that although the pigments are closely packed the transition frequencies of neighboring pigments are essentially uncorrelated. We present the simulated linear absorption spectra for the LH2 complex and provide a detailed explanation of the states responsible for the observed two-band structure. Finally, we discuss the energy transfer within the complex by analyzing population transfer calculations and 2D spectra for different waiting times. We conclude that the energy transfer from the B800 ring to the B850 ring is mediated by intermediate states that are delocalized over both rings, allowing for a stepwise downhill energy transport.

  17. Solid-state NMR applied to photosynthetic light-harvesting complexes

    NARCIS (Netherlands)

    Pandit, A.; Groot, de H.J.M.

    2012-01-01

    This short review describes how solid-state NMR has provided a mechanistic and electronic picture of pigment–protein and pigment–pigment interactions in photosynthetic antenna complexes. NMR results on purple bacterial antenna complexes show how the packing of the protein and the pigments inside the

  18. Solid-state NMR applied to photosynthetic light-harvesting complexes

    NARCIS (Netherlands)

    Pandit, A.; Groot, de H.J.M.

    2012-01-01

    This short review describes how solid-state NMR has provided a mechanistic and electronic picture of pigment–protein and pigment–pigment interactions in photosynthetic antenna complexes. NMR results on purple bacterial antenna complexes show how the packing of the protein and the pigments inside the

  19. Entanglement and entangling power of the dynamics in light-harvesting complexes

    CERN Document Server

    Caruso, Filippo; Datta, Animesh; Huelga, Susana F; Plenio, Martin B

    2009-01-01

    We study the evolution of quantum entanglement during exciton energy transfer (EET) in a network model of the Fenna-Matthews-Olson (FMO) complex, a biological pigment-protein complex involved in the early steps of photosynthesis in sulphur bacteria. The influence of Markovian, as well as spatially and temporally correlated (non-Markovian) noise on the generation of entanglement across distinct chromophores (site entanglement) and different excitons (mode entanglement) is studied for different injection mechanisms, like thermal and coherent laser excitation. Additionally, we study the entangling power of the FMO complex under natural operating conditions. While quantum information processing tends to favor maximal entanglement, near unit EET is achieved when the initial part of the evolution displays intermediate values of both forms of entanglement which is the result of an intricate interplay between coherent and noisy processes in these complex systems.

  20. Coherent excitons at different orientation arrangements of local transition dipole moments in circular light-harvesting complexes

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The coherent exciton plays an important role in the photosynthetic primary process, and its functions are deeply dependent on the orientation arrangements of local transition dipole moments (TDMs). We theoretically and systematically study the physical property of the coherent exciton at different orientation arrangements of the local TDMs in circular light-harvesting (LH) complexes. Especially, if the orientation arrangements are different, the delocalized TDMs of the coherent excitons and the energy locations of the optically active coherent excitons (OACEs) can be obviously different, and then there are more manners to capture, store and transfer light energy in and between LH complexes.Similarly, if the orientation arrangements are altered, light absorption and radiative intensities can be converted fully between the OACEs in the upper and lower coherent exciton bands, and then the blue and red shifts of the absorption and radiative bands of the pigment molecules can occur simultaneously at some orientation arrangements. If the systems are in the vicinities of the critical orientation arrangements, the weak static disorder or small thermal excitation can destroy the coherent electronic excitations, and then the coherent exciton cannot exist any more.

  1. Probing energy transfer events in the light harvesting complex 2 (LH2) of Rhodobacter sphaeroides with two-dimensional spectroscopy.

    Science.gov (United States)

    Fidler, Andrew F; Singh, Ved P; Long, Phillip D; Dahlberg, Peter D; Engel, Gregory S

    2013-10-21

    Excitation energy transfer events in the photosynthetic light harvesting complex 2 (LH2) of Rhodobacter sphaeroides are investigated with polarization controlled two-dimensional electronic spectroscopy. A spectrally broadened pulse allows simultaneous measurement of the energy transfer within and between the two absorption bands at 800 nm and 850 nm. The phased all-parallel polarization two-dimensional spectra resolve the initial events of energy transfer by separating the intra-band and inter-band relaxation processes across the two-dimensional map. The internal dynamics of the 800 nm region of the spectra are resolved as a cross peak that grows in on an ultrafast time scale, reflecting energy transfer between higher lying excitations of the B850 chromophores into the B800 states. We utilize a polarization sequence designed to highlight the initial excited state dynamics which uncovers an ultrafast transfer component between the two bands that was not observed in the all-parallel polarization data. We attribute the ultrafast transfer component to energy transfer from higher energy exciton states to lower energy states of the strongly coupled B850 chromophores. Connecting the spectroscopic signature to the molecular structure, we reveal multiple relaxation pathways including a cyclic transfer of energy between the two rings of the complex.

  2. Comparison of the light-harvesting networks of plant and cyanobacterial photosystem I.

    Science.gov (United States)

    Sener, Melih K; Jolley, Craig; Ben-Shem, Adam; Fromme, Petra; Nelson, Nathan; Croce, Roberta; Schulten, Klaus

    2005-09-01

    With the availability of structural models for photosystem I (PSI) in cyanobacteria and plants it is possible to compare the excitation transfer networks in this ubiquitous photosystem from two domains of life separated by over one billion years of divergent evolution, thus providing an insight into the physical constraints that shape the networks' evolution. Structure-based modeling methods are used to examine the excitation transfer kinetics of the plant PSI-LHCI supercomplex. For this purpose an effective Hamiltonian is constructed that combines an existing cyanobacterial model for structurally conserved chlorophylls with spectral information for chlorophylls in the Lhca subunits. The plant PSI excitation migration network thus characterized is compared to its cyanobacterial counterpart investigated earlier. In agreement with observations, an average excitation transfer lifetime of approximately 49 ps is computed for the plant PSI-LHCI supercomplex with a corresponding quantum yield of 95%. The sensitivity of the results to chlorophyll site energy assignments is discussed. Lhca subunits are efficiently coupled to the PSI core via gap chlorophylls. In contrast to the chlorophylls in the vicinity of the reaction center, previously shown to optimize the quantum yield of the excitation transfer process, the orientational ordering of peripheral chlorophylls does not show such optimality. The finding suggests that after close packing of chlorophylls was achieved, constraints other than efficiency of the overall excitation transfer process precluded further evolution of pigment ordering.

  3. The composition and spectral properties of three different forms of light-harvesting complex II

    Institute of Scientific and Technical Information of China (English)

    LENG; Jing; (冷静); LI; Liangbi; (李良璧); KUANG; Tingyun; (匡廷云)

    2003-01-01

    Different aggregates of LHC II play a very important role in regulating the light absorption and excitation energy transfer of plant. Trimeric LHC II was purified from spinach thylakoid membrane. In order to obtain the dimeric and monomeric LHC II, the trimer was treated with the mixture of 2% OGP and 10 ?g/mL PLA2, then loaded onto the sucrose density gradient in the presence of 0.06% triton X-100. The LHC II trimer, dimer and monomer isolated by sucrose density gradient all contained three polypeptides with molecular weight of 29, 28 and 26 kd respectively. The pigment composition showed much difference in the content of Chl b and xanthophyll among three forms of LHC II. To study the light capture and excitation energy transfer in different forms of LHC II, the absorption and fluorescence spectra were analyzed. The results clearly showed that the efficiency of energy absorption and transfer was different in the three kinds of LHC II, the highest for trimeric LHC II, intermediate for dimeric LHC II, and the lowest for monomeric LHC II. It was suggested that there might be a physiological homeostasis of different aggregates of LHC II in plants, which is significant for the plant self-regulating upon exposure to variable light environment.

  4. Nanometer arrays of functional light harvesting antenna complexes by nanoimprint lithography and host-guest interactions

    NARCIS (Netherlands)

    Escalante, Maryana; Zhao, Yiping; Ludden, Manon J.W.; Vermeij, Rolf; Olsen, John D.; Berenschot, Erwin; Hunter, C. Neil; Huskens, Jurriaan; Subramaniam, Vinod; Otto, Cees

    2008-01-01

    We show an approach based on a combination of site-directed mutagenesis, NIL and multivalent host−guest interactions for the realization of engineered ordered functional arrays of purified components of the photosynthetic system, the membrane-bound LH2 complex. In addition to micrometer-scale patter

  5. Nanoscale Confinement and Fluorescence Effects of Bacterial Light Harvesting Complex LH2 in Mesoporous Silicas

    DEFF Research Database (Denmark)

    Ikemoto, Hideki; Tubasum, Sumera; Pullerits, Tonu;

    2013-01-01

    harvesting complex LH2 in nanoscale chemical environments. Mesoporous silicas (SBA-15 family) with different shapes and pore sizes were synthesized and used to create nanoscale biomimetic environments for molecular confinement of LH2. A combination of UV-vis absorption, wide-field fluorescence microscopy...

  6. Characterization of the Main Light-Harvesting Chlorophyll a/b-Protein Complex of Green Alga, Bryopsis corticulans

    Institute of Scientific and Technical Information of China (English)

    CHENHuil; SHENShi-Hua; GONGYan-Dao; HEJun-Fang; WANGGuang-Ce; LILiang-Bi; KUANGTing-Yun

    2004-01-01

    The main light-harvesting chlorophyll a/b -protein complex (LHC Ⅱ) has been isolated directly from thylakoid membranes of shiphonous 8Teen alga, Bryopsis corticulans Setch. by using two consecutive runs of anion exchange and gel-filtration chromatography. Monomeric and trimeric subcomplexes of LHC Ⅱ were obtained by using sucrose gradient ultracentrifugation. Pigment analysis by reversed-phase high performance liquid chromatography showed that chlorophyll a (Chl a), chlorophyll b (Chl b), neoxanthin, violaxanthin and siphonaxanthin were involved in LHC Ⅱ from B. corticulans. The properties of electronictransition of monomeric LHC Ⅱ showed similarities to those of trimeric LHC Ⅱ. Circular dichroism spectroscopy showed that strong intramolecular interaction of excitonic dipoles between Chl a and between Chl b exist in one LHC Ⅱ apoprotein, while the intermolecular interaction of these dipoles can be intensified in the trimeric structure. The monomer has high efficient energy transfer from Chl b and siphonaxanthin to Chl a similarly to that of the trimer. Our results suggest that in B. corticulans, LHC Ⅱ monomer has high ordered pigment organization that play effective physiological function as the trimer, and thus it might be also a functional organization existing in thylakoid membrane of B.corticulans.

  7. Ab initio molecular orbital calculations of electronic couplings in the LH2 bacterial light-harvesting complex of Rps. acidophila

    Energy Technology Data Exchange (ETDEWEB)

    Scholes, G.D.; Fleming, G.R. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry]|[Lawrence Berkeley National Lab., CA (United States). Physical Biosciences Div.; Gould, I.R. [Imperial Coll. of Science, Technology and Medicine, London (United Kingdom). Dept. of Chemistry; Cogdell, R.J. [Univ. of Glasgow (United Kingdom). Div. of Biochemistry and Molecular Biology

    1999-04-01

    The results of ab initio molecular orbital calculations of excited states and electronic couplings (for energy transfer) between the B800 and B850 bacteriochlorophyll a (Bchl) chromophores in the peripheral light-harvesting complex (LH2) of the purple photosynthetic bacterium Rhodopseudomonas acidophila are reported. Electronic couplings are estimated from supermolecule calculations of Bchl dimers using the Ci-singles methodology and 3-21G{sup *} or 6-31G{sup *} basis sets. A scheme for dissecting the coupling into contributions from the Coulombic coupling and the short-range coupling (i.e., dependent on interchromophore orbital overlap) is reported. B850 couplings are calculated to be [total (Coulombic + short)]: intrapolypeptide dimer 320 (265 + 55) cm{sup {minus}1} and interpolypeptide dimer 255 (195 + 60) cm{sup {minus}1} at the CIS/6-31G{sup *} level. These results differ significantly from those estimated using the point dipole approximation. The effect of including Mg ligands (His residues) and H-bonding residues (Trp and Tyr) is also investigated. The consequences for superradiance and energy transfer dynamics and mechanism are discussed.

  8. Self-assembly and energy transfer in artificial light-harvesting complexes of bacteriochlorophyll c with astaxanthin.

    Science.gov (United States)

    Alster, J; Polívka, T; Arellano, J B; Hříbek, P; Vácha, F; Hála, J; Pšenčík, J

    2012-03-01

    Chlorosomes, the light-harvesting antennae of green photosynthetic bacteria, are based on large aggregates of bacteriochlorophyll molecules. Aggregates with similar properties to those in chlorosomes can also be prepared in vitro. Several agents were shown to induce aggregation of bacteriochlorophyll c in aqueous environments, including certain lipids, carotenes, and quinones. A key distinguishing feature of bacteriochlorophyll c aggregates, both in vitro and in chlorosomes, is a large (>60 nm) red shift of their Q(y) absorption band compared with that of the monomers. In this study, we investigate the self-assembly of bacteriochlorophyll c with the xanthophyll astaxanthin, which leads to the formation of a new type of complexes. Our results indicate that, due to its specific structure, astaxanthin molecules competes with bacteriochlorophylls for the bonds involved in the aggregation, thus preventing the formation of any significant red shift compared with pure bacteriochlorophyll c in aqueous buffer. A strong interaction between both the types of pigments in the developed assemblies, is manifested by a rather efficient (~40%) excitation energy transfer from astaxanthin to bacteriochlorophyll c, as revealed by fluorescence excitation spectroscopy. Results of transient absorption spectroscopy show that the energy transfer is very fast (<500 fs) and proceeds through the S(2) state of astaxanthin.

  9. Towards in vivo mutation analysis: knock-out of specific chlorophylls bound to the light-harvesting complexes of Arabidopsis thaliana - the case of CP24 (Lhcb6).

    Science.gov (United States)

    Passarini, Francesca; Xu, Pengqi; Caffarri, Stefano; Hille, Jacques; Croce, Roberta

    2014-09-01

    In the last ten years, a large series of studies have targeted antenna complexes of plants (Lhc) with the aim of understanding the mechanisms of light harvesting and photoprotection. Combining spectroscopy, modeling and mutation analyses, the role of individual pigments in these processes has been highlighted in vitro. In plants, however, these proteins are associated with multiple complexes of the photosystems and function within this framework. In this work, we have envisaged a way to bridge the gap between in vitro and in vivo studies by knocking out in vivo pigments that have been proposed to play an important role in excitation energy transfer between the complexes or in photoprotection. We have complemented a CP24 knock-out mutant of Arabidopsis thaliana with the CP24 (Lhcb6) gene carrying a His-tag and with a mutated version lacking the ligand for chlorophyll 612, a specific pigment that in vitro experiments have indicated as the lowest energy site of the complex. Both complexes efficiently integrated into the thylakoid membrane and assembled into the PSII supercomplexes, indicating that the His-tag does not impair the organization in vivo. The presence of the His-tag allowed the purification of CP24-WT and of CP24-612 mutant in their native states. It is shown that CP24-WT coordinates 10 chlorophylls and 2 carotenoid molecules and has properties identical to those of the reconstituted complex, demonstrating that the complex self-assembled in vitro assumes the same folding as in the plant. The absence of the ligand for chlorophyll 612 leads to the loss of one Chl a and of lutein, again as in vitro, indicating the feasibility of the method. This article is part of a special issue entitled: photosynthesis research for sustainability: keys to produce clean energy.

  10. Could light harvesting complexes exhibit non-classical effects at room temperature?

    CERN Document Server

    Wilde, Mark M; Mizel, Ari

    2009-01-01

    Mounting experimental and theoretical evidence suggests that coherent quantum effects play a role in the efficient transfer of an excitation from a chlorosome antenna to a reaction center in the Fenna-Matthews-Olson protein complex. However, it is conceivable that a satisfying alternate interpretation of the results is possible in terms of a classical theory. To address this possibility, we consider a class of classical theories satisfying the minimal postulates of macrorealism and frame Leggett-Garg-type tests that could rule them out. Our numerical simulations indicate that even in the presence of decoherence, several tests could exhibit the required violations of the Leggett-Garg inequality. Remarkably, some violations persist even at room temperature for our decoherence model.

  11. New insights into the photochemistry of carotenoid spheroidenone in light-harvesting complex 2 from the purple bacterium Rhodobacter sphaeroides.

    Science.gov (United States)

    Niedzwiedzki, Dariusz M; Dilbeck, Preston L; Tang, Qun; Martin, Elizabeth C; Bocian, David F; Hunter, C Neil; Holten, Dewey

    2017-03-01

    Light-harvesting complex 2 (LH2) from the semi-aerobically grown purple phototrophic bacterium Rhodobacter sphaeroides was studied using optical (static and time-resolved) and resonance Raman spectroscopies. This antenna complex comprises bacteriochlorophyll (BChl) a and the carotenoid spheroidenone, a ketolated derivative of spheroidene. The results indicate that the spheroidenone-LH2 complex contains two spectral forms of the carotenoid: (1) a minor, "blue" form with an S2 (1(1)B u(+) ) spectral origin band at 522 nm, shifted from the position in organic media simply by the high polarizability of the binding site, and (2) the major, "red" form with the origin band at 562 nm that is associated with a pool of pigments that more strongly interact with protein residues, most likely via hydrogen bonding. Application of targeted modeling of excited-state decay pathways after carotenoid excitation suggests that the high (92%) carotenoid-to-BChl energy transfer efficiency in this LH2 system, relative to LH2 complexes binding carotenoids with comparable double-bond conjugation lengths, derives mainly from resonance energy transfer from spheroidenone S2 (1(1)B u(+) ) state to BChl a via the Qx state of the latter, accounting for 60% of the total transfer. The elevated S2 (1(1)B u(+) ) → Qx transfer efficiency is apparently associated with substantially decreased energy gap (increased spectral overlap) between the virtual S2 (1(1)B u(+) ) → S0 (1(1)A g(-) ) carotenoid emission and Qx absorption of BChl a. This reduced energetic gap is the ultimate consequence of strong carotenoid-protein interactions, including the inferred hydrogen bonding.

  12. Effects of pH on the peripheral light-harvesting antenna complex for Rhodopseudomonas palustris

    Institute of Scientific and Technical Information of China (English)

    FENG Juan; LI XueFeng; LIU Yan

    2008-01-01

    In this work steady-state absorption spectroscopy, circular dichroism spectroscopy and sub-micro-second time-resolved absorption spectroscopy were used to investigate the effect of pH on the struc-tures and functions of LH2 complex for Rhodopseudomonas palustris. The results revealed that: (1) B800 Bchla was gradually transformed to free pigments absorbing around 760 nm on the minutes timescale upon the induction of strong acidic pH, and subsequently there disappeared the CD signal for Qy band of B800 in the absence of B800. In addition, Carotenoids changed with the similar tendency to B850 BChl. (2) The introduction of strong basic pH gave rise to no significant changes for B800 Bchla, while B850 BChla experienced remarkable spectral blue-shift from 852 to 837 nm. Similar phe-nomenon was seen for the CD signal for Qy band of B850. Carotenoids displayed strong and pH-independent CD signals in the visible range. (3) In the case of both physiological and basic pH, broad and asymmetrical positive Tn←T1 transient absorption appeared following the pulsed photo-excitation of Car at 532 nm. By contrast, the featureless and weak positive signal was observed on the sub-microsecond timescale in the acidic pH environment. The aforementioned experimental results indicated that acidic pH-induced removal of B800 Bchla prevented the generation of the caro-tenoid triplet state (3Car*), which is known to be essential for the photo-protection function. Neverthe-less, carotenoids can still perform this important physiological role under the basic pH condition, where the spectral blue shift of B850 exerts little effect on the overall structure of the cyclic aggregate, therefore favoring the formation of carotenoid triplet state.

  13. Static and dynamic protein impact on electronic properties of light-harvesting complex LH2.

    Science.gov (United States)

    Zerlauskiene, O; Trinkunas, G; Gall, A; Robert, B; Urboniene, V; Valkunas, L

    2008-12-11

    A comparative analysis of the temperature dependence of the absorption spectra of the LH2 complexes from different species of photosynthetic bacteria, i.e., Rhodobacter sphaeroides, Rhodoblastus acidophilus, and Phaeospirillum molischianum, was performed in the temperature range from 4 to 300 K. Qualitatively, the temperature dependence is similar for all of the species studied. The spectral bandwidths of both B800 and B850 bands increases with temperature while the band positions shift in opposite directions: the B800 band shifts slightly to the red while the B850 band to the blue. These results were analyzed using the modified Redfield theory based on the exciton model. The main conclusion drawn from the analysis was that the spectral density function (SDF) is the main factor underlying the strength of the temperature dependence of the bandwidths for the B800 and B850 electronic transitions, while the bandwidths themselves are defined by the corresponding inhomogeneous distribution function (IDF). Slight variation of the slope of the temperature dependence of the bandwidths between species can be attributed to the changes of the values of the reorganization energies and characteristic frequencies determining the SDF. To explain the shift of the B850 band position with temperature, which is unusual for the conventional exciton model, a temperature dependence of the IDF must be postulated. This dependence can be achieved within the framework of the modified (dichotomous) exciton model. The slope of the temperature dependence of the B850 bandwidth is then defined by the value of the reorganization energy and by the difference between the transition energies of the dichotomous states of the pigment molecules. The equilibration factor between these dichotomous states mainly determines the temperature dependence of the peak shift.

  14. Highly efficient energy transfer from a carbonyl carotenoid to chlorophyll a in the main light harvesting complex of Chromera velia.

    Science.gov (United States)

    Durchan, Milan; Keşan, Gürkan; Slouf, Václav; Fuciman, Marcel; Staleva, Hristina; Tichý, Josef; Litvín, Radek; Bína, David; Vácha, František; Polívka, Tomáš

    2014-10-01

    We report on energy transfer pathways in the main light-harvesting complex of photosynthetic relative of apicomplexan parasites, Chromera velia. This complex, denoted CLH, belongs to the family of FCP proteins and contains chlorophyll (Chl) a, violaxanthin, and the so far unidentified carbonyl carotenoid related to isofucoxanthin. The overall carotenoid-to-Chl-a energy transfer exhibits efficiency over 90% which is the largest among the FCP-like proteins studied so far. Three spectroscopically different isofucoxanthin-like molecules were identified in CLH, each having slightly different energy transfer efficiency that increases from isofucoxanthin-like molecules absorbing in the blue part of the spectrum to those absorbing in the reddest part of spectrum. Part of the energy transfer from carotenoids proceeds via the ultrafast S2 channel of both the violaxanthin and isofucoxanthin-like carotenoid, but major energy transfer pathway proceeds via the S1/ICT state of the isofucoxanthin-like carotenoid. Two S1/ICT-mediated channels characterized by time constants of ~0.5 and ~4ps were found. For the isofucoxanthin-like carotenoid excited at 480nm the slower channel dominates, while those excited at 540nm employs predominantly the fast 0.5ps channel. Comparing these data with the excited-state properties of the isofucoxanthin-like carotenoid in solution we conclude that, contrary to other members of the FCP family employing carbonyl carotenoids, CLH complex suppresses the charge transfer character of the S1/ICT state of the isofucoxanthin-like carotenoid to achieve the high carotenoid-to-Chl-a energy transfer efficiency.

  15. Mapping Out the Structure of a Spinach Light-Harvester

    Institute of Scientific and Technical Information of China (English)

    2004-01-01

    @@ The major light-harvesting complex of photosystem Ⅱ(LHC-Ⅱ) serves as the principal solar energy collector in the photosynthesis of green plants and presumably also functions in photoprotection under high-light conditions. Many of its structures were revealed by a work of a 3.2A electron crystallographic model of LHC-Ⅱ in 1994. Since then researchers have eagerly awaited a higher-resolution structure to extend knowledge of the light harvesting and energy transfer processes involved in photosynthesis to the level of full atomic data.

  16. Energy transfer dynamics in trimers and aggregates of light-harvesting complex II probed by 2D electronic spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Enriquez, Miriam M.; Zhang, Cheng; Tan, Howe-Siang, E-mail: howesiang@ntu.edu.sg [Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371 (Singapore); Akhtar, Parveen; Garab, Győző; Lambrev, Petar H., E-mail: lambrev@brc.hu [Institute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, P.O. Box 521, H-6701 Szeged (Hungary)

    2015-06-07

    The pathways and dynamics of excitation energy transfer between the chlorophyll (Chl) domains in solubilized trimeric and aggregated light-harvesting complex II (LHCII) are examined using two-dimensional electronic spectroscopy (2DES). The LHCII trimers and aggregates exhibit the unquenched and quenched excitonic states of Chl a, respectively. 2DES allows direct correlation of excitation and emission energies of coupled states over population time delays, hence enabling mapping of the energy flow between Chls. By the excitation of the entire Chl b Q{sub y} band, energy transfer from Chl b to Chl a states is monitored in the LHCII trimers and aggregates. Global analysis of the two-dimensional (2D) spectra reveals that energy transfer from Chl b to Chl a occurs on fast and slow time scales of 240–270 fs and 2.8 ps for both forms of LHCII. 2D decay-associated spectra resulting from the global analysis identify the correlation between Chl states involved in the energy transfer and decay at a given lifetime. The contribution of singlet–singlet annihilation on the kinetics of Chl energy transfer and decay is also modelled and discussed. The results show a marked change in the energy transfer kinetics in the time range of a few picoseconds. Owing to slow energy equilibration processes, long-lived intermediate Chl a states are present in solubilized trimers, while in aggregates, the population decay of these excited states is significantly accelerated, suggesting that, overall, the energy transfer within the LHCII complexes is faster in the aggregated state.

  17. Energy transfer dynamics in trimers and aggregates of light-harvesting complex II probed by 2D electronic spectroscopy.

    Science.gov (United States)

    Enriquez, Miriam M; Akhtar, Parveen; Zhang, Cheng; Garab, Győző; Lambrev, Petar H; Tan, Howe-Siang

    2015-06-07

    The pathways and dynamics of excitation energy transfer between the chlorophyll (Chl) domains in solubilized trimeric and aggregated light-harvesting complex II (LHCII) are examined using two-dimensional electronic spectroscopy (2DES). The LHCII trimers and aggregates exhibit the unquenched and quenched excitonic states of Chl a, respectively. 2DES allows direct correlation of excitation and emission energies of coupled states over population time delays, hence enabling mapping of the energy flow between Chls. By the excitation of the entire Chl b Qy band, energy transfer from Chl b to Chl a states is monitored in the LHCII trimers and aggregates. Global analysis of the two-dimensional (2D) spectra reveals that energy transfer from Chl b to Chl a occurs on fast and slow time scales of 240-270 fs and 2.8 ps for both forms of LHCII. 2D decay-associated spectra resulting from the global analysis identify the correlation between Chl states involved in the energy transfer and decay at a given lifetime. The contribution of singlet-singlet annihilation on the kinetics of Chl energy transfer and decay is also modelled and discussed. The results show a marked change in the energy transfer kinetics in the time range of a few picoseconds. Owing to slow energy equilibration processes, long-lived intermediate Chl a states are present in solubilized trimers, while in aggregates, the population decay of these excited states is significantly accelerated, suggesting that, overall, the energy transfer within the LHCII complexes is faster in the aggregated state.

  18. Nuclear, Virescent Mutants of Zea mays L. with High Levels of Chlorophyll (a/b) Light-Harvesting Complex during Thylakoid Assembly.

    Science.gov (United States)

    Polacco, M L; Chang, M T; Neuffer, M G

    1985-04-01

    We have found nuclear, recessive mutants in Zea mays L. where assembly of the major chlorophyll (a/b) light-harvesting complex (LHC) was not delayed relative to most other thylakoid protein complexes during thylakoid biogenesis. This contrasts with the normal development of maize chloroplasts (NR Baker, R Leech 1977 Plant Physiol 60: 640-644). All four mutants examined were allelic and virescent, and displayed visibly higher yields of leaf Chl fluorescence during greening. Fully greened mutants had normal leaf Chl fluorescence yield and normal levels of LHC, and grew to maturity under field conditions. Therefore, delayed LHC assembly is not an obligate feature of thylakoid differentiation.Assigning the molecular basis for the mutation should provide information concerning reguation of LHC assembly. Several possibilities are discussed. The pleiotropic mutant phenotype is not attributable to defects in thylakoid glycerolipid synthesis. Thylakoids isolated from greening mutant leaf sections had elevated glycerolipid/Chl ratios. In addition, both the molar distribution and acyl composition of four major glycerolipids were normal for developing mutant thylakoids.

  19. Nuclear, Virescent Mutants of Zea mays L. with High Levels of Chlorophyll (a/b) Light-Harvesting Complex during Thylakoid Assembly 1

    Science.gov (United States)

    Polacco, Mary L.; Chang, M. T.; Neuffer, M. Gerald

    1985-01-01

    We have found nuclear, recessive mutants in Zea mays L. where assembly of the major chlorophyll (a/b) light-harvesting complex (LHC) was not delayed relative to most other thylakoid protein complexes during thylakoid biogenesis. This contrasts with the normal development of maize chloroplasts (NR Baker, R Leech 1977 Plant Physiol 60: 640-644). All four mutants examined were allelic and virescent, and displayed visibly higher yields of leaf Chl fluorescence during greening. Fully greened mutants had normal leaf Chl fluorescence yield and normal levels of LHC, and grew to maturity under field conditions. Therefore, delayed LHC assembly is not an obligate feature of thylakoid differentiation. Assigning the molecular basis for the mutation should provide information concerning reguation of LHC assembly. Several possibilities are discussed. The pleiotropic mutant phenotype is not attributable to defects in thylakoid glycerolipid synthesis. Thylakoids isolated from greening mutant leaf sections had elevated glycerolipid/Chl ratios. In addition, both the molar distribution and acyl composition of four major glycerolipids were normal for developing mutant thylakoids. Images Fig. 2 PMID:16664140

  20. Charge-transfer character of the low-energy Chl a Q(y) absorption band in aggregated light harvesting complexes II.

    Science.gov (United States)

    Kell, Adam; Feng, Ximao; Lin, Chen; Yang, Yiqun; Li, Jun; Reus, Michael; Holzwarth, Alfred R; Jankowiak, Ryszard

    2014-06-12

    One of the key functions of the major light harvesting complex II (LHCII) of higher plants is to protect Photosystem II from photodamage at excessive light conditions in a process called "non-photochemical quenching" (NPQ). Using hole-burning (HB) spectroscopy, we investigated the nature of the low-energy absorption band in aggregated LHCII complexes - which are highly quenched and have been established as a good in vitro model for NPQ. Nonresonant holes reveal that the lowest energy state (located near 683.3 nm) is red-shifted by ~4 nm and significantly broader (by a factor of 4) as compared to nonaggregated trimeric LHCII. Resonant holes burned in the low-energy wing of the absorption spectrum (685-710 nm) showed a high electron-phonon (el-ph) coupling strength with a Huang-Rhys factor S of 3-4. This finding combined with the very low HB efficiency in the long-wavelength absorption tail is consistent with a dominant charge-transfer (CT) character of the lowest energy transition(s) in aggregated LHCII. The value of S decreases at shorter wavelengths (energy excitonic state is strongly mixed with the CT states. Our findings support the mechanistic model in which Chl-Chl CT states formed in aggregated LHCII are intermediates in the efficient excited state quenching process (M. G. Müller et al., Chem. Phys. Chem. 2010, 11, 1289-1296; Y. Miloslavina et al., FEBS Lett. 2008, 582, 3625-3631).

  1. Modeling of the N-terminal Section and the Lumenal Loop of Trimeric Light Harvesting Complex II (LHCII) by Using EPR.

    Science.gov (United States)

    Fehr, Niklas; Dietz, Carsten; Polyhach, Yevhen; von Hagens, Tona; Jeschke, Gunnar; Paulsen, Harald

    2015-10-23

    The major light harvesting complex II (LHCII) of green plants plays a key role in the absorption of sunlight, the regulation of photosynthesis, and in preventing photodamage by excess light. The latter two functions are thought to involve the lumenal loop and the N-terminal domain. Their structure and mobility in an aqueous environment are only partially known. Electron paramagnetic resonance (EPR) has been used to measure the structure of these hydrophilic protein domains in detergent-solubilized LHCII. A new technique is introduced to prepare LHCII trimers in which only one monomer is spin-labeled. These heterogeneous trimers allow to measure intra-molecular distances within one LHCII monomer in the context of a trimer by using double electron-electron resonance (DEER). These data together with data from electron spin echo envelope modulation (ESEEM) allowed to model the N-terminal protein section, which has not been resolved in current crystal structures, and the lumenal loop domain. The N-terminal domain covers only a restricted area above the superhelix in LHCII, which is consistent with the "Velcro" hypothesis to explain thylakoid grana stacking (Standfuss, J., van Terwisscha Scheltinga, A. C., Lamborghini, M., and Kühlbrandt, W. (2005) EMBO J. 24, 919-928). The conformation of the lumenal loop domain is surprisingly different between LHCII monomers and trimers but not between complexes with and without neoxanthin bound.

  2. Nanoantenna enhanced emission of light-harvesting complex 2: the role of resonance, polarization, and radiative and non-radiative rates.

    Science.gov (United States)

    Wientjes, Emilie; Renger, Jan; Curto, Alberto G; Cogdell, Richard; van Hulst, Niek F

    2014-12-01

    Nanoantennae show potential for photosynthesis research for two reasons; first by spatially confining light for experiments which require high spatial resolution, and second by enhancing the photon emission of single light-harvesting complexes. For effective use of nanoantennae a detailed understanding of the interaction between the nanoantenna and the light-harvesting complex is required. Here we report how the excitation and emission of multiple purple bacterial LH2s (light-harvesting complex 2) are controlled by single gold nanorod antennae. LH2 complexes were chemically attached to such antennae, and the antenna length was systematically varied to tune the resonance with respect to the LH2 absorption and emission. There are three main findings. (i) The polarization of the LH2 emission is fully controlled by the resonant nanoantenna. (ii) The largest fluorescence enhancement, of 23 times, is reached for excitation with light at λ = 850 nm, polarized along the long antenna-axis of the resonant antenna. The excitation enhancement is found to be 6 times, while the emission efficiency is increased 3.6 times. (iii) The fluorescence lifetime of LH2 depends strongly on the antenna length, with shortest lifetimes of ∼40 ps for the resonant antenna. The lifetime shortening arises from an 11 times resonant enhancement of the radiative rate, together with a 2-3 times increase of the non-radiative rate, compared to the off-resonant antenna. The observed length dependence of radiative and non-radiative rate enhancement is in good agreement with simulations. Overall this work gives a complete picture of how the excitation and emission of multi-pigment light-harvesting complexes are influenced by a dipole nanoantenna.

  3. Towards building artificial light harvesting complexes: enhanced singlet-singlet energy transfer between donor and acceptor pairs bound to albumins.

    Science.gov (United States)

    Kumar, Challa V; Duff, Michael R

    2008-12-01

    -assembled which can capture donor-acceptor pairs and facilitate singlet-singlet energy transfer. Such systems may form a basis for the design and construction of protein-based multi-chromophore self-assemblies for solar light harvesting, conversion and storage.

  4. The fine tuning of carotenoid-chlorophyll interactions in light-harvesting complexes: an important requisite to guarantee efficient photoprotection via triplet-triplet energy transfer in the complex balance of the energy transfer processes

    Science.gov (United States)

    Di Valentin, Marilena; Carbonera, Donatella

    2017-08-01

    Triplet-triplet energy transfer (TTET) from the chlorophyll to the carotenoid triplet state is the process exploited by photosynthetic systems to protect themselves from singlet oxygen formation under light-stress conditions. A deep comprehension of the molecular strategies adopted to guarantee TTET efficiency, while at the same time maintaining minimal energy loss and efficient light-harvesting capability, is still lacking. The paramagnetic nature of the triplet state makes electron paramagnetic resonance (EPR) the method of choice when investigating TTET. In this review, we focus on our extended comparative study of two photosynthetic antenna complexes, the Peridinin-chlorophyll a-protein of dinoflagellates and the light-harvesting complex II of higher plants, in order to point out important aspects of the molecular design adopted in the photoprotection strategy. We have demonstrated that a proper analysis of the EPR data allows one to identify the pigments involved in TTET and, consequently, gain an insight into the structure of the photoprotective sites. The structural information has been complemented by a detailed description of the electronic structure provided by hyperfine spectroscopy. All these elements represent the fundamental building blocks toward a deeper understanding of the requirements for efficient photoprotection, which is fundamental to guarantee the prolonged energy conversion action of photosynthesis.

  5. Effect of metal nanoparticles on energy spectra and optical properties of peripheral light-harvesting LH2 complexes from photosynthetic bacteria

    Energy Technology Data Exchange (ETDEWEB)

    Goliney, I.Yu., E-mail: igoliney@kinr.kiev.ua [Institute for Nuclear Research, National Academy of Science of Ukraine, 47 Nauki pr., 03680 Kyiv (Ukraine); Sugakov, V.I. [Institute for Nuclear Research, National Academy of Science of Ukraine, 47 Nauki pr., 03680 Kyiv (Ukraine); Valkunas, L. [Center for Physical Sciences and Technology, Savanoriu Ave. 231, 02300 Vilnius (Lithuania); Department of Theoretical Physics, Vilnius University, Sauletekio 9, Build. 3, 10222 Vilnius (Lithuania); Vertsimakha, G.V. [Institute for Nuclear Research, National Academy of Science of Ukraine, 47 Nauki pr., 03680 Kyiv (Ukraine)

    2012-08-24

    Highlights: Black-Right-Pointing-Pointer Excitons of light-harvesting complexes (LH2) hybridize with plasmon modes. Black-Right-Pointing-Pointer Light absorption of LH2 is enhanced by a metal nanoparticle. Black-Right-Pointing-Pointer Using nanoshells allows reaching resonance between molecular and plasmons. Black-Right-Pointing-Pointer Metal nanoparticles introduce additional channel of excitation decay. Black-Right-Pointing-Pointer Light-harvesting may gain from the proper positioning of nanoshells. -- Abstract: The paper explores the theoretical possibility of affecting optical spectra and the quantum yield of the energy transfer in the peripheral light-harvesting complexes (LH2) from photosynthetic bacteria by placing a metal nanoparticle or a nanoshell nearby. An increased probability of the excitonic transition in the LH2 arises due to the borrowing of the oscillator strength from surface plasmons of the metal particle or the nanoshell. While both absorption and quenching of the excitations increase in the vicinity to a metal nanoparticle, having opposite effects, the total yield of the excitation transfer to reaction centers is shown to grow in the certain range of parameters.

  6. Exploring the mechanism(s) of energy dissipation in the light harvesting complex of the photosynthetic algae Cyclotella meneghiniana.

    Science.gov (United States)

    Ramanan, Charusheela; Berera, Rudi; Gundermann, Kathi; van Stokkum, Ivo; Büchel, Claudia; van Grondelle, Rienk

    2014-09-01

    Photosynthetic organisms have developed vital strategies which allow them to switch from a light-harvesting to an energy dissipative state at the level of the antenna system in order to survive the detrimental effects of excess light illumination. These mechanisms are particularly relevant in diatoms, which grow in highly fluctuating light environments and thus require fast and strong response to changing light conditions. We performed transient absorption spectroscopy on FCPa, the main light-harvesting antenna from the diatom Cyclotella meneghiniana, in the unquenched and quenched state. Our results show that in quenched FCPa two quenching channels are active and are characterized by differing rate constants and distinct spectroscopic signatures. One channel is associated with a faster quenching rate (16ns⁻¹) and virtually no difference in spectral shape compared to the bulk unquenched chlorophylls, while a second channel is associated with a slower quenching rate (2.7ns⁻¹) and exhibits an increased population of red-emitting states. We discuss the origin of the two processes in the context of the models proposed for the regulation of photosynthetic light-harvesting. This article is part of a special issue entitled: photosynthesis research for sustainability: keys to produce clean energy.

  7. Molecular Basis of Light Harvesting and Photoprotection in CP24 UNIQUE FEATURES OF THE MOST RECENT ANTENNA COMPLEX

    NARCIS (Netherlands)

    Passarini, Francesca; Wientjes, Emilie; Hienerwadel, Rainer; Croce, Roberta

    2009-01-01

    CP24 is a minor antenna complex of Photosystem II, which is specific for land plants. It has been proposed that this complex is involved in the process of excess energy dissipation, which protects plants from photodamage in high light conditions. Here, we have investigated the functional

  8. Effect of the mutation of carotenoids on the dynamics of energy transfer in light- harvesting complexes (LH2) from Rhodobacter sphaeroides 601 at room temperature

    Institute of Scientific and Technical Information of China (English)

    Liu Wei-Min; Liu Yuan; Liu Rang-Jun; Yan Yong-Li; Guo Li-Jun; Xu Chun-He; Qian Shi-Xiong

    2006-01-01

    Energy transfers in two kinds of peripheral light-harvesting complexes (LH2) of Rhodobacter sphaeroides (RS) 601 are studied by using femtosecond pump-probe spectroscopy with tunable laser wavelength at room temperature. These two complexes are native LH2 (RS601) and green carotenoid mutated LH2 (GM309). The obtained results demonstrate that, compared with spheroidenes with ten conjugated double bonds in native RS601, carotenoid in GM309 containing neurosporenes with nine conjugated double bonds can lead to a reduction in energy transfer rate in the B800-to-B850 band and the disturbance in the energy relaxation processes within the excitonic B850 band.

  9. Synchrotron Small-Angle X-Ray Scattering Investigation on Integral Membrane Protein Light-Harvesting Complex LH2 from Photosynthetic Bacterium Rhodopseudomonas Acidophila

    Institute of Scientific and Technical Information of China (English)

    DU Lu-Chao; WENG Yu-Xiang; HONG Xin-Guo; XIAN Ding-Chang; Kobayashi Katsumi

    2006-01-01

    @@ Structures of membrane protein in solution are different from that in crystal phase. We present the primary results of small angle x-ray scattering (SAXS) resolved topological structures of a light harvesting antenna membrane protein complex LH2 from photosynthetic bacteria Rhodopseudomonas acidophila in detergent solution for the first time. Our results show that the elliptical shape of the LH2 complex in solution clearly deviates from its circular structure in crystal phase determined by x-ray diffraction. This result provides an insight into the structure and function interplay in LH2.

  10. Spectroscopic studies of two spectral variants of light-harvesting complex 2 (LH2) from the photosynthetic purple sulfur bacterium Allochromatium vinosum.

    Science.gov (United States)

    Niedzwiedzki, Dariusz M; Bina, David; Picken, Nichola; Honkanen, Suvi; Blankenship, Robert E; Holten, Dewey; Cogdell, Richard J

    2012-09-01

    Two spectral forms of the peripheral light-harvesting complex (LH2) from the purple sulfur photosynthetic bacterium Allochromatium vinosum were purified and their photophysical properties characterized. The complexes contain bacteriochlorophyll a (BChl a) and multiple species of carotenoids. The composition of carotenoids depends on the light conditions applied during growth of the cultures. In addition, LH2 grown under high light has a noticeable split of the B800 absorption band. The influence of the change of carotenoid distribution as well as the spectral change of the excitonic absorption of the bacteriochlorophylls on the light-harvesting ability was studied using steady-state absorption, fluorescence and femtosecond time-resolved absorption at 77K. The results demonstrate that the change of the distribution of the carotenoids when cells were grown at low light adapts the absorptive properties of the complex to the light conditions and maintains maximum photon-capture performance. In addition, an explanation for the origin of the enigmatic split of the B800 absorption band is provided. This spectral splitting is also observed in LH2 complexes from other photosynthetic sulfur purple bacterial species. According to results obtained from transient absorption spectroscopy, the B800 band split originates from two spectral forms of the associated BChl a monomeric molecules bound within the same complex.

  11. The regulation of TiO2 nanoparticles on the expression of light-harvesting complex II and photosynthesis of chloroplasts of Arabidopsis thaliana.

    Science.gov (United States)

    Ze, Yuguan; Liu, Chao; Wang, Ling; Hong, Mengmeng; Hong, Fashui

    2011-11-01

    Recent studies demonstrated that titanium dioxide nanoparticles (TiO2 NPs) could significantly promote photosynthesis and plant growth, but its mechanism is still unclear. In this article, we studied the mechanism of light absorption and transfer of chloroplasts of Arabidopsis thaliana caused by TiO2 NPs treated. The results showed that TiO2 NPs could induce significant increases of light-harvesting complex II (LHCII) b gene expression and LHCII II content on the thylakoid membrane in A. thaliana, and the increases in LHCII were higher than the non-nano TiO2 (bulk-TiO2) treatment. Meanwhile, spectroscopy assays indicated that TiO2 NPs obviously increased the absorption peak intensity of the chloroplast in red and blue region, the fluorescence quantum yield near 680 nm, the excitation peak intensity near 440 and 480 nm and/or near 650 and 680 nm of the chloroplast. TiO2 NPs treatment could reduce F480/F440 ratio and increase F650/F680 ratio and accelerate the rate of whole chain electron transport and oxygen evolution of the chloroplast. However, the photosynthesis improvement of the non-nanoTiO2 treatment was far less effective than TiO2 NPs treatment. Taken together, TiO2 NPs could promote the light absorption of chloroplast, regulate the distribution of light energy from PS I to PS II by increasing LHCII and accelerate the transformation from light energy to electronic energy, water photolysis, and oxygen evolution.

  12. The light intensity under which cells are grown controls the type of peripheral light-harvesting complexes that are assembled in a purple photosynthetic bacterium.

    Science.gov (United States)

    Brotosudarmo, Tatas H P; Collins, Aaron M; Gall, Andrew; Roszak, Aleksander W; Gardiner, Alastair T; Blankenship, Robert E; Cogdell, Richard J

    2011-11-15

    The differing composition of LH2 (peripheral light-harvesting) complexes present in Rhodopseudomonas palustris 2.1.6 have been investigated when cells are grown under progressively decreasing light intensity. Detailed analysis of their absorption spectra reveals that there must be more than two types of LH2 complexes present. Purified HL (high-light) and LL (low-light) LH2 complexes have mixed apoprotein compositions. The HL complexes contain PucAB(a) and PucAB(b) apoproteins. The LL complexes contain PucAB(a), PucAB(d) and PucB(b)-only apoproteins. This mixed apoprotein composition can explain their resonance Raman spectra. Crystallographic studies and molecular sieve chromatography suggest that both the HL and the LL complexes are nonameric. Furthermore, the electron-density maps do not support the existence of an additional Bchl (bacteriochlorophyll) molecule; rather the density is attributed to the N-termini of the α-polypeptide.

  13. Minor Complexes at Work : Light-Harvesting by Carotenoids in the Photosystem II Antenna Complexes CP24 and CP26

    NARCIS (Netherlands)

    Marin, Alessandro; Passarini, Francesca; van Stokkum, Ivo H. M.; van Grondelle, Rienk; Croce, Roberta; Brown, Leonid S.

    2011-01-01

    Plant photosynthesis relies on the capacity of chlorophylls and carotenoids to absorb light. One of the roles of carotenoids is to harvest green-blue light and transfer the excitation energy to the chlorophylls. The corresponding dynamics were investigated here for the first time, to our knowledge,

  14. The light intensity under which cells are grown controls the type of peripheral light-harvesting complexes that are assembled in a purple photosynthetic bacterium

    Energy Technology Data Exchange (ETDEWEB)

    Brotosudarmo, Tatas H. P. [Univ. of Glasgow, Scotland (United Kingdom). Inst. of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences; Collins, Aaron M. [Washington Univ., St. Louis, MO (United States). Depts. of Biology and Chemistry; Gall, Andrew [Commissariat a l' Energie Atomique et aux Energies Alternatives (CEA-Saclay), Gif-sur-Yvette (France). Inst. de Biologie et Technologies de Saclay et CNRS; Roszak, Aleksander W. [Univ. of Glasgow, Scotland (United Kingdom). Dept. of Chemistry, WestChem; Gardiner, Alastair T. [Univ. of Glasgow, Scotland (United Kingdom). Inst. of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences; Blankenship, Robert E. [Washington Univ., St. Louis, MO (United States). Depts. of Biology and Chemistry; Cogdell, Richard J. [Univ. of Glasgow, Scotland (United Kingdom). Inst. of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences

    2011-11-15

    The differing composition of LH2 (peripheral light-harvesting) complexes present in Rhodopseudomonas palustris 2.1.6 have been investigated when cells are grown under progressively decreasing light intensity. Analysis of the absorption spectra reveals there must be more than two types of LH2 complexes present. Purified HL (high-light) and LL (low-light) LH2 complexes have mixed apoprotein compositions. The HL complexes contain PucABa and PucABb apoproteins. The LL complexes contain PucABa, PucABd and PucBb-only apoproteins. This mixed apoprotein composition can explain their resonance Raman spectra.

  15. Quenching Capabilities of Long-Chain Carotenoids in Light-Harvesting-2 Complexes from Rhodobacter sphaeroides with an Engineered Carotenoid Synthesis Pathway.

    Science.gov (United States)

    Dilbeck, Preston L; Tang, Qun; Mothersole, David J; Martin, Elizabeth C; Hunter, C Neil; Bocian, David F; Holten, Dewey; Niedzwiedzki, Dariusz M

    2016-06-23

    Six light-harvesting-2 complexes (LH2) from genetically modified strains of the purple photosynthetic bacterium Rhodobacter (Rb.) sphaeroides were studied using static and ultrafast optical methods and resonance Raman spectroscopy. These strains were engineered to incorporate carotenoids for which the number of conjugated groups (N = NC═C + NC═O) varies from 9 to 15. The Rb. sphaeroides strains incorporate their native carotenoids spheroidene (N = 10) and spheroidenone (N = 11), as well as longer-chain analogues including spirilloxanthin (N = 13) and diketospirilloxantion (N = 15) normally found in Rhodospirillum rubrum. Measurements of the properties of the carotenoid first singlet excited state (S1) in antennas from the Rb. sphaeroides set show that carotenoid-bacteriochlorophyll a (BChl a) interactions are similar to those in LH2 complexes from various other bacterial species and thus are not significantly impacted by differences in polypeptide composition. Instead, variations in carotenoid-to-BChl a energy transfer are primarily regulated by the N-determined energy of the carotenoid S1 excited state, which for long-chain (N ≥ 13) carotenoids is not involved in energy transfer. Furthermore, the role of the long-chain carotenoids switches from a light-harvesting supporter (via energy transfer to BChl a) to a quencher of the BChl a S1 excited state B850*. This quenching is manifested as a substantial (∼2-fold) reduction of the B850* lifetime and the B850* fluorescence quantum yield for LH2 housing the longest carotenoids.

  16. Novel Evidence for a Reversible Dissociation of Light-harvesting Complex Ⅱ from Photosystem Ⅱ Reaction Center Complex Induced by Saturating Light Illumination in Soybean Leaves

    Institute of Scientific and Technical Information of China (English)

    Yi Liao; Da-Quan Xu

    2007-01-01

    After saturating light illumination for 3 h the potential photochemical efficiency of photosystem Ⅱ (PSⅡ) (Fv/Fm, the ratio of variable to maximal fluorescence) decreased markedly and recovered basically to the level before saturating light illumination after dark recovery for 3 h in both soybean and wheat leaves, indicating that the decline in Fv/Fm is a reversible down-regulation. Also, the saturating light illumination led to significant decreases in the low temperature (77 K) chlorophyll fluorescence parameters F685 (chlorophyll a fluorescence peaked at 685 nm ) and F685/F735 (F735, chlorophyll a fluorescence peaked at 735 nm) in soybean leaves but not in wheat leaves. Moreover,trypsin (a protease) treatment resulted in a remarkable decrease in the amounts of PsbS protein (a nuclear gene psbS-encoded 22 kDa protein) in the thylakoids from saturating light-illuminated (SI), but not in those from darkadapted (DT) and dark-recovered (DRT) soybean leaves. However, the treatment did not cause such a decrease in amounts of the PsbS protein in the thylakoids from saturating light-illuminated wheat leaves. These results support the conclusion that saturating light illumination induces a reversible dissociation of some light-harvesting complex Ⅱ (LHCⅡ) from PSⅡ reaction center complex in soybean leaf but not in wheat leaf.

  17. Light-harvesting complex gene expression is controlled by both transcriptional and post-transcriptional mechanisms during photoacclimation in Chlamydomonas reinhardtii

    CERN Document Server

    Durnford Dion, G; McKim, Sarah M; Sarchfield, Michelle L

    2003-01-01

    To compensate for increases in photon flux density (PFD), photosynthetic organisms possess mechanisms for reversibly modulating their photosynthetic apparatus to minimize photodamage. The photoacclimation response in Chlamydomonas reinhardtii was assessed following a 10-fold increase in PFD over 24h. In addition to a 50% reduction in the amount of chlorophyll and light-harvesting complexes (LHC) per cell, the expression of genes encoding polypeptides of the light-harvesting antenna were also affected. The abundance of Lhcb (a LHCH gene), Lhcb4 (a CP29-like gene), and Lhca (a LHCI gene) transcripts were reduced by 65 to 80%, within 1-2 h; however, the RNA levels of all three genes recovered to their low-light (LL) concentrations within 6-8 h. To determine the role of transcript turnover in this transient decline in abundance, the stability of all transcripts was measured. Although there was no change in the Lhcb or Lhca transcript turnover time, the Lhcb4 mRNA stability decreased 2.5-fold immediately following...

  18. Superior Light-Harvesting Heteroleptic Ruthenium(II) Complexes with Electron-Donating Antennas for High Performance Dye-Sensitized Solar Cells.

    Science.gov (United States)

    Chen, Wang-Chao; Kong, Fan-Tai; Li, Zhao-Qian; Pan, Jia-Hong; Liu, Xue-Peng; Guo, Fu-Ling; Zhou, Li; Huang, Yang; Yu, Ting; Dai, Song-Yuan

    2016-08-03

    Three heteroleptic polypyridyl ruthenium complexes, RC-41, RC-42, and RC-43, with efficient electron-donating antennas in the ancillary ligands were designed, synthesized, and characterized as sensitizers for dye-sensitized solar cell. All the RC dye sensitizers showed remarkable light-harvesting capacity and broadened absorption range. Significantly, RC-43 obtained the lower energy metal-ligand charge transfer (MLCT) band peaked at 557 nm with a high molar extinction coefficient of 27 400 M(-1) cm(-1). In conjunction with TiO2 photoanode of submicrospheres and iodide-based electrolytes, the DSSCs sensitizing with the RC sensitizers, achieved impressively high short-circuit current density (19.04 mA cm(-2) for RC-41, 19.83 mA cm(-2) for RC-42, and 20.21 mA cm(-2) for RC-43) and power conversion efficiency (10.07% for RC-41, 10.52% for RC-42, and 10.78% for RC-43). The superior performances of RC dye sensitizers were attributed to the enhanced light-harvesting capacity and incident-photon-to-current efficiency (IPCE) caused by the introduction of electron-donating antennas in the ancillary ligands. The interfacial charge recombination/regeneration kinetics and electron lifetime were further evaluated by the electrochemical impedance spectroscopy (EIS) and transient absorption spectroscopy (TAS). These data decisively revealed the dependences on the photovoltaic performance of ruthenium sensitizers incorporating electron-donating antennas.

  19. Scalable High-Performance Algorithm for the Simulation of Exciton Dynamics. Application to the Light-Harvesting Complex II in the Presence of Resonant Vibrational Modes.

    Science.gov (United States)

    Kreisbeck, Christoph; Kramer, Tobias; Aspuru-Guzik, Alán

    2014-09-09

    The accurate simulation of excitonic energy transfer in molecular complexes with coupled electronic and vibrational degrees of freedom is essential for comparing excitonic system parameters obtained from ab initio methods with measured time-resolved spectra. Several exact methods for computing the exciton dynamics within a density-matrix formalism are known but are restricted to small systems with less than 10 sites due to their computational complexity. To study the excitonic energy transfer in larger systems, we adapt and extend the exact hierarchical equation of motion (HEOM) method to various high-performance many-core platforms using the Open Compute Language (OpenCL). For the light-harvesting complex II (LHC II) found in spinach, the HEOM results deviate from predictions of approximate theories and clarify the time scale of the transfer process. We investigate the impact of resonantly coupled vibrations on the relaxation and show that the transfer does not rely on a fine-tuning of specific modes.

  20. Changes in Thermostability of Photosystem Ⅱ and Leaf Lipid Composition of Rice Mutant with Deficiency of Light-harvesting Chlorophyll Protein Complexes

    Institute of Scientific and Technical Information of China (English)

    Yunlai Tang; Mei Chen; Yinong Xu; Tingyun Kuang

    2007-01-01

    We studied the difference in thermostability of photosystem Ⅱ (PSⅡ) and leaf lipid composition between a T-DNA insertion mutant rice (Oryza sativa L.) VG28 and its wild type Zhonghua11. Native green gel and SDS-PAGE electrophoreses revealed that the mutant VG28 lacked all light-harvesting chlorophyll a/b protein complexes. Both the mutant and wild type were sensitive to high temperatures, and the maximal efficiency of PSⅡ photochemistry (Fv/Fm) and oxygen-evolving activity of PSⅡ in leaves significantly decreased with increasing temperature. However, the PSⅡ activity of the mutant was markedly more sensitive to high temperatures than that of the wild type. Lipid composition analysis showed that the mutant had less phosphatidylglycerol and sulfoquinovosyl diacylglycerol compared with the wild type. Fatty acid analysis revealed that the mutant had an obvious decrease in the content of unsaturation of membrane lipids on the thermostability of PSll are discussed.

  1. High Yield Non-detergent Isolation of Photosystem I-Light-harvesting Chlorophyll II Membranes from Spinach Thylakoids: IMPLICATIONS FOR THE ORGANIZATION OF THE PS I ANTENNAE IN HIGHER PLANTS.

    Science.gov (United States)

    Bell, Adam J; Frankel, Laurie K; Bricker, Terry M

    2015-07-24

    Styrene-maleic acid copolymer was used to effect a non-detergent partial solubilization of thylakoids from spinach. A high density membrane fraction, which was not solubilized by the copolymer, was isolated and was highly enriched in the Photosystem (PS) I-light-harvesting chlorophyll (LHC) II supercomplex and depleted of PS II, the cytochrome b6/f complex, and ATP synthase. The LHC II associated with the supercomplex appeared to be energetically coupled to PS I based on 77 K fluorescence, P700 photooxidation, and PS I electron transport light saturation experiments. The chlorophyll (Chl) a/b ratio of the PS I-LHC II membranes was 3.2 ± 0.9, indicating that on average, three LHC II trimers may associate with each PS I. The implication of these findings within the context of higher plant PS I antenna organization is discussed.

  2. Evolutionary loss of light-harvesting proteins Lhcb6 and Lhcb3 in major land plant groups--break-up of current dogma.

    Science.gov (United States)

    Kouřil, Roman; Nosek, Lukáš; Bartoš, Jan; Boekema, Egbert J; Ilík, Petr

    2016-05-01

    Photosynthesis in plants and algae relies on the coordinated function of photosystems (PS) I and II. Their efficiency is augmented by finely-tuned light-harvesting proteins (Lhcs) connected to them. The most recent Lhcs (in evolutionary terms), Lhcb6 and Lhcb3, evolved during the transition of plants from water to land and have so far been considered to be an essential characteristic of land plants. We used single particle electron microscopy and sequence analysis to study architecture and composition of PSII supercomplex from Norway spruce and related species. We have found that there are major land plant families that lack functional lhcb6 and lhcb3 genes, which notably changes the organization of PSII supercomplexes. The Lhcb6 and Lhcb3 proteins have been lost in the gymnosperm genera Picea and Pinus (family Pinaceae) and Gnetum (Gnetales). We also revealed that the absence of these proteins in Norway spruce modifies the PSII supercomplex in such a way that it resembles its counterpart in the alga Chlamydomonas reinhardtii, an evolutionarily older organism. Our results break a deep-rooted concept of Lhcb6 and Lhcb3 proteins being the essential characteristic of land plants, and beg the question of what the evolutionary benefit of their loss could be.

  3. Elucidation of structure-function relationships in photosynthetic light-harvesting antenna complexes by non-linear polarization spectroscopy in the frequency domain (NLPF).

    Science.gov (United States)

    Lokstein, Heiko; Krikunova, Maria; Teuchner, Klaus; Voigt, Bernd

    2011-08-15

    Photosynthetically active pigments are usually organized into pigment-protein complexes. These include light-harvesting antenna complexes (LHCs) and reaction centers. Site energies of the bound pigments are determined by interactions with their environment, i.e., by pigment-protein as well as pigment-pigment interactions. Thus, resolution of spectral substructures of the pigment-protein complexes may provide valuable insight into structure-function relationships. By means of conventional (linear) and time-resolved spectroscopic techniques, however, it is often difficult to resolve the spectral substructures of complex pigment-protein assemblies. Nonlinear polarization spectroscopy in the frequency domain (NLPF) is shown to be a valuable technique in this regard. Based on initial experimental work with purple bacterial antenna complexes as well as model systems NLPF has been extended to analyse the substructure(s) of very complex spectra, including analyses of interactions between chlorophylls and "optically dark" states of carotenoids in LHCs. The paper reviews previous work and outlines perspectives regarding the application of NLPF spectroscopy to disentangle structure-function relationships in pigment-protein complexes.

  4. [Formation of 55-kDa Fragments under Impaired Coordination Bonds and Hydrophobic Interactions in Peripheral Light-Harvesting Complexes Isolated from Photosynthetic Purple Bacteria].

    Science.gov (United States)

    Solov'ev, A A; Erokhin, Y E

    2015-01-01

    Size exclusion chromatography was used to assess the relative size of intact and diphenylamine-treated (DPA, with suppressed carotenoid synthesis) peripheral light-harvesting complexes (LH2 complexes) of the sulfurbacterium Allochromatium minutissimum. Both LH2 complexes were nonamers and had the same elution volume V(e), coinciding with that for the LH2 complex of Rhodoblastus acidophilus (strain 10050). Their molecular mass was 150 kDa. Bot pheophytinization of bacteriochlorophyll (BChl) at low pH and treatment with the detergent LDAO, affecting the hydrophobic interactions between the neighboring protomers, result in the fragmentation of the ring of the isolated LH2 complexes and formation of 55-kDa fragments with molecular masses corresponding to one-third of the initial value. Fragmentation caused by both pheophytinization and detergent treatment was much more rapid in DPA-treated LH2 complexes than in the intact ones. The 55-kDa fragments formed at low pH values contained monomeric bacteriopheophytin, while the fragments of a similar molecular mass formed at pH 8.0 in the presence of the detergent contained monomeric BChl. The observed fragmentation was hypothesized to reflect the inherent C3 symmetry of the LH2 complexes, with the preliminarily assembled trimers used as building blocks.

  5. Influence of phospholipid composition on self-assembly and energy-transfer efficiency in networks of light-harvesting 2 complexes.

    Science.gov (United States)

    Sumino, Ayumi; Dewa, Takehisa; Noji, Tomoyasu; Nakano, Yuki; Watanabe, Natsuko; Hildner, Richard; Bösch, Nils; Köhler, Jürgen; Nango, Mamoru

    2013-09-12

    In the photosynthetic membrane of purple bacteria networks of light-harvesting 2 (LH2) complexes capture the sunlight and transfer the excitation energy. In order to investigate the mutual relationship between the supramolecular organization of the pigment-protein complexes and their biological function, the LH2 complexes were reconstituted into three types of phospholipid membranes, consisting of L-α-phosphatidylglycerol (PG), L-α-phosphatidylcholine (PC), and L-α-phosphatidylethanolamine (PE)/PG/cardiolipin (CL). Atomic force microscopy (AFM) revealed that the type of phospholipids had a crucial influence on the clustering tendency of the LH2 complexes increased from PG over PC to PE/PG/CL, where the LH2 complexes formed large, densely packed clusters. Time-resolved spectroscopy uncovered a strong quenching of the LH2 fluorescence that is ascribed to singlet-singlet and singlet-triplet annihilation by an efficient energy transfer between the LH2 complexes in the artificial membrane systems. Quantitative analysis reveals that the intercomplex energy transfer efficiency varies strongly as a function of the morphology of the nanostructure, namely in the order PE/PG/CL > PC > PG, which is in line with the clustering tendency of LH2 observed by AFM. These results suggest a strong influence of the phospholipids on the self-assembly of LH2 complexes into networks and concomitantly on the intercomplex energy transfer efficiency.

  6. High efficiency light harvesting by carotenoids in the LH2 complex from photosynthetic bacteria: unique adaptation to growth under low-light conditions.

    Science.gov (United States)

    Magdaong, Nikki M; LaFountain, Amy M; Greco, Jordan A; Gardiner, Alastair T; Carey, Anne-Marie; Cogdell, Richard J; Gibson, George N; Birge, Robert R; Frank, Harry A

    2014-09-25

    Rhodopin, rhodopinal, and their glucoside derivatives are carotenoids that accumulate in different amounts in the photosynthetic bacterium, Rhodoblastus (Rbl.) acidophilus strain 7050, depending on the intensity of the light under which the organism is grown. The different growth conditions also have a profound effect on the spectra of the bacteriochlorophyll (BChl) pigments that assemble in the major LH2 light-harvesting pigment-protein complex. Under high-light conditions the well-characterized B800-850 LH2 complex is formed and accumulates rhodopin and rhodopin glucoside as the primary carotenoids. Under low-light conditions, a variant LH2, denoted B800-820, is formed, and rhodopinal and rhodopinal glucoside are the most abundant carotenoids. The present investigation compares and contrasts the spectral properties and dynamics of the excited states of rhodopin and rhodopinal in solution. In addition, the systematic differences in pigment composition and structure of the chromophores in the LH2 complexes provide an opportunity to explore the effect of these factors on the rate and efficiency of carotenoid-to-BChl energy transfer. It is found that the enzymatic conversion of rhodopin to rhodopinal by Rbl. acidophilus 7050 grown under low-light conditions results in nearly 100% carotenoid-to-BChl energy transfer efficiency in the LH2 complex. This comparative analysis provides insight into how photosynthetic systems are able to adapt and survive under challenging environmental conditions.

  7. Molecular factors controlling photosynthetic light harvesting by carotenoids.

    Science.gov (United States)

    Polívka, Tomás; Frank, Harry A

    2010-08-17

    Carotenoids are naturally occurring pigments that absorb light in the spectral region in which the sun irradiates maximally. These molecules transfer this energy to chlorophylls, initiating the primary photochemical events of photosynthesis. Carotenoids also regulate the flow of energy within the photosynthetic apparatus and protect it from photoinduced damage caused by excess light absorption. To carry out these functions in nature, carotenoids are bound in discrete pigment-protein complexes in the proximity of chlorophylls. A few three-dimensional structures of these carotenoid complexes have been determined by X-ray crystallography. Thus, the stage is set for attempting to correlate the structural information with the spectroscopic properties of carotenoids to understand the molecular mechanism(s) of their function in photosynthetic systems. In this Account, we summarize current spectroscopic data describing the excited state energies and ultrafast dynamics of purified carotenoids in solution and bound in light-harvesting complexes from purple bacteria, marine algae, and green plants. Many of these complexes can be modified using mutagenesis or pigment exchange which facilitates the elucidation of correlations between structure and function. We describe the structural and electronic factors controlling the function of carotenoids as energy donors. We also discuss unresolved issues related to the nature of spectroscopically dark excited states, which could play a role in light harvesting. To illustrate the interplay between structural determinations and spectroscopic investigations that exemplifies work in the field, we describe the spectroscopic properties of four light-harvesting complexes whose structures have been determined to atomic resolution. The first, the LH2 complex from the purple bacterium Rhodopseudomonas acidophila, contains the carotenoid rhodopin glucoside. The second is the LHCII trimeric complex from higher plants which uses the carotenoids

  8. PS2013 Satellite Workshop on Photosynthetic Light-Harvesting Systems

    Energy Technology Data Exchange (ETDEWEB)

    Niederman, Robert A. [Rutgers Univ., New Brunswick, NJ (United States); Blankenship, Robert E. [Washington Univ., St. Louis, MO (United States); Frank, Harry A. [Univ. of Connecticut, Storrs, CT (United States)

    2015-02-07

    represented a diverse international and multidisciplinary group, with over 160 individuals attending from a total of 17 different countries. Attendees came from a wide range of fields assuring that the widest possible interdisciplinary exchanges. They included prominent biochemists, biophysicists, plant physiologists, chemical physicists, as well as theoretical and computational physical chemists, who presented their research findings or to hear the latest advances in this very dynamic field. In the choice of speakers, a balance was created between established scientists and young, emerging researchers, given this opportunity to showcase their results. Sessions were held on electronic and vibrational coherence including coherent sharing of excitations among donor and acceptor molecules during excitation energy transfer, nonphotochemical quenching, acclimation to light environments, evolution, adaptation and biodiversity of light-harvesting pigment-protein complexes, their structure and membrane organization, spectroscopy and dynamics, as well as artificial antenna systems. A joint session was also held with the participants from the Cyanobacterial Satellite Conference. A special issue of Photosynthesis Research devoted to light harvesting (Volume 121, Issue No. 1, July 2014) has recently appeared which contains peer-reviewed original research contributions arising from talks and posters presented at the PS2013 Satellite Workshop on Photosynthetic Light-Harvesting Systems. Edited by the Organizers of the Workshop, Robert E. Blankenship, Harry A. Frank and Robert A. Niederman, it includes topics ranging from the isolation of new bacteriochlorophyll species from green bacteria, temperature effects on the excited states of the newly discovered chlorophyll (Chl) ƒ, new architectures for enhancing energy capture by biohybrid light-harvesting complexes, forces governing the formation of light-harvesting rings, spectroscopy of carotenoids of algae and diatoms and the supramolecular

  9. Crystallization and preliminary X-ray diffraction analysis of the peripheral light-harvesting complex LH2 from Marichromatium purpuratum.

    Science.gov (United States)

    Cranston, Laura J; Roszak, Aleksander W; Cogdell, Richard J

    2014-06-01

    LH2 from the purple photosynthetic bacterium Marichromatium (formerly known as Chromatium) purpuratum is an integral membrane pigment-protein complex that is involved in harvesting light energy and transferring it to the LH1-RC `core' complex. The purified LH2 complex was crystallized using the sitting-drop vapour-diffusion method at 294 K. The crystals diffracted to a resolution of 6 Å using synchrotron radiation and belonged to the tetragonal space group I4, with unit-cell parameters a=b=109.36, c=80.45 Å. The data appeared to be twinned, producing apparent diffraction symmetry I422. The tetragonal symmetry of the unit cell and diffraction for the crystals of the LH2 complex from this species reveal that this complex is an octamer.

  10. Temperature-induced dissociation reaction and dynamics of light-harvesting complex Ⅱ isolated from purple photosynthetic bacterium Rps. palustris

    Institute of Scientific and Technical Information of China (English)

    FENG Juan; LI XueFeng; LIU Yuan

    2007-01-01

    Steady-state absorption spectroscopy, circular dichroism, and resonance Raman spectroscopy have been used to investigate the thermal stability of LH2 complex isolated from purple photosynthetic bacterium Rps. Palustris. The results show that: 1) upon increasing the temperature, a transition from B800 and B850 to free bacteriochlorophyll (B780) happens; 2) a gradual decrease and disappearance of CD signal in visible region occur; 3) a shift of the frequency, belonging to C=C and C-C stretching vibration, to higher wavenumber takes place. It is suggested that LH2 complex can be dissociated in the presence of B800, B850 and carotenoids simultaneously. Single-exponential fitting on the dynamic decay curves gives the apparent time constants of hundreds of minutes for various pigments.

  11. Distribution of colored carotenoids between light-harvesting complexes in the process of recovering carotenoid biosynthesis in Ectothiorhodospira haloalkaliphila cells.

    Science.gov (United States)

    Ashikhmin, Aleksandr; Makhneva, Zoya; Bolshakov, Maksim; Moskalenko, Andrey

    2014-12-01

    The processes of recovering colored-carotenoid (Car) biosynthesis in Car-less cells of the purple sulfur bacterium Ectothiorhodospira haloalkaliphila grown with diphenylamine (DPA-cells) have been studied. It has been found that (1) the rate of recovering colored-Car biosynthesis in the lag-phase is far ahead of the growth rate of the cells themselves; (2) several Cars (ζ-carotene, neurosporene etc.) act as intermediates in Car biosynthesis; (3) because filling the "empty" Car pockets in the LH1-RC complexes is faster than in LH2, available spirilloxanthin is preferentially incorporated into the nascent LH1-RC core particles; (4) as a consequence of the resulting lack of spirilloxanthin availability, the biosynthetic intermediates (anhydrorhodovibrin, rhodopin and lycopene) fill the empty nascent LH2 Car pockets. In the present report, we further discuss the process of colored Car incorporation into LH complexes during the recovery of Car biosynthesis in the DPA-cells of Ect.haloalkaliphila.

  12. The upstream regulatory sequence of the light harvesting complex Lhcf2 gene of the marine diatom Phaeodactylum tricornutum enhances transcription in an orientation- and distance-independent fashion.

    Science.gov (United States)

    Russo, Monia Teresa; Annunziata, Rossella; Sanges, Remo; Ferrante, Maria Immacolata; Falciatore, Angela

    2015-12-01

    Diatoms are a key phytoplankton group in the contemporary ocean, showing extraordinary adaptation capacities to rapidly changing environments. The recent availability of whole genome sequences from representative species has revealed distinct features in their genomes, like novel combinations of genes encoding distinct metabolisms and a significant number of diatom-specific genes. However, the regulatory mechanisms driving diatom gene expression are still largely uncharacterized. Considering the wide variety of fields of study orbiting diatoms, ranging from ecology, evolutionary biology to biotechnology, it is thus essential to increase our understanding of fundamental gene regulatory processes such as transcriptional regulation. To this aim, we explored the functional properties of the 5'-flanking region of the Phaeodatylum tricornutum Lhcf2 gene, encoding a member of the Light Harvesting Complex superfamily and we showed that this region enhances transcription of a GUS reporter gene in an orientation- and distance-independent fashion. This represents the first example of a cis-regulatory sequence with enhancer-like features discovered in diatoms and it is instrumental for the generation of novel genetic tools and diatom exploitation in different areas of study. Copyright © 2015 Elsevier B.V. All rights reserved.

  13. Analysis of Chloroplast Ultrastructure, Photosystem Ⅱ Light Harvesting Complexes and Chlorophyll Synthesis in a Chlorophyll-Less Rice Mutant W2555

    Institute of Scientific and Technical Information of China (English)

    XU Pei-zhou; LI Yun; YUAN Shu; ZHANG Hong-yu; WANG Xu-dong; LIN Hong-hui; WU Xian-jun

    2006-01-01

    A comparative study on chloroplast ultrastructure and light harvesting complex of photosystem Ⅱ (LHC Ⅱ) was conducted between a new rice mutant (W2555) and its wild type (WT). The chloroplasts of W2555 had less thylakoids and grana stacks compared with the wild type. There was no significant change in the composition of LHC Ⅱ polypeptide in W2555, while a decline had been noted in LHC Ⅱ content. Northern blot analysis with a specific cab gene probe showed no appreciable difference in the LHC Ⅱ mRNA level between the W2555 and its wild type. The precursors of chlorophyll synthesis, δ-aminolevulinic acid (ALA)and porphobilinogen (PBG) were over accumulated in W2555, but the other precursors were all decreased. These results indicated that the decreased level of LHC Ⅱ in the mutant W2555 was attributed to the change of cab gene transcription, but a blockage in chlorophyll biosynthesis due to the formation of uroporphyrinogen Ⅲ (Urogen Ⅲ).

  14. Lessons from nature about solar light harvesting

    Science.gov (United States)

    Scholes, Gregory D.; Fleming, Graham R.; Olaya-Castro, Alexandra; van Grondelle, Rienk

    2011-10-01

    Solar fuel production often starts with the energy from light being absorbed by an assembly of molecules; this electronic excitation is subsequently transferred to a suitable acceptor. For example, in photosynthesis, antenna complexes capture sunlight and direct the energy to reaction centres that then carry out the associated chemistry. In this Review, we describe the principles learned from studies of various natural antenna complexes and suggest how to elucidate strategies for designing light-harvesting systems. We envisage that such systems will be used for solar fuel production, to direct and regulate excitation energy flow using molecular organizations that facilitate feedback and control, or to transfer excitons over long distances. Also described are the notable properties of light-harvesting chromophores, spatial-energetic landscapes, the roles of excitonic states and quantum coherence, as well as how antennas are regulated and photoprotected.

  15. Functional characteristics of spirilloxanthin and keto-bearing Analogues in light-harvesting LH2 complexes from Rhodobacter sphaeroides with a genetically modified carotenoid synthesis pathway.

    Science.gov (United States)

    Niedzwiedzki, Dariusz M; Dilbeck, Preston L; Tang, Qun; Mothersole, David J; Martin, Elizabeth C; Bocian, David F; Holten, Dewey; Hunter, C Neil

    2015-01-01

    Light-harvesting 2 (LH2) complexes from a genetically modified strain of the purple photosynthetic bacterium Rhodobacter (Rba.) sphaeroides were studied using static and ultrafast optical methods and resonance Raman spectroscopy. Carotenoid synthesis in the Rba. sphaeroides strain was engineered to redirect carotenoid production away from spheroidene into the spirilloxanthin synthesis pathway. The strain assembles LH2 antennas with substantial amounts of spirilloxanthin (total double-bond conjugation length N=13) if grown anaerobically and of keto-bearing long-chain analogs [2-ketoanhydrorhodovibrin (N=13), 2-ketospirilloxanthin (N=14) and 2,2'-diketospirilloxanthin (N=15)] if grown semi-aerobically (with ratios that depend on growth conditions). We present the photophysical, electronic, and vibrational properties of these carotenoids, both isolated in organic media and assembled within LH2 complexes. Measurements of excited-state energy transfer to the array of excitonically coupled bacteriochlorophyll a molecules (B850) show that the mean lifetime of the first singlet excited state (S1) of the long-chain (N≥13) carotenoids does not change appreciably between organic media and the protein environment. In each case, the S1 state appears to lie lower in energy than that of B850. The energy-transfer yield is ~0.4 in LH2 (from the strain grown aerobically or semi-aerobically), which is less than half that achieved for LH2 that contains short-chain (N≤11) analogues. Collectively, the results suggest that the S1 excited state of the long-chain (N≥13) carotenoids participates little if at all in carotenoid-to-BChl a energy transfer, which occurs predominantly via the carotenoid S2 excited state in these antennas.

  16. Photodynamics of Light Harvesting Systems

    NARCIS (Netherlands)

    Ruijter, Ward Piet Frans de

    2005-01-01

    Light harvesting (LH) lies at the basis of photosynthesis, the process in which energy from the sun is stored by a photochemical reaction. The photophysics of light absorption and energy transfer is the key to a detailed understanding of the first steps in this process. This thesis describes the

  17. Photodynamics of Light Harvesting Systems

    NARCIS (Netherlands)

    Ruijter, Ward Piet Frans de

    2005-01-01

    Light harvesting (LH) lies at the basis of photosynthesis, the process in which energy from the sun is stored by a photochemical reaction. The photophysics of light absorption and energy transfer is the key to a detailed understanding of the first steps in this process. This thesis describes the inv

  18. A Zea mays 39-kDa thylakoid transglutaminase catalyses the modification by polyamines of light-harvesting complex II in a light-dependent way.

    Science.gov (United States)

    Della Mea, M; Di Sandro, A; Dondini, L; Del Duca, S; Vantini, F; Bergamini, C; Bassi, R; Serafini-Fracassini, D

    2004-09-01

    A transglutaminase (TGase; EC 2.3.2.13) activity, which shared many properties with the TGase activity of the Helianthus tuberosus chloroplast, was observed in the Zea mays L. chloroplast and in its fractions. This activity was found to be prevalent in thylakoids; bis-(glutamyl) spermidine and bis-(glutamyl) putrescine were the main polyamine conjugates formed. Light stimulated the endogenous thylakoid activity. Putrescine, spermidine and spermine were conjugated to the isolated light-harvesting complex of photosystem II (LHCII) with different degrees of efficiency, spermine being the polyamine most efficiently conjugated. A TGase with a light-sensitive activity was identified in the photosystem II-enriched fraction. Its partial purification on a sucrose gradient allowed the separation of a 39-kDa band, which was immunorecognised by two anti-TGase antibodies (Ab-3 and rat prostatic gland-TGase). Both a colorimetric and a radiometric assay for TGase activity, the former carried out in the presence of biotinylated cadaverine and the latter in the presence of polyamines labelled with radioactive isotopes and resulting in the isolation of glutamyl-polyamines, further confirmed that the thylakoid enzyme is indeed a calcium-dependent transglutaminase (Thyl-TGase). At variance with guinea pig liver and erythrocyte TGases, which are insensitive to light, the activity of the thylakoid transglutaminase is affected by light. Moreover, this enzyme, when tested with purified LHCII as substrate, catalysed the production of mono- and bis-glutamyl-polyamines in equal amounts, whereas the 'animal' enzymes produced mainly mono-derivatives. Herein, it is discussed whether this light sensitivity is due to the enzyme or the substrate.

  19. Photosynthetic light harvesting: excitons and coherence.

    Science.gov (United States)

    Fassioli, Francesca; Dinshaw, Rayomond; Arpin, Paul C; Scholes, Gregory D

    2014-03-06

    Photosynthesis begins with light harvesting, where specialized pigment-protein complexes transform sunlight into electronic excitations delivered to reaction centres to initiate charge separation. There is evidence that quantum coherence between electronic excited states plays a role in energy transfer. In this review, we discuss how quantum coherence manifests in photosynthetic light harvesting and its implications. We begin by examining the concept of an exciton, an excited electronic state delocalized over several spatially separated molecules, which is the most widely available signature of quantum coherence in light harvesting. We then discuss recent results concerning the possibility that quantum coherence between electronically excited states of donors and acceptors may give rise to a quantum coherent evolution of excitations, modifying the traditional incoherent picture of energy transfer. Key to this (partially) coherent energy transfer appears to be the structure of the environment, in particular the participation of non-equilibrium vibrational modes. We discuss the open questions and controversies regarding quantum coherent energy transfer and how these can be addressed using new experimental techniques.

  20. Spectroscopic Investigations of the Photophysics of Cryptophyte Light-Harvesting

    Science.gov (United States)

    Dinshaw, Rayomond

    The biological significance of photosynthesis is indisputable as it is necessary for nearly all life on earth. Photosynthesis provides chemical energy for plants, algae, and bacteria, while heterotrophic organisms rely on these species as their ultimate food source. The initial step in photosynthesis requires the absorption of sunlight to create electronic excitations. Light-harvesting proteins play the functional role of capturing solar radiation and transferring the resulting excitation to the reaction centers where it is used to carry out the chemical reactions of photosynthesis. Despite the wide variety of light-harvesting protein structures and arrangements, most light-harvesting proteins are able to utilize the captured solar energy for charge separation with near perfect quantum efficiency.1 This thesis will focus on understanding the energy transfer dynamics and photophysics of a specific subset of light-harvesting antennae known as phycobiliproteins. These proteins are extracted from cryptophyte algae and are investigated using steady-state and ultrafast spectroscopic techniques.

  1. Design principles of natural light-harvesting as revealed by single molecule spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Krüger, T.P.J., E-mail: tjaart.kruger@up.ac.za [Department of Physics, University of Pretoria, Private bag X20, Hatfield 0028 (South Africa); Grondelle, R. van [Department of Physics and Astronomy, VU University Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam (Netherlands)

    2016-01-01

    Biology offers a boundless source of adaptation, innovation, and inspiration. A wide range of photosynthetic organisms exist that are capable of harvesting solar light in an exceptionally efficient way, using abundant and low-cost materials. These natural light-harvesting complexes consist of proteins that strongly bind a high density of chromophores to capture solar photons and rapidly transfer the excitation energy to the photochemical reaction centre. The amount of harvested light is also delicately tuned to the level of solar radiation to maintain a constant energy throughput at the reaction centre and avoid the accumulation of the products of charge separation. In this Review, recent developments in the understanding of light-harvesting by plants will be discussed, based on results obtained from single molecule spectroscopy studies. Three design principles of the main light-harvesting antenna of plants will be highlighted: (a) fine, photoactive control over the intrinsic protein disorder to efficiently use intrinsically available thermal energy dissipation mechanisms; (b) the design of the protein microenvironment of a low-energy chromophore dimer to control the amount of shade absorption; (c) the design of the exciton manifold to ensure efficient funneling of the harvested light to the terminal emitter cluster.

  2. Heterologous Production of the Photosynthetic Reaction Center and Light Harvesting 1 Complexes of the Thermophile Thermochromatium tepidum in the Mesophile Rhodobacter sphaeroides and Thermal Stability of a Hybrid Core Complex.

    Science.gov (United States)

    Jun, D; Huang, V; Beatty, J T

    2017-10-15

    The photosynthetic complexes of the thermophile Thermochromatium tepidum are of considerable interest in biohybrid solar cell applications because of the ability of thermophilic proteins to tolerate elevated temperatures. Synthetic operons encoding reaction center (RC) and light harvesting 1 (LH1) pigment-protein complexes of T. tepidum were expressed in the mesophile Rhodobacter sphaeroides The T. tepidum RC (TRC) was assembled and was found to be functional with the addition of menadione to populate the QA pocket. The production of T. tepidum LH1 (TLH1) was increased by selection of a phototrophy-capable mutant after UV irradiation mutagenesis, which yielded a hybrid RC-TLH1 core complex consisting of the R. sphaeroides RC and T. tepidum TLH1, confirmed by the absorbance peak of TLH1 at 915 nm. Affinity chromatography partial purification and subsequent sucrose gradient analysis of the hybrid RC-TLH1 core complex indicated that this core complex assembled as a monomer. Furthermore, the RC-TLH1 hybrid core complex was more tolerant of a temperature of 70°C than the R. sphaeroides RC-LH1 core complexes in both the dimeric and monomeric forms; after 1 h, the hybrid complex retained 58% of the initial starting value, compared to values of 11% and 53% for the R. sphaeroides RC-LH1 dimer and monomer forms, respectively.IMPORTANCE This work is important because it is a new approach to bioengineering of photosynthesis proteins for potential use in biophotovoltaic solar energy capture. The work establishes a proof of principle for future biohybrid solar cell applications. Copyright © 2017 American Society for Microbiology.

  3. A structure-based model of energy transfer reveals the principles of light harvesting in photosystem II supercomplexes.

    Science.gov (United States)

    Bennett, Doran I G; Amarnath, Kapil; Fleming, Graham R

    2013-06-19

    Photosystem II (PSII) initiates photosynthesis in plants through the absorption of light and subsequent conversion of excitation energy to chemical energy via charge separation. The pigment binding proteins associated with PSII assemble in the grana membrane into PSII supercomplexes and surrounding light harvesting complex II trimers. To understand the high efficiency of light harvesting in PSII requires quantitative insight into energy transfer and charge separation in PSII supercomplexes. We have constructed the first structure-based model of energy transfer in PSII supercomplexes. This model shows that the kinetics of light harvesting cannot be simplified to a single rate limiting step. Instead, substantial contributions arise from both excitation diffusion through the antenna pigments and transfer from the antenna to the reaction center (RC), where charge separation occurs. Because of the lack of a rate-limiting step, fitting kinetic models to fluorescence lifetime data cannot be used to derive mechanistic insight on light harvesting in PSII. This model will clarify the interpretation of chlorophyll fluorescence data from PSII supercomplexes, grana membranes, and leaves.

  4. Economic photoprotection in photosystem II that retains a complete light-harvesting system with slow energy traps.

    Science.gov (United States)

    Belgio, Erica; Kapitonova, Ekaterina; Chmeliov, Jevgenij; Duffy, Christopher D P; Ungerer, Petra; Valkunas, Leonas; Ruban, Alexander V

    2014-07-11

    The light-harvesting antenna of higher plant photosystem II has an intrinsic capability for self-defence against intense sunlight. The thermal dissipation of excess energy can be measured as the non-photochemical quenching of chlorophyll fluorescence. It has recently been proposed that the transition between the light-harvesting and self-defensive modes is associated with a reorganization of light-harvesting complexes. Here we show that despite structural changes, the photosystem II cross-section does not decrease. Our study reveals that the efficiency of energy trapping by the non-photochemical quencher(s) is lower than the efficiency of energy capture by the reaction centres. Consequently, the photoprotective mechanism works effectively for closed rather than open centres. This type of defence preserves the exceptional efficiency of electron transport in a broad range of light intensities, simultaneously ensuring high photosynthetic productivity and, under hazardous light conditions, sufficient photoprotection for both the reaction centre and the light-harvesting pigments of the antenna.

  5. Economic photoprotection in photosystem II that retains a complete light-harvesting system with slow energy traps

    Science.gov (United States)

    Belgio, Erica; Kapitonova, Ekaterina; Chmeliov, Jevgenij; Duffy, Christopher D. P.; Ungerer, Petra; Valkunas, Leonas; Ruban, Alexander V.

    2014-07-01

    The light-harvesting antenna of higher plant photosystem II has an intrinsic capability for self-defence against intense sunlight. The thermal dissipation of excess energy can be measured as the non-photochemical quenching of chlorophyll fluorescence. It has recently been proposed that the transition between the light-harvesting and self-defensive modes is associated with a reorganization of light-harvesting complexes. Here we show that despite structural changes, the photosystem II cross-section does not decrease. Our study reveals that the efficiency of energy trapping by the non-photochemical quencher(s) is lower than the efficiency of energy capture by the reaction centres. Consequently, the photoprotective mechanism works effectively for closed rather than open centres. This type of defence preserves the exceptional efficiency of electron transport in a broad range of light intensities, simultaneously ensuring high photosynthetic productivity and, under hazardous light conditions, sufficient photoprotection for both the reaction centre and the light-harvesting pigments of the antenna.

  6. Energizing the light harvesting antenna: Insight from CP29.

    Science.gov (United States)

    Ioannidis, Nikolaos E; Papadatos, Sotiris; Daskalakis, Vangelis

    2016-10-01

    How do plants cope with excess light energy? Crop health and stress tolerance are governed by molecular photoprotective mechanisms. Protective exciton quenching in plants is activated by membrane energization, via unclear conformational changes in proteins called antennas. Here we show that pH and salt gradients stimulate the response of such an antenna under low and high energization by all-atom Molecular Dynamics Simulations. Novel insight establishes that helix-5 (H5) conformation in CP29 from spinach is regulated by chemiosmotic factors. This is selectively correlated with the chl-614 macrocycle deformation and interactions with nearby pigments, that could suggest a role in plant photoprotection. Adding to the significance of our findings, H5 domain is conserved among five antennas (LHCB1-5). These results suggest that light harvesting complexes of Photosystem II, one of the most abundant proteins on earth, can sense chemiosmotic gradients via their H5 domains in an upgraded role from a solar detector to also a chemiosmotic sensor.

  7. Natural Light Harvesting Systems: Unraveling the quantum puzzles

    CERN Document Server

    Thilagam, A

    2013-01-01

    In natural light harvesting systems, the sequential quantum events of photon absorption by specialized biological antenna complexes, charge separation, exciton formation and energy transfer to localized reaction centers culminates in the conversion of solar to chemical energy. A notable feature in these processes is the exceptionally high efficiencies (> 95 %) at which excitation is transferred from the illuminated protein complex site to the reaction centers. Such high exciton propagation rates within a system of interwoven biomolecular network structures, is yet to be replicated in artificial light harvesting complexes. A clue to unraveling the quantum puzzles of nature may lie in the observation of long lived coherences lasting several picoseconds in the electronic spectra of photosynthetic complexes, even in noisy environmental baths. A number of experimental and theoretical studies have been devoted to unlocking the links between quantum processes and information protocols, in the hope of finding answers...

  8. Limits of quantum speedup in photosynthetic light harvesting

    CERN Document Server

    Hoyer, Stephan; Whaley, K Birgitta

    2009-01-01

    In the initial stages of photosynthesis, energy collected from light is transferred across a network of chlorophyll molecules to a reaction center. Recent experimental evidence showing long lived quantum coherences in this energy transport in several photosynthetic light-harvesting complexes has suggested that coherence may play an important role in the function of these systems. In particular, it has been hypothesized that excitation transport in such systems may feature speedups analogous to those found in quantum algorithms. The most direct analogy to such transport is found in quantum walks, which form the basis of a powerful class of quantum algorithms including quantum search. Unlike idealized quantum walks, however, real light harvesting complexes are characterized by disorder, energy funnels and decoherence. Whether any quantum speedup can be found in this situation is unclear. Here we characterize quantum speedup for excitation energy transfer in the Fenna-Matthews-Olson (FMO) complex of green sulfur...

  9. A light-harvesting array of synthetic porphyrins

    Science.gov (United States)

    Davila, Jorge; Harriman, Anthony; Milgrom, Lionel R.

    1987-05-01

    An array of five porphyrin molecules has been synthesized and used as a simple model of the light-harvesting complex found in natural photosynthesis. Efficient Förster energy transfer occurs from antenna zinc porphyrins to a central free-base porphyrin molecule. This central porphyrin retains long-lived singlet and triplet excited states that can be quenched by diffusional processes, Both electron and energy transfer quenching reactions can be observed.

  10. Structural characterization of the B800-850 and B875 light-harvesting antenna complexes from Rhodobacter sphaeroides by electron microscopy

    NARCIS (Netherlands)

    Boonstra, Arjen F.; Visschers, Ronald W.; Calkoen, Florentine; Grondelle, Rienk van; Bruggen, Ernst F.J. van; Boekema, Egbert J.

    1993-01-01

    The structure and aggregation behavior of B800-850 (LHII) and B875 (LHI) antenna complexes of Rhodobacter sphaeroides were studied by electron microscopy. Single molecular projections (top views and side views) of isolated particles were analyzed. The B800-850 complexes, isolated as 150 kDa particle

  11. Optimization of light harvesting and photoprotection: molecular mechanisms and physiological consequences

    OpenAIRE

    Horton, Peter

    2012-01-01

    The distinctive lateral organization of the protein complexes in the thylakoid membrane investigated by Jan Anderson and co-workers is dependent on the balance of various attractive and repulsive forces. Modulation of these forces allows critical physiological regulation of photosynthesis that provides efficient light-harvesting in limiting light but dissipation of excess potentially damaging radiation in saturating light. The light-harvesting complexes (LHCII) are central to this regulation,...

  12. The Effect of Dye Density on the Efficiency of Photosensitization of TiO2 Films: Light-Harvesting by Phenothiazine-Labelled Dendritic Ruthenium Complexes

    Directory of Open Access Journals (Sweden)

    Lin-Yong Zhu

    2009-09-01

    Full Text Available A family of dendritic tris-bipyridyl ruthenium coordination complexes incorporating two or four carboxylate groups for binding to a TiO2 surface site and another dendritic linker between the metal complex and highly absorptive dyes were formulated as thin films on TiO2 coated glass. The family included phenothiazine-substituted dendrons of increasing structural complexity and higher optical density. The dye-loaded films were characterized by steady-state emission and absorption measurements and by kinetic studies of luminescence and transient absorption. Upon photoexcitation of the bound dyes, rapid electron injection into the metal oxide film was the dominant observed process, producing oxidized dye that persisted for hundreds of milliseconds. Complex decay profiles for emission, transient absorption, and optical bleaching of the dendritic dyes point to highly heterogeneous behavior for the films, with observed persistence lifetimes related directly to structurally enhance electronic coupling between the metal oxide support and the dendritic dyes.

  13. Photosystem I light-harvesting complex Lhca4 adopts multiple conformations : Red forms and excited-state quenching are mutually exclusive

    NARCIS (Netherlands)

    Passarini, Francesca; Wientjes, Emilie; van Amerongen, Herbert; Croce, Roberta

    2010-01-01

    In this work we have investigated the origin of the multi-exponential fluorescence decay and of the short excited-state lifetime of Lhca4. Lhca4 is the antenna complex of Photosystem I which accommodates the red-most chlorophyll forms and it has been proposed that these chlorophylls can play a role

  14. Photosystem I light-harvesting complex Lhca4 adopts multiple conformations: red forms and excited-state quenching are mutually exclusive

    NARCIS (Netherlands)

    Passarini, F.; Wientjes, E.; Amerongen, van H.; Croce, R.

    2010-01-01

    In this work we have investigated the origin of the multi-exponential fluorescence decay and of the short excited-state lifetime of Lhca4. Lhca4 is the antenna complex of Photosystem I which accommodates the red-most chlorophyll forms and it has been proposed that these chlorophylls can play a role

  15. Coupling of metal-based light-harvesting antennas and electron-donor subunits: Trinuclear Ruthenium(II) complexes containing tetrathiafulvalene-substituted polypyridine ligands

    DEFF Research Database (Denmark)

    Campagna, Sebastiano; Serroni, Scolastica; Puntoriero, Fausto

    2002-01-01

    Three new tetrathiafulvalene-substituted 2,2'-bipyridine ligands, cis-bpy-TTF1, trans-bpy-TTF1, and cis-bpy-TTF2 have been prepared and characterized. X-ray analysis of trans-bpy-TTF1, is also reported. Such ligands have been used to prepare two new trinuclear Ru-II complexes, namely, [{(bpy)(2)R...

  16. Production of superoxide from photosystem II-light harvesting complex II supercomplex in STN8 kinase knock-out rice mutants under photoinhibitory illumination.

    Science.gov (United States)

    Poudyal, Roshan Sharma; Nath, Krishna; Zulfugarov, Ismayil S; Lee, Choon-Hwan

    2016-09-01

    When phosphorylation of Photosystem (PS) II core proteins is blocked in STN8 knock-out mutants of rice (Oryza sativa) under photoinhibitory illumination, the mobilization of PSII supercomplex is prevented. We have previously proposed that more superoxide (O2(-)) is produced from PSII in the mutant (Nath et al., 2013, Plant J. 76, 675-686). Here, we clarify the type and site for the generation of reactive oxygen species (ROS). Using both histochemical and fluorescence probes, we observed that, compared with wild-type (WT) leaves, levels of ROS, including O2(-) and hydrogen peroxide (H2O2), were increased when leaves from mutant plants were illuminated with excess light. However, singlet oxygen production was not enhanced under such conditions. When superoxide dismutase was inhibited, O2(-) production was increased, indicating that it is the initial event prior to H2O2 production. In thylakoids isolated from WT leaves, kinase was active in the presence of ATP, and spectrophotometric analysis of nitrobluetetrazolium absorbance for O2(-) confirmed that PSII-driven superoxide production was greater in the mutant thylakoids than in the WT. This contrast in levels of PSII-driven superoxide production between the mutants and the WT plants was confirmed by conducting protein oxidation assays of PSII particles from osstn8 leaves under strong illumination. Those assays also demonstrated that PSII-LHCII supercomplex proteins were oxidized more in the mutant, thereby implying that PSII particles incur greater damage even though D1 degradation during PSII-supercomplex mobilization is partially blocked in the mutant. These results suggest that O2(-) is the major form of ROS produced in the mutant, and that the damaged PSII in the supercomplex is the primary source of O2(-).

  17. Natural strategies for photosynthetic light harvesting

    NARCIS (Netherlands)

    Croce, R.; Amerongen, van H.

    2014-01-01

    Photosynthetic organisms are crucial for life on Earth as they provide food and oxygen and are at the basis of most energy resources. They have a large variety of light-harvesting strategies that allow them to live nearly everywhere where sunlight can penetrate. They have adapted their pigmentation

  18. Discrete cyclic porphyrin arrays as artificial light-harvesting antenna.

    Science.gov (United States)

    Aratani, Naoki; Kim, Dongho; Osuka, Atsuhiro

    2009-12-21

    The importance of photosynthesis has driven researchers to seek ways to mimic its fundamental features in simplified systems. The absorption of a photon by light-harvesting (antenna) complexes made up of a large number of protein-embedded pigments initiates photosynthesis. Subsequently the many pigments within the antenna system shuttle that photon via an efficient excitation energy transfer (EET) until it encounters a reaction center. Since the 1995 discovery of the circularly arranged chromophoric assemblies in the crystal structure of light-harvesting antenna complex LH2 of purple bacteria Rps. Acidophila, many designs of light-harvesting antenna systems have focused on cyclic porphyrin wheels that allow for efficient EET. In this Account, we review recent research in our laboratories in the synthesis of covalently and noncovalently linked discrete cyclic porphyrin arrays as models of the photosynthetic light-harvesting antenna complexes. On the basis of the silver(I)-promoted oxidative coupling strategy, we have prepared a series of extremely long yet discrete meso-meso-linked porphyrin arrays and covalently linked large porphyrin rings. We examined the photophysical properties of these molecules using steady-state absorption, fluorescence, fluorescence lifetime, fluorescence anisotropy decay, and transient absorption measurements. Both the pump-power dependence on the femtosecond transient absorption and the transient absorption anisotropy decay profiles are directly related to the EET processes within the porphyrin rings. Within these structures, the exciton-exciton annihilation time and the polarization anisotropy rise time are well-described in terms of the Forster-type incoherent energy hopping model. In noncoordinating solvents such as CHCl(3), meso-pyridine-appended zinc(II) porphyrins and their meso-meso-linked dimers spontaneously assemble to form tetrameric porphyrin squares and porphyrin boxes, respectively. In the latter case, we have demonstrated

  19. Scalable high-performance algorithm for the simulation of exciton-dynamics. Application to the light harvesting complex II in the presence of resonant vibrational modes

    DEFF Research Database (Denmark)

    Kreisbeck, Christoph; Kramer, Tobias; Aspuru-Guzik, Alán

    2014-01-01

    The accurate simulation of excitonic energy transfer in molecular complexes with coupled electronic and vibrational degrees of freedom is essential for comparing excitonic system-parameters obtained from ab-initio methods with measured time-resolved spectra. Several exact methods for computing...... the exciton dynamics within a density-matrix formalism are known, but are restricted to small systems with less than ten sites due to their computational complexity. To study the excitonic energy transfer in larger systems, we adapt and extend the exact hierarchical equation of motion (HEOM) method to various...... coupled vibrations on the relaxation and show that the transfer does not rely on a fine-tuning of specific modes....

  20. Programming Light-Harvesting Efficiency Using DNA Origami

    Science.gov (United States)

    2016-01-01

    The remarkable performance and quantum efficiency of biological light-harvesting complexes has prompted a multidisciplinary interest in engineering biologically inspired antenna systems as a possible route to novel solar cell technologies. Key to the effectiveness of biological “nanomachines” in light capture and energy transport is their highly ordered nanoscale architecture of photoactive molecules. Recently, DNA origami has emerged as a powerful tool for organizing multiple chromophores with base-pair accuracy and full geometric freedom. Here, we present a programmable antenna array on a DNA origami platform that enables the implementation of rationally designed antenna structures. We systematically analyze the light-harvesting efficiency with respect to number of donors and interdye distances of a ring-like antenna using ensemble and single-molecule fluorescence spectroscopy and detailed Förster modeling. This comprehensive study demonstrates exquisite and reliable structural control over multichromophoric geometries and points to DNA origami as highly versatile platform for testing design concepts in artificial light-harvesting networks. PMID:26906456

  1. Optimal Energy Transfer in Light-Harvesting Systems

    Directory of Open Access Journals (Sweden)

    Lipeng Chen

    2015-08-01

    Full Text Available Photosynthesis is one of the most essential biological processes in which specialized pigment-protein complexes absorb solar photons, and with a remarkably high efficiency, guide the photo-induced excitation energy toward the reaction center to subsequently trigger its conversion to chemical energy. In this work, we review the principles of optimal energy transfer in various natural and artificial light harvesting systems. We begin by presenting the guiding principles for optimizing the energy transfer efficiency in systems connected to dissipative environments, with particular attention paid to the potential role of quantum coherence in light harvesting systems. We will comment briefly on photo-protective mechanisms in natural systems that ensure optimal functionality under varying ambient conditions. For completeness, we will also present an overview of the charge separation and electron transfer pathways in reaction centers. Finally, recent theoretical and experimental progress on excitation energy transfer, charge separation, and charge transport in artificial light harvesting systems is delineated, with organic solar cells taken as prime examples.

  2. Optimal Energy Transfer in Light-Harvesting Systems.

    Science.gov (United States)

    Chen, Lipeng; Shenai, Prathamesh; Zheng, Fulu; Somoza, Alejandro; Zhao, Yang

    2015-08-20

    Photosynthesis is one of the most essential biological processes in which specialized pigment-protein complexes absorb solar photons, and with a remarkably high efficiency, guide the photo-induced excitation energy toward the reaction center to subsequently trigger its conversion to chemical energy. In this work, we review the principles of optimal energy transfer in various natural and artificial light harvesting systems. We begin by presenting the guiding principles for optimizing the energy transfer efficiency in systems connected to dissipative environments, with particular attention paid to the potential role of quantum coherence in light harvesting systems. We will comment briefly on photo-protective mechanisms in natural systems that ensure optimal functionality under varying ambient conditions. For completeness, we will also present an overview of the charge separation and electron transfer pathways in reaction centers. Finally, recent theoretical and experimental progress on excitation energy transfer, charge separation, and charge transport in artificial light harvesting systems is delineated, with organic solar cells taken as prime examples.

  3. PucC and LhaA direct efficient assembly of the light-harvesting complexes in Rhodobacter sphaeroides

    DEFF Research Database (Denmark)

    Mothersole, David; Jackson, Philip J.; Vasilev, Cvetelin

    2016-01-01

    interactions between pigments newly arriving from BchG and nascent proteins within the SecYEG-SecDF-YajC-YidC assembly machinery, thereby co-ordinating pigment delivery, the co-translational insertion of LH polypeptides and their folding and assembly to form photosynthetic complexes.......The mature architecture of the photosynthetic membrane of the purple phototroph Rhodobacter sphaeroides has been characterised to a level where an atomic-level membrane model is available, but the roles of the putative assembly proteins LhaA and PucC in establishing this architecture are unknown...

  4. Energy transfer pathways in light-harvesting complexes of purple bacteria as revealed by global kinetic analysis of two-dimensional transient spectra.

    Science.gov (United States)

    Ostroumov, Evgeny E; Mulvaney, Rachel M; Anna, Jessica M; Cogdell, Richard J; Scholes, Gregory D

    2013-09-26

    Excited state dynamics in LH2 complexes of two purple bacterial species were studied by broad-band two-dimensional electronic spectroscopy. The optical response was measured in the 500-600 nm spectral region on the 0-400 fs time scale. Global target analysis of two-dimensional (2D) transient spectra revealed the main energy transfer pathways between carotenoid S2, 1Bu(-) and S1 states and bacteriochlorophyll Qx state. Global analysis ascertained the evolutionary and vibration-associated spectra, which also indicated the presence of a higher-lying vibrational level in the carotenoid S1 state. The estimation of the spectral overlap between the 1Bu(-) state and the Qx state indicated a significant contribution of the 1Bu(-) state to the overall S2-to-Qx excitation energy transfer.

  5. Stimulus-responsive light-harvesting complexes based on the pillararene-induced co-assembly of β-carotene and chlorophyll

    Science.gov (United States)

    Sun, Yan; Guo, Fang; Zuo, Tongfei; Hua, Jingjing; Diao, Guowang

    2016-06-01

    The locations and arrangements of carotenoids at the subcellular level are responsible for their designated functions, which reinforces the necessity of developing methods for constructing carotenoid-based suprastructures beyond the molecular level. Because carotenoids lack the binding sites necessary for controlled interactions, functional structures based on carotenoids are not easily obtained. Here, we show that carotene-based suprastructures were formed via the induction of pillararene through a phase-transfer-mediated host-guest interaction. More importantly, similar to the main component in natural photosynthesis, complexes could be synthesized after chlorophyll was introduced into the carotene-based suprastructure assembly process. Remarkably, compared with molecular carotene or chlorophyll, this synthesized suprastructure exhibits some photocatalytic activity when exposed to light, which can be exploited for photocatalytic reaction studies of energy capture and solar conversion in living organisms.

  6. Two-dimensional electronic spectroscopy and photosynthesis: Fundamentals and applications to photosynthetic light-harvesting

    Energy Technology Data Exchange (ETDEWEB)

    Schlau-Cohen, Gabriela S.; Ishizaki, Akihito [Department of Chemistry, University of California, Berkeley, CA 94720 (United States); Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Fleming, Graham R., E-mail: grfleming@lbl.gov [Department of Chemistry, University of California, Berkeley, CA 94720 (United States); Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States)

    2011-07-28

    Graphical abstract: 2D electronic spectroscopy, when combined with theoretical approaches, can investigate structure-function relationships in photosynthetic complexes by probing electronic energy transfer and excited state orientations. Display Omitted Highlights: {yields} We review theoretical principles and experimental implementation of 2D spectroscopy. {yields} 2DES monitors energy transfer, observes coherence, determines excited state geometry, and compares to homology models. {yields} 2DES reveals structure-function relationships in the Photosystem II supercomplex. - Abstract: In natural light harvesting systems, pigment-protein complexes are able to harvest sunlight with near unity quantum efficiency. These complexes exhibit emergent properties that cannot be simply extrapolated from knowledge of their component parts. In this perspective, we focus on how two-dimensional electronic spectroscopy (2DES) can provide an incisive tool to probe the electronic, energetic, and spatial landscapes that must be understood to describe photosynthetic light-harvesting. We review the theoretical and experimental principles of 2DES, and demonstrate its application to the study of the Photosystem II supercomplex of green plants. We illustrate several capabilities of 2DES, including monitoring energy transfer pathways, observing excitonic coherence, determining excitonic geometry, and informing on the atomic structure.

  7. Modeling the NMR signatures associated with the functional conformational switch in the major light-harvesting antenna of photosystem II in higher plants.

    Science.gov (United States)

    Duffy, Christopher D P; Pandit, Anjali; Ruban, Alexander V

    2014-03-28

    The major photosystem II antenna complex, LHCII, possesses an intrinsic conformational switch linked to the formation of a photoprotective, excitation-quenching state. Recent solid state NMR experiments revealed that aggregation-induced quenching in (13)C-enriched LHCII from C. reinhardtii is associated with changes to the chemical shifts of three specific (13)C atoms in the Chla conjugated macrocycle. We performed DFT-based NMR calculations on the strongly-quenched crystal structure of LHCII (taken from spinach). We demonstrate that specific Chla-xanthophyll interactions in the quenched structure lead to changes in the Chla(13)C chemical shifts that are qualitatively similar to those observed by solid state NMR. We propose that these NMR changes are due to modulations in Chla-xanthophyll associations that occur due to a quenching-associated functional conformation change in the lutein and neoxanthin domains of LHCII. The combination of solid-state NMR and theoretical modeling is therefore a powerful tool for assessing functional conformational switching in the photosystem II antenna.

  8. The structural basis of light-harvesting in purple bacteria.

    Science.gov (United States)

    Cogdell, Richard J; Isaacs, Neil W; Freer, Andrew A; Howard, Tina D; Gardiner, Alastair T; Prince, Steve M; Papiz, Miroslavr Z

    2003-11-27

    A typical purple bacterial photosynthetic unit consists of two types of light-harvesting complex (LH1 and LH2) together with a reaction centre. This short review presents a description of the structure of the LH2 complex from Rhodopseudomonas acidophila, which has recently been improved to a resolution of 2.0 A [Papiz et al., J. Mol. Biol. 326 (2003) 1523-1538]. We show how this structure has helped to reveal the details of the various excitation energy transfer events in which it is involved.

  9. Energy Transfer Pathways in the CP24 and CP26 Antenna Complexes of Higher Plant Photosystem II : A Comparative Study

    NARCIS (Netherlands)

    Marin, Alessandro; Passarini, Francesca; Croce, Roberta; van Grondelle, Rienk; Brown, Leonid S.

    2010-01-01

    Antenna complexes are key components of plant photosynthesis, the process that converts sunlight, CO(2), and water into oxygen and sugars. We report the first (to our knowledge) femtosecond transient absorption study on the light-harvesting pigment-protein complexes CP26 (Lhcb5) and CP24 (Lhcb6) of

  10. The Light-Harvesting Chlorophyll a/b Binding Proteins Lhcb1 and Lhcb2 Play Complementary Roles during State Transitions in Arabidopsis[C][W][OPEN

    Science.gov (United States)

    Pietrzykowska, Malgorzata; Suorsa, Marjaana; Semchonok, Dmitry A.; Tikkanen, Mikko; Boekema, Egbert J.; Aro, Eva-Mari

    2014-01-01

    Photosynthetic light harvesting in plants is regulated by phosphorylation-driven state transitions: functional redistributions of the major trimeric light-harvesting complex II (LHCII) to balance the relative excitation of photosystem I and photosystem II. State transitions are driven by reversible LHCII phosphorylation by the STN7 kinase and PPH1/TAP38 phosphatase. LHCII trimers are composed of Lhcb1, Lhcb2, and Lhcb3 proteins in various trimeric configurations. Here, we show that despite their nearly identical amino acid composition, the functional roles of Lhcb1 and Lhcb2 are different but complementary. Arabidopsis thaliana plants lacking only Lhcb2 contain thylakoid protein complexes similar to wild-type plants, where Lhcb2 has been replaced by Lhcb1. However, these do not perform state transitions, so phosphorylation of Lhcb2 seems to be a critical step. In contrast, plants lacking Lhcb1 had a more profound antenna remodeling due to a decrease in the amount of LHCII trimers influencing thylakoid membrane structure and, more indirectly, state transitions. Although state transitions are also found in green algae, the detailed architecture of the extant seed plant light-harvesting antenna can now be dated back to a time after the divergence of the bryophyte and spermatophyte lineages, but before the split of the angiosperm and gymnosperm lineages more than 300 million years ago. PMID:25194026

  11. Effects of nitrogen-deficiency on efficiency of light-harvesting apparatus in radish.

    Science.gov (United States)

    Cetner, M D; Kalaji, H M; Goltsev, V; Aleksandrov, V; Kowalczyk, K; Borucki, W; Jajoo, A

    2017-10-01

    Nitrogen starvation has been stated to reduce chlorophyll a and accessory pigments, decrease photosynthetic efficiency, as well as modify chloroplast thylakoid membranes. However, the impact of N-deficiency on light-dependent reactions of photosynthesis has not been well understood. In this study, efficiency and structure of light-harvesting complex under N-deficiency conditions were investigated in two radish cultivars (Raphanus sativus var. sativus 'Fluo HF1' and 'Suntella F1'). Light-dependent reactions of photosynthesis were investigated by measuring in vivo chlorophyll a prompt fluorescence signal. Acquired data were utilised in two ways: by plotting fast induction curves and calculating OJIP-test biophysical parameters. Detailed analysis of difference curves as well as OJIP-test results showed that major disturbances were associated with photosystem II and its subunits, including decoupling of light-harvesting complexes, dysfunction of oxygen-evolving complex, and reaction centres inactivation. The maximum quantum yield of photosystem II primary photochemistry was severely restricted, causing an inhibition in electron transport through successive protein complexes in the thylakoid membrane. Structural changes were demonstrated by recording images using Transmission Electron Microscopy (TEM). TEM investigations showed intensive starch accumulation under N-deficiency. Rare thylakoid stacks distributed in tiny layers of stroma around grains and chloroplast periphery were observed in cells of N-deficient plants. The application of principal component analysis (PCA) on OJIP-test results allowed characterizing the dynamics of stress response and separating parameters according to their influence on plants stress response. 'Suntella F1' genotype was found to be more sensitive to nitrogen deficiency as compared to 'Fluo HF1' genotype. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

  12. Light harvesting by dye linked conducting polymers

    DEFF Research Database (Denmark)

    Nielsen, Kim Troensegaard

    2006-01-01

    The fact that the fossil fuel is finite and that the detrimental long-term effects of letting CO2 into our atmosphere exist, have created an enormous interest in developing new, cheap, renewable and less polluting energy resources. One of the most obviousabundant sources of energy in the solar......,15-dibromoporphinato]zinc(II) (P-domain). It is shown that the N domains in NPN work as effective light harvesting antennas for the P domain and effectively transfer electrically generated excitons in the N domain to the P domain.Unfortunately the P domain does not separate the charge carriers but instead works...

  13. Rod-like nano-light harvester.

    Science.gov (United States)

    Ling, Jun; Zheng, Zhicheng; Köhler, Anna; Müller, Axel H E

    2014-01-01

    Imitating the natural "energy cascade" architecture, we present a single-molecular rod-like nano-light harvester (NLH) based on a cylindrical polymer brush. Block copolymer side chains carrying (9,9-diethylfluoren-2-yl)methyl methacrylate units as light absorbing antennae (energy donors) are tethered to a linear polymer backbone containing 9-anthracenemethyl methacrylate units as emitting groups (energy acceptors). These NLHs exhibit very efficient energy absorption and transfer. Moreover, we manipulate the energy transfer by tuning the donor-acceptor distance.

  14. DNA-directed spatial assembly of photosynthetic light-harvesting proteins.

    Science.gov (United States)

    Henry, Sarah L; Withers, Jamie M; Singh, Ishwar; Cooper, Jonathan M; Clark, Alasdair W; Burley, Glenn A; Cogdell, Richard J

    2016-01-28

    This manuscript describes the surface immobilization of a light-harvesting complex to prescribed locations directed by the sequence-selective recognition of duplex DNA. An engineered light-harvesting complex (RC-LH1) derived from Rhodopseudomonas (Rps.) palustris containing the zinc finger (ZF) domain zif268 was prepared. The zif268 domain directed the binding of zfRC-LH1 to target double-stranded DNA sequences both in solution and when immobilized on lithographically defined micro-patterns. Excitation energy transfer from the carotenoids to the bacteriochlorophyll pigments within zfRC-LH1 confirmed that the functional and structural integrity of the complex is retained after surface immobilization.

  15. Light harvesting by dye linked conducting polymers

    Energy Technology Data Exchange (ETDEWEB)

    Troensegaard Nielsen, K.

    2006-06-15

    The fact that the fossil fuel is finite and that the detrimental long-term effects of letting CO2 into our atmosphere exist, have created an enormous interest in developing new, cheap, renewable and less polluting energy resources. One of the most obvious abundant sources of energy in the solar system is the sun. Unfortunately the well developed silicon solar cells are very costly to produce. In an attempt to produce cheap and flexible solar cells, plastic solar cells have received a lot of attention in the last decades. There are still a lot of parameters to optimize if the plastic solar cell shall be able to compete with the silicon solar cells. One of the parameters is to ensure a high degree of charge carrier separation. Charge carrier separation can only happen at heterojunctions, which cover for example the interfaces between the polymers and the electrodes or the interface between an n-conductor and a p-conductor. The facts that the charge carrier separation only happens at the heterojunctions limits the thickness of the active layer in solar cells and thereby the effectiveness of the solar cells. In this project the charge carrier separation is attempted optimized by making plastic solar cells with a molecular heterojunction. The molecular heterojunction has been obtained by synthesizing a three domain super molecular assembly termed NPN. NPN consists of two poly[1-(2,5-dioctyltolanyl)ethynylene] chains (N-domains) coupled to the [10,20-bis(3,5-bistert-butylphenyl]-5,15-dibromoporphinato]zinc(II) (P-domain). It is shown that the N domains in NPN work as effective light harvesting antennas for the P domain and effectively transfer electrically generated excitons in the N domain to the P domain. Unfortunately the P domain does not separate the charge carriers but instead works as a charge carrier trap. This results in a performance of solar cells made of NPN that is much lower than the performance of solar cells made of pure poly[1-(2,5-dioctyltolanyl

  16. Green grasses as light harvesters in dye sensitized solar cells

    Science.gov (United States)

    Shanmugam, Vinoth; Manoharan, Subbaiah; Sharafali, A.; Anandan, Sambandam; Murugan, Ramaswamy

    2015-01-01

    Chlorophylls, the major pigments presented in plants are responsible for the process of photosynthesis. The working principle of dye sensitized solar cell (DSSC) is analogous to natural photosynthesis in light-harvesting and charge separation. In a similar way, natural dyes extracted from three types of grasses viz. Hierochloe Odorata (HO), Torulinium Odoratum (TO) and Dactyloctenium Aegyptium (DA) were used as light harvesters in dye sensitized solar cells (DSSCs). The UV-Vis absorption spectroscopy, Fourier transform infrared (FT-IR), and liquid chromatography-mass spectrometry (LC-MS) were used to characterize the dyes. The electron transport mechanism and internal resistance of the DSSCs were investigated by the electrochemical impedance spectroscopy (EIS). The performance of the cells fabricated with the grass extract shows comparable efficiencies with the reported natural dyes. Among the three types of grasses, the DSSC fabricated with the dye extracted from Hierochloe Odorata (HO) exhibited the maximum efficiency. LC-MS investigations indicated that the dominant pigment present in HO dye was pheophytin a (Pheo a).

  17. Robustness and Optimality of Light Harvesting in Cyanobacterial Photosystem I

    CERN Document Server

    Sener, M K; Ritz, T; Park, S; Fromme, P; Schulten, K; Sener, Melih K.; Lu, Deyu; Ritz, Thorsten; Park, Sanghyun; Fromme, Petra; Schulten, Klaus

    2002-01-01

    As most biological species, photosynthetic lifeforms have evolved to function optimally, despite thermal disorder and with fault tolerance. It remains a challenge to understand how this is achieved. To address this challenge the function of the protein-pigment complex photosystem I (PSI) of the cyanobacterium Synechococcus elongatus is investigated theoretically. The recently obtained high resolution structure of this complex exhibits an aggregate of 96 chlorophylls that are electronically coupled to function as a light-harvesting antenna complex. This paper constructs an effective Hamiltonian for the chlorophyll aggregate to describe excitation transfer dynamics and spectral properties of PSI. For this purpose, a new kinetic expansion method, the sojourn expansion, is introduced. Our study shows that at room temperature fluctuations of site energies have little effect on the calculated excitation lifetime and quantum yield, which compare favorably with experimental results. The efficiency of the system is fo...

  18. Light harvesting, electron transfer and electron cycling of a native photosynthetic membrane adsorbed onto a gold surface

    NARCIS (Netherlands)

    Magis, G.J; Hollander, den M. -J.; Onderwaater, W. G.; Olsen, J.D.; Hunter, C.N.; Aartsma, T.J.; Frese, R.N.

    2010-01-01

    Photosynthetic membranes comprise a network of light harvesting and reaction center pigment–protein complexes responsible for the primary photoconversion reactions: light absorption, energy transfer and electron cycling. The structural organization of membranes of the purple bacterial species Rb. sp

  19. Light harvesting for quantum solar energy conversion

    Science.gov (United States)

    Markvart, Tomas

    2000-05-01

    Despite wide structural and functional differences, the laws that govern quantum solar energy conversion to chemical energy or electricity share many similarities. In the photosynthetic membrane, in common with semiconductor solar cells, the conversion process proceeds from the creation of electron-hole pairs by a photon of light, followed by charge separation to produce the required high-energy product. In many cases, however, mechanisms are needed to enhance the optical absorption cross-section and extend the spectral range of operation. A common way of achieving this is by light harvesting: light absorption by a specialised unit which transfers the energy to the conversion apparatus. This paper considers two examples of light harvesting - semiconductor solar cells and the photosynthetic apparatus - to illustrate the basic operation and principles that apply. The existence of a light harvesting unit in photosynthesis has been known since the early 1930's but details of the process - relating, in particular, to the relationship between the structure and spectral properties - are still being unravelled. The excitation energy carriers are excitons but the precise nature of the transport - via the solid state Frenkel-Peierls variety or by Förster's resonant energy transfer - is still subject to debate. In semiconductor solar cells, the energy of the absorbed photon is collected by minority carriers but the broad principles remain the same. In both cases it is shown that the rate of energy conversion is described by a law which parallels the Shockley's solar cell equation, and the light harvesting energy collection is subject to reciprocity relations which resemble Onsager's reciprocity relations between coefficients which couple appropriate forces and flows in non-equilibrium thermodynamics. Differences in the basic atomic make-up in the two systems lead to different energy transport equations. In both cases, however, similar mathematical techniques based on Green

  20. Structure of the light harvesting antenna from Rhodospirillum molischianum studied by electron microscopy

    NARCIS (Netherlands)

    Boonstra, Arjen F.; Germeroth, Lothar; Boekema, Egbert J.

    1994-01-01

    The structure of two types of isolated light-harvesting antenna complexes from Rhodospirillum molischianum was studied by electron microscopy and image analysis. The B870 reaction center complex forms an almost circular particle with a diameter in the plane of the membrane of about 10.7-11.2 nm. A

  1. Spectroscopic properties of a reconstituted light-harvesting complex from the green sulfur bacterium Chlorobium tepidum containing CsmA and bacteriochlorophyll a

    DEFF Research Database (Denmark)

    Pedersen, Marie Østergaard; Pham, Lan; Steensgaard, Dorte Bjerre

    2008-01-01

    Green sulfur bacteria possess two light-harvesting antenna systems, the chlorosome and the Fenna-Matthews-Olson (FMO) protein. In addition to self-aggregated bacteriochlorophyll (BChl) c, chlorosomes of Chlorobium tepidum contain a small amount of BChl a (ratio 100:1). The chlorosomal BChl......-PAGE. Mass spectrometric analysis showed an m/z of 6154.8, in agreement with the calculated mass of the csmA gene product after C-terminal processing. CD spectroscopy of the isolated protein showed that the main structural motif was an R-helix. We have reconstituted the isolated CsmA protein with BChl...

  2. Assembly of the light-harvesting chlorophyll antenna in the green alga Chlamydomonas reinhardtii requires expression of the TLA2-CpFTSY gene.

    Science.gov (United States)

    Kirst, Henning; García-Cerdán, Jose Gines; Zurbriggen, Andreas; Melis, Anastasios

    2012-02-01

    The truncated light-harvesting antenna2 (tla2) mutant of Chlamydomonas reinhardtii showed a lighter-green phenotype, had a lower chlorophyll (Chl) per-cell content, and higher Chl a/b ratio than corresponding wild-type strains. Physiological analyses revealed a higher intensity for the saturation of photosynthesis and greater P(max) values in the tla2 mutant than in the wild type. Biochemical analyses showed that the tla2 strain was deficient in the Chl a-b light-harvesting complex, and had a Chl antenna size of the photosystems that was only about 65% of that in the wild type. Molecular and genetic analyses showed a single plasmid insertion in the tla2 strain, causing a chromosomal DNA rearrangement and deletion/disruption of five nuclear genes. The TLA2 gene, causing the tla2 phenotype, was cloned by mapping the insertion site and upon complementation with each of the genes that were deleted. Successful complementation was achieved with the C. reinhardtii TLA2-CpFTSY gene, whose occurrence and function in green microalgae has not hitherto been investigated. Functional analysis showed that the nuclear-encoded and chloroplast-localized CrCpFTSY protein specifically operates in the assembly of the peripheral components of the Chl a-b light-harvesting antenna. In higher plants, a cpftsy null mutation inhibits assembly of both the light-harvesting complex and photosystem complexes, thus resulting in a seedling-lethal phenotype. The work shows that cpftsy deletion in green algae, but not in higher plants, can be employed to generate tla mutants. The latter exhibit improved solar energy conversion efficiency and photosynthetic productivity under mass culture and bright sunlight conditions.

  3. Self-assembled photosynthesis-inspired light harvesting material and solar cells containing the same

    Science.gov (United States)

    Lindsey, Jonathan S.; Chinnasamy, Muthiah; Fan, Dazhong

    2009-12-15

    A solar cell is described that comprises: (a) a semiconductor charge separation material; (b) at least one electrode connected to the charge separation material; and (c) a light-harvesting film on the charge separation material, the light-harvesting film comprising non-covalently coupled, self-assembled units of porphyrinic macrocycles. The porphyrinic macrocycles preferably comprise: (i) an intramolecularly coordinated metal; (ii) a first coordinating substituent; and (iii) a second coordinating substituent opposite the first coordinating substituent. The porphyrinic macrocycles can be assembled by repeating intermolecular coordination complexes of the metal, the first coordinating substituent and the second coordinating substituent.

  4. Long range excitonic transport in a biomimetic system inspired by the bacterial light-harvesting apparatus

    Energy Technology Data Exchange (ETDEWEB)

    Harel, Elad [Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208 (United States)

    2012-05-07

    Photosynthesis, the process by which energy from sunlight drives cellular metabolism, relies on a unique organization of light-harvesting and reaction center complexes. Recently, the organization of light-harvesting LH2 complexes and dimeric reaction center-light-harvesting I-PufX core complexes in membranes of purple non-sulfur bacteria was revealed by atomic force microscopy [S. Bahatyrova et al., Nature (London) 430, 1058 (2004)]. Here, we discuss optimal exciton transfer in a biomimetic system closely modeled on the structure of LH2 and its organization within the membrane using a Markovian quantum model with dissipation and trapping added phenomenologically. In a deliberate manner, we neglect the high level detail of the bacterial light-harvesting complex and its interaction with the phonon bath in order to elucidate a set of design principles that may be incorporated in artificial pigment-scaffold constructs in a supramolecular assembly. We show that our scheme reproduces many of the most salient features found in their natural counterpart and may be largely explained by simple electrostatic considerations. Most importantly, we show that quantum effects act primarily to enforce robustness with respect to spatial and spectral disorder between and within complexes. The implications of such an arrangement are discussed in the context of biomimetic photosynthetic analogs capable of transferring energy efficiently across tens to hundreds of nanometers.

  5. Organization of the Bacterial Light-Harvesting Apparatus Rationalized by Exciton Transport Optimization

    CERN Document Server

    Harel, Elad

    2011-01-01

    Photosynthesis, the process by which energy from sunlight drives cellular metabolism, relies on a unique organization of light-harvesting and reaction center complexes. Recently, the organization of light-harvesting LH2 complexes and dimeric reaction center-light harvesting I-PufX (RC-LH1-PufX) core complexes in membranes of purple non-sulfur bacteria was revealed by atomic force microscopy (AFM)1. Here, we report that the structure of LH2 and its organization within the membrane can be largely rationalized by a simple physical model that relies primarily on exciton transfer optimization. The process through which the light-harvesting complexes transfer excitation energy has been recognized to incorporate both coherent and incoherent processes mediated by the surrounding protein environment. Using the Haken-Strobl model, we show that the organization of the complexes in the membrane can be almost entirely explained by simple electrostatic considerations and that quantum effects act primarily to enforce robust...

  6. Long range excitonic transport in a biomimetic system inspired by the bacterial light-harvesting apparatus

    Science.gov (United States)

    Harel, Elad

    2012-05-01

    Photosynthesis, the process by which energy from sunlight drives cellular metabolism, relies on a unique organization of light-harvesting and reaction center complexes. Recently, the organization of light-harvesting LH2 complexes and dimeric reaction center-light-harvesting I-PufX core complexes in membranes of purple non-sulfur bacteria was revealed by atomic force microscopy [S. Bahatyrova et al., Nature (London) 430, 1058 (2004)]. Here, we discuss optimal exciton transfer in a biomimetic system closely modeled on the structure of LH2 and its organization within the membrane using a Markovian quantum model with dissipation and trapping added phenomenologically. In a deliberate manner, we neglect the high level detail of the bacterial light-harvesting complex and its interaction with the phonon bath in order to elucidate a set of design principles that may be incorporated in artificial pigment-scaffold constructs in a supramolecular assembly. We show that our scheme reproduces many of the most salient features found in their natural counterpart and may be largely explained by simple electrostatic considerations. Most importantly, we show that quantum effects act primarily to enforce robustness with respect to spatial and spectral disorder between and within complexes. The implications of such an arrangement are discussed in the context of biomimetic photosynthetic analogs capable of transferring energy efficiently across tens to hundreds of nanometers.

  7. Multireference excitation energies for bacteriochlorophylls A within light harvesting system 2

    DEFF Research Database (Denmark)

    Anda, Andre; Hansen, Thorsten; De Vico, Luca

    2016-01-01

    Light-harvesting system 2 (LH2) of purple bacteria is one of the most popular antenna complexes used to study Nature's way of collecting and channeling solar energy. The dynamics of the absorbed energy is probed by ultrafast spectroscopy. Simulation of these experiments relies on fitting a range...

  8. The back and forth of energy transfer between carotenoids and chlorophylls and its role in the regulation of light harvesting.

    Science.gov (United States)

    Holleboom, Christoph-Peter; Walla, Peter J

    2014-02-01

    Many aspects in the regulation of photosynthetic light-harvesting of plants are still quite poorly understood. For example, it is still a matter of debate which physical mechanism(s) results in the regulation and dissipation of excess energy in high light. Many researchers agree that electronic interactions between chlorophylls (Chl) and certain states of carotenoids are involved in these mechanisms. However, in particular, the role of the first excited state of carotenoids (Car S1) is not easily revealed, because of its optical forbidden character. The use of two-photon excitation is an elegant approach to address directly this state and to investigate the energy transfer in the direction Car S1 → Chl. Meanwhile, it has been applied to a large variety of systems starting from simple carotenoid-tetrapyrrole model compounds up to entire plants. Here, we present a systematic summary of the observations obtained by two-photon excitation about Car S1 → Chl energy transfer in systems with increasing complexity and the correlation to fluorescence quenching. We compare these observations directly with the energy transfer in the opposite direction, Chl → Car S1, for the same systems as obtained in pump-probe studies. We discuss what surprising aspects of this comparison led us to the suggestion that quenching excitonic Car-Chl interactions could contribute to the regulation of light harvesting, and how this suggestion can be connected to other models proposed.

  9. Optimization of light harvesting and photoprotection: molecular mechanisms and physiological consequences.

    Science.gov (United States)

    Horton, Peter

    2012-12-19

    The distinctive lateral organization of the protein complexes in the thylakoid membrane investigated by Jan Anderson and co-workers is dependent on the balance of various attractive and repulsive forces. Modulation of these forces allows critical physiological regulation of photosynthesis that provides efficient light-harvesting in limiting light but dissipation of excess potentially damaging radiation in saturating light. The light-harvesting complexes (LHCII) are central to this regulation, which is achieved by phosphorylation of stromal residues, protonation on the lumen surface and de-epoxidation of bound violaxanthin. The functional flexibility of LHCII derives from a remarkable pigment composition and configuration that not only allow efficient absorption of light and efficient energy transfer either to photosystem II or photosystem I core complexes, but through subtle configurational changes can also exhibit highly efficient dissipative reactions involving chlorophyll-xanthophyll and/or chlorophyll-chlorophyll interactions. These changes in function are determined at a macroscopic level by alterations in protein-protein interactions in the thylakoid membrane. The capacity and dynamics of this regulation are tuned to different physiological scenarios by the exact protein and pigment content of the light-harvesting system. Here, the molecular mechanisms involved will be reviewed, and the optimization of the light-harvesting system in different environmental conditions described.

  10. Molecular Design, Modification and Assembly of Light Harvesting Pigment-protein Complexes from Photosynthetic Membrane With the Aim of Constructing Devices Simulating Photosynthetic Light Harvesting Process%以构建光合作用模拟器为目标的光合膜天线色素蛋白复合体的分子修饰,改造和组装立项报告

    Institute of Scientific and Technical Information of China (English)

    杨春虹; 刘成; 李阳; 刘华英; 涂文凤

    2016-01-01

    The fossil energy was still the main part of world energy consumption. It has been a critical problem to social development and national security that the fossil energy gradually exhausted. The fossil energy consumption also brings about serious environmental pollution and global warming problem. Therefore increasing utilization of renewable clear energy, mastering key technology and keeping independence in making use of renewable clear energy are very important to the nation's economy and the people's livelihood.Solar energy is main resource for most renewable clear energy and photosynthesis is the only way to harvest, convert and store solar energy at ambient temperature and pressure conditions on the earth. Photosynthetic membrane proteins in plants are responsible for harvesting and converting solar energy. The simulation of such processes is one of hot points in scientific research. Studies about the relationship between structure and function of photosynthetic membrane proteins and the mechanism of excitation energy transfer are the basis of such simulation. This project will be based on the new achievement in photosynthetic researches, for example, the atomic resolution crystal structure of major light harvesting complexes, to explore the functions of photosynthetic membrane proteins and further unveil the relationship between structure and function on different levels. Finally, we can (1)accomplish molecular design and modification for stability improvement;(2)increase photosynthetic quantum efficiency and stability by modifying key domains and environment;(3) study the relationship between structure and function in Berteroa incana, which contains a series of photosynthetic membrane proteins with high stability and efficiency;(4)design, and reconstitute photosynthetic proteins which can absorb light at all wavelength in visible region. Collaborating with other project, we plan to modify photosynthetic membrane proteins with organic or nano particles to

  11. An ancient light-harvesting protein is critical for the regulation of algal photosynthesis.

    Science.gov (United States)

    Peers, Graham; Truong, Thuy B; Ostendorf, Elisabeth; Busch, Andreas; Elrad, Dafna; Grossman, Arthur R; Hippler, Michael; Niyogi, Krishna K

    2009-11-26

    Light is necessary for photosynthesis, but its absorption by pigment molecules such as chlorophyll can cause severe oxidative damage and result in cell death. The excess absorption of light energy by photosynthetic pigments has led to the evolution of protective mechanisms that operate on the timescale of seconds to minutes and involve feedback-regulated de-excitation of chlorophyll molecules in photosystem II (qE). Despite the significant contribution of eukaryotic algae to global primary production, little is known about their qE mechanism, in contrast to that in flowering plants. Here we show that a qE-deficient mutant of the unicellular green alga Chlamydomonas reinhardtii, npq4, lacks two of the three genes encoding LHCSR (formerly called LI818). This protein is an ancient member of the light-harvesting complex superfamily, and orthologues are found throughout photosynthetic eukaryote taxa, except in red algae and vascular plants. The qE capacity of Chlamydomonas is dependent on environmental conditions and is inducible by growth under high light conditions. We show that the fitness of the npq4 mutant in a shifting light environment is reduced compared to wild-type cells, demonstrating that LHCSR is required for survival in a dynamic light environment. Thus, these data indicate that plants and algae use different proteins to dissipate harmful excess light energy and protect the photosynthetic apparatus from damage.

  12. Plasmon enhanced light harvesting: multiscale modeling of the FMO protein coupled with gold nanoparticles.

    Science.gov (United States)

    Andreussi, Oliviero; Caprasecca, Stefano; Cupellini, Lorenzo; Guarnetti-Prandi, Ingrid; Guido, Ciro A; Jurinovich, Sandro; Viani, Lucas; Mennucci, Benedetta

    2015-05-28

    Plasmonic systems, such as metal nanoparticles, are becoming increasingly important in spectroscopies and devices because of their ability to enhance, even by several orders of magnitude, the photophysical properties of neighboring systems. In particular, it has been shown both theoretically and experimentally that combining nanoplasmonic devices with natural light-harvesting proteins substantially increases the fluorescence and absorption properties of the system. This kind of biohybrid device can have important applications in the characterization and design of efficient light-harvesting systems. In the present work, the FMO light-harvesting protein was combined with gold nanoparticles of different sizes, and its photophysical properties were characterized using a multiscale quantum-mechanical classical-polarizable and continuum model (QM/MMPol/PCM). By optimal tuning of the plasmon resonance of the metal nanoparticles, fluorescence enhancements of up to 2 orders of magnitude were observed. Orientation effects were found to be crucial: amplifications by factors of up to 300 were observed for the absorption process, while the radiative decay of the emitting state increased at most by a factor of 10, mostly as a result of poor alignment of the emitting state with the considered metal aggregates. Despite being a limiting factor for high-fluorescence-enhancement devices, the strong orientation dependence may represent an important feature of the natural light-harvesting system that could allow selective enhancement of a specific excited state of the complex.

  13. The chlorosome: a prototype for efficient light harvesting in photosynthesis

    OpenAIRE

    Oostergetel, G.; Amerongen, van, H.; Boekema, E.J.

    2010-01-01

    Three phyla of bacteria include phototrophs that contain unique antenna systems, chlorosomes, as the principal light-harvesting apparatus. Chlorosomes are the largest known supramolecular antenna systems and contain hundreds of thousands of BChl c/d/e molecules enclosed by a single membrane leaflet and a baseplate. The BChl pigments are organized via self-assembly and do not require proteins to provide a scaffold for efficient light harvesting. Their excitation energy flows via a small protei...

  14. Excitation migration in fluctuating light-harvesting antenna systems.

    Science.gov (United States)

    Chmeliov, Jevgenij; Trinkunas, Gediminas; van Amerongen, Herbert; Valkunas, Leonas

    2016-01-01

    Complex multi-exponential fluorescence decay kinetics observed in various photosynthetic systems like photosystem II (PSII) have often been explained by the reversible quenching mechanism of the charge separation taking place in the reaction center (RC) of PSII. However, this description does not account for the intrinsic dynamic disorder of the light-harvesting proteins as well as their fluctuating dislocations within the antenna, which also facilitate the repair of RCs, state transitions, and the process of non-photochemical quenching. Since dynamic fluctuations result in varying connectivity between pigment-protein complexes, they can also lead to non-exponential excitation decay kinetics. Based on this presumption, we have recently proposed a simple conceptual model describing excitation diffusion in a continuous medium and accounting for possible variations of the excitation transfer pathways. In the current work, this model is further developed and then applied to describe fluorescence kinetics originating from very diverse antenna systems, ranging from PSII of various sizes to LHCII aggregates and even the entire thylakoid membrane. In all cases, complex multi-exponential fluorescence kinetics are perfectly reproduced on the entire relevant time scale without assuming any radical pair equilibration at the side of the excitation quencher, but using just a few parameters reflecting the mean excitation energy transfer rate as well as the overall average organization of the photosynthetic antenna.

  15. Plasmon-controlled light-harvesting: design rules for biohybrid devices via multiscale modeling.

    Science.gov (United States)

    Andreussi, Oliviero; Biancardi, Alessandro; Corni, Stefano; Mennucci, Benedetta

    2013-09-11

    Photosynthesis is triggered by the absorption of light by light-harvesting (LH) pigment-protein complexes followed by excitation energy transfer to the reaction center(s). A promising strategy to achieve control on and to improve light harvesting is to complement the LH complexes with plasmonic particles. Here a recently developed QM/MM/continuum approach is used to investigate the LH process of the peridinin-chlorophyll-protein (PCP) complex on a silver island film. The simulations not only reproduce and interpret the experiments but they also suggest general rules to design novel biohybrid devices; hot-spot configurations in which the LH complex is sandwiched between couples of metal aggregates are found to produce the largest amplifications. Indications about the best distances and orientations are also reported together with illumination and emission geometries of the PCP-NP system necessary to achieve the maximum enhancement.

  16. Environmental correlation effects on excitation energy transfer in photosynthetic light harvesting

    CERN Document Server

    Sarovar, Mohan; Whaley, K Birgitta

    2009-01-01

    Several recent studies of energy transfer in photosynthetic light harvesting complexes have revealed a subtle interplay between coherent and decoherent dynamic contributions to the overall transfer efficiency in these open quantum systems. In this work we systematically investigate the impact of temporal and spatial correlations in environmental fluctuations on excitation transport in the Fenna-Matthews-Olson photosynthetic complex. We demonstrate that the exact nature of the correlations can have a large impact on the efficiency of light harvesting. In particular, we find that spatial correlations can enhance coherences in the site basis while at the same time slowing transport, and that the overall efficiency of transport is maximized at a finite temporal correlation that results in optimal driving of transitions between excitonic states.

  17. The chlorosome: a prototype for efficient light harvesting in photosynthesis.

    Science.gov (United States)

    Oostergetel, Gert T; van Amerongen, Herbert; Boekema, Egbert J

    2010-06-01

    Three phyla of bacteria include phototrophs that contain unique antenna systems, chlorosomes, as the principal light-harvesting apparatus. Chlorosomes are the largest known supramolecular antenna systems and contain hundreds of thousands of BChl c/d/e molecules enclosed by a single membrane leaflet and a baseplate. The BChl pigments are organized via self-assembly and do not require proteins to provide a scaffold for efficient light harvesting. Their excitation energy flows via a small protein, CsmA embedded in the baseplate to the photosynthetic reaction centres. Chlorosomes allow for photosynthesis at very low light intensities by ultra-rapid transfer of excitations to reaction centres and enable organisms with chlorosomes to live at extraordinarily low light intensities under which no other phototrophic organisms can grow. This article reviews several aspects of chlorosomes: the supramolecular and molecular organizations and the light-harvesting and spectroscopic properties. In addition, it provides some novel information about the organization of the baseplate.

  18. Aluminum Nanoarrays for Plasmon-Enhanced Light Harvesting.

    Science.gov (United States)

    Lee, Minah; Kim, Jong Uk; Lee, Ki Joong; Ahn, SooHoon; Shin, Yong-Beom; Shin, Jonghwa; Park, Chan Beum

    2015-06-23

    The practical limits of coinage-metal-based plasmonic materials demand sustainable, abundant alternatives with a wide plasmonic range of the solar energy spectrum. Aluminum (Al) is an emerging alternative, but its instability in aqueous environments critically limits its applicability to various light-harvesting systems. Here, we report a design strategy to achieve a robust platform for plasmon-enhanced light harvesting using Al nanostructures. The incorporation of mussel-inspired polydopamine nanolayers in the Al nanoarrays allowed for the reliable use of Al plasmonic resonances in a highly corrosive photocatalytic redox solution and provided nanoscale arrangement of organic photosensitizers on Al surfaces. The Al-photosensitizer core-shell assemblies exhibited plasmon-enhanced light absorption, which resulted in a 300% efficiency increase in photo-to-chemical conversion. Our strategy enables stable and advanced use of aluminum for plasmonic light harvesting.

  19. Clustered Geometries Exploiting Quantum Coherence Effects for Efficient Energy Transfer in Light Harvesting

    CERN Document Server

    Ai, Qing; Jin, Bih-Yaw; Cheng, Yuan-Chung

    2013-01-01

    Elucidating quantum coherence effects and geometrical factors for efficient energy transfer in photosynthesis has the potential to uncover non-classical design principles for advanced organic materials. We study energy transfer in a linear light-harvesting model to reveal that dimerized geometries with strong electronic coherences within donor and acceptor pairs exhibit significantly improved efficiency, which is in marked contrast to predictions of the classical F\\"orster theory. We reveal that energy tuning due to coherent delocalization of photoexcitations is mainly responsible for the efficiency optimization. This coherence-assisted energy-tuning mechanism also explains the energetics and chlorophyll arrangements in the widely-studied Fenna-Matthews-Olson complex. We argue that a clustered network with rapid energy relaxation among donors and resonant energy transfer from donor to acceptor states provides a basic formula for constructing efficient light-harvesting systems, and the general principles revea...

  20. Purple-bacterial light harvesting benefits more from energy funnelling than from delocalisation

    CERN Document Server

    Baghbanzadeh, Sima

    2015-01-01

    Light-harvesting complexes of purple bacteria have two properties that are thought to contribute to the efficiency of their exciton transport: an energy funnel that directs excitons towards the reaction centre as well as substantial excitonic delocalisation, which can enhance transport through supertransfer. To determine the relative importance of these two features, we compared models of the light-harvesting apparatus with thousands of counterfactual situations in which the extent of delocalisation and the energy landscape were altered. We find that the influence of delocalisation is usually minor and sometimes deleterious, especially when compared to the decisive importance of a funnel in the energy landscape. Consequently, delocalisation is most likely a side-effect of the dense chlorophyll packing that evolved to increase light absorption per reaction centre.

  1. Functionalized dye encapsulated polymer nanoparticles attached with a BSA scaffold as efficient antenna materials for artificial light harvesting.

    Science.gov (United States)

    Jana, Bikash; Bhattacharyya, Santanu; Patra, Amitava

    2016-09-21

    A potential strategy for a new generation light harvesting system is multi-chromophoric donor-acceptor pairs where light energy is absorbed by an antenna complex and subsequently transfers its energy to the acceptor via energy transfer. Here, we design a system of a functionalized polymer nanoparticle-protein scaffold for efficient light harvesting and white light generation where a dye doped polymer nanoparticle acts as a donor and a dye encapsulated BSA protein acts as an acceptor. Analysis reveals that 91.3% energy transfer occurs from the dye doped polymer nanoparticle to the dye encapsulated BSA protein. The antenna effect of this light harvesting system is found to be 31 at a donor to acceptor ratio of 0.82 : 1 which is unprecedented. The enhanced effective molar extinction coefficient of the acceptor dye is potential for the light harvesting system. Bright white light emission with a quantum yield of 14% under single wavelength excitation is obtained by changing the ratio of donor to acceptor. Analysis reveals that the efficient energy transfer in this polymer-protein assembly may open up new possibilities in designing artificial light harvesting systems for future applications.

  2. Geometry, supertransfer, and optimality in the light harvesting of purple bacteria

    CERN Document Server

    Baghbanzadeh, Sima

    2016-01-01

    The remarkable rotational symmetry of the photosynthetic antenna complexes of purple bacteria has long been thought to enhance their light harvesting and excitation energy transport. We study the role of symmetry by modeling hypothetical antennas whose symmetry is broken by altering the orientations of the bacteriochlorophyll pigments. We find that in both LH2 and LH1 complexes, symmetry increases energy transfer rates by enabling the cooperative, coherent process of supertransfer. The enhancement is particularly pronounced in the LH1 complex, whose natural geometry outperforms the average randomized geometry by 5.5 standard deviations, one of the most significant increase due to coherent effects in any photosynthetic complex studied to date.

  3. Light harvesting in a fluctuating antenna

    NARCIS (Netherlands)

    Chmeliov, J.; Trinkunas, G.; Amerongen, van H.; Valkunas, L.

    2014-01-01

    One of the major players in oxygenic photosynthesis, photosystem II (PSII), exhibits complex multiexponential fluorescence decay kinetics that for decades has been ascribed to reversible charge separation taking place in the reaction center (RC). However, in this description the protein dynamics is

  4. Light harvesting and photoprotection in Cyanobacteria

    NARCIS (Netherlands)

    Tian, L.

    2013-01-01

    The process of photosynthesis has been studied for centuries, but despite a large amount of progress, there are still many aspects that are not fully understood. An important part of the progress is the fact that many structures of photosynthetic complexes have been resolved 1,2and these

  5. The chlorosome: a prototype for efficient light harvesting in photosynthesis

    NARCIS (Netherlands)

    Oostergetel, G.; Amerongen, van H.; Boekema, E.J.

    2010-01-01

    Three phyla of bacteria include phototrophs that contain unique antenna systems, chlorosomes, as the principal light-harvesting apparatus. Chlorosomes are the largest known supramolecular antenna systems and contain hundreds of thousands of BChl c/d/e molecules enclosed by a single membrane leaflet

  6. The chlorosome : a prototype for efficient light harvesting in photosynthesis

    NARCIS (Netherlands)

    Oostergetel, Gert T.; van Amerongen, Herbert; Boekema, Egbert J.

    Three phyla of bacteria include phototrophs that contain unique antenna systems, chlorosomes, as the principal light-harvesting apparatus. Chlorosomes are the largest known supramolecular antenna systems and contain hundreds of thousands of BChl c/d/e molecules enclosed by a single membrane leaflet

  7. Discrete redox signaling pathways regulate photosynthetic light-harvesting and chloroplast gene transcription.

    Directory of Open Access Journals (Sweden)

    John F Allen

    Full Text Available In photosynthesis in chloroplasts, two related regulatory processes balance the actions of photosystems I and II. These processes are short-term, post-translational redistribution of light-harvesting capacity, and long-term adjustment of photosystem stoichiometry initiated by control of chloroplast DNA transcription. Both responses are initiated by changes in the redox state of the electron carrier, plastoquinone, which connects the two photosystems. Chloroplast Sensor Kinase (CSK is a regulator of transcription of chloroplast genes for reaction centres of the two photosystems, and a sensor of plastoquinone redox state. We asked whether CSK is also involved in regulation of absorbed light energy distribution by phosphorylation of light-harvesting complex II (LHC II. Chloroplast thylakoid membranes isolated from a CSK T-DNA insertion mutant and from wild-type Arabidopsis thaliana exhibit similar light- and redox-induced (32P-labelling of LHC II and changes in 77 K chlorophyll fluorescence emission spectra, while room-temperature chlorophyll fluorescence emission transients from Arabidopsis leaves are perturbed by inactivation of CSK. The results indicate indirect, pleiotropic effects of reaction centre gene transcription on regulation of photosynthetic light-harvesting in vivo. A single, direct redox signal is transmitted separately to discrete transcriptional and post-translational branches of an integrated cytoplasmic regulatory system.

  8. Nucleus-encoded light-harvesting chlorophyll a/b proteins are imported normally into chlorophyll b-free chloroplasts of Arabidopsis.

    Science.gov (United States)

    Nick, Sabine; Meurer, Jörg; Soll, Jürgen; Ankele, Elisabeth

    2013-05-01

    Chloroplast-located proteins which are encoded by the nuclear genome have to be imported from the cytosol into the organelle in a posttranslational manner. Among these nuclear-encoded chloroplast proteins are the light-harvesting chlorophyll a/b-binding proteins (LHCPs). After translation in the cytosol, precursor proteins of LHCPs are imported via the TOC/TIC translocase, processed to their mature size to insert into thylakoid membranes where they recruit chlorophylls a and b to form pigment-protein complexes. The translocation of proteins is a highly regulated process which employs several regulators. To analyze whether CAO (chlorophyll a oxigenase) which converts chlorophyll a to chlorophyll b at the inner chloroplast membrane, is one of these regulators, we performed import reactions utilizing a homozygous loss-of-function mutant (cao-1). We imported in vitro translated and (35)S-labeled precursor proteins of light-harvesting proteins of photosystem II LHCB1, LHCB4, and LHCB5 into chloroplasts isolated from cao-1 and show that import of precursor proteins and their processing to mature forms are not impaired in the mutant. Therefore, regulation of the import machinery cannot be responsible for the decreased steady-state levels of light-harvesting complex (LHC) proteins. Regulation does not take place at the transcriptional level either, because Lhcb mRNAs are not down-regulated. Additionally, reduced steady-state levels of LHCPs also do not occur due to posttranslational turnover of non-functional LHCPs in chloroplasts. Taken together, our data show that plants in the absence of CAO and therefore devoid of chlorophyll b are not influenced in their import behavior of LHC proteins.

  9. Coherent open-loop optimal control of light-harvesting dynamics

    CERN Document Server

    Caruso, Filippo; Calarco, Tommaso; Huelga, Susana F; Plenio, Martin B

    2011-01-01

    We apply theoretically open-loop quantum optimal control techniques to provide methods for the verification of various quantum coherent transport mechanisms in natural and artificial light-harvesting complexes under realistic experimental constraints. We demonstrate that optimally shaped laser pulses allow to faithfully prepare the photosystem in specified initial states (such as localized excitation or coherent superposition, i.e. propagating and non-propagating states) and to probe efficiently the dynamics. These results provide a path towards the discrimination of the different transport pathways and to the characterization of environmental properties, enhancing our understanding of the role that coherent processes may play in biological complexes.

  10. Probing the effect of the binding site on the electrostatic behavior of a series of carotenoids reconstituted into the light-harvesting 1 complex from purple photosynthetic bacterium Rhodospirillum rubrum detected by stark spectroscopy.

    Science.gov (United States)

    Nakagawa, Katsunori; Suzuki, Satoru; Fujii, Ritsuko; Gardiner, Alastair T; Cogdell, Richard J; Nango, Mamoru; Hashimoto, Hideki

    2008-08-01

    Reconstitutions of the LH1 complexes from the purple photosynthetic bacterium Rhodospirillum rubrum S1 were performed with a range of carotenoid molecules having different numbers of C=C conjugated double bonds. Since, as we showed previously, some of the added carotenoids tended to aggregate and then to remain with the reconstituted LH1 complexes (Nakagawa, K.; Suzuki, S.; Fujii, R.; Gardiner, A.T.; Cogdell, R.J.; Nango, M.; Hashimoto, H. Photosynth. Res. 2008, 95, 339-344), a further purification step using a sucrose density gradient centrifugation was introduced to improve purity of the final reconstituted sample. The measured absorption, fluorescence-excitation, and Stark spectra of the LH1 complex reconstituted with spirilloxanthin were identical with those obtained with the native, spirilloxanthin-containing, LH1 complex of Rs. rubrum S1. This shows that the electrostatic environments surrounding the carotenoid and bacteriochlorophyll a (BChl a) molecules in both of these LH1 complexes were essentially the same. In the LH1 complexes reconstituted with either rhodopin or spheroidene, however, the wavelength maximum at the BChl a Qy absorption band was slightly different to that of the native LH1 complexes. These differences in the transition energy of the BChl a Qy absorption band can be explained using the values of the nonlinear optical parameters of this absorption band, i.e., the polarizability change Tr(Deltaalpha) and the static dipole-moment change |Deltamu| upon photoexcitation, as determined using Stark spectroscopy. The local electric field around the BChl a in the native LH1 complex (ES) was determined to be approximately 3.0x10(6) V/cm. Furthermore, on the basis of the values of the nonlinear optical parameters of the carotenoids in the reconstituted LH1 complexes, it is possible to suggest that the conformations of carotenoids, anhydrorhodovibrin and spheroidene, in the LH1 complex were similar to that of rhodopin glucoside in crystal structure of

  11. Potential sustainable energy source: Pheroid™ with incorporated light harvesting materials

    CSIR Research Space (South Africa)

    Smit, Jacoba E

    2010-09-01

    Full Text Available . In the photosynthetic system light energy is absorbed by antenna chlorophylls and this energy is then passed onto a reaction centre chlorophyll molecule where charge separation occurs [1] in less than 100 ps and at about 95% efficiency [2]. It has been shown...-based combinations, which enables the production of small, elastic artificial vesicles, called Pheroid™. Previous work has shown that photosynthetic light harvesting material can be incorporated into the Pheroid™ (Figure 1). Figure 1: Examples of photosynthetic...

  12. Light-harvesting materials: Soft support for energy conversion

    Energy Technology Data Exchange (ETDEWEB)

    Stolley, Ryan M.; Helm, Monte L.

    2014-11-10

    To convert solar energy into viable fuel sources, coupling light-harvesting materials to catalysts is a critical challenge. Now, coupling between an organic supramolecular hydrogel and a non precious metal catalyst has been demonstrated to be effective for photocatalytic H2 production. Ryan M. Stolley and Monte L. Helm are at Pacific Northwest National Laboratory (PNNL), Richland, WA, USA 99352. PNNL is operated by Battelle for the US Department of Energy. e-mail: Monte.Helm@pnnl.gov

  13. Artificial photosynthetic reaction centers coupled to light-harvesting antennas.

    Science.gov (United States)

    Ghosh, Pulak Kumar; Smirnov, Anatoly Yu; Nori, Franco

    2011-12-01

    We analyze a theoretical model for energy and electron transfer in an artificial photosynthetic system. The photosystem consists of a molecular triad (i.e., with a donor, a photosensitive unit, and an acceptor) coupled to four accessory light-harvesting-antenna pigments. The resonant energy transfer from the antennas to the artificial reaction center (the molecular triad) is described here by the Förster mechanism. We consider two different kinds of arrangements of the accessory light-harvesting pigments around the reaction center. The first arrangement allows direct excitation transfer to the reaction center from all the surrounding pigments. The second configuration transmits energy via a cascade mechanism along a chain of light-harvesting chromophores, where only one chromophore is connected to the reaction center. We show that the artificial photosynthetic system using the cascade energy transfer absorbs photons in a broader wavelength range and converts their energy into electricity with a higher efficiency than the system based on direct couplings between all the antenna chromophores and the reaction center.

  14. Functionalized Nanoparticles and Surfaces for Controlled Chemical Catalysis and Effective Light Harvesting

    Energy Technology Data Exchange (ETDEWEB)

    Marye Anne Fox, James K. Whitesell

    2012-11-02

    We have prepared a range of such arrays as key components for biotechnology and photonic applications. These involve self-assembled arrays of increasing complexity with three-dimensionally disposed multilayer interactions. These arrays also include dendrimers as the distinguishing structural building blocks. These photoactive integrated systems have a regular, highly-branched, three-dimensional architecture. Structural modifications of these units include variation of the core, bridging layers, and terminal groups. These modifications result in a large array of dendritic molecules with potential applications for light harvesting.

  15. Functionalized Nanoparticles and Surfaces for Controlled Chemical Catalysis and Effective Light Harvesting

    Energy Technology Data Exchange (ETDEWEB)

    Marye Anne Fox, James K. Whitesell

    2012-11-02

    We have prepared a range of such arrays as key components for biotechnology and photonic applications. These involve self-assembled arrays of increasing complexity with three-dimensionally disposed multilayer interactions. These arrays also include dendrimers as the distinguishing structural building blocks. These photoactive integrated systems have a regular, highly-branched, three-dimensional architecture. Structural modifications of these units include variation of the core, bridging layers, and terminal groups. These modifications result in a large array of dendritic molecules with potential applications for light harvesting.

  16. Single-residue insertion switches the quaternary structure and exciton states of cryptophyte light-harvesting proteins.

    Science.gov (United States)

    Harrop, Stephen J; Wilk, Krystyna E; Dinshaw, Rayomond; Collini, Elisabetta; Mirkovic, Tihana; Teng, Chang Ying; Oblinsky, Daniel G; Green, Beverley R; Hoef-Emden, Kerstin; Hiller, Roger G; Scholes, Gregory D; Curmi, Paul M G

    2014-07-01

    Observation of coherent oscillations in the 2D electronic spectra (2D ES) of photosynthetic proteins has led researchers to ask whether nontrivial quantum phenomena are biologically significant. Coherent oscillations have been reported for the soluble light-harvesting phycobiliprotein (PBP) antenna isolated from cryptophyte algae. To probe the link between spectral properties and protein structure, we determined crystal structures of three PBP light-harvesting complexes isolated from different species. Each PBP is a dimer of αβ subunits in which the structure of the αβ monomer is conserved. However, we discovered two dramatically distinct quaternary conformations, one of which is specific to the genus Hemiselmis. Because of steric effects emerging from the insertion of a single amino acid, the two αβ monomers are rotated by ∼73° to an "open" configuration in contrast to the "closed" configuration of other cryptophyte PBPs. This structural change is significant for the light-harvesting function because it disrupts the strong excitonic coupling between two central chromophores in the closed form. The 2D ES show marked cross-peak oscillations assigned to electronic and vibrational coherences in the closed-form PC645. However, such features appear to be reduced, or perhaps absent, in the open structures. Thus cryptophytes have evolved a structural switch controlled by an amino acid insertion to modulate excitonic interactions and therefore the mechanisms used for light harvesting.

  17. Two Cyanobacterial Photoreceptors Regulate Photosynthetic Light Harvesting by Sensing Teal, Green, Yellow, and Red Light.

    Science.gov (United States)

    Wiltbank, Lisa B; Kehoe, David M

    2016-02-09

    The genomes of many photosynthetic and nonphotosynthetic bacteria encode numerous phytochrome superfamily photoreceptors whose functions and interactions are largely unknown. Cyanobacterial genomes encode particularly large numbers of phytochrome superfamily members called cyanobacteriochromes. These have diverse light color-sensing abilities, and their functions and interactions are just beginning to be understood. One of the best characterized of these functions is the regulation of photosynthetic light-harvesting antenna composition in the cyanobacterium Fremyella diplosiphon by the cyanobacteriochrome RcaE in response to red and green light, a process known as chromatic acclimation. We have identified a new cyanobacteriochrome named DpxA that maximally senses teal (absorption maximum, 494 nm) and yellow (absorption maximum, 568 nm) light and represses the accumulation of a key light-harvesting protein called phycoerythrin, which is also regulated by RcaE during chromatic acclimation. Like RcaE, DpxA is a two-component system kinase, although these two photoreceptors can influence phycoerythrin expression through different signaling pathways. The peak responsiveness of DpxA to teal and yellow light provides highly refined color discrimination in the green spectral region, which provides important wavelengths for photosynthetic light harvesting in cyanobacteria. These results redefine chromatic acclimation in cyanobacteria and demonstrate that cyanobacteriochromes can coordinately impart sophisticated light color sensing across the visible spectrum to regulate important photosynthetic acclimation processes. The large number of cyanobacteriochrome photoreceptors encoded by cyanobacterial genomes suggests that these organisms are capable of extremely complex light color sensing and responsiveness, yet little is known about their functions and interactions. Our work uncovers previously undescribed cooperation between two photoreceptors with very different light

  18. Role of ions in the regulation of light-harvesting

    Directory of Open Access Journals (Sweden)

    Radek Kana

    2016-12-01

    Full Text Available Regulation of photosynthetic light harvesting in the thylakoids is one of the major key factors affecting the efficiency of photosynthesis. Thylakoid membrane is negatively charged and influences both the structure and the function of the primarily photosynthetic reactions through its electrical double layer. Further, there is a heterogeneous organization of soluble ions (K+, Mg2+, Cl- attached to the thylakoid membrane that, together with fixed charges (negatively charged amino acids, lipids, provides an electrical field. The electrical double layer is affected by the valence of the ions and interferes with the regulation of state transitions, protein interactions, and excitation energy spillover from Photosystem II to Photosystem I. These effects are reflected in changes in the intensity of chlorophyll a fluorescence, which is also a measure of photoprotective non-photochemical quenching of the excited state of chlorophyll a. A triggering of non-photochemical quenching proceeds via lumen acidification and is coupled to the export of positive counter-ions (Mg2+, K+ to the stroma or/and negative ions (e.g., Cl- into the lumen. The effect of protons and anions in the lumen and of the cations (Mg2+, K+ in the stroma are, thus, functionally tightly interconnected. In this review, we discuss the consequences of the model of electrical double layer, proposed by James Barber (J. Barber (1980 Biochim Biophys Acta 594:253-308 in light of light-harvesting regulation. Further, we explain differences between electrostatic screening and neutralization, and we emphasize the opposite effect of monovalent (K+ and divalent (Mg2+ ions on light-harvesting and on screening of the negative charges on the thylakoid membrane; this effect needs to be incorporated in all future models of photosynthetic regulation by ion channels and transporters.

  19. Iterative linearized density matrix propagation for modeling coherent excitation energy transfer in photosynthetic light harvesting.

    Science.gov (United States)

    Huo, P; Coker, D F

    2010-11-14

    Rather than incoherent hopping between chromophores, experimental evidence suggests that the excitation energy transfer in some biological light harvesting systems initially occurs coherently, and involves coherent superposition states in which excitation spreads over multiple chromophores separated by several nanometers. Treating such delocalized coherent superposition states in the presence of decoherence and dissipation arising from coupling to an environment is a significant challenge for conventional theoretical tools that either use a perturbative approach or make the Markovian approximation. In this paper, we extend the recently developed iterative linearized density matrix (ILDM) propagation scheme [E. R. Dunkel et al., J. Chem. Phys. 129, 114106 (2008)] to study coherent excitation energy transfer in a model of the Fenna-Matthews-Olsen light harvesting complex from green sulfur bacteria. This approach is nonperturbative and uses a discrete path integral description employing a short time approximation to the density matrix propagator that accounts for interference between forward and backward paths of the quantum excitonic system while linearizing the phase in the difference between the forward and backward paths of the environmental degrees of freedom resulting in a classical-like treatment of these variables. The approach avoids making the Markovian approximation and we demonstrate that it successfully describes the coherent beating of the site populations on different chromophores and gives good agreement with other methods that have been developed recently for going beyond the usual approximations, thus providing a new reliable theoretical tool to study coherent exciton transfer in light harvesting systems. We conclude with a discussion of decoherence in independent bilinearly coupled harmonic chromophore baths. The ILDM propagation approach in principle can be applied to more general descriptions of the environment.

  20. Light harvesting via energy transfer in the dye solar cell

    Energy Technology Data Exchange (ETDEWEB)

    Siegers, Conrad

    2007-11-09

    The PhD-thesis ''Light Harvesting via Energy Transfer in the Dye Solar Cell'' (University of Freiburg, July 2007) describes the conceptual design, synthesis and testing of energy donor acceptor sensitizers for the dye solar cell (DSC). Under monochromatic illumination solar cells sensitized with the novel donor acceptor systems revealed a higher power conversion efficiency than cells containing exclusively the acceptor component. The following approach led to this conclusion: (i) the choice of suitable chromophores as energy donor and acceptor moieties according to the Foerster-theory, (ii) the synthesis of different donor acceptor systems, (iii) the development of a methodology allowing the quantification of energy transfer within dye solar cells, and (iv) the evaluation of characteristics of DSCs that were sensitized with the different donor acceptor systems. The acceptor chromophores used in this work were derived from [Ru(dcbpy)2acac]Cl (dcbpy = 4,4'-dicarboxy-2,2'-bipyridin, acac = acetylacetonato). This complex offered the opportunity to introduce substituents at the acac-ligand's terminal CH3 groups without significantly affecting its excellent photoelectrochemical properties. Alkylated 4-amino-1,8-naphthalimides (termed Fluorols in the following) were used as energy donor chromophores. This class of compounds fulfils the requirements for efficient energy transfer to [Ru(dcbpy)2acac]Cl. Covalently linking donor and acceptor chromophores to one another was achieved by two different concepts. A dyad comprising one donor and one acceptor chromophore was synthesized by subsequent hydrosilylation steps of an olefin-bearing donor and an acceptor precursor to the dihydrosilane HSiMe2-CH2CH2-SiMe2H. A series of polymers comprising multiple donor and acceptor units was made by the addition of alkyne-bearing chromophores to hyperbranched polyglycerol azide (''Click-chemistry''). In this series the donor acceptor

  1. Light harvesting via energy transfer in the dye solar cell

    Energy Technology Data Exchange (ETDEWEB)

    Siegers, Conrad

    2007-11-09

    The PhD-thesis ''Light Harvesting via Energy Transfer in the Dye Solar Cell'' (University of Freiburg, July 2007) describes the conceptual design, synthesis and testing of energy donor acceptor sensitizers for the dye solar cell (DSC). Under monochromatic illumination solar cells sensitized with the novel donor acceptor systems revealed a higher power conversion efficiency than cells containing exclusively the acceptor component. The following approach led to this conclusion: (i) the choice of suitable chromophores as energy donor and acceptor moieties according to the Foerster-theory, (ii) the synthesis of different donor acceptor systems, (iii) the development of a methodology allowing the quantification of energy transfer within dye solar cells, and (iv) the evaluation of characteristics of DSCs that were sensitized with the different donor acceptor systems. The acceptor chromophores used in this work were derived from [Ru(dcbpy)2acac]Cl (dcbpy = 4,4'-dicarboxy-2,2'-bipyridin, acac = acetylacetonato). This complex offered the opportunity to introduce substituents at the acac-ligand's terminal CH3 groups without significantly affecting its excellent photoelectrochemical properties. Alkylated 4-amino-1,8-naphthalimides (termed Fluorols in the following) were used as energy donor chromophores. This class of compounds fulfils the requirements for efficient energy transfer to [Ru(dcbpy)2acac]Cl. Covalently linking donor and acceptor chromophores to one another was achieved by two different concepts. A dyad comprising one donor and one acceptor chromophore was synthesized by subsequent hydrosilylation steps of an olefin-bearing donor and an acceptor precursor to the dihydrosilane HSiMe2-CH2CH2-SiMe2H. A series of polymers comprising multiple donor and acceptor units was made by the addition of alkyne-bearing chromophores to hyperbranched polyglycerol azide (''Click-chemistry''). In this series the donor acceptor

  2. Triplet Energy Transport in Platinum-Acetylide Light Harvesting Arrays.

    Science.gov (United States)

    Chen, Zhuo; Hsu, Hsien-Yi; Arca, Mert; Schanze, Kirk S

    2015-06-18

    Light harvesting and triplet energy transport is investigated in chromophore-functionalized polystyrene polymers featuring light harvesting and energy acceptor chromophores (traps) at varying loading. The series of precision polymers was constructed via reversible addition-fragmentation transfer polymerization and functionalized with platinum acetylide triplet chromophores by using an azide-alkyne "click" reaction. The polymers have narrow polydispersity and degree of polymerization ∼60. The chromophores have the general structure, trans-[-R-C6H4-C≡C-Pt(PBu3)2-C≡C-Ar], where R is the attachment point to the polystyrene backbone and Ar is either -C6H4-C≡C-Ph or -pyrenyl (PE2-Pt and Py-Pt, respectively, with triplet energies of 2.35 and 1.88 eV). The polychromophores contain mainly the high-energy PE2-Pt units (light absorber and energy donor), with randomly distributed Py-Pt units (3-20% loading, energy acceptor). Photophysical methods are used to study the dynamics and efficiency of energy transport from the PE2-Pt to Py-Pt units in the polychromophores. The energy transfer efficiency is >90% for copolymers that contain 5% of the Py-Pt acceptor units. Time-resolved phosphorescence measurements combined with Monte Carlo exciton dynamics simulations suggest that the mechanism of exciton transport is exchange energy transfer hopping between PE2-Pt units.

  3. The terminal phycobilisome emitter, LCM: A light-harvesting pigment with a phytochrome chromophore.

    Science.gov (United States)

    Tang, Kun; Ding, Wen-Long; Höppner, Astrid; Zhao, Cheng; Zhang, Lun; Hontani, Yusaku; Kennis, John T M; Gärtner, Wolfgang; Scheer, Hugo; Zhou, Ming; Zhao, Kai-Hong

    2015-12-29

    Photosynthesis relies on energy transfer from light-harvesting complexes to reaction centers. Phycobilisomes, the light-harvesting antennas in cyanobacteria and red algae, attach to the membrane via the multidomain core-membrane linker, L(CM). The chromophore domain of L(CM) forms a bottleneck for funneling the harvested energy either productively to reaction centers or, in case of light overload, to quenchers like orange carotenoid protein (OCP) that prevent photodamage. The crystal structure of the solubly modified chromophore domain from Nostoc sp. PCC7120 was resolved at 2.2 Å. Although its protein fold is similar to the protein folds of phycobiliproteins, the phycocyanobilin (PCB) chromophore adopts ZZZssa geometry, which is unknown among phycobiliproteins but characteristic for sensory photoreceptors (phytochromes and cyanobacteriochromes). However, chromophore photoisomerization is inhibited in L(CM) by tight packing. The ZZZssa geometry of the chromophore and π-π stacking with a neighboring Trp account for the functionally relevant extreme spectral red shift of L(CM). Exciton coupling is excluded by the large distance between two PCBs in a homodimer and by preservation of the spectral features in monomers. The structure also indicates a distinct flexibility that could be involved in quenching. The conclusions from the crystal structure are supported by femtosecond transient absorption spectra in solution.

  4. Separating annihilation and excitation energy transfer dynamics in light harvesting systems.

    Science.gov (United States)

    Vengris, Mikas; Larsen, Delmar S; Valkunas, Leonas; Kodis, Gerdenis; Herrero, Christian; Gust, Devens; Moore, Thomas; Moore, Ana; van Grondelle, Rienk

    2013-09-26

    The dependence of excitation energy transfer kinetics on the electronic state of the acceptor (ground vs excited) has been resolved with a novel multipulse prePump-Pump-Probe spectroscopy. The primary energy transfer and annihilation dynamics in two model light-harvesting systems were explored: an artificially synthesized carotenoid-zinc-phthalocyanine dyad and a naturally occurring light-harvesting peridinin-chlorophyll protein complex from Amphidinium carterae. Both systems use carotenoid as the primary excitation energy donor with porphyrin chromophores as the acceptor molecules. The prePump-Pump-Probe transient signals were analyzed with Monte Carlo modeling to explicitly address the underlying step-by-step kinetics involved in both excitation migration and annihilation processes. Both energy transfer and annihilation dynamics were demonstrated to occur with approximately the same rate in both systems, regardless of the excitation status of the acceptor pigments. The possible reasons for these observations are discussed in the framework of the Förster energy transfer model.

  5. Multireference Excitation Energies for Bacteriochlorophylls A within Light Harvesting System 2.

    Science.gov (United States)

    Anda, André; Hansen, Thorsten; De Vico, Luca

    2016-03-08

    Light-harvesting system 2 (LH2) of purple bacteria is one of the most popular antenna complexes used to study Nature's way of collecting and channeling solar energy. The dynamics of the absorbed energy is probed by ultrafast spectroscopy. Simulation of these experiments relies on fitting a range of parameters to reproduce the spectra. Here, we present a method that can determine key parameters to chemical accuracy. These will eliminate free variables in the modeling, thus reducing the problem. Using MS-RASPT2/RASSCF calculations, we compute excitation energies and transition dipole moments of all bacteriochlorophylls in LH2. We find that the excitation energies vary among the bacteriochlorophyll monomers and that they are regulated by the curvature of the macrocycle ring and the dihedral angle of an acetyl moiety. Increasing the curvature lifts the ground state energy, which causes a red shift of the excitation energy. Increasing the torsion of the acetyl moiety raises the excited state energy, resulting in a blue shift of the excitation energy. The obtained results mark a giant leap for multiconfigurational multireference quantum chemical methods in the photochemistry of biological systems, which can prove instrumental in exposing the underlying physics of photosynthetic light-harvesting.

  6. Development of Scaffolds for Light Harvesting and Photocatalysis from the Coat Protein of Tobacco Mosaic Virus

    Science.gov (United States)

    Dedeo, Michel Toussaint

    The utility of a previously developed TMV-based light harvesting system has been dramatically expanded through the introduction of reactive handles for the site-specific modification of the interior and exterior surfaces. Further experiments to reengineer the coat protein have produced structures with unique, unexpected, and useful assembly properties that complement the newly available surface modifications. Energy transfer from chromophores in the RNA channel of self-assembled TMV structures to the exterior was made possible by conjugation of acceptor dyes and porphyrins to the N-terminus. By repositioning the N-terminus to the pore through circular permutation, this process was repeated to create structures that mimic the light harvesting 1 complex of photosynthetic bacteria. To study and improve upon natural photosynthesis, closely packed chromophore arrays and gold nanoparticles were tethered to the pore of stabilized TMV disks through introduction of a uniquely reactive lysine. Finally, a dimeric TMV coat protein was produced to control the distribution and arrangement of synthetic groups with synergistic activity.

  7. Semiconductor Nanocrystals as Light Harvesters in Solar Cells

    Directory of Open Access Journals (Sweden)

    Lioz Etgar

    2013-02-01

    Full Text Available Photovoltaic cells use semiconductors to convert sunlight into electrical current and are regarded as a key technology for a sustainable energy supply. Quantum dot-based solar cells have shown great potential as next generation, high performance, low-cost photovoltaics due to the outstanding optoelectronic properties of quantum dots and their multiple exciton generation (MEG capability. This review focuses on QDs as light harvesters in solar cells, including different structures of QD-based solar cells, such as QD heterojunction solar cells, QD-Schottky solar cells, QD-sensitized solar cells and the recent development in organic-inorganic perovskite heterojunction solar cells. Mechanisms, procedures, advantages, disadvantages and the latest results obtained in the field are described. To summarize, a future perspective is offered.

  8. Semiconductor Nanocrystals as Light Harvesters in Solar Cells

    Science.gov (United States)

    Etgar, Lioz

    2013-01-01

    Photovoltaic cells use semiconductors to convert sunlight into electrical current and are regarded as a key technology for a sustainable energy supply. Quantum dot-based solar cells have shown great potential as next generation, high performance, low-cost photovoltaics due to the outstanding optoelectronic properties of quantum dots and their multiple exciton generation (MEG) capability. This review focuses on QDs as light harvesters in solar cells, including different structures of QD-based solar cells, such as QD heterojunction solar cells, QD-Schottky solar cells, QD-sensitized solar cells and the recent development in organic-inorganic perovskite heterojunction solar cells. Mechanisms, procedures, advantages, disadvantages and the latest results obtained in the field are described. To summarize, a future perspective is offered. PMID:28809318

  9. Semiconductor Nanocrystals as Light Harvesters in Solar Cells.

    Science.gov (United States)

    Etgar, Lioz

    2013-02-04

    Photovoltaic cells use semiconductors to convert sunlight into electrical current and are regarded as a key technology for a sustainable energy supply. Quantum dot-based solar cells have shown great potential as next generation, high performance, low-cost photovoltaics due to the outstanding optoelectronic properties of quantum dots and their multiple exciton generation (MEG) capability. This review focuses on QDs as light harvesters in solar cells, including different structures of QD-based solar cells, such as QD heterojunction solar cells, QD-Schottky solar cells, QD-sensitized solar cells and the recent development in organic-inorganic perovskite heterojunction solar cells. Mechanisms, procedures, advantages, disadvantages and the latest results obtained in the field are described. To summarize, a future perspective is offered.

  10. Optimal light harvesting structures at optical and infrared frequencies

    CERN Document Server

    Villate-Guío, F; García-Vidal, F J; Martín-Moreno, L; de León-Pérez, F

    2012-01-01

    One-dimensional light harvesting structures with a realistic geometry nano-patterned on an opaque metallic film are optimized to render high transmission efficiencies at optical and infrared frequencies. Simple design rules are developed for the particular case of a slit-groove array with a given number of grooves that are symmetrically distributed with respect to a central slit. These rules take advantage of the hybridization of Fabry-Perot modes in the slit and surface modes of the corrugated metal surface. Same design rules apply for optical and infrared frequencies. The parameter space of the groove array is also examined with a conjugate gradient optimization algorithm that used as a seed the geometries optimized following physical intuition. Both uniform and nonuniform groove arrays are considered. The largest transmission enhancement, with respect to a uniform array, is obtained for a chirped groove profile. Such enhancement is a function of the wavelength. It decreases from 39% in the optical part of ...

  11. Dendrimer light-harvesting: intramolecular electrodynamics and mechanisms.

    Science.gov (United States)

    Andrews, David L; Bradshaw, David S; Jenkins, Robert D; Rodríguez, Justo

    2009-12-01

    In the development of highly efficient materials for harvesting solar energy, there is an increasing focus on purpose-built dendrimers and allied multi-chromophore systems. A proliferation of antenna chromophores is not the only factor determining the sought light-harvesting efficiency; the internal geometry and photophysics of these molecules are also crucially important. In particular, the mechanisms by means of which radiant energy is ultimately trapped depends on an intricate interplay of electronic, structural, energetic and symmetry properties. To better understand these processes a sound theoretical representation of the intramolecular electrodynamics is required. A suitable formalism, based on quantum electrodynamics, readily delivers physical insights into the necessary excitation channelling processes, and it affords a rigorous basis for modelling the intramolecular flow of energy.

  12. Primary light harvesting system: phycobilisomes and associated membranes. Progress report, January 1, 1976--December 31, 1976

    Energy Technology Data Exchange (ETDEWEB)

    Gantt, E.

    1976-01-01

    Phycobilisomes, which function as light harvesting antennae in red and blue-green algae, are structured for maximum energy transfer from the phycobiliproteins to chlorophyll in the photosynthetic lamellae. An immunoelectron microscopic procedure was devised by which it was possible to show that allophycocyanin is located on the photosynthetic membrane, but apparently is not a structural component thereof. Location of allophycocyanin on the membrane is significant because it facilitates the energy transfer to chlorophyll. In attempts at reconstitution of phycobilisomes, from isolated phycobiliproteins, it was found that association of these pigments is more complex than had thus far been inferred from in vitro studies. In reconstituting complexes of phycocyanin and phycoerythrin, the previous apparent confirmational state of each protein was very important. Several allophycocyanin fms, derived from phycobilisomes, similarly showed absorption, fluorescence and sedimentation behavior which suggested minor but significant changes in the state of confirmation and or aggregation.

  13. The fundamental role of localised vibrations in excitation dynamics in photosynthetic light-harvesting systems

    CERN Document Server

    Kolli, Avinash; Scholes, Gregory D; Olaya-Castro, Alexandra

    2012-01-01

    The importance of fast vibrations in enhancing and controlling energy transfer and conversion in biomolecules is an issue of current debate. In this article we show that coupling between localised high-frequency vibrations and electronic degrees of freedom is fundamental for efficient excitation transport in photosynthetic light-harvesting systems with high degree of disorder. We consider the cryptophyte antennae protein phycoerythrin 545 and discuss how the balance between electronic interactions and coupling to fast vibronic modes supports the biological function of these antennae by generating a non-cascaded transport that leads to a rapid, directed and wider spatial distribution of excitation energy across the complex. Furthermore, we illustrate signatures of vibronic influence in the beating of excitonic coherences and show that mechanisms supporting coherent evolution of excitons also assist coupling to selected modes that enhance energy transfer to preferential sites in the complex. We therefore argue ...

  14. Identification of light-harvesting chlorophyll a/b-binding protein genes of Zostera marina L. and their expression under different environmental conditions

    Science.gov (United States)

    Kong, Fanna; Zhou, Yang; Sun, Peipei; Cao, Min; Li, Hong; Mao, Yunxiang

    2016-02-01

    Photosynthesis includes the collection of light and the transfer of solar energy using light-harvesting chlorophyll a/b-binding (LHC) proteins. In high plants, the LHC gene family includes LHCA and LHCB sub-families, which encode proteins constituting the light-harvesting complex of photosystems I and II. Zostera marina L. is a monocotyledonous angiosperm and inhabits submerged marine environments rather than land environments. We characterized the Lhca and Lhcb gene families of Z. marina from the expressed sequence tags (EST) database. In total, 13 unigenes were annotated as ZmLhc, 6 in Lhca family and 7 in ZmLhcb family. ZmLHCA and ZmLHCB contained the conservative LHC motifs and amino acid residues binding chlorophyll. The average similarity among mature ZmLHCA and ZmLHCB was 48.91% and 48.66%, respectively, which indicated a high degree of divergence within ZmLHChc gene family. The reconstructed phylogenetic tree showed that the tree topology and phylogenetic relationship were similar to those reported in other high plants, suggesting that the Lhc genes were highly conservative and the classification of ZmLhc genes was consistent with the evolutionary position of Z. marina. Real-time reverse transcription (RT) PCR analysis showed that different members of ZmLhca and ZmLhcb responded to a stress in different expression patterns. Salinity, temperature, light intensity and light quality may affect the expression of most ZmLhca and ZmLhcb genes. Inorganic carbon concentration and acidity had no obvious effect on ZmLhca and ZmLhcb gene expression, except for ZmLhca6.

  15. Primary light harvesting system: phycobilisomes and associated membranes. Progress report, January 1, 1978--December 31, 1978

    Energy Technology Data Exchange (ETDEWEB)

    Gantt, E.

    1978-01-01

    Phycobilisomes, attached to photosynthetic membranes of the red and blue-green algae, function as the major light harvesters for photosynthesis. They represent one of the most efficient energy transfer systems in photosynthetic organisms. Allophycocyanin is the terminal pigment in the transfer chain. One of the far emitting allophycocyanin forms has been under study because it is the probable bridging pigment between the phycobilisomes and the photosynthetic membrane. Vesicles with attached phycobilisomes from Anabaena variabilis have been isolated and shown to transfer excitation energy from phycobiliproteins to photosystem II chlorophy11 and to actively evolving oxygen. With the availability of such conditions, and with the capability of being able to isolate phycobilisomes from any algae, probes for the phycobilisome attachment site can now be undertaken. Our isolation, characterization, and in vitro recombination of a phycocyanin and phycoerythrin complex represents the first crucial step in being able to explore the in vitro formation of phycobilisomes.

  16. Multireference excitation energies for bacteriochlorophylls A within light harvesting system 2

    DEFF Research Database (Denmark)

    Anda, Andre; Hansen, Thorsten; De Vico, Luca

    2016-01-01

    of the excitation energy. Increasing the torsion of the acetyl moiety raises the excited state energy, resulting in a blue shift of the excitation energy. The obtained results mark a giant leap for multiconfigurational multireference quantum chemical methods in the photochemistry of biological systems, which can......Light-harvesting system 2 (LH2) of purple bacteria is one of the most popular antenna complexes used to study Nature's way of collecting and channeling solar energy. The dynamics of the absorbed energy is probed by ultrafast spectroscopy. Simulation of these experiments relies on fitting a range...... of parameters to reproduce the spectra. Here, we present a method that can determine key parameters to chemical accuracy. These will eliminate free variables in the modeling, thus reducing the problem. Using MS-RASPT2/RASSCF calculations, we compute excitation energies and transition dipole moments of all...

  17. Excitation energy transfer in light-harvesting system: Effect of initial state

    CERN Document Server

    Cui, B; Oh, C H

    2012-01-01

    The light-harvesting is a problem of long interest. It becomes active again in recent years stimulated by suggestions of quantum effects in energy transport. Recent experiments found evidence that BChla 1 and BChla 6 are the first to be excited in the Fenna-Matthews-Olson(FMO) protein, theoretical studies, however, are mostly restricted to consider the exciton in BChla 1 initially. In this paper, we study the energy transport in the FMO complex by taking different initial states into account. Optimizations are performed for the decoherence rates as to maximal transport efficiency. Dependence of the energy transfer efficiency on the initial states is given and discussed. Effects of fluctuations in the site energies and couplings are also examined.

  18. Distinguishing the roles of energy funnelling and delocalization in photosynthetic light harvesting.

    Science.gov (United States)

    Baghbanzadeh, Sima; Kassal, Ivan

    2016-03-14

    Photosynthetic complexes improve the transfer of excitation energy from peripheral antennas to reaction centers in several ways. In particular, a downward energy funnel can direct excitons in the right direction, while coherent excitonic delocalization can enhance transfer rates through the cooperative phenomenon of supertransfer. However, isolating the role of purely coherent effects is difficult because any change to the delocalization also changes the energy landscape. Here, we show that the relative importance of the two processes can be determined by comparing the natural light-harvesting apparatus with counterfactual models in which the delocalization and the energy landscape are altered. Applied to the example of purple bacteria, our approach shows that although supertransfer does enhance the rates somewhat, the energetic funnelling plays the decisive role. Because delocalization has a minor role (and is sometimes detrimental), it is most likely not adaptive, being a side-effect of the dense chlorophyll packing that evolved to increase light absorption per reaction center.

  19. Consequences of Decreased Light Harvesting Capability on Photosystem II Function in Synechocystis sp. PCC 6803

    Science.gov (United States)

    Nagarajan, Aparna; Page, Lawrence E.; Liberton, Michelle; Pakrasi, Himadri B.

    2014-01-01

    Cyanobacteria use large pigment-protein complexes called phycobilisomes to harvest light energy primarily for photosystem II (PSII). We used a series of mutants with partial to complete reduction of phycobilisomes to examine the effects of antenna truncation on photosystem function in Synechocystis sp. PCC 6803. The antenna mutants CB, CK, and PAL expressed increasing levels of functional PSII centers to compensate for the loss of phycobilisomes, with a concomitant decrease in photosystem I (PSI). This increased PSII titer led to progressively higher oxygen evolution rates on a per chlorophyll basis. The mutants also exhibited impaired S-state transition profiles for oxygen evolution. Additionally, P700+ re-reduction rates were impacted by antenna reduction. Thus, a decrease in antenna size resulted in overall physiological changes in light harvesting and delivery to PSII as well as changes in downstream electron transfer to PSI. PMID:25513759

  20. Self-Assembly Strategies for Integrating Light Harvesting and Charge Separation in Artificial Photosynthetic Systems

    Energy Technology Data Exchange (ETDEWEB)

    Wasielewski, Michael R. (NWU)

    2017-02-15

    In natural photosynthesis, organisms optimize solar energy conversion through organized assemblies of photofunctional chromophores and catalysts within proteins that provide specifically tailored environments for chemical reactions. As with their natural counterparts, artificial photosynthetic systems for practical solar fuels production must collect light energy, separate charge, and transport charge to catalytic sites where multielectron redox processes will occur. While encouraging progress has been made on each aspect of this complex problem, researchers have not yet developed self-ordering and self-assembling components and the tailored environments necessary to realize a fully-functional artificial system. Previously researchers have used complex, covalent molecular systems comprised of chromophores, electron donors, and electron acceptors to mimic both the light-harvesting and the charge separation functions of photosynthetic proteins. These systems allow for study of the dependencies of electron transfer rate constants on donor?acceptor distance and orientation, electronic interaction, and the free energy of the reaction. The most useful and informative systems are those in which structural constraints control both the distance and the orientation between the electron donors and acceptors. Self-assembly provides a facile means for organizing large numbers of molecules into supramolecular structures that can bridge length scales from nanometers to macroscopic dimensions. The resulting structures must provide pathways for migration of light excitation energy among antenna chromophores, and from antennas to reaction centers. They also must incorporate charge conduits, that is, molecular 'wires' that can efficiently move electrons and holes between reaction centers and catalytic sites. The central scientific challenge is to develop small, functional building blocks with a minimum number of covalent linkages, which also have the appropriate molecular

  1. Light harvesting and Blue-Green light induced non-photochemical quenching in two different C-phycocyanin mutants of synechocytis PCC 6803

    NARCIS (Netherlands)

    Tian, L.; Stokkum, van I.H.M.; Koehorst, R.B.M.; Amerongen, van H.

    2013-01-01

    Cyanobacteria are oxygen-evolving photosynthetic organisms that harvest sunlight and convert excitation energy into chemical energy. Most of the light is absorbed by large light harvesting complexes called phycobilisomes (PBs). In high-light conditions, cyanobacteria switch on a photoprotective mech

  2. Designing dye-nanochannel antenna hybrid materials for light harvesting, transport and trapping.

    Science.gov (United States)

    Calzaferri, Gion; Méallet-Renault, Rachel; Brühwiler, Dominik; Pansu, Robert; Dolamic, Igor; Dienel, Thomas; Adler, Pauline; Li, Huanrong; Kunzmann, Andreas

    2011-02-25

    We discuss artificial photonic antenna systems that are built by incorporating chromophores into one-dimensional nanochannel materials and by organizing the latter in specific ways. Zeolite L (ZL) is an excellent host for the supramolecular organization of different kinds of molecules and complexes. The range of possibilities for filling its one-dimensional channels with suitable guests has been shown to be much larger than one might expect. Geometrical constraints imposed by the host structure lead to supramolecular organization of the guests in the channels. The arrangement of dyes inside the ZL channels is what we call the first stage of organization. It allows light harvesting within the volume of a dye-loaded ZL crystal and also the radiationless transport of energy to either the channel ends or center. One-dimensional FRET transport can be realized in these guest-host materials. The second stage of organization is realized by coupling either an external acceptor or donor stopcock fluorophore at the ends of the ZL channels, which can then trap or inject electronic excitation energy. The third stage of organization is obtained by interfacing the material to an external device via a stopcock intermediate. A possibility to achieve higher levels of organization is by controlled assembly of the host into ordered structures and preparation of monodirectional materials. The usually strong light scattering of ZL can be suppressed by refractive-index matching and avoidance of microphase separation in hybrid polymer/dye-ZL materials. The concepts are illustrated and discussed in detail on a bidirectional dye antenna system. Experimental results of two materials with a donor-to-acceptor ratio of 33:1 and 52:1, respectively, and a three-dye system illustrate the validity and challenges of this approach for synthesizing dye-nanochannel hybrid materials for light harvesting, transport, and trapping.

  3. Evolution under the sun: optimizing light harvesting in photosynthesis.

    Science.gov (United States)

    Ruban, Alexander V

    2015-01-01

    The emergence and evolution of life on our planet was possible because the sun provides energy to our biosphere. Indeed, all life forms need energy for existence and proliferation in space and time. Light-energy conversion takes place in photosynthetic organisms that evolve in various environments featuring an impressive range of light intensities that span several orders of magnitude. This property is achieved by the evolution of mechanisms of efficient energy capture that involved development of antenna pigments and pigment-protein complexes as well as the emergence of various strategies on the organismal, cellular, and molecular levels to counteract the detrimental effects of high light intensity on the delicate photosynthetic apparatus. Darwin was one of the first to describe the behaviour of plants towards light. He noticed that some plants try to avoid full daylight and called this reaction paraheliotropism. However, it was only in the second half of the 20th century, when scientists began to discover the structure and molecular mechanisms of the photosynthetic machinery, that the reasons for paraheliotropisms became clear. This review explains the need for the evolution of light adaptations using the example of higher plants. The review focuses on short-term adaptation mechanisms that occur on the minute scale, showing that these processes are fast enough to track rapid fluctuations in light intensity and that they evolved to be effective, allowing for the expansion of plant habitats and promoting diversification and survival. Also introduced are the most recent developments in methods that enable quantification of the light intensities that can be tolerated by plants. © The Author 2014. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.

  4. Forster Energy Transfer Theory as Reflected in the Structures of Photosynthetic Light-Harvesting Systems

    Energy Technology Data Exchange (ETDEWEB)

    Sener, Melih [Univ. of Illinois, Urbana-Champaign, IL (United States); Strumpfer, Johan [Univ. of Illinois, Urbana-Champaign, IL (United States); Hsin, Jen [Univ. of Illinois, Urbana-Champaign, IL (United States); Chandler, Danielle [Univ. of Illinois, Urbana-Champaign, IL (United States); Scheuring, Simon [Institut National de la Sante Et Recherche Medicale, Paris (France); Hunter, C. Neil [Univ. of Sheffield (United Kingdom); Schulten, Klaus [Univ. of Illinois, Urbana-Champaign, IL (United States)

    2011-02-22

    Förster's theory of resonant energy transfer underlies a fundamental process in nature, namely the harvesting of sunlight by photosynthetic life forms. The theoretical framework developed by Förster and others describes how electronic excitation migrates in the photosynthetic apparatus of plants, algae, and bacteria from light absorbing pigments to reaction centers where light energy is utilized for the eventual conversion into chemical energy. The demand for highest possible efficiency of light harvesting appears to have shaped the evolution of photosynthetic species from bacteria to plants which, despite a great variation in architecture, display common structural themes founded on the quantum physics of energy transfer as described first by Förster. Herein, Förster’s theory of excitation transfer is summarized, including recent extensions, and the relevance of the theory to photosynthetic systems as evolved in purple bacteria, cyanobacteria, and plants is demonstrated. Förster's energy transfer formula, as used widely today in many fields of science, is also derived.

  5. Enhancing light-harvesting power with coherent vibrational interactions: A quantum heat engine picture.

    Science.gov (United States)

    Killoran, N; Huelga, S F; Plenio, M B

    2015-10-21

    Recent evidence suggests that quantum effects may have functional importance in biological light-harvesting systems. Along with delocalized electronic excitations, it is now suspected that quantum coherent interactions with certain near-resonant vibrations may contribute to light-harvesting performance. However, the actual quantum advantage offered by such coherent vibrational interactions has not yet been established. We investigate a quantum design principle, whereby coherent exchange of single energy quanta between electronic and vibrational degrees of freedom can enhance a light-harvesting system's power above what is possible by thermal mechanisms alone. We present a prototype quantum heat engine which cleanly illustrates this quantum design principle and quantifies its quantum advantage using thermodynamic measures of performance. We also demonstrate the principle's relevance in parameter regimes connected to natural light-harvesting structures.

  6. Enhancing light-harvesting power with coherent vibrational interactions: A quantum heat engine picture

    Energy Technology Data Exchange (ETDEWEB)

    Killoran, N.; Huelga, S. F.; Plenio, M. B. [Institut für Theoretische Physik, Universität Ulm, Albert-Einstein-Allee 11, D-89069 Ulm (Germany)

    2015-10-21

    Recent evidence suggests that quantum effects may have functional importance in biological light-harvesting systems. Along with delocalized electronic excitations, it is now suspected that quantum coherent interactions with certain near-resonant vibrations may contribute to light-harvesting performance. However, the actual quantum advantage offered by such coherent vibrational interactions has not yet been established. We investigate a quantum design principle, whereby coherent exchange of single energy quanta between electronic and vibrational degrees of freedom can enhance a light-harvesting system’s power above what is possible by thermal mechanisms alone. We present a prototype quantum heat engine which cleanly illustrates this quantum design principle and quantifies its quantum advantage using thermodynamic measures of performance. We also demonstrate the principle’s relevance in parameter regimes connected to natural light-harvesting structures.

  7. Molecular design of the photosystem II light-harvesting antenna: photosynthesis and photoprotection

    National Research Council Canada - National Science Library

    Peter Horton; Alexander Ruban

    The photosystem II (PSII) light-harvesting system carries out two essential functions, the efficient collection of light energy for photosynthesis, and the regulated dissipation of excitation energy in excess of that which can be used...

  8. Tetrastyryl-BODIPY-based dendritic light harvester and estimation of energy transfer efficiency.

    Science.gov (United States)

    Kostereli, Ziya; Ozdemir, Tugba; Buyukcakir, Onur; Akkaya, Engin U

    2012-07-20

    Versatile BODIPY dyes can be transformed into bright near-IR-emitting fluorophores by quadruple styryl substitutions. When clickable functionalities on the styryl moieties are inserted, an efficient synthesis of a light harvester is possible. In addition, clear spectral evidence is presented showing that, in dendritic light harvesters, calculations commonly based on quantum yield or emission lifetime changes of the donor are bound to yield large overestimations of energy transfer efficiency.

  9. The architecture and function of the light-harvesting apparatus of purple bacteria: from single molecules to in vivo membranes.

    Science.gov (United States)

    Cogdell, Richard J; Gall, Andrew; Köhler, Jürgen

    2006-08-01

    This review describes the structures of the two major integral membrane pigment complexes, the RC-LH1 'core' and LH2 complexes, which together make up the light-harvesting system present in typical purple photosynthetic bacteria. The antenna complexes serve to absorb incident solar radiation and to transfer it to the reaction centres, where it is used to 'power' the photosynthetic redox reaction and ultimately leads to the synthesis of ATP. Our current understanding of the biosynthesis and assembly of the LH and RC complexes is described, with special emphasis on the roles of the newly described bacteriophytochromes. Using both the structural information and that obtained from a wide variety of biophysical techniques, the details of each of the different energy-transfer reactions that occur, between the absorption of a photon and the charge separation in the RC, are described. Special emphasis is given to show how the use of single-molecule spectroscopy has provided a more detailed understanding of the molecular mechanisms involved in the energy-transfer processes. We have tried, with the help of an Appendix, to make the details of the quantum mechanics that are required to appreciate these molecular mechanisms, accessible to mathematically illiterate biologists. The elegance of the purple bacterial light-harvesting system lies in the way in which it has cleverly exploited quantum mechanics.

  10. Spectroscopic Studies of Cryptophyte Light Harvesting Proteins: Vibrations and Coherent Oscillations.

    Science.gov (United States)

    Arpin, Paul C; Turner, Daniel B; McClure, Scott D; Jumper, Chanelle C; Mirkovic, Tihana; Challa, J Reddy; Lee, Joohyun; Teng, Chang Ying; Green, Beverley R; Wilk, Krystyna E; Curmi, Paul M G; Hoef-Emden, Kerstin; McCamant, David W; Scholes, Gregory D

    2015-08-06

    The first step of photosynthesis is the absorption of light by antenna complexes. Recent studies of light-harvesting complexes using two-dimensional electronic spectroscopy have revealed interesting coherent oscillations. Some contributions to those coherences are assigned to electronic coherence and therefore have implications for theories of energy transfer. To assign these femtosecond data and to gain insight into the interplay among electronic and vibrational resonances, we need detailed information on vibrations and coherences in the excited electronic state compared to the ground electronic state. Here, we used broad-band transient absorption and femtosecond stimulated Raman spectroscopies to record ground- and excited-state coherences in four related photosynthetic proteins: PC577 from Hemiselmis pacifica CCMP706, PC612 from Hemiselmis virescens CCAC 1635 B, PC630 from Chroomonas CCAC 1627 B (marine), and PC645 from Chroomonas mesostigmatica CCMP269. Two of those proteins (PC630 and PC645) have strong electronic coupling while the other two proteins (PC577 and PC612) have weak electronic coupling between the chromophores. We report vibrational spectra for the ground and excited electronic states of these complexes as well as an analysis of coherent oscillations observed in the broad-band transient absorption data.

  11. Dimeric carotenoid interaction in the light-harvesting antenna of purple phototrophic bacteria.

    Science.gov (United States)

    Zurdo, J; Lozano, R M; Fernandez-Cabrera, C; Ramirez, J M

    1991-03-15

    The carotenoid content of intracytoplasmic membrane vesicles isolated from purple phototrophic bacteria was reduced to a variable extent by mild extraction with light petroleum. Using preparations obtained from Rhodobacter capsulatus strains that contained the Light Harvesting System I (LHI) complex as the only major photosynthetic holochrome, it was shown that the visible circular dichroism of the carotenoids increased with the square of the membrane carotenoid content, as expected from being caused by dimeric exciton interaction. No chirality resulting from twists of the individual planar chromophore was detected. Therefore the contribution to carotenoid optical activity of non-degenerate interactions with bacteriochlorophyll or the apoprotein does not appear to be significant. The broadening of the absorption band of the bound pigment, caused by the splitting of the monomer transition, was demonstrated in membrane vesicles of both Rb, capsulatus and Rhodospirillum rubrum as a decrease of the fine structure of the band. Furthermore, the dimeric organization of the carotenoid pigments in the bacterial LHI complex accounted for the observed quantitative relationship between the fine structure of the band and the carotenoid content of the membrane.

  12. AplA, a member of a new class of phycobiliproteins lacking a traditional role in photosynthetic light harvesting.

    Science.gov (United States)

    Montgomery, Beronda L; Casey, Elena Silva; Grossman, Arthur R; Kehoe, David M

    2004-11-01

    All known phycobiliproteins have light-harvesting roles during photosynthesis and are found in water-soluble phycobilisomes, the light-harvesting complexes of cyanobacteria, cyanelles, and red algae. Phycobiliproteins are chromophore-bearing proteins that exist as heterodimers of alpha and beta subunits, possess a number of highly conserved amino acid residues important for dimerization and chromophore binding, and are invariably 160 to 180 amino acids long. A new and unusual group of proteins that is most closely related to the allophycocyanin members of the phycobiliprotein superfamily has been identified. Each of these proteins, which have been named allophycocyanin-like (Apl) proteins, apparently contains a 28-amino-acid extension at its amino terminus relative to allophycocyanins. Apl family members possess the residues critical for chromophore interactions, but substitutions are present at positions implicated in maintaining the proper alpha-beta subunit interactions and tertiary structure of phycobiliproteins, suggesting that Apl proteins are able to bind chromophores but fail to adopt typical allophycocyanin conformations. AplA isolated from the cyanobacterium Fremyella diplosiphon contained a covalently attached chromophore and, although present in the cell under a number of conditions, was not detected in phycobilisomes. Thus, Apl proteins are a new class of photoreceptors with a different cellular location and structure than any previously described members of the phycobiliprotein superfamily.

  13. Cascade exciton-pumping engines with manipulated speed and efficiency in light-harvesting porous π-network films.

    Science.gov (United States)

    Gu, Cheng; Huang, Ning; Xu, Fei; Gao, Jia; Jiang, Donglin

    2015-03-09

    Light-harvesting antennae are the machinery for exciton pumping in natural photosynthesis, whereas cascade energy transfer through chlorophyll is key to long-distance, efficient energy transduction. Numerous artificial antennae have been developed. However, they are limited in their cascade energy-transfer abilities because of a lack of control over complex chromophore aggregation processes, which has impeded their advancement. Here we report a viable approach for addressing this issue by using a light-harvesting porous polymer film in which a three-dimensional π-network serves as the antenna and micropores segregate multiple dyes to prevent aggregation. Cascade energy-transfer engines are integrated into the films; the rate and efficiency of the energy-funneling engines are precisely manipulated by tailoring the dye components and contents. The nanofilms allow accurate and versatile luminescence engineering, resulting in the production of thirty emission hues, including blue, green, red and white. This advance may open new pathways for realising photosynthesis and photoenergy conversion.

  14. Mixed-organic-cation perovskite photovoltaics for enhanced solar-light harvesting.

    Science.gov (United States)

    Pellet, Norman; Gao, Peng; Gregori, Giuliano; Yang, Tae-Youl; Nazeeruddin, Mohammad K; Maier, Joachim; Grätzel, Michael

    2014-03-17

    Hybrid organic-inorganic lead halide perovskite APbX3 pigments, such as methylammonium lead iodide, have recently emerged as excellent light harvesters in solid-state mesoscopic solar cells. An important target for the further improvement of the performance of perovskite-based photovoltaics is to extend their optical-absorption onset further into the red to enhance solar-light harvesting. Herein, we show that this goal can be reached by using a mixture of formamidinium (HN=CHNH3 (+), FA) and methylammonium (CH3 NH3 (+), MA) cations in the A position of the APbI3 perovskite structure. This combination leads to an enhanced short-circuit current and thus superior devices to those based on only CH3 NH3 (+). This concept has not been applied previously in perovskite-based solar cells. It shows great potential as a versatile tool to tune the structural, electrical, and optoelectronic properties of the light-harvesting materials.

  15. Enhancing light-harvesting power with coherent vibrational interactions: a quantum heat engine picture

    CERN Document Server

    Killoran, Nathan; Plenio, Martin B

    2014-01-01

    Recent evidence suggests that quantum effects may have functional importance in biological light-harvesting systems. Along with delocalized electronic excitations, it is now suspected that quantum coherent interactions with certain near-resonant vibrations contribute to light-harvesting performance. However, the actual quantum advantage offered by such coherent vibrational interactions has not yet been established. We investigate a quantum design principle, whereby coherent exchange of single energy quanta between electronic and vibrational degrees of freedom can enhance a light-harvesting system's power above what is possible by thermal mechanisms alone. We present a prototype quantum heat engine which cleanly illustrates this quantum design principle, and quantify its quantum advantage using thermodynamic measures of performance. We also demonstrate the principle's applicability for realistic biological structures.

  16. Multichromophoric organic molecules encapsulated in polymer nanoparticles for artificial light harvesting.

    Science.gov (United States)

    Bhattacharyya, Santanu; Jana, Bikash; Patra, Amitava

    2015-03-16

    We designed a self-assembled multichromophoric organic molecular arrangement inside polymer nanoparticles for light-harvesting antenna materials. The self-assembled molecular arrangement of quaterthiophene molecules was found to be an efficient light-absorbing antenna material, followed by energy transfer to Nile red (NR) dye molecules, which was confined in polymer nanoparticles. The efficiency of the antenna effect was found to be 3.2 and the effective molar extinction coefficient of acceptor dye molecules was found to be enhanced, which indicates an efficient light-harvesting system. Based on this energy-transfer process, tunable photo emission and white light emission has been generated with 14 % quantum yield. Such self-assembled oligothiophene-NR systems encapsulated in polymer nanoparticles may open up new possibilities for fabrication of artificial light harvesting system.

  17. Limiting Factors in Photosynthesis: IV. Iron Stress-Mediated Changes in Light-Harvesting and Electron Transport Capacity and its Effects on Photosynthesis in Vivo.

    Science.gov (United States)

    Terry, N

    1983-04-01

    Using iron stress to reduce the total amount of light-harvesting and electron transport components per unit leaf area, the influence of light-harvesting and electron transport capacity on photosynthesis in sugar beet (Beta vulgaris L. cv F58-554H1) leaves was explored by monitoring net CO(2) exchange rate (P) in relation to changes in the content of Chl.In most light/CO(2) environments, and especially those with high light (>/=1000 microeinsteins photosynthetically active radiation per square meter per second) and high CO(2) (>/=300 microliters CO(2) per liter air), P per area was positively correlated with changes in Chl (a + b) content (used here as an index of the total amount of light-harvesting and electron transport components). This positive correlation of P per area with Chl per area was obtained not only with Fe-deficient plants, but also over the normal range of variation in Chl contents found in healthy, Fe-sufficient plants. For example, light-saturated P per area at an ambient CO(2) concentration close to normal atmospheric levels (300 microliters CO(2) per liter air) increased by 36% with increase in Chl over the normal range, i.e. from 40 to 65 micrograms Chl per square centimeter. Iron deficiency-mediated changes in Chl content did not affect dark respiration rate or the CO(2) compensation point. The results suggest that P per area of sugar beet may be colimited by light-harvesting and electron transport capacity (per leaf area) even when CO(2) is limiting photosynthesis as occurs under field conditions.

  18. Biohydrogen production with the light-harvesting function of grana from spirulina and colloidal platinum

    Energy Technology Data Exchange (ETDEWEB)

    Amao, Yutaka; Nakamura, Naoki [Department of Applied Chemistry, Oita University Dannoharu 700, Oita 870-1192 (Japan)

    2006-01-15

    Biohydrogen production with the light-harvesting function of grana from spirulina by use of three-component system consisting of NADH, methylviologen (MV{sup 2+}) and colloidal platinum was investigated. The decay rate of chlorophyll included in grana was suppressed by addition of NADH and little degradation was observed in 120min irradiation. The biohydrogen production system was developed using the light-harvesting function of grana and platinum colloid in the presence of NADH and MV{sup 2+} and the amount of hydrogen produced was estimated to be 0.14{mu}mol after 4h irradiation. (author)

  19. Enhanced Light Harvesting in Dye-Sensitized Solar Cell Using External Lightguide

    Directory of Open Access Journals (Sweden)

    Chi-Hui Chien

    2011-01-01

    Full Text Available An external lightguide (EL for enhancing the light-harvesting efficiency of dye-sensitized solar cells (DSSCs was designed and developed. The EL attached to the exterior of a DSSC photoelectrode directed light on a dye-covered nanoporous TiO2 film (D-NTF of the photoelectrode. Experimental tests confirmed that the EL increased the light-harvesting efficiency of a DSSC with an active area of 0.25 cm2 by 30.69%. Photocurrent density and the power conversion efficiency were also increased by 38.12% and 25.09%, respectively.

  20. Powering the future of molecular artificial photosynthesis with light-harvesting metallosupramolecular dye assemblies.

    Science.gov (United States)

    Frischmann, Peter D; Mahata, Kingsuk; Würthner, Frank

    2013-02-21

    Chemical ingenuity will play a significant role in solving the greatest challenge currently facing society: providing clean and carbon neutral energy for all of humanity. Molecular artificial photosynthesis is an emerging technology based on principles learned from Nature where individual components perform the essential light-harvesting, charge-separation, and water splitting functions to store solar energy in the form of chemical bonds. This tutorial review focuses specifically on the application of metallosupramolecular self-assembly strategies to interface solar fuel catalysts with photosensitizers and construct light-harvesting antennae capable of achieving panchromatic absorption and directional energy concentration.

  1. Salt-induced redox-independent phosphorylation of light harvesting chlorophyll a/b proteins in Dunaliella salina thylakoid membranes.

    Science.gov (United States)

    Liu, Xian-De; Shen, Yun-Gang

    2005-02-17

    This study investigated the regulation of the major light harvesting chlorophyll a/b protein (LHCII) phosphorylation in Dunaliella salina thylakoid membranes. We found that both light and NaCl could induce LHCII phosphorylation in D. salina thylakoid membranes. Treatments with oxidants (ferredoxin and NADP) or photosynthetic electron flow inhibitors (DCMU, DBMIB, and stigmatellin) inhibited LHCII phosphorylation induced by light but not that induced by NaCl. Furthermore, neither addition of CuCl(2), an inhibitor of cytochrome b(6)f complex reduction, nor oxidizing treatment with ferricyanide inhibited light- or NaCl-induced LHCII phosphorylation, and both salts even induced LHCII phosphorylation in dark-adapted D. salina thylakoid membranes as other salts did. Together, these results indicate that the redox state of the cytochrome b(6)f complex is likely involved in light- but not salt-induced LHCII phosphorylation in D. salina thylakoid membranes.

  2. Excitation migration in fluctuating light-harvesting antenna systems

    NARCIS (Netherlands)

    Chmeliov, J.; Trinkunas, G.; Amerongen, van H.; Valkunas, L.

    2016-01-01

    Complex multi-exponential fluorescence decay kinetics observed in various photosynthetic systems like photosystem II (PSII) have often been explained by the reversible quenching mechanism of the charge separation taking place in the reaction center (RC) of PSII. However, this description does not ac

  3. Improving light harvesting in polymer photodetector devices through nanoindented metal mask films

    NARCIS (Netherlands)

    Macedo, A. G.; Zanetti, F.; Mikowski, A.; Hummelen, J. C.; Lepienski, C. M.; da Luz, M. G. E.; Roman, L. S.

    2008-01-01

    To enhance light harvesting in organic photovoltaic devices, we propose the incorporation of a metal (aluminum) mask film in the system's usual layout. We fabricate devices in a sandwich geometry, where the mask (nanoindented with a periodic array of holes of sizes d and spacing s) is added between

  4. Quantum coherence controls the charge separation in a prototypical artificial light harvesting system

    Directory of Open Access Journals (Sweden)

    Schramm H.

    2013-03-01

    Full Text Available Ultrafast spectroscopy and quantum-dynamics simulations of an artificial supramolecular light-harvesting system — a supramolecular triad - provide strong evidence that the quantum-correlated wavelike motion of electrons and nuclei on a timescale of few tens of femtoseconds governs the ultrafast electronic charge transfer.

  5. Hidden symmetries enhance quantum transport in Light Harvesting systems

    CERN Document Server

    Zech, Tobias; Wellens, Thomas; Buchleitner, Andreas

    2012-01-01

    For more than 50 years we have known that photosynthetic systems harvest solar energy with almost unit {\\it quantum efficiency}. However, recent experimental evidence of {\\it quantum coherence} during the excitonic energy transport in photosynthetic organisms challenges our understanding of this fundamental biological function. Currently, and despite numerous efforts, the causal connection between coherence and efficiency is still a matter of debate. We show, through the study of extensive simulations of quantum coherent transport on networks, that three dimensional structures characterized by centro-symmetric Hamiltonians are statistically more efficient than random arrangements. Moreover, we demonstrate that the experimental data available for the electronic Hamiltonians of the Fenna-Mathew-Olson (FMO) complex of sulfur bacteria and of the crypophyte PC645 complex of marine algae are consistent with this strong correlation of centro-symmetry with quantum efficiency. These results show that what appears to b...

  6. Efficient light harvesting and energy transfer in a red phosphorescent iridium dendrimer.

    Science.gov (United States)

    Cho, Yang-Jin; Hong, Seong Ahn; Son, Ho-Jin; Han, Won-Sik; Cho, Dae Won; Kang, Sang Ook

    2014-12-15

    A series of red phosphorescent iridium dendrimers of the type [Ir(btp)2(pic-PCn)] (Ir-Gn; n = 0, 1, 2, and 3) with two 2-(benzo[b]thiophen-2-yl)pyridines (btp) and 3-hydroxypicolinate (pic) as the cyclometalating and ancillary ligands were prepared in good yields. Dendritic generation was grown at the 3 position of the pic ligand with 4-(9H-carbazolyl)phenyl dendrons connected to 3,5-bis(methyleneoxy)benzyloxy branches (PCn; n = 0, 2, 4, and 8). The harvesting photons on the PCn dendrons followed by efficient energy transfer to the iridium center resulted in high red emissions at ∼600 nm by metal-to-ligand charge transfer. The intensity of the phosphorescence gradually increased with increasing dendrimer generation. Steady-state and time-resolved spectroscopy were used to investigate the energy-transfer mechanism. On the basis of the fluorescence quenching rate constants of the PCn dendrons, the energy-transfer efficiencies for Ir-G1, Ir-G2, and Ir-G3 were 99, 98, and 96%, respectively. The energy-transfer efficiency for higher-generation dendrimers decreased slightly because of the longer distance between the PC dendrons and the core iridium(III) complex, indicating that energy transfer in Ir-Gn is a Förster-type energy transfer. Finally, the light-harvesting efficiencies for Ir-G1, Ir-G2, and Ir-G3 were determined to be 162, 223, and 334%, respectively.

  7. Comparative study of energy-transfer processes in several porphyrin-based artificial light-harvesting molecules

    Energy Technology Data Exchange (ETDEWEB)

    Hauschild, R. [Institut fuer Angewandte Physik, Universitaet Karlsruhe Wolfgang-Gaede-Str. 1, D-76131 Karlsruhe (Germany)]. E-mail: robert.hauschild@physik.uni-karlsruhe.de; Riedel, G. [Institut fuer Angewandte Physik, Universitaet Karlsruhe Wolfgang-Gaede-Str. 1, D-76131 Karlsruhe (Germany); Zeller, J. [Institut fuer Angewandte Physik, Universitaet Karlsruhe Wolfgang-Gaede-Str. 1, D-76131 Karlsruhe (Germany); Center for Functional Nanostructures, Universitaet Karlsruhe (Germany); Balaban, T.S. [Center for Functional Nanostructures, Universitaet Karlsruhe (Germany); Forschungszentrum Karlsruhe, Institute for Nanotechnology (Germany); Prokhorenko, V.I. [Center for Functional Nanostructures, Universitaet Karlsruhe (Germany); Kalt, H. [Institut fuer Angewandte Physik, Universitaet Karlsruhe Wolfgang-Gaede-Str. 1, D-76131 Karlsruhe (Germany); Center for Functional Nanostructures, Universitaet Karlsruhe (Germany); Berova, N. [Columbia University, Department of Chemistry, New York (United States); Huang, X. [Columbia University, Department of Chemistry, New York (United States); Pescitelli, R. [Columbia University, Department of Chemistry, New York (United States); University of Pisa, Department of Chemistry, Pisa (Italy); Nakanishi, K. [Columbia University, Department of Chemistry, New York (United States)

    2005-04-15

    Time resolved fluorescence spectroscopy was carried out on porphyrin-based artificial light harvesting molecules (ALHM). The ALHMs are dyads consisting of zinc-tetraphenylporphyrin (Zn-TPP) as an antenna complex and a free-base tetraphenylporphyrin (TPP) as an energy trap. Both chromophores are covalently bound by a steroidal bridge in different configurations. We have observed energy transfer in the ALHMs with transfer times on the order of approximately 1 ns. We have also compared the energy transfer dynamics of these ALHMs differing in the link between the energy donor and the energy trap. Only when connected by a chemical bond does energy transfer from Zn-TPP to TPP occur. A spread in the energy transfer times was found which is attributed to the different configurations of the ALHMs under study.

  8. Efficient energy transfer in light-harvesting systems, I: optimal temperature, reorganization energy, and spatial-temporal correlations

    CERN Document Server

    Wu, Jianlan; Shen, Young; Cao, Jianshu; Silbey, Robert J

    2010-01-01

    Understanding the mechanisms of efficient and robust energy transfer in light-harvesting systems provides new insights for the optimal design of artificial systems. In this paper, we use the Fenna-Matthews-Olson (FMO) protein complex and phycocyanin 645 (PC 645) to explore the general dependence on physical parameters that help maximize the efficiency and maintain its stability. With the Haken-Strobl model, the maximal energy transfer efficiency (ETE) is achieved under an intermediate optimal value of dephasing rate. Guided by the insight, we use the generalized Bloch-Redfield (GBR) equation approach to correctly describe dissipative exciton dynamics and find that maximal ETE can be achieved under various physical conditions, including temperature, reorganization energy, and spatial-temporal correlations in noise. We also identify regimes of reorganization energy where the ETE changes monotonically with temperature or spatial correlation and therefore cannot be optimized with respect to these two variables.

  9. Supercomplexes of photosystem I and antenna proteins in cyanobacteria and green plants

    NARCIS (Netherlands)

    Kouril, R.; Zygadlo, A.; Jensen, P. E.; Yeremenko, N.; Matthijs, H.C.P.; D'Haene, S.; Dekker, J.P.; Boekema, E.J.; Matthijs, H.C.P.

    2005-01-01

    Photosystem I (PSI) and Photosystem II (PSII) can form supercomplexes with various types of antenna proteins. One such protein is Light-harvesting complex II (LHCII). In plants it is bound in its trimeric form to dimeric PSII. In spinach and Arabidopsis thaliana most dimers bind 2-4 LHCII trimers. W

  10. Remodeling of the major light-harvesting antenna protein of PSII protects the young leaves of barley (Hordeum vulgare L.) from photoinhibition under prolonged iron deficiency.

    Science.gov (United States)

    Saito, Akihiro; Iino, Tomohisa; Sonoike, Kintake; Miwa, Eitaro; Higuchi, Kyoko

    2010-12-01

    Because of the high demand for iron of the photosynthetic apparatus in thylakoid membranes, iron deficiency primarily affects the electron transfer between the two photosystems (PSI and PSII), resulting in photooxidative damage in plants. However, in barley, PSII is protected against photoinhibition, and the plant survives even with a low iron content in its chlorotic leaves. In this study, we report an adaptation mechanism of the photosynthetic apparatus in barley to iron deficiency, which is concomitant with the remodeling of a PSII antenna system. Transcriptome analysis revealed that long-term iron deficiency induced the expression of two genes of the major light-harvesting Chl a/b-binding protein of PSII (LHCII), namely HvLhcb1.11 and HvLhcb1.12. Chl fluorescence analysis of the wild type and Lhcb1-less chlorina mutants clearly showed that non-photochemical quenching (NPQ) of the wild type was increased by approximately 200% by iron deficiency, whereas NPQ of chlorina mutants did not change significantly under iron deficiency. The mutant showed severe photodamage in young leaves under prolonged iron deficiency, suggesting that the HvLhcb1 protein is essential for both thermal dissipation and photoprotection in iron-deficient barley. Analysis of thylakoid protein complexes revealed that the proportion of the monomeric form of Lhcb1 significantly increased in barley grown under iron-deficient conditions. We hypothesize that alteration of the HvLhcb1 subpopulations modifies the organization of LHCII in the thylakoid membranes, which is a key step for thermal dissipation to compensate for excess excitation energy and thereby protect the photosystems from serious damage in iron-deficient barley leaves.

  11. Vibronic origin of long-lived coherence in an artificial molecular light harvester.

    Science.gov (United States)

    Lim, James; Paleček, David; Caycedo-Soler, Felipe; Lincoln, Craig N; Prior, Javier; von Berlepsch, Hans; Huelga, Susana F; Plenio, Martin B; Zigmantas, Donatas; Hauer, Jürgen

    2015-07-09

    Natural and artificial light-harvesting processes have recently gained new interest. Signatures of long-lasting coherence in spectroscopic signals of biological systems have been repeatedly observed, albeit their origin is a matter of ongoing debate, as it is unclear how the loss of coherence due to interaction with the noisy environments in such systems is averted. Here we report experimental and theoretical verification of coherent exciton-vibrational (vibronic) coupling as the origin of long-lasting coherence in an artificial light harvester, a molecular J-aggregate. In this macroscopically aligned tubular system, polarization-controlled 2D spectroscopy delivers an uncongested and specific optical response as an ideal foundation for an in-depth theoretical description. We derive analytical expressions that show under which general conditions vibronic coupling leads to prolonged excited-state coherence.

  12. Verification of the vibronic origin of long-lived coherence in an artificial molecular light harvester

    CERN Document Server

    Lim, James; Caycedo-Soler, Felipe; Lincoln, Craig N; Prior, Javier; von Berlepsch, Hans; Huelga, Susana F; Plenio, Martin B; Zigmantas, Donatas; Hauer, Jürgen

    2015-01-01

    Is quantum coherence responsible for the surprisingly high efficiency of natural light harvesters? If so, how do such systems avoid the loss of coherence due to interaction with their warm, wet and noisy environments? The answer to these important questions rests in the beneficial interplay between electronic and vibrational degrees of freedom. Here we report experimental and theoretical verification of coherent exciton-vibrational (vibronic) coupling as the origin of long-lasting coherence in an artificial light harvester, a molecular J-aggregate. In this macroscopically aligned tubular system, polarization controlled 2D spectroscopy delivers an uncongested and specific optical response. This clarity of signal provided the opportunity to unambiguously assign the origin of the observed long-lived coherences to vibronic coupling and rule out other explanations based upon correlated fluctuations. The discussed vibronic coupling is functionally relevant, as it describes interaction between vibrations and electro...

  13. Improving photosynthesis of microalgae by changing the ratio of light-harvesting pigments

    Institute of Scientific and Technical Information of China (English)

    WANG Gaohong; CHEN Lanzhou; LI Genbao; LI Dunhai; HU Chunxiang; CHEN Haofeng; LIU Yongding; SONG Lirong

    2005-01-01

    Changing the ratio of light-harvesting pigments was regarded as an efficient way to improve the photosynthesis rate in microalgae, but the underlying mechanism is still unclear. In the present study, a mutant of Anabeana simensis (called SP) was selected from retrieved satellite cultures. Several parameters related with photosynthesis, such as the growth, photosynthesis rate, the content of photosynthetic pigment, low temperature fluorescence spectrum (77K) and electron transport rate, were compared with those of the wild type. It was found that the change in the ratio of light-harvesting pigments in the mutant led to more efficient light energy transfer and usage in mutant than in the wild type. This may be the reason why the mutant had higher photosynthesis and growth rates.

  14. Photoinduced Electronic Energy Transfer: Theoretical and Experimental Issues for Light Harvesting Applications

    Science.gov (United States)

    2013-10-21

    harvesting systems. Summary of key results: 1. Coherence in photosynthetic light harvesting (experiment) The initial step in photosynthesis ...two dihydrobiliverdins (DBV) with a peak absorption of 580 nm, two mesobiliverdins (MBV) with absorption peaks near 610 nm and four...phycocyanobilins (PCB) two with peak absorptions of 630 nm and two with peaks at 645 nm – covalently bound to a protein matrix. The presence of three distinct types

  15. Phycobilisome Mobility and Its Role in the Regulation of Light Harvesting in Red Algae1[W

    Science.gov (United States)

    Kaňa, Radek; Kotabová, Eva; Lukeš, Martin; Papáček, Štěpán; Matonoha, Ctirad; Liu, Lu-Ning; Prášil, Ondřej; Mullineaux, Conrad W.

    2014-01-01

    Red algae represent an evolutionarily important group that gave rise to the whole red clade of photosynthetic organisms. They contain a unique combination of light-harvesting systems represented by a membrane-bound antenna and by phycobilisomes situated on thylakoid membrane surfaces. So far, very little has been revealed about the mobility of their phycobilisomes and the regulation of their light-harvesting system in general. Therefore, we carried out a detailed analysis of phycobilisome dynamics in several red alga strains and compared these results with the presence (or absence) of photoprotective mechanisms. Our data conclusively prove phycobilisome mobility in two model mesophilic red alga strains, Porphyridium cruentum and Rhodella violacea. In contrast, there was almost no phycobilisome mobility in the thermophilic red alga Cyanidium caldarium that was not caused by a decrease in lipid desaturation in this extremophile. Experimental data attributed this immobility to the strong phycobilisome-photosystem interaction that highly restricted phycobilisome movement. Variations in phycobilisome mobility reflect the different ways in which light-harvesting antennae can be regulated in mesophilic and thermophilic red algae. Fluorescence changes attributed in cyanobacteria to state transitions were observed only in mesophilic P. cruentum with mobile phycobilisomes, and they were absent in the extremophilic C. caldarium with immobile phycobilisomes. We suggest that state transitions have an important regulatory function in mesophilic red algae; however, in thermophilic red algae, this process is replaced by nonphotochemical quenching. PMID:24948833

  16. Förster energy transfer theory as reflected in the structures of photosynthetic light-harvesting systems.

    Science.gov (United States)

    Şener, Melih; Strümpfer, Johan; Hsin, Jen; Chandler, Danielle; Scheuring, Simon; Hunter, C Neil; Schulten, Klaus

    2011-02-25

    Förster’s theory of resonant energy transfer underlies a fundamental process in nature, namely the harvesting of sunlight by photosynthetic life forms. The theoretical framework developed by Förster and others describes how electronic excitation migrates in the photosynthetic apparatus of plants, algae, and bacteria from light absorbing pigments to reaction centers where light energy is utilized for the eventual conversion into chemical energy. The demand for highest possible efficiency of light harvesting appears to have shaped the evolution of photosynthetic species from bacteria to plants which, despite a great variation in architecture, display common structural themes founded on the quantum physics of energy transfer as described first by Förster. Herein, Förster’s theory of excitation transfer is summarized, including recent extensions, and the relevance of the theory to photosynthetic systems as evolved in purple bacteria, cyanobacteria, and plants is demonstrated. Förster’s energy transfer formula, as used widely today in many fields of science, is also derived.

  17. A hybrid photocatalytic system comprising ZnS as light harvester and an [Fe(2)S(2)] hydrogenase mimic as hydrogen evolution catalyst.

    Science.gov (United States)

    Wen, Fuyu; Wang, Xiuli; Huang, Lei; Ma, Guijun; Yang, Jinhui; Li, Can

    2012-05-01

    Photo opportunity: A highly efficient and stable hybrid artificial photosynthetic H(2) evolution system is assembled by using a semiconductor (ZnS) as light-harvester and an [Fe(2)S(2)] hydrogenase mimic ([(μ-SPh-4-NH(2) )(2) Fe(2) (CO)(6)]) as catalyst for H(2) evolution. Photocatalytic H(2) production is achieved with more than 2607 turnovers (based on [Fe(2)S(2)]) and an initial turnover frequency of 100 h(-1) through the efficient transfer of photogenerated electrons from ZnS to the [Fe(2)S(2)] complex.

  18. Differential control of xanthophylls and light-induced stress proteins, as opposed to light-harvesting chlorophyll a/b proteins, during photosynthetic acclimation of barley leaves to light irradiance

    Science.gov (United States)

    Montane; Tardy; Kloppstech; Havaux

    1998-09-01

    Barley (Hordeum vulgare L.) plants were grown at different photon flux densities ranging from 100 to 1800 &mgr;mol m-2 s-1 in air and/or in atmospheres with reduced levels of O2 and CO2. Low O2 and CO2 partial pressures allowed plants to grow under high photosystem II (PSII) excitation pressure, estimated in vivo by chlorophyll fluorescence measurements, at moderate photon flux densities. The xanthophyll-cycle pigments, the early light-inducible proteins, and their mRNA accumulated with increasing PSII excitation pressure irrespective of the way high excitation pressure was obtained (high-light irradiance or decreased CO2 and O2 availability). These findings indicate that the reduction state of electron transport chain components could be involved in light sensing for the regulation of nuclear-encoded chloroplast gene expression. In contrast, no correlation was found between the reduction state of PSII and various indicators of the PSII light-harvesting system, such as the chlorophyll a-to-b ratio, the abundance of the major pigment-protein complex of PSII (LHCII), the mRNA level of LHCII, the light-saturation curve of O2 evolution, and the induced chlorophyll-fluorescence rise. We conclude that the chlorophyll antenna size of PSII is not governed by the redox state of PSII in higher plants and, consequently, regulation of early light-inducible protein synthesis is different from that of LHCII.

  19. Hierarchical Self-Assembly of a Biomimetic Light-Harvesting Antenna Based on DNA G-Quadruplexes

    NARCIS (Netherlands)

    Oltra, Nuria Sancho; Browne, Wesley R.; Roelfes, Gerard

    2013-01-01

    A new modular approach to an artificial light-harvesting antenna system is presented. The approach involves the hierarchical self-assembly of porphyrin acceptor molecules to G-quadruplexes tethered to coumarin donor moieties.

  20. Efficiency Enhancement of InGaN-Based Solar Cells via Stacking Layers of Light-Harvesting Nanospheres

    OpenAIRE

    Amal M. Al-Amri; Po-Han Fu; Kun-Yu Lai; Hsin-Ping Wang; Lain-Jong Li; Jr-Hau He

    2016-01-01

    An effective light-harvesting scheme for InGaN-based multiple quantum well solar cells is demonstrated using stacking layers of polystyrene nanospheres. Light-harvesting efficiencies on the solar cells covered with varied stacks of nanospheres are evaluated through numerical and experimental methods. The numerical simulation reveals that nanospheres with 3 stacking layers exhibit the most improved optical absorption and haze ratio as compared to those obtained by monolayer nanospheres. The ex...

  1. Molecular cloning and characterization of the light-harvesting chlorophyll a/b gene from the pigeon pea (Cajanus cajan).

    Science.gov (United States)

    Qiao, Guang; Wen, Xiao-Peng; Zhang, Ting

    2015-12-01

    Light-harvesting chlorophyll a/b-binding proteins (LHCB) have been implicated in the stress response. In this study, a gene encoding LHCB in the pigeon pea was cloned and characterized. Based on the sequence of a previously obtained 327 bp Est, a full-length 793 bp cDNA was cloned using the rapid amplification of cDNA ends (RACE) method. It was designated CcLHCB1 and encoded a 262 amino acid protein. The calculated molecular weight of the CcLHCB1 protein was 27.89 kDa, and the theoretical isoelectric point was 5.29. Homology search and sequence multi-alignment demonstrated that the CcLHCB1 protein sequence shared a high identity with LHCB from other plants. Bioinformatics analysis revealed that CcLHCB1 was a hydrophobic protein with three transmembrane domains. By fluorescent quantitative real-time polymerase chain reaction (PCR), CcLHCB1 mRNA transcripts were detectable in different tissues (leaf, stem, and root), with the highest level found in the leaf. The expression of CcLHCB1 mRNA in the leaves was up-regulated by drought stimulation and AM inoculation. Our results provide the basis for a better understanding of the molecular organization of LCHB and might be useful for understanding the interaction between plants and microbes in the future.

  2. Primary light-harvesting system: phycobilisomes and associated membranes. Progress report, January 1, 1981-December 31, 1981

    Energy Technology Data Exchange (ETDEWEB)

    Gantt, E.

    1981-01-01

    Phycobilisomes, serving as primary light harvesting complexes in cyanobacteria and red algae, were investigated. Structurally the phycobilisomes of both groups have the same fundamental phycobiliprotein arrangement. Allophycocyanin is in the center near the thylakoid. Stacked rods composed of phycocyanin, or phycocyanin-phycoerythrin radiate peripherally from the allophycocyanin core. Phycobilisomes of Nostoc sp. and Fremyella diplosiphon, after separation into separate allophycocyanin and phycoerythrin-phycocyanin fractions have been associated in vitro. Hybrid phycobilisomes, derived from mixtures of phycobiliprotein from these species were also obtained. The interaction is specific since reassociation was not obtained with phycobiliprotein complexes of some other algae. Phycobilisomes, whether native, or associated in vitro, were similar in their sedimentation, absorption, fluorescence excitation, fluorescence emission, and by electron microscopy. Furthermore, many of the colorless polypeptides were also highly similar between Nostoc and Fremyella. The similarity formed may reflect an evolutionary relationship between the two species. The polypeptide composition of Porphyridium cruentum phycobilisomes is the most complex of any thus far examined. The phycobiliprotein containing polypeptides comprised 84% of the total stainable protein, while the remaining were colorless. Most of the colorless polypeptides occurred in a pelletable fraction, which was enriched in allophycocyanin and phycocyanin, it is probable that some are involved in the linking of these phycobiliproteins.

  3. Spectroscopic study of the light-harvesting protein C-phycocyanin associated with colorless linker peptides

    Energy Technology Data Exchange (ETDEWEB)

    Pizarro, Shelly A.

    2000-05-12

    The phycobilisome (PBS) light-harvesting antenna is composed of chromophore-containing biliproteins and 'colorless' linker peptides and is structurally designed to support unidirectional transfer of excitation energy from the periphery of the PBS to its core. The linker peptides have a unique role in this transfer process by modulating the spectral properties of the associated biliprotein. There is only one three-dimensional structure of a biliprotein/linker complex available to date (APC/LC7.8) and the mechanism of interaction between these two proteins remains unknown. This study brings together a detailed spectroscopic characterization of C-Phycocyanin (PC)-linker complexes (isolated from Synechococcus sp. PCC 7002) with proteomic analysis of the linker amino acid sequences to produce a model for biliprotein/linker interaction. The amino acid sequences of the rod linkers [LR8.9, LR32.3 and LRC28.5] were examined to identify evolutionarily conserved regions important to either the structure or function of this protein family. Although there is not one common homologous site among all the linkers, there are strong trends across each separate subset (LC, LR and LRC) and the N-terminal segments of both LR32.3 and LRC28.5 display multiple regions of similarity with other linkers. Predictions of the secondary structure of LR32.3 and LRC28.5, and comparison to the crystal structure of LC7.8, further narrowed the candidates for interaction sites with the PC chromophores. Measurements of the absorption, fluorescence, CD and excitation anisotropy of PC trimer, PC/LR32.3, and PC/LRC28.5, document the spectroscopic effect of each linker peptide on the PC chromophores at a series of temperatures (298 to 77 K). Because LR32.3 and LRC28.5 modulate the PC trimer spectral properties in distinct manners, it suggests different chromophore-interaction mechanisms for each linker. The low temperature absorbance spectrum of the PC trimer is consistent with an excitonic

  4. Spectroscopic study of the light-harvesting protein C-phycocyanin associated with colorless linker peptides

    Energy Technology Data Exchange (ETDEWEB)

    Pizarro, Shelly Ann [Univ. of California, Berkeley, CA (United States)

    2000-05-01

    The phycobilisome (PBS) light-harvesting antenna is composed of chromophore-containing biliproteins and 'colorless' linker peptides and is structurally designed to support unidirectional transfer of excitation energy from the periphery of the PBS to its core. The linker peptides have a unique role in this transfer process by modulating the spectral properties of the associated biliprotein. There is only one three-dimensional structure of a biliprotein/linker complex available to date (APC/LC7.8) and the mechanism of interaction between these two proteins remains unknown. This study brings together a detailed spectroscopic characterization of C-Phycocyanin (PC)-linker complexes (isolated from Synechococcus sp. PCC 7002) with proteomic analysis of the linker amino acid sequences to produce a model for biliprotein/linker interaction. The amino acid sequences of the rod linkers [LR8.9, LR32.3 and LRC28.5] were examined to identify evolutionarily conserved regions important to either the structure or function of this protein family. Although there is not one common homologous site among all the linkers, there are strong trends across each separate subset (LC, LR and LRC) and the N-terminal segments of both LR32.3 and LRC28.5 display multiple regions of similarity with other linkers. Predictions of the secondary structure of LR32.3 and LRC28.5, and comparison to the crystal structure of LC7.8, further narrowed the candidates for interaction sites with the PC chromophores. Measurements of the absorption, fluorescence, CD and excitation anisotropy of PC trimer, PC/LR32.3, and PC/LRC28.5, document the spectroscopic effect of each linker peptide on the PC chromophores at a series of temperatures (298 to 77 K

  5. Facile Synthesis of Colloidal CuO Nanocrystals for Light-Harvesting Applications

    Directory of Open Access Journals (Sweden)

    Yee-Fun Lim

    2012-01-01

    Full Text Available CuO is an earth-abundant, nontoxic, and low band-gap material; hence it is an attractive candidate for application in solar cells. In this paper, a synthesis of CuO nanocrystals by a facile alcohothermal route is reported. The nanocrystals are dispersible in a solvent mixture of methanol and chloroform, thus enabling the processing of CuO by solution. A bilayer solar cell comprising of CuO nanocrystals and phenyl-C61-butyric acid methyl ester (PCBM achieved a power conversion efficiency of 0.04%, indicating the potential of this material for light-harvesting applications.

  6. Pixelated speckle image holography carrier fringes for efficient superimposed light harvesting in organic solar cells

    Science.gov (United States)

    Zhou, Lei; Li, Yan-Qing; Chen, Jing-De; Ou, Qing-Dong; Tang, Jian-Xin; Zhou, Yun; Lin, Yi; Wei, Huai-Xin

    2017-06-01

    An inverted organic solar cell (OSC) device structure by incorporating pixelated speckle image holography carrier fringes (SIHFs) for efficient superimposed light harvesting is demonstrated. The proposed SIHF based OSCs yield an 18.2% increase in power conversion efficiency (PCE) compared to that of the flat control devices. Moreover, compared to the common two-dimensional (2D) periodic grating patterned OSCs, SIHF based devices achieve 7.8% higher short-circuit current (JSC) and 10.0% higher PCE. This observable improvement in PCE of SIHF based OSCs is mainly ascribed to the geometric effect due to the unique chaotic carrier fringes of SIHFs.

  7. Facile Synthesis of Colloidal CuO Nanocrystals for Light-Harvesting Applications

    KAUST Repository

    Lim, Yee-Fun

    2012-01-01

    CuO is an earth-abundant, nontoxic, and low band-gap material; hence it is an attractive candidate for application in solar cells. In this paper, a synthesis of CuO nanocrystals by a facile alcohothermal route is reported. The nanocrystals are dispersible in a solvent mixture of methanol and chloroform, thus enabling the processing of CuO by solution. A bilayer solar cell comprising of CuO nanocrystals and phenyl-C61-butyric acid methyl ester (PCBM) achieved a power conversion efficiency of 0.04%, indicating the potential of this material for light-harvesting applications.

  8. Photovoltaic nanopillar radial junction diode architecture enhanced by integrating semiconductor quantum dot nanocrystals as light harvesters

    Science.gov (United States)

    Güzeltürk, Burak; Mutlugün, Evren; Wang, Xiaodong; Pey, Kin Leong; Demir, Hilmi Volkan

    2010-08-01

    We propose and demonstrate colloidal quantum dot hybridized, radial p-n junction based, nanopillar solar cells with photovoltaic performance enhanced by intimately integrating nanocrystals to serve as light harvesting agents around the light trapping pillars. By furnishing Si based nanopillar photovoltaic diodes with CdSe quantum dots, we experimentally showed up to sixfold enhancement in UV responsivity and ˜13% enhancement in overall solar conversion efficiency. The maximum responsivity enhancement achieved by incorporation of nanocrystals in the nanopillar architecture is found to be spectrally more than four times larger than the responsivity enhancement obtained using planar architecture of the same device.

  9. Long-distance electronic energy transfer in light-harvesting supramolecular polymers.

    Science.gov (United States)

    Winiger, Christian B; Li, Shaoguang; Kumar, Ganesh R; Langenegger, Simon M; Häner, Robert

    2014-12-01

    The efficient collection of solar energy relies on the design and construction of well-organized light-harvesting systems. Herein we report that supramolecular phenanthrene polymers doped with pyrene are effective collectors of light energy. The linear polymers are formed through the assembly of short amphiphilic oligomers in water. Absorption of light by phenanthrene residues is followed by electronic energy transfer along the polymer over long distances (>100 nm) to the accepting pyrene molecules. The high efficiency of the energy transfer, which is documented by large fluorescence quantum yields, suggests a quantum coherent process.

  10. Recent trends in mesoscopic solar cells based on molecular and nanopigment light harvesters

    Directory of Open Access Journals (Sweden)

    Carole Grätzel

    2013-01-01

    Full Text Available Mesoscopic solar cells are one of the most promising photovoltaic technologies among third generation photovoltaics due to their low cost and high efficiency. The morphology of wide-band semiconductors, sensitized with molecular or nanosized light harvesters, used as electron collectors contribute substantially to the device performance. Recent developments in the use of organic–inorganic layer structured perovskites as light absorbers and as electron or hole transport materials allows reduction in the thickness of photoanodes to the submicron level and have raised the power conversion efficiency of solid state mesoscopic solar cells above the 10% level.

  11. Efficient Light Harvester Layer Prepared by Solid/Mist Interface Reaction for Perovskite Solar Cells.

    Science.gov (United States)

    Xia, Xiang; Li, Hongcui; Wu, Wenyi; Li, Yanhua; Fei, Dehou; Gao, Chunxiao; Liu, Xizhe

    2015-08-12

    A solid/mist reaction method is developed to produce well-crystallized light harvester layers without pinhole defects for perovskite solar cells. The reaction based on mist precursor can be facilely operated with low process temperature. And it can effectively control the volume of CH3NH3I solution and the reaction temperature, which affect the quality of perovskite harvester layers and the performance of perovskite solar cells remarkably. Under optimized condition, the efficiencies of devices reach 16.2% with the average efficiency of 14.9%. The solid/mist reaction is also used to fabricate planar junction solar cells and a PCE of 14.9% is obtained.

  12. Recent trends in mesoscopic solar cells based on molecular and nanopigment light harvesters

    KAUST Repository

    Grätzel, Carole

    2013-01-01

    Mesoscopic solar cells are one of the most promising photovoltaic technologies among third generation photovoltaics due to their low cost and high efficiency. The morphology of wide-band semiconductors, sensitized with molecular or nanosized light harvesters, used as electron collectors contribute substantially to the device performance. Recent developments in the use of organic-inorganic layer structured perovskites as light absorbers and as electron or hole transport materials allows reduction in the thickness of photoanodes to the submicron level and have raised the power conversion efficiency of solid state mesoscopic solar cells above the 10% level.

  13. Ruthenium based metallopolymer grafted reduced graphene oxide as a new hybrid solar light harvester in polymer solar cells

    Science.gov (United States)

    Vinoth, R.; Babu, S. Ganesh; Bharti, Vishal; Gupta, V.; Navaneethan, M.; Bhat, S. Venkataprasad; Muthamizhchelvan, C.; Ramamurthy, Praveen C.; Sharma, Chhavi; Aswal, Dinesh K.; Hayakawa, Yasuhiro; Neppolian, B.

    2017-01-01

    A new class of pyridyl benzimdazole based Ru complex decorated polyaniline assembly (PANI-Ru) was covalently grafted onto reduced graphene oxide sheets (rGO) via covalent functionalization approach. The covalent attachment of PANI-Ru with rGO was confirmed from XPS analysis and Raman spectroscopy. The chemical bonding between PANI-Ru and rGO induced the electron transfer from Ru complex to rGO via backbone of the conjugated PANI chain. The resultant hybrid metallopolymer assembly was successfully demonstrated as an electron donor in bulk heterojunction polymer solar cells (PSCs). A PSC device fabricated with rGO/PANI-Ru showed an utmost ~6 fold and 2 fold enhancement in open circuit potential (Voc) and short circuit current density (Jsc) with respect to the standard device made with PANI-Ru (i.e., without rGO) under the illumination of AM 1.5 G. The excellent electronic properties of rGO significantly improved the electron injection from PANI-Ru to PCBM and in turn the overall performance of the PSC device was enhanced. The ultrafast excited state charge separation and electron transfer role of rGO sheet in hybrid metallopolymer was confirmed from ultrafast spectroscopy measurements. This covalent modification of rGO with metallopolymer assembly may open a new strategy for the development of new hybrid nanomaterials for light harvesting applications. PMID:28225039

  14. Lutein epoxide cycle, light harvesting and photoprotection in species of the tropical tree genus Inga.

    Science.gov (United States)

    Matsubara, Shizue; Krause, G Heinrich; Seltmann, Martin; Virgo, Aurelio; Kursar, Thomas A; Jahns, Peter; Winter, Klaus

    2008-04-01

    Dynamics and possible function of the lutein epoxide (Lx) cycle, that is, the reversible conversion of Lx to lutein (L) in the light-harvesting antennae, were investigated in leaves of tropical tree species. Photosynthetic pigments were quantified in nine Inga species and species from three other genera. In Inga, Lx levels were high in shade leaves (mostly above 20 mmol mol(-1) chlorophyll) and low in sun leaves. In Virola surinamensis, both sun and shade leaves exhibited very high Lx contents (about 60 mmol mol(-1) chlorophyll). In Inga marginata grown under high irradiance, Lx slowly accumulated within several days upon transfer to deep shade. When shade leaves of I. marginata were briefly exposed to the sunlight, both violaxanthin and Lx were quickly de-epoxidized. Subsequently, overnight recovery occurred only for violaxanthin, not for Lx. In such leaves, containing reduced levels of Lx and increased levels of L, chlorophyll fluorescence induction showed significantly slower reduction of the photosystem II electron acceptor, Q(A), and faster formation as well as a higher level of non-photochemical quenching. The results indicate that slow Lx accumulation in Inga leaves may improve light harvesting under limiting light, while quick de-epoxidation of Lx to L in response to excess light may enhance photoprotection.

  15. Light-harvesting cross-linked polymers for efficient heterogeneous photocatalysis.

    Science.gov (United States)

    Wang, Cheng; Xie, Zhigang; deKrafft, Kathryn E; Lin, Wenbin

    2012-04-01

    Nonporous, phosphorescent cross-linked polymers (Ru-CP and Ir-CP) were synthesized via Pd-catalyzed Sonogashira cross-coupling reactions between tetra(p-ethynylphenyl)methane and dibrominated Ru(bpy)(3)(2+) or Ir(ppy)(2)(bpy)(+), respectively. The resultant particulate cross-linked polymer (CP) materials have very high catalyst loadings (76.3 wt % for Ru-CP and 71.6 wt % for Ir-CP), and are nonporous with negligibly small surface areas (2.9 m(2)/g for Ru-CP and 2.7 m(2)/g for Ir-CP). Despite their nonporous nature, the insoluble CP materials serve as highly active and recyclable heterogeneous photocatalysts for a range of organic transformations such as aza-Henry reaction, aerobic amine coupling, and dehalogenation of benzyl bromoacetate. An efficient light-harvesting mechanism, which involves collection of photons by exciting the (3)MLCT states of the phosphors and migration of the excited states to the particle surface, is proposed to account for the very high catalytic activities of these nonporous CPs. Steady-state and time-resolved emission data, as well as the reduced catalytic activity of Os(bpy)(3)(2+)-doped Ru-CPs supports efficient excited state migration for the CP frameworks. This work uncovers a new strategy in designing highly efficient photocatalysts based on light-harvesting cross-linked polymers.

  16. Exploiting Collective Effects to Direct Light Absorption in Natural and Artificial Light-Harvesters

    Science.gov (United States)

    Schroeder, Christopher

    Photosynthesis---the conversion of sunlight to chemical energy---is fundamental for supporting life on our planet. Despite its importance, the physical principles that underpin the primary steps of photosynthesis, from photon absorption to electronic charge separation, remain to be understood in full. Electronic coherence within tightly-packed light-harvesting (LH) units or within individual reaction centers (RCs) has been recognized as an important ingredient for a complete understanding of the excitation energy transfer (EET) dynamics. However, the electronic coherence across units---RC and LH or LH and LH---has been consistently neglected as it does not play a significant role during these relatively slow transfer processes. Here, we turn our attention to the absorption process, which, as we will show, has a much shorter built-in timescale. We demonstrate that the---often overlooked---spatially extended but short-lived excitonic delocalization plays a relevant role in general photosynthetic systems. Most strikingly, we find that absorption intensity is, quite generally, redistributed from LH units to the RC, increasing the number of excitations which can effect charge separation without further transfer steps. A biomemetic nano-system is proposed which is predicted to funnel excitation to the RC-analogue, and hence is the first step towards exploiting these new design principles for efficient artificial light-harvesting.

  17. Cyanobacterial flv4-2 Operon-Encoded Proteins Optimize Light Harvesting and Charge Separation in Photosystem II.

    Science.gov (United States)

    Chukhutsina, Volha; Bersanini, Luca; Aro, Eva-Mari; van Amerongen, Herbert

    2015-05-01

    Photosystem II (PSII) complexes drive the water-splitting reaction necessary to transform sunlight into chemical energy. However, too much light can damage and disrupt PSII. In cyanobacteria, the flv4-2 operon encodes three proteins (Flv2, Flv4, and Sll0218), which safeguard PSII activity under air-level CO2 and in high light conditions. However, the exact mechanism of action of these proteins has not been clarified yet. We demonstrate that the PSII electron transfer properties are influenced by the flv4-2 operon-encoded proteins. Accelerated secondary charge separation kinetics was observed upon expression/overexpression of the flv4-2 operon. This is likely induced by docking of the Flv2/Flv4 heterodimer in the vicinity of the QB pocket of PSII, which, in turn, increases the QB redox potential and consequently stabilizes forward electron transfer. The alternative electron transfer route constituted by Flv2/Flv4 sequesters electrons from QB(-) guaranteeing the dissipation of excess excitation energy in PSII under stressful conditions. In addition, we demonstrate that in the absence of the flv4-2 operon-encoded proteins, about 20% of the phycobilisome antenna becomes detached from the reaction centers, thus decreasing light harvesting. Phycobilisome detachment is a consequence of a decreased relative content of PSII dimers, a feature observed in the absence of the Sll0218 protein.

  18. Adaptation of light-harvesting systems of Arthrospira platensis to light conditions, probed by time-resolved fluorescence spectroscopy.

    Science.gov (United States)

    Akimoto, Seiji; Yokono, Makio; Hamada, Fumiya; Teshigahara, Ayaka; Aikawa, Shimpei; Kondo, Akihiko

    2012-08-01

    Cyanobacteria change the quantity and/or quality of their pigment-protein complexes in response to light conditions. In the present study, we analyzed excitation relaxation dynamics in the cyanobacterium, Arthrospira (Spirulina) platensis, grown under lights exhibiting different spectral profiles, by means of steady-state absorption and picosecond time-resolved fluorescence spectroscopies. It was found that F760, which is the PSI red-chlorophyll characteristic of A. platensis, contributes to slower energy-transfer phase in the PSI of A. platensis. Excitation energy transfers in phycobilisome and those from PSII to PSI were modified depending on the light quality. Existence of quencher was suggested in PSI of the blue-light grown cells. Phycobilisomes in the green-light grown cells and the far-red-light grown cells transferred excitation energy from phycobilisome to chlorophyll without loss of energy. In these cells, excitation energy was shared between two photosystems. Fast energy transfer was established in phycobilisome under the yellow-light condition where only the phycobilisome can absorb the cultivation light. Differences in light-harvesting and energy-transfer processes under different cultivation-light conditions are discussed. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.

  19. The trade-off between the light-harvesting and photoprotective functions of fucoxanthin-chlorophyll proteins dominates light acclimation in Emiliania huxleyi (clone CCMP 1516).

    Science.gov (United States)

    McKew, Boyd A; Davey, Phillip; Finch, Stewart J; Hopkins, Jason; Lefebvre, Stephane C; Metodiev, Metodi V; Oxborough, Kevin; Raines, Christine A; Lawson, Tracy; Geider, Richard J

    2013-10-01

    Mechanistic understanding of the costs and benefits of photoacclimation requires knowledge of how photophysiology is affected by changes in the molecular structure of the chloroplast. We tested the hypothesis that changes in the light dependencies of photosynthesis, nonphotochemical quenching and PSII photoinactivation arises from changes in the abundances of chloroplast proteins in Emiliania huxleyi strain CCMP 1516 grown at 30 (Low Light; LL) and 1000 (High Light; HL) μmol photons m(-2) s(-1) photon flux densities. Carbon-specific light-saturated gross photosynthesis rates were not significantly different between cells acclimated to LL and HL. Acclimation to LL benefited cells by increasing biomass-specific light absorption and gross photosynthesis rates under low light, whereas acclimation to HL benefited cells by reducing the rate of photoinactivation of PSII under high light. Differences in the relative abundances of proteins assigned to light-harvesting (Lhcf), photoprotection (LI818-like), and the photosystem II (PSII) core complex accompanied differences in photophysiology: specifically, Lhcf:PSII was greater under LL, whereas LI818:PSII was greater in HL. Thus, photoacclimation in E. huxleyi involved a trade-off amongst the characteristics of light absorption and photoprotection, which could be attributed to changes in the abundance and composition of proteins in the light-harvesting antenna of PSII.

  20. Surface modifications of photoanodes in dye sensitized solar cells: enhanced light harvesting and reduced recombination

    Science.gov (United States)

    Saxena, Vibha; Aswal, D. K.

    2015-06-01

    In a quest to harvest solar power, dye-sensitized solar cells (DSSCs) have potential for low-cost eco-friendly photovoltaic devices. The major processes which govern the efficiency of a DSSC are photoelectron generation, injection of photo-generated electrons to the conduction band (CB) of the mesoporous nanocrystalline semiconductor (nc-SC); transport of CB electrons through nc-SC and subsequent collection of CB electrons at the counter electrode (CE) through the external circuit; and dye regeneration by redox couple or hole transport layer (HTL). Most of these processes occur at various interfaces of the photoanode. In addition, recombination losses of photo-generated electrons with either dye or redox molecules take place at the interfaces. Therefore, one of the key requirements for high efficiency is to improve light harvesting of the photoanode and to reduce the recombination losses at various interfaces. In this direction, surface modification of the photoanode is the simplest method among the various other approaches available in the literature. In this review, we present a comprehensive discussion on surface modification of the photoanode, which has been adopted in the literature for not only enhancing light harvesting but also reducing recombination. Various approaches towards surface modification of the photoanode discussed are (i) fluorine-doped tin oxide (FTO)/nc-SC interface modified via a compact layer of semiconductor material which blocks exposed sites of FTO to electrolyte (or HTL), (ii) nc-SC/dye interface modification either through acid treatment resulting in enhanced dye loading due to a positively charged surface or by depositing insulating/semiconducting blocking layer on the nc-SC surface, which acts as a tunneling barrier for recombination, (iii) nc-SC/dye interface modified by employing co-adsorbents which helps in reducing the dye aggregation and thereby recombination, and (iv) dye/electrolyte (or dye/HTL) interface modification using

  1. Multi-step excitation energy transfer engineered in genetic fusions of natural and synthetic light-harvesting proteins.

    Science.gov (United States)

    Mancini, Joshua A; Kodali, Goutham; Jiang, Jianbing; Reddy, Kanumuri Ramesh; Lindsey, Jonathan S; Bryant, Donald A; Dutton, P Leslie; Moser, Christopher C

    2017-02-01

    Synthetic proteins designed and constructed from first principles with minimal reference to the sequence of any natural protein have proven robust and extraordinarily adaptable for engineering a range of functions. Here for the first time we describe the expression and genetic fusion of a natural photosynthetic light-harvesting subunit with a synthetic protein designed for light energy capture and multi-step transfer. We demonstrate excitation energy transfer from the bilin of the CpcA subunit (phycocyanin α subunit) of the cyanobacterial photosynthetic light-harvesting phycobilisome to synthetic four-helix-bundle proteins accommodating sites that specifically bind a variety of selected photoactive tetrapyrroles positioned to enhance energy transfer by relay. The examination of combinations of different bilin, chlorin and bacteriochlorin cofactors has led to identification of the preconditions for directing energy from the bilin light-harvesting antenna into synthetic protein-cofactor constructs that can be customized for light-activated chemistry in the cell.

  2. Evolution of the land plant Exocyst complexes

    Directory of Open Access Journals (Sweden)

    Fatima eCvrckova

    2012-07-01

    Full Text Available Exocyst is an evolutionarily conserved vesicle tethering complex functioning especially in the last stage of exocytosis. Homologs of its eight canonical subunits -Sec3, Sec5, Sec6, Sec8, Sec10, Sec15, Exo70 and Exo84 - were found also in higher plants and confirmed to form complexes in vivo, and to participate in cell growth including polarized expansion of pollen tubes and root hairs. Here we present results of a phylogenetic study of land plant exocyst subunits encoded by a selection of completely sequenced genomes representing a variety of plant, mostly angiosperm, lineages. According to their evolution histories, plant exocyst subunits can be divided into several groups. The core subunits Sec6, Sec8 and Sec10, together with Sec3 and Sec5, underwent few, if any fixed duplications in the tracheophytes (though they did amplify in the moss Physcomitrella patens, while others form larger families, with the number of paralogs ranging typically from two to eight per genome (Sec15, Exo84 to several dozens per genome (Exo70. Most of the diversity, which can be in some cases traced down to the origins of land plants, can be attributed to the peripheral subunits Exo84 and, in particular, Exo70. As predicted previously, early land plants (including possibly also the Rhyniophytes encoded three basal Exo70 paralogs which further diversified in the course of land plant evolution. Our results imply that plants do not have a single "Exocyst complex" – instead, they appear to possess a diversity of exocyst variants unparalleled among other organisms studied so far. This feature might perhaps be directly related to the demands of building and maintenance of the complicated and spatially diverse structures of the endomembranes and cell surfaces in multicellular land plants.

  3. Third order nonlinear optical properties of bacteriochlorophylls in bacterial photosynthetic light-harvesting proteins

    Science.gov (United States)

    Chen, Lin X.; Laible, Philip D.

    1997-05-01

    The third order hyperpolarizability, , of the ground state S 0 of bacteriochlorophyll a (BChl a) has been determined using degenerate four wave mixing. The for BChl a in vivo (the B875 and B850 arrays of light harvesting proteins) is enhanced relative to that in vitro (THF). A significantly higher in B875 than that in B850 suggests stronger pigment interactions in the former resulting from superior overlap of adjacent macrocycles. In addition, a 50-160 fold increase in for the S 1 excited state of relative to S 0 of BChl a in vivo provides an alternative methods for probing excited state dynamics and a potential application for molecular switching.

  4. Light-Harvesting Nanoparticle Core-Shell Clusters with Controllable Optical Output.

    Science.gov (United States)

    Sun, Dazhi; Tian, Ye; Zhang, Yugang; Xu, Zhihua; Sfeir, Matthew Y; Cotlet, Mircea; Gang, Oleg

    2015-06-23

    We used DNA self-assembly methods to fabricate a series of core-shell gold nanoparticle-DNA-colloidal quantum dot (AuNP-DNA-Qdot) nanoclusters with satellite-like architecture to modulate optical (photoluminescence) response. By varying the intercomponent distance through the DNA linker length designs, we demonstrate precise tuning of the plasmon-exciton interaction and the optical behavior of the nanoclusters from regimes characterized by photoluminescence quenching to photoluminescence enhancement. The combination of detailed X-ray scattering probing with photoluminescence intensity and lifetime studies revealed the relation between the cluster structure and its optical output. Compared to conventional light-harvesting systems like conjugated polymers and multichromophoric dendrimers, the proposed nanoclusters bring enhanced flexibility in controlling the optical behavior toward a desired application, and they can be regarded as controllable optical switches via the optically pumped color.

  5. Design principles and fundamental trade-offs in biomimetic light harvesting

    CERN Document Server

    Sarovar, Mohan

    2012-01-01

    Recent developments in synthetic and supramolecular chemistry have created opportunities to design organic systems with tailored nanoscale structure for various technological applications. A key application area is the capture of light energy and its conversion into electrochemical or chemical forms for photovoltaic or sensing applications. In this work we consider cylindrical assemblies of chromophores that model structures produced by several supramolecular techniques. Our study is especially guided by the versatile structures produced by virus-templated assembly. We use a multi-objective optimization framework to determine design principles and limitations in light harvesting performance for such assemblies, both in the presence and absence of disorder. We identify a fundamental trade-off in cylindrical assemblies that is encountered when attempting to maximize both efficiency of energy transfer and absorption bandwidth. We also rationalize the optimal design strategies and provide explanations for why var...

  6. Periodically arranged colloidal gold nanoparticles for enhanced light harvesting in organic solar cells

    DEFF Research Database (Denmark)

    Mirsafaei, Mina; Fernandes Cauduro, André Luis; Kunstmann-Olsen, Casper

    of thinner devices without compromising light absorption. In this work, we theoretically and experimentally investigate periodically arranged colloidal gold nanoparticles in organic solar cells, and demonstrate the use of such nanostructures to improve the light absorption in and thus the efficiency...... nanostructures as well as the period of the periodical arrangements in organic bulk hetero-junction solar cells. In addition, we investigate experimentally the light absorption enhancement in the organic active layer by incorporating surface-ordered gold nanoparticle arrangements at the bottom of the organic...... active layer. The latter are fabricated with a lithography-free stamp technique, creating a centimeter scaled area with defined inter-particle spacing. Our study presents the light harvesting ability of template-assisted nanoparticle assemblies in organic solar cells and as the approach is easily...

  7. Enhancement of coherent energy transfer by disorder and temperature in light harvesting processes

    CERN Document Server

    Xiong, Shi-Jie; Zhao, Yang

    2012-01-01

    We investigate the influence of static disorder and thermal excitations on excitonic energy transport in the light-harvesting apparatus of photosynthetic systems by solving the Schr\\"{o}dinger equation and taking into account the coherent hoppings of excitons, the rates of exciton creation and annihilation in antennas and reaction centers, and the coupling to thermally excited phonons. The antennas and reaction centers are modeled, respectively, as the sources and drains which provide the channels for creation and annihilation of excitons. Phonon modes below a maximum frequency are coupled to the excitons that are continuously created in the antennas and depleted in the reaction centers, and the phonon population in these modes obeys the Bose-Einstein distribution at a given temperature. It is found that the energy transport is not only robust against the static disorder and the thermal noise, but it can also be enhanced by increasing the randomness and temperature in most parameter regimes. Relevance of our ...

  8. Bio-hydrogen Production Using the Visible Light-harvesting Function of Chlorophyll-a

    Energy Technology Data Exchange (ETDEWEB)

    Yutaka Amao; Noriko Himeshima [Department of Applied Chemistry, Oita University, Dannoharu 700, Oita 870-1192, (Japan)

    2006-07-01

    A Bio-hydrogen production system, coupling D-maltose hydrolysis by gluco-amylase and glucose dehydrogenase (GDH) and hydrogen production with platinum nano-particle colloid catalyst using the photo-sensitization based on the visible light harvesting of Mg chlorophyll-a (Mg Chl-a), was developed. Hydrogen gas was continuously produced when the reaction mixture containing D-maltose, gluco-amylase, GDH, nicotinamide adenine dinucleotide (NAD+), Mg Chl-a, methyl-viologen (MV2+) and platinum nano-particle colloid was irradiated by visible light. The amount of hydrogen production was estimated to be 5.0 {mu}mol after 4 h irradiation and the yield of conversion of D-maltose to hydrogen gas was about 1.8%. The quantum yield was 3.1%. (authors)

  9. Efficiency Enhancement of InGaN-Based Solar Cells via Stacking Layers of Light-Harvesting Nanospheres

    KAUST Repository

    Al-Amri, Amal M.

    2016-06-24

    An effective light-harvesting scheme for InGaN-based multiple quantum well solar cells is demonstrated using stacking layers of polystyrene nanospheres. Light-harvesting efficiencies on the solar cells covered with varied stacks of nanospheres are evaluated through numerical and experimental methods. The numerical simulation reveals that nanospheres with 3 stacking layers exhibit the most improved optical absorption and haze ratio as compared to those obtained by monolayer nanospheres. The experimental demonstration, agreeing with the theoretical analyses, shows that the application of 3-layer nanospheres improves the conversion efficiency of the solar cell by ~31%.

  10. Circular dichroism measured on single chlorosomal light-harvesting complexes of green photosynthetic bacteria

    KAUST Repository

    Furumaki, Shu

    2012-12-06

    We report results on circular dichroism (CD) measured on single immobilized chlorosomes of a triple mutant of green sulfur bacterium Chlorobaculum tepidum. The CD signal is measured by monitoring chlorosomal bacteriochlorphyll c fluorescence excited by alternate left and right circularly polarized laser light with a fixed wavelength of 733 nm. The excitation wavelength is close to a maximum of the negative CD signal of a bulk solution of the same chlorosomes. The average CD dissymmetry parameter obtained from an ensemble of individual chlorosomes was gs = -0.025, with an intrinsic standard deviation (due to variations between individual chlorosomes) of 0.006. The dissymmetry value is about 2.5 times larger than that obtained at the same wavelength in the bulk solution. The difference can be satisfactorily explained by taking into account the orientation factor in the single-chlorosome experiments. The observed distribution of the dissymmetry parameter reflects the well-ordered nature of the mutant chlorosomes. © 2012 American Chemical Society.

  11. Photoenergy Harvesting Organic PV Cells Using Modified Photosynthetic Light-Harvesting Complex for Energy Harvesting Materials

    Science.gov (United States)

    2008-07-03

    radical cation of the dye sensitizer (Chl  ) blocks the reverse electron transfer from TiO2  and stabilizes the resultant charge-separated state...different kinds of pigments on various electrodes such as TiO2 glass or plastic films (Scheme 3), collaborated with Prof. Minoru Taya, University of...Washinton in Seattle,US (see Time table 2). Scheme 3. Schemetic model of dye sensitized solar cell ( DSSC ) 10 One testable example

  12. Functional analysis of Photosystem I light-harvesting complexes (Lhca) gene products of Chlamydomonas reinhardtii

    NARCIS (Netherlands)

    Mozzo, Milena; Mantelli, Manuela; Passarini, Francesca; Caffarri, Stefano; Croce, Roberta; Bassi, Roberto

    2010-01-01

    The outer antenna system of Chlamydomonas reinhardtii Photosystem I is composed of nine gene products, but due to difficulty in purification their individual properties are not known. In this work, the functional properties of the nine Lhca antennas of Chlamydomonas, have been investigated upon expr

  13. Thermo-optically induced reorganizations in the main light harvesting antenna of plants. II

    DEFF Research Database (Denmark)

    Holm, Jens Kai; Varkonyi, Zsuzsanna; Kovacs, Laszlo

    2005-01-01

    from the same membranes. These reorganizations have earlier been assigned to originate from a thermo-optic effect. According to the thermo-optic mechanism, fast local thermal transients due to dissipation of the excess excitation energy induce elementary structural changes in the close vicinity......, together with other close similarities between the two systems, strongly suggests that the gross short-term, thermo-optically induced structural reorganizations in the membranes occur mainly, albeit probably not exclusively, in the LHCII-only domains [Boekema et al. (2000) J Mol Biol 301: 1123–1133]. Hence...

  14. Allelic variations of a light harvesting chlorophyll a/b-binding protein gene (Lhcb1 associated with agronomic traits in barley.

    Directory of Open Access Journals (Sweden)

    Yanshi Xia

    Full Text Available Light-harvesting chlorophyll a/b-binding protein (LHCP is one of the most abundant chloroplast proteins in plants. Its main function is to collect and transfer light energy to photosynthetic reaction centers. However, the roles of different LHCPs in light-harvesting antenna systems remain obscure. Exploration of nucleotide variation in the genes encoding LHCP can facilitate a better understanding of the functions of LHCP. In this study, nucleotide variations in Lhcb1, a LHCP gene in barley, were investigated across 292 barley accessions collected from 35 different countries using EcoTILLING technology, a variation of the Targeting Induced Local Lesions In Genomes (TILLING. A total of 23 nucleotide variations were detected including three insert/deletions (indels and 20 single nucleotide polymorphisms (SNPs. Among them, 17 SNPs were in the coding region with nine missense changes. Two SNPs with missense changes are predicted to be deleterious to protein function. Seventeen SNP formed 31 distinguishable haplotypes in the barley collection. The levels of nucleotide diversity in the Lhcb1 locus differed markedly with geographic origins and species of accessions. The accessions from Middle East Asia exhibited the highest nucleotide and haplotype diversity. H. spontaneum showed greater nucleotide diversity than H. vulgare. Five SNPs in Lhcb1 were significantly associated with at least one of the six agronomic traits evaluated, namely plant height, spike length, number of grains per spike, thousand grain weight, flag leaf area and leaf color, and these SNPs may be used as potential markers for improvement of these barley traits.

  15. Engineering of complex protein sialylation in plants

    Science.gov (United States)

    Kallolimath, Somanath; Castilho, Alexandra; Strasser, Richard; Grünwald-Gruber, Clemens; Altmann, Friedrich; Strubl, Sebastian; Galuska, Christina Elisabeth; Zlatina, Kristina; Galuska, Sebastian Peter; Werner, Stefan; Thiesler, Hauke; Werneburg, Sebastian; Hildebrandt, Herbert; Gerardy-Schahn, Rita; Steinkellner, Herta

    2016-01-01

    Sialic acids (Sias) are abundant terminal modifications of protein-linked glycans. A unique feature of Sia, compared with other monosaccharides, is the formation of linear homo-polymers, with its most complex form polysialic acid (polySia). Sia and polySia mediate diverse biological functions and have great potential for therapeutic use. However, technological hurdles in producing defined protein sialylation due to the enormous structural diversity render their precise investigation a challenge. Here, we describe a plant-based expression platform that enables the controlled in vivo synthesis of sialylated structures with different interlinkages and degree of polymerization (DP). The approach relies on a combination of stably transformed plants with transient expression modules. By the introduction of multigene vectors carrying the human sialylation pathway into glycosylation-destructed mutants, transgenic plants that sialylate glycoproteins in α2,6- or α2,3-linkage were generated. Moreover, by the transient coexpression of human α2,8-polysialyltransferases, polySia structures with a DP >40 were synthesized in these plants. Importantly, plant-derived polySia are functionally active, as demonstrated by a cell-based cytotoxicity assay and inhibition of microglia activation. This pathway engineering approach enables experimental investigations of defined sialylation and facilitates a rational design of glycan structures with optimized biotechnological functions. PMID:27444013

  16. Light harvesting proteins for solar fuel generation in bioengineered photoelectrochemical cells.

    Science.gov (United States)

    Ihssen, Julian; Braun, Artur; Faccio, Greta; Gajda-Schrantz, Krisztina; Thöny-Meyer, Linda

    2014-01-01

    The sun is the primary energy source of our planet and potentially can supply all societies with more than just their basic energy needs. Demand of electric energy can be satisfied with photovoltaics, however the global demand for fuels is even higher. The direct way to produce the solar fuel hydrogen is by water splitting in photoelectrochemical (PEC) cells, an artificial mimic of photosynthesis. There is currently strong resurging interest for solar fuels produced by PEC cells, but some fundamental technological problems need to be solved to make PEC water splitting an economic, competitive alternative. One of the problems is to provide a low cost, high performing water oxidizing and oxygen evolving photoanode in an environmentally benign setting. Hematite, α-Fe2O3, satisfies many requirements for a good PEC photoanode, but its efficiency is insufficient in its pristine form. A promising strategy for enhancing photocurrent density takes advantage of photosynthetic proteins. In this paper we give an overview of how electrode surfaces in general and hematite photoanodes in particular can be functionalized with light harvesting proteins. Specifically, we demonstrate how low-cost biomaterials such as cyanobacterial phycocyanin and enzymatically produced melanin increase the overall performance of virtually no-cost metal oxide photoanodes in a PEC system. The implementation of biomaterials changes the overall nature of the photoanode assembly in a way that aggressive alkaline electrolytes such as concentrated KOH are not required anymore. Rather, a more environmentally benign and pH neutral electrolyte can be used.

  17. Photophysical characterization of low-molecular weight organogels for energy transfer and light harvesting

    Science.gov (United States)

    Atsbeha, T.; Bussotti, L.; Cicchi, S.; Foggi, P.; Ghini, G.; Lascialfari, L.; Marcelli, A.

    2011-05-01

    The choice of a donor and an acceptor with suitable optical and self-assembly properties is essential in the design of organogel-based light harvesting systems. Organogels can provide supramolecular structures capable of enhancing energy transfer processes. In this work, we present the characterization of N-(naphthalene-1-carboxyamide)-(3 S,4 S)-pyrrolidin-(3,4)-bisdodecyl-carbamoyldiester ( 1) and N-(4-nitrobenzofurazan-7-amino)-(3 S,4 S)-pyrrolidin-(3,4)-bisdodecyl-carbamoyldiester ( 2) which are used as donor and acceptor moieties, respectively. The donor molecule is hardly capable to form a gelon its own but it can be assembled at reasonable concentrations with the acceptor gelator to form a two-component donor-acceptor organogels in cyclohexane. Stable organogels are formed from cyclohexane for gelator concentrations as low as ≈10 -3 M. UV-vis and steady-state fluorescence spectroscopies were used to provide a characterization of their molecular interactions. The optical changes observed during the cooling of two-component solutions of these systems are indicative of typical sol-gel transitions. The occurrence of excitation energy transfer processes in the gels is confirmed by comparison of their excitation and absorption spectra.

  18. Highly Efficient Photon Upconversion in Self-Assembled Light-Harvesting Molecular Systems

    Science.gov (United States)

    Ogawa, Taku; Yanai, Nobuhiro; Monguzzi, Angelo; Kimizuka, Nobuo

    2015-06-01

    To meet the world’s demands on the development of sunlight-powered renewable energy production, triplet-triplet annihilation-based photon upconversion (TTA-UC) has raised great expectations. However, an ideal highly efficient, low-power, and in-air TTA-UC has not been achieved. Here, we report a novel self-assembly approach to achieve this, which enabled highly efficient TTA-UC even in the presence of oxygen. A newly developed lipophilic 9,10-diphenylanthracene-based emitter molecule functionalized with multiple hydrogen-bonding moieties spontaneously coassembled with a triplet sensitizer in organic media, showing efficient triplet sensitization and subsequent triplet energy migration among the preorganized chromophores. This supramolecular light-harvesting system shows a high UC quantum yield of 30% optimized at low excitation power in deaerated conditions. Significantly, the UC emission largely remains even in an air-saturated solution, and this approach is facilely applicable to organogel and solid-film systems.

  19. Combining light-harvesting with detachability in high-efficiency thin-film silicon solar cells.

    Science.gov (United States)

    Ram, Sanjay K; Desta, Derese; Rizzoli, Rita; Bellettato, Michele; Lyckegaard, Folmer; Jensen, Pia B; Jeppesen, Bjarke R; Chevallier, Jacques; Summonte, Caterina; Larsen, Arne Nylandsted; Balling, Peter

    2017-06-01

    Efforts to realize thin-film solar cells on unconventional substrates face several obstacles in achieving good energy-conversion efficiency and integrating light-management into the solar cell design. In this report a technique to circumvent these obstacles is presented: transferability and an efficient light-harvesting scheme are combined for thin-film silicon solar cells by the incorporation of a NaCl layer. Amorphous silicon solar cells in p-i-n configuration are fabricated on reusable glass substrates coated with an interlayer of NaCl. Subsequently, the solar cells are detached from the substrate by dissolution of the sacrificial NaCl layer in water and then transferred onto a plastic sheet, with a resultant post-transfer efficiency of 9%. The light-trapping effect of the surface nanotextures originating from the NaCl layer on the overlying solar cell is studied theoretically and experimentally. The enhanced light absorption in the solar cells on NaCl-coated substrates leads to significant improvement in the photocurrent and energy-conversion efficiency in solar cells with both 350 and 100 nm thick absorber layers, compared to flat-substrate solar cells. Efficient transferable thin-film solar cells hold a vast potential for widespread deployment of off-grid photovoltaics and cost reduction.

  20. Porphyrin-based polymeric nanostructures for light harvesting applications: Ab initio calculations

    Science.gov (United States)

    Orellana, Walter

    The capture and conversion of solar energy into electricity is one of the most important challenges to the sustainable development of mankind. Among the large variety of materials available for this purpose, porphyrins concentrate great attention due to their well-known absorption properties in the visible range. However, extended materials like polymers with similar absorption properties are highly desirable. In this work, we investigate the stability, electronic and optical properties of polymeric nanostructures based on free-base porphyrins and phthalocyanines (H2P, H2Pc), within the framework of the time-dependent density functional perturbation theory. The aim of this work is the stability, electronic, and optical characterization of polymeric sheets and nanotubes obtained from H2P and H2Pc monomers. Our results show that H2P and H2Pc sheets exhibit absorption bands between 350 and 400 nm, slightly different that the isolated molecules. However, the H2P and H2Pc nanotubes exhibit a wide absorption in the visible and near-UV range, with larger peaks at 600 and 700 nm, respectively, suggesting good characteristic for light harvesting. The stability and absorption properties of similar structures obtained from ZnP and ZnPc molecules is also discussed. Departamento de Ciencias Físicas, República 220, 037-0134 Santiago, Chile.

  1. Third order nonlinear optical properties of stacked bacteriochlorophylls in bacterial photosynthetic light-harvesting proteins

    Energy Technology Data Exchange (ETDEWEB)

    Chen, L.X.; Laible, P.D. [Argonne National Lab., IL (United States). Chemistry Div.; Spano, F.C.; Manas, E.S. [Temple Univ., Philadelphia, PA (United States). Dept. of Chemistry

    1997-09-01

    Enhancement of the nonresonant second order molecular hyperpolarizabilities {gamma} were observed in stacked macrocyclic molecular systems, previously in a {micro}-oxo silicon phthalocyanine (SiPcO) monomer, dimer and trimer series, and now in bacteriochlorophyll a (BChla) arrays of light harvesting (LH) proteins. Compared to monomeric BChla in a tetrahydrofuran (THF) solution, the <{gamma}> for each macrocycle was enhanced in naturally occurring stacked macrocyclic molecular systems in the bacterial photosynthetic LH proteins where BChla`s are arranged in tilted face-to-face arrays. In addition, the {gamma} enhancement is more significant in B875 of LH1 than in B850 in LH2. Theoretical modeling of the nonresonant {gamma} enhancement using simplified molecular orbitals for model SiPcO indicated that the energy level of the two photon state is crucial to the {gamma} enhancement when a two photon process is involved, whereas the charge transfer between the monomers is largely responsible when one photon near resonant process is involved. The calculated results can be extended to {gamma} enhancement in B875 and B850 arrays, suggesting that BChla in B875 are more strongly coupled than in B850. In addition, a 50--160 fold increase in <{gamma}> for the S{sub 1} excited state of relative to S{sub 0} of bacteriochlorophyll in vivo was observed which provides an alternative method for probing excited state dynamics and a potential application for molecular switching.

  2. The regulation of light sensing and light harvesting impacts the use of cyanobacteria as biotechnology platforms

    Directory of Open Access Journals (Sweden)

    Beronda L Montgomery

    2014-07-01

    Full Text Available Light is harvested in cyanobacteria by chlorophyll-containing photosystems embedded in the thylakoid membranes and phycobilisomes (PBSs, photosystem-associated light-harvesting antennae. Light absorbed by the PBSs and photosystems can be converted to chemical energy through photosynthesis. Photosynthetically-fixed carbon pools, which are constrained by photosynthetic light capture versus the dissipation of excess light absorbed, determine the available organismal energy budget. The molecular bases of the environmental regulation of photosynthesis, photoprotection and photomorphogenesis are still being elucidated in cyanobacteria. Thus, the potential impacts of these phenomena on the efficacy of developing cyanobacteria as robust biotechnological platforms require additional attention. Current advances and persisting needs for developing cyanobacterial production platforms that are related to light sensing and harvesting include the development of tools to balance the utilization of absorbed photons for conversion to chemical energy and biomass versus light dissipation in photoprotective mechanisms. Such tools can be used to direct energy to more effectively support the production of desired bioproducts from sunlight.

  3. Kernel methods for phenotyping complex plant architecture.

    Science.gov (United States)

    Kawamura, Koji; Hibrand-Saint Oyant, Laurence; Foucher, Fabrice; Thouroude, Tatiana; Loustau, Sébastien

    2014-02-07

    The Quantitative Trait Loci (QTL) mapping of plant architecture is a critical step for understanding the genetic determinism of plant architecture. Previous studies adopted simple measurements, such as plant-height, stem-diameter and branching-intensity for QTL mapping of plant architecture. Many of these quantitative traits were generally correlated to each other, which give rise to statistical problem in the detection of QTL. We aim to test the applicability of kernel methods to phenotyping inflorescence architecture and its QTL mapping. We first test Kernel Principal Component Analysis (KPCA) and Support Vector Machines (SVM) over an artificial dataset of simulated inflorescences with different types of flower distribution, which is coded as a sequence of flower-number per node along a shoot. The ability of discriminating the different inflorescence types by SVM and KPCA is illustrated. We then apply the KPCA representation to the real dataset of rose inflorescence shoots (n=1460) obtained from a 98 F1 hybrid mapping population. We find kernel principal components with high heritability (>0.7), and the QTL analysis identifies a new QTL, which was not detected by a trait-by-trait analysis of simple architectural measurements. The main tools developed in this paper could be use to tackle the general problem of QTL mapping of complex (sequences, 3D structure, graphs) phenotypic traits.

  4. B Plant Complex preclosure work plan

    Energy Technology Data Exchange (ETDEWEB)

    ADLER, J.G.

    1999-02-02

    This preclosure work plan describes the condition of the dangerous waste treatment storage, and/or disposal (TSD) unit after completion of the B Plant Complex decommissioning Transition Phase preclosure activities. This description includes waste characteristics, waste types, locations, and associated hazards. The goal to be met by the Transition Phase preclosure activities is to place the TSD unit into a safe and environmentally secure condition for the long-term Surveillance and Maintenance (S&M) Phase of the facility decommissioning process. This preclosure work plan has been prepared in accordance with Section 8.0 of the Hanford Federal Facility Agreement and Consent Order (Tri-Party Agreement) (Ecology et al. 1996). The preclosure work plan is one of three critical Transition Phase documents, the other two being: B Plant End Points Document (WHC-SD-WM-TPP-054) and B Plant S&M plan. These documents are prepared by the U.S. Department of Energy, Richland Operations Office (DOE-RL) and its contractors with the involvement of Washington State Department of Ecology (Ecology). The tanks and vessels addressed by this preclosure work plan are limited to those tanks end vessels included on the B Plant Complex Part A, Form 3, Permit Application (DOE/RL-88-21). The criteria for determining which tanks or vessels are in the Part A, Form 3, are discussed in the following. The closure plan for the TSD unit will not be prepared until the Disposition Phase of the facility decommissioning process is initiated, which follows the long-term S&M Phase. Final closure will occur during the Disposition Phase of the facility decommissioning process. The Waste Encapsulation Storage Facility (WESF) is excluded from the scope of this preclosure work plan.

  5. Vibronic coupling explains the ultrafast carotenoid-to-bacteriochlorophyll energy transfer in natural and artificial light harvesters

    CERN Document Server

    Perlík, Václav; Cranston, Laura J; Cogdell, Richard J; Lincoln, Craig N; Savolainen, Janne; Šanda, František; Mančal, Tomáš; Hauer, Jürgen

    2015-01-01

    The initial energy transfer in photosynthesis occurs between the light-harvesting pigments and on ultrafast timescales. We analyze the carotenoid to bacteriochlorophyll energy transfer in LH2 Marichromatium purpuratum as well as in an artificial light-harvesting dyad system by using transient grating and two-dimensional electronic spectroscopy with 10 fs time resolution. We find that F\\"orster-type models reproduce the experimentally observed 60 fs transfer times, but overestimate coupling constants, which leads to a disagreement with both linear absorption and electronic 2D-spectra. We show that a vibronic model, which treats carotenoid vibrations on both electronic ground and excited state as part of the system's Hamiltonian, reproduces all measured quantities. Importantly, the vibronic model presented here can explain the fast energy transfer rates with only moderate coupling constants, which are in agreement with structure based calculations. Counterintuitively, the vibrational levels on the carotenoid el...

  6. Advanced nanostructured materials and their application for improvement of sun-light harvesting and efficiency of solar cells

    Science.gov (United States)

    Dimova-Malinovska, D.

    2016-02-01

    This review describes the application of different nanostructured materials in solar cells technology for improvement of sun-light harvesting and their efficiency. Several approaches have recently been proposed to increase the efficiency of solar cells above the theoretical limit which are based on a “photon management” concept that employs such phenomena as: (i) down-conversion, and (ii) surface plasmon resonance effect (iii) decreasing of the loss due to the reflection of the radiation, (iv) increasing of the reflection from the back contact, v) increasing of the effective solar cells surface, etc. The results demonstrate the possibility for to increasing of light harvesting, short circuit current and efficiency by application of nanomaterials in thin film and hetero-junction (HJ) solar cells. The first promising results allow an expectation for application of advanced nanomaterials in the 3d generation solar cells.

  7. Supramolecularly self-organized nanomaterials: A voyage from inorganic particles to organic light-harvesting materials

    Science.gov (United States)

    Varotto, Alessandro

    In 2009 the U.S. National Science Foundation announced the realignment of the Chemistry Divisions introducing the new interdisciplinary program of "Macromolecular, Supramolecular and Nanochemistry." This statement officially recognizes a field of studies that has already seen the publication of many thousands of works in the past 20 years. Nanotechnology and supramolecular chemistry can be found in the most diverse disciplines, from biology to engineering, to physics. Furthermore, many technologies rely on nanoscale dimensions for more than one component. Nanomaterials and technologies are on the market with a range of applications from composite materials, to electronics, to medicine, to sensing and more. This thesis will introduce a variety of studies and applications of supramolecular chemistry to form nanoscale photonic materials from soft matter. We will first illustrate a method to synthesize metallic nanoparticles using plasmids DNA as a mold. The circular DNA functions as a sacrificial template to shape the particles into narrowly monodispersed nanodiscs. Secondly, we will describe the synthesis of a highly fluorinated porphyrin derivative and how the fluorines improve the formation of ultra thin films when the porphyrin is blended with fullerene C60. Finally, we will show how to increase the short-circuit current in a solar cell built with an internal parallel tandem light harvesting design. A blend of phthalocyanines, each with a decreasing optical band gap, is supramolecularly self-organized with pyridyl-C60 within thin films. The different band gaps of the single phthalocyanines capture a wider segment of the solar spectrum increasing the overall efficiency of the device. In conclusion, we have presented a number of studies for the preparation of inorganic and organic nanomaterials and their application in supramolecularly organized photonic devices.

  8. A structural role of the carotenoid in the light-harvesting II protein of Rhodobacter capsulatus.

    Science.gov (United States)

    Zurdo, J; Fernandez-Cabrera, C; Ramirez, J M

    1993-03-01

    The membrane-linked light-harvesting II protein (LHII) of Rhodobacter capsulatus was partly depleted of carotenoids by selective extraction with light petroleum. Carotenoid removal was accompanied by bleaching of the Qy(S1<--S0) absorption band of bacteriochlorophyll (Bchl) a near 800 nm, by a bathochromic shift and a broadening of the other Bchl Qy band at 850 nm, and by the formation of a weak Qy band of dissociated Bchl near 770 nm. The changes in the 800 and 850 nm bands seemed to reflect alterations in only those Bchl molecules that had lost their associated carotenoids, firstly, because the extent of the changes was closely correlated to the degree of carotenoid extraction, and, secondly, because the residual fraction of carotenoid-containing LHII, which could be almost quantitatively recovered from the membrane after detergent solubilization and ion-exchange chromatography, showed an unmodified LHII absorption spectrum. The Bchl responsible for the shifted 850 nm band remained bound to protein, since its visible (Qx) transition seemed to retain the induced optical activity of the native bound pigment. Besides, the shifted Bchl could act as an efficient acceptor of singlet excitation energy from the pigments of the intact LHII fraction. The close similarity between the spectroscopic Bchl changes that accompany carotenoid extraction and the differential spectral features of carotenoidless LHII of Rhodobacter mutants, previously reported, strongly suggests that the direct cause of the spectral modifications is the absence of carotenoid and not any independent effect of the experimental manipulation of the membrane. Several interpretations of the structural changes that underlie the observed spectral changes are possible. The simplest one is to assume that carotenoid removal elicits an alteration in the angle between the Qy transition moments of two strongly interacting Bchl molecules.

  9. Crystal structure of archaeal photolyase from Sulfolobus tokodaii with two FAD molecules: implication of a novel light-harvesting cofactor.

    Science.gov (United States)

    Fujihashi, Masahiro; Numoto, Nobutaka; Kobayashi, Yukiko; Mizushima, Akira; Tsujimura, Masanari; Nakamura, Akira; Kawarabayasi, Yutaka; Miki, Kunio

    2007-01-26

    UV exposure of DNA molecules induces serious DNA lesions. The cyclobutane pyrimidine dimer (CPD) photolyase repairs CPD-type - lesions by using the energy of visible light. Two chromophores for different roles have been found in this enzyme family; one catalyzes the CPD repair reaction and the other works as an antenna pigment that harvests photon energy. The catalytic cofactor of all known photolyases is FAD, whereas several light-harvesting cofactors are found. Currently, 5,10-methenyltetrahydrofolate (MTHF), 8-hydroxy-5-deaza-riboflavin (8-HDF) and FMN are the known light-harvesting cofactors, and some photolyases lack the chromophore. Three crystal structures of photolyases from Escherichia coli (Ec-photolyase), Anacystis nidulans (An-photolyase), and Thermus thermophilus (Tt-photolyase) have been determined; however, no archaeal photolyase structure is available. A similarity search of archaeal genomic data indicated the presence of a homologous gene, ST0889, on Sulfolobus tokodaii strain7. An enzymatic assay reveals that ST0889 encodes photolyase from S. tokodaii (St-photolyase). We have determined the crystal structure of the St-photolyase protein to confirm its structural features and to investigate the mechanism of the archaeal DNA repair system with light energy. The crystal structure of the St-photolyase is superimposed very well on the three known photolyases including the catalytic cofactor FAD. Surprisingly, another FAD molecule is found at the position of the light-harvesting cofactor. This second FAD molecule is well accommodated in the crystal structure, suggesting that FAD works as a novel light-harvesting cofactor of photolyase. In addition, two of the four CPD recognition residues in the crystal structure of An-photolyase are not found in St-photolyase, which might utilize a different mechanism to recognize the CPD from that of An-photolyase.

  10. Enhanced light-harvesting capacity by micellar assembly of free accessory chromophores and LH1-like antennas.

    Science.gov (United States)

    Harris, Michelle A; Sahin, Tuba; Jiang, Jianbing; Vairaprakash, Pothiappan; Parkes-Loach, Pamela S; Niedzwiedzki, Dariusz M; Kirmaier, Christine; Loach, Paul A; Bocian, David F; Holten, Dewey; Lindsey, Jonathan S

    2014-01-01

    Biohybrid light-harvesting antennas are an emerging platform technology with versatile tailorability for solar-energy conversion. These systems combine the proven peptide scaffold unit utilized for light harvesting by purple photosynthetic bacteria with attached synthetic chromophores to extend solar coverage beyond that of the natural systems. Herein, synthetic unattached chromophores are employed that partition into the organized milieu (e.g. detergent micelles) that house the LH1-like biohybrid architectures. The synthetic chromophores include a hydrophobic boron-dipyrrin dye (A1) and an amphiphilic bacteriochlorin (A2), which transfer energy with reasonable efficiency to the bacteriochlorophyll acceptor array (B875) of the LH1-like cyclic oligomers. The energy-transfer efficiencies are markedly increased upon covalent attachment of a bacteriochlorin (B1 or B2) to the peptide scaffold, where the latter likely acts as an energy-transfer relay site for the (potentially diffusing) free chromophores. The efficiencies are consistent with a Förster (through-space) mechanism for energy transfer. The overall energy-transfer efficiency from the free chromophores via the relay to the target site can approach those obtained previously by relay-assisted energy transfer from chromophores attached at distant sites on the peptides. Thus, the use of free accessory chromophores affords a simple design to enhance the overall light-harvesting capacity of biohybrid LH1-like architectures.

  11. Optimizing Photovoltaic Response by Tuning Light-Harvesting Nanocrystal Shape Synthesized Using a Quick Liquid-Gas Phase Reaction.

    Science.gov (United States)

    Mazumdar, Sayantan; Tamilselvan, Muthusamy; Bhattacharyya, Aninda J

    2015-12-30

    The electron recombination lifetime in a sensitized semiconductor assembly is greatly influenced by the crystal structure and geometric form of the light-harvesting semiconductor nanocrystal. When such light harvesters with varying structural characteristics are configured in a photoanode, its interface with the electrolyte becomes equally important and directly influences the photovoltaic efficiency. We have systematically probed here the influence of nanocrystal crystallographic structure and shape on the electron recombination lifetime and its eventual influence on the light to electricity conversion efficiency of a liquid junction semiconductor sensitized solar cell. The light-harvesting cadmium sulfide (CdS) nanocrystals of distinctly different and controlled shapes are obtained using a novel and simple liquid-gas phase synthesis method performed at different temperatures involving very short reaction times. High-resolution synchrotron X-ray diffraction and spectroscopic studies respectively exhibit different crystallographic phase content and optical properties. When assembled on a mesoscopic TiO2 film by a linker molecule, they exhibit remarkable variation in electron recombination lifetime by 1 order of magnitude, as determined by ac-impedance spectroscopy. This also drastically affects the photovoltaic efficiency of the differently shaped nanocrystal sensitized solar cells.

  12. Exciton coherence and energy transport in the light-harvesting dimers of allophycocyanin.

    Science.gov (United States)

    Womick, Jordan M; Moran, Andrew M

    2009-12-03

    Femtosecond transient grating and photon echo spectroscopies with a sub-20 fs time resolution are applied to allophycocyanin (APC), a protein located at the base of the phycobilisome antenna of cyanobacteria. Coupling between pairs of phycocyanobilin pigments with nondegenerate energy levels gives rise to the four-level exciton electronic structure of APC. Spectroscopic signals obtained in multiple experiments (e.g., linear absorption, fluorescence, transient grating, 2D Fourier transform photon echo) are used to constrain the parameters of a Frenkel exciton Hamiltonian. Comparison between experiment and theory yields a robust microscopic understanding of the electronic and nuclear relaxation dynamics. In agreement with previous work, transient absorption anisotropy establishes that internal conversion between the exciton states of the dimer occurs with time constants of 35, 220, and 280 fs. The sub-100 fs dynamics are decomposed into three distinct relaxation processes: electronic population transfer, intramolecular vibrational energy redistribution, and the dephasing of electronic and nuclear coherences. Model calculations show that the sub-100 fs red-shift in the transient absorption signal spectrum reflects interference between stimulated emission (ESE) and excited state absorption (ESA) signal components. It is also established that the pigment fluctuations in the dimer are not well-correlated, although further experiments will be required to precisely quantify the amount of correlation. The findings of this paper suggest that the light harvesting function of APC is enhanced by nondegeneracy of the pigments comprising the dimer and strong vibronic coupling of intramolecular modes on the phycocyanobilins. We find that the exciton states are 96% localized to the individual molecular sites within a particular dimer. Localization of the transition densities, in turn, is suggested to promote significant vibronic coupling which serves to both broaden the absorption

  13. Light-harvesting host-guest antenna materials for solar energy conversion devices

    Science.gov (United States)

    Huber, Stefan; Calzaferri, Gion

    2006-04-01

    In natural photosynthesis, light is absorbed by photonic antenna systems consisting of a few hundred chlorophyll molecules. These devices allow fast energy transfer from an electronically excited molecule to an unexcited neighbour molecule in such a way that the excitation energy reaches the reaction centre with high probability. Trapping occurs there. The anisotropic arrangement of the chlorophyll molecules is important for efficient energy migration. In natural antennae the formation of aggregates is prevented by fencing the chlorophyll molecules in polypeptide cages. A similar approach is possible by enclosing dyes inside a microporous material and by choosing conditions such that the cavities are able to uptake only monomers but not aggregates. In most of our experiments we have been using zeolite L as a host because it was found to be very versatile. Its crystals are of cylindrical shape and consist of an extended one-dimensional tube system. They can be prepared in wide size range. We have filled the individual tubes with successive chains of different dye molecules and we have shown that photonic antenna materials can be prepared. Moreover, fluorescent dye molecules can be bound covalently to the channel entrances. Dependent on the spectral properties of these stopcock molecules, the electronic excitation energy is transported radiationless to the stopcock fixed at the ends of the nanochannels or injected from the stopcock to the dyes inside the zeolite. The radiationless energy migration is in competition with spontaneous emission, thermal deactivation, quenching, and photochemically induced degradation. Fast energy migration is therefore crucial for an efficient antenna material. - The supramolecular organization of the dyes inside the channels is a first stage of organization. It allows light harvesting within the volume of a dye-loaded zeolite L crystal and radiationless transport to both ends of the cylinder or from the ends to the centre. The second

  14. All organic host-guest crystals based on a dumb-bell-shaped conjugated host for light harvesting through resonant energy transfer.

    Science.gov (United States)

    Winkler, Reingard; Berger, Ricarda; Manca, Marianna; Hulliger, Jürg; Weber, Edwin; Loi, Maria A; Botta, Chiara

    2012-01-16

    Together we glow: Fully organic host-guest crystals with two dyes inserted in their parallel nanochannels display broad emission in the visible range thanks to resonant energy transfer. The conjugated host crystal provides light harvesting in the UV region.

  15. The specificity of controlled protein disorder in the photoprotection of plants.

    Science.gov (United States)

    Krüger, Tjaart P J; Ilioaia, Cristian; Johnson, Matthew P; Belgio, Erica; Horton, Peter; Ruban, Alexander V; van Grondelle, Rienk

    2013-08-20

    Light-harvesting pigment-protein complexes of photosystem II of plants have a dual function: they efficiently use absorbed energy for photosynthesis at limiting sunlight intensity and dissipate the excess energy at saturating intensity for photoprotection. Recent single-molecule spectroscopy studies on the trimeric LHCII complex showed that environmental control of the intrinsic protein disorder could in principle explain the switch between their light-harvesting and photoprotective conformations in vivo. However, the validity of this proposal depends strongly on the specificity of the protein dynamics. Here, a similar study has been performed on the minor monomeric antenna complexes of photosystem II (CP29, CP26, and CP24). Despite their high structural homology, similar pigment content and organization compared to LHCII trimers, the environmental response of these proteins was found to be rather distinct. A much larger proportion of the minor antenna complexes were present in permanently weakly fluorescent states under most conditions used; however, unlike LHCII trimers the distribution of the single-molecule population between the strongly and weakly fluorescent states showed no significant sensitivity to low pH, zeaxanthin, or low detergent conditions. The results support a unique role for LHCII trimers in the regulation of light harvesting by controlled fluorescence blinking and suggest that any contribution of the minor antenna complexes to photoprotection would probably involve a distinct mechanism. Copyright © 2013 Biophysical Society. Published by Elsevier Inc. All rights reserved.

  16. Binary ionic porphyrin nanosheets: electronic and light-harvesting properties regulated by crystal structure

    Science.gov (United States)

    Tian, Yongming; M. Beavers, Christine; Busani, Tito; Martin, Kathleen E.; Jacobsen, John L.; Mercado, Brandon Q.; Swartzentruber, Brian S.; van Swol, Frank; Medforth, Craig J.; Shelnutt, John A.

    2012-02-01

    Crystalline solids self-assembled from anionic and cationic porphyrins provide a new class of multifunctional optoelectronic micro- and nanomaterials. A 1 : 1 combination of zinc(ii) tetra(4-sulfonatophenyl)porphyrin (ZnTPPS) and tin(iv) tetra(N-methyl-4-pyridiniumyl)porphyrin (SnTNMePyP) gives porphyrin nanosheets with high aspect ratios and varying thickness. The room temperature preparation of the nanosheets has provided the first X-ray crystal structure of a cooperative binary ionic (CBI) solid. The unit cell contains one and one-half molecules of aquo-ZnTPPS4- (an electron donor) and three half molecules of dihydroxy-SnTNMePyP4+ (an electron acceptor). Charge balance in the solid is reached without any non-porphyrinic ions, as previously determined for other CBI nanomaterials by non-crystallographic means. The crystal structure reveals a complicated molecular arrangement with slipped π-π stacking only occurring in isolated dimers of one of the symmetrically unique zinc porphyrins. Consistent with the crystal structure, UV-visible J-aggregate bands indicative of exciton delocalization and extended π-π stacking are not observed. XRD measurements show that the structure of the Zn/Sn nanosheets is distinct from that of Zn/Sn four-leaf clover-like CBI solids reported previously. In contrast with the Zn/Sn clovers that do exhibit J-aggregate bands and are photoconductive, the nanosheets are not photoconductive. Even so, the nanosheets act as light-harvesting structures in an artificial photosynthesis system capable of reducing water to hydrogen but not as efficiently as the Zn/Sn clovers.Crystalline solids self-assembled from anionic and cationic porphyrins provide a new class of multifunctional optoelectronic micro- and nanomaterials. A 1 : 1 combination of zinc(ii) tetra(4-sulfonatophenyl)porphyrin (ZnTPPS) and tin(iv) tetra(N-methyl-4-pyridiniumyl)porphyrin (SnTNMePyP) gives porphyrin nanosheets with high aspect ratios and varying thickness. The room

  17. A Novel Soluble Tin(IV Porphyrin Modified Single-Walled Carbon Nanotube Nanohybrid With Light Harvesting Properties

    Directory of Open Access Journals (Sweden)

    Jian-Yu Zheng

    2008-01-01

    Full Text Available A dihydroxotin(IV porphyrin functionalized single-walled carbon nanotubes (SWNTs nanohybrid is obtained. Solubility of the nanohybrid in organic solvents is determined by UV-Vis-NIR absorption spectroscopy. Electron absorption and fluorescence spectra investigations demonstrate that efficient electron transfer occurs within the nanohybrid at the photoexcited state and the charge-separated state of the nanohybrid is observed by transient absorption spectrum. The results illustrate that this soluble electron donor–acceptor nanohybrid might be a good candidate as a light harvesting material in molecular photoelectronic devices.

  18. Enhanced photoresponse of CdS/CMK-3 composite as a candidate for light-harvesting assembly

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Bin; Chen Xudong; Yang Jin; Yu Dingshan; Chen Yujie; Wu Dingcai; Fu Ruowen; Zhang Mingqiu, E-mail: cescxd@mail.sysu.edu.cn, E-mail: ceszmq@mail.sysu.edu.cn [Key Laboratory of the Ministry of Education for Polymer Composite and Functional Materials, DSAPM Lab, School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou, 510275 (China)

    2010-01-29

    Two typical carbon materials (ordered mesoporous carbon and carbon nanotube) were chosen as scaffolds in combination with semiconductor quantum dots (SQDs) for making light-harvesting assemblies. The effects of interfacial morphology on photoelectric performance of the carbon-based heterostructures have been investigated in detail. The enhanced photoresponse shows a strong dependence on the interfacial morphology as a result of direct interfacial contacts between SQDs and carbon materials, which plays a major role in increasing charge generation at the interface and transport pathways for photoinduced electron transfer. The methodology to enhance the photoresponse through tuning interfacial morphology proves to be a potent alternative in fabricating photochemical energy conversion systems.

  19. Enhanced photoresponse of CdS/CMK-3 composite as a candidate for light-harvesting assembly.

    Science.gov (United States)

    Zhang, Bin; Chen, Xudong; Yang, Jin; Yu, Dingshan; Chen, Yujie; Wu, Dingcai; Fu, Ruowen; Zhang, Mingqiu

    2010-01-29

    Two typical carbon materials (ordered mesoporous carbon and carbon nanotube) were chosen as scaffolds in combination with semiconductor quantum dots (SQDs) for making light-harvesting assemblies. The effects of interfacial morphology on photoelectric performance of the carbon-based heterostructures have been investigated in detail. The enhanced photoresponse shows a strong dependence on the interfacial morphology as a result of direct interfacial contacts between SQDs and carbon materials, which plays a major role in increasing charge generation at the interface and transport pathways for photoinduced electron transfer. The methodology to enhance the photoresponse through tuning interfacial morphology proves to be a potent alternative in fabricating photochemical energy conversion systems.

  20. Enhancement of a Two-Photon-Induced Reaction in Solution Using Light-Harvesting Gold Nanodimer Structures.

    Science.gov (United States)

    Wu, Botao; Ueno, Kosei; Yokota, Yukie; Sun, Kai; Zeng, Heping; Misawa, Hiroaki

    2012-06-07

    We performed a quantitative analysis of plasmon-assisted two-photon photochromic reactions on light-harvesting gold nanodimer structures. Our strategy for the quantitative analysis of two-photon-induced photochemical reactions on gold nanostructures is using not only a confined photochemical reaction chamber but also a solution system. The strong intensification of near-field light at the nanogap positions on gold nanodimer pairs promoted two-photon absorption by a closed-form diarylethene derivative, resulting in highly efficient photochromic conversion to the open-form structure.

  1. Plant Mediator complex and its critical functions in transcription regulation.

    Science.gov (United States)

    Yang, Yan; Li, Ling; Qu, Li-Jia

    2016-02-01

    The Mediator complex is an important component of the eukaryotic transcriptional machinery. As an essential link between transcription factors and RNA polymerase II, the Mediator complex transduces diverse signals to genes involved in different pathways. The plant Mediator complex was recently purified and comprises conserved and specific subunits. It functions in concert with transcription factors to modulate various responses. In this review, we summarize the recent advances in understanding the plant Mediator complex and its diverse roles in plant growth, development, defense, non-coding RNA production, response to abiotic stresses, flowering, genomic stability and metabolic homeostasis. In addition, the transcription factors interacting with the Mediator complex are also highlighted.

  2. Plant mitochondrial Complex I composition and assembly: A review.

    Science.gov (United States)

    Subrahmanian, Nitya; Remacle, Claire; Hamel, Patrice Paul

    2016-07-01

    In the mitochondrial inner membrane, oxidative phosphorylation generates ATP via the operation of several multimeric enzymes. The proton-pumping Complex I (NADH:ubiquinone oxidoreductase) is the first and most complicated enzyme required in this process. Complex I is an L-shaped enzyme consisting of more than 40 subunits, one FMN molecule and eight Fe-S clusters. In recent years, genetic and proteomic analyses of Complex I mutants in various model systems, including plants, have provided valuable insights into the assembly of this multimeric enzyme. Assisted by a number of key players, referred to as "assembly factors", the assembly of Complex I takes place in a sequential and modular manner. Although a number of factors have been identified, their precise function in mediating Complex I assembly still remains to be elucidated. This review summarizes our current knowledge of plant Complex I composition and assembly derived from studies in plant model systems such as Arabidopsis thaliana and Chlamydomonas reinhardtii. Plant Complex I is highly conserved and comprises a significant number of subunits also present in mammalian and fungal Complexes I. Plant Complex I also contains additional subunits absent from the mammalian and fungal counterpart, whose function in enzyme activity and assembly is not clearly understood. While 14 assembly factors have been identified for human Complex I, only two proteins, namely GLDH and INDH, have been established as bona fide assembly factors for plant Complex I. This article is part of a Special Issue entitled Respiratory complex I, edited by Volker Zickermann and Ulrich Brandt.

  3. Exploring the effect of vibronic contributions on light harvesting efficiency of NKX-2587 derivatives through vibrationally resolved electronic spectra

    Science.gov (United States)

    Yang, Pan; Shen, Wei; Li, Ming; He, Rongxing

    2017-01-01

    The vibrationally resolved electronic spectra of five metal-free NKX-2587 derivatives containing heteroatom with different atomic sizes and electronegativity, were simulated within the Franck-Condon approximation including the Herzberg-Teller and Duschinsky effects, aimed at exploring the correlation of vibronic structure associated with the spectrum and efficiency of dye sensitized solar cells (DSSCs). The parameters of short-circuit current density (Jsc) and open circuit voltage (Voc) involving efficiency of DSSCs, such as total dipole moments (μnormal), the light harvesting efficiency (LHE), injection driving force (∆ Ginject), and the number of electrons in the conduction band (nc), were calculated and discussed in detail. Results showed that the heteroatoms in the same period with large size and weak electronegativity and the ones in the same main group with large size and weak electronegativity are beneficial to Voc. The sizes and electronegativity of the heteroatoms have a weak effect on Jsc. The low-frequency modes play important roles in enhancing the intensities of the electronic spectra and structures can affect light harvesting efficiency (LHE). In this sense, our results provided guidance for understanding the sources of spectral intensities of dye molecules, and a valuable help for rational design of new molecules to improve the energy conversion efficiency (η) of DSSCs.

  4. Effects of system-bath entanglement on the performance of light-harvesting systems: A quantum heat engine perspective

    CERN Document Server

    Xu, Dazhi; Zhao, Yang; Cao, Jianshu

    2015-01-01

    We explore energy transfer in a generic three-level system, which is coupled to three non-equilibrium baths. Built on the concept of quantum heat engine, our three-level model describes non-equilibrium quantum processes including light-harvesting energy transfer, nano-scale heat transfer, photo-induced isomerization, and photovoltaics in double quantum-dots. In the context of light-harvesting, the excitation energy is first pumped up by sunlight, then is transferred via two excited states which are coupled to a phonon bath, and finally decays to the ground state. The efficiency of this process is evaluated by steady state analysis via a polaron-transformed master equation; thus a wide range of the system-phonon coupling strength can be covered. We show that the coupling with the phonon bath not only modifies the steady state, resulting in population inversion, but also introduces a finite steady state coherence which optimizes the energy transfer flux and efficiency. In the strong coupling limit, the steady s...

  5. Loss of CpSRP54 function leads to a truncated light-harvesting antenna size in Chlamydomonas reinhardtii.

    Science.gov (United States)

    Jeong, Jooyeon; Baek, Kwangryul; Kirst, Henning; Melis, Anastasios; Jin, EonSeon

    2017-01-01

    The Chlamydomonas reinhardtii truncated light-harvesting antenna 4 (tla4) DNA transposon mutant has a pale green phenotype, a lower chlorophyll (Chl) per cell and a higher Chl a/b ratio in comparison with the wild type. It required a higher light intensity for the saturation of photosynthesis and displayed a greater per chlorophyll light-saturated rate of oxygen evolution than the wild type. The Chl antenna size of the photosystems in the tla4 mutant was only about 65% of that measured in the wild type. Molecular genetic analysis revealed that a single plasmid DNA insertion disrupted two genes on chromosome 11 of the mutant. A complementation study identified the "chloroplast signal recognition particle 54" gene (CpSRP54), as the lesion causing the tla4 phenotype. Disruption of this gene resulted in partial failure to assemble and, therefore, lower levels of light-harvesting Chl-binding proteins in the C. reinhardtii thylakoids. A comparative in silico 3-D structure-modeling analysis revealed that the M-domain of the CpSRP54 of C. reinhardtii possesses a more extended finger loop structure, due to different amino acid composition, as compared to that of the Arabidopsis CpSRP54. The work demonstrated that CpSRP54 deletion in microalgae can serve to generate tla mutants with a markedly smaller photosystem Chl antenna size, improved solar energy conversion efficiency, and photosynthetic productivity in high-density cultures under bright sunlight conditions.

  6. Core–shell heterostructured metal oxide arrays enable superior light-harvesting and hysteresis-free mesoscopic perovskite solar cells

    KAUST Repository

    Mahmood, Khalid

    2015-01-01

    To achieve highly efficient mesoscopic perovskite solar cells (PSCs), the structure and properties of an electron transport layer (ETL) or material (ETM) have been shown to be of supreme importance. Particularly, the core-shell heterostructured mesoscopic ETM architecture has been recognized as a successful electrode design, because of its large internal surface area, superior light-harvesting efficiency and its ability to achieve fast charge transport. Here we report the successful fabrication of a hysteresis-free, 15.3% efficient PSC using vertically aligned ZnO nanorod/TiO2 shell (ZNR/TS) core-shell heterostructured ETMs for the first time. We have also added a conjugated polyelectrolyte polymer into the growth solution to promote the growth of high aspect ratio (AR) ZNRs and substantially improve the infiltration of the perovskite light absorber into the ETM. The PSCs based on the as-synthesized core-shell ZnO/TiO2 heterostructured ETMs exhibited excellent performance enhancement credited to the superior light harvesting capability, larger surface area, prolonged charge-transport pathways and lower recombination rate. The unique ETM design together with minimal hysteresis introduces core-shell ZnO/TiO2 heterostructures as a promising mesoscopic electrode approach for the fabrication of efficient PSCs. This journal is © The Royal Society of Chemistry.

  7. Two-dimensional artificial light-harvesting antennae with predesigned high-order structure and robust photosensitising activity

    Science.gov (United States)

    Feng, Xiao; Ding, Xuesong; Chen, Long; Wu, Yang; Liu, Lili; Addicoat, Matthew; Irle, Stephan; Dong, Yuping; Jiang, Donglin

    2016-09-01

    Highly ordered discrete assemblies of chlorophylls that are found in natural light-harvesting antennae are key to photosynthesis, which converts light energy to chemical energy and is the principal producer of organic matter on Earth. Porphyrins and phthalocyanines, which are analogues of chlorophylls, exhibit a strong absorbance of visible and near-infrared light, respectively. A highly ordered porphyrin-co-phthalocyanine antennae would harvest photons over the entire solar spectrum for chemical transformation. However, such a robust antennae has not yet been synthesised. Herein, we report a strategy that merges covalent bonds and noncovalent forces to produce highly ordered two-dimensional porphyrin-co-phthalocyanine antennae. This methodology enables control over the stoichiometry and order of the porphyrin and phthalocyanine units; more importantly, this approach is compatible with various metalloporphyrin and metallophthalocyanine derivatives and thus may lead to the generation of a broad structural diversity of two-dimensional artificial antennae. These ordered porphyrin-co-phthalocyanine two-dimensional antennae exhibit unique optical properties and catalytic functions that are not available with single-component or non-structured materials. These 2D artificial antennae exhibit exceptional light-harvesting capacity over the entire solar spectrum as a result of a synergistic light-absorption effect. In addition, they exhibit outstanding photosensitising activities in using both visible and near-infrared photons for producing singlet oxygen.

  8. Light harvesting and blue-green light induced non-photochemical quenching in two different C-phycocyanin mutants of Synechocystis PCC 6803.

    Science.gov (United States)

    Tian, Lijin; van Stokkum, Ivo H M; Koehorst, Rob B M; van Amerongen, Herbert

    2013-09-26

    Cyanobacteria are oxygen-evolving photosynthetic organisms that harvest sunlight and convert excitation energy into chemical energy. Most of the light is absorbed by large light harvesting complexes called phycobilisomes (PBs). In high-light conditions, cyanobacteria switch on a photoprotective mechanism called non-photochemical quenching (NPQ): During this process, absorption of blue-green light transforms the inactive orange form of the orange carotenoid protein OCP (OCP(o)) into the red active form OCP(r) that subsequently binds to the PB, resulting in a substantial loss of excitation energy and corresponding decrease of the fluorescence. In wild-type cells, the quenching site is a bilin chomophore that fluoresces at 660 nm and which is called APC(Q)(660). In the present work, we studied NPQ in two different types of mutant cells (CB and CK) that possess significantly truncated PBs, using spectrally resolved picosecond fluorescence spectroscopy. The results are in very good agreement with earlier in vitro experiments on quenched and unquenched PBs, although the fraction of quenched PBs is far lower in vivo. It is also lower than the fraction of PBs that is quenched in wild-type cells, but the site, rate, and location of quenching appear to be very similar.

  9. Normal mode analysis of the spectral density of the Fenna-Matthews-Olson light-harvesting protein: how the protein dissipates the excess energy of excitons.

    Science.gov (United States)

    Renger, Thomas; Klinger, Alexander; Steinecker, Florian; Schmidt am Busch, Marcel; Numata, Jorge; Müh, Frank

    2012-12-20

    We report a method for the structure-based calculation of the spectral density of the pigment-protein coupling in light-harvesting complexes that combines normal-mode analysis with the charge density coupling (CDC) and transition charge from electrostatic potential (TrEsp) methods for the computation of site energies and excitonic couplings, respectively. The method is applied to the Fenna-Matthews-Olson (FMO) protein in order to investigate the influence of the different parts of the spectral density as well as correlations among these contributions on the energy transfer dynamics and on the temperature-dependent decay of coherences. The fluctuations and correlations in excitonic couplings as well as the correlations between coupling and site energy fluctuations are found to be 1 order of magnitude smaller in amplitude than the site energy fluctuations. Despite considerable amplitudes of that part of the spectral density which contains correlations in site energy fluctuations, the effect of these correlations on the exciton population dynamics and dephasing of coherences is negligible. The inhomogeneous charge distribution of the protein, which causes variations in local pigment-protein coupling constants of the normal modes, is responsible for this effect. It is seen thereby that the same building principle that is used by nature to create an excitation energy funnel in the FMO protein also allows for efficient dissipation of the excitons' excess energy.

  10. The PufX quinone channel enables the light-harvesting 1 antenna to bind more carotenoids for light collection and photoprotection.

    Science.gov (United States)

    Olsen, John D; Martin, Elizabeth C; Hunter, C Neil

    2017-02-01

    Photosynthesis in some phototrophic bacteria requires the PufX component of the reaction centre-light-harvesting 1-PufX (RC-LH1-PufX) complex, which creates a pore for quinone/quinol (Q/QH2 ) exchange across the LH1 barrier surrounding the RC. However, photosynthetic bacteria such as Thermochromatium (T.) tepidum do not require PufX because there are fewer carotenoid binding sites, which creates multiple pores in the LH1 ring for Q/QH2 exchange. We show that an αTrp-24 →Phe alteration of the Rhodobacter (Rba.) sphaeroides LH1 antenna impairs carotenoid binding and allows photosynthetic growth in the absence of PufX. We propose that acquisition of PufX and confining Q/QH2 traffic to a pore adjacent to the RC QB site is an evolutionary upgrade that allows increased LH1 carotenoid content for enhanced light absorption and photoprotection. © 2017 The Authors. FEBS Letters published by John Wiley & Sons Ltd on behalf of Federation of European Biochemical Societies.

  11. Self-aggregation behavior of synthetic zinc 3-hydroxymethyl-13/15-carbonyl-chlorins as models of main light-harvesting components in photosynthetic green bacteria.

    Science.gov (United States)

    Tamiaki, Hitoshi; Yoshimura, Hideaki; Shimamura, Yasuhide; Kunieda, Michio

    2008-01-01

    Zinc complexes of 3-hydroxymethyl-13/15-carbonyl-chlorins having a six-membered lactone as the E-ring were prepared by modifying purpurin-18 as models of bacteriochlorophyll-d, one of the chlorophyllous pigments in the main light-harvesting antenna systems (chlorosomes) of green photosynthetic bacteria. The synthetic 13-carbonylated compound self-aggregated in 1%(v/v) tetrahydrofuran and hexane to give large oligomers possessing red-shifted and broadened electronic absorption bands and intense circular dichroism bands at the shifted Q ( y ) region, indicating that the supramolecular structure of the resulting self-aggregate was similar to those of natural and artificial chlorosomal aggregates. The red-shift value observed here was smaller than the reported values in chlorosomal pigments having a five-membered keto-ring, which was ascribable to a weaker intermolecular hydrogen-bonding of 13-C=O with 3(1)-OH in a supramolecule of the former self-aggregate and suppression of the pi-pi interaction among the composite chlorins. On the other hand, the isomeric 15-carbonylated molecule was monomeric even in the nonpolar organic solvent, confirming the reported proposal that the linear orientation of three interactive moieties, OH, C=O and Zn, in a molecule is requisite for its chlorosomal self-aggregation.

  12. Complex plant traits : time for polygenic analysis

    NARCIS (Netherlands)

    Jansen, Ritsert C.

    1996-01-01

    Currently, mapping of genes for complex traits is an area of active theoretical research at the interface of genetics and statistics. Much progress has been made over the past few years in handling statistically complex but realistic multilocus models. Here, I describe the state of the art and discu

  13. Broadband Light-Harvesting Molecular Triads with High FRET Efficiency Based on the Coumarin-Rhodamine-BODIPY Platform.

    Science.gov (United States)

    He, Longwei; Zhu, Sasa; Liu, Yong; Xie, Yinan; Xu, Qiuyan; Wei, Haipeng; Lin, Weiying

    2015-08-17

    Broadband capturing and FRET-based light-harvesting molecular triads, CRBs, based on the coumarin-rhodamine-BODIPY platform were rationally designed and synthesized. The absorption band of CRBs starts from blue-green to yellow-orange regions (330-610 nm), covering the strong radiation scope of sunlight. The peripheral coumarin and BODIPY chromophore energy could transfer to the central acceptor rhodamine by a one-step direct way. The energy of the coumarin moiety could also transfer to the BODIPY unit, subsequently transferring to the rhodamine core by two-step sequential ways. Both the efficiencies of the coumarin moiety and the BODIPY unit to the rhodamine core in CRBs, determined by two different ways, are very high.

  14. Ultrafast exciton-exciton coherent transfer in molecular aggregates and its application to light-harvesting systems.

    Science.gov (United States)

    Hyeon-Deuk, Kim; Tanimura, Yoshitaka; Cho, Minheang

    2007-08-21

    Effects of the exciton-exciton coherence transfer (EECT) in strongly coupled molecular aggregates are investigated from the reduced time-evolution equation which we have developed to describe EECT. Starting with the nonlinear response function, we obtained explicit contributions from EECT to four-wave-mixing spectrum such as photon echo, taking into account double exciton states, static disorder, and heat-bath coupling represented by arbitrary spectral densities. By using the doorway-window picture and the projection operator technique, the transfer rates between two different electronic coherent states are obtained within a framework of cumulant expansion at high temperature. Applications of the present theory to strongly coupled B850 chlorophylls in the photosynthetic light harvesting system II (LH2) are discussed. It is shown that EECT is indispensable in properly describing ultrafast phenomena of strongly coupled molecular aggregates such as LH2 and that the EECT contribution to the two-dimensional optical spectroscopy is not negligible.

  15. Efficient light harvesting by photon downconversion and light trapping in hybrid ZnS nanoparticles/Si nanotips solar cells.

    Science.gov (United States)

    Huang, Chun-Ying; Wang, Di-Yan; Wang, Chun-Hsiung; Chen, Yung-Ting; Wang, Yaw-Tyng; Jiang, You-Ting; Yang, Ying-Jay; Chen, Chia-Chun; Chen, Yang-Fang

    2010-10-26

    A hybrid colloidal ZnS nanoparticles/Si nanotips p-n active layer has been demonstrated to have promising potential for efficient solar spectrum utilization in crystalline silicon-based solar cells. The hybrid solar cell shows an enhancement of 20% in the short-circuit current and approximately 10% in power conversion efficiency compared to its counterpart without integrating ZnS nanoparticles. The enhancement has been investigated by external quantum efficiency, photoluminescence excitation spectrum, photoluminescence, and reflectance to distinct the role of ZnS quantum dots for light harvesting. It is concluded that ZnS nanoparticles not only act as frequency downconversion centers in the ultraviolet region but also serve as antireflection coating for light trapping in the measured spectral regime. Our approach is ready to be extended to many other material systems for the creation of highly efficient photovoltaic devices.

  16. Efficient light harvesting of a luminescent solar concentrator using excitation energy transfer from an aggregation-induced emitter.

    Science.gov (United States)

    Banal, James L; Ghiggino, Kenneth P; Wong, Wallace W H

    2014-12-14

    The compromise between light absorption and reabsorption losses limits the potential light conversion efficiency of luminescent solar concentrators (LSCs). Current approaches do not fully address both issues. By using the excitation energy transfer (EET) strategy with a donor chromophore that exhibits aggregation-induced emission (AIE) behaviour, it is shown that both transmission and reabsorption losses can be minimized in a LSC device achieving high light collection and concentration efficiencies. The light harvesting performance of the LSC developed has been characterized using fluorescence quantum yield measurements and Monte Carlo ray tracing simulations. Comparative incident photon conversion efficiency and short-circuit current data based on the LSC coupled to a silicon solar cell provide additional evidence for improved performance.

  17. Role of delocalized exciton states of light-harvesting pigments in excitation energy transfer in natural photosynthesis

    Science.gov (United States)

    Fetisova, Zoya; Mauring, Koit; Taisova, Alexandra

    1995-02-01

    Photosynthesis is an extremely efficient converter of light into chemical energy, with an observed quantum yield for primary photochemistry approximately 90%. To achieve this the photosynthetic apparatus must be highly optimized, and some of the design principles that may be involved have been suggested. The role of delocalized exciton states of light-harvesting pigments in the energy transfer process has been considered by mathematical simulation of the light-harvesting process in model systems. Namely, it has been shown that aggregation of antenna pigments (allowing to consider each aggregate as a supermolecule) is biologically expedient, as an efficient strategy for light harvesting in photosynthesis. The question of whether this design principle is realized in a natural antenna has been examined for the 3D chlorosomal superantenna of green bacteria with the hole-burning spectroscopy. Spectral hole burning studies of intact cells of green bacteria Chlorobium phaeovibriodes. Chloroflexus aurantiacus and Chlorobium limicola have proven that the Qy- absorption system of antenna bacteriochlorophylls e or c (BChl e or BChl c) should be interpreted in terms of the delocalized exciton level structure of an aggregate. For the first time the 0-0 transition band of the lowest exciton state of BChl e and BChl c aggregates has been directly detected as the lowest energy inhomogeneously broadened band of the 1.8 K near-infrared excitation spectrum. These lowest energy bands have different spectral position of their maximums: approximately 739 nm in C.phaeovibriodes (BChl e band), approximately 752 nm in C.aurantiacus (BChl c band) and approximately 774 nm in C.limicola (BChl c band) cells. However, these bands display a number of fundamentally similar spectral features: (1) The magnitude of inhomogeneous broadening of these bands is 90 - 100 cm-1; (2) The width of each band is 2 - 3 times less than that of the monomeric BChl c (or BChl e) in vitro at 5 K; (3) Each band

  18. Aperiodic TiO2 nanotube photonic crystal: full-visible-spectrum solar light harvesting in photovoltaic devices.

    Science.gov (United States)

    Guo, Min; Xie, Keyu; Wang, Yu; Zhou, Limin; Huang, Haitao

    2014-09-23

    Bandgap engineering of a photonic crystal is highly desirable for photon management in photonic sensors and devices. Aperiodic photonic crystals (APCs) can provide unprecedented opportunities for much more versatile photon management, due to increased degrees of freedom in the design and the unique properties brought about by the aperiodic structures as compared to their periodic counterparts. However, many efforts still remain on conceptual approaches, practical achievements in APCs are rarely reported due to the difficulties in fabrication. Here, we report a simple but highly controllable current-pulse anodization process to design and fabricate TiO2 nanotube APCs. By coupling an APC into the photoanode of a dye-sensitized solar cell, we demonstrate the concept of using APC to achieve nearly full-visible-spectrum light harvesting, as evidenced by both experimental and simulated results. It is anticipated that this work will lead to more fruitful practical applications of APCs in high-efficiency photovoltaics, sensors and optoelectronic devices.

  19. Light harvesting with Ge quantum dots embedded in SiO2 or Si3N4

    Science.gov (United States)

    Cosentino, Salvatore; Sungur Ozen, Emel; Raciti, Rosario; Mio, Antonio M.; Nicotra, Giuseppe; Simone, Francesca; Crupi, Isodiana; Turan, Rasit; Terrasi, Antonio; Aydinli, Atilla; Mirabella, Salvo

    2014-01-01

    Germanium quantum dots (QDs) embedded in SiO2 or in Si3N4 have been studied for light harvesting purposes. SiGeO or SiGeN thin films, produced by plasma enhanced chemical vapor deposition, have been annealed up to 850 °C to induce Ge QD precipitation in Si based matrices. By varying the Ge content, the QD diameter can be tuned in the 3-9 nm range in the SiO2 matrix, or in the 1-2 nm range in the Si3N4 matrix, as measured by transmission electron microscopy. Thus, Si3N4 matrix hosts Ge QDs at higher density and more closely spaced than SiO2 matrix. Raman spectroscopy revealed a higher threshold for amorphous-to-crystalline transition for Ge QDs embedded in Si3N4 matrix in comparison with those in the SiO2 host. Light absorption by Ge QDs is shown to be more effective in Si3N4 matrix, due to the optical bandgap (0.9-1.6 eV) being lower than in SiO2 matrix (1.2-2.2 eV). Significant photoresponse with a large measured internal quantum efficiency has been observed for Ge QDs in Si3N4 matrix when they are used as a sensitive layer in a photodetector device. These data will be presented and discussed, opening new routes for application of Ge QDs in light harvesting devices.

  20. Maximizing photosynthetic efficiency and culture productivity in cyanobacteria upon minimizing the phycobilisome light-harvesting antenna size.

    Science.gov (United States)

    Kirst, Henning; Formighieri, Cinzia; Melis, Anastasios

    2014-10-01

    A phycocyanin-deletion mutant of Synechocystis (cyanobacteria) was generated upon replacement of the CPC-operon with a kanamycin resistance cassette. The Δcpc transformant strains (Δcpc) exhibited a green phenotype, compared to the blue-green of the wild type (WT), lacked the distinct phycocyanin absorbance at 625nm, and had a lower Chl per cell content and a lower PSI/PSII reaction center ratio compared to the WT. Molecular and genetic analyses showed replacement of all WT copies of the Synechocystis DNA with the transgenic version, thereby achieving genomic DNA homoplasmy. Biochemical analyses showed the absence of the phycocyanin α- and β-subunits, and the overexpression of the kanamycin resistance NPTI protein in the Δcpc. Physiological analyses revealed a higher, by a factor of about 2, intensity for the saturation of photosynthesis in the Δcpc compared to the WT. Under limiting intensities of illumination, growth of the Δcpc was slower than that of the WT. This difference in the rate of cell duplication diminished gradually as growth irradiance increased. Identical rates of cell duplication of about 13h for both WT and Δcpc were observed at about 800μmolphotonsm(-2)s(-1) or greater. Culture productivity analyses under simulated bright sunlight and high cell-density conditions showed that biomass accumulation by the Δcpc was 1.57-times greater than that achieved by the WT. Thus, the work provides first-time direct evidence of the applicability of the Truncated Light-harvesting Antenna (TLA)-concept in cyanobacteria, entailing substantial improvements in the photosynthetic efficiency and productivity of mass cultures upon minimizing the phycobilisome light-harvesting antenna size.

  1. Engineering Chemically Exfoliated Large-Area Two-Dimensional MoS2 Nanolayers with Porphyrins for Improved Light Harvesting.

    Science.gov (United States)

    Zhang, Hanyu; Choi, Jungwook; Ramani, Arjun; Voiry, Damien; Natoli, Sean N; Chhowalla, Manish; McMillin, David R; Choi, Jong Hyun

    2016-09-19

    Molybdenum disulfide (MoS2 ) is a promising candidate for electronic and optoelectronic applications. However, its application in light harvesting has been limited in part due to crystal defects, often related to small crystallite sizes, which diminish charge separation and transfer. Here we demonstrate a surface-engineering strategy for 2D MoS2 to improve its photoelectrochemical properties. Chemically exfoliated large-area MoS2 thin films were interfaced with eight molecules from three porphyrin families: zinc(II)-, gallium(III)-, iron(III)-centered, and metal-free protoporphyrin IX (ZnPP, GaPP, FePP, H2 PP); metal-free and zinc(II) tetra-(N-methyl-4-pyridyl)porphyrin (H2 T4, ZnT4); and metal-free and zinc(II) tetraphenylporphyrin (H2 TPP, ZnTPP). We found that the photocurrents from MoS2 films under visible-light illumination are strongly dependent on the interfacial molecules and that the photocurrent enhancement is closely correlated with the highest occupied molecular orbital (HOMO) levels of the porphyrins, which suppress the recombination of electron-hole pairs in the photoexcited MoS2 films. A maximum tenfold increase was observed for MoS2 functionalized with ZnPP compared with pristine MoS2 films, whereas ZnT4-functionalized MoS2 demonstrated small increases in photocurrent. The application of bias voltage on MoS2 films can further promote photocurrent enhancements and control current directions. Our results suggest a facile route to render 2D MoS2 films useful for potential high-performance light-harvesting applications.

  2. Fingerprinting the macro-organisation of pigment-protein complexes in plant thylakoid membranes in vivo by circular-dichroism spectroscopy.

    Science.gov (United States)

    Tóth, Tünde N; Rai, Neha; Solymosi, Katalin; Zsiros, Ottó; Schröder, Wolfgang P; Garab, Győző; van Amerongen, Herbert; Horton, Peter; Kovács, László

    2016-09-01

    Macro-organisation of the protein complexes in plant thylakoid membranes plays important roles in the regulation and fine-tuning of photosynthetic activity. These delicate structures might, however, undergo substantial changes during isolating the thylakoid membranes or during sample preparations, e.g., for electron microscopy. Circular-dichroism (CD) spectroscopy is a non-invasive technique which can thus be used on intact samples. Via excitonic and psi-type CD bands, respectively, it carries information on short-range excitonic pigment-pigment interactions and the macro-organisation (chiral macrodomains) of pigment-protein complexes (psi, polymer or salt-induced). In order to obtain more specific information on the origin of the major psi-type CD bands, at around (+)506, (-)674 and (+)690nm, we fingerprinted detached leaves and isolated thylakoid membranes of wild-type and mutant plants and also tested the effects of different environmental conditions in vivo. We show that (i) the chiral macrodomains disassemble upon mild detergent treatments, but not after crosslinking the protein complexes; (ii) in different wild-type leaves of dicotyledonous and monocotyledonous angiosperms the CD features are quite robust, displaying very similar excitonic and psi-type bands, suggesting similar protein composition and (macro-) organisation of photosystem II (PSII) supercomplexes in the grana; (iii) the main positive psi-type bands depend on light-harvesting protein II contents of the membranes; (iv) the (+)506nm band appears only in the presence of PSII-LHCII supercomplexes and does not depend on the xanthophyll composition of the membranes. Hence, CD spectroscopy can be used to detect different macro-domains in the thylakoid membranes with different outer antenna compositions in vivo.

  3. Versatile design of biohybrid light-harvesting architectures to tune location, density, and spectral coverage of attached synthetic chromophores for enhanced energy capture.

    Science.gov (United States)

    Harris, Michelle A; Jiang, Jianbing; Niedzwiedzki, Dariusz M; Jiao, Jieying; Taniguchi, Masahiko; Kirmaier, Christine; Loach, Paul A; Bocian, David F; Lindsey, Jonathan S; Holten, Dewey; Parkes-Loach, Pamela S

    2014-07-01

    Biohybrid antennas built upon chromophore-polypeptide conjugates show promise for the design of efficient light-capturing modules for specific purposes. Three new designs, each of which employs analogs of the β-polypeptide from Rhodobacter sphaeroides, have been investigated. In the first design, amino acids at seven different positions on the polypeptide were individually substituted with cysteine, to which a synthetic chromophore (bacteriochlorin or Oregon Green) was covalently attached. The polypeptide positions are at -2, -6, -10, -14, -17, -21, and -34 relative to the 0-position of the histidine that coordinates bacteriochlorophyll a (BChl a). All chromophore-polypeptides readily formed LH1-type complexes upon combination with the α-polypeptide and BChl a. Efficient energy transfer occurs from the attached chromophore to the circular array of 875 nm absorbing BChl a molecules (denoted B875). In the second design, use of two attachment sites (positions -10 and -21) on the polypeptide affords (1) double the density of chromophores per polypeptide and (2) a highly efficient energy-transfer relay from the chromophore at -21 to that at -10 and on to B875. In the third design, three spectrally distinct bacteriochlorin-polypeptides were prepared (each attached to cysteine at the -14 position) and combined in an ~1:1:1 mixture to form a heterogeneous mixture of LH1-type complexes with increased solar coverage and nearly quantitative energy transfer from each bacteriochlorin to B875. Collectively, the results illustrate the great latitude of the biohybrid approach for the design of diverse light-harvesting systems.

  4. Distance-Dependent Long-Range Electron Transfer in Protein: a Case Study of Photosynthetic Bacterial Light-Harvesting Antenna Complex LH2 Assembled on TiO2 Nanoparticle by Femto-Second Time-Resolved Spectroscopy%应用飞秒时间分辨瞬态吸收光谱研究蛋白质中距离相关长程电荷转移:光合细菌天线复合体LH2与TiO2纳米颗粒超分子组装体个例初探

    Institute of Scientific and Technical Information of China (English)

    翁羽翔; 张蕾; 杨健; 全冬晖; 汪力; 杨国桢; 藤井律子; 小山泰; 张建平; 冯娟; 余军华; 张宝文

    2003-01-01

    The function of protein in long-range biological electron transfer is a question of debate. We report some preliminary results in femtosecond spectroscopic study of photosynthetic bacterial light-harvesting antenna complex assembled onto TiO2 nanoparticle with an average size of 8 nm in diameter. Crystal structure shows that photosynthetic bacterial antenna complex LH2 has a ring-like structure composed by α- and β-apoprotein helices. The α- and β-transmembrance helices construct two concentric cylinders with pigments bacteriochlorophyll a (Bchl a) and carotenoid (Car) buried inside the protein. We attempt to insert TiO2 nanoparticle into the cavity of the inner cylindrical hollow of LH2 to investigate the nature of the electron transfer between the excited-state Bchl a and the TiO2 nanoparticle. A significant decrease in the ground state bleaching recovery time constant for Bchl a at 850 nm (B850) in respect to that of the Bchl a in free LH2 has been observed. By using the relation of distance-dependent long-range electron transfer rate in protein, the distance between the donor B850 and the acceptor TiO2 nanoparticle has been estimated, which is about 0.6 nm. The proposed method of assembling proteins onto wide-gap semiconductor nanoparticle can be a promising way to determine the role of the protein playing in biological electron transfer processes.%蛋白质在生物体内电荷转移过程中所起的作用迄今仍然是一个有争议的问题.其争论焦点是蛋白质在生物电荷转移过程中是否提供特殊的电子传递通道或者是仅仅作为普通的有机介质.应用飞秒时间分辨瞬态吸收光谱研究由光合细菌天线分子和平均粒径为8 nm的TiO2组装而成的超分子系统中长程电荷转移.晶体结构研究表明,光合细菌天线分子具有由多个α-脱辅基和β-脱辅基蛋白跨膜螺旋构成的双层空心柱面体结构,其中α-脱辅基蛋白跨膜螺旋构成的小环状体套于β-脱辅基蛋

  5. Using complex plant pedigrees to map valuable genes

    NARCIS (Netherlands)

    Jannink, Jean-Luc; Bink, Marco C.A.M.; Jansen, Ritsert C.

    2001-01-01

    Statistical methods pioneered by human and animal geneticists use marker and pedigree information to detect quantitative trait loci within complex pedigrees. These methods, adapted to plants, promise to expand the range of data useful for identifying the genetic factors influencing plant growth, dev

  6. Using Plants to Explore the Nature & Structural Complexity of Life

    Science.gov (United States)

    Howard, Ava R.

    2014-01-01

    Use of real specimens brings the study of biology to life. This activity brings easily acquired plant specimens into the classroom to tackle common alternative conceptions regarding life, size, complexity, the nature of science, and plants as multicellular organisms. The activity occurs after a discussion of the characteristics of life and engages…

  7. Using Plants to Explore the Nature & Structural Complexity of Life

    Science.gov (United States)

    Howard, Ava R.

    2014-01-01

    Use of real specimens brings the study of biology to life. This activity brings easily acquired plant specimens into the classroom to tackle common alternative conceptions regarding life, size, complexity, the nature of science, and plants as multicellular organisms. The activity occurs after a discussion of the characteristics of life and engages…

  8. Targeted Interactomics in Plants Through Protein Complex Isolation

    Institute of Scientific and Technical Information of China (English)

    Geert De Jaeger

    2012-01-01

    TAPtag technology is the most widely applied tool to pick up in situ protein interactions in a proteome wide setting.Our research team has developed a versatile TAP technology platform for protein complex isolation from plants.We isolated complexes for hundreds of proteins and extensively demonstrated the power of our technology for protein discovery,functional analysis of proteins and protein complexes,and the modelling of protein networks.Complexes are purified from Arabidopsis cell suspension cultures or seedlings and we are currently translating the technology towards crop plants to bring complex purification in a developmental context.Besides protein complexes,we are deriving protocol variations to isolate chromatin complexes.

  9. Thermal treatment synthesis of SnO2 nanoparticles and investigation of its light harvesting application

    Science.gov (United States)

    Dadkhah, Mahnaz; Ansari, Fatemeh; Salavati-Niasari, Masoud

    2016-07-01

    In this research, nanostructured SnO2 materials have been prepared via thermal treatment method with the aid of new Schiff base complex. N, N'-bis(salicylidene)-1,2-propylenediamine (H2salpn) has been used as Schiff base to prepare a new Schiff base complex. The products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and TEM. Then, as-prepared SnO2 nanoparticles have been applied as working electrode in dye-sensitized solar cells sensitizing with two different natural dyes: madder and mignonette.

  10. SORPTION PROPERTIES OF PLANT POLYSACCHARIDE COMPLEXES

    Directory of Open Access Journals (Sweden)

    L. E. Glagoleva

    2012-01-01

    Full Text Available The article presents information on the laws of the sorption of water to grow-negative polysaccharide complexes of the pumpkin and briar, deter-mined the rate constant of swelling as a function of temperature and pH, the maximum degree of swelling and limit the time to achieve it.

  11. Semiconductor Nanocrystals for New-generation Lightening and Light Harvesting Applications

    Energy Technology Data Exchange (ETDEWEB)

    Acharya, Krishna [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2015-02-20

    Research works: I. QDs: CdSe/ZnSe and ZnSe/CdS; Synthetic complexities and mitigations. II. Photovoltaics: PLD graphite counter electrode; PbS, PbSe sensitization on TiO2; NW sensitized solar cell. III. Photocatalysis:ZnSe/CdS/Pt & ZnTe/CdS/Pt

  12. A nanoscale bio-inspired light-harvesting system developed from self-assembled alkyl-functionalized metallochlorin nano-aggregates

    KAUST Repository

    Ocakoǧlu, Kasim

    2014-01-01

    Self-assembled supramolecular organization of nano-structured biomimetic light-harvesting modules inside solid-state nano-templates can be exploited to develop excellent light-harvesting materials for artificial photosynthetic devices. We present here a hybrid light-harvesting system mimicking the chlorosomal structures of the natural photosynthetic system using synthetic zinc chlorin units (ZnChl-C6, ZnChl-C12 and ZnChl-C 18) that are self-aggregated inside the anodic aluminum oxide (AAO) nano-channel membranes. AAO nano-templates were modified with a TiO2 matrix and functionalized with long hydrophobic chains to facilitate the formation of supramolecular Zn-chlorin aggregates. The transparent Zn-chlorin nano-aggregates inside the alkyl-TiO2 modified AAO nano-channels have a diameter of ∼120 nm in a 60 μm length channel. UV-Vis studies and fluorescence emission spectra further confirm the formation of the supramolecular ZnChl aggregates from monomer molecules inside the alkyl-functionalized nano-channels. Our results prove that the novel and unique method can be used to produce efficient and stable light-harvesting assemblies for effective solar energy capture through transparent and stable nano-channel ceramic materials modified with bio-mimetic molecular self-assembled nano-aggregates. © 2014 the Partner Organisations.

  13. Tunable and highly efficient light-harvesting antenna systems based on 1,7-perylene-3,4,9,10-tetracarboxylic acid derivatives

    NARCIS (Netherlands)

    Dubey,R.K.; Inan, D.; Sengupta, S.; Sudhölter,E.J.R.; Grozema, F.C.; Jager, W.F.

    2016-01-01

    We report the synthesis and excited-state dynamics of a series of five bichromophoric light-harvesting antenna systems, which are capable of efficient harvesting of solar energy in the spectral range of 350–580 nm. These antenna systems have been synthesized in a modular fashion by the covalent

  14. How can the green sulfur bacteria use quantum computing for light harvesting?

    CERN Document Server

    Drakova, D

    2016-01-01

    Long lasting coherence in photosynthetic pigment-protein complexes has been observed even at physiological temperatures. Experiments have demonstrated quantum coherent behaviour in the long-time operation of the D-Wave quantum computer as well. Quantum coherence is the common feature between the two phenomena. An explanations for eight orders of magnitude discrepancy between the single flux qubit coherence time and the long-time quantum behaviour of an array of thousand flux qubits in the quantum computer was suggested within a theory where the flux qubits are coupled to an environment of particles called gravonons of high density of states The coherent evolution is in high dimensional spacetime and can be understood as a solution of Schroedinger's time-dependent equation. Explanations for the quantum beats observed in 2D Fourier transform electronic spectroscopy of the Fenna-Matthews-Olson (FMO) protein complex in the green sulfur bacteria are presently sought in constructing transport theories based on quan...

  15. Cooperative Subunit Refolding of a Light-Harvesting Protein through a Self-Chaperone Mechanism.

    Science.gov (United States)

    Laos, Alistair J; Dean, Jacob C; Toa, Zi S D; Wilk, Krystyna E; Scholes, Gregory D; Curmi, Paul M G; Thordarson, Pall

    2017-01-27

    The fold of a protein is encoded by its amino acid sequence, but how complex multimeric proteins fold and assemble into functional quaternary structures remains unclear. Here we show that two structurally different phycobiliproteins refold and reassemble in a cooperative manner from their unfolded polypeptide subunits, without biological chaperones. Refolding was confirmed by ultrafast broadband transient absorption and two-dimensional electronic spectroscopy to probe internal chromophores as a marker of quaternary structure. Our results demonstrate a cooperative, self-chaperone refolding mechanism, whereby the β-subunits independently refold, thereby templating the folding of the α-subunits, which then chaperone the assembly of the native complex, quantitatively returning all coherences. Our results indicate that subunit self-chaperoning is a robust mechanism for heteromeric protein folding and assembly that could also be applied in self-assembled synthetic hierarchical systems.

  16. A small polypeptide triggers complete degradation of light-harvesting phycobiliproteins in nutrient-deprived cyanobacteria.

    Science.gov (United States)

    Collier, J L; Grossman, A R

    1994-03-01

    Phycobilisomes are the multiprotein complexes predominantly responsible for harvesting light energy in cyanobacteria and some eukaryotic algae. When the cyanobacterium Synechococcus sp. strain PCC 7942 is deprived of an essential nutrient, the phycobilisomes are specifically and rapidly degraded. Degradation may be either partial (after phosphorus deprivation) or complete (after sulfur or nitrogen deprivation). We have developed a visual screen to obtain mutants unable to degrade their phycobilisomes upon nutrient starvation. Complementation of one of these mutants led to the identification of a gene, designated nblA, that encodes a 59 amino acid polypeptide essential for phycobilisome degradation. Transcription of nblA increases dramatically in sulfur- or nitrogen-deprived cells and moderately in phosphorus-deprived cells. Using the phosphorus-regulated alkaline phosphatase (phoA) promoter as a tool, we engineered constructs from which we could control the expression of either sense or antisense nblA. Increased expression of sense nbLA caused complete phycobilisome degradation during phosphorus deprivation, while expression of antisense nblA prevented phycobilisome degradation. Hence, nblA is necessary, and may be sufficient, for the degradation of phycobilisomes under adverse environmental conditions. Further investigation of the mechanism by which nblA causes phycobilisome destruction may reveal general principles that govern the specificity of macromolecular complex degradation.

  17. Photoactive Nanomaterials Inspired by Nature: LTL Zeolite Doped with Laser Dyes as Artificial Light Harvesting Systems

    Directory of Open Access Journals (Sweden)

    Leire Gartzia-Rivero

    2017-05-01

    Full Text Available The herein reported work describes the development of hierarchically-organized fluorescent nanomaterials inspired by plant antenna systems. These hybrid materials are based on nanostructured zeolitic materials (LTL zeolite doped with laser dyes, which implies a synergism between organic and inorganic moieties. The non-interconnected channeled structure and pore dimensions (7.1 Å of the inorganic host are ideal to order and align the allocated fluorophores inside, inferring also high thermal and chemical stability. These artificial antennae harvest a broad range of chromatic radiation and convert it into predominant red-edge or alternatively white-light emission, just choosing the right dye combination and concentration ratio to modulate the efficiency of the ongoing energy transfer hops. A further degree of organization can be achieved by functionalizing the channel entrances of LTL zeolite with specific tailor-made (stopcock molecules via a covalent linkage. These molecules plug the channels to avoid the leakage of the guest molecules absorbed inside, as well as connect the inner space of the zeolite with the outside thanks to energy transfer processes, making the coupling of the material with external devices easier.

  18. Vibronic resonances sustain excited state coherence in light harvesting proteins at room temperature

    CERN Document Server

    Novelli, Fabio; Roozbeh, Ashkan; Wilk, Krystyna E; Curmi, Paul M G; Davis, Jeffrey A

    2015-01-01

    Until recently it was believed that photosynthesis, a fundamental process for life on earth, could be fully understood with semi-classical models. However, puzzling quantum phenomena have been observed in several photosynthetic pigment-protein complexes, prompting questions regarding the nature and role of these effects. Recent attention has focused on discrete vibrational modes that are resonant or quasi-resonant with excitonic energy splittings and strongly coupled to these excitonic states. Here we report a series of experiments that unambiguously identify excited state coherent superpositions that dephase on the timescale of the excited state lifetime. Low energy (56 cm-1) oscillations on the signal intensity provide direct experimental evidence for the role of vibrational modes resonant with excitonic splittings in sustaining coherences involving different excited excitonic states at physiological temperature.

  19. Ultrafast pump-probe spectroscopy of Zinc Phthalocynine (ZnPc) and light harvesting complex II (LHC II)

    CSIR Research Space (South Africa)

    Ombinda-Lemboumba, Saturnin

    2009-07-01

    Full Text Available The presentation discusses basic principles of pump-probe technique, possible transient absorption signals, LHC II and ZnPc, experimental setup, chirp measurement and correction methods. The results of the study, conclusion and future work are also...

  20. Femtosecond pump probe spectroscopy for the study of energy transfer of light-harvesting complexes from extractions of spinach leaves

    CSIR Research Space (South Africa)

    Ombinda-Lemboumba, Saturnin

    2009-09-01

    Full Text Available :sapphire femtosecond oscillator (Coherent Mira 900-F), operating at a repetition rate of 76 MHz and pumped by the 5 W output of a continuous diode-pumped Nd:YVO4 laser (Coherent Verdi V5), produced pulses of approximately 130 fs duration, as measured by a home...

  1. Kinetics and heterogeneity of energy transfer from light harvesting complex II to photosystem I in the supercomplex isolated from Arabidopsis.

    Science.gov (United States)

    Santabarbara, Stefano; Tibiletti, Tania; Remelli, William; Caffarri, Stefano

    2017-03-29

    State transitions are a phenomenon that maintains the excitation balance between photosystem II (PSII) and photosystem I (PSI-LHCI) by controlling their relative absorption cross-sections. Under light conditions exciting PSII preferentially, a trimeric LHCII antenna moves from PSII to PSI-LHCI to form the PSI-LHCI-LHCII supercomplex. In this work, the excited state dynamics in the PSI-LHCI and PSI-LHCI-LHCII supercomplexes isolated from Arabidopsis have been investigated by picosecond time-resolved fluorescence spectroscopy. The excited state decays were analysed using two approaches based on either (i) a sum of discrete exponentials or (ii) a continuous distribution of lifetimes. The results indicate that the energy transfer from LHCII to the bulk of the PSI antenna occurs with an average macroscopic transfer rate in the 35-65 ns(-1) interval. Yet, the most satisfactory description of the data is obtained when considering a heterogeneous population containing two PSI-LHCI-LHCII supercomplexes characterised by a transfer time of ∼15 and ∼60 ns(-1), likely due to the differences in the strength and orientation of LHCII harboured to PSI. Both these values are of the same order of magnitude of those estimated for the average energy transfer rates from the low energy spectral forms of LHCI to the bulk of the PSI antenna (15-40 ns(-1)), but they are slower than the transfer from the bulk antenna of PSI to the reaction centre (>150 ns(-1)), implying a relatively small kinetics bottleneck for the energy transfer from LHCII. Nevertheless, the kinetic limitation imposed by excited state diffusion has a negligible impact on the photochemical quantum efficiency of the supercomplex, which remains about 98% in the case of PSI-LHCI.

  2. Plant polyadenylation factors: conservation and variety in the polyadenylation complex in plants.

    Science.gov (United States)

    Hunt, Arthur G; Xing, Denghui; Li, Qingshun Q

    2012-11-20

    Polyadenylation, an essential step in eukaryotic gene expression, requires both cis-elements and a plethora of trans-acting polyadenylation factors. The polyadenylation factors are largely conserved across mammals and fungi. The conservation seems also extended to plants based on the analyses of Arabidopsis polyadenylation factors. To extend this observation, we systemically identified the orthologs of yeast and human polyadenylation factors from 10 plant species chosen based on both the availability of their genome sequences and their positions in the evolutionary tree, which render them representatives of different plant lineages. The evolutionary trajectories revealed several interesting features of plant polyadenylation factors. First, the number of genes encoding plant polyadenylation factors was clearly increased from "lower" to "higher" plants. Second, the gene expansion in higher plants was biased to some polyadenylation factors, particularly those involved in RNA binding. Finally, while there are clear commonalities, the differences in the polyadenylation apparatus were obvious across different species, suggesting an ongoing process of evolutionary change. These features lead to a model in which the plant polyadenylation complex consists of a conserved core, which is rather rigid in terms of evolutionary conservation, and a panoply of peripheral subunits, which are less conserved and associated with the core in various combinations, forming a collection of somewhat distinct complex assemblies. The multiple forms of plant polyadenylation complex, together with the diversified polyA signals may explain the intensive alternative polyadenylation (APA) and its regulatory role in biological functions of higher plants.

  3. Assembly of Photosynthetic Antenna Protein / Pigments Complexes from Algae and Plants for Development of Nanobiodevices

    Science.gov (United States)

    2012-07-10

    bacterial photosynthesis . The structure of the reaction center (RC, the first membrane protein to have its structure determined to high resolution) revealed...the mechanisms of efficient light -harvesting but also those of photo-protection. In order to understand these reactions both structural and functional...binding protein and its effect on the stability of reconstituted light -harvesting core antenna complex” , Photosynthesis Res.. 111,63-69(2012)(Doi

  4. Triplet excitons in natural photosynthetic and artificial light harvesting systems: Measurement and modeling

    Science.gov (United States)

    Hartzler, Daniel Allen

    Under full sunlight, unprotected (Bacterio)Chlorophyll ((B)Chl) molecules photodegrade in a matter of minutes. This is the result of the generation of highly reactive singlet oxygen (1O2) by energy transfer from the (B)Chl triplet state (3(B)Chl) to the oxygen ground state. Natural photosynthetic systems must protect themselves from 1O2, typically done by positioning carotenoids within a few angstroms of each (B)Chl molecule to quench 3(B)Chl states. Using phosphorescence spectroscopy and computational modeling, we investigated alternative, carotenoid independent, mechanisms which nature may employ to prevent 1O2 sensitization by lowering the energy of 3(B)Chl below that of 1O2. The two proposed triplet lowering mechanisms investigated were: triplet state lowering by strong pigment-pigment interactions (i.e. triplet exciton formation) and triplet state lowering by pigment-protein interactions. Possible natural examples employing these mechanisms are two structures found in green sulfur bacteria: the chlorosome (an antenna containing ~100000 coupled BChl c, d, or e molecules with unexpectedly high photostability) and the Fenna-Matthews-Olson (FMO) complex (an auxiliary antenna containing eight seemingly unprotected BChl a molecules). Measurements performed on linear aggregates of the dye perylene diimide (PDI) show that triplet exciton formation does reduce the triplet state energy. However, direct measurement of triplet state energies for the chlorosome and FMO complex proved experimentally difficult, thus an alternative approach was used to calculate these energies using empirical and excitonic models. Since the use of excitonic modeling requires knowledge of both the pigment site energies and the pigment-pigment interactions (i.e. couplings), work was performed to catalog the monomeric singlet and triplet state energies of all known natural (B)Chl pigments by direct measurement or computational modeling and to characterize the triplet-triplet (T-T) coupling in

  5. Consecutive binding of chlorophylls a and b during the assembly in vitro of light-harvesting chlorophyll-a/b protein (LHCIIb).

    Science.gov (United States)

    Horn, Ruth; Grundmann, Götz; Paulsen, Harald

    2007-02-23

    The apoprotein of the major light-harvesting chlorophyll a/b complex (LHCIIb) is post-translationally imported into the chloroplast, where membrane insertion, protein folding, and pigment binding take place. The sequence and molecular mechanism of the latter steps is largely unknown. The complex spontaneously self-organises in vitro to form structurally authentic LHCIIb upon reconstituting the unfolded recombinant protein with the pigments chlorophyll a, b, and carotenoids in detergent micelles. Former measurements of LHCIIb assembly had revealed two apparent kinetic phases, a faster one (tau1) in the range of 10 s to 1 min, and a slower one (tau2) in the range of several min. To unravel the sequence of events we analysed the binding of chlorophylls into the complex by using time-resolved fluorescence measurements of resonance energy transfer from chlorophylls to an acceptor dye attached to the apoprotein. Chlorophyll a, offered in the absence of chlorophyll b, bound with the faster kinetics (tau1) exclusively whereas chlorophyll b, in the absence of chlorophyll a, bound predominantly with the slower kinetics (tau2). In double-jump experiments, LHCIIb assembly could be dissected into a faster chlorophyll a and a subsequent, predominantly slower chlorophyll b-binding step. The assignment of the faster and the slower kinetic phase to predominantly chlorophyll a and exclusively chlorophyll b binding, respectively, was verified by analysing the assembly kinetics with a circular dichroism signal in the visible domain presumably reflecting the establishment of pigment-pigment interactions. We propose that slow chlorophyll binding is confined to the exclusively chlorophyll b binding sites whereas faster binding occurs to the chlorophyll a binding sites. The latter sites can bind both chlorophylls a and b but in a reversible fashion as long as the complex is not stabilised by proper occupation of the chlorophyll b sites. The resulting two-step model of LHCIIb assembly is

  6. Electrospray-assisted characterization and deposition of chlorosomes to fabricate a biomimetic light-harvesting device

    Energy Technology Data Exchange (ETDEWEB)

    Modesto-Lopez, Luis B.; Thimsen, Elijah J.; Collins, Aaron M.; Blankenship, R. E.; Biswas, Pratim

    2010-01-01

    Photosynthesis is an efficient process by which solar energy is converted into chemical energy. Green photosynthetic bacteria such as Chloroflexus aurantiacus have supramolecular antenna complexes called chlorosomes attached to their cytoplasmic membrane that increase the cross section for light absorption even in low-light conditions. Self-assembled bacteriochlorophyll pigments in the chlorosome interior play a key role in the efficient transfer and funneling of the harvested energy. In this work it was demonstrated that chlorosomes can be rapidly and precisely size-characterized online in real time using an electrospray-assisted mobility-based technique. Chlorosomes were electrospray-deposited onto TiO{sub 2} nanostructured films with columnar morphology to fabricate a novel biomimetic device to overcome the solvent compatibility issues associated with biological particles and synthetic dyes. The assembled unit retained the viability of the chlorosomes, and the harvesting of sunlight over a broader range of wavelengths was demonstrated. It was shown that the presence of chlorosomes in the biomimetic device had a 30-fold increase in photocurrent.

  7. Efficiency of light harvesting in a photosynthetic bacterium adapted to different levels of light.

    Science.gov (United States)

    Timpmann, Kõu; Chenchiliyan, Manoop; Jalviste, Erko; Timney, John A; Hunter, C Neil; Freiberg, Arvi

    2014-10-01

    In this study, we use the photosynthetic purple bacterium Rhodobacter sphaeroides to find out how the acclimation of photosynthetic apparatus to growth conditions influences the rates of energy migration toward the reaction center traps and the efficiency of charge separation at the reaction centers. To answer these questions we measured the spectral and picosecond kinetic fluorescence responses as a function of excitation intensity in membranes prepared from cells grown under different illumination conditions. A kinetic model analysis yielded the microscopic rate constants that characterize the energy transfer and trapping inside the photosynthetic unit as well as the dependence of exciton trapping efficiency on the ratio of the peripheral LH2 and core LH1 antenna complexes, and on the wavelength of the excitation light. A high quantum efficiency of trapping over 80% was observed in most cases, which decreased toward shorter excitation wavelengths within the near infrared absorption band. At a fixed excitation wavelength the efficiency declines with the LH2/LH1 ratio. From the perspective of the ecological habitat of the bacteria the higher population of peripheral antenna facilitates growth under dim light even though the energy trapping is slower in low light adapted membranes. The similar values for the trapping efficiencies in all samples imply a robust photosynthetic apparatus that functions effectively at a variety of light intensities. Copyright © 2014 Elsevier B.V. All rights reserved.

  8. Screening π-conjugated bridges of organic dyes for dye-sensitized solar cells with panchromatic visible light harvesting

    Science.gov (United States)

    Yang, Zhenqing; Liu, Chunmeng; Shao, Changjin; Zeng, Xiaofei; Cao, Dapeng

    2016-07-01

    Developing highly efficient organic dyes with panchromatic visible light harvesting for dye-sensitized solar cells (DSSCs) is still one of the most important scientific challenges. Here, we design a series of phenothiazine derivative organic dyes with donor-π-acceptor (D-π-A) structure using density functional theory (DFT) and time-dependent DFT (TDDFT) based on experimentally synthesized typical SH-6 organic dyes. Results indicate that the newly designed BUCT13 - BUCT30 dyes show smaller HOMO-LUMO energy gaps, higher molar extinction coefficients and obvious redshifts compared to the SH-6 dye, and the maximum absorption peaks of eight dyes are greater than 650 nm among the newly designed dyes. In particular, BUCT27 exhibits a 234 nm redshift and the maximum molar extinction coefficient with an increment of about 80% compared to the SH-6 dye. BUCT19 exhibits not only a 269 nm redshift and higher molar extinction coefficient with an increment of about 50% compared to the SH-6 dye, but the extremely broad absorption spectrum covering the entire visible range up to the near-IR region of 1200 nm. It is expected that this work can provide a new strategy and guidance for the investigation of these dye-sensitized devices.

  9. Broadband and omnidirectional light harvesting enhancement in photovoltaic devices with aperiodic TiO2 nanotube photonic crystal

    Science.gov (United States)

    Guo, Min; Su, Haijun; Zhang, Jun; Liu, Lin; Fu, Nianqing; Yong, Zehui; Huang, Haitao; Xie, Keyu

    2017-03-01

    Design of more effective broadband light-trapping elements to improve the light harvesting efficiency under both normal and tilted light for solar cells and other photonic devices is highly desirable. Herein we present a theoretical analysis on the optical properties of a novel TiO2 nanotube aperiodic photonic crystal (NT APC) following an aperiodic sequences and its photocurrent enhancement effect for dye-sensitized solar cells (DSSCs) under various incidence angles. It is found that, compared to regular PC, the designed TiO2 NT APC owns broader reflection region and a desired omnidirectional reflection (ODR) bandgaps, leading to considerable and stable photocurrent enhancement under both normal and oblique light. The effects of the structural parameters of the TiO2 NT APC, including the average lattice constant and the common sequence difference, on the optical properties, ODR bandgaps and absorption magnification of the integrated DSSCs are investigated in detail. Moreover, the angular dependence of photocurrent enhancement and angular compensation effect of such TiO2 NT APCs are also provided to offer a guidance on the optimum structural parameters design under different engineering application conditions.

  10. Theoretical design of multi-colored semi-transparent organic solar cells with both efficient color filtering and light harvesting.

    Science.gov (United States)

    Wen, Long; Chen, Qin; Sun, Fuhe; Song, Shichao; Jin, Lin; Yu, Yan

    2014-11-13

    Solar cells incorporated with multi-coloring capability not only offer an aesthetic solution to bridge the gap between solar modules and building decorations but also open up the possibility for self-powered colorful display. In this paper, we proposed a multi-colored semi-transparent organic solar cells (TOSCs) design containing metallic nanostructures with the both high color purity and efficiency based on theoretical considerations. By employing guided mode resonance effect, the multi-colored TOSC behave like an efficient color filter that selectively transmits light with the desired wavelengths and generates electricity with light of other wavelengths. Broad range of coloring and luminosity adjusting for the transmission light can be achieved by simply tuning the period and the duty cycle of the metallic nanostructures. Furthermore, accompanying with the efficient color filtering characteristics, the optical absorption of TOSCs was improved due to the marked suppression of transmission loss at the off-resonance wavelengths and the increased light trapping in TOSCs. The mechanisms of the light guiding in photoactive layer and broadband backward scattering from the metallic nanostructures were identified to make an essential contribution to the improved light-harvesting. By enabling efficient color control and high efficiency simultaneously, this approach holds great promise for future versatile photovoltaic energy utilization.

  11. Facile synthesis of light harvesting semiconductor bismuth oxychloride nano photo-catalysts for efficient removal of hazardous organic pollutants.

    Science.gov (United States)

    Seddigi, Zaki S; Gondal, Mohammed A; Baig, Umair; Ahmed, Saleh A; Abdulaziz, M A; Danish, Ekram Y; Khaled, Mazen M; Lais, Abul

    2017-01-01

    In the present work, bismuth oxychloride nanoparticles-a light harvesting semiconductor photocatalyst-were synthesized by a facile hydrolysis route, with sodium bismuthate and hydroxylammonium chloride as the precursor materials. The as-synthesized semiconductor photocatalysts were characterized using X-ray diffraction analysis, Fourier transform infra-red spectroscopy, Raman spectroscopy, Field emission scanning electron microscopy, X-ray photoelectron spectroscopy and Photoluminescence spectroscopy techniques. The crystal structure, morphology, composition, and optical properties of these facile synthesized bismuth oxychloride nanoparticles (BiOCl NPs) were compared to those of traditional bismuth oxychloride. In addition, the photocatalytic performance of facile-synthesized BiOCl NPs and traditional BiOCl, as applied to the removal of hazardous organic dyes under visible light illumination, is thoroughly investigated. Our results reveal that facile-synthesized BiOCl NPs display strong UV-Vis light adsorption, improved charge carrier mobility and an inhibited rate of charge carrier recombination, when compared to traditional BiOCl. These enhancements result in an improved photocatalytic degradation rate of hazardous organic dyes under UV-Vis irradiance. For instance, the facile-synthesized BiOCl NPs attained 100% degradation of methylene blue and methyl orange dyes in approximately 30 mins under UV-Vis irradiation, against 55% degradation for traditional BiOCl under similar experimental conditions.

  12. Vibronic coupling explains the ultrafast carotenoid-to-bacteriochlorophyll energy transfer in natural and artificial light harvesters

    Energy Technology Data Exchange (ETDEWEB)

    Perlík, Václav; Seibt, Joachim; Šanda, František; Mančal, Tomáš [Institute of Physics, Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 5, Prague 121 16 (Czech Republic); Cranston, Laura J.; Cogdell, Richard J. [Institute of Molecular Cell and System Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow Biomedical Research Centre, 120 University Place, Glasgow G12 8TA, Scotland (United Kingdom); Lincoln, Craig N.; Hauer, Jürgen, E-mail: juergen.hauer@tuwien.ac.at [Photonics Institute, Vienna University of Technology, Gusshausstrasse 27, 1040 Vienna (Austria); Savolainen, Janne [Department of Physical Chemistry II, Ruhr-University Bochum, 44780 Bochum (Germany)

    2015-06-07

    The initial energy transfer steps in photosynthesis occur on ultrafast timescales. We analyze the carotenoid to bacteriochlorophyll energy transfer in LH2 Marichromatium purpuratum as well as in an artificial light-harvesting dyad system by using transient grating and two-dimensional electronic spectroscopy with 10 fs time resolution. We find that Förster-type models reproduce the experimentally observed 60 fs transfer times, but overestimate coupling constants, which lead to a disagreement with both linear absorption and electronic 2D-spectra. We show that a vibronic model, which treats carotenoid vibrations on both electronic ground and excited states as part of the system’s Hamiltonian, reproduces all measured quantities. Importantly, the vibronic model presented here can explain the fast energy transfer rates with only moderate coupling constants, which are in agreement with structure based calculations. Counterintuitively, the vibrational levels on the carotenoid electronic ground state play the central role in the excited state population transfer to bacteriochlorophyll; resonance between the donor-acceptor energy gap and the vibrational ground state energies is the physical basis of the ultrafast energy transfer rates in these systems.

  13. Vibronic coupling explains the ultrafast carotenoid-to-bacteriochlorophyll energy transfer in natural and artificial light harvesters

    Science.gov (United States)

    Perlík, Václav; Seibt, Joachim; Cranston, Laura J.; Cogdell, Richard J.; Lincoln, Craig N.; Savolainen, Janne; Šanda, František; Mančal, Tomáš; Hauer, Jürgen

    2015-06-01

    The initial energy transfer steps in photosynthesis occur on ultrafast timescales. We analyze the carotenoid to bacteriochlorophyll energy transfer in LH2 Marichromatium purpuratum as well as in an artificial light-harvesting dyad system by using transient grating and two-dimensional electronic spectroscopy with 10 fs time resolution. We find that Förster-type models reproduce the experimentally observed 60 fs transfer times, but overestimate coupling constants, which lead to a disagreement with both linear absorption and electronic 2D-spectra. We show that a vibronic model, which treats carotenoid vibrations on both electronic ground and excited states as part of the system's Hamiltonian, reproduces all measured quantities. Importantly, the vibronic model presented here can explain the fast energy transfer rates with only moderate coupling constants, which are in agreement with structure based calculations. Counterintuitively, the vibrational levels on the carotenoid electronic ground state play the central role in the excited state population transfer to bacteriochlorophyll; resonance between the donor-acceptor energy gap and the vibrational ground state energies is the physical basis of the ultrafast energy transfer rates in these systems.

  14. Nerium oleander indirect leaf photosynthesis and light harvesting reductions after clipping injury or Spodoptera eridania herbivory: high sensitivity to injury.

    Science.gov (United States)

    Delaney, Kevin J

    2012-04-01

    Variable indirect photosynthetic rate (P(n)) responses occur on injured leaves after insect herbivory. It is important to understand factors that influence indirect P(n) reductions after injury. The current study examines the relationship between gas exchange and chlorophyll a fluorescence parameters with injury intensity (% single leaf tissue removal) from clipping or Spodoptera eridania Stoll (Noctuidae) herbivory on Nerium oleander L. (Apocynaceae). Two experiments showed intercellular [CO(2)] increases but P(n) and stomatal conductance reductions with increasing injury intensity, suggesting non-stomatal P(n) limitation. Also, P(n) recovery was incomplete at 3d post-injury. This is the first report of a negative exponential P(n) impairment function with leaf injury intensity to suggest high N. oleander leaf sensitivity to indirect P(n) impairment. Negative linear functions occurred between most other gas exchange and chlorophyll a fluorescence parameters with injury intensity. The degree of light harvesting impairment increased with injury intensity via lower (1) photochemical efficiency indicated lower energy transfer efficiency from reaction centers to PSII, (2) photochemical quenching indicated reaction center closure, and (3) electron transport rates indicated less energy traveling through PSII. Future studies can examine additional mechanisms (mesophyll conductance, carbon fixation, and cardenolide induction) to cause N. oleander indirect leaf P(n) reductions after injury. Published by Elsevier Ireland Ltd.

  15. Facile synthesis of light harvesting semiconductor bismuth oxychloride nano photo-catalysts for efficient removal of hazardous organic pollutants

    Science.gov (United States)

    Seddigi, Zaki S.; Baig, Umair; Ahmed, Saleh A.; Abdulaziz, M. A.; Danish, Ekram Y.; Khaled, Mazen M.; Lais, Abul

    2017-01-01

    In the present work, bismuth oxychloride nanoparticles–a light harvesting semiconductor photocatalyst–were synthesized by a facile hydrolysis route, with sodium bismuthate and hydroxylammonium chloride as the precursor materials. The as-synthesized semiconductor photocatalysts were characterized using X-ray diffraction analysis, Fourier transform infra-red spectroscopy, Raman spectroscopy, Field emission scanning electron microscopy, X-ray photoelectron spectroscopy and Photoluminescence spectroscopy techniques. The crystal structure, morphology, composition, and optical properties of these facile synthesized bismuth oxychloride nanoparticles (BiOCl NPs) were compared to those of traditional bismuth oxychloride. In addition, the photocatalytic performance of facile-synthesized BiOCl NPs and traditional BiOCl, as applied to the removal of hazardous organic dyes under visible light illumination, is thoroughly investigated. Our results reveal that facile-synthesized BiOCl NPs display strong UV-Vis light adsorption, improved charge carrier mobility and an inhibited rate of charge carrier recombination, when compared to traditional BiOCl. These enhancements result in an improved photocatalytic degradation rate of hazardous organic dyes under UV-Vis irradiance. For instance, the facile-synthesized BiOCl NPs attained 100% degradation of methylene blue and methyl orange dyes in approximately 30 mins under UV-Vis irradiation, against 55% degradation for traditional BiOCl under similar experimental conditions. PMID:28245225

  16. Bifunctional Polymer Nanocomposites as Hole-Transport Layers for Efficient Light Harvesting: Application to Perovskite Solar Cells.

    Science.gov (United States)

    Wang, Jhong-Yao; Hsu, Fang-Chi; Huang, Jeng-Yeh; Wang, Leeyih; Chen, Yang-Fang

    2015-12-23

    A new approach to largely enhancing light harvesting of solar cells by employing bifunctional polymer nanocomposites as hole-transport layers (HTLs) is proposed. To illustrate our working principle, CH3NH3PbI3-xClx perovskite solar cells are used as examples. Gold nanoparticles (Au-NPs) are added into a conjugated poly(3-hexylthiophene-2,5-diyl) (P3HT) matrix, resulting in a ∼4-fold enhancement in the electrical conductivity and carrier mobility of the native P3HT film. The improved electrical properties are attributed to enhanced polymer chain ordering caused by Au-NPs. By integration of those P3HT:Au-NP films with an optimum loading concentration of 20% into perovskite solar cells as HTLs, this leads to a more than 25% enhancement in the power conversion efficiency (PCE) compared with that of the NP-free one. In addition to the modulated electrical properties of the HTL, the improved performance can also be attributed to the scattering effect from the incorporated Au-NPs, which effectively extends the optical pathway to amplify photon absorption of the photoactive layer. The design principle shown here can be generalized to other organic materials as well, which should be very useful for the further development of high-performance optoelectronic devices.

  17. Upright nanopyramid structured cover glass with light harvesting and self-cleaning effects for solar cell applications

    Science.gov (United States)

    Amalathas, Amalraj Peter; Alkaisi, Maan M.

    2016-11-01

    In this paper, we demonstrate the effect of upright nanopyramid (UNP) structured cover glass with light harvesting and self-cleaning functions on the device performance of monocrystalline Si solar cells. The UNP structures were fabricated on the surface of the glass substrate by simple, high throughput and low cost UV nanoimprint lithography, using a Si master mold with inverted nanopyramid (INP) structures. The diffuse transmittance and haze ratio values were significantly increased for UNP patterned glass, especially in the wavelength range 300-600 nm compared to the bare glass; this implies that antireflection and strong light scattering are due to the UNP structures. By replacing a bare cover glass with UNP patterned glass, the power conversion efficiency of the monocrystalline Si solar cell was substantially enhanced by about 10.97%; this is mainly due to the increased short-circuit current density J SC of 32.39 mA cm-2 compared to the reference cell with bare cover glass (i.e. J SC  =  31.60 mA cm-2). In addition, unlike the bare cover glass (i.e. θ CA ~ 36°), the fluorinated UNP structured cover glass exhibited a hydrophobic surface with a water contact angle (θ CA) of ~132° and excellent self-cleaning of dust particles by rolling down water droplets.

  18. Optimal spectral coordination of subantennae in natural antennae as an efficient strategy for light harvesting in photosynthesis.

    Science.gov (United States)

    Novikov, A A; Taisova, A S; Fetisova, Z G

    2006-08-01

    This work continues a series of our investigations on efficient strategies of functioning of natural light-harvesting antennae, initiated by a concept of rigorous optimization of photosynthetic apparatus by functional criterion, and deals with the problem of an optimal spectral coordination of subantennae in photosynthetic superantenna of the green bacterium Oscillochloris trichoides from a new family of green bacteria Oscillochloridaceae based in 2000. At present, two subantennae were identified surely: chlorosomal BChl c subantenna B750 and membrane BChl a subantennae B805-860. Some indirect experiments indicated on the presence of minor amounts of BChl a in isolated chlorosomes which allowed us to propose on the existence of an intermediate-energy subantenna which can connect the chlorosomal BChl c and the membrane BChl a ones. However, in the absorption spectra of isolated chlorosomes, this BChl a subantenna was not visually identified. This promoted us to perform a theoretical analysis of the optimality of spectral coordination of Oscillochloris trichoides subantennae. Using mathematical modeling for the functioning of the natural superantenna, we showed that an intermediate-energy subantenna, connecting B750 and B805-860 ones, allows one to control superantenna efficiency, i.e. to optimize the excitation energy transfer from B750 to B805 by functional criterion, and hence, the existence of such intermediate-energy subantenna is biologically expedient.

  19. Layered co-sensitization of gardenia and monascus for panchromatic light harvesting in dye-sensitized solar cells

    Science.gov (United States)

    Kwon, Oh Oun; Lee, Hyo Jung; Kim, Sang-Wook; Kim, Jung-Hun; Kim, Tae-Young; Park, Kyung-Hee; Lee, Jae-Wook

    2015-04-01

    TiO2 electrodes adsorbed with two natural dyes (gardenia yellow and monascus) were used as sensitizers to improve the conversion efficiency of cocktail dye-sensitized solar cells (CDSC) for light harvesting over a wide range of wavelength. Adsorption and electrochemical properties of two dyes were evaluated based on adsorption kinetics and electrochemical measurements. In addition, the photovoltaic performance of a photo-electrode adsorbed with single-dye (gardenia yellow and monascus) or the mixture or successive adsorption of the two dyes, was evaluated from current-voltage measurements. Layered co-sensitization of the two natural dyes was compared depending on the adsorption modes. As for the TiO2 electrode with successive adsorption of monascus and gardenia yellow dyes, the solar cell yields a short-circuit current density (Jsc) of 2.04 mA/cm2, a photovoltage (Voc) of 0.63 V, and a fill factor of 0.64, corresponding to an energy conversion efficiency (η) of 0.82%.

  20. Vibronic coupling explains the ultrafast carotenoid-to-bacteriochlorophyll energy transfer in natural and artificial light harvesters.

    Science.gov (United States)

    Perlík, Václav; Seibt, Joachim; Cranston, Laura J; Cogdell, Richard J; Lincoln, Craig N; Savolainen, Janne; Šanda, František; Mančal, Tomáš; Hauer, Jürgen

    2015-06-07

    The initial energy transfer steps in photosynthesis occur on ultrafast timescales. We analyze the carotenoid to bacteriochlorophyll energy transfer in LH2 Marichromatium purpuratum as well as in an artificial light-harvesting dyad system by using transient grating and two-dimensional electronic spectroscopy with 10 fs time resolution. We find that Förster-type models reproduce the experimentally observed 60 fs transfer times, but overestimate coupling constants, which lead to a disagreement with both linear absorption and electronic 2D-spectra. We show that a vibronic model, which treats carotenoid vibrations on both electronic ground and excited states as part of the system's Hamiltonian, reproduces all measured quantities. Importantly, the vibronic model presented here can explain the fast energy transfer rates with only moderate coupling constants, which are in agreement with structure based calculations. Counterintuitively, the vibrational levels on the carotenoid electronic ground state play the central role in the excited state population transfer to bacteriochlorophyll; resonance between the donor-acceptor energy gap and the vibrational ground state energies is the physical basis of the ultrafast energy transfer rates in these systems.

  1. [Protective properties of avermectine complex and plant growth regulators].

    Science.gov (United States)

    Iamborko, N A; Pindrus, A A

    2009-01-01

    Antimutagen properties of avermectine complex of Avercom synthesized by Streptomyces avermitilis UCM Ac-2161, and growth regulators of plants (GRP) of bioagrostim-extra, ivin and emistim-C have been revealed in experiments with test-cultures of Salmonella typhimurium TA 100, TA 98. Avercom and plant growth regulators neutralize by toxication 27-48% and mutagen action of pesticides on soil microbial associations by 19.0-30.0%.

  2. Space, time and complexity in plant dispersal ecology.

    Science.gov (United States)

    Robledo-Arnuncio, Juan J; Klein, Etienne K; Muller-Landau, Helene C; Santamaría, Luis

    2014-01-01

    Dispersal of pollen and seeds are essential functions of plant species, with far-reaching demographic, ecological and evolutionary consequences. Interest in plant dispersal has increased with concerns about the persistence of populations and species under global change. We argue here that advances in plant dispersal ecology research will be determined by our ability to surmount challenges of spatiotemporal scales and heterogeneities and ecosystem complexity. Based on this framework, we propose a selected set of research questions, for which we suggest some specific objectives and methodological approaches. Reviewed topics include multiple vector contributions to plant dispersal, landscape-dependent dispersal patterns, long-distance dispersal events, spatiotemporal variation in dispersal, and the consequences of dispersal for plant communities, populations under climate change, and anthropogenic landscapes.

  3. A light-harvesting antenna protein retains its folded conformation in the absence of protein-lipid and protein-pigment interactions.

    Science.gov (United States)

    Kikuchi, J; Asakura, T; Loach, P A; Parkes-Loach, P S; Shimada, K; Hunter, C N; Conroy, M J; Williamson, M P

    1999-04-15

    The first study by nmr of the integral membrane protein, the bacterial light-harvesting (LH) antenna protein LH1 beta, is reported. The photosynthetic apparatus of purple bacteria contains two different kinds of antenna complexes (LH1 and LH2), which consist of two small integral membrane proteins alpha and beta, each of approximately 6 kDa, and bacteriochlorophyll and carotenoid pigments. We have purified the antenna polypeptide LH1 beta from Rhodobacter sphaeroides, and have recorded CD spectra and a series of two-dimensional nmr spectra. A comparison of CD spectra of LH1 beta observed in organic solvents and detergent micelles shows that the helical character of the peptide does not change appreciably between the two milieus. A significantly high-field shifted methyl signal was observed both in organic solvents and in detergent micelles, implying that a similar three-dimensional structure is present in each case. However, the 1H-nmr signals observed in organic solvents had a narrower line width and better resolution, and it is shown that in this case organic solvents provide a better medium for nmr studies than detergent micelles. A sequential assignment has been carried out on the C-terminal transmembrane region, which is the region in which the pigment is bound. The region is shown to have a helical structure by the chemical shift values of the alpha-CH protons and the presence of nuclear Overhauser effects characteristic of helices. An analysis of the amide proton chemical shifts of the residues surrounding the histidine chlorophyll ligand suggests that the local structure is well ordered even in the absence of protein-lipid and protein-pigment interactions. Its structure was determined from 348 nmr-derived constraints by using distance geometry calculations. The polypeptide contains an alpha-helix extending from Leu19 (position of cytoplasmic surface) to Trp44 (position of periplasmic surface). The helix is bent, as expected from the amide proton chemical

  4. A nanoscale bio-inspired light-harvesting system developed from self-assembled alkyl-functionalized metallochlorin nano-aggregates

    Science.gov (United States)

    Ocakoglu, Kasim; Joya, Khurram S.; Harputlu, Ersan; Tarnowska, Anna; Gryko, Daniel T.

    2014-07-01

    Self-assembled supramolecular organization of nano-structured biomimetic light-harvesting modules inside solid-state nano-templates can be exploited to develop excellent light-harvesting materials for artificial photosynthetic devices. We present here a hybrid light-harvesting system mimicking the chlorosomal structures of the natural photosynthetic system using synthetic zinc chlorin units (ZnChl-C6, ZnChl-C12 and ZnChl-C18) that are self-aggregated inside the anodic aluminum oxide (AAO) nano-channel membranes. AAO nano-templates were modified with a TiO2 matrix and functionalized with long hydrophobic chains to facilitate the formation of supramolecular Zn-chlorin aggregates. The transparent Zn-chlorin nano-aggregates inside the alkyl-TiO2 modified AAO nano-channels have a diameter of ~120 nm in a 60 μm length channel. UV-Vis studies and fluorescence emission spectra further confirm the formation of the supramolecular ZnChl aggregates from monomer molecules inside the alkyl-functionalized nano-channels. Our results prove that the novel and unique method can be used to produce efficient and stable light-harvesting assemblies for effective solar energy capture through transparent and stable nano-channel ceramic materials modified with bio-mimetic molecular self-assembled nano-aggregates.Self-assembled supramolecular organization of nano-structured biomimetic light-harvesting modules inside solid-state nano-templates can be exploited to develop excellent light-harvesting materials for artificial photosynthetic devices. We present here a hybrid light-harvesting system mimicking the chlorosomal structures of the natural photosynthetic system using synthetic zinc chlorin units (ZnChl-C6, ZnChl-C12 and ZnChl-C18) that are self-aggregated inside the anodic aluminum oxide (AAO) nano-channel membranes. AAO nano-templates were modified with a TiO2 matrix and functionalized with long hydrophobic chains to facilitate the formation of supramolecular Zn-chlorin aggregates. The

  5. Enhanced light harvesting of dye-sensitized solar cells with TiO2 microspheres as light scattering layer

    Science.gov (United States)

    Guan, Yingli; Song, Lixin; Zhou, Yangyang; Yin, Xin; Xie, Xueyao; Xiong, Jie

    2017-03-01

    Two kinds of TiO2 microspheres (TMS) with average diameter of 1500 nm but different surface were fabricated by solvothermal method from different Ti source. The effect of TMS on the light harvesting and photovoltaic performance of dye-sensitized solar cells (DSSCs)was investigated. The UV-Vis diffusion reflectance spectra and absorption spectra of N719 dye in detached solutions proved that the TMS showed dual functions of light scattering and dye-adsorption which was an important functional material in DSSCs. The results showed that the TMS made from titanium(IV) isopropoxide with rough surface (TMSR) exhibited better photovoltaic performance than that of TMS made from tetrabutyl titanate with smooth surface (TMSS). To further improve the photovoltaic performance, the double-layered DSSCs made of P25 as an underlayer and TMS as a light-scattering layer (P25-TMS) were fabricated. The photovoltaic performance of double-layered DSSCs was higher than that of the single-layered DSSCs with similar thickness. Especially, the DSSCs made of P25 as an underlayer and the TMSR as a light-scattering layer (P25-TMSR) had a highest power conversion efficiency of 7.62%. This was higher than that of single-layered TMSR-based cell (5.54%), P25-based cell (5.75%), and double-layered P25-TMSS-based cell (6.78%) with similar thickness. This was mainly attributed to the large specific surface area, superior light scattering ability, and fast electron transport of TMSR.

  6. Effects of temperature on the astaxanthin productivity and light harvesting characteristics of the green alga Haematococcus pluvialis.

    Science.gov (United States)

    Giannelli, Luca; Yamada, Hiroyuki; Katsuda, Tomohisa; Yamaji, Hideki

    2015-03-01

    The green alga Haematococcus pluvialis, which accumulates astaxanthin at an optimal temperature of 20°C, was cultivated under temperatures of 20°C, 23.5°C, 27°C, and 30.5°C, in order to assess the effects on algal metabolism during the growth phase. The culture growth rate declined with above-optimal increases in temperature, and the final maximum cell concentration at 30.5°C reached only 35% of that attained at 20°C. On the contrary, the biomass productivity was increased under all the high-temperature conditions, probably reflecting the metabolism switch from cell duplication to energy accumulation that is typically observed in algal cultures subjected to environmental stress. Moreover, an increase in the light-harvesting capability of the alga was observed by means of the total pigment balance and the photosynthesis-intensity (PI) curve measured under the different cultivation conditions. Cultures kept at higher temperatures were able to better harvest and utilize the impinging light due to photo-acclimation. Finally, the differences in the astaxanthin metabolism were elucidated by subjecting the cultures to nitrogen starvation at 20°C and 27°C. In the culture at 27°C, a 1.4-fold increase in the astaxanthin productivity was observed when compared to that at 20°C, and the latter required almost two-fold more energy for the astaxanthin production compared with the 27°C culture.

  7. Resonance Raman spectroscopic investigation of the light-harvesting chromophore in escherichia coli photolyase and Vibrio cholerae cryptochrome-1.

    Science.gov (United States)

    Sokolova, Olga; Cecala, Christine; Gopal, Anand; Cortazar, Frank; McDowell-Buchanan, Carla; Sancar, Aziz; Gindt, Yvonne M; Schelvis, Johannes P M

    2007-03-27

    Photolyases and cryptochromes are flavoproteins that belong to the class of blue-light photoreceptors. They usually bind two chromophores: flavin adenine dinucleotide (FAD), which forms the active site, and a light-harvesting pigment, which is a 5,10-methenyltetrahydrofolate polyglutamate (MTHF) in most cases. In Escherichia coli photolyase (EcPhr), the MTHF cofactor is present in substoichiometric amounts after purification, while in Vibrio cholerae cryptochrome-1 (VcCry1) the MTHF cofactor is bound more strongly and is present at stoichiometric levels after purification. In this paper, we have used resonance Raman spectroscopy to monitor the effect of loss of MTHF on the protein-FAD interactions in EcPhr and to probe the protein-MTHF interactions in both EcPhr and VcCry1. We find that removal of MTHF does not perturb protein-FAD interactions, suggesting that it may not affect the physicochemical properties of FAD in EcPhr. Our data demonstrate that the pteridine ring of MTHF in EcPhr has different interactions with the protein matrix than that of MTHF in VcCry1. Comparison to solution resonance Raman spectra of MTHF suggests that the carbonyl of its pteridine ring in EcPhr experiences stronger hydrogen bonding and a more polar environment than in VcCry1, but that hydrogen bonding to the pteridine ring amine hydrogens is stronger in VcCry-1. These differences in hydrogen bonding may account for the higher binding affinity of MTHF in VcCry1 compared to EcPhr.

  8. Plasmon-enhanced light harvesting of chlorophylls on near-percolating silver films via one-photon anti-Stokes upconversion.

    Science.gov (United States)

    Wang, Ya-Lan; Nan, Fan; Liu, Xiao-Li; Zhou, Li; Peng, Xiao-Niu; Zhou, Zhang-Kai; Yu, Ying; Hao, Zhong-Hua; Wu, Yan; Zhang, Wei; Wang, Qu-Quan; Zhang, Zhenyu

    2013-01-01

    There exists a wealth of means of efficient utilization of solar energy in nature, with photosynthesis of chlorophylls as a prime example. Separately, artificially structured plasmonic materials are versatile in light harvesting and energy conversion. Using a simple and scalable design of near-percolating silver nanostructures, we demonstrate that the light-harvesting efficiency of chlorophylls can be drastically enhanced by tuning the plasmon frequency of the constituent silver nanoparticles to coincide with the maximal photon flux of sunlight. In particular, we show that the photon upconversion efficiency can be readily enhanced by over 20 folds, with the room-temperature fluorescence quantum yield increased by a factor of 2.63. The underlying mechanism for the upconversion enhancement is attributed to a one-electron-per-photon anti-Stokes process, involving absorption of a characteristic phonon mode of the chlorophylls. These findings suggest that chlorophylls can serve as molecular building blocks for high-efficiency light harvesting and solar energy conversion.

  9. Light Harvesting and White-Light Generation in a Composite of Carbon Dots and Dye-Encapsulated BSA-Protein-Capped Gold Nanoclusters.

    Science.gov (United States)

    Barman, Monoj Kumar; Paramanik, Bipattaran; Bain, Dipankar; Patra, Amitava

    2016-08-08

    Several strategies have been adopted to design an artificial light-harvesting system in which light energy is captured by peripheral chromophores and it is subsequently transferred to the core via energy transfer. A composite of carbon dots and dye-encapsulated BSA-protein-capped gold nanoclusters (AuNCs) has been developed for efficient light harvesting and white light generation. Carbon dots (C-dots) act as donor and AuNCs capped with BSA protein act as acceptor. Analysis reveals that energy transfer increases from 63 % to 83 % in presence of coumarin dye (C153), which enhances the cascade energy transfer from carbon dots to AuNCs. Bright white light emission with a quantum yield of 19 % under the 375 nm excitation wavelength is achieved by changing the ratio of components. Interesting findings reveal that the efficient energy transfer in carbon-dot-metal-cluster nanocomposites may open up new possibilities in designing artificial light harvesting systems for future applications.

  10. RNAseq and Proteomics for Analysing Complex Oomycete Plant Interactions.

    Science.gov (United States)

    Burra, Dharani D; Vetukuri, Ramesh R; Resjö, Svante; Grenville-Briggs, Laura J; Andreasson, Erik

    2016-01-01

    The oomycetes include some of the most devastating plant pathogens. In this review we discuss the latest results from oomycete and plant studies with emphasis on interaction studies. We focus on the outcomes of RNAseq and proteomics studies and some pitfalls of these approaches. Both pathogenic interactions and biological control are discussed. We underline the usefulness of studies at several levels of complexity from studies of one organism, up to two or more and within agricultural fields (managed settings) up to wild ecosystems. Finally we identify areas of future interest such as detailed interactome studies, dual RNAseq studies, peptide modification studies and population/meta omics with or without biological control agents.

  11. Deep Plant Phenomics: A Deep Learning Platform for Complex Plant Phenotyping Tasks.

    Science.gov (United States)

    Ubbens, Jordan R; Stavness, Ian

    2017-01-01

    Plant phenomics has received increasing interest in recent years in an attempt to bridge the genotype-to-phenotype knowledge gap. There is a need for expanded high-throughput phenotyping capabilities to keep up with an increasing amount of data from high-dimensional imaging sensors and the desire to measure more complex phenotypic traits (Knecht et al., 2016). In this paper, we introduce an open-source deep learning tool called Deep Plant Phenomics. This tool provides pre-trained neural networks for several common plant phenotyping tasks, as well as an easy platform that can be used by plant scientists to train models for their own phenotyping applications. We report performance results on three plant phenotyping benchmarks from the literature, including state of the art performance on leaf counting, as well as the first published results for the mutant classification and age regression tasks for Arabidopsis thaliana.

  12. Deep Plant Phenomics: A Deep Learning Platform for Complex Plant Phenotyping Tasks

    Directory of Open Access Journals (Sweden)

    Jordan R. Ubbens

    2017-07-01

    Full Text Available Plant phenomics has received increasing interest in recent years in an attempt to bridge the genotype-to-phenotype knowledge gap. There is a need for expanded high-throughput phenotyping capabilities to keep up with an increasing amount of data from high-dimensional imaging sensors and the desire to measure more complex phenotypic traits (Knecht et al., 2016. In this paper, we introduce an open-source deep learning tool called Deep Plant Phenomics. This tool provides pre-trained neural networks for several common plant phenotyping tasks, as well as an easy platform that can be used by plant scientists to train models for their own phenotyping applications. We report performance results on three plant phenotyping benchmarks from the literature, including state of the art performance on leaf counting, as well as the first published results for the mutant classification and age regression tasks for Arabidopsis thaliana.

  13. The Polycomb Complex PRC1: Composition and Function in Plants

    Institute of Scientific and Technical Information of China (English)

    Anne Molitor; Wen-Hui Shen

    2013-01-01

    Polycomb group (PcG) proteins are crucial epigenetic regulators conferring transcriptional memory to cell lineages.They assemble into multi-protein complexes,e.g.,Polycomb Repressive Complex 1 and 2 (PRC1,PRC2),which are thought to act in a sequential manner to stably maintain gene repression.PRC2 induces histone H3 lysine 27 (H3K27) trimethylation (H3K27me3),which is subsequently read by PRC1 that further catalyzes H2A monoubiquitination (H2Aubl),creating a transcriptional silent chromatin conformation.PRC2 components are conserved in plants and have been extensively characterized in Arabidopsis.In contrast,PRC1 composition and function are more diverged between animals and plants.Only more recently,PRC1 existence in plants has been documented.Here we review the aspects of plant specific and conserved PRC1 and highlight critical roles of PRC1 components in seed embryonic trait determinacy,shoot stem cell fate determinacy,and flower development in Arabidopsis.

  14. Chlorophyll-binding proteins revisited - a multigenic family of light-harvesting and stress proteins from a brown algal perspective

    Directory of Open Access Journals (Sweden)

    Collén Jonas

    2010-11-01

    Full Text Available Abstract Background Chlorophyll-binding proteins (CBPs constitute a large family of proteins with diverse functions in both light-harvesting and photoprotection. The evolution of CBPs has been debated, especially with respect to the origin of the LI818 subfamily, members of which function in non-photochemical quenching and have been found in chlorophyll a/c-containing algae and several organisms of the green lineage, but not in red algae so far. The recent publication of the Ectocarpus siliculosus genome represents an opportunity to expand on previous work carried out on the origin and function of CBPs. Results The Ectocarpus genome codes for 53 CBPs falling into all major families except the exclusively green family of chlorophyll a/b binding proteins. Most stress-induced CBPs belong to the LI818 family. However, we highlight a few stress-induced CBPs from Phaeodactylum tricornutum and Chondrus crispus that belong to different sub-families and are promising targets for future functional studies. Three-dimensional modeling of two LI818 proteins revealed features common to all LI818 proteins that are likely to interfere with their capacity to bind chlorophyll b and lutein, but may enable binding of chlorophyll c and fucoxanthin. In the light of this finding, we examined the possibility that LI818 proteins may have originated in a chlorophyll c/fucoxanthin containing organism and compared this scenario to three alternatives: an independent evolution of LI818 proteins in different lineages, an ancient origin together with the first CBPs, before the separation of the red and the green lineage, or an origin in the green lineage and a transfer to an ancestor of haptophytes and heterokonts during a cryptic endosymbiosis event. Conclusions Our findings reinforce the idea that the LI818 family of CBPs has a role in stress response. In addition, statistical analyses of phylogenetic trees show an independent origin in different eukaryotic lineages or a

  15. A proteomic strategy for global analysis of plant protein complexes.

    Science.gov (United States)

    Aryal, Uma K; Xiong, Yi; McBride, Zachary; Kihara, Daisuke; Xie, Jun; Hall, Mark C; Szymanski, Daniel B

    2014-10-01

    Global analyses of protein complex assembly, composition, and location are needed to fully understand how cells coordinate diverse metabolic, mechanical, and developmental activities. The most common methods for proteome-wide analysis of protein complexes rely on affinity purification-mass spectrometry or yeast two-hybrid approaches. These methods are time consuming and are not suitable for many plant species that are refractory to transformation or genome-wide cloning of open reading frames. Here, we describe the proof of concept for a method allowing simultaneous global analysis of endogenous protein complexes that begins with intact leaves and combines chromatographic separation of extracts from subcellular fractions with quantitative label-free protein abundance profiling by liquid chromatography-coupled mass spectrometry. Applying this approach to the crude cytosolic fraction of Arabidopsis thaliana leaves using size exclusion chromatography, we identified hundreds of cytosolic proteins that appeared to exist as components of stable protein complexes. The reliability of the method was validated by protein immunoblot analysis and comparisons with published size exclusion chromatography data and the masses of known complexes. The method can be implemented with appropriate instrumentation, is applicable to any biological system, and has the potential to be further developed to characterize the composition of protein complexes and measure the dynamics of protein complex localization and assembly under different conditions.

  16. Biological significance of complex N-glycans in plants and their impact on plant physiology

    Directory of Open Access Journals (Sweden)

    Richard eStrasser

    2014-07-01

    Full Text Available Asparagine (N-linked protein glycosylation is a ubiquitous co- and post-translational modification which can alter the biological function of proteins and consequently affects the development, growth and physiology of organisms. Despite an increasing knowledge of N-glycan biosynthesis and processing, we still understand very little about the biological function of individual N-glycan structures in plants. In particular, the N-glycan processing steps mediated by Golgi-resident enzymes create a structurally diverse set of protein-linked carbohydrate structures. Some of these complex N-glycan modifications like the presence of beta1,2-xylose, core alpha1,3-fucose or the Lewis a-epitope are characteristic for plants and are evolutionary highly conserved. In mammals, complex N-glycans are involved in different cellular processes including molecular recognition and signalling events. By contrast, the complex N-glycan function is still largely unknown in plants. Here, in this short review I focus on important recent developments and discuss their implications for future research in plant glycobiology and plant biotechnology.

  17. Inter-plant communication through mycorrhizal networks mediates complex adaptive behaviour in plant communities.

    Science.gov (United States)

    Gorzelak, Monika A; Asay, Amanda K; Pickles, Brian J; Simard, Suzanne W

    2015-01-01

    Adaptive behaviour of plants, including rapid changes in physiology, gene regulation and defence response, can be altered when linked to neighbouring plants by a mycorrhizal network (MN). Mechanisms underlying the behavioural changes include mycorrhizal fungal colonization by the MN or interplant communication via transfer of nutrients, defence signals or allelochemicals. We focus this review on our new findings in ectomycorrhizal ecosystems, and also review recent advances in arbuscular mycorrhizal systems. We have found that the behavioural changes in ectomycorrhizal plants depend on environmental cues, the identity of the plant neighbour and the characteristics of the MN. The hierarchical integration of this phenomenon with other biological networks at broader scales in forest ecosystems, and the consequences we have observed when it is interrupted, indicate that underground 'tree talk' is a foundational process in the complex adaptive nature of forest ecosystems.

  18. A mechanistic model for the light response of photosynthetic electron transport rate based on light harvesting properties of photosynthetic pigment molecules.

    Science.gov (United States)

    Ye, Zi-Piao; Robakowski, Piotr; Suggett, David J

    2013-03-01

    Models describing the light response of photosynthetic electron transport rate (ETR) are routinely used to determine how light absorption influences energy, reducing power and yields of primary productivity; however, no single model is currently able to provide insight into the fundamental processes that implicitly govern the variability of light absorption. Here we present development and application of a new mechanistic model of ETR for photosystem II based on the light harvesting (absorption and transfer to the core 'reaction centres') characteristics of photosynthetic pigment molecules. Within this model a series of equations are used to describe novel biophysical and biochemical characteristics of photosynthetic pigment molecules and in turn light harvesting; specifically, the eigen-absorption cross-section and the minimum average lifetime of photosynthetic pigment molecules in the excited state, which describe the ability of light absorption of photosynthetic pigment molecules and retention time of excitons in the excited state but are difficult to be measured directly. We applied this model to a series of previously collected fluorescence data and demonstrated that our model described well the light response curves of ETR, regardless of whether dynamic down-regulation of PSII occurs, for a range of photosynthetic organisms (Abies alba, Picea abies, Pinus mugo and Emiliania huxleyi). Inherent estimated parameters (e.g. maximum ETR and the saturation irradiance) by our model are in very close agreement with the measured data. Overall, our mechanistic model potentially provides novel insights into the regulation of ETR by light harvesting properties as well as dynamical down-regulation of PSII.

  19. A compact model for the complex plant circadian clock

    Directory of Open Access Journals (Sweden)

    Didier eGonze

    2016-02-01

    Full Text Available The circadian clock is an endogenous timekeeper that allows organisms to anticipate and adapt to the daily variations of their environment. The plant clock is an intricate network of interlocked feedback loops, in which transcription factors regulate each other to generate oscillations with expression peaks at specific times of the day. Over the last decade, mathematical modeling approaches have been used to understand the inner workings of the clock in the model plant Arabidopsis thaliana. Those efforts have produced a number of models of ever increasing complexity. Here, we present an alternative model that combines a low number of equations and parameters, similar to the very earliest models, with the complex network structure found in more recent ones. This simple model describes the temporal evolution of the abundance of eight clock genes and captures key features of the clock on a qualitative level, namely the entrained and free-running behaviors of the wild type clock, as well as the defects found in knockout mutants (such as altered free-running periods, lack of entrainment, or changes in the expression of other clock genes. Additionally, our model produces complex responses to various light cues, such as extreme photoperiods and non-24h environmental cycles, and can describe the control of hypocotyl growth by the clock. Our model constitutes a useful tool to probe dynamical properties of the clock as well as model more clock-dependent processes.

  20. Exotic plant species around Jeongeup Research Complex and RFT industrial complex

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Jin Kyu; Cha, Min Kyoung; Ryu, Tae Ho; Lee, Yun Jong; Kim, Jin Hong [Advanced Radiation Technology Institute, Korea Atomic Energy Research Institute, Jeongeup(Korea, Republic of)

    2015-08-15

    In Shinjeong-dong of Jeongeup, there are three government-supported research institutes and an RFT industrial complex which is currently being established. Increased human activities can affect flora and fauna as a man-made pressure onto the region. As a baseline study, status of exotic plants was investigated prior to a full operation of the RFT industrial complex. A total of 54 species and 1 variety of naturalized or introduced plants were found in the study area. Among them, three species (Ambrosia artemisifolia var. elatior, Rumex acetocella and Aster pilosus) belong to 'nuisance species', and four species (Phytolacca americana, Iopomoea hederacea, Ereechtites hieracifolia and Rudbeckia laciniata) to ‘monitor species’ designated by the ministry of Environment. Some of naturalized trees and plants were intentionally introduced in this area, while others naturally immigrated. Physalis angulata seems to immigrate in the study area in the form of mixture with animal feeds as its distribution coincided with the transportation route of the animal feeds. Liquidambar styraciflua is amenable to the ecological investigation on the possible expansion of the species to the nearby Naejang National Park as its leave shape and autumn color are very similar to those of maple trees. The number of naturalized plants around the RFT industrial complex will increase with an increase in floating population, in human activities in association with constructions of factories and operations of the complex. The result of this study provides baseline data for assessing the ecological change of the region according to the operation of the RFT industrial complex.