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Sample records for excited-state proton transfer

  1. Excited state Intramolecular Proton Transfer in Anthralin

    DEFF Research Database (Denmark)

    Møller, Søren; Andersen, Kristine B.; Spanget-Larsen, Jens

    1998-01-01

    Quantum chemical calculations performed on anthralin (1,8-dihydroxy-9(10H)-anthracenone) predict the possibility of an excited-state intramolecular proton transfer process. Fluorescence excitation and emission spectra of the compound dissolved in n-hexane at ambient temperature results in an unus......Quantum chemical calculations performed on anthralin (1,8-dihydroxy-9(10H)-anthracenone) predict the possibility of an excited-state intramolecular proton transfer process. Fluorescence excitation and emission spectra of the compound dissolved in n-hexane at ambient temperature results......, associated with an excited-state intramolecular proton transfer process....

  2. Dual fluorescence of ellipticine: excited state proton transfer from solvent versus solvent mediated intramolecular proton transfer.

    Science.gov (United States)

    Banerjee, Sanghamitra; Pabbathi, Ashok; Sekhar, M Chandra; Samanta, Anunay

    2011-08-25

    Photophysical properties of a natural plant alkaloid, ellipticine (5,11-dimethyl-6H-pyrido[4,3-b]carbazole), which comprises both proton donating and accepting sites, have been studied in different solvents using steady state and time-resolved fluorescence techniques primarily to understand the origin of dual fluorescence that this molecule exhibits in some specific alcoholic solvents. Ground and excited state calculations based on density functional theory have also been carried out to help interpretation of the experimental data. It is shown that the long-wavelength emission of the molecule is dependent on the hydrogen bond donating ability of the solvent, and in methanol, this emission band arises solely from an excited state reaction. However, in ethylene glycol, both ground and excited state reactions contribute to the long wavelength emission. The time-resolved fluorescence data of the system in methanol and ethylene glycol indicates the presence of two different hydrogen bonded species of ellipticine of which only one participates in the excited state reaction. The rate constant of the excited state reaction in these solvents is estimated to be around 4.2-8.0 × 10(8) s(-1). It appears that the present results are better understood in terms of solvent-mediated excited state intramolecular proton transfer reaction from the pyrrole nitrogen to the pyridine nitrogen leading to the formation of the tautomeric form of the molecule rather than excited state proton transfer from the solvents leading to the formation of the protonated form of ellipticine. © 2011 American Chemical Society

  3. Size effect of water cluster on the excited-state proton transfer in aqueous solvent

    Science.gov (United States)

    Liu, Yu-Hui; Chu, Tian-Shu

    2011-03-01

    Time-dependent density functional theory (TDDFT) was used to investigate the excited-state proton transfer (ESPT) dynamics of 6-hydroxyquinolinium (6HQc) in aqueous solvent, resulting in the excited zwitterionic form (6HQz). The optimized excited-state energy profiles of 6HQc:(H 2O) n complexes have been calculated along the phenolic O sbnd H bond to simulate the minimum energy pathway (MEP) in the excited state. The results suggested that the threshold of the size of the water cluster is 3 for the excited-state proton transfer of 6HQc in aqueous solvent, since the conformation of the stable hydrated proton requires proton transferring to the second or deeper shell of water solvent. Moreover, the stability of the hydrated proton can be improved significantly by adding one more H 2O molecule to form an Eigen cation in the excited-state 6HQz:H 9O 4+. The effect of the size of water cluster on the proton transfer is investigated theoretically in the excited state for the first time.

  4. TDDFT study on the excited-state proton transfer of 8-hydroxyquinoline: key role of the excited-state hydrogen-bond strengthening.

    Science.gov (United States)

    Lan, Sheng-Cheng; Liu, Yu-Hui

    2015-03-15

    Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations have been employed to study the excited-state intramolecular proton transfer (ESIPT) reaction of 8-hydroxyquinoline (8HQ). Infrared spectra of 8HQ in both the ground and the lowest singlet excited states have been calculated, revealing a red-shift of the hydroxyl group (-OH) stretching band in the excited state. Hence, the intramolecular hydrogen bond (O-H···N) in 8HQ would be significantly strengthened upon photo-excitation to the S1 state. As the intramolecular proton-transfer reaction occurs through hydrogen bonding, the ESIPT reaction of 8HQ is effectively facilitated by strengthening of the electronic excited-state hydrogen bond (O-H···N). As a result, the intramolecular proton-transfer reaction would occur on an ultrafast timescale with a negligible barrier in the calculated potential energy curve for the ESIPT reaction. Therefore, although the intramolecular proton-transfer reaction is not favorable in the ground state, the ESIPT process is feasible in the excited state. Finally, we have identified that radiationless deactivation via internal conversion (IC) becomes the main dissipative channel for 8HQ by analyzing the energy gaps between the S1 and S0 states for the enol and keto forms. Copyright © 2014 Elsevier B.V. All rights reserved.

  5. Prototropic studies in vitreous and in solid phases: Pyranine and 2-naphthol excited state proton transfer

    Energy Technology Data Exchange (ETDEWEB)

    Silva, Fátima Aparecida das Chagas [Departamento de Química Fundamental, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, SP (Brazil); Rezende, Eduardo Triboni [Universidade Nove de Julho, São Paulo, SP (Brazil); Filho, Décio Briotto [Departamento de Bioquímica Instituto de Química, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, SP (Brazil); Brito Rezende, Daisy de [Departamento de Química Fundamental, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, SP (Brazil); Cuccovia, Iolanda Midea [Departamento de Bioquímica Instituto de Química, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, SP (Brazil); Gome, Ligia Ferreira [Departamento de Análises Clínicas, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, SP (Brazil); Silva, Mauro Francisco Pinheiro da [Departamento de Química Fundamental, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, SP (Brazil); and others

    2014-02-15

    Excited state proton transfer processes in vitreous glasses and in solid mixtures are investigated by steady state fluorimetry and laser flash photolysis kinetic studies with the photoacids pyranine and 2-naphthol. Glasses were derived from TEOS by the sol–gel condensation process and hydrated solid mixtures from NaCl or KH{sub 2}PO{sub 4}/K{sub 2}HPO{sub 4} crystals. The extent of the water content necessary for the reaction is determined. Shrinkage of TEOS derived monoliths from water loss leads to an increase in proton transfer extent due to the increase in local concentrations of accepting and donor buffer species, but the concomitant increase in the ionic strength actuates in an opposite direction. Furthermore, water losses by aging of air-exposed gel goes to a critical 20% weight fraction, beyond it proton transfer reactions are hindered. Similar studies with solid NaCl or solid phosphate buffer mixtures demonstrated the same critical water level indicating that free water molecules are crucial for the proton to escape from the original cage where the geminate ion pair [–||RO{sup −⁎}H{sup +}||–] is formed and can undergo coupled proton transfer reactions. -- Highlights: • Pyranine and 2-naphthol excited state proton transfer in SiO{sub 2} gel, solid phosphate buffer and NaCl. • Sol–gel formation leads to contraction and concentration of donor and accepting species. • 20% weight fraction water is required for the ESPT to go forward.

  6. Theoretical Insights Into the Excited State Double Proton Transfer Mechanism of Deep Red Pigment Alkannin.

    Science.gov (United States)

    Zhao, Jinfeng; Dong, Hao; Zheng, Yujun

    2018-01-24

    As the most important component of deep red pigments, alkannin is investigated theoretically in detail based on time-dependent density functional theory (TDDFT) method. Exploring the dual intramolecular hydrogen bonds (O1-H2···O3 and O4-H5···O6) of alkannin, we confirm the O1-H2···O3 may play a more important role in the first excited state than the O4-H5···O6 one. Infrared (IR) vibrational analyses and subsequent charge redistribution also support this viewpoint. Via constructing the S1-state potential energy surface (PES) and searching transition state (TS) structures, we illuminate the excited state double proton transfer (ESDPT) mechanism of alkannin is the stepwise process that can be first launched by the O1-H2···O3 hydrogen bond wire in gas state, acetonitrile (CH3CN) and cyclohexane (CYH) solvents. We present a novel mechanism that polar aprotic solvents can contribute to the first-step proton transfer (PT) process in the S1 state, and nonpolar solvents play important roles in lowering the potential energy barrier of the second-step PT reaction.

  7. Photophysical Model of 10-Hydroxybenzo[h]quinoline: Internal Conversion and Excited State Intramolecular Proton Transfer

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Junghwa; Joo, Taiha [Pohang Univ. of Science and Technology, Pohang (Korea, Republic of)

    2014-03-15

    Photophysics of 10-hydroxybenzo[h]quinoline (HBQ) has been in controversy, in particular, on the nature of the electronic states before and after the excited state intramolecular proton transfer (ESIPT), even though the dynamics and mechanism of the ESIPT have been well established. We report highly time resolved fluorescence spectra over the full emission frequency regions of the enol and keto isomers and the anisotropy in time domain to determine the accurate rates of the population decay, spectral relaxation and anisotropy decay of the keto isomer. We have shown that the ∼300 fs component observed frequently in ESIPT dynamics arises from the S{sub 2}→S{sub 1} internal conversion in the reaction product keto isomer and that the ESIPT occurs from the enol isomer in S{sub 1} state to the keto isomer in S{sub 2} state.

  8. Excited state proton transfer in 9-aminoacridine carboxamides in water and in DNA

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Charles A. [Iowa State Univ., Ames, IA (United States)

    1995-09-26

    The 9-aminoacridine molecule is important in several different fields of chemistry. The absorption and fluorescence spectra of this compound are pH sensitive and it is this property that allowed it to be used as a pH probe in different chemical environments. The compound exhibits proton transfer reactions which are among the most fundamental of chemical reactions. The planarity of 9-aminoacridine allows it to intercalate into DNA. Intercalation is a process in which the aromatic flat surface of the intercalator inserts between adjacent base pairs of DNA. The large surface area of 9-aminoacridine`s fused tricyclic ring system allows strong intercalative binding through van der Waals attractions. 9-aminoacridine and many of its derivatives have been tried as possible antitumor drugs. The cytotoxicity of an antitumor agent can be dramatically increased through the addition of one or two cationic side chains. This increase in cytotoxicity using the 9-aminoacridine compound as a parent molecule has been investigated through various derivatives with cationic side chains consisting of different number of carbon atoms between the proximal and distal N atoms. Similar derivatives varied the position of the carboxamide side chain on the aromatic ring system. The objective of this work is to first create a baseline study of the excited state kinetics of the 9-aminoacridine carboxamides in the absence of DNA. The baseline study will allow the excited state kinetics of these antitumor drugs when placed in DNA to be more fully understood.

  9. Theoretical study on water-mediated excited-state multiple proton transfer in 7-azaindole: significance of hydrogen bond rearrangement.

    Science.gov (United States)

    Yu, Xue-fang; Yamazaki, Shohei; Taketsugu, Tetsuya

    2012-11-01

    Excited-state multiple proton transfer (ESMPT) in the cluster of 7-azaindole with three water molecules [7-azaindole(H(2)O)(3)] is theoretically investigated by the TDDFT, CASPT2, and CC2 methods. Examination of the potential energy surface in the first excited state indicates that ESMPT in 7-azaindole(H(2)O)(3) proceeds initially with the rearrangement of hydrogen bond structure of water molecules from a bridged-planar isomer to a cyclic-nonplanar isomer, followed by triple proton transfer in the latter. This reaction is found to be energetically more favorable than quadruple proton transfer in the bridged-planar isomer without hydrogen bond reorganization. It is also shown that all proton-transfer processes follow a concerted mechanism rather than a stepwise mechanism. The computational results show good consistency with the unexpected experimental observations as to the electronic spectra and excited-state lifetime. In particular, the barrier of the hydrogen bond rearrangement is found to be less than 1 kcal/mol, consistent with the missing vibronic bands for 7-azaindole(H(2)O)(3) with an excess energy of more than 200 cm(-1) in the S(1) state.

  10. Stepwise vs concerted excited state tautomerization of 2-hydroxypyridine: Ammonia dimer wire mediated hydrogen/proton transfer

    Energy Technology Data Exchange (ETDEWEB)

    Esboui, Mounir, E-mail: mounir.esboui@fst.rnu.tn [Laboratoire de Spectroscopie Atomique, Moléculaire et Applications, Département de Physique, Faculté des Sciences de Tunis, 2092 Tunis (Tunisia); Technical and Vocational Training Corporation, Hail College of Technology, P.O. Box 1960, Hail 81441 (Saudi Arabia)

    2015-07-21

    The stepwise and concerted excited state intermolecular proton transfer (PT) and hydrogen transfer (HT) reactions in 2-hydroxypyridine-(NH{sub 3}){sub 2} complex in the gas phase under Cs symmetry constraint and without any symmetry constraints were performed using quantum chemical calculations. It shows that upon excitation, the hydrogen bonded in 2HP-(NH{sub 3}){sub 2} cluster facilitates the releasing of both hydrogen and proton transfer reactions along ammonia wire leading to the formation of the 2-pyridone tautomer. For the stepwise mechanism, it has been found that the proton and the hydrogen may transfer consecutively. These processes are distinguished from each other through charge translocation analysis and the coupling between the motion of the proton and the electron density distribution along ammonia wire. For the complex under Cs symmetry, the excited state HT occurs on the A″({sup 1}πσ{sup ∗}) and A′({sup 1}nσ{sup ∗}) states over two accessible energy barriers along reaction coordinates, and excited state PT proceeds mainly through the A′({sup 1}ππ{sup ∗}) and A″({sup 1}nπ{sup ∗}) potential energy surfaces. For the unconstrained complex, potential energy profiles show two {sup 1}ππ{sup ∗}-{sup 1}πσ{sup ∗} conical intersections along enol → keto reaction path indicating that proton and H atom are localized, respectively, on the first and second ammonia of the wire. Moreover, the concerted excited state PT is competitive to take place with the stepwise process, because it proceeds over low barriers of 0.14 eV and 0.11 eV with respect to the Franck-Condon excitation of enol tautomer, respectively, under Cs symmetry and without any symmetry constraints. These barriers can be probably overcome through tunneling effect.

  11. Does excited-state proton-transfer reaction contribute to the emission behaviour of 4-aminophthalimide in aqueous media?

    Science.gov (United States)

    Khara, Dinesh Chandra; Banerjee, Sanghamitra; Samanta, Anunay

    2014-06-23

    4-Aminophthalimide (AP) is an extensively used molecule both for fundamental studies and applications primarily due to its highly solvent-sensitive fluorescence properties. The fluorescence spectrum of AP in aqueous media was recently shown to be dependent on the excitation wavelength. A time-dependent blue shift of its emission spectrum is also reported. On the basis of these findings, the excited-state solvent-mediated proton-transfer reaction of the molecule, which was proposed once but discarded at a later stage, is reintroduced. We report on the fluorescence behaviour of AP and its imide-H protected derivative, N-BuAP, to prove that a solvent-assisted excited-state keto-enol transformation does not contribute to the steady-state and time-resolved emission behaviour of AP in aqueous media. Our results also reveal that the fluorescence of AP in aqueous media arises from two distinct hydrogen-bonded species. The deuterium isotope effect on the fluorescence quantum yield and lifetime of AP, which was thought to be a reflection of the excited-state proton-transfer reaction in the system, is explained by considering the difference in the influence of H(2)O and D(2)O on the nonradiative rates and ground-state exchange of the proton with the solvent. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Excited-state proton transfer from pyranine to acetate in methanol

    Indian Academy of Sciences (India)

    trisulphonate, HPTS) to acetate in methanol has been studied by steady-state and time-resolved fluorescence spectroscopy. The rate constant of direct proton transfer from pyranine to acetate (1) is calculated to be ∼ 1 × 109 M-1 s-1. This is slower by ...

  13. Low-threshold wavelength-switchable organic nanowire lasers based on excited-state intramolecular proton transfer.

    Science.gov (United States)

    Zhang, Wei; Yan, Yongli; Gu, Jianmin; Yao, Jiannian; Zhao, Yong Sheng

    2015-06-08

    Coherent light signals generated at the nanoscale are crucial to the realization of photonic integrated circuits. Self-assembled nanowires from organic dyes can provide both a gain medium and an effective resonant cavity, which have been utilized for fulfilling miniaturized lasers. Excited-state intramolecular proton transfer (ESIPT), a classical molecular photoisomerization process, can be used to build a typical four-level system, which is more favorable for population inversion. Low-power driven lasing in proton-transfer molecular nanowires with an optimized ESIPT energy-level process has been achieved. With high gain and low loss from the ESIPT, the wires can be applied as effective FP-type resonators, which generated single-mode lasing with a very low threshold. The lasing wavelength can be reversibly switched based on a conformation conversion of the excited keto form in the ESIPT process. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Excited state and ground state proton transfer rates of 3-hydroxyflavone and its derivatives studied by shpol'skii spectroscopy: The influence of redistribution of electron density

    NARCIS (Netherlands)

    Bader, A.N.; Pivovarenko, V.; Demchenko, A.P.; Ariese, F.; Gooijer, C.

    2004-01-01

    We studied the mechanisms of excited-state intramolecular proton transfer (ESIPT) and ground-state back proton transfer (BPT) in 3-hydroxyflavone (3HF) at cryogenic temperatures. The focus was on substituents that change the distribution of electronic density on the chromophore and their influence

  15. Effect of NaCl Salts on the Activation Energy of Excited-State Proton Transfer Reaction of Coumarin 183.

    Science.gov (United States)

    Joung, Joonyoung F; Kim, Sangin; Park, Sungnam

    2015-12-17

    Coumarin 183 (C183) was used as a photoacid to study excited-state proton transfer (ESPT) reactions. Here, we studied the effect of ions on the ESPT of C183 in aqueous NaCl solutions using a steady-state fluorescence spectroscopy and time-correlated single photon counting (TCSPC) method. The acid dissociation equilibrium of excited-state C183 and the activation energy for the ESPT of C183 were determined as a function of NaCl concentration. The change in the equilibrium constant was found to be correlated with the solvation energy of deprotonated C183. Frequency-resolved TCSPC signals measured at several temperatures were analyzed by using a global fitting analysis method which enabled us to extract all the rate constants involving the ESPT reaction and the spectra of individual species. The activation energy for the ESPT reaction of C183 was highly dependent on NaCl concentration. Quantum chemical calculations were used to calculate the local hydrogen-bond (H-bond) configurations around C183 in aqueous NaCl solutions. It was found that the activation energy for the ESPT was determined by the local H-bond configurations around C183 which were significantly influenced by the dissolved ions.

  16. Excited-state proton-transfer dynamics of 1-methyl-6-hydroxyquinolinium embedded in a solid matrix of poly(2-hydroxyethyl methacrylate).

    Science.gov (United States)

    Park, Sun-Young; Lee, Young-Shin; Jang, Du-Jeon

    2008-11-28

    The excited-state intrinsic proton transfer and its geminate recombination, as well as the ground-state equilibria, of 1-methyl-6-hydroxyquinolinium embedded in a solid matrix of poly(2-hydroxyethyl methacrylate) have been studied by measuring time-resolved and steady-state fluorescence spectra along with absorption and excitation spectra. Proton transfer takes place within 3.3 ns to form ion pairs while its back-reaction occurs on the time scale of 3.7 ns. The ion pairs in the rigid alcoholic matrix go through neither diffusion to form free ions nor subsequent electronic rearrangement to form the keto species within their excited-state lifetimes.

  17. Excited-state proton transfer from pyranine to acetate in methanol

    Indian Academy of Sciences (India)

    TECS

    This is slower by about two orders of magnitude than that in bulk water (8 × 10. 10. M. –1 ... termolecular reactions observed in bulk water. In the .... mode for the diffusion of the proton to the bulk. To analyse the observed decay characteristics of. HPTS in the presence of acetate, we now use a sim- ple kinetic model. 14,15.

  18. Wagging motion of hydrogen-bonded wire in the excited-state multiple proton transfer process of 7-hydroxyquinoline·(NH3)3 cluster.

    Science.gov (United States)

    Liu, Yu-Hui; Lan, Sheng-Cheng; Li, Chun-Ran

    2013-08-01

    In this work, the dynamics of hydrogen bonds (as well as the hydrogen-bonded wire) in excited-state tautomerization of 7-hydroxyquinoline·(NH3)3 (7HQ·(NH3)3) cluster has been investigated by using time-dependent density functional theory (TDDFT). It shows that upon an excitation, the hydrogen bond between -OH group in 7-hydroxyquinoline (7HQ) and NH3 moiety would extremely strengthened in S1 state, which could effectively facilitate the releasing of the proton from the phenolic group of 7HQ moiety to the hydrogen-bonded wire and the forming an Eigen-like cationic wire (NH3···NH4(+)···NH3) in the cluster. To fulfill the different optimal angles of NH4(+) in the wire, a wagging motion of hydrogen-bonded wire would occur in excited state. Moreover, the wagging motion of the hydrogen-bonded wire would effectively promote excited-state proton transfer reaction. As the results, an excited-state multiple proton transfer (ESMPT) mechanism containing two concerted and asymmetrical processes has been proposed for the proton transfer dynamics of 7HQ·(NH3)3 cluster. Copyright © 2013 Elsevier B.V. All rights reserved.

  19. Theoretical study on the excited-state intramolecular proton-transfer reaction of 10-hydroxybenzo[h]quinoline in methanol and cyclohexane

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Meng [Department of Chemistry, Liaoning University, Shenyang 110036 (China); State Key Lab of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023 (China); Zhao, Jinfeng [Department of Physics, Liaoning University, Shenyang 110036 (China); State Key Lab of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023 (China); Cui, Yanling; Wang, Qianyu [Department of Physics, Liaoning University, Shenyang 110036 (China); Dai, Yumei [Normal College, Shenyang University, Shenyang 110044 (China); Song, Peng, E-mail: songpeng@lnu.edu.cn [Department of Physics, Liaoning University, Shenyang 110036 (China); Xia, Lixin, E-mail: lixinxia@lnu.edu.cn [Department of Chemistry, Liaoning University, Shenyang 110036 (China)

    2015-05-15

    The dynamics of the excited-state intramolecular proton-transfer (ESIPT) reaction of 10-hydroxybenzoquinoline (HBQ) in different solvents, have been investigated based on the time-dependent density functional theory (TD-DFT) in detail. Upon excitation, the intramolecular hydrogen bond between the hydroxyl and phenanthrene functionality is significantly strengthened in the S{sub 1} state, which can be used as a reasonable tendency for facilitating the ESIPT process. In addition, the calculated vertical excitation energies in the S{sub 0} state and S{sub 1} state reproduce the experimental UV–vis absorbance and fluorescence emission spectra well. Through calculating the fluorescence spectra of the HBQ chromophore, two outcomes for this chromophore were found in the S{sub 1} state, which demonstrates that the ESIPT process occurs. The potential energy curves have been calculated to account for the mechanism of the proton-transfer process in the excited-state. As a result, the barrierless ESIPT process can occur in the S{sub 1} state with proton transfer from the O atom to the N atom. And maybe the ESIPT process is easier in methanol solvent due to the higher potential energy difference. - Highlights: • The hydrogen bond between the hydroxyl and phenanthrene is strengthened. • The hydrogen bond facilitates the proton transfer from the hydroxyl group to the N atom. • The spontaneous excited-state intramolecular proton transfer reaction can be observed.

  20. External Electric Field Effects on Excited-State Intramolecular Proton Transfer in 4'-N,N-Dimethylamino-3-hydroxyflavone in Poly(methyl methacrylate) Films.

    Science.gov (United States)

    Furukawa, Kazuki; Hino, Kazuyuki; Yamamoto, Norifumi; Awasthi, Kamlesh; Nakabayashi, Takakazu; Ohta, Nobuhiro; Sekiya, Hiroshi

    2015-09-17

    The external electric field effects on the steady-state electronic spectra and excited-state dynamics were investigated for 4'-N,N-(dimethylamino)-3-hydroxyflavone (DMHF) in a poly(methyl methacrylate) (PMMA) film. In the steady-state spectrum, dual emission was observed from the excited states of the normal (N*) and tautomer (T*) forms. Application of an external electric field of 1.0 MV·cm(-1) enhanced the N* emission and reduced the T* emission, indicating that the external electric field suppressed the excited-state intramolecular proton transfer (ESIPT). The fluorescence decay profiles were measured for the N* and T* forms. The change in the emission intensity ratio N*/T* induced by the external electric field is dominated by ESIPT from the Franck-Condon excited state of the N* form and vibrational cooling in potential wells of the N* and T* forms occurring within tens of picoseconds. Three manifolds of fluorescent states were identified for both the N* and T* forms. The excited-state dynamics of DMHF in PMMA films has been found to be very different from that in solution due to intermolecular interactions in a rigid environment.

  1. Role of intramolecular hydrogen bonding in the excited-state intramolecular double proton transfer (ESIDPT of calix[4]arene: A TDDFT study

    Directory of Open Access Journals (Sweden)

    Wang Se

    2016-01-01

    Full Text Available The time-dependent density functional theory (TDDFT method was performed to investigate the excited-state intramolecular double proton transfer (ESIDPT reaction of calix[4]arene (C4A and the role of the intramolecular hydrogen bonds in the ESIDPT process. The geometries of C4A in the ground state and excited states (S1, S2 and T1 were optimized. Four intramolecular hydrogen bonds formed in the C4A are strengthened or weakened in the S2 and T1 states compared to those in the ground state. Interestingly, upon excitation to the S1 state of C4A, two protons H1 and H2 transfer along the two intramolecular hydrogen bonds O1-H1···O2 and O2-H2···O3, while the other two protons do not transfer. The ESIDPT reaction breaks the primary symmetry of C4A in the ground state. The potential energy curves of proton transfer demonstrate that the ESIDPT process follows the stepwise mechanism but not the concerted mechanism. Findings indicate that intramolecular hydrogen bonding is critical to the ESIDPT reactions in intramolecular hydrogen-bonded systems.

  2. The theoretical study of excited-state intramolecular proton transfer of 2,5-bis(benzoxazol-2-yl)thiophene-3,4-diol

    Science.gov (United States)

    Lan, Rui-Fang; Yang, Yun-Fan; Ma, Yan-Zhen; Li, Yong-Qing

    2017-08-01

    The symmetrical structures 2,5-bis(benzoxazol-2-yl)thiophene-3,4-diol (BBTD) can take shape two intramolecular hydrogen bonds in chloroform. In order to research the molecular dynamic behavior of BBTD upon photo-induced process, we utilize density functional theory (DFT) and time-dependent density functional theory (TDDFT) to complete theoretical calculation. Through the comparison of bond length, bond angle, IR spectra, and frontier molecular orbitals between ground state (S0) and first excited state (S1), it clearly indicates that photoexcitation have slightly influence for intensity of hydrogen bond. For the sake of understanding the mechanism of excited state intramolecular proton transfer (ESIPT) of BBTD in chloroform, potential energy surfaces have been scanned along with the orientation of O1-H2 and O4-H5 in S0 and S1 state, respectively. A intrigued hydrogen bond dynamic phenomenon has been found that ESIPT of BBTD is not a synergetic double proton transfer process, but a stepwise single proton transfer process BBTD → BBTD-S → BBTD-D. Moreover, the proton transfer process of BBTD-S → BBTD-D is easier to occur than that of BBTD → BBTD-S in S1 state.

  3. Theoretical study of excited-state proton transfer of 2,7-diazaindole·(H2O)2 cluster via hydrogen bonding dynamics

    Science.gov (United States)

    Liu, Yuan; Tang, Zhe; Wang, Yi; Tian, Jing; Fei, Xu; Cao, Fang; Li, GuangYue

    2017-12-01

    A new chromophore, 2,7-diazaindole (2,7-DAI), has been designed to surpass the limitation of 7-azaindole (7AI). It exhibits remarkable water catalyzed proton-transfer properties. Excited-state proton transfer (ESPT) has been investigated based on the time-dependent density functional theory method. The calculated vertical excitation energies in the S0 and S1 states agree well with the experimental values. Proton transfer couples with hydrogen-bonding dynamics between the 2,7-diazaindole and the surrounding water molecules. Hydrogen bond strengthening has been testified in the S1 state based on a comparison of primary bond lengths and hydrogen bond energy that is involved in the intermolecular hydrogen bond between the S0 and S1 states. Frontier molecular further suggest that the electron density changes between the ground and excited states serve as basic driving forces for proton transfer. We determined the potential-energy curves of the S0 and S1 states to characterize the ESPT process. This work explains that the ESPT process for 2,7-DAI·(H2O)2 clusters at the molecular level, and highlights the importance of hydrogen bonding in ESPT.

  4. Tunable excited-state intramolecular proton transfer reactions with Nsbnd H or Osbnd H as a proton donor: A theoretical investigation

    Science.gov (United States)

    Li, Yuanyuan; Wen, Keke; Feng, Songyan; Yuan, Huijuan; An, Beibei; Zhu, Qiuling; Guo, Xugeng; Zhang, Jinglai

    2017-12-01

    Excited-state intramolecular proton transfer (ESIPT) reactions occurring in the S1 state for five molecules, which possess five/six-membered ring intramolecular Nsbnd H···N or Osbnd H···N hydrogen bonds bearing quinoline or 2-phenylpyridine moiety, have been described in detail by the time-dependent density functional theory (TD-DFT) approach using the B3LYP hybrid functional. For the five molecules, the constrained potential energy profiles along the ESIPT reactions show that proton transfer is barrierless in molecules possessing six-membered ring intramolecular H-bonds, which is smoother than that with certain barriers in five-membered ring H-bonding systems. For the latter, chemical modification by a more strong acid group can lower the ESIPT barrier significantly, which harnesses the ESIPT reaction from a difficult type to a fast one. The energy barrier of the ESIPT reaction depends on the intensity of the intramolecular H-bond, which can be measured with the topological descriptors by topology analysis of the bond critical point (BCP) of the intramolecular H-bond. It is found that when the value of electron density ρ(r) at BCP is bigger than 0.025 a.u., the corresponding molecule might go through an ultrafast and barrierless ESIPT process, which opens a new scenario to explore the ESIPT reactions.

  5. Excited-state intramolecular proton transfer and conformational relaxation in 4'-N,N-dimethylamino-3-hydroxyflavone doped in acetonitrile crystals.

    Science.gov (United States)

    Furukawa, Kazuki; Yamamoto, Norifumi; Hino, Kazuyuki; Sekiya, Hiroshi

    2016-10-19

    The effect of intermolecular interactions on excited-state intramolecular proton transfer (ESIPT) in 4'-N,N-dimethylamino-3-hydroxyflavone (DMHF) doped in acetonitrile crystals was investigated by measuring its temperature dependence of steady-state fluorescence excitation and fluorescence spectra and picosecond time-resolved spectra. The relative intensity of emission from the excited state of the normal form (N*) to that from the excited state of the tautomer form (T*) and spectral features changed markedly with temperature. Unusual changes in the spectral shift and spectral features were observed in the fluorescence spectra measured between 200 and 218 K, indicating that a solid-solid phase transition of DMHF-doped acetonitrile crystals occurred. Time-resolved fluorescence spectra suggested conformational relaxation of the N* state competed with ESIPT after photoexcitation and the ESIPT rate increased with temperature in the low-temperature phase of acetonitrile. However, the intermolecular interaction of N* with acetonitrile in the high-temperature phase markedly stabilized the potential minimum of the fluorescent N* state and slowed the ESIPT. This stabilization can be explained by reorganization of acetonitrile originating from the strong electric dipole-dipole interaction between DMHF and acetonitrile molecules.

  6. Water-assisted self-photoredox of 2-(1-hydroxyethyl)-9,10-anthraquinone through a triplet excited state intra-molecular proton transfer pathway.

    Science.gov (United States)

    Dai, Jingze; Han, Juan; Chen, Xuebo; Fang, Weihai; Ma, Jiani; Phillips, David Lee

    2015-10-28

    Using multi-configurational perturbation theory (CASPT2//CASSCF), a novel self-photoredox reaction for 2-(1-hydroxyethyl)-9,10-anthraquinone was proposed to effectively occur through two steps of triplet excited state intra-molecular proton transfer (ESIPT) reaction aided by water wires without the introduction of an external oxidant or reductant. The photoinduced charge transfer along the desired direction was determined to be the major driving force for the occurrence of the energetically favorable ESIPT in the triplet state, in which the water wires function as an effective proton relay and photocatalyst to lower the reaction barrier. The computational results provide convincing evidence that the deprotonation of the hydroxyl group in the triplet state and connecting water molecule(s) between that hydroxyl group and the carbonyl group that is protonated by a nearby water molecule in the water wire is the initial reaction step that triggers the protonation of the carbonyl group seen in the previously reported time-resolved spectroscopy experiments that produces a protonated carbonyl triplet intermediate that then undergoes a subsequent deprotonation of the methylene C-H in the triplet and ground states to complete the self-photoredox reaction of anthraquinone. Comparison of the theoretical results with previously reported results from time-resolved spectroscopy experiments indicate the photoredox reactions can occur either via a concerted or non-concerted deprotonation-protonation of distal sites of the molecule assisted by the connecting water molecules. These new insights will help provide benchmarks to elucidate the photochemistry of the anthraquinone and benzophenone compounds in acidic and/or neutral aqueous solutions.

  7. Correlation among Singlet-Oxygen Quenching, Free-Radical Scavenging, and Excited-State Intramolecular-Proton-Transfer Activities in Hydroxyflavones, Anthocyanidins, and 1-Hydroxyanthraquinones.

    Science.gov (United States)

    Nagaoka, Shin-Ichi; Bandoh, Yuki; Nagashima, Umpei; Ohara, Keishi

    2017-10-26

    Singlet-oxygen (1O2) quenching, free-radical scavenging, and excited-state intramolecular proton-transfer (ESIPT) activities of hydroxyflavones, anthocyanidins, and 1-hydroxyanthraquinones were studied by means of laser, stopped-flow, and steady-state spectroscopies. In hydroxyflavones and anthocyanidins, the 1O2 quenching activity positively correlates to the free-radical scavenging activity. The reason for this correlation can be understood by considering that an early step of each reaction involves electron transfer from the unfused phenyl ring (B-ring), which is singly bonded to the bicyclic chromen or chromenylium moiety (A- and C-rings). Substitution of an electron-donating OH group at B-ring enhances the electron transfer leading to activation of the 1O2 quenching and free-radical scavenging. In 3-hydroxyflavones, the OH substitution at B-ring reduces the activity of ESIPT within C-ring, which can be explained in terms of the nodal-plane model. As a result, the 1O2 quenching and free-radical scavenging activities negatively correlate to the ESIPT activity. A catechol structure at B-ring is another factor that enhances the free-radical scavenging in hydroxyflavones. In contrast to these hydroxyflavones, 1-hydroxyanthraquinones having an electron-donating OH substituent adjacent to the O-H---O═C moiety susceptible to ESIPT do not show a simple correlation between their 1O2 quenching and ESIPT activities, because the OH substitution modulates these reactions.

  8. The excited-state intramolecular proton transfer in Nsbnd H-type dye molecules with a seven-membered-ring intramolecular hydrogen bond: A theoretical insight

    Science.gov (United States)

    Yuan, Huijuan; Feng, Songyan; Wen, Keke; Guo, Xugeng; Zhang, Jinglai

    2018-02-01

    Excited-state intramolecular proton transfer (ESIPT) reactions of a series of N(R)sbnd H ⋯ N-type seven-membered-ring hydrogen-bonding compounds were explored by employing density functional theory/time-dependent density functional theory calculations with the PBE0 functional. Our results indicate that the absorption and emission spectra predicted theoretically match very well the experimental findings. Additionally, as the electron-withdrawing strength of R increases, the intramolecular H-bond of the Nsbnd S1 form gradually enhances, and the forward energy barrier along the ESIPT reaction gradually decreases. For compound 4, its ESIPT reaction is found to be a barrierless process due to the involvement of a strong electron-withdrawing COCF3 group. It is therefore a reasonable presumption that the ESIPT efficiency of these N(R)sbnd H ⋯ N-type seven-membered-ring H-bonding systems can be improved when a strong electron-withdrawing group in R is introduced.

  9. A comprehensive spectroscopic and computational investigation of intramolecular proton transfer in the excited states of 2-(2′-hydroxyphenyl) benzoxazole and its derivatives

    Energy Technology Data Exchange (ETDEWEB)

    Padalkar, Vikas S. [Tinctorial Chemistry Group, Institute of Chemical Technology, Matunga, Mumbai 400019 (India); Ramasami, Ponnadurai, E-mail: ramchemi@intnet.mu [Computational Chemistry Group, Department of Chemistry, Faculty of Science, University of Mauritius, Réduit (Mauritius); Sekar, Nagaiyan, E-mail: n.sekar@ictmumbai.edu.in [Tinctorial Chemistry Group, Institute of Chemical Technology, Matunga, Mumbai 400019 (India)

    2014-02-15

    The excited-state intramolecular proton transfer (ESIPT) fluorescence of the 2-(2′ hydroxyphenyl) benzoxazole (HBO) and its derivatives with NO{sub 2} as electron acceptor and NH{sub 2} as electron donor at the 4 and 5 position of benzoxazole ring was studied by spectroscopic and computational methods. The changes in the electronic transition, energy levels, and orbital diagrams of the HBO derivatives were investigated using the DFT computations and they were correlated with the experimental spectral emission. The benzoxazole derivatives are fluorescent under UV-light in solution. Photophysical properties of the compounds were also studied in solvents of different polarities. Experimental absorption and emission wavelengths are in agreement with those computed with a deviation ranging between 0 and 50%. The computational methods have been useful for molecular understanding of the transitions responsible for the fluorescent spectra. -- Highlights: • Experimental photophysical properties of 2-substituted benzoxazoles in different solvents have been studied and compared with the computational data. • Compounds show dual emission due to ESIPT process and was supported by DFT and TD-DFT computations. • Experimental results and computational results are in good agreements.

  10. Synthesis and Optical Properties of Excited-State Intramolecular Proton Transfer Active π-Conjugated Benzimidazole Compounds: Influence of Structural Rigidification by Ring Fusion.

    Science.gov (United States)

    Takagi, Koji; Ito, Kaede; Yamada, Yoshihiro; Nakashima, Takuya; Fukuda, Ryoichi; Ehara, Masahiro; Masu, Hyuma

    2017-12-01

    Two excited-state intramolecular proton transfer (ESIPT) active benzimidazole derivatives (1 and 2) were synthesized by acid-catalyzed intramolecular cyclization. The steady-state fluorescence spectrum in THF revealed that ring-fused derivative 1 exhibits a dual emission, namely, the major emission was from the K* (keto) form (ESIPT emission) at 515 nm with a large Stokes shift of 11 100 cm-1 and the minor emission was from the E* (enol) form at below 400 nm. In contrast, the normal emission from the E* form was dominant and the fluorescence quantum yield was very low (Φ ∼ 0.002) for nonfused derivative 2. The time-resolved fluorescence spectroscopy of 1 suggested that ESIPT effectively occurs due to the restricted conformational transition to the S1-TICT state, and the averaged radiative and nonradiative decay rate constants were estimated as ⟨kf⟩ = 0.15 ns-1 and ⟨knr⟩ = 0.60 ns-1, respectively. The fluorescence emission of 1 was influenced by the measurement conditions, such as solvent polarity and basicity, as well as the presence of Lewis base. The ESIPT process and solvatochromic behavior were nicely reproduced by the DFT/TDDFT calculation using the PCM model. In the single-crystal fluorescent spectra, the ESIPT emissions were exclusively observed for both fused and nonfused compounds as a result of hydrogen-bonding interactions.

  11. Synthesis, structural, and photophysical studies of π-fused acenaphtho[1,2-d]imidazole-based excited-state intramolecular proton transfer molecules

    Science.gov (United States)

    Somasundaram, Sivaraman; Kamaraj, Eswaran; Hwang, Su Jin; Jung, Sooyoung; Choi, Moon Gun; Park, Sanghyuk

    2017-06-01

    Orange-red fluorescent molecules are promising materials for use in a new generation of displays, light sources, and chemosensors because conventional red-emitters have lower fluorescence quantum efficiencies. In this work, a set of orange-emitting fused imidazole series 2-(7-(4-fluorophenyl)-7H-acenaphtho[1,2-d]imidazol-8-yl)phenol (AHPI-F), 2-(7-(4-chlorophenyl)-7H-acenaphtho[1,2-d]imidazol-8-yl)phenol (AHPI-Cl), and 2-(7-(4-bromophenyl)-7H-acenaphtho[1,2-d]imidazol-8-yl)phenol (AHPI-Br) have been synthesized via multicomponent reaction method with high yield. Synthesized molecules were fully characterized by 1H NMR, 13C NMR, GC-Mass, UV-vis. absorption, PL, and TGA-DSC. The compounds AHPI-F, AHPI-Cl, AHPI-Br showed large Stokes' shifted emission due to excited-state intramolecular proton transfer (ESIPT) process, and they effectively formed large single crystals. The crystal structure of each compound was identified by X-ray crystallographic analysis. To elucidate the photophysical properties of the molecule, theoretical calculation were performed by density functional theory (DFT) with B3LYP 6-31G(d,p) basis sets using the identified molecular conformations from X-ray analysis. Calculated electronic properties including HOMO-LUMO levels were compared with the experimental results. As a result of ESIPT process, extended conjugation length through acenaphto[1,2-d]imidazole, and charge transfer characteristics by the introduction of halogen atoms, all of the materials showed orange ESIPT emission with no spatial overlap between absorption (λmax,abs = 325 nm) and emission (λmax,ems = 578 nm).

  12. Photophysical properties and excited state intramolecular proton transfer in 2-hydroxy-5-[(E)-(4-methoxyphenyl)diazenyl]benzoic acid in homogeneous solvents and micro-heterogeneous environments

    Energy Technology Data Exchange (ETDEWEB)

    Gashnga, Pynsakhiat Miki [Centre for Advanced Studies, Department of Chemistry, North-Eastern Hill University, Shillong 793022, Meghalaya (India); Singh, T. Sanjoy [Department of Chemistry, Assam University, Silchar 788011, Assam (India); Baul, Tushar S. Basu [Centre for Advanced Studies, Department of Chemistry, North-Eastern Hill University, Shillong 793022, Meghalaya (India); Mitra, Sivaprasad, E-mail: smitra@nehu.ac.in [Centre for Advanced Studies, Department of Chemistry, North-Eastern Hill University, Shillong 793022, Meghalaya (India)

    2014-04-15

    A systematic study on the photophysical properties and excited state intramolecular proton transfer (ESIPT) behavior of 2-hydroxy-5-[(E)-(4-methoxyphenyl)diazenyl]benzoic acid, is reported using steady-state and time-resolved fluorescence spectroscopy in homogeneous solvents as well as in different micro-heterogeneous environments. Depending on the nature of intramolecular hydrogen bond (IHB), the salicylic acid derivative may exist in two different ground state conformers (I and II). Structure I having IHB between the carbonyl oxygen and phenolic hydrogen can undergo ESIPT upon excitation as evidenced by largely Stokes-shifted fluorescence at ∼455 nm; whereas, normal fluorescence in the blue side of the spectrum (∼410 nm) is due to the spontaneous emission from conformer II. The results in homogeneous solvents were compared with those in bio-mimicking environments of β-cyclodextrin (CD) and surfactants. The intensity of the ESIPT fluorescence increases substantially upon encapsulation of the probe into the cyclodextrin as well as micellar nano-cavities. Detailed analysis of the spectroscopic data indicates that the probe forms 1:1 complex with CD in aqueous medium. Binding constant of the probe with the micelles as well as critical micelle concentration was obtained from the variation of fluorescence intensity on increasing concentration of different surfactants in aqueous medium. -- Highlights: • Steady state and time resolved fluorescence study on ESIPT in HMBA. • Dual fluorescence corresponding to the pro- and non-ESIPT structures. • Modulation of ESIPT fluorescence in micro-heterogeneous environments. • 1:1 stoichiometry for interaction with cyclodextrin. • Calculation of binding constant and other physico-chemical properties from fluorescence titration data in surfactants.

  13. Excited state intramolecular proton transfer (ESIPT) in the Photoresponsive Prototropic Schiff-Base N‧-(2-hydroxybenzylidene)-4-hydroxybenzohydrazide: Computational Modeling Study

    Science.gov (United States)

    Abdel-Mottaleb, M. S. A.

    2017-09-01

    Computations within Density Functional Theory (DFT) and its Time-Dependent (TD) extension at the B3LYP/6-31G(d) level are performed for both S0 and S1 states to obtain the optimum molecular geometry of the keto-enol photochromic material of the title molecule and to explain the photo-induced ESIPT to generate the corresponding enol tautomer. The choice of the compound is interesting, and deserves attention due to geometrical changes in the electronic structure of the Nsbnd N linkage during the proton transfer (PT) reaction coordinate. In particular, PT path is followed by relaxed scan technique for computing potential energy surface (PES) to identify the transition state and to obtain barrier heights in S0 and S1 states. The photoresponsive H-transfer tautomerism is discussed in terms of different computational parameters including enthalpies and free energies. Both electronic reactivity as well as the thermodynamic stability plays together to facilitate proton transfer in the excited- and ground states of the tautomeric forms.

  14. New insights into the solvent-assisted excited-state double proton transfer of 2-(1H-pyrazol-5-yl)pyridine with alcoholic partners: A TDDFT investigation

    Science.gov (United States)

    Li, Hui; Shi, Ying; Yin, Hang; Wang, Ye; Cong, Lin; Jin, Mingxing; Ding, Dajun

    2015-04-01

    Excited-state double proton transfer (ESDPT) in the hydrogen-bonded 2-(1H-pyrazol-5-yl)pyridine with propyl alcoholic partner (PPP) was theoretically investigated by time-dependent density functional theory (TDDFT) method. Great changes have taken place for the calculated geometric structures, the electron density features and vibrational spectrum of PPP system in S0 and S1 state. Our results have demonstrated that ESDPT reaction happens within the system upon photoexcitation. We also found that the ESDPT process is facilitated by the electronically excited state intermolecular hydrogen bond strengthening. Particularly, after the photoexcitation from HOMO(π) to the LUMO(π∗), the rearrangement of electronic density distribution of frontier molecular orbitals (MOs) on pyridine and the pyrazol moieties exhibits a very important positive factor for the ESDPT. Furthermore, by the investigation of the stretching vibrations of Nsbnd H and Osbnd H groups, the infrared (IR) spectroscopic results provide us not only a theoretical evidence of ESDPT, but also a considerable clue to characterize the nature of intermolecular reaction. In addition, efforts have also been devoted towards calculating the absorption peak, which shows good consistency with the experimental result of the studied system.

  15. Excited state intramolecular charge transfer reaction in 4-(1 ...

    Indian Academy of Sciences (India)

    Administrator

    Abstract. Excited state intramolecular charge transfer reaction of 4-(1-azetidinyl) benzonitrile (P4C) in deuterated and normal methanol, ethanol and acetonitrile has been studied in order to investigate the solvent isotope effects on reaction rates and yields. These quantities (reaction rates and yields) along with several.

  16. Excited state intramolecular charge transfer reaction in 4-(1 ...

    Indian Academy of Sciences (India)

    Excited state intramolecular charge transfer reaction of 4-(1-azetidinyl) benzonitrile (P4C) in deuterated and normal methanol, ethanol and acetonitrile has been studied in order to investigate the solvent isotope effects on reaction rates and yields. These quantities (reaction rates and yields) along with several other ...

  17. A new insight into the chemistry of iridium(III) complexes bearing phenyl phenylphosphonite cyclometalate and chelating pyridyl triazolate: the excited-state proton transfer tautomerism via an inter-ligand PO-H···N hydrogen bond.

    Science.gov (United States)

    Lin, Cheng-Huei; Liao, Jia-Ling; Wu, Yu-Sin; Liao, Kuan-Yu; Chi, Yun; Chen, Chi-Lin; Lee, Gene-Hsiang; Chou, Pi-Tai

    2015-05-14

    Treatment of [IrCl3(tht)3], where tht = tetrahydrothiophene, with two equiv. of phenyl diphenylphosphinite (pdpitH) gave [Ir(pdpitH)(pdpit)(tht)Cl2] (1), which on further reaction with 3-t-butyl-5-(2-pyridyl)-1,2,4-triazole (bptzH) and NaOAc using a one-pot reaction afforded [Ir(pdpit)2(bptz)] (2). In sharp contrast, the reaction of [IrCl3(tht)3], pdpitH, and bptzH in the presence of a stronger base, Na2CO3, afforded a phenyl phenylphosphonite (pppo)-containing Ir(III) complex [Ir(pdpit)(pppo)(bptz)] (3) that reveals a strong PO-H-N inter-ligand hydrogen bond (H-bond), as evidenced by the single crystal X-ray structural analysis. For confirmation, addition of diazomethane to a diethylether solution of 3 led to the isolation of two methylated Ir(III) isomeric complexes, i.e. [Ir(pdpit)(pppoMe)(bptz)] (4) and [Ir(pdpit)(pppo)(bptzMe)] (5), possessing either a PO-Me or N-Me bonding fragment, respectively. The absorption spectrum of 3 in CH2Cl2 resembles that of 4, implying the dominant PO-H character in solution. Despite the prevailing PO-H character both in the solid crystal and in solution, its corresponding emission resembles that of 5, leading us to propose a mechanism incorporating the excited-state inter-ligand proton transfer (ESILPT) from PO-H to N-H isomeric form via the pre-existing PO···H···N hydrogen bond. The thermodynamics of proton transfer tautomerism are discussed on the basis of absorption/emission spectroscopy in combination with computational approaches; additional support is given by the relationship between emission pattern versus the position of protons and methyl substituents. The results demonstrate for the first time a paradigm of excited-state proton transfer for the transition metal complexes in the triplet manifold.

  18. Formation of H-atom in 2s excited state of proton-lithium and proton ...

    Indian Academy of Sciences (India)

    Abstract. The differential and total cross-sections have been investigated in the forma- tion of H-atom in the 2s excited state of proton-lithium and proton-sodium scattering by using the Coulomb projected Born (CPB) approximation in the energy range from 50 to. 10,000 keV. The results thus obtained are compared with the ...

  19. Unique photophysical behavior of 2,2'-bipyridine-3,3'-diol in DMSO-water binary mixtures: potential application for fluorescence sensing of Zn2+ based on the inhibition of excited-state intramolecular double proton transfer.

    Science.gov (United States)

    Mandal, Sarthak; Ghosh, Surajit; Banerjee, Chiranjib; Kuchlyan, Jagannath; Sarkar, Nilmoni

    2013-10-10

    In this work we have investigated the anomalous behavior of DMSO-water binary mixtures using 2,2'-bipyridine-3,3'-diol (BP(OH)2) as a microenvironment-sensitive excited-state-intramolecular-double-proton-transfer (ESIDPT) probe. Here we present results on the UV-vis absorption and fluorescence properties of BP(OH)2 in the binary solutions. DMSO-water binary mixtures at various compositions are an intriguing hydrogen bonded system, where DMSO acts to diminish the hydrogen bonding ability of water with the dissolved solutes. As a result, we observe unusual changes in the photophysical properties of BP(OH)2 with increasing DMSO content in complete correlation with the prior simulation and experimental results on the solvent structures and dynamics. The fluorescence quantum yield and fluorescence lifetime of BP(OH)2 depend strongly on the DMSO content and become maximum at very low mole fraction (∼0.12) of DMSO. The anomalous behavior at this particular region likely arises from the enhanced pair hydrophobicity of the medium as demonstrated by Bagchi and co-workers (Banerjee, S.; Roy, S.; Bagchi, B. J. Phys. Chem. B 2010, 114, 12875-12882). In addition we have also shown the utilization of BP(OH)2 as a potential Zn(2+)-selective fluorescent sensor in a 1:1 DMSO-water binary mixture useful for biological applications. We observed highly enhanced fluorescence emission of BP(OH)2 selectively for binding with the Zn(2+) metal ion. Moreover, the fluorescence emission maximum of BP(OH)2-Zn(2+) is significantly blue-shifted with a reduced Stokes shift due to the inhibition of the ESIDPT process of BP(OH)2 through strong coordination.

  20. Excited-state behavior of tryptamine and related indoles. Remarkably efficient intramolecular proton-induced quenching

    Energy Technology Data Exchange (ETDEWEB)

    Shizuka, H.; Serizawa, M.; Kobayashi, H.; Kameta, K.; Sugiyama, H.; Matsuura, T.; Saito, I.

    1988-03-16

    The excited state behavior of tryptamine and 1,2,3,4-tetrahydrocarbazoles possessing alkylamino side chains in the absence and presence of 18-crown-6 in MeOH-H/sub 2/O (9:1) mixtures has been studied by means of nanosecond single-photon counting, fluorimetry, and photochemical H-D isotope exchange. The fluorescence intensity of these indoles increases significantly with increasing concentration of 18-crown-6. The relatively short lifetime of the tryptamine ammonium ion 1 is not ascribed to external quenching but rather to internal quenching. The rate constant k/sub q/ for internal quenching can be estimated from the equation k/sub q/ = tau/sub 0//sup -1/ - tau/sub max//sup -1/, where tau/sub 0/ and tau/sub max/ represent the fluorescence lifetimes for free 1 and the 1:1 1-crown ether complex, respectively. Internal quenching originates from electrophilic proton attack by the -N/sup +/H/sub 3/ (or -N/sup +/D/sub 3/) group of 1 at the C-4 position of the excited indole ring. For 3 (the tetrahydrocarbazole derivative R(CH/sub 2/)/sub 3/N/sup +/H/sub 3/) the k/sub q/ value comprises the electrophilic proton attack at the C-8 position plus other quenching (probably charge-transfer quenching) between the excited indole moiety (R*) and the -N/sup +/H/sub 3/ (or -N/sup +/D/sub 3/) group. The stabilization constant K/sub g/ for the corresponding ammonium ion and 18-crown-6 can be determined by fluorimetry. The kinetic and thermodynamic parameters for the internal quenching and the complex formation, respectively, have been described.

  1. Excited state intramolecular charge transfer reaction of 4 ...

    Indian Academy of Sciences (India)

    Administrator

    We will use the twisted intramolecular charge transfer (TICT) model to explain the photo-induced charge transfer ..... full width at half maxima (Γ) are expressed in 103 cm–1. –ΔGr are in kJ mol–1 units. PFH: per- ..... incorrect values of thermodynamic and kinetic parameters calculated using these reaction times, leading to ...

  2. Excited state intramolecular charge transfer reaction in non-aqueous ...

    Indian Academy of Sciences (India)

    concentration dependent reaction rate constant of a. TICT reaction already measured in bulk electrolyte solutions.44–46 Here, we report such a study where photo-induced intramolecular charge transfer reaction has been investigated in AOT/heptane non-aqueous reverse micelles at different Ws values, and also in.

  3. Excited state charge transfer reaction in (mixed solvent + electrolyte ...

    Indian Academy of Sciences (India)

    charge transfer reaction of 4-(1-azetidinyl)benzonitrile (P4C) in two sets of mixed solvents, (1-propanol + ethyl acetate) and (propylene ...... Harun Al Rasid Gazi and Ranjit Biswas. PrOH+EA. Normalized F.I.. 0. 1. Normalized F.I.. 0. 1. -3. 0. 3. 3000. 4000. 5000. 6000. Residual. -3. 0. 3. Residual. -3. 0. 3. Time(ps). 3000. 4000.

  4. Excited states populated via nucleon transfer in the reaction [sup 32]S+[sup 208]Pb

    Energy Technology Data Exchange (ETDEWEB)

    Corradi, L.; Petrache, C.M.; Ackermann, D.; De Angelis, G.; Moreno, H.; Napoli, D.R.; Spolaore, P.; Stefanini, A.M. (INFN, Lab. Nazionali di Legnaro (Italy)); Beghini, S.; Montagnoli, G.; Scarlassara, F.; Segato, G.F.; Signorini, C. (Padua Univ. (Italy). Dipt. di Fisica INFN, Padua (Italy)); Pollarolo, G. (Turin Univ. (Italy). Dipt. di Fisica INFN, Turin (Italy))

    1993-01-01

    The population strengths of excited states in nuclei produced via transfer reactions in the 185 MeV[sup 32]S+[sup 208]Pb reaction have been investigated by heavy-ion-[gamma] coincidence techniques. The cross sections extracted from the [gamma] spectra, have been analyzed in the framework of the Complex WKB approximation theory. (orig.).

  5. Symmetry-breaking intramolecular charge transfer in the excited state of meso-linked BODIPY dyads

    KAUST Repository

    Whited, Matthew T.

    2012-01-01

    We report the synthesis and characterization of symmetric BODIPY dyads where the chromophores are attached at the meso position, using either a phenylene bridge or direct linkage. Both molecules undergo symmetry-breaking intramolecular charge transfer in the excited state, and the directly linked dyad serves as a visible-light-absorbing analogue of 9,9′-bianthryl.

  6. Dynamics of charge-transfer excited states relevant to photochemical energy conversion

    Energy Technology Data Exchange (ETDEWEB)

    Lim, E.C.

    1991-11-01

    The primary objective of the research program is to gain a fundamental understanding of the factors governing the efficiency of excited-state charge transfer CT interactions between two chromophores that are brought together in close proximity, either by a very short covalent linkage or by ground-state complex formation. CT and van der Walls (vdW), interactions in covalently bonded bichromophoric compounds in condensed phase, as well as those in vdW complexes in supersonic jets, are being investigated using laser-based techniques under a variety of experimental conditions. This progress report is divided into three parts, according to the class of molecular systems and the phase (liquid vs. gas) in which the excited-state interactions are probed. The first is concerned with the excited states of bridged diaryl compounds in the condensed phase. The second involves the excited states of vdW complexes in supersonic jets. Finally, the third, is concerned with the excited states of electron donor-acceptor (EDA) systems in both the condensed phase and supersonic jets. In each of these studies, we are concerned with the interchromophore interactions ranging from weak vdW forces to strong CT forces, and the factors determining whether the interaction forces are weak or strong in related molecules.

  7. Solvent-dependent excited-state hydrogen transfer and intersystem crossing in 2-(2′-hydroxyphenyl)-benzothiazole

    KAUST Repository

    Aly, Shawkat Mohammede

    2015-02-12

    The excited-state intramolecular hydrogen transfer (ESIHT) of 2-(2′-hydroxyphenyl) benzothiazole (HBT) has been investigated in a series of nonpolar, polar aprotic, and polar protic solvents. A variety of state-of-the-art experimental methods were employed, including femto- and nanosecond transient absorption and fluorescence upconversion spectroscopy with broadband capabilities. We show that the dynamics and mechanism of ESIHT of the singlet excited HBT are strongly solvent-dependent. In nonpolar solvents, the data demonstrate that HBT molecules adopt a closed form stabilized by O-H⋯N chelated hydrogen bonds with no twisting angle, and the photoinduced H transfer occurs within 120 fs, leading to the formation of a keto tautomer. In polar solvents, owing to dipole-dipole cross talk and hydrogen bonding interactions, the H transfer process is followed by ultrafast nonradiative deactivation channels, including ultrafast internal conversion (IC) and intersystem crossing (ISC). This is likely to be driven by the twisting motion around the C-C bond between the hydroxyphenyl and thiazole moieties, facilitating the IC back to the enol ground state or to the keto triplet state. In addition, our femtosecond time-resolved fluorescence experiments indicate, for the first time, that the lifetime of the enol form in ACN is approximately 280 fs. This observation indicates that the solvent plays a crucial role in breaking the H bond and deactivating the excited state of the HBT. Interestingly, the broadband transient absorption and fluorescence up-conversion data clearly demonstrate that the intermolecular proton transfer from the excited HBT to the DMSO solvent is about 190 fs, forming the HBT anion excited state.

  8. Solvent control of intramolecular proton transfer

    DEFF Research Database (Denmark)

    Manolova, Y.; Marciniak, Heinz; Tschierlei, S.

    2017-01-01

    The solvent dependent excited state dynamics of 4-hydroxy-3-(piperidin-1-ylmethyl)-1-naphthaldehyde (compound 2), a candidate for a molecular switch based on intramolecular proton transfer, was investigated by ultrafast spectroscopy and quantum-chemical calculations. In acetonitrile a mixture...... of molecules in the enol and zwitterionic proton transfer (PT) form exists in the ground state. However, the zwitterion is the energetically favored one in the electronically excited state. Optical excitation of the enol form results in intramolecular proton transfer and formation of the PT form within 1.4 ps....... In addition we observe the appearance of a long living species with a rate of 1/(330 ps) which returns to the original ground state on time scales beyond 2 ns and which is attributed to the triplet state. In toluene the enol form is the only observed ground state tautomer, but no light induced proton transfer...

  9. Electronic and photophysical properties of 2-(2′-hydroxyphenyl)benzoxazole and its derivatives enhancing in the excited-state intramolecular proton transfer processes: A TD-DFT study on substitution effect

    Energy Technology Data Exchange (ETDEWEB)

    Daengngern, Rathawat; Kungwan, Nawee, E-mail: naweekung@gmail.com

    2015-11-15

    The effect of electron donating and withdrawing substituents on the enol absorption and keto emission spectra of 2-(2′-hydroxyphenyl)benzoxazole (HBO) and its derivatives has been systematically investigated by means of density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The enol absorption spectra of HBO were simulated by using five different DFTs with various exchange-correlation functions to validate a suitable functional prior to being further used as a method of choice to study the effect of substituents on the spectral characteristics of HBO derivatives. The popular B3LYP (Becke, three-parameter, Lee–Yang–Parr) exchange-correlation functional is found to provide the best desirable result in predicting the absorption spectrum close to experimental data. In the ground state, enol forms of HBO and its derivatives are more stable than those of keto forms, while in the first lowest excited state, keto forms are found to be more stable than their enol forms. Overall, simulated absorption and emission spectra of HBO and its derivatives from TD-B3LYP calculations are in good agreement with the experimental data. For enol, absorption maxima of HBO derivatives having electron-withdrawing groups are red-shift corresponding to their lower HOMO–LUMO energy gaps compared to that of HBO. For keto emission, HBO having electron donating groups (m-MeHBO and MHBO) and withdrawing group (CNHBO) at 4′-position on the phenol fragment as well as electron donating groups (HBOMe and HBOM) at 6-position on the benzoxazole fragment make the position of keto emission peak shift to shorter wavelength (blue-shift). However, HBO derivatives with electron withdrawing groups (HBOF, HBOCl, HBOA and HBOE) at 6-position give redshifted emission compared to the parent compound (HBO). The type of substituent on both 4′- and 6-positions certainly has a pronounced effect on the absorption and emission spectra of HBO derivatives. - Highlights: • Simulated spectra

  10. Construction of Vibronic Diabatic Hamiltonian for Excited-State Electron and Energy Transfer Processes.

    Science.gov (United States)

    Xie, Yu; Jiang, Shengshi; Zheng, Jie; Lan, Zhenggang

    2017-12-21

    Photoinduced excited-state electron and energy transfer processes are crucial in biological photoharvesting systems and organic photovoltaic devices. We discuss the construction of a diabatic vibronic Hamiltonian for the proper treatment of these processes involving the projection approach acting on both electronic wave functions and vibrational modes. In the electronic part, the wave function projection approach is used to construct the diabatic Hamiltonian in which both local excited states and charge-transfer states are included on the same footing. For the vibrational degrees of freedom, the vibronic couplings in the diabatic Hamiltonian are obtained in the basis of the pseudonormal modes localized on each monomer site by applying delocalized-to-localized mode projection. This systematic approach allows us to construct the vibronic diabatic Hamiltonian in molecular aggregates.

  11. Charge-transfer excited states in aqueous DNA: Insights from many-body Green's function theory.

    Science.gov (United States)

    Yin, Huabing; Ma, Yuchen; Mu, Jinglin; Liu, Chengbu; Rohlfing, Michael

    2014-06-06

    Charge-transfer (CT) excited states play an important role in the excited-state dynamics of DNA in aqueous solution. However, there is still much controversy on their energies. By ab initio many-body Green's function theory, together with classical molecular dynamics simulations, we confirm the existence of CT states at the lower energy side of the optical absorption maximum in aqueous DNA as observed in experiments. We find that the hydration shell can exert strong effects (∼1  eV) on both the electronic structure and CT states of DNA molecules through dipole electric fields. In this case, the solvent cannot be simply regarded as a macroscopic screening medium as usual. The influence of base stacking and base pairing on the CT states is also discussed.

  12. Assignment of the Charge-Transfer Excited States of Bis(N-Heterocyclic) Complexes of Copper(I)

    Science.gov (United States)

    1989-03-21

    Excited States of Bis (N-Heterocyclic) Complexes of Copper ( I) 12 PERSONAL AUTHOR(S( W. L. Parker and G. A. Crosby 3a 7YPE OF REPORT i b ’!ME COVERED ~ aDATE...Assignment of the Charge-Transfer Excited States of Bis (N-Heterocyclic) Complexes of Copper (I) by W. L. Parker and G. A. Crosby Prepared for Publication in...IHmited. Assignment of the Charge-Transfer Excited States of Bis (N-Heterocycl ic) Complexes of Copper (I) W. L. Parker and G. A. Crosby* Chemical

  13. Excited state conformational dynamics in carotenoids: dark intermediates and excitation energy transfer.

    Science.gov (United States)

    Beck, Warren F; Bishop, Michael M; Roscioli, Jerome D; Ghosh, Soumen; Frank, Harry A

    2015-04-15

    A consideration of the excited state potential energy surfaces of carotenoids develops a new hypothesis for the nature of the conformational motions that follow optical preparation of the S2 (1(1)Bu(+)) state. After an initial displacement from the Franck-Condon geometry along bond length alternation coordinates, it is suggested that carotenoids pass over a transition-state barrier leading to twisted conformations. This hypothesis leads to assignments for several dark intermediate states encountered in femtosecond spectroscopic studies. The Sx state is assigned to the structure reached upon the onset of torsional motions near the transition state barrier that divides planar and twisted structures on the S2 state potential energy surface. The X state, detected recently in two-dimensional electronic spectra, corresponds to a twisted structure well past the barrier and approaching the S2 state torsional minimum. Lastly, the S(∗) state is assigned to a low lying S1 state structure with intramolecular charge transfer character (ICT) and a pyramidal conformation. It follows that the bent and twisted structures of carotenoids that are found in photosynthetic light-harvesting proteins yield excited-state structures that favor the development of an ICT character and optimized energy transfer yields to (bacterio)chlorophyll acceptors. Copyright © 2015 Elsevier Inc. All rights reserved.

  14. Observation of excited state charge transfer with fs/ps-CARS

    Energy Technology Data Exchange (ETDEWEB)

    Blom, Alex Jason [Iowa State Univ., Ames, IA (United States)

    2009-01-01

    Excited state charge transfer processes are studied using the fs/ps-CARS probe technique. This probe allows for multiplexed detection of Raman active vibrational modes. Systems studied include Michler's Ketone, Coumarin 120, 4-dimethylamino-4'-nitrostilbene, and several others. The vibrational spectrum of the para di-substituted benzophenone Michler's Ketone in the first excited singlet state is studied for the first time. It is found that there are several vibrational modes indicative of structural changes of the excited molecule. A combined experimental and theoretical approach is used to study the simplest 7-amino-4-methylcoumarin, Coumarin 120. Vibrations observed in FTIR and spontaneous Raman spectra are assigned using density functional calculations and a continuum solvation model is used to predict how observed modes are affected upon inclusion of a solvent. The low frequency modes of the excited state charge transfer species 4-dimethylamino-4{prime}-nitrostilbene are studied in acetonitrile. Results are compared to previous work on this molecule in the fingerprint region. Finally, several partially completed projects and their implications are discussed. These include the two photon absorption of Coumarin 120, nanoconfinement in cyclodextrin cavities and sensitization of titania nanoparticles.

  15. Theoretical Modelling for the Ground State Rotamerisation and Excited State Intramolecular Proton Transfer of 2-(2’-hydroxyphenyloxazole, 2-(2’-hydroxyphenylimidazole, 2-(2’-hydroxyphenylthiazole and Their Benzo Analogues

    Directory of Open Access Journals (Sweden)

    Nitin Chattopadhyay

    2003-05-01

    Full Text Available Abstract: Two series of compounds, one comprising of 2-(2′-hydroxyphenylbenzoxazole (HBO, 2-(2′-hydroxyphenylbenzimidazole (HBI, 2-(2′-hydroxyphenylbenzothiazole (HBT, and the other of 2-(2′-hydroxyphenyloxazole (HPO, 2-(2′-hydroxyphenylimidazole (HPI and 2-(2′-hydroxyphenylthiazole (HPT are susceptible to ground state rotamerization as well as excited state intramolecular proton transfer (ESIPT reactions. Some of these compounds show experimental evidence of the existence of two ground state conformers. Out of these two one undergoes ESIPT reaction leading to the formation of the tautomer. The two photophysical processes, in combination, result in the production of a number of fluorescence bands each one of which corresponding to a particular species. Semiempirical AM1-SCI calculations have been performed to rationalize the photophysical behaviour of the compounds. The calculations suggest that for the first series of compounds, two rotational isomers are present in the ground state of HBO and HBI while HBT has a single conformer under similar circumstances. For the molecules of the other series existence of rotamers depends very much on the polarity of the environment. The potential energy curves (PEC for the ESIPT process in different electronic states of the molecules have been generated theoretically. The simulated PECs reveal that for all these systems the IPT reaction is unfavourable in the ground state but feasible, both kinetically and thermodynamically, in the S1 as well as T1 states.

  16. Dynamics of charge-transfer excited states relevant to photochemical energy conversion

    Energy Technology Data Exchange (ETDEWEB)

    Lim, E.C.

    1993-01-01

    A systematic study of intramolecular photoassociation and photoinduced charge transfer (CT) was initiated in bichromophoric systems of M-X-M, where two identical aromatic hydrocarbons M are joined by X=CH[sub 2], O, NH, etc. Dinaphthylamines, dinaphthylethers, and dinaphthylmethanes in nonpolar solvents form triplet excimers, following inter system crossing of singlets to the triplet manifold; in polar solvents, the molecule forms an intramolecular CT state. The interchromophore interaction study was extended to N-phenyl-2-naphthylamine. The lowest excited singlet states of the dinaphthylamines were studied by semiempirical quantum chemical methods. Exciplex formation was studied in excited states of jet-cooled van der Waals complexes, such as fluorene/substituted benzenes and 1-cyanonaphthalene-aliphatic amines.

  17. Bimolecular Excited-State Electron Transfer with Surprisingly Long-Lived Radical Ions

    KAUST Repository

    Alsam, Amani Abdu

    2015-09-02

    We explored the excited-state interactions of bimolecular, non-covalent systems consisting of cationic poly[(9,9-di(3,3’-N,N’-trimethyl-ammonium) propyl fluorenyl-2,7-diyl)-alt-co-(9,9-dioctyl-fluorenyl-2,7-diyl)] diiodide salt (PFN) and 1,4-dicyanobenzene (DCB) using steady-state and time-resolved techniques, including femto- and nanosecond transient absorption and femtosecond infrared spectroscopies with broadband capabilities. The experimental results demonstrated that photo-induced electron transfer from PFN to DCB occurs on the picosecond time scale, leading to the formation of PFN+• and DCB-• radical ions. Interestingly, real-time observations of the vibrational marker modes on the acceptor side provided direct evidence and insight into the electron transfer process indirectly inferred from UV-Vis experiments. The band narrowing on the picosecond time scale observed on the antisymmetric C-N stretching vibration of the DCB radical anion provides clear experimental evidence that a substantial part of the excess energy is channeled into vibrational modes of the electron transfer product and that the geminate ion pairs dissociate. More importantly, our nanosecond time-resolved data indicate that the charge-separated state is very long lived ( 30 ns) due to the dissociation of the contact radical ion pair into free ions. Finally, the fast electron transfer and slow charge recombination anticipate the current donor−acceptor system with potential applications in organic solar cells.

  18. Characterising excited states in and around the semi-magic nucleus $^{68}$ Ni using Coulomb excitation and one-neutron transfer

    CERN Multimedia

    It is proposed to investigate the structure of excited states in $^{68, 70}$Ni(Z =28, N=40, 42) via the measurement of electromagnetic matrix elements in a Coulomb excitation experiment in order to study the N = 40 harmonic-oscillator shell and the Z = 28 proton shell closures. The measured B(E2) values connecting low-lying 0$^{+}$ and 2$^{+}$ can be compared to shell-model predictions. It is also proposed to perform the one-neutron transfer reaction ${d}$($^{68}$Ni,$^{69}$Ni)${p}$, with the aim of populating excited states in $^{69}$Ni. Comparisons with the states populated in the recently performed ${d}$($^{66}$Ni,$^{67}$Ni)${p}$ reaction will be useful in determining the role of the neutron $d_{5/2}$ orbital in the semi-magic properties of $^{68}$Ni.

  19. Charge-Transfer Dynamics in the Lowest Excited State of a Pentacene–Fullerene Complex: Implications for Organic Solar Cells

    KAUST Repository

    Joseph, Saju

    2017-10-02

    We characterize the dynamic nature of the lowest excited state in a pentacene/C60 complex on the femtosecond time scale, via a combination of ab initio molecular dynamics and time-dependent density functional theory. We analyze the correlations between the molecular vibrations of the complex and the oscillations in the electron-transfer character of its lowest excited state, which point to vibration-induced coherences between the (pentacene-based) local-excitation (LE) state and the complex charge-transfer (CT) state. We discuss the implications of our results on this model system for the exciton-dissociation process in organic solar cells.

  20. Manipulating charge transfer excited state relaxation and spin crossover in iron coordination complexes with ligand substitution

    DEFF Research Database (Denmark)

    Zhang, Wenkai; Kjær, Kasper Skov; Alonso-Mori, Roberto

    2017-01-01

    state lifetime of iron based complexes due to spin crossover-the extremely fast intersystem crossing and internal conversion to high spin metal-centered excited states. We revitalize a 30 year old synthetic strategy for extending the MLCT excited state lifetimes of iron complexes by making mixed ligand...... iron complexes with four cyanide (CN-;) ligands and one 2,2′-bipyridine (bpy) ligand. This enables MLCT excited state and metal-centered excited state energies to be manipulated with partial independence and provides a path to suppressing spin crossover. We have combined X-ray Free-Electron Laser (XFEL......) Kβ hard X-ray fluorescence spectroscopy with femtosecond time-resolved UV-visible absorption spectroscopy to characterize the electronic excited state dynamics initiated by MLCT excitation of [Fe(CN)4(bpy)]2-. The two experimental techniques are highly complementary; the time-resolved UV...

  1. Excited State Structural Dynamics of Carotenoids and ChargeTransfer Systems

    Energy Technology Data Exchange (ETDEWEB)

    Van Tassle, Aaron Justin [Univ. of California, Berkeley, CA (United States)

    2006-01-01

    This dissertation describes the development andimplementation of a visible/near infrared pump/mid-infrared probeapparatus. Chapter 1 describes the background and motivation ofinvestigating optically induced structural dynamics, paying specificattention to solvation and the excitation selection rules of highlysymmetric molecules such as carotenoids. Chapter 2 describes thedevelopment and construction of the experimental apparatus usedthroughout the remainder of this dissertation. Chapter 3 will discuss theinvestigation of DCM, a laser dye with a fluorescence signal resultingfrom a charge transfer state. By studying the dynamics of DCM and of itsmethyl deuterated isotopomer (an otherwise identical molecule), we areable to investigate the origins of the charge transfer state and provideevidence that it is of the controversial twisted intramolecular (TICT)type. Chapter 4 introduces the use of two-photon excitation to the S1state, combined with one-photon excitation to the S2 state of thecarotenoid beta-apo-8'-carotenal. These 2 investigations show evidencefor the formation of solitons, previously unobserved in molecular systemsand found only in conducting polymers Chapter 5 presents an investigationof the excited state dynamics of peridinin, the carotenoid responsiblefor the light harvesting of dinoflagellates. This investigation allowsfor a more detailed understanding of the importance of structuraldynamics of carotenoids in light harvesting.

  2. Shape coexistence at the proton drip-line: First identification of excited states in 180Pb

    CERN Document Server

    Rahkila, P; Pakarinen, J; Gray-Jones, C; Greenlees, P T; Jakobsson, U; Jones, P; Julin, R; Juutinen, S; Ketelhut, S; Koivisto, H; Leino, M; Nieminen, P; Nyman, M; Papadakis, P; Paschalis, S; Petri, M; Peura, P; Roberts, O J; Ropponen, T; Ruotsalainen, P; Saren, J; Scholey, C; Sorri, J; Tuff, A G; Uusitalo, J; Wadsworth, R; Bender, M; Heenen, P -H

    2010-01-01

    Excited states in the extremely neutron-deficient nucleus, 180Pb, have been identified for the first time using the JUROGAM II array in conjunction with the RITU recoil separator at the Accelerator Laboratory of the University of Jyvaskyla. This study lies at the limit of what is presently achievable with in-beam spectroscopy, with an estimated cross-section of only 10 nb for the 92Mo(90Zr,2n)180Pb reaction. A continuation of the trend observed in 182Pb and 184Pb is seen, where the prolate minimum continues to rise beyond the N=104 mid-shell with respect to the spherical ground state. Beyond mean-field calculations are in reasonable correspondence with the trends deduced from experiment.

  3. Coherence, energy and charge transfers in de-excitation pathways of electronic excited state of biomolecules in photosynthesis

    DEFF Research Database (Denmark)

    Bohr, Henrik; Malik, F. Bary

    2013-01-01

    The observed multiple de-excitation pathways of photo-absorbed electronic excited state in the peridinin–chlorophyll complex, involving both energy and charge transfers among its constituents, are analyzed using the bio-Auger (B-A) theory. It is also shown that the usually used F¨orster–Dexter th...

  4. An excited-state intramolecular photon transfer fluorescence probe for localizable live cell imaging of cysteine

    Science.gov (United States)

    Liu, Wei; Chen, Wen; Liu, Si-Jia; Jiang, Jian-Hui

    2017-03-01

    Small molecule probes suitable for selective and specific fluorescence imaging of some important but low-concentration intracellular reactive sulfur species such as cysteine (Cys) pose a challenge in chemical biology. We present a readily available, fast-response fluorescence probe CHCQ-Ac, with 2-(5‧-chloro-2-hydroxyl-phenyl)-6-chloro-4(3 H)-quinazolinone (CHCQ) as the fluorophore and acrylate group as the functional moiety, that enables high-selectivity and high-sensitivity for detecting Cys in both solution and biological system. After specifically reacted with Cys, the probe undergoes a seven-membered intramolecular cyclization and released the fluorophore CHCQ with excited-state intramolecular photon transfer effect. A highly fluorescent, insoluble aggregate was then formed to facilitate high-sensitivity and high-resolution imaging. The results showed that probe CHCQ-Ac affords a remarkably large Stokes shift and can detect Cys under physiological pH condition with no interference from other analytes. Moreover, this probe was proved to have excellent chemical stability, low cytotoxicity and good cell permeability. Our design of this probe provides a novel potential tool to visualize and localize cysteine in bioimaging of live cells that would greatly help to explore various Cys-related physiological and pathological cellular processes in cell biology and diagnostics.

  5. Proton decay of excited states in 12N and 13O and the astrophysical 11C(p,γ)12N reaction rate

    Science.gov (United States)

    Sobotka, L. G.; Buhro, W. W.; Charity, R. J.; Elson, J. M.; Jager, M. F.; Manfredi, J.; Mahzoon, M. H.; Mukhamedzhanov, A. M.; Eremenko, V.; McCleskey, M.; Pizzone, R. G.; Roeder, B. T.; Spiridon, A.; Simmons, E.; Trache, L.; Kurokawa, M.; Navrátil, P.

    2013-05-01

    Using a 13O beam, we have observed proton decays of 12N and 13O excited states following proton-knockout and inelastic interactions on a 9Be target. The excited states were determined from detected two- and three-body exit channels using the invariant mass method. The width of the second excited state of 12N was determined to be 55(20) keV, considerably smaller than the value listed in the ENSDF data base. Three new excited states of narrow width (Γ<50 keV) were observed in 13O from the p+12N and 2p+11C exit channels. One of these states (E* = 3.67 MeV) was found to sequentially decay to the second excited of 12N. We again found these data to be inconsistent with the listed decay width. The ramifications for the astrophysically interesting 11C(p,γ)12N reaction are given.

  6. Excited states

    CERN Document Server

    Lim, Edward C

    1974-01-01

    Excited States, Volume I reviews radiationless transitions, phosphorescence microwave double resonance through optical spectra in molecular solids, dipole moments in excited states, luminescence of polar molecules, and the problem of interstate interaction in aromatic carbonyl compounds. The book discusses the molecular electronic radiationless transitions; the double resonance techniques and the relaxation mechanisms involving the lowest triplet state of aromatic compounds; as well as the optical spectra and relaxation in molecular solids. The text also describes dipole moments and polarizab

  7. Dynamics of charge-transfer excited states relevant to photochemical energy conversion. Progress report, June 1, 1991--November 15, 1991

    Energy Technology Data Exchange (ETDEWEB)

    Lim, E.C.

    1991-11-01

    The primary objective of the research program is to gain a fundamental understanding of the factors governing the efficiency of excited-state charge transfer CT interactions between two chromophores that are brought together in close proximity, either by a very short covalent linkage or by ground-state complex formation. CT and van der Walls (vdW), interactions in covalently bonded bichromophoric compounds in condensed phase, as well as those in vdW complexes in supersonic jets, are being investigated using laser-based techniques under a variety of experimental conditions. This progress report is divided into three parts, according to the class of molecular systems and the phase (liquid vs. gas) in which the excited-state interactions are probed. The first is concerned with the excited states of bridged diaryl compounds in the condensed phase. The second involves the excited states of vdW complexes in supersonic jets. Finally, the third, is concerned with the excited states of electron donor-acceptor (EDA) systems in both the condensed phase and supersonic jets. In each of these studies, we are concerned with the interchromophore interactions ranging from weak vdW forces to strong CT forces, and the factors determining whether the interaction forces are weak or strong in related molecules.

  8. First identification of excited states in 117Ba using the recoil-β -delayed proton tagging technique

    Science.gov (United States)

    Ding, B.; Liu, Z.; Seweryniak, D.; Woods, P. J.; Wang, H. L.; Yang, J.; Liu, H. L.; Davids, C. N.; Carpenter, M. P.; Davinson, T.; Janssens, R. V. F.; Page, R. D.; Robinson, A. P.; Shergur, J.; Sinha, S.; Zhu, S.; Tang, X. D.; Wang, J. G.; Huang, T. H.; Zhang, W. Q.; Sun, M. D.; Liu, X. Y.; Lu, H. Y.

    2017-02-01

    Excited states have been observed for the first time in the neutron-deficient nucleus 117Ba using the recoil-decay tagging technique following the heavy-ion fusion-evaporation reaction 64Zn(58Ni, 2p3n)117Ba. Prompt γ rays have been assigned to 117Ba through correlations with β -delayed protons following the decay of A =117 recoils. Through the analysis of the γ -γ coincidence relationships, a high-spin level scheme consisting of two bands has been established in 117Ba. Based on the systematics of the level spacings in the neighboring barium isotopes, the two bands are proposed to have ν h11 /2[532 ] 5 /2- and ν d5 /2[413 ] 5 /2+ configurations, respectively. The observed band-crossing properties are interpreted in the framework of cranked shell model.

  9. Proton-hole and core-excited states in the semi-magic nucleus 131In82

    Energy Technology Data Exchange (ETDEWEB)

    Taprogge, J.; Jungclaus, A.; Grawe, H.; Borzov, I. N.; Nishimura, S.; Doornenbal, P.; Lorusso, G.; Simpson, G. S.; Söderström, P. -A.; Sumikama, T.; Xu, Z. Y.; Baba, H.; Browne, F.; Fukuda, N.; Gernhäuser, R.; Gey, G.; Inabe, N.; Isobe, T.; Jung, H. S.; Kameda, D.; Kim, G. D.; Kim, Y. -K.; Kojouharov, I.; Kubo, T.; Kurz, N.; Kwon, Y. K.; Li, Z.; Sakurai, H.; Schaffner, H.; Shimizu, Y.; Steiger, K.; Suzuki, H.; Takeda, H.; Vajta, Zs.; Watanabe, H.; Wu, J.; Yagi, A.; Yoshinaga, K.; Benzoni, G.; Bönig, S.; Chae, K. Y.; Coraggio, L.; Daugas, J. -M.; Drouet, F.; Gadea, A.; Gargano, A.; Ilieva, S.; Itaco, N.; Kondev, F. G.; Kröll, T.; Lane, G. J.; Montaner-Pizá, A.; Moschner, K.; Mücher, D.; Naqvi, F.; Niikura, M.; Nishibata, H.; Odahara, A.; Orlandi, R.; Patel, Z.; Podolyák, Zs.; Wendt, A.

    2016-11-01

    The decay of the N = 83 nucleus Cd-131 has been studied at the RIBF facility at the RIKEN Nishina Center. The main purpose of the study was to identify the position of the and proton-hole states and the energies of core-excited configurations in the semi-magic nucleus In-131. From the radiation emitted following the decay, a level scheme of In-131 was established and the feeding to each excited state determined. Similarities between the single-particle transitions observed in the decays of the N = 83 isotones In-132 and Cd-131 are discussed. Finally the excitation energies of several core-excited configurations in In-131 are compared to QRPA and shell-model calculations.

  10. Proton-hole and core-excited states in the semi-magic nucleus {sup 131}In{sub 82}

    Energy Technology Data Exchange (ETDEWEB)

    Taprogge, J. [Instituto de Estructura de la Materia, CSIC, Madrid (Spain); Universidad Autonoma de Madrid, Departamento de Fisica Teorica, Madrid (Spain); RIKEN Nishina Center, RIKEN, Saitama (Japan); Jungclaus, A. [Instituto de Estructura de la Materia, CSIC, Madrid (Spain); Grawe, H. [GSI Helmholtzzentrum fuer Schwerionenforschung GmbH, Darmstadt (Germany); Borzov, I.N. [Kurchatov Institute, Moscow (Russian Federation); Joint Institute for Nuclear Research, Dubna (Russian Federation); Nishimura, S.; Doornenbal, P.; Soederstroem, P.A.; Baba, H.; Fukuda, N.; Inabe, N.; Isobe, T.; Kameda, D.; Kubo, T.; Shimizu, Y.; Suzuki, H.; Takeda, H.; Watanabe, H. [RIKEN Nishina Center, RIKEN, Saitama (Japan); Lorusso, G. [RIKEN Nishina Center, RIKEN, Saitama (Japan); National Physical Laboratory, NPL, Teddington, Middlesex (United Kingdom); University of Surrey, Department of Physics, Guildford (United Kingdom); Simpson, G.S.; Drouet, F. [LPSC, Universite Joseph Fourier Grenoble 1, CNRS/IN2P3, Institut National Polytechnique de Grenoble, Grenoble Cedex (France); Sumikama, T. [Tohoku University, Department of Physics, Sendai, Miyagi (Japan); Xu, Z.Y.; Niikura, M. [University of Tokyo, Department of Physics, Tokyo (Japan); Browne, F. [RIKEN Nishina Center, RIKEN, Saitama (Japan); University of Brighton, School of Computing, Engineering and Mathematics, Brighton (United Kingdom); Gernhaeuser, R.; Steiger, K.; Muecher, D. [Technische Universitaet Muenchen, Physik Department E12, Garching (Germany); Gey, G. [RIKEN Nishina Center, RIKEN, Saitama (Japan); LPSC, Universite Joseph Fourier Grenoble 1, CNRS/IN2P3, Institut National Polytechnique de Grenoble, Grenoble Cedex (France); Institut Laue-Langevin, B.P. 156, Grenoble Cedex 9 (France); Jung, H.S. [Chung-Ang University, Department of Physics, Seoul (Korea, Republic of); Kim, G.D.; Kwon, Y.K. [Institute for Basic Science, Rare Isotope Science Project, Daejeon (Korea, Republic of); Kim, Y.K. [Institute for Basic Science, Rare Isotope Science Project, Daejeon (Korea, Republic of); Hanyang University, Department of Nuclear Engineering, Seoul (Korea, Republic of); Kojouharov, I.; Kurz, N.; Schaffner, H. [Joint Institute for Nuclear Research, Dubna (Russian Federation); Li, Z. [Peking University, School of Physics and State key Laboratory of Nuclear Physics and Technology, Beijing (China); Sakurai, H. [RIKEN Nishina Center, RIKEN, Saitama (Japan); University of Tokyo, Department of Physics, Tokyo (Japan); Vajta, Zs. [RIKEN Nishina Center, RIKEN, Saitama (Japan); MTA Atomki, P.O. Box 51, Debrecen (Hungary); Wu, J. [RIKEN Nishina Center, RIKEN, Saitama (Japan); Peking University, School of Physics and State key Laboratory of Nuclear Physics and Technology, Beijing (China); Yagi, A.; Nishibata, H.; Odahara, A. [Osaka University, Department of Physics, Toyonaka (Japan); Yoshinaga, K. [Tokyo University of Science, Department of Physics, Faculty of Science and Technology, Noda, Chiba (Japan); Benzoni, G. [INFN, Sezione di Milano, Milano (Italy); Boenig, S.; Ilieva, S.; Kroell, T. [Technische Universitaet Darmstadt, Institut fuer Kernphysik, Darmstadt (Germany); Chae, K.Y. [Sungkyunkwan University, Department of Physics, Suwon (Korea, Republic of); Coraggio, L.; Gargano, A. [Complesso Universitario di Monte S. Angelo, Istituto Nazionale di Fisica Nucleare, Napoli (Italy); Daugas, J.M. [CEA, DAM, DIF, Arpajon cedex (France); Gadea, A.; Montaner-Piza, A. [CSIC-Univ. of Valencia, Instituto de Fisica Corpuscular, Paterna (Spain); Itaco, N. [Seconda Universita di Napoli, Dipartimento di Matematica e Fisica, Caserta (Italy); Kondev, F.G. [Argonne National Laboratory, Nuclear Engineering Division, Argonne, IL (United States); Lane, G.J. [Australian National University, Department of Nuclear Physics, Research School of Physical Sciences and Engineering, Canberra (Australia); Moschner, K.; Wendt, A. [University of Cologne, IKP, Cologne (Germany); Naqvi, F. [Yale University, Wright Nuclear Structure Laboratory, New Haven, CT (United States); Orlandi, R. [K.U. Leuven, Instituut voor Kern- en StralingsFysica, Heverlee (Belgium); Japan Atomic Energy Agency, Advanced Science Research Center, Tokai, Ibaraki (Japan); Patel, Z.; Podolyak, Zs. [University of Surrey, Department of Physics, Guildford (United Kingdom)

    2016-11-15

    The β decay of the N = 83 nucleus {sup 131}Cd has been studied at the RIBF facility at the RIKEN Nishina Center. The main purpose of the study was to identify the position of the 1p{sub 3/2} and 0f{sub 5/2} proton-hole states and the energies of core-excited configurations in the semi-magic nucleus {sup 131}In. From the radiation emitted following the β decay, a level scheme of {sup 131}In was established and the β feeding to each excited state determined. Similarities between the single-particle transitions observed in the β decays of the N = 83 isotones {sup 132}In and {sup 131}Cd are discussed. Finally the excitation energies of several core-excited configurations in {sup 131}In are compared to QRPA and shell-model calculations. (orig.)

  11. Excited-State Dynamics of Biological Molecules in Solution: Photoinduced Charge Transfer in Oxidatively Damaged DNA and Deactivation of Violacein in Viscous Solvents

    Science.gov (United States)

    Beckstead, Ashley Ann

    UV radiation from the sun is strongly absorbed by DNA, and the resulting electronic excited states can lead to the formation of mutagenic photoproducts. Decades of research have brought to light the excited-state dynamics of single RNA and DNA nucleobases, but questions remain about the nature of excited states accessed in DNA strands. In this thesis, I present ultrafast spectroscopic observations of photoinduced electron transfer from the oxidatively damaged bases, 8-oxo-7,8-dihydro-2'-deoxyguanosine, 5-hydroxy-2'-deoxycytidine and 5-hydroxy-2'-deoxyuridine, to adenine in three dinucleotides. The results reveal that charge transfer states are formed on a timescale faster than our instrumental resolution (electron transfer efficiently returns the excited-state population to the ground state on timescales from tens to hundreds of ps. In addition to recent spectroscopic observations of charge transfer state species in DNA by other groups, our results have augmented understanding of the long-lived transient signals observed in DNA strands. The observation of photoinduced electron transfer in these oxidatively damaged nucleobases also supports a recent proposal regarding the role of oxidative products in pre-RNA catalysis. I discuss these observations in the contexts of fundamental DNA excited-state dynamics and prebiotic chemical evolution. In this thesis, I also present the first ultrafast spectroscopic investigation of violacein, a pigment isolated from Antarctic bacteria. Despite claims for the photoprotective role of this pigment, there has never been a spectroscopic analysis of excited-state deactivation in violacein. Emission spectra, fluorescence quantum yields and excited-state lifetimes of violacein in various solvents were measured for the first time. Both the fluorescence quantum yield and excited-state lifetime of violacein increase in increasingly viscous solvents, suggesting a large-scale motion mediates excited-state deactivation. I compare these

  12. Measurement of Polarization Observables in the Electro-Excitation of the Proton to its First Excited State

    Energy Technology Data Exchange (ETDEWEB)

    Roche, Rikki [Florida State Univ., Tallahassee, FL (United States)

    2003-08-01

    This thesis reports results from the Thomas Jefferson National Accelerator Facility (Jefferson Lab) Hall A experiment E91-011, which measured double-polarization observables in the pion electroproduction reaction from the proton. Specifically, the experiment measured the recoil proton polarization, polarized response functions, and cross section for the p($\\vec{e}$, e' $\\vec{p}$) π° reaction at a center-of-mass energy centered at W = 1232 MeV--the peak of the Δ(1232) resonance--and at a four-momentum transfer squared of Q2 = 1.0 GeV2/c2. Both the recoil proton polarization and polarized response function results will be presented in this thesis. Data were collected at Jefferson Lab, located in Newport News, Virginia during the summer of 2000. A 4.53 GeV polarized electron beam was scattered off of a cryogenic hydrogen target. The recoil proton polarization was measured in the Focal Plane Polarimeter (FPP), located in one of the two High Resolution Spectrometers (HRS) in Hall A. A maximum likelihood method was used to determine the polarized response functions directly from the measured polarizations and cross sections. A simultaneous fit of the cross sections, the recoil proton polarizations, and angular distributions of the polarized response functions will provide a determination of individual multipole amplitudes. Some of these multipole amplitudes are related to the concept of proton deformation. Both the recoil proton polarizations and polarized response functions were compared to two phenomenological models: MAID and SAID, which have all free parameters fixed, based on fits to previous world data. The measured helicity dependent observables, which are dominated by imaginary parts of Δ(1232)-resonance excitation multipole amplitudes, agree very well with the two models. The measured helicity independent observables, which are dominated by real parts of background multipole amplitudes, do not agree completely with

  13. Proton transfer events in GFP

    NARCIS (Netherlands)

    Di Donato, M.; van Wilderen, L.J.; van Stokkum, I.H.M.; Stuart, T. C.; Kennis, J.T.M.; Hellingwerf, K.J.; van Grondelle, R.; Groot, M.L.

    2011-01-01

    Proton transfer is one of the most important elementary processes in biology. Green fluorescent protein (GFP) serves as an important model system to elucidate the mechanistic details of this reaction, because in GFP proton transfer can be induced by light absorption. Illumination initiates proton

  14. Dynamics of charge-transfer excited states relevant to photochemical energy conversion. Technical report, June 1, 1992--March 30, 1993

    Energy Technology Data Exchange (ETDEWEB)

    Lim, E.C.

    1993-06-01

    A systematic study of intramolecular photoassociation and photoinduced charge transfer (CT) was initiated in bichromophoric systems of M-X-M, where two identical aromatic hydrocarbons M are joined by X=CH{sub 2}, O, NH, etc. Dinaphthylamines, dinaphthylethers, and dinaphthylmethanes in nonpolar solvents form triplet excimers, following inter system crossing of singlets to the triplet manifold; in polar solvents, the molecule forms an intramolecular CT state. The interchromophore interaction study was extended to N-phenyl-2-naphthylamine. The lowest excited singlet states of the dinaphthylamines were studied by semiempirical quantum chemical methods. Exciplex formation was studied in excited states of jet-cooled van der Waals complexes, such as fluorene/substituted benzenes and 1-cyanonaphthalene-aliphatic amines.

  15. Proton and hydride affinities in excited states: magnitude reversals in proton and hydride affinities between the lowest singlet and triplet states of annulenyl and benzannulenyl anions and cations.

    Science.gov (United States)

    Rosenberg, Martin; Ottosson, Henrik; Kilså, Kristine

    2010-04-02

    Aromaticity has importance for proton and hydride affinities in the singlet ground state (S(0)) of annulenyl anions and cations so that, e.g., cyclopentadiene is an acidic hydrocarbon. For the lowest pipi* excited triplet state (T(1)), Baird's rule concludes that annulenes with 4n pi-electrons are aromatic and those with 4n+2 pi-electrons are antiaromatic, opposite to Huckel's rule for aromaticity in S(0). Our hypothesis is now that the relative magnitudes of proton and hydride affinities of annulenyl anions and cations reverts systematically as one goes from S(0) to T(1) as a result of the opposite electron counting rules for aromaticity in the two states. Using quantum chemical calculations at the G3(MP2)//(U)B3LYP/6-311+G(d,p) level we have examined the validity of this hypothesis for eight proton and eight hydride addition reactions of anions and cations, respectively, of annulenyl and benzannulenyl type. We categorize the (4n+2)pi-electron systems in S(0) and the 4npi-electron systems in T(1) to be of A-character and 4npi-electron systems in S(0) and (4n+2)pi-electron systems in T(1) to be of AA-character (A, aromatic; AA, anti/nonaromatic). The average proton affinities of anions of A- and AA-characters in S(0) are 1447 and 1521 kJ/mol, respectively, and in T(1) they are 1365 and 1493 kJ/mol. The average hydride affinities of A- and AA-character cations in S(0) are 826 and 996 kJ/mol, and in T(1) they are 790 and 879 kJ/mol, respectively. Thus, the calculated proton and hydride affinities are in general lower for anions and cations of A-character than for those of AA-character, in good support of our hypothesis. The findings could likely be applied in synthetic organic photochemistry and other areas where excited state acid-base chemistry plays a role.

  16. Observation of Ground- and Excited-State Charge Transfer at the C60/Graphene Interface.

    Science.gov (United States)

    Jnawali, Giriraj; Rao, Yi; Beck, Jonathan H; Petrone, Nicholas; Kymissis, Ioannis; Hone, James; Heinz, Tony F

    2015-07-28

    We examine charge transfer interactions in the hybrid system of a film of C60 molecules deposited on single-layer graphene using Raman spectroscopy and Terahertz (THz) time-domain spectroscopy. In the absence of photoexcitation, we find that the C60 molecules in the deposited film act as electron acceptors for graphene, yielding increased hole doping in the graphene layer. Hole doping of the graphene film by a uniform C60 film at a level of 5.6 × 10(12)/cm(2) or 0.04 holes per interfacial C60 molecule was determined by the use of both Raman and THz spectroscopy. We also investigate transient charge transfer occurring upon photoexcitation by femtosecond laser pulses with a photon energy of 3.1 eV. The C60/graphene hybrid exhibits a short-lived (ps) decrease in THz conductivity, followed by a long-lived increase in conductivity. The initial negative photoconductivity transient, which decays within 2 ps, reflects the intrinsic photoresponse of graphene. The longer-lived positive conductivity transient, with a lifetime on the order of 100 ps, is attributed to photoinduced hole doping of graphene by interfacial charge transfer. We discuss possible microscopic pathways for hot carrier processes in the hybrid system.

  17. Ligand manipulation of charge transfer excited state relaxation and spin crossover in [Fe(2,2′-bipyridine2(CN2

    Directory of Open Access Journals (Sweden)

    Kasper S. Kjær

    2017-07-01

    Full Text Available We have used femtosecond resolution UV-visible and Kβ x-ray emission spectroscopy to characterize the electronic excited state dynamics of [Fe(bpy2(CN2], where bpy=2,2′-bipyridine, initiated by metal-to-ligand charge transfer (MLCT excitation. The excited-state absorption in the transient UV-visible spectra, associated with the 2,2′-bipyridine radical anion, provides a robust marker for the MLCT excited state, while the transient Kβ x-ray emission spectra provide a clear measure of intermediate and high spin metal-centered excited states. From these measurements, we conclude that the MLCT state of [Fe(bpy2(CN2] undergoes ultrafast spin crossover to a metal-centered quintet excited state through a short lived metal-centered triplet transient species. These measurements of [Fe(bpy2(CN2] complement prior measurement performed on [Fe(bpy3]2+ and [Fe(bpy(CN4]2− in dimethylsulfoxide solution and help complete the chemical series [Fe(bpyN(CN6–2N]2N-4, where N = 1–3. The measurements confirm that simple ligand modifications can significantly change the relaxation pathways and excited state lifetimes and support the further investigation of light harvesting and photocatalytic applications of 3d transition metal complexes.

  18. Ultrafast Excited-State Dynamics of Diketopyrrolopyrrole (DPP)-Based Materials: Static versus Diffusion-Controlled Electron Transfer Process

    KAUST Repository

    Alsulami, Qana

    2015-06-25

    Singlet-to-triplet intersystem crossing (ISC) and photoinduced electron transfer (PET) of platinum(II) containing diketopyrrolopyrrole (DPP) oligomer in the absence and presence of strong electron-acceptor tetracyanoethylene (TCNE) were investigated using femtosecond and nanosecond transient absorption spectroscopy with broadband capabilities. The role of platinum(II) incorporation in those photophysical properties was evaluated by comparing the excited-state dynamics of DPP with and without the metal centers. The steady-state measurements reveal that platinum(II) incorporation facilitates dramatically the interactions between DPP-Pt(acac) and TCNE, resulting in charge transfer (CT) complex formation. The transient absorption spectra in the absence of TCNE reveal ultrafast ISC of DPP-Pt(acac) followed by their long-lived triplet state. In the presence of TCNE, PET from the excited DPP-Pt(acac) and DPP to TCNE, forming the radical ion pairs. The ultrafast PET which occurs statically from DPP-Pt(acac) to TCNE in picosecond regime, is much faster than that from DPP to TCNE (nanosecond time scale) which is diffusion-controlled process, providing clear evidence that PET rate is eventually controlled by the platinum(II) incorporation.

  19. Search for excited states in 25O

    Science.gov (United States)

    Jones, M. D.; Fossez, K.; Baumann, T.; DeYoung, P. A.; Finck, J. E.; Frank, N.; Kuchera, A. N.; Michel, N.; Nazarewicz, W.; Rotureau, J.; Smith, J. K.; Stephenson, S. L.; Stiefel, K.; Thoennessen, M.; Zegers, R. G. T.

    2017-11-01

    Background: Theoretical calculations suggest the presence of low-lying excited states in 25O. Previous experimental searches by means of proton knockout on 26F produced no evidence for such excitations. Purpose: We search for excited states in 25O using the 24O(d ,p ) 25O reaction. The theoretical analysis of excited states in unbound O,2725 is based on the configuration interaction approach that accounts for couplings to the scattering continuum. Method: We use invariant-mass spectroscopy to measure neutron-unbound states in 25O. For the theoretical approach, we use the complex-energy Gamow Shell Model and Density Matrix Renormalization Group method with a finite-range two-body interaction optimized to the bound states and resonances of O-2623, assuming a core of 22O. We predict energies, decay widths, and asymptotic normalization coefficients. Results: Our calculations in a large s p d f space predict several low-lying excited states in 25O of positive and negative parity, and we obtain an experimental limit on the relative cross section of a possible Jπ=1/2 + state with respect to the ground state of 25O at σ1 /2 +/σg .s .=0 .25-0.25+1.0 . We also discuss how the observation of negative parity states in 25O could guide the search for the low-lying negative parity states in 27O. Conclusion: Previous experiments based on the proton knockout of 26F suffered from the low cross sections for the population of excited states in 25O because of low spectroscopic factors. In this respect, neutron transfer reactions carry more promise.

  20. Multiconfiguration Pair-Density Functional Theory Outperforms Kohn-Sham Density Functional Theory and Multireference Perturbation Theory for Ground-State and Excited-State Charge Transfer.

    Science.gov (United States)

    Ghosh, Soumen; Sonnenberger, Andrew L; Hoyer, Chad E; Truhlar, Donald G; Gagliardi, Laura

    2015-08-11

    The correct description of charge transfer in ground and excited states is very important for molecular interactions, photochemistry, electrochemistry, and charge transport, but it is very challenging for Kohn-Sham (KS) density functional theory (DFT). KS-DFT exchange-correlation functionals without nonlocal exchange fail to describe both ground- and excited-state charge transfer properly. We have recently proposed a theory called multiconfiguration pair-density functional theory (MC-PDFT), which is based on a combination of multiconfiguration wave function theory with a new type of density functional called an on-top density functional. Here we have used MC-PDFT to study challenging ground- and excited-state charge-transfer processes by using on-top density functionals obtained by translating KS exchange-correlation functionals. For ground-state charge transfer, MC-PDFT performs better than either the PBE exchange-correlation functional or CASPT2 wave function theory. For excited-state charge transfer, MC-PDFT (unlike KS-DFT) shows qualitatively correct behavior at long-range with great improvement in predicted excitation energies.

  1. Excited-state intramolecular hydrogen transfer (ESIHT) of 1,8-Dihydroxy-9,10-anthraquinone (DHAQ) characterized by ultrafast electronic and vibrational spectroscopy and computational modeling

    KAUST Repository

    Mohammed, Omar F.

    2014-05-01

    We combine ultrafast electronic and vibrational spectroscopy and computational modeling to investigate the photoinduced excited-state intramolecular hydrogen-transfer dynamics in 1,8-dihydroxy-9,10-anthraquinone (DHAQ) in tetrachloroethene, acetonitrile, dimethyl sulfoxide, and methanol. We analyze the electronic excited states of DHAQ with various possible hydrogen-bonding schemes and provide a general description of the electronic excited-state dynamics based on a systematic analysis of femtosecond UV/vis and UV/IR pump-probe spectroscopic data. Upon photoabsorption at 400 nm, the S 2 electronic excited state is initially populated, followed by a rapid equilibration within 150 fs through population transfer to the S 1 state where DHAQ exhibits ESIHT dynamics. In this equilibration process, the excited-state population is distributed between the 9,10-quinone (S2) and 1,10-quinone (S1) states while undergoing vibrational energy redistribution, vibrational cooling, and solvation dynamics on the 0.1-50 ps time scale. Transient UV/vis pump-probe data in methanol also suggest additional relaxation dynamics on the subnanosecond time scale, which we tentatively ascribe to hydrogen bond dynamics of DHAQ with the protic solvent, affecting the equilibrium population dynamics within the S2 and S1 electronic excited states. Ultimately, the two excited singlet states decay with a solvent-dependent time constant ranging from 139 to 210 ps. The concomitant electronic ground-state recovery is, however, only partial because a large fraction of the population relaxes to the first triplet state. From the similarity of the time scales involved, we conjecture that the solvent plays a crucial role in breaking the intramolecular hydrogen bond of DHAQ during the S2/S1 relaxation to either the ground or triplet state. © 2014 American Chemical Society.

  2. Qualitative assessment of ultra-fast non-Grotthuss proton dynamics in S1 excited state of liquid H2O from ab initio time-dependent density functional theory★

    Science.gov (United States)

    Ziaei, Vafa; Bredow, Thomas

    2017-11-01

    We study qualitatively ultra-fast proton transfer (PT) in the first singlet (S1) state of liquid water (absorption onset) through excited-state dynamics by means of time-dependent density functional theory and ab initio Born-Oppenheimer molecular dynamics. We find that after the initial excitation, a PT occurs in S1 in form of a rapid jump to a neighboring water molecule, on which the proton either may rest for a relatively long period of time (as a consequence of possible defect in the hydrogen bond network) followed by back and forth hops to its neighboring water molecule or from which it further moves to the next water molecule accompanied by back and forth movements. In this way, the proton may become delocalized over a long water wire branch, followed again by back and forth jumps or short localization on a water molecule for some femtoseconds. As a result, the mechanism of PT in S1 is in most cases highly non-Grotthuss-like, delayed and discrete. Furthermore, upon PT an excess charge is ejected to the solvent trap, the so-called solvated electron. The spatial extent of the ejected solvated electron is mainly localized within one solvent shell with overlappings on the nearest neighbor water molecules and delocalizing (diffuse) tails extending beyond the first solvent sphere. During the entire ultra-short excited-state dynamics the remaining OH radical from the initially excited water molecule exhibits an extremely low mobility and is non-reactive. Supplementary material in the form of one pdf file available from the Journal web page at http://https://doi.org/10.1140/epjb/e2017-80329-7.

  3. Femtosecond laser selective intramolecular double proton transfer in [2,2'-bipyridyl]-3,3'-diol

    NARCIS (Netherlands)

    Marks, D.R.A.; Prosposito, P.; Zhang, H.; Glasbeek, M.

    1998-01-01

    We report an excitation energy dependence of the dynamics of the excited-state intramolecular double-proton transfer of [2,2'-bipyridyl]-3,3'-diol in liquid solution. By means of femtosecond fluorescence upconversion experiments it is shown that an increase of the vibrational energy in the excited

  4. Influence of 2'-deoxy sugar moiety on excited-state protonation equilibrium of adenine and adenosine with acridine inside SDS micelles: a time-resolved study with quantum chemical calculations.

    Science.gov (United States)

    Sarangi, Manas Kumar; Bhattacharyya, Dhananjay; Basu, Samita

    2012-02-01

    The protonation dynamics of the DNA base adenine (Ade) and its nucleoside 2'-deoxyadenosine (d-Ade) are investigated by monitoring the deprotonation kinetics of an N-heterocyclic DNA intercalator, acridine (Acr), in the confined environment of sodium dodecyl sulfate (SDS) micelles. Protonation of acridine (AcrH(+)) occurs at the hydrophilic interface and this species remains in dynamic equilibrium with its deprotonated counterpart (Acr) inside the hydrophobic core of SDS micelles. Quenching of the fluorescence of AcrH(+)* at 478 nm is observed after addition of Ade and d-Ade with Stern-Volmer constant (K(SV)) 298 and 75 M(-1), respectively, with a concomitant increment in Acr* at 425 nm. Time-resolved fluorescence studies reveal quenching in the lifetime of AcrH(+)*. The relative amplitude of AcrH(+)* decreases from 0.97 to 0.51 and 0.97 to 0.89 with equimolar addition of Ade and d-Ade, respectively. These observations are explained by excited-state proton transfer (ESPT) from AcrH(+)* to the bases. The reduced K(SV) value and negligible change in the relative amplitudes of AcrH(+)* with d-Ade infer that ESPT is hindered substantially by the presence of a 2'-deoxy sugar unit. Transient time-resolved absorption spectra of Acr reflect that Ade reduces the absorbance of (3)AcrH(+)*; however, d-Ade keeps it unaltered for more than a time delay of 2 μs. The optimized geometries calculated by quantum chemical methods reflect deprotonation of AcrH(+)* with protonation at the N1 position of Ade, while it remains protonated with d-Ade. The hindered ESPT between AcrH(+)* and d-Ade singles out the significance of the 2'-deoxy sugar moiety in controlling the deprotonation kinetics. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Photochemistry of Eumelanin Precursors Role of Excited State Proton Transfer for UV Photoprotection

    OpenAIRE

    Corani, Alice

    2015-01-01

    Melanin is an epidermal pigment commonly known to give darker skin coloration under sun exposure. It is also present in the hair, eyes, inner ear and brain. The first function of epidermis melanin is believed to be photoprotective against harmful ultraviolet (UV) light, but the recent increase of skin cancer correlated to an increase of sun exposure questions the properties of melanin. Its presence in different body parts suggests that its function is not solely protective against...

  6. Dynamics of Excited State Proton Transfer in Nitro Substituted 10-Hydroxybenzo[h]quinolines

    DEFF Research Database (Denmark)

    Marciak, H; Hristova, S.; Deneva, V

    2017-01-01

    of the ground state enol–keto tautomeric equilibrium (ΔG values of 1.03 and 0.62 kcal mol−1 respectively for 2 and 3). The fluorescence stems from the keto form even if the enol form is optically excited as proven by the shape of the excitation spectra indicating that ESIPT takes place. The Stokes shift...... of the substituted compounds is substantially lower compared to HBQ, which follows from the fact that the substitution occurs in the formal cyclohexa-2,4-dienone moiety and leads to a decrease of the HOMO level of the keto tautomer. The pump–probe experiments show that in the nitro substituted HBQs 2 and 3 ESIPT...

  7. Concerted and asynchronous mechanism of ground state proton transfer in alcohol mediated 7-hydroxyquinoline

    Science.gov (United States)

    Kang, Baotao; Jang, Du-Jeon; Lee, Jin Yong

    2015-07-01

    Alcohols mediated 7-hydroxyquinoline (7-HQ) complex has received enormous attractions on the issue of proton transfer reaction in the ground and excited states. In the present paper, concentrating on the ground state proton transfer (GSPT), density functional theory (DFT) calculations were carried out to investigate the intrinsic insight into the reaction mechanism. We found that the GSPT is concerted and asynchronous process and can be accelerated by more acidic alcohol. Such GSPT was initiated by the proton transfer from alcohol to keto group of 7-HQ and finished by the proton transfer from nitrogen to alcohol. Our findings were in agreement with experimental conclusions quite well. Our results would be helpful to understand the proton transfer reaction for 7-HQ and related systems.

  8. Concerted and asynchronous mechanism of ground state proton transfer in alcohol mediated 7-hydroxyquinoline

    Energy Technology Data Exchange (ETDEWEB)

    Kang, Baotao [Department of Chemistry, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Jang, Du-Jeon [Department of Chemistry, Seoul National University, Seoul 151-742 (Korea, Republic of); Lee, Jin Yong, E-mail: jinylee@skku.edu [Department of Chemistry, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of)

    2015-07-29

    Highlights: • Reaction rate constants obtained by DFT agree with experimental ones quite well. • Experimental postulate of concerted and asynchronous GSPT was confirmed. • The GSPT reaction can be decomposed into three asynchronous steps. - Abstract: Alcohols mediated 7-hydroxyquinoline (7-HQ) complex has received enormous attractions on the issue of proton transfer reaction in the ground and excited states. In the present paper, concentrating on the ground state proton transfer (GSPT), density functional theory (DFT) calculations were carried out to investigate the intrinsic insight into the reaction mechanism. We found that the GSPT is concerted and asynchronous process and can be accelerated by more acidic alcohol. Such GSPT was initiated by the proton transfer from alcohol to keto group of 7-HQ and finished by the proton transfer from nitrogen to alcohol. Our findings were in agreement with experimental conclusions quite well. Our results would be helpful to understand the proton transfer reaction for 7-HQ and related systems.

  9. Proton and hydride affinities in excited states: magnitude reversals in proton and hydride affinities between the lowest singlet and triplet states of annulenyl and benzannulenyl anions and cations

    DEFF Research Database (Denmark)

    Rosenberg, Martin; Ottosson, Henrik; Kilså, Kristine

    2010-01-01

    Aromaticity has importance for proton and hydride affinities in the singlet ground state (S(0)) of annulenyl anions and cations so that, e.g., cyclopentadiene is an acidic hydrocarbon. For the lowest pipi* excited triplet state (T(1)), Baird's rule concludes that annulenes with 4n pi......-electrons are aromatic and those with 4n+2 pi-electrons are antiaromatic, opposite to Huckel's rule for aromaticity in S(0). Our hypothesis is now that the relative magnitudes of proton and hydride affinities of annulenyl anions and cations reverts systematically as one goes from S(0) to T(1) as a result of the opposite...... electron counting rules for aromaticity in the two states. Using quantum chemical calculations at the G3(MP2)//(U)B3LYP/6-311+G(d,p) level we have examined the validity of this hypothesis for eight proton and eight hydride addition reactions of anions and cations, respectively, of annulenyl...

  10. Excited states 2

    CERN Document Server

    Lim, Edward C

    2013-01-01

    Excited States, Volume 2 is a collection of papers that deals with molecules in the excited states. The book describes the geometries of molecules in the excited electronic states. One paper describes the geometries of a diatomic molecule and of polyatomic molecules; it also discusses the determination of the many excited state geometries of molecules with two, three, or four atoms by techniques similar to diatomic spectroscopy. Another paper introduces an ordered theory related to excitons in pure and mixed molecular crystals. This paper also presents some experimental data such as those invo

  11. Proton Transfer in Perfluorosulfonic Acid Fuel Cell Membranes with Differing Pendant Chains and Equivalent Weights.

    Science.gov (United States)

    Thomaz, Joseph E; Lawler, Christian M; Fayer, Michael D

    2017-05-04

    Proton transfer in the nanoscopic water channels of polyelectrolyte fuel cell membranes was studied using a photoacid, 8-hydroxypyrene-1,3,6-trisulfonic acid sodium salt (HPTS), in the channels. The local environment of the probe was determined using 8-methoxypyrene-1,3,6-trisulfonic acid sodium salt (MPTS), which is not a photoacid. Three fully hydrated membranes, Nafion (DuPont) and two 3M membranes, were studied to determine the impact of different pendant chains and equivalent weights on proton transfer. Fluorescence anisotropy and excited state population decay data that characterize the local environment of the fluorescent probes and proton transfer dynamics were measured. The MPTS lifetime and anisotropy results show that most of the fluorescent probes have a bulk-like water environment with a relatively small fraction interacting with the channel wall. Measurements of the HPTS protonated and deprotonated fluorescent bands' population decays provided information on the proton transport dynamics. The decay of the protonated band from ∼0.5 ns to tens of nanoseconds is in part determined by dissociation and recombination with the HPTS, providing information on the ability of protons to move in the channels. The dissociation and recombination is manifested as a power law component in the protonated band fluorescence decay. The results show that equivalent weight differences between two 3M membranes resulted in a small difference in proton transfer. However, differences in pendant chain structure did significantly influence the proton transfer ability, with the 3M membranes displaying more facile transfer than Nafion.

  12. Synergy effects of electric and magnetic fields on locally excited-state fluorescence of photoinduced electron transfer systems in a polymer film.

    Science.gov (United States)

    Awasthi, Kamlesh; Iimori, Toshifumi; Ohta, Nobuhiro

    2009-10-08

    Photoluminescence of electron donor-acceptor pairs that show photoinduced electron transfer (PIET) has been measured in a polymer film under simultaneous application of electric field and magnetic field. Fluorescence emitted from the locally excited state (LE fluorescence) of 9-methylanthracene (MAnt) and pyrene (Py) is quenched by an electric field in a mixture of 1,3-dicyanobenzene (DCB) with MAnt or Py, indicating that PIET from the excited state of MAnt or Py to DCB is enhanced by an electric field. Simultaneous application of electric and magnetic fields enhances the reverse process from the radical-ion pair produced by PIET to the LE fluorescent state of MAnt or Py. As a result, the electric-field-induced quenching of the LE fluorescence is reduced by application of the magnetic fields. Thus, the synergy effect of electric and magnetic fields is observed on the LE fluorescence of MAnt or Py. Exciplex fluorescence spectra resulting from PIET can be obtained by analyzing the field effects on photoluminescence spectra, even when the exciplex fluorescence is too weak to be determined from the steady-state or time-resolved photoluminescence spectra at zero field.

  13. Femtosecond double proton transfer dynamics in [2,2'-bipyridyl]-3,3'-diol in sol-gel glasses

    NARCIS (Netherlands)

    Prosposito, P.; Marks, D.R.A.; Zhang, H.; Glasbeek, M.

    1998-01-01

    Abstract: Intramolecular excited state double proton-transfer dynamics has been studied for [2,2'-bipyridyl]-3,3'-diol (BP(OH)2) in sol-gel glass. By means of the femtosecond fluorescence up-conversion technique, the spectral dependence of the fluorescence transients obtained for BP(OH)2 in a few

  14. Kinetic isotope effect of proton-coupled electron transfer in a hydrogen bonded phenol-pyrrolidino[60]fullerene

    NARCIS (Netherlands)

    Ravensbergen, J.; Brown, C.L.; Moore, G.F.; Frese, R.N.; van Grondelle, R.; Gust, D.; Moore, T.A.; Moore, A.L.; Kennis, J.T.M.

    2015-01-01

    Proton-coupled electron transfer (PCET) plays a central role in photosynthesis and potentially in solar-to-fuel systems. We report a spectroscopy study on a phenol-pyrrolidino[60]fullerene. Quenching of the singlet excited state from 1 ns to 250 ps is assigned to PCET. A H/D exchange study reveals a

  15. Excited states 4

    CERN Document Server

    Lim, Edward C

    2013-01-01

    Excited States, Volume 4 is a collection of papers that deals with the excited states of molecular activity. One paper investigates the resonance Raman spectroscopy as the key to vibrational-electronic coupling. This paper reviews the basic theory of Raman scattering; it also explains the derivation of the Raman spectra, excitation profiles, and depolarization ratios for simple resonance systems. Another paper reviews the magnetic properties of triplet states, including the zero-field resonance techniques, the high-field experiments, and the spin Hamiltonian. This paper focuses on the magnetic

  16. Photochemical transformations. 37. Electron-transfer requirements for photosolvolysis and photo-Wagner-Meerwein reactions of some dichlorodibenzobicyclo(2. 2. 2)octadienes in singlet and triplet excited states

    Energy Technology Data Exchange (ETDEWEB)

    Cristol, S.J.; Bindel, T.H.; Hoffmann, D.; Aeling, E.O.

    1984-06-29

    Substituted trans-7,8-dichloro-10-X-2,3:5,6-dibenzobicyclo(2.2.2)octa-2,5-dienes (X = COCH/sub 3/, CN, and NO/sub 2/) and corresponding dinitro-substituted compounds (10,15-dinitro) were solvolyzed with silver acetate in acetic acid and were irradiated in glacial acetic acid or acetonitrile with 254- and 300-nm light. The structures of the monoring-substituted diastereoisomeric dichlorides were demonstrated by proof of structures of the daughter solvolysis products. Unlike compounds previously studied, these compounds were either photochemically inert or photoinactive with respect to Wagner-Meerwein rearrangement or to solvolysis. These results have been rationalized in terms of the inability of the excited states of the light-absorbing chromophores in these compounds to transfer electrons to the carbon-chlorine bonds remote from these chromophores. While triplet states of a variety of cis- and trans-7,8-dichloro-2,3:5,6-dibenzobicyclo(2.2.2)octa-2,5-dienes are reported to be similarly inert, the 10,11-dimethoxy derivatives all were photoactive with acetone sensitization. The migration stereochemistries of the sensitized reactions were quite different from those of direct irradiations or of ground-state reactions. Estimations of the free energies of electron transfer were consistent with these and previously reported results. 26 references, 1 table.

  17. Proton transfer in phenol-amine complexes: phenol electronic effects on free energy profile in solution.

    Science.gov (United States)

    Aono, Shinji; Kato, Shigeki

    2010-12-01

    Free energy profiles for the proton transfer reactions in hydrogen-bonded complex of phenol with trimethylamine in methyl chloride solvent are studied with the reference interaction site model self-consistent field method. The reactions in both the electronic ground and excited states are considered. The second-order Møller-Plesset perturbation (MP) theory or the second-order multireference MP theory is used to evaluate the effect of the dynamical electron correlation on the free energy profiles. The free energy surface in the ground state shows a discrepancy with the experimental results for the related hydrogen-bonded complexes. To resolve this discrepancy, the effects of chloro-substitutions in phenol are examined, and its importance in stabilizing the ionic form is discussed. The temperature effect is also studied. In contrast to the ground state, the ππ* excited state of phenol-trimethylamine complex exhibits the proton transfer reaction with a low barrier. The reaction is almost thermoneutral. This is attributed to the reduction of proton affinity of phenol by the ππ* electronic excitation. We further examine the possibility of the electron-proton-coupled transfer in the ππ* state through the surface crossing with the charge transfer type πσ* state. © 2010 Wiley Periodicals, Inc.

  18. Dual electron transfer pathways from 4,4'-dimethoxybenzophenone ketyl radical in the excited state to parent molecule in the ground state.

    Science.gov (United States)

    Sakamoto, Masanori; Cai, Xichen; Fujitsuka, Mamoru; Majima, Tetsuro

    2005-08-11

    Dual intermolecular electron transfer (ELT) pathways from 4,4'-dimethoxybenzophenone (1) ketyl radical (1H*) in the excited state [1H*(D1)] to the ground-state 4,4'-dimethoxybenzophenone [1(S0)] were found in 2-methyltetrahydrofuran (MTHF) by observing bis(4-methoxyphenyl)methanol cation (1H+) and 4,4'-dimethoxybenzophenone radical anion (1*-) during nanosecond-picosecond two-color two-laser flash photolysis. ELT pathway I involved the two-photon ionization of 1H* following the injection of electron to the solvent. The solvated electron was quickly trapped by 1(S0) to produce 1*-. ELT pathway II was a self-quenching-like ELT from 1H*(D1) to 1(S0) to give 1H+ and 1*-. From the fluorescence quenching of 1H*(D1), the ELT rate constant was determined to be 1.0 x 10(10) M(-1) s(-1), which is close to the diffusion-controlled rate constant of MTHF. The self-quenching-like ELT mechanism was discussed on the basis of Marcus' ELT theory.

  19. A NOVEL PROTON TRANSFER COMPOUND (A NEW ...

    African Journals Online (AJOL)

    Preferred Customer

    2011-11-22

    . ITS X-RAY STRUCTURE. Iran Sheikhshoaie* and Mahdeieh Ghazizadeh. Department of Chemistry, Shahid Bahonar University of Kerman, Iran. (Received November 22, 2011; revised August 14, 2012). ABSTRACT. A novel proton transfer ...

  20. A novel chalcone-analogue as an optical sensor based on ground and excited states intramolecular charge transfer: A combined experimental and theoretical study

    Energy Technology Data Exchange (ETDEWEB)

    Fayed, Tarek A. [Chemistry Department, Faculty of Science, Tanta University, 31527-Tanta (Egypt)], E-mail: tfayed2003@yahoo.co.uk

    2006-05-31

    Steady-state absorption and emission spectroscopic techniques as well as semiempirical quantum calculations at the AM1 and ZINDO/S levels have been used to investigate the intramolecular charge transfer (ICT) behaviour of a novel chalcone namely; 1-(2-pyridyl)-5-(4-dimethylaminophenyl)-penta-2,4-diene-1-one, DMAC. The ground state DMAC has a significant ICT character and a great sensitivity to the hydrogen bond donating ability of the medium as reflected from the change of the absorption spectra in pure and mixed organic solvents. On the other hand, its excited singlet state exhibits high ICT characters as manifested by the drastic solvatochromic effects. These results are consistent with the data of charge density calculations in both the ground and excited state, which indicates enhancement of the charge transfer from the dimethyl-amino group to the carbonyl oxygen upon excitation. Also, the dipole moment calculations indicates a highly dipolar excited singlet state ({delta}{mu} {sub eg} = 15.5 D). The solvent dependence of the fluorescence quantum yield of DMAC was interpreted on the basis of positive and negative solvatokinetic as well as the hydrogen bonding effects. Incorporation of the 2-pyridyl group in the chemical structure of the present DMAC led to design of a potential optical sensor for probing acidity of the medium and metal cations such as Zn{sup 2+}, Cd{sup 2+} and Hg{sup 2+}. This was concluded from the high acidochromic and metallochromic behaviour of DMAC on adding such cations to its acetonitrile solutions.

  1. Femtosecond dynamics of fundamental reaction processes in liquids: Proton transfer, geminate recombination, isomerization and vibrational relaxation

    Energy Technology Data Exchange (ETDEWEB)

    Schwartz, Benjamin Joel [Univ. of California, Berkeley, CA (United States)

    1992-11-01

    The fast excited state intramolecular proton transfer of 3-hydroxyflavone is measured and effects of external hydrogen-bonding interactions on the proton transfer are studied. The proton transfer takes place in ~240 fsec in nonpolar environments, but becomes faster than instrumental resolution of 110 fsec in methanol solution. The dynamics following photodissociation of CH2I2 and other small molecules provide the first direct observations of geminate recombination. The recombination of many different photodissociating species occurs on a ~350 fsec time scale. Results show that recombination yields but not rates depend on the solvent environment and suggest that recombination kinetics are dominated by a single collision with surrounding solvent cage. Studies of sterically locked phenyl-substituted butadienes offer new insights into the electronic structure and isomerization behavior of conjugated polyenes. Data show no simple correlation between hinderance of specific large amplitude motions and signatures of isomerizative behavior such as viscosity dependent excited state lifetimes, implying that the isomerization does not provide a suitable for simple condensed phase reaction rate theories. The spectral dynamics of a photochromic spiropyran indicate that recombination, isomerization and vibrational relaxation all play important roles in photoreactivity of complex molecules. The interplay of these microscopic phenomena and their effect on macroscopic properties such as photochromism are discussed. All the results indicate that the initial steps of the photochromic reaction process occur extremely rapidly. Laser system and computer codes for data analysis are discussed.

  2. Spectroscopic study on the intermolecular double proton transfer in 4-(naphthalen-1-yl)-6-octyl-1,3,5-triazin-2-amine with acid

    Energy Technology Data Exchange (ETDEWEB)

    Li Zongyao [Key Lab for Special Functional Materials of Ministry of Education, Henan University, Kaifeng 475004 (China); Research Institute of Henan Coal and Chemical Industry Group, Zhengzhou 450046 (China); Li Chunli [Key Lab for Special Functional Materials of Ministry of Education, Henan University, Kaifeng 475004 (China); Zhao Chunmei [Key Lab for Special Functional Materials of Ministry of Education, Henan University, Kaifeng 475004 (China); Institute for Functional Nanomaterials, Huanghe Science and Technology College, Zhengzhou 450000 (China); Wu Wei [Key Lab for Special Functional Materials of Ministry of Education, Henan University, Kaifeng 475004 (China); Wang Hua, E-mail: hwang@henu.edu.cn [Key Lab for Special Functional Materials of Ministry of Education, Henan University, Kaifeng 475004 (China)

    2012-10-15

    With 2,4,6-trichloro-1,3,5-triazine as starting material, a functionalized triazine derivative, 4-(naphthalen-1-yl)-6-octyl-1,3,5-triazin-2-amine (NOTA) was synthesized in 14% yield through three steps: Kumada cross-coupling, Suzuki coupling and amination. Intermolecular double proton transfer of NOTA with acetic acid (HOAc) and trifluoroacetic acid (TFA) in chloroform was investigated by UV-vis absorption and fluorescence emission. It is found that both NOTA/HOAc and NOTA/TFA undergo excited state double proton transfer, resulting in amino-imino tautomerization emission in excited state. - Highlights: Black-Right-Pointing-Pointer A functionalized triazine derivative, 4-(naphthalen-1-yl)-6-octyl-1,3,5-triazin-2-amine (NOTA) was synthesized in 14% yield through three steps: Kumada cross-coupling, Suzuki coupling and amination. Black-Right-Pointing-Pointer Intermolecular double proton transfer of NOTA with acetic acid (HOAc) and trifluoroacetic acid (TFA) in chloroform was investigated. Black-Right-Pointing-Pointer Both NOTA/HOAc and NOTA/TFA undergo excited state double proton transfer. Black-Right-Pointing-Pointer Amino-imino tautomerization emission in excited state are proposed.

  3. Hydrogen-bond dynamics and proton transfer in nanoconfinement

    NARCIS (Netherlands)

    van der Loop, T.H.

    2015-01-01

    Proton transfer is of fundamental importance to both biology and chemistry. Much is known about proton transfer in large water volumes but often proton transfer reactions take place in very small nanometer sized volumes for example between lipid layers and in proton channels in mitochondria and

  4. Non-typical fluorescence studies of excited and ground state proton and hydrogen transfer

    Science.gov (United States)

    Gil, Michał; Kijak, Michał; Piwoński, Hubert; Herbich, Jerzy; Waluk, Jacek

    2017-03-01

    Fluorescence studies of tautomerization have been carried out for various systems that exhibit single and double proton or hydrogen translocation in various environments, such as liquid and solid condensed phases, ultracold supersonic jets, and finally, polymer matrices with single emitters. We focus on less explored areas of application of fluorescence for tautomerization studies, using porphycene, a porphyrin isomer, as an example. Fluorescence anisotropy techniques allow investigations of self-exchange reactions, where the reactant and product are formally identical. Excitation with polarized light makes it possible to monitor tautomerization in single molecules and to detect their three-dimensional orientation. Analysis of fluorescence from single vibronic levels of jet-isolated porphycene not only demonstrates coherent tunneling of two internal protons, but also indicates that the process is vibrational mode-specific. Next, we present bifunctional proton donor-acceptor systems, molecules that are able, depending on the environment, to undergo excited state single intramolecular or double intermolecular proton transfer. For molecules that have donor and acceptor groups located in separate moieties linked by a single bond, excited state tautomerization can be coupled to mutual twisting of the two subunits.

  5. Non-typical fluorescence studies of excited and ground state proton and hydrogen transfer

    KAUST Repository

    Gil, Michał

    2017-02-03

    Fluorescence studies of tautomerization have been carried out for various systems that exhibit single and double proton or hydrogen translocation in various environments, such as liquid and solid condensed phases, ultracold supersonic jets, and finally, polymer matrices with single emitters.We focus on less explored areas of application of fluorescence for tautomerization studies, using porphycene, a porphyrin isomer, as an example. Fluorescence anisotropy techniques allow investigations of self-exchange reactions, where the reactant and product are formally identical. Excitation with polarized light makes it possible to monitor tautomerization in single molecules and to detect their three-dimensional orientation. Analysis of fluorescence from single vibronic levels of jet-isolated porphycene not only demonstrates coherent tunneling of two internal protons, but also indicates that the process is vibrational mode-specific. Next, we present bifunctional proton donoracceptor systems, molecules that are able, depending on the environment, to undergo excited state single intramolecular or double intermolecular proton transfer. For molecules that have donor and acceptor groups located in separate moieties linked by a single bond, excited state tautomerization can be coupled to mutual twisting of the two subunits.

  6. Polarization Transfer in Proton Compton Scattering at High Momentum Transfer

    CERN Document Server

    Hamilton, D J; Aniol, K A; Annand, J R M; Bertin, P Y; Bimbot, L; Bosted, P; Calarco, J R; Camsonne, A; Chang, G C; Chang, T H; Chen, J P; Seonho Choi; Chudakov, E; Danagulyan, A S; Degtyarenko, P; De Jager, C W; Deur, A; Dutta, D; Egiyan, K; Gao, H; Garibaldi, F; Gayou, O; Gilman, R; Glamazdin, A; Glashausser, C; Gómez, J; Hansen, J O; Hayes, D; Higinbotham, D W; Hinton, W; Horn, T; Howell, C; Hunyady, T; Hyde-Wright, C E; Jiang, X; Jones, M K; Khandaker, M; Ketikyan, A; Koubarovski, V; Krämer, K; Kumbartzki, G; Laveissière, G; Le Rose, J J; Lindgren, R A; Margaziotis, D J; Markowitz, P; McCormick, K; Meziani, Z E; Michaels, R; Moussiegt, P; Nanda, S; Nathan, A M; Nikolenko, D M; Nelyubin, V V; Norum, B E; Paschke, K; Pentchev, L; Perdrisat, C F; Piasetzky, E; Pomatsalyuk, R I; Punjabi, V A; Rachek, Igor A; Radyushkin, A V; Reitz, B; Roché, R; Roedelbronn, M; Ron, G; Sabatie, F; Saha, A; Savvinov, N; Shahinyan, A; Shestakov, Yu V; Sirca, S; Slifer, K J; Solvignon, P; Stoler, P; Tajima, S; Sulkosky, V; Todor, L; Vlahovic, B; Weinstein, L B; Wang, K; Wojtsekhowski, B; Voskanyan, H; Xiang, H; Zheng, X; Zhu, L

    2004-01-01

    Compton scattering from the proton was investigated at s=6.9 (GeV/c)**2 and \\t=-4.0 (GeV/c)**2 via polarization transfer from circularly polarized incident photons. The longitudinal and transverse components of the recoil proton polarization were measured. The results are in excellent agreement with a prediction based on a reaction mechanism in which the photon interacts with a single quark carrying the spin of the proton and in disagreement with a prediction of pQCD based on a two-gluon exchange mechanism.

  7. Polarisation Transfer in Proton Compton Scattering at High Momentum Transfer

    Energy Technology Data Exchange (ETDEWEB)

    Hamilton, David Jonathan [Univ. of Glasgow, Scotland (United Kingdom)

    2004-01-01

    The Jefferson Lab Hall A experiment E99-114 comprised a series of measurements to explore proton Compton scattering at high momentum transfer. For the first time, the polarisation transfer observables in the p ($\\vec{γ}$, γ' \\vec{p}$) reaction were measured in the GeV energy range, where it is believed that quark-gluon degrees of freedom begin to dominate. The experiment utilised a circularly polarised photon beam incident on a liquid hydrogen target, with the scattered photon and recoil proton detected in a lead-glass calorimeter and a magnetic spectrometer, respectively.

  8. Excited state kinetics of anthracene-bridge-aniline intramolecular exciplexes

    DEFF Research Database (Denmark)

    Thyrhaug, Erling; Hammershøj, Peter; Kjær, Kasper Skov

    2014-01-01

    excited anthracene state (LE) and an excited state complex (exciplex, EP) in non-polar solvents. The kinetics of the excited state processes were established in decalin from the time-resolved emission, and was shown to be strongly influenced by an electron-transfer state (ET). For quantitative studies...

  9. Excited state intramolecular proton transfer of 2-(2′,6′-dihydroxyphenyl)benzoxazole: Insights using computational methods

    Energy Technology Data Exchange (ETDEWEB)

    Tathe, Abhinav B.; Gupta, Vinod D.; Shreykar, Milind R. [Tinctorial Chemistry Group, Department of Dyestuff Technology, Institute of Chemical Technology, N. P. Marg, Matunga, Mumbai, Maharashtra 400019 (India); Ramasami, Ponnadurai, E-mail: ramchemi@intnet.mu [Computational Chemistry Group, Department of Chemistry, Faculty of Science University of Mauritius, Réduit (Mauritius); Sekar, Nagaiyan, E-mail: n.sekar@ictmumbai.edu.in [Tinctorial Chemistry Group, Department of Dyestuff Technology, Institute of Chemical Technology, N. P. Marg, Matunga, Mumbai, Maharashtra 400019 (India)

    2014-10-15

    The photo-physical behaviour of 2-(2′,6′-dihydroxyphenyl) benzoxazole was studied using the Density Functional Theory (DFT), Time Dependent Density Functional Theory (TD-DFT) and Configuration Interaction Singles (CIS). Different functionals including the hybrid and M06X series were used to compute the absorption and emission. Experimental absorption and emission wavelengths are in good agreement with those predicted using TD-DFT [TD-B3LYP/6–31 G(d)]. The further improvement was not observed with the larger basis sets like 6–31 G(d,p) and 6–311 G(d,p). The rotational barrier was also calculated theoretically in chloroform (10.5–14.1 kcal/mol) and it was found to be close to the experimental energy value (10.5 kcal/mol). - Highlights: • Photo-physical data of 2-(2′,6′-dihydroxyphenyl)benzoxazole was studied theoretically. • The methods employed are DFT, TD-DFT and CIS. • The rotational barriers evaluated computationally. • The results of DFT and TD-DFT are in good agreement with the experiments. • This study can lead to a better understanding of ESIPT phenomenon computationally.

  10. Theoretical study of the mechanism of proton transfer in tautomeric ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Chemical Sciences; Volume 113; Issue 4 ... Proton transfers; tautomerism; dissociative process; direct proton transfer. Abstract. Semiempirical SCF-MO studies of tautomerism in alloxan preclude the possibility of direct proton transfer in the gas phase due to the strain in the four-centred transition ...

  11. Intramolecular photoinduced proton transfer in 2-(2′-hydroxyphenyl)benzazole family: A TD-DFT quantum chemical study

    Energy Technology Data Exchange (ETDEWEB)

    Roohi, Hossein, E-mail: hroohi@guilan.ac.ir; Mohtamedifar, Nafiseh; Hejazi, Fahemeh

    2014-11-24

    Highlights: • PBE1PBE/TD method was used to study the ESIPT process in the benzazole family. • Potential energy curves in ground and excited states were calculated. • Effect of substitution in benzazole ring on the ESIPT process was investigated. • In contrast to S{sub 0} state, keto form of the molecules can be formed at the S{sub 1} state. • The photophysical properties of the compounds were calculated. - Abstract: In this work, intramolecular photoinduced proton transfer in 2-(2′-hydroxyphenyl)benzazole family (HBO, HBI and HBT) was investigated using TD-DFT calculations at PBE1PBE/6-311++G(2d,2p) level of theory. The potential energy surfaces were employed to explore the proton transfer reactions in both states. In contrast to the ground state, photoexcitation from S{sub 0} state to S{sub 1} one encourages the operation of the excited-state intramolecular proton transfer process. Structural parameters, H-bonding energy, absorption and emission bands, vertical excitation and emission energies, oscillator strength, fluorescence rate constant, dipole moment, atomic charges and electron density at critical points were calculated. Molecular orbital analysis shows that vertical S{sub 0} → S{sub 1} transition in the studied molecules corresponds essentially to the excitation from HOMO (π) to LUMO (π{sup ∗}). Our calculated results are in good agreement with the experimental observations.

  12. Femtosecond dynamics of fundamental reaction processes in liquids: Proton transfer, geminate recombination, isomerization and vibrational relaxation. [Spiropyrans

    Energy Technology Data Exchange (ETDEWEB)

    Schwartz, B.J.

    1992-11-01

    The fast excited state intramolecular proton transfer of 3-hydroxyflavone is measured and effects of external hydrogen-bonding interactions on the proton transfer are studied. The proton transfer takes place in [approximately]240 fsec in nonpolar environments, but becomes faster than instrumental resolution of 110 fsec in methanol solution. The dynamics following photodissociation of CH[sub 2]I[sub 2] and other small molecules provide the first direct observations of geminate recombination. The recombination of many different photodissociating species occurs on a [approximately]350 fsec time scale. Results show that recombination yields but not rates depend on the solvent environment and suggest that recombination kinetics are dominated by a single collision with surrounding solvent cage. Studies of sterically locked phenyl-substituted butadienes offer new insights into the electronic structure and isomerization behavior of conjugated polyenes. Data show no simple correlation between hinderance of specific large amplitude motions and signatures of isomerizative behavior such as viscosity dependent excited state lifetimes, implying that the isomerization does not provide a suitable for simple condensed phase reaction rate theories. The spectral dynamics of a photochromic spiropyran indicate that recombination, isomerization and vibrational relaxation all play important roles in photoreactivity of complex molecules. The interplay of these microscopic phenomena and their effect on macroscopic properties such as photochromism are discussed. All the results indicate that the initial steps of the photochromic reaction process occur extremely rapidly. Laser system and computer codes for data analysis are discussed.

  13. Excited-State Dynamics of Oxyluciferin in Firefly Luciferase.

    Science.gov (United States)

    Snellenburg, Joris J; Laptenok, Sergey P; DeSa, Richard J; Naumov, Panče; Solntsev, Kyril M

    2016-12-21

    The color variations of light emitted by some natural and mutant luciferases are normally attributed to collective factors referred to as microenvironment effects; however, the exact nature of these interactions between the emitting molecule (oxyluciferin) and the active site remains elusive. Although model studies of noncomplexed oxyluciferin and its variants have greatly advanced the understanding of its photochemistry, extrapolation of the conclusions to the real system requires assumptions about the polarity and proticity of the active site. To decipher the intricate excited-state dynamics, global and target analysis is performed here for the first time on the steady-state and time-resolved spectra of firefly oxyluciferin complexed with luciferase from the Japanese firefly (Luciola cruciata). The experimental steady-state and time-resolved luminescence spectra of the oxyluciferin/luciferase complex in solution are compared with the broadband time-resolved firefly bioluminescence recorded in vivo. The results demonstrate that de-excitation of the luminophore results in a complex cascade of photoinduced proton transfer processes and can be interpreted by the pH dependence of the emitted light. It is confirmed that proton transfer is the central event in the spectrochemistry of this system for which any assignment of the pH-dependent emission to a single chemical species would be an oversimplification.

  14. Excited-State Dynamics of Oxyluciferin in Firefly Luciferase

    KAUST Repository

    Snellenburg, Joris J.

    2016-11-23

    The color variations of light emitted by some natural and mutant luciferases are normally attributed to collective factors referred to as microenvironment effects; however, the exact nature of these interactions between the emitting molecule (oxyluciferin) and the active site remains elusive. Although model studies of noncomplexed oxyluciferin and its variants have greatly advanced the understanding of its photochemistry, extrapolation of the conclusions to the real system requires assumptions about the polarity and proticity of the active site. To decipher the intricate excited-state dynamics, global and target analysis is performed here for the first time on the steady-state and time-resolved spectra of firefly oxyluciferin complexed with luciferase from the Japanese firefly (Luciola cruciata). The experimental steady-state and time resolved luminescence spectra of the oxyluciferin/luciferase complex in solution are compared with the broadband time-resolved firefly bioluminescence recorded in vivo. The results demonstrate that de-excitation of the luminophore results in a complex cascade of photoinduced proton transfer processes and can be interpreted by the pH dependence of the emitted light. It is confirmed that proton transfer is the central event in the spectrochemistry of this system for which any assignment of the pH dependent emission to a single chemical species would be an oversimplification.

  15. 10-hydroxybenzo[h]quinoline: Switching between single and double-well proton transfer through structural modifications

    DEFF Research Database (Denmark)

    Hristova, S; Dobrikov, G; Kamounah, F. S.

    2015-01-01

    and excited singlet state. We observed that the incorporation of electron acceptor substituents on position 7 of the HBQ backbone led to appearance of a keto tautomer in ground state and changes in the excited state potential energy surface. Both processes were strongly solvent dependent. In the ground state...... the equilibrium could be driven from the enol to the keto form by change of solvent. The theoretical calculations explain the substitution-determined transition from a single- to a double-well proton transfer mechanism...

  16. Proton Transfer in Nucleobases is Mediated by Water

    Energy Technology Data Exchange (ETDEWEB)

    Khistyaev, Kirill; Golan, Amir; Bravaya, Ksenia B.; Orms, Natalie; Krylov, Anna I.; Ahmed, Musahid

    2013-08-08

    Water plays a central role in chemistry and biology by mediating the interactions between molecules, altering energy levels of solvated species, modifying potential energy proles along reaction coordinates, and facilitating ecient proton transport through ion channels and interfaces. This study investigates proton transfer in a model system comprising dry and microhydrated clusters of nucleobases. With mass spectrometry and tunable vacuum ultraviolet synchrotron radiation, we show that water shuts down ionization-induced proton transfer between nucleobases, which is very ecient in dry clusters. Instead, a new pathway opens up in which protonated nucleo bases are generated by proton transfer from the ionized water molecule and elimination of a hydroxyl radical. Electronic structure calculations reveal that the shape of the potential energy prole along the proton transfer coordinate depends strongly on the character of the molecular orbital from which the electron is removed, i.e., the proton transfer from water to nucleobases is barrierless when an ionized state localized on water is accessed. The computed energetics of proton transfer is in excellent agreement with the experimental appearance energies. Possible adiabatic passage on the ground electronic state of the ionized system, while energetically accessible at lower energies, is not ecient. Thus, proton transfer is controlled electronically, by the character of the ionized state, rather than statistically, by simple energy considerations.

  17. Theory of interrelated electron and proton transfer processes

    DEFF Research Database (Denmark)

    Kuznetsov, A.M.; Ulstrup, Jens

    2003-01-01

    A simple theory of elementary act of interrelated reactions of electron and proton transfer is developed. Mechanisms of synchronous and multistage transfer and coherent transitions via a dynamically populated intermediate state are discussed. Formulas for rate constants of adiabatic and nonadiaba......A simple theory of elementary act of interrelated reactions of electron and proton transfer is developed. Mechanisms of synchronous and multistage transfer and coherent transitions via a dynamically populated intermediate state are discussed. Formulas for rate constants of adiabatic...

  18. Parallel proton transfer pathways in aqueous acid-base reactions

    NARCIS (Netherlands)

    Cox, M.J.; Bakker, H.J.

    2008-01-01

    We study the mechanism of proton transfer (PT) between the photoacid 8-hydroxy-1,3, 6-pyrenetrisulfonic acid (HPTS) and the base chloroacetate in aqueous solution. We investigate both proton and deuteron transfer reactions in solutions with base concentrations ranging from 0.25M to 4M. Using

  19. Excited states in {sup 155}Yb and

    Energy Technology Data Exchange (ETDEWEB)

    Ding, K. Y.; Cizewski, J. A.; Seweryniak, D.; Amro, H.; Carpenter, M. P.; Davids, C. N.; Fotiades, N.; Janssens, R. V. F.; Lauritsen, T.; Lister, C. J. (and others)

    2001-09-01

    The 270-MeV {sup 58}Ni+{sup 102}Pd reaction was used for the first recoil-decay tagging measurement with Gammasphere coupled to the Fragment Mass Analyzer at Argonne National Laboratory. Level structures of {sup 155}Yb, {sup 156}Lu, and {sup 157}Lu, as well as the excited states associated with the 25/2{sup -} isomer in {sup 155}Lu, are identified for the first time. The systematical behavior of the energy levels is compared with that of neighboring isotones and isotopes. The attractive interaction between h{sub 11/2} protons and h{sub 9/2} neutrons plays an important role in the structure of {sup 155}Yb and {sup 155,156}Lu.

  20. New insights into the nonadiabatic state population dynamics of model proton-coupled electron transfer reactions from the mixed quantum-classical Liouville approach

    Energy Technology Data Exchange (ETDEWEB)

    Shakib, Farnaz A.; Hanna, Gabriel, E-mail: gabriel.hanna@ualberta.ca [Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2 (Canada)

    2016-01-14

    In a previous study [F. A. Shakib and G. Hanna, J. Chem. Phys. 141, 044122 (2014)], we investigated a model proton-coupled electron transfer (PCET) reaction via the mixed quantum-classical Liouville (MQCL) approach and found that the trajectories spend the majority of their time on the mean of two coherently coupled adiabatic potential energy surfaces. This suggested a need for mean surface evolution to accurately simulate observables related to ultrafast PCET processes. In this study, we simulate the time-dependent populations of the three lowest adiabatic states in the ET-PT (i.e., electron transfer preceding proton transfer) version of the same PCET model via the MQCL approach and compare them to the exact quantum results and those obtained via the fewest switches surface hopping (FSSH) approach. We find that the MQCL population profiles are in good agreement with the exact quantum results and show a significant improvement over the FSSH results. All of the mean surfaces are shown to play a direct role in the dynamics of the state populations. Interestingly, our results indicate that the population transfer to the second-excited state can be mediated by dynamics on the mean of the ground and second-excited state surfaces, as part of a sequence of nonadiabatic transitions that bypasses the first-excited state surface altogether. This is made possible through nonadiabatic transitions between different mean surfaces, which is the manifestation of coherence transfer in MQCL dynamics. We also investigate the effect of the strength of the coupling between the proton/electron and the solvent coordinate on the state population dynamics. Drastic changes in the population dynamics are observed, which can be understood in terms of the changes in the potential energy surfaces and the nonadiabatic couplings. Finally, we investigate the state population dynamics in the PT-ET (i.e., proton transfer preceding electron transfer) and concerted versions of the model. The PT

  1. Excited-state free energy surfaces in solution: time-dependent density functional theory∕reference interaction site model self-consistent field method.

    Science.gov (United States)

    Minezawa, Noriyuki

    2013-06-28

    Constructing free energy surfaces for electronically excited states is a first step toward the understanding of photochemical processes in solution. For that purpose, the analytic free energy gradient is derived and implemented for the linear-response time-dependent density functional theory combined with the reference interaction site model self-consistent field method. The proposed method is applied to study (1) the fluorescence spectra of aqueous acetone and (2) the excited-state intramolecular proton transfer reaction of ortho-hydroxybenzaldehyde in an acetonitrile solution.

  2. Search for excited states of light and heavy flavor quarks in the $\\gamma$+jet final state in proton-proton collisions at $\\sqrt{s} =$ 13 TeV

    Energy Technology Data Exchange (ETDEWEB)

    Sirunyan, Albert M; et al.

    2017-11-13

    A search is presented for excited quarks of light and heavy flavor that decay to $\\gamma$+jet final states. The analysis is based on data corresponding to an integrated luminosity of 35.9 fb$^{-1}$ collected by the CMS experiment in proton-proton collisions at $\\sqrt{s}=$ 13 TeV at the LHC. A signal would appear as a resonant contribution to the invariant mass spectrum of the $\\gamma$+jet system, above the background expected from standard model processes. No resonant excess is found, and upper limits are set on the product of the excited quark cross section and its branching fraction as a function of its mass. These are the most stringent limits to date in the $\\gamma$+jet final state, and exclude excited light quarks with masses below 5.5 TeV and excited b quarks with masses below 1.8 TeV, assuming standard model couplings.

  3. Synthesis, spectral behaviour and photophysics of donor-acceptor kind of chalcones: Excited state intramolecular charge transfer and fluorescence quenching studies

    Science.gov (United States)

    Pannipara, Mehboobali; Asiri, Abdullah M.; Alamry, Khalid A.; Arshad, Muhammad N.; El-Daly, Samy A.

    2015-02-01

    The spectral and photophysical properties of two chalcones containing electron donating and accepting groups with intramolecular charge transfer characteristics were synthesized and characterized by 1H NMR, 13C NMR and X-ray crystallography. Both compounds show very strong solvent polarity dependent changes in their photophysical characteristics, namely, remarkable red shift in the emission spectra with increasing solvent polarity, large change in Stokes shift, significant reduction in the fluorescence quantum yield; indicating that the fluorescence states of these compounds are of intramolecular charge transfer (ICT) character. The solvent effect on the photophysical parameters such as singlet absorption, molar absorptivity, oscillator strength, dipole moment, fluorescence spectra, and fluorescence quantum yield of both compounds have been investigated comprehensively. For both dyes, Lippert-Mataga and Reichardt's correlations were used to estimate the difference between the excited and ground state dipole moments (Δμ). The interactions of dyes with colloidal silver nanoparticles (Ag NPs) were also studied in ethanol using steady state fluorescence quenching measurements. The fluorescence quenching data reveal that dynamic quenching and energy transfer play a major role in the fluorescence quenching of dyes by Ag NPs.

  4. Two-neutron decay of excited states of 11Li

    Science.gov (United States)

    Smith, Jenna; MoNA Collaboration

    2013-10-01

    One prominent example of a Borromean nucleus is the two-neutron halo nucleus, 11Li. All excited states of this nucleus are unbound to two-neutron decay. Many theories propose that the two valence neutrons exhibit dineutron behavior in the ground state, but it is unclear what effect such a structure would have on the decay of the excited states. We have recently completed an experiment designed to study the decay of one of these excited states. Unbound 11Li was populated via a two-proton knockout from 13B. The two emitted neutrons were detected with the Modular Neutron Array (MoNA) and the Large-area multi-Institutional Scintillator Array (LISA) in coincidence with the daughter fragment, 9Li. Preliminary results will be discussed.

  5. Resonance Raman examination of the electronic excited states of glycylglycine and other dipeptides: Observation of a carboxylate{yields}amide charge transfer transition

    Energy Technology Data Exchange (ETDEWEB)

    Chen, X.G.; Li, P.; Holtz, J.S.W.; Chi, Z.; Pajcini, V.; Asher, S.A. [Univ. of Pittsburgh, PA (United States); Kelly, L.A. [Brookhaven National Lab., Upton, NY (United States)

    1996-10-09

    We have examined the UV resonance Raman and the VUV absorption spectra of aqueous glycylglycine and other dipeptides. We observe strong resonance Raman enhancement of the amide I, II, and III bands and the amide C{sub {alpha}}H bending mode in a manner similar to that we observed previously with excitation within the {pi}{yields}{pi}{sup *} transition of N-methylacetamide. However, in addition, we observe strong resonance Raman enhancement of the ca. 1400 cm{sup -1} symmetric COO{sup -} stretching vibration, whose 206.5 nm Raman cross section is increased 20-fold compared to that of the carboxylate in sodium acetate, for example. Addition of a methylene spacer between the amide and carboxylate groups causes the resonance Raman enhancement of this symmetric COO{sup -} stretch to disappear. The UV resonance Raman excitation profiles, the Raman depolarization ratio dispersion, and the VUV absorption spectra of glycylglycine and other dipeptides demonstrate the existence of a new 197 nm charge transfer band which involves electron transfer from a nonbonding carboxylate orbital to the amide-like {pi}{sup *} orbital. This transition occurs at the penultimate carboxylate end of all peptides and proteins. 18 refs., 9 figs., 3 tabs.

  6. Faster photoinduced electron transfer in a diluted mixture than in a neat donor solvent: effect of excited-state H-bonding.

    Science.gov (United States)

    Barman, Nabajeet; Singha, Debabrata; Sahu, Kalyanasis

    2014-04-07

    In a neat electron-donating solvent (in this case aniline), photoinduced electron transfer (PET) from the solvent to an excited acceptor (e.g. a coumarin fluorophore) may be anticipated to be the most efficient because of the close contact of the acceptor with many donors. Addition of an inert component would most likely retard the PET process by replacing some donors from the neighbourhood of the acceptors. Surprisingly, we found dramatic acceleration of PET (6-10 fold enhancement compared to neat aniline), for coumarin 102 (C102) dissolved in a binary mixture of aniline and an inert solvent (cyclohexane or toluene). The PET induced fluorescence follows an anomalous trend against the mole fraction of aniline (XAN); first quenches up to certain XAN (0.075 for cyclohexane; 0.13 for toluene), thereafter, enhances with increase in XAN. Although the non-interacting component cannot directly participate in the PET process, it may modulate C102-aniline H-bonding association by changing the polarity of the medium or by disrupting the aniline-aniline H-bond. The study clearly illustrates the dominant role of hydrogen bonding in activating the electron transfer rate where standard thermodynamics predicts very weak donor-acceptor interaction.

  7. Generation of Triplet Excited States via Photoinduced Electron Transfer in meso-anthra-BODIPY: Fluorogenic Response toward Singlet Oxygen in Solution and in Vitro

    KAUST Repository

    Filatov, Mikhail A.

    2017-04-14

    Heavy atom-free BODIPY-anthracene dyads (BADs) generate locally excited triplet states by way of photoinduced electron transfer (PeT), followed by recombination of the resulting charge-separated states (CSS). Subsequent quenching of the triplet states by molecular oxygen produces singlet oxygen (1O2), which reacts with the anthracene moiety yielding highly fluorescent species. The steric demand of the alkyl substituents in the BODIPY subunit defines the site of 1O2 addition. Novel bis- and tetraepoxides and bicyclic acetal products, arising from rearrangements of anthracene endoperoxides were isolated and characterized. 1O2 generation by BADs in living cells enables visualization of the dyads distribution, promising new imaging applications.

  8. Excited state of {sup 7}He and its unique structure

    Energy Technology Data Exchange (ETDEWEB)

    Korsheninnikov, A.A.; Golovkov, M.S.; Ozawa, A.; Yoshida, K.; Tanihata, I.; Fulop, Z.; Kusaka, K.; Morimoto, K.; Otsu, H.; Petrascu, H.; Tokanai, F. [Institute of Physical and Chemical Research, Wako, Saitama (Japan); Kuzmin, E.A.; Nikolskii, E.Yu.; Novatskii, B.G.; Ogloblin, A.A. [Russian Research Centre Kurchatov Inst., Moscow (Russian Federation)

    2000-07-01

    The transfer reaction p({sup 8}He,d){sup 7}He with the exotic {sup 8}He-beam has been studied by correlational measurements, and an excited state of {sup 7}He was observed. Most likely, it has a structure with a neutron in an excited state coupled to the {sup 6}He-core which itself is in the excited 2{sup +}-state. The transfer reaction p({sup 8}He,{sup 2}He){sup 7}H was also studied, and manifestation on the possible existence of the resonance {sup 7}H was obtained. (orig.)

  9. Intracluster proton transfer in aniline-amine complex ions

    OpenAIRE

    Inokuchi, Yoshiya; Ohashi, Kazuhiko; Honkawa, Yoshiki; Sekiya, Hiroshi; Nishi, Nobuyuki

    2002-01-01

    The intracluster proton transfer in aniline-amine complex ions is investigated by infrared photodissociation spectroscopy and density functional theory calculations. The proton acceptors include ammonia, methylamine, dimethylamine and trimethylamine in ascending order of proton affinity. The spectra of (aniline-ammonia)+ and (aniline-methylamine)+ demonstrate the persistence of the aniline ion unit in the complexes. For (aniline-dimethylamine)+ and (aniline-trimethylamine)+, the spectra imply...

  10. Characterization of excited-state reactions with instant spectra of fluorescence kinetics

    Energy Technology Data Exchange (ETDEWEB)

    Tomin, Vladimir I., E-mail: tomin@apsl.edu.pl; Ushakou, Dzmitryi V.

    2015-10-15

    Comprehensible knowledge of the excited-state proton transfer processes in organic compounds is overwhelmingly important not only for physics, but also chemistry and Life Sciences, since they play a key role in main processes of photosynthesis and functioning of biological organisms. Moreover compounds with Excited-State Intramolecular Proton Transfer (ESIPT) are in the focus of the interest of scientists throughout the world, because dual fluorescence spectra of such objects corresponding to two forms of molecular structure (normal and photoproduct) are very sensitive to characteristics of molecular microenvironment. This property allows to use such substances as fluorescent probes for diverse applications in chemistry and Life Sciences. But at the same time studying of proton transfer processes is not simple, because this process is characterized by extremely fast times (on picoseconds time scale and less order) and very often contribution of reverse reactions is essentially complicates an interpretation of observed properties of dual fluorescence. Hence, understanding of a role of reversible reactions is crucial for a comprehensive description of all processes accompanying excited state reactions. We discuss new approach for treatment ESIPT reaction on the basis of experimentally measured instant spectra of dual fluorescence and temporal behavior of ratiometric signal of normal to tautomer form intensities. Simple analytical expressions show in transparent way how to distinguish a degree of reverse reaction contribution to ratiometric signal. A validation of the approach under consideration is fulfilled with two different flavonols – 3-hydroxyflavone and 4′-(Dimethylamino)-3-hydroxyflavone – representing two extreme cases in affecting reversible reaction on dual emission. A comparing of new approach and traditional method when we analyze kinetics of separate the N* and T* fluorescence bands decays, has been carried out. - Highlights: • The excited-state

  11. Proton-Coupled Electron Transfer in Artificial Photosynthetic Systems.

    Science.gov (United States)

    Mora, S Jimena; Odella, Emmanuel; Moore, Gary F; Gust, Devens; Moore, Thomas A; Moore, Ana L

    2018-01-08

    Artificial photosynthetic constructs can in principle operate more efficiently than natural photosynthesis because they can be rationally designed to optimize solar energy conversion for meeting human demands rather than the multiple needs of an organism competing for growth and reproduction in a complex ecosystem. The artificial photosynthetic constructs described in this Account consist primarily of covalently linked synthetic chromophores, electron donors and acceptors, and proton donors and acceptors that carry out the light absorption, electron transfer, and proton-coupled electron transfer (PCET) processes characteristic of photosynthetic cells. PCET is the movement of an electron from one site to another accompanied by proton transfer. PCET and the transport of protons over tens of angstroms are important in all living cells because they are a fundamental link between redox processes and the establishment of transmembrane gradients of proton electrochemical potential, known as proton-motive force (PMF), which is the unifying concept in bioenergetics. We have chosen a benzimidazole phenol (BIP) system as a platform for the study of PCET because with appropriate substitutions it is possible to design assemblies in which one or multiple proton transfers can accompany oxidation of the phenol. In BIP, oxidation of the phenol increases its acidity by more than ten pKa units; thus, electrochemical oxidation of the phenol is associated with a proton transfer to the imidazole. This is an example of a PCET process involving transfer of one electron and one proton, known as electron-proton transfer (EPT). When the benzimidazole moiety of BIP is substituted at the 4-position with good proton acceptor groups such as aliphatic amines, experimental and theoretical results indicate that two proton transfers occur upon one-electron oxidation of the phenol. This phenomenon is described as a one-electron-two-proton transfer (E2PT) process and results in translocation of

  12. Dynamics of competitive reactions: endothermic proton transfer and exothermic substitution.

    Science.gov (United States)

    Ren, Jianhua; Brauman, John I

    2004-03-03

    Dynamics of an endothermic proton-transfer reaction, F(-) with dimethyl sulfoxide, and an endothermic proton-transfer reaction with a competing exothermic substitution (S(N)2) channel, F(-) with borane-methyl sulfide complex, were investigated using a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR) and kinetic modeling. The two proton-transfer reactions have slightly positive and a small negative overall free energy changes, respectively. Energy-dependent rate constants were measured as a function of F(-) ion translational energy, and the resulting kinetics were modeled with the RRKM (Rice-Ramsperger-Kassel-Marcus) theory. The observed rate constants for the proton-transfer reactions of F(-) with dimethyl sulfoxide and with borane-methyl sulfide complex are identical, with a value of 0.17 x 10(-9) cm(3) molecule(-1) s(-1); for the S(N)2 reaction, k = 0.90 x 10(-9) cm(3) molecule(-1) s(-1) at 350 K. Both proton-transfer reactions have positive entropy changes in the forward direction and show positive energy dependences. The competing S(N)2 reaction exhibits negative energy dependence and becomes less important at higher energies. The changes of the observed rate constants agree with RRKM theory predictions for a few kcal/mol of additional kinetic energy. The dynamic change of the branching ratio for the competing proton transfer and the substitution reactions results from the competition between the microscopic rate constants associated with each channel.

  13. Excited-state Wigner crystals

    Science.gov (United States)

    Rogers, Fergus J. M.; Loos, Pierre-François

    2017-01-01

    Wigner crystals (WCs) are electronic phases peculiar to low-density systems, particularly in the uniform electron gas. Since its introduction in the early twentieth century, this model has remained essential to many aspects of electronic structure theory and condensed-matter physics. Although the (lowest-energy) ground-state WC (GSWC) has been thoroughly studied, the properties of excited-state WCs (ESWCs) are basically unknown. To bridge this gap, we present a well-defined procedure to obtain an entire family of ESWCs in a one-dimensional electron gas using a symmetry-broken mean-field approach. While the GSWC is a commensurate crystal (i.e., the number of density maxima equals the number of electrons), these ESWCs are incommensurate crystals exhibiting more or less maxima. Interestingly, they are lower in energy than the (uniform) Fermi fluid state. For some of these ESWCs, we have found asymmetrical band gaps, which would lead to anisotropic conductivity. These properties are associated with unusual characteristics in their electronic structure.

  14. The mechanisms of Excited states in enzymes

    DEFF Research Database (Denmark)

    Petersen, Frederic Nicolas Rønne; Bohr, Henrik

    2010-01-01

    Enzyme catalysis is studied on the basis of excited state processes, which are of electronic, vibrational and thermal nature. The ways of achieving the excited state, such as photo-absorption and ligand binding, are discussed and exemplified by various cases of enzymes.......Enzyme catalysis is studied on the basis of excited state processes, which are of electronic, vibrational and thermal nature. The ways of achieving the excited state, such as photo-absorption and ligand binding, are discussed and exemplified by various cases of enzymes....

  15. Competitive Energy and Electron Transfer in β-Functionalized Free-Base Porphyrin-Zinc Porphyrin Dimer Axially Coordinated to C60 : Synthesis, Supramolecular Formation and Excited-State Processes.

    Science.gov (United States)

    Hu, Yi; Thomas, Michael B; Jinadasa, R G Waruna; Wang, Hong; D'Souza, Francis

    2017-09-18

    Simultaneous occurrence of energy and electron transfer events involving different acceptor sites in a newly assembled supramolecular triad comprised of covalently linked free-base porphyrin-zinc porphyrin dyad, H2 P-ZnP axially coordinated to electron acceptor fullerene, has been successfully demonstrated. The dyad was connected through the β-pyrrole positions of the porphyrin macrocycle instead of the traditionally used meso-positions for better electronic communication. Interestingly, the β-pyrrole functionalization modulated the optical properties to such an extent that it was possible to almost exclusively excite the zinc porphyrin entity in the supramolecular triad. The measured binding constant for the complex with 1:1 molecular stoichiometry was in the order of 104  m-1 revealing moderately stable complex formation. An energy level diagram constructed using optical, electrochemical and computational results suggested that both the anticipated energy and electron events are thermodynamically feasible in the triad. Consequently, it was possible to demonstrate occurrence of excited state energy transfer to the covalently linked H2 P, and electron transfer to the coordinated ImC60 from studies involving steady-state and time-resolved emission, and femto- and nanosecond transient absorption studies. The estimated energy transfer was around 67 % in the dyad with a rate constant of 1.1×109  s-1 . In the supramolecular triad, the charge separated state was rather long-lived although it was difficult to arrive the exact lifetime of charge separated state from nanosecond transient spectral studies due to overlap of strong triplet excited signals of porphyrin in the monitoring wavelength window. Nevertheless, simultaneous occurrence of energy and electron transfer in the appropriately positioned energy and electron acceptor entities in a supramolecular triad was possible to demonstrate in the present study, a step forward to unraveling the complex

  16. Explicit proton transfer in classical molecular dynamics simulations

    OpenAIRE

    Wolf, Maarten G.; Groenhof, Gerrit

    2014-01-01

    We present Hydrogen Dynamics (HYDYN), a method that allows explicit proton transfer in classical force field molecular dynamics simulations at thermodynamic equilibrium. HYDYN reproduces the characteristic properties of the excess proton in water, from the special pair dance, to the continuous fluctuation between the limiting Eigen and Zundel complexes, and the water reorientation beyond the first solvation layer. Advantages of HYDYN with respect to existing methods are computational efficien...

  17. Proton transfer in acetylacetone and its α-halo derivatives.

    Science.gov (United States)

    Dolati, Fatemeh; Tayyari, Sayyed Faramarz; Vakili, Mohammad; Wang, Yan Alexander

    2016-01-07

    A two-dimensional potential energy surface was utilized to treat the proton transfer in acetylacetone (AA) and its α-halo derivatives: α-fluoro-(FAA), α-chloro-(ClAA), and α-bromo-acetylacetone (BrAA). This potential energy function, which couples O-H stretching and in-plane bending vibrations, was acquired through ab initio calculations for a fixed skeleton geometry. The resulting potential energy surfaces were then used to calculate the proton tunneling frequencies and proton transfer barrier heights. The barrier heights (the energy difference between the saddle point and the minima) calculated at the MP2/6-31G(2d,p) level of theory for proton transfers in AA, FAA, ClAA, and BrAA are 7.2, 9.4, 6.3, and 5.9 kcal mol(-1), respectively. The theoretically predicted proton transfer barrier heights exhibit excellent linear correlations with geometrical, electronic structural, and topological parameters evaluated by the atoms-in-molecule (AIM) and natural bond orbital (NBO) analyses.

  18. 4-Hydroxy-1-naphthaldehydes: proton transfer or deprotonation

    DEFF Research Database (Denmark)

    Manolova, Y; Kurteva, V; Antonov, L

    2015-01-01

    A series of naphthaldehydes, including a Mannich base, have been investigated by UV-Vis spectroscopy, NMR and theoretical methods to explore their potential tautomerism. In the case of 4-hydroxy-1-naphthaldehyde concentration dependent deprotonation has been detected in methanol and acetonitrile....... For 4-hydroxy-3-(piperidin-1-ylmethyl)-1-naphthaldehyde (a Mannich base) an intramolecular proton transfer involving the OH group and the piperidine nitrogen occurs. In acetonitrile the equilibrium is predominantly at the OH-form, whereas in methanol the proton transferred tautomer is the preferred form...

  19. Alternating electron and proton transfer steps in photosynthetic water oxidation.

    Science.gov (United States)

    Klauss, André; Haumann, Michael; Dau, Holger

    2012-10-02

    Water oxidation by cyanobacteria, algae, and plants is pivotal in oxygenic photosynthesis, the process that powers life on Earth, and is the paradigm for engineering solar fuel-production systems. Each complete reaction cycle of photosynthetic water oxidation requires the removal of four electrons and four protons from the catalytic site, a manganese-calcium complex and its protein environment in photosystem II. In time-resolved photothermal beam deflection experiments, we monitored apparent volume changes of the photosystem II protein associated with charge creation by light-induced electron transfer (contraction) and charge-compensating proton relocation (expansion). Two previously invisible proton removal steps were detected, thereby filling two gaps in the basic reaction-cycle model of photosynthetic water oxidation. In the S(2) → S(3) transition of the classical S-state cycle, an intermediate is formed by deprotonation clearly before electron transfer to the oxidant (Y Z OX). The rate-determining elementary step (τ, approximately 30 µs at 20 °C) in the long-distance proton relocation toward the protein-water interface is characterized by a high activation energy (E(a) = 0.46 ± 0.05 eV) and strong H/D kinetic isotope effect (approximately 6). The characteristics of a proton transfer step during the S(0) → S(1) transition are similar (τ, approximately 100 µs; E(a) = 0.34 ± 0.08 eV; kinetic isotope effect, approximately 3); however, the proton removal from the Mn complex proceeds after electron transfer to . By discovery of the transient formation of two further intermediate states in the reaction cycle of photosynthetic water oxidation, a temporal sequence of strictly alternating removal of electrons and protons from the catalytic site is established.

  20. Water-assisted Proton Transfer in Ferredoxin I*

    Science.gov (United States)

    Lutz, Stephan; Tubert-Brohman, Ivan; Yang, Yonggang; Meuwly, Markus

    2011-01-01

    The role of water molecules in assisting proton transfer (PT) is investigated for the proton-pumping protein ferredoxin I (FdI) from Azotobacter vinelandii. It was shown previously that individual water molecules can stabilize between Asp15 and the buried [3Fe-4S]0 cluster and thus can potentially act as a proton relay in transferring H+ from the protein to the μ2 sulfur atom. Here, we generalize molecular mechanics with proton transfer to studying proton transfer reactions in the condensed phase. Both umbrella sampling simulations and electronic structure calculations suggest that the PT Asp15-COOH + H2O + [3Fe-4S]0 → Asp15-COO− + H2O + [3Fe-4S]0 H+ is concerted, and no stable intermediate hydronium ion (H3O+) is expected. The free energy difference of 11.7 kcal/mol for the forward reaction is in good agreement with the experimental value (13.3 kcal/mol). For the reverse reaction (Asp15-COO− + H2O + [3Fe-4S]0H+ → Asp15-COOH + H2O + [3Fe-4S]0), a larger barrier than for the forward reaction is correctly predicted, but it is quantitatively overestimated (23.1 kcal/mol from simulations versus 14.1 from experiment). Possible reasons for this discrepancy are discussed. Compared with the water-assisted process (ΔE ≈ 10 kcal/mol), water-unassisted proton transfer yields a considerably higher barrier of ΔE ≈ 35 kcal/mol. PMID:21531725

  1. Vibrational Förster transfer to hydrated protons.

    Science.gov (United States)

    Timmer, R L A; Tielrooij, K J; Bakker, H J

    2010-05-21

    We have studied the influence of excess protons on the vibrational energy relaxation of the O-H and O-D stretching modes in water using femtosecond pump-probe spectroscopy. Without excess protons, we observe exponential decays with time constants of 1.7 and 4.3 ps for the bulk and anion bound O-D stretch vibrations. The addition of protons introduces a new energy relaxation pathway, which leads to an increasingly nonexponential decay of the O-D stretch vibration. This new pathway is attributed to a distance-dependent long range dipole-dipole (Forster) interaction between the O-D stretching vibration and modes associated with dissolved protons. The high efficiency of hydrated protons as receptors of vibrational energy follows from the very large absorption cross section and broad bandwidth of protons in water. For a proton concentration of 1M we find that Forster energy transfer occurs over an average distance of 4.5 A, which corresponds to a separation of about two water molecules.

  2. Experimental and Theoretical Aspects of Excited State Electron Transfer and Related Phenomena: Conference Held in Honour of Zbigniew R. Grabowski in Pultusk, Poland on September 27-October 2, 1992

    Science.gov (United States)

    1992-10-01

    linear law , also typi:al for complex formation in the excited state. These data give evidence for the formation of long lived ( up to 30 ns...Dr. MIaria Amparo Olba-Torrent Department of Physical Chemuistry ProE Jai Pat Mittal University (if Valencia Chemiistry Division Dr. Moliner 5(0

  3. Photophysics of a proton transfer phototautomer within biological confinement of a protein: Spectroscopic and molecular docking studies

    Energy Technology Data Exchange (ETDEWEB)

    Paul, Bijan K., E-mail: bijan.paul.chem.cu@gmail.com; Guchhait, Nikhil, E-mail: nguchhait@yahoo.com

    2014-09-15

    The present work demonstrates the effect of biological confinement on the photophysics of a proton transfer phototautomer viz., 2-hydroxy-1-naphthaldehyde (HN21). HN21 is a potential candidate exhibiting excited-state intramolecular proton transfer (ESIPT) reaction and thereby generating the phototautomer (i.e., proton transferred keto form) in the excited-state. The ESIPT photophysics of the probe (HN21) is found to be remarkably modified within the confined bio-environment of a model transport protein Bovine Serum Albumin (BSA). Such considerable modification of the ESIPT photophysics of the probe has been exploited to determine the probe–protein binding strength (binding constant, K(±10%)=1.23×10{sup 4} M{sup −1}). The probe–protein binding process is found to be thermodynamically feasible (ΔG=−24.25 kJ mol{sup −1}). The present work also delves into evaluation of the probable binding location of the probe (HN21) within the biomacromolecular assembly of the protein by blind docking simulation technique, which reveals that HN21 favorably binds to the hydrophobic subdomain IIIA of BSA. Circular dichroism (CD) spectroscopy delineates the effect of probe binding on the protein secondary structure in terms of decrease of α-helical content of BSA with increasing probe concentration. Apart from this, excitation–emission matrix fluorescence technique is found to hint at the effect on protein tertiary structure upon binding to the probe. The modulated dynamics of the proton transfer phototautomer of HN21 within the biological confinement is investigated in this context by time-resolved fluorescence decay measurements. The present work also accentuates the mutually corroborating data found from experimental and computational studies. - Highlights: • Remarkable modification of ESIPT emission of HN21 in protein is explored. • Probe–protein binding efficiency is evaluated from fluorescence spectral data. • Binding to the probe accompanies perturbation

  4. Rearrangements in ground and excited states

    CERN Document Server

    de Mayo, Paul

    1980-01-01

    Rearrangements in Ground and Excited States, Volume 3 presents essays on the chemical generation of excited states; the cis-trans isomerization of olefins; and the photochemical rearrangements in trienes. The book also includes essays on the zimmerman rearrangements; the photochemical rearrangements of enones; the photochemical rearrangements of conjugated cyclic dienones; and the rearrangements of the benzene ring. Essays on the photo rearrangements via biradicals of simple carbonyl compounds; the photochemical rearrangements involving three-membered rings or five-membered ring heterocycles;

  5. Role of Electron-Driven Proton-Transfer Processes in the Ultrafast Deactivation of Photoexcited Anionic 8-oxoGuanine-Adenine and 8-oxoGuanine-Cytosine Base Pairs

    Directory of Open Access Journals (Sweden)

    Xiuxiu Wu

    2017-01-01

    Full Text Available It has been reported that 8-oxo-7,8-dihydro-guanosine (8-oxo-G, which is the main product of oxidative damage of DNA, can repair cyclobutane pyrimidine dimer (CPD lesions when incorporated into DNA or RNA strands in proximity to such lesions. It has therefore been suggested that the 8-oxo-G nucleoside may have been a primordial precursor of present-day flavins in DNA or RNA repair. Because the electron transfer leading to the splitting of a thymine-thymine pair in a CPD lesion occurs in the photoexcited state, a reasonably long excited-state lifetime of 8-oxo-G is required. The neutral (protonated form of 8-oxo-G exhibits a very short (sub-picosecond intrinsic excited-state lifetime which is unfavorable for repair. It has therefore been argued that the anionic (deprotonated form of 8-oxo-G, which exhibits a much longer excited-state lifetime, is more likely to be a suitable cofactor for DNA repair. Herein, we have investigated the exited-state quenching mechanisms in the hydrogen-bonded complexes of deprotonated 8-oxo-G− with adenine (A and cytosine (C using ab initio wave-function-based electronic-structure calculations. The calculated reaction paths and potential-energy profiles reveal the existence of barrierless electron-driven inter-base proton-transfer reactions which lead to low-lying S1/S0 conical intersections. The latter can promote ultrafast excited-state deactivation of the anionic base pairs. While the isolated deprotonated 8-oxo-G− nucleoside may have been an efficient primordial repair cofactor, the excited states of the 8-oxo-G−-A and 8-oxo-G−-C base pairs are likely too short-lived to be efficient electron-transfer repair agents.

  6. Proton-transfer reactions in "super" photoacids and supramolecular assemblies

    NARCIS (Netherlands)

    Kumpulainen, T.S.

    2015-01-01

    Transfer of a proton is undoubtedly one of the most elementary and yet one of the most significant reactions in chemical and biological processes and have received great attention during the last 60 years. Surprisingly, the exact mechanism of this elementary reaction is still not fully understood

  7. Variation of kinetic isotope effect in multiple proton transfer reactions

    Indian Academy of Sciences (India)

    Variation of kinetic isotope effect in multiple proton transfer reactions. #. B SARITHA and M DURGA PRASAD. ∗. School of Chemistry, University of Hyderabad, Hyderabad 500 046, India e-mail: mdpsc@uohyd.ernet.in. Abstract. Recently, we had suggested that the motion along the promoter mode in the first part of the IRC.

  8. Nonradiative charge transfer in collisions of protons with rubidium atoms

    Science.gov (United States)

    Yan, Ling-Ling; Qu, Yi-Zhi; Liu, Chun-Hua; Zhang, Yu; Wang, Jian-Guo; Buenker, Robert J.

    2012-06-01

    The nonradiative charge-transfer cross sections for protons colliding with Rb(5s) atoms are calculated by using the quantum-mechanical molecularorbital close-coupling method in an energy range of 10-3 keV-10 keV. The total and state-selective charge-transfer cross sections are in good agreement with the experimental data in the relatively low energy region. The importance of rotational coupling for chargetransfer process is stressed. Compared with the radiative charge-transfer process, nonradiative charge transfer is a dominant mechanism at energies above 15 eV. The resonance structures of state-selective charge-transfer cross sections arising from the competition among channels are analysed in detail. The radiative and nonradiative charge-transfer rate coefficients from low to high temperature are presented.

  9. Potential energy construction in the diabatic picture for quantum mechanical rate constants of intermolecular proton transfer.

    Science.gov (United States)

    Hori, Yuta; Ida, Tomonori; Mizuno, Motohiro

    2017-06-28

    We propose a simple method for potential construction in the diabatic picture and the estimation of thermal rate constants for intermolecular proton transfer reactions using quantum dynamics simulations carried out on the constructed potentials. For symmetrical and asymmetrical proton transfer pairs, the obtained potentials and rate constants were in good agreement with the reference values. Furthermore, our method is used for the analysis of proton transfer in crystalline imidazolium succinate and discusses the proton conductivity in terms of intermolecular proton transfer. This approach can be used to estimate proton transfer rate constants for large molecular systems, even when the calculation of the transition state is impossible.

  10. Excited-state structural dynamics of a dual-emission calmodulin-green fluorescent protein sensor for calcium ion imaging.

    Science.gov (United States)

    Oscar, Breland G; Liu, Weimin; Zhao, Yongxin; Tang, Longteng; Wang, Yanli; Campbell, Robert E; Fang, Chong

    2014-07-15

    Fluorescent proteins (FPs) have played a pivotal role in bioimaging and advancing biomedicine. The versatile fluorescence from engineered, genetically encodable FP variants greatly enhances cellular imaging capabilities, which are dictated by excited-state structural dynamics of the embedded chromophore inside the protein pocket. Visualization of the molecular choreography of the photoexcited chromophore requires a spectroscopic technique capable of resolving atomic motions on the intrinsic timescale of femtosecond to picosecond. We use femtosecond stimulated Raman spectroscopy to study the excited-state conformational dynamics of a recently developed FP-calmodulin biosensor, GEM-GECO1, for calcium ion (Ca(2+)) sensing. This study reveals that, in the absence of Ca(2+), the dominant skeletal motion is a ∼ 170 cm(-1) phenol-ring in-plane rocking that facilitates excited-state proton transfer (ESPT) with a time constant of ∼ 30 ps (6 times slower than wild-type GFP) to reach the green fluorescent state. The functional relevance of the motion is corroborated by molecular dynamics simulations. Upon Ca(2+) binding, this in-plane rocking motion diminishes, and blue emission from a trapped photoexcited neutral chromophore dominates because ESPT is inhibited. Fluorescence properties of site-specific protein mutants lend further support to functional roles of key residues including proline 377 in modulating the H-bonding network and fluorescence outcome. These crucial structural dynamics insights will aid rational design in bioengineering to generate versatile, robust, and more sensitive optical sensors to detect Ca(2+) in physiologically relevant environments.

  11. Ab initio study on the mechanism of C2H2++NH3 reaction: Efficient charge transfer and proton transfer processes competing with stable complex formation

    Science.gov (United States)

    Cui, Qiang; Morokuma, Keiji

    1998-03-01

    High level ab initio calculations have been performed to investigate the mechanism of the ion-molecule reaction NH3+C2H2+. Three channels, covalent complex formation (CC), proton transfer (PT), and charge transfer (CT) have been studied. Among the two pathways found for the PT channel, one leads the reactants NH3+C2H2+ to NH4++C2H(2Π) through a moderately bound complex without any barrier, and the other leads NH3++C2H2 to the H-atom transferred products NH4++C2H(2Σ+) with a modest barrier. These findings support the fast "stripping" mechanism proposed by Anderson et al. As to the CC channel, several isomers of C2H5N+ and the isomerization transition states have been located. No significant barrier relative to the reactants has been found on either the ground or the 2A″ excited state. To rationalize the experimental fact that no CC channel products have been observed, it is argued that the reactants NH3+C2H2+ correlate adiabatically to excited states of covalent C2H5N+ species, whose formation requires significant alternation of the C2H2+ geometry and electronic structure. Therefore, the system is most likely to follow the PT or the CT channel instead of visiting the CC channel. For the CT channel, limited potential energy surface scans of the three electronic states (1,2 2A'+2A″) indicate that CT at different approach angles or between electronic states of different symmetries (A'→A',A″→A') may produce final products of different characteristics, and might account for the two pathways proposed by Anderson et al.

  12. Solvent influence on excited-state intramolecular proton transfer in 3-hydroxychromone derivatives studied by cryogenic high-resolution fluorescence spectroscopy

    NARCIS (Netherlands)

    Bader, A.N.; Pivovarenko, V.; Demchenko, A.P.; Ariese, F.; Gooijer, C.

    2003-01-01

    High-resolution Shpol'skii spectra (recorded at 10 K in n-octane) of 3-hydroxychromone (3HC) substituted at the 2-position with a furan (3HC-F), a benzofuran (3HC-BF) or a naphthofuran group (3HC-NF) are presented. Being close analogues of 3-hydroxyflavone (3HF), these compounds can undergo

  13. Excited-State Deactivation of Branched Phthalocyanine Compounds.

    Science.gov (United States)

    Zhu, Huaning; Li, Yang; Chen, Jun; Zhou, Meng; Niu, Yingli; Zhang, Xinxing; Guo, Qianjin; Wang, Shuangqing; Yang, Guoqiang; Xia, Andong

    2015-12-21

    The excited-state relaxation dynamics and chromophore interactions in two phthalocyanine compounds (bis- and trisphthalocyanines) are studied by using steady-state and femtosecond transient absorption spectral measurements, where the excited-state energy-transfer mechanism is explored. By exciting phthalocyanine compounds to their second electronically excited states and probing the subsequent relaxation dynamics, a multitude of deactivation pathways are identified. The transient absorption spectra show the relaxation pathway from the exciton state to excimer state and then back to the ground state in bisphthalocyanine (bis-Pc). In trisphthalocyanine (tris-Pc), the monomeric and dimeric subunits are excited and the excitation energy transfers from the monomeric vibrationally hot S1 state to the exciton state of a pre-associated dimer, with subsequent relaxation to the ground state through the excimer state. The theoretical calculations and steady-state spectra also show a face-to-face conformation in bis-Pc, whereas in tris-Pc, two of the three phthalocyanine branches form a pre-associated face-to-face dimeric conformation with the third one acting as a monomeric unit; this is consistent with the results of the transient absorption experiments from the perspective of molecular structure. The detailed structure-property relationships in phthalocyanine compounds is useful for exploring the function of molecular aggregates in energy migration of natural photosynthesis systems. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Proton Transfer Time-of-Flight Mass Spectrometer

    Energy Technology Data Exchange (ETDEWEB)

    Watson, Thomas B. [Brookhaven National Lab. (BNL), Upton, NY (United States)

    2016-03-01

    The Proton Transfer Reaction Mass Spectrometer (PTRMS) measures gas-phase compounds in ambient air and headspace samples before using chemical ionization to produce positively charged molecules, which are detected with a time-of-flight (TOF) mass spectrometer. This ionization method uses a gentle proton transfer reaction method between the molecule of interest and protonated water, or hydronium ion (H3O+), to produce limited fragmentation of the parent molecule. The ions produced are primarily positively charged with the mass of the parent ion, plus an additional proton. Ion concentration is determined by adding the number of ions counted at the molecular ion’s mass-to-charge ratio to the number of air molecules in the reaction chamber, which can be identified according to the pressure levels in the reaction chamber. The PTRMS allows many volatile organic compounds in ambient air to be detected at levels from 10–100 parts per trillion by volume (pptv). The response time is 1 to 10 seconds.

  15. Charmonium excited state spectrum in lattice QCD

    Energy Technology Data Exchange (ETDEWEB)

    Jozef Dudek; Robert Edwards; Nilmani Mathur; David Richards

    2008-02-01

    Working with a large basis of covariant derivative-based meson interpolating fields we demonstrate the feasibility of reliably extracting multiple excited states using a variational method. The study is performed on quenched anisotropic lattices with clover quarks at the charm mass. We demonstrate how a knowledge of the continuum limit of a lattice interpolating field can give additional spin-assignment information, even at a single lattice spacing, via the overlap factors of interpolating field and state. Excited state masses are systematically high with respect to quark potential model predictions and, where they exist, experimental states. We conclude that this is most likely a result of the quenched approximation.

  16. Computing correct truncated excited state wavefunctions

    Science.gov (United States)

    Bacalis, N. C.; Xiong, Z.; Zang, J.; Karaoulanis, D.

    2016-12-01

    We demonstrate that, if a wave function's truncated expansion is small, then the standard excited states computational method, of optimizing one "root" of a secular equation, may lead to an incorrect wave function - despite the correct energy according to the theorem of Hylleraas, Undheim and McDonald - whereas our proposed method [J. Comput. Meth. Sci. Eng. 8, 277 (2008)] (independent of orthogonality to lower lying approximants) leads to correct reliable small truncated wave functions. The demonstration is done in He excited states, using truncated series expansions in Hylleraas coordinates, as well as standard configuration-interaction truncated expansions.

  17. Microscopic models for proton transfer in water and strongly hydrogen-bonded complexes with a single-well proton potential

    DEFF Research Database (Denmark)

    Kuznetsov, A.M.; Ulstrup, Jens

    2004-01-01

    A new mechanism and formalism for proton transfer in donor-acceptor complexes with long hydrogen bonds introduced recently [1], is applied to a proton transfer in liquid water. "Structural diffusion" of hydroxonium ions is regarded as totally adiabatic process, with synchronous hindered translation...

  18. Excited states of muonium in atomic hydrogen

    Indian Academy of Sciences (India)

    Muonium formation in excited states in muon-hydrogen charge-exchange collision is investigated using a method developed in a previous paper. Differential cross-section results are found to resemble positronium formation cross-section results of positron-hydrogen charge-exchange problem. Forward differential and ...

  19. Insights into Proton-Coupled Electron Transfer from Computation

    Science.gov (United States)

    Provorse, Makenzie R.

    Proton-coupled electron transfer (PCET) is utilized throughout Nature to facilitate essential biological processes, such as photosynthesis, cellular respiration, and DNA replication and repair. The general approach to studying PCET processes is based on a two-dimensional More O'Ferrall-Jencks diagram in which electron transfer (ET) and proton transfer (PT) occur in a sequential or concerted fashion. Experimentally, it is difficult to discern the contributing factors of concerted PCET mechanisms. Several theoretical approaches have arisen to qualitatively and quantitatively investigate these reactions. Here, we present a multistate density functional theory (MSDFT) method to efficiently and accurately model PCET mechanisms. The MSDFT method is validated against experimental and computational data previously reported on an isoelectronic series of small molecule self-exchange hydrogen atom transfer reactions and a model complex specifically designed to study long-range ET through a hydrogen-bonded salt-bridge interface. Further application of this method to the hydrogen atom abstraction of ascorbate by a nitroxyl radical demonstrates the sensitivity of the thermodynamic and kinetic properties to solvent effects. In particular, the origin of the unusual kinetic isotope effect is investigated. Lastly, the MSDFT is employed in a combined quantum mechanical/molecular mechanical (QM/MM) approach to explicitly model PCET in condensed phases.

  20. Kinetics of proton transfer in a green fluorescent protein: A laser ...

    Indian Academy of Sciences (India)

    Unknown

    protonation kinetics showed dependence on the bulk viscosity of the solvent, and therefore implicates bulk solvent-controlled protein dynamics in the protonation process. The protonation is proposed to be a sequential process involving two steps: (a) proton transfer from solvent to the chromophore, and (b) internal structural.

  1. Pathway of proton transfer in bacterial reaction centers: replacement of serine-L223 by alanine inhibits electron and proton transfers associated with reduction of quinone to dihydroquinone.

    Science.gov (United States)

    Paddock, M L; McPherson, P H; Feher, G; Okamura, M Y

    1990-01-01

    The pathway of proton transfer in the reaction center (RC) from Rhodobacter sphaeroides was investigated by site-directed mutagenesis. Ser-L223, a putative proton donor that forms a hydrogen bond with the secondary quinone acceptor QB, was replaced with Ala and Thr. RCs with Ala-L223 displayed reduced electron transfer and proton uptake rates in the reaction QA-QB- + 2H+----QAQBH2. The rate constant for this reaction, k(2)AB, was found to be reduced approximately 350-fold to 4.0 +/- 0.2 s-1. Proton uptake measurements using a pH indicator dye showed a rapid uptake of 1 H+ per RC followed by a slower uptake of 1 H+ per RC at a rate of 4.1 +/- 0.1 s-1; native RCs showed a rapid uptake of 2H+ per RC. Evidence is provided that these changes were not due to gross structural changes in the binding site of QB. RCs with Thr-L223 showed little reduction in the rates of electron and proton transfer. These results indicate that proton transfer from the hydroxyl group of Ser-L223 or Thr-L223 is required for fast electron and proton transfer associated with the formation of the dihydroquinone QH2. In contrast, previous work showed that replacing Glu-L212, another putative proton donor to QB, with Gln slowed proton uptake from solution without significantly altering electron transfer. We propose a model that involves two distinct proton transfer steps. The first step occurs prior to transfer of the second electron to QB and involves proton transfer from Ser-L223. The second step occurs after this electron transfer through a pathway involving Glu-L212. PMID:2168561

  2. Proton Linear Energy Transfer measurement using Emulsion Cloud Chamber

    Energy Technology Data Exchange (ETDEWEB)

    Shin, Jae-ik [Proton Therapy Center, National Cancer Center (Korea, Republic of); Division of Heavy Ion Clinical Research, Korea Institute of Radiological & Medical Sciences (KIRAMS), Seoul (Korea, Republic of); Park, Seyjoon [Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University, School of Medicine, Seoul (Korea, Republic of); Kim, Haksoo; Kim, Meyoung [Proton Therapy Center, National Cancer Center (Korea, Republic of); Jeong, Chiyoung [Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul (Korea, Republic of); Cho, Sungkoo [Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University, School of Medicine, Seoul (Korea, Republic of); Lim, Young Kyung; Shin, Dongho [Proton Therapy Center, National Cancer Center (Korea, Republic of); Lee, Se Byeong, E-mail: sblee@ncc.re.kr [Proton Therapy Center, National Cancer Center (Korea, Republic of); Morishima, Kunihiro; Naganawa, Naotaka; Sato, Osamu [Department of Physics, Nagoya University, Nagoya (Japan); Kwak, Jungwon [Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul (Korea, Republic of); Kim, Sung Hyun [Center for Underground Physics, Institute for Basic Science (IBS), Daejeon (Korea, Republic of); Cho, Jung Sook [Department of refinement education, Dongseo University, Busan (Korea, Republic of); Ahn, Jung Keun [Department of Physics, Korea University, Seoul (Korea, Republic of); Kim, Ji Hyun; Yoon, Chun Sil [Gyeongsang National University, Jinju (Korea, Republic of); Incerti, Sebastien [CNRS, IN2P3, CENBG, UMR 5797, F-33170 Gradignan (France); Université Bordeaux 1, CENBG, UMR 5797, F-33170 Gradignan (France)

    2015-04-15

    This study proposes to determine the correlation between the Volume Pulse Height (VPH) measured by nuclear emulsion and Linear Energy Transfer (LET) calculated by Monte Carlo simulation based on Geant4. The nuclear emulsion was irradiated at the National Cancer Center (NCC) with a therapeutic proton beam and was installed at 5.2 m distance from the beam nozzle structure with various thicknesses of water-equivalent material (PMMA) blocks to position with specific positions along the Bragg curve. After the beam exposure and development of the emulsion films, the films were scanned by S-UTS developed in Nagoya University. The proton tracks in the scanned films were reconstructed using the ‘NETSCAN’ method. Through this procedure, the VPH can be derived from each reconstructed proton track at each position along the Bragg curve. The VPH value indicates the magnitude of energy loss in proton track. By comparison with the simulation results obtained using Geant4, we found the correlation between the LET calculated by Monte Carlo simulation and the VPH measured by the nuclear emulsion.

  3. Proton Linear Energy Transfer measurement using Emulsion Cloud Chamber

    Science.gov (United States)

    Shin, Jae-ik; Park, Seyjoon; Kim, Haksoo; Kim, Meyoung; Jeong, Chiyoung; Cho, Sungkoo; Lim, Young Kyung; Shin, Dongho; Lee, Se Byeong; Morishima, Kunihiro; Naganawa, Naotaka; Sato, Osamu; Kwak, Jungwon; Kim, Sung Hyun; Cho, Jung Sook; Ahn, Jung Keun; Kim, Ji Hyun; Yoon, Chun Sil; Incerti, Sebastien

    2015-04-01

    This study proposes to determine the correlation between the Volume Pulse Height (VPH) measured by nuclear emulsion and Linear Energy Transfer (LET) calculated by Monte Carlo simulation based on Geant4. The nuclear emulsion was irradiated at the National Cancer Center (NCC) with a therapeutic proton beam and was installed at 5.2 m distance from the beam nozzle structure with various thicknesses of water-equivalent material (PMMA) blocks to position with specific positions along the Bragg curve. After the beam exposure and development of the emulsion films, the films were scanned by S-UTS developed in Nagoya University. The proton tracks in the scanned films were reconstructed using the 'NETSCAN' method. Through this procedure, the VPH can be derived from each reconstructed proton track at each position along the Bragg curve. The VPH value indicates the magnitude of energy loss in proton track. By comparison with the simulation results obtained using Geant4, we found the correlation between the LET calculated by Monte Carlo simulation and the VPH measured by the nuclear emulsion.

  4. Restrained Proton Indicator in Combined Quantum-Mechanics/Molecular-Mechanics Dynamics Simulations of Proton Transfer through a Carbon Nanotube.

    Science.gov (United States)

    Duster, Adam W; Lin, Hai

    2017-09-14

    Recently, a collective variable "proton indicator" was purposed for tracking an excess proton solvated in bulk water in molecular dynamics simulations. In this work, we demonstrate the feasibility of utilizing the position of this proton indicator as a reaction coordinate to model an excess proton migrating through a hydrophobic carbon nanotube in combined quantum-mechanics/molecular-mechanics simulations. Our results indicate that applying a harmonic restraint to the proton indicator in the bulk solvent near the nanotube pore entrance leads to the recruitment of water molecules into the pore. This is consistent with an earlier study that employed a multistate empirical valence bond potential and a different representation (center of excess charge) of the proton. We attribute this water recruitment to the delocalized nature of the solvated proton, which prefers to be in high-dielectric bulk solvent. While water recruitment into the pore is considered an artifact in the present simulations (because of the artificially imposed restraint on the proton), if the proton were naturally restrained, it could assist in building water wires prior to proton transfer through the pore. The potential of mean force for a proton translocation through the water-filled pore was computed by umbrella sampling, where the bias potentials were applied to the proton indicator. The free energy curve and barrier heights agree reasonably with those in the literature. The results suggest that the proton indicator can be used as a reaction coordinate in simulations of proton transport in confined environments.

  5. Protonation and strong H-bonding as the factors controlling structural changes in excited azaaromatics

    Energy Technology Data Exchange (ETDEWEB)

    Grabowska, A. (Polska Akademia Nauk, Warsaw. Inst. Chemii Fizycznej)

    1981-11-01

    The relationship between the structure of a molecule and electron density distribution in excited states of protonated N-heteroaromatics has been discussed, basing on (1) Walsh rules (2) dihydroflavines as model compounds. Two selected examples of inter- and intramolecular proton transfer have been quoted, namely the net charge distribution in 7-azaindole and proton transfer kinetics in 2(2'-hydroxyphenyl)benzoxazole.

  6. Spectral and electrooptical absorption and emission studies on internally hydrogen bonded benzoxazole 'double' derivatives: 2,5-bis(benzoxazolyl)hydroquinone (BBHQ) and 3,6-bis(benzoxazolyl)pyrocatechol (BBPC). Single versus double proton transfer in the excited BBPC revisited

    Energy Technology Data Exchange (ETDEWEB)

    Wortmann, R.; Lebus, S.; Reis, H. [Institute of Physical Chemistry, University of Mainz, Jakob-Welder-Weg 11, 55099 Mainz (Germany); Grabowska, A.; Kownacki, K. [Institute of Physical Chemistry, Polish Academy of Sciences, 44/52 Kasprzaka, 01-224 Warsaw (Poland); Jarosz, S. [Institute of Organic Chemistry, Polish Academy of Sciences, 44/52 Kasprzaka, 01-224 Warsaw (Poland)

    1999-05-15

    Ground and excited state dipole moments and polarizabilities of 2,5-bis(benzoxazolyl)hydroquinone (BBHQ) and 3,6-bis(benzoxazolyl)pyrocatechol (BBPC) are determined by means of electrooptical absorption and emission measurements. BBHQ is found to exhibit a small, while BBPC a large increase of the static polarizability in the Franck-Condon (FC) excited singlet state. The change of the dipole moments upon excitation to the FC state is zero within experimental error. However, both molecules show dipole moments in the fluorescent states of their phototautomers, of about 5 D, the major component being parallel to the long molecular axis. The experimental and theoretical results strongly suggest that the fluorescent species of BBHQ and BBPC are monoketo-tautomers created by single proton transfer in the course of the excited state relaxation. For BBPC this was confirmed by a comparative photophysical study with its monomethoxy-derivative (MeBBPC), in which one active proton is replaced by the CH{sub 3} group. These results lead to the revision of previous conclusions [Grabowska et al., Chem. Phys. Lett. 177 (1991) 17] stating that BBPC undergoes a double proton transfer in the excited state. For BBHQ the previously found single proton transfer mechanism of tautomerization is fully confirmed. (Copyright (c) 1999 Elsevier Science B.V., Amsterdam. All rights reserved.)

  7. Umbrella sampling of proton transfer in a creatine-water system

    Science.gov (United States)

    Ivchenko, Olga; Bachert, Peter; Imhof, Petra

    2014-04-01

    Proton transfer reactions are among the most common processes in chemistry and biology. Proton transfer between creatine and surrounding solvent water is underlying the chemical exchange saturation transfer used as a contrast in magnetic resonance imaging. The free energy barrier, determined by first-principles umbrella sampling simulations (EaDFT 3 kcal/mol) is in the same order of magnitude as the experimentally obtained activation energy. The underlying mechanism is a first proton transfer from the guanidinium group to the water pool, followed by a second transition where a proton is "transferred back" from the nearest water molecule to the deprotonated nitrogen atom of creatine.

  8. Rearrangements in ground and excited states

    CERN Document Server

    de Mayo, Paul

    1980-01-01

    Rearrangements in Ground and Excited States, Volume 2 covers essays on the theoretical approach of rearrangements; the rearrangements involving boron; and the molecular rearrangements of organosilicon compounds. The book also includes essays on the polytopal rearrangement at phosphorus; the rearrangement in coordination complexes; and the reversible thermal intramolecular rearrangements of metal carbonyls. Chemists and people involved in the study of rearrangements will find the book invaluable.

  9. New memory devices based on the proton transfer process

    Science.gov (United States)

    Wierzbowska, Małgorzata

    2016-01-01

    Memory devices operating due to the fast proton transfer (PT) process are proposed by the means of first-principles calculations. Writing information is performed using the electrostatic potential of scanning tunneling microscopy (STM). Reading information is based on the effect of the local magnetization induced at the zigzag graphene nanoribbon (Z-GNR) edge—saturated with oxygen or the hydroxy group—and can be realized with the use of giant magnetoresistance (GMR), a magnetic tunnel junction or spin-transfer torque devices. The energetic barriers for the hop forward and backward processes can be tuned by the distance and potential of the STM tip; this thus enables us to tailor the non-volatile logic states. The proposed system enables very dense packing of the logic cells and could be used in random access and flash memory devices.

  10. Collective proton transfer in ordinary ice: local environments, temperature dependence and deuteration effects.

    Science.gov (United States)

    Drechsel-Grau, Christof; Marx, Dominik

    2017-01-25

    The transfer of multiple protons in hydrogen-bonded networks usually occurs one proton at a time. At sufficiently high temperatures, each proton transfers via thermally activated hopping along its hydrogen bond, thereby moving a charge defect through the network. At low temperatures, quantum-mechanical tunnelling might set in instead, thus avoiding hopping over the energy barriers. In the case of several transferring protons, independent thermal hopping or quantum tunnelling of the individual protons becomes less favourable because of a significant creation of charge defects. In individual molecules or hydrogen-bonded molecular complexes, for instance, double proton transfer is often found to be concerted. Multiple proton transfer that avoids charge defects can occur in cyclic topologies built from several hydrogen bonds that allow for directional chains of proton transfer. This requires perfect proton order within these rings, which imposes handedness and thus chirality, and changes parity upon transfer of all protons. Ordinary ice, which is hexagonal ice Ih, is the most stable form of crystalline ice obtained upon freezing liquid water at ambient pressure and consists of interconnected six rings of oxygen atoms that host six protons each. These hexagonal rings remain proton disordered even down to low temperatures, as heralded by the residual entropy of ice Ih. However, owing to combinatorics, a certain number of these six rings is proton ordered in macroscopic crystals. These chiral hexameric rings might support coherent tunnelling of the hosted protons. Indeed, there is some evidence in the recent literature, both experimental and simulational, that correlated tunnelling of all six protons might be possible in proton-ordered six rings in ice Ih if temperatures are low enough. In this Perspective, the key ideas and previous findings will be reviewed in the light of relevant experiments with a focus on available ab initio path integral simulation work

  11. Proton Transfer and Low-Barrier Hydrogen Bonding: a Shifting Vibrational Landscape Dictated by Large Amplitude Tunneling

    Science.gov (United States)

    Vealey, Zachary; Foguel, Lidor; Vaccaro, Patrick

    2017-06-01

    Our fundamental understanding of synergistic hydrogen-bonding and proton-transfer phenomena has been advanced immensely by studies of model systems in which the coherent transduction of hydrons is mediated by two degenerate equilibrium configurations that are isolated from one another by a potential barrier of substantial height. This topography advantageously affords unambiguous signatures for the underlying state-resolved dynamics in the form of tunneling-induced spectral bifurcations, the magnitudes of which encode both the overall efficacy and the detailed mechanism of the unimolecular transformation. As a prototypical member of this class of compounds, 6-hydroxy-2-formylfulvene (HFF) supports an unusual quasi-linear O-H...O \\leftrightarrow O...H-O reaction coordinate that presents a minimal impediment to proton migration - a situation commensurate with the concepts of low-barrier hydrogen bonding (which are characterized by great strength, short distance, and a vanishingly small barrier for hydron migration). A variety of fluorescence-based, laser-spectroscopic probes have been deployed in a cold supersonic free-jet expansion to explore the vibrational landscape and anomalously large tunneling-induced shifts that dominate the ˜{X}^{1}A_{1} potential-energy surface of HFF, thus revealing the most rapid proton tunneling ever reported for a molecular ground state (τ_{pt}≤120fs). The surprising efficiency of such tunneling-mediated processes stems from proximity of the zero-point level to the barrier crest and produces a dramatic alteration in the canonical pattern of vibrational features that reflects, in part, the subtle transition from quantum-mechanical barrier penetration to classical over-the-barrier dynamics. The ultrafast proton-transfer regime that characterizes the ˜{X}^{1}A_{1} manifold will be juxtaposed against analogous findings for the lowest-lying singlet excited state ˜{A}^{1}B_{2} (π*←π), where a marked change in the nature of the

  12. Application of spectroscopy and super-resolution microscopy: Excited state

    Energy Technology Data Exchange (ETDEWEB)

    Bhattacharjee, Ujjal [Iowa State Univ., Ames, IA (United States)

    2016-02-19

    Photophysics of inorganic materials and organic molecules in complex systems have been extensively studied with absorption and emission spectroscopy.1-4 Steady-state and time-resolved fluorescence studies are commonly carried out to characterize excited-state properties of fluorophores. Although steady-state fluorescence measurements are widely used for analytical applications, time-resolved fluorescence measurements provide more detailed information about excited-state properties and the environment in the vicinity of the fluorophore. Many photophysical processes, such as photoinduced electron transfer (PET), rotational reorientation, solvent relaxation, and energy transfer, occur on a nanosecond (10-9 s) timescale, thus affecting the lifetime of the fluorophores. Moreover, time-resolved microscopy methods, such as lifetimeimaging, combine the benefits of the microscopic measurement and information-rich, timeresolved data. Thus, time-resolved fluorescence spectroscopy combined with microscopy can be used to quantify these processes and to obtain a deeper understanding of the chemical surroundings of the fluorophore in a small area under investigation. This thesis discusses various photophysical and super-resolution microscopic studies of organic and inorganic materials, which have been outlined below.

  13. Analytical calculation of proton linear energy transfer in voxelized geometries including secondary protons

    Science.gov (United States)

    Sanchez-Parcerisa, D.; Cortés-Giraldo, M. A.; Dolney, D.; Kondrla, M.; Fager, M.; Carabe, A.

    2016-02-01

    In order to integrate radiobiological modelling with clinical treatment planning for proton radiotherapy, we extended our in-house treatment planning system FoCa with a 3D analytical algorithm to calculate linear energy transfer (LET) in voxelized patient geometries. Both active scanning and passive scattering delivery modalities are supported. The analytical calculation is much faster than the Monte-Carlo (MC) method and it can be implemented in the inverse treatment planning optimization suite, allowing us to create LET-based objectives in inverse planning. The LET was calculated by combining a 1D analytical approach including a novel correction for secondary protons with pencil-beam type LET-kernels. Then, these LET kernels were inserted into the proton-convolution-superposition algorithm in FoCa. The analytical LET distributions were benchmarked against MC simulations carried out in Geant4. A cohort of simple phantom and patient plans representing a wide variety of sites (prostate, lung, brain, head and neck) was selected. The calculation algorithm was able to reproduce the MC LET to within 6% (1 standard deviation) for low-LET areas (under 1.7 keV μm-1) and within 22% for the high-LET areas above that threshold. The dose and LET distributions can be further extended, using radiobiological models, to include radiobiological effectiveness (RBE) calculations in the treatment planning system. This implementation also allows for radiobiological optimization of treatments by including RBE-weighted dose constraints in the inverse treatment planning process.

  14. Analytical calculation of proton linear energy transfer in voxelized geometries including secondary protons.

    Science.gov (United States)

    Sanchez-Parcerisa, D; Cortés-Giraldo, M A; Dolney, D; Kondrla, M; Fager, M; Carabe, A

    2016-02-21

    In order to integrate radiobiological modelling with clinical treatment planning for proton radiotherapy, we extended our in-house treatment planning system FoCa with a 3D analytical algorithm to calculate linear energy transfer (LET) in voxelized patient geometries. Both active scanning and passive scattering delivery modalities are supported. The analytical calculation is much faster than the Monte-Carlo (MC) method and it can be implemented in the inverse treatment planning optimization suite, allowing us to create LET-based objectives in inverse planning. The LET was calculated by combining a 1D analytical approach including a novel correction for secondary protons with pencil-beam type LET-kernels. Then, these LET kernels were inserted into the proton-convolution-superposition algorithm in FoCa. The analytical LET distributions were benchmarked against MC simulations carried out in Geant4. A cohort of simple phantom and patient plans representing a wide variety of sites (prostate, lung, brain, head and neck) was selected. The calculation algorithm was able to reproduce the MC LET to within 6% (1 standard deviation) for low-LET areas (under 1.7 keV μm(-1)) and within 22% for the high-LET areas above that threshold. The dose and LET distributions can be further extended, using radiobiological models, to include radiobiological effectiveness (RBE) calculations in the treatment planning system. This implementation also allows for radiobiological optimization of treatments by including RBE-weighted dose constraints in the inverse treatment planning process.

  15. Excited state dynamics of DNA bases

    Czech Academy of Sciences Publication Activity Database

    Kleinermanns, K.; Nachtigallová, Dana; de Vries, M. S.

    2013-01-01

    Roč. 32, č. 2 (2013), s. 308-342 ISSN 0144-235X R&D Projects: GA ČR GAP208/12/1318 Grant - others:National Science Foundation(US) CHE-0911564; NASA(US) NNX12AG77G; Deutsche Forschungsgemeinschaft(DE) SFB 663; Deutsche Forschungsgemeinschaft(DE) KI 531-29 Institutional support: RVO:61388963 Keywords : DNA bases * nucleobases * excited state * dynamics * computations * gas phase * conical intersections Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 4.920, year: 2013

  16. Absorption and tunneling effects in one- and two-proton transfer reactions

    Energy Technology Data Exchange (ETDEWEB)

    Marta, H.D. [Facultad de Ingenieria, Montevideo (Uruguay). Inst. de Fisica; Donangelo, R. [Universidade Federal, Rio de Janeiro, RJ (Brazil). Inst. de Fisica; Tomasi, D.; Fernandez Niello, J.O.; Pacheco, A.J. [Comision Nacional de Energia Atomica, Buenos Aires (Argentina). Dept. de Fisica. Lab. TANDAR

    1997-12-31

    We analyze proton transfer data for the {sup 12} C + {sup 197} Au system. Our semiclassical model reproduces the observed energy dependence of the transfer probabilities at large distances. (author) 3 refs., 1 fig.

  17. Probing the Locality of Excited States with Linear Algebra.

    Science.gov (United States)

    Etienne, Thibaud

    2015-04-14

    This article reports a novel theoretical approach related to the analysis of molecular excited states. The strategy introduced here involves gathering two pieces of physical information, coming from Hilbert and direct space operations, into a general, unique quantum mechanical descriptor of electronic transitions' locality. Moreover, the projection of Hilbert and direct space-derived indices in an Argand plane delivers a straightforward way to visually probe the ability of a dye to undergo a long- or short-range charge-transfer. This information can be applied, for instance, to the analysis of the electronic response of families of dyes to light absorption by unveiling the trend of a given push-pull chromophore to increase the electronic cloud polarization magnitude of its main transition with respect to the size extension of its conjugated spacer. We finally demonstrate that all the quantities reported in this article can be reliably approximated by a linear algebraic derivation, based on the contraction of detachment/attachment density matrices from canonical to atomic space. This alternative derivation has the remarkable advantage of a very low computational cost with respect to the previously used numerical integrations, making fast and accurate characterization of large molecular systems' excited states easily affordable.

  18. Theoretical studies on proton transfer reaction of 3(5)-substituted ...

    Indian Academy of Sciences (India)

    Abstract. The inter and intra molecular proton transfer reactions of a series of pyrazole derivatives have been studied by using density functional theory (DFT) and MP2 methods implementing 6-311++G(d,p) atomic basis set. The substituents have been selected to cover a wide range of electronic effects. Proton transfer ...

  19. Proton transfer in ba(3) cytochrome c oxidase from Thermus thermophilus.

    Science.gov (United States)

    von Ballmoos, Christoph; Adelroth, Pia; Gennis, Robert B; Brzezinski, Peter

    2012-04-01

    The respiratory heme-copper oxidases catalyze reduction of O(2) to H(2)O, linking this process to transmembrane proton pumping. These oxidases have been classified according to the architecture, location and number of proton pathways. Most structural and functional studies to date have been performed on the A-class oxidases, which includes those that are found in the inner mitochondrial membrane and bacteria such as Rhodobacter sphaeroides and Paracoccus denitrificans (aa(3)-type oxidases in these bacteria). These oxidases pump protons with a stoichiometry of one proton per electron transferred to the catalytic site. The bacterial A-class oxidases use two proton pathways (denoted by letters D and K, respectively), for the transfer of protons to the catalytic site, and protons that are pumped across the membrane. The B-type oxidases such as, for example, the ba(3) oxidase from Thermus thermophilus, pump protons with a lower stoichiometry of 0.5 H(+)/electron and use only one proton pathway for the transfer of all protons. This pathway overlaps in space with the K pathway in the A class oxidases without showing any sequence homology though. Here, we review the functional properties of the A- and the B-class ba(3) oxidases with a focus on mechanisms of proton transfer and pumping. Copyright © 2012 Elsevier B.V. All rights reserved.

  20. Quantum marginals from pure doubly excited states

    Science.gov (United States)

    Maciążek, Tomasz; Tsanov, Valdemar

    2017-11-01

    The possible spectra of one-particle reduced density matrices that are compatible with a pure multipartite quantum system of finite dimension form a convex polytope. We introduce a new construction of inner- and outer-bounding polytopes that constrain the polytope for the entire quantum system. The outer bound is sharp. The inner polytope stems only from doubly excited states. We find all quantum systems, where the bounds coincide giving the entire polytope. We show, that those systems are: (i) any system of two particles (ii) L qubits, (iii) three fermions on N≤slant 7 levels, (iv) any number of bosons on any number of levels and (v) fermionic Fock space on N≤slant 5 levels. The methods we use come from symplectic geometry and representation theory of compact Lie groups. In particular, we study the images of proper momentum maps, where our method describes momentum images for all representations that are spherical.

  1. Excited States in Solution through Polarizable Embedding

    DEFF Research Database (Denmark)

    Olsen, Jógvan Magnus; Aidas, Kestutis; Kongsted, Jacob

    2010-01-01

    We present theory and implementation of an advanced quantum mechanics/molecular mechanics (QM/MM) approach using a fully self-consistent polarizable embedding (PE) scheme. It is a polarizable layered model designed for effective yet accurate inclusion of an anisotropic medium in a quantum...... mechanical calculation. The polarizable embedding potential is described by an atomistic representation including terms up to localized octupoles and anisotropic polarizabilities. It is generally applicable to any quantum chemical description but is here implemented for the case of Kohn−Sham density...... functional theory which we denote the PE-DFT method. It has been implemented in combination with time-dependent quantum mechanical linear and nonlinear response techniques, thus allowing for assessment of electronic excitation processes and dynamic ground- and excited-state molecular properties using...

  2. Excited states of {sup 4}He droplets

    Energy Technology Data Exchange (ETDEWEB)

    Guardiola, R.; Navarro, J.; Portesi, M.

    2001-06-01

    We study low-lying excited states of {sup 4}He clusters up to a cluster size of 40 atoms in a variational framework. The ansatz wave function combines two- and three-body correlations, coming from a translationally invariant configuration interaction description, and Jastrow-type short-range correlation. We have previously used this scheme to determine the ground-state energies of {sup 4}He and {sup 3}He clusters. Here we present an extension of this ansatz wave function having a good quantum angular momentum L. The variational procedure is applied independently to the cases with L=0,2,4, and upper bounds for the corresponding energies are thus obtained. Moreover, centroid energies for L excitations are calculated through the use of sum rules. A comparison with previous calculations is also made.

  3. The Bending Magnets for the Proton Transfer Line of CNGS

    CERN Document Server

    Schirm, K M; Anashin, V; Kiselev, O; Maraev, V; Ogurtsov, A; Pupkov, Yu; Ruvinsky, E; Zhilyaev, K; Konstantinov, Yu S; Kosjakin, M; Peregud, V

    2006-01-01

    The project "CERN neutrinos to Gran Sasso (CNGS)", a collaboration between CERN and the INFN (Gran Sasso Laboratory) in Italy, will study neutrino oscillations in a long base-line experiment. High-energy protons will be extracted from the CERN SPS accelerator, transported through a 727 m long transfer line and focused onto a graphite target to produce a beam of pions and kaons and subsequently neutrinos. The transfer line requires a total of 78 dipole magnets. They were produced in the framework of an in-kind contribution of Germany via DESY to the CNGS project. The normal conducting dipoles, built from laminated steel cores and copper coils, have a core length of 6.3 m, a 37 mm gap height and a nominal field range of 1.38 T - 1.91 T at a maximum current of 4950 A. The magnet design was a collaboration between CERN and BINP. The half-core production was subcontracted to EFREMOV Institute; the coil fabrication, magnet assembly and the field measurements were concluded at BINP in June 2004. The main design issu...

  4. First 3- excited state of Fe56

    Science.gov (United States)

    Fotiades, N.; Nelson, R. O.; Devlin, M.

    2010-03-01

    There is no reliable evidence for the existence of the 3.076 MeV (3-) level adopted in the ENSDF evaluation for Fe56 although it has been reported in a few experiments. Previous reports of the observation of this level appear to be based on an incorrect assignment in early (e,e') work. Recent neutron inelastic scattering measurements by Demidov [Phys. At. Nucl. 67, 1884, (2004)] show that the assigned γ-ray decay of this state does not occur at a level consistent with known properties of inelastic scattering. In the present work the Fe56(n,n'γ) reaction was used to populate excited states in Fe56. Neutrons in the energy range from 1 to 250 MeV were provided by the pulsed neutron source of the Los Alamos Neutron Science Center’s WNR facility. Deexciting γ rays were detected with the GEANIE spectrometer, a Compton suppressed array of 26 Ge detectors. The γ-γ data obtained with GEANIE were used to establish coincidence relations between transitions. All previously reported levels up to Ex=3.6 MeV excitation energy were observed except for the 3.076 MeV (3-) level. The 991- and 2229-keV transitions, previously reported to deexcite this level, were not observed in the γ-γ coincidence data obtained in the present experiment. The present work supports the assignment of the 4509.6 keV level as the first 3- excited state in Fe56 by observation of two previously known transitions deexciting this state.

  5. A treatment of excited states in nucleosynthesis

    Science.gov (United States)

    Gupta, Sanjib Shankar

    2002-10-01

    Many isotopes of importance to nucleosynthesis have metastable states whose decay to the ground state is strongly inhibited by a high angular momentum difference. Traditionally, excited states of a nucleus have been treated by assuming attainment of thermal equilibrium; a Hauser-Feshbach calculation is then performed on the whole nucleus to determine nuclear reaction rates. A description of the nucleus when it is not in equilibrium, and a method for computing reaction rates that does not presume thermalization are presented in this work. In nucleosynthesis calculations, we may characterize the internal electromagnetic transitions of a nucleus as a Markov process. This allows us to decompose the interaction of radiation with nucleons into effective interactions between ensembles. Rather than consider a single isotope, we construct the canonical ensembles which are the true nuclear species of interest. We are then in a position to specify nonequilibrium occupations of the ensembles by discretizing the Nuclear Level Density function. The generality of the stochastic process identified at the outset now permits the description of nucleosynthesis as Markov flows in networks of suitably populated ensembles. This allows us to use as many excited states as we wish in nucleosyn thesis while tracking their nonequilibrium evolution as substochastic processes. A website utilizing these principles is discussed in some detail. It accesses the theoretical NLD database from the Brussels Intitute of Astrophysics to supplement adopted experimental data from the ENSDF database (maintained by Brookhaven National Laboratories). The composite is processed by a CGI (Common Gateway Interface) application to dynamically obtain plots and tables of rates on a specified temperature grid. Beta-decay rates are discussed for an isotope important to nuclear astrophysics ( 180TA) as a test-bed for the techniques implemented.

  6. Influence of Proton Acceptors on the Proton-Coupled Electron Transfer Reaction Kinetics of a Ruthenium-Tyrosine Complex.

    Science.gov (United States)

    Lennox, J Christian; Dempsey, Jillian L

    2017-11-22

    A polypyridyl ruthenium complex with fluorinated bipyridine ligands and a covalently bound tyrosine moiety was synthesized, and its photo-induced proton-coupled electron transfer (PCET) reactivity in acetonitrile was investigated with transient absorption spectroscopy. Using flash-quench methodology with methyl viologen as an oxidative quencher, a Ru 3+ species is generated that is capable of initiating the intramolecular PCET oxidation of the tyrosine moiety. Using a series of substituted pyridine bases, the reaction kinetics were found to vary as a function of proton acceptor concentration and identity, with no significant H/D kinetic isotope effect. Through analysis of the kinetics traces and comparison to a control complex without the tyrosine moiety, PCET reactivity was found to proceed through an equilibrium electron transfer followed by proton transfer (ET-PT) pathway in which irreversible deprotonation of the tyrosine radical cation shifts the ET equilibrium, conferring a base dependence on the reaction. Comprehensive kinetics modeling allowed for deconvolution of complex kinetics and determination of rate constants for each elementary step. Across the five pyridine bases explored, spanning a range of 4.2 pK a units, a linear free-energy relationship was found for the proton transfer rate constant with a slope of 0.32. These findings highlight the influence that proton transfer driving force exerts on PCET reaction kinetics.

  7. Scientific Computation Application Partnerships in Materials and Chemical Sciences, Charge Transfer and Charge Transport in Photoactivated Systems, Developing Electron-Correlated Methods for Excited State Structure and Dynamics in the NWChem Software Suite

    Energy Technology Data Exchange (ETDEWEB)

    Cramer, Christopher J. [Univ. of Minnesota, Minneapolis, MN (United States)

    2017-11-12

    Charge transfer and charge transport in photoactivated systems are fundamental processes that underlie solar energy capture, solar energy conversion, and photoactivated catalysis, both organometallic and enzymatic. We developed methods, algorithms, and software tools needed for reliable treatment of the underlying physics for charge transfer and charge transport, an undertaking with broad applicability to the goals of the fundamental-interaction component of the Department of Energy Office of Basic Energy Sciences and the exascale initiative of the Office of Advanced Scientific Computing Research.

  8. Linear energy transfer incorporated intensity modulated proton therapy optimization

    Science.gov (United States)

    Cao, Wenhua; Khabazian, Azin; Yepes, Pablo P.; Lim, Gino; Poenisch, Falk; Grosshans, David R.; Mohan, Radhe

    2018-01-01

    The purpose of this study was to investigate the feasibility of incorporating linear energy transfer (LET) into the optimization of intensity modulated proton therapy (IMPT) plans. Because increased LET correlates with increased biological effectiveness of protons, high LETs in target volumes and low LETs in critical structures and normal tissues are preferred in an IMPT plan. However, if not explicitly incorporated into the optimization criteria, different IMPT plans may yield similar physical dose distributions but greatly different LET, specifically dose-averaged LET, distributions. Conventionally, the IMPT optimization criteria (or cost function) only includes dose-based objectives in which the relative biological effectiveness (RBE) is assumed to have a constant value of 1.1. In this study, we added LET-based objectives for maximizing LET in target volumes and minimizing LET in critical structures and normal tissues. Due to the fractional programming nature of the resulting model, we used a variable reformulation approach so that the optimization process is computationally equivalent to conventional IMPT optimization. In this study, five brain tumor patients who had been treated with proton therapy at our institution were selected. Two plans were created for each patient based on the proposed LET-incorporated optimization (LETOpt) and the conventional dose-based optimization (DoseOpt). The optimized plans were compared in terms of both dose (assuming a constant RBE of 1.1 as adopted in clinical practice) and LET. Both optimization approaches were able to generate comparable dose distributions. The LET-incorporated optimization achieved not only pronounced reduction of LET values in critical organs, such as brainstem and optic chiasm, but also increased LET in target volumes, compared to the conventional dose-based optimization. However, on occasion, there was a need to tradeoff the acceptability of dose and LET distributions. Our conclusion is that the

  9. Linear energy transfer incorporated intensity modulated proton therapy optimization.

    Science.gov (United States)

    Cao, Wenhua; Khabazian, Azin; Yepes, Pablo P; Lim, Gino J; Poenisch, Falk; Grosshans, David R; Mohan, Radhe

    2017-11-13

    The purpose of this study was to investigate the feasibility of incorporating linear energy transfer (LET) into the optimization of intensity modulated proton therapy (IMPT) plans. Because increased LET correlates with increased biological effectiveness of protons, high LETs in target volumes and low LETs in critical structures and normal tissues are preferred in an IMPT plan. However, if not explicitly incorporated into the optimization criteria, different IMPT plans may yield similar physical dose distributions but greatly different LET, specifically dose-averaged LET, distributions. Conventionally, the IMPT optimization criteria (or cost function) only includes dose-based objectives in which the relative biological effectiveness (RBE) is assumed to have a constant value of 1.1. In this study, we added LET-based objectives for maximizing LET in target volumes and minimizing LET in critical structures and normal tissues. Due to the fractional programming nature of the resulting model, we used a variable reformulation approach so that the optimization process is computationally equivalent to conventional IMPT optimization. In this study, five brain tumor patients who had been treated with proton therapy at our institution were selected. Two plans were created for each patient based on the proposed LET-incorporated optimization (LETOpt) and the conventional dose-based optimization (DoseOpt). The optimized plans were compared in terms of both dose (assuming a constant RBE of 1.1 as adopted in clinical practice) and LET. Both optimization approaches were able to generate comparable dose distributions. The LET-incorporated optimization achieved not only pronounced reduction of LET values in critical organs, such as brainstem and optic chiasm, but also increased LET in the target volumes, compared to the conventional dose-based optimization. However, on occasion, there was a need to tradeoff the acceptability of dose and LET distributions. Our conclusion is that the

  10. Supporting Information for the article entitled, “Excited State Charge ...

    Indian Academy of Sciences (India)

    Supporting Information for the article entitled, “Excited State Charge Transfer Reaction in (Mixed Solvent + Electrolyte) Systems: Role of Reactant-Solvent and ... S2: Composition dependence of the reaction time (, upper panels) and long time ( , lower panels) constants obtained from bi-exponential fit of the collected LE ...

  11. Excited state electron affinity calculations for aluminum

    Science.gov (United States)

    Hussein, Adnan Yousif

    2017-08-01

    Excited states of negative aluminum ion are reviewed, and calculations of electron affinities of the states (3s^23p^2)^1D and (3s3p^3){^5}{S}° relative to the (3s^23p)^2P° and (3s3p^2)^4P respectively of the neutral aluminum atom are reported in the framework of nonrelativistic configuration interaction (CI) method. A priori selected CI (SCI) with truncation energy error (Bunge in J Chem Phys 125:014107, 2006) and CI by parts (Bunge and Carbó-Dorca in J Chem Phys 125:014108, 2006) are used to approximate the valence nonrelativistic energy. Systematic studies of convergence of electron affinity with respect to the CI excitation level are reported. The calculated value of the electron affinity for ^1D state is 78.675(3) meV. Detailed Calculations on the ^5S°c state reveals that is 1216.8166(3) meV below the ^4P state.

  12. Ultrafast Excited State Relaxation of a Metalloporphyrin Revealed by Femtosecond X-ray Absorption Spectroscopy

    DEFF Research Database (Denmark)

    Shelby, Megan L.; Lestrange, Patrick J.; Jackson, Nicholas E.

    2016-01-01

    and nuclear structure for critical excited electronic states in the relaxation pathway characterize the dependence of the complex's geometry on the electron occupation of the 3d orbitals. Calculated XANES transitions for these excited states assign a short-lived transient signal to the spectroscopic signature...... of the Ni(I) species, resulting from intramolecular charge transfer on a time scale that has eluded previous synchrotron studies. These combined results enable us to examine the excited state structural dynamics of NiTMP prior to thermal relaxation and to capture intermediates of potential photocatalytic...

  13. Enhanced negative ion formation via electron attachment to electronically-excited states

    Energy Technology Data Exchange (ETDEWEB)

    Pinnaduwage, L.A. [Oak Ridge National Lab., TN (United States). Health Sciences Research Div.]|[Univ. of Tennessee, Knoxville, TN (United States). Dept. of Physics

    1995-12-31

    Recent basic studies on electron attachment to laser-excited molecules show that electron attachment to electronically-excited states can have orders of magnitude larger cross sections compared to the respective ground electronic states. Even though systematic studies have not been conducted, there are indications that electronically-excited states may play a significant role in negative ion formation in gas discharges. The high-lying Rydberg states could be of particular significance since, (i) their production efficiencies are high, and (ii) they have comparatively long lifetimes. Such states could be populated in discharge sources via direct electron impact or via excitation transfer from metastable states of inert gases.

  14. Kinetic isotope effect on the proton-transfer in indigo carmine

    Science.gov (United States)

    Iwakura, Izumi; Yabushita, Atsushi; Kobayashi, Takayoshi

    2010-01-01

    We have found that photo-excited indigo carmine causes stepwise proton transfer to generate mono-alcohol intermediate, which immediately returns to the parent molecule [I. Iwakura, A. Yabushita, T. Kobayashi, Chem. Lett. 38 (2009) 1020]. The kinetic isotope effect in the proton transfer of this system has been studied by direct observation of the real-time molecular vibrational amplitude during the reaction including the transition state using a sub-5-fs laser pulse. The kaH/kaD ratio for the proton transfer after photo-excitation is observed to be 1.5 ± 0.1.

  15. Excited State Spectra and Dynamics of Phenyl-Substituted Butadienes

    DEFF Research Database (Denmark)

    Wallace-Williams, Stacie E.; Schwartz, Benjamin J.; Møller, Søren

    1994-01-01

    A combination of steady-state and dynamic spectral measurements are used to provide new insights into the nature of the excited-state processes of all-trans-1,4-diphenyl-1,3-butadiene and several analogs: 1,4-diphenyl- 1,3-cyclopentadiene, 1,1,4,4-tetraphenylbutadiene, 1,2,3,4-tetraphenyl-1,3-cyc...... indicate that phenyl torsional motion is not important to the excited-state dynamics and reveal alternative excited-state reaction pathways. The results demonstrate how molecular systems that are structually similar can exhibit different electronic properties and excited-state dynamics....

  16. Excited-State Effective Masses in Lattice QCD

    Energy Technology Data Exchange (ETDEWEB)

    George Fleming, Saul Cohen, Huey-Wen Lin

    2009-10-01

    We apply black-box methods, i.e. where the performance of the method does not depend upon initial guesses, to extract excited-state energies from Euclidean-time hadron correlation functions. In particular, we extend the widely used effective-mass method to incorporate multiple correlation functions and produce effective mass estimates for multiple excited states. In general, these excited-state effective masses will be determined by finding the roots of some polynomial. We demonstrate the method using sample lattice data to determine excited-state energies of the nucleon and compare the results to other energy-level finding techniques.

  17. Investigation of two-photon absorption induced excited state absorption in a fluorenyl-based chromophore.

    Science.gov (United States)

    Li, Changwei; Yang, Kun; Feng, Yan; Su, Xinyan; Yang, Junyi; Jin, Xiao; Shui, Min; Wang, Yuxiao; Zhang, Xueru; Song, Yinglin; Xu, Hongyao

    2009-12-03

    Two-photon absorption induced excited state absorption in the solution of a new fluorenyl-based chromophore is investigated by a time-resolved pump-probe technique using femtosecond pulses. With the help of an additional femtosecond open-aperture Z-scan technique, numerical simulations based on a three-energy level model are used to interpret the experimental results, and we determine the nonlinear optical parameters of this new chromophore uniquely. Large two-photon absorption cross section and excited state absorption cross section for singlet excited state are obtained, indicating a good candidate for optical limiting devices. Moreover, the influence of two-beam coupling induced energy transfer in neat N,N'-dimethylformamide solvent is also considered, although this effect is strongly restrained by the instantaneous two-photon absorption.

  18. Excited state evolution towards ligand loss and ligand chelation at group 6 metal carbonyl centres.

    Science.gov (United States)

    Manton, Jennifer C; Amirjalayer, Saeed; Coleman, Anthony C; McMahon, Suzanne; Harvey, Emma C; Greetham, Gregory M; Clark, Ian P; Buma, Wybren Jan; Woutersen, Sander; Pryce, Mary T; Long, Conor

    2014-12-21

    The photochemistry and photophysics of three model "half-sandwich" complexes (η(6)-benzophenone)Cr(CO)3, (η(6)-styrene)Cr(CO)3, and (η(6)-allylbenzene)Cr(CO)3 were investigated using pico-second time-resolved infrared spectroscopy and time-dependent density functional theory methods. The (η(6)-benzophenone)Cr(CO)3 complex was studied using two excitation wavelengths (470 and 320 nm) while the remaining complexes were irradiated using 400 nm light. Two independent excited states were detected spectroscopically for each complex, one an unreactive excited state of metal-to-arene charge-transfer character and the other with metal-to-carbonyl charge transfer character. This second excited state leads to an arrested release of CO on the pico-second time-scale. Low-energy excitation (470 nm) of (η(6)-benzophenone)Cr(CO)3 populated only the unreactive excited state which simply relaxes to the parent complex. Higher energy irradiation (320 nm) induced CO-loss. Irradiation of (η(6)-styrene)Cr(CO)3, or (η(6)-allylbenzene)Cr(CO)3 at 400 nm provided evidence for the simultaneous population of both the reactive and unreactive excited states. The efficiency at which the unreactive excited state is populated depends on the degree of conjugation of the substituent with the arene π-system and this affects the efficiency of the CO-loss process. The quantum yield of CO-loss is 0.50 for (η(6)-allylbenzene)Cr(CO)3 and 0.43 for (η(6)-styrene)Cr(CO)3. These studies provide evidence for the existence of two photophysical routes to CO loss, a minor ultrafast route and an arrested mechanism involving the intermediate population of a reactive excited state. This reactive excited state either relaxes to reform the parent species or eject CO. Thus the quantum yield of the CO-loss is strongly dependent on the excitation wavelength. Time-dependent density functional theory calculations confirm that the state responsible for ultrafast CO-loss has significant metal-centred character while

  19. Electron affinity and excited states of methylglyoxal

    Science.gov (United States)

    Dauletyarov, Yerbolat; Dixon, Andrew R.; Wallace, Adam A.; Sanov, Andrei

    2017-07-01

    Using photoelectron imaging spectroscopy, we characterized the anion of methylglyoxal (X2A″ electronic state) and three lowest electronic states of the neutral methylglyoxal molecule: the closed-shell singlet ground state (X1A'), the lowest triplet state (a3A″), and the open-shell singlet state (A1A″). The adiabatic electron affinity (EA) of the ground state, EA(X1A') = 0.87(1) eV, spectroscopically determined for the first time, compares to 1.10(2) eV for unsubstituted glyoxal. The EAs (adiabatic attachment energies) of two excited states of methylglyoxal were also determined: EA(a3A″) = 3.27(2) eV and EA(A1A″) = 3.614(9) eV. The photodetachment of the anion to each of these two states produces the neutral species near the respective structural equilibria; hence, the a3A″ ← X2A″ and A1A″ ← X2A″ photodetachment transitions are dominated by intense peaks at their respective origins. The lowest-energy photodetachment transition, on the other hand, involves significant geometry relaxation in the X1A' state, which corresponds to a 60° internal rotation of the methyl group, compared to the anion structure. Accordingly, the X1A' ← X2A″ transition is characterized as a broad, congested band, whose vertical detachment energy, VDE = 1.20(4) eV, significantly exceeds the adiabatic EA. The experimental results are in excellent agreement with the ab initio predictions using several equation-of-motion methodologies, combined with coupled-cluster theory.

  20. Insight into the structure and the mechanism of the slow proton transfer in the GFP double mutant T203V/S205A.

    Science.gov (United States)

    Wineman-Fisher, Vered; Simkovitch, Ron; Shomer, Shay; Gepshtein, Rinat; Huppert, Dan; Saif, Mari; Kallio, Karen; Remington, S James; Miller, Yifat

    2014-06-21

    Mutations near the fluorescing chromophore of the green fluorescent protein (GFP) have direct effects on the absorption and emission spectra. Some mutants have significant band shifts and most of the mutants exhibit a loss of fluorescence intensity. In this study we continue our investigation of the factors controlling the excited state proton transfer (PT) process of GFP, in particular to study the effects of modifications to the key side chain Ser205 in wt-GFP, proposed to participate in the proton wire. To this aim we combined mutagenesis, X-ray crystallography, steady-state spectroscopy, time-resolved emission spectroscopy and all-atom explicit molecular dynamics (MD) simulations to study the double mutant T203V/S205A. Our results show that while in the previously described GFP double mutant T203V/S205V the PT process does not occur, in the T203V/S205A mutant the PT process does occur, but with a 350 times slower rate than in wild-type GFP (wt-GFP). Furthermore, the kinetic isotope effect in the GFP double mutant T203V/S205A is twice smaller than in the wt-GFP and in the GFP single mutant S205V, which forms a novel PT pathway. On the other hand, the crystal structure of GFP T203V/S205A does not reveal a viable proton transfer pathway. To explain PT in GFP T203V/S205A, we argue on the basis of the MD simulations for an alternative, novel proton-wire pathway which involves the phenol group of the chromophore and water molecules infrequently entering from the bulk. This alternative pathway may explain the dramatically slow PT in the GFP double mutant T203V/S205A compared to wt-GFP.

  1. Vibrational Förster transfer to hydrated protons

    NARCIS (Netherlands)

    Timmer, R.L.A.; Tielrooij, K.J.; Bakker, H.J.

    2010-01-01

    We have studied the influence of excess protons on the vibrational energy relaxation of the O-H and O-D stretching modes in water using femtosecond pump-probe spectroscopy. Without excess protons, we observe exponential decays with time constants of 1.7 and 4.3 ps for the bulk and anion bound O-D

  2. Effect of electrostatic interactions on the formation of proton transfer ...

    Indian Academy of Sciences (India)

    WINTEC

    mining step. But at low buffer concentration, a rate limiting contribution24–26 comes from an intermo- lecular exchange of proton(s) between His-64 and bulk solvent or buffer when His-64 has its sidechain pointing ..... date the effect of water re-organization as well as that of electrostatic interactions on the rotation of His-64.

  3. Fluorescence and picosecond induced absorption from the lowest singlet excited states of quercetin in solutions and polymer films

    Science.gov (United States)

    Bondarev, S. L.; Tikhomirov, S. A.; Buganov, O. V.; Knyukshto, V. N.; Raichenok, T. F.

    2017-03-01

    The spectroscopic and photophysical properties of the biologically important plant antioxidant quercetin in organic solvents, polymer films of polyvinyl alcohol, and a buffer solution at pH 7.0 are studied by stationary luminescence and femtosecond laser spectroscopy at room temperature and 77 K. The large magnitude of the dipole moment of the quercetin molecule in the excited Franck-Condon state μ e FC = 52.8 C m indicates the dipolar nature of quercetin in this excited state. The transient induced absorption spectra S 1→ S n in all solvents are characterized by a short-wave band at λ abs max = 460 nm with exponential decay times in the range of 10.0-20.0 ps. In the entire spectral range at times of >100 ps, no residual induced absorption was observed that could be attributed to the triplet-triplet transitions T 1 → T k in quercetin. In polar solvents, two-band fluorescence was also recorded at room temperature, which is due to the luminescence of the initial enol form of quercetin ( 415 nm) and its keto form with a transferred proton (550 nm). The short-wave band is absent in nonpolar 2-methyltetrahydrofuran (2-MTHF). The spectra of fluorescence and fluorescence excitation exhibit a low dependence on the wavelength of excitation and detection, which may be related to the solvation and conformational changes in the quercetin molecule. Decreasing the temperature of a glassy-like freezing quercetin solution in ethanol and 2-MTHF to 77 K leads to a strong increase in the intensity (by a factor of 100) of both bands. The energy circuits for the proton transfer process are proposed depending on the polarity of the medium. The main channel for the exchange of electronic excitation energy in the quercetin molecule at room temperature is the internal conversion S 1 ⇝ S 0, induced by the state with a proton transfer.

  4. Density Functional Reactivity Theory Characterizes Charge Separation Propensity in Proton-Coupled Electron Transfer Reactions

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Shubin [Univ. of North Carolina, Chapel Hill, NC (United States); Ess, Daniel H. [Brigham Young Univ., Provo, UT (United States); Univ. of North Carolina, Chapel Hill, NC (United States); Schauer, Cynthia [Univ. of North Carolina, Chapel Hill, NC (United States)

    2011-04-20

    Proton-coupled electron transfer (PCET) reactions occur in many biological and artificial solar energy conversion processes. In these reactions the electron is often transferred to a site distant to the proton acceptor site. In this work, we employ the dual descriptor and the electrophilic Fukui function from density functional reactivity theory (DFRT) to characterize the propensity for an electron to be transferred to a site other than the proton acceptor site. The electrophilic regions of hydrogen bond or van der Waal reactant complexes were examined using these DFRT descriptors to determine the region of space to which the electron is most likely to be transferred. This analysis shows that in PCET reactions the electrophilic region of the reactant complex does not include the proton acceptor site.

  5. Recent aspects of the proton transfer reaction in H-bonded complexes

    Science.gov (United States)

    Szafran, Mirosław

    1996-07-01

    Proton transfer processes cover a very wide range of situations and time scales and they are of great interest from the viewpoint of chemical reactions in solution. These processes can occur via thermally activated crossing or tunneling. This review considers various aspects of this many-faceted field. Spectroscopic, dielectric, colligative and energetic properties and structures of various species with H-bonds are examined. Proton transfer reactions in water and organic solvents, and the contribution of various H-bonded species and ions to these processes are discussed. Among other topics, this survey includes the effects of solvent, acid-base stoichiometry, concentration, temperature and impurity on proton transfer reactions in complexes of phenols and carboxylic acids with amines, pyridines and pyridine N-oxides. The contribution of the nonstoichiometric acid-base complexes and ionic species to the reversible proton transfer mechanism is discussed.

  6. Interplay between singlet and triplet excited states in a conformationally locked donor–acceptor dyad

    KAUST Repository

    Filatov, Mikhail A.

    2015-10-13

    The synthesis and photophysical characterization of a palladium(II) porphyrin – anthracene dyad bridged via short and conformationally rigid bicyclo[2.2.2]octadiene spacer were achieved. A spectroscopic investigation of the prepared molecule in solution has been undertaken to study electronic energy transfer in excited singlet and triplet states between the anthracene and porphyrin units. By using steady-state and time-resolved photoluminescence spectroscopy it was shown that excitation of the singlet excited state of the anthracene leads to energy transfer to the lower-lying singlet state of porphyrin. Alternatively, excitation of the porphyrin followed by intersystem crossing to the triplet state leads to very fast energy transfer to the triplet state of anthracene. The rate of this energy transfer has been determined by transient absorption spectroscopy. Comparative studies of the dynamics of triplet excited states of the dyad and reference palladium octaethylporphyrin (PdOEP) have been performed.

  7. Vibronic coupling in the excited-states of carotenoids

    Energy Technology Data Exchange (ETDEWEB)

    Miki, Takeshi [Physikalisch-Chemisches Institut; Ruprecht-Karls-Universität Heidelberg; D-69120 Heidelberg, Germany; Buckup, Tiago [Physikalisch-Chemisches Institut; Ruprecht-Karls-Universität Heidelberg; D-69120 Heidelberg, Germany; Krause, Marie S. [Physikalisch-Chemisches Institut; Ruprecht-Karls-Universität Heidelberg; D-69120 Heidelberg, Germany; Southall, June [College of Medical; Veterinary, and Life Science; University of Glasgow; G12 8QQ Glasgow, UK; Cogdell, Richard J. [College of Medical; Veterinary, and Life Science; University of Glasgow; G12 8QQ Glasgow, UK; Motzkus, Marcus [Physikalisch-Chemisches Institut; Ruprecht-Karls-Universität Heidelberg; D-69120 Heidelberg, Germany

    2016-01-01

    The ultrafast femtochemistry of carotenoids is governed by the interaction between electronic excited states, which has been explained by the relaxation dynamics within a few hundred femtoseconds from the lowest optically allowed excited state S2to the optically dark state S1.

  8. Proton transfer reactions and hydrogen-bond networks in protein environments.

    Science.gov (United States)

    Ishikita, Hiroshi; Saito, Keisuke

    2014-02-06

    In protein environments, proton transfer reactions occur along polar or charged residues and isolated water molecules. These species consist of H-bond networks that serve as proton transfer pathways; therefore, thorough understanding of H-bond energetics is essential when investigating proton transfer reactions in protein environments. When the pKa values (or proton affinity) of the H-bond donor and acceptor moieties are equal, significantly short, symmetric H-bonds can be formed between the two, and proton transfer reactions can occur in an efficient manner. However, such short, symmetric H-bonds are not necessarily stable when they are situated near the protein bulk surface, because the condition of matching pKa values is opposite to that required for the formation of strong salt bridges, which play a key role in protein-protein interactions. To satisfy the pKa matching condition and allow for proton transfer reactions, proteins often adjust the pKa via electron transfer reactions or H-bond pattern changes. In particular, when a symmetric H-bond is formed near the protein bulk surface as a result of one of these phenomena, its instability often results in breakage, leading to large changes in protein conformation.

  9. Proton transfer and complex formation of angiotensin I ions with gaseous molecules at various temperature

    Energy Technology Data Exchange (ETDEWEB)

    Nonose, Shinji, E-mail: nonose@yokohama-cu.ac.jp; Yamashita, Kazuki; Sudo, Ayako; Kawashima, Minami

    2013-09-23

    Highlights: • Proton transfer from angiotensin I ions (z = 2, 3) to gaseous molecules was studied. • Temperature dependence of absolute reaction rate constants was measured. • Remarkable changes were obtained for distribution of product ions and reaction rate constants. • Proton transfer reaction was enhanced and reduced by complex formation. • Conformation changes are induced by complex formation and or by thermal collision with He. - Abstract: Proton transfer reactions of angiotensin I ions for +2 charge state, [M + 2H]{sup 2+}, to primary, secondary and aromatic amines were examined in the gas phase. Absolute reaction rate constants for proton transfer were determined from intensities of parent and product ions in the mass spectra. Temperature dependence of the reaction rate constants was measured. Remarkable change was observed for distribution of product ions and reaction rate constants. Proton transfer reaction was enhanced or reduced by complex formation of [M + 2H]{sup 2+} with gaseous molecules. The results relate to conformation changes of [M + 2H]{sup 2+} with change of temperature, which are induced by complex formation and or by thermal collision with He. Proton transfer reactions of angiotensin I ions for +3 charge state, [M + 3H]{sup 3+}, were also studied. The reaction rates did not depend on temperature so definitely.

  10. Proton-coupled electron transfer dynamics in the catalytic mechanism of a [NiFe]-hydrogenase.

    Science.gov (United States)

    Greene, Brandon L; Wu, Chang-Hao; McTernan, Patrick M; Adams, Michael W W; Dyer, R Brian

    2015-04-08

    The movement of protons and electrons is common to the synthesis of all chemical fuels such as H2. Hydrogenases, which catalyze the reversible reduction of protons, necessitate transport and reactivity between protons and electrons, but a detailed mechanism has thus far been elusive. Here, we use a phototriggered chemical potential jump method to rapidly initiate the proton reduction activity of a [NiFe] hydrogenase. Coupling the photochemical initiation approach to nanosecond transient infrared and visible absorbance spectroscopy afforded direct observation of interfacial electron transfer and active site chemistry. Tuning of intramolecular proton transport by pH and isotopic substitution revealed distinct concerted and stepwise proton-coupled electron transfer mechanisms in catalysis. The observed heterogeneity in the two sequential proton-associated reduction processes suggests a highly engineered protein environment modulating catalysis and implicates three new reaction intermediates; Nia-I, Nia-D, and Nia-SR(-). The results establish an elementary mechanistic understanding of catalysis in a [NiFe] hydrogenase with implications in enzymatic proton-coupled electron transfer and biomimetic catalyst design.

  11. Ultrafast Excited State Relaxation of a Metalloporphyrin Revealed by Femtosecond X-ray Absorption Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Shelby, Megan L. [Chemical; Department; Lestrange, Patrick J. [Department; Jackson, Nicholas E. [Department; Haldrup, Kristoffer [Physics; Mara, Michael W. [Chemical; Department; Stickrath, Andrew B. [Chemical; Zhu, Diling [LCLS, SLAC National Laboratory, Menlo Park, California 94025, United States; Lemke, Henrik T. [LCLS, SLAC National Laboratory, Menlo Park, California 94025, United States; Chollet, Matthieu [LCLS, SLAC National Laboratory, Menlo Park, California 94025, United States; Hoffman, Brian M. [Department; Li, Xiaosong [Department; Chen, Lin X. [Chemical; Department

    2016-07-06

    Photoexcited Nickel(II) tetramesitylporphyrin (NiTMP), like many open-shell metalloporphyrins, relaxes rapidly through multiple electronic states following an initial porphyrin-based excitation, some involving metal centered electronic configuration changes that could be harnessed catalytically before excited state relaxation. While a NiTMP excited state present at 100 ps was previously identified by X-ray transient absorption (XTA) spectroscopy at a synchrotron source as a relaxed (d,d) state, the lowest energy excited state (J. Am. Chem. Soc., 2007, 129, 9616 and Chem. Sci., 2010, 1, 642), structural dynamics before thermalization were not resolved due to the similar to 100 ps duration of the available X-ray probe pulse. Using the femtosecond (fs) X-ray pulses of the Linac Coherent Light Source (LCLS), the Ni center electronic configuration from the initial excited state to the relaxed (d,d) state has been obtained via ultrafast Ni K-edge XANES (X-ray absorption near edge structure) on a time scale from hundreds of femtoseconds to 100 ps. This enabled the identification of a short-lived Ni(I) species aided by time-dependent density functional theory (TDDFT) methods. Computed electronic and nuclear structure for critical excited electronic states in the relaxation pathway characterize the dependence of the complex's geometry on the electron occupation of the 3d orbitals. Calculated XANES transitions for these excited states assign a short-lived transient signal to the spectroscopic signature of the Ni(I) species, resulting from intramolecular charge transfer on a time scale that has eluded previous synchrotron studies. These combined results enable us to examine the excited state structural dynamics of NiTMP prior to thermal relaxation and to capture intermediates of potential photocatalytic significance.

  12. Spectroscopic signatures of proton transfer dynamics in the water dimer cation

    Energy Technology Data Exchange (ETDEWEB)

    Kamarchik, Eugene; Kostko, Oleg; Bowman, Joel M.; Ahmed, Musahid; Krylov, Anna I.

    2009-12-21

    Using full dimensional EOM-IP-CCSD/aug-cc-pVTZ potential energy surfaces, the photoelectron spectrum, vibrational structure, and ionization dynamics of the water dimer radical cation, (H2O)+2, were computed. We also report an experimental photoelectron spectrum which is derived from photoionization efficiency measurements and compares favorably with the theoretical spectrum. The vibrational structure is also compared with the recent experimental work of Gardenier et al. [J. Phys. Chem. A 113, 4772 (2009)] and the recent theoretical calculations by Cheng et al. [J. Phys. Chem. A 113 13779 (2009)]. A reduced dimensionality nuclear Hamiltonian was used to compute the ionization dynamics for both the ground state and first excited state of the cation. The dynamics show markedly different behavior and spectroscopic signatures depending on which state of the cation is accessed by the ionization. Ionization to the ground-state cation surface induces a hydrogen transfer which is complete within 50 femtoseconds, whereas ionization to the first excited state results in a much slower process.

  13. Competing Pathways in the photo- Proton-Coupled Electron Transfer Reduction of fac -[Re(bpy)(CO) 3 (4,4'-bpy] +* by Hydroquinone

    Energy Technology Data Exchange (ETDEWEB)

    Stewart, David J.; Brennaman, M. Kyle; Bettis, Stephanie E.; Wang, Li; Binstead, Robert A.; Papanikolas, John M.; Meyer, Thomas J.

    2011-08-04

    The emitting metal-to-ligand charge transfer (MLCT) excited state of fac-[Re{sup I}(bpy)(CO)₃(4,4'-bpy)]+ (1) (bpy is 2,2'-bipyridine, 4,4'-bpy is 4,4'-bipyridine), [Re II(bpy –•)(CO)₃(4,4'-bpy)]+*, is reductively quenched by 1,4-hydroquinone (H₂Q) in CH₃CN at 23 ± 2 °C by competing pathways to give a common electron–proton-transfer intermediate. In one pathway, electron transfer (ET) quenching occurs to give Re{sup I}(bpy –•)(CO)₃(4,4'-bpy)]⁰ with k = (1.8 ± 0.2) × 10⁹ M –1 s –1, followed by proton transfer from H₂Q to give [ReI(bpy)(CO)₃(4,4'-bpyH )]+. Protonation triggers intramolecular bpy –•→ 4,4'-bpyH{sup +} electron transfer. In the second pathway, preassociation occurs between the ground state and H₂Q at high concentrations. Subsequent Re → bpy MLCT excitation of the adduct is followed by electron–proton transfer from H₂Q in concert with intramolecular bpy –•→ 4,4'-bpyH+ electron transfer to give [ReI(bpy)(CO)₃(4,4'-bpyH)]+ with k = (1.0 ± 0.4) × 10⁹ s–1 in 3:1 CH₃CN/H₂O.

  14. Amide Proton Transfer (APT) MR imaging and Magnetization Transfer (MT) MR imaging of pediatric brain development

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Hong; Kang, Huiying; Peng, Yun [Beijing Children' s Hospital, Capital Medical University, Imaging Center, Department of Radiology, Beijing (China); Zhao, Xuna [Philips Healthcare, Beijing (China); Jiang, Shanshan; Zhang, Yi; Zhou, Jinyuan [Johns Hopkins University, Division of MR Research, Department of Radiology, Baltimore, MD (United States)

    2016-10-15

    To quantify the brain maturation process during childhood using combined amide proton transfer (APT) and conventional magnetization transfer (MT) imaging at 3 Tesla. Eighty-two neurodevelopmentally normal children (44 males and 38 females; age range, 2-190 months) were imaged using an APT/MT imaging protocol with multiple saturation frequency offsets. The APT-weighted (APTW) and MT ratio (MTR) signals were quantitatively analyzed in multiple brain areas. Age-related changes in MTR and APTW were evaluated with a non-linear regression analysis. The APTW signals followed a decreasing exponential curve with age in all brain regions measured (R{sup 2} = 0.7-0.8 for the corpus callosum, frontal and occipital white matter, and centrum semiovale). The most significant changes appeared within the first year. At maturation, larger decreases in APTW and lower APTW values were found in the white matter. On the contrary, the MTR signals followed an increasing exponential curve with age in the same brain regions measured, with the most significant changes appearing within the initial 2 years. There was an inverse correlation between the MTR and APTW signal intensities during brain maturation. Together with MT imaging, protein-based APT imaging can provide additional information in assessing brain myelination in the paediatric population. (orig.)

  15. Simulating the proton transfer in gramicidin A by a sequential dynamical Monte Carlo method.

    Science.gov (United States)

    Till, Mirco S; Essigke, Timm; Becker, Torsten; Ullmann, G Matthias

    2008-10-23

    The large interest in long-range proton transfer in biomolecules is triggered by its importance for many biochemical processes such as biological energy transduction and drug detoxification. Since long-range proton transfer occurs on a microsecond time scale, simulating this process on a molecular level is still a challenging task and not possible with standard simulation methods. In general, the dynamics of a reactive system can be described by a master equation. A natural way to describe long-range charge transfer in biomolecules is to decompose the process into elementary steps which are transitions between microstates. Each microstate has a defined protonation pattern. Although such a master equation can in principle be solved analytically, it is often too demanding to solve this equation because of the large number of microstates. In this paper, we describe a new method which solves the master equation by a sequential dynamical Monte Carlo algorithm. Starting from one microstate, the evolution of the system is simulated as a stochastic process. The energetic parameters required for these simulations are determined by continuum electrostatic calculations. We apply this method to simulate the proton transfer through gramicidin A, a transmembrane proton channel, in dependence on the applied membrane potential and the pH value of the solution. As elementary steps in our reaction, we consider proton uptake and release, proton transfer along a hydrogen bond, and rotations of water molecules that constitute a proton wire through the channel. A simulation of 8 mus length took about 5 min on an Intel Pentium 4 CPU with 3.2 GHz. We obtained good agreement with experimental data for the proton flux through gramicidin A over a wide range of pH values and membrane potentials. We find that proton desolvation as well as water rotations are equally important for the proton transfer through gramicidin A at physiological membrane potentials. Our method allows to simulate long

  16. Structure of excited states in nuclei near doubly magic {sup 100}SN

    Energy Technology Data Exchange (ETDEWEB)

    Gorska, M.

    1998-11-01

    The three neutron-deficient nuclei {sup 94}Pd, {sup 98}Cd and {sup 104}Sn in the vicinity of {sup 100}Sn were investigated by means of in-beam {gamma}-ray spectroscopy of excited states. The isomeric decays in {sup 94}Pd and {sup 98}Cd were studied for the first time with an exclusive experimental setup for delayed {gamma}-ray detection with complete exit channel identification based on information from neutron and charged-particle filter detectors. The structure of excited states of {sup 94}Pd showed the first indication of increasing proton-neutron interaction towards the N=Z line in this region of nuclei, that in turn might be related to increased proton-neutron pairing correlations predicted in T{sub z}=0 nuclei. The closest neighbours of {sup 100}Sn with two active particles, {sup 98}Cd and {sup 102}Sn, are now known with their lowest excited states. The measured reduced transition probabilities for the decay of the isomeric 8{sup +} and 6{sup +} states in {sup 98}Cd and {sup 102}Sn, respectively, allowed to extract an effective quadrupole charge for neutron and proton in this region of nuclei based on the high configurational purity of the states. While the neutron effective charge appeared to be large and in agreement with expectation, the proton effective charge value is very small (e{sub {pi}}{<=}1). This controversial result, which would indicate that {sup 100}Sn is a very good closed shell nucleus with respect to quadrupole excitation, is not understood. An experimental reason for this result, related to existence of a core excited isomer, observed in the experiment by means of its half life but not {gamma}-rays, which may have escaped observation, can not be definitely excluded and is left as possible explanation. (orig.)

  17. Excited-state kinetics of the carotenoid S//1 state in LHC II and two-photon excitation spectra of lutein and beta-carotene in solution Efficient Car S//1 yields Chl electronic energy transfer via hot S//1 states?

    CERN Document Server

    Walla, P J; Linden, Patricia A; Ohta, Kaoru

    2002-01-01

    The excited-state dynamics of the carotenoids (Car) in light- harvesting complex II (LHC II) of Chlamydomonas reinhardtii were studied by transient absorption measurements. The decay of the Car S //1 population ranges from similar to 200 fs to over 7 ps, depending on the excitation and detection wavelengths. In contrast, a 200 fs Car S//1 yields Chlorophyll (Chl) energy transfer component was the dominant time constant for our earlier two-photon fluorescence up- conversion measurements (Walla, P.J. ; et al. J. Phys. Chem. B 2000, 104, 4799-4806). We also present the two-photon excitation (TPE) spectra of lutein and beta-carotene in solution and compare them with the TPE spectrum of LHC II. The TPE-spectrum of LHC II has an onset much further to the blue and a width that is narrower than expected from comparison to the S//1 fluorescence of lutein and beta-carotene in solution. Different environments may affect the shape of the S//1 spectrum significantly. To explain the blue shift of the TPE spectrum and the d...

  18. Excited state intramolecular charge transfer reaction of 4 ...

    Indian Academy of Sciences (India)

    Author Affiliations. Tuhin Pradhan1 Harun Al Rasid Gazi1 Ranjit Biswas1. Department of Chemical, Biological and Macromolecular Sciences, S.N. Bose National Centre for Basic Sciences, J.D. Block, Sector III, Salt Lake, Kolkata 700 098 ...

  19. Excited state charge transfer reaction in (mixed solvent+ electrolyte ...

    Indian Academy of Sciences (India)

    Author Affiliations. Harun Al Rasid Gazi1 Ranjit Biswas1. Department of Chemical, Biological and Macromolecular Sciences, S. N. Bose National Centre for Basic Sciences, JD Block, Sector III, Salt Lake, Kolkata, 700 098, India ...

  20. Proton electromagnetic form factors at large momentum transfer

    Indian Academy of Sciences (India)

    Keywords. Proton; electromagnetic form factors; Rosenbluth seperation; quark orbital angular momentum ... factor describes the amplitude for chirality flip at the electromagnetic vertex. Besides the form factors F1 ... Rosenbluth separation. This is clearly a serious problem and has attracted considerable attention in the litera-.

  1. The JLab polarization transfer measurements of proton elastic form ...

    Indian Academy of Sciences (India)

    the recoil proton, P and Pt, in the elastic scattering of polarized electrons, ep ep. Together these ... a greater challenge experimentally: there are no free neutron targets, the free neutron has a 15 min life time, and in addition .... ments made at fixed Q2, and over a range of values of the kinematic factor ε, with the. Rosenbluth ...

  2. Effect of electrostatic interactions on the formation of proton transfer ...

    Indian Academy of Sciences (India)

    We report here a theoretical study on the effect of electrostatic interactions on the formation of dynamical, proton-conducting hydrogen-bonded networks in the protein HCA II. The conformational fluctuations of His-64 is found to contribute crucially to the mechanism of such path formation irrespective of the way electrostatic ...

  3. Direct conversion of graphite into diamond through electronic excited states

    CERN Document Server

    Nakayama, H

    2003-01-01

    An ab initio total energy calculation has been performed for electronic excited states in diamond and rhombohedral graphite by the full-potential linearized augmented plane wave method within the framework of the local density approximation (LDA). First, calculations for the core-excited state in diamond have been performed to show that the ab initio calculations based on the LDA describe the wavefunctions in the electronic excited states as well as in the ground state quite well. Fairly good coincidence with both experimental data and theoretical prediction has been obtained for the lattice relaxation of the core exciton state. The results of the core exciton state are compared with nitrogen-doped diamond. Next, the structural stability of rhombohedral graphite has been investigated to examine the possibility of the transition into the diamond structure through electronic excited states. While maintaining the rhombohedral symmetry, rhombohedral graphite can be spontaneously transformed to cubic diamond. Tota...

  4. Excited State Dynamics of DNA and RNA bases

    Science.gov (United States)

    Hudock, Hanneli; Levine, Benjamin; Martinez, Todd

    2007-03-01

    Recent ultrafast spectroscopic experiments have reported excited state lifetimes for DNA and RNA bases and assigned these lifetimes to various electronic states. We have used theoretical and simulation methods to describe the excited state dynamics of these bases in an effort to provide a mechanistic explanation for the observed lifetimes. Our simulations are based on ab initio molecular dynamics, where the electronic and nuclear Schrodinger equations are solved simultaneously. The results are further verified by comparison to high-level ab initio electronic structure methods, including dynamic electron correlation effects through multireference perturbation theory, at important points along the dynamical pathways. Our results provide an explanation of the photochemical mechanism leading to nonradiative decay of the electronic excited states and some suggestions as to the origin of the different lifetimes. Comparisons between pyrimidines illustrate how chemical differences impact excited state dynamics and may play a role in explaining the propensity for dimer formation in thymine.

  5. Excited state dynamics of liquid water near the surface

    Directory of Open Access Journals (Sweden)

    Schultz Thomas

    2013-03-01

    Full Text Available Time resolved photoelectron spectroscopy explores the excited state dynamics of liquid water in presence of cations close to the surface. A transient hydrated electroncation complex is observed.

  6. Communication: Charge transfer dominates over proton transfer in the reaction of nitric acid with gas-phase hydrated electrons

    Science.gov (United States)

    Lengyel, Jozef; Med, Jakub; Slavíček, Petr; Beyer, Martin K.

    2017-09-01

    The reaction of HNO3 with hydrated electrons (H2O)n- (n = 35-65) in the gas phase was studied using Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and ab initio molecular dynamics simulations. Kinetic analysis of the experimental data shows that OH-(H2O)m is formed primarily via a reaction of the hydrated electron with HNO3 inside the cluster, while proton transfer is not observed and NO3-(H2O)m is just a secondary product. The reaction enthalpy was determined using nanocalorimetry, revealing a quite exothermic charge transfer with -241 ± 69 kJ mol-1. Ab initio molecular dynamics simulations indicate that proton transfer is an allowed reaction pathway, but the overall thermochemistry favors charge transfer.

  7. Cyclopropyl Group: An Excited-State Aromaticity Indicator?

    Science.gov (United States)

    Ayub, Rabia; Papadakis, Raffaello; Jorner, Kjell; Zietz, Burkhard; Ottosson, Henrik

    2017-10-04

    The cyclopropyl (cPr) group, which is a well-known probe for detecting radical character at atoms to which it is connected, is tested as an indicator for aromaticity in the first ππ* triplet and singlet excited states (T 1 and S 1 ). Baird's rule says that the π-electron counts for aromaticity and antiaromaticity in the T 1 and S 1 states are opposite to Hückel's rule in the ground state (S 0 ). Our hypothesis is that the cPr group, as a result of Baird's rule, will remain closed when attached to an excited-state aromatic ring, enabling it to be used as an indicator to distinguish excited-state aromatic rings from excited-state antiaromatic and nonaromatic rings. Quantum chemical calculations and photoreactivity experiments support our hypothesis; calculated aromaticity indices reveal that openings of cPr substituents on [4n]annulenes ruin the excited-state aromaticity in energetically unfavorable processes. Yet, polycyclic compounds influenced by excited-state aromaticity (e.g., biphenylene), as well as 4nπ-electron heterocycles with two or more heteroatoms represent limitations. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. First experimental evidence of 2He decay from 18Ne excited states

    CERN Document Server

    Rapisarda, E; Cardella, G; De Napoli, M; Raciti, G; Sfienti, C

    2010-01-01

    Two-proton decay from 18Ne excited states has been studied by complete kinematical detection of the decay products. The 18Ne nucleus has been produced as a radioactive beam by 20Ne projectile fragmentation at 45 AMeV on a 9Be target, using the FRIBs in-flight facility of the LNS. The 18Ne at 33 AMeV incident energy has been excited via Coulomb excitation on a natPb target. The correlated 2p emission has been disentangled from the uncorrelated 2p emission using a high granularity particle detector setup allowing the reconstruction of momentum and angle correlations of the two emitted protons. The obtained results unambiguously show that the 6.15 MeV 18Ne state two-proton decay proceeds through 2He emission (31%) and democratic or virtual sequential decay (69%).

  9. An S-N2-model for proton transfer in hydrogen-bonded systems

    DEFF Research Database (Denmark)

    Kuznetsov, A.M.; Ulstrup, Jens

    2004-01-01

    A new mechanism of proton transfer in donor-acceptor complexes with long hydrogen bonds is suggested. The transition is regarded as totally adiabatic. Two closest water molecules that move synchronously by hindered translation to and from the reaction complex are crucial. The water molecules induce...... a shift of the proton from the donor to the acceptor with simultaneous breaking/formation of hydrogen bonds between these molecules and the proton donor and acceptor. Expressions for the activation barrier and kinetic hydrogen isotope effect are derived. The general scheme is illustrated with the use...

  10. Quantitative dissection of hydrogen bond-mediated proton transfer in the ketosteroid isomerase active site

    Science.gov (United States)

    Sigala, Paul A.; Fafarman, Aaron T.; Schwans, Jason P.; Fried, Stephen D.; Fenn, Timothy D.; Caaveiro, Jose M. M.; Pybus, Brandon; Ringe, Dagmar; Petsko, Gregory A.; Boxer, Steven G.; Herschlag, Daniel

    2013-01-01

    Hydrogen bond networks are key elements of protein structure and function but have been challenging to study within the complex protein environment. We have carried out in-depth interrogations of the proton transfer equilibrium within a hydrogen bond network formed to bound phenols in the active site of ketosteroid isomerase. We systematically varied the proton affinity of the phenol using differing electron-withdrawing substituents and incorporated site-specific NMR and IR probes to quantitatively map the proton and charge rearrangements within the network that accompany incremental increases in phenol proton affinity. The observed ionization changes were accurately described by a simple equilibrium proton transfer model that strongly suggests the intrinsic proton affinity of one of the Tyr residues in the network, Tyr16, does not remain constant but rather systematically increases due to weakening of the phenol–Tyr16 anion hydrogen bond with increasing phenol proton affinity. Using vibrational Stark spectroscopy, we quantified the electrostatic field changes within the surrounding active site that accompany these rearrangements within the network. We were able to model these changes accurately using continuum electrostatic calculations, suggesting a high degree of conformational restriction within the protein matrix. Our study affords direct insight into the physical and energetic properties of a hydrogen bond network within a protein interior and provides an example of a highly controlled system with minimal conformational rearrangements in which the observed physical changes can be accurately modeled by theoretical calculations. PMID:23798390

  11. Challenges in reduction of dinitrogen by proton and electron transfer.

    Science.gov (United States)

    van der Ham, Cornelis J M; Koper, Marc T M; Hetterscheid, Dennis G H

    2014-08-07

    Ammonia is an important nutrient for the growth of plants. In industry, ammonia is produced by the energy expensive Haber-Bosch process where dihydrogen and dinitrogen form ammonia at a very high pressure and temperature. In principle one could also reduce dinitrogen upon addition of protons and electrons similar to the mechanism of ammonia production by nitrogenases. Recently, major breakthroughs have taken place in our understanding of biological fixation of dinitrogen, of molecular model systems that can reduce dinitrogen, and in the electrochemical reduction of dinitrogen at heterogeneous surfaces. Yet for efficient reduction of dinitrogen with protons and electrons major hurdles still have to be overcome. In this tutorial review we give an overview of the different catalytic systems, highlight the recent breakthroughs, pinpoint common grounds and discuss the bottlenecks and challenges in catalytic reduction of dinitrogen.

  12. Proton-transfer in hydrogenated guanine-cytosine trimer neutral species, cations, and anions embedded in B-form DNA.

    Science.gov (United States)

    Lin, Yuexia; Wang, Hongyan; Wu, Yingxi; Gao, Simin; Schaefer, Henry F

    2014-04-14

    The neutral DNA trimers with the hydrogen atom added to the C8 site of the middle guanine-cytosine (GC) base pair, the DNA trimers protonated at the N7 site of the middle GC base pair, and the anionic species resulting from hydride addition to the C6 site of the middle GC base pair are investigated using theoretical methods. The canonical Watson-Crick structures (WC), transition state structures (TS) and proton-transferred structures (PT) of each relevant system are optimized in the gas phase and in aqueous solution, in order to understand the processes of proton transfer. The proton transfer reactions of the DNA trimers are compared with the corresponding isolated hydrogenated GC base pairs to explore the influence of the surrounding molecules and the base sequence. The proton transfer reactions of the neutral species, cations, and anions are compared, aiming to clarify the effects of the system's total charge. The results reveal that the surrounding molecules decrease the reaction energies of proton-transfer in aqueous solution. The structures with the dATGCAT and dGCGCGC sequences facilitate proton H4a transfer, but hinder proton H1 transfer. The structures with the dCGGCCG and dTAGCTA sequences facilitate proton H1 transfer. The net charge on the system plays an important role in determining the single and double proton-transfer patterns. Anions are more likely to experience proton-transfer reactions than neutral species and cations, and all the proton-transfer reactions of the anions are exothermic.

  13. Spectroscopy and dynamics of double proton transfer in formic acid dimer

    DEFF Research Database (Denmark)

    Mackeprang, Kasper; Xu, Zhen-Hao; Maroun, Zeina

    2016-01-01

    . Building on the previous development of the Molecular Mechanics with Proton Transfer (MMPT) force field for simulating proton transfer reactions, molecular dynamics (MD) simulations were carried out to interpret the experimental spectra in the OH-stretching region. Within the framework of MMPT...... that recorded at a higher pressure. The spectra of formic acid vapor contain features from both formic acid monomer and formic acid dimer, but at low and high pressures of formic acid, the equilibrium is pushed towards the monomer and dimer, respectively. A similar approach was used for the formic-d acid dimer...... for estimating barriers for proton transfer in gas phase systems is generic and holds promise for further improved PESs and energetics of these important systems. Additional MD simulations at the semi-empirical DFTB level of theory agree quite well for the center band position but underestimate the width...

  14. 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.

  15. Charge-displacement analysis for excited states

    Energy Technology Data Exchange (ETDEWEB)

    Ronca, Enrico, E-mail: enrico@thch.unipg.it; Tarantelli, Francesco, E-mail: francesco.tarantelli@unipg.it [Istituto CNR di Scienze e Tecnologie Molecolari, via Elce di Sotto 8, I-06123 Perugia (Italy); Dipartimento di Chimica, Biologia e Biotecnologie, Università degli Studi di Perugia, via Elce di Sotto 8, I-06123 Perugia (Italy); Pastore, Mariachiara, E-mail: chiara@thch.unipg.it; Belpassi, Leonardo; De Angelis, Filippo [Istituto CNR di Scienze e Tecnologie Molecolari, via Elce di Sotto 8, I-06123 Perugia (Italy); Angeli, Celestino; Cimiraglia, Renzo [Dipartimento di Scienze Chimiche e Farmaceutiche, Università degli Studi di Ferrara, via Borsari 46, I-44100 Ferrara (Italy)

    2014-02-07

    We extend the Charge-Displacement (CD) analysis, already successfully employed to describe the nature of intermolecular interactions [L. Belpassi et al., J. Am. Chem. Soc. 132, 13046 (2010)] and various types of controversial chemical bonds [L. Belpassi et al., J. Am. Chem. Soc. 130, 1048 (2008); N. Salvi et al., Chem. Eur. J. 16, 7231 (2010)], to study the charge fluxes accompanying electron excitations, and in particular the all-important charge-transfer (CT) phenomena. We demonstrate the usefulness of the new approach through applications to exemplary excitations in a series of molecules, encompassing various typical situations from valence, to Rydberg, to CT excitations. The CD functions defined along various spatial directions provide a detailed and insightful quantitative picture of the electron displacements taking place.

  16. Microsecond light-induced proton transfer to flavin in the blue light sensor plant cryptochrome.

    Science.gov (United States)

    Langenbacher, Thomas; Immeln, Dominik; Dick, Bernhard; Kottke, Tilman

    2009-10-14

    Plant cryptochromes are blue light photoreceptors that regulate key responses in growth and daily rhythm of plants and might be involved in magnetoreception. They show structural homology to the DNA repair enzyme photolyase and bind flavin adenine dinucleotide as chromophore. Blue light absorption initiates the photoreduction from the oxidized dark state of flavin to the flavin neutral radical, which is the signaling state of the sensor. Previous time-resolved studies of the photoreduction process have been limited to observation of the decay of the radical in the millisecond time domain. We monitored faster, light-induced changes in absorption of an algal cryptochrome covering a spectral range of 375-750 nm with a streak camera setup. Electron transfer from tryptophan to flavin is completed before 100 ns under formation of the flavin anion radical. Proton transfer takes place with a time constant of 1.7 micros leading to the flavin neutral radical. Finally, the flavin radical and a tryptophan neutral radical decay with a time constant >200 micros in the millisecond and second time domain. The microsecond proton transfer has not been observed in animal cryptochromes from insects or photolyases. Furthermore, the strict separation in time of electron and proton transfer is novel in the field of flavin-containing photoreceptors. The reaction rate implies that the proton donor is not in hydrogen bonding distance to the flavin N5. Potential candidates for the proton donor and the involvement of the tryptophan triad are discussed.

  17. Triplet excited state properties in variable gap π-conjugated donor–acceptor–donor chromophores

    KAUST Repository

    Cekli, Seda

    2016-02-12

    A series of variable band-gap donor–acceptor–donor (DAD) chromophores capped with platinum(II) acetylide units has been synthesized and fully characterized by electrochemical and photophysical methods, with particular emphasis placed on probing triplet excited state properties. A counter-intuitive trend of increasing fluorescence quantum efficiency and lifetime with decreasing excited state energy (optical gap) is observed across the series of DAD chromophores. Careful study of the excited state dynamics, including triplet yields (as inferred from singlet oxygen sensitization), reveals that the underlying origin of the unusual trend in the fluorescence parameters is that the singlet–triplet intersystem crossing rate and yield decrease with decreasing optical gap. It is concluded that the rate of intersystem crossing decreases as the LUMO is increasingly localized on the acceptor unit in the DAD chromophore, and this result is interpreted as arising because the extent of spin–orbit coupling induced by the platinum heavy metal centers decreases as the LUMO is more localized on the acceptor. In addition to the trend in intersystem crossing, the results show that the triplet decay rates follow the Energy Gap Law correlation over a 1.8 eV range of triplet energy and 1000-fold range of triplet decay rates. Finally, femtosecond transient absorption studies for the DAD chromophores reveals a strong absorption in the near-infrared region which is attributed to the singlet excited state. This spectral band appears to be general for DAD chromophores, and may be a signature of the charge transfer (CT) singlet excited state.

  18. Tracking the charge and spin dynamics of electronic excited states in inorganic complexes

    Science.gov (United States)

    Gaffney, Kelly

    2015-03-01

    Inorganic complexes have many advantageous properties for solar energy applications, including strong visible absorption and photocatalytic activity. Whether used as a photocatalyst or a photosensitizer, the lifetime of electronic excited states and the earth abundance of the molecular components represent a key property for solar energy applications. These dual needs have undermined the usefulness of many coordination compounds. Isoelectronic iron and ruthenium based complexes represent a clear example. Ru-polypyridal based molecules have been the workhorse of solar energy related research and dye sensitized solar cells for decades, but the replacement of low abundance Ru with Fe leads to million-fold reductions in metal to ligand charge transfer (MLCT) excited state lifetimes. Understanding the origin of this million-fold reduction in lifetime and how to control excited state relaxation in 3d-metal complexes motivates the work I will discuss. We have used the spin sensitivity of hard x-ray fluorescence spectroscopy and the intense femtosecond duration pulses generated by the LCLS x-ray laser to probe the spin dynamics in a series of electronically excited [Fe(CN)6-2N(2,2'-bipyridine)N]2 N - 4 complexes, with N = 1-3. These femtosecond resolution measurements demonstrate that modification of the solvent and ligand environment can lengthen the MLCT excited state lifetime by more than two orders of magnitude. They also verify the role of triplet ligand field excited states in the spin crossover dynamics from singlet to quintet spin configurations. Work supported by the AMOS program within the Chemical Sciences, Geosciences, and Biosciences Division of the Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

  19. Proton transfer reaction-mass spectrometry applications in medical research.

    Science.gov (United States)

    Herbig, Jens; Amann, Anton

    2009-06-01

    Gathering information about a subject's physiological and pathophysiological condition from the `smell' of breath is an idea that dates back to antiquity. This intriguing concept of non-invasive diagnosis has been revitalized by `exhaled breath analysis' in recent decades. A main driving force was the development of sensitive and versatile gas-chromatographic and mass-spectrometric instruments for trace gas analysis. Ironically, only non-smelling constituents of breath, such as O(2), CO(2), H(2), and NO have so far been included in routine clinical breath analysis. The `smell' of human breath, on the other hand, arises through a combination of volatile organic compounds (VOCs) of which several hundred have been identified to date. Most of these volatiles are systemic and are released in the gas-exchange between blood and air in the alveoli. The concentration of these compounds in the alveolar breath is related to the respective concentrations in blood. Measuring VOCs in exhaled breath allows for screening of disease markers, studying the uptake and effect of medication (pharmacokinetics), or monitoring physiological processes. There is a range of requirements for instruments for the analysis of a complex matrix, such as human breath. Mass-spectrometric techniques are particularly well suited for this task since they offer the possibility of detecting a large variety of interesting compounds. A further requirement is the ability to measure accurately in the concentration range of breath VOCs, i.e. between parts-per-trillion (pptv) and parts-per-million (ppmv) range. In the mid 1990's proton transfer reaction-mass spectrometry (PTR-MS) was developed as a powerful and promising tool for the analysis of VOCs in gaseous media. Soon thereafter these instruments became commercially available to a still growing user community and have now become standard equipment in many fields including environmental research, food and flavour science, as well as life sciences. Their

  20. Carotenoids as electron or excited-state energy donors in artificial photosynthesis: an ultrafast investigation of a carotenoporphyrin and a carotenofullerene dyad

    NARCIS (Netherlands)

    Pillai, S.; Ravensbergen, J.; Antoniuk-Pablant, A.; Sherman, B.D.; van Grondelle, R.; Frese, R.N.; Moore, T.A.; Gust, D.; Moore, A.L.; Kennis, J.T.M.

    2013-01-01

    Photophysical investigations of molecular donor-acceptor systems have helped elucidate many details of natural photosynthesis and revealed design principles for artificial photosynthetic systems. To obtain insights into the factors that govern the partition between excited-state energy transfer

  1. Excited-State N2 Dissociation Pathway on Fe-Functionalized Au.

    Science.gov (United States)

    Martirez, John Mark P; Carter, Emily A

    2017-03-29

    Localized surface plasmon resonances (LSPRs) offer the possibility of light-activated chemical catalysis on surfaces of strongly plasmonic metal nanoparticles. This technology relies on lower-barrier bond formation and/or dissociation routes made available through energy transfer following the eventual decay of LSPRs. The coupling between these decay processes and a chemical trajectory (nuclear motion, charge-transfer, intersystem crossing, etc.) dictates the availability of these alternative (possibly lower barrier) excited-state channels. The Haber-Bosch method of NH3 synthesis from N2 and H2 is notoriously energy intensive. This is due to the difficulty of N2 dissociation despite the overall reaction being thermodynamically favorable at ambient temperatures and pressures. LSPRs may provide means to improve the kinetics of N2 dissociation via induced resonance electronic excitation. In this work, we calculate, via embedded n-electron valence second-order perturbation theory within the density functional embedding theory, the excited-state potential energy surfaces for dissociation of N2 on an Fe-doped Au(111) surface. This metal alloy may take advantage simultaneously of the strong LSPR of Au and the catalytic activity of Fe toward N2 dissociation. We find the ground-state dissociation activation energy to be 4.74 eV/N2, with Fe as the active site on the surface. Consecutive resonance energy transfers (RETs) may be accessed due to the availability of many electronically excited states with intermediate energies arising from the metal surface that may couple to states induced by the Fe-dopant and the adsorbate molecule, and crossing between excited states may effectively lower the dissociation barrier to 1.33 eV. Our work illustrates that large energetic barriers, prohibitive toward chemical reaction, may be overcome through multiple RETs facilitating an otherwise difficult chemical process.

  2. Electrostatic models of electron-driven proton transfer across a lipid membrane

    Energy Technology Data Exchange (ETDEWEB)

    Smirnov, Anatoly Yu; Nori, Franco [Advanced Science Institute, RIKEN, Wako-shi, Saitama, 351-0198 (Japan); Mourokh, Lev G [Department of Physics, Queens College, The City University of New York, Flushing, NY 11367 (United States)

    2011-06-15

    We present two models for electron-driven uphill proton transport across lipid membranes, with the electron energy converted to the proton gradient via the electrostatic interaction. In the first model, associated with the cytochrome c oxidase complex in the inner mitochondria membranes, the electrostatic coupling to the site occupied by an electron lowers the energy level of the proton-binding site, making proton transfer possible. In the second model, roughly describing the redox loop in a nitrate respiration of E. coli bacteria, an electron displaces a proton from the negative side of the membrane to a shuttle, which subsequently diffuses across the membrane and unloads the proton to its positive side. We show that both models can be described by the same approach, which can be significantly simplified if the system is separated into several clusters, with strong Coulomb interaction inside each cluster and weak transfer couplings between them. We derive and solve the equations of motion for the electron and proton creation/annihilation operators, taking into account the appropriate Coulomb terms, tunnel couplings, and the interaction with the environment. For the second model, these equations of motion are solved jointly with a Langevin-type equation for the shuttle position. We obtain expressions for the electron and proton currents and determine their dependence on the electron and proton voltage build-ups, on-site charging energies, reorganization energies, temperature, and other system parameters. We show that the quantum yield in our models can be up to 100% and the power-conversion efficiency can reach 35%.

  3. Direct observation of photoinduced bent nitrosyl excited-state complexes

    Energy Technology Data Exchange (ETDEWEB)

    Sawyer, Karma R.; Steele, Ryan P.; Glascoe, Elizabeth A.; Cahoon, James F.; Schlegel, Jacob P.; Head-Gordon, Martin; Harris, Charles B.

    2008-06-28

    Ground state structures with side-on nitrosyl ({eta}{sup 2}-NO) and isonitrosyl (ON) ligands have been observed in a variety of transition-metal complexes. In contrast, excited state structures with bent-NO ligands have been proposed for years but never directly observed. Here we use picosecond time-resolved infrared spectroscopy and density functional theory (DFT) modeling to study the photochemistry of Co(CO){sub 3}(NO), a model transition-metal-NO compound. Surprisingly, we have observed no evidence for ON and {eta}{sup 2}-NO structural isomers, but have observed two bent-NO complexes. DFT modeling of the ground and excited state potentials indicates that the bent-NO complexes correspond to triplet excited states. Photolysis of Co(CO){sub 3}(NO) with a 400-nm pump pulse leads to population of a manifold of excited states which decay to form an excited state triplet bent-NO complex within 1 ps. This structure relaxes to the ground triplet state in ca. 350 ps to form a second bent-NO structure.

  4. Molecular dynamics simulations reveal proton transfer pathways in cytochrome C-dependent nitric oxide reductase.

    Directory of Open Access Journals (Sweden)

    Andrei V Pisliakov

    Full Text Available Nitric oxide reductases (NORs are membrane proteins that catalyze the reduction of nitric oxide (NO to nitrous oxide (N(2O, which is a critical step of the nitrate respiration process in denitrifying bacteria. Using the recently determined first crystal structure of the cytochrome c-dependent NOR (cNOR [Hino T, Matsumoto Y, Nagano S, Sugimoto H, Fukumori Y, et al. (2010 Structural basis of biological N2O generation by bacterial nitric oxide reductase. Science 330: 1666-70.], we performed extensive all-atom molecular dynamics (MD simulations of cNOR within an explicit membrane/solvent environment to fully characterize water distribution and dynamics as well as hydrogen-bonded networks inside the protein, yielding the atomic details of functionally important proton channels. Simulations reveal two possible proton transfer pathways leading from the periplasm to the active site, while no pathways from the cytoplasmic side were found, consistently with the experimental observations that cNOR is not a proton pump. One of the pathways, which was newly identified in the MD simulation, is blocked in the crystal structure and requires small structural rearrangements to allow for water channel formation. That pathway is equivalent to the functional periplasmic cavity postulated in cbb(3 oxidase, which illustrates that the two enzymes share some elements of the proton transfer mechanisms and confirms a close evolutionary relation between NORs and C-type oxidases. Several mechanisms of the critical proton transfer steps near the catalytic center are proposed.

  5. Molecular Dynamics Simulations Reveal Proton Transfer Pathways in Cytochrome C-Dependent Nitric Oxide Reductase

    Science.gov (United States)

    Pisliakov, Andrei V.; Hino, Tomoya; Shiro, Yoshitsugu; Sugita, Yuji

    2012-01-01

    Nitric oxide reductases (NORs) are membrane proteins that catalyze the reduction of nitric oxide (NO) to nitrous oxide (N2O), which is a critical step of the nitrate respiration process in denitrifying bacteria. Using the recently determined first crystal structure of the cytochrome c-dependent NOR (cNOR) [Hino T, Matsumoto Y, Nagano S, Sugimoto H, Fukumori Y, et al. (2010) Structural basis of biological N2O generation by bacterial nitric oxide reductase. Science 330: 1666–70.], we performed extensive all-atom molecular dynamics (MD) simulations of cNOR within an explicit membrane/solvent environment to fully characterize water distribution and dynamics as well as hydrogen-bonded networks inside the protein, yielding the atomic details of functionally important proton channels. Simulations reveal two possible proton transfer pathways leading from the periplasm to the active site, while no pathways from the cytoplasmic side were found, consistently with the experimental observations that cNOR is not a proton pump. One of the pathways, which was newly identified in the MD simulation, is blocked in the crystal structure and requires small structural rearrangements to allow for water channel formation. That pathway is equivalent to the functional periplasmic cavity postulated in cbb 3 oxidase, which illustrates that the two enzymes share some elements of the proton transfer mechanisms and confirms a close evolutionary relation between NORs and C-type oxidases. Several mechanisms of the critical proton transfer steps near the catalytic center are proposed. PMID:22956904

  6. Electrochemical proton-coupled electron transfer of an osmium aquo complex: theoretical analysis of asymmetric tafel plots and transfer coefficients.

    Science.gov (United States)

    Ludlow, Michelle K; Soudackov, Alexander V; Hammes-Schiffer, Sharon

    2010-02-03

    Electrochemical proton-coupled electron transfer of an osmium aquo complex attached to a self-assembled monolayer on a gold electrode is studied with a recently developed theoretical formulation. The calculated hydrogen/deuterium kinetic isotope effect for the standard rate constant, the cathodic transfer coefficient at zero overpotential, and the Tafel plot are in excellent agreement with experimental data. The input quantities to the heterogeneous rate constant expressions were calculated with density functional theory in conjunction with dielectric continuum models, and no parameters were fit to experimental data. The theoretical calculations indicate that the asymmetry of the Tafel plot and the deviation of the transfer coefficient at zero overpotential from the standard value of one-half arise from the change in the equilibrium proton donor-acceptor distance upon electron transfer. The direction of the asymmetry and deviation from one-half is determined by the sign of this distance change, and the magnitude of these effects is determined by the magnitude of this distance change, as well as the reorganization energy and the distance dependence of the overlap between the initial and final proton vibrational wave functions. This theory provides experimentally testable predictions for the impact of specific system properties on the qualitative behavior of the Tafel plots.

  7. Proton transfer in histidine-tryptophan heterodimers embedded in helium droplets

    Energy Technology Data Exchange (ETDEWEB)

    Bellina, Bruno; Merthe, Daniel J.; Kresin, Vitaly V. [Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089-0484 (United States)

    2015-03-21

    We used cold helium droplets as nano-scale reactors to form and ionize, by electron bombardment and charge transfer, aromatic amino acid heterodimers of histidine with tryptophan, methyl-tryptophan, and indole. The molecular interaction occurring through an N–H ⋅ ⋅ ⋅ N hydrogen bond leads to a proton transfer from the indole group of tryptophan to the imidazole group of histidine in a radical cationic environment.

  8. Entanglement entropy in excited states of the quantum Lifshitz model

    Science.gov (United States)

    Parker, Daniel E.; Vasseur, Romain; Moore, Joel E.

    2017-06-01

    We investigate the entanglement properties of an infinite class of excited states in the quantum Lifshitz model (QLM). The presence of a conformal quantum critical point in the QLM makes it unusually tractable for a model above one spatial dimension, enabling the ground state entanglement entropy for an arbitrary domain to be expressed in terms of geometrical and topological quantities. Here we extend this result to excited states and find that the entanglement can be naturally written in terms of quantities which we dub ‘entanglement propagator amplitudes’ (EPAs). EPAs are geometrical probabilities that we explicitly calculate and interpret. A comparison of lattice and continuum results demonstrates that EPAs are universal. This work shows that the QLM is an example of a 2  +  1d field theory where the universal behavior of excited-state entanglement may be computed analytically.

  9. A Simple Hubbard Model for the Excited States of Dibenzoterrylene

    CERN Document Server

    Sadeq, Z S

    2016-01-01

    We use a simple Hubbard model to characterize the electronic excited states of the dibenzoterrylene (DBT) molecule; we compute the excited state transition energies and oscillator strengths from the ground state to several singlet excited states. We consider the lowest singlet and triplet states of the molecule, examine their wavefunctions, and compute the density correlation functions that describe these states. We find that the DBT ground state is mostly a closed shell singlet with very slight radical character. We predict a relatively small singlet-triplet splitting of 0.75 eV, which is less than the mid-sized -acenes but larger than literature predictions for this state; this is because the Hubbard interaction makes a very small correction to the singlet and triplet states.

  10. Polarization transfer from remote protons in 13C CP/MAS

    Science.gov (United States)

    Tripon, Carmen; Aluas, Mihaela; Filip, Xenia; Filip, Claudiu

    2006-11-01

    An experimental procedure for CP/MAS polarization transfer from remote 1H nuclear spins is introduced, which is applicable to protonated carbons in organic solids. It is based on preparing a state of non-uniform polarization, where directly bonded 13C- 1H nuclei are de-polarized prior to recording the CP buildup curve. This curve is then expected to quantify the polarization transfer from remote protons only. The ability of the cross-polarization/polarization-inversion (CPPI) sequence to generate an initial state suitable for remote 1H CP/MAS scheme is analyzed both theoretically and experimentally. Confining to aliphatic groups, it was found that complete de-polarization of bonded proton is possible in the case of CH, whereas for CH 2 and CH 3 moieties only a partial de-polarization can be achieved. The theoretical predictions have been verified in practice for the particular case of L-alanine. The significance of the results from fundamental, as well as practical point of view, is also discussed. In particular, it is shown that: (i) the coherent description of polarization transfer under CP/MAS, including 1H polarization redistribution, is valid over time-scales longer than commonly assumed in many treatments of cross-polarization, and (ii) the remote protons polarization transfer curve can be used in combination with the conventional CP/MAS curve to get additional structural and dynamical information in organic systems.

  11. Proton Transfer in Aqueous Solution: Exploring the Boundaries of Adaptive QM/MM

    NARCIS (Netherlands)

    Jiang, Tao|info:eu-repo/dai/nl/371572118; Boereboom, J.M.|info:eu-repo/dai/nl/369185463; Michel, C.; Fleurat-Lessard, P.; Bulo, R.E.|info:eu-repo/dai/nl/272561495

    2015-01-01

    In this chapter, we review the current state-of-the-art in quantum mechanical/molecular mechanical (QM/MM) simulations of reactions in aqueous solutions, and we discuss how proton transfer poses new challenges for its successful application. In the QM/MM description of an aqueous reaction, solvent

  12. Accurate Excited State Geometries within Reduced Subspace TDDFT/TDA.

    Science.gov (United States)

    Robinson, David

    2014-12-09

    A method for the calculation of TDDFT/TDA excited state geometries within a reduced subspace of Kohn-Sham orbitals has been implemented and tested. Accurate geometries are found for all of the fluorophore-like molecules tested, with at most all valence occupied orbitals and half of the virtual orbitals included but for some molecules even fewer orbitals. Efficiency gains of between 15 and 30% are found for essentially the same level of accuracy as a standard TDDFT/TDA excited state geometry optimization calculation.

  13. Identifying involvement of Lys251/Asp252 pair in electron transfer and associated proton transfer at the quinone reduction site of Rhodobacter capsulatus cytochrome bc1.

    Science.gov (United States)

    Kuleta, Patryk; Sarewicz, Marcin; Postila, Pekka; Róg, Tomasz; Osyczka, Artur

    2016-10-01

    Describing dynamics of proton transfers in proteins is challenging, but crucial for understanding processes which use them for biological functions. In cytochrome bc1, one of the key enzymes of respiration or photosynthesis, proton transfers engage in oxidation of quinol (QH2) and reduction of quinone (Q) taking place at two distinct catalytic sites. Here we evaluated by site-directed mutagenesis the contribution of Lys251/Asp252 pair (bacterial numbering) in electron transfers and associated with it proton uptake to the quinone reduction site (Qi site). We showed that the absence of protonable group at position 251 or 252 significantly changes the equilibrium levels of electronic reactions including the Qi-site mediated oxidation of heme bH, reverse reduction of heme bH by quinol and heme bH/Qi semiquinone equilibrium. This implicates the role of H-bonding network in binding of quinone/semiquinone and defining thermodynamic properties of Q/SQ/QH2 triad. The Lys251/Asp252 proton path is disabled only when both protonable groups are removed. With just one protonable residue from this pair, the entrance of protons to the catalytic site is sustained, albeit at lower rates, indicating that protons can travel through parallel routes, possibly involving water molecules. This shows that proton paths display engineering tolerance for change as long as all the elements available for functional cooperation secure efficient proton delivery to the catalytic site. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.

  14. Measurement of Proton-Induced Transfer Reactions with JENSA

    Science.gov (United States)

    Chatterjee, Sidharth; Chipps, Kelly; Pain, Steven; Cizewski, Jolie; Jensa Collaboration

    2017-09-01

    Reaction measurements of radioactive nuclei on light targets are important to understanding the origin of and the trends in the structure of nuclei. To efficiently measure nuclear reactions, measurements require highly localized and pure light targets and need to accommodate arrays of light charged particles, gamma rays, and recoiling heavy ions. The Jet Experiments in Nuclear Structure and Astrophysics (JENSA) jet target system was designed to facilitate high resolution, low background nuclear reaction studies. To demonstrate the capability of the JENSA system, the 20Ne(p,3He)18F reaction was studied during the commissioning phase. The radioisotope 18F is one of the galactic gamma-ray sources targeted by next-generation space-based telescopes. In addition, the 20Ne(p,3He) reaction has not been previously used for the spectroscopic study of 18F. The JENSA system gives us the opportunity to study this reaction with high resolution and low background. The measurement was performed with a proton beam from the Holifield Radioactive Ion Beam Facility tandem on a neon jet of natural isotopic abundance from JENSA. The experimental setup of JENSA and preliminary results will be discussed. Oak Ridge National Laboratory; Rutgers University Department of Physics and Astronomy.

  15. Formation of Bonded Exciplex in the Excited States of Dicyanoanthracene-Pyridine System : Time Dependent Density Functional Theory Study

    NARCIS (Netherlands)

    Setiawan, D.; Sethio, D.; Martoprawiro, M.A.; Filatov, M.; Gaol, FL; Nguyen, QV

    2012-01-01

    Strong quenching of fluorescence was recently observed in pyridine solutions of 9,10-dicyanoanthracene chromophore. It was hypothesized that quenching may be attributed to the formation of bound charge transfer complexes in the excited states of the molecules. In this work, using time-dependent

  16. First-principles molecular dynamics study of proton transfer mechanism in bovine cytochrome c oxidase

    Energy Technology Data Exchange (ETDEWEB)

    Kamiya, Katsumasa [Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577 (Japan); Boero, Mauro [Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577 (Japan); Tateno, Masaru [Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577 (Japan); Shiraishi, Kenji [CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan); Oshiyama, Atsushi [Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577 (Japan)

    2007-09-12

    Density functional based first-principles molecular dynamics calculations, performed on a model system extracted from the bovine cytochrome c oxidase, have been performed in an attempt to inspect the proton transfer mechanism across a peptide group. Our model system includes the specific Tyr440-Ser441 peptide group involved in a novel proton transfer path and shows that the Y440-S441 enol peptide group [-C(OH) = N-], which is a structural isomer of a keto form [-CO-NH-], is the product of the deprotonation of an imidic acid [-C(OH)-NH-] occurring in the vicinity of the deprotonated aspartic acid residue. For the subsequent enol-to-keto tautomerization, a direct H{sup +} transfer path in the Y440-S441 peptide group has been identified, in which the transition state takes a distorted four-membered ring structure.

  17. Long-Range Electrostatics-Induced Two-Proton Transfer Captured by Neutron Crystallography in an Enzyme Catalytic Site.

    Science.gov (United States)

    Gerlits, Oksana; Wymore, Troy; Das, Amit; Shen, Chen-Hsiang; Parks, Jerry M; Smith, Jeremy C; Weiss, Kevin L; Keen, David A; Blakeley, Matthew P; Louis, John M; Langan, Paul; Weber, Irene T; Kovalevsky, Andrey

    2016-04-11

    Neutron crystallography was used to directly locate two protons before and after a pH-induced two-proton transfer between catalytic aspartic acid residues and the hydroxy group of the bound clinical drug darunavir, located in the catalytic site of enzyme HIV-1 protease. The two-proton transfer is triggered by electrostatic effects arising from protonation state changes of surface residues far from the active site. The mechanism and pH effect are supported by quantum mechanics/molecular mechanics (QM/MM) calculations. The low-pH proton configuration in the catalytic site is deemed critical for the catalytic action of this enzyme and may apply more generally to other aspartic proteases. Neutrons therefore represent a superb probe to obtain structural details for proton transfer reactions in biological systems at a truly atomic level. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Insights into the Proton Transfer Mechanism of a Bilin Reductase PcyA Following Neutron Crystallography.

    Science.gov (United States)

    Unno, Masaki; Ishikawa-Suto, Kumiko; Kusaka, Katsuhiro; Tamada, Taro; Hagiwara, Yoshinori; Sugishima, Masakazu; Wada, Kei; Yamada, Taro; Tomoyori, Katsuaki; Hosoya, Takaaki; Tanaka, Ichiro; Niimura, Nobuo; Kuroki, Ryota; Inaka, Koji; Ishihara, Makiko; Fukuyama, Keiichi

    2015-04-29

    Phycocyanobilin, a light-harvesting and photoreceptor pigment in higher plants, algae, and cyanobacteria, is synthesized from biliverdin IXα (BV) by phycocyanobilin:ferredoxin oxidoreductase (PcyA) via two steps of two-proton-coupled two-electron reduction. We determined the neutron structure of PcyA from cyanobacteria complexed with BV, revealing the exact location of the hydrogen atoms involved in catalysis. Notably, approximately half of the BV bound to PcyA was BVH(+), a state in which all four pyrrole nitrogen atoms were protonated. The protonation states of BV complemented the protonation of adjacent Asp105. The "axial" water molecule that interacts with the neutral pyrrole nitrogen of the A-ring was identified. His88 Nδ was protonated to form a hydrogen bond with the lactam O atom of the BV A-ring. His88 and His74 were linked by hydrogen bonds via H3O(+). These results imply that Asp105, His88, and the axial water molecule contribute to proton transfer during PcyA catalysis.

  19. Photoionization of excited states of neon-like Mg III

    Indian Academy of Sciences (India)

    The close coupling -matrix method is used to calculate cross-sections for photoionization of Mg III from its first three excited states. Configuration interaction wave functions are used to represent two target states of Mg III retained in the -matrix expansion. The positions and effective quantum numbers for the Rydberg ...

  20. The excited state antiaromatic benzene ring: a molecular Mr Hyde?

    Science.gov (United States)

    Papadakis, Raffaello; Ottosson, Henrik

    2015-09-21

    The antiaromatic character of benzene in its first ππ* excited triplet state (T1) was deduced more than four decades ago by Baird using perturbation molecular orbital (PMO) theory [J. Am. Chem. Soc. 1972, 94, 4941], and since then it has been confirmed through a range of high-level quantum chemical calculations. With focus on benzene we now first review theoretical and computational studies that examine and confirm Baird's rule on reversal in the electron count for aromaticity and antiaromaticity of annulenes in their lowest triplet states as compared to Hückel's rule for the ground state (S0). We also note that the rule according to quantum chemical calculations can be extended to the lowest singlet excited state (S1) of benzene. Importantly, Baird, as well as Aihara [Bull. Chem. Soc. Jpn. 1978, 51, 1788], early put forth that the destabilization and excited state antiaromaticity of the benzene ring should be reflected in its photochemical reactivity, yet, today these conclusions are often overlooked. Thus, in the second part of the article we review photochemical reactions of a series of benzene derivatives that to various extents should stem from the excited state antiaromatic character of the benzene ring. We argue that benzene can be viewed as a molecular "Dr Jekyll and Mr Hyde" with its largely unknown excited state antiaromaticity representing its "Mr Hyde" character. The recognition of the "Jekyll and Hyde" split personality feature of the benzene ring can likely be useful in a range of different areas.

  1. Size dependent deactivation of the excited state of DHICA

    DEFF Research Database (Denmark)

    Gauden, Magdalena; Pezzella, Alessandro; Panzella, Lucia

    2008-01-01

    Melanin is a natural pigment mainly responsible for the protection of skin and eyes from UV damage. 5,6- dihydroxyindole- 2 carboxylic acid (DHICA) is a key melanin building block. We have investigated the excited state dynamics of DHICA as well as its derivatives and oligomeric units using...

  2. Role of solvent dynamics in ultrafast photoinduced proton-coupled electron transfer reactions in solution.

    Science.gov (United States)

    Hazra, Anirban; Soudackov, Alexander V; Hammes-Schiffer, Sharon

    2010-09-30

    A theoretical formulation for modeling photoinduced nonequilibrium proton-coupled electron transfer (PCET) reactions in solution is presented. In this formulation, the PCET system is described by donor and acceptor electron-proton vibronic free energy surfaces that depend on a single collective solvent coordinate. Dielectric continuum theory is used to obtain a generalized Langevin equation of motion for this collective solvent coordinate. The terms in this equation depend on the solvent properties, such as the dielectric constants, relaxation time, and molecular moment of inertia, as well as the solute properties characterizing the vibronic surfaces. The ultrafast dynamics following photoexcitation is simulated using a surface hopping method in conjunction with the Langevin equation of motion. This methodology is used to examine a series of model photoinduced PCET systems, where the initial nonequilibrium state is prepared by vertical photoexcitation from the ground electronic state to the donor electronic state. Analysis of the dynamical trajectories provides insight into the interplay between the solvent dynamics and the electron-proton transfer for these types of processes. In addition, these model studies illustrate how the coupling between the electron-proton transfer and the solvent dynamics can be tuned by altering the solute and solvent properties.

  3. New Oxime Ligand with Potential for Proton-Coupled Electron-Transfer Reactions

    DEFF Research Database (Denmark)

    Deville, Claire; Sundberg, Jonas; McKenzie, Christine Joy

    .2 Metal complex of ligands possessing both H-donor and H-acceptor sites in the second coordination sphere should be interesting candidates for proton transfer reactions induced by photooxidation of the metal ion. We have prepared new oxime-containing ligands which coordinate to metal ions...... such that a pyridine group is sterically restricted so it does not coordinate. Instead it can act as proximal base for accepting the oxime proton. [1] M. H. V. Huynh, T. J. Meyer, Chem. Rev. 2007, 107, 5004-5064. [2] T. Irebo, O. Johansson, L. Hammarström, J. Am. Chem. Soc., 2008, 130, 9194-9195....

  4. Excited state potential energy surfaces of bistridentate RuII complexes - A TD-DFT study

    Science.gov (United States)

    Österman, Tomas; Persson, Petter

    2012-10-01

    Time-dependent density functional theory (TD-DFT) calculations have been used to investigate low-energy singlet and triplet excited state potential energy surfaces (PES) of two prototype RuII-bistridentate complexes: [RuII(tpy)2]2+ (tpy is 2,2':6',2''-terpyridine) and [RuII(dqp)2]2+ (dqp is 2,6-di(quinolin-8-yl)pyridine). Solvent effects were considered using a self-consistent reaction field scheme. The calculations provide information about the excited state manifold along pathways for activated decay of metal-to-ligand charge-transfer (MLCT) excited states via metal-centered (MC) states for the two complexes. Significant differences in the energy profiles of the investigated PESs are explained through characterization of the electronic properties of the involved states calculated by the TD-DFT calculations. Finally, implications of the computational results for the design of octahedral metal complexes utilizing ligand field splitting (LFS) strategies for efficient light-harvesting in photochemical applications such as artificial photosynthesis are discussed.

  5. Negative electron transfer dissociation of deprotonated phosphopeptide anions: choice of radical cation reagent and competition between electron and proton transfer.

    Science.gov (United States)

    Huzarska, Malwina; Ugalde, Israel; Kaplan, Desmond A; Hartmer, Ralf; Easterling, Michael L; Polfer, Nick C

    2010-04-01

    Despite significant developments in mass spectrometry technology in recent years, no routine proteomics sequencing tool is currently available for peptide anions. The use of a molecular open-shell cation is presented here as a possible reaction partner to induce electron transfer dissociation with deprotonated peptide anions. In this negative electron transfer dissociation (NETD) scheme, an electron is abstracted from the peptide anion and transferred to the radical cation. This is demonstrated for the example of the fluoranthene cation, C(16)H(10)(+*), which is reacted with deprotonated phosphorylated peptides in a 3-D ion trap mass spectrometer. Selective backbone cleavage at the C(alpha)-C bond is observed to yield a and x fragments, similarly to electron detachment dissociation (EDD) of peptide anions. Crucially, the phosphorylation site is left intact in the dissociation process, allowing an identification and localization of the post-translational modification (PTM) site. In contrast, NETD using Xe(+*) as the reagent cation results in sequential neutral losses (CO(2) and H(3)PO(4)) from a/x fragments, which complicate the interpretation of the mass spectra. This difference in dissociation behavior can be understood in the framework of the reduced recombination energy of the electron transfer process for fluoranthene, which is estimated at 2.5-4.5 eV, compared to 6.7-8.7 eV for xenon. Similarly to ETD, proton transfer is found to compete with electron transfer processes in NETD. Isotope fitting of the charge-reduced species shows that in the case of fluoranthene-mediated NETD, proton transfer only accounts for anions.

  6. Proton transfer pathways, energy landscape, and kinetics in creatine-water systems.

    Science.gov (United States)

    Ivchenko, Olga; Whittleston, Chris S; Carr, Joanne M; Imhof, Petra; Goerke, Steffen; Bachert, Peter; Wales, David J

    2014-02-27

    We study the exchange processes of the metabolite creatine, which is present in both tumorous and normal tissues and has NH2 and NH groups that can transfer protons to water. Creatine produces chemical exchange saturation transfer (CEST) contrast in magnetic resonance imaging (MRI). The proton transfer pathway from zwitterionic creatine to water is examined using a kinetic transition network constructed from the discrete path sampling approach and an approximate quantum-chemical energy function, employing the self-consistent-charge density-functional tight-binding (SCC-DFTB) method. The resulting potential energy surface is visualized by constructing disconnectivity graphs. The energy landscape consists of two distinct regions corresponding to the zwitterionic creatine structures and deprotonated creatine. The activation energy that characterizes the proton transfer from the creatine NH2 group to water was determined from an Arrhenius fit of rate constants as a function of temperature, obtained from harmonic transition state theory. The result is in reasonable agreement with values obtained in water exchange spectroscopy (WEX) experiments.

  7. Proton transfer to flavin stabilizes the signaling state of the blue light receptor plant cryptochrome.

    Science.gov (United States)

    Hense, Anika; Herman, Elena; Oldemeyer, Sabine; Kottke, Tilman

    2015-01-16

    Plant cryptochromes regulate the circadian rhythm, flowering time, and photomorphogenesis in higher plants as responses to blue light. In the dark, these photoreceptors bind oxidized FAD in the photolyase homology region (PHR). Upon blue light absorption, FAD is converted to the neutral radical state, the likely signaling state, by electron transfer via a conserved tryptophan triad and proton transfer from a nearby aspartic acid. Here we demonstrate, by infrared and time-resolved UV-visible spectroscopy on the PHR domain, that replacement of the aspartic acid Asp-396 with cysteine prevents proton transfer. The lifetime of the radical is decreased by 6 orders of magnitude. This short lifetime does not permit to drive conformational changes in the C-terminal extension that have been associated with signal transduction. Only in the presence of ATP do both the wild type and mutant form a long-lived radical state. However, in the mutant, an anion radical is formed instead of the neutral radical, as found previously in animal type I cryptochromes. Infrared spectroscopic experiments demonstrate that the light-induced conformational changes of the PHR domain are conserved in the mutant despite the lack of proton transfer. These changes are not detected in the photoreduction of the non-photosensory d-amino acid oxidase to the anion radical. In conclusion, formation of the anion radical is sufficient to generate a protein response in plant cryptochromes. Moreover, the intrinsic proton transfer is required for stabilization of the signaling state in the absence of ATP. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

  8. Simulation and optimization of beam losses during continuous transfer extraction at the CERN Proton Synchrotron

    CERN Document Server

    Garcia, J B

    2011-01-01

    The proton beams used for the fixed target physics at the Super Proton Synchrotron (SPS) are extracted from the Proton Synchrotron ( PS) by a multiturn technique called continuous transfer (CT). During the CT extraction, large losses are observed in locations where the machine aperture should be large enough to accommodate the circulating beam. This limits the maximum intensity deliverable due to the induced stray radiation outside the PS tunnel. Scattered particles from the interaction with the electrostatic septum are identified as the possible source of these losses. This article presents a detailed study aiming to understand the origin of losses and propose possible cures. The simulations could reproduce accurately the beam loss pattern measured in real machine operation and determine the beam shaving, intrinsic to the extraction process, as the cause for the unexpected losses. Since these losses are unavoidable, the proposed solution implies a new optics scheme displacing the losses to a region with bett...

  9. Proton transfer dynamics in the propionic acid dimer from path integral molecular dynamics calculations.

    Science.gov (United States)

    Durlak, Piotr; Latajka, Zdzisław

    2011-09-01

    The double proton transfer process in the cyclic dimer of propionic acid in the gas phase was studied using a path integral molecular dynamics method. Structures, energies and proton trajectories were determined. Very large amplitude motions of the skeleton of a propionic acid molecule were observed during the simulations, and almost free rotation of the C(2)H(5) group around the C(α)-C bond. A double-well symmetric potential with a very small energy barrier was determined from the free energy profile for the proton motions. Infrared spectra for different isotopomers were calculated, and comparative vibrational analysis was performed. The vibrational results from CPMD appear to be in qualitative agreement with the experimental ones.

  10. Investigations into photo-excited state dynamics in colloidal quantum dots

    Science.gov (United States)

    Singh, Gaurav

    Colloidal Quantum dots (QDs) have garnered considerable scientific and technological interest as a promising material for next generation solar cells, photo-detectors, lasers, bright light-emitting diodes (LEDs), and reliable biomarkers. However, for practical realization of these applications, it is crucial to understand the complex photo-physics of QDs that are very sensitive to surface chemistry and chemical surroundings. Depending on the excitation density, QDs can support single or multiple excitations. The first part of this talk addresses evolution of QD excited state dynamics in the regime of low excitation intensity. We use temperature-resolved time-resolved fluorescence spectroscopy to study exciton dynamics from picoseconds to microseconds and use kinetic modeling based on classical electron transfer to show the effect of surface trap states on dynamics of ground-state exciton manifold in core-shell CdSe/CdS QDs. We show that the thickness of CdS shell plays an important role in interaction of CdSe core exciton states with nanocrystal environment, and find that a thicker shell can minimize the mixing of QD exciton states with surface trap states. I will then present an investigation into the dynamics of multiply-excited states in QDs. One of the key challenges in QD spectroscopy is to reliably distinguish multi- from single-excited states that have similar lifetime components and spectroscopic signatures. I will describe the development of a novel multi-pulse fluorescence technique to selectively probe multi-excited states in ensemble QD samples and determine the nature of the multi-excited state contributing to the total fluorescence even in the limit of low fluorescent yields. We find that in our sample of CdSe/CdS core/shell QDs the multi-excited emission is dominated by emissive trion states rather than biexcitons. Next, I will discuss the application of this technique to probe exciton-plasmon coupling in layered hybrid films of QD/gold nanoparticles

  11. Simultaneous measurements of absorbed dose and linear energy transfer in therapeutic proton beams

    Science.gov (United States)

    Granville, Dal A.; Sahoo, Narayan; Sawakuchi, Gabriel O.

    2016-02-01

    The biological response resulting from proton therapy depends on both the absorbed dose in the irradiated tissue and the linear energy transfer (LET) of the beam. Currently, optimization of proton therapy treatment plans is based only on absorbed dose. However, recent advances in proton therapy delivery have made it possible to vary the LET distribution for potential therapeutic gain, leading to investigations of using LET as an additional parameter in plan optimization. Having a method to measure and verify both absorbed dose and LET as part of a quality assurance program would be ideal for the safe delivery of such plans. Here we demonstrated the potential of an optically stimulated luminescence (OSL) technique to simultaneously measure absorbed dose and LET. We calibrated the ratio of ultraviolet (UV) to blue emission intensities from Al2O3:C OSL detectors as a function of LET to facilitate LET measurements. We also calibrated the intensity of the blue OSL emission for absorbed dose measurements and introduced a technique to correct for the LET-dependent dose response of OSL detectors exposed to therapeutic proton beams. We demonstrated the potential of our OSL technique by using it to measure LET and absorbed dose under new irradiation conditions, including patient-specific proton therapy treatment plans. In the beams investigated, we found the OSL technique to measure dose-weighted LET within 7.9% of Monte Carlo-simulated values and absorbed dose within 2.5% of ionization chamber measurements.

  12. Proton-Coupled Electron Transfer in Organic Synthesis: Fundamentals, Applications, and Opportunities

    Science.gov (United States)

    Miller, David C.; Tarantino, Kyle T.; Knowles, Robert R.

    2016-01-01

    Proton-coupled electron transfers (PCETs) are unconventional redox processes in which both protons and electrons are exchanged, often in a concerted elementary step. While PCET is now recognized to play a central a role in biological redox catalysis and inorganic energy conversion technologies, its applications in organic synthesis are only beginning to be explored. In this chapter we aim to highlight the origins, development and evolution of PCET processes most relevant to applications in organic synthesis. Particular emphasis is given to the ability of PCET to serve as a non-classical mechanism for homolytic bond activation that is complimentary to more traditional hydrogen atom transfer processes, enabling the direct generation of valuable organic radical intermediates directly from their native functional group precursors under comparatively mild catalytic conditions. The synthetically advantageous features of PCET reactivity are described in detail, along with examples from the literature describing the PCET activation of common organic functional groups. PMID:27573270

  13. Ferrous iron reduction of superoxide, a proton-coupled electron-transfer four-point test.

    Science.gov (United States)

    Wander, Matthew C F; Kubicki, James D; Clark, Aurora E; Schoonen, Martin A A

    2009-02-12

    Nelsen's four-point method of separating oxidants and reductants has been tested to evaluate its applicability to proton-coupled electron-transfer reactions. An efficient computational method was developed to determine rate-limiting steps in complex, multistep redox reactions. Geochemical redox reactions are rarely single-step, and by identifying the rate-limiting steps, computational time can be greatly reduced. The reaction of superoxide and ferrous oxide was selected as a test case for its simplicity and its importance in environmental radical generation chemistry (Fenton's reaction). Two approaches, one quantum mechanical and the other semiempirical, were compared. In both approaches, hybrid density functional theory (DFT) was used with the B3LYP/6-31+G(d,p) basis set and a polarized continuum model of the solvent to minimize the structures and determine the energies. In the quantum mechanical case, DFT was used to determine both the Gibbs free energies and the values for the intrinsic component of the reorganization energy of possible combinations of reactants and products. In the latter, experimental DeltaG(f) values were combined with calculated intrinsic reorganization energy values. The computational results matched the relative difference in rate barriers between the reduction of superoxide by ferrous iron above and below pH 4.8. In the acidic pH range, the proton is coupled to the electron transfer, whereas in the neutral case, the proton initiates the electron transfer.

  14. Ionization-induced proton transfer in thymine-ammonia van der Waals clusters

    Science.gov (United States)

    Kim, Nam Joon; Kim, Hyung Min; Kim, Seong Keun

    2007-03-01

    Ion intensity distribution of thymine-ammonia clusters produced in a supersonic jet was investigated using the resonant 2-photon ionization technique. The mass spectrum of Thym(NH3)n (m = 1-7) exhibited an anomalously strong ion intensity for n = 1 in contrast to the nearly negligible ion signals for n > 1. We suggest that proton transfer from the thymine radical cation to an ammonia molecule following the ionization of the clusters is responsible for the observed anomaly. It is also proposed that charge migration occurring with the proton transfer leads to an ion core switch from the thymine radical cation to the newly formed ammonium ion. The subsequent evaporation of other ammonia molecules in the cluster ion as a consequence of the energy released from the reaction results in extensive loss of ion signals for n > 1, and at their expense, an anomalously large ion intensity for n = 1. This mechanism is supported by density functional theory calculations on the thymine-ammonia 1:1 complex ion performed along the reaction coordinate of the proton transfer. The formation of the ammonium ion in the cluster is also confirmed by the fragmentation feature of metastable Thym(NH3)1+ (m = 1-4) obtained using reflectron time-of-flight mass spectrometry.

  15. Intramolecular proton transfer and tunnelling reactions of hydroxyphenylbenzoxazole derivatives in Xenon at 15 K

    Energy Technology Data Exchange (ETDEWEB)

    Walla, Peter J. [Max-Planck-Institute for Biophysical Chemistry, Department 010, Spectroscopy and Photochemical Kinetics, Am Fassberg 11, D-37077 Goettingen (Germany) and Department for Biophysical Chemistry, Technical University of Brunswick, Institute for Physical and Theoretical Chemistry, Hans-Sommerstr. 10, D-38106 Braunschweig (Germany)]. E-mail: pwalla@gwdg.de; Nickel, Bernhard [Max-Planck-Institute for Biophysical Chemistry, Department 010, Spectroscopy and Photochemical Kinetics, Am Fassberg 11, D-37077 Goettingen (Germany)

    2005-06-06

    We investigated the site dependence and the tunnelling processes of the intramolecular proton and deuteron transfer in the triplet state of the compounds 2-(2'-hydroxy-4'-methylphenyl)benzoxazole (m-MeHBO) and 2-(2'-hydroxy-3'-methylphenyl)benzoxazoles (o-MeHBO) and their deuterio-oxy analogues in a solid xenon matrix. After singlet excitation there occurs an ultrafast intramolecular enol {yields} keto proton transfer and subsequent intersystem crossing mainly to the keto triplet state. In the triplet state of m-MeHBO, the proton transfer back to the lower enol triplet state is governed by tunnelling processes. In o-MeHBO, however, the enol triplet state is higher and therefore normally no tunnel reaction can be observed. Because of the external heavy atom-effect in a xenon matrix, we were able to investigate the reverse enol-keto-tunnelling after exciting directly the enol triplet state of deuterated o-MeHBO. The time constants of the reverse enol-keto tautomerization are similar to those of the normal keto-enol tautomerization. In a xenon matrix, the observed site-selective phosphorescence spectra are very well-resolved vibrationally. This allowed the study of the tunnel rates in different well-defined sites. The vibrational energies obtained in the spectra are in good agreement with vibrational energies found in resonant Raman and IR spectra of 2-(2'-hydroxyphenyl)benzoxazole (HBO)

  16. Proton-Transfer-Driven Water Exchange Mechanism in the Na+ Solvation Shell.

    Science.gov (United States)

    Hellström, Matti; Behler, Jörg

    2017-04-27

    Ligand exchange plays an important role for organic and inorganic chemical reactions. We demonstrate the existence of a novel water exchange mechanism, the "proton transfer pathway" (PTP), around Na+(aq) in basic (high pH) solution, using reactive molecular dynamics simulations employing a high-dimensional neural network potential. An aqua ligand in the first solvation (hydration) shell around a sodium ion is only very weakly acidic, but if a hydroxide ion is present in the second solvation shell, thermal fluctuations can cause the aqua ligand to transfer a proton to the neighboring OH-, resulting in a transient direct-contact ion pair, Na+-OH-, which is only weakly bound and easily dissociates. The extent to which water exchange events follow the PTP is pH-dependent: in dilute NaOH(aq) solutions, only very few exchanges occur, whereas in saturated NaOH(aq) solutions up to a third of water self-exchange events are induced by proton transfer. The principles and results outlined here are expected to be relevant for chemical synthesis involving bases and alkali metal cations.

  17. Protonated serotonin: Geometry, electronic structures and photophysical properties

    Science.gov (United States)

    Omidyan, Reza; Amanollahi, Zohreh; Azimi, Gholamhassan

    2017-07-01

    The geometry and electronic structures of protonated serotonin have been investigated by the aim of MP2 and CC2 methods. The relative stabilities, transition energies and geometry of sixteen different protonated isomers of serotonin have been presented. It has been predicted that protonation does not exhibit essential alteration on the S1 ← S0 electronic transition energy of serotonin. Instead, more complicated photophysical nature in respect to its neutral analogue is suggested for protonated system owing to radiative and non-radiative deactivation pathways. In addition to hydrogen detachment (HD), hydrogen/proton transfer (H/PT) processes from ammonium to indole ring along the NH+⋯ π hydrogen bond have been predicted as the most important photophysical consequences of SERH+ at S1 excited state. The PT processes is suggested to be responsible for fluorescence of SERH+ while the HD driving coordinate is proposed for elucidation of its nonradiative deactivation mechanism.

  18. Can $\\beta$-decay probe excited state halos?

    CERN Multimedia

    2002-01-01

    In the first experiment at the newly constructed ISOLDE Facility the first-forbidden $\\beta$-decay of $^{17}$Ne into the first excited state of $^{17}$F has been measured. It is a factor two faster than the corresponding mirror decay and thus gives one of the largest recorded asymmetries for $\\beta$-decays feeding bound final states. Shell-model calculations can only reproduce the asymmetry if the halo structure of the $^{17}$F state is taken into account.

  19. A Molecular Dynamic Simulation of Hydrated Proton Transfer in Perfluorosulfonate Ionomer Membranes (Nafion 117

    Directory of Open Access Journals (Sweden)

    Hong Sun

    2015-01-01

    Full Text Available A molecular dynamic model based on Lennard-Jones Potential, the interaction force between two particles, molecular diffusion, and radial distribution function (RDF is presented. The diffusion of the hydrated ion, triggered by both Grotthuss and vehicle mechanisms, is used to study the proton transfer in Nafion 117. The hydrated ion transfer mechanisms and the effects of the temperature, the water content in the membrane, and the electric field on the diffusion of the hydrated ion are analyzed. The molecular dynamic simulation results are in good agreement with those reported in the literature. The modeling results show that when the water content in Nafion 117 is low, H3O+ is the main transfer ion among the different hydrated ions. However, at higher water content, the hydrated ion in the form of H+(H2O2 is the main transfer ion. It is also found that the negatively charged sulfonic acid group as the fortified point facilitates the proton transfer in Nafion 117 better than the free water molecule. The diffusion of the hydrated ion can be improved by increasing the cell temperature, the water content in Nafion, and the electric field intensity.

  20. Reactions of excited states of phenoxazin-3-one dyes with amino acids.

    Science.gov (United States)

    Villegas, M L; Bertolotti, S G; Previtali, C M; Encinas, M V

    2005-01-01

    The interaction with amino acids of the excited states of the N-oxide resazurin and its deoxygenation product resorufin, has been studied in aqueous solution at pH 7.5. Steady-state and time-resolved studies show that the fluorescence is quenched by amino acids. Complexation of the dyes in the ground state with aromatic amino acids was also observed. The singlet quenching is attributed to electron transfer from the amino acids to the excited dye based on the dependence of the bimolecular rate constants with the ionization potential of quenchers. Flash photolysis experiments allowed determination of the quenching rate constants for the triplet deactivation of dyes by several amino acids, as well as the characterization of the transients formed in the process. These data show that the triplet is also deactivated by an electron transfer process. However, the deactivation of the N-oxide dye by tryptophan can be described by a hydrogen atom transfer. The protolytic dissociation constants of the dye radical ions are reported. The irradiation of rezasurin in the presence of amino acids leads to deoxygenation of the dye to give resorufin. This process involves the triplet excited state of resazurin and is efficient only in the presence of amino acids containing the -SH group.

  1. Signature of nonadiabatic coupling in excited-state vibrational modes.

    Science.gov (United States)

    Soler, Miguel A; Nelson, Tammie; Roitberg, Adrian E; Tretiak, Sergei; Fernandez-Alberti, Sebastian

    2014-11-13

    Using analytical excited-state gradients, vibrational normal modes have been calculated at the minimum of the electronic excited-state potential energy surfaces for a set of extended conjugated molecules with different coupling between them. Molecular model systems composed of units of polyphenylene ethynylene (PPE), polyphenylenevinylene (PPV), and naphthacene/pentacene (NP) have been considered. In all cases except the NP model, the influence of the nonadiabatic coupling on the excited-state equilibrium normal modes is revealed as a unique highest frequency adiabatic vibrational mode that overlaps with the coupling vector. This feature is removed by using a locally diabatic representation in which the effect of NA interaction is removed. Comparison of the original adiabatic modes with a set of vibrational modes computed in the locally diabatic representation demonstrates that the effect of nonadiabaticity is confined to only a few modes. This suggests that the nonadiabatic character of a molecular system may be detected spectroscopically by identifying these unique state-specific high frequency vibrational modes.

  2. Lifetimes of excited states in neutron-rich Xe isotopes

    Energy Technology Data Exchange (ETDEWEB)

    Ilieva, Stoyanka; Kroell, Thorsten [Institut fuer Kernphysik, TU Darmstadt (Germany); Collaboration: EXILL-FATIMA-Collaboration

    2016-07-01

    The EXILL and FATIMA campaign at ILL, Grenoble is the first prompt-fission γ-ray spectroscopy experiment performed with a mixed array of Ge detectors (EXILL) and fast LaBr{sub 3}(Ce) scintillators (FATIMA). The lifetimes of excited states, populated by neutron-induced fission of {sup 235}U and {sup 241}Pu targets, were directly measured. The high-resolution EXILL detector gives us the possibility to identify the nuclides of interest among the large amount of produced fission fragments. Using the generalized centroid difference method to analyse the data from FATIMA we could measure lifetimes down to ∼ 10 ps. The lifetime of an excited state is a direct measure for the strength (collectivity) of a transition. The properties of the excited states in even-even nuclei can be largely described by quadrupole and octupole degrees of freedom. This contribution will present the current status of the analysis for the neutron-rich even-even {sup 138,140,142}Xe isotopes which lie in the vicinity of the double shell closure Z=50 and N=82. Through the direct lifetime measurement we aim to study the evolution of quadrupole and octupole collectivity above {sup 132}Sn.

  3. Controlling excited-state contamination in nucleon matrix elements

    Energy Technology Data Exchange (ETDEWEB)

    Yoon, Boram; Gupta, Rajan; Bhattacharya, Tanmoy; Engelhardt, Michael; Green, Jeremy; Joó, Bálint; Lin, Huey-Wen; Negele, John; Orginos, Kostas; Pochinsky, Andrew; Richards, David; Syritsyn, Sergey; Winter, Frank

    2016-06-01

    We present a detailed analysis of methods to reduce statistical errors and excited-state contamination in the calculation of matrix elements of quark bilinear operators in nucleon states. All the calculations were done on a 2+1 flavor ensemble with lattices of size $32^3 \\times 64$ generated using the rational hybrid Monte Carlo algorithm at $a=0.081$~fm and with $M_\\pi=312$~MeV. The statistical precision of the data is improved using the all-mode-averaging method. We compare two methods for reducing excited-state contamination: a variational analysis and a two-state fit to data at multiple values of the source-sink separation $t_{\\rm sep}$. We show that both methods can be tuned to significantly reduce excited-state contamination and discuss their relative advantages and cost-effectiveness. A detailed analysis of the size of source smearing used in the calculation of quark propagators and the range of values of $t_{\\rm sep}$ needed to demonstrate convergence of the isovector charges of the nucleon to the $t_{\\rm sep} \\to \\infty $ estimates is presented.

  4. Proton transport and the water environment in nafion fuel cell membranes and AOT reverse micelles.

    Science.gov (United States)

    Spry, D B; Goun, A; Glusac, K; Moilanen, David E; Fayer, M D

    2007-07-04

    The properties of confined water and diffusive proton-transfer kinetics in the nanoscopic water channels of Nafion fuel cell membranes at various hydration levels are compared to water in a series of well-characterized AOT reverse micelles with known water nanopool sizes using the photoacid pyranine as a molecular probe. The side chains of Nafion are terminated by sulfonate groups with sodium counterions that are arrayed along the water channels. AOT has sulfonate head groups with sodium counterions that form the interface with the reverse micelle's water nanopool. The extent of excited-state deprotonation is observed by steady-state fluorescence measurements. Proton-transfer kinetics and orientational relaxation are measured by time-dependent fluorescence using time-correlated single photon counting. The time dependence of deprotonation is related to diffusive proton transport away from the photoacid. The fluorescence reflecting the long time scale proton transport has an approximately t-0.8 power law decay in contrast to bulk water, which has a t-3/2 power law. For a given hydration level of Nafion, the excited-state proton transfer and the orientational relaxation are similar to those observed for a related size AOT water nanopool. The effective size of the Nafion water channels at various hydration levels are estimated by the known size of the AOT reverse micelles that display the corresponding proton-transfer kinetics and orientational relaxation.

  5. Ground- and excited-state structural orientation of 2-(2`-hydroxyphenyl)benzazoles in cyclodextrins

    Energy Technology Data Exchange (ETDEWEB)

    Roberts, E.L.; Dey, J.; Warner, I.M. [Louisiana State Univ., Baton Rouge, LA (United States)

    1996-12-12

    The effects of {alpha}-, {beta}-, {gamma}-, and 2,6-di-O-methyl-{beta}-cyclodextrins (CDs) on the ground- and excited-state properties of 2-(2`-hydroxyphenyl)benzoxazole, 2-(2`-hydroxyphenyl)benzothiazole, and 2-(2`-hydroxyphenyl)benzimidazole in aqueous media are investigated. Steady-state fluorescence measurements are used to characterize the interaction of CDs with these azoles. Absorbance measurements indicate increased solubility of the azoles in aqueous solutions of CDs. Measurements of acidity constants (pK{sub a}) and data from induced circular dichroism indicate increased ground- and excited-state acidities of the phenolic protons of the molecules in the presence of CDs and axial orientation of the molecules within the CD cavity, respectively. The data further suggest a planar structure for HBO and a twisted confirmation for both HBT and HBI. The association constants of the inclusion complexes have also been estimated. These studies are further supplemented by comparative spectroscopic studies of 2-(2`-methoxyphenyl)benzothiazole in aqueous solutions of CDs. On the basis of the spectral data acquired, it is believed that the HBA molecules exist as zwitterionic tautomers in the presence of CDs. 35 refs., 6 figs., 2 tabs.

  6. Unbound Excited States of the N = 16 Closed Shell Nucleus 24O

    Science.gov (United States)

    Rogers, W. F.; MoNA Collaboration

    2015-10-01

    The energies of two low-lying neutron-unbound excited states of 24O, which were populated by proton-knockout reactions on 26F, have been measured using the MoNA and LISA arrays in combination with the Sweeper Magnet at the Coupled Cyclotron Facility at the NSCL using invariant mass spectroscopy. The current measurement confirms for the first time the separate identity of 2+ and (1+) neutron-unbound excited states in 24O with decay energies 0.51(5) MeV state and 1.20(7) MeV, respectively, to the 23O ground state. These measured decay energies are consistent with two previous lower resolution measurements to within 2 σ. The level energies for the two states are computed using the decay energies and the 1-neutron separation energy for 24O, resulting in 4.70(15) MeV for the 2+ state and 5.39(16) MeV for the (1+) state. Errors in the level energies are dominated by uncertainty in the 24O neutron separation energy, underscoring the need for a higher resolution 24O ground state mass measurement. Results will be compared with 3 phenomenological and 2 ab initio model calculations. Work Supported by NSF Grants PHY-0922335, PHY-0922409, PHY-0922446, PHY-0922462, PHY-0922473, PHY-0922537, PHY-0922559, PHY-0922622, PHY-0922794, PHY-0969173, PHY-1101745, PHY-1205357, PHY- 1205537.

  7. Surprisingly Long-Lived Ascorbyl Radicals in Acetonitrile: Concerted Proton-Electron Transfer Reactions and Thermochemistry

    Science.gov (United States)

    Warren, Jeffrey J.; Mayer, James M.

    2008-01-01

    Proton-coupled electron transfer (PCET) reactions and thermochemistry of 5,6-isopropylidene ascorbate (iAscH−) have been examined in acetonitrile solvent.iAscH− is oxidized by 2,4,6-tBu3C6H2O• and by excess TEMPO• to give the corresponding 5,6-isopropylidene ascorbyl radical anion (iAsc•−), which persists for hours at 298 K in dry MeCN solution. The stability of iAsc•− is surprising in light of the transience of the ascorbyl radical in aqueous solutions, and is due to the lack of the protons needed for radical disproportionation. A concerted proton-electron transfer (CPET) mechanism is indicated for the reactions of iAscH−. Redox potential, pKa and equilibrium measurements define the thermochemical landscape for 5,6-isopropylidene ascorbic acid and its derivatives in MeCN. These measurements give an O–H bond dissociation free energy (BDFE) for iAscH−of 65.4 ± 1.5 kcal mol−1 in MeCN. Similar studies on underivatized ascorbate indicate a BDFE of 67.8 ± 1.2 kcal mol−1. These values are much lower than the aqueous BDFE for ascorbate of 74.0 ± 1.5 kcal mol−1 derived from reported data. PMID:18505256

  8. Sustainable power generation in microbial fuel cells using bicarbonate buffer and proton transfer mechanisms.

    Science.gov (United States)

    Fan, Yanzhen; Hu, Hongqiang; Liu, Hong

    2007-12-01

    Phosphate buffer solution has been commonly used in MFC studiesto maintain a suitable pH for electricity-generating bacteria and/or to increase the solution conductivity. However, addition of a high concentration of phosphate buffer in MFCs could be expensive, especially for wastewater treatment. In this study, the performances of MFCs with cloth electrode assemblies (CEA) were evaluated using bicarbonate buffer solutions. A maximum power density of 1550 W/m3 (2770 mW/ m2) was obtained at a current density of 0.99 mA/cm2 using a pH 9 bicarbonate buffer solution. Such a power density was 38.6% higher than that using a pH 7 phosphate buffer at the same concentration of 0.2 M. Based on the quantitative comparison of free proton transfer rates, diffusion rates of pH buffer species, and the current generated, a facilitated proton transfer mechanism was proposed for MFCs in the presence of the pH buffers. The excellent performance of MFCs using bicarbonate as pH buffer and proton carrier indicates that bicarbonate buffer could be served as a low-cost and effective pH buffer for practical applications, especially for wastewater treatment.

  9. Intracellular Proton-Transfer Mutants in a CLC Cl-/H+ Exchanger

    Energy Technology Data Exchange (ETDEWEB)

    Lim, H.; Miller, C

    2009-01-01

    CLC-ec1, a bacterial homologue of the CLC family's transporter subclass, catalyzes transmembrane exchange of Cl- and H+. Mutational analysis based on the known structure reveals several key residues required for coupling H+ to the stoichiometric countermovement of Cl-. E148 (Gluex) transfers protons between extracellular water and the protein interior, and E203 (Gluin) is thought to function analogously on the intracellular face of the protein. Mutation of either residue eliminates H+ transport while preserving Cl- transport. We tested the role of Gluin by examining structural and functional properties of mutants at this position. Certain dissociable side chains (E, D, H, K, R, but not C and Y) retain H+/Cl- exchanger activity to varying degrees, while other mutations (V, I, or C) abolish H+ coupling and severely inhibit Cl- flux. Transporters substituted with other nonprotonatable side chains (Q, S, and A) show highly impaired H+ transport with substantial Cl- transport. Influence on H+ transport of side chain length and acidity was assessed using a single-cysteine mutant to introduce non-natural side chains. Crystal structures of both coupled (E203H) and uncoupled (E203V) mutants are similar to wild type. The results support the idea that Gluin is the internal proton-transfer residue that delivers protons from intracellular solution to the protein interior, where they couple to Cl- movements to bring about Cl-/H+ exchange.

  10. Nonadiabatic dynamics of photoinduced proton-coupled electron transfer: comparison of explicit and implicit solvent simulations.

    Science.gov (United States)

    Auer, Benjamin; Soudackov, Alexander V; Hammes-Schiffer, Sharon

    2012-07-05

    Theoretical approaches for simulating the ultrafast dynamics of photoinduced proton-coupled electron transfer (PCET) reactions in solution are developed and applied to a series of model systems. These processes are simulated by propagating nonadiabatic surface hopping trajectories on electron-proton vibronic surfaces that depend on the solute and solvent nuclear coordinates. The PCET system is represented by a four-state empirical valence bond model, and the solvent is treated either as explicit solvent molecules or as a dielectric continuum, in which case the solvent dynamics is described in terms of two collective solvent coordinates corresponding to the energy gaps associated with electron and proton transfer. The explicit solvent simulations reveal two distinct solvent relaxation time scales, where the faster time scale relaxation corresponds to librational motions of solvent molecules in the first solvation shell, and the slower time scale relaxation corresponds to the bulk solvent dielectric response. The charge transfer dynamics is strongly coupled to both the fast and slow time scale solvent dynamics. The dynamical multistate continuum theory is extended to include the effects of two solvent relaxation time scales, and the resulting coupled generalized Langevin equations depend on parameters that can be extracted from equilibrium molecular dynamics simulations. The implicit and explicit solvent approaches lead to qualitatively similar charge transfer and solvent dynamics for model PCET systems, suggesting that the implicit solvent treatment captures the essential elements of the nonequilibrium solvent dynamics for many systems. A combination of implicit and explicit solvent approaches will enable the investigation of photoinduced PCET processes in a variety of condensed phase systems.

  11. Excited-State Interaction of Semiconducting Single-Walled Carbon Nanotubes with Their Wrapping Polymers.

    Science.gov (United States)

    Kahmann, Simon; Salazar Rios, Jorge M; Zink, Matthias; Allard, Sybille; Scherf, Ullrich; Dos Santos, Maria C; Brabec, Christoph J; Loi, Maria A

    2017-11-16

    We employ photoluminescence and pump-probe spectroscopy on films of semiconducting single-walled carbon nanotubes (CNTs) of different chirality wrapped with either a wide band gap polyfluorene derivative (PF12) or a polythiophene with narrower gap (P3DDT) to elucidate the excited states' interplay between the two materials. Excitation above the polymer band gap gives way to an ultrafast electron transfer from both polymers toward the CNTs. By monitoring the hole polaron on the polymer via its mid infrared signature, we show that also illumination below the polymer band gap leads to the formation of this fingerprint and infer that holes are also transferred toward the polymer. As this contradicts the standard way of discussing the involved energy levels, we propose that polymer-wrapped CNTs should be considered as a single hybrid system, exhibiting states shared between the two components. This proposition is validated through quantum chemical calculations that show hybridization of the first excited states, especially for the thiophene-CNT sample.

  12. Femtosecond Studies of Charge-Transfer Mediated Proton Transfer in 2-Butylamino-6-methyl-4-nitropyridine N-Oxide

    NARCIS (Netherlands)

    Poor, B.; Michniewicz, N.; Kallay, M.; Buma, W.J.; Kubinyi, M.; Szemik-Hojniak, A.; Deperasinska, I.; Puszko, A.; Zhang, H.

    2006-01-01

    Abstract: We have unraveled the effects of an amino substituent in the ortho position on the excited-state dynamics of 4-nitropyridine N-oxide by studying the picosecond fluorescence kinetics and femtosecond transient absorption of a newly synthesized compound, 2-butylamino-6-methyl-4-nitropyridine

  13. Monovalent counterion distributions at highly charged water interfaces: proton-transfer and Poisson-Boltzmann theory.

    Science.gov (United States)

    Bu, Wei; Vaknin, David; Travesset, Alex

    2005-12-01

    Surface sensitive synchrotron-x-ray scattering studies reveal the distributions of monovalent ions next to highly charged interfaces. A lipid phosphate (dihexadecyl hydrogen phosphate) was spread as a monolayer at the air-water interface, containing CsI at various concentrations. Using anomalous reflectivity off and at the L3 Cs+ resonance, we provide spatial counterion distributions (Cs+) next to the negatively charged interface over a wide range of ionic concentrations. We argue that at low salt concentrations and for pure water the enhanced concentration of hydroniums H3O+ at the interface leads to proton transfer back to the phosphate group by a high contact potential, whereas high salt concentrations lower the contact potential resulting in proton release and increased surface charge density. The experimental ionic distributions are in excellent agreement with a renormalized-surface-charge Poisson-Boltzmann theory without fitting parameters or additional assumptions.

  14. Proton transfer in the K-channel analog of B-type Cytochrome c oxidase from Thermus thermophilus.

    Science.gov (United States)

    Woelke, Anna Lena; Wagner, Anke; Galstyan, Gegham; Meyer, Tim; Knapp, Ernst-Walter

    2014-11-04

    A key enzyme in aerobic metabolism is cytochrome c oxidase (CcO), which catalyzes the reduction of molecular oxygen to water in the mitochondrial and bacterial membranes. Substrate electrons and protons are taken up from different sides of the membrane and protons are pumped across the membrane, thereby generating an electrochemical gradient. The well-studied A-type CcO uses two different entry channels for protons: the D-channel for all pumped and two consumed protons, and the K-channel for the other two consumed protons. In contrast, the B-type CcO uses only a single proton input channel for all consumed and pumped protons. It has the same location as the A-type K-channel (and thus is named the K-channel analog) without sharing any significant sequence homology. In this study, we performed molecular-dynamics simulations and electrostatic calculations to characterize the K-channel analog in terms of its energetic requirements and functionalities. The function of Glu-15B as a proton sink at the channel entrance is demonstrated by its rotational movement out of the channel when it is deprotonated and by its high pKA value when it points inside the channel. Tyr-244 in the middle of the channel is identified as the valve that ensures unidirectional proton transfer, as it moves inside the hydrogen-bond gap of the K-channel analog only while being deprotonated. The electrostatic energy landscape was calculated for all proton-transfer steps in the K-channel analog, which functions via proton-hole transfer. Overall, the K-channel analog has a very stable geometry without large energy barriers.

  15. Excited-state annihilation reduces power dependence of single-molecule FRET experiments.

    Science.gov (United States)

    Nettels, Daniel; Haenni, Dominik; Maillot, Sacha; Gueye, Moussa; Barth, Anders; Hirschfeld, Verena; Hübner, Christian G; Léonard, Jérémie; Schuler, Benjamin

    2015-12-28

    Single-molecule Förster resonance energy transfer (FRET) experiments are an important method for probing biomolecular structure and dynamics. The results from such experiments appear to be surprisingly independent of the excitation power used, in contradiction to the simple photophysical mechanism usually invoked for FRET. Here we show that excited-state annihilation processes are an essential cause of this behavior. Singlet-singlet annihilation (SSA) is a mechanism of fluorescence quenching induced by Förster-type energy transfer between two fluorophores while they are both in their first excited singlet states (S1S1), which is usually neglected in the interpretation of FRET experiments. However, this approximation is only justified in the limit of low excitation rates. We demonstrate that SSA is evident in fluorescence correlation measurements for the commonly used FRET pair Alexa 488/Alexa 594, with a rate comparable to the rate of energy transfer between the donor excited state and the acceptor ground state (S1S0) that is exploited in FRET experiments. Transient absorption spectroscopy shows that SSA occurs exclusively via energy transfer from Alexa 488 to Alexa 594. Excitation-power dependent microsecond correlation experiments support the conclusion based on previously reported absorption spectra of triplet states that singlet-triplet annihilation (STA) analogously mediates energy transfer if the acceptor is in the triplet state. The results indicate that both SSA and STA have a pronounced effect on the overall FRET process and reduce the power dependence of the observed FRET efficiencies. The existence of annihilation processes thus seems to be essential for using FRET as a reliable spectroscopic ruler at the high excitation rates commonly employed in single-molecule spectroscopy.

  16. Rotational Spectra in 29 Vibrationally Excited States of Interstellar Aminoacetonitrile

    Energy Technology Data Exchange (ETDEWEB)

    Kolesniková, L.; Alonso, E. R.; Mata, S.; Alonso, J. L. [Grupo de Espectroscopia Molecular (GEM), Edificio Quifima, Área de Química-Física, Laboratorios de Espectroscopia y Bioespectroscopia, Parque Científico UVa, Unidad Asociada CSIC, Universidad de Valladolid, E-47011 Valladolid (Spain)

    2017-04-01

    We report a detailed spectroscopic investigation of the interstellar aminoacetonitrile, a possible precursor molecule of glycine. Using a combination of Stark and frequency-modulation microwave and millimeter wave spectroscopies, we observed and analyzed the room-temperature rotational spectra of 29 excited states with energies up to 1000 cm{sup −1}. We also observed the {sup 13}C isotopologues in the ground vibrational state in natural abundance (1.1%). The extensive data set of more than 2000 new rotational transitions will support further identifications of aminoacetonitrile in the interstellar medium.

  17. Modular Hamiltonian for Excited States in Conformal Field Theory.

    Science.gov (United States)

    Lashkari, Nima

    2016-07-22

    We present a novel replica trick that computes the relative entropy of two arbitrary states in conformal field theory. Our replica trick is based on the analytic continuation of partition functions that break the Z_{n} replica symmetry. It provides a method for computing arbitrary matrix elements of the modular Hamiltonian corresponding to excited states in terms of correlation functions. We show that the quantum Fisher information in vacuum can be expressed in terms of two-point functions on the replica geometry. We perform sample calculations in two-dimensional conformal field theories.

  18. Switching of the triplet excited state of rhodamine/naphthaleneimide dyads: an experimental and theoretical study.

    Science.gov (United States)

    Cui, Xiaoneng; Zhao, Jianzhang; Lou, Zhangrong; Li, Shujing; Wu, Huijian; Han, Ke-Li

    2015-01-02

    Rhodamine-bromonaphthaleneimide (RB-NI) and rhodamine-bromonaphthalenediimide (RB-NDI) dyads were prepared for switching of the triplet excited states. Bromo-NI or bromo-NDI parts in the dyads are the spin converters, i.e., the triplet state producing modules, whereas the RB unit is the acid-activatable electron donor/energy acceptor. NI and NDI absorb at 359 and 541 nm, and the T1 state energy levels are 2.25 and 1.64 eV, respectively. RB undertakes the reversible spirolactam (RB-c) ↔ opened amide (RB-o) transformation. RB-c shows no visible light absorption, and the triplet-state energy level is ET1 = 3.36 eV. Conversely RB-o shows strong absorption at 557 nm, and ET1 is 1.73 eV. Thus, the acid-activated fluorescence-resonance-energy-transfer (FRET) competes with the ISC of NI or NDI. No triplet state was observed for the dyads with nanosecond time-resolved transient absorption spectroscopy. Upon addition of acid, strong fluorescence and long-living triplet excited states were observed. Thus, the producing of triplet state is acid-activatable. The triplet state of RB-NI is localized on RB-o part, whereas in RB-NDI the triplet state is delocalized on both the NDI and RB-o units. The ISC of spin converter was not outcompeted by RET. These studies are useful for switching of triplet excited state.

  19. Characterizing the modulation transfer function (MTF) of proton/carbon radiography using Monte Carlo simulations.

    Science.gov (United States)

    Seco, Joao; Oumano, Michael; Depauw, Nicolas; Dias, Marta F; Teixeira, Rui P; Spadea, Maria F

    2013-09-01

    To characterize the modulation transfer function (MTF) of proton/carbon radiography using Monte Carlo simulations. To assess the spatial resolution of proton/carbon radiographic imaging. A phantom was specifically modeled with inserts composed of two materials with three different densities of bone and lung. The basic geometry of the phantom consists of cube-shaped inserts placed in water. The thickness of the water, the thickness of the cubes, the depth of the cubes in the water, and the particle beam energy have all been varied and studied. There were two phantom thicknesses considered 20 and 28 cm. This represents an average patient thickness and a thicker sized patient. Radiographs were produced for proton beams at 230 and 330 MeV and for a carbon ion beam at 400 MeV per nucleon. The contrast-to-noise ratio (CNR) was evaluated at the interface of two materials on the radiographs, i.e., lung-water and bone-water. The variation in CNR at interface between lung-water and bone-water were study, where a sigmoidal fit was performed between the lower and the higher CNR values. The full width half-maximum (FWHM) value was then obtained from the sigmoidal fit. Ultimately, spatial resolution was defined by the 10% point of the modulation-transfer-function (MTF10%), in units of line-pairs per mm (lp/mm). For the 20 cm thick phantom, the FWHM values varied between 0.5 and 0.7 mm at the lung-water and bone-water interfaces, for the proton beam energies of 230 and 330 MeV and the 400 MeV/n carbon beam. For the 28 cm thick phantom, the FWHM values varied between 0.5 and 1.2 mm at the lung-water and bone-water interface for the same inserts and beam energies. For the 20 cm phantom the MTF10% for lung-water interface is 2.3, 2.4, and 2.8 lp/mm, respectively, for 230, 330, and 400 MeV/n beams. For the same 20 cm thick phantom but for the bone-water interface the MTF10% yielded 1.9, 2.3, and 2.7 lp/mm, respectively, for 230, 330, and 400 MeV/n beams. In the case of the thicker 28

  20. Excited state carbene formation from UV irradiated diazomethane.

    Science.gov (United States)

    Lee, Hosik; Miyamoto, Yoshiyuki; Tateyama, Yoshitaka

    2009-01-16

    The laser flash photolysis process of diazomethane has been studied by using a real time propagation time-dependent density functional theory (RTP-TDDFT) combined with molecular dynamics. The activation energy barrier for disintegrating diazomethane into nitrogen (N(2)) and carbene (CH(2)) molecules significantly decreases in the electronic excited S(1) state compared to that in the S(0) ground state. Furthermore, the produced carbene molecule can be in the electronic excited state of (1)CH(2) ((1)B(1)) instead of the lowest state among singlet states (1)CH(2) ((1)A(1)), which is evident in the wave function characteristics of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) throughout the disintegration. This is regarded as the initial stage of the rearrangement in the excited state (RIES), the evidence of which has been given by experiments in the past decade. In the RIES mechanism scheme, we suggest that the photoreaction in the S(1) state contributes considerably to the photochemistry of carbene formation. The passing near the S(1)/S(0) conical intersection, which allows the transition to ground state diazomethane producing the lowest singlet state carbene molecule, is considered a rare event from our molecular dynamics, although this has been regarded as the dominant mechanism in previous theoretical studies.

  1. Calculations on the electronic excited states of ureas and oligoureas.

    Science.gov (United States)

    Oakley, Mark T; Guichard, Gilles; Hirst, Jonathan D

    2007-03-29

    We report CASPT2 calculations on the electronic excited states of several ureas. For monoureas, we find an electric dipole forbidden n --> pi* transition between 180 and 210 nm, dependent on the geometry and substituents of the urea. We find two intense pinb --> pi* transitions between 150 and 210 nm, which account for the absorptions seen in the experimental spectra. The n' --> pi* and pib --> pi* transitions are at wavelengths below 125 nm, which is below the lower limit of the experimental spectra. Parameter sets modeling the charge densities of the electronic transitions have been derived and permit calculations on larger oligoureas, using the exciton matrix method. For glycouril, a urea dimer, both the CASPT2 method and the matrix method yield similar results. Calculations of the electronic circular dichroism spectrum of an oligourea containing eight urea groups indicate that the experimental spectrum cannot be reproduced without the inclusion of electronic excitations involving the side chains. These calculations are one of the first attempts to understand the relationship between the structure and excited states of this class of macromolecule.

  2. Excited state mass spectra of singly charmed baryons

    Energy Technology Data Exchange (ETDEWEB)

    Shah, Zalak; Kumar Rai, Ajay [Sardar Vallabhbhai National Institute of Technology, Department of Applied Physics, Surat, Gujarat (India); Thakkar, Kaushal [GIDC Degree Engineering College, Department of Applied Sciences and Humanities, Abrama (India); Vinodkumar, P.C. [Sardar Patel University, Department of Physics, V.V. Nagar (India)

    2016-10-15

    Mass spectra of excited states of the singly charmed baryons are calculated using the hypercentral description of the three-body system. The baryons consist of a charm quark and light quarks (u, d and s) are studied in the framework of QCD motivated constituent quark model. The form of the confinement potential is hyper-Coloumb plus power potential with potential index ν, varying from 0.5 to 2.0. The first-order correction to the confinement potential is also incorporated in this approach. The radial as well as orbital excited state masses of Σ{sub c}{sup ++}, Σ{sub c}{sup +}, Σ{sub c}{sup 0}, Ξ{sub c}{sup +}, Ξ{sub c}{sup 0}, Λ{sub c}{sup +}, Ω{sub c}{sup 0} baryons, are reported in this paper. We have incorporated spin-spin, spin-orbit and tensor interactions perturbatively in the present study. The semi-electronic decay of Ω{sub c} and Ξ{sub c} are also calculated using the spectroscopic parameters of these baryons. The computed results are compared with other theoretical predictions as well as with the available experimental observations. We also construct the Regge trajectory in (n{sub r},M{sup 2}) and (J,M{sup 2}) planes for these baryons. (orig.)

  3. Chemical modulation of electronic structure at the excited state

    Science.gov (United States)

    Li, F.; Song, C.; Gu, Y. D.; Saleem, M. S.; Pan, F.

    2017-12-01

    Spin-polarized electronic structures are the cornerstone of spintronics, and have thus attracted a significant amount of interest; in particular, researchers are looking into how to modulate the electronic structure to enable multifunctional spintronics applications, especially in half-metallic systems. However, the control of the spin polarization has only been predicted in limited two-dimensional systems with spin-polarized Dirac structures and is difficult to achieve experimentally. Here, we report the modulation of the electronic structure in the light-induced excited state in a typical half-metal, L a1 /2S r1 /2Mn O3 -δ . According to the spin-transport measurements, there appears a light-induced increase in magnetoresistance due to the enhanced spin scattering, which is closely associated with the excited spin polarization. Strikingly, the light-induced variation can be enhanced via alcohol processing and reduced by oxygen annealing. X-ray photoelectron spectroscopy measurements show that in the chemical process, a redox reaction occurs with a change in the valence of Mn. Furthermore, first-principles calculations reveal that the change in the valence of Mn alters the electronic structure and consequently modulates the spin polarization in the excited state. Our findings thus report a chemically tunable electronic structure, demonstrating interesting physics and the potential for multifunctional applications and ultrafast spintronics.

  4. Proposed linear energy transfer areal detector for protons using radiochromic film

    Energy Technology Data Exchange (ETDEWEB)

    Mayer, Rulon [Henry M. Jackson Foundation for the Advancement of Military Medicine, Bethesda, Maryland 20817 (United States); Lin, Liyong; Fager, Marcus; Douglas, Dan; McDonough, James; Carabe, Alejandro [Department of Radiation Oncology, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania 19104 (United States)

    2015-04-15

    Radiation therapy depends on predictably and reliably delivering dose to tumors and sparing normal tissues. Protons with kinetic energy of a few hundred MeV can selectively deposit dose to deep seated tumors without an exit dose, unlike x-rays. The better dose distribution is attributed to a phenomenon known as the Bragg peak. The Bragg peak is due to relatively high energy deposition within a given distance or high Linear Energy Transfer (LET). In addition, biological response to radiation depends on the dose, dose rate, and localized energy deposition patterns or LET. At present, the LET can only be measured at a given fixed point and the LET spatial distribution can only be inferred from calculations. The goal of this study is to develop and test a method to measure LET over extended areas. Traditionally, radiochromic films are used to measure dose distribution but not for LET distribution. We report the first use of these films for measuring the spatial distribution of the LET deposited by protons. The radiochromic film sensitivity diminishes for large LET. A mathematical model correlating the film sensitivity and LET is presented to justify relating LET and radiochromic film relative sensitivity. Protons were directed parallel to radiochromic film sandwiched between solid water slabs. This study proposes the scaled-normalized difference (SND) between the Treatment Planning system (TPS) and measured dose as the metric describing the LET. The SND is correlated with a Monte Carlo (MC) calculation of the LET spatial distribution for a large range of SNDs. A polynomial fit between the SND and MC LET is generated for protons having a single range of 20 cm with narrow Bragg peak. Coefficients from these fitted polynomial fits were applied to measured proton dose distributions with a variety of ranges. An identical procedure was applied to the protons deposited from Spread Out Bragg Peak and modulated by 5 cm. Gamma analysis is a method for comparing the calculated

  5. A proton polarimeter for {sup 3}He(d,p){sup 4}He polarization transfer studies

    Energy Technology Data Exchange (ETDEWEB)

    Fletcher, K.A. E-mail: fletcher@geneseo.edu; Geist, W.H.; Brune, C.R.; Fisher, B.M.; Fitzgerald, R.P.; Karwowski, H.J.; Kruse, D.E.; Leonard, D.S.; Ludwig, E.J.; Runkle, R.C.; Veal, K.D.; Wood, M.H

    2000-12-11

    A compact polarimeter has been constructed and calibrated to measure the polarization of 13-16 MeV protons, such as those emitted from the {sup 3}He(d,p){sup 4}He reaction near the E{sub d}=430 keV resonance. The polarimeter uses p-{sup 4}He elastic scattering as an analyzer. It consists of a {sup 4}He gas cell pressurized to 2.76 MPa and a left-right pair of CsI detectors collimated at 65 deg. to maximize the figure of merit for the device. The effective analyzing power and efficiency of the polarimeter have been measured as a function of energy using a collimated polarized proton beam. These measured values are in good agreement with a Monte Carlo computer simulation that forms the basis for the calibration curve for the device. Preliminary results from the {sup 3}He(d,p){sup 4}He reaction with polarized deuterons confirm that the proton polarimeter can be used to determine polarization transfer coefficients near the low-energy resonance.

  6. First observation of ultrafast intramolecular proton transfer rate between electronic ground states in solution.

    Science.gov (United States)

    Masuda, Yuichi; Nakano, Tomoko; Sugiyama, Midori

    2012-05-10

    Despite the importance of ultrafast (time scale exceeding 10(-11) s) intramolecular proton transfer (PT) events between electronic ground states in solution, experimental determination of the rates of such reactions has not yet been accomplished because of the limitations of the utilized methods. The objective of this study was to evaluate the PT rates of intramolecular O···H···O hydrogen-bonded systems in solution through the (1)H spin-lattice relaxation times of the hydroxyl protons, induced by the (1)H-(17)O dipolar interactions (T(1dd)(OH)), taking into account the contribution of the OH reorientational motion to T(1dd)(OH). Solutions of the benzoic acid dimer (BA dimer), 1-benzoyl-6-hydroxy-6-phenylfulvene (Fulvene), and dibenzoylmethane (DBM) were chosen as test systems. For Fulvene in CCl(4), the PT time, τ(PT), was deduced to be 7 × 10(-11) s. In the case of the BA dimer in CCl(4), the τ(PT) value was considerably greater than the OH reorientational correlation time, τ(R(OH)) = 4.3 × 10(-11) s. In contrast, the experimental results for DBM in CCl(4) indicated that the proton is located about midway between the two oxygen atoms, that is, the PT potential energy surface is a single well or a double well with a PT barrier near or below the zero-point energy.

  7. Simulation and optimization of beam losses during continuous transfer extraction at the CERN Proton Synchrotron

    Science.gov (United States)

    Barranco García, Javier; Gilardoni, Simone

    2011-03-01

    The proton beams used for the fixed target physics at the Super Proton Synchrotron (SPS) are extracted from the Proton Synchrotron (PS) by a multiturn technique called continuous transfer (CT). During the CT extraction, large losses are observed in locations where the machine aperture should be large enough to accommodate the circulating beam. This limits the maximum intensity deliverable due to the induced stray radiation outside the PS tunnel. Scattered particles from the interaction with the electrostatic septum are identified as the possible source of these losses. This article presents a detailed study aiming to understand the origin of losses and propose possible cures. The simulations could reproduce accurately the beam loss pattern measured in real machine operation and determine the beam shaving, intrinsic to the extraction process, as the cause for the unexpected losses. Since these losses are unavoidable, the proposed solution implies a new optics scheme displacing the losses to a region with better shielding. New simulations demonstrate the satisfactory performance of the new extraction optics and its suitability to be implemented in the machine. Finally, beam loss measurements in these new operation conditions confirmed the previous simulation results.

  8. Catalytic role of calix[4]hydroquinone in acetone-water proton exchange: a quantum chemical study of proton transfer via keto-enol tautomerism.

    Science.gov (United States)

    Zakharov, M; Masunov, A E; Dreuw, A

    2008-10-16

    Calix[4]hydroquinone has recently attracted considerable interest since it forms stable tubular aggregates mediated solely by hydrogen bonding and pi-pi-stacking interactions. These aggregates trap specifically various small organic molecules and, in particular, catalyze the proton exchange of water with acetone. Using correlated quantum chemical methods, the mechanism of the observed proton exchange mediated by keto-enol tautomerism of acetone is investigated in detail. Starting with an investigation of keto-enol tautomerism of acetone-water clusters, it appears that four catalytic water molecules are optimal for the catalysis and that additional solvent water molecules lead to a decrease in efficiency. Analyses of the partial charges revealed a decrease of the polarization of the reactive hydrogen bonds due to the additional water molecules. As a next step, hydroquinone-acetone-water complexes were studied as models for the situation in the CHQ moieties. However, the computations revealed that the proton transfer reaction becomes less efficient when one catalytic water molecule is replaced by hydroquinone. Although concerted proton transfer via keto-enol tautomerism of acetone seems to be the predominant mechanism in supercritical water, it is no longer the rate-determining reaction mechanism for the catalyzed acetone-water proton exchange observed in tubular CHQ. Nevertheless, a key feature of the catalytic function of tubular CHQ has been identified to be the stiff hydrogen bonding network and the exclusion of additional solvent water molecules.

  9. Photoproduction of the rho^0 Meson on the Proton at Large Momentum Transfer

    Energy Technology Data Exchange (ETDEWEB)

    M. Battaglieri; E. Anciant; M. Anghinolfi; R. De Vita; E. Golovach; J. M. Laget; V. Mokeev; M. Ripani; G. Adams; M. J. Amaryan; D. S. Armstrong; B. Asavapibhop; G. Asryan; G. Audit; T. Auger; H. Avakian; S. Barrow; K. Beard; M. Bektasoglu; B. L. Berman; N. Bianchi; A. S. Biselli; S. Boiarinov; D. Branford; W. J. Briscoe; W. K. Brooks; V. D. Burkert; J. R. Calarco; G. P. Capitani; D. S. Carman; B. Carnahan; A. Cazes; C. Cetina; P. L. Cole; A. Coleman; D. Cords; P. Corvisiero; D. Crabb; H. Crannell; J. P. Cummings; E. DeSanctis; P. V. Degtyarenko; R. Demirchyan; H. Denizli; L. Dennis; K. V. Dharmawardane; K. S. Dhuga; C. Djalali; G. E. Dodge; D. Doughty; P. Dragovitsch; M. Dugger; S. Dytman; M. Eckhause; H. Egiyan; K. S. Egiyan; L. Elouadrhiri; L. Farhi; R. J. Feuerbach; J. Ficenec; T. A. Forest; A. P. Freyberger; V. Frolov; H. Funsten; S. J. Gaff; M. Gai; S. Gilad; G. P. Gilfoyle; K. L. Giovanetti; K. Griffioen; M. Guidal; M. Guillo; V. Gyurjyan; D. Hancock; J. Hardie; D. Heddle; F. W. Hersman; K. Hicks; R. S. Hicks; M. Holtrop; C. E. Hyde-Wright; M. M. Ito; K. Joo; J. H. Kelley; M. Khandaker; W. Kim; A. Klein; F. J. Klein; M. Klusman; M. Kossov; L. H. Kramer; Y. Kuang; S. E. Kuhn; D. Lawrence; M. Lucas; K. Lukashin; R. W. Major; J. J. Manak; C. Marchand; S. McAleer; J. McCarthy; J. W. C. McNabb; B. A. Mecking; M. D. Mestayer; C. A. Meyer; K. Mikhailov; R. Minehart; M. Mirazita; R. Miskimen; V. Muccifora; J. Mueller; G. S. Mutchler; J. Napolitano; S. O. Nelson; B. B. Niczyporuk; R. A. Niyazov; J. T. O' Brien; A. K. Opper; G. Peterson; S. A. Philips; N. Pivnyuk; D. Pocanic; O. Pogorelko; E. Polli; B. M. Preedom; J. W. Price; D. Protopopescu; L. M. Qin; B. A. Raue; A. R. Reolon; G. Riccardi; G. Ricco; B. G. Ritchie; F. Ronchetti; P. Rossi; D. Rowntree; P. D. Rubin; K. Sabourov; C. Salgado; M. Sanzone-Arenhovel; V. Sapunenko; R. A. Schumacher; V. S. Serov; A. Shafi; Y. G. Sharabian; J. Shaw; A. V. Skabelin; E. S. Smith; T. Smith; L. C. Smith; D. I. Sober; M. Spraker; A. Stavinsky; S. Stepanyan; P. Stoler; M. Taiuti; S. Taylor; D. J. Tedeschi; L. Todor; R. Thompson; M. F. Vineyard; A. V. Vlassov; L. B. Weinstein; A. Weisberg; H. Weller; D. P. Weygand; C. S. Whisnant; E. Wolin; M. Wood; A. Yegneswaran; J. Yun; B. Zhang; J. Zhao; Z. Zhou

    2001-10-01

    The differential cross section, d{sigma}/dt, for p0 meson photoproduction on the proton above the resonance region was measured up to a momentum transfer -t = 5 GeV2 using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The p0 channel was extracted from the measured two charged-pion cross sections by fitting the {pi}+{pi}- and p{pi}+ invariant masses. The low momentum transfer region shows the typical diffractive pattern expected from Reggeon exchange. The flatter behavior at large -t cannot be explained solely in terms of QCD-inspired two-gluon exchange models. The data indicate that other processes, like quark interchange, are important to fully describe p photoproduction.

  10. Electronic structures and population dynamics of excited states of xanthione and its derivatives

    Science.gov (United States)

    Fedunov, Roman G.; Rogozina, Marina V.; Khokhlova, Svetlana S.; Ivanov, Anatoly I.; Tikhomirov, Sergei A.; Bondarev, Stanislav L.; Raichenok, Tamara F.; Buganov, Oleg V.; Olkhovik, Vyacheslav K.; Vasilevskii, Dmitrii A.

    2017-09-01

    A new compound, 1,3-dimethoxy xanthione (DXT), has been synthesized and its absorption (stationary and transient) and luminescence spectra have been measured in n-hexane and compared with xanthione (XT) spectra. The pronounced broadening of xanthione vibronic absorption band related to the electronic transition to the second singlet excited state has been observed. Distinctions between the spectra of xanthione and its methoxy derivatives are discussed. Quantum chemical calculations of these compounds in the ground and excited electronic states have been accomplished to clarify the nature of electronic spectra changes due to modification of xanthione by methoxy groups. Appearance of a new absorption band of DXT caused by symmetry changes has been discussed. Calculations of the second excited state structure of xanthione and its methoxy derivatives confirm noticeable charge transfer (about 0.1 of the charge of an electron) from the methoxy group to thiocarbonyl group. Fitting of the transient spectra of XT and DXT has been fulfilled and the time constants of internal conversion S2 →S1 and intersystem crossing S1 →T1 have been determined. A considerable difference between the time constants of internal conversion S2 →S1 in XT and DXT is uncovered.

  11. Fermionic Basis in Conformal Field Theory and Thermodynamic Bethe Ansatz for Excited States

    Directory of Open Access Journals (Sweden)

    Hermann Boos

    2011-01-01

    Full Text Available We generalize the results of [Comm. Math. Phys. 299 (2010, 825-866] (hidden Grassmann structure IV to the case of excited states of the transfer matrix of the six-vertex model acting in the so-called Matsubara direction. We establish an equivalence between a scaling limit of the partition function of the six-vertex model on a cylinder with quasi-local operators inserted and special boundary conditions, corresponding to particle-hole excitations, on the one hand, and certain three-point correlation functions of conformal field theory (CFT on the other hand. As in hidden Grassmann structure IV, the fermionic basis developed in previous papers and its conformal limit are used for a description of the quasi-local operators. In paper IV we claimed that in the conformal limit the fermionic creation operators generate a basis equivalent to the basis of the descendant states in the conformal field theory modulo integrals of motion suggested by A. Zamolodchikov (1987. Here we argue that, in order to completely determine the transformation between the above fermionic basis and the basis of descendants in the CFT, we need to involve excitations. On the side of the lattice model we use the excited-state TBA approach. We consider in detail the case of the descendant at level 8.

  12. Direct simulation of proton-coupled electron transfer reaction dynamics and mechanisms

    Science.gov (United States)

    Kretchmer, Joshua S.; Miller, Thomas F., III

    2014-03-01

    Proton-coupled electron transfer (PCET) reactions, in which both an electron and an associated proton undergo reactive transfer, play an important role in many chemical and biological systems. Due to the complexity of this class of reactions, a variety of different mechanisms fall under the umbrella of PCET. However, the physical driving forces that determine the preferred mechanism in a given system still remain poorly understood. Towards this end, we extend ring polymer molecular dynamics (RPMD), a path-integral quantum dynamics method, to enable the direct simulation and characterization of PCET reaction dynamics in both fully atomistic and system-bath models of organometallic catalysts. In addition to providing validation for the simulation method via extensive comparison with existing PCET rate theories, we analyze the RPMD trajectories to investigate the competition between the concerted and sequential reaction mechanisms for PCET, elucidating the large role of the solvent in controlling the preferred mechanism. We further employ RPMD to determine the kinetics and mechanistic features of concerted PCET reactions across different regimes of electronic and vibrational coupling, providing evidence for a new and distinct PCET reaction mechanism.

  13. New Rh2(II,II) Complexes for Solar Energy Applications: Panchromatic Absorption and Excited-State Reactivity.

    Science.gov (United States)

    Whittemore, Tyler J; Sayre, Hannah J; Xue, Congcong; White, Travis A; Gallucci, Judith C; Turro, Claudia

    2017-10-18

    The new heteroleptic paddlewheel complexes cis-[Rh 2 (μ-form) 2 (μ-np) 2 ][BF 4 ] 2 , where form = p-ditolylformamidinate (DTolF) or p-difluorobenzylformamidinate (F-form) and np = 1,8-napthyridyine, and cis-Rh 2 (μ-form) 2 (μ-npCOO) 2 (npCOO - = 1,8-naphthyridine-2-carboxylate), were synthesized and characterized. The complexes absorb strongly throughout the ultraviolet (λ max = 300 nm, ε = 20 300 M -1 cm -1 ) and visible regions (λ max = 640 nm ε = 3500 M -1 cm -1 ), making them potentially useful new dyes with panchromatic light absorption for solar energy conversion applications. Ultrafast and nanosecond transient absorption and time-resolved infrared spectroscopies were used to characterize the identity and dynamics of the excited states, where singlet and triplet Rh 2 /form-to-naphthyridine, metal/ligand-to-ligand charge-transfer (ML-LCT) excited states were observed in all four complexes. The npCOO - complexes exhibit red-shifted absorption profiles extending into the near-IR and undergo photoinitiated electron transfer to generate reduced methyl viologen, a species that persists in the presence of a sacrificial donor. The energy of the triplet excited state of each complex was estimated from energy-transfer quenching experiments using a series of organic triplet donors (E( 3 ππ*) from 1.83 to 0.78 eV). The singlet reduction (+0.6 V vs Ag/AgCl) potentials, and singlet and triplet oxidation potentials (-1.1 and -0.5 V vs Ag/AgCl, respectively) were determined. Based on the excited-state lifetimes and redox properties, these complexes represent a new class of light absorbers with potential application as dyes for charge injection into semiconductor solar cells and in sensitizer-catalyst assemblies for photocatalysis that operate with irradiation from the ultraviolet to ∼800 nm.

  14. On the maximum charge state and proton transfer reactivity of peptide and protein ions formed by electrospray ionization.

    Science.gov (United States)

    Schnier, P D; Gross, D S; Williams, E R

    1995-11-01

    A relatively simple model for calculation of the energetics of gas-phase proton transfer reactions and the maximum charge state of multiply protonated ions formed by electrospray ionization is presented. This model is based on estimates of the intrinsic proton transfer reactivity of sites of protonation and point charge Coulomb interactions. From this model, apparent gas-phase basicities (GB(app)) of multiply protonated ions are calculated. Comparison of this value to the gas-phase basicity of the solvent from which an ion is formed enables a maximum charge state to be calculated. For 13 commonly electrosprayed proteins, our calculated maximum charge states are within an average of 6% of the experimental values reported in the literature. This indicates that the maximum charge state for proteins is determined by their gas-phase reactivity. Similar results are observed for peptides with many basic residues. For peptides with few basic residues, we find that the maximum charge state is better correlated to the charge state in solution. For low charge state ions, we find that the most basic sites Arg, Lys, and His are preferentially protonated. A significant fraction of the less basic residues Pro, Trp, and Gln are protonated in high charge state ions. The calculated GB(app) of individual protonation sites varies dramatically in the high charge state ions. From these values, we calculate a reduced cross section for proton transfer reactivity that is significantly lower than the Langevin collision frequency when the GB(app) of the ion is approximately equal to the GB of the neutral base.

  15. Vibrational kinetics of electronically excited states in H2 discharges

    Science.gov (United States)

    Colonna, Gianpiero; Pietanza, Lucia D.; D'Ammando, Giuliano; Celiberto, Roberto; Capitelli, Mario; Laricchiuta, Annarita

    2017-11-01

    The evolution of atmospheric pressure hydrogen plasma under the action of repetitively ns electrical pulse has been investigated using a 0D state-to-state kinetic model that self-consistently couples the master equation of heavy particles and the Boltzmann equation for free electrons. The kinetic model includes, together with atomic hydrogen states and the vibrational kinetics of H2 ground state, vibrational levels of singlet states, accounting for the collisional quenching, having a relevant role because of the high pressure. The mechanisms of excitations, radiative decay and collisional quenching involving the excited H2 states and the corresponding cross sections, integrated over the non-equilibrium electron energy distribution function (EEDF) to obtain kinetic rates, are discussed in the light of the kinetic simulation results, i.e. the time evolution during the pulse of the plasma composition, of the EEDF and of the vibrational distributions of ground and singlet excited states.

  16. Ultrafast excited state dynamics in 9,9'-bifluorenylidene.

    Science.gov (United States)

    Conyard, Jamie; Heisler, Ismael A; Browne, Wesley R; Feringa, Ben L; Amirjalayer, Saeed; Buma, Wybren Jan; Woutersen, Sander; Meech, Stephen R

    2014-08-07

    9,9'-Bifluorenylidene has been proposed as an alternative and flexible electron acceptor in organic photovoltaic cells. Here we characterize its excited state properties and photokinetics, combining ultrafast fluorescence and transient IR measurements with quantum chemical calculations. The fluorescence decay is ultrafast (sub-100 fs) and remarkably independent of viscosity. This suggests that large scale structure change is not the primary relaxation mode. The ultrafast decay populates a dark state characterized by distinct vibrational and electronic spectra. This state decays with a 6 ps time constant to a hot ground state that ultimately populates the initial state with a 20 ps time constant; these times are also insensitive to solvent viscosity. No metastable intermediate structures are resolved in the photocycle after population of the dark state. The implications of these results for the operation of 9,9'-bifluorenylidene as an electron acceptor and as a potential molecular switch are discussed.

  17. Excited state mass spectra and Regge trajectories of bottom baryons

    Science.gov (United States)

    Thakkar, Kaushal; Shah, Zalak; Rai, Ajay Kumar; C. Vinodkumar, P.

    2017-09-01

    We present the mass spectra of radial and orbital excited states of singly heavy bottom baryons; Σb+, Σb-, Ξb-, Ξb0, Λb0 and Ωb-. The QCD motivated hypercentral quark model is employed for the three body description of baryons and the form of confinement potential is hyper Coulomb plus linear. The first order correction to the confinement potential is also incorporated in this work. The semi-electronic decay of Ωb and Ξb are calculated using the spectroscopic parameters of the baryons. The computed results are compared with other theoretical predictions as well as with the available experimental observations. The Regge trajectories are plotted in (n ,M2) plane.

  18. Excited state mass spectra of doubly heavy Ξ baryons

    Energy Technology Data Exchange (ETDEWEB)

    Shah, Zalak; Rai, Ajay Kumar [Sardar Vallabhbhai National Institute of Technology, Department of Applied Physics, Surat, Gujarat (India)

    2017-02-15

    In this paper, the mass spectra are obtained for doubly heavy Ξ baryons, namely, Ξ{sub cc}{sup +}, Ξ{sub cc}{sup ++}, Ξ{sub bb}{sup -}, Ξ{sub bb}{sup 0}, Ξ{sub bc}{sup 0} and Ξ{sub bc}{sup +}. These baryons consist of two heavy quarks (cc, bb, and bc) with a light (d or u) quark. The ground, radial, and orbital states are calculated in the framework of the hypercentral constituent quark model with Coulomb plus linear potential. Our results are also compared with other predictions, thus, the average possible range of excited states masses of these Ξ baryons can be determined. The study of the Regge trajectories is performed in (n, M{sup 2}) and (J, M{sup 2}) planes and their slopes and intercepts are also determined. Lastly, the ground state magnetic moments of these doubly heavy baryons are also calculated. (orig.)

  19. Electronic excited states at ultrathin dielectric-metal interfaces

    Science.gov (United States)

    Sementa, L.; Marini, A.; Barcaro, G.; Negreiros, F. R.; Fortunelli, A.

    2013-09-01

    Electronic excited states at a bcc(110) lithium surface, both bare and covered by ionic ultrathin (1-2 monolayers) LiF epitaxial films, are investigated via many-body perturbation theory calculations achieving an atomistic level of detail. The full self-consistent solution of the GW equations is used to account for correlation effects and to properly describe the screened potential in the vacuum. In addition to the correct prediction of image-potential states, we find that the mixing between resonances and image states and the charge compression due to the dielectric ultrathin overlayer give rise to excitations with a hybrid localized but low-lying character whose accurate description cannot intrinsically be achieved via simple models or low-level calculations, but which are expected to play a crucial role in determining the electronic response and transport properties of these systems.

  20. Excited states using semistochastic heat-bath configuration interaction

    Science.gov (United States)

    Holmes, Adam A.; Umrigar, C. J.; Sharma, Sandeep

    2017-10-01

    We extend our recently developed heat-bath configuration interaction (HCI) algorithm, and our semistochastic algorithm for performing multireference perturbation theory, to calculate excited-state wavefunctions and energies. We employ time-reversal symmetry, which reduces the memory requirements by more than a factor of two. An extrapolation technique is introduced to reliably extrapolate HCI energies to the full CI limit. The resulting algorithm is used to compute fourteen low-lying potential energy surfaces of the carbon dimer using the cc-pV5Z basis set, with an estimated error in energy of 30-50 μHa compared to full CI. The excitation energies obtained using our algorithm have a mean absolute deviation of 0.02 eV compared to experimental values.

  1. Intramolecular Halogen Atom Coordinated H Transfer via Ion-Neutral Complex in the Gas Phase Dissociation of Protonated Dichlorvos Derivatives

    Science.gov (United States)

    Zhang, Xiaoping; Cheng, Shuai

    2017-10-01

    Intramolecular halogen atom coordinated H transfer reaction in the gas phase dissociation of protonated dichlorvos derivatives has been explored by electrospray ionization tandem mass spectrometry. Upon collisional activation, protonated dichlorvos underwent dissociation reaction via cleavage of the P-O bond to give reactive ion-neutral complex (INC) intermediate, [dimethoxylphosphinoylium + dichloroacetaldehyde]. Besides direct dissociation of the complex, intramolecular chlorine atom coordinated H transfer reaction within the complex takes place, leading to the formation of protonated dimethyl chlorophosphate. To investigate the fragmentation mechanism, deuterium-labeled experiments and several other halogen-substituted (Br and F) analogs of dichlorvos were prepared and evaluated, which display a similar intramolecular halogen transfer. Density functional theory (DFT)-based calculations were performed and the computational results also support the mechanism. [Figure not available: see fulltext.

  2. Twisting in the excited state of an N-methylpyridinium fluorescent dye modulated by nano-heterogeneous micellar systems.

    Science.gov (United States)

    Cesaretti, A; Carlotti, B; Gentili, P L; Germani, R; Spalletti, A; Elisei, F

    2016-04-01

    A push-pull N-methylpyridinium fluorescent dye with a pyrenyl group as the electron-donor portion was investigated within the nano-heterogeneous media provided by some micellar systems. The molecule was studied by stationary and time-resolved spectroscopic techniques in spherical micellar solutions and viscoelastic hydrogels, in order to throw light on the role played by twisting in its excited state deactivation. As proven by femtosecond fluorescence up-conversion and transient absorption experiments, the excited state dynamics of the molecule is ruled by charge transfer and twisting processes, which, from the locally excited (LE) state initially populated upon excitation, progressively lead to twisted (TICT) and planar (PICT) intramolecular charge transfer states. The inclusion within micellar aggregates was found to slow down and/or limit the rotation of the molecule with respect to what had previously been observed in water, while its confinement within the hydrophobic domains of the gel matrixes prevents any molecular torsion. The increasing viscosity of the medium, when passing from water to micellar systems, implies that the detected steady-state fluorescence comes from an excited state which is not fully relaxed, as is the case with the TICT state in micelles or the LE state in hydrogels, where the detected emission changes its usual orange colour to yellow.

  3. Theoretical analysis of co-solvent effect on the proton transfer reaction of glycine in a water-acetonitrile mixture.

    Science.gov (United States)

    Kasai, Yukako; Yoshida, Norio; Nakano, Haruyuki

    2015-05-28

    The co-solvent effect on the proton transfer reaction of glycine in a water-acetonitrile mixture was examined using the reference interaction-site model self-consistent field theory. The free energy profiles of the proton transfer reaction of glycine between the carboxyl oxygen and amino nitrogen were computed in a water-acetonitrile mixture solvent at various molar fractions. Two types of reactions, the intramolecular proton transfer and water-mediated proton transfer, were considered. In both types of the reactions, a similar tendency was observed. In the pure water solvent, the zwitterionic form, where the carboxyl oxygen is deprotonated while the amino nitrogen is protonated, is more stable than the neutral form. The reaction free energy is -10.6 kcal mol(-1). On the other hand, in the pure acetonitrile solvent, glycine takes only the neutral form. The reaction free energy from the neutral to zwitterionic form gradually increases with increasing acetonitrile concentration, and in an equally mixed solvent, the zwitterionic and neutral forms are almost isoenergetic, with a difference of only 0.3 kcal mol(-1). The free energy component analysis based on the thermodynamic cycle of the reaction also revealed that the free energy change of the neutral form is insensitive to the change of solvent environment but the zwitterionic form shows drastic changes. In particular, the excess chemical potential, one of the components of the solvation free energy, is dominant and contributes to the stabilization of the zwitterionic form.

  4. Reactivity of hydropersulfides toward the hydroxyl radical unraveled: disulfide bond cleavage, hydrogen atom transfer, and proton-coupled electron transfer.

    Science.gov (United States)

    Anglada, Josep M; Crehuet, Ramon; Adhikari, Sarju; Francisco, Joseph S; Xia, Yu

    2018-02-14

    Hydropersulfides (RSSH) are highly reactive as nucleophiles and hydrogen atom transfer reagents. These chemical properties are believed to be key for them to act as antioxidants in cells. The reaction involving the radical species and the disulfide bond (S-S) in RSSH, a known redox-active group, however, has been scarcely studied, resulting in an incomplete understanding of the chemical nature of RSSH. We have performed a high-level theoretical investigation on the reactions of the hydroxyl radical (˙OH) toward a set of RSSH (R = -H, -CH 3 , -NH 2 , -C(O)OH, -CN, and -NO 2 ). The results show that S-S cleavage and H-atom abstraction are the two competing channels. The electron inductive effect of R induces selective ˙OH substitution at one sulfur atom upon S-S cleavage, forming RSOH and ˙SH for the electron donating groups (EDGs), whereas producing HSOH and ˙SR for the electron withdrawing groups (EWGs). The H-Atom abstraction by ˙OH follows a classical hydrogen atom transfer (hat) mechanism, producing RSS˙ and H 2 O. Surprisingly, a proton-coupled electron transfer (pcet) process also occurs for R being an EDG. Although for RSSH having EWGs hat is the leading channel, S-S cleavage can be competitive or even dominant for the EDGs. The overall reactivity of RSSH toward ˙OH attack is greatly enhanced with the presence of an EDG, with CH 3 SSH being the most reactive species found in this study (overall rate constant: 4.55 × 10 12 M -1 s -1 ). Our results highlight the complexity in RSSH reaction chemistry, the extent of which is closely modulated by the inductive effect of the substituents in the case of the oxidation by hydroxyl radicals.

  5. Ultrafast excited state dynamics of tris-(2,2'-bipyridine) Ruthenium (II)

    Energy Technology Data Exchange (ETDEWEB)

    Yeh, Alvin T.W. [Univ. of California, Berkeley, CA (United States)

    2000-03-01

    Time resolved anisotropy measurements and time dependent transient absorption measurements are used to study the evolution of the photoexcited Franck-Condon state to the formation of the long-lived triplet metal-to-ligand charge-transfer (3MLCT) state in tris-(2,2’-bipyridine) ruthenium. [Ru(bpy)3]2+ represents a large class of inorganic compounds with interesting and potentially applicable photophysical properties. These compounds have generated much interest in the inorganic chemistry community because their photophysical properties are easily manipulated by synthetic chemistry methods. However, little remains known about the processes which govern the evolution horn initial photoexcitation to the formation of the long-lived excited state.

  6. Rotation around the glycosidic bond as driving force of proton transfer in protonated 2‧-deoxyriboadenosine monophosphate (dAMP)

    Science.gov (United States)

    Shishkin, Oleg V.; Dopieralski, Przemyslaw; Palamarchuk, Gennady V.; Latajka, Zdzislaw

    2010-04-01

    Theoretical investigation of the conformation of 2'-deoxyriboadenosine monophosphate protonated at the N7 atom and stabilized by a very strong C8-H⋯O-P hydrogen bond indicates that this hydrogen bond may be disrupted by rotation of the adenine moiety around the glycosidic bond. A B3LYP/aug-cc-pVDZ scan of the relaxed potential energy surface demonstrates that this rotation is a multi-stage process, accompanying proton transfer from the N7 atom of adenine to the oxygen atom of the phosphate group with a change of conformation of the nucleotide from south/anti to north/syn conformation. Car-Parrinello molecular dynamics simulation indicates that rotation around the glycosidic bond is the preferred way for relaxation of the molecular geometry of this conformer. Both processes, i.e. conformational transition and proton transfer, are strongly coupled. However, the conformer containing a strong C-H⋯O hydrogen bond also corresponds to a local minimum on the Gibbs free energy surface. A specific property of this hydrogen bond is the large variation of the H⋯O distance (ranging from 1.3 to 2.2 Å), which is not caused by proton movement between the carbon and oxygen atoms, but rather by relative motions of the adenine and phosphate moieties.

  7. Multidimensional treatment of stochastic solvent dynamics in photoinduced proton-coupled electron transfer processes: sequential, concerted, and complex branching mechanisms.

    Science.gov (United States)

    Soudackov, Alexander V; Hazra, Anirban; Hammes-Schiffer, Sharon

    2011-10-14

    A theoretical approach for the multidimensional treatment of photoinduced proton-coupled electron transfer (PCET) processes in solution is presented. This methodology is based on the multistate continuum theory with an arbitrary number of diabatic electronic states representing the relevant charge distributions in a general PCET system. The active electrons and transferring proton(s) are treated quantum mechanically, and the electron-proton vibronic free energy surfaces are represented as functions of multiple scalar solvent coordinates corresponding to the single electron and proton transfer reactions involved in the PCET process. A dynamical formulation of the dielectric continuum theory is used to derive a set of coupled generalized Langevin equations of motion describing the time evolution of these collective solvent coordinates. The parameters in the Langevin equations depend on the solvent properties, such as the dielectric constants, relaxation time, and molecular moment of inertia, as well as the solute properties. The dynamics of selected intramolecular nuclear coordinates, such as the proton donor-acceptor distance or a torsional angle within the PCET complex, may also be included in this formulation. A surface hopping method in conjunction with the Langevin equations of motion is used to simulate the nonadiabatic dynamics on the multidimensional electron-proton vibronic free energy surfaces following photoexcitation. This theoretical treatment enables the description of both sequential and concerted mechanisms, as well as more complex processes involving a combination of these mechanisms. The application of this methodology to a series of model systems corresponding to collinear and orthogonal PCET illustrates fundamental aspects of these different mechanisms and elucidates the significance of proton vibrational relaxation and nonequilibrium solvent dynamics. © 2011 American Institute of Physics

  8. Spectroscopic and excited-state properties of tri-9-anthrylborane I: Solvent polarity effects.

    Science.gov (United States)

    Kitamura, Noboru; Sakuda, Eri

    2005-08-25

    Spectroscopic and excited-state properties of tri-9-anthrylborane (TAB), showing unique absorption and fluorescence characteristics originating from p(boron)-pi(anthryl group) orbital interactions, were studied in 12 solvents. Although the absorption maximum energy (nu(a)) of TAB which appeared at around 21 x 10(3) cm(-1) (band I) was almost independent of the solvent polarity parameter, f(X) (f(X) = (D(s) - 1)/(2D(s) + 1) - (n(2) - 1)/(2n(2) + 1) where D(s) and n represent the static dielectric constant and the refractive index of a solvent, respectively), the fluorescence maximum energy (nu(f)) showed a linear correlation with f(X). The f(X) dependence of the value of nu(a) - nu(f) demonstrated that the change in the dipole moment of TAB upon light excitation was approximately 8.0 D, indicating that absorption band I was ascribed to an intramolecular charge-transfer transition in nature. The excited electron of TAB was thus concluded to localize primarily on the p orbital of the boron atom. Furthermore, it was shown that the fluorescence lifetime and quantum yield of TAB varied from 11.8 to 1.1 ns and from 0.41 to 0.02, respectively, with an increase in f(X). The present results indicated that the nonradiative decay rate constant (k(nr)) of TAB was influenced significantly by f(X). Excited-state decay of TAB was understood by intramolecular back-electron (charge) transfer from the p orbital of the boron atom to the pi orbital of the anthryl group, which was discussed in terms of the energy gap dependence of k(nr). Specific solvent interactions of TAB revealed by the present spectroscopic and photophysical studies are also discussed.

  9. Proton-coupled electron transfer promotes the reduction of ferrylmyoglobin by uric acid under physiological conditions

    DEFF Research Database (Denmark)

    de Zawadzki, Andressa; Cardoso, Daniel R.; Skibsted, Leif Horsfelt

    2017-01-01

    The hypervalent muscle pigment ferrylmyoglobin, MbFe(IV)]O, is not reduced by urate monoanions at physiological conditions despite a strong driving force of around 30 kJ mol1 while for low pH, uric acid was found to reduce protonated ferrylmyoglobin, MbFe(IV)]O,H+, efficiently in a bimolecular...... reaction with k1 ¼ 1.1 0.1 103 L mol1 s1, DH‡ ¼ 66.1 0.1 kJ mol1 and DS‡ ¼ 35.2 0.2 J mol1 K1. For intermediate pH, like for anaerobic muscles and for meat, proton-oupled electron transfer occurs in a transition state, {MbFe(IV)]O/H+/urate}‡, which is concluded to be formed from uric acid and Mb......Fe(IV)]O rather than from urate and MbFe(IV)]O,H+ with k3 ¼ 9.7 0.6 102 L mol1 s1, DH‡ ¼ 59.2 0.1 kJ mol1 and DS‡ ¼ 11.5 0.3 J mol1 K1. The activation parameters as calculated from the temperature dependence of the pH-reduction profile in aqueous 0.067 mol L1 NaCl (from 25 C up to 40 C), support a mechanism...

  10. Keto-enol tautomerization and intermolecular proton transfer in photoionized cyclopentanone dimer in the gas phase

    Energy Technology Data Exchange (ETDEWEB)

    Ghosh, Arup K.; Chatterjee, Piyali; Chakraborty, Tapas, E-mail: pctc@iacs.res.in [Department of Physical Chemistry, Indian Association for the Cultivation of Science, 2A Raja S. C. Mullick Road, Jadavpur, Kolkata 700032 (India)

    2014-07-28

    Time-of-flight mass spectra of cyclopentanone and its clusters cooled in a supersonic jet expansion have been measured following 4-, 3-, and 2-photon ionizations by the 2nd, 3rd, and 4th harmonic wavelengths, respectively, of a Q-switched Nd:YAG laser. The mass spectra reveal signatures of energetically favored keto to enol tautomerization of the molecular ion leading to intermolecular proton transfer, and this observation is found sharply dependent on the ionization wavelengths used. Electronic structure calculation predicts that in spite of the energetic preference, keto-enol conversion barrier of isolated molecular ion is high. However, the barrier is significantly reduced in a CH⋯O hydrogen-bonded dimer of the molecule. The transition states associated with tautomeric conversion of both cyclopentanone monomer and dimer cations have been identified by means of intrinsic reaction co-ordinate calculation. In a supersonic jet expansion, although a weakly bound dimer is readily generated, the corresponding cation and also the protonated counterpart are observed only for ionization by 532 nm. For other two ionization wavelengths, these species do not register in the mass spectra, where the competing reaction channels via α-cleavage of the ring become dominant. In contrast to the report of a recent study, we notice that the intact molecular ion largely survives fragmentations when ionized from the 2-photon resonant 3p Rydberg state as intermediate using nanosecond laser pulses, and the corresponding resonant 3-photon ionization spectrum has been recorded probing the intact molecular ion.

  11. The “Autothixotropic” Phenomenon of Water and its Role in Proton Transfer

    Directory of Open Access Journals (Sweden)

    Peter Bukovec

    2011-10-01

    Full Text Available In an experimental study, significantly higher conductivity values than those of freshly prepared chemically analogous solutions were found in aged (~one year old aqueous solutions, except for those stored frozen. The results surprisingly resemble a previously noticed phenomenon in liquid water, which develops when water is stored in closed vessels. This was observed as a disturbing phenomenon in gravimetric measurements and in luminescence spectroscopy measurements. The phenomenon was termed “autothixotropy of water” due to the weak gel-like behavior which develops spontaneously over time, in which ions seem to play an important role. Here, according to experimental results we propose that contact with hydrophilic surfaces also plays an important role. The role of the “autothixotropy of water” in proton transfer is also discussed.

  12. Kinematically complete investigation of momentum transfer for single ionization in fast proton-helium collisions

    Energy Technology Data Exchange (ETDEWEB)

    Weber, T.; Mergel, V.; Jagutzki, O.; Schmidt, L.; Afaneh, F.; Schmidt-Boecking, H. [Institut fuer Kernphysik, August-Euler-Strasse 6, 60486 Frankfurt am Main (Germany); Khayyat, K. [Department of Physics, University of Missouri, Rolla, MO (United States); Doerner, R. [Fakultaet fuer Physik, Universitaet Freiburg (Germany); Gonzalez, A. [Centro Atomico Bariloche, 8400 S C de Bariloche (Argentina); Cocke, C.L. [Department of Physics, Kansas State University, Manhatten, KS (United States); Landers, A.L. [Department of Physics, Western Michigan University, Kalamazoo, MI (United States)

    2000-09-14

    The dynamics of singly ionizing proton-helium collisions have been studied experimentally for several energies of the projectile (0.2, 0.5, 1.0 and 1.3 MeV) with the technique of cold target recoil-ion momentum spectroscopy (COLTRIMS). The complete final-state distribution in momentum space of all three particles was determined by measuring the three momentum components of the emitted electron and the coincident recoiling target ion. The momentum transfer and energy loss of the outgoing projectile was determined by momentum and energy conservation laws. Doubly differential cross sections of the kinematically complete experimental investigation are presented. The present data are compared with results from fast highly charged heavy-ion impact experiments. (author)

  13. Probing water micro-solvation in proteins by water catalysed proton-transfer tautomerism.

    Science.gov (United States)

    Shen, Jiun-Yi; Chao, Wei-Chih; Liu, Chun; Pan, Hsiao-An; Yang, Hsiao-Ching; Chen, Chi-Lin; Lan, Yi-Kang; Lin, Li-Ju; Wang, Jinn-Shyan; Lu, Jyh-Feng; Chun-Wei Chou, Steven; Tang, Kuo-Chun; Chou, Pi-Tai

    2013-01-01

    Scientists have made tremendous efforts to gain understanding of the water molecules in proteins via indirect measurements such as molecular dynamic simulation and/or probing the polarity of the local environment. Here we present a tryptophan analogue that exhibits remarkable water catalysed proton-transfer properties. The resulting multiple emissions provide unique fingerprints that can be exploited for direct sensing of a site-specific water environment in a protein without disrupting its native structure. Replacing tryptophan with the newly developed tryptophan analogue we sense different water environments surrounding the five tryptophans in human thromboxane A₂ synthase. This development may lead to future research to probe how water molecules affect the folding, structures and activities of proteins.

  14. Formaldehyde measurements by Proton transfer reaction – Mass Spectrometry (PTR-MS: correction for humidity effects

    Directory of Open Access Journals (Sweden)

    A. Vlasenko

    2010-08-01

    Full Text Available Formaldehyde measurements can provide useful information about photochemical activity in ambient air, given that HCHO is formed via numerous oxidation processes. Proton transfer reaction mass spectrometry (PTR-MS is an online technique that allows measurement of VOCs at the sub-ppbv level with good time resolution. PTR-MS quantification of HCHO is hampered by the humidity dependence of the instrument sensitivity, with higher humidity leading to loss of PTR-MS signal. In this study we present an analytical, first principles approach to correct the PTR-MS HCHO signal according to the concentration of water vapor in sampled air. The results of the correction are validated by comparison of the PTR-MS results to those from a Hantzsch fluorescence monitor which does not have the same humidity dependence. Results are presented for an intercomparison made during a field campaign in rural Ontario at Environment Canada's Centre for Atmospheric Research Experiments.

  15. Proton transfer bis-benzazole fluors and their use in scintillator detectors

    Science.gov (United States)

    Kauffman, J.M.

    1994-03-29

    A novel class of proton transfer, bis-benzazole, fluorescent compounds, i.e., fluors, is disclosed. The novel fluors include substituted or unsubstituted 1,4-bis(2-benzazolyl)-2-hydroxybenzenes and 1,4-bis(2-benzazolyl)-2-amidobenzenes wherein the benzazolyl group may be benzoxazolyl, benzimidazolyl, benzothiazolyl, and the like. The benzazolyl groups may be substituted with one or more alkyl groups to improve solubility in organic matrix materials such as solvents, monomers, resins, polymers, and the like. The novel fluors may be used in the manufacture of fluorescent coatings, objects, scintillators, light sources and the like. The novel fluors are particularly useful for radiation-hard, solid scintillators for the detection and measurement of high energy particles and radiation.

  16. Reaction Coordinate, Free Energy and Rate of Intramolecular Proton Transfer in Human Carbonic Anhydrase II.

    Science.gov (United States)

    Paul, Sanjib; Paul, Tanmoy Kumar; Taraphder, Srabani

    2018-02-21

    The role of structure and dynamics of an enzyme has been investigated at three different stages of its function including the chemical event it catalyzes. A one-pot computational method has been designed for each of these stages based on classical and/or QM-MM molecular dynamics and transition path sampling simulations. For a pair of initial and final states A and B separated by a high free energy barrier, using a two-stage selection process, several collective variables (CVs) are identified that can delineate A and B. However, these CVs are found to exhibit strong cross-coupling over the transition paths. A set of mutually orthogonal order parameters is then derived from these CVs and an optimal reaction coordinate, r determined applying half trajectory likelihood maximization along with a Bayesian information criterion. The transition paths are also used to project the multi-dimensional free energy surface and barrier crossing dynamics along r. The proposed scheme has been applied to the rate determining intramolecular proton transfer reaction of the well known enzyme human carbonic anhydrase II (HCA II). The potential-of-mean force, F(r) in the absence of the chemical step is found to reproduce earlier results on the equilibrium population of two sidechain orientations of the key residue His-64. Estimation of rate constants, k from mean first passage times for the three different stages of catalysis shows that the rate determining step of intramolecular proton transfer occurs with k ≃ 1.0 X 10 6 sec -1 , in close agreement with known experimental results.

  17. Humidity independent mass spectrometry for gas phase chemical analysis via ambient proton transfer reaction

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Hongying; Huang, Guangming, E-mail: gmhuang@ustc.edu.cn

    2015-03-31

    Graphical abstract: Direct and humidity independent mass spectrometry analysis of gas phase chemicals could be achieved via ambient proton transfer ionization, ion intensity was found to be stable with humidity ranged from ∼10% to ∼100%. - Highlights: • A humidity independent mass spectrometric method for gas phase samples analysis. • A universal and good sensitivity method. • The method can real time identify plant released raw chemicals. - Abstract: In this work, a humidity independent mass spectrometric method was developed for rapid analysis of gas phase chemicals. This method is based upon ambient proton transfer reaction between gas phase chemicals and charged water droplets, in a reaction chamber with nearly saturate humidity under atmospheric pressure. The humidity independent nature enables direct and rapid analysis of raw gas phase samples, avoiding time- and sample-consuming sample pretreatments in conventional mass spectrometry methods to control sample humidity. Acetone, benzene, toluene, ethylbenzene and meta-xylene were used to evaluate the analytical performance of present method. The limits of detection for benzene, toluene, ethylbenzene and meta-xylene are in the range of ∼0.1 to ∼0.3 ppbV; that of benzene is well below the present European Union permissible exposure limit for benzene vapor (5 μg m{sup −3}, ∼1.44 ppbV), with linear ranges of approximately two orders of magnitude. The majority of the homemade device contains a stainless steel tube as reaction chamber and an ultrasonic humidifier as the source of charged water droplets, which makes this cheap device easy to assemble and facile to operate. In addition, potential application of this method was illustrated by the real time identification of raw gas phase chemicals released from plants at different physiological stages.

  18. Proton-transfer reaction dynamics and energetics in calcification and decalcification.

    Science.gov (United States)

    Suwa, Ryota; Hatta, Masayuki; Ichikawa, Kazuhiko

    2014-10-13

    CaCO3 -saturated saline waters at pH values below 8.5 are characterized by two stationary equilibrium states: reversible chemical calcification/decalcification associated with acid dissociation, Ca(2+) +HCO3 (-) ⇌CaCO3 +H(+) ; and reversible static physical precipitation/dissolution, Ca(2+) +CO3 (2-) ⇌CaCO3 . The former reversible reaction was determined using a strong base and acid titration. The saturation state described by the pH/PCO2 -independent solubility product, [Ca(2+) ][CO3 (2-) ], may not be observed at pH below 8.5 because [Ca(2+) ][CO3 (2-) ]/([Ca(2+) ][HCO3 (-) ]) ≪1. Since proton transfer dynamics controls all reversible acid dissociation reactions in saline waters, the concentrations of calcium ion and dissolved inorganic carbon (DIC) were expressed as a function of dual variables, pH and PCO2 . The negative impact of ocean acidification on marine calcifying organisms was confirmed by applying the experimental culture data of each PCO2 /pH-dependent coral polyp skeleton weight (Wskel) to the proton transfer idea. The skeleton formation of each coral polyp was performed in microspaces beneath its aboral ectoderm. This resulted in a decalcification of 14 weight %, a normalized CaCO3 saturation state Λ of 1.3 at PCO2 ≈400 ppm and pH ≈8.0, and serious decalcification of 45 % and Λ 2.5 at PCO2 ≈1000 ppm and pH ≈7.8. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Using Diffusion Monte Carlo to Probe Rotational Excited States

    Science.gov (United States)

    Petit, Andrew S.; McCoy, Anne B.

    2009-06-01

    Since its inception in 1975 by Anderson, has been successfully applied to a wide range of electronic and vibrational problems. In the latter case, it has been shown to be a powerful method for studying highly fluxional systems exhibiting large amplitude vibrational motions. We report here our recent work developing a new DMC algorithm capable of treating rotational excited states. We first develop the appropriate coordinates, nodal structures, and re-crossing corrections for this problem. Then, using H_3O^+ and D_3O^+ as model systems, we show that our method can successfully describe a range of rotational states from mid0,0,0> to {1}/{√{2}} (mid10,10,0 > + mid 10,-10,0 >). In particular, we examine the combined effects of rotational and zero-point vibrational motion on the geometric structure of the molecules. Finally, we find the mid 10,0,0 > state to be somewhat problematic but show that the problem is straightforward to identify and has a well-defined solution. J. B. Anderson, J. Chem. Phys., 63, 1499 (1975). X. Huang, S. Carter, and J. Bowman, J. Chem. Phys., 118, 5431 (2003).

  20. Amide proton transfer imaging in clinics: Basic concepts and current and future use in brain tumors and stoke

    Energy Technology Data Exchange (ETDEWEB)

    Park, Ji Eun [Dept. of Radiology and Research Institute of Radiology, University of Ulsan College of Medicine, Asan Medical Center, Seoul (Korea, Republic of); Jahng, Geon Ho [Dept. of Radiology, Kyung Hee University Hospital at Gangdong, College of Medicine, Kyung Hee University, Seoul (Korea, Republic of); Jeong, Ha Kyu [Philips Korea, Seoul (Korea, Republic of)

    2016-12-15

    Amide proton transfer (APT) imaging is gaining attention as a relatively new in vivo molecular imaging technique that has higher sensitivity and spatial resolution than magnetic resonance spectroscopy imaging. APT imaging is a subset of the chemical exchange saturation transfer mechanism, which can offer unique image contrast by selectively saturating protons in target molecules that get exchanged with protons in bulk water. In this review, we describe the basic concepts of APT imaging, particularly with regard to the benefit in clinics from the current literature. Clinical applications of APT imaging are described from two perspectives: in the diagnosis and monitoring of the treatment response in brain glioma by reflecting endogenous mobile proteins and peptides, and in the potential for stroke imaging with respect to tissue acidity.

  1. Detection of trace gases from fermentation processes using photoacoustic spectroscopy and proton-transfer-reaction mass spectrometry

    NARCIS (Netherlands)

    Boamfă-Ivan, Elena Iuliana

    2005-01-01

    This thesis presents novel interdisciplinary Physics - Biology research work that employed Photoacoustic Spectroscopy and Proton-Transfer-Reaction Mass Spectrometry. Both techniques were used in biological studies of trace gasses emitted by crop plants and fruit under stress situations. The findings

  2. Intermolecular Proton Transfer in Microhydrated Guanine-Cytosine Base Pairs: a New Mechanism for Spontaneous Mutation in DNA

    Science.gov (United States)

    Cerón-Carrasco, J. P.; Requena, A.; Zúñiga, J.; Michaux, C.; Perpête, E. A.; Jacquemin, D.

    2009-09-01

    Accurate calculations of the double proton transfer (DPT) in the adenine-thymine base pair (AT) were presented in a previous work [ J. Phys. Chem. A 2009, 113, 7892. ] where we demonstrated that the mechanism of the reaction in solution is strongly affected by surrounding water. Here we extend our methodology to the guanine-cytosine base pair (GC), for which it turns out that the proton transfer in the gas phase is a synchronous concerted mechanism. The O(G)-H-N(C) hydrogen bond strength emerges as the key parameter in this process, to the extent that complete transfer takes place by means of this hydrogen bond. Since the main effect of the molecular environment is precisely to weaken this bond, the direct proton transfer is not possible in solution, and thus the tautomeric equilibrium must be assisted by surrounding water molecules in an asynchronous concerted mechanism. This result demonstrates that water plays a crucial role in proton reactions. It does not act as a passive element but actually catalyzes the DPT.

  3. Geographical provenancing of purple grape juices from different farming systems by proton transfer reaction mass spectrometry using supervised statistical techniques

    NARCIS (Netherlands)

    Granato, Daniel; Koot, Alex; Ruth, van S.M.

    2015-01-01

    BACKGROUND: Organic, biodynamic and conventional purple grape juices (PGJ; n = 79) produced in Brazil and Europe were characterized by volatile organic compounds (m/z 20-160) measured by proton transfer reaction mass spectrometry (PTR-MS), and classification models were built using supervised

  4. Hydrogen Bond Switching among Flavin and Amino Acids Determines the Nature of Proton-Coupled Electron Transfer in BLUF Photoreceptors

    NARCIS (Netherlands)

    Mathes, T.; Zhu, J.; van Stokkum, I.H.M.; Groot, M.L.; Hegemann, P.; Kennis, J.T.M.

    2012-01-01

    BLUF domains are flavin-binding photoreceptors that can be reversibly switched from a dark-adapted state to a light-adapted state. Proton-coupled electron transfer (PCET) from a conserved tyrosine to the flavin that results in a neutral flavin semiquinone/tyrosyl radical pair constitutes the

  5. In vitro and in vivo volatile flavour analysis of red kidney beans by proton transfer reaction-mass spectrometry

    NARCIS (Netherlands)

    Ruth, van S.M.; Dings, L.; Buhr, K.; Posthumus, M.A.

    2004-01-01

    The volatile flavour released from red kidney beans was evaluated in vitro (in a model mouth system) and in vivo (in-nose). The dynamic release of the volatile flavour compounds was analysed by proton transfer reaction¿mass spectrometry. The flavour compounds were identified by gas

  6. Online monitoring of air quality at the postanesthetic care unit by proton-transfer-reaction mass spectrometry

    NARCIS (Netherlands)

    Rieder, J.; Prazeller, P.; Boehler, M.; Lirk, P.; Lindinger, W.; Amann, A.

    2001-01-01

    The subthreshold exposure to trace anesthetic gases is not associated with considerable risk of adverse health effects. Online control of ambient air exchange at the postoperative workplace may help in supervising air quality and lead to cost reduction. A proton-transfer-reaction mass spectrometer

  7. Interference through the resonant Auger process via multiple core-excited states

    Science.gov (United States)

    Chatterjee, Souvik; Nakajima, Takashi

    2017-12-01

    We theoretically investigate the resonant Auger process via multiple core-excited states. The presence of multiple core-excited states sets off interference into the common final continuum, and we show that the degree of interference depends on the various parameters such as the intensity of the employed x-ray pulse and the lifetimes of the core-excited states. For the specific examples we employ the double (1 s-13 p and 1 s-14 p ) core-excited states of Ne atom and numerically solve the time-dependent Schrödinger equation to demonstrate that the energy-resolved electron spectra clearly exhibit the signature of interference.

  8. Combined quantum-mechanical molecular mechanics calculations with NWChem and AMBER: Excited state properties of green fluorescent protein chromophore analogue in aqueous solution.

    Science.gov (United States)

    Pirojsirikul, Teerapong; Götz, Andreas W; Weare, John; Walker, Ross C; Kowalski, Karol; Valiev, Marat

    2017-07-05

    Combined quantum mechanical molecular mechanics (QM/MM) calculations have become a popular methodology for efficient and accurate description of large molecular systems. In this work we introduce our development of a QM/MM framework based on two well-known codes-NWChem and AMBER. As an initial application area we are focused on excited state properties of small molecules in an aqueous phase using an analogue of the green fluorescent protein (GFP) chromophore as a particular test case. Our approach incorporates high level coupled cluster theory for the analysis of excited states providing a reliable theoretical analysis of effects of an aqueous solvation environment on the photochemical properties of the GFP chromophore. Using a systematic approach, which involves comparison of gas phase and aqueous phase results for different protonation states and conformations, we resolve existing uncertainties regarding the theoretical interpretation of experimental data. We observe that the impact of aqueous environment on charged states generally results in blue shifts of the absorption spectra, but the magnitude of the effect is sensitive to both protonation state and conformation and can be rationalized based on charge movement into the area of higher/lower external electrostatic potentials. At neutral pH levels the experimentally observed absorption signal is most likely coming from the phenol protonated form. Our results also show that the high level electron correlated method is essential for a proper description of excited states of GFP. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  9. A semiempirical study for the ground and excited states of free-base and zinc porphyrin-fullerene dyads

    Science.gov (United States)

    Parusel, A. B.

    2000-01-01

    The ground and excited states of a covalently linked porphyrin-fullerene dyad in both its free-base and zinc forms (D. Kuciauskas et al., J. Phys. Chem. 100 (1996) 15926) have been investigated by semiempirical methods. The excited-state properties are discussed by investigation of the character of the molecular orbitals. All frontier MOs are mainly localized on either the donor or the acceptor subunit. Thus, the absorption spectra of both systems are best described as the sum of the spectra of the single components. The experimentally observed spectra are well reproduced by the theoretical computations. Both molecules undergo efficient electron transfer in polar but not in apolar solvents. This experimental finding is explained theoretically by explicitly considering solvent effects. The tenth excited state in the gas phase is of charge-separated character where an electron is transferred from the porphyrin donor to the fullerene acceptor subunit. This state is stabilized in energy in polar solvents due to its large formal dipole moment. The stabilization energy for an apolar environment such as benzene is not sufficient to lower this state to become the first excited singlet state. Thus, no electron transfer is observed, in agreement with experiment. In a polar environment such as acetonitrile, the charge-separated state becomes the S, state and electron transfer takes place, as observed experimentally. The flexible single bond connecting both the donor and acceptor subunits allows free rotation by ca. +/- 30 degrees about the optimized ground-state conformation. For the charge-separated state this optimized geometry has a maximum dipole moment. The geometry of the charge-separated state thus does not change relatively to the ground-state conformation. The electron-donating properties of porphyrin are enhanced in the zinc derivative due to a reduced porphyrin HOMO-LUMO energy gap. This yields a lower energy for the charge-separated state compared to the free

  10. Tyrosine oxidation in heme oxygenase: examination of long-range proton-coupled electron transfer.

    Science.gov (United States)

    Smirnov, Valeriy V; Roth, Justine P

    2014-10-01

    Heme oxygenase is responsible for the degradation of a histidine-ligated ferric protoporphyrin IX (Por) to biliverdin, CO, and the free ferrous ion. Described here are studies of tyrosyl radical formation reactions that occur after oxidizing Fe(III)(Por) to Fe(IV)=O(Por(·+)) in human heme oxygenase isoform-1 (hHO-1) and the structurally homologous protein from Corynebacterium diphtheriae (cdHO). Site-directed mutagenesis on hHO-1 probes the reduction of Fe(IV)=O(Por(·+)) by tyrosine residues within 11 Å of the prosthetic group. In hHO-1, Y58· is implicated as the most likely site of oxidation, based on the pH and pD dependent kinetics. The absence of solvent deuterium isotope effects in basic solutions of hHO-1 and cdHO contrasts with the behavior of these proteins in the acidic solution, suggesting that long-range proton-coupled electron transfer predominates over electron transfer.

  11. Characterizing amide proton transfer imaging in haemorrhage brain lesions using 3T MRI

    Energy Technology Data Exchange (ETDEWEB)

    Jeong, Ha-Kyu [Philips Korea, Seoul (Korea, Republic of); Korea Basic Science Institute, Chungcheongbuk-do (Korea, Republic of); Han, Kyunghwa [Yonsei University College of Medicine, Department of Radiology and Research Institute of Radiological Science, Seodaemun-gu, Seoul (Korea, Republic of); Yonsei University College of Medicine, Yonsei Biomedical Research Institute, Seoul (Korea, Republic of); Zhou, Jinyuan [Johns Hopkins University School of Medicine, Division of MRI Research, Department of Radiology, Baltimore, MD (United States); Zhao, Yansong [Philips Healthcare, MR Clinical Science, Cleveland, OH (United States); Choi, Yoon Seong; Lee, Seung-Koo; Ahn, Sung Soo [Yonsei University College of Medicine, Department of Radiology and Research Institute of Radiological Science, Seodaemun-gu, Seoul (Korea, Republic of)

    2017-04-15

    The aim of this study was to characterize amide proton transfer (APT)-weighted signals in acute and subacute haemorrhage brain lesions of various underlying aetiologies. Twenty-three patients with symptomatic haemorrhage brain lesions including tumorous (n = 16) and non-tumorous lesions (n = 7) were evaluated. APT imaging was performed and analyzed with magnetization transfer ratio asymmetry (MTR{sub asym}). Regions of interest were defined as the enhancing portion (when present), acute or subacute haemorrhage, and normal-appearing white matter based on anatomical MRI. MTR{sub asym} values were compared among groups and components using a linear mixed model. MTR{sub asym} values were 3.68 % in acute haemorrhage, 1.6 % in subacute haemorrhage, 2.65 % in the enhancing portion, and 0.38 % in normal white matter. According to the linear mixed model, the distribution of MTR{sub asym} values among components was not significantly different between tumour and non-tumour groups. MTR{sub asym} in acute haemorrhage was significantly higher than those in the other regions regardless of underlying pathology. Acute haemorrhages showed high MTR{sub asym} regardless of the underlying pathology, whereas subacute haemorrhages showed lower MTR{sub asym} than acute haemorrhages. These results can aid in the interpretation of APT imaging in haemorrhage brain lesions. (orig.)

  12. Reply to the 'Comment on "Proton transport in barium stannate: classical, semi-classical and quantum regime"'.

    Science.gov (United States)

    Geneste, Grégory; Hermet, Jessica; Dezanneau, Guilhem

    2017-08-09

    We respond to the erroneous criticisms about our modeling of proton transport in barium stannate [G. Geneste et al., Phys. Chem. Chem. Phys., 2015, 17, 19104]. In this previous work, we described, on the basis of density-functional calculations, proton transport in the classical and semi-classical regimes, and provided arguments in favor of an adiabatic picture for proton transfer at low temperature. We re-explain here our article (with more detail and precision), the content of which has been distorted in the Comment, and reiterate our arguments in this reply. We refute all criticisms. They are completely wrong in the context of our article. Even though a few of them are based on considerations probably true in some metals, they make no sense here since they do not correspond to the content of our work. It has not been understood in the Comment that two competitive configurations, associated with radically different transfer mechanisms, have been studied in our work. It has also not been understood in the Comment that the adiabatic regime described for transfer occurs in the protonic ground state, in a very-low barrier configuration with the protonic ground state energy larger than the barrier. Serious confusion has been made in the Comment with the case of H in metals like Nb or Ta, leading to the introduction of the notion of (protonic) "excited-state proton transfer", relevant for H in some metals, but (i) that does not correspond to the (ground state) adiabatic transfers here described, and (ii) that does not correspond to what is commonly described as the "adiabatic limit for proton transfer" in the scientific literature. We emphasize, accordingly, the large differences between proton transfer in the present oxide and hydrogen jumps in metals like Nb or Ta, and the similarities between proton transfer in the present oxide and in acid-base solutions. We finally describe a scenario for proton transfer in the present oxide regardless of the temperature regime.

  13. Minimal-excitation states for electron quantum optics using levitons.

    Science.gov (United States)

    Dubois, J; Jullien, T; Portier, F; Roche, P; Cavanna, A; Jin, Y; Wegscheider, W; Roulleau, P; Glattli, D C

    2013-10-31

    The on-demand generation of pure quantum excitations is important for the operation of quantum systems, but it is particularly difficult for a system of fermions. This is because any perturbation affects all states below the Fermi energy, resulting in a complex superposition of particle and hole excitations. However, it was predicted nearly 20 years ago that a Lorentzian time-dependent potential with quantized flux generates a minimal excitation with only one particle and no hole. Here we report that such quasiparticles (hereafter termed levitons) can be generated on demand in a conductor by applying voltage pulses to a contact. Partitioning the excitations with an electronic beam splitter generates a current noise that we use to measure their number. Minimal-excitation states are observed for Lorentzian pulses, whereas for other pulse shapes there are significant contributions from holes. Further identification of levitons is provided in the energy domain with shot-noise spectroscopy, and in the time domain with electronic Hong-Ou-Mandel noise correlations. The latter, obtained by colliding synchronized levitons on a beam splitter, exemplifies the potential use of levitons for quantum information: using linear electron quantum optics in ballistic conductors, it is possible to imagine flying-qubit operation in which the Fermi statistics are exploited to entangle synchronized electrons emitted by distinct sources. Compared with electron sources based on quantum dots, the generation of levitons does not require delicate nanolithography, considerably simplifying the circuitry for scalability. Levitons are not limited to carrying a single charge, and so in a broader context n-particle levitons could find application in the study of full electron counting statistics. But they can also carry a fraction of charge if they are implemented in Luttinger liquids or in fractional quantum Hall edge channels; this allows the study of Abelian and non-Abelian quasiparticles in the

  14. Implementation of proton transfer reaction-mass spectrometry (PTR-MS) for advanced bioprocess monitoring.

    Science.gov (United States)

    Luchner, Markus; Gutmann, Rene; Bayer, Karl; Dunkl, Jürgen; Hansel, Armin; Herbig, Jens; Singer, Wolfgang; Strobl, Florian; Winkler, Klaus; Striedner, Gerald

    2012-12-01

    We report on the implementation of proton transfer reaction-mass spectrometry (PTR-MS) technology for on-line monitoring of volatile organic compounds (VOCs) in the off-gas of bioreactors. The main part of the work was focused on the development of an interface between the bioreactor and an analyzer suitable for continuous sampling of VOCs emanating from the bioprocess. The permanently heated sampling line with an inert surface avoids condensation and interaction of volatiles during transfer to the PTR-MS. The interface is equipped with a sterile sinter filter unit directly connected to the bioreactor headspace, a condensate trap, and a series of valves allowing for dilution of the headspace gas, in-process calibration, and multiport operation. To assess the aptitude of the entire system, a case study was conducted comprising three identical cultivations with a recombinant E. coli strain, and the volatiles produced in the course of the experiments were monitored with the PTR-MS. The high reproducibility of the measurements proved that the established sampling interface allows for reproducible transfer of volatiles from the headspace to the PTR-MS analyzer. The set of volatile compounds monitored comprises metabolites of different pathways with diverse functions in cell physiology but also volatiles from the process matrix. The trends of individual compounds showed diverse patterns. The recorded signal levels covered a dynamic range of more than five orders of magnitude. It was possible to assign specific volatile compounds to distinctive events in the bioprocess. The presented results clearly show that PTR-MS was successfully implemented as a powerful bioprocess-monitoring tool and that access to volatiles emitted by the cells opens promising perspectives in terms of advanced process control. Copyright © 2012 Wiley Periodicals, Inc.

  15. Spin-locking vs. chemical exchange saturation transfer MRI for investigating chemical exchange process between water and labile metabolite protons

    Science.gov (United States)

    Jin, Tao; Autio, Joonas; Obata, Takayuki; Kim, Seong-Gi

    2010-01-01

    Chemical exchange saturation transfer (CEST) and spin-locking (SL) experiments were both able to probe the exchange process between protons of non-equivalent chemical environments. To compare the characteristics of the CEST and SL approaches in the study of chemical exchange effects, we performed CEST and SL experiments at varied pH and concentrated metabolites with exchangeable amide, amine, and hydroxyl protons at 9.4 T. Our results show that: i) On-resonance SL is most sensitive to chemical exchanges in the intermediate exchange regime and is able to detect hydroxyl and amine protons on a millimolar concentration scale. Off-resonance SL and CEST approaches are sensitive to slow-exchanging protons when an optimal SL or saturation pulse power matches the exchanging rate, respectively. ii) Offset frequency-dependent SL and CEST spectra are very similar, and can be explained well with an SL model recently developed by Trott and Palmer. iii) The exchange rate and population of metabolite protons can be determined from offset-dependent SL or CEST spectra or from on-resonance SL relaxation dispersion measurements. iv) The asymmetry of the magnetization transfer ratio (MTRasym) is highly dependent on the choice of saturation pulse power. In the intermediate exchange regime, MTRasym becomes complicated and should be interpreted with care. PMID:21500270

  16. Spin-locking versus chemical exchange saturation transfer MRI for investigating chemical exchange process between water and labile metabolite protons.

    Science.gov (United States)

    Jin, Tao; Autio, Joonas; Obata, Takayuki; Kim, Seong-Gi

    2011-05-01

    Chemical exchange saturation transfer (CEST) and spin-locking (SL) experiments were both able to probe the exchange process between protons of nonequivalent chemical environments. To compare the characteristics of the CEST and SL approaches in the study of chemical exchange effects, we performed CEST and SL experiments at varied pH and concentrated metabolite phantoms with exchangeable amide, amine, and hydroxyl protons at 9.4 T. Our results show that: (i) on-resonance SL is most sensitive to chemical exchanges in the intermediate-exchange regime and is able to detect hydroxyl and amine protons on a millimolar concentration scale. Off-resonance SL and CEST approaches are sensitive to slow-exchanging protons when an optimal SL or saturation pulse power matches the exchanging rate, respectively. (ii) Offset frequency-dependent SL and CEST spectra are very similar and can be explained well with an SL model recently developed by Trott and Palmer (J Magn Reson 2002;154:157-160). (iii) The exchange rate and population of metabolite protons can be determined from offset-dependent SL or CEST spectra or from on-resonance SL relaxation dispersion measurements. (iv) The asymmetry of the magnetization transfer ratio (MTR(asym)) is highly dependent on the choice of saturation pulse power. In the intermediate-exchange regime, MTR(asym) becomes complicated and should be interpreted with care. Copyright © 2010 Wiley-Liss, Inc.

  17. Reoptimization of Intensity Modulated Proton Therapy Plans Based on Linear Energy Transfer

    Energy Technology Data Exchange (ETDEWEB)

    Unkelbach, Jan, E-mail: junkelbach@mgh.harvard.edu [Department of Radiation Oncology, Massachusetts General Hospital, Boston, Massachusetts (United States); Botas, Pablo [Department of Radiation Oncology, Massachusetts General Hospital, Boston, Massachusetts (United States); Faculty of Physics, Ruprecht-Karls-Universität Heidelberg, Heidelberg (Germany); Giantsoudi, Drosoula; Gorissen, Bram L.; Paganetti, Harald [Department of Radiation Oncology, Massachusetts General Hospital, Boston, Massachusetts (United States)

    2016-12-01

    Purpose: We describe a treatment plan optimization method for intensity modulated proton therapy (IMPT) that avoids high values of linear energy transfer (LET) in critical structures located within or near the target volume while limiting degradation of the best possible physical dose distribution. Methods and Materials: To allow fast optimization based on dose and LET, a GPU-based Monte Carlo code was extended to provide dose-averaged LET in addition to dose for all pencil beams. After optimizing an initial IMPT plan based on physical dose, a prioritized optimization scheme is used to modify the LET distribution while constraining the physical dose objectives to values close to the initial plan. The LET optimization step is performed based on objective functions evaluated for the product of LET and physical dose (LET×D). To first approximation, LET×D represents a measure of the additional biological dose that is caused by high LET. Results: The method is effective for treatments where serial critical structures with maximum dose constraints are located within or near the target. We report on 5 patients with intracranial tumors (high-grade meningiomas, base-of-skull chordomas, ependymomas) in whom the target volume overlaps with the brainstem and optic structures. In all cases, high LET×D in critical structures could be avoided while minimally compromising physical dose planning objectives. Conclusion: LET-based reoptimization of IMPT plans represents a pragmatic approach to bridge the gap between purely physical dose-based and relative biological effectiveness (RBE)-based planning. The method makes IMPT treatments safer by mitigating a potentially increased risk of side effects resulting from elevated RBE of proton beams near the end of range.

  18. Chemical rescue of enzymes: proton transfer in mutants of human carbonic anhydrase II.

    Science.gov (United States)

    Maupin, C Mark; Castillo, Norberto; Taraphder, Srabani; Tu, Chingkuang; McKenna, Robert; Silverman, David N; Voth, Gregory A

    2011-04-27

    In human carbonic anhydrase II (HCA II), the mutation of position 64 from histidine to alanine (H64A) disrupts the rate limiting proton transfer (PT) event, resulting in a reduction of the catalytic activity of the enzyme as compared to the wild-type. Potential of mean force (PMF) calculations utilizing the multistate empirical valence bond (MS-EVB) methodology for H64A HCA II yields a PT free energy barrier significantly higher than that found in the wild-type enzyme. This high barrier, determined in the absence of exogenous buffer and assuming no additional ionizable residues in the PT pathway, indicates the likelihood of alternate enzyme pathways that utilize either ionizable enzyme residues (self-rescue) and/or exogenous buffers (chemical rescue). It has been shown experimentally that the catalytic activity of H64A HCA II can be chemically rescued to near wild-type levels by the addition of the exogenous buffer 4-methylimidazole (4MI). Crystallographic studies have identified two 4MI binding sites, yet site-specific mutations intended to disrupt 4MI binding have demonstrated these sites to be nonproductive. In the present work, MS-EVB simulations show that binding of 4MI near Thr199 in the H64A HCA II mutant, a binding site determined by NMR spectroscopy, results in a viable chemical rescue pathway. Additional viable rescue pathways are also identified where 4MI acts as a proton transport intermediary from the active site to ionizable residues on the rim of the active site, revealing a probable mode of action for the chemical rescue pathway.

  19. High-energy excited states in {sup 98}Cd

    Energy Technology Data Exchange (ETDEWEB)

    Braun, Norbert; Blazhev, Andrey; Jolie, Jan [Institut fuer Kernphysik, Universitaet Koeln (Germany); Boutachkov, Plamen; Gorska, Magda; Grawe, Hubert; Pietri, Stephane [GSI, Darmstadt (Germany); Brock, Tim; Nara Singh, B.S.; Wadsworth, Robert [Department of Physics, University of York, York (United Kingdom); Liu, Zhong [University of Edinburgh, Edinburgh (United Kingdom)

    2009-07-01

    Studies of isomerism in the proton-rich N {approx_equal}Z nuclei around {sup 100}Sn give important insights into the role of proton-neutron pairing and also serve as testing grounds for nuclear models. In summer 2008, an experiment on {sup 96,97,98}Cd was performed using the FRS fragment separator and the RISING germanium array at GSI. These exotic nuclei of interest were produced using fragmentation of a 850 MeV/u {sup 124}Xe beam on a 4 g/cm{sup 2} {sup 9}Be target and finally implanted into an active stopper consisting of 9 double-sided silicon strip detectors. In {sup 98}Cd, a new high-energy isomeric transition was identified. Preliminary results on {sup 98}Cd are presented and their implications for the high-excitation level scheme are discussed.

  20. In situ measurements of water transfer due to different mechanisms in a proton exchange membrane fuel cell

    Science.gov (United States)

    Husar, Attila; Higier, Andrew; Liu, Hongtan

    Water management is of critical importance in a proton exchange membrane (PEM) fuel cell, in particular, those based on a sulfonic acid polymer, which requires water to conduct protons. Yet there are limited in situ studies of water transfer through the membrane and no data are available for water transfer due to individual mechanisms through the membrane in an operational fuel cell. Thus it is the objective of this study to measure water transfer through the membrane due to each individual mechanism in an operational PEM fuel cell. The three different mechanisms of water transfer, i.e., electro-osmotic drag, diffusion and hydraulic permeation are isolated by specially imposed boundary conditions. Therefore water transfer through the membrane due to each mechanism is measured separately. In this study, all the data is collected in an actual assembled operational fuel cell. The experimental results show that water transfer due to hydraulic permeation, i.e. the pressure difference between the anode and cathode is at least an order of magnitude lower than those due to the other two mechanisms. The data for water transfer due to diffusion through the membrane are in good agreement with some of the ex situ data in the literature. The data for electro-osmosis show that the number of water molecules dragged per proton increases not only with temperature but also with current density, which is different from existing data in the literature. The methodology used in this study is simple and can be easily adopted for in situ water transfer measurement due to different mechanisms in other PEM fuel cells without any cell modifications.

  1. Effects of external electric fields on double proton transfer kinetics in the formic acid dimer.

    Science.gov (United States)

    Arabi, Alya A; Matta, Chérif F

    2011-08-14

    Molecules can be exposed to strong local electric fields of the order of 10(8)-10(10) V m(-1) in the biological milieu. The effects of such fields on the rate constant (k) of a model reaction, the double-proton transfer reaction in the formic acid dimer (FAD), are investigated. The barrier heights and shapes are calculated in the absence and presence of several static homogenous external fields ranging from 5.14 × 10(8) to 5.14 × 10(9) V m(-1) using density functional theory (DFT/B3LYP) and second order Møller-Plesset perturbation theory (MP2) in conjunction with the 6-311++G(d,p) Pople basis set. Conventional transition state theory (CTST) followed by Wigner tunneling correction is then applied to estimate the rate constants at 25 °C. It is found that electric fields parallel to the long axis of the dimer (the line joining the two carbon atoms) lower the uncorrected barrier height, and hence increase the raw k. These fields also flatten the potential energy surface near the transition state region and, hence, decrease the multiplicative tunneling correction factor. The net result of these two opposing effects is that fields increase k(corrected) by a factor of ca. 3-4 (DFT-MP2, respectively) compared to the field-free k. Field strengths of ∼3 × 10(9) V m(-1) are found to be sufficient to double the tunneling-corrected double proton transfer rate constant at 25 °C. Field strengths of similar orders of magnitudes are encountered in the scanning tunneling microscope (STM), in the microenvironment of a DNA base-pair, in an enzyme active site, and in intense laser radiation fields. It is shown that the net (tunneling corrected) effect of the field on k can be closely fitted to an exponential relationship of the form k = aexp(bE), where a and b are constants and E the electric field strength.

  2. A benchmark study of electronic excitation energies, transition moments, and excited-state energy gradients on the nicotine molecule

    Energy Technology Data Exchange (ETDEWEB)

    Egidi, Franco, E-mail: franco.egidi@sns.it; Segado, Mireia; Barone, Vincenzo, E-mail: vincenzo.barone@sns.it [Scuola Normale Superiore, Piazza dei Cavalieri, 7 I-56126 Pisa (Italy); Koch, Henrik [Department of Chemistry, Norwegian University of Science and Technology, 7491 Trondheim (Norway); Cappelli, Chiara [Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via G. Moruzzi, 3 I-56124 Pisa (Italy)

    2014-12-14

    In this work, we report a comparative study of computed excitation energies, oscillator strengths, and excited-state energy gradients of (S)-nicotine, chosen as a test case, using multireference methods, coupled cluster singles and doubles, and methods based on time-dependent density functional theory. This system was chosen because its apparent simplicity hides a complex electronic structure, as several different types of valence excitations are possible, including n-π{sup *}, π-π{sup *}, and charge-transfer states, and in order to simulate its spectrum it is necessary to describe all of them consistently well by the chosen method.

  3. Photoluminescence and excited states dynamics in PbWO4:Pr3+ crystals

    CERN Document Server

    Auffray, E; Shalapska, T; Zazubovich, S

    2014-01-01

    Luminescence and photo-thermally stimulated defects creation processes are studied for a Pr3+-doped PbWO4 crystal at 4.2-400 K under excitation in the band-to-band, exciton, and charge-transfer transitions regions, as well as in the Pr3+-related absorption bands. Emission spectra of Pr3+ centers depend on the excitation energy, indicating the presence of Pr3+ centers of two types. The origin of these centers is discussed. The 2.03-2.06 eV emission, arising from the D-1(2) -> H-3(4) transitions of Pr3+ ions, is found to be effectively excited in a broad intense absorption band peaking at 4.2 K at 3.92 eV. By analogy with some other Pe(3+)-doped compounds, this band is suggested to arise from an electron transfer from an impurity Pr3+ ion to the crystal lattice W6+ or Pb2+ ions. The dynamics of the Pr3+-related excited states is clarified. In the PbWO4:Pr crystal studied, the concentration of single oxygen and lead vacancies as traps for electrons and holes is found to be negligible.

  4. Excited state properties of the chromophore of the asFP595 chromoprotein: 2D and 3D theoretical analyses

    Science.gov (United States)

    Sun, Mengtao

    The ground and excited state properties (e.g., the intramolecular charge and energy transfer, and electron-hole coherence) of the chromophore of the asFP595 chromoprotein from Anemonia sulcata in the neutral and anionic forms are theoretically studied with quantum chemistry methods. The ground-state properties of the asFP595 in the neutral and anionic forms, such as the alternations of the bond lengths and the Mulliken charge distributions, are compared. The calculated transition energies of the asFP595 in the neutral and anionic form are consistent with the experimental results. To study the excited state properties of the asFP595 chromophore, the energies and densities of highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs), as well as the CI main coefficients, are compared between the two forms. The intramolecular charge and energy transfer in the neutral and anionic forms are investigated and compared with the three-dimensional (3D) real-space analysis methods, including the strength and orientation of the transition dipoles with transition density, and the orientation and result of the intramolecular charge transfer with charge difference density. The electron-hole coherence and delocalization on the excitation are studied with the 2D real-space analysis method of the transition density matrix. In all, the calculated results are remain in good agreement with the experimental data, and the theoretical analysis results supported the proposed models in the experiment.

  5. Measurement of the proton form factor ratio at low momentum transfer

    Energy Technology Data Exchange (ETDEWEB)

    Friedman, Moshe [Hebrew Univ. of Jerusalem (Israel)

    2016-08-01

    Experiment E08-007-II measured the proton elastic form factor ratio μGE=GM in the momentum transfer range of Q2 ~ 0.02 - 0.08 GeV2, the lowest ever measured by polarization transfer techniques. The experiment was performed at the Thomas Jefferson National Accelerator Facility in Newport News, Virginia, USA during 2012. A polarized electron beam with energies of 1.1, 1.7, and 2.2 GeV was elastically scattered off a polarized solid NH3 target. The asymmetries between the cross section of positive and negative helicity states of the beam were determined. These asymmetries can be used to determine the form factor ratio. In this thesis, we present the asymmetry analysis of the experiment, discuss the main challenges and show preliminary results for part of the data. Preliminary asymmetries indicate an increase in the form factor ratio above unity. However, a complete analysis is required before any conclusion can be made. Further analysis is ongoing, and final asymmetry results and form factor extraction is expected during 2017. We also present first results for 14N asymmetries for elastic and quasi-elastic scattering. The measured asymmetries are in agreement with the shell model approximation, within the low accuracy of the measurement. A change in the asymmetry sign between the elastic and the quasi-elastic processes is seen, and should motivate further theoretical studies. These experimental asymmetries will also be useful for systematic studies of other experiments using polarized NH3 targets.

  6. Hydrogen bonding and coordination bonding in the electronically excited states of Cu2(L)2 (L = 5-(4-pyridyl)tetrazole)MeOH: A TDDFT study

    Science.gov (United States)

    Meng, Yanfang; Zhang, Chunqing; Ji, Min; Hao, Ce; Qiu, Jieshan

    2013-05-01

    The luminescent metal organic framework (MOF), Cu2(L)2·MeOH (L = 5-(4-pyridyl)tetrazole), was studied using time-dependent density functional theory (TDDFT). A combination of frontier molecular orbitals and electronic configuration analysis revealed that the emission mechanism was a ligand to metal charge transition (LMCT) rather than a metal to ligand charge transfer (MLCT). Hydrogen bonding significantly changed the nature of the frontier orbital and the luminescence. Electronic transition energies predicted that the hydrogen bonding in excited state would become weaker with an electronic spectral blue-shift. The bond lengths, frequencies, and binding energies indicated weakening of the hydrogen bonding in the excited state, which can affect emissions in two ways, including: (i) a decrease in the electronic coupling between methanol and the motif and suppressing the occurrence of the photo-induced electron transfer (PET); and (ii) increasing the energy gap between S1 and S0, leading to radiative transition. Coordination bonding was also investigated in the excited state through bond lengths, frequencies, and bond orders. Coordination bonds were found to become stronger in the excited state leading to an enhancement of the luminescence.

  7. Experimental and computational studies on creatininium 4-nitrobenzoate - An organic proton transfer complex

    Science.gov (United States)

    Thirumurugan, R.; Anitha, K.

    2017-10-01

    A new organic proton transfer complex of creatininium 4-nitrobenzoate (C4NB) has been synthesized and its single crystals were grown successfully by slow evaporation technique. The grown single crystal was subjected to various characterization techniques like single crystal X-ray diffraction (SCXRD), FTIR, FT-Raman and Kurtz-Perry powder second harmonic generation (SHG). The SCXRD analysis revealed that C4NB was crystallized into orthorhombic crystal system, with noncentrosymmetric (NCS), P212121 space group. The creatininium cation and 4-nitrobenzoate anion were connected through a pair of N__H⋯O hydrogen bonds (N(3)__H(6) ⋯ O(3) (x+1, y, z) and N(2)__H(5) &ctdot O(2) (x-1/2, -y-1/2, -z+2)) and fashioned a R22(8) ring motif. The crystal structure was stabilized by strong N__H⋯O and weak C__H⋯O intermolecular interactions and it was quantitatively analysed by Hirshfeld surface and fingerprint (FP) analysis. FTIR and FT-Raman studies confirmed the vibrational modes of functional groups present in C4NB compound indubitably. SHG efficiency of grown crystal was 4.6 times greater than that of standard potassium dihydrogen phosphate (KDP) material. Moreover, density functional theory (DFT) studies such as Mulliken charge distribution, frontier molecular orbitals (FMOs), molecular electrostatic potential (MEP) map, natural bond orbital analysis (NBO) and first order hyperpolarizability (β0) were calculated to explore the structure-property relationship.

  8. Static and dynamic headspace analysis of instant coffee blends by proton-transfer-reaction mass spectrometry.

    Science.gov (United States)

    Romano, Andrea; Gaysinsky, Sylvia; Czepa, Andreas; Del Pulgar, José Sanchez; Cappellin, Luca; Biasioli, Franco

    2015-09-01

    Instant coffee is a widespread product, generally related to a high consumer acceptability, also because of its ease of preparation. The present work addresses the characterization of the headspace of freshly brewed instant coffees resulting from different blends, during and immediately after preparation. The sample set consisted of 10 coffees, obtained by mixing three different blends in different proportions. The employment of Proton Transfer Reaction-Mass Spectrometry (PTR-MS) allowed for direct and real-time sampling from the headspace, under conditions that mimic those that are encountered above the cup during and right after brewing. Different coffee brews were separated on the basis of the respective volatile profiles, and data showed good consistency with the respective blend compositions. When the headspace evolution was monitored during preparation, similar results were obtained in terms of blend separation; moreover, different blends displayed different and reproducible 'signatures' in terms of time evolution. A straightforward method for the prediction of headspace composition is proposed, allowing to predict the volatile profiles of two-component and three-component blends on the basis of the respective parent components. Overall, the results constitute a successful example of the applicability of PTR-MS as a tool for product development in food science. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.

  9. Applying protein-based amide proton transfer MR imaging to distinguish solitary brain metastases from glioblastoma

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Hao; Zou, Tianyu; Wang, Xianlong; Du, Yongxing; Jiang, Chunxiu; Ma, Ling; Zhu, Jianbin; He, Wen; Rui, Qihong; Wen, Zhibo [Zhujiang Hospital, Southern Medical University, Department of Radiology, Guangzhou, Guangdong (China); Lou, Huiling [The First People' Hospital of Guangzhou, Department of Geriatrics, Guangzhou, Guangdong (China); Jiang, Shanshan [Zhujiang Hospital, Southern Medical University, Department of Radiology, Guangzhou, Guangdong (China); Johns Hopkins University School of Medicine, Division of MR Research, Department of Radiology, Baltimore, MD (United States); Huang, Zhongqing [Shantou University Medical College, Department of Medical Image Center, Yuebei People' s Hospital, Shantou, Guangdong (China); Zhou, Jianyuan [Johns Hopkins University School of Medicine, Division of MR Research, Department of Radiology, Baltimore, MD (United States)

    2017-11-15

    To determine the utility of amide proton transfer-weighted (APTw) MR imaging in distinguishing solitary brain metastases (SBMs) from glioblastomas (GBMs). Forty-five patients with SBMs and 43 patients with GBMs underwent conventional and APT-weighted sequences before clinical intervention. The APTw parameters and relative APTw (rAPTw) parameters in the tumour core and the peritumoral brain zone (PBZ) were obtained and compared between SBMs and GBMs. The receiver-operating characteristic (ROC) curve was used to assess the best parameter for distinguishing between the two groups. The APTw{sub max}, APTw{sub min}, APTw{sub mean}, rAPTw{sub max}, rAPTw{sub min} or rAPTw{sub mean} values in the tumour core were not significantly different between the SBM and GBM groups (P = 0.141, 0.361, 0.221, 0.305, 0.578 and 0.448, respectively). However, the APTw{sub max}, APTw{sub min}, APTw{sub mean}, rAPTw{sub max}, rAPTw{sub min} or rAPTw{sub mean} values in the PBZ were significantly lower in the SBM group than in the GBM group (P < 0.001). The APTw{sub min} values had the highest area under the ROC curve 0.905 and accuracy 85.2% in discriminating between the two neoplasms. As a noninvasive imaging method, APT-weighted MR imaging can be used to distinguish SBMs from GBMs. (orig.)

  10. Measuring odour emission and biofilter efficiency in composting plants by proton transfer reaction-mass spectrometry.

    Science.gov (United States)

    Biasioli, F; Aprea, E; Gasperi, F; Märk, T D

    2009-01-01

    PTR-MS (Proton Transfer Reaction-Mass Spectrometry) is an innovative technique that allows the rapid detection of most volatile organic compounds (VOCs) with high sensitivity (sub-ppb) and by direct injection. We describe here the possible use of PTR-MS in waste managements and composting plants both for the real time monitoring of volatile emissions and, after calibration with olfactometric assessments, for the instrumental determination of odour concentration. Beside a short description of the technique, we will report on the calibration of PTR-MS data with olfactometric assessment of odour concentration showing the possibility of a relatively good estimation of odour concentration by instrumental data. We will also show how the rapid PTR-MS fingerprint can be used to visualise the overall effect of a biofilter on the VOCs concentration and to calculate the reduction of the concentration of single masses and, finally, we will provide examples of the performances of a new implementation of this technique based on a time of flight (TOF) analyser. Instead of the usual quadrupole mass filter, the TOF provides an increase of analytical information and the possibility to separate important compounds that in the quadrupole version were not or only indirectly quantifiable. In conclusion we suggest that PTR-MS analysis can be a valuable tool for the rapid and on site monitoring of odour emission and plant operation.

  11. Application of proton-transfer-reaction-mass-spectrometry for Indoor Air Quality research.

    Science.gov (United States)

    Schripp, T; Etienne, S; Fauck, C; Fuhrmann, F; Märk, L; Salthammer, T

    2014-04-01

    In the field of Indoor Air Quality research, the measurement of volatile organic compounds (VOCs) demands instruments that are rapid, mobile, robust, highly sensitive and allow for simultaneous monitoring of multiple compounds. These instruments should also compensate for possible interferences from permanent gases and air humidity. Proton-transfer-reaction-mass-spectrometry (PTR-MS) has proved to be a valuable and promising technique that fits the mentioned requirements for a suitable online measuring device. In this study, five exemplary applications of PTR-MS are described: (i) release of paint additives during drying process, (ii) emission of VOCs from active hardcopy devices, (iii) reference material evaluation, (iv) diffusion studies, and (v) emission testing of building products. The examples are selected to illustrate possibilities and limitations of the PTR technique in this field of research. The quadruple-based PTR-QMS was able to determine the emission characteristics during the experiments, especially in case of depleting emission sources (e.g., reference material). This allows for chemometrical analysis of the measured release patterns and detection of underlying processes. However, PTR-QMS reaches a functional limit in case of compound identification. If identification of VOCs is necessary, the measurements need to be accompanied by GC/MS analytics or a PTR instrument with higher mass-resolution (e.g., PTR-TOF-MS). © 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  12. OH clock determination by proton transfer reaction mass spectrometry at an environmental chamber

    Directory of Open Access Journals (Sweden)

    P. Barmet

    2012-03-01

    Full Text Available The hydroxyl free radical (OH is the major oxidizing species in the lower atmosphere. Measuring the OH concentration is generally difficult and involves elaborate, expensive, custom-made experimental setups. Thus other more economical techniques, capable of determining OH concentrations at environmental chambers, would be valuable. This work is based on an indirect method of OH concentration measurement, by monitoring an appropriate OH tracer by proton transfer reaction mass spectrometry (PTR-MS. 3-pentanol, 3-pentanone and pinonaldehyde (PA were used as OH tracers in α-pinene (AP secondary organic aerosol (SOA aging studies. In addition we tested butanol-d9 as a potential "universal" OH tracer and determined its reaction rate constant with OH: kbutanol-d9 = 3.4(±0.88 × 10−12 cm3 molecule−1 s−1. In order to make the chamber studies more comparable among each other as well as to atmospheric measurements we suggest the use of a chemical (time dimension: the OH clock, which corresponds to the integrated OH concentration over time.

  13. Humidity independent mass spectrometry for gas phase chemical analysis via ambient proton transfer reaction.

    Science.gov (United States)

    Zhu, Hongying; Huang, Guangming

    2015-03-31

    In this work, a humidity independent mass spectrometric method was developed for rapid analysis of gas phase chemicals. This method is based upon ambient proton transfer reaction between gas phase chemicals and charged water droplets, in a reaction chamber with nearly saturate humidity under atmospheric pressure. The humidity independent nature enables direct and rapid analysis of raw gas phase samples, avoiding time- and sample-consuming sample pretreatments in conventional mass spectrometry methods to control sample humidity. Acetone, benzene, toluene, ethylbenzene and meta-xylene were used to evaluate the analytical performance of present method. The limits of detection for benzene, toluene, ethylbenzene and meta-xylene are in the range of ∼0.1 to ∼0.3 ppbV; that of benzene is well below the present European Union permissible exposure limit for benzene vapor (5 μg m(-3), ∼1.44 ppbV), with linear ranges of approximately two orders of magnitude. The majority of the homemade device contains a stainless steel tube as reaction chamber and an ultrasonic humidifier as the source of charged water droplets, which makes this cheap device easy to assemble and facile to operate. In addition, potential application of this method was illustrated by the real time identification of raw gas phase chemicals released from plants at different physiological stages. Copyright © 2015 Elsevier B.V. All rights reserved.

  14. Proton-Transfer Mechanisms at the Water-ZnO Interface: The Role of Presolvation.

    Science.gov (United States)

    Quaranta, Vanessa; Hellström, Matti; Behler, Jörg

    2017-04-06

    The dissociation of water is an important step in many chemical processes at solid surfaces. In particular, water often spontaneously dissociates near metal oxide surfaces, resulting in a mixture of H2O, H+, and OH- at the interface. Ubiquitous proton-transfer (PT) reactions cause these species to dynamically interconvert, but the underlying mechanisms are poorly understood. Here, we develop and use a reactive high-dimensional neural-network potential based on density functional theory data to elucidate the structural and dynamical properties of the interfacial species at the liquid-water-metal-oxide interface, using the nonpolar ZnO(101̅0) surface as a prototypical case. Molecular dynamics simulations reveal that water dissociation and recombination proceed via two types of PT reactions: (i) to and from surface oxide and hydroxide anions ("surface-PT") and (ii) to and from neighboring adsorbed hydroxide ions and water molecules ("adlayer-PT"). We find that the adlayer-PT rate is significantly higher than the surface-PT rate. Water dissociation is, for both types of PT, governed by a predominant presolvation mechanism, i.e., thermal fluctuations that cause the adsorbed water molecules to occasionally accept a hydrogen bond, resulting in a decreased PT barrier and an increased dissociation rate as compared to when no hydrogen bond is present. Consequently, we are able to show that hydrogen bond fluctuations govern PT events at the water-metal-oxide interface in a way similar to that in acidic and basic aqueous bulk solutions.

  15. Triacetone triperoxide detection using low reduced-field proton transfer reaction mass spectrometer

    Science.gov (United States)

    Shen, Chengyin; Li, Jianquan; Han, Haiyan; Wang, Hongmei; Jiang, Haihe; Chu, Yannan

    2009-08-01

    Proton transfer reaction mass spectrometry (PTR-MS) was applied to on-line detection of the explosive triacetone triperoxide (TATP) using a discharge gas of water vapor or alternative ammonia in the ion source. The dependence of ionic intensity on reduced-field in the drift tube was investigated, and the results indicate that an irregular operation using low reduced-field can enhance TATP detection due to reduced collision-induced dissociation in the drift tube. When water vapor is used as the discharge gas, the characteristic ions for TATP identification are [TATP + H]+ which are detectable at a reduced-field about 50 Td. If ammonia is the discharge gas, PTR-MS exhibits a better sensitivity, the explosive TATP can be discriminated according to the adduct ions [TATP + NH4]+, and a limit of detection at ppb level can be achieved at a reduced-field around 100 Td in this PTR-MS apparatus. PTR-MS is suggested as a potential tool for on-site detection of the explosive TATP with the advantages of rapid response and high sensitivity without sample pretreatment.

  16. Ground- and excited-state scattering potentials for the stopping of protons in an electron gas

    Science.gov (United States)

    Matias, F.; Fadanelli, R. C.; Grande, P. L.; Koval, N. E.; Díez Muiño, R.; Borisov, A. G.; Arista, N. R.; Schiwietz, G.

    2017-09-01

    The self-consistent electron-ion potential V(r) is calculated for H+ ions in an electron gas system as a function of the projectile energy to model the electronic stopping power for conduction-band electrons. The results show different self-consistent potentials at low projectile-energies, related to different degrees of excitation of the electron cloud surrounding the intruder ion. This behavior can explain the abrupt change of velocity dependent screening-length of the potential found by the use of the extended Friedel sum rule and the possible breakdown of the standard free electron gas model for the electronic stopping at low projectile energies. A dynamical interpolation of V(r) is proposed and used to calculate the stopping power for H+ interacting with the valence electrons of Al. The results are in good agreement with the TDDFT benchmark calculations as well as with experimental data.

  17. [Two-dimensional model of a double-well potential: proton transfer when a hydrogen bond is deformed].

    Science.gov (United States)

    Krasilnikov, P M

    2014-01-01

    The potential energy cross-section profile along a hydrogen bond may contain two minima in certain conditions; it is so-called a double well potential. The H-bond double well potential is essential for proton transfer along this hydrogen bond. We have considered the two-dimensional model of such double well potential in harmonic approximation, and we have also investigated the proton tunneling in it. In real environments thermal motion of atoms or conformational changes may cause reorientation and relative shift of molecule fragment forming the hydrogen bond and, as a result, the hydrogen bond isdeformed. This deformation is liable to change the double well potential form and, hence, the probability of the proton tunneling is changed too. As it is shown the characteristic time of proton tunneling is essentially increased by even small relative shift of heavy atoms forming the H-bond and also rotational displacement of covalent bond generated by one of heavy atoms and the proton (hydrogen atom). However, it is also shown, at the certain geometry of the H-bond deformation the opposite effect occurred, i.e., the characteristic time is not increased and even decreased. Notice that such its behavior arises from two-dimensionality of potential wells; this and other properties of our model are discussed in detail.

  18. Intramolecular proton transfer through the adjoining π-conjugated system in Shiff base: Application for colorimetric sensing of fluoride anion

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Xudong, E-mail: 081022009@fudan.edu.cn [College of Chemistry and Material Sciences, Hebei Normal University, Yuhua Road 113, Shijiazhuang 050024 (China); College of Science and Hebei Research Center of Pharmaceutical and Chemical Engineering, Hebei University of Science and Technology, Yuhua Road 70, Shijiazhuang 050080 (China); Zhang, Ping [College of Chemistry and Material Sciences, Hebei Normal University, Yuhua Road 113, Shijiazhuang 050024 (China); Li, Yajuan; Zhen, Xiaoli; Geng, Lijun; Wang, Yanqiu [College of Science and Hebei Research Center of Pharmaceutical and Chemical Engineering, Hebei University of Science and Technology, Yuhua Road 70, Shijiazhuang 050080 (China); Ma, Zichuan, E-mail: ma7405@hebtu.edu.cn [College of Chemistry and Material Sciences, Hebei Normal University, Yuhua Road 113, Shijiazhuang 050024 (China)

    2014-07-01

    In this paper, a new kind of phenol-based chemsensor L2 comprised of a Schiff base and azo groups was rationally designed and synthesized. It could selectively recognize fluoride anion among tested anions such as F{sup −}, AcO{sup −}, H{sub 2}PO{sub 4}{sup −}, Cl{sup −}, Br{sup −}, and I{sup −} with obvious color changes from yellow to fuchsia. The intramolecular PT (proton transfer) in L1 and L2 was responsible for the sensing ability, which was certified by the {sup 1}H NMR and Uv–vis experiments. - Highlights: • The phenol derivative L2 could selectively sense F{sup −} among test anions. • Intramolecular proton transfer happened when L2 was bonded with F{sup −}. • It is the first antipyrine-based anion receptor.

  19. Resonance-Enhanced Excited-State Raman Spectroscopy of Conjugated Thiophene Derivatives: Combining Experiment with Theory

    Science.gov (United States)

    Barclay, Matthew S.; Quincy, Timothy J.; Caricato, Marco; Elles, Christopher G.

    2017-06-01

    Resonance-enhanced Femtosecond Stimulated Raman Spectroscopy (FSRS) is an ultrafast experimental method that allows for the study of excited-state structural behaviors, as well as the characterization of higher electronically excited states accessible through the resonant conditions of the observed vibrations. However, interpretation of the experiment is difficult without an accurate vibrational assignment of the resonance-enhanced spectra. We therefore utilize simulations of off-resonant excited-state Raman spectra, in which we employ a numerical derivative of the analytical excited-state polarizabilities along the normal mode displacements, in order to identify and interpret the resonance-enhanced vibrations observed in experiment. We present results for a benchmark series of conjugated organic thiophene derivatives, wherein we have computed the off-resonant excited-state Raman spectra for each molecule and matched it with its resonance-enhanced experimental spectrum. This comparison allows us to successfully identify the vibrational displacements of the observed FSRS bands, as well as validate the accuracy of the theoretical results through an experimental benchmark. The agreement between the experimental and computed results demonstrates that we are able to predict qualitatively accurate excited-state Raman spectra for these conjugated thiophenes, allowing for a more thorough interpretation of excited-state Raman signals at relatively low computational cost.

  20. Detection of trace gases from fermentation processes using photoacoustic spectroscopy and proton-transfer-reaction mass spectrometry

    OpenAIRE

    Boamfă-Ivan, Elena Iuliana

    2005-01-01

    This thesis presents novel interdisciplinary Physics - Biology research work that employed Photoacoustic Spectroscopy and Proton-Transfer-Reaction Mass Spectrometry. Both techniques were used in biological studies of trace gasses emitted by crop plants and fruit under stress situations. The findings of this research bring to light essential new features in plant physiology. A line tuneable (5 - 8 ?m) infrared CO-laser based photoacoustic detector was adapted to achieve fast, non-invasive and ...

  1. Charge transfer in green fluorescent protein.

    Science.gov (United States)

    van Thor, Jasper J; Sage, J Timothy

    2006-06-01

    Charge transfer reactions that contribute to the photoreactions of the wild type green fluorescent protein (GFP) do not occur in the isolated p-hydroxybenzylidene-imidazolidinone chromophore, demonstrating the role of the protein environment. The high quantum efficiency of the fluorescence photocycle that includes excited state proton transfer and the suppression of non-radiative pathways by the protein environment have been correlated with structural dynamics in the chromophore environment. A low quantum efficiency competing phototransformation reaction of GFP is accompanied by both proton and electron transfer, and closely mimics the charge redistribution that is occurring in the fluorescence photocycle. The protein response to this destabilising event has been demonstrated by cryo-trapping of early products in the reaction pathway and is found to be strong even at 100 K, including displacements of chromophore, protein, solvent and a photogenerated CO2 molecule derived from the decarboxylated Glu 222 side chain. We discuss the ramifications of the observation of strong conformational perturbations below the protein dynamical transition at approximately 200 K, in view of low temperature work on other light sensitive proteins such as myoglobin and bacteriorhodopsin. The proton and electron transfer in the phototransformation pathway mimics the proton and charge transfer which occurs during the fluorescence cycle, which leads to common structural responses in both photoreactions as shown by ultrafast spectroscopy. We review and discuss literature on light-induced and thermal charge transfer events, focusing on recent findings addressing conformational dynamics and implications for thermodynamic properties.

  2. Evolution of the N=82 shell gap below {sup 132}Sn inferred from core excited states in {sup 131}In

    Energy Technology Data Exchange (ETDEWEB)

    Gorska, M. [Gesellschaft fuer Schwerionenforschung (GSI), D-64291 Darmstadt (Germany)], E-mail: m.gorska@gsi.de; Caceres, L. [Gesellschaft fuer Schwerionenforschung (GSI), D-64291 Darmstadt (Germany); Departamento de Fisica Teorica, Universidad Autonoma de Madrid, E-28049 Madrid (Spain); Grawe, H. [Gesellschaft fuer Schwerionenforschung (GSI), D-64291 Darmstadt (Germany); Pfuetzner, M. [IEP, University of Warsaw, PL-00681 Warsaw (Poland); Jungclaus, A. [Departamento de Fisica Teorica, Universidad Autonoma de Madrid, E-28049 Madrid (Spain); Instituto de Estructuras de la Materia, CSIC, Serrano113bis, E-28006 Madrid (Spain); Pietri, S. [Department of Physics, University of Surrey, Guildford, GU2 7XH (United Kingdom); Werner-Malento, E. [IEP, University of Warsaw, PL-00681 Warsaw (Poland); Podolyak, Z.; Regan, P.H. [Department of Physics, University of Surrey, Guildford, GU2 7XH (United Kingdom); Rudolph, D. [Department of Physics, Lund University, S-22100 Lund (Sweden); Detistov, P. [Faculty of Physics, University of Sofia, BG-1164 Sofia (Bulgaria); Lalkovski, S. [Faculty of Physics, University of Sofia, BG-1164 Sofia (Bulgaria); School of Enviroment and Technology, University of Brighton, Brighton, BN2 4GJ (United Kingdom); Modamio, V.; Walker, J. [Departamento de Fisica Teorica, Universidad Autonoma de Madrid, E-28049 Madrid (Spain); Beck, T. [Gesellschaft fuer Schwerionenforschung (GSI), D-64291 Darmstadt (Germany); Bednarczyk, P. [Gesellschaft fuer Schwerionenforschung (GSI), D-64291 Darmstadt (Germany); Henryk Niewodniczanski Institute of Nuclear Physics, PAN, PL-31342 Krakow (Poland); Doornenbal, P. [Gesellschaft fuer Schwerionenforschung (GSI), D-64291 Darmstadt (Germany); Institut fuer Kernphysik, Universitaet zu Koeln, D-50937 Koeln (Germany); Geissel, H.; Gerl, J. [Gesellschaft fuer Schwerionenforschung (GSI), D-64291 Darmstadt (Germany)] (and others)

    2009-03-02

    The {gamma}-ray decay of an excited state in {sup 131}In, the one proton hole neighbor of the doubly magic {sup 132}Sn has been measured. A high-spin, core-excited isomer with T{sub 1/2}=630(60) ns was identified following production by both relativistic fragmentation of a {sup 136}Xe beam and fission of a {sup 238}U beam. This state deexcites by a single {gamma}-ray branch of 3782(2) keV from which direct evidence for the size of the N=82 shell gap is inferred. The results are discussed in comparison to a shell-model calculation including configurations across the closed shells at N=82 and Z=50.

  3. Escherichia coli dihydrofolate reductase catalyzed proton and hydride transfers: temporal order and the roles of Asp27 and Tyr100.

    Science.gov (United States)

    Liu, C Tony; Francis, Kevin; Layfield, Joshua P; Huang, Xinyi; Hammes-Schiffer, Sharon; Kohen, Amnon; Benkovic, Stephen J

    2014-12-23

    The reaction catalyzed by Escherichia coli dihydrofolate reductase (ecDHFR) has become a model for understanding enzyme catalysis, and yet several details of its mechanism are still unresolved. Specifically, the mechanism of the chemical step, the hydride transfer reaction, is not fully resolved. We found, unexpectedly, the presence of two reactive ternary complexes [enzyme:NADPH:7,8-dihydrofolate (E:NADPH:DHF)] separated by one ionization event. Furthermore, multiple kinetic isotope effect (KIE) studies revealed a stepwise mechanism in which protonation of the DHF precedes the hydride transfer from the nicotinamide cofactor (NADPH) for both reactive ternary complexes of the WT enzyme. This mechanism was supported by the pH- and temperature-independent intrinsic KIEs for the C-H→C hydride transfer between NADPH and the preprotonated DHF. Moreover, we showed that active site residues D27 and Y100 play a synergistic role in facilitating both the proton transfer and subsequent hydride transfer steps. Although D27 appears to have a greater effect on the overall rate of conversion of DHF to tetrahydrofolate, Y100 plays an important electrostatic role in modulating the pKa of the N5 of DHF to enable the preprotonation of DHF by an active site water molecule.

  4. Unbound excited states in $^{19}$,$^{17}$C

    CERN Document Server

    Satou, Y; Fukuda, N; Sugimoto, T; Kondo, Y; Matsui, N; Hashimoto, Y; Nakabayashi, T; Okumura, T; Shinohara, M; Motobayashi, T; Yanagisawa, Y; Aoi, N; Takeuchi, S; Gomi, T; Togano, Y; Kawai, S; Sakuraï, H; Ong, H J; Onishi, T K; Shimoura, S; Tamaki, M; Kobayashi, T; Otsu, H; Matsuda, Y; Endo, N; Kitayama, M; Ishihara, M

    2008-01-01

    The neutron-rich carbon isotopes 19,17C have been investigated via proton inelastic scattering on a liquid hydrogen target at 70 MeV/nucleon. The invariant mass method in inverse kinematics was employed to reconstruct the energy spectrum, in which fast neutrons and charged fragments were detected in coincidence using a neutron hodoscope and a dipole magnet system. A peak has been observed with an excitation energy of 1.46(10) MeV in 19C, while three peaks with energies of 2.20(3), 3.05(3), and 6.13(9) MeV have been observed in 17C. Deduced cross sections are compared with microscopic DWBA calculations based on p-sd shell model wave functions and modern nucleon-nucleus optical potentials. Jpi assignments are made for the four observed states as well as the ground states of both nuclei.

  5. Transport properties of local thermodynamic equilibrium hydrogen plasmas including electronically excited states.

    Science.gov (United States)

    Capitelli, M; Celiberto, R; Gorse, C; Laricchiuta, A; Pagano, D; Traversa, P

    2004-02-01

    A study of the dependence of transport coefficients (thermal conductivity, viscosity, electrical conductivity) of local thermodynamic equilibrium H2 plasmas on the presence of electronically atomic excited states, H(n), is reported. The results show that excited states with their "abnormal" cross sections strongly affect the transport coefficients especially at high pressure. Large relative errors are found when comparing the different quantities with the corresponding values obtained by using ground-state transport cross sections. The accuracy of the present calculation is finally discussed in the light of the selection of transport cross sections and in dependence of the considered number of excited states.

  6. Strategic modulation of the photonic properties of conjugated organometallic Pt-Ir polymers exhibiting hybrid CT-excited states.

    Science.gov (United States)

    Soliman, Ahmed M; Zysman-Colman, Eli; Harvey, Pierre D

    2015-04-01

    Polymer 6, ([trans-Pt(PBu3 )2 (C≡C)2 ]-[Ir(dFMeppy)2 (N^N)](PF6 ))n , (([Pt]-[Ir](PF6 ))n ; N^N = 5,5'-disubstituted-2,2'-bipyridyl; dFMeppy = 2-(2,4-difluoro-phenyl)-5-methylpyridine) is prepared along with model compounds. These complexes are investigated by absorption and emission spectroscopy and their photophysical and electrochemical properties are measured and compared with their corresponding non fluorinated complexes. Density functional theory (DFT) and time-dependent DFT computations corroborate the nature of the excited state as being a hybrid between the metal-to-ligand charge transfer ((1,3) MLCT) for the trans-Pt(PBu3 )2 (C≡CAr)2 unit, [Pt] and the metal-to-ligand/ligand-to-ligand' charge transfer ((1,3) ML'CT/LL'CT) for [Ir] with L = dFMeppy. Overall, the fluorination of the phenylpyridine group expectedly does not change the nature of the excited state but desirably induces a small blue shift of the absorption and emission bands along a slight decrease in emission quantum yields and lifetimes. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Relaxation dynamics in the excited states of a ketocyanine dye ...

    Indian Academy of Sciences (India)

    WINTEC

    Pramanik et al proposed the twisted intramolecular charge transfer (TICT) process in the S1 state, which .... trile clearly suggests that a photon of 400 nm light excites the molecule to its S2 state, the higher energy emission .... 400 nm photon as well as the dynamics of the re- laxation processes taking place in the S1 state. At.

  8. Calibration and intercomparison of acetic acid measurements using proton transfer reaction mass spectrometry (PTR-MS)

    Science.gov (United States)

    Haase, K.B.; Keene, W.C.; Pszenny, A.A.P.; Mayne, H.R.; Talbot, R.W.; Sive, B.C.

    2012-01-01

    Acetic acid is one of the most abundant organic acids in the ambient atmosphere, with maximum mixing ratios reaching into the tens of parts per billion by volume (ppbv) range. The identities and associated magnitudes of the major sources and sinks for acetic acid are poorly characterized, due in part to the limitation in available measurement techniques. This paper demonstrates that Proton Transfer Reaction Mass Spectrometry (PTR-MS) can reliably quantify acetic acid vapor in ambient air. Three different PTR-MS configurations were calibrated at low ppbv mixing ratios using permeation tubes, which yielded calibration factors between 7.0 and 10.9 normalized counts per second per ppbv (ncps ppbv−1) at a drift tube field strength of 132 townsend (Td). Detection limits ranged from 0.06 to 0.32 ppbv with dwell times of 5 s. These calibration factors showed negligible humidity dependence. Using the experimentally determined calibration factors, PTR-MS measurements of acetic acid during the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) campaign were validated against results obtained using Mist Chambers coupled with Ion Chromatography (MC/IC). An orthogonal least squares linear regression of paired data yielded a slope of 1.14 ± 0.06 (2σ), an intercept of 0.049 ± 20 (2σ) ppbv, and an R2 of 0.78. The median mixing ratio of acetic acid on Appledore Island, ME during the ICARTT campaign was 0.530 ± 0.025 ppbv with a minimum of 0.075 ± 0.004 ppbv, and a maximum of 3.555 ± 0.171 ppbv.

  9. Predicting IDH mutation status in grade II gliomas using amide proton transfer-weighted (APTw) MRI.

    Science.gov (United States)

    Jiang, Shanshan; Zou, Tianyu; Eberhart, Charles G; Villalobos, Maria A V; Heo, Hye-Young; Zhang, Yi; Wang, Yu; Wang, Xianlong; Yu, Hao; Du, Yongxing; van Zijl, Peter C M; Wen, Zhibo; Zhou, Jinyuan

    2017-09-01

    To assess the amide proton transfer-weighted (APTw) MRI features of isocitrate dehydrogenase (IDH)-wildtype and IDH-mutant grade II gliomas and to test the hypothesis that the APTw signal is a surrogate imaging marker for identifying IDH mutation status preoperatively. Twenty-seven patients with pathologically confirmed low-grade glioma, who were previously scanned at 3T, were retrospectively analyzed. The Mann-Whitney test was used to evaluate relationships between APTw intensities for IDH-mutant and IDH-wildtype groups, and receiver operator characteristic (ROC) analysis was used to assess the diagnostic performance of APTw. Based on histopathology and molecular analysis, seven cases were diagnosed as IDH-wildtype grade II gliomas and 20 cases as IDH-mutant grade II gliomas. The maximum and minimum APTw values, based on multiple regions of interest, as well as the whole-tumor histogram-based mean and 50th percentile APTw values, were significantly higher in the IDH-wildtype gliomas than in the IDH-mutant groups. This corresponded to the areas under the ROC curves of 0.89, 0.76, 0.75, and 0.75, respectively, for the prediction of the IDH mutation status. IDH-wildtype lesions typically were associated with relatively high APTw signal intensities as compared with IDH-mutant lesions. The APTw signal could be a valuable imaging biomarker by which to identify IDH1 mutation status in grade II gliomas. Magn Reson Med 78:1100-1109, 2017. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

  10. The π-Tetrel Bond and its Influence on Hydrogen Bonding and Proton Transfer.

    Science.gov (United States)

    Wei, Yuanxin; Li, Qingzhong; Scheiner, Steve

    2017-12-01

    The positive region that lies above the plane of F 2 TO (T=C and Si) interacts with malondialdehyde (MDA), which contains an intramolecular H-bond. The T atom of F 2 TO can lie either in the MDA molecular plane, forming a T⋅⋅⋅O tetrel bond, or F 2 TO can stack directly above MDA in a parallel arrangement. The former structure is more stable than the latter, and in either case, F 2 SiO engages in a much stronger interaction than does F 2 CO, reaching nearly 200 kJ mol -1 . The π-tetrel bond strengthens/weakens the MDA H-bond when the bond is formed to the hydroxyl/carbonyl group of MDA, and causes an accompanying inhibition/promotion of proton transfer within this H-bond; this effect is stronger for F 2 SiO. These same aspects can be tuned by substituents placed on any of the C atoms of MDA, although their effects are not fully correlated with the electron-withdrawing or electron-releasing properties of the substituent. A new type of π-π tetrel bond occurs when the π-hole on the T atom of F 2 TO approaches the middle carbon atom of MDA from above, and a similar configuration is also found between F 2 TO and benzene. Evidence for extensive C⋅⋅⋅C π-π tetrel bonding in crystal materials is presented. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. The reactions of ground and excited state sodium atoms with hydrogen halide molecules

    Science.gov (United States)

    Weiss, P. S.; Mestdagh, J. M.; Covinsky, M. H.; Balko, B. A.; Lee, Y. T.

    1988-10-01

    The reactions of ground and excited state Na atoms with hydrogen halide (HX) molecules have been studied using the crossed molecular beams method. With both increasing translational and increasing electronic energy, the reactive cross sections increase in the reactions of HCl and HBr. From product angular and velocity distributions detailed center-of-mass information is derived. For the reactions of Na (3 2S 1/2, 3 2P 1/2, 4 2D 5/2, 5 2S 1/2) with HCl, the product NaCl is back-scattered with respect to the incoming Na atom in the center-of-mass frame of reference. The reaction of each Na state studied with HCl is direct and proceeds via collinear and near-collinear Na-Cl-H approach geometries. For the Na (3 2P 3/2) and Na (4 2D 5/2) reactions with HCl the predominant transition state symmetry is 2Σ in a collinear (C ∞ν) Na-Cl-H geometry. This is consistent with the reaction proceeding via electron transfer from the Na atom to the halide atom. Absolute reactive cross sections for each state of Na studied with HCl were determined by comparison with both small and large angle elastic scattering. We were unable to observe Na atoms with over 4 eV of electronic energy react with HF up to collision energies of 13 kcal/mole.

  12. Triphenylamine-benzimidazole derivatives: synthesis, excited-state characterization, and DFT studies.

    Science.gov (United States)

    Pina, João; Seixas de Melo, J Sérgio; Batista, Rosa M F; Costa, Susana P G; Raposo, M Manuela M

    2013-11-15

    The synthesis and comprehensive characterization of the excited states of four novel triphenylamine-benzimidazole derivatives has been undertaken in solution (ethanol and methylcyclohexane) at room temperature. This includes the determination of the absorption, fluorescence, and triplet-triplet absorption spectra, together with quantum yields of fluorescence, internal conversion, intersystem crossing, and singlet oxygen. From the overall data the radiative and radiationless rate constants could be obtained, and it is shown that the compounds are highly emissive with the radiative decay dominating, with more than 70% of the quanta loss through this deactivation channel. The basic structure of the triphenylamine-benzimidazole derivatives (1a) was modified at position 5 of the heterocyclic moiety with electron-donating (OH (1b), OCH3 (1c)) or electron-withdrawing groups (CN, (1d)). It was found that the photophysical properties remain basically unchanged with the different substitutions, although a marked Stokes shift was observed with 1d. The presence and nature of a charge-transfer transition is discussed with the help of theoretical (DFT and TDFT) data. All compounds displayed exceptionally high thermal stability (between 399 and 454 °C) as seen by thermogravimetric analysis.

  13. Termolecular proton transfer reactions assisted by ionic hydrogen bond formation: Reactions of aromatic cations with polar molecules

    Science.gov (United States)

    Daly, G. M.; Meot-Ner, M.; Pithawalla, Y. B.; El-Shall, M. S.

    1996-05-01

    We present a new method that applies resonant-two-photon ionization to generate reactant ions selectively in the source of a high-pressure mass spectrometer (R2PI-HPMS) for kinetic and equilibrium studies. Applications to reactions that would be obscured otherwise in a complex system are illustrated in mixtures of benzene with polar solvent molecules (S). We observe a novel type of proton transfer reactions from C6H6+• to two S molecules where S=CH3CN, CH3OH, C2H5OH and CH3COOC2H5, and from C6H5CH3+• to two S molecules where S=CH3OH and C2H5OH to form protonated solvent S2H+ dimers. The reactions are driven by the strong hydrogen bonds in the S2H+ dimers and therefore require the formation of the hydrogen bond concertedly with proton transfer, to make the process energetically feasible. The adducts (C6H6+•)S are observed with blocked solvent molecules where the subsequent switching reaction to yield S2H+ is slow, but not with alcohol reactants that can form hydrogen-bonded chains that facilitate fast subsequent proton extraction. Correspondingly, kinetic simulations suggest that the mechanism proceeds through (C6H6+•)S+S→S2H++C6H5• and C6H6+•+2S→S2H++C6H5• reactions, respectively. The rate coefficients of these reactions are in the range 10-13-10-12 cm3 s-1 for the reaction through a bimolecular switching channel and in the range 10-26-10-28 cm6 s-1 for reaction through a direct termolecular proton extraction mechanism. The relation to energetics and reactant structure is examined.

  14. Conserved phosphoryl transfer mechanisms within kinase families and the role of the C8 proton of ATP in the activation of phosphoryl transfer

    Directory of Open Access Journals (Sweden)

    Kenyon Colin P

    2012-03-01

    Full Text Available Abstract Background The kinome is made up of a large number of functionally diverse enzymes, with the classification indicating very little about the extent of the conserved kinetic mechanisms associated with phosphoryl transfer. It has been demonstrated that C8-H of ATP plays a critical role in the activity of a range of kinase and synthetase enzymes. Results A number of conserved mechanisms within the prescribed kinase fold families have been identified directly utilizing the C8-H of ATP in the initiation of phosphoryl transfer. These mechanisms are based on structurally conserved amino acid residues that are within hydrogen bonding distance of a co-crystallized nucleotide. On the basis of these conserved mechanisms, the role of the nucleotide C8-H in initiating the formation of a pentavalent intermediate between the γ-phosphate of the ATP and the substrate nucleophile is defined. All reactions can be clustered into two mechanisms by which the C8-H is induced to be labile via the coordination of a backbone carbonyl to C6-NH2 of the adenyl moiety, namely a "push" mechanism, and a "pull" mechanism, based on the protonation of N7. Associated with the "push" mechanism and "pull" mechanisms are a series of proton transfer cascades, initiated from C8-H, via the tri-phosphate backbone, culminating in the formation of the pentavalent transition state between the γ-phosphate of the ATP and the substrate nucleophile. Conclusions The "push" mechanism and a "pull" mechanism are responsible for inducing the C8-H of adenyl moiety to become more labile. These mechanisms and the associated proton transfer cascades achieve the proton transfer via different family-specific conserved sets of amino acids. Each of these mechanisms would allow for the regulation of the rate of formation of the pentavalent intermediate between the ATP and the substrate nucleophile. Phosphoryl transfer within kinases is therefore a specific event mediated and regulated via the

  15. Sterics level the rates of proton transfer to [Ni(XPh){PhP(CH₂CH₂PPh₂)₂}]⁺ (X = O, S or Se).

    Science.gov (United States)

    Alwaaly, Ahmed; Henderson, Richard A

    2014-09-04

    Rates of proton transfers between lutH(+) (lut = 2,6-dimethylpyridine) and [Ni(XPh)(PhP{CH2CH2PPh2}2)](+) (X = O, S or Se) are slow and show little variation (k(O) : k(S) : k(Se) = 1 : 12 : 9). This unusual behaviour is a consequence of sterics affecting the optimal interaction between the reactants prior to proton transfer.

  16. Probing an Excited-State Atomic Transition Using Hyperfine Quantum Beat Spectroscopy

    CERN Document Server

    Wade, Christopher G; Keaveney, James; Adams, Charles S; Weatherill, Kevin J

    2014-01-01

    We describe a method to observe the dynamics of an excited-state transition in a room temperature atomic vapor using hyperfine quantum beats. Our experiment using cesium atoms consists of a pulsed excitation of the D2 transition, and continuous-wave driving of an excited-state transition from the 6P$_{3/2}$ state to the 7S$_{1/2}$ state. We observe quantum beats in the fluorescence from the 6P$_{3/2}$ state which are modified by the driving of the excited-state transition. The Fourier spectrum of the beat signal yields evidence of Autler-Townes splitting of the 6P$_{3/2}$, F = 5 hyperfine level and Rabi oscillations on the excited-state transition. A detailed model provides qualitative agreement with the data, giving insight to the physical processes involved.

  17. A Simple Hubbard Model for the Excited States of $\\pi$ Conjugated -acene Molecules

    CERN Document Server

    Sadeq, Z S

    2015-01-01

    In this paper we present a model that elucidates in a simple way the electronic excited states of $\\pi$ conjugated -acene molecules such as tetracene, pentacene, and hexacene. We use a tight-binding and truncated Hubbard model written in the electron-hole basis to describe the low lying excitations with reasonable quantitative accuracy. We are able to produce semi-analytic wavefunctions for the electronic states of the system, which allows us to compute the density correlation functions for various states such as the ground state, the first two singly excited states, and the lowest lying doubly excited state. We show that in this lowest lying doubly excited state, a state which has been speculated as to being involved in the singlet fission process, the electrons and holes behave in a triplet like manner.

  18. Tracking the Excited-State Time Evolution of the Visual Pigment with Multiconfigurational Quantum Chemistry

    National Research Council Canada - National Science Library

    Luis Manuel Frutos; Tadeusz Andruniów; Fabrizio Santoro; Nicolas Ferré; Massimo Olivucci

    2007-01-01

    ...). Here, we use a scaled quantum mechanics/molecular mechanics potential that reproduces the isomerization path determined with multiconfigurational perturbation theory to follow the excited-state evolution of bovine Rh...

  19. Role of the electronically excited-state hydrogen bonding and water clusters in the luminescent metal-organic framework.

    Science.gov (United States)

    Sui, Xiao; Ji, Min; Lan, Xin; Mi, Weihong; Hao, Ce; Qiu, Jieshan

    2013-05-20

    The electronically excited state and luminescence property of metal-organic framework Zn(3-tzba)(2,2'-bipy)(H2O)·nH2O have been investigated using the density functional theory (DFT) and time-dependent DFT (TDDFT). The calculated geometry and infrared spectra in the ground state are consistent with the experimental results. The frontier molecular orbitals and electronic configuration indicated that the origin of luminescence is attributed to a ligand-to-ligand charge transfer (LLCT). We theoretically demonstrated that the hydrogen bond H47···O5═C is weakened in the excited state S1; the weakening of the excited-state hydrogen bonding should be beneficial to the luminescence. To explore the effect of the water clusters on the luminescence, we studied four complexes Zn(3-tzba)(2,2'-bipy)(H2O)·3H2O, Zn(3-tzba)(2,2'-bipy)(H2O)·2H2O, Zn(3-tzba)(2,2'-bipy)(H2O)·H2O, and Zn(3-tzba)(2,2'-bipy)(H2O). The results reveal that the presence of water should play an important role in the emission characteristics of the MOF. Also, the UV-vis absorption and emission spectra of Zn(3-tzba)(2,2'-bipy)(H2O)·3H2O are in good agreement with the experimental results.

  20. OPTIMIZATION OF A BOXCAR INTEGRATOR AVERAGER SYSTEM FOR EXCITED-STATE LIFETIME MEASUREMENTS

    OpenAIRE

    NOVO, JBM; PESSINE, FBT

    1992-01-01

    The instrumental distortions due to adjustable parameters of the SR250 boxcar integrator/averager system and a pulsed-laser luminescence spectrometer on the excited-state lifetime decay waveforms were investigated. A theoretical model which takes into account the exponential moving average for this instrument and also RC distortion on the time-dependent luminescence signal is presented. An analytical expression relating the sample's excited-state lifetime and the adjustable instrumental param...

  1. Vibronic energy map and excited state vibrational characteristics of magnesium myoglobin determined by energy-selective fluorescence.

    OpenAIRE

    Kaposi, A D; Vanderkooi, J. M.

    1992-01-01

    The vibrational frequencies of the singlet excited state of Mg-substituted myoglobin and relative absorption probabilities were determined by fluorescence line-narrowing spectroscopy. These spectra contain information on the structure of the excited state species, and the availability of vibrationally resolved spectra from excited state biomolecules should aid in elucidating their structure and reactivity.

  2. Fourier transform infrared difference and time-resolved infrared detection of the electron and proton transfer dynamics in photosynthetic water oxidation.

    Science.gov (United States)

    Noguchi, Takumi

    2015-01-01

    Photosynthetic water oxidation, which provides the electrons necessary for CO₂ reduction and releases O₂ and protons, is performed at the Mn₄CaO₅ cluster in photosystem II (PSII). In this review, studies that assessed the mechanism of water oxidation using infrared spectroscopy are summarized focusing on electron and proton transfer dynamics. Structural changes in proteins and water molecules between intermediates known as Si states (i=0-3) were detected using flash-induced Fourier transform infrared (FTIR) difference spectroscopy. Electron flow in PSII and proton release from substrate water were monitored using the infrared changes in ferricyanide as an exogenous electron acceptor and Mes buffer as a proton acceptor. Time-resolved infrared (TRIR) spectroscopy provided information on the dynamics of proton-coupled electron transfer during the S-state transitions. In particular, a drastic proton movement during the lag phase (~200μs) before electron transfer in the S3→S0 transition was detected directly by monitoring the infrared absorption of a polarizable proton in a hydrogen bond network. Furthermore, the proton release pathways in the PSII proteins were analyzed by FTIR difference measurements in combination with site-directed mutagenesis, isotopic substitutions, and quantum chemical calculations. Therefore, infrared spectroscopy is a powerful tool for understanding the molecular mechanism of photosynthetic water oxidation. This article is part of a Special Issue entitled: Vibrational spectroscopies and bioenergetic systems. Copyright © 2014 Elsevier B.V. All rights reserved.

  3. One dimensional transient numerical study of the mass heat and charge transfer in a proton exchange membrane for PEMFC

    Energy Technology Data Exchange (ETDEWEB)

    Haddad, Djamel; Benmoussa, Hocine [Laboratory (LESEI), Faculty of Engineering, University of Batna (Algeria); Bourmada, Noureddine; Oulmi, Kafia [Laboratory LCCE, Faculty of Science, University of Batna (Algeria); Mahmah, Bouziane; Belhamel, Maiouf [CDER, BP, 62 Avenue-Observatoire, Bouzareah, Alger (Algeria)

    2009-06-15

    The objective of our study is to quantify the mass water transferred by various modes: diffusion, convection and migration. For the water transfer, the principal forces considered in the model are, the convection force, the osmotic force (i.e. diffusion) and the electric force (migration). The first of these forces results from a pressure gradient, the second of a concentration gradient and the third of a protons' migration from the anode to the cathode, which has an effect on the dipole of the water molecules (resistance force to the advancement). The numerical tool used to solve the equations' system is the finite element method. The results obtained numerically considering this method are concentration profiles and concentration variation with time and membrane thickness. These results illustrate the contribution of each mass transfer mode. (author)

  4. Phonon driven proton transfer in crystals with short strong hydrogen bonds

    NARCIS (Netherlands)

    Fontaine-Vive, F.; Johnson, M.R.; Kearley, G.J.; Cowan, J.A.; Howard, J.A.K.; Parker, S.F.

    2006-01-01

    Recent work on understanding why protons migrate with increasing temperature in short, strong hydrogen bonds is extended here to three more organic, crystalline systems. Inelastic neutron scattering and density functional theory based simulations are used to investigate structure, vibrations, and

  5. Quantum dynamical simulation of non-adiabatic proton transfers in aqueous solution methodology, molecular models and applications

    CERN Document Server

    Billeter, S R

    1998-01-01

    This thesis describes the methodology of quantum dynamical (QD) simulation of proton transfers in aqueous solutions, its implementation in the simulation program QDGROMOS and its application to protonated water and aqueous solutions of acetic acid. QDGROMOS is based on the GROMOS96 molecular dynamics (MD) program package. Many of the solutions to partial problems such as the representation of the quantum state, the solution of the time-dependent Schrodinger equation, the forces from the quantum subsystem, the time-ordering of the propagations and the correlations between the subsystems, are complementary. In chapter 1, various numerical propagation algorithms for solving the time-dependent Schrodinger equation under the influence of a constant Hamilton operator are compared against each other, mainly in one dimension. A Chebysheff series expansion and the expansion in terms of eigenstates of the Hamilton operator were found to be most stable. Chapter 2 describes the theory, the methods and the algorithms of Q...

  6. Detection of Ketones by a Novel Technology: Dipolar Proton Transfer Reaction Mass Spectrometry (DP-PTR-MS).

    Science.gov (United States)

    Pan, Yue; Zhang, Qiangling; Zhou, Wenzhao; Zou, Xue; Wang, Hongmei; Huang, Chaoqun; Shen, Chengyin; Chu, Yannan

    2017-05-01

    Proton transfer reaction mass spectrometry (PTR-MS) has played an important role in the field of real-time monitoring of trace volatile organic compounds (VOCs) due to its advantages such as low limit of detection (LOD) and fast time response. Recently, a new technology of proton extraction reaction mass spectrometry (PER-MS) with negative ions OH- as the reagent ions has also been presented, which can be applied to the detection of VOCs and even inorganic compounds. In this work, we combined the functions of PTR-MS and PER-MS in one instrument, thereby developing a novel technology called dipolar proton transfer reaction mass spectrometry (DP-PTR-MS). The selection of PTR-MS mode and PER-MS mode was achieved in DP-PTR-MS using only water vapor in the ion source and switching the polarity. In this experiment, ketones (denoted by M) were selected as analytes. The ketone (molecular weight denoted by m) was ionized as protonated ketone [M + H]+ [mass-to-charge ratio (m/z) m + 1] in PTR-MS mode and deprotonated ketone [M - H]- (m/z m - 1) in PER-MS mode. By comparing the m/z value of the product ions in the two modes, the molecular weight of the ketone can be positively identified as m. Results showed that whether it is a single ketone sample or a mixed sample of eight kinds of ketones, the molecular weights can be detected with DP-PTR-MS. The newly developed DP-PTR-MS not only maintains the original advantages of PTR-MS and PER-MS in sensitive and rapid detection of ketones, but also can estimate molecular weight of ketones. Graphical Abstract ᅟ.

  7. Detection of Ketones by a Novel Technology: Dipolar Proton Transfer Reaction Mass Spectrometry (DP-PTR-MS)

    Science.gov (United States)

    Pan, Yue; Zhang, Qiangling; Zhou, Wenzhao; Zou, Xue; Wang, Hongmei; Huang, Chaoqun; Shen, Chengyin; Chu, Yannan

    2017-05-01

    Proton transfer reaction mass spectrometry (PTR-MS) has played an important role in the field of real-time monitoring of trace volatile organic compounds (VOCs) due to its advantages such as low limit of detection (LOD) and fast time response. Recently, a new technology of proton extraction reaction mass spectrometry (PER-MS) with negative ions OH- as the reagent ions has also been presented, which can be applied to the detection of VOCs and even inorganic compounds. In this work, we combined the functions of PTR-MS and PER-MS in one instrument, thereby developing a novel technology called dipolar proton transfer reaction mass spectrometry (DP-PTR-MS). The selection of PTR-MS mode and PER-MS mode was achieved in DP-PTR-MS using only water vapor in the ion source and switching the polarity. In this experiment, ketones (denoted by M) were selected as analytes. The ketone (molecular weight denoted by m) was ionized as protonated ketone [M + H]+ [mass-to-charge ratio ( m/z) m + 1] in PTR-MS mode and deprotonated ketone [M - H]- ( m/z m - 1) in PER-MS mode. By comparing the m/z value of the product ions in the two modes, the molecular weight of the ketone can be positively identified as m. Results showed that whether it is a single ketone sample or a mixed sample of eight kinds of ketones, the molecular weights can be detected with DP-PTR-MS. The newly developed DP-PTR-MS not only maintains the original advantages of PTR-MS and PER-MS in sensitive and rapid detection of ketones, but also can estimate molecular weight of ketones.

  8. Proton transfers in a channelrhodopsin-1 studied by Fourier transform infrared (FTIR) difference spectroscopy and site-directed mutagenesis.

    Science.gov (United States)

    Ogren, John I; Yi, Adrian; Mamaev, Sergey; Li, Hai; Spudich, John L; Rothschild, Kenneth J

    2015-05-15

    Channelrhodopsin-1 from the alga Chlamydomonas augustae (CaChR1) is a low-efficiency light-activated cation channel that exhibits properties useful for optogenetic applications such as a slow light inactivation and a red-shifted visible absorption maximum as compared with the more extensively studied channelrhodopsin-2 from Chlamydomonas reinhardtii (CrChR2). Previously, both resonance Raman and low-temperature FTIR difference spectroscopy revealed that unlike CrChR2, CaChR1 under our conditions exhibits an almost pure all-trans retinal composition in the unphotolyzed ground state and undergoes an all-trans to 13-cis isomerization during the primary phototransition typical of other microbial rhodopsins such as bacteriorhodopsin (BR). Here, we apply static and rapid-scan FTIR difference spectroscopy along with site-directed mutagenesis to characterize the proton transfer events occurring upon the formation of the long-lived conducting P2 (380) state of CaChR1. Assignment of carboxylic C=O stretch bands indicates that Asp-299 (homolog to Asp-212 in BR) becomes protonated and Asp-169 (homolog to Asp-85 in BR) undergoes a net change in hydrogen bonding relative to the unphotolyzed ground state of CaChR1. These data along with earlier FTIR measurements on the CaChR1 → P1 transition are consistent with a two-step proton relay mechanism that transfers a proton from Glu-169 to Asp-299 during the primary phototransition and from the Schiff base to Glu-169 during P2 (380) formation. The unusual charge neutrality of both Schiff base counterions in the P2 (380) conducting state suggests that these residues may function as part of a cation selective filter in the open channel state of CaChR1 as well as other low-efficiency ChRs. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

  9. Properties of electronically excited states of four squaraine dyes and their complexes with fullerene C70: A theoretical investigation

    Science.gov (United States)

    Zhang, Jian; Li, Tingyu

    2017-09-01

    Solar cells sensitized by polypyridyl Ru(II) complexes exhibit relatively high efficiency, however those photo-sensitizers did not absorb the photons in the far-red and near-infrared region. At present, squaraine dyes have received considerable attention as their attractively intrinsic red light absorption and unusual high molar extinction coefficient. Here we applied density functional theory and time dependent density functional theory to investigate the properties of electronically excited states of four squaraine dyes and their complexes with fullerene C70. The influences of different functionals, basis sets and solvent effects are evaluated. To understand the photophysical properties, the investigations are basing on a classification method which splits the squaraine dyes and their complexes with fullerene C70 into two units to characterize the intramolecular density distribution. We present the signatures of their electronically excited states which are characterized as local excitation or charge-transfer excitation. The relationship between open-circuit voltage and the number of intramolecular hydrogen bonds in squaraine dyes are discussed.

  10. Ergodicity, configurational entropy and free energy in pigment solutions and plant photosystems: influence of excited state lifetime.

    Science.gov (United States)

    Jennings, Robert C; Zucchelli, Giuseppe

    2014-01-01

    We examine ergodicity and configurational entropy for a dilute pigment solution and for a suspension of plant photosystem particles in which both ground and excited state pigments are present. It is concluded that the pigment solution, due to the extreme brevity of the excited state lifetime, is non-ergodic and the configurational entropy approaches zero. Conversely, due to the rapid energy transfer among pigments, each photosystem is ergodic and the configurational entropy is positive. This decreases the free energy of the single photosystem pigment array by a small amount. On the other hand, the suspension of photosystems is non-ergodic and the configurational entropy approaches zero. The overall configurational entropy which, in principle, includes contributions from both the single excited photosystems and the suspension which contains excited photosystems, also approaches zero. Thus the configurational entropy upon photon absorption by either a pigment solution or a suspension of photosystem particles is approximately zero. Copyright © 2014 Elsevier B.V. All rights reserved.

  11. Design, synthesis and excited-state properties of mononuclear Ru(II) complexes of tridentate heterocyclic ligands.

    Science.gov (United States)

    Pal, Amlan K; Hanan, Garry S

    2014-09-07

    Artificial photosynthetic systems that contain light-harvesting coordination complexes may one day replace conventional non-renewable sources of energy with renewable solar energy sources. Light-Harvesting Complexes (LHC) are important components of natural photosynthetic systems and are also sought after in artificial systems as well. Polynuclear photoactive complexes are therefore very attractive, and those based on stereogenic [Ru(2,2'-bipyridine)3](2+) are photophysically appealing, but difficult to obtain in a stereochemically pure form. On the other hand, polynuclear complexes based on the achiral [Ru(2,2':6',2''-terpyridine)2](2+) motif are easy to synthesise, however, these complexes are devoid of attractive excited-state properties. Hence strategies to increase the r.t. excited-state lifetime of these complexes would be of practical importance in vectorial electron and/or electron transfer in various optoelectronic applications. This tutorial review will report on the sophisticated synthetic strategies currently in use to enhance the photophysical properties of mononuclear Ru(II) complexes of tridentate ligands at room temperature.

  12. Electronic excited states responsible for dimer formation upon UV absorption directly by thymine strands: joint experimental and theoretical study.

    Science.gov (United States)

    Banyasz, Akos; Douki, Thierry; Improta, Roberto; Gustavsson, Thomas; Onidas, Delphine; Vayá, Ignacio; Perron, Marion; Markovitsi, Dimitra

    2012-09-12

    The study addresses interconnected issues related to two major types of cycloadditions between adjacent thymines in DNA leading to cyclobutane dimers (TTs) and (6-4) adducts. Experimental results are obtained for the single strand (dT)(20) by steady-state and time-resolved optical spectroscopy, as well as by HPLC coupled to mass spectrometry. Calculations are carried out for the dinucleoside monophosphate in water using the TD-M052X method and including the polarizable continuum model; the reliability of TD-M052X is checked against CASPT2 calculations regarding the behavior of two stacked thymines in the gas phase. It is shown that irradiation at the main absorption band leads to cyclobutane dimers (TTs) and (6-4) adducts via different electronic excited states. TTs are formed via (1)ππ* excitons; [2 + 2] dimerization proceeds along a barrierless path, in line with the constant quantum yield (0.05) with the irradiation wavelength, the contribution of the (3)ππ* state to this reaction being less than 10%. The formation of oxetane, the reaction intermediate leading to (6-4) adducts, occurs via charge transfer excited states involving two stacked thymines, whose fingerprint is detected in the fluorescence spectra; it involves an energy barrier explaining the important decrease in the quantum yield of (6-4) adducts with the irradiation wavelength.

  13. Conserved phosphoryl transfer mechanisms within kinase families and the role of the C8 proton of ATP in the activation of phosphoryl transfer

    CSIR Research Space (South Africa)

    Kenyon, CP

    2012-03-01

    Full Text Available , with the concomitant re-protonation of C8. Groups 8 There is only one member in each of Group 8, Group 9, Group 10 and Group 11 kinases. Group 8 consists of ribo- flavin kinase from Schizosaccharomyces pombe and Homo sapiens (flavokinase family) (Additional file 1... 3) in that the latter two are pyrophosphotrans- ferases transferring a pyrophosphate group from a nucleo- side triphosphate, such as ATP to the hydroxyl of thiamine. All enzymes in Group 7 are homo-dimeric, with the active site comprising amino...

  14. Analytical linear energy transfer model including secondary particles: calculations along the central axis of the proton pencil beam.

    Science.gov (United States)

    Marsolat, F; De Marzi, L; Pouzoulet, F; Mazal, A

    2016-01-21

    In proton therapy, the relative biological effectiveness (RBE) depends on various types of parameters such as linear energy transfer (LET). An analytical model for LET calculation exists (Wilkens' model), but secondary particles are not included in this model. In the present study, we propose a correction factor, L sec, for Wilkens' model in order to take into account the LET contributions of certain secondary particles. This study includes secondary protons and deuterons, since the effects of these two types of particles can be described by the same RBE-LET relationship. L sec was evaluated by Monte Carlo (MC) simulations using the GATE/GEANT4 platform and was defined by the ratio of the LET d distributions of all protons and deuterons and only primary protons. This method was applied to the innovative Pencil Beam Scanning (PBS) delivery systems and L sec was evaluated along the beam axis. This correction factor indicates the high contribution of secondary particles in the entrance region, with L sec values higher than 1.6 for a 220 MeV clinical pencil beam. MC simulations showed the impact of pencil beam parameters, such as mean initial energy, spot size, and depth in water, on L sec. The variation of L sec with these different parameters was integrated in a polynomial function of the L sec factor in order to obtain a model universally applicable to all PBS delivery systems. The validity of this correction factor applied to Wilkens' model was verified along the beam axis of various pencil beams in comparison with MC simulations. A good agreement was obtained between the corrected analytical model and the MC calculations, with mean-LET deviations along the beam axis less than 0.05 keV μm(-1). These results demonstrate the efficacy of our new correction of the existing LET model in order to take into account secondary protons and deuterons along the pencil beam axis.

  15. Excited state solvatochromic and prototropic behaviour of 4-aminodiphenylamine and 4,4'-diaminodiphenylamine—A comparative study by electronic spectra

    Science.gov (United States)

    Nayaki, S. Kothai; Swaminathan, M.

    2006-06-01

    Solvatochromic and prototropic behaviour of 4-aminodiphenylamine (4ADA) and 4,4'-diaminodiphenylamine (DADA) have been investigated in the solvents of different polarity and at various acid-base concentrations in the ground and excited states using absorption and fluorescence spectra. Solvatochromic shifts have been analysed and observed shifts are explained by the hydrogen bonding interactions. The prototropic study reveals that (i) absorption maximum of monocation of DADA is red shifted to its neutral form, and (ii) the fluorescence of 4ADA is red shifted on protonation. The abnormal fluorescence of 4ADA + is found to be due to large solvent relaxation in polar medium.

  16. Excited state solvatochromic and prototropic behaviour of 4-aminodiphenylamine and 4,4'-diaminodiphenylamine--a comparative study by electronic spectra.

    Science.gov (United States)

    Nayaki, S Kothai; Swaminathan, M

    2006-06-01

    Solvatochromic and prototropic behaviour of 4-aminodiphenylamine (4ADA) and 4,4'-diaminodiphenylamine (DADA) have been investigated in the solvents of different polarity and at various acid-base concentrations in the ground and excited states using absorption and fluorescence spectra. Solvatochromic shifts have been analysed and observed shifts are explained by the hydrogen bonding interactions. The prototropic study reveals that (i) absorption maximum of monocation of DADA is red shifted to its neutral form, and (ii) the fluorescence of 4ADA is red shifted on protonation. The abnormal fluorescence of 4ADA+ is found to be due to large solvent relaxation in polar medium.

  17. Effect of Basic Site Substituents on Concerted Proton-Electron Transfer in Hydrogen Bonded-Pyridyl Phenols

    Science.gov (United States)

    Markle, Todd F.; Tronic, Tristan A.; DiPasquale, Antonio G.; Kaminsky, Werner

    2012-01-01

    Separated concerted proton-electron transfer (sCPET) reactions of two series of phenols with pendent substituted pyridyl moieties are described. The pyridine is either attached directly to the phenol (HOAr-pyX) or connected through a methylene linker (HOArCH2pyX) (X = 4-NO2, 5-CF3, 4-CH3, 4-NMe2). Electron-donating and -withdrawing substituents also have a substantial effect on the chemical environment of the transferring proton, as indicated by IR and 1H NMR spectra, X-ray structures and computational studies. One-electron oxidation of the phenols occurs concomitantly with proton transfer from the phenolic oxygen to the pyridyl nitrogen. The oxidation potentials vary linearly with the pKa of the free pyridine (pyX), with slopes slightly below the Nerstian value of 59 mV/pKa. For the HOArCH2pyX series, the rate constants ksCPET for oxidation by NAr3•+ or [Fe(diimine)3]3+ vary primarily with the thermodynamic driving force (ΔG°sCPET), whether ΔG° is changed by varying the potential of the oxidant or the substituent on the pyridine, indicating a constant intrinsic barrier λ. In contrast, the substituents in the HOAr-pyX series affect λ as well as ΔG°sCPET, and compounds with electron-withdrawing substituents have significantly lower reactivity. The relationship between the structural and spectroscopic properties of the phenols and their CPET reactivity is discussed. PMID:23176252

  18. Effect of basic site substituents on concerted proton-electron transfer in hydrogen-bonded pyridyl-phenols.

    Science.gov (United States)

    Markle, Todd F; Tronic, Tristan A; DiPasquale, Antonio G; Kaminsky, Werner; Mayer, James M

    2012-12-20

    Separated concerted proton-electron transfer (sCPET) reactions of two series of phenols with pendent substituted pyridyl moieties are described. The pyridine is either attached directly to the phenol (HOAr-pyX) or connected through a methylene linker (HOArCH(2)pyX) (X = 4-NO(2), 5-CF(3), 4-CH(3), and 4-NMe(2)). Electron-donating and -withdrawing substituents have a substantial effect on the chemical environment of the transferring proton, as indicated by IR and (1)H NMR spectra, X-ray structures, and computational studies. One-electron oxidation of the phenols occurs concomitantly with proton transfer from the phenolic oxygen to the pyridyl nitrogen. The oxidation potentials vary linearly with the pK(a) of the free pyridine (pyX), with slopes slightly below the Nerstian value of 59 mV/pK(a). For the HOArCH(2)pyX series, the rate constants k(sCPET) for oxidation by NAr(3)(•+) or [Fe(diimine)(3)](3+) vary primarily with the thermodynamic driving force (ΔG°(sCPET)), whether ΔG° is changed by varying the potential of the oxidant or the substituent on the pyridine, indicating a constant intrinsic barrier λ. In contrast, the substituents in the HOAr-pyX series affect λ as well as ΔG°(sCPET), and compounds with electron-withdrawing substituents have significantly lower reactivity. The relationship between the structural and spectroscopic properties of the phenols and their CPET reactivity is discussed.

  19. Below-band-gap ionization of liquid-to-supercritical ammonia: geminate recombination via proton-coupled back electron transfer.

    Science.gov (United States)

    Urbanek, Janus; Vöhringer, Peter

    2014-01-09

    Femtosecond multiphoton ionization experiments have been conducted on ammonia over a wide range of temperature (225 K ≤ T ≤ 490 K) and density (0.18 g/cm(3) ≤ ρ ≤ 0.7 g/cm(3)), thereby covering the liquid and supercritical phases. The experiments were carried out with excitation pulses having a wavelength of 400 nm, and the ionization was found to involve two photons. Therefore, the total ionization energy in this study corresponds to 6.2 eV, which is roughly 2 eV below the valence-to-conduction band gap of the fluid. The ionization generates solvated electrons, which have been detected through their characteristic near-infrared resonance, and must be facilitated through a coupling to nuclear degrees of freedom of the liquid. The recombination of the solvated electron with the geminate fragments was found to obey predominantly single-exponential kinetics with time constants between 500 fs and 1 ps. Only a very minor fraction of the photogenerated electrons is able to escape from the geminate recombination. The results indicate that the majority of electrons are injected into suitable trapping sites located between the first and second solvation shells of the initially ionized ammonia molecules. Such configurations can be considered as instantly reactive and facilitate an ultrafast barrierless electron annihilation. This process is found to exhibit a pronounced kinetic isotope effect, which indicates that the electronic decay is accompanied by the transfer of a proton. The sequence of ionization and recombination events can therefore be described appropriately as a proton-coupled electron transfer (PCET) followed by a proton-coupled back electron transfer (PCBET).

  20. Photocatalytic Conversion of Nitrobenzene to Aniline through Sequential Proton-Coupled One-Electron Transfers from a Cadmium Sulfide Quantum Dot.

    Science.gov (United States)

    Jensen, Stephen C; Homan, Stephanie Bettis; Weiss, Emily A

    2016-02-10

    This paper describes the use of cadmium sulfide quantum dots (CdS QDs) as visible-light photocatalysts for the reduction of nitrobenzene to aniline through six sequential photoinduced, proton-coupled electron transfers. At pH 3.6-4.3, the internal quantum yield of photons-to-reducing electrons is 37.1% over 54 h of illumination, with no apparent decrease in catalyst activity. Monitoring of the QD exciton by transient absorption reveals that, for each step in the catalytic cycle, the sacrificial reductant, 3-mercaptopropionic acid, scavenges the excitonic hole in ∼5 ps to form QD(•-); electron transfer to nitrobenzene or the intermediates nitrosobenzene and phenylhydroxylamine then occurs on the nanosecond time scale. The rate constants for the single-electron transfer reactions are correlated with the driving forces for the corresponding proton-coupled electron transfers. This result suggests, but does not prove, that electron transfer, not proton transfer, is rate-limiting for these reactions. Nuclear magnetic resonance analysis of the QD-molecule systems shows that the photoproduct aniline, left unprotonated, serves as a poison for the QD catalyst by adsorbing to its surface. Performing the reaction at an acidic pH not only encourages aniline to desorb but also increases the probability of protonated intermediates; the latter effect probably ensures that recruitment of protons is not rate-limiting.

  1. Measurement of Lactate Content and Amide Proton Transfer Values in the Basal Ganglia of a Neonatal Piglet Hypoxic-Ischemic Brain Injury Model Using MRI.

    Science.gov (United States)

    Zheng, Y; Wang, X-M

    2017-04-01

    As amide proton transfer imaging is sensitive to protein content and intracellular pH, it has been widely used in the nervous system, including brain tumors and stroke. This work aimed to measure the lactate content and amide proton transfer values in the basal ganglia of a neonatal piglet hypoxic-ischemic brain injury model by using MR spectroscopy and amide proton transfer imaging. From 58 healthy neonatal piglets (3-5 days after birth; weight, 1-1.5 kg) selected initially, 9 piglets remained in the control group and 43 piglets, in the hypoxic-ischemic brain injury group. Single-section amide proton transfer imaging was performed at the coronal level of the basal ganglia. Amide proton transfer values of the bilateral basal ganglia were measured in all piglets. The ROI of MR spectroscopy imaging was the right basal ganglia, and the postprocessing was completed with LCModel software. After hypoxic-ischemic insult, the amide proton transfer values immediately decreased, and at 0-2 hours, they remained at their lowest level. Thereafter, they gradually increased and finally exceeded those of the control group at 48-72 hours. After hypoxic-ischemic insult, the lactate content increased immediately, was maximal at 2-6 hours, and then gradually decreased to the level of the control group. The amide proton transfer values were negatively correlated with lactate content (r = -0.79, P < .05). This observation suggests that after hypoxic-ischemic insult, the recovery of pH was faster than that of lactate homeostasis. © 2017 by American Journal of Neuroradiology.

  2. The Proton Elastic Form Factor Ratio mu(p) G**p(E)/G**p(M) at Low Momentum Transfer

    Energy Technology Data Exchange (ETDEWEB)

    G. Ron; J. Glister; B. Lee; K. Allada; W. Armstrong; J. Arrington; A. Beck; F. Benmokhtar; B.L. Berman; W. Boeglin; E. Brash; A. Camsonne; J. Calarco; J. P. Chen; Seonho Choi; E. Chudakov; L. Coman; B. Craver; F. Cusanno; J. Dumas; C. Dutta; R. Feuerbach; A. Freyberger; S. Frullani; F. Garibaldi; R. Gilman; O. Hansen; D. W. Higinbotham; T. Holmstrom; C.E. Hyde; H. Ibrahim; Y. Ilieva; C. W. de Jager; X. Jiang; M. K. Jones; A. Kelleher; E. Khrosinkova; E. Kuchina; G. Kumbartzki; J. J. LeRose; R. Lindgren; P. Markowitz; S. May-Tal Beck; E. McCullough; D. Meekins; M. Meziane; Z.-E. Meziani; R. Michaels; B. Moffit; B.E. Norum; Y. Oh; M. Olson; M. Paolone; K. Paschke; C. F. Perdrisat; E. Piasetzky; M. Potokar; R. Pomatsalyuk; I. Pomerantz; A. Puckett; V. Punjabi; X. Qian; Y. Qiang; R. Ransome; M. Reyhan; J. Roche; Y. Rousseau; A. Saha; A.J. Sarty; B. Sawatzky; E. Schulte; M. Shabestari; A. Shahinyan; R. Shneor; S. ˇ Sirca; K. Slifer; P. Solvignon; J. Song; R. Sparks; R. Subedi; S. Strauch; G. M. Urciuoli; K. Wang; B. Wojtsekhowski; X. Yan; H. Yao; X. Zhan; X. Zhu

    2007-11-01

    High precision measurements of the proton elastic form factor ratio have been made at four-momentum transfers, Q^2, between 0.2 and 0.5 GeV^2. The new data, while consistent with previous results, clearly show a ratio less than unity and significant differences from the central values of several recent phenomenological fits. By combining the new form-factor ratio data with an existing cross-section measurement, one finds that in this Q^2 range the deviation from unity is primarily due to GEp being smaller than the dipole parameterization.

  3. Thermally induced double proton transfer in GG and wobble GT base pairs: A possible origin of the mutagenic guanine

    Science.gov (United States)

    Padermshoke, Adchara; Katsumoto, Yukiteru; Masaki, Ryuta; Aida, Misako

    2008-05-01

    Double proton transfer (DPT) reactions in three guanine-guanine (GG) dimers, a guanine-thymine wobble (wGT) base pair, and a model compound 4(3H)-pyrimidinone (k-PP) dimer have been investigated using ab initio MO calculations and liquid-phase infrared (IR) spectroscopy. The calculations suggest that the DPT processes in these dimers are energetically accessible. Temperature-dependent IR measurements of the model compound reveal that slight thermal energy can induce the DPT reaction, and hence the enol tautomer can result. The present study demonstrates a potential pathway for the generation of the mutagenic amino-enol form of guanine.

  4. Photochemistry of excited-state species in natural waters: a role for particulate organic matter.

    Science.gov (United States)

    Cottrell, Barbara A; Timko, Stephen A; Devera, Lianne; Robinson, Alice K; Gonsior, Michael; Vizenor, Ashley E; Simpson, André J; Cooper, William J

    2013-09-15

    Laser flash photolysis (LFP) was used to characterize a triplet excited state species isolated from Black River and San Joaquin wetlands particulate organic matter (POM). The solubilized organic matter, isolated from POM by pH-independent diffusion in distilled water, was named PdOM. UV-visible absorption spectroscopy, excitation-emission matrix spectroscopy (EEMs), and (1)H NMR were used to characterize the PdOM. While LFP of dissolved organic matter (DOM) is known to generate the solvated electron, LFP of the PdOM transient in argon-, air-, and nitrous oxide-saturated solutions indicated that this was a triplet excited state species ((3)PdOM*). The lifetime and the reactivity of (3)PdOM* with sorbic acid, a triplet state quencher, were compared with that of the triplet excited state of benzophenone, a DOM proxy. A second excited state species (designated DOM*), with a longer lifetime, was reported in a number of previous studies but not characterized. The lifetime of DOM*, measured for seventeen organic matter isolates, lignin, tannic acid, and three wetlands plant extracts, was shown to differentiate allochthonous from autochthonous DOM. (3)POM* and DOM* were also observed in lake water and a constructed wetlands' water. Aqueous extracts of fresh and aged plant material from the same wetland were shown to be one source of these excited state species. This study provides evidence of a role for POM in the photochemistry of natural and constructed wetland waters. Copyright © 2013 Elsevier Ltd. All rights reserved.

  5. Effect of xanthophyll composition on the chlorophyll excited state lifetime in plant leaves and isolated LHCII

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, Matthew P.; Zia, Ahmad [School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS (United Kingdom); Horton, Peter [Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN (United Kingdom); Ruban, Alexander V., E-mail: a.ruban@qmul.ac.uk [School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS (United Kingdom)

    2010-07-19

    Xanthophyll excited states have been implicated by transient absorption and two-photon excitation studies in playing a key role in the regulation of photosynthetic light harvesting via photoprotective energy dissipation. For any proposed quenching mechanism to be effective it must reduce the chlorophyll excited state lifetime from 2 ns to {approx}0.5-0.4 ns. In the presented study the effect of xanthophyll composition on the chlorophyll excited state lifetime in Arabidopsis leaves in the light harvesting (F{sub m}) and photoprotective (NPQ) states was determined. The data was compared to the chlorophyll excited state lifetime of native isolated LHCII and CP26 in detergent micelles with varying xanthophyll composition. It was found that although the differences in xanthophyll composition between LHC complexes from various Arabidopsis mutants were sufficient to explain the varying F{sub m} lifetime (and varying PSII efficiency), they were not of a sufficient scale to fully explain the observed differences in the NPQ lifetimes. Only when the LHC complexes were exposed to a low detergent/low pH media, a condition known to mimic the conformational state of LHCII associated with NPQ in vivo, were variations in excited state lifetime large enough to explain the differences observed in leaves. Furthermore, the data reveal that the replacement of lutein by either zeaxanthin or violaxanthin in the internal xanthophyll binding sites of LHCII and CP26 reduces the efficiency of energy dissipation in the photoprotective state in leaves and isolated complexes.

  6. Protonated nitrosamide

    DEFF Research Database (Denmark)

    Egsgaard, H.; Carlsen, L.; Øgaard Madsen, J.

    1994-01-01

    The protonated nitrosamide, NH3NO+, has been generated by chemical ionization mass spectrometry. Although a direct search for this species in ammonia flames has proved negative, fast proton transfer to major flame constituents is supported experimentally as well as by MO calculations....

  7. Pulsed radiation studies of carotenoid radicals and excited states

    Energy Technology Data Exchange (ETDEWEB)

    Burke, M

    2001-04-01

    The one-electron reduction potentials of the radical cations of five dietary carotenoids, in aqueous micellar environments, have been obtained from a pulse radiolysis study of electron transfer between the carotenoids and tryptophan radical cations as a function of pH, and lie in the range 980 to 1060 mV. The decays of the carotenoid radical cations suggest a distribution of exponential lifetimes. The radicals persist for up to about one second, depending on the medium and may re-orientate within a biological environment to react with other biomolecules, such as tyrosine, cysteine or ascorbic acid, which was indeed confirmed. Spectral information of carotenoid pigmented liposomes has been collected, subsequently pulse radiolysis was used to generate the radical cations of {beta}-carotene, zeaxanthin and lutein, in unilamellar vesicles of dipalmitoyl phosphatidyl choline. The rate constants for the 'repair' of these carotenoid radical cations by water-soluble vitamin C were found to be similar ({approx}1 x 10{sup 7} M{sup -1}s{sup -1}) for {beta}-carotene and zeaxanthin and somewhat lower ({approx}0.5 x 10{sup 7} M{sup -1}s{sup -1}) for lutein. The results are discussed in terms of the microenvironment of the carotenoids and suggest that for {beta}-carotene, a hydrocarbon carotenoid, the radical cation is able to interact with a water-soluble species even though the parent hydrocarbon carotenoid is probably entirely in the non-polar region of the liposome. Studies investigating the ability of ingested lycopene to protect human lymphoid cells against singlet oxygen and nitrogen dioxide radical mediated cell damage have shown that a high lycopene diet is beneficial in protecting human cells against reactive oxygen species. Triplet states of carotenoids were produced in benzene solvent and their triplet lifetimes were found to depend on the concentration of the parent molecule. The rate constants obtained for ground state quenching correlate with the number

  8. Characterisation of Dissolved Organic Carbon by Thermal Desorption - Proton Transfer Reaction - Mass Spectrometry

    Science.gov (United States)

    Materić, Dušan; Peacock, Mike; Kent, Matthew; Cook, Sarah; Gauci, Vincent; Röckmann, Thomas; Holzinger, Rupert

    2017-04-01

    Dissolved organic carbon (DOC) is an integral component of the global carbon cycle. DOC represents an important terrestrial carbon loss as it is broken down both biologically and photochemically, resulting in the release of carbon dioxide (CO2) to the atmosphere. The magnitude of this carbon loss can be affected by land management (e.g. drainage). Furthermore, DOC affects autotrophic and heterotrophic processes in aquatic ecosystems, and, when chlorinated during water treatment, can lead to the release of harmful trihalomethanes. Numerous methods have been used to characterise DOC. The most accessible of these use absorbance and fluorescence properties to make inferences about chemical composition, whilst high-performance size exclusion chromatography can be used to determine apparent molecular weight. XAD fractionation has been extensively used to separate out hydrophilic and hydrophobic components. Thermochemolysis or pyrolysis Gas Chromatography - Mass Spectrometry (GC-MS) give information on molecular properties of DOC, and 13C NMR spectroscopy can provide an insight into the degree of aromaticity. Proton Transfer Reaction - Mass Spectrometry (PTR-MS) is a sensitive, soft ionisation method suitable for qualitative and quantitative analysis of volatile and semi-volatile organic vapours. So far, PTR-MS has been used in various environmental applications such as real-time monitoring of volatile organic compounds (VOCs) emitted from natural and anthropogenic sources, chemical composition measurements of aerosols etc. However, as the method is not compatible with water, it has not been used for analysis of organic traces present in natural water samples. The aim of this work was to develop a method based on thermal desorption PTR-MS to analyse water samples in order to characterise chemical composition of dissolved organic carbon. We developed a clean low-pressure evaporation/sublimation system to remove water from samples and thermal desorption system to introduce

  9. Patterns of Failure After Proton Therapy in Medulloblastoma; Linear Energy Transfer Distributions and Relative Biological Effectiveness Associations for Relapses

    Energy Technology Data Exchange (ETDEWEB)

    Sethi, Roshan V. [Harvard Medical School, Massachusetts General Hospital, Boston, Massachusetts (United States); Giantsoudi, Drosoula; Raiford, Michael; Malhi, Imran; Niemierko, Andrzej [Department of Radiation Oncology, Massachusetts General Hospital, Boston, Massachusetts (United States); Rapalino, Otto; Caruso, Paul [Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts (United States); Yock, Torunn I.; Tarbell, Nancy J.; Paganetti, Harald [Department of Radiation Oncology, Massachusetts General Hospital, Boston, Massachusetts (United States); MacDonald, Shannon M., E-mail: smacdonald@partners.org [Department of Radiation Oncology, Massachusetts General Hospital, Boston, Massachusetts (United States)

    2014-03-01

    Purpose: The pattern of failure in medulloblastoma patients treated with proton radiation therapy is unknown. For this increasingly used modality, it is important to ensure that outcomes are comparable to those in modern photon series. It has been suggested this pattern may differ from photons because of variations in linear energy transfer (LET) and relative biological effectiveness (RBE). In addition, the use of matching fields for delivery of craniospinal irradiation (CSI) may influence patterns of relapse. Here we report the patterns of failure after the use of protons, compare it to that in the available photon literature, and determine the LET and RBE values in areas of recurrence. Methods and Materials: Retrospective review of patients with medulloblastoma treated with proton radiation therapy at Massachusetts General Hospital (MGH) between 2002 and 2011. We documented the locations of first relapse. Discrete failures were contoured on the original planning computed tomography scan. Monte Carlo calculation methods were used to estimate the proton LET distribution. Models were used to estimate RBE values based on the LET distributions. Results: A total of 109 patients were followed for a median of 38.8 months (range, 1.4-119.2 months). Of the patients, 16 experienced relapse. Relapse involved the supratentorial compartment (n=8), spinal compartment (n=11), and posterior fossa (n=5). Eleven failures were isolated to a single compartment; 6 failures in the spine, 4 failures in the supratentorium, and 1 failure in the posterior fossa. The remaining patients had multiple sites of disease. One isolated spinal failure occurred at the spinal junction of 2 fields. None of the 70 patients treated with an involved-field-only boost failed in the posterior fossa outside of the tumor bed. We found no correlation between Monte Carlo-calculated LET distribution and regions of recurrence. Conclusions: The most common site of failure in patients treated with protons for

  10. Excited-State Dynamics of Carotenoids Studied by Femtosecond Transient Absorption Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Ingu; Pang, Yoonsoo [Department of Physics and Photon Science, Gwangju (Korea, Republic of); Lee, Sebok [Gwangju Institute of Science and Technology, Gwangju (Korea, Republic of)

    2014-03-15

    Carotenoids, natural antenna pigments in photosynthesis share a symmetric backbone of conjugated polyenes. Contrary to the symmetric and almost planar geometries of carotenoids, excited state structure and dynamics of carotenoids are exceedingly complex. In this paper, recent infrared and visible transient absorption measurements and excitation dependent dynamics of 8'-apo-β-caroten-8'-al and 7',7'-dicyano-7'-apo-β-carotene will be reviewed. The recent visible transient absorption measurements of 8'-apo-β-caroten-8'-al in polar and nonpolar solvents will also be introduced to emphasize the complex excited-state dynamics and unsolved problems in the S{sub 2} and S{sub 1} excited states.

  11. On excited states in real-time AdS/CFT

    Energy Technology Data Exchange (ETDEWEB)

    Botta-Cantcheff, Marcelo; Martínez, Pedro J.; Silva, Guillermo A. [Instituto de Física de La Plata - CONICET & Departamento de Física - UNLP,C.C. 67, 1900 La Plata (Argentina)

    2016-02-25

    The Skenderis-van Rees prescription, which allows the calculation of time-ordered correlation functions of local operators in CFT’s using holographic methods is studied and applied for excited states. Calculation of correlators and matrix elements of local CFT operators between generic in/out states are carried out in global Lorentzian AdS. We find the precise form of such states, obtain an holographic formula to compute the inner product between them, and using the consistency with other known prescriptions, we argue that the in/out excited states built according to the Skenderis-Van Rees prescription correspond to coherent states in the (large-N) AdS-Hilbert space. This is confirmed by explicit holographic computations. The outcome of this study has remarkable implications on generalizing the Hartle-Hawking construction for wave functionals of excited states in AdS quantum gravity.

  12. Tracking excited-state charge and spin dynamics in iron coordination complexes

    DEFF Research Database (Denmark)

    Zhang, Wenkai; Alonso-Mori, Roberto; Bergmann, Uwe

    2014-01-01

    Crucial to many light-driven processes in transition metal complexes is the absorption and dissipation of energy by 3d electrons(1-4). But a detailed understanding of such non-equilibrium excited-state dynamics and their interplay with structural changes is challenging: a multitude of excited...... states and possible transitions result in phenomena too complex to unravel when faced with the indirect sensitivity of optical spectroscopy to spin dynamics(5) and the flux limitations of ultrafast X-ray sources(6,7). Such a situation exists for archetypal poly-pyridyl iron complexes, such as [Fe(2......,2'-bipyridine)(3)](2+), where the excited-state charge and spin dynamics involved in the transition from a low-to a high-spin state (spin crossover) have long been a source of interest and controversy(6-15). Here we demonstrate that femtosecond resolution X-ray fluorescence spectroscopy, with its sensitivity...

  13. Analysis of Native-Like Proteins and Protein Complexes Using Cation to Anion Proton Transfer Reactions (CAPTR).

    Science.gov (United States)

    Laszlo, Kenneth J; Bush, Matthew F

    2015-12-01

    Mass spectra of native-like protein complexes often exhibit narrow charge-state distributions, broad peaks, and contributions from multiple, coexisting species. These factors can make it challenging to interpret those spectra, particularly for mixtures with significant heterogeneity. Here we demonstrate the use of ion/ion proton transfer reactions to reduce the charge states of m/z-selected, native-like ions of proteins and protein complexes, a technique that we refer to as cation to anion proton transfer reactions (CAPTR). We then demonstrate that CAPTR can increase the accuracy of charge state assignments and the resolution of interfering species in native mass spectrometry. The CAPTR product ion spectra for pyruvate kinase exhibit ~30 peaks and enable unambiguous determination of the charge state of each peak, whereas the corresponding precursor spectra exhibit ~6 peaks and the assigned charge states have an uncertainty of ±3%. 15+ bovine serum albumin and 21+ yeast enolase dimer both appear near m/z 4450 and are completely unresolved in a mixture. After a single CAPTR event, the resulting product ions are baseline resolved. The separation of the product ions increases dramatically after each subsequent CAPTR event; 12 events resulted in a 3000-fold improvement in separation relative to the precursor ions. Finally, we introduce a framework for interpreting and predicting the figures of merit for CAPTR experiments. More generally, these results suggest that CAPTR strongly complements other mass spectrometry tools for analyzing proteins and protein complexes, particularly those in mixtures. Graphical Abstract ᅟ.

  14. Crystal structure of acetanilide at 15 and 295 K by neutron diffraction. Lack of evidence for proton transfer along the N-H...O hydrogen bond

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, S.W.; Eckert, J. [Los Alamos National Lab., NM (United States); Barthes, M. [Universite Montpellier II (France); McMullan, R.K. [Brookhaven National Lab., Upton, NY (United States); Muller, M. [Universite Lille I, Villeneuve d`Ascq (France)

    1995-11-02

    The crystal structure of acetanilide C{sub 8}H{sub 9}NO, M{sub r} = 135.17, orthorhombic, space group Pbca, Z=8, has been determined from neutron diffraction data at 15 and 295 K. The crystal data obtained are presented. This new investigation of the structure of acetanilide has been undertaken in order to assess a recent suggestion that confirmational substates in the amide proton position may be responsible for the vibrational anomalies. We found no evidence for multiple conformations or transfer along the N-H...O hydrogen bond of the amide proton at either temperature. However the intramolecular O...H6 distance from O to the nearest phenyl ring proton is unusually short and the amide proton has relatively close contacts with one of the phenyl and one of the methyl protons, which may well affect the vibrational parameters of the respective molecular groups. 44 refs., 6 figs., 5 tabs.

  15. Dual fluorescent polyaniline model compounds: steric and temperature effects on excited state charge separation.

    Science.gov (United States)

    Kapelle, Sabine; Rettig, Wolfgang; Lapouyade, René

    2002-07-01

    Low temperature dual fluorescence of several derivatives of 4-aminodiphenylamine is investigated quantitatively. A strong thermochromic and solvatochromic redshift is indicative of the high dipole moment of the CT state emitting at long wavelength. The combination of steady state and time-resolved data allowed the calculation of the excited-state equilibrium. The absence of CT-risetimes in diethyl ether and their presence in butyronitrile points to the complication by additional ground state conformational equilibria. Both ground and excited state equilibria depend on solvent polarity and temperature. High solvent polarity favours one of the ground state conformers.

  16. Shannon information entropy in position space for doubly excited states of helium with finite confinements

    Science.gov (United States)

    Ou, Jen-Hao; Ho, Yew Kam

    2017-12-01

    Quantifying electron localization in quantum confined systems remains challenging, especially for excited states. A quantum dot (QD) is represented by a helium atom in a finite oscillator potential. The effect of dot width variation on the electron localization in QD is systematically examined via Shannon entropy for low-lying doubly excited states (2s21Se, 2p21Se, 2s3s 1Se) obtained using highly correlated Hylleraas functions. In particular, the most effective dot width where the electron density is the most localized is determined successfully and justified by the electron density plot for all three states.

  17. Combined quantum-mechanical molecular mechanics calculations with NWChem and AMBER: Excited state properties of green fluorescent protein chromophore analogue in aqueous solution

    Energy Technology Data Exchange (ETDEWEB)

    Pirojsirikul, Teerapong [Department of Chemistry and Biochemistry, University of California San Diego, 9500 Gilman Drive La Jolla California 92093; Götz, Andreas W. [San Diego Supercomputer Center, University of California San Diego, 9500 Gilman Drive La Jolla California 92093; Weare, John [Department of Chemistry and Biochemistry, University of California San Diego, 9500 Gilman Drive La Jolla California 92093; Walker, Ross C. [Department of Chemistry and Biochemistry, University of California San Diego, 9500 Gilman Drive La Jolla California 92093; GlaxoSmithKline, 1250 S. Collegeville Road Collegeville Pennsylvania 19426; Kowalski, Karol [Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P. O. Box 999 Richland Washington 99352; Valiev, Marat [Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P. O. Box 999 Richland Washington 99352

    2017-05-03

    Green Fluorescent Protein (GFP) is a widely used fluorescent biomarker for the study of biological systems. Our investigation is focused on providing a reliable theoretical description of the GFP chromophore, the photochemical properties of which can be influenced through both the surrounding protein environment and pH levels. In this work we are specifically addressing the effect of an aqueous solvation environment , where a number of experimental measurements have been performed. Our approach is based on a combined quantum mechanics molecular mechanics (QM/MM) methodology, which incorporates high level coupled cluster theory for the analysis of excited states. It also presents the first application of the newly developed NWChem/AMBER QM/MM interface. Using a systematic approach, which involves comparison of gas phase and aqueous results for different protonation states and conformations, we have resolved existing uncertainties regarding theoretical interpretation of the experimental data. We observe that the impact of aqueous environment on charged states generally results in blue shifts, but the magnitude of the effect is sensitive to charge state and conformation and can be rationalized based on charge movement into the area of higher/lower external electrostatic potentials. At neutral pH levels the experimentally observed absorption signal is most likely coming from the phenol protonated form. Our results also show that the high level coupled description is essential for proper description of excited states of GFP.

  18. Quantum effect on the internal proton transfer and structural fluctuation in the H+ 5 cluster.

    Science.gov (United States)

    Ohta, Yasuhito; Ohta, Koji; Kinugawa, Kenichi

    2004-12-08

    The thermal equilibrium state of H+(5) is investigated by means of an ab initio path integral molecular dynamics (PIMD) method, in which degrees of freedom of both nuclei and electrons at finite temperature are quantized within the adiabatic approximation. The second-order Moller-Plesset force field has been employed for the present ab initio PIMD. At 5-200 K, H+(5) is shown to have the structure that the proton is surrounded by the two H(2) units without any exchange of an atom between the central proton and the H(2) unit. At 5 K, the quantum tunneling of the central proton occurs more easily when the distance between the two H(2) units is shortened. At the high temperature of 200 K, the central proton is more delocalized in space between the two H(2) units, with less correlation with the stretching of the distance between the two H(2) units. As for the rotation of the H(2) units around the C(2) axis of H+(5) , the dihedral angle distribution is homogeneous at all temperatures, suggesting that the two H(2) units freely rotate around the C(2) axis, while this quantum effect on the rotation of the H(2) units becomes more weakened with increasing temperature. The influence of the structural fluctuation of H+(5) on molecular orbital energies has been examined to conclude that the highest occupied molecular orbital-lowest unoccupied molecular orbital energy gap is largely reduced with the increase of temperature because of the spatial expansion of the whole cluster. (c) 2004 American Institute of Physics.

  19. The effect of oxygen transfer mechanism on the cathode performance based on proton-conducting solid oxide fuel cells

    KAUST Repository

    Hou, Jie

    2015-01-01

    Two types of proton-blocking composites, La2NiO4+δ-LaNi0.6Fe0.4O3-δ (LNO-LNF) and Sm0.2Ce0.8O2-δ-LaNi0.6Fe0.4O3-δ (SDC-LNF), were evaluated as cathode materials for proton-conducting solid oxide fuel cells (H-SOFCs) based on the BaZr0.1Ce0.7Y0.2O3-δ (BZCY) electrolyte, in order to compare and investigate the influence of two different oxygen transfer mechanism on the performance of the cathode for H-SOFCs. The X-ray diffraction (XRD) results showed that the chemical compatibility of the components in both compounds was excellent up to 1000°C. Electrochemical studies revealed that LNO-LNF showed lower area specific polarization resistances in symmetrical cells and better electrochemical performance in single cell tests. The single cell with LNO-LNF cathode generated remarkable higher maximum power densities (MPDs) and lower interfacial polarization resistances (Rp) than that with SDC-LNF cathode. Correspondingly, the MPDs of the single cell with the LNO-LNF cathode were 490, 364, 266, 180 mW cm-2 and the Rp were 0.103, 0.279, 0.587, 1.367 Ω cm2 at 700, 650, 600 and 550°C, respectively. Moreover, after the single cell with LNO-LNF cathode optimized with an anode functional layer (AFL) between the anode and electrolyte, the power outputs reached 708 mW cm-2 at 700°C. These results demonstrate that the LNO-LNF composite cathode with the interstitial oxygen transfer mechanism is a more preferable alternative for H-SOFCs than SDC-LNF composite cathode with the oxygen vacancy transfer mechanism.

  20. Rotational dependence of the proton-transfer reaction HBr+ + CO2-->HOCO+ + Br. I. Energy versus angular momentum effects.

    Science.gov (United States)

    Paetow, Lisa; Unger, Franziska; Beichel, Witali; Frenking, Gernot; Weitzel, Karl-Michael

    2010-05-07

    Cross sections for the endothermic proton-transfer reactions of rotationally state-selected HBr(+) and DBr(+) ions with CO(2) were measured in a guided ion beam apparatus in order to determine the influence of rotational excitation and collision energy in the center of mass (c.m.) system on the cross section. Ab initio calculations were performed to obtain energetic information about reactants, intermediates, and products. In the experiment HBr(+) and DBr(+) ions were prepared with the same mean rotational quantum number but different mean rotational energies as the rotational constants differ by about a factor of two. The mean rotational energy was varied from 1.4 to 66.3 meV for HBr(+) and from 0.7 to 43.0 meV for DBr(+). Collision energies (E(c.m.)) ranged from 0.32 to 1.00 eV. Under all conditions considered, an increase in the rotational excitation leads to a decrease in the cross section for both reactions. However, the effect is more pronounced for the higher collision energies. For E(c.m.)=1.00 and 0.85 eV; a comparison between the results for HBr(+) and DBr(+) indicates that the cross section is dominated by effects of rotational energy rather than angular momentum. For lower collision energies the cross sections for the deuteron transfer and the proton transfer are in best agreement if not compared for the same c.m. collision energy but for the same value of the difference between the collision energy and the reaction enthalpy.

  1. The rate of second electron transfer to QB(-) in bacterial reaction center of impaired proton delivery shows hydrogen-isotope effect.

    Science.gov (United States)

    Maróti, Ágnes; Wraight, Colin A; Maróti, Péter

    2015-02-01

    The 2nd electron transfer in reaction center of photosynthetic bacterium Rhodobacter sphaeroides is a two step process in which protonation of QB(-) precedes interquinone electron transfer. The thermal activation and pH dependence of the overall rate constants of different RC variants were measured and compared in solvents of water (H2O) and heavy water (D2O). The electron transfer variants where the electron transfer is rate limiting (wild type and M17DN, L210DN and H173EQ mutants) do not show solvent isotope effect and the significant decrease of the rate constant of the second electron transfer in these mutants is due to lowering the operational pKa of QB(-)/QBH: 4.5 (native), 3.9 (L210DN), 3.7 (M17DN) and 3.1 (H173EQ) at pH7. On the other hand, the proton transfer variants where the proton transfer is rate limiting demonstrate solvent isotope effect of pH-independent moderate magnitude (2.11±0.26 (WT+Ni(2+)), 2.16±0.35 (WT+Cd(2+)) and 2.34±0.44 (L210DN/M17DN)) or pH-dependent large magnitude (5.7 at pH4 (L213DN)). Upon deuteration, the free energy and the enthalpy of activation increase in all proton transfer variants by about 1 kcal/mol and the entropy of activation becomes negligible in L210DN/M17DN mutant. The results are interpreted as manifestation of equilibrium and kinetic solvent isotope effects and the structural, energetic and kinetic possibility of alternate proton delivery pathways are discussed. Copyright © 2014 Elsevier B.V. All rights reserved.

  2. Deactivation of 6-Aminocoumarin Intramolecular Charge Transfer Excited State through Hydrogen Bonding

    Science.gov (United States)

    Krystkowiak, Ewa; Dobek, Krzysztof; Maciejewski, Andrzej

    2014-01-01

    This paper presents results of the spectral (absorption and emission) and photophysical study of 6-aminocoumarin (6AC) in various aprotic hydrogen-bond forming solvents. It was established that solvent polarity as well as hydrogen-bonding ability influence solute properties. The hydrogen-bonding interactions between S1-electronic excited solute and solvent molecules were found to facilitate the nonradiative deactivation processes. The energy-gap dependence on radiationless deactivation in aprotic solvents was found to be similar to that in protic solvents. PMID:25244014

  3. Locally Excited State-Charge Transfer State Coupled Dyes as Optically Responsive Neuron Firing Probes.

    Science.gov (United States)

    Sirbu, Dumitru; Butcher, John B; Waddell, Paul G; Andras, Peter; Benniston, Andrew C

    2017-10-17

    A selection of NIR-optically responsive neuron probes was produced comprising of a donor julolidyl group connected to a BODIPY core and several different styryl and vinylpyridinyl derived acceptor moieties. The strength of the donor-acceptor interaction was systematically modulated by altering the electron withdrawing nature of the aryl unit. The fluorescence quantum yield was observed to decrease as the electron withdrawing effect of the aryl subunit increased in line with changes of the Hammett parameter. The effectiveness of these fluorophores as optically responsive dyes for neuronal imaging was assessed by measuring the toxicity and signal-to-noise ratio (SNR) of each dye. A great improvement of SNR was obtained when compared to the first-generation BODIPY-based voltage sensitive dyes with concomitant toxicity decrease. The mechanism for the optical response is disparate from conventional cyanine-based dyes, opening up a new way to produce effective voltage sensitive dyes that respond well into the NIR region. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Before there was light : Excited state dynamics in luminescent (nano)materials

    NARCIS (Netherlands)

    Rabouw, F.T.|info:eu-repo/dai/nl/413318036

    2015-01-01

    In this thesis we examine two types of luminescent materials: colloidal semiconductor nanocrystals (also known as quantum dots), and crystals doped with lanthanide ions. These materials convert one color of light to another. By investigating the dynamics of the excited state, we gain new insights

  5. Structural Monitoring of the Onset of Excited-State Aromaticity in a Liquid Crystal Phase.

    Science.gov (United States)

    Hada, Masaki; Saito, Shohei; Tanaka, Sei'ichi; Sato, Ryuma; Yoshimura, Masahiko; Mouri, Kazuhiro; Matsuo, Kyohei; Yamaguchi, Shigehiro; Hara, Mitsuo; Hayashi, Yasuhiko; Röhricht, Fynn; Herges, Rainer; Shigeta, Yasuteru; Onda, Ken; Miller, R J Dwayne

    2017-11-08

    Aromaticity of photoexcited molecules is an important concept in organic chemistry. Its theory, Baird's rule for triplet aromaticity since 1972 gives the rationale of photoinduced conformational changes and photochemical reactivities of cyclic π-conjugated systems. However, it is still challenging to monitor the dynamic structural change induced by the excited-state aromaticity, particularly in condensed materials. Here we report direct structural observation of a molecular motion and a subsequent packing deformation accompanied by the excited-state aromaticity. Photoactive liquid crystal (LC) molecules featuring a π-expanded cyclooctatetraene core unit are orientationally ordered but loosely packed in a columnar LC phase, and therefore a photoinduced conformational planarization by the excited-state aromaticity has been successfully observed by time-resolved electron diffractometry and vibrational spectroscopy. The structural change took place in the vicinity of excited molecules, producing a twisted stacking structure. A nanoscale torque driven by the excited-state aromaticity can be used as the working mechanism of new photoresponsive materials.

  6. Switching of the triplet excited state of rhodamine-C60 dyads.

    Science.gov (United States)

    Wang, Fen; Cui, Xiaoneng; Lou, Zhangrong; Zhao, Jianzhang; Bao, Ming; Li, Xingwei

    2014-12-21

    Acid-switching of the triplet excited state in rhodamine-C60 dyads was achieved. The rhodamine moiety acts as an acid-activated visible light-harvesting antenna and C60 as the singlet energy acceptor and the spin converter, and production of the triplet state was enhanced in the presence of acid.

  7. Two-Photon Excitation of Conjugated Molecules in Solution: Spectroscopy and Excited-State Dynamics

    Science.gov (United States)

    Elles, Christopher G.; Houk, Amanda L.; de Wergifosse, Marc; Krylov, Anna

    2017-06-01

    We examine the two-photon absorption (2PA) spectroscopy and ultrafast excited-state dynamics of several conjugated molecules in solution. By controlling the relative wavelength and polarization of the two photons, the 2PA measurements provide a more sensitive means of probing the electronic structure of a molecule compared with traditional linear absorption spectra. We compare experimental spectra of trans-stilbene, cis-stilbene, and phenanthrene in solution with the calculated spectra of the isolated molecules using EOM-EE-CCSD. The calculated spectra show good agreement with the low-energy region of the experimental spectra (below 6 eV) after suppressing transitions with strong Rydberg character and accounting for solvent and method-dependent shifts of the valence transitions. We also monitor the excited state dynamics following two-photon excitation to high-lying valence states of trans-stilbene up to 6.5 eV. The initially excited states rapidly relax to the lowest singlet excited state and then follow the same reaction path as observed following direct one-photon excitation to the lowest absorption band at 4.0 eV.

  8. Thermality and excited state Rényi entropy in two-dimensional CFT

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Feng-Li [Department of Physics, National Taiwan Normal University,Taipei 11677, Taiwan (China); Wang, Huajia [Department of Physics, University of Illinois,Urbana-Champaign, IL 61801 (United States); Zhang, Jia-ju [Dipartimento di Fisica, Università degli Studi di Milano-Bicocca,Piazza della Scienza 3, I-20126 Milano (Italy); Theoretical Physics Division, Institute of High Energy Physics, Chinese Academy of Sciences,19B Yuquan Rd, Beijing 100049 (China); Theoretical Physics Center for Science Facilities, Chinese Academy of Sciences,19B Yuquan Rd, Beijing 100049 (China)

    2016-11-21

    We evaluate one-interval Rényi entropy and entanglement entropy for the excited states of two-dimensional conformal field theory (CFT) on a cylinder, and examine their differences from the ones for the thermal state. We assume the interval to be short so that we can use operator product expansion (OPE) of twist operators to calculate Rényi entropy in terms of sum of one-point functions of OPE blocks. We find that the entanglement entropy for highly excited state and thermal state behave the same way after appropriate identification of the conformal weight of the state with the temperature. However, there exists no such universal identification for the Rényi entropy in the short-interval expansion. Therefore, the highly excited state does not look thermal when comparing its Rényi entropy to the thermal state one. As the Rényi entropy captures the higher moments of the reduced density matrix but the entanglement entropy only the average, our results imply that the emergence of thermality depends on how refined we look into the entanglement structure of the underlying pure excited state.

  9. Temperature dependent excited state relaxation of a red emitting DNA-templated silver nanocluster

    DEFF Research Database (Denmark)

    Cerretani, Cecilia; Carro-Temboury, Miguel R.; Krause, Stefan

    2017-01-01

    The nanosecond excited state temporal and spectral relaxation of a purified, red-emitting DNA-templated silver nanocluster (DNA–AgNC) was characterized as a function of temperature. The findings are explained by introducing a phenomenological electronic structure diagram. The reproducibility...

  10. Excited-State Dynamics of Melamine and Its Lysine Derivative Investigated by Femtosecond Transient Absorption Spectroscopy

    Directory of Open Access Journals (Sweden)

    Yuyuan Zhang

    2016-11-01

    Full Text Available Melamine may have been an important prebiotic information carrier, but its excited-state dynamics, which determine its stability under UV radiation, have never been characterized. The ability of melamine to withstand the strong UV radiation present on the surface of the early Earth is likely to have affected its abundance in the primordial soup. Here, we studied the excited-state dynamics of melamine (a proto-nucleobase and its lysine derivative (a proto-nucleoside using the transient absorption technique with a UV pump, and UV and infrared probe pulses. For melamine, the excited-state population decays by internal conversion with a lifetime of 13 ps without coupling significantly to any photochemical channels. The excited-state lifetime of the lysine derivative is slightly longer (18 ps, but the dominant deactivation pathway is otherwise the same as for melamine. In both cases, the vast majority of excited molecules return to the electronic ground state on the aforementioned time scales, but a minor population is trapped in a long-lived triplet state.

  11. Ponderomotive dressing of doubly-excited states with intensity-controlled laser light

    Directory of Open Access Journals (Sweden)

    Ding Thomas

    2013-03-01

    Full Text Available We laser-dress several doubly-excited states in helium. Tuning the coupling-laser intensity from perturbative to the strong-coupling regime, we are able to measure phases imprinted on the two-electron wavefunctions, and observe a new continuum coupling mechanism.

  12. Polarization of the excited states of twisted ethylene in a non-symmetrical environment

    NARCIS (Netherlands)

    Zijlstra, R.W J; van Duijnen, P.T.; de Vries, Alex

    1996-01-01

    The polarization behavior of the low lying excited states in the vicinity of the perpendicularly twisted (D-2d) ethylene has been investigated in a quantum mechanical CISD approach, in which the quantum system was embedded in a polarized dielectric continuum modeling a non-symmetrical distribution

  13. Influence of base stacking geometry on the nature of excited states in G-quadruplexes: a time-dependent DFT study.

    Science.gov (United States)

    Lech, Christopher J; Phan, Anh Tuân; Michel-Beyerle, Maria-Elisabeth; Voityuk, Alexander A

    2015-03-05

    G-quadruplexes are four-stranded structures of nucleic acids that are formed from the association of guanine nucleobases into cyclical arrangements known as tetrads. G-quadruplexes are involved in a host of biological processes and are of interest in nanomaterial applications. However, not much is known about their electronic properties. In this paper, we analyze electronic excited states of G-quadruplexes using a combination of time-dependent DFT calculations and molecular dynamics simulations. We systematically consider experimentally observed arrangements of stacked guanine tetrads. The effects of structural features on exciton delocalization and photoinduced charge separation are explored using a quantitative analysis of the transition electron density. It is shown that collective coherent excitations shared between two guanine nucleobases dominate in the absorption spectrum of stacked G-tetrads. These excitations may also include a significant contribution of charge transfer states. Large variation in exciton localization is also observed between different structures with a general propensity toward localization between two bases. We reveal large differences in how charge separation occurs within different nucleobase arrangements, with some geometries favoring separation within a single tetrad and others favoring separation between tetrads. We also investigate the effects of the coordinating K(+) ion located in the central cavity of G-quadruplexes on the relative excited state properties of such systems. Our results demonstrate how the nature of excited states in G-quadruplexes depends on the nucleobase stacking geometry resulting from the mutual arrangement of guanine tetrads.

  14. Proton-transfer and H2-elimination reactions of trimethylamine alane: role of dihydrogen bonding and Lewis acid-base interactions.

    Science.gov (United States)

    Filippov, Oleg A; Tsupreva, Victoria N; Golubinskaya, Lyudmila M; Krylova, Antonina I; Bregadze, Vladimir I; Lledos, Agusti; Epstein, Lina M; Shubina, Elena S

    2009-04-20

    Proton-transfer and H(2)-elimination reactions of aluminum hydride AlH(3)(NMe(3)) (TMAA) with XH acids were studied by means of IR and NMR spectroscopy and DFT calculations. The dihydrogen-bonded (DHB) intermediates in the interaction of the TMAA with XH acids (CH(3)OH, (i)PrOH, CF(3)CH(2)OH, adamantyl acetylene, indole, 2,3,4,5,6-pentafluoroaniline, and 2,3,5,6-tetrachloroaniline) were examined experimentally at low temperatures, and the spectroscopic characteristics, dihydrogen bond strength and structures, and the electronic and energetic characteristics of these complexes were determined by combining experimental and theoretical approaches. The possibility of two different types of DHB complexes with polydentate proton donors (typical monodentate and bidentate coordination with the formation of a symmetrical chelate structure) was shown by DFT calculations and was experimentally proven in solution. The DHB complexes are intermediates of proton-transfer and H(2)-elimination reactions. The extent of this reaction is very dependent on the acid strength and temperature. With temperature increases the elimination of H(2) was observed for OH and NH acids, yielding the reaction products with Al-O and Al-N bonds. The reaction mechanism was computationally studied. Besides the DHB pathway for proton transfer, another pathway starting from a Lewis complex was discovered. Preference for one of the pathways is related to the acid strength and the nucleophilicity of the proton donor. As a consequence of the dual Lewis acid-base nature of neutral aluminum hydride, participation of a second ROH molecule acting as a bifunctional catalyst forming a six-member cycle connecting aluminum and hydride sites notably reduces the reaction barrier. This mechanism could operate for proton transfer from weak OH acids to TMAA in the presence of an excess of proton donor.

  15. Mechanisms underlying dioxygen reduction in laccases. Structural and modelling studies focusing on proton transfer

    Science.gov (United States)

    2010-01-01

    Background Laccases are enzymes that couple the oxidation of substrates with the reduction of dioxygen to water. They are the simplest members of the multi-copper oxidases and contain at least two types of copper centres; a mononuclear T1 and a trinuclear that includes two T3 and one T2 copper ions. Substrate oxidation takes place at the mononuclear centre whereas reduction of oxygen to water occurs at the trinuclear centre. Results In this study, the CotA laccase from Bacillus subtilis was used as a model to understand the mechanisms taking place at the molecular level, with a focus in the trinuclear centre. The structures of the holo-protein and of the oxidised form of the apo-protein, which has previously been reconstituted in vitro with Cu(I), have been determined. The former has a dioxygen moiety between the T3 coppers, while the latter has a monoatomic oxygen, here interpreted as a hydroxyl ion. The UV/visible spectra of these two forms have been analysed in the crystals and compared with the data obtained in solution. Theoretical calculations on these and other structures of CotA were used to identify groups that may be responsible for channelling the protons that are needed for reduction of dioxygen to water. Conclusions These results present evidence that Glu 498 is the only proton-active group in the vicinity of the trinuclear centre. This strongly suggests that this residue may be responsible for channelling the protons needed for the reduction. These results are compared with other data available for these enzymes, highlighting similarities and differences within laccases and multicopper oxidases. PMID:20822511

  16. Mechanisms underlying dioxygen reduction in laccases. Structural and modelling studies focusing on proton transfer

    Directory of Open Access Journals (Sweden)

    Bento Isabel

    2010-09-01

    Full Text Available Abstract Background Laccases are enzymes that couple the oxidation of substrates with the reduction of dioxygen to water. They are the simplest members of the multi-copper oxidases and contain at least two types of copper centres; a mononuclear T1 and a trinuclear that includes two T3 and one T2 copper ions. Substrate oxidation takes place at the mononuclear centre whereas reduction of oxygen to water occurs at the trinuclear centre. Results In this study, the CotA laccase from Bacillus subtilis was used as a model to understand the mechanisms taking place at the molecular level, with a focus in the trinuclear centre. The structures of the holo-protein and of the oxidised form of the apo-protein, which has previously been reconstituted in vitro with Cu(I, have been determined. The former has a dioxygen moiety between the T3 coppers, while the latter has a monoatomic oxygen, here interpreted as a hydroxyl ion. The UV/visible spectra of these two forms have been analysed in the crystals and compared with the data obtained in solution. Theoretical calculations on these and other structures of CotA were used to identify groups that may be responsible for channelling the protons that are needed for reduction of dioxygen to water. Conclusions These results present evidence that Glu 498 is the only proton-active group in the vicinity of the trinuclear centre. This strongly suggests that this residue may be responsible for channelling the protons needed for the reduction. These results are compared with other data available for these enzymes, highlighting similarities and differences within laccases and multicopper oxidases.

  17. Excited-state dynamics of mononucleotides and DNA strands in a deep eutectic solvent.

    Science.gov (United States)

    Zhang, Yuyuan; de La Harpe, Kimberly; Hariharan, Mahesh; Kohler, Bern

    2018-01-31

    The photophysics of several mono- and oligonucleotides were investigated in a deep eutectic solvent for the first time. The solvent glyceline, prepared as a 1 : 2 mole ratio mixture of choline chloride and glycerol, was used to study excited-state deactivation in a non-aqueous solvent by the use of steady-state and time-resolved spectroscopy. DNA strands in glyceline retain the secondary structures that are present in aqueous solution to some degree, thus enabling a study of the effects of solvent properties on the excited states of stacked bases and stacked base pairs. The excited-state lifetime of the mononucleotide 5'-AMP in glyceline is 630 fs, or twice as long as in aqueous solution. Even slower relaxation is seen for 5'-TMP in glyceline, and a possible triplet state with a lifetime greater than 3 ns is observed. Circular dichroism spectra show that the single strand (dA)18 and the duplex d(AT)9·d(AT)9 adopt similar structures in glyceline and in aqueous solution. Despite having similar conformations in both solvents, femtosecond transient absorption experiments reveal striking changes in the dynamics. Excited-state decay and vibrational cooling generally take place more slowly in glyceline than in water. Additionally, the fraction of long-lived excited states in both oligonucleotide systems is lower in glyceline than in aqueous solution. For a DNA duplex, water is suggested to favor decay pathways involving intrastrand charge separation, while the deep eutectic solvent favors interstrand deactivation channels involving neutral species. Slower solvation dynamics in the viscous deep eutectic solvent may also play a role. These results demonstrate that the dynamics of excitations in stacked bases and stacked base pairs depend not only on conformation, but are also highly sensitive to the solvent.

  18. Variation of excited-state dynamics in trifluoromethyl functionalized C60 fullerenes.

    Science.gov (United States)

    Park, Jaehong; Ramirez, Jessica J; Clikeman, Tyler T; Larson, Bryon W; Boltalina, Olga V; Strauss, Steven H; Rumbles, Garry

    2016-08-17

    We report on electronically excited-state dynamics of three different trifluoromethyl C60 fullerenes (TMFs, C60(CF3)n: C60/4-1, C60/6-2, and C60/10-1, featuring four, six, and ten trifluoromethyl groups, respectively) using steady-state and time-resolved optical spectroscopy as well as ultrafast pump/probe transient absorption spectroscopy. C60/4-1 and C60/6-2 dissolved in toluene solvent show near-unity S1 → T1 intersystem crossing quantum yield (ΦISC), ca. 1 ns S1-state lifetimes, and microsecond-timescale T1-state lifetimes, which are typical of the fullerene class. On the other hand, C60/10-1 exhibits a dominant sub-nanosecond nonradiative S1 → S0 relaxation mechanism and negligible ΦISC, therefore decreasing the average excited-state lifetime (τavg) by about 5 orders of magnitude compared to that of C60/4-1 and C60/6-2 (τavg ≈ 17 μs and 54 μs for C60/4-1 and C60/6-2, respectively, whereas τavg ≈ 100 ps for C60/10-1). These excited-state characteristics of C60/4-1 and C60/6-2 are preserved in polymer matrix, suggesting that fullerene/polymer interactions do not modulate intrinsic photophysics of trifluoromethyl-substituted fullerenes. The contrasting excited-state study results of C60/4-1 and C60/6-2 to that of C60/10-1 infer that intrinsic optical properties and excited-state dynamics can be affected by the substitution on the fullerene.

  19. Variation of excited-state dynamics in trifluoromethyl functionalized C 60 fullerenes

    Energy Technology Data Exchange (ETDEWEB)

    Park, Jaehong; Ramirez, Jessica J.; Clikeman, Tyler T.; Larson, Bryon W.; Boltalina, Olga V.; Strauss, Steven H.; Rumbles, Garry

    2016-01-01

    We report on electronically excited-state dynamics of three different trifluoromethyl C60 fullerenes (TMFs, C60(CF3)n: C60/4-1, C60/6-2, and C60/10-1, featuring four, six, and ten trifluoromethyl groups, respectively) using steady-state and time-resolved optical spectroscopy as well as ultrafast pump/probe transient absorption spectroscopy. C60/4-1 and C60/6-2 dissolved in toluene solvent show near-unity S1--T1 intersystem crossing quantum yield (..phi..ISC), ca. 1 ns S1-state lifetimes, and microsecond-timescale T1-state lifetimes, which are typical of the fullerene class. On the other hand, C60/10-1 exhibits a dominant sub-nanosecond nonradiative S1--S0 relaxation mechanism and negligible ..phi..ISC, therefore decreasing the average excited-state lifetime (..tau..avg) by about 5 orders of magnitude compared to that of C60/4-1 and C60/6-2 (..tau..avg approx. 17 us and 54 us for C60/4-1 and C60/6-2, respectively, whereas ..tau..avg approx. 100 ps for C60/10-1). These excited-state characteristics of C60/4-1 and C60/6-2 are preserved in polymer matrix, suggesting that fullerene/polymer interactions do not modulate intrinsic photophysics of trifluoromethyl-substituted fullerenes. The contrasting excited- state study results of C60/4-1 and C60/6-2 to that of C60/10-1 infer that intrinsic optical properties and excited-state dynamics can be affected by the substitution on the fullerene.

  20. Tetracarboxy-phthalocyanines: From excited state dynamics to photodynamic inactivation against Bovine herpesvirus type 1.

    Science.gov (United States)

    Cocca, Leandro H Z; Oliveira, Taise M A; Gotardo, Fernando; Teles, Amanda V; Menegatti, Ricardo; Siqueira, Jonathas P; Mendonça, Cleber R; Bataus, Luiz A M; Ribeiro, Anderson O; Souza, Thalita F M; Souza, Guilherme R L; Gonçalves, Pablo J; De Boni, Leonardo

    2017-10-01

    Herein we present the excited state dynamic of zinc and aluminum tetracarboxy-phthalocyanines (ZnPc and AlPc) and its application in the photodynamic inactivation (PDI) of Bovine herpesvirus type 1 (BoHV-1) in vitro. The excited state dynamic provides valuable data to describe the excited state properties of potential optical limiters and/or photosensitizers (PSs), such as: the excited state cross-sections, fluorescence lifetime and triplet state quantum yield. The excited state characterization was performed using three different Z-scan techniques: Single Pulse, White Light Continuum and Pulse Train. Considering the photodynamic inactivation of BoHV-1, an initial viral suspension containing 10 5.75 TCID 50 /mL was incubated with the PSs for 1h at 37°C under agitation and protected from light. The samples were placed in microtiter plates and irradiated (180mW/cm 2 ). During irradiation, a sample was taken every 15min and the viability of the virus was evaluated. The results show that both phthalocyanines were efficient against viruses. However, a higher photodynamic efficiency was observed by ZnPc, which can be attributed to its higher triplet and singlet quantum yields. The results presented here are important for animal health (treatment of BoHV-1) and also open up a field of studies to use AlPc and ZnPc as potential agents against a wide range of microorganisms of veterinary interest. Copyright © 2017 Elsevier B.V. All rights reserved.

  1. Picosecond spectral relaxation of curcumin excited state in toluene–alcohol mixtures

    Energy Technology Data Exchange (ETDEWEB)

    Saini, R.K.; Das, K., E-mail: kaustuv@rrcat.gov.in

    2013-12-15

    Excited state photophysics of Curcumin in a binary solvent mixture of toluene and five different alcohols (Methanol, Ethanol, 1-Propanol, 1-Butanol and 1-Octanol) are compared with an instrument time resolution of ∼40 ps. As the alcohol mole-fraction is varied from zero to unity, the observed trends in the fluorescence quantum yield and lifetime of the pigment in toluene–alcohol mixtures changes significantly in going from Methanol to 1-Octanol. This is attributed to the different degree of modulation of the non-radiative rates associated with the excited state intermolecular H bonding between the pigment and the alcohol. Fluorescence decays taken at the red edge of the emission spectrum started to show measurable rise times (200–30 ps) the magnitude of which decreased gradually with increasing alcohol mole-fraction. As a consequence the solvation times in the binary mixture were observed to slow down considerably at certain solvent compositions compared to that in neat alcohol. However, in toluene-1-Octanol mixture, the rise times and corresponding solvation times did not show a dependence on the 1-Octanol mole-fraction. The observed results suggest that viscosity, polarity and hydrogen bonding property of the alcohol solvent plays an important role in the excited state processes of the pigment in toluene–alcohol mixture. -- Highlights: • Excited state photophysics of Curcumin in a binary solvent mixture of toluene and five different alcohols were studied. • The observed trends in the fluorescence properties are attributed to intermolecular H bonding between the pigment and the alcohol. • Except 1-Octanol, the average solvation times of the pigment were observed to depend upon alcohol mole-fraction. • Viscosity, polarity and hydrogen bonding play an important role in the excited state processes of the pigment.

  2. Compton Scattering Cross Section on the Proton at High Momentum Transfer

    CERN Document Server

    Danagoulian, A; Annand, J R M; Bertin, P Y; Bimbot, L; Bosted, P; Calarco, J R; Camsonne, A; Chang, C C; Chang, T H; Chen, J P; Choi, Seonho; Chudakov, E; De Jager, C W; Degtyarenko, P; Deur, A; Dutta, D; Egiyan, K; Gao, H; Garibaldi, F; Gayou, O; Gilman, R; Glamazdin, A; Glashausser, C; Gómez, J; Hamilton, D J; Hansen, J O; Hayes, D; Higinbotham, D W; Hinton, W; Horn, T; Howell, C; Hunyady, T; Hyde-Wright, C E; Jiang, X; Jones, M K; Ketikyan, A; Khandaker, M; Koubarovski, V; Krämer, K; Kumbartzki, G; Laveissière, G; Le Rose, J; Lindgren, R A; Mamyan, V H; Margaziotis, D J; Markowitz, P; McCormick, K; Meziani, Z E; Michaels, R; Moussiegt, P; Nanda, S; Nathan, A M; Nelyubin, V V; Nikolenko, D M; Norum, B E; Paschke, K; Pentchev, L; Perdrisat, C F; Piasetzky, E; Pomatsalyuk, R I; Punjabi, V A; Rachek, Igor A; Radyushkin, A; Reitz, B; Roché, R; Roedelbronn, M; Ron, G; Sabatie, F; Saha, A; Savvinov, N; Shahinyan, A; Shestakov, Yu V; Sirca, S; Slifer, K J; Solvignon, P; Stoler, P; Sulkosky, V; Tajima, S; Todor, L; Vlahovic, B; Voskanyan, H; Wang, K; Weinstein, L B; Wojtsekhowski, B; Xiang, H; Zheng, X; Zhu, L

    2007-01-01

    Cross-section values for Compton scattering on the proton were measured at 25 kinematic settings over the range s = 5-11 and -t = 2-7 GeV2 with statistical accuracy of a few percent. The scaling power for the s-dependence of the cross section at fixed center of mass angle was found to be 8.0 +/ 0.2, strongly inconsistent with the prediction of perturbative QCD. The observed cross-section values are in fair agreement with the calculations using the handbag mechanism, in which the external photons couple to a single quark.

  3. Proton transfer unlocks inactivation in cyclic nucleotide-gated A1 channels.

    Science.gov (United States)

    Marchesi, Arin; Arcangeletti, Manuel; Mazzolini, Monica; Torre, Vincent

    2015-02-15

    Desensitization and inactivation provide a form of short-term memory controlling the firing patterns of excitable cells and adaptation in sensory systems. Unlike many of their cousin K(+) channels, cyclic nucleotide-gated (CNG) channels are thought not to desensitize or inactivate. Here we report that CNG channels do inactivate and that inactivation is controlled by extracellular protons. Titration of a glutamate residue within the selectivity filter destabilizes the pore architecture, which collapses towards a non-conductive, inactivated state in a process reminiscent of the usual C-type inactivation observed in many K(+) channels. These results indicate that inactivation in CNG channels represents a regulatory mechanism that has been neglected thus far, with possible implications in several physiological processes ranging from signal transduction to growth cone navigation. Ion channels control ionic fluxes across biological membranes by residing in any of three functionally distinct states: deactivated (closed), activated (open) or inactivated (closed). Unlike many of their cousin K(+) channels, cyclic nucleotide-gated (CNG) channels do not desensitize or inactivate. Using patch recording techniques, we show that when extracellular pH (pHo ) is decreased from 7.4 to 6 or lower, wild-type CNGA1 channels inactivate in a voltage-dependent manner. pHo titration experiments show that at pHo  < 7 the I-V relationships are outwardly rectifying and that inactivation is coupled to current rectification. Single-channel recordings indicate that a fast mechanism of proton blockage underlines current rectification while inactivation arises from conformational changes downstream from protonation. Furthermore, mutagenesis and ionic substitution experiments highlight the role of the selectivity filter in current decline, suggesting analogies with the C-type inactivation observed in K(+) channels. Analysis with Markovian models indicates that the non-independent binding of two

  4. Effect of active-site mutation at Asn67 on the proton transfer mechanism of human carbonic anhydrase II.

    Science.gov (United States)

    Maupin, C Mark; Zheng, Jiayin; Tu, Chingkuang; McKenna, Robert; Silverman, David N; Voth, Gregory A

    2009-08-25

    The rate-limiting proton transfer (PT) event in the site-specific mutant N67L of human carbonic anhydrase II (HCA II) has been examined by kinetic, X-ray, and simulation approaches. The X-ray crystallography studies, which were previously reported, and molecular dynamics (MD) simulations indicate that the proton shuttling residue, His64, predominantly resides in the outward orientation with a significant disruption of the ordered water in the active site for the dehydration pathway. While disorder is seen in the active-site water, water cluster analysis indicates that the N67L mutant may form water clusters similar to those seen in the wild-type (WT). For the hydration pathway of the enzyme, the active site water cluster analysis reveals an inability of the N67L mutant to stabilize water clusters when His64 is in the inward orientation, thereby favoring PT when His64 is in the outward orientation. The preference of the N67L mutant to carry out the PT when His64 is in the outward orientation for both the hydration and dehydration pathway is reasoned to be the main cause of the observed reduction in the overall rate. To probe the mechanism of PT, solvent H/D kinetic isotope effects (KIEs) were experimentally studied with catalysis measured by the exchange of (18)O between CO(2) and water. The values obtained from the KIEs were determined as a function of the deuterium content of solvent, using the proton inventory method. No differences were detected in the overarching mechanism of PT between WT and N67L HCA II, despite changes in the active-site water structure and/or the orientation of His64.

  5. Mixed quantum classical calculation of proton transfer reaction rates: from deep tunneling to over the barrier regimes.

    Science.gov (United States)

    Xie, Weiwei; Xu, Yang; Zhu, Lili; Shi, Qiang

    2014-05-07

    We present mixed quantum classical calculations of the proton transfer (PT) reaction rates represented by a double well system coupled to a dissipative bath. The rate constants are calculated within the so called nontraditional view of the PT reaction, where the proton motion is quantized and the solvent polarization is used as the reaction coordinate. Quantization of the proton degree of freedom results in a problem of non-adiabatic dynamics. By employing the reactive flux formulation of the rate constant, the initial sampling starts from the transition state defined using the collective reaction coordinate. Dynamics of the collective reaction coordinate is treated classically as over damped diffusive motion, for which the equation of motion can be derived using the path integral, or the mixed quantum classical Liouville equation methods. The calculated mixed quantum classical rate constants agree well with the results from the numerically exact hierarchical equation of motion approach for a broad range of model parameters. Moreover, we are able to obtain contributions from each vibrational state to the total reaction rate, which helps to understand the reaction mechanism from the deep tunneling to over the barrier regimes. The numerical results are also compared with those from existing approximate theories based on calculations of the non-adiabatic transmission coefficients. It is found that the two-surface Landau-Zener formula works well in calculating the transmission coefficients in the deep tunneling regime, where the crossing point between the two lowest vibrational states dominates the total reaction rate. When multiple vibrational levels are involved, including additional crossing points on the free energy surfaces is important to obtain the correct reaction rate using the Landau-Zener formula.

  6. Energy loss and charge transfer effects of low energy protons in thin organic films

    CERN Document Server

    Byrne, C M

    2000-01-01

    observed in TRIM simulations. It is possible that this might be attributed to a quasi-channelling effect in the 12-8 PDA at these low energies. Attempts were made to apply the same techniques to the study of thin films of double-stranded DNA. It proved difficult to produce reliable measurements over the considerable lengths of time the samples had to reside in a high vacuum. Energy loss measurements were nevertheless made for some of the DNA films although these, together with the estimates of film thickness, could not be used for any quantitative measurements. The energy loss and stopping power of protons with incident energies between 4.93 and 15 keV has been determined for self-supporting Langmiur-Blodgett films of polymerised 12-8 diacetylene (12-8 PDA), of 54 and 60 nm thicknesses, in a transmission mode. Energy loss as a function of both incident proton energy and energy loss as a function of angle has been determined for the two thicknesses of 12-8 PDA in this energy range and the experimental data com...

  7. The H2 + + He proton transfer reaction: quantum reactive differential cross sections to be linked with future velocity mapping experiments

    Science.gov (United States)

    Hernández Vera, Mario; Wester, Roland; Gianturco, Francesco Antonio

    2018-01-01

    We construct the velocity map images of the proton transfer reaction between helium and molecular hydrogen ion {{{H}}}2+. We perform simulations of imaging experiments at one representative total collision energy taking into account the inherent aberrations of the velocity mapping in order to explore the feasibility of direct comparisons between theory and future experiments planned in our laboratory. The asymptotic angular distributions of the fragments in a 3D velocity space is determined from the quantum state-to-state differential reactive cross sections and reaction probabilities which are computed by using the time-independent coupled channel hyperspherical coordinate method. The calculations employ an earlier ab initio potential energy surface computed at the FCI/cc-pVQZ level of theory. The present simulations indicate that the planned experiments would be selective enough to differentiate between product distributions resulting from different initial internal states of the reactants.

  8. Interfacial solvation and excited state photophysical properties of 7-aminocoumarins at silica/liquid interfaces

    Science.gov (United States)

    Roy, Debjani

    The properties of solutes adsorbed at interfaces can be very different compared to bulk solution limits. This thesis examines how polar, hydrophilic silica surfaces and different solvents systematically change a solute's equilibrium and dynamic solvation environment at solid/liquid interfaces. The primary tools used in these studies are steady state fluorescence spectroscopy and time correlated single photon counting (TCSPC) --a fluorescence method capable resolving fluorescence emission on the picosecond timescale. To sample adsorbed solutes, TCSPC experiments were carried out in total internal reflection (TIR) geometry. These studies used total of six different 7-aminocoumarin dyes to isolate the effects of molecular and electronic structure on solute photophysical behavior. Fluorescence lifetimes measured in the TIR geometry are compared to the lifetimes of coumarins in bulk solution using different solvents to infer interfacial polarity and excited state solute conformation and dynamics. Steady state emission experiments measuring the behavior of the coumarins adsorbed at silica surfaces from bulk methanol solutions show that all coumarins had a similar affinity DeltaG ads ˜ - 25-30 kJ/mole. Despite these similar adsorption energetics solute structure had a very pronounced effect on the tendency of solutes to aggregate and form multilayers. Our finding suggests that hydrogen bonding donating properties of the silica surface plays a dominant role in determining the interfacial behavior of these solutes. The silica surface also had pronounced effects on the time dependent emission of some solutes. In particular, the strong hydrogen bond donating properties of the silica surface inhibit formation of a planar, charge transfer state through hydrogen bond donation to the solute's amine group. A consequence of this interaction is that the time dependent emission from solutes adsorbed at the surface appears to be more similar to emission from solutes in nonpolar

  9. On-line analysis of organic compounds in diesel exhaust using a proton transfer reaction mass spectrometer (PTR-MS)

    Science.gov (United States)

    Jobson, B. T.; Alexander, M. L.; Maupin, G. D.; Muntean, G. G.

    2005-08-01

    Chemical ionization mass spectrometry using H3O+ proton transfer in an ion drift tube (PTR-MS) was used to measure volatile organic compound (VOC) concentrations on-line in diesel engine exhaust as a function of engine load. The purpose of the study was to evaluate the PTR-MS instrument as an analytical tool for diesel engine emissions abatement research. Measured sensitivities determined from gas standards were found to agree well with calculated sensitivities for non-polar species. A slight humidity dependent sensitivity was observed for non-polar species, implying that reactions with H+(H2O)2 were important for some organics. The diesel exhaust mass spectra were complex but displayed a pattern of strong ion signals at 14n + 1 (n = 3.8) masses, with a relative ion abundance similar to that obtained from electron impact ionization of alkanes. Laboratory experiments verified that C8-C16 n-alkanes and C8-C13 1-alkenes react with H3O+ in dissociative proton transfer reaction resulting in alkyl cation ion products, primarily m/z 41, 43, 57, 71 and 85. Monitoring the sum of these ion signals may be useful for estimating alkane emissions from unburnt diesel fuel. Alkane fragmentation likely simplified the diesel exhaust mass spectrum and reduced potential mass interferences with isobaric aromatic compounds. Concentrations of aldehydes and ketones dominated those of aromatic species with formaldehyde and acetaldehyde estimated to be the most abundant VOCs in the PTR-MS mass spectrum at all engine loads. The relative abundances of benzene and toluene increased with engine load indicating their pyrogenic origin. The relative abundance of alkanes, aromatics, aldehydes and alcohols was broadly consistent with literature publications of diesel exhaust analysis by gas chromatography. About 75% of the organic ion signal could be assigned. On-line analysis of diesel exhaust using this technology may be valuable tool for diesel engine emission research.

  10. Energy-decomposition analysis of ion-neutral complexes along reaction coordinates of unimolecular proton-transfer reaction in gas phase: Comparison between 2-butanol radical ion and protonated 2-ethoxypropane ion

    Science.gov (United States)

    Sugimura, Natsuhiko; Igarashi, Yoko; Aoyama, Reiko; Shibue, Toshimichi

    2017-10-01

    An energy-decomposition analysis clarified the physical origins that change in gas-phase unimolecular proton-transfer reactions via ion-neutral complexes of the 2-butanol radical ion and protonated 2-ethoxypropane ion. In the bond cleavage and new bond-formation parts of the reaction coordinates, exchange and polarization energies provide a major source of the attraction. In the ion-neutral complex-formation part of the reaction coordinate, different major attractive sources, dispersion, and electrostatic energies were observed. The physical origins of weak interaction in the ion-neutral complexes were affected by the local charges and distances between the ion moieties and the neutral moieties.

  11. Proton-coupled electron transfer in the electrocatalysis of CO2 reduction: prediction of sequential vs. concerted pathways using DFT.

    Science.gov (United States)

    Göttle, Adrien J; Koper, Marc T M

    2017-01-01

    Herein we investigate computationally in detail the mechanism of the formation of the carboxylate adduct during the electroreduction of CO2 in water catalysed by cobalt porphyrin complexes. Specifically, we address qualitatively the competition between the concerted and sequential pathways for the proton-coupled electron transfer. We use a simple methodology for accurate computation of the pKa of the neutral and anionic carboxylate intermediates, [CoP-COOH] and [CoP-COOH]- (where CoP is a cobalt porphine complex), based on the isodesmic proton-exchange reaction scheme. The predicted values are used as in input for a theoretical model that describes the transition between the sequential and concerted pathways. The activation of the sequential pathway (ET-PT) that leads to the formation of the neutral [CoP-COOH] intermediate at pH ≈ 3.5 (pKa[CoP-COOH] = 3.5 ± 0.4), as predicted by the calculations, is in good agreement with the drastic increase in the faradaic efficiency of the CO2 reduction reaction towards CO at pH = 3 compared to pH = 1, as experimentally observed. This confirms the existence of the CO2 anionic adduct [CoP-CO2]- as a viable intermediate at pH = 3 and its crucial role for the pH dependence of the faradaic efficiency for the CO2 reduction. The analysis also shows that when the pH is significantly higher than the pKa of the neutral carboxylate adduct, the CO2 reduction has to go through an alternative pathway with the formation of the anionic carboxylate intermediate [CoP-COOH]-. It is formed through a concerted proton-electron transfer step from the anionic CO2 adduct [CoP-CO2]- when the pH is below ∼8.6 (pKa[CoP-COOH]- = 8.6 ± 0.4). At pH ≈ 8.6 and above, another decoupled ET-PT is predicted to take place, leading to the formation of a dianionic CO2 adduct [CoP-CO2]2-.

  12. Dynamics of Energy Transfer and Soft-Landing in Collisions of Protonated Dialanine with Perfluorinated Self-Assembled Monolayer Surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Pratihar, Subha; Kohale, Swapnil C.; Bhakta, Dhruv G.; Laskin, Julia; Hase, William L.

    2014-11-21

    Chemical dynamics simulations are reported which provide atomistic details of collisions of protonated dialanine, ala2-H+, with a perfluorinateted octanethiolate self-assembled monolayer (F-SAM ) surface. The simulations are performed at collisions energy Ei of 5.0, 13.5, 22.5, 30.00, and 70 eV, and incident angles 0o 0 (normal) and grazing 45o. Excellent agreement with experiment (J. Am. Chem. Soc. 2000, 122, 9703-9714) is found for both the average fraction and distribution of the collision energy transferred to the ala2-H+ internal degrees of freedom. The dominant pathway for this energy transfer is to ala2-H+ vibration, but for Ei = 5.0 eV ~20% of the energy transfer is to ala2-H+ rotation. Energy transfer to ala2-H+ rotation decreases with increase in Ei and becomes negligible at high Ei. Three types of collisions are observed in the simulations: i.e. those for which ala2-H+ (1) directly scatters off the F-SAM surface; (2) sticks/physisorbs on//in the surface, but desorbs within the 10 ps numerical integration of the simulations; and (3) remains trapped (i.e. soft-landed) on/in the surface when the simulations are terminated. Penetration of the F-SAM by ala2-H+ is important for the latter two types of events. The trapped trajectories are expected to have relatively long residence times on the surface, since a previous molecular dynamics simulation (J. Phys. Chem. B 2014, 118, 5577-5588) shows that thermally accommodated ala2-H+ ions have an binding energy with the F-SAM surface of at least ~15 kcal/mol.

  13. Dynamic flexibility in the light reactions of photosynthesis governed by both electron and proton transfer reactions.

    Science.gov (United States)

    Kramer, David M; Avenson, Thomas J; Edwards, Gerald E

    2004-07-01

    Plant photosynthesis performs the remarkable feat of converting light energy into usable chemical forms, which involves taming highly reactive intermediates without harming plant cells. This requires an apparatus that is not only efficient and robust but also flexible in its responses to changing environmental conditions. It also requires that the output of the energy-storing reactions be matched with the demands of metabolism. This article addresses the mechanisms by which this flexibility is achieved for short-term environmental changes. We argue that chloroplasts need two types of flexible mechanisms: one for modulating the output ratio of ATP:NADPH, which involves cyclic electron flux around photosystem I; and another for changing the regulatory sensitivity of the light-harvesting antenna to electron (and proton) flow.

  14. Energy cascades, excited state dynamics, and photochemistry in cob(III)alamins and ferric porphyrins.

    Science.gov (United States)

    Rury, Aaron S; Wiley, Theodore E; Sension, Roseanne J

    2015-03-17

    Porphyrins and the related chlorins and corrins contain a cyclic tetrapyrrole with the ability to coordinate an active metal center and to perform a variety of functions exploiting the oxidation state, reactivity, and axial ligation of the metal center. These compounds are used in optically activated applications ranging from light harvesting and energy conversion to medical therapeutics and photodynamic therapy to molecular electronics, spintronics, optoelectronic thin films, and optomagnetics. Cobalt containing corrin rings extend the range of applications through photolytic cleavage of a unique axial carbon-cobalt bond, permitting spatiotemporal control of drug delivery. The photochemistry and photophysics of cyclic tetrapyrroles are controlled by electronic relaxation dynamics including internal conversion and intersystem crossing. Typically the electronic excitation cascades through ring centered ππ* states, ligand to metal charge transfer (LMCT) states, metal to ligand charge transfer (MLCT) states, and metal centered states. Ultrafast transient absorption spectroscopy provides a powerful tool for the investigation of the electronic state dynamics in metal containing tetrapyrroles. The UV-visible spectrum is sensitive to the oxidation state, electronic configuration, spin state, and axial ligation of the central metal atom. Ultrashort broadband white light probes spanning the range from 270 to 800 nm, combined with tunable excitation pulses, permit the detailed unravelling of the time scales involved in the electronic energy cascade. State-of-the-art theoretical calculations provide additional insight required for precise assignment of the states. In this Account, we focus on recent ultrafast transient absorption studies of ferric porphyrins and corrin containing cob(III)alamins elucidating the electronic states responsible for ultrafast energy cascades, excited state dynamics, and the resulting photoreactivity or photostability of these compounds. Iron

  15. Water oxidation by amorphous cobalt-based oxides: volume activity and proton transfer to electrolyte bases.

    Science.gov (United States)

    Klingan, Katharina; Ringleb, Franziska; Zaharieva, Ivelina; Heidkamp, Jonathan; Chernev, Petko; Gonzalez-Flores, Diego; Risch, Marcel; Fischer, Anna; Dau, Holger

    2014-05-01

    Water oxidation in the neutral pH regime catalyzed by amorphous transition-metal oxides is of high interest in energy science. Crucial determinants of electrocatalytic activity were investigated for a cobalt-based oxide film electrodeposited at various thicknesses on inert electrodes. For water oxidation at low current densities, the turnover frequency (TOF) per cobalt ion of the bulk material stayed fully constant for variation of the thickness of the oxide film by a factor of 100 (from about 15 nm to 1.5 μm). Thickness variation changed neither the nanostructure of the outer film surface nor the atomic structure of the oxide catalyst significantly. These findings imply catalytic activity of the bulk hydrated oxide material. Nonclassical dependence on pH was observed. For buffered electrolytes with pKa values of the buffer base ranging from 4.7 (acetate) to 10.3 (hydrogen carbonate), the catalytic activity reflected the protonation state of the buffer base in the electrolyte solution directly and not the intrinsic catalytic properties of the oxide itself. It is proposed that catalysis of water oxidation occurs within the bulk hydrated oxide film at the margins of cobalt oxide fragments of molecular dimensions. At high current densities, the availability of a proton-accepting base at the catalyst-electrolyte interface controls the rate of water oxidation. The reported findings may be of general relevance for water oxidation catalyzed at moderate pH by amorphous transition-metal oxides. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Proton Transfer Reaction Mass Spectrometry detects rapid changes in volatile metabolite emission by Mycobacterium smegmatis after the addition of specific antimicrobial agents

    NARCIS (Netherlands)

    Crespo, E.; Cristescu, S. M.; de Ronde, H.; Kuijper, S.; Kolk, A.H.J.; Anthony, R.M.; Harren, F. J. M.

    2011-01-01

    The metabolic activity of plants, animals or microbes can be monitored by gas headspace analysis. This can be achieved using Proton Transfer Reaction Mass Spectrometry (PTR-MS), a highly sensitive detection method for trace gas analysis. PTR-MS is rapid and can detect metabolic responses on-line as

  17. Characterisation of the volatile profiles of infant formulas by proton transfer reaction-mass spectrometry and gas chromatography-mass spectrometry

    NARCIS (Netherlands)

    Ruth, van S.M.; Floris, V.; Fayoux, S.

    2006-01-01

    The volatile profiles of 13 infant formulas were evaluated by proton transfer reaction-mass spectrometry (PTR-MS) and gas chromatography¿mass spectrometry (GC¿MS). The infant formulas varied in brand (Aptamil, Cow & Gate, SMA), type (for different infant target groups) and physical form

  18. Proton-Transfer-Steered Mechanism of Photo lesion Repair by (6-4)-Photolyases

    NARCIS (Netherlands)

    Faraji, Shirin; Dreuw, Andreas

    2012-01-01

    DNA (6-4)-photolyases are enzymes initiating cleavage of mutagenic pyrimidine (6-4) pyrimidone photolesions by a photoinitiated electron transfer from flavin adenine dinucleotide to the lesion. Using state-of-the-art quantum chemical calculations, we present the first energetically feasible

  19. Concentration-Dependent Proton Transfer Mechanisms in Aqueous NaOH Solutions: From Acceptor-Driven to Donor-Driven and Back.

    Science.gov (United States)

    Hellström, Matti; Behler, Jörg

    2016-09-01

    Proton transfer processes play an important role in many fields of chemistry. In dilute basic aqueous solutions, proton transfer from water molecules to hydroxide ions is aided by "presolvation", i.e., thermal fluctuations that modify the hydrogen-bonding environment around the proton-receiving OH(-) ion to become more similar to that of a neutral H2O molecule. In particular at high concentrations, however, the underlying mechanisms and especially the role of the counterions are little understood. As a prototypical case, we investigate aqueous NaOH solutions using molecular dynamics simulations employing a reactive high-dimensional neural-network potential constructed from density functional theory reference data. We find that with increasing concentration the predominant proton transfer mechanism changes from being "acceptor-driven", i.e., governed by the presolvation of OH(-), to "donor-driven", i.e., governed by the presolvation of H2O, and back to acceptor-driven near the room-temperature solubility limit of 19 mol/L, which corresponds to an extremely solvent-deficient system containing only about one H2O molecule per ion. Specifically, we identify concentration ranges where the proton transfer rate is mostly affected by OH(-) losing an accepted hydrogen bond, OH(-) forming a donated hydrogen bond, H2O forming an accepted hydrogen bond, or H2O losing a coordinated Na(+). Presolvation also manifests itself in the shortening of the Na(+)-OH2 distances, in that the Na(+) "pushes" one of the H2O protons away.

  20. Unrestricted density functional theory based on the fragment molecular orbital method for the ground and excited state calculations of large systems

    Energy Technology Data Exchange (ETDEWEB)

    Nakata, Hiroya, E-mail: nakata.h.ab@m.titech.ac.jp [Center for Biological Resources and Informatics, Tokyo Institute of Technology, B-62 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8501 (Japan); RIKEN, Research Cluster for Innovation, Nakamura Lab, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Fedorov, Dmitri G. [NRI, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan); Yokojima, Satoshi [RIKEN, Research Cluster for Innovation, Nakamura Lab, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Tokyo University of Pharmacy and Life Sciences, 1423-1 Horinouchi, Hachioji-shi, Tokyo 192-0392 (Japan); Kitaura, Kazuo [Graduate School of System Informatics, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501 (Japan); Sakurai, Minoru [Center for Biological Resources and Informatics, Tokyo Institute of Technology, B-62 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8501 (Japan); Nakamura, Shinichiro [RIKEN, Research Cluster for Innovation, Nakamura Lab, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan)

    2014-04-14

    We extended the fragment molecular orbital (FMO) method interfaced with density functional theory (DFT) into spin unrestricted formalism (UDFT) and developed energy gradients for the ground state and single point excited state energies based on time-dependent DFT. The accuracy of FMO is evaluated in comparison to the full calculations without fragmentation. Electronic excitations in solvated organic radicals and in the blue copper protein, plastocyanin (PDB code: 1BXV), are reported. The contributions of solvent molecules to the electronic excitations are analyzed in terms of the fragment polarization and quantum effects such as interfragment charge transfer.

  1. Role of the electronic excited-state hydrogen bonding in the nitro-explosives detection by [Zn2(oba)2(bpy)

    Science.gov (United States)

    Wang, Peipei; Song, Xuedan; Zhao, Zhengyan; Liu, Lei; Mu, Wensheng; Hao, Ce

    2016-09-01

    This paper investigates the luminescent properties of luminescent metal-organic framework (LMOF) [Zn2(oba)2(bpy)], and its selectivity for the detection of nitro-explosives via fluorescence quenching, using the density functional and time-dependent density functional theories. The luminescent mechanism of the LMOF follows the electron transfer from ligand to ZnO quantum dot. The hydrogen bondings formed between LMOF and electron-withdrawing nitro-explosives as well as electron-donating aromatic compounds have different influences on the luminescent mechanism of the LMOF. The hydrogen bonding in the excited state was investigated to display the relationship between hydrogen bonding and fluorescence.

  2. Measurement of muon transfer from proton to triton and {ital pp}{mu} molecular formation in solid hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Mulhauser, F.; Beveridge, J.L.; Marshall, G.M. [TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia, V6T 2A3 (CANADA); Bailey, J.M. [Chester Technology, Chester (England); Beer, G.A.; Knowles, P.E.; Mason, G.R.; Olin, A. [University of Victoria, Victoria, British Columbia, V8W 2Y2 (CANADA); Fujiwara, M.C. [University of British Columbia, Vancouver, British Columbia, V6T 2A6 (CANADA); Huber, T.M. [Gustavus Adolphus College, St. Peter, Minnesota 56082 (United States); Jacot-Guillarmod, R. [Institut de Physique, Universite de Fribourg, CH-1700 Fribourg (Switzerland); Kammel, P.; Zmeskal, J. [Austrian Academy of Sciences, A-1090 Vienna (Austria); Kim, S.K. [Jeonbuk National University, Jeonju City 560-756, South (Korea); Kunselman, A.R. [University of Wyoming, Laramie, Wyoming 82071 (United States); Markushin, V.E. [Russian Research Center, Kurchatov Institute, Moscow 123182 (Russia); Martoff, C.J. [Temple University, Philadelphia, Pennsylvania 19122 (United States); Petitjean, C. [Paul Scherrer Institute, PSI, CH-5232 Villigen (Switzerland)

    1996-05-01

    An alternate approach was used to study the reactions of muonic atoms and molecules in solid layers of hydrogen isotopes. Muons stopped in a protium layer with a small admixture of tritium producing {mu}{ital p} atoms. Muon transfer from a proton to a triton generated {mu}{ital t} atoms, which were emitted into a deuterium layer. Subsequent epithermal {ital dt}{mu} molecular formation followed by {ital dt} fusion gave a prompt signal for the {mu}{ital t} emission. Fusion time spectra at various tritium concentrations were measured by detecting neutrons and {alpha} particles and the {mu}{ital p} disappearance rates were determined. The rates of {mu}{ital p}{r_arrow}{mu}{ital t} transfer and {ital pp}{mu} formation were measured to be {lambda}{sub {ital pt}}=[5.86{plus_minus}(0.10){sub {ital stat}}{plus_minus}(0.15){sub {ital syst}}({sub {minus}0}{sup +0.30}){sub {ital model}}]{times}10{sup 9} s{sup {minus}1} and {lambda}{sub {ital pp}}{sub {mu}}=[3.21 {plus_minus}(0.10){sub {ital stat}}{plus_minus}(0.14){sub {ital syst}}({sub {minus}0.06}{sup +0}){sub {ital model}(}]{times}10{sup 6} s{sup {minus}1}, respectively. Comparisons are made with the most recent theoretical values. {copyright} {ital 1996 The American Physical Society.}

  3. Microscopic theory of the two-proton radioactivity

    Energy Technology Data Exchange (ETDEWEB)

    Rotureau, J.; Chatterjee, R.; Ploszajczak, M. [CEA/DSM-CNRS/IN2P3, Grand Accelerateur National d' Ions Lourds (GANIL), Caen (France); Okolowicz, J. [CEA/DSM-CNRS/IN2P3, Grand Accelerateur National d' Ions Lourds (GANIL), Caen (France); Radzikowskiego, Institute of Nuclear Physics, Krakow (Poland)

    2005-09-01

    We formulate the microscopic theory of the two-proton radioactivity based on the real-energy continuum shell model. This microscopic approach is applied to describe the two-proton decay from the 1{sup -}{sub 2} excited state in {sup 18}Ne. (orig.)

  4. Excited-state spectroscopy of singly, doubly and triply-charmed baryons from lattice QCD

    CERN Document Server

    Padmanath, M; Mathur, Nilmani; Peardon, Michael

    2013-01-01

    We present the ground and excited state spectra of singly, doubly and triply-charmed baryons by using dynamical lattice QCD. A large set of baryonic operators that respect the symmetries of the lattice and are obtained after subduction from their continuum analogues are utilized. These operators transform as irreducible representations of SU(3)$_F$ symmetry for flavour, SU(4) symmetry for Dirac spins of quarks and O(3) symmetry for orbital angular momenta. Using novel computational techniques correlation functions of these operators are generated and the variational method is exploited to extract excited states. The lattice spectra that we obtain have baryonic states with well-defined total spins up to 7/2 and the low lying states remarkably resemble the expectations of quantum numbers from SU(6)$\\otimes$O(3) symmetry.

  5. Heat capacity for systems with excited-state quantum phase transitions

    Energy Technology Data Exchange (ETDEWEB)

    Cejnar, Pavel; Stránský, Pavel, E-mail: stransky@ipnp.troja.mff.cuni.cz

    2017-03-18

    Heat capacities of model systems with finite numbers of effective degrees of freedom are evaluated using canonical and microcanonical thermodynamics. Discrepancies between both approaches, which are observed even in the infinite-size limit, are particularly large in systems that exhibit an excited-state quantum phase transition. The corresponding irregularity of the spectrum generates a singularity in the microcanonical heat capacity and affects smoothly the canonical heat capacity. - Highlights: • Thermodynamics of systems with excited-state quantum phase transitions • ESQPT-generated singularities of the microcanonical heat capacity • Non-monotonous dependences of the canonical heat capacity • Discord between canonical and microcanonical pictures in the infinite-size limit.

  6. Excited-state spectroscopy of singly, doubly and triply-charmed baryons from lattice QCD

    Energy Technology Data Exchange (ETDEWEB)

    Padmanath, M. [Tata Institute; Edwards, Robert G. [JLAB; Mathur, Nilmani [Tata Institute; Peardon, Michael [Trinity College

    2014-07-01

    We present the ground and excited state spectra of singly, doubly and triply-charmed baryons by using dynamical lattice QCD. A large set of baryonic operators that respect the symmetries of the lattice and are obtained after subduction from their continuum analogues are utilized. These operators transform as irreducible representations of SU(3)F symmetry for flavour, SU(4) symmetry for Dirac spins of quarks and O(3) symmetry for orbital angular momenta. Using novel computational techniques correlation functions of these operators are generated and the variational method is exploited to extract excited states. The lattice spectra that we obtain have baryonic states with well-defined total spins up to 7/2 and the low lying states remarkably resemble the expectations of quantum numbers from SU(6)ⓍO(3) symmetry.

  7. Measurement of the excited-state transverse hyperfine coupling in NV centers via dynamic nuclear polarization

    Science.gov (United States)

    Poggiali, F.; Cappellaro, P.; Fabbri, N.

    2017-05-01

    Precise knowledge of a quantum system's Hamiltonian is a critical pre-requisite for its use in many quantum information technologies. Here, we report a method for the precise characterization of the nonsecular part of the excited-state Hamiltonian of an electronic-nuclear spin system in diamond. The method relies on the investigation of the dynamic nuclear polarization mediated by the electronic spin, which is currently exploited as a primary tool for initializing nuclear qubits and performing enhanced nuclear magnetic resonance. By measuring the temporal evolution of the population of the ground-state hyperfine levels of a nitrogen-vacancy center, we obtain the first direct estimation of the excited-state transverse hyperfine coupling between its electronic and nitrogen nuclear spin. Our method could also be applied to other electron-nuclear spin systems, such as those related to defects in silicon carbide.

  8. 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.

  9. First-order derivative couplings between excited states from adiabatic TDDFT response theory.

    Science.gov (United States)

    Ou, Qi; Bellchambers, Gregory D; Furche, Filipp; Subotnik, Joseph E

    2015-02-14

    We present a complete derivation of derivative couplings between excited states in the framework of adiabatic time-dependent density functional response theory. Explicit working equations are given and the resulting derivative couplings are compared with derivative couplings from a pseudo-wavefunction ansatz. For degenerate excited states, i.e., close to a conical intersection (CI), the two approaches are identical apart from an antisymmetric overlap term. However, if the difference between two excitation energies equals another excitation energy, the couplings from response theory exhibit an unphysical divergence. This spurious behavior is a result of the adiabatic or static kernel approximation of time-dependent density functional theory leading to an incorrect analytical structure of the quadratic response function. Numerical examples for couplings close to a CI and for well-separated electronic states are given.

  10. Ab initio QM/MM excited-state molecular dynamics study of coumarin 151 in water solution

    Science.gov (United States)

    Kina, Daisuke; Arora, Pooja; Nakayama, Akira; Noro, Takeshi; Gordon, Mark S.; Taketsugu, Tetsuya

    Ab initio molecular dynamics (AIMD) simulations are performed to investigate the excited state dynamics of coumarin 151 (C151) in the gas phase and in water solution at the CASSCF level of theory with segmented DZP basis sets, where in the latter case effective fragment potentials (EFP) are used. The dipole moment of an isolated C151 molecule increases considerably upon electronic vertical excitation, from 5.0 D (S0 state) to 11.1 D (S1 state). Two equilibrium structures have been identified in the S1 state, i.e., a charge-transfer state with a planar amino group and a deformed structure of the six-membered ring with the carbonyl group, and a structure that is similar to the S0 equilibrium structure. In AIMD simulations for an isolated C151 molecule (presumably similar to dynamics in nonpolar solvents), C151 decays from S1 to S0 via a crossing point of the charge-transfer state in some trajectories, while in the AIMD simulations for C151-EFP (including solvent), the S1 and S0 energies show an almost parallel energy variation with structural changes, and no crossing point is observed. This result