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Sample records for circular dichroism spectroscopy

  1. Structural characterization of chiral molecules using vibrational circular dichroism spectroscopy

    DEFF Research Database (Denmark)

    Lassen, Peter Rygaard

    2006-01-01

    compounds of pharmaceutical interest. Others are transition metal complexes relevant for the search for parity-violation effects in vibrational spectroscopy (rhenium complexes), for asymmetric catalysis (Schiff-base complexes), or as model systems for metal centres in biology (Schiff-bases and heme....... Currently, only part of the enhancement can be reproduced theoretically, as demonstrated for the Schiff-bases. Their conformers and absolute configurations were also identified. As for proteins, the interpretation of their spectra is different, because the immense number of overlapping vibrational modes...... chiral molecules. This project is about application of one such technique, circular dichroism (CD) spectroscopy, which measures the difference in absorption of left- and right circularly polarized light - hence the name circular dichroism. This study has focused on the infrared (IR) range because...

  2. Photoelectron circular dichroism of isopropanolamine

    Science.gov (United States)

    Catone, D.; Turchini, S.; Contini, G.; Prosperi, T.; Stener, M.; Decleva, P.; Zema, N.

    2017-01-01

    Spectroscopies based on circular polarized light are sensitive to the electronic and structural properties of chiral molecules. Photoelectron circular dichroism (PECD) is a powerful technique that combines the chiral sensitivity of the circular polarized light and the electronic information obtained by photoelectron spectroscopy. An experimental and theoretical PECD study of the outer valence and C 1s core states of 1-amino-2-propanol in the gas phase is presented. The experimental dichroic dispersions in the photoelectron kinetic energy are compared with theoretical calculations employing a multicentric basis set of B-spline functions and a Kohn-Sham Hamiltonian. In order to understand analogies and differences in the dichroism of structural isomers bearing the same functional groups, a comparison with previous PECD study of valence band of 2-amino-1-propanol is carried out.

  3. Magnetic circular dichroism spectroscopy as a probe of the structures of the metal sites in metalloproteins.

    Science.gov (United States)

    McMaster, Jonathan; Oganesyan, Vasily S

    2010-10-01

    Magnetic circular dichroism (MCD) is a powerful probe of the electronic and geometric structures of metal centres in metalloproteins. MCD has provided significant insight into the nature of the axial donors at haem centres and, more recently, sophisticated methods for the analysis of MCD spectra have had a major impact on the study of the electronic structures of the ground states of a range of Cu, non-haem iron and Mo-containing active sites. This detail, together with data from other complimentary spectroscopies, has played a major role in defining the chemistry underpinning the catalysis achieved by these metal centres.

  4. Structure and Absolute Configuration of Nyasol and Hinokiresinol via Synthesis and Vibrational Circular Dichroism Spectroscopy

    DEFF Research Database (Denmark)

    Lassen, Peter Rygaard

    2005-01-01

    The absolute configuration of the norlignan (+)-nyasol was determined to be S by comparison of the experimental vibrational circular dichroism data with first-principle calculations taking into account the eight lowest energy conformations. The established absolute configuration of (+)-nyasol...

  5. Stereochemical study of tolperisone, a muscle relaxant agent, by circular dichroism and ultraviolet spectroscopy.

    Science.gov (United States)

    Zsila, F; Hollósi, M; Gergely, A

    2000-11-01

    The stereochemistry of tolperisone, a chiral aryl-alkyl basic ketone was investigated by means of circular dichroism (CD) and ultraviolet (UV) spectroscopy. The unusually high optical activity of tolperisone hydrochloride in the n-->pi* region is interpreted by the presence of a chiral conformer in solution. For stereochemical reasons, the C = O group and the aromatic moiety lack coplanarity by forming an inherently dissymetric chromophore, of M helicity. Similar helicity prevails in the crystal phase, according to the solid-state CD spectrum of (-)-tolperisone HCl salt. The chirality rule proposed by Snatzke for nonplanar benzoyl chromophores predicts the absolute configuration of (-)-tolperisone hydrochloride to be R, in agreement with other alpha-methyl-beta-amino-ketones.

  6. Strong K-edge Magnetic Circular Dichroism Observed in Photon-in-Photon-out Spectroscopy

    NARCIS (Netherlands)

    Sikora, Marcin; Juhin, Amelie; Weng, Tsu-Chien; Sainctavit, Philippe; Detlefs, Carsten; de Groot, Frank; Glatzel, Pieter

    2010-01-01

    A large enhancement of the x-ray magnetic circular dichroism is observed at the iron K absorption preedge of magnetite. This is achieved by performing resonant inelastic x-ray scattering (RIXS) experiments with a 2p hole in the final state of the second-order optical process. We measured and calcula

  7. Elucidating second coordination sphere effects in heme proteins using low-temperature magnetic circular dichroism spectroscopy.

    Science.gov (United States)

    Lehnert, Nicolai

    2012-05-01

    This paper reviews recent findings on how the second coordination sphere of heme proteins fine-tunes the properties of the heme active site via hydrogen bonding. This insight is obtained from low-temperature magnetic circular dichroism (MCD) spectroscopy. In the case of high-spin ferric hemes, MCD spectroscopy allows for the identification of a multitude of charge-transfer (CT) transitions. Using optically-detected magnetic saturation curves, out-of-plane polarized CT transitions between the heme and its axial ligand(s) can be identified. In the case of ferric Cytochrome P450cam, the corresponding S(σ)→Fe(III) CT transition can be used as a probe for the {Fe(III)-axial ligand} interaction, indicating that the hydrogen bonding network of the proximal Cys only plays a limited role for fine-tuning the Fe(III)-S(Cys) interaction. In the case of high-spin ferrous hemes with axial His/imidazole coordination, our MCD-spectroscopic investigations have uncovered a direct correlation between the strength of the hydrogen bond to the proximal imidazole ligand and the ground state of the complexes. With neutral imidazole coordination, the doubly occupied d-orbital of high-spin iron(II) is of d(π) character, located orthogonal to the heme plane. As the strength of the hydrogen bond increases, this orbital rotates into the heme plane, changing the ground state of the complex.

  8. The thermal and storage stability of bovine haemoglobin by ultraviolet–visible and circular dichroism spectroscopies

    Directory of Open Access Journals (Sweden)

    Ruchir Bhomia

    2016-08-01

    Full Text Available The effects of temperature, pH and long-term storage on the secondary structure and conformation changes of bovine haemoglobin (bHb were studied using circular dichroism (CD and ultraviolet--visible (UV–vis spectroscopies. Neural network software was used to deconvolute the CD data to obtain the fractional content of the five secondary structures. The storage stability of bHb solutions in pH 6, 7 and 8 buffers was significantly higher at 4 °C than at 23 °C for the first 3 days. A complete denaturation of bHb was observed after 40 days irrespective of storage temperature or pH. The bHb solutions were also exposed to heating and cooling cycles between 25 and 65 °C and structural changes were followed by UV–vis and CD spectroscopies. These experiments demonstrated that α-helix content of bHb decreased steadily with the increasing temperature above 35 °C at all pH values. The loss in α-helicity and gain in random coil conformations was pH-dependent and the greatest under alkaline conditions. Furthermore, there was minimal recovery of the secondary structure content upon cooling to 25 °C. The use of bHb as a model drug is very common and this study elucidates the significance of storage and processing conditions on its stability.

  9. The thermal and storage stability of bovine haemoglobin by ultraviolet-visible and circular dichroism spectroscopies$

    Institute of Scientific and Technical Information of China (English)

    Ruchir Bhomia; Vivek Trivedi n; Nichola J. Coleman; John C. Mitchell

    2016-01-01

    The effects of temperature, pH and long-term storage on the secondary structure and conformation changes of bovine haemoglobin (bHb) were studied using circular dichroism (CD) and ultraviolet–visible (UV–vis) spectroscopies. Neural network software was used to deconvolute the CD data to obtain the fractional content of the five secondary structures. The storage stability of bHb solutions in pH 6, 7 and 8 buffers was significantly higher at 4 °C than at 23 °C for the first 3 days. A complete denaturation of bHb was observed after 40 days irrespective of storage temperature or pH. The bHb solutions were also ex-posed to heating and cooling cycles between 25 and 65 °C and structural changes were followed by UV–vis and CD spectroscopies. These experiments demonstrated that α-helix content of bHb decreased steadily with the increasing temperature above 35 °C at all pH values. The loss inα-helicity and gain in random coil conformations was pH-dependent and the greatest under alkaline conditions. Furthermore, there was minimal recovery of the secondary structure content upon cooling to 25 °C. The use of bHb as a model drug is very common and this study elucidates the significance of storage and processing con-ditions on its stability.

  10. Magnetic circular dichroism spectroscopy of weakly exchange coupled transition metal dimers: A model study

    DEFF Research Database (Denmark)

    Piligkos, S.; Slep, L.D.; Weyhermuller, T.

    2009-01-01

    bands of the minority spin Ni(II) ligand field bands were observed to change sign relative to the parent complex 2. This behavior has been analyzed. The present work hence provides a benchmark study for the application of MCD spectroscopy to weakly interacting transition metal dinners. (C) 2008 Elsevier......A detailed study of the magnetic circular dichroism (MCD) spectra of weakly exchange coupled transition metal heterodimers is reported. The systems consist of three isostructural complexes of the type [LM(III)(PyA)(3)M(II)](ClO4)(2) where L represents 1,4,7-trimethyl-1,4,7-triazacyclonanane and Py......A- is the monoanion of pyridine-2-aldoxime. The trivalent metal ion M(III) is either diamagnetic Ga(III) or paramagnetic Cr(III) (S-Cr = 3/2). The divalent metal ion M(II) is either diamagnetic Zn(II) or paramagnetic Ni(II) (S-Ni = 1). The three systems 1 (CrZn), 2 (GaNi) and 3 (CrNi) have been structurally...

  11. Interaction of fisetin with human serum albumin by fluorescence, circular dichroism spectroscopy and DFT calculations: binding parameters and conformational changes

    Energy Technology Data Exchange (ETDEWEB)

    Matei, Iulia; Ionescu, Sorana [Department of Physical Chemistry, Faculty of Chemistry, University of Bucharest, Bd. Regina Elisabeta 4-12, 030018 Bucharest (Romania); Hillebrand, Mihaela, E-mail: mihh@gw-chimie.math.unibuc.ro [Department of Physical Chemistry, Faculty of Chemistry, University of Bucharest, Bd. Regina Elisabeta 4-12, 030018 Bucharest (Romania)

    2011-08-15

    The interaction between fisetin, an antioxidant and neuroprotective flavonoid, and human serum albumin (HSA) is investigated by means of fluorescence (steady-state, synchronous, time-resolved) and circular dichroism (CD) spectroscopy. The formation of a 1:1 complex with a constant of about 10{sup 5} M{sup -1} was evidenced. Foerster's resonance energy transfer and competitive binding with site markers warfarin and ibuprofen were considered and discussed. Changes in the CD band of HSA indicate a decrease in the {alpha}-helix content upon binding. An induced CD signal for bound fisetin was observed and rationalized in terms of density functional theory calculations. - Highlights: > Fisetin-BSA system was studied by fluorescence spectroscopy. > Binding parameters, association constant and number of sites were estimated. > Binding site of fisetin was identified by competitive experiments. > Conformational changes in HSA and fisetin were evidenced by circular dichroism. > TDDFT calculated CD spectra supported the experimental data.

  12. Calcium Binding Ability of Recombinant Buffalo Regucalcin: A Study Using Circular Dichroism Spectroscopy.

    Science.gov (United States)

    Harikrishna, P; Thomas, Jobin; Shende, A M; Bhure, S K

    2017-02-13

    Regucalcin is a calcium regulating multifunctional protein reported to have many important functions like calcium homeostasis, anti-oxidative, anti-apoptotic and anti-cancerous functions. Although it is demonstrated as a calcium regulating protein, the calcium binding ability of regucalcin is still a controversy. The main reason for the controversy is that it lacks a typical EF hand motif which is common to most of the calcium binding proteins. Even though many studies reported regucalcin as a calcium binding protein, there are some studies reporting regucalcin as non-calcium binding also. In the present study, we investigated the calcium binding ability of recombinant buffalo regucalcin by assessing the secondary structural changes of the protein using circular dichroism spectroscopy after adding Ca(2+) to the protein solution. Two types of calcium binding studies were done, one with different concentration of calcium chloride (0.5 mM CaCl2, 1 mM CaCl2, 2 mM CaCl2) and other at different time interval (no incubation and 10 min incubation) after addition of calcium chloride. Significant structural changes were observed in both studies which prove the calcium binding ability of recombinant regucalcin. A constant increase in the α-helix (1.1% with 0.5 mM CaCl2, 1.4% with 1 mM CaCl2, 3.5% with 2 mM CaCl2) and a decrease in β-sheets (78.5% with 0.5 mM CaCl2, 77.4% with 1 mM CaCl2, 75.7% with 2 mM CaCl2) were observed with the increase in calcium chloride concentration. There was a rapid increase in α-helix and decrease in β-sheets immediately after addition of calcium chloride, which subsides after 10 min incubation.

  13. Lipid membrane association of myelin proteins and peptide segments studied by oriented and synchrotron radiation circular dichroism spectroscopy.

    Science.gov (United States)

    Muruganandam, Gopinath; Bürck, Jochen; Ulrich, Anne S; Kursula, Inari; Kursula, Petri

    2013-12-01

    Myelin-specific proteins are either integral or peripheral membrane proteins that, in complex with lipids, constitute a multilayered proteolipid membrane system, the myelin sheath. The myelin sheath surrounds the axons of nerves and enables rapid conduction of axonal impulses. Myelin proteins interact intimately with the lipid bilayer and play crucial roles in the assembly, function, and stability of the myelin sheath. Although myelin proteins have been investigated for decades, their structural properties upon membrane surface binding are still largely unknown. In this study, we have used simplified model systems consisting of synthetic peptides and membrane mimics, such as detergent micelles and/or lipid vesicles, to probe the conformation of peptides using synchrotron radiation circular dichroism spectroscopy (SRCD). Additionally, oriented circular dichroism spectroscopy (OCD) was employed to examine the orientation of myelin peptides in macroscopically aligned lipid bilayers. Various representative peptides from the myelin basic protein (MBP), P0, myelin/oligodencrocyte glycoprotein, and connexin32 (cx32) were studied. A helical peptide from the central immunodominant epitope of MBP showed a highly tilted orientation with respect to the membrane surface, whereas the N-terminal cytoplasmic segment of cx32 folded into a helical structure that was only slightly tilted. The folding of full-length myelin basic protein was, furthermore, studied in a bicelle environment. Our results provide information on the conformation and membrane alignment of important membrane-binding peptides in a membrane-mimicking environment, giving novel insights into the mechanisms of membrane binding and stacking by myelin proteins.

  14. Conformational analysis of quinine and its pseudo enantiomer quinidine: a combined jet-cooled spectroscopy and vibrational circular dichroism study.

    Science.gov (United States)

    Sen, Ananya; Bouchet, Aude; Lepère, Valeria; Le Barbu-Debus, Katia; Scuderi, D; Piuzzi, F; Zehnacker-Rentien, A

    2012-08-16

    Laser-desorbed quinine and quinidine have been studied in the gas phase by combining supersonic expansion with laser spectroscopy, namely, laser-induced fluorescence (LIF), resonance-enhanced multiphoton ionization (REMPI), and IR-UV double resonance experiments. Density funtional theory (DFT) calculations have been done in conjunction with the experimental work. The first electronic transition of quinine and quinidine is of π-π* nature, and the studied molecules weakly fluoresce in the gas phase, in contrast to what was observed in solution (Qin, W. W.; et al. J. Phys. Chem. C2009, 113, 11790). The two pseudo enantiomers quinine and quinidine show limited differences in the gas phase; their main conformation is of open type as it is in solution. However, vibrational circular dichroism (VCD) experiments in solution show that additional conformers exist in condensed phase for quinidine, which are not observed for quinine. This difference in behavior between the two pseudo enantiomers is discussed.

  15. Optical and structural properties of plasma-treated Cordyceps bassiana spores as studied by circular dichroism, absorption, and fluorescence spectroscopy

    Science.gov (United States)

    Lee, Geon Joon; Sim, Geon Bo; Choi, Eun Ha; Kwon, Young-Wan; Kim, Jun Young; Jang, Siun; Kim, Seong Hwan

    2015-01-01

    To understand the killing mechanism of fungal spores by plasma treatment, the optical, structural, and biological properties of the insect pathogenic fungus Cordyceps bassiana spores were studied. A nonthermal atmospheric-pressure plasma jet (APPJ) was used to treat the spores in aqueous solution. Optical emission spectra of the APPJ acquired in air indicated emission peaks corresponding to hydroxyl radicals and atomic oxygen. When the APPJ entered the aqueous solution, additional reactive species were derived from the interaction of plasma radicals with the aqueous solution. Fluorescence and absorption spectroscopy confirmed the generation of hydroxyl radicals and hydrogen peroxide in the plasma-activated water (PAW). Spore counting showed that plasma treatment significantly reduced spore viability. Absorption spectroscopy, circular dichroism (CD) spectroscopy, and agarose gel electrophoresis of the DNA extracted from plasma-treated spores showed a reduction in spore DNA content. The magnitude of the dip in the CD spectrum was lower in the plasma-treated spores than in the control, indicating that plasma treatment causes structural modifications and/or damage to cellular components. Tryptophan fluorescence intensity was lower in the plasma-treated spores than in the control, suggesting that plasma treatment modified cell wall proteins. Changes in spore viability and DNA content were attributed to structural modification of the cell wall by reactive species coming from the APPJ and the PAW. Our results provided evidence that the plasma radicals and the derived reactive species play critical roles in fungal spore inactivation.

  16. Optical and structural properties of plasma-treated Cordyceps bassiana spores as studied by circular dichroism, absorption, and fluorescence spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Geon Joon, E-mail: gjlee@kw.ac.kr; Sim, Geon Bo; Choi, Eun Ha [Plasma Bioscience Research Center/Department of Electrical and Biological Physics, Kwangwoon University, Seoul 139-701 (Korea, Republic of); Kwon, Young-Wan [KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul 136-701 (Korea, Republic of); Kim, Jun Young; Jang, Siun; Kim, Seong Hwan, E-mail: piceae@naver.com [Department of Microbiology and Institute of Basic Sciences, Dankook University, Cheonan 330-714 (Korea, Republic of)

    2015-01-14

    To understand the killing mechanism of fungal spores by plasma treatment, the optical, structural, and biological properties of the insect pathogenic fungus Cordyceps bassiana spores were studied. A nonthermal atmospheric-pressure plasma jet (APPJ) was used to treat the spores in aqueous solution. Optical emission spectra of the APPJ acquired in air indicated emission peaks corresponding to hydroxyl radicals and atomic oxygen. When the APPJ entered the aqueous solution, additional reactive species were derived from the interaction of plasma radicals with the aqueous solution. Fluorescence and absorption spectroscopy confirmed the generation of hydroxyl radicals and hydrogen peroxide in the plasma-activated water (PAW). Spore counting showed that plasma treatment significantly reduced spore viability. Absorption spectroscopy, circular dichroism (CD) spectroscopy, and agarose gel electrophoresis of the DNA extracted from plasma-treated spores showed a reduction in spore DNA content. The magnitude of the dip in the CD spectrum was lower in the plasma-treated spores than in the control, indicating that plasma treatment causes structural modifications and/or damage to cellular components. Tryptophan fluorescence intensity was lower in the plasma-treated spores than in the control, suggesting that plasma treatment modified cell wall proteins. Changes in spore viability and DNA content were attributed to structural modification of the cell wall by reactive species coming from the APPJ and the PAW. Our results provided evidence that the plasma radicals and the derived reactive species play critical roles in fungal spore inactivation.

  17. Alkali-hydrolysis of D-glucono-delta-lactone studied by chiral Raman and circular dichroism spectroscopies

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The alkali-hydrolysis of D-glucono-delta-lactone (GDL) was investigated by chiral Raman and circular dichroism (CD) spectroscopies in combination with density functional theory calculation. Based on the characteristic CD bands of GDL and its hydrolysis product, the dynamics of hydrolysis was studied using stopped-flow CD method. Using chiral Raman spectroscopy (CRS), the stereochemical change of GDL owing to the hydrolysis reaction was discussed on the vibrational scale. The CRS results show that the ring-opening due to hydrolysis has a great influence on the chiral structure around the car-bonyl group, which was evidenced by the disappearance of the CRS band at 1735 cm-1 (C== O stretching vibrational mode). In addition, the change of positions and intensity of CRS bands was also observed, which was ascribed to the perturbation around the C2, C3, C4 and C5 carbons due to ring-opening. It is worthy to note that the stereochemistry of C2, C3, C4 and C5 had no fundamental change during the hydrolysis reaction, which was reflected in the maintenance of the signs of the CRS bands. Our results demonstrate that in comparison with CD technique, CRS may provide more detailed structural information of chiral molecules and open up new vistas of research for chiral reactions.

  18. Ultraviolet-circular dichroism spectroscopy and potentiometric study of the interaction between human serum albumin and sodium perfluorooctanoate.

    Science.gov (United States)

    Messina, Paula; Prieto, Gerardo; Dodero, Verónica; Ruso, Juan M; Schulz, Pablo; Sarmiento, Félix

    2005-12-15

    The interaction of a fluorinated surfactant, sodium perfluorooctanoate, with human serum albumin (HSA) has been investigated by a combination of ultraviolet-circular dichroism (UV-CD) spectroscopy and potentiometry (by a home-built ion-selective electrode) techniques to detect and characterize the conformational transitions of HSA. By using difference spectroscopy, the transition was followed as a function of temperature, and the data were analyzed to obtain the parameters characterizing the thermodynamics of unfolding. The results indicate that the presence of surfactant drastically changes the melting unfolding, acting as a structure stabilizer and delaying the unfolding process. Potentiometric measurements were used to determine the binding isotherms and binding capacity for this system. The isotherm shows a high affinity of surfactant molecules for HSA. The average number of surfactant molecules absorbed per protein molecule (at 28 mM of surfactant concentration) was found to be approximately 900, about 6 g of surfactant per gram of protein. The shape of the binding capacity curve and the relation between binding capacity and extend of cooperativity were examined. From these analysis, the values of g (number of ligand-binding sites), KH (Hill binding constant), and nH (Hill coefficient) were determined.

  19. Chiral Surface Waves for Enhanced Circular Dichroism

    CERN Document Server

    Pellegrini, Giovanni; Celebrano, Michele; Duò, Lamberto; Biagioni, Paolo

    2016-01-01

    We present a novel chiral sensing platform that combines a one-dimensional photonic crystal design with a birefringent surface defect. The platform sustains simultaneous transverse electric and transverse magnetic surface modes, which are exploited to generate chiral surface waves. The present design provides homogeneous and superchiral fields of both handednesses over arbitrarily large areas in a wide spectral range, resulting in the enhancement of the circular dichroism signal by two orders of magnitude, thus paving the road toward the successful combination of surface-enhanced spectroscopies and electromagnetic superchirality.

  20. Novel Secondary Structure of Calcitonin in Solid State as Revealed by Circular Dichroism Spectroscopy

    Institute of Scientific and Technical Information of China (English)

    DU,Hai-Ning(杜海宁); DING,Jin-Guo(丁金国); CUI,Da-Fu(崔大敷); HU,Hong-Yu(胡红雨)

    2002-01-01

    The solid-state circular dichroic study reveals that salmon calcitonin presents a typical α-helical structure while human calcitonin appears to form a β-sheet in solid state, although both of them adopt random coil structures in aqueous solution.

  1. IR and Vibrational Circular Dichroism Spectroscopy of Matrine- and Artemisinin-Type Herbal Products: Stereochemical Characterization and Solvent Effects.

    Science.gov (United States)

    Zhang, Yuefei; Poopari, M Reza; Cai, Xiaoli; Savin, Aliaksandr; Dezhahang, Zahra; Cheramy, Joseph; Xu, Yunjie

    2016-04-22

    Five Chinese herbal medicines--matrine, oxymatrine, sophoridine, artemisinin, and dihydroartemisinin--were investigated using vibrational circular dichroism (VCD) experiments and density functional theory calculations to extract their stereochemical information. The three matrine-type alkaloids are available from the dry roots of Sophora flavescens and have long been used in various traditional Chinese herbal medicines to combat diseases such as cancer and cardiac arrhythmia. Artemisinin and the related dihydroartemisinin, discovered in 1979 by Professor Youyou Tu, a 2015 Nobel laureate in medicine, are effective drugs for the treatment of malaria. The VCD measurements were carried out in CDCl3 and DMSO-d6, two solvents with different dielectric constants and hydrogen-bonding characteristics. A "clusters-in-a-liquid" approach was used to model both explicit and implicit solvent effects. The studies show that effectively accounting for solvent effects is critical to using IR and VCD spectroscopy to provide unique spectroscopic features to differentiate the potential stereoisomers of these Chinese herbal medicines.

  2. X-ray absorption spectroscopy and magnetic circular dichroism studies of L10-Mn-Ga thin films

    Science.gov (United States)

    Glas, M.; Sterwerf, C.; Schmalhorst, J. M.; Ebke, D.; Jenkins, C.; Arenholz, E.; Reiss, G.

    2013-11-01

    Tetragonally distorted Mn3-xGax thin films with 0.1magnetic anisotropy and low magnetization and thus have the potential to serve as electrodes in spin transfer torque magnetic random access memory. Because a direct capping of these films with MgO is problematic due to oxide formation, we examined the influence of a CoFeB interlayer and of two different deposition methods for the MgO barrier on the formation of interfacial Mn-O for Mn62Ga38 by element specific X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD). A highly textured L10 crystal structure of the Mn-Ga films was verified by X-ray diffraction measurements. For samples with e-beam evaporated MgO barrier no evidence for Mn-O was found whereas in samples with magnetron sputtered MgO, Mn-O was detected, even for the thickest interlayer thickness. Both XAS and XMCD measurements showed an increasing interfacial Mn-O amount with decreasing CoFeB interlayer thickness. Additional element specific full hysteresis loops determined an out-of-plane magnetization axis for the Mn and Co, respectively.

  3. Alkali-hydrolysis of D-glucono-delta-lactone studied by chiral Raman and circular dichroism spectroscopies

    Institute of Scientific and Technical Information of China (English)

    JIA GuoQing; QIU Shi; LI GuanNa; ZHOU Jun; FENG ZhaoChi; LI Can

    2009-01-01

    The alkali-hydrolysis of D-glucono-delta-lactone (GDL) was investigated by chiral Raman and circular dichroism (CD) spectroecopies in combination with density functional theory calculation. Based on the characteristic CD bands of GDL and its hydrolysis product, the dynamics of hydrolysis was studied using stopped-flow CD method. Using chiral Raman spectroscopy (CRS), the stereochemical change of GDL owing to the hydrolysis reaction was discussed on the vibrational scale. The CRS results show that the ring-opening due to hydrolysis has a great influence on the chiral structure around the cer-bonyl group, which was evidenced by the disappearance of the CRS band at 1735 cm-1 (C=0 stretching vibrational mode). In addition, the change of positions and intensity of CRS bands was also observed, which was ascribed to the perturbation around the C2, C3, C4 and C5 carbons due to ring-opening. It is worthy to note that the stereochemistry of C2, C3, C4 and C5 had no fundamental change during the hydrolysis reaction, which was reflected in the maintenance of the signs of the CRS bands. Our results demonstrate that in comparison with CD technique, CRS may provide more detailed structural infor-mation of chiral molecules and open up new vistas of research for chirel reactions.

  4. X-ray magnetic circular dichroism and reflection anisotropy spectroscopy Kerr effect studies of capped magnetic nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Cunniffe, J. P.; McNally, D.E.; Liberati, M.; Arenholz, E.; McGuinness, C.; McGilp, J. F.

    2010-03-02

    Aligned Co wires grown on Pt(997) under ultra-high vacuum conditions have been capped successfully by the epitaxial growth of Au monolayers (ML) at room temperature. The samples were kept under vacuum except when transferring between apparatus or when making some of the measurements. No degradation of the Co wires was detected during the measurements. The magneto-optic response of the system was measured using X-ray magnetic circular dichroism (XMCD) at the Co L{sub 2,3} edge and reflection anisotropy spectroscopy (RAS) at near normal incidence, which is sensitive to the normal component of the out-of-plane magnetization via the Kerr effect (MOKE). Capping the wires significantly impacts their magnetic properties. Comparison of the magneto-optic response of the system at X-ray and optical energies reveals small differences that are attributed to the induced moment in the Pt substrate and Au capping layer not picked up by the element specific XMCD measurements. The sensitivity of RAS-MOKE is sufficient to allow the determination of the easy axis direction of the capped wires to within a few degrees. The results for a 6-atom-wide Co wire sample, capped with 6 ML of Au, are consistent with the capped wires possessing perpendicular magnetization.

  5. Silica as a Matrix for Encapsulating Proteins: Surface Effects on Protein Structure Assessed by Circular Dichroism Spectroscopy

    Directory of Open Access Journals (Sweden)

    Genet H. Zemede

    2012-08-01

    Full Text Available The encapsulation of biomolecules in solid materials that retain the native properties of the molecule is a desired feature for the development of biosensors and biocatalysts. In the current study, protein entrapment in silica-based materials is explored using the sol-gel technique. This work surveys the effects of silica confinement on the structure of several model polypeptides, including apomyoglobin, copper-zinc superoxide dismutase, polyglutamine, polylysine, and type I antifreeze protein. Changes in the secondary structure of each protein following encapsulation are monitored by circular dichroism spectroscopy. In many cases, silica confinement reduces the fraction of properly-folded protein relative to solution, but addition of a secondary solute or modification of the silica surface leads to an increase in structure. Refinement of the glass surface by addition of a monosubstituted alkoxysilane during sol-gel processing is shown to be a valuable tool for testing the effects of surface chemistry on protein structure. Because silica entrapment prevents protein aggregation by isolating individual protein molecules in the pores of the glass material, one may monitor aggregation-prone polypeptides under solvent conditions that are prohibited in solution, as demonstrated with polyglutamine and a disease-related variant of superoxide dismutase.

  6. X-ray absorption spectroscopy and magnetic circular dichroism studies of L1{sub 0}-Mn-Ga thin films

    Energy Technology Data Exchange (ETDEWEB)

    Glas, M., E-mail: mglas@physik.uni-bielefeld.de; Sterwerf, C.; Schmalhorst, J. M.; Reiss, G. [Thin Films and Physics of Nanostructures, Bielefeld University, Bielefeld (Germany); Ebke, D. [Thin Films and Physics of Nanostructures, Bielefeld University, Bielefeld (Germany); Max Planck Institute for Chemical Physics of Solids, Dresden (Germany); Jenkins, C.; Arenholz, E. [ALS Berkeley, California 94720-8229 (United States)

    2013-11-14

    Tetragonally distorted Mn{sub 3−x}Ga{sub x} thin films with 0.1spectroscopy (XAS) and magnetic circular dichroism (XMCD). A highly textured L1{sub 0} crystal structure of the Mn-Ga films was verified by X-ray diffraction measurements. For samples with e-beam evaporated MgO barrier no evidence for Mn-O was found whereas in samples with magnetron sputtered MgO, Mn-O was detected, even for the thickest interlayer thickness. Both XAS and XMCD measurements showed an increasing interfacial Mn-O amount with decreasing CoFeB interlayer thickness. Additional element specific full hysteresis loops determined an out-of-plane magnetization axis for the Mn and Co, respectively.

  7. Electrochemical reduction of the biliverdin-serum albumin complex as monitored by absorption and circular dichroism spectroscopy.

    Science.gov (United States)

    Claret, J; Ibars, O; Lang, K; Trull, F R; Lightner, D A

    1995-02-23

    The cathodic reduction at the mercury electrode of a biliverdin IX alpha-serum albumin complex at physiological pH in an aqueous buffer containing percentages of DMSO ranging from 4% to 20% is studied by cyclic voltametry and controlled potential coulometry. The progression of pigment disappearance and the (stereochemical) nature of the product are monitored by chromatography, UV-visible absorption and circular dichroism spectroscopy. Upon reduction, albumin-bound biliverdin IX alpha, with a slight preference for the P-helicity, affords the corresponding bound bilirubin IX alpha -with an M-chirality conformation. The complex is reduced at -0.64 V (vs. SCE; 8% DMSO), only a little shifted compared to reduction of free biliverdin IX alpha under the same conditions. In contrast, an analogous bilirubin IX alpha-serum albumin complex is essentially inert towards cathodic reduction under conditions where free bilirubin IX alpha is reduced, indicating a better shielding by the protein of the bilirubin IX alpha molecule from the electrode surface. The presence of relative position (as in the biliverdins IX alpha and XIII alpha) or absence (as in mesobiliverdin IX alpha) of vinyl groups in the pigment does not have a significant effect upon its electroreduction behaviour, indicating that the process is not sensitive to the subtle differences imposed by vinyl groups upon the structure of the corresponding biliverdin-albumin complexes.

  8. Enhanced biocatalysis mechanism under microwave irradiation in isoquercitrin production revealed by circular dichroism and surface plasmon resonance spectroscopy.

    Science.gov (United States)

    Gong, An; Zhu, Dan; Mei, Yi-Yuan; Xu, Xiao-Hui; Wu, Fu-An; Wang, Jun

    2016-04-01

    An efficient and rapid process for isoquercitrin production by hesperidinase-catalyzed hydrolysis of rutin was successfully developed under microwave irradiation detecting the affinity by circular dichroism (CD) and surface plasmon resonance (SPR) spectroscopy. A maximum isoquercitrin yield of 91.5±2.7% was obtained in 10min with the conditions of 10g/L hesperidinase, 2g/L rutin, 30°C and microwave power density 88.9W/L. Enzymatic reaction rate and Vm/Km in the microwave reactor were 6.34-fold higher than in a continuous flow microreactor and 1.24-fold higher than in a biphasic system. CD and SPR analysis results also showed that hesperidinase has a better selectivity and affinity (3.3-fold than in a batch reactor) to generate isoquercitrin under microwave irradiation. Microwave irradiation greatly improved the reaction efficiency and productivity, leading to a more positive economical assessment. The binding affinity indicates the presence of strong multivalent interactions between rutin and hesperidinase under microwave irradiation.

  9. Spin state transition in LaCoO3 studied using soft x-ray absorption spectroscopy and magnetic circular dichroism.

    Science.gov (United States)

    Haverkort, M W; Hu, Z; Cezar, J C; Burnus, T; Hartmann, H; Reuther, M; Zobel, C; Lorenz, T; Tanaka, A; Brookes, N B; Hsieh, H H; Lin, H-J; Chen, C T; Tjeng, L H

    2006-10-27

    Using soft x-ray absorption spectroscopy and magnetic circular dichroism at the Co-L(2,3) edge, we reveal that the spin state transition in LaCoO3 can be well described by a low-spin ground state and a triply degenerate high-spin first excited state. From the temperature dependence of the spectral line shapes, we find that LaCoO3 at finite temperatures is an inhomogeneous mixed-spin state system. It is crucial that the magnetic circular dichroism signal in the paramagnetic state carries a large orbital momentum. This directly shows that the currently accepted low- or intermediate-spin picture is at variance. Parameters derived from these spectroscopies fully explain existing magnetic susceptibility, electron spin resonance, and inelastic neutron data.

  10. Absolute Configuration Assignment of a Paraconic Acid Derivative via Vibrational Circular Dichroism Spectroscopy and Density Functional Theory Calculation.

    Science.gov (United States)

    Meninno, Sara; Rizzo, Paola; Abbate, Sergio; Longhi, Giovanna; Mazzeo, Giuseppe; Monaco, Guglielmo; Lattanzi, Alessandra; Zanasi, Riccardo

    2016-02-01

    Density functional theory calculation of the vibrational circular dichroism spectrum was used to assign the absolute configuration of an all-carbon quaternary β-stereocenter of a γ-butyrolactone recently synthesized through an asymmetric organocatalytic tandem aldol/lactonization sequence. Comparison with the experimental spectrum is satisfactory, on account of the fact that spectroscopic features are weak due to the presence of multiple conformers. As a result, the (R) absolute configuration was assigned to the (+) optical isomer.

  11. SIMULTANEOUS MEASUREMENT OF CIRCULAR DICHROISM AND FLUORESCENCE POLARIZATION ANISOTROPY.

    Energy Technology Data Exchange (ETDEWEB)

    SUTHERLAND,J.C.

    2002-01-19

    Circular dichroism and fluorescence polarization anisotropy are important tools for characterizing biomolecular systems. Both are used extensively in kinetic experiments involving stopped- or continuous flow systems as well as titrations and steady-state spectroscopy. This paper presents the theory for determining circular dichroism and fluorescence polarization anisotropy simultaneously, thus insuring the two parameters are recorded under exactly the same conditions and at exactly the same time in kinetic experiments. The approach to measuring circular dichroism is that used in almost all conventional dichrographs. Two arrangements for measuring fluorescence polarization anisotropy are described. One uses a single fluorescence detector and signal processing with a lock-in amplifier that is similar to the measurement of circular dichroism. The second approach uses classic ''T'' format detection optics, and thus can be used with conventional photon-counting detection electronics. Simple extensions permit the simultaneous measurement of the absorption and excitation intensity corrected fluorescence intensity.

  12. Polyglutamine- and temperature-dependent conformational rigidity in mutant huntingtin revealed by immunoassays and circular dichroism spectroscopy.

    Directory of Open Access Journals (Sweden)

    Valentina Fodale

    Full Text Available BACKGROUND: In Huntington's disease, expansion of a CAG triplet repeat occurs in exon 1 of the huntingtin gene (HTT, resulting in a protein bearing>35 polyglutamine residues whose N-terminal fragments display a high propensity to misfold and aggregate. Recent data demonstrate that polyglutamine expansion results in conformational changes in the huntingtin protein (HTT, which likely influence its biological and biophysical properties. Developing assays to characterize and measure these conformational changes in isolated proteins and biological samples would advance the testing of novel therapeutic approaches aimed at correcting mutant HTT misfolding. Time-resolved Förster energy transfer (TR-FRET-based assays represent high-throughput, homogeneous, sensitive immunoassays widely employed for the quantification of proteins of interest. TR-FRET is extremely sensitive to small distances and can therefore provide conformational information based on detection of exposure and relative position of epitopes present on the target protein as recognized by selective antibodies. We have previously reported TR-FRET assays to quantify HTT proteins based on the use of antibodies specific for different amino-terminal HTT epitopes. Here, we investigate the possibility of interrogating HTT protein conformation using these assays. METHODOLOGY/PRINCIPAL FINDINGS: By performing TR-FRET measurements on the same samples (purified recombinant proteins or lysates from cells expressing HTT fragments or full length protein at different temperatures, we have discovered a temperature-dependent, reversible, polyglutamine-dependent conformational change of wild type and expanded mutant HTT proteins. Circular dichroism spectroscopy confirms the temperature and polyglutamine-dependent change in HTT structure, revealing an effect of polyglutamine length and of temperature on the alpha-helical content of the protein. CONCLUSIONS/SIGNIFICANCE: The temperature- and polyglutamine

  13. Linear dichroism and circular dichroism in photosynthesis research

    NARCIS (Netherlands)

    Garab, G.; Amerongen, van H.

    2009-01-01

    The efficiency of photosynthetic light energy conversion depends largely on the molecular architecture of the photosynthetic membranes. Linear- and circular-dichroism (LD and CD) studies have contributed significantly to our knowledge of the molecular organization of pigment systems at different lev

  14. All-dielectric metasurface circular dichroism waveplate

    Science.gov (United States)

    Hu, Jingpei; Zhao, Xiaonan; Lin, Yu; Zhu, Aijiao; Zhu, Xiaojun; Guo, Peiji; Cao, Bing; Wang, Chinhua

    2017-01-01

    We propose and experimentally demonstrate a high efficient circularly polarizing dichroism waveplate (CPDW) using a Si-based all-dielectric 2Dchiral metasurface. We demonstrate that the CPDW exhibits a unique dichroism in that it functions as a transmissive quarter waveplate for one of either left-or right-handed circularly polarized incident lightand a reflective mirror for the opposite polarization. The circular polarization dichroism (CPD = IRCP ‑ ILCP) in transmission at wavelength ~1.5 μm reaches 97% and the extinction ratio (ER = IRCP/ILCP) is as high as 345:1. Experimental fabrications and measurements of the proposed all-dielectric metasurface are implemented and found to be in excellent agreement with the simulations. The proposed all-dielectric chiral metasurface is of advantages of high-dichroism, easy-fabrication and standard semiconductor fabrication techniques compatible, which could lead to enhanced security in fiber and free-space communications, as well as imaging and sensing applications for circularly polarized light with a highly integrated photonic platform.

  15. All-dielectric metasurface circular dichroism waveplate

    Science.gov (United States)

    Hu, Jingpei; Zhao, Xiaonan; Lin, Yu; Zhu, Aijiao; Zhu, Xiaojun; Guo, Peiji; Cao, Bing; Wang, Chinhua

    2017-01-01

    We propose and experimentally demonstrate a high efficient circularly polarizing dichroism waveplate (CPDW) using a Si-based all-dielectric 2Dchiral metasurface. We demonstrate that the CPDW exhibits a unique dichroism in that it functions as a transmissive quarter waveplate for one of either left-or right-handed circularly polarized incident lightand a reflective mirror for the opposite polarization. The circular polarization dichroism (CPD = IRCP − ILCP) in transmission at wavelength ~1.5 μm reaches 97% and the extinction ratio (ER = IRCP/ILCP) is as high as 345:1. Experimental fabrications and measurements of the proposed all-dielectric metasurface are implemented and found to be in excellent agreement with the simulations. The proposed all-dielectric chiral metasurface is of advantages of high-dichroism, easy-fabrication and standard semiconductor fabrication techniques compatible, which could lead to enhanced security in fiber and free-space communications, as well as imaging and sensing applications for circularly polarized light with a highly integrated photonic platform. PMID:28139753

  16. Evaluation of cathepsin B activity for degrading collagen IV using a surface plasmon resonance method and circular dichroism spectroscopy.

    Science.gov (United States)

    Shoji, Atsushi; Kabeya, Mitsutaka; Ishida, Yuuki; Yanagida, Akio; Shibusawa, Yoichi; Sugawara, Masao

    2014-07-01

    Evaluation of cathepsin B activities for degrading collagen IV and heat-denatured collagen IV (gelatin) were performed by surface plasmon resonance (SPR) and circular dichroism (CD) measurements. The optimal pH of cathepsin B activity for degrading each substrate was around 4.0. The ΔRU(15 min), which is a decrease in the SPR signal at 15 min after injection of cathepsin B, was smaller for collagen IV than for heat-denatured collagen IV owing to the presence of triple-helical conformation. An unstable nature of the triple-helical conformation of collagen IV at pH 4.0 was shown by the CD study. Degrading collagen IV by cathepsin B was facilitated owing to a local unwinding of the triple-helical conformation caused by proteolytic cleavage of the non-helical region. The concentration dependence of the initial velocity for degrading collagen IV by cathepsin B at pH 4.0 was biphasic, showing that cathepsin B at low concentration exhibits exopeptidase activity, while the enzyme at high concentration exhibits endopeptidase activity. The kinetic parameters for the exopeptidase activity of cathepsin B toward collagen IV and heat-treated collagen IV were evaluated and discussed in terms of the protease mechanism.

  17. Conformational analysis of XA and AX dipeptides in water by electronic circular dichroism and 1H NMR spectroscopy.

    Science.gov (United States)

    Hagarman, Andrew; Measey, Thomas; Doddasomayajula, Ravi S; Dragomir, Isabelle; Eker, Fatma; Griebenow, Kai; Schweitzer-Stenner, Reinhard

    2006-04-06

    We measured the temperature-dependent electronic circular dichroism (ECD) spectra of AX, XA, and XG dipeptides in D2O. The spectra of all XA and AX peptides indicate a substantial population of the polyproline II (PPII) conformation, while the ECD spectra of LG, KG, PG, and AG were found to be quantitatively different from the alanine-based dipeptides. Additional UV absorption data indicate that the ECD spectra of the XG peptides stem from electronic coupling between the peptide and the C-terminal group, and that spectral differences reflect different orientations of the latter. We also measured the 1H NMR spectra of the investigated dipeptides to determine the 3JHalphaNH coupling constants for the C-terminal residue. The observed temperature dependence of the ECD spectra and the respective room-temperature 3JHalphaNH coupling constants were analyzed by a two-state model encompassing PPII and a beta-like conformation. The PPII propensity of alanine in the XA series is only slightly modulated by the N-terminal side chain, and is larger than 50%. As compared to AA, XA peptides containing L, P, S, K V, E, T, and I all cause a relative stabilization of the extended beta-strand conformation. The PPII fractions of XA peptides varied between 0.64 for AA and 0.58 for DA, whereas the PPII fractions of AX peptides were much lower. From the investigated AX peptides, only AL and AQ showed the expected PPII propensity. We found that AT, AI, and AV clearly prefer an extended beta-strand conformation. A quantitative comparison of AA, AAA, and AAAA revealed a hierarchy AAAA > AAA approximately AA for the PPII population, in agreement with predictions from MD calculations and results from Raman optical activity studies (McColl et al. J. Am. Chem. Soc. 2004, 126, 5076).

  18. Direct observation of high-spin states in manganese dimer and trimer cations by x-ray magnetic circular dichroism spectroscopy in an ion trap

    Energy Technology Data Exchange (ETDEWEB)

    Zamudio-Bayer, V. [Physikalisches Institut, Universität Freiburg, Stefan-Meier-Straße 21, 79104 Freiburg (Germany); Institut für Methoden und Instrumentierung der Forschung mit Synchrotronstrahlung, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Straße 15, 12489 Berlin (Germany); Hirsch, K.; Langenberg, A.; Kossick, M. [Institut für Methoden und Instrumentierung der Forschung mit Synchrotronstrahlung, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Straße 15, 12489 Berlin (Germany); Institut für Optik und Atomare Physik, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin (Germany); Ławicki, A.; Lau, J. T., E-mail: tobias.lau@helmholtz-berlin.de [Institut für Methoden und Instrumentierung der Forschung mit Synchrotronstrahlung, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Straße 15, 12489 Berlin (Germany); Terasaki, A. [Cluster Research Laboratory, Toyota Technological Institute, 717-86 Futamata, Ichikawa, Chiba 272-0001 (Japan); Department of Chemistry, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581 (Japan); Issendorff, B. von [Physikalisches Institut, Universität Freiburg, Stefan-Meier-Straße 21, 79104 Freiburg (Germany)

    2015-06-21

    The electronic structure and magnetic moments of free Mn{sub 2}{sup +} and Mn{sub 3}{sup +} are characterized by 2p x-ray absorption and x-ray magnetic circular dichroism spectroscopy in a cryogenic ion trap that is coupled to a synchrotron radiation beamline. Our results directly show that localized magnetic moments of 5 μ{sub B} are created by 3d{sup 5}({sup 6}S) states at each ionic core, which are coupled ferromagnetically to form molecular high-spin states via indirect exchange that is mediated in both cases by a delocalized valence electron in a singly occupied 4s derived antibonding molecular orbital with an unpaired spin. This leads to total magnetic moments of 11 μ{sub B} for Mn{sub 2}{sup +} and 16 μ{sub B} for Mn{sub 3}{sup +}, with no contribution of orbital angular momentum.

  19. Simulation of magnetic circular dichroism in the electron microscope

    Science.gov (United States)

    Rubino, Stefano; Schattschneider, Peter; Rusz, Jan; Verbeeck, Johan; Leifer, Klaus

    2010-12-01

    As electron energy-loss spectroscopy (EELS) and x-ray absorption spectroscopy (XAS) probe the same transitions from core-shell states to unoccupied states above the Fermi energy, it should always be possible to apply the two techniques to the same physical phenomena, such as magnetic dichroism, and obtain the same information. Indeed, the similarity in the expression of the electron and x-ray cross-sections had been already exploited to prove the equivalence of x-ray magnetic linear dichroism and anisotropy in EELS, by noting that the polarization vector of a photon plays the same role as the momentum transfer in electron scattering. Recently, the same was proven true for x-ray magnetic circular dichroism (XMCD) by establishing a new TEM technique called EMCD (electron energy-loss magnetic chiral dichroism) (Schattschneider P et al 2006 Nature 441 486-8), which makes use of special electron scattering conditions to force the absorption of a circularly polarized virtual photon. The intrinsic advantage of EMCD over XMCD is the high spatial resolution of electron microscopes, which are readily available. Among the particular obstacles in EMCD that do not exist for synchrotron radiation, is the notoriously low signal and the very particular scattering conditions necessary to observe a chiral dichroic signal. In spite of that, impressive progress has been made in recent years. The signal strength could be considerably increased, and some innovations such as using a convergent beam have been introduced. EMCD has evolved into several techniques, which make full use of the versatility of the TEM and energy filtering, spectroscopy or STEM conditions (Rubino S 2007 Magnetic circular dichroism in the transmission electron microscope PhD Thesis Vienna University of Technology, Vienna, Austria).

  20. Stereochemistry of the tadalafil diastereoisomers: a critical assessment of vibrational circular dichroism, electronic circular dichroism, and optical rotatory dispersion.

    Science.gov (United States)

    Qiu, Shi; De Gussem, Ewoud; Tehrani, Kourosch Abbaspour; Sergeyev, Sergey; Bultinck, Patrick; Herrebout, Wouter

    2013-11-14

    The stereochemistry of all four stereoisomers of tadalafil is determined using vibrational circular dichroism (VCD), electronic circular dichroism (ECD), and optical rotatory dispersion (ORD) spectroscopy. By comparing experimentally obtained VCD spectra to computationally simulated ones, the absolute configuration of the enantiomeric pair (6R, 12aR)/(6S, 12aS) can be confidently assigned without prior knowledge of their relative stereochemistry. IR and NMR spectra are used to aid the assignment of the relative stereochemistry. The IR and VCD difference spectra further confirm the assignment of all stereoisomers. ECD and ORD spectra are used to investigate the complementarity of the three chiroptical techniques. VCD spectroscopy itself is found to have the ability to identify diastereoisomers, and simultaneous use of these chiroptical spectroscopic methods and NMR chemical shifts aids in increasing the reliability of stereochemistry assignment of diastereoisomers.

  1. Circular Dichroism in Multiphoton Ionization of Resonantly Excited He+ Ions

    Science.gov (United States)

    Ilchen, M.; Douguet, N.; Mazza, T.; Rafipoor, A. J.; Callegari, C.; Finetti, P.; Plekan, O.; Prince, K. C.; Demidovich, A.; Grazioli, C.; Avaldi, L.; Bolognesi, P.; Coreno, M.; Di Fraia, M.; Devetta, M.; Ovcharenko, Y.; Düsterer, S.; Ueda, K.; Bartschat, K.; Grum-Grzhimailo, A. N.; Bozhevolnov, A. V.; Kazansky, A. K.; Kabachnik, N. M.; Meyer, M.

    2017-01-01

    Intense, circularly polarized extreme-ultraviolet and near-infrared (NIR) laser pulses are combined to double ionize atomic helium via the oriented intermediate He+(3 p ) resonance state. Applying angle-resolved electron spectroscopy, we find a large photon helicity dependence of the spectrum and the angular distribution of the electrons ejected from the resonance by NIR multiphoton absorption. The measured circular dichroism is unexpectedly found to vary strongly as a function of the NIR intensity. The experimental data are well described by theoretical modeling and possible mechanisms are discussed.

  2. Proteolytically-induced changes of secondary structural protein conformation of bovine serum albumin monitored by Fourier transform infrared (FT-IR) and UV-circular dichroism spectroscopy

    Science.gov (United States)

    Güler, Günnur; Vorob'ev, Mikhail M.; Vogel, Vitali; Mäntele, Werner

    2016-05-01

    Enzymatically-induced degradation of bovine serum albumin (BSA) by serine proteases (trypsin and α-chymotrypsin) in various concentrations was monitored by means of Fourier transform infrared (FT-IR) and ultraviolet circular dichroism (UV-CD) spectroscopy. In this study, the applicability of both spectroscopies to monitor the proteolysis process in real time has been proven, by tracking the spectral changes together with secondary structure analysis of BSA as proteolysis proceeds. On the basis of the FTIR spectra and the changes in the amide I band region, we suggest the progression of proteolysis process via conversion of α-helices (1654 cm- 1) into unordered structures and an increase in the concentration of free carboxylates (absorption of 1593 and 1402 cm- 1). For the first time, the correlation between the degree of hydrolysis and the concentration of carboxylic groups measured by FTIR spectroscopy was revealed as well. The far UV-CD spectra together with their secondary structure analysis suggest that the α-helical content decreases concomitant with an increase in the unordered structure. Both spectroscopic techniques also demonstrate that there are similar but less spectral changes of BSA for the trypsin attack than for α-chymotrypsin although the substrate/enzyme ratio is taken the same.

  3. Vibrational circular dichroism spectroscopy of a spin-triplet bis-(biuretato) cobaltate(III) coordination compound with low-lying electronic transitions.

    Science.gov (United States)

    Johannessen, Christian; Thulstrup, Peter W

    2007-03-14

    Vibrational absorption (VA) and vibrational circular dichroism (VCD) spectroscopy was applied in the analysis of vibrational and low lying electronic transitions of a triplet ground state cobalt(III) coordination compound. The spectroscopic measurements were performed on the tetrabutylammonium salt of (6S,7S)-1,3,5,8,10,12-hexaaza-2,4,9,11-tetraoxo-6,7-diphenyl-dodecanato(4-)cobaltate(III) in DMSO solution and in potassium bromide pellets. The chiral anion exhibits an unusual geometry for cobalt(III), being four-coordinate, planar, and paramagnetic with an intermediate spin state. The spectroscopic results were compared to measurements performed on the free ligand and to theoretical calculations using density functional theory (B3LYP/TZVP). The results of the VCD analysis of the coordination compound identified an electronic, dipole-forbidden, magnetic dipole-allowed low-lying d-d transition located in the mid infrared, as well as several amide stretch transitions located in the fingerprint region (1800-1100 cm(-1)), in both the liquid and solid phase. VCD signals were found to be 5-10 times higher than expected, indicating enhancement of the vibrational CD signals, caused by coupling of the vibrational transitions with the close-lying electronic transition.

  4. Probing the Interaction of Human Serum Albumin with Norfloxacin in the Presence of High-Frequency Electromagnetic Fields: Fluorescence Spectroscopy and Circular Dichroism Investigations

    Directory of Open Access Journals (Sweden)

    Jamshidkhan Chamani

    2011-11-01

    Full Text Available The present study describes an investigation by fluorescence quenching, circular dichroism and UV-visible spectroscopy of the interaction between norfloxacin (NRF and human serum albumin (HSA in the presence of electromagnetic fields (EMFs. The results obtained from this study indicated that NRF had a strong ability to quench HSA at λex = 280 nm. In addition, a slight blue shift occurred, which suggested that the microenvironment of the protein became more hydrophobic after addition of NRF. The interaction between the NRF and HSA, whether in the absence or presence of an EMF, was considered to be a static quenching mechanism. Moreover, synchronous fluorescence demonstrated that the microenvironment around Trp became modified. Data of HSA-NRF in the presence of EMFs between 1 Hz–1 MHz confirmed the results of quenching and blue shifts. Corresponding Stern-Volmer plots were also drawn and the resultant Ksv and kq values were compared. Moreover, the binding parameters, including the number of binding sites, the binding constant and the distance, r, between donor and acceptor, were calculated based on Förster’s non-radiative energy transfer theory. According to far and near UV-CD, the formation of the complex caused changes of the secondary and tertiary structures of HSA. The obtained results are significant for patients who are subjected to high-frequency radiation as this was found to reduce the affinity of NRF to HSA.

  5. Fingerprinting the macro-organisation of pigment-protein complexes in plant thylakoid membranes in vivo by circular-dichroism spectroscopy.

    Science.gov (United States)

    Tóth, Tünde N; Rai, Neha; Solymosi, Katalin; Zsiros, Ottó; Schröder, Wolfgang P; Garab, Győző; van Amerongen, Herbert; Horton, Peter; Kovács, László

    2016-09-01

    Macro-organisation of the protein complexes in plant thylakoid membranes plays important roles in the regulation and fine-tuning of photosynthetic activity. These delicate structures might, however, undergo substantial changes during isolating the thylakoid membranes or during sample preparations, e.g., for electron microscopy. Circular-dichroism (CD) spectroscopy is a non-invasive technique which can thus be used on intact samples. Via excitonic and psi-type CD bands, respectively, it carries information on short-range excitonic pigment-pigment interactions and the macro-organisation (chiral macrodomains) of pigment-protein complexes (psi, polymer or salt-induced). In order to obtain more specific information on the origin of the major psi-type CD bands, at around (+)506, (-)674 and (+)690nm, we fingerprinted detached leaves and isolated thylakoid membranes of wild-type and mutant plants and also tested the effects of different environmental conditions in vivo. We show that (i) the chiral macrodomains disassemble upon mild detergent treatments, but not after crosslinking the protein complexes; (ii) in different wild-type leaves of dicotyledonous and monocotyledonous angiosperms the CD features are quite robust, displaying very similar excitonic and psi-type bands, suggesting similar protein composition and (macro-) organisation of photosystem II (PSII) supercomplexes in the grana; (iii) the main positive psi-type bands depend on light-harvesting protein II contents of the membranes; (iv) the (+)506nm band appears only in the presence of PSII-LHCII supercomplexes and does not depend on the xanthophyll composition of the membranes. Hence, CD spectroscopy can be used to detect different macro-domains in the thylakoid membranes with different outer antenna compositions in vivo.

  6. Anisotropic elliptical dichroism and influence of imperfection of circular polarization upon anisotropic circular dichroism

    Energy Technology Data Exchange (ETDEWEB)

    Wakabayashi, Masamitsu [Department of Biomolecular Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8501 (Japan); RIKEN, Research Cluster for Innovation, Nakamura Lab, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Yokojima, Satoshi, E-mail: yokojima@toyaku.ac.jp [Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachiouji-shi, Tokyo 192-0392 (Japan); RIKEN, Research Cluster for Innovation, Nakamura Lab, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Fukaminato, Tuyoshi [Research Institute for Electronic Science, Hokkaido University, N20, W10, Kita-ku, Sapporo 001-0020 (Japan); PRESTO, Japan Science and Technology Agency (JST), Sanbancho, Chiyoda-ku, Tokyo 102-0075 (Japan); Ohtani, Hiroyuki [Department of Biomolecular Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8501 (Japan); Nakamura, Shinichiro, E-mail: snakamura@riken.jp [RIKEN, Research Cluster for Innovation, Nakamura Lab, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan)

    2015-04-21

    In spite of the importance of anisotropic circular dichroism, in practice, it is difficult to get rid of the artifacts that arise from the imperfection of the circular polarization. Undesirable linear dichroism, interference of two orthogonal polarization states, and linear birefringence prevent us from making accurate measurements. We propose a theoretical method for evaluating the contributions of the first two, which are thought to be the main artifacts when specimens are not thick enough. Using the time-dependent perturbation theory and taking into account the direction of light propagation toward an orientationally fixed molecule, we formulated the transition probability of systems perturbed by arbitrarily polarized light and the absorption difference associated with two kinds of polarized light. We also formulated, as an extension of the dissymmetry factor of circular dichroism, a newly defined dissymmetry factor associated with two arbitrary polarization states. Furthermore, we considered a mixed-state of photon ensemble in which polarization states distribute at a certain width around a certain average. Although the purity of polarization and ellipticity does not correspond immediately, by considering the mixed state it is possible to treat them consistently. We used quantum statistical mechanics to describe the absorption difference for two kinds of photon ensembles and applied the consequent formula to examine the reported experimental results of single-molecule chiroptical responses under discussion in the recent past. The artifacts are theoretically suggested to be sensitive to the incident direction of elliptically polarized light and to the oriented systems, the ellipticity, and the orientation of ellipse. The mixed state has little, if any, effect when the polarization state distribution is narrow.

  7. The circular dichroism of ribosomal ribonucleic acids.

    Science.gov (United States)

    Cox, R A; Hirst, W; Godwin, E; Kaiser, I

    1976-05-01

    1. The c.d. (circular dichroism) of Drosophila melanogaster rRNA (42% G+C) and of G+C-rich fragments (78% G+C) obtained by partial hydrolysis of rabbit L-rRNA (the largest RNA species isolated from the large subribosomal particle) were measured and found to differ substantially. 2. To interpret these spectra a relation between c.d. of bihelical RNA and % G+C was derived, namely delta epsilonfG = AFG2+bfG+c, where deltaepsilonfG is the c.d. of RNA characterized by a mole fraction, fG, of guanine nucleotides and a, b and c are constants. 3. A frame of reference was established by studying the c.d. of a range of rRNA species, including S-rRNA (the RNA species isolated from the smaller subribosomal particle) and L-rRNA of Escherichia coli. 4. It was found for the rRNA species studied that 0.60+/-0.05 of residues appear to form bihelical secondary structure. 5. A higher helical content, 0.66+/-0.05, was found for the G+C-rich fragment of L-rRNA. The difference in the c.d. of rabbit L-rRNA and of D. melanogaster rRNA is attributable to the dependence of c.d. of the bihelical parts on %G+C. 6. The minimum in c.d. at 295 nm increases with increasing %G+C. The c.d. of rRNA was compared with that of the parent subparticle in this region of the spectrum, where high precision may be attained.

  8. Uncertainty in measurement of protein circular dichroism spectra

    Science.gov (United States)

    Cox, Maurice G.; Ravi, Jascindra; Rakowska, Paulina D.; Knight, Alex E.

    2014-02-01

    Circular dichroism (CD) spectroscopy of proteins is widely used to measure protein secondary structure, and to detect changes in secondary and higher orders of structure, for applications in research and in the quality control of protein products such as biopharmaceuticals. However, objective comparison of spectra is challenging because of a limited quantitative understanding of the sources of error in the measurement. Statistical methods can be used for comparisons, but do not provide a mechanism for dealing with systematic, as well as random, errors. Here we present a measurement model for CD spectroscopy of proteins, incorporating the principal sources of uncertainty, and use the model in conjunction with experimental data to derive an uncertainty budget. We show how this approach could be used in practice for the objective comparison of spectra, and discuss the benefits and limitations of this strategy.

  9. Circular dichroism induced by Fano resonances in planar chiral oligomers

    CERN Document Server

    Hopkins, Ben; Miroshnichenko, Andrey E; Kivshar, Yuri S

    2016-01-01

    We present a general theory of circular dichroism induced in planar chiral nanostructures with rotational symmetry. It is demonstrated, analytically, that the handedness of the incident field's polarization can control whether a nanostructure induces either absorption or scattering losses, even when the total loss (extinction) is polarization-independent. We then show that this effect is a consequence of modal interference so that strong circular dichroism in absorption and scattering can be engineered by combining Fano resonances with chiral nanoparticle clusters.

  10. Circular dichroism beamline B23 at the Diamond Light Source.

    Science.gov (United States)

    Hussain, Rohanah; Jávorfi, Tamás; Siligardi, Giuliano

    2012-01-01

    Synchrotron radiation circular dichroism (SRCD) is a well established technique in structural biology. The first UV-VIS beamline, dedicated to circular dichroism, at Diamond Light Source Ltd, a third-generation synchrotron facility in south Oxfordshire, UK, has recently become operational and it is now available for the user community. Herein the main characteristics of the B23 SRCD beamline, the ancillary facilities available for users, and some of the recent advances achieved are summarized.

  11. Circular dichroism in drug discovery and development: an abridged review.

    Science.gov (United States)

    Bertucci, Carlo; Pistolozzi, Marco; De Simone, Angela

    2010-09-01

    Chirality plays a fundamental role in determining the pharmacodynamic and pharmacokinetic properties of drugs, and contributes significantly to our understanding of the mechanisms that lie behind biorecognition phenomena. Circular dichroism spectroscopy is the technique of choice for determining the stereochemistry of chiral drugs and proteins, and for monitoring and characterizing molecular recognition phenomena in solution. The role of chirality in our understanding of recognition phenomena at the molecular level is discussed here via several selected systems of interest in the drug discovery and development area. The examples were selected in order to underline the utility of circular dichroism in emerging studies of protein-protein interactions in biological context. In particular, the following aspects are discussed here: the relationship between stereochemistry and pharmacological activity--stereochemical characterization of new leads and drugs; stereoselective binding of leads and drugs to target proteins--the binding of drugs to serum albumins; conformational transitions of peptides and proteins of physiological relevance, and the stereochemical characterization of therapeutic peptides.

  12. Structural characterization of recombinant therapeutic proteins by circular dichroism.

    Science.gov (United States)

    Bertucci, Carlo; Pistolozzi, Marco; De Simone, Angela

    2011-10-01

    Most of the protein therapeutics are now produced by recombinant DNA technology. The advantages of recombinant proteins are related to their higher specificity and to their safety as exposure to animal or human diseases. However, several problems are still present in development of recombinant proteins as therapeutics, such as low bioavailability, short serum half-life, and immune response. Their successful application hinges on the protein stereochemical stability, and on the folding and the tendency to aggregate induced by purification steps and storage. All these aspects determine the failure of many potential protein therapies, and limitations in the development of the formulation. The application of multiple analytical techniques is important in order to obtain a detailed product profile and to understand how manufacturing can influence product structure and activity. Surely the protein conformation is a key aspect to be assessed, because a specific conformation is often essential for the biological function of the protein. Thus, there is a growing need to perform structural studies under the conditions in which the proteins operate, and to monitor the structural changes of the protein. Circular dichroism has been increasingly recognised as a valuable and reliable technique to get this information. In particular, examples will be here reported on the use of circular dichroism spectroscopy in the structural characterization of free and formulated recombinant proteins, looking at the prediction of the secondary structure, propensity to conformational changes, stability, and tendency to aggregate.

  13. High orbital angular momentum quantum numbers in the electronic ground states of Fe$_2^+$ and Co$_2^+$ as determined by x-ray absorption and x-ray magnetic circular dichroism spectroscopy

    CERN Document Server

    Zamudio-Bayer, V; Langenberg, A; Lawicki, A; Terasaki, A; Issendorff, B v; Lau, J T

    2015-01-01

    The $^6\\Delta$ electronic ground state of the Co$_2^+$ diatomic molecular cation has been assigned experimentally by x-ray absorption and x-ray magnetic circular dichroism spectroscopy in a cryogenic ion trap. Three candidates, $^6\\Phi$, $^6\\Gamma$, and $^8\\Gamma$, for the electronic ground state of Fe$_2^+$ have been identified. These states carry sizable ground-state orbital angular momenta that disagree with theoretical predictions from multireference configuration interaction and density functional theory. Our results show that the ground states of neutral and cationic diatomic molecules of $3d$ elements cannot be assumed to be connected by a one-electron process.

  14. Magnetic circular dichroism of porphyrin lanthanide M3+ complexes.

    Science.gov (United States)

    Andrushchenko, Valery; Padula, Daniele; Zhivotova, Elena; Yamamoto, Shigeki; Bouř, Petr

    2014-10-01

    Lanthanide complexes exhibit interesting spectroscopic properties yielding many applications as imaging probes, natural chirality amplifiers, and therapeutic agents. However, many properties are not fully understood yet. Therefore, we applied magnetic circular dichroism (MCD) spectroscopy, which provides enhanced information about the underlying electronic structure to a series of lanthanide compounds. The metals in the M(3+) state included Y, La, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu; the spectra were collected for selected tetraphenylporphin (TPP) and octaethylporphin (OEP) complexes in chloroform. While the MCD and UV-VIS absorption spectra were dominated by the porphyrin signal, metal binding significantly modulated them. MCD spectroscopy was found to be better suited to discriminate between various species than absorption spectroscopy alone. The main features and trends in the lanthanide series observed in MCD and absorption spectra of the complexes could be interpreted at the Density Functional Theory (DFT) level, with effective core potentials on metal nuclei. The sum over state (SOS) method was used for simulation of the MCD intensities. The combination of the spectroscopy and quantum-chemical computations is important for understanding the interactions of the metals with the organic compounds.

  15. Effect of colloidal gold size on the conformational changes of adsorbed cytochrome c: probing by circular dichroism, UV-visible, and infrared spectroscopy.

    Science.gov (United States)

    Jiang, Xiue; Jiang, Junguang; Jin, Yongdong; Wang, Erkang; Dong, Shaojun

    2005-01-01

    The conformational changes of bovine heart cytochrome c (cyt c) induced by the adsorption on gold nanoparticles with different sizes have been investigated by electronic absorption, circular dichroism (CD), and Fourier transform infrared spectra. The combination of these techniques can give complementary information about adsorption-induced conformational changes. The results show that there are different conformational changes for cyt c adsorbed on gold nanoparticles with different sizes due to the different interaction forces between cyt c and gold nanoparticles. The colloidal gold concentration-dependent conformation distribution curves of cyt c obtained by analysis of CD spectra using the singular value decomposition least-squares method show that the coverage of cyt c on the gold nanoparticles surface also affects the conformational changes of the adsorbed cyt c.

  16. Large Enhancement of Circular Dichroism Using an Embossed Chiral Metamaterial

    CERN Document Server

    Mousavi, S Hamed Shams; El-Sayed, Mostafa A; Eftekhar, Ali A; Adibi, Ali

    2016-01-01

    In the close vicinity of a chiral nanostructure, the circular dichroism of a biomolecule could be greatly enhanced, due to the interaction with the local superchiral fields. Modest enhancement of optical activity using a planar metamaterial, with some chiral properties, and achiral nanoparticles has been previously reported. A more substantial chirality enhancement can be achieved in the local filed of a chiral nanostructure with a three-dimensional arrangement. Using an embossed chiral nanostructure designed for chiroptical sensing, we measure the circular dichroism spectra of two biomolecules, Chlorophylls A and B, at the molecular level, using a simple polarization resolved reflection measurement. This experiment is the first realization of the on-resonance surface-enhanced circular dichroism, achieved by matching the chiral resonances of a strongly chiral metamaterial with that of a chiral molecule, resulting in an unprecedentedly large differential CD spectrum from a monolayer of a chiral material.

  17. Transient vibrational circular dichroism spectrometer: technical development

    Directory of Open Access Journals (Sweden)

    Helbing J.

    2010-06-01

    Full Text Available We recently reported the first measurements of transient VCD in the C-H-stretch region following visible excitation of cobalt(--spartein complex (Co(spCl2 with picosecond time resolution [1]. This poster presents the detailed description of the setup based on the synchronization of a femtosecond laser system with a photo elastic modulator [2]. A very precise control of the probe pulse polarization is a requirement to avoid linear dichroism artefacts. This is particularly important in crossed polarizer “quasi-null” technique which can be used to significantly enhance chiral signals [3].

  18. Circular dichroism as a means to follow DNA gymnastics: on the shoulders of giants

    Directory of Open Access Journals (Sweden)

    H.H. Klump

    2010-01-01

    Full Text Available This is the first report of DNA stem-loops self-assembled by ‘foot-loop’ interactions into either two-dimensional strings or three-dimensional spirals, distinguished by circular dichroism spectroscopy. All subunits are linked by cooperative Watson-Crick hydrogen bonds.

  19. Circular Dichroism Investigation of Dess-Martin Periodinane Oxidation in the Organic Chemistry Laboratory

    Science.gov (United States)

    Reed, Nicole A.; Rapp, Robert D.; Hamann, Christian S.; Artz, Pamela G.

    2005-01-01

    Dess-Martin periodinane oxidation is an experiment that provides an avenue to the introduction of Circular Dichroism (CD) spectroscopy in organic chemistry curriculum as a diagnostic tool for examination of the results of a familiar reaction, and absolute configuration. From the experiment, students increased their understanding of CD theory and…

  20. Experimental determination of excitonic band structures of single-walled carbon nanotubes using circular dichroism spectra

    Science.gov (United States)

    Wei, Xiaojun; Tanaka, Takeshi; Yomogida, Yohei; Sato, Naomichi; Saito, Riichiro; Kataura, Hiromichi

    2016-10-01

    Experimental band structure analyses of single-walled carbon nanotubes have not yet been reported, to the best of our knowledge, except for a limited number of reports using scanning tunnelling spectroscopy. Here we demonstrate the experimental determination of the excitonic band structures of single-chirality single-walled carbon nanotubes using their circular dichroism spectra. In this analysis, we use gel column chromatography combining overloading selective adsorption with stepwise elution to separate 12 different single-chirality enantiomers. Our samples show higher circular dichroism intensities than the highest values reported in previous works, indicating their high enantiomeric purity. Excitonic band structure analysis is performed by assigning all observed Eii and Eij optical transitions in the circular dichroism spectra. The results reproduce the asymmetric structures of the valence and conduction bands predicted by density functional theory. Finally, we demonstrate that an extended empirical formula can estimate Eij optical transition energies for any (n,m) species.

  1. Circular dichroism of graphene oxide: the chiral structure model

    Institute of Scientific and Technical Information of China (English)

    Jing CAO; Hua-Jie YIN; Rui SONG

    2013-01-01

    We have observed the circular dichroism signal of dilute graphene oxide (GO), then systematically investigated the chirality of GO and established a probable chiral unit model, This study may open up a new field for understanding the structure of GO and lay the foundation for fabrication of GO-based materials.

  2. Enhanced circular dichroism via slow light in dispersive structured media

    DEFF Research Database (Denmark)

    Pedersen, Jesper Goor; Mortensen, Asger

    2007-01-01

    Circular dichroism (CD) is in widespread use as a means of determining enantiomeric excess. We show how slow-light phenomena in dispersive structured media allow for a reduction in the required optical path length of an order of magnitude. The same ideas may be used to enhance the sensitivity of CD...

  3. Cyanobacterial phycobilisomes: selective dissociation monitored by fluorescence and circular dichroism

    Energy Technology Data Exchange (ETDEWEB)

    Rigbi, M.; Rosinski, J.; Siegelman, H.W.; Sutherland, J.C.

    1980-04-01

    Phycobilisomes are supramolecular assemblies of phycobiliproteins responsible for photosynthetic light collection in red algae and cyanobacteria. They can be selectively dissociated by reduction of temperature and buffer concentration. Phycobilisomes isolated from Fremyella diplosiphon transfer energy collected by C-phycoerythrin and C-phycocyanin to allophycocyanin. The energy transfer to allophycocyanin is nearly abolished at 2/sup 0/C, as indicated by a blue shift in fluorescence emission, and is accompanied by a decrease in the circular dichroism in the region of allophycocyanin absorbance. Further dissociation of the phycobilisomes can be attained by reduction of buffer concentration and holding at 2/sup 0/C. Energy transfer to C-phycocyanin is nearly abolished, and decreases occur in the circular dichroism in the region of C-phycocyanin and C-phycoerythrin absorbance. Complete dissociation of the phycobilisomes at low buffer concentration and 2/sup 0/C requires extended time. Energy transfer to C-phycocyanin is further reduced and the circular dichroism maximum of C-phycoerythrin at 575 nm is lost. Circular dichroism provides information on the hexamer-monomer transitions of the phycobiliproteins, whereas fluorescence is indicative of hexamer-hexamer interactions. We consider that hydrophobic interactions are fundamental to the maintenance of the structure and function of phycobilisomes.

  4. Circular and linear dichroism of periodical helical media with large dielectric anisotropy

    CERN Document Server

    Arakelian, H M; Eritsyan, H S

    2000-01-01

    The interaction of light with a layer of periodical helical media is considered. Features of circular and linear dichroism at large dielectric anisotropy are studied. Influence of dielectric boundaries on circular and linear dichroism is investigated.

  5. The optical properties of CuA in bovine cytochrome c oxidase determined by low-temperature magnetic-circular-dichroism spectroscopy.

    Science.gov (United States)

    Greenwood, C; Hill, B C; Barber, D; Eglinton, D G; Thomson, A J

    1983-11-01

    The visible-near-i.r.-region m.c.d. (magnetic-circular-dichroism) spectrum recorded at low temperature in the range 450-900 nm is reported for oxidized resting mammalian cytochrome c oxidase. M.c.d. magnetization curves determined at different wavelengths reveal the presence of two paramagnetic species. Curves at 576, 613 and 640 nm fit well to those expected for an x,y-polarized haem transition with g values of 3.03, 2.21 and 1.45, i.e. cytochrome a3+. The m.c.d. features at 515, 785 and 817 nm magnetize as a S = 1/2 paramagnet with average g values close to 2, and simulated m.c.d. magnetization curves obtained by using the observed g values of CuA2+, i.e. 2.18, 2.03 and 1.99, fit well to the experimental observations. The form of the m.c.d. magnetization curve at 466 nm is curious, but it can be explained if CuA2+ and cytochrome a3+ contribute with oppositely signed bands at this wavelength. By comparing the m.c.d. spectrum of the enzyme with that of extracted haem a-bisimidazole complex it has been possible to deconvolute the m.c.d. spectrum of CuA2+, which shows transitions throughout the spectral region from 450 to 950 nm. The m.c.d.-spectral properties of CuA2+ were compared with those of a well-defined type I blue copper centre in azurin isolated from Pseudomonas aeruginosa. The absolute intensities of the m.c.d. signals at equal fields and temperatures for CuA2+ are 10-20-fold greater than those for azurin. The optical spectrum of CuA2+ strongly suggests an assignment as a d9 ion rather than Cu(I) bound to a thiyl radical.

  6. Electronic and vibrational circular dichroism spectra of (R)-(-)-apomorphine

    Energy Technology Data Exchange (ETDEWEB)

    Abbate, Sergio, E-mail: abbate@med.unibs.it [Dipartimento di Scienze Biomediche e Biotecnologie, Universita di Brescia, Viale Europa 11, 25123 Brescia (Italy); CNISM, Consorzio Interuniversitario Scienze Fisiche della Materia, Via della Vasca Navale 84, 00146 Roma (Italy); Longhi, Giovanna; Lebon, France [Dipartimento di Scienze Biomediche e Biotecnologie, Universita di Brescia, Viale Europa 11, 25123 Brescia (Italy); CNISM, Consorzio Interuniversitario Scienze Fisiche della Materia, Via della Vasca Navale 84, 00146 Roma (Italy); Tommasini, Matteo [Dipartimento di Chimica, Materiali e Ingegneria Chimica ' G. Natta' , Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano (Italy); Consorzio Interuniversitario per la Scienza e Tecnologia dei Materiali (INSTM), Unita di Ricerca del Politecnico di Milano (Dip. CMIC), Piazza Leonardo da Vinci 32, 20133 Milano (Italy)

    2012-09-11

    Highlights: Black-Right-Pointing-Pointer ECD and VCD Spectra of (R)-(-)-apomorphine measured in various solvents. Black-Right-Pointing-Pointer DFT calculations allow to study the protonation state and conformations. Black-Right-Pointing-Pointer Contributions from catechol OH vibrations to the VCD spectra is studied. -- Abstract: Apomorphine is a chiral drug molecule; notwithstanding its extraordinary importance, little attention has been paid to the characterization of its chiroptical properties. Here we report on its electronic circular dichroism (ECD) spectra, recorded in methanol and water, and vibrational circular dichroism (VCD) in methanol and dimethyl sulfoxide (DMSO) solutions. Density functional theory (DFT) calculations have allowed us to interpret the spectra and to evaluate the role of possible conformations, charge-states and interactions with counter ions.

  7. Photoemission and magnetic circular dichroism studies of magnetic semiconductors

    Science.gov (United States)

    Fujimori, Atsushi

    2005-03-01

    Recently, a series of novel ferromagnetic semiconductors have been synthesized using MBE and related techniques and have attracted much attention because of unknown mechanisms of carrier-induced ferromagnetism and potential applications as "spin electronics" devices. Some new materials show ferromagnetism even well above room temperature. Photoemission spectroscopy has been used to study the d orbitals of the dilute transition-metal atoms, mostly Mn, and their hybridization with the host band states [1]. Soft x-ray absorption spectroscopy (XAS) and magnetic circular dichroism (MCD) at the transition-metal 2p-3d absorption edges are useful techniques to study the valence and spin states of the transition-metal atoms. Furthermore, since MCD has different sensitivities to the ferromagnetic and paramagnetic components at different temperatures and magnetic fileds, if the sample is a mixture of ferromagnetic and non-ferromagnetic transition- metal atoms, it can be used to separate the two components and to study their electronic structures. In this talk, results are presented for the prototypical diluted ferromagnetic semiconductor Ga1-xMnxAs [2] and the room-temperature ferromagnets Zn1-xCoxO and Ti1-xCoxO2.I acknowledge collaboration with Y. Ishida, J.-I. Hwang, M. Kobayashi, Y. Takeda, Y. Saitoh, J. Okamoto, T. Okane, Y. Muramatsu, K. Mamiya, T. Koide, A. Tanaka, M. Tanaka, Hayashi, S. Ohya, T. Kondo, H. Munekata, H. Saeki, H. Tabata, T. Kawai, Y. Matsumoto, H. Koinuma, T. Fukumura and M. Kawasaki. This work was supported by a Grant-in-Aid for Scientific Research in Priority Area "Semiconductor nano-spintronics" (14076209) from MEXT, Japan.1. J. Okabayashi et al., Phys. Rev. B 64, 125304 (2001).2. A. Fujimori et al., J. Electron Spectrosc. Relat. Phenom., in press.

  8. Complex polarization propagator calculations of magnetic circular dichroism spectra

    Science.gov (United States)

    Solheim, Harald; Ruud, Kenneth; Coriani, Sonia; Norman, Patrick

    2008-03-01

    It is demonstrated that the employment of the nonlinear complex polarization propagator enables the calculation of the complete magnetic circular dichroism spectra of closed-shell molecules, including at the same time both the so-called Faraday A and B terms. In this approach, the differential absorption of right and left circularly polarized light in the presence of a static magnetic field is determined from the real part of the magnetic field-perturbed electric dipole polarizability. The introduction of the finite lifetimes of the electronically excited states into the theory results in response functions that are well behaved in the entire spectral region, i.e., the divergencies that are found in conventional response theory approaches at the transition energies of the system are not present. The applicability of the approach is demonstrated by calculations of the ultraviolet magnetic circular dichroism spectra of para-benzoquinone, tetrachloro-para-benzoquinone, and cyclopropane. The present results are obtained with the complex polarization propagator approach in conjunction with Kohn-Sham density functional theory and the standard adiabatic density functionals B3LYP, CAM-B3LYP, and BHLYP.

  9. Bright circularly polarized soft X-ray high harmonics for X-ray magnetic circular dichroism.

    Science.gov (United States)

    Fan, Tingting; Grychtol, Patrik; Knut, Ronny; Hernández-García, Carlos; Hickstein, Daniel D; Zusin, Dmitriy; Gentry, Christian; Dollar, Franklin J; Mancuso, Christopher A; Hogle, Craig W; Kfir, Ofer; Legut, Dominik; Carva, Karel; Ellis, Jennifer L; Dorney, Kevin M; Chen, Cong; Shpyrko, Oleg G; Fullerton, Eric E; Cohen, Oren; Oppeneer, Peter M; Milošević, Dejan B; Becker, Andreas; Jaroń-Becker, Agnieszka A; Popmintchev, Tenio; Murnane, Margaret M; Kapteyn, Henry C

    2015-11-17

    We demonstrate, to our knowledge, the first bright circularly polarized high-harmonic beams in the soft X-ray region of the electromagnetic spectrum, and use them to implement X-ray magnetic circular dichroism measurements in a tabletop-scale setup. Using counterrotating circularly polarized laser fields at 1.3 and 0.79 µm, we generate circularly polarized harmonics with photon energies exceeding 160 eV. The harmonic spectra emerge as a sequence of closely spaced pairs of left and right circularly polarized peaks, with energies determined by conservation of energy and spin angular momentum. We explain the single-atom and macroscopic physics by identifying the dominant electron quantum trajectories and optimal phase-matching conditions. The first advanced phase-matched propagation simulations for circularly polarized harmonics reveal the influence of the finite phase-matching temporal window on the spectrum, as well as the unique polarization-shaped attosecond pulse train. Finally, we use, to our knowledge, the first tabletop X-ray magnetic circular dichroism measurements at the N4,5 absorption edges of Gd to validate the high degree of circularity, brightness, and stability of this light source. These results demonstrate the feasibility of manipulating the polarization, spectrum, and temporal shape of high harmonics in the soft X-ray region by manipulating the driving laser waveform.

  10. Vibrational Circular Dichroism Absolute Configuration of 9,12-Cyclomulin-13-ol, a Diterpene from Azorella and Laretia Species.

    Science.gov (United States)

    Muñoz, Marcelo A; San-Martín, Aurelio; Joseph-Nathan, Pedro

    2015-08-01

    The absolute configuration of the diterpenoid 9,12-cyclomulin-13-ol (1), a constituent of Azorella and Laretia species, has been established by vibrational circular dichroism spectroscopy in combination with density functional theory calculations. The obtained normal diterpene absolute configuration confirms that of azorellanol (2), which was determined by single crystal X-ray diffraction.

  11. Using Circular Dichroism Spectra to Estimate Protein Secondary Structure

    Energy Technology Data Exchange (ETDEWEB)

    Greenfield, N.

    2006-01-01

    Circular dichroism (CD) is an excellent tool for rapid determination of the secondary structure and folding properties of proteins that have been obtained using recombinant techniques or purified from tissues. The most widely used applications of protein CD are to determine whether an expressed, purified protein is folded, or if a mutation affects its conformation or stability. In addition, it can be used to study protein interactions. This protocol details the basic steps of obtaining and interpreting CD data and methods for analyzing spectra to estimate the secondary structural composition of proteins. CD has the advantage that it is that measurements may be made on multiple samples containing 20 {mu}g or less of proteins in physiological buffers in a few hours. However, it does not give the residue-specific information that can be obtained by X-ray crystallography or NMR.

  12. Large circular dichroism and optical rotation in titanium doped chiral silver nanorods

    Energy Technology Data Exchange (ETDEWEB)

    Titus, Jitto; Perera, A.G. Unil [Department of Physics and Astronomy, Optoelectronics Laboratory, GSU, Atlanta, GA (United States); Larsen, George; Zhao, Yiping [Department of Physics and Astronomy, Nanolab, UGA, Athens, GA (United States)

    2016-10-15

    The circular dichroism of titanium-doped silver chiral nanorod arrays grown using the glancing angle deposition (GLAD) method is investigated in the visible and near infrared ranges using transmission ellipsometry and spectroscopy. These films are found to have significant circular polarization effects across broad ranges of the visible to NIR spectrum, including large values for optical rotation. The characteristics of these circular polarization effects are strongly influenced by the morphology of the deposited arrays. Thus, the morphological control of the optical activity in these nanostructures demonstrates significant optimization capability of the GLAD technique for fabricating chiral plasmonic materials. (copyright 2016 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  13. Three-dimensional structural imaging of starch granules by second-harmonic generation circular dichroism.

    Science.gov (United States)

    Zhuo, G-Y; Lee, H; Hsu, K-J; Huttunen, M J; Kauranen, M; Lin, Y-Y; Chu, S-W

    2014-03-01

    Chirality is one of the most fundamental and essential structural properties of biological molecules. Many important biological molecules including amino acids and polysaccharides are intrinsically chiral. Conventionally, chiral species can be distinguished by interaction with circularly polarized light, and circular dichroism is one of the best-known approaches for chirality detection. As a linear optical process, circular dichroism suffers from very low signal contrast and lack of spatial resolution in the axial direction. It has been demonstrated that by incorporating nonlinear interaction with circularly polarized excitation, second-harmonic generation circular dichroism can provide much higher signal contrast. However, previous circular dichroism and second-harmonic generation circular dichroism studies are mostly limited to probe chiralities at surfaces and interfaces. It is known that second-harmonic generation, as a second-order nonlinear optical effect, provides excellent optical sectioning capability when combined with a laser-scanning microscope. In this work, we combine the axial resolving power of second-harmonic generation and chiral sensitivity of second-harmonic generation circular dichroism to realize three-dimensional chiral detection in biological tissues. Within the point spread function of a tight focus, second-harmonic generation circular dichroism could arise from the macroscopic supramolecular packing as well as the microscopic intramolecular chirality, so our aim is to clarify the origins of second-harmonic generation circular dichroism response in complicated three-dimensional biological systems. The sample we use is starch granules whose second-harmonic generation-active molecules are amylopectin with both microscopic chirality due to its helical structure and macroscopic chirality due to its crystallized packing. We found that in a starch granule, the second-harmonic generation for right-handed circularly polarized excitation is

  14. Circular dichroism and fluorescence spectroscopy of cysteinyl-tRNA synthetase from Halobacterium salinarum ssp. NRC-1 demonstrates that group I cations are particularly effective in providing structure and stability to this halophilic protein.

    Directory of Open Access Journals (Sweden)

    Christopher J Reed

    Full Text Available Proteins from extremophiles have the ability to fold and remain stable in their extreme environment. Here, we investigate the presence of this effect in the cysteinyl-tRNA synthetase from Halobacterium salinarum ssp. NRC-1 (NRC-1, which was used as a model halophilic protein. The effects of salt on the structure and stability of NRC-1 and of E. coli CysRS were investigated through far-UV circular dichroism (CD spectroscopy, fluorescence spectroscopy, and thermal denaturation melts. The CD of NRC-1 CysRS was examined in different group I and group II chloride salts to examine the effects of the metal ions. Potassium was observed to have the strongest effect on NRC-1 CysRS structure, with the other group I salts having reduced strength. The group II salts had little effect on the protein. This suggests that the halophilic adaptations in this protein are mediated by potassium. CD and fluorescence spectra showed structural changes taking place in NRC-1 CysRS over the concentration range of 0-3 M KCl, while the structure of E. coli CysRS was relatively unaffected. Salt was also shown to increase the thermal stability of NRC-1 CysRS since the melt temperature of the CysRS from NRC-1 was increased in the presence of high salt, whereas the E. coli enzyme showed a decrease. By characterizing these interactions, this study not only explains the stability of halophilic proteins in extremes of salt, but also helps us to understand why and how group I salts stabilize proteins in general.

  15. Circular dichroism in laser-assisted proton-hydrogen collisions

    Science.gov (United States)

    Niederhausen, Thomas; Feuerstein, Bernold; Thumm, Uwe

    2004-08-01

    We investigate the effects of a strong laser field on the dynamics of electron capture and emission in ion-atom collisions within a reduced dimensionality model of the scattering system in which the motion of the active electron and the laser electric field vector are confined to the scattering plane. We examine the probabilities for electron capture and ionization as a function of the laser intensity, the projectile impact parameter b , and the laser phase ϕ that determines the orientation of the laser electric field with respect to the internuclear axis at the time of closest approach between target and projectile. Our results for the b -dependent ionization and capture probabilities show a strong dependence on both ϕ and the helicity of the circularly polarized laser light. For intensities above 5×1012W/cm2 our model predicts a noticeable circular dichroism in the capture probability for slow proton-hydrogen collisions, which persists after averaging over ϕ . Capture and electron emission probabilities defer significantly from results for laser-unassisted collisions. Furthermore, we find evidence for a charge-resonance-enhanced ionization mechanism that may enable the measurement of the absolute laser phase ϕ .

  16. Optical properties and circular dichroism of chiral metal nanoparticles

    Science.gov (United States)

    Fan, Zhiyuan; Govorov, Alexander; OU Team

    2013-03-01

    In nature, biological systems are built up by homochiral building blocks, such as a sugar and protein. Circular dichroism (CD) is an effective tool of resolving molecular conformations. It utilizes circularly polarized light to detect differential absorption of chiral materials. In medicine, it will help us to develop new drugs and therapies, if we understand the connection between the physical or chemical properties of drug molecules and their conformations. With the rapid development of nanotechnologies, chiral nanomaterials attract lots of attention nowadays. CD signals of chiral molecules can be enhanced or shifted to the visible band in the presence of plasmonic nanocrystals. Here we present a plasmonic CD mechanism from a single chiral metal nanocrystal. The mechanism is essentially different from the dipolar plasmon-plasmon interaction in a chiral NP assembly, which mimics the CD mechanism of chiral molecules. Chiral metal nanocrystals are expected to have promising applications in biosensing. Recently a few experimental papers reported successful realizations of chiral nanocrystals in a macroscopic ensemble in solution. Particularly the paper described silver nanoparticles grown on chiral template molecules and demonstrating characteristic CD signals at a plasmonic wavelength. The plasmonic CD signals in Ref. can come from a dipolar plasmon-molecule interaction or from a chiral shape of nanocrystals. This work was supported by the NSF (project: CBET- 0933782) and by the Volkswagen Foundation.

  17. Room temperature high circular dichroism ultraviolet lasing from planar spiral metal-GaN nanowire cavity (Conference Presentation)

    Science.gov (United States)

    Shih, Min-Hsiung

    2016-09-01

    Circularly polarized light and chiroptical effect have received considerable attention in advanced photonic and electronic technologies including optical spintronics, quantum-based optical information processing and communication, and high-efficiency liquid crystal display backlights. Moreover, the development of circularly polarized photon sources has played a major role in circular dichroism (CD) spectroscopy, which is important for analyses of optically active molecules, chiral synthesis in biology and chemistry, and ultrafast magnetization control. However, the conventional collocation of light-emitting devices and additional circular-polarization converters that produce circularly polarized beams makes the setup bulky and hardly compatible with nanophotonic devices in ultrasmall scales. In fact, the direct generation of circularly polarized photons may simplify the system integration, compact the setup, lower the cost of external components, and perhaps enhance the power efficiency. In this work, with the spiral-type metal-gallium nitride (GaN) nanowire cavity, we demonstrated an ultrasmall semiconductor laser capable of emitting circularly-polarized photons. The left- and right-hand spiral metal nanowire cavities with varied periods were designed at ultraviolet wavelengths to achieve the high quality factor circular dichroism metastructures. The dissymmetry factors characterizing the degrees of circular polarizations of the left- and right-hand chiral lasers were 1.4 and -1.6 (2 if perfectly circular polarized), respectively. The results show that the chiral cavities with only 5 spiral periods can achieve lasing signals with decently high degrees of circular polarizations.

  18. Circular dichroism measurements at an x-ray free-electron laser with polarization control

    Science.gov (United States)

    Hartmann, G.; Lindahl, A. O.; Knie, A.; Hartmann, N.; Lutman, A. A.; MacArthur, J. P.; Shevchuk, I.; Buck, J.; Galler, A.; Glownia, J. M.; Helml, W.; Huang, Z.; Kabachnik, N. M.; Kazansky, A. K.; Liu, J.; Marinelli, A.; Mazza, T.; Nuhn, H.-D.; Walter, P.; Viefhaus, J.; Meyer, M.; Moeller, S.; Coffee, R. N.; Ilchen, M.

    2016-08-01

    A non-destructive diagnostic method for the characterization of circularly polarized, ultraintense, short wavelength free-electron laser (FEL) light is presented. The recently installed Delta undulator at the LCLS (Linac Coherent Light Source) at SLAC National Accelerator Laboratory (USA) was used as showcase for this diagnostic scheme. By applying a combined two-color, multi-photon experiment with polarization control, the degree of circular polarization of the Delta undulator has been determined. Towards this goal, an oriented electronic state in the continuum was created by non-resonant ionization of the O2 1s core shell with circularly polarized FEL pulses at hν ≃ 700 eV. An also circularly polarized, highly intense UV laser pulse with hν ≃ 3.1 eV was temporally and spatially overlapped, causing the photoelectrons to redistribute into so-called sidebands that are energetically separated by the photon energy of the UV laser. By determining the circular dichroism of these redistributed electrons using angle resolving electron spectroscopy and modeling the results with the strong-field approximation, this scheme allows to unambiguously determine the absolute degree of circular polarization of any pulsed, ultraintense XUV or X-ray laser source.

  19. FTIR Vibrational Circular Dichroism Of Oligopeptides Related To Polyproline

    Science.gov (United States)

    Dukor, R. K.; Keiderling, Timothy A.

    1989-12-01

    Vibrational Circular Dichroism (VCD) data can be routinely measured by FTIR. On our FTIR VCD instrument it is possible to obtain a spectrum where baseline correction is accomplished with solvent only. Such capability is important for measuring biological systems. Several polypeptides that have been assigned to be in 'random coil' conformation all give an amide I VCD pattern which has the same sign and bandshape as poly-L-proline II but a smaller magnitude. This is consistent with a previous proposal by Tiffany & Krimm that the 'random coil' conformation of charged polypeptides actually has a significant local ordering in the form of a left-handed extended helix. To investigate this problem further we have studied the effects of temperature and chain length on the VCD bandshape of this conformational type. The latter studies were done with (Pro)n, n=2-7. Our results indicate that even at the level of (Pro)4 the VCD spectrum has the same bandshape, sign and intensity as found in the 'random coil' poly-L-glutamic acid spectrum. Data on various 'random coil' systems will be compared to the model studies we have done.

  20. Structures of plant viruses from vibrational circular dichroism.

    Science.gov (United States)

    Shanmugam, Ganesh; Polavarapu, Prasad L; Kendall, Amy; Stubbs, Gerald

    2005-08-01

    Vibrational circular dichroism (VCD) spectra in the amide I and II regions have been measured for viruses for the first time. VCD spectra were recorded for films prepared from aqueous buffer solutions and also for solutions using D(2)O buffers at pH 8. Investigations of four filamentous plant viruses, Tobacco mosaic virus (TMV), Papaya mosaic virus, Narcissus mosaic virus (NMV) and Potato virus X (PVX), as well as a deletion mutant of PVX, are described in this paper. The film VCD spectra of the viruses clearly revealed helical structures in the virus coat proteins; the nucleic acid bases present in the single-stranded RNA could also be characterized. In contrast, the solution VCD spectra showed the characteristic VCD bands for alpha-helical structures in the coat proteins but not for RNA. Both sets of results clearly indicated that the coat protein conformations are dominated by helical structures, in agreement with earlier reports. VCD results also indicated that the coat protein structures in PVX and NMV are similar to each other and somewhat different from that of TMV. The present study demonstrates the feasibility of measuring VCD spectra for viruses and extracting structural information from these spectra.

  1. Conformational effects on the circular dichroism of Human Carbonic Anhydrase II: a multilevel computational study.

    Directory of Open Access Journals (Sweden)

    Tatyana G Karabencheva-Christova

    Full Text Available Circular Dichroism (CD spectroscopy is a powerful method for investigating conformational changes in proteins and therefore has numerous applications in structural and molecular biology. Here a computational investigation of the CD spectrum of the Human Carbonic Anhydrase II (HCAII, with main focus on the near-UV CD spectra of the wild-type enzyme and it seven tryptophan mutant forms, is presented and compared to experimental studies. Multilevel computational methods (Molecular Dynamics, Semiempirical Quantum Mechanics, Time-Dependent Density Functional Theory were applied in order to gain insight into the mechanisms of interaction between the aromatic chromophores within the protein environment and understand how the conformational flexibility of the protein influences these mechanisms. The analysis suggests that combining CD semi empirical calculations, crystal structures and molecular dynamics (MD could help in achieving a better agreement between the computed and experimental protein spectra and provide some unique insight into the dynamic nature of the mechanisms of chromophore interactions.

  2. Helical Inversion of Gel Fibrils by Elongation of Perfluoroalkyl Chains as Studied by Vibrational Circular Dichroism.

    Science.gov (United States)

    Sato, Hisako; Yajima, Tomoko; Yamagishi, Akihiko

    2016-05-01

    Vibrational circular dichroism (VCD) spectroscopy was applied to gelation by a chiral low-molecular mass weight gelator, N,N'-diperfluoroalkanoyl-1,2-trans-diaminocyclohexane. Attention was focused on the winding effects of (-CF2 )n chains on the gelating ability. For this purpose, a series of gelators were synthesized with perfluoroalkyl chains of different length (n = 6-8). When gelation was studied using acetonitrile as a solvent, the fibrils took different morphologies, depending on the chain length: twisted saddle-like ribbon or helical ribbon from fibril (n = 6) and a helical ribbon from platelet (n = 8). The signs of VCD peaks assigned to the couplet of C=O stretching and to the C-F stretching were also dependent on n, indicating that a gelator molecule changed conformation on elongating perfluoroalkyl chains. A model is proposed for the aggregation modes in fibrils. Chirality 28:361-364, 2016. © 2016 Wiley Periodicals, Inc.

  3. Effects of Trehalose on Thermodynamic Properties of Alpha-synuclein Revealed through Synchrotron Radiation Circular Dichroism

    Directory of Open Access Journals (Sweden)

    Paolo Ruzza

    2015-05-01

    Full Text Available Many neurodegenerative diseases, including Huntington’s, Alzheimer’s and Parkinson’s diseases, are characterized by protein misfolding and aggregation. The capability of trehalose to interfere with protein misfolding and aggregation has been recently evaluated by several research groups. In the present work, we studied, by means of synchrotron radiation circular dichroism (SRCD spectroscopy, the dose-effect of trehalose on α-synuclein conformation and/or stability to probe the capability of this osmolyte to interfere with α-synuclein’s aggregation. Our study indicated that a low trehalose concentration stabilized α-synuclein folding much better than at high concentration by blocking in vitro α-synuclein’s polymerisation. These results suggested that trehalose could be associated with other drugs leading to a new approach for treating Parkinson’s and other brain-related diseases.

  4. Crystal structures, circular dichroism spectra and absolute configurations of some ?-ascorbic acid derivatives

    Science.gov (United States)

    Wittine, Karlo; Gazivoda, Tatjana; Markuš, Marko; Mrvoš-Sermek, Draginja; Hergold-Brundić, Antonija; Cetina, Mario; Žiher, Dinko; Gabelica, Vesna; Mintas, Mladen; Raić-Malić, Silvana

    2004-01-01

    Chiral 2,3-O,O-dibenzyl ethers of L-ascorbic acid with 4-(5,6-epoxy)- (4) and 6-O-tosyl- (8) functional groups were studied by X-ray crystallography and circular dichroism (CD) spectroscopy. The stereostructure of 2,3-O,O-dibenzyl-5,6-isopropylidene-L-ascorbic acid (6) and 8 was determined by X-ray crystal structure analysis. Comparison of the CD-spectra of 4 and 8 with the CD-spectra of their synthetic precursors (2-3, 5-7) and L-ascorbic acid (1) itself, as well as crystal structures of 6 and 8 permitted to deduce the absolute configuration of 4. Thus, the chiral atoms C-4 and C-5 in 4 have R and S configurations, which is consistent with the configuration of 1.

  5. Ligand induced circular dichroism and circularly polarized luminescence in CdSe quantum dots.

    Science.gov (United States)

    Tohgha, Urice; Deol, Kirandeep K; Porter, Ashlin G; Bartko, Samuel G; Choi, Jung Kyu; Leonard, Brian M; Varga, Krisztina; Kubelka, Jan; Muller, Gilles; Balaz, Milan

    2013-12-23

    Chiral thiol capping ligands L- and D-cysteines induced modular chiroptical properties in achiral cadmium selenide quantum dots (CdSe QDs). Cys-CdSe prepared from achiral oleic acid capped CdSe by postsynthetic ligand exchange displayed size-dependent electronic circular dichroism (CD) and circularly polarized luminescence (CPL). Opposite CPL signals were measured for the CdSe QDs capped with D- and L-cysteine. The CD profile and CD anisotropy varied with size of CdSe nanocrystals with largest anisotropy observed for CdSe nanoparticles of 4.4 nm. Magic angle spinning solid state NMR (MAS ssNMR) experiments suggested bidentate interaction between cysteine and the surface of CdSe. Time Dependent Density Functional Theory (TDDFT) calculations verified that attachment of L- and D-cysteine to the surface of model (CdSe)13 nanoclusters induces measurable opposite CD signals for the exitonic band of the nanocluster. The origin of the induced chirality is consistent with the hybridization of highest occupied CdSe molecular orbitals with those of the chiral ligand.

  6. Anisotropic Circular Dichroism Signatures of Oriented Thylakoid Membranes and Lamellar Aggregates of LHCII

    Energy Technology Data Exchange (ETDEWEB)

    Miloslavina, Y.; Hind, G.; Lambrev, P. H.; Javorfi, T.; Varkonyi, Z.; Karlicky, V.; Wall, J. S.; Garab, G.

    2011-06-12

    In photosynthesis research, circular dichroism (CD) spectroscopy is an indispensable tool to probe molecular architecture at virtually all levels of structural complexity. At the molecular level, the chirality of the molecule results in intrinsic CD; pigment-pigment interactions in protein complexes and small aggregates can give rise to excitonic CD bands, while 'psi-type' CD signals originate from large, densely packed chiral aggregates. It has been well established that anisotropic CD (ACD), measured on samples with defined non-random orientation relative to the propagation of the measuring beam, carries specific information on the architecture of molecules or molecular macroassemblies. However, ACD is usually combined with linear dichroism and can be distorted by instrumental imperfections, which given the strong anisotropic nature of photosynthetic membranes and complexes, might be the reason why ACD is rarely studied in photosynthesis research. In this study, we present ACD spectra, corrected for linear dichroism, of isolated intact thylakoid membranes of granal chloroplasts, washed unstacked thylakoid membranes, photosystem II (PSII) membranes (BBY particles), grana patches, and tightly stacked lamellar macroaggregates of the main light-harvesting complex of PSII (LHCII). We show that the ACD spectra of face- and edge-aligned stacked thylakoid membranes and LHCII lamellae exhibit profound differences in their psi-type CD bands. Marked differences are also seen in the excitonic CD of BBY and washed thylakoid membranes. Magnetic CD (MCD) spectra on random and aligned samples, and the largely invariable nature of the MCD spectra, despite dramatic variations in the measured isotropic and anisotropic CD, testify that ACD can be measured without substantial distortions and thus employed to extract detailed information on the (supra)molecular organization of photosynthetic complexes. An example is provided showing the ability of CD data to indicate such an

  7. Anisotropic Circular Dichroism Signatures of Oriented Thylakoid Membranes and Lamellar Aggregates of LHCII

    Energy Technology Data Exchange (ETDEWEB)

    Miloslavina Y.; Hind G.; Lambrev, P. H.; Javorfi, T.; Varkonyi, Z.; Karlicky, V.; Wall, J. S.; Garab, G.

    2012-03-01

    In photosynthesis research, circular dichroism (CD) spectroscopy is an indispensable tool to probe molecular architecture at virtually all levels of structural complexity. At the molecular level, the chirality of the molecule results in intrinsic CD; pigment-pigment interactions in protein complexes and small aggregates can give rise to excitonic CD bands, while 'psi-type' CD signals originate from large, densely packed chiral aggregates. It has been well established that anisotropic CD (ACD), measured on samples with defined non-random orientation relative to the propagation of the measuring beam, carries specific information on the architecture of molecules or molecular macroassemblies. However, ACD is usually combined with linear dichroism and can be distorted by instrumental imperfections, which given the strong anisotropic nature of photosynthetic membranes and complexes, might be the reason why ACD is rarely studied in photosynthesis research. In this study, we present ACD spectra, corrected for linear dichroism, of isolated intact thylakoid membranes of granal chloroplasts, washed unstacked thylakoid membranes, photosystem II (PSII) membranes (BBY particles), grana patches, and tightly stacked lamellar macroaggregates of the main light-harvesting complex of PSII (LHCII). We show that the ACD spectra of face- and edge-aligned stacked thylakoid membranes and LHCII lamellae exhibit profound differences in their psi-type CD bands. Marked differences are also seen in the excitonic CD of BBY and washed thylakoid membranes. Magnetic CD (MCD) spectra on random and aligned samples, and the largely invariable nature of the MCD spectra, despite dramatic variations in the measured isotropic and anisotropic CD, testify that ACD can be measured without substantial distortions and thus employed to extract detailed information on the (supra)molecular organization of photosynthetic complexes. An example is provided showing the ability of CD data to indicate such an

  8. A computational protocol for the study of circularly polarized phosphorescence and circular dichroism in spin-forbidden absorption

    DEFF Research Database (Denmark)

    Kaminski, Maciej; Cukras, Janusz; Pecul, Magdalena;

    2015-01-01

    on the response function formalism and is implemented at the level of time-dependent density functional theory. It has been employed to calculate the spin-forbidden circular dichroism and circularly polarized phosphorescence signals of valence n - p* and n ’ p* transitions, respectively, in several chiral enones......We present a computational methodology to calculate the intensity of circular dichroism (CD) in spinforbidden absorption and of circularly polarized phosphorescence (CPP) signals, a manifestation of the optical activity of the triplet–singlet transitions in chiral compounds. The protocol is based...... structure. In many cases the sign of the spin-forbidden CD and CPP signals are opposite. For the b,g-enones under investigation, where there are two minima on the lowest triplet excited state potential energy surface, each minimum exhibits a CPP signal of a different sign....

  9. A Simple Spreadsheet Program to Simulate and Analyze the Far-UV Circular Dichroism Spectra of Proteins

    Science.gov (United States)

    Abriata, Luciano A.

    2011-01-01

    A simple algorithm was implemented in a spreadsheet program to simulate the circular dichroism spectra of proteins from their secondary structure content and to fit [alpha]-helix, [beta]-sheet, and random coil contents from experimental far-UV circular dichroism spectra. The physical basis of the method is briefly reviewed within the context of…

  10. Characterization of dry globular proteins and protein fibrils by synchrotron radiation vacuum UV circular dichroism

    DEFF Research Database (Denmark)

    Nesgaard, Lise W.; Hoffmann, Søren Vrønning; Andersen, Christian Beyschau

    2008-01-01

    Circular dichroism using synchrotron radiation (SRCD) can extend the spectral range down to approximately 130 nm for dry proteins, potentially providing new structural information. Using a selection of dried model proteins, including alpha-helical, beta-sheet, and mixed-structure proteins, we obs...

  11. Energetics, structures, vibrational frequencies, vibrational absorption, vibrational circular dichroism and Raman intensities of Leu-enkephalin

    DEFF Research Database (Denmark)

    Jalkanen, Karl J.

    2003-01-01

    , similar to the characteristic features in electronic circular dichroism spectra with respect to those in the UV-vis electronic absorption spectra. Finally, we have also attempted to stabilize the zwitterionic species by treating the aqueous environment by using a continuum solvent approach, the Onsager...

  12. Protein Circular Dichroism Data Bank (PCDDB): data bank and website design.

    Science.gov (United States)

    Whitmore, Lee; Janes, Robert W; Wallace, B A

    2006-06-01

    The Protein Circular Dichroism Data Bank (PCDDB) is a new deposition data bank for validated circular dichroism spectra of biomacromolecules. Its aim is to be a resource for the structural biology and bioinformatics communities, providing open access and archiving facilities for circular dichroism and synchrotron radiation circular dichroism spectra. It is named in parallel with the Protein Data Bank (PDB), a long-existing valuable reference data bank for protein crystal and NMR structures. In this article, we discuss the design of the data bank structure and the deposition website located at http://pcddb.cryst.bbk.ac.uk. Our aim is to produce a flexible and comprehensive archive, which enables user-friendly spectral deposition and searching. In the case of a protein whose crystal structure and sequence are known, the PCDDB entry will be linked to the appropriate PDB and sequence data bank files, respectively. It is anticipated that the PCDDB will provide a readily accessible biophysical catalogue of information on folded proteins that may be of value in structural genomics programs, for quality control and archiving in industrial and academic labs, as a resource for programs developing spectroscopic structural analysis methods, and in bioinformatics studies.

  13. Probing electronic coupling between adenine bases in RNA strands from synchrotron radiation circular dichroism experiments

    DEFF Research Database (Denmark)

    Nielsen, Lisbeth Munksgård; Hoffmann, Søren Vrønning; Nielsen, Steen Brøndsted

    2012-01-01

    Circular dichroism spectra (176–330 nm) of RNA adenine oligomers, (rA)n (n = 1–10, 12, 15, and 20), reveal electronic coupling between two bases in short strands. The number of interacting bases in long strands is more and larger than that reported previously for the corresponding DNA strands....

  14. Detection Limits for Natural Circular Dichroism of Chiral Complexes in the X-ray Range

    NARCIS (Netherlands)

    Goulon, José; Sette, Francesco; Moise, Claude; Fontaine, Alain; Perey, Danièle; Rudolf, Petra; Baudelet, François

    1993-01-01

    Whereas both Magnetic Circular Dichroism and Faraday Rotation studies have been successfully carried out at the K-, L- and M- absorption edges of metal atoms in ferromagnetic systems, Natural optical activity of chiral complexes has not yet been detected quite unambiguously in the X-ray range. We re

  15. Circular dichroism spectroscopic investigation of double-decker phthalocyanine with G-Quadruplex as promising telomerase inhibitor

    Science.gov (United States)

    Baǧda, Efkan; Baǧda, Esra; Yabaş, Ebru

    2017-01-01

    In the present study, interaction of a double-decker phthalocyanine with two G-quadruplex DNA, Tel 21 and cMYC, was investigated. To the best of our knowledge, this is the first study about G-quadruplex-double decker phthalocyanine interaction. The spectrophotometric titration method was used for binding constant calculations. From the binding constants, it can be said that double-decker phthalocyanine more likely to bind Tel 21 rather than cMYC. The conformational changes upon binding were monitored via circular dichroism spectroscopy. The ethidium bromide replacement assay was investigated spectrofluorometrically.

  16. Electrically induced circular dichroism of multi-domain layers of a long-pitch cholesteric liquid crystal

    Science.gov (United States)

    Yakovlev, Dmitry D.; Sherman, Maria M.; Yakovlev, Dmitry A.

    2014-01-01

    Circular dichroism is typical of cholesteric materials with a cholesteric pitch of the order of light wavelength, where it is connected with selective reflection of one of the circularly polarized components of light. In this work we report, for the first time, on our observations of circular dichroism on multi-domain layers of a nonabsorbing cholesteric LC material whose natural cholesteric pitch is much larger than the wavelength of incident light. It is demonstrated that the degree of manifestation of the circular dichroism depends heavily on the LC layer thickness, voltage applied to the layer, and wavelength.

  17. Circular dichroism and superdiffusive transport at the surface of BiTeI.

    Science.gov (United States)

    Mauchain, J; Ohtsubo, Y; Hajlaoui, M; Papalazarou, E; Marsi, M; Taleb-Ibrahimi, A; Faure, J; Kokh, K A; Tereshchenko, O E; Eremeev, S V; Chulkov, E V; Perfetti, L

    2013-09-20

    We investigate the electronic states of BiTeI after the optical pumping with circularly polarized photons. Our data show that photoexcited electrons reach an internal thermalization within 300 fs of the arrival of the pump pulse. Instead, the dichroic contrast generated by the circularly polarized light relaxes on a time scale shorter than 80 fs. This result implies that orbital and spin polarization created by the circular pump pulse rapidly decays via manybody interaction. The persistent dichroism at longer delay times is due to the helicity dependence of superdiffussive transport. We ascribe it to the lack of inversion symmetry in an electronic system far from equilibrium conditions.

  18. [Study of collagen mimetic peptide's triple-helix structure and its thermostability by circular dichroism].

    Science.gov (United States)

    Zhang, Zhi-Bao; Wang, Jing-Jie; Chen, Hui-Juan; Xiong, Qing-Qing; Liu, Ling-Rong; Zhang, Qi-Qing

    2014-04-01

    In the present study, the authors explore the triple-helix conformation and thermal stability of collagen mimetic peptides (CMPs) as a function of peptide sequence and/or chain length by circular dichroism(CD). Five CMPs were designed and synthetized varying the number of POG triplets or incorporating an integrin alpha2beta1 binding motif Gly-Phe-Hyp-Gly-Glu-Arg (GFOGER). CD spectroscopy from 260 to 190 nm was recorded to confirm the existence of triple-helix conformation at room temperature, while thermal melting and thermal annealing of triple-helix (thermal unfolding and refolding of triple-helix, respectively) was characterized by monitoring ellipticity at 225 nm as a function of temperature. The results demonstrated that all the CMPs adopted triple-helix conformation, and the thermal stability of the CMPs was enhanced with increasing the number of POG triplets. In contrast to natural collagen, the thermal denaturation processes of CMPs were reversible, i. e. the triple-helix unfolded upon heating while refolded upon cooling. Meanwhile, the phenomenon of "hysteresis" was observed by comparing melting and thermal curves. These findings add new insights to the mechanisms of collagen and CMPs assembly, as well as provide an alternative approach to the fabrication of artificial collagen-likes biomaterials.

  19. Study of Structural Stability of Cyclophilin A by NMR and Circular Dichroism Spectra

    Institute of Scientific and Technical Information of China (English)

    SHI, Yan-Hong; LIN, Dong-Hai; HUANG, Jian-Ying; SHEN, Xu

    2006-01-01

    The structural stability of cyclophilin A (CypA) was investigated using H/D exchange and temperature coefficients of chemical shifts of amide protons, monitored by 2D heteronuclear NMR spectroscopy. Amide proton exchange rates were measured by H/D exchange experiments for slow-exchange protons and measured by SEA (Solvent Exposed Amides)-HSQC experiments for fast-exchange protons. Temperature coefficients of chemical shifts and hydrogen exchange rates of amide protons show reasonably good correlation with the protein structure. Totally,44 out of 153 non-proline assigned residues still exist in 86 d of hydrogen-deuterium exchange at 4 ℃, suggesting that CypA structure should be highly stable. Residues in secondary structures of α2, β1, β2, β5,β6 and β7 might constitute the hydrophobic core of the protein. The change in free energy of unfolding ( AGuH2O ) of CypA was estimated to be (21.99± 1.53) kJ·mol-1 by circular dichroism (CD). The large free energy change is also an indicator of the high structural stability.

  20. The use of Coulomb-attenuated methods for the calculation of electronic circular dichroism spectra

    Science.gov (United States)

    Shcherbin, Dmitry; Ruud, Kenneth

    2008-06-01

    We explore different parametrizations of the Coulomb-attenuated method B3LYP functional (CAM-B3LYP) for the calculation of circular dichroism spectra. In order to assess the performance of the different parametrizations, the calculated results are compared with high-level coupled-cluster calculations at the CC2 and CCSD levels of theory. We demonstrate that it is not possible to directly obtain good results both for the excitation energies and the rotational strengths simultaneously for any of the parametrizations of the CAM-B3LYP functional that we have tested. However, using the lowest excited state as a reference instead of the ground state—that is, shifting uniformly all excitation energies—leads to one parametrization which performs better than the others and thus can be recommended for studies of circular dichroism using the CAM-B3LYP functional.

  1. The use of Coulomb-attenuated methods for the calculation of electronic circular dichroism spectra

    Energy Technology Data Exchange (ETDEWEB)

    Shcherbin, Dmitry [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromso, N-9037 Tromso (Norway); Ruud, Kenneth [Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromso, N-9037 Tromso (Norway)], E-mail: kenneth.ruud@chem.uit.no

    2008-06-16

    We explore different parametrizations of the Coulomb-attenuated method B3LYP functional (CAM-B3LYP) for the calculation of circular dichroism spectra. In order to assess the performance of the different parametrizations, the calculated results are compared with high-level coupled-cluster calculations at the CC2 and CCSD levels of theory. We demonstrate that it is not possible to directly obtain good results both for the excitation energies and the rotational strengths simultaneously for any of the parametrizations of the CAM-B3LYP functional that we have tested. However, using the lowest excited state as a reference instead of the ground state-that is, shifting uniformly all excitation energies-leads to one parametrization which performs better than the others and thus can be recommended for studies of circular dichroism using the CAM-B3LYP functional.

  2. Resonant second-harmonic-generation circular-dichroism microscopy reveals molecular chirality in native biological tissues

    CERN Document Server

    Chen, Mei-Yu; Kan, Che-Wei; Lin, Yen-Yin; Ye, Cin-Wei; Wu, Meng-Jer; Liu, Hsiang-Lin; Chu, Shi-Wei

    2016-01-01

    Conventional linear optical activity effects are widely used for studying chiral materials. However, poor contrast and artifacts due to sample anisotropy limit the applicability of these methods. Here we demonstrate that nonlinear second-harmonic-generation circular dichroism spectral microscopy can overcome these limits. In intact collagenous tissues, clear spectral resonance is observed with sub-micrometer spatial resolution. By performing gradual protein denaturation studies, we show that the resonant responses are dominantly due to the molecular chirality.

  3. Levels of Supramolecular Chirality of Polyglutamine Aggregates Revealed by Vibrational Circular Dichroism

    OpenAIRE

    Kurouski, Dmitry; Kar, Karunakar; Wetzel, Ronald; Dukor, Rina K.; Lednev, Igor K.; Nafie, Laurence A.

    2013-01-01

    Polyglutamine (PolyQ) aggregates are a hallmark of several severe neurodegenerative diseases, expanded CAG-repeat diseases in which inheritance of an expanded polyQ sequence above a pathological threshold is associated with a high risk of disease. Application of vibrational circular dichroism (VCD) reveals that these PolyQ fibril aggregates exhibit a chiral supramolecular organization that is distinct from the supramolecular organization of previously observed amyloid fibrils. PolyQ fibrils g...

  4. Magnetic moments in a gadolinium iron garnet studied by soft-X-ray magnetic circular dichroism

    NARCIS (Netherlands)

    Rudolf, P.; Sette, F.; Tjeng, L.H.; Meigs, G.; Chen, C.T.

    1992-01-01

    The magnetic moments of Gd and Fe in gadolinium iron garnet (Gd3Fe5O12) were probed at 77 and 300 K by soft-X-ray magnetic circular dichroism (SXMCD) measurements at the GdMa4,5 and at the FeL2,3 absorption edges. The SXMCD signal at each edge allows one to independently determine the magnetic order

  5. X-ray magnetic circular dichroism in Co2FeGa: First-principles calculations

    Science.gov (United States)

    Kukusta, D. A.; Antonov, V. N.; Yaresko, A. N.

    2011-08-01

    The electronic structure and x-ray magnetic circular dichroism (XMCD) spectra of the Heusler alloy Co2FeGa were investigated theoretically from first principles, using the fully relativistic Dirac linear MT-orbital (LMTO) band structure method. Densities of valence states, orbital and spin magnetic moments are analyzed and discussed. The origin of the XMCD spectra in the Co2FeGa compound is examined. The calculated results are compared with available experimental data.

  6. Circular dichroism in free-free transitions of high energy electron-atom scattering

    CERN Document Server

    Cionga, Aurelia; Zloh, Gabriela; 10.1103/PhysRevA.62.063406

    2013-01-01

    We consider high energy electron scattering by hydrogen atoms in the presence of a laser field of moderate power and higher frequencies. If the field is a superposition of a linearly and a circularly polarized laser beam in a particular configuration, then we can show that circular dichroism in two photon transitions can be observed not only for the differential but also for the integrated cross sections, provided the laser-dressing of the atomic target is treated in second order perturbation theory and the coupling between hydrogenic bound and continuum states is involved.

  7. Circular dichroism in the two-colour two-photon ionization of hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Cionga, Aurelia [Institute of Space Sciences, PO Box MG-23, R-76900 Bucharest-Magurele (Romania); Fifirig, Magda [Department of Chemistry, University of Bucharest, Bd Regina Elisabeta 4-12, R-70346 Bucharest (Romania); Ehlotzky, Fritz [Institute for Theoretical Physics, University of Innsbruck, Technikerstrasse 25, A-6020 Innsbruck (Austria)

    2002-12-14

    We study dichroic effects in the two-photon ionization of hydrogen from its ground state due to the interaction with a bichromatic field of commensurate frequencies. The two field components have different polarization: one is linearly polarized and the other is circularly polarized (CP). Circular dichroism (CD) in the angular distribution of the photoelectrons appears if the helicity of the CP field is reversed. Numerical results reveal the influence of the photon frequencies chosen on the CD in the azimuthal angular distribution of the ejected photoelectrons.

  8. Correction: Absolute stereochemistry and preferred conformations of urate degradation intermediates from computed and experimental circular dichroism spectra.

    Science.gov (United States)

    Pipolo, Silvio; Percudani, Riccardo; Cammi, Roberto

    2016-04-14

    Correction for 'Absolute stereochemistry and preferred conformations of urate degradation intermediates from computed and experimental circular dichroism spectra' by Silvio Pipolo et al., Org. Biomol. Chem., 2011, 9, 5149-5155.

  9. Direct determination of absolute configuration: a vibrational circular dichroism study on dimethyl-substituted phenyloxiranes synthesized by Shi epoxidation

    DEFF Research Database (Denmark)

    Fristrup, Peter; Lassen, Peter Rygaard; Tanner, David Ackland;

    2008-01-01

    The three possible dimethylsubstituted phenyloxiranes (cis, trans and geminal) were synthesized in both racemic (mCPBA) and enantiomerically enriched forms (Shi epoxidation) and subjected to a vibrational circular dichroism study. The experimental spectra were compared to theoretical spectra obta...

  10. Surface characterization of human serum albumin and sodium perfluorooctanoate mixed solutions by pendant drop tensiometry and circular dichroism.

    Science.gov (United States)

    Messina, Paula; Prieto, Gerardo; Dodero, Verónica; Cabrerizo-Vílchez, M A; Maldonado-Valderrama, J; Ruso, Juan M; Sarmiento, Félix

    2006-06-15

    The interfacial behavior of mixed human serum albumin (HSA)/sodium perfluorooctanoate (C8FONa) solutions is examined by using two experimental techniques, pendant drop tensiometry and circular dichroism spectroscopy. Through the analysis of the surface tension of the mixed solutions, surface competitive adsorption at the air-water interface between C8FONa and HSA is detected. The dynamic adsorption curves exhibit the distinct regimes in their time-dependent surface tension. The nature of these regimes is further analyzed in terms of the variation of the molecules surface areas. As a consequence, a compact and dense structure was formed where protein molecules were interconnected and overlapped. Thus, a reduction of the area occupied per molecule from 100 to 0.2 nm(2) is interpreted as a gel-like structure at the surface. The presence of the surfactant seems to favor the formation of this interfacial structure. Finally, measurements of circular dichroism suggests a compaction of the protein due to the association with the surfactant given by an increase of alpha-helix structure in the complexes as compared to that of pure protein.

  11. An X-ray magnetic circular dichroism study of the interface Magnetism in titanate Heterostructures

    Science.gov (United States)

    Salluzzo, Marco; CNR-SPIN Team

    2014-03-01

    The 2D-electron system (2DES) created at the interface between LaAlO3 and SrTiO3 have attracted strong interest in recent years. This system shows an intriguing inversion the Ti3d bands hierarchy at the interface respect the bulk, and some reports even suggested coexistence between ferromagnetism and superconductivity. By using x-ray magnetic circular dichroism we show that oxygen vacancies induce magnetic interfacial localized Ti3 + states, which couple to the 2DES, with a negative exchange interaction. The magnetic dichroism signal is quenched in standard LAO/STO interfaces annealed in high oxygen pressure after the deposition and showing a homogeneous superconducting ground state, suggesting a decisive role of oxygen vacancies in the magnetism of these oxide interfaces.

  12. Circular dichroism and infrared spectroscopic characterization of secondary structure components of protein Z during mashing and boiling processes.

    Science.gov (United States)

    Han, Yupeng; Wang, Jinjing; Li, Yongxian; Hang, Yu; Yin, Xiangsheng; Li, Qi

    2015-12-01

    In beer brewing, protein Z is hypothesized to stabilize beer foam. However, few investigations have revealed the relationship between conformational alterations to protein Z during the brewing process and beer foam. In this report, protein Z from sweet wort was isolated during mashing and boiling processes. Circular dichroism (CD) and Fourier transform infrared spectroscopy (FTIR) were used to monitor the structural characteristics of protein Z. The results showed that the α-helix and β-sheet content decreased, whereas the content of β-turn and random coil increased. The complex environment rich in polysaccharides may facilitate conformational alterations and modifications to protein Z. Additionally, the formation of extended structural features to protein Z provides access to reactive amino acid side chains that can undergo modifications and the exposure of hydrophobic core regions of the protein. Analyzing structural transformations should provide a deeper understanding of the mechanism of protein Z on maintaining beer foam.

  13. Local X-ray magnetic circular dichroism study of Fe/Cu(111) using a tunneling smart tip

    Energy Technology Data Exchange (ETDEWEB)

    DiLullo, Andrew; Shirato, Nozomi; Cummings, Marvin [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Kersell, Heath; Chang, Hao [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Ohio University, Athens, OH 45701 (United States); Rosenmann, Daniel; Miller, Dean; Freeland, John W. [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Hla, Saw-Wai [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Ohio University, Athens, OH 45701 (United States); Rose, Volker, E-mail: vrose@anl.gov [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States)

    2016-01-28

    A tunneling smart tip of a synchrotron X-ray scanning tunneling microscope provides simultaneously localized topographic, elemental and magnetic information. Localized spectroscopy with simultaneous topographic, elemental and magnetic information is presented. A synchrotron X-ray scanning tunneling microscope has been employed for the local study of the X-ray magnetic circular dichroism at the Fe L{sub 2,3}-edges of a thin iron film grown on Cu(111). Polarization-dependent X-ray absorption spectra have been obtained through a tunneling smart tip that serves as a photoelectron detector. In contrast to conventional spin-polarized scanning tunneling microscopy, X-ray excitations provide magnetic contrast even with a non-magnetic tip. Intensity variations in the photoexcited tip current point to chemical variations within a single magnetic Fe domain.

  14. Vibrational circular dichroism spectra for large molecules and molecules with heavy elements

    Science.gov (United States)

    Reiter, Kevin; Kühn, Michael; Weigend, Florian

    2017-02-01

    We present an implementation of vibrational circular dichroism (VCD) spectra in TURBOMOLE. We mainly followed the route proposed by Cheeseman [Chem. Phys. Lett. 252, 211 (1996)] and extended the modules for calculating the magnetic response and vibrational frequencies accordingly. The implementation allows for gauge origin invariant employment of effective core potentials, as demonstrated for Co(ppy)3, ppy = 2-Phenylpyridine. In this way, scalar relativistic effects are covered and heavy elements can be treated. Further, with the present implementation molecular symmetry may be efficiently exploited, which makes the calculation of large (symmetric) systems feasible. The calculation of the VCD spectrum of icosahedral C6202+ is shown as an illustrative application.

  15. Assignment of absolute stereostructures through quantum mechanics electronic and vibrational circular dichroism calculations.

    Science.gov (United States)

    Dai, Peng; Jiang, Nan; Tan, Ren-Xiang

    2016-01-01

    Elucidation of absolute configuration of chiral molecules including structurally complex natural products remains a challenging problem in organic chemistry. A reliable method for assigning the absolute stereostructure is to combine the experimental circular dichroism (CD) techniques such as electronic and vibrational CD (ECD and VCD), with quantum mechanics (QM) ECD and VCD calculations. The traditional QM methods as well as their continuing developments make them more applicable with accuracy. Taking some chiral natural products with diverse conformations as examples, this review describes the basic concepts and new developments of QM approaches for ECD and VCD calculations in solution and solid states.

  16. Circular dichroism spectroscopic studies on structures formed by telomeric DNA sequences in vitro

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Telomere plays an important role in cellular processes, such as cell aging, death and carcinogenisis. Having special sequences, it can form quadruplex structure in vitro. Circular dichroism (CD) spectroscopic studies show that TTAGGG, (TTAGGG)2 and (TTAGGG)4 can all form quadruplex in vitro and exist mainly as parallel quadruplex without metal ions. Both K+ and Na+ can stabilize the tetrameric structure and facilitate the forming of anti-parallel conformation. Furthermore, the conformations of quadruplex can also be affected by sequence length, the nature and concentration of metal ions.

  17. Similar structures, different characteristics: circular dichroism of metallic helix arrays with single-, double-, and triple-helical structures.

    Science.gov (United States)

    Zhang, Peng; Yang, Zhenyu; Zhao, Ming; Wu, Lin; Lu, Zeqin; Cheng, Yongzhi; Gong, Rongzhou; Zheng, Yu; Duan, Jian

    2013-04-01

    We fabricated three-dimensional metallic helix arrays with single-, double-, and triple-helical structures. The transmission performances with the normal incident angle were measured in the microwave frequency of 12-18 GHz. For the single- and double-helical structures, giant circular dichroism with fairly wide bands is observed in the transmission spectra. However, the triple-helical structure does not exhibit circular dichroism. Based on the phenomenon of circular dichroism, the single- and double-helical structures can be used as broadband circular polarizers in the microwave region, but triple-helical ones cannot. The experiments have a good agreement with our simulation results, which were studied by the finite-difference time domain method.

  18. Experimental demonstration of the microscopic origin of circular dichroism (Conference Presentation)

    Science.gov (United States)

    Shvets, Gennady B.

    2016-09-01

    Fully two-dimensional metamaterials, also known as metasurfaces comprised of planar-chiral plasmonic metamolecules that are just nanometers thick, have been shown to exhibit chiral dichroism in transmission. The origin of the resulting circular dichroism is rather subtle. Theoretical calculations indicate that this surprising effect relies on finite non-radiative (Ohmic) losses of the metasurface. In the absence of such losses on the nanoscale, the chiral dichroism in transmission (CDT) defined as the difference between the transmission coefficients of the RCP and LCP waves, must identically vanish. This surprising theoretical prediction has never been experimentally verified because of the challenge of measuring non-radiative loss on the nanoscale. We use a combination of nanoscale characterization techniques to demonstrate that the RCP and LCP states of the incident light produce drastically different distributions of optical energy and Ohmic heat dissipation in the two-dimensional chiral nanoantennas, thereby producing a strong chiral dichroism in absorption (CDA). A planar-chiral metasurface, along with its chiral enantiomer, was designed to maximize the CDA in mid-IR range. The CDA gives rise to the CDT observed experimentally in the far-field measurements. We then use scattering-type near-field scanning optical microscopy to map the optical energy distribution on the nanoantennas and their enantiomers in response to the RCP and LCP light. Photo-expansion microscopy, also known as AFM-IR, was then utilized to experimentally demonstrate drastically different Ohmic heating of the nanoantennas under RCP and LCP light illumination. In collaboration with: A.B.Khanikaev, N.Arju, Z.Fan, D.Purtseladze, F.Lu, J.Lee, P.Sarriugarte, M.Schnell, R.Hillenbrand, M.A.Belkin

  19. A molecular dynamics and circular dichroism study of a novel synthetic antimicrobial peptide

    Science.gov (United States)

    Rodina, N. P.; Yudenko, A. N.; Terterov, I. N.; Eliseev, I. E.

    2013-08-01

    Antimicrobial peptides are a class of small, usually positively charged amphiphilic peptides that are used by the innate immune system to combat bacterial infection in multicellular eukaryotes. Antimicrobial peptides are known for their broad-spectrum antimicrobial activity and thus can be used as a basis for a development of new antibiotics against multidrug-resistant bacteria. The most challengeous task on the way to a therapeutic use of antimicrobial peptides is a rational design of new peptides with enhanced activity and reduced toxicity. Here we report a molecular dynamics and circular dichroism study of a novel synthetic antimicrobial peptide D51. This peptide was earlier designed by Loose et al. using a linguistic model of natural antimicrobial peptides. Molecular dynamics simulation of the peptide folding in explicit solvent shows fast formation of two antiparallel beta strands connected by a beta-turn that is confirmed by circular dichroism measurements. Obtained from simulation amphipatic conformation of the peptide is analysed and possible mechanism of it's interaction with bacterial membranes together with ways to enhance it's antibacterial activity are suggested.

  20. Photon energy dependence of circular dichroism of the Au(111) surface state

    Science.gov (United States)

    Ärrälä, M.; Nieminen, J.; Braun, J.; Ebert, H.; Lindroos, M.

    2013-11-01

    Through relativistic photoemission calculations for the Au(111) surface state at the Fermi level, we study the photon energy dependence of circular dichroism. The dichromatic signal (DS) pattern changes 23 times with photon energies between 7 and 100 eV, and we have found 13 different patterns in the k∥ map at the Fermi level for the DS from the Au(111) surface state with normal incidence light. We show that the photon energy dependence of DS is very complex even in the simplest case. The sign change in the circular dichroism as a function of photon energy is related to the relative phases of the complex expansion coefficients of different outgoing partial waves in a time-reversed low-energy electron diffraction state. With off-normal incidence, the z component of the incoming photon field is dominant, and the fine structure seen in the DS in the normal incidence case is lost very rapidly, moving from a normal to an off-normal incidence. We also report that the Rashba split surface state of Au(111) has a significant component of d-type orbital due to relativistic effects and the computational setup used.

  1. Spectral characteristics of fluorescence and circular dichroism of aflatoxin B1 reaction with its anti-idiotypic antibody

    Science.gov (United States)

    Liu, Aiping; Yang, Hongxiu; Wang, Xiaohong; Chen, Fusheng

    2012-11-01

    Aflatoxin B1 (AFB1) is a toxic secondary metabolite and sensitive methods for its analysis have been developed. In our lab, a number of works have been carried out, including exploitation of detection methods and production of anti-idiotypic antibody (Ab2) against Fab fragment of anti-AFB1 antibody (Ab1). In this paper, Ab2 was generated upon the immunization of mice with F(ab')2 fragment, which was specific to AFB1 and obtained by pepsin digestion of Ab1. The characteristics of Ab2 was primarily investigated by indirect competitive enzyme-linked immunosorbent assay (icELISA), which indicated that Ab2, might bear an internal image of antigen AFB1 and was able to combine to F(ab')2 in competition with AFB1, and the concentration of Ab2 to cause 50% inhibition of binding (IC50) was 131.8 μg/mL. In addition, fluorescence and circular dichroism studies were designed to explore the mutual relationship among AFB1, F(ab')2 and Ab2. The fluorescence spectroscopy implied that both AFB1 and Ab2 act as a quencher upon F(ab')2, and the Ab2 could compete with AFB1 when both of Ab2 and AFB1 reacted with F(ab')2. The circular dichroism (CD) spectrum suggested that both the binding of Ab2 and AFB1 on F(ab')2 brought secondary conformation change of F(ab')2, especially in the changes of α helix and β sheet. The research performed would provide unique insight into the comprehension of interaction among AFB1, F(ab')2 and Ab2 as well as offer structural information for substitution researches of toxic antigen like AFB1.

  2. Circular dichroism study of the interaction between mutagens and bilirubin bound to different binding sites of serum albumins

    Science.gov (United States)

    Orlov, Sergey; Goncharova, Iryna; Urbanová, Marie

    Although recent investigations have shown that bilirubin not only has a negative role in the organism but also exhibits significant antimutagenic properties, the mechanisms of interactions between bilirubin and mutagens are not clear. In this study, interaction between bilirubin bound to different binding sites of mammalian serum albumins with structural analogues of the mutagens 2-aminofluorene, 2,7-diaminofluorene and mutagen 2,4,7-trinitrofluorenone were investigated by circular dichroism and absorption spectroscopy. Homological human and bovine serum albumins were used as chiral matrices, which preferentially bind different conformers of bilirubin in the primary binding sites and make it observable by circular dichroism. These molecular systems approximated a real system for the study of mutagens in blood serum. Differences between the interaction of bilirubin bound to primary and to secondary binding sites of serum albumins with mutagens were shown. For bilirubin bound to secondary binding sites with low affinity, partial displacement and the formation of self-associates were observed in all studied mutagens. The associates of bilirubin bound to primary binding sites of serum albumins are formed with 2-aminofluorene and 2,4,7-trinitrofluorenone. It was proposed that 2,7-diaminofluorene does not interact with bilirubin bound to primary sites of human and bovine serum albumins due to the spatial hindrance of the albumins binding domains. The spatial arrangement of the bilirubin bound to serum albumin along with the studied mutagens was modelled using ligand docking, which revealed a possibility of an arrangement of the both bilirubin and 2-aminofluorene and 2,4,7-trinitrofluorenone in the primary binding site of human serum albumin.

  3. Enantioselective semi-preparative HPLC separation of PCB metabolites and their absolute structures determined by electronic and vibrational circular dichroism

    Energy Technology Data Exchange (ETDEWEB)

    Tuan, H.P.; Larsson, C.; Huehnerfuss, H. [Hamburg Univ. (Germany). Inst. fuer Organische Chemie; Hoffmann, F.; Froeba, M. [Giessen Univ. (Germany). Inst. fuer Anorganische und Analytische Chemie; Bergmann, Aa. [Stockholm Univ. (Sweden). Dept. of Environmental Chemistry

    2004-09-15

    The present paper represents a first result of an ongoing systematic study of atropisomeric methylsulfonyl, methylthionyl, hydroxy, and methoxy metabolites of environmentally most relevant PCBs. This involves semi-preparative enantioselective HPLC separation to obtain pure atropisomers from synthesized PCB metabolite standards, their configuration estimation using the electronic circular dichroism (UV-CD) method and the determination / confirmation of these absolute configurations applying the combined vibrational circular dichroism (VCD) / ab initio approach. The following substances have been investigated: 4-HO-, 4-MeO-, 4-MeS-, 4-MeSO2-, 3-MeS- and 3-MeSO{sub 2}-CB149.

  4. Chirality study inside biological tissue by second harmonic generation circular dichroism

    Science.gov (United States)

    Hsu, Kuo-Jen; Lee, Hsuan; Zhuo, Guan-Yu; Chao, Pen-Hsiu; Chu, Shi-Wei

    2013-02-01

    Many biological systems are composed of chiral molecules and their functions depend strongly on their chirality. For example, most amino acids are of left-handed chirality while most polysaccharides are of right-handed chirality. Both of them are vital for human life, so it is important to perform chiral detection inside bio-tissues. Here we demonstrated second harmonic generation circular dichroism (SHG-CD) as a novel chiral imaging contrast in thick biotissue. Compared with conventional chiral detection, SHG-CD provides at least three orders higher contrast. In addition, due to the nonlinear nature of SHG, this technique provides optical sectioning capability, so the axial contrast is much better. The advantages of nonlinear optical microscopy are optical sectioning and deep penetration capabilities. The SHG-CD achieved 100% signal contrast with sub-micrometer spatial resolution. This method is expected to offer a novel contrast mechanism of imaging chirality inside complex bio-tissues.

  5. Detection of magnetic circular dichroism on the two-nanometer scale

    Science.gov (United States)

    Schattschneider, Peter; Stöger-Pollach, Michael; Rubino, Stefano; Sperl, Matthias; Hurm, Christian; Zweck, Josef; Rusz, Ján

    2008-09-01

    Magnetic circular dichroism (MCD) is a standard technique for the study of magnetic properties of materials in synchrotron beamlines. We present here a scattering geometry in the transmission electron microscope through which MCD can be observed with unprecedented spatial resolution. A convergent electron beam is used to scan a cross sectional preparation of a Fe/Au multilayer sample. Differences in the energy-loss spectra induced by the magnetic moments of the Fe atoms can be resolved with a resolution of better than 2 nm. This is a breakthrough achievement when compared both to the previous energy-loss MCD resolution (200 nm) or the best x-ray MCD experiments (approximately 20 nm).

  6. Levels of Supramolecular Chirality of Polyglutamine Aggregates Revealed by Vibrational Circular Dichroism

    Science.gov (United States)

    Kurouski, Dmitry; Kar, Karunakar; Wetzel, Ronald; Dukor, Rina K.; Lednev, Igor K.; Nafie, Laurence A.

    2013-01-01

    Polyglutamine (PolyQ) aggregates are a hallmark of several severe neurodegenerative diseases, expanded CAG-repeat diseases in which inheritance of an expanded polyQ sequence above a pathological threshold is associated with a high risk of disease. Application of vibrational circular dichroism (VCD) reveals that these PolyQ fibril aggregates exhibit a chiral supramolecular organization that is distinct from the supramolecular organization of previously observed amyloid fibrils. PolyQ fibrils grown from monomers with Q repeats 35 and above (Q≥35) exhibit approximately 10-fold enhancement of the same VCD spectrum compared to the already enhanced VCD of fibrils formed from Q repeats 30 and below (Q≤30). PMID:23583713

  7. Feasibility of non-invasive optical blood-glucose detection using overtone circular dichroism

    CERN Document Server

    Hokr, Brett H; Meng, Zhaokai; Petrov, Georgi I; Yakovlev, Vladislav V

    2016-01-01

    Diabetes is one of the most debilitating and costly diseases currently plaguing humanity. It is a leading cause of death and dismemberment in the world, and we know how to treat it. Accurate, continuous monitoring and control of blood glucose levels via insulin treatments are widely known to mitigate the majority of detrimental effects caused by the disease. The primary limitation of continuous glucose monitoring is patient non-compliance due to the unpleasant nature of "finger-stick" testing methods. This limitation can be largely, or even completely, removed by non-invasive testing methods. In this report, we demonstrate the vibrational overtone circular dichroism properties of glucose and analyze its use as a method of non-invasive glucose monitoring, capable of assuaging this trillion dollar scourge.

  8. X-Ray Magnetic Circular Dichroism Measurement of Fe-Co Alloy Films Prepared by Electrodeposition

    Institute of Scientific and Technical Information of China (English)

    LI Zong-Mu; XU Fa-Qiang; WANG Li-Wu; WANG Jie; ZHU Jun-Fa; ZHANG Wen-Hua

    2007-01-01

    The macro- and micro-magnetic properties of Fe-Co alloy films eletrodeposited on GaAs(100) are studied by synchrotron radiation x-ray magnetic circular dichroism (XMCD) in combination with the magneto-optical Kerr effect (MOKE) measurements and magnetic force microscopy (MFM). The orbital and spin magnetic moments of each element in the Fe-Co alloy are determined by the sum rules of XMCD. Element-specific hysteresis loops (ESHL) are obtained by recording the La MCD signals as a function of applied magnetic field. MOKE results reveal that the amorphous films are magnetically isotropic in the surface plane. The MFM image shows that the dimension of the magnetic domains is about 1-2 μm, which is much larger than that of the grains, indicating that there are intergranular correlations among these grains. Both ESHL and MOKE hysteresis loops indicate the strong ferromagnetic coupling of Fe and Co in the alloy films.

  9. Optically detected electron paramagnetic resonance by microwave modulated magnetic circular dichroism

    Science.gov (United States)

    Börger, Birgit; Bingham, Stephen J.; Gutschank, Jörg; Schweika, Marc Oliver; Suter, Dieter; Thomson, Andrew J.

    1999-11-01

    Electron paramagnetic resonance (EPR) can be detected optically, with a laser beam propagating perpendicular to the static magnetic field. As in conventional EPR, excitation uses a resonant microwave field. The detection process can be interpreted as coherent Raman scattering or as a modulation of the laser beam by the circular dichroism of the sample oscillating at the microwave frequency. The latter model suggests that the signal should show the same dependence on the optical wavelength as the MCD signal. We check this for two different samples [cytochrome c-551, a metalloprotein, and ruby (Cr3+:Al2O3)]. In both cases, the observed wavelength dependence is almost identical to that of the MCD signal. A quantitative estimate of the amplitude of the optically detected EPR signal from the MCD also shows good agreement with the experimental results.

  10. Photoemission and core-level magnetic circular dichroism studies of diluted magnetic semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Fujimori, A. [Department of Complexity Science and Engineering, Universtiy of Tokyo, 1-5-1 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan) and Synchrotron Radiation Research Center, Japan Atomic Energy Research Institute, SPring-8, Mikazuki, Hyogo 679-5148 (Japan)]. E-mail: fujimori@phys.s.u-tokyo.ac.jp; Okabayashi, J. [Department of Applied Chemistry, University of Tokyo, 7-3-1 Hongo, Bunkyou-ku, Tokyo 113-8656 (Japan); Takeda, Y. [Synchrotron Radiation Research Center, Japan Atomic Energy Research Institute, SPring-8, Mikazuki, Hyogo 679-5148 (Japan); Mizokawa, T. [Department of Complexity Science and Engineering, Universtiy of Tokyo, 1-5-1 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan); Okamoto, J. [Synchrotron Radiation Research Center, Japan Atomic Energy Research Institute, SPring-8, Mikazuki, Hyogo 679-5148 (Japan); Mamiya, K. [Photon Factory, IMSS, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305 (Japan); Saitoh, Y. [Synchrotron Radiation Research Center, Japan Atomic Energy Research Institute, SPring-8, Mikazuki, Hyogo 679-5148 (Japan); Muramatsu, Y. [Synchrotron Radiation Research Center, Japan Atomic Energy Research Institute, SPring-8, Mikazuki, Hyogo 679-5148 (Japan); Oshima, M. [Department of Applied Chemistry, University of Tokyo, 7-3-1 Hongo, Bunkyou-ku, Tokyo 113-8656 (Japan); Ohya, S. [Department of Electronic Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Tanaka, M. [Department of Electronic Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

    2005-06-15

    An overview is given on the photoemission studies of the electronic structure of diluted magnetic semiconductors (DMS's), in particular of the prototypical ferromagnetic DMS Ga{sub 1-x}Mn{sub x}As. Configuration-interaction cluster-model analyses of the photoemission data allow us to estimate the p-d exchange coupling constant and hence to predict how to increase the Curie temperature in new materials. Spectra near the Fermi level combined with the transport and optical properties suggest a highly incoherent metallic state for the ferromagnetic metallic phase. It is shown that new insight into the chemically and magnetically inhomogeneous states of DMS's can be gained by the temperature and magnetic field dependence of core-level magnetic circular dichroism signals.

  11. Stability of some Cactaceae proteins based on fluorescence, circular dichroism, and differential scanning calorimetry measurements.

    Science.gov (United States)

    Gorinstein, S; Zemser, M; Vargas-Albores, F; Ochoa, J L; Paredes-Lopez, O; Scheler, C; Aksu, S; Salnikow, J

    1999-02-01

    Characterization of three cactus proteins (native and denatured) from Machaerocereus gummosus (Pitahaya agria), Lophocereu schottii (Garambullo), and Cholla opuntia (Cholla), was based on electrophoretic, fluorescence, CD (circular dichroism), DSC (differential scanning calorimetry), and FT-IR (Fourier transform infrared) measurements. The obtained results of intrinsic fluorescence, DSC, and CD were dissimilar for the three species of cactus, providing evidence of differences in secondary and tertiary structures. Cactus proteins may be situated in the following order corresponding to their relative stability: Machaerocereus gummosus (Pitahaya agria) > Cholla opuntia (Cholla) > Lophocereu schottii (Garambullo). Thermodynamic properties of proteins and their changes upon denaturation (temperature of denaturation, enthalphy, and the number of ruptured hydrogen bonds) were correlated with the secondary structure of proteins and disappearance of alpha-helix.

  12. Fano resonance assisting plasmonic circular dichroism from nanorice heterodimers for extrinsic chirality

    CERN Document Server

    Hu, Li; Fang, Liang; Chen, Guo; Wei, Hua; Fang, Yurui

    2015-01-01

    In this work, the circular dichroisms (CD) of nanorice heterodimers consisting of two parallel arranged nanorices with the same size but different materials are investigated theoretically. Symmetry-breaking is introduced by using different materials and oblique incidence to achieve strong CD at the vicinity of Fano resonance peaks. We demonstrate that all Au-Ag heterodimers exhibit multipolar Fano resonances and strong CD effect. A simple quantitative analysis shows that the structure with larger Fano asymmetry factor has stronger CD. The intensity and peak positions of the CD effect can be flexibly tuned in a large range by changing particle size, shape, the inter-particle distance and surroundings. Furthermore, CD spectra exhibit high sensitivity to ambient medium in visible and near infrared regions. Our results here are beneficial for the design and application of high sensitive CD sensors and other related fields.

  13. Circular dichroism and Raman spectroscopic study of the spider venom toxin V50F17

    Science.gov (United States)

    Alix, A. J. P.; Berjot, M.; Dauchez, M. A. M.; Dhalluin, C.; Lippens, G.

    1999-05-01

    V50F17 is a small 45 amino acid neurotoxin fractionated (F17) from the venom V50 of the spider Segestria florentina, which has eight cysteine residues constituting four disulfide bridges. Using circular dichroism data and vibrational Raman data at both pH 2.9 and 7.0 and preliminary NMR results obtained at pH 2.9, we derived structural information for this small protein. From these data, it is seen that it is possible to characterise well the local conformation of the disulfide bridges and the overall shape of the globular protein. Moreover, using optical spectroscopic data, it is shown that consequent local and/or global modifications are obtained on changing the pH. Results of the secondary structure states, the local conformations of the disulfide bridges, the exposure of side chains of residues and particularly of Tyr41 are discussed.

  14. Light flux density threshold at which protein denaturation is induced by synchrotron radiation circular dichroism beamlines.

    Science.gov (United States)

    Miles, A J; Janes, Robert W; Brown, A; Clarke, D T; Sutherland, J C; Tao, Y; Wallace, B A; Hoffmann, S V

    2008-07-01

    New high-flux synchrotron radiation circular dichroism (SRCD) beamlines are providing important information for structural biology, but can potentially cause denaturation of the protein samples under investigation. This effect has been studied at the new CD1 dedicated SRCD beamline at ISA in Denmark, where radiation-induced thermal damage effects were observed, depending not only on the radiation flux but also on the focal spot size of the light. Comparisons with similar studies at other SRCD facilities worldwide has lead to the estimation of a flux density threshold under which SRCD beamlines should be operated when samples are to be exposed to low-wavelength vacuum ultraviolet radiation for extended periods of time.

  15. A study of aliphatic amino acids using simulated vibrational circular dichroism and Raman optical activity spectra

    CERN Document Server

    Ganesan, Aravindhan; Wang, Feng

    2013-01-01

    Vibrational optical activity (VOA) spectra, such as vibrational circular dichroism (VCD) and Raman optical activity (ROA) spectra, of aliphatic amino acids are simulated using density functional theory (DFT) methods in both gas phase (neutral form) and solution (zwitterionic form), together with their respective infrared (IR) and Raman spectra of the amino acids. The DFT models, which are validated by excellent agreements with the available experimental Raman and ROA spectra of alanine in solution, are employed to study other aliphatic amino acids. The inferred (IR) intensive region (below 2000 cm-1) reveals the signature of alkyl side chains, whereas the Raman intensive region (above 3000 cm-1) contains the information of the functional groups in the amino acids. Furthermore, the chiral carbons of the amino acids (except for glycine) dominate the VCD and ROA spectra in the gas phase, but the methyl group vibrations produce stronger VCD and ROA signals in solution. The C-H related asymmetric vibrations domina...

  16. 4-Arylflavan-3-ols as Proanthocyanidin Models: Absolute Configuration via Density Functional Calculation of Electronic Circular Dichroism

    Science.gov (United States)

    Density functional theory/B3LYP has been employed to optimize the conformations of selected 4-arylflavan-3-ols and their phenolic methyl ether 3-O-acetates. The electronic circular dichroism spectra of the major conformers have been calculated using time-dependent density functional theory to valida...

  17. Circular dichroism spectrum of [Co(en)(3)](3+) in water : A discrete solvent reaction field study

    NARCIS (Netherlands)

    Jensen, L.; Swart, Marcel; Van Duijnen, Piet Th.; Autschbach, J.

    2006-01-01

    In this work we investigate the circular dichroism (CD) spectrum of [Co(en)(3)](3+) in water, using the discrete solvent reaction field (DRF) model. The DRF model is a polarizable quantum mechanics/molecular mechanics (QM/MM) model. The implementation of the DRF model for CD spectra calculations bas

  18. Soft-X-ray magnetic circular dichroism : a new technique for probing magnetic properties of magnetic surfaces and ultrathin films

    NARCIS (Netherlands)

    Tjeng, L.H.; Idzerda, Y.U.; Rudolf, P.; Sette, F.; Chen, C.T.

    1992-01-01

    We demonstrate the feasibility of applying the novel soft-X-ray magnetic circular dichroism (SXMCD) technique to investigate the magnetic properties of magnetic surfaces and uitrathin films. Measurements have been carried out on Ni films of various thickness on a Cu(100) substrate at the Ni L2,3 abs

  19. X-ray magnetic circular dichroism spectra and distortions at Fe2+ L(2,3) edges

    NARCIS (Netherlands)

    Wang, X.; de Groot, F.M.F.; Cramer, S.P.

    1996-01-01

    We have shown from ligand field multiplet calculations that the shape of X-ray magnetic circular dichroism (XMCD) spectra changes drastically with the distortion parameter Ds. The temperature dependence study of XMCD makes it possible to determine both Ds and spin-orbit coupling.

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

    NARCIS (Netherlands)

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

    2007-01-01

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

  1. A new, model-free calculation method to determine the coordination modes and distribution of copper(II) among the metal binding sites of multihistidine peptides using circular dichroism spectroscopy.

    Science.gov (United States)

    Osz, Katalin

    2008-12-01

    A new calculation method to determine microscopic protonation processes from CD spectra measured at different pH and Cu(II):ligand ratios was developed and used to give the relative binding strengths for the three histidines of hsPrP(84-114), a 31-mer polypeptide modeling the N-terminal copper(II) binding region of human (homo sapiens) prion protein. Mutants of hsPrP(84-114) with two or one histidyl residues have also been synthesized and their copper(II) complexes studied by CD spectroscopy. The 1-His models were analyzed first, and the molar CD spectra for the different coordination modes on the different histidines were calculated using the general computational program PSEQUAD. These spectra were deconvoluted into the sum of Gaussian curves and used as a first parameter set to calculate the molar spectra for the different coordination modes (3N and 4N coordination) and coordination positions (His85, His96 and His111) of the 2-His peptides. The calculation method therefore does not require the direct use of CD spectra measured in the smaller peptide models. This is a significant improvement over earlier calculation methods. In the same runs, the stepwise deprotonation pK(mic) values were refined and the pH-dependent distribution of copper(II) between the two histidines was determined. The results revealed the high, but different copper(II) binding affinities of the three separate histidines in the following order: His85 copper(II) binding preferences are transferable from the 2-His peptides to the 3-His hsPrP(84-114).

  2. Circular dichroism measured on single chlorosomal light-harvesting complexes of green photosynthetic bacteria

    KAUST Repository

    Furumaki, Shu

    2012-12-06

    We report results on circular dichroism (CD) measured on single immobilized chlorosomes of a triple mutant of green sulfur bacterium Chlorobaculum tepidum. The CD signal is measured by monitoring chlorosomal bacteriochlorphyll c fluorescence excited by alternate left and right circularly polarized laser light with a fixed wavelength of 733 nm. The excitation wavelength is close to a maximum of the negative CD signal of a bulk solution of the same chlorosomes. The average CD dissymmetry parameter obtained from an ensemble of individual chlorosomes was gs = -0.025, with an intrinsic standard deviation (due to variations between individual chlorosomes) of 0.006. The dissymmetry value is about 2.5 times larger than that obtained at the same wavelength in the bulk solution. The difference can be satisfactorily explained by taking into account the orientation factor in the single-chlorosome experiments. The observed distribution of the dissymmetry parameter reflects the well-ordered nature of the mutant chlorosomes. © 2012 American Chemical Society.

  3. Optimized Spiral Metal-Gallium-Nitride Nanowire Cavity for Ultra-High Circular Dichroism Ultraviolet Lasing at Room Temperature.

    Science.gov (United States)

    Liao, Wei-Chun; Liao, Shu-Wei; Chen, Kuo-Ju; Hsiao, Yu-Hao; Chang, Shu-Wei; Kuo, Hao-Chung; Shih, Min-Hsiung

    2016-05-25

    Circularly polarized laser sources with small footprints and high efficiencies can possess advanced functionalities in optical communication and biophotonic integrated systems. However, the conventional lasers with additional circular-polarization converters are bulky and hardly compatible with nanophotonic circuits, and most active chiral plasmonic nanostructures nowadays exhibit broadband emission and low circular dichroism. In this work, with spirals of gallium nitride (GaN) nanowires (NWRs) covered by a metal layer, we demonstrated an ultrasmall semiconductor laser capable of emitting circularly-polarized photons. The left- and right-hand spiral metal nanowire cavities with varied periods were designed at ultraviolet wavelengths to achieve the high quality factor circular dichroism metastructures. The dissymmetry factors characterizing the degrees of circular polarizations of the left- and right-hand chiral lasers were 1.4 and -1.6 (±2 if perfectly circular polarized), respectively. The results show that the chiral cavities with only 5 spiral periods can achieve lasing signals with the high degrees of circular polarizations.

  4. International comparability in spectroscopic measurements of protein structure by circular dichroism: CCQM-P59.1

    Science.gov (United States)

    Ravi, Jascindra; Rakowska, Paulina D.; Garfagnini, Tommaso; Baron, Bruno; Charlet, Philippe; Jones, Christopher; Milev, Stoyan; DeSa Lorenz, Julie; Plusquellic, David; Wien, Frank; Wu, Liqing; Meuse, Curtis W.; Knight, Alex E.

    2010-12-01

    Circular dichroism (CD) is a spectroscopic technique that is widely used to obtain information about protein structure, and hence is an important tool with many applications, including the characterization of biopharmaceuticals. A previous inter-laboratory study, CCQM-P59, showed that there was a poor level of comparability between laboratories in CD spectroscopy. In a follow-up study reported here, we achieved our goal of demonstrating improved comparability and data quality, primarily by addressing the problems identified in the previous study, which included cell path-length measurement, instrument calibration and good practice in general. Multivariate analysis techniques (principal component analysis and soft independent modelling of class analogies) were shown to be useful in comparing large spectral data sets and in classifying spectra. However, our results also show that there is more work to be done to improve confidence in the technique as the discrepancies observed were partially due to systematic effects, which the statistical approaches do not consider. We therefore conclude that there is a need for an improved understanding of the uncertainties in CD measurement.

  5. Competitive binding of (-)-epigallocatechin-3-gallate and 5-fluorouracil to human serum albumin: A fluorescence and circular dichroism study

    Science.gov (United States)

    Yuan, Lixia; Liu, Min; Liu, Guiqin; Li, Dacheng; Wang, Zhengping; Wang, Bingquan; Han, Jun; Zhang, Min

    2017-02-01

    Combination therapy with more than one therapeutic agent can improve therapeutic efficiency and decrease drug resistance. In this study, the interactions of human serum albumin (HSA) with individual or combined anticancer drugs, (-)-epigallocatechin-3-gallate (EGCG) and 5-fluorouracil (FU), were investigated by fluorescence and circular dichroism (CD) spectroscopy. The results demonstrated that the interaction of EGCG or FU with HSA is a process of static quenching and EGCG formed a more stable complex. The competitive experiments of site markers suggested that both anti-carcinogens mainly bound to site I (subdomain IIA). The interaction forces which play important roles in the binding process were discussed based on enthalpy and entropy changes. Moreover, the competition binding model for a ternary system was proposed so as to precisely calculate the binding parameters. The results demonstrated that one drug decreased the binding affinity of another drug with HSA, resulting in the increasing free drug concentration at the action sites. CD studies indicated that there was an alteration in HSA secondary structure due to the binding of EGCG and FU. It can be concluded that the combination of EGCG with FU may enhance anticancer efficacy. This finding may provide a theoretical basis for clinical treatments.

  6. Site-specific conformational determination in thermal unfolding studies of helical peptides using vibrational circular dichroism with isotopic substitution

    Science.gov (United States)

    Silva, R. A. G. D.; Kubelka, Jan; Bour, Petr; Decatur, Sean M.; Keiderling, Timothy A.

    2000-01-01

    Understanding the detailed mechanism of protein folding requires dynamic, site-specific stereochemical information. The short time response of vibrational spectroscopies allows evaluation of the distribution of populations in rapid equilibrium as the peptide unfolds. Spectral shifts associated with isotopic labels along with local stereochemical sensitivity of vibrational circular dichroism (VCD) allow determination of the segment sequence of unfolding. For a series of alanine-rich peptides that form α-helices in aqueous solution, we used isotopic labeling and VCD to demonstrate that the α-helix noncooperatively unwinds from the ends with increasing temperature. For these blocked peptides, the C-terminal is frayed at 5°C. Ab initio level theoretical simulations of the IR and VCD band shapes are used to analyze the spectra and to confirm the conformation of the labeled components. The VCD signals associated with the labeled residues are amplified by coupling to the nonlabeled parts of the molecule. Thus small labeled segments are detectable and stereochemically defined in moderately large peptides in this report of site-specific peptide VCD conformational analysis. PMID:10880566

  7. Dimethyl Sulfoxide Induced Destabilization and Disassembly of Various Structural Variants of Insulin Fibrils Monitored by Vibrational Circular Dichroism.

    Science.gov (United States)

    Zhang, Ge; Babenko, Viktoria; Dzwolak, Wojciech; Keiderling, Timothy A

    2015-12-15

    Dimethyl sulfoxide (DMSO) induced destabilization of insulin fibrils has been previously studied by Fourier transform infrared spectroscopy and interpreted in terms of secondary structural changes. The variation of this process for fibrils with different types of higher-order morphological structures remained unclear. Here, we utilize vibrational circular dichroism (VCD), which has been reported to provide a useful biophysical probe of the supramolecular chirality of amyloid fibrils, to characterize changes in the macroscopic chirality following DMSO-induced disassembly for two types of insulin fibrils formed under different conditions, at different reduced pH values with and without added salt and agitation. We confirm that very high concentrations of DMSO can disaggregate both types of insulin fibrils, which initially maintained a β-sheet conformation and eventually changed their secondary structure to a disordered form. The two types responded to varying concentrations of DMSO, and disaggregation followed different mechanisms. Interconversion of specific insulin fibril morphological types also occurred during the destabilization process as monitored by VCD. With transmission electron microscopy, we were able to correlate the changes in VCD sign patterns to alteration of morphology of the insulin fibrils.

  8. Core-level magnetic circular dichroism in 3d and 4f magnetic systems (invited) (abstract)

    Science.gov (United States)

    Koide, T.

    1994-05-01

    With the recent availability of circulary polarized synchrotron radiation over a wide photon energy range from VUV to hard X rays, the magnetic circular dichroism (MCD) in core-level photoabsorption has rapidly attracted growing interest, both experimentally and theoretically. This novel technique can provide element-specific and site-selective information about the magnetic and the electronic states in various magnetic substances because the core-level MCD process involves optical transitions in which the one-electron initial states are well localized and have well-defined angular momenta. In order to get insight into the local magnetic states in 3d and 4f magnetic systems, we have studied MCD of ferrites, Fe1-xPtx alloys, and mixed-valence CeRh3B2 at the core-absorption edges in the VUV˜soft x-ray region. The experiments were performed by utilizing directly characterized, circularly polarized undulator radiation and off-plane synchrotron radiation1 in conjunction with an ultrahigh vacuum compatible superconducting magnet of special design.2 Clear MCD signals were observed for CeRh3B2 in the prethreshold region of the Ce 4d→4f (N4,5) edges. A comparison of the experimental MCD spectrum with theoretical ones3 for uniaxial crystal fields of Δc=0 and 0.2 eV shows that the experimental spectrum qualitatively agrees with the theoretical one for Δc=0 eV. Theory predicts that the MCD pattern for ΔcCeRh3B2. We will also present the MCD data in the M2,3 core-absorption region for ferrites (Fe3O4 and CoFe2O4) and Fe1-xPtx alloys, discussing the results.

  9. Can circular dichroism in core-level photoemission provide a spectral fingerprint of adsorbed chiral molecules?

    Energy Technology Data Exchange (ETDEWEB)

    Allegretti, F [Physics Department, University of Warwick, Coventry CV4 7AL (United Kingdom); Polcik, M [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D 14195 Berlin (Germany); Sayago, D I [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D 14195 Berlin (Germany); Demirors, F [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D 14195 Berlin (Germany); O' Brien, S [Physics Department, University of Warwick, Coventry CV4 7AL (United Kingdom); Nisbet, G [Centre for Applied Catalysis, Department of Chemical and Biological Sciences, University of Huddersfield, Queensgate, Huddersfield HD1 3DH (United Kingdom); Lamont, C L A [Centre for Applied Catalysis, Department of Chemical and Biological Sciences, University of Huddersfield, Queensgate, Huddersfield HD1 3DH (United Kingdom); Woodruff, D P [Physics Department, University of Warwick, Coventry CV4 7AL (United Kingdom)

    2005-04-01

    The results of experimental measurements and theoretical simulations of circular dichroism in the angular distribution (CDAD) of photoemission from atomic core levels of each of the enantiomers of a chiral molecule, alanine, adsorbed on Cu(1 1 0) are presented. Measurements in, and out of, substrate mirror planes allow one to distinguish the CDAD due to the chirality of the sample from that due to a chiral experimental geometry. For these studies of oriented chiral molecules, the CDAD is seen not only in photoemission from the molecular chiral centre, but also from other atoms which have chiral geometries as a result of the adsorption. The magnitude of the CDAD due to the sample chirality differs for different adsorption phases of alanine, and for different emission angles and energies, but is generally small compared with CDAD out of the substrate mirror planes which is largely unrelated to the molecular chirality. While similar measurements of other molecules may reveal larger CDAD due to molecular chirality, the fact that the results for one chiral molecule show weak effects means that such CDAD is unlikely to provide a simple and routine general spectral fingerprint of adsorbed molecular chirality.

  10. Induced circular dichroism of the interaction between pinacyanol and algal alginates.

    Science.gov (United States)

    Khouri, Sa'ib J; Knierim, Robert; Buss, Volker

    2009-09-08

    The interaction between pinacyanol chloride and sodium alginate or guluronate-rich alginate is found to effect profound changes in the visible absorbance and circular dichroism spectra. Two different types of aggregates are observed depending on the relative dye/alginate concentrations. With a dye/alginate ratio at 1:1, a complex is deduced based on an analysis of Job's method and conductometric titrations. Another complex forms at 1:10 dye/alginate ratio and only in the presence of alginate or guluronate-rich alginate. The two aggregates are in dynamic equilibrium according to the presence of isosbestic points in the visible spectra. The effects of pH and divalent cations on the spectra are studied. The 1:10 complex is damaged by addition of hydrochloric acid and divalent cations; however, at low concentration of these agents the spectra indicate conversion of the complex into the 1:1 aggregate. Models for the two complexes are proposed taking into account the preference of guluronate binding sites for chelating ions.

  11. Reversible Plasmonic Circular Dichroism via Hybrid Supramolecular Gelation of Achiral Gold Nanorods.

    Science.gov (United States)

    Jin, Xue; Jiang, Jian; Liu, Minghua

    2016-12-27

    The fabrication of chiroptical plasmonic nanomaterials such as chiral plasmonic gold nanorods (GNRs) has been attracting great interest. Generally, in order to realize the plasmonic circular dichroism (PCD) from achiral GNRs, it is necessary to partially replace the surface-coated cetyltrimethylammonium bromide with chiral molecules. Here, we present a supramolecular approach to generate and modulate the PCD of GNRs through the hybrid gelation of GNRs with an amphiphilic chiral dendron gelator. Upon gelation, the PCD could be produced and further regulated depending on the ratio of the dendrons to GNRs. It was revealed that the wrapping of the self-assembled nanofibers around the GNRs is crucial for generating the PCD. Furthermore, the hybrid gel underwent a thermotriggered gel-sol and sol-gel transformation, during which the PCD can disappear (solution) and reappear (gel), respectively, and such process can be repeated many times. In addition, the hybrid gel could also undergo shrinkage upon addition of a slight amount of Mg(2+) ions, during which the PCD disappeared also. Thus, through the gel formation and subsequent metal ion- or temperature-triggered phase transition, PCD can be reversibly modulated. The results not only clarified the generation mechanism of PCD from the achiral GNRs without the chiral modification on the surface but also offered a simple and efficient way to modulate the PCD.

  12. Studies on fish and pork paste gelation by dynamic rheology and circular dichroism.

    Science.gov (United States)

    Liu, R; Zhao, S-M; Xiong, S-B; Xie, B-J; Liu, H-M

    2007-09-01

    The muscle paste of fish, pork, and their mixtures were prepared to study the gelling characteristics by dynamic rheological measurement. The gelation mechanisms of muscle paste were also investigated by circular dichroism. Gel formation of fish paste occurred in 2 steps of 5 to 35 and 51 to 90 degrees C respectively, while pork paste mainly in 1 step of 49 to 72 degrees C. Gel formation was relative to the alpha-helix unfolding of myosin, which responded the melting temperatures of 40 and 50 degrees C for fish myosin and 50 and 60 degrees C for pork myosin, respectively. Alpha-helix unfolding of myosin was beneficial for gel formation. During gel formation, G' of muscle paste was linearly related to alpha-helical content of myosin. The interactions of fish and pork proteins at high temperature (>35 degrees C) could change the gel forming characteristics of muscle paste. Mixed paste exhibited a similar gelation pattern to individual fish paste with 2 visible increases in G'. Addition of pork could suppress the breakdown of fish gel structure at approximately 50 degrees C. Mixing pork and silver carp in a certain ratio could improve the gel properties of silver carp products.

  13. Simultaneous Analysis of Secondary Structure and Light Scattering from Circular Dichroism Titrations: Application to Vectofusin-1

    Science.gov (United States)

    Vermeer, Louic S.; Marquette, Arnaud; Schoup, Michel; Fenard, David; Galy, Anne; Bechinger, Burkhard

    2016-12-01

    Circular Dichroism data are often decomposed into their constituent spectra to quantify the secondary structure of peptides or proteins but the estimation of the secondary structure content fails when light scattering leads to spectral distortion. If peptide-induced liposome self-association occurs, subtracting control curves cannot correct for this. We show that if the cause of the light scattering is independent from the peptide structural changes, the CD spectra can be corrected using principal component analysis (PCA). The light scattering itself is analysed and found to be in good agreement with backscattering experiments. This method therefore allows to simultaneously follow structural changes related to peptide-liposome binding as well as peptide induced liposome self-association. We apply this method to study the structural changes and liposome binding of vectofusin-1, a transduction enhancing peptide used in lentivirus based gene therapy. Vectofusin-1 binds to POPC/POPS liposomes, causing a reversal of the negative liposome charge at high peptide concentrations. When the peptide charges exactly neutralise the lipid charges on both leaflets reversible liposome self-association occurs. These results are in good agreement with biological observations and provide further insight into the conditions required for efficent transduction enhancement.

  14. Interaction of polyphenolic metabolites with human serum albumin: a circular dichroism study.

    Science.gov (United States)

    Nozaki, Akiko; Kimura, Toshikiro; Ito, Hideyuki; Hatano, Tsutomu

    2009-09-01

    Binding sites of polyphenolic compounds on human serum albumin (HSA) were investigated using induced Cotton effects on the circular dichroism (CD) spectra. Polyphenolic compounds used in this study are known to be metabolites from tannins and their related polyphenols in food and medicinal plants. The present investigation revealed that the structural differences markedly affected the binding of the compounds to HSA. Protocatechuic acid, together with its methylated compounds vanillic and isovanillic acids, were assigned to be bound to sites I and II of HSA, based on the competitive relationships with site-I-binding phenylbutazone (PB) and site-II-binding diazepam (DP). 4-O-Methylgallic acid, which is the metabolite from gallic acid, was bound to site I on HSA, while gallic acid did not affect the binding of PB and DP at the concentration examined. Neither ellagic acid nor its metabolite urolithin A was competitive with PB and DP on HSA. The addition of digitoxin did not affect the induced CD of the polyphenolic acids examined.

  15. Applied Circular Dichroism: A Facile Spectroscopic Tool for Configurational Assignment and Determination of Enantiopurity

    Directory of Open Access Journals (Sweden)

    Macduff O. Okuom

    2015-01-01

    Full Text Available In order to determine if electronic circular dichroism (ECD is a good tool for the qualitative evaluation of absolute configuration and enantiopurity in the absence of chiral high performance liquid chromatography (HPLC, ECD studies were performed on several prescriptions and over-the-counter drugs. Cotton effects (CE were observed for both S and R isomers between 200 and 300 nm. For the drugs examined in this study, the S isomers showed a negative CE, while the R isomers displayed a positive CE. The ECD spectra of both enantiomers were nearly mirror images, with the amplitude proportional to the enantiopurity. Plotting the differential extinction coefficient (Δε versus enantiopurity at the wavelength of maximum amplitude yielded linear standard curves with coefficients of determination (R2 greater than 97% for both isomers in all cases. As expected, Equate, Advil, and Motrin, each containing a racemic mixture of ibuprofen, yielded no chiroptical signal. ECD spectra of Suphedrine and Sudafed revealed that each of them is rich in 1S,2S-pseudoephedrine, while the analysis of Equate vapor inhaler is rich in R-methamphetamine.

  16. Utilization of circular dichroism experiment to distinguish acanthoside D and eleutheroside E.

    Science.gov (United States)

    Kil, Yun-Seo; Park, Ji-Yeon; Kim, Youngmee; Nam, Sang-Jip; Kim, Sung-Jin; Kim, Yeong Shik; Seo, Eun Kyoung

    2015-11-01

    Two lignan glycosides, acanthoside D (1) (=liriodendrin, (+)-syringaresinol di-O-β-D-glucopyranoside) and eleutheroside E (2) have been confused each other for so long time, and hard to be distinguished each other. Now, this two compounds need to be defined properly so that all the commercial mistakes and confusions should not be made. They have identical planar structures except for the configurations at C-7 and C-8 in each structure according to the chemistry database, SciFinder(®). The systematic name of acanthoside D is [(1S,3aR,4S,6aR)-tetrahydro-1H,3H-furo[3,4-c]furan-1,4-diyl]bis(2,6-dimethoxy-4,1-phenylene) bis-β-D-glucopyranoside (1), and the name of eleutheroside E is [(1R,3aR,4S,6aS)-tetrahydro-1H,3H-furo[3,4-c]furan-1,4-diyl]bis(2,6-dimethoxy-4,1-phenylene) bis-β-D-glucopyranoside (2). The differences at two chiral centers do not make any differences in the NMR spectra. Thus, the circular dichroism were utilized to dissolve this difficult problem. Acanthoside D (1) showed a positive Cotton effect at 200 nm, whereas eleutheroside E (2) exhibited a negative cotton effect at 200 nm. The absolute structure of acanthoside D was also confirmed by X-ray crystallography.

  17. Conformational flexibility of a scorpion toxin active on mammals and insects: a circular dichroism study.

    Science.gov (United States)

    Loret, E P; Sampieri, F; Roussel, A; Granier, C; Rochat, H

    1990-01-01

    Three scorpion toxins have been analyzed by circular dichroism in water and in 2,2,2-trifluoroethanol (TFE) solutions. These toxins were chosen because they are representative of three kinds of pharmacological activities: (1) toxin AaH IT2, an antiinsect toxin purified from the venom of Androctonus australis Hector, which is able to bind to insect nervous system preparation, (2) toxin Css II, from the venom of Centruroides suffusus suffusus, which is a beta-type antimammal toxin capable of binding to mammal nervous system preparation, and (3) the toxin Ts VII from the venom of Tityus serrulatus, which is able to bind to both types of nervous systems. In order to minimize bias, CD data were analyzed by a predictive algorithm to assess secondary structure content. Among the three molecules, Ts VII presented the most unordered secondary structure in water, but it gained in ordered forms when solubilized in TFE. These results indicated that the Ts VII backbone is the most flexible, which might result in a more pronounced tendency for this toxin molecule to undergo conformational changes. This is consistent with the fact that it competes with both antiinsect and beta-type antimammal toxins for the binding to the sodium channel.

  18. Applications of Circular Dichroism for Structural Analysis of Gelatin and Antimicrobial Peptides

    Directory of Open Access Journals (Sweden)

    Yoonkyung Park

    2012-03-01

    Full Text Available Circular dichroism (CD is a useful technique for monitoring changes in the conformation of antimicrobial peptides or gelatin. In this study, interactions between cationic peptides and gelatin were observed without affecting the triple helical content of the gelatin, which was more strongly affected by anionic surfactant. The peptides did not adopt a secondary structure in the presence of aqueous solution or Tween 80, but a peptide secondary structure formed upon the addition of sodium dodecyl sulfate (SDS. The peptides bound to the phosphate group of lipopolysaccharide (LPS and displayed an alpha-helical conformation while (KW4 adopted a folded conformation. Further, the peptides did not specifically interact with the fungal cell wall components of mannan or laminarin. Tryptophan blue shift assay indicated that these peptides interacted with SDS, LPS, and gelatin but not with Tween 80, mannan, or laminarin. The peptides also displayed antibacterial activity against P. aeruginosa without cytotoxicity against HaCaT cells at MIC, except for HPA3NT3-analog peptide. In this study, we used a CD spectroscopic method to demonstrate the feasibility of peptide characterization in numerous environments. The CD method can thus be used as a screening method of gelatin-peptide interactions for use in wound healing applications.

  19. Density functional calculations on electronic circular dichroism spectra of chiral transition metal complexes.

    Science.gov (United States)

    Autschbach, Jochen; Jorge, Francisco E; Ziegler, Tom

    2003-05-05

    Time-dependent density functional theory (TD-DFT) has for the first time been applied to the computation of circular dichroism (CD) spectra of transition metal complexes, and a detailed comparison with experimental spectra has been made. Absorption spectra are also reported. Various Co(III) complexes as well as [Rh(en)(3)](3+) are studied in this work. The resulting simulated CD spectra are generally in good agreement with experimental spectra after corrections for systematic errors in a few of the lowest excitation energies are applied. This allows for an interpretation and assignment of the spectra for the whole experimentally accessible energy range (UV/vis). Solvent effects on the excitations are estimated via inclusion of a continuum solvent model. This significantly improves the computed excitation energies for charge-transfer bands for complexes of charge +3, but has only a small effect on those for neutral or singly charged complexes. The energies of the weak d-to-d transitions of the Co complexes are systematically overestimated due to deficiencies of the density functionals. These errors are much smaller for the 4d metal complex. Taking these systematic errors and the effect of a solvent into consideration, TD-DFT computations are demonstrated to be a reliable tool in order to assist with the assignment and interpretation of CD spectra of chiral transition metal complexes.

  20. First-principles analysis of X-ray magnetic circular dichroism for transition metal complex oxides

    Science.gov (United States)

    Ikeno, Hidekazu

    2016-10-01

    X-ray magnetic circular dichroism (XMCD) is widely used for the characterization of magnetism of materials. However, information from XMCD related to the atomic, electronic, and magnetic structures is not fully utilized due to the lack of reliable theoretical tools for spectral analysis. In this work, the first-principles configuration interaction (CI) calculations for X-ray absorption spectra developed by the author were extended for the calculation of XMCD, where the Zeeman energy was taken into the Hamiltonian of the CI to mimic magnetic polarization in the solid state. This technique was applied to interpret the L2,3 XMCD from 3d transition metal complex oxides, such as NiFe2O4 and FeTiO3. The experimental XMCD spectra were quantitatively reproduced using this method. The oxidation states as well as the magnetic ordering between transition metal ions on crystallographically different sites in NiFe2O4 can be unambiguously determined. A first-principles analysis of XMCD in FeTiO3 revealed the presence of Fe3+ and Ti3+ ions, which indicates that the charge transfer from Fe to Ti ions occurs. The origin of magnetic polarization of Ti ions in FeTiO3 was also discussed.

  1. Introducing DInaMo: A Package for Calculating Protein Circular Dichroism Using Classical Electromagnetic Theory

    Directory of Open Access Journals (Sweden)

    Igor V. Uporov

    2015-09-01

    Full Text Available The dipole interaction model is a classical electromagnetic theory for calculating circular dichroism (CD resulting from the π-π* transitions of amides. The theoretical model, pioneered by J. Applequist, is assembled into a package, DInaMo, written in Fortran allowing for treatment of proteins. DInaMo reads Protein Data Bank formatted files of structures generated by molecular mechanics or reconstructed secondary structures. Crystal structures cannot be used directly with DInaMo; they either need to be rebuilt with idealized bond angles and lengths, or they need to be energy minimized to adjust bond lengths and bond angles because it is common for crystal structure geometries to have slightly short bond lengths, and DInaMo is sensitive to this. DInaMo reduces all the amide chromophores to points with anisotropic polarizability and all nonchromophoric aliphatic atoms including hydrogens to points with isotropic polarizability; all other atoms are ignored. By determining the interactions among the chromophoric and nonchromophoric parts of the molecule using empirically derived polarizabilities, the rotational and dipole strengths are determined leading to the calculation of CD. Furthermore, ignoring hydrogens bound to methyl groups is initially explored and proves to be a good approximation. Theoretical calculations on 24 proteins agree with experiment showing bands with similar morphology and maxima.

  2. Measuring circular dichroism in a capillary cell using the b23 synchrotron radiation CD beamline at diamond light source.

    Science.gov (United States)

    Jávorfi, Tamás; Hussain, Rohanah; Myatt, Daniel; Siligardi, Giuliano

    2010-01-01

    Synchrotron radiation circular dichroism (SRCD) is a well-established method in structural biology. The first UV-VIS beamline dedicated to circular dichroism at Diamond Light Source, a third generation synchrotron facility in South Oxfordshire, has recently become operational and it is now available for the user community. Herein we present an important application of SRCD: the CD measurement of protein solutions in fused silica rectangular capillary cells. This was achieved without the use of any lens between the photoelastic modulator and the photomultiplier tube detectors by exploiting the high photon flux of the collimated beam that can be as little as half a millimeter squared. Measures to minimize or eliminate vacuum-UV protein denaturation effects are discussed. The CD spectra measured in capillaries is a proof of principle to address CD measurements in microdevice systems using the new B23 SRCD beamline.

  3. A new soft X-ray magnetic circular dichroism facility at the BSRF beamline 4B7B

    CERN Document Server

    Guo, Zhi-Ying; Xing, Hai-Ying; Tang, Kun; Xui, Wei; Chen, Dong-liang; Cui, Ming-Qi; Zhao, YI-Dong

    2014-01-01

    X-ray magnetic circular dichroism (XMCD) has become an important and powerful tool because it allows the study of material properties in combination with elemental specificity, chemical state specificity, and magnetic specificity. A new soft X-ray magnetic circular dichroism apparatus has been developed at the Beijing Synchrotron Radiation Facility (BSRF). The apparatus combines three experimental conditions: ultra-high-vacuum environment, moderate magnetic fields and in-situ sample preparation to measure the absorption signal. We designed a C type dipole electromagnet that provides magnetic fields up to 0.5T in parallel (or anti-parallel) direction relative to the incoming X-ray beam. The performances of the electromagnet are measured and the results show good agreement with the simulation ones. Following film grown in situ by evaporation methods, XMCD measurements are performed. Combined polarization corrections, the magnetic moments of the Fe and Co films determined by sum rules are consistent with other t...

  4. Photoelectron circular dichroism of chiral molecules studied with a continuum-state-corrected strong-field approximation

    Science.gov (United States)

    Dreissigacker, Ingo; Lein, Manfred

    2014-05-01

    Motivated by recent experiments on circular dichroism in the photoelectron momentum distributions from strong-field ionization of chiral molecules [C. Lux et al., Angew. Chem. Int. Ed. 51, 5001 (2012), 10.1002/anie.201109035; C. S. Lehmann et al., J. Chem. Phys. 139, 234307 (2013), 10.1063/1.4844295], we investigate the origin of this effect theoretically. We show that it is not possible to describe photoelectron circular dichroism with the commonly used strong-field approximation due to its plane-wave nature. We therefore apply the Born approximation to the scattering state and use this as a continuum-state correction in the strong-field approximation. We obtain electron distributions for the molecules camphor and fenchone. In order to gain physical insight into the process, we study the contributions of individual molecular orientations.

  5. Simulations of circular dichroism spectra of a pair of diterpene enantiomers by time-dependent density functional theory

    Science.gov (United States)

    Liaw, Chih-Chuang; Chang, Jia-Lin; Chen, Shou-Fong; Huang, Jhih-Hong; Sie, Jyun-Fu; Cheng, Yung-Yi

    2011-11-01

    We present the first theoretical study on a pair of diterpene enantiomers of formula C 21H 34O 5, which were newly isolated from plants and identified as 3β,5β-dihydroxy-16 α/ β-methoxyhalima-13(14)-en-15,16-olide. The equilibrium geometries and harmonic vibrational frequencies of their low-lying conformers were obtained by using the AM1 and B3LYP/6-31+G(d) methods. At the optimized geometries, rotatory strengths of six excited states of each conformer were computed by the time-dependent density functional theory. The electronic circular dichroism spectra were simulated by taking Boltzmann averaging and considering the solvent effect, from which the absolute configurations of the enantiomers were determined. Their vibrational circular dichroism spectra were also predicted.

  6. Measurement of the polarization for soft x-ray magnetic circular dichroism at the BSRF beamline 4B7B

    CERN Document Server

    Zhi-Ying, Guo; Jing-Tao, Zhu; YI-Dong, Zhao; Lei, Zheng; Cai-Hao, Hong; Kun, Tang; Dong-Liang, Yang; Ming-Qi, Cui

    2012-01-01

    Three ultra-short-period W/B4C multilayers (1.244nm, 1.235nm and 1.034nm) have been fabricated and used for polarization measurement at the 4B7B Beamline of Beijing Synchrotron Radiation Facility (BSRF). By rotating analyzer ellipsometry method, the linear polarization degree of light emerging from this beamline has been measured and the circular polarization evaluated for 700eV-860eV. The first soft x-ray magnetic circular dichroism measurements are carried out at BSRF by positioning the beamline aperture out of the plane of the electron storage ring.

  7. Ab initio study of the one- and two-photon circular dichroism of R-(+)-3-methyl-cyclopentanone

    Science.gov (United States)

    Rizzo, Antonio; Lin, Na; Ruud, Kenneth

    2008-04-01

    One- and two-photon circular dichroism spectra of R-(+)-3-methyl-cyclopentanone, a system that has been the subject of recent experimental studies of (2+1) resonance-enhanced multiphoton ionization circular dichroism, have been calculated with an origin-invariant density functional theory approximation in the region of the lowest electronic excited states, both for the gas phase and for a selection of solvents. A polarizable continuum model is used in the calculations performed on the solvated system. Two low-lying conformers are analyzed, and a comparison of the intensities and characteristic features is made with the corresponding two-photon absorption for each species, also for the Boltzmann-averaged spectra. The effect of the choice of geometry, basis set, and exchange-correlation functional is carefully analyzed. It is found that a density functional theory approach using the Coulomb attenuating method variant of Becke's three-parameter exchange and the Lee-Yang-Parr correlation functionals with correlation-consistent basis sets of double-zeta quality can reproduce the experimental electronic circular dichroism spectra very well. The features appearing in experiment are characterized in terms of molecular excitations, and the differences in the response of each state in the one- and two-photon processes are highlighted.

  8. Influence of hybridization in the Magnetic Circular X-ray Dichroism at the Ce-M4,5 absorption edges of Ce-Fe systems

    NARCIS (Netherlands)

    Finazzi, M.; de Groot, F.M.F.; Dias, A.-M.; Kappler, J.-P.; Schulte, O.; Felsch, W.; Krill, G.

    2013-01-01

    We have performed a Magnetic Circular X-ray Dichroism (XMCD) study at the Ce-M*,s absorption edges on some Ce-Fe systems. We find that the dichroism signal in these systems is very sensitive to the degree of hybridization of the 4f electrons with the valence band. XMCD is able to demonstrate that th

  9. Influence of hybridization in the magnetic circular X-ray dichroism at the Ce-M(4,5) absorption edges of Ce-Fe systems

    NARCIS (Netherlands)

    Finazzi, M; deGroot, FMF; Dias, AM; Kappler, JP; Schulte, O; Felsch, W; Krill, G

    1996-01-01

    We have performed a Magnetic Circular X-ray Dichroism (XMCD) study at the Ce-M(4,5) absorption edges on some Ce-Fe systems. We find that the dichroism signal in these systems is very sensitive to the degree of hybridization of the 4f electrons with the valence band. XMCD is able to demonstrate that

  10. Circular dichroism sensor based on cadmium sulfide quantum dots for chiral identification and detection of penicillamine

    Energy Technology Data Exchange (ETDEWEB)

    Ngamdee, Kessarin [Materials Chemistry Research Center, Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Khon Kaen University, Khon Kaen, 40002 (Thailand); Puangmali, Theerapong [Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen, 40002 (Thailand); Tuntulani, Thawatchai [Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok, 10330 (Thailand); Ngeontae, Wittaya, E-mail: wittayange@kku.ac.th [Materials Chemistry Research Center, Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Khon Kaen University, Khon Kaen, 40002 (Thailand)

    2015-10-22

    A new chemical sensor based on the measuring of circular dichroism signal (CD) was fabricated from cysteamine capped cadmium sulfide quantum dots (Cys-CdS QDs). The chiral-thiol molecules, D-penicillamine (DPA) and L-penicillamine (LPA), were used to evaluate potentials of this sensor. Basically, DPA and LPA provide very low CD signals. However, the CD signals of DPA and LPA can be enhanced in the presence of Cys-CdS QDs. The CD spectra of DPA and LPA exhibited a mirror image profile. Parameters affecting the determination of DPA and LPA were thoroughly investigated in details. Under the optimized condition, the CD signals of DPA and LPA displayed a linear relationship with the concentrations of both enantiomers, ranging from 1 to 35 μM. Detection limits of this sensor were 0.49 and 0.74 μM for DPA and LPA, respectively. To demonstrate a potential application of this sensor, the proposed sensor was used to determine DPA and LPA in real urine samples. It was confirmed that the proposed detection technique was reliable and could be utilized in a broad range of applications. - Highlights: • This paper demonstrates a new CD sensor based on cadmium sulfide quantum dots. • Achiral quantum dots are used for the detection and chiral identification of thiol-chiral containing compounds. • The sensor show highest selectivity towards penicillamine. • The detection limits of the sensor less than 1 μM. • The sensor can potentially be used in physiological urine samples.

  11. Species-dependent stereoselective drug binding to albumin: a circular dichroism study.

    Science.gov (United States)

    Pistolozzi, Marco; Bertucci, Carlo

    2008-03-01

    Drug binding to albumins from different mammalian species was investigated to disclose evidence of species-dependent stereoselectivity in drug-binding processes and affinities. This aspect is important for evaluating the reliability of extrapolating distribution data among species. The circular dichroism (CD) signal induced by drug binding to the albumins [human serum albumin (HSA), bovine serum albumin (BSA), rat serum albumin (RSA), and dog serum albumin (DSA)] were measured and analyzed. The binding of selected drugs and metabolites to HSA significantly differed from the binding to the other albumins in terms of affinity and conformation of the bound ligands. In particular, phenylbutazone, a marker of site one on HSA, showed a higher affinity for binding to BSA with respect to RSA, HSA, and DSA, respectively. In the case of diazepam, a marker of site two on HSA, the affinity decreased in order from HSA to DSA, RSA, and BSA. The induced CD spectra were similar in terms of energy and band signs, suggesting almost the same conformation for the bound drug to the different albumins. Stereoselectivity was high for the binding of ketoprofen to HSA and RSA. A different sign was observed for the CD spectra induced by the drug to the two albumins because of the prevalence of a different conformation of the bound drug. Interestingly, the same induced CD spectra were obtained using either the racemic form or the (S)-enantiomer. Finally, significant differences were observed in the affinity of bilirubin, being highest for BSA, then decreasing for RSA, HSA, and DSA. A more complex conformational equilibrium was observed for bound bilirubin.

  12. Prediction of protein secondary structure from circular dichroism using theoretically derived spectra.

    Science.gov (United States)

    Louis-Jeune, Caroline; Andrade-Navarro, Miguel A; Perez-Iratxeta, Carol

    2012-02-01

    Circular dichroism (CD) is a spectroscopic technique commonly used to investigate the structure of proteins. Major secondary structure types, alpha-helices and beta-strands, produce distinctive CD spectra. Thus, by comparing the CD spectrum of a protein of interest to a reference set consisting of CD spectra of proteins of known structure, predictive methods can estimate the secondary structure of the protein. Currently available methods, including K2D2, use such experimental CD reference sets, which are very small in size when compared to the number of tertiary structures available in the Protein Data Bank (PDB). Conversely, given a PDB structure, it is possible to predict a theoretical CD spectrum from it. The methodological framework for this calculation was established long ago but only recently a convenient implementation called DichroCalc has been developed. In this study, we set to determine whether theoretically derived spectra could be used as reference set for accurate CD based predictions of secondary structure. We used DichroCalc to calculate the theoretical CD spectra of a nonredundant set of structures representing most proteins in the PDB, and applied a straightforward approach for predicting protein secondary structure content using these theoretical CD spectra as reference set. We show that this method improves the predictions, particularly for the wavelength interval between 200 and 240 nm and for beta-strand content. We have implemented this method, called K2D3, in a publicly accessible web server at http://www. ogic.ca/projects/k2d3.

  13. Theoretical modeling of peptide α-helical circular dichroism in aqueous solution.

    Science.gov (United States)

    Kaminský, Jakub; Kubelka, Jan; Bour, Petr

    2011-03-10

    Reliable modeling of protein and peptide circular dichroism (CD) spectra in the far UV presents a challenge for current theoretical approaches. In this study, the time-dependent density functional theory (TDDFT), configuration interaction with single excitation (CIS), and transition dipole coupling (TDC) were used to assess the most important factors contributing to the CD spectra of the α-helical secondary structure. The dependence on the peptide chain length and also the role of the flexibility and solvent environment were investigated with a model oligopeptide Ac-(Ala)(N)-NH-Me, (N = 1, ..., 18). Both the TDDFT and TDC-like methods suggest that the CD curve typical for the α-helix arises gradually, but its basic characteristic is discernible already for peptides with 4-5 amino acid residues. The calculated dependence was in a qualitative agreement with experimental spectra of short α-helices stabilized by the histidine-metal binding. The TDDFT computations of the CD were found to be unusually sensitive to the basis set and solvent model. Explicit hydration and temperature fluctuations of the peptide geometry, simulated with the aid of molecular dynamics (MD), significantly influenced the CD and absorption spectral shapes. An extensive averaging over MD configurations is thus required to obtain a converged spectral profile in cluster simulations. On the other hand, both the TDDFT and TDC models indicate only a minor influence of the alanine side chains. The CIS and TDC calculations also point toward a relatively small effect of the helix-helix interaction on the CD spectral profiles. For a model system of two helices, the CIS method predicted larger changes in the spectra than TDC. This suggests other than interactions between peptide chains, such as mutual polarization, can have a minor, but measurable, effect on the CD spectrum.

  14. Vibronic coupling effect on circular dichroism spectrum: Carotenoid-retinal interaction in xanthorhodopsin

    Science.gov (United States)

    Fujimoto, Kazuhiro J.; Balashov, Sergei P.

    2017-03-01

    The role of vibronic coupling of antenna carotenoid and retinal in xanthorhodopsin (XR) in its circular dichroism (CD) spectrum is examined computationally. A vibronic exciton model combined with a transition-density-fragment interaction (TDFI) method is developed, and applied to absorption and CD spectral calculations of XR. The TDFI method is based on the electronic Coulomb and exchange interactions between transition densities for individual chromophores [K. J. Fujimoto, J. Chem. Phys. 137, 034101 (2012)], which provides a quantitative description of electronic coupling energy. The TDFI calculation reveals a dominant contribution of the Coulomb interaction to the electronic coupling energy and a negligible contribution of the exchange interaction, indicating that the antenna function of carotenoid results from the Förster type of excitation-energy transfer, not from the Dexter one. The calculated absorption and CD spectra successfully reproduce the main features of the experimental results, which allow us to investigate the mechanism of biphasic CD spectrum observed in XR. The results indicate that vibronic coupling between carotenoid and retinal plays a significant role in the shape of the CD spectrum. Further analysis reveals that the negative value of electronic coupling directly contributes to the biphasic shape of CD spectrum. This study also reveals that the C6—C7 bond rotation of salinixanthin is not the main factor for the biphasic CD spectrum although it gives a non-negligible contribution to the spectral shift. The present method is useful for analyzing the molecular mechanisms underlying the chromophore-chromophore interactions in biological systems.

  15. Soft-x-ray linear-dichroism and magnetic-circular-dichroism studies of CeRh3B2: Large crystal-field splitting and anomalous ferromagnetism

    Science.gov (United States)

    Yamaguchi, K.; Namatame, H.; Fujimori, A.; Koide, T.; Shidara, T.; Nakamura, M.; Misu, A.; Fukutani, H.; Yuri, M.; Kasaya, M.; Suzuki, H.; Kasuya, T.

    1995-05-01

    CeRh3B2 shows an anomalously high Curie temperature (Tc=115 K) for a Ce compound with nonmagnetic constituents, strong anisotropy in the magnetic susceptibility, and ferromagnetic ordering. We have studied its electronic structure by measuring linear dichroism (LD) and magnetic circular dichroism (MCD) in the Ce 4d core-level x-ray-absorption spectra. The result for LD indicates a highly anisotropic distribution of Ce 4f electrons along the hexagonal c axis, while the MCD result shows that the magnetic moment of the Ce 4f electron is dominated by the orbital moment as in the case of a small crystal field. Using the Anderson-impurity model including the axial crystal field, the strong interatomic Ce 4f-Ce 5d hybridization and the Ce 4f-Rh 4d hybridization, we show that there is a range of parameter sets for the axial crystal field and the Ce 4f-valence-band transfer integral which explains the results of the LD and MCD experiments. Using the same parameter set, we have also attempted to explain the Kondo temperature and the unusually high Curie temperature.

  16. Conformation and stability properties of B17: I. Analytical investigations using circular dichroism.

    Science.gov (United States)

    Khachfe, Hassan M; Atkinson, David

    2012-08-01

    Structural characterization of B17, the 17% N-terminal domain of apo B, was carried out using circular dichroic (CD) spectroscopy, where secondary and tertiary structures were studied as a function of temperature and pH. Mild acidic conditions that correlate with histidine protonation invoked a change in the α-helix and random coil contents of the protein, with no apparent change in the β-sheet structural content. Specific changes in the structure of the protein that occur in response to temperature were also investigated to understand the stability and conformational changes of B17. Far- and near-UV CDs were used to probe the thermal changes in the protein. The protonation of some histidine residues was attributed to underlie the increase in the helical content of the protein.

  17. Domain imaging on multiferroic BiFeO{sub 3}(001) by linear and circular dichroism in threshold photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Sander, Anke; Christl, Maik [Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, Von-Danckelmann-Platz 3, 06120 Halle(Saale) (Germany); Chiang, Cheng-Tien [Max Planck Institute of Microstructure Physics, Weinberg 2, 06120 Halle(Saale) (Germany); Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, Von-Danckelmann-Platz 3, 06120 Halle(Saale) (Germany); Alexe, Marin [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom); Widdra, Wolf, E-mail: wolf.widdra@physik.uni-halle.de [Institute of Physics, Martin-Luther-Universität Halle-Wittenberg, Von-Danckelmann-Platz 3, 06120 Halle(Saale) (Germany); Max Planck Institute of Microstructure Physics, Weinberg 2, 06120 Halle(Saale) (Germany)

    2015-12-14

    We demonstrate ferroelectric domain imaging at BiFeO{sub 3}(001) single crystal surfaces with laser-based threshold photoemission electron microscopy (PEEM). Work function differences and linear dichroism allow for the identification of the eight independent ferroelectric domain configurations in the PEEM images. There, the determined domain structure is consistent with piezoresponse force microscopy of the sample surface and can also be related to the circular dichroic PEEM images. Our results provide a method for efficient mapping of complex ferroelectric domains with laser-excited PEEM and may allow lab-based time-resolved studies of the domain dynamics in the future.

  18. Theoretical description of circular dichroism in photoelectron angular distributions of randomly oriented chiral molecules after multi-photon photoionization

    CERN Document Server

    Goetz, R E; Nikoobakht, B; Berger, R; Koch, C P

    2016-01-01

    Photoelectron circular dichroism refers to the forward/backward asymmetry in the photoelectron angular distribution with respect to the propagation axis of circularly polarized light. It has recently been demonstrated in femtosecond multi-photon photoionization experiments with randomly oriented camphor and fenchone molecules [C. Lux et al., Angew. Chem. Int. Ed. 51, 5001 (2012);C. S. Lehmann et al., J. Chem. Phys. 139, 234307 (2013)]. A theoretical framework describing this process as (2+1) resonantly enhanced multi-photon ionization is constructed, which consists of two-photon photoselection from randomly oriented molecules and successive one-photon ionisation of the photoselected molecules. It combines perturbation theory for the light-matter interaction with ab initio calculations for the two-photon absorption and a single-center expansion of the photoelectron wavefunction in terms of hydrogenic continuum functions. It is verified that the model correctly reproduces the basic symmetry behavior expected un...

  19. Relaxation Dynamics in Photoexcited Chiral Molecules Studied by Time-Resolved Photoelectron Circular Dichroism: Toward Chiral Femtochemistry

    CERN Document Server

    Comby, Antoine; Boggio-Pasqua, Martial; Descamps, Dominique; Légaré, Francois; Nahon, Laurent; Petit, Stéphane; Pons, Bernard; Fabre, Baptiste; Mairesse, Yann; Blanchet, Valérie

    2016-01-01

    Unravelling the main initial dynamics responsible for chiral recognition is a key stepin the understanding of many biological processes. However this challenging task requires a sensitive enantiospecic probe to investigate molecular dynamics on their natural femtosecond timescale. Here we show that, in the gas phase, the ultrafast relaxationdynamics of photoexcited chiral molecules can be tracked by recording Time-ResolvedPhotoElectron Circular Dichroism (TR-PECD) resulting from the photoionisation bya circularly polarized probe pulse. A large forward/backward asymmetry along theprobe propagation axis is observed in the photoelectron angular distribution. Its evolution with pump-probe delay reveals ultrafast dynamics that are inaccessible in theangle-integrated photoelectron spectrum nor via the usual electron emission anisotropyparameter ($\\beta$). PECD, which originates from the electron scattering in the chiral molecular potential, appears as a new sensitive observable for ultrafast molecular dynamicsin ch...

  20. Wavelength dependent photoelectron circular dichroism of limonene studied by femtosecond multiphoton laser ionization and electron-ion coincidence imaging

    Science.gov (United States)

    Rafiee Fanood, Mohammad M.; Janssen, Maurice H. M.; Powis, Ivan

    2016-09-01

    Enantiomers of the monoterpene limonene have been investigated by (2 + 1) resonance enhanced multiphoton ionization and photoelectron circular dichroism employing tuneable, circularly polarized femtosecond laser pulses. Electron imaging detection provides 3D momentum measurement while electron-ion coincidence detection can be used to mass-tag individual electrons. Additional filtering, by accepting only parent ion tagged electrons, can be then used to provide discrimination against higher energy dissociative ionization mechanisms where more than three photons are absorbed to better delineate the two photon resonant, one photon ionization pathway. The promotion of different vibrational levels and, tentatively, different electronic ion core configurations in the intermediate Rydberg states can be achieved with different laser excitation wavelengths (420 nm, 412 nm, and 392 nm), in turn producing different state distributions in the resulting cations. Strong chiral asymmetries in the lab frame photoelectron angular distributions are quantified, and a comparison made with a single photon (synchrotron radiation) measurement at an equivalent photon energy.

  1. PILOT STUDY International comparability in spectroscopic measurements of protein structure by circular dichroism: CCQM-P59

    Science.gov (United States)

    Ravi, Jascindra; Schiffmann, David; Tantra, Ratna; Cox, Simon; Eady, Jonathan; Jones, Christopher; Vrettos, John S.; Affleck, Richard P.; DeSa Lorenz, Julie; Shigeri, Yasushi; Linghui, Sheng; Jun, Liu; Willows, Robert; Charlet, Philippe; Dupont, Yves; Meuse, Curtis W.; Bailey, Marc J. A.; Knight, Alex E.

    2010-01-01

    Circular dichroism is a spectroscopic technique that is widely used to obtain information about protein structure, and hence is an important tool with many applications, including the characterization of biopharmaceuticals. However, there is a lack of confidence in the technique, arising from an observed lack of comparability in the data obtained by different laboratories, or even different operators. In this study, we set out to determine the extent of comparability in the technique, by comparing the results obtained from identical protein samples by a panel of worldwide laboratories. The laboratories chosen were either national measurement institutes (NMIs) or expert laboratories nominated by an NMI. We also aimed to identify the main factors contributing to any lack of measurement comparability. Data were analysed using PCA and SIMCA methods, and we show these statistical techniques are ideal for analysing large amounts of this type of spectroscopic data. We found a startling lack of comparability among laboratories, but we also found that most of the variability arose from relatively simple problems, which can be avoided by following simple guidelines. We believe that the lack of an absolute reference or measurement traceability in circular dichroism contributes to a lack of confidence in the technique. Main text. To reach the main text of this paper, click on Final Report. The final report has been peer-reviewed and approved for publication by the CCQM Working Group on Bioanalysis (BAWG).

  2. A circular dichroism sensor for Ni(2+) and Co(2+) based on L-cysteine capped cadmium sulfide quantum dots.

    Science.gov (United States)

    Tedsana, Wimonsiri; Tuntulani, Thawatchai; Ngeontae, Wittaya

    2015-03-31

    A new circular dichroism sensor for detecting Ni(2+) and Co(2+) was proposed for the first time using chiral chelating quantum dots. The detection principle was based on changing of circular dichroism signals of the chiral quantum dots when forming a chiral complex with Ni(2+) or Co(2+). L-Cysteine capped cadmium sulfide quantum dots (L-Cyst-CdS QDs) were proposed as a chiral probe. The CD spectrum of L-Cyst-CdS QDs was significantly changed in the presence of Ni(2+) and Co(2+). On the other hand, other studied cations did not alter the original CD spectrum. Moreover, when increasing the concentration of Ni(2+) or Co(2+), the intensity of the CD spectrum linearly increased as a function of concentration and could be useful for the quantitative analysis. The proposed CD sensor showed linear working concentration ranges of 10-60 μM and 4-80 μM with low detection limits of 7.33 μМ and 1.13 μM for the detection of Ni(2+) and Co(2+), respectively. Parameters possibly affected the detection sensitivity such as solution pH and incubation time were studied and optimized. The proposed sensor was applied to detect Ni(2+) and Co(2+) in real water samples, and the results agreed well with the analysis using the standard ICP-OES.

  3. Structural alterations of human serum albumin caused by glycative and oxidative stressors revealed by circular dichroism analysis.

    Science.gov (United States)

    Monacelli, Fiammetta; Storace, Daniela; D'Arrigo, Cristina; Sanguineti, Roberta; Borghi, Roberta; Pacini, Davide; Furfaro, Anna L; Pronzato, Maria A; Odetti, Patrizio; Traverso, Nicola

    2013-01-01

    The aim of this work was to evaluate the ability of oxidative and glycative stressors to modify properties of human serum albumin (HSA) by analyzing markers of glycation (pentosidine) and oxidation (advanced oxidative protein products (AOPPs)) and assessing fluorescence and circular dichroism. HSA was incubated for up to 21 days with ribose, ascorbic acid (AA) and diethylenetriamine pentacetate (DTPA) in various combinations in order to evaluate influences of these substances on the structure of HSA. Ribose was included as a strong glycative molecule, AA as a modulator of oxidative stress, and DTPA as an inhibitor of metal-catalyzed oxidation. Ribose induced a significant increase in pentosidine levels. AA and DTPA prevented the accumulation of pentosidine, especially at later time points. Ribose induced a mild increase in AOPP formation, while AA was a strong inducer of AOPP formation. Ribose, in combination with AA, further increased the formation of AOPP. DTPA prevented the AA-induced generation of AOPP. Ribose was also a potent inducer of fluorescence at 335nm ex/385nm em, which is typical of pentosidine. AA and DTPA prevented this fluorescence. Circular dichroism showed complex results, in which AA and DTPA were strong modifiers of the percentages of the alpha-helical structure of HSA, while ribose affected the structure of HSA only at later time points.

  4. A new soft X-ray magnetic circular dichroism facility at the BSRF beamline 4B7B

    Science.gov (United States)

    Guo, Zhi-Ying; Hong, Cai-Hao; Xing, Hai-Ying; Tang, Kun; Zheng, Lei; Xui, Wei; Chen, Dong-Liang; Cui, Ming-Qi; Zhao, Yi-Dong

    2015-04-01

    X-ray magnetic circular dichroism (XMCD) has become an important and powerful tool because it allows the study of material properties in combination with elemental specificity, chemical state specificity, and magnetic specificity. A new soft X-ray magnetic circular dichroism apparatus has been developed at the Beijing Synchrotron Radiation Facility (BSRF). The apparatus combines three experimental conditions: an ultra-high-vacuum environment, moderate magnetic fields and in-situ sample preparation to measure the absorption signal. We designed a C-type dipole electromagnet that provides magnetic fields up to 0.5 T in parallel (or anti-parallel) direction relative to the incoming X-ray beam. The performances of the electromagnet are measured and the results show good agreement with the simulation ones. Following film grown in situ by evaporation methods, XMCD measurements are performed. Combined polarization corrections, the magnetic moments of the Fe and Co films determined by sum rules are consistent with other theoretical predictions and experimental measurements. Supported by National Natural Science Foundation of China (61204008)

  5. Circular Dichroism and Superdiffusive Transport at the Surface of BiTeI

    OpenAIRE

    Mauchain, J; Kokh, K. A.; Tereshchenko, O. E.; Eremeev, S. V.; Chulkov, Eugene V.; Perfetti, L

    2013-01-01

    International audience; We investigate the electronic states of BiTeI after the optical pumping with circularly polarized photons. Our data show that photoexcited electrons reach an internal thermalization within 300 fs from the arrival of the pump pulse. Instead, the dichroic contrast generated by the circularly polarized light relaxes on a timescale shorter than 80 fs. This result implies that orbital and spin polarization created by the circular pump pulse rapidly decays via manybody inter...

  6. Magnetism of unconventional nanoscaled materials. An X-ray circular dichroism and muon spin rotation study

    Energy Technology Data Exchange (ETDEWEB)

    Tietze, Thomas Hermann

    2014-12-15

    The physical properties of nanoparticles deviate strongly from its bulk counterparts. In particular, the magnetic properties change strongly due to an elevated number of surface compared to bulk atoms. As a consequence the orbital magnetic moment in nanoparticles as well as the magnetic anisotropy is enhanced. Therefore, such nanoparticles have great potential in e.g. next generation high density data storage devices. A promising way to realize such devices is to deposit nanoparticles on graphene. Depending on the preparation conditions the templated growth of nanocluster arrays with different particle size and shape is possible. Since graphene possesses outstanding properties as well it is congruous to combine the advantages of both systems and to investigate its principle properties in more detail. Thus, one part of this work is dedicated to the size and shape dependence of electronic and magnetic properties of Ni nanoclusters on graphene. The magnetic properties were investigated using X-ray Magnetic Circular Dichroism (XMCD). From the corresponding absorption spectra, the electronic structure and the nanoparticle substrate interaction could be determined. Two sets of nanoparticles were investigated, with triangular and spherical shape. For each set the size was varied. Nonmagnetic absorption spectra indicate a strong interaction between the Ni nanoclusters and the graphene substrate. The integrated absorption signal which is a measure of the number of unoccupied states in the Ni d shell decreases strongly with decreasing cluster size. This means an enhanced occupancy of the Ni d states, most likely caused by charge transfer at the Ni nanocluster/graphene interface. As a consequence the magnetic moment was much smaller than expected for nanoclusters for all samples investigated. The smallest value obtained was only 50% of the respective bulk magnetic moment. The magnetic moment increases disproportionally and converges towards bulk properties above 2 ML. No

  7. Absorption and Magnetic Circular Dichroism Analyses of Giant Zeeman Splittings in Diffusion-Doped Colloidal Cd(1-x)Mn(x)Se Quantum Dots.

    Science.gov (United States)

    Barrows, Charles J; Vlaskin, Vladimir A; Gamelin, Daniel R

    2015-08-06

    Impurity ions can transform the electronic, magnetic, or optical properties of colloidal quantum dots. Magnetic impurities introduce strong dopant-carrier exchange coupling that generates giant Zeeman splittings (ΔEZ) of excitonic excited states. To date, ΔEZ in colloidal doped quantum dots has primarily been quantified by analysis of magnetic circular dichroism (MCD) intensities and absorption line widths (σ). Here, we report ΔEZ values detected directly by absorption spectroscopy for the first time in such materials, using colloidal Cd(1-x)Mn(x)Se quantum dots prepared by diffusion doping. A convenient method for decomposing MCD and absorption data into circularly polarized absorption spectra is presented. These data confirm the widely applied MCD analysis in the low-field, high-temperature regime, but also reveal a breakdown at low temperatures and high fields when ΔEZ/σ approaches unity, a situation not previously encountered in doped quantum dots. This breakdown is apparent for the first time here because of the extraordinarily large ΔEZ and small σ achieved by nanocrystal diffusion doping.

  8. Kaempferol-human serum albumin interaction: Characterization of the induced chirality upon binding by experimental circular dichroism and TDDFT calculations

    Science.gov (United States)

    Matei, Iulia; Ionescu, Sorana; Hillebrand, Mihaela

    2012-10-01

    The experimental induced circular dichroism (ICD) and absorption spectra of the achiral flavonoid kaempferol upon binding to human serum albumin (HSA) were correlated to electronic CD and UV-vis spectra theoretically predicted by time-dependent density functional theory (TDDFT). The neutral and four anionic species of kaempferol in various conformations were considered in the calculations. The appearance of the experimental ICD signal was rationalized in terms of kaempferol binding to HSA in a distorted, chiral, rigid conformation. The comparison between the experimental and simulated spectra allowed for the identification of the kaempferol species that binds to HSA, namely the anion generated by deprotonation of the hydroxyl group in position 7. This approach constitutes a convenient method for evidencing the binding species and for determining its conformation in the binding pocket of the protein. Its main advantage over the UV-vis absorption method lays in the fact that only the bound ligand species gives an ICD signal.

  9. A QM/MM-MD study on protein electronic properties: Circular dichroism spectra of oxytocin and insulin

    Science.gov (United States)

    Kitagawa, Yuya; Akinaga, Yoshinobu; Kawashima, Yukio; Jung, Jaewoon; Ten-no, Seiichiro

    2012-06-01

    A QM/MM (quantum-mechanical/molecular-mechanical) molecular-dynamics approach based on the generalized hybrid-orbital (GHO) method, in conjunction with the second-order perturbation (MP2) theory and the second-order approximate coupled-cluster (CC2) model, is employed to calculate electronic property accounting for a protein environment. Circular dichroism (CD) spectra originating from chiral disulfide bridges of oxytocin and insulin at room temperature are computed. It is shown that the sampling of thermal fluctuation of molecular geometries facilitated by the GHO-MD method plays an important role in the obtained spectra. It is demonstrated that, while the protein environments in an oxytocin molecule have significant electrostatic influence on its chiral center, it is compensated by solvent induced charges. This gives a reasonable explanation to experimental observations. GHO-MD simulations starting from different experimental structures of insulin indicate that existence of the disulfide bridges with negative dihedral angles is crucial.

  10. A QM/MM-MD study on protein electronic properties: Circular dichroism spectra of oxytocin and insulin

    Energy Technology Data Exchange (ETDEWEB)

    Kitagawa, Yuya [Graduate School of System Informatics, Kobe University, Kobe 657-8501 (Japan); CREST, Japan Science and Technology Agency (JST), 4-1-8 Honcho Kawaguchi, Saitama 332-0012 (Japan); Akinaga, Yoshinobu [RIKEN Advanced Institute for Computational Science, Kobe 650-0047 (Japan); Kawashima, Yukio [Department of Chemistry, Graduate School of Sciences, Kyushu University, Fukuoka 812-8581 (Japan); Institute of Advanced Research, Kyushu University, Fukuoka 812-8581 (Japan); Jung, Jaewoon [RIKEN Advanced Institute for Computational Science, Kobe 650-0047 (Japan); Ten-no, Seiichiro, E-mail: tenno@cs.kobe-u.ac.jp [Graduate School of System Informatics, Kobe University, Kobe 657-8501 (Japan); CREST, Japan Science and Technology Agency (JST), 4-1-8 Honcho Kawaguchi, Saitama 332-0012 (Japan)

    2012-06-05

    A QM/MM (quantum-mechanical/molecular-mechanical) molecular-dynamics approach based on the generalized hybrid-orbital (GHO) method, in conjunction with the second-order perturbation (MP2) theory and the second-order approximate coupled-cluster (CC2) model, is employed to calculate electronic property accounting for a protein environment. Circular dichroism (CD) spectra originating from chiral disulfide bridges of oxytocin and insulin at room temperature are computed. It is shown that the sampling of thermal fluctuation of molecular geometries facilitated by the GHO-MD method plays an important role in the obtained spectra. It is demonstrated that, while the protein environments in an oxytocin molecule have significant electrostatic influence on its chiral center, it is compensated by solvent induced charges. This gives a reasonable explanation to experimental observations. GHO-MD simulations starting from different experimental structures of insulin indicate that existence of the disulfide bridges with negative dihedral angles is crucial.

  11. On the interplay between chirality and exciton coupling: a DFT calculation of the circular dichroism in π-stacked ethylene.

    Science.gov (United States)

    Norman, Patrick; Linares, Mathieu

    2014-09-01

    The chirality of stacked weakly interacting π-systems was interpreted in terms of Frenkel exciton states and the formation of excitonic circular dichroism (CD) bands was monitored for ethylene stacks of varying sizes. Convergence of CD bands with respect to the system size was observed for stacks involving around 10 molecules. By means of rotation around the C-C double bond in ethylene, chirality was induced in the monomeric system and which was shown to dominate the spectral responses, even for polymer aggregates. In helical assemblies of chiral entities, there will always be a mix of excitonic and monomeric contributions to the CD signal and it is demonstrated that the complex polarization propagator approach in combination with Density Functional Theory is a suitable method to address this situation.

  12. Drug binding to human serum albumin: abridged review of results obtained with high-performance liquid chromatography and circular dichroism.

    Science.gov (United States)

    Ascoli, Giorgio A; Domenici, Enrico; Bertucci, Carlo

    2006-09-01

    The drug binding to plasma and tissue proteins are fundamental factors in determining the overall pharmacological activity of a drug. Human serum albumin (HSA), together with alpha1-acid glycoprotein (AGP), are the most important plasma proteins, which act as drug carriers, with drug pharmacokinetic implications, resulting in important clinical impacts for drugs that have a relatively narrow therapeutic index. This review focuses on the combination of biochromatography and circular dichroism as an effective approach for the characterization of albumin binding sites and their enantioselectivity. Furthermore, their applications to the study of changes in the binding properties of the protein arising by the reversible or covalent binding of drugs are discussed, and examples of physiological relevance reported. Perspectives of these studies reside in supporting the development of new drugs, which require miniaturization to facilitate the screening of classes of compounds for their binding to the target protein, and a deeper characterization of the mechanisms involved in the molecular recognition processes.

  13. Toroidal Interaction and Propeller Chirality of Hexaarylbenzenes. Dynamic Domino Inversion Revealed by Combined Experimental and Theoretical Circular Dichroism Studies.

    Science.gov (United States)

    Kosaka, Tomoyo; Inoue, Yoshihisa; Mori, Tadashi

    2016-03-01

    Hexaarylbenzenes (HABs) have greatly attracted much attention due to their unique propeller-shaped structure and potential application in materials science, such as liquid crystals, molecular capsules/rotors, redox materials, nonlinear optical materials, as well as molecular wires. Less attention has however been paid to their propeller chirality. By introducing small point-chiral group(s) at the periphery of HABs, propeller chirality was effectively induced, provoking strong Cotton effects in the circular dichroism (CD) spectrum. Temperature and solvent polarity manipulate the dynamics of propeller inversion in solution. As such, whizzing toroids become more substantial in polar solvents and at an elevated temperature, where radial aromatic rings (propeller blades) prefer orthogonal alignment against the central benzene ring (C6 core), maximizing toroidal interactions.

  14. Present status of vacuum ultraviolet natural circular dichroism measurement system using polarizing undulator at TERAS BL5 beamline

    Energy Technology Data Exchange (ETDEWEB)

    Tanaka, Masahito, E-mail: masahito-tanaka@aist.go.j [Research Institute of Instrumentation Frontier, National Institute of Advanced Industrial Science and Technology (AIST), Central 2, Umezono 1-1-1, Tsukuba, Ibaraki 305-8568 (Japan); Yagi-Watanabe, Kazutoshi; Kaneko, Fusae [Research Institute of Instrumentation Frontier, National Institute of Advanced Industrial Science and Technology (AIST), Central 2, Umezono 1-1-1, Tsukuba, Ibaraki 305-8568 (Japan); Nakagawa, Kazumichi [Graduate School of Human Development and Environment, Kobe University, Tsurukabuto 3-11, Nada-ku, Kobe 657-8501 (Japan)

    2010-08-15

    The study of natural circular dichroism (CD) in the vacuum and extreme ultraviolet (VUV and EUV) regions has been providing us with chirality and structural information on biomolecules. We have developed the beamline BL5 at TERAS, Tsukuba, which is equipped with a compact Onuki-type polarizing undulator. This beamline is dedicated to measuring the CD spectra in the VUV and EUV regions for the photon energy region of 5-40 eV. The use of a polarization modulation technique with a polarizing undulator is essential for detecting a weak CD signal. Using this CD system, the natural CD spectrum has been measured in the EUV region up to 40 eV for the first time. In addition, the differences and the similarities between the CD spectra of four amino acid films (alanine, valine, leucine, and phenylalanine) in the VUV region up to 9.5 eV are determined.

  15. Domain wall velocity measurement in permalloy nanowires with X-ray magnetic circular dichroism imaging and single shot Kerr microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Moore, T.A., E-mail: t.a.moore@physics.or [Fachbereich Physik, Universitaet Konstanz, Universitaetsstrasse 10, 78457 Konstanz (Germany); Klaeui, M.; Heyne, L.; Moehrke, P. [Fachbereich Physik, Universitaet Konstanz, Universitaetsstrasse 10, 78457 Konstanz (Germany); Backes, D.; Rhensius, J. [Fachbereich Physik, Universitaet Konstanz, Universitaetsstrasse 10, 78457 Konstanz (Germany); Laboratory for Micro- and Nanotechnology, Paul Scherrer Institut, 5232 Villigen PSI (Switzerland); Ruediger, U. [Fachbereich Physik, Universitaet Konstanz, Universitaetsstrasse 10, 78457 Konstanz (Germany); Heyderman, L.J. [Laboratory for Micro- and Nanotechnology, Paul Scherrer Institut, 5232 Villigen PSI (Switzerland); Mentes, T.O.; Nino, M.A.; Locatelli, A. [Sincrotrone Trieste, 34012 Basovizza-Trieste (Italy); Potenza, A.; Marchetto, H.; Cavill, S.; Dhesi, S.S. [Diamond Light Source Ltd., Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0DE (United Kingdom)

    2010-05-15

    Domain walls (DWs) propagated along nanoscale magnetic wires by current or field pulses could potentially be used for data storage or logic applications, but the understanding of the DW dynamics, particularly under the influence of spin-polarized current, is incomplete. Measuring the velocity can give insights into the physics of the DW motion. Here we demonstrate DW velocity measurements in permalloy (Ni{sub 80}Fe{sub 20}) nanowires (1500 nm width and 20 nm thickness) using the techniques of X-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM) to image the magnetic contrast in the nanowires, and single shot Kerr microscopy, which allows for dynamic measurements. The magnetic imaging yields the average velocity as well as information on the DW spin structure, whereas the single shot method highlights the stochastic nature of the DW motion.

  16. X-ray magnetic circular dichroism and small angle neutron scattering study of thiol capped gold nanoparticles.

    Energy Technology Data Exchange (ETDEWEB)

    de la Venta, J.; Bouzas, V.; Pucci, A.; Laguna-Marco, M. A.; Haskel, D.; Pinel, E. F.; te Velthuis, S. G. E.; Hoffmann, A.; Lal, J.; Bleuel, M.; Ruggeri, G.; de Julian, C.; Garcia, M. A.; Univ. Complutense de Madrid; Inst. de Magnetismo Aplicado UCM; Univ. Pisa; Univ. di Padova

    2009-11-01

    X-ray magnetic circular dichroism (XMCD) and Small Angle Neutron Scattering (SANS) measurements were performed on thiol capped Au nanoparticles (NPs) embedded into polyethylene. An XMCD signal of 0.8 {center_dot} 10{sup -4} was found at the Au L{sub 3} edge of thiol capped Au NPs embedded in a polyethylene matrix for which Superconducting Quantum Interference Device (SQUID) magnetometry yielded a saturation magnetization, M{sub s}, of 0.06 emu/g{sub Au}. SANS measurements showed that the 3.2 nm average-diameter nanoparticles are 28% polydispersed, but no detectable SANS magnetic signal was found with the resolution and sensitivity accessible with the neutron experiment. A comparison with previous experiments carried out on Au NPs and multilayers, yield to different values between XMCD signals and magnetization measured by SQUID magnetometer. We discuss the origin of those differences.

  17. X-ray magnetic circular dichroism and small angle neutron scattering studies of thiol capped gold nanoparticles.

    Energy Technology Data Exchange (ETDEWEB)

    de la Venta, J.; Bouzas, V.; Pucci, A.; Laguna-Marco, M. A.; Haskel, D.; te Velthuis, S. G. E; Hoffmann, A.; Lal, J.; Bleuel, M.; Ruggeri, G.; de Julian Fernandez, C.; Garcia, M. A.; Univ.Complutense de Madrid; Inst. de Magnetismo Aplicado; Univ. of Pisa; Lab. di Magnetismo Molecolare

    2009-01-01

    X-ray magnetic circular dichroism (XMCD) and Small Angle Neutron Scattering (SANS) measurements were performed on thiol capped Au nanoparticles (NPs) embedded into polyethylene. An XMCD signal of 0.8 {center_dot} 10{sup -4} was found at the Au L{sub 3} edge of thiol capped Au NPs embedded in a polyethylene matrix for which Superconducting Quantum Interference Device (SQUID) magnetometry yielded a saturation magnetization, M{sub s}, of 0.06 emu/g{sub Au}. SANS measurements showed that the 3.2 nm average-diameter nanoparticles are 28% polydispersed, but no detectable SANS magnetic signal was found with the resolution and sensitivity accessible with the neutron experiment. A comparison with previous experiments carried out on Au NPs and multilayers, yield to different values between XMCD signals and magnetization measured by SQUID magnetometer. We discuss the origin of those differences.

  18. Soft x-ray circular dichroism and scattering using a modulated elliptically polarizing wiggler and double synchronous detection

    Energy Technology Data Exchange (ETDEWEB)

    Sutherland, J.C.; Polewski, K.; Monteleone, D.C. [and others

    1998-01-23

    We have constructed an experimental station (beamline) at the National Synchrotron Light Source to measure circular dichroism (CD) using soft x-rays (250 {le} hv {le} 900 eV) from a time modulated elliptically polarizing wiggler. The polarization of the soft x-ray beam switches periodically between two opposite polarizations, hence permitting the use of phase-sensitive (lock-in) detection. While the wiggler can be modulated at frequencies up to 100 Hz, switching transients limit the actual practical frequency to {approx}25 Hz. With analog detection, switching transients are blocked by a chopper synchronized to the frequency and phase of the wiggler. The CD is obtained from the ratio of the signal recovered at the frequency of polarization modulation, f, to the average beam intensity, which is recovered by synchronous detection at frequency 2f.

  19. 4f orbital and spin magnetism in cerium intermetallic compounds studied by magnetic circular x-ray dichroism

    Science.gov (United States)

    Schillé, J. Ph.; Bertran, F.; Finazzi, M.; Brouder, Ch.; Kappler, J. P.; Krill, G.

    1994-08-01

    Magnetic circular x-ray dichroism experiments at the M4,5 absorption edges of cerium in the intermetallic compounds CeCuSi, CeRh3B2, and CeFe2 are reported. By applying general sum rules, it is shown that these experiments are able to yield both the magnitude and the direction of the 4f magnetic moment on Ce. An estimation of the orbital contribution to those 4f moments is given. Our experiments demonstrate the existence of a 4f magnetic moment on Ce in CeFe2 and confirm the extreme sensitivity of the 4f orbital contribution to the degree of localization of the 4f electrons. This 4f orbital contribution is significantly higher than the one predicted from spin-resolved band-structure calculations.

  20. Determination of levamisole and tetramisole in seized cocaine samples by enantioselective high-performance liquid chromatography and circular dichroism detection.

    Science.gov (United States)

    Bertucci, Carlo; Tedesco, Daniele; Fabini, Edoardo; Di Pietra, Anna Maria; Rossi, Francesca; Garagnani, Marco; Del Borrello, Elia; Andrisano, Vincenza

    2014-10-10

    Levamisole, an anthelmintic drug, has been increasingly employed as an adulterant of illicit street cocaine over the last decade; recently, the use of tetramisole, the racemic mixture of levamisole and its enantiomer dexamisole, was also occasionally observed. A new enantioselective high-performance liquid chromatography (HPLC) method, performed on cellulose tris(3,5-dimethylphenylcarbamate) chiral stationary phases in normal-phase mode, was validated to determine the enantiomeric composition of tetramisole enantiomers in seized cocaine samples. Furthermore, the hyphenation of the validated HPLC method with a circular dichroism (CD) detection system allowed the direct determination of elution order and a selective monitoring of levamisole and dexamisole in the presence of possible interferences. The method was applied to the identification and quantitation of the two enantiomers of tetramisole in seized street cocaine samples.

  1. A vibrational circular dichroism implementation within a Slater-type-orbital based density functional framework and its application to hexa- and hepta-helicenes

    NARCIS (Netherlands)

    Baerends, Evert; Neugebauer, Johannes; Nicu, Valentin; Wolff, Stephen

    2008-01-01

    We describe the implementation of the rotational strengths for vibrational circular dichroism (VCD) in the Slater-type orbital based Amsterdam Density Functional (ADF) package. We show that our implementation, which makes use of analytical derivative techniques and London atomic orbitals, yields o

  2. Infrared and circular dichroism spectroscopic characterisation of secondary structure components of a water treatment coagulant protein extracted from Moringa oleifera seeds.

    Science.gov (United States)

    Kwaambwa, H M; Maikokera, R

    2008-06-15

    The secondary structure of a water treatment coagulant protein extracted from Moringa oleifera (MO) seeds has been investigated by Fourier transform infrared spectroscopy (FTIR) in the dried state, and by circular dichroism (CD) spectroscopy. The FTIR and CD spectra indicate that the secondary structure of the protein is dominated by alpha-helix. The FTIR spectrum recorded two distinct and strong absorption bands at 1656 cm(-1) and 1542 cm(-1), in the usual range of absorption of helices of proteins. The CD spectrum showed the shape of mainly alpha-helical secondary structure (estimated to be 58+/-4%) characteristic of negative ellipticity bands near 222 nm and 208 nm and a positive band at 192 nm. The beta-sheet structure composition was estimated to be 10+/-3% whereas unordered structures were around 33%. Changes in solution pH affected the protein secondary structure significantly only at pH values above 10, as indicated by CD spectra, whereas ionic strength had minimal effect. CD data also showed that sodium dodecyl sulphate (SDS) interacts with the coagulant protein and modifies the protein conformation. The surfactant-induced conformational change of the coagulant protein was confirmed by quenching of tryptophan fluorescence of the protein.

  3. Theoretical description of circular dichroism in photoelectron angular distributions of randomly oriented chiral molecules after multi-photon photoionization

    Science.gov (United States)

    Goetz, R. E.; Isaev, T. A.; Nikoobakht, B.; Berger, R.; Koch, C. P.

    2017-01-01

    Photoelectron circular dichroism refers to the forward/backward asymmetry in the photoelectron angular distribution with respect to the propagation axis of circularly polarized light. It has recently been demonstrated in femtosecond multi-photon photoionization experiments with randomly oriented camphor and fenchone molecules [C. Lux et al., Angew. Chem., Int. Ed. 51, 4755 (2012) and C. S. Lehmann et al., J. Chem. Phys. 139, 234307 (2013)]. A theoretical framework describing this process as (2+1) resonantly enhanced multi-photon ionization is constructed, which consists of two-photon photoselection from randomly oriented molecules and successive one-photon ionization of the photoselected molecules. It combines perturbation theory for the light-matter interaction with ab initio calculations for the two-photon absorption and a single-center expansion of the photoelectron wavefunction in terms of hydrogenic continuum functions. It is verified that the model correctly reproduces the basic symmetry behavior expected under exchange of handedness and light helicity. When applied to fenchone and camphor, semi-quantitative agreement with the experimental data is found, for which a sufficient d wave character of the electronically excited intermediate state is crucial.

  4. X-ray magnetic circular dichroism study of Dy-doped Bi2Te3 topological insulator thin films

    Science.gov (United States)

    Figueroa, A. I.; Baker, A. A.; Harrison, S. E.; Kummer, K.; van der Laan, G.; Hesjedal, T.

    2017-01-01

    Magnetic doping of topological insulators (TIs) is crucial for unlocking novel quantum phenomena, paving the way for spintronics applications. Recently, we have shown that doping with rare earth ions introduces large magnetic moments and allows for high doping concentrations without the loss of crystal quality, however no long range magnetic order was observed. In Dy-doped Bi2Te3 we found a band gap opening above a critical doping concentration, despite the paramagnetic bulk behavior. Here, we present a surface-sensitive x-ray magnetic circular dichroism (XMCD) study of an in situ cleaved film in the cleanest possible environment. The Dy M4,5 absorption spectra measured with circularly polarized x-rays are fitted using multiplet calculations to obtain the effective magnetic moment. Arrott-Noakes plots, measured by the Dy M5 XMCD as a function of field at low temperatures, give a negative transition temperature. The evaporation of a ferromagnetic Co thin film did not introduce ferromagnetic ordering of the Dy dopants either; instead a lowering of the transition temperature was observed, pointing towards an antiferromagnetic ordering scenario. This result shows that there is a competition between the magnetic exchange interaction and the Zeeman interaction. The latter favors the Co and Dy magnetic moments to be both aligned along the direction of the applied magnetic field, while the exchange interaction is minimized if the Dy and Co atoms are antiferromagnetically coupled, as in zero applied field.

  5. Direct evidence of Ni magnetic moment in TbNi{sub 2}Mn—X-ray magnetic circular dichroism

    Energy Technology Data Exchange (ETDEWEB)

    Yu, D.H., E-mail: dyu@ansto.gov.au [Bragg Institute, Australian Nuclear Science and Technology Organisation, Lucas Heights, Sydney, NSW 2234 (Australia); Huang, Meng-Jie [National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30076, Taiwan (China); Wang, J.L. [Bragg Institute, Australian Nuclear Science and Technology Organisation, Lucas Heights, Sydney, NSW 2234 (Australia); School of Physical, Environmental and Mathematical Sciences, University of New South Wales, Canberra at the Australian Defense Force Academy, Sydney, ACT 2600 (Australia); Institute for Superconductivity and Electronic Materials, University of Wollongong, Wollongong, NSW 2522 (Australia); Su, Hui-Chia; Lin, Hong-Ji; Chen, Chien-Te [National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30076, Taiwan (China); Campbell, S.J. [School of Physical, Environmental and Mathematical Sciences, University of New South Wales, Canberra at the Australian Defense Force Academy, Sydney, ACT 2600 (Australia)

    2014-12-15

    We have investigated the individual magnetic moments of Ni, Mn and Tb atoms in the intermetallic compound TbNi{sub 2}Mn in the Laves phase (magnetic phase transition temperature T{sub C} ∼131 K) by X-ray magnetic circular dichroism (XMCD) studies at 300 K, 80 K and 20 K. Analyses of the experimental results reveal that Ni atoms at 20 K in an applied magnetic field of 1 T carry an intrinsic magnetic moment of spin and orbital magnetic moment contributions 0.53±0.01 μ{sub B} and 0.05±0.01 μ{sub B}, respectively. These moment values are similar to those of the maximum saturated moment of Ni element. A very small magnetic moment of order <0.1 μ{sub B} has been measured for Mn. This suggests that Mn is antiferromagnetically ordered across the two nearly equally occupied sites of 16d and 8a. A magnetic moment of up to ∼0.3 μ{sub B} has been observed for the Tb atoms. Identification of a magnetic moment on the Ni atoms has provided further evidence for the mechanism of enhancement of the magnetic phase transition temperature in TbNi{sub 2}Mn compared with TbNi{sub 2} (T{sub C}∼37.5 K) and TbMn{sub 2} (T{sub C}∼54 K) due to rare earth–transition metal (R–T) and transition metal–transition metal (T–T) interactions. The behaviour of the X-ray magnetic circular dichroism spectra of TbNi{sub 2}Mn at 300 K, 80 K and 20 K – above and below the magnetic ordering temperature T{sub C} ∼131 K – is discussed. - Highlights: • We study the magnetic moment of TbNi{sub 2}Mn with XMCD. • We observe directly the Ni intrinsic magnetic moment in TbNi{sub 2}Mn. • We find that Mn ordered antiferromagnetically across the 16d and 8a sites. • We confirm the mechanism for increasing the magnetic phase transition temperature.

  6. All-optical switching in granular ferromagnets caused by magnetic circular dichroism

    Science.gov (United States)

    Ellis, Matthew O. A.; Fullerton, Eric E.; Chantrell, Roy W.

    2016-07-01

    Magnetic recording using circularly polarised femto-second laser pulses is an emerging technology that would allow write speeds much faster than existing field driven methods. However, the mechanism that drives the magnetisation switching in ferromagnets is unclear. Recent theories suggest that the interaction of the light with the magnetised media induces an opto-magnetic field within the media, known as the inverse Faraday effect. Here we show that an alternative mechanism, driven by thermal excitation over the anisotropy energy barrier and a difference in the energy absorption depending on polarisation, can create a net magnetisation over a series of laser pulses in an ensemble of single domain grains. Only a small difference in the absorption is required to reach magnetisation levels observed experimentally and the model does not preclude the role of the inverse Faraday effect but removes the necessity that the opto-magnetic field is 10 s of Tesla in strength.

  7. Dispersion of rotation of polarization plane and circular dichroism for alkaline atoms in intense radiation fields

    Science.gov (United States)

    Karagodova, Tamara Y.; Kuptsova, Anna V.

    1998-10-01

    The method of computer simulations on nonlinear resonant magneto-optical effects developed for real multi-level atoms in the two laser fields of arbitrary intensity and external magnetic field is applied for the polarization effects of different types calculations and investigations of the dependence of the characteristics of these effects on magnetic field strength, intensities, polarizations and detunings of laser fields for alkaline atoms. The essence of the method consists in simulations and analysis of the plots of dependence of quasienergies on parameters (detunings and intensities of radiation fields, magnetic field strength), which are obtained with the help of sorting subprogram, and selection of suitable algorithms for calculations of characteristics of nonlinear resonant magneto-optical effects. One-photon and two photon resonant effects are investigated for wide range of magnetic field strength from Zeeman to Paschen Back effects. Some new features in the spectra of rotation of plane of polarization and circular dicohroizm of different types are predicted. The results show the agreement with known experiments. Such calculations of nonlinear resonant magneto-optical effects in the intense laser fields resonant to adjacent transitions and magnetic field show the opportunity of investigation the modifications of electronic structure due to intense radiation fields and strong external magnetic field in atomic gases and also may be used for the treatment of new methods of phase-polarization selection of modes of tunable lasers.

  8. Plasmonic circular dichroism of 310- and α-helix using a discrete interaction model/quantum mechanics method.

    Science.gov (United States)

    Chulhai, Dhabih V; Jensen, Lasse

    2015-05-28

    Plasmonic circular dichroism (CD) of chiral molecules in the near field of plasmonic nanoparticles (NPs) may be used to enhance molecular CD signatures or to induce a CD signal at the plasmon resonance. A recent few-states theory explored these effects for model systems and showed an orientation dependence of the sign of the induced CD signal for spherical NPs. Here, we use the discrete interaction model/quantum mechanical (DIM/QM) method to simulate the CD and plasmonic CD of the 310- and α-helix conformations of a short alanine peptide. We find that the interactions between the molecule and the plasmon lead to significant changes in the CD spectra. In the plasmon region, we find that the sign of the CD depends strongly on the orientation of the molecule as well as specific interactions with the NP through image dipole effects. A small enhancement of the CD is found in the molecular region of the spectrum, however, the molecular signatures may be significantly altered through interactions with the NP. We also show that the image dipole effect can result in induced plasmonic CD even for achiral molecules. Overall, we find that the specific interactions with the NP can lead to large changes to the CD spectrum that complicates the interpretation of the results.

  9. An atomic orbital based real-time time-dependent density functional theory for computing electronic circular dichroism band spectra.

    Science.gov (United States)

    Goings, Joshua J; Li, Xiaosong

    2016-06-21

    One of the challenges of interpreting electronic circular dichroism (ECD) band spectra is that different states may have different rotatory strength signs, determined by their absolute configuration. If the states are closely spaced and opposite in sign, observed transitions may be washed out by nearby states, unlike absorption spectra where transitions are always positive additive. To accurately compute ECD bands, it is necessary to compute a large number of excited states, which may be prohibitively costly if one uses the linear-response time-dependent density functional theory (TDDFT) framework. Here we implement a real-time, atomic-orbital based TDDFT method for computing the entire ECD spectrum simultaneously. The method is advantageous for large systems with a high density of states. In contrast to previous implementations based on real-space grids, the method is variational, independent of nuclear orientation, and does not rely on pseudopotential approximations, making it suitable for computation of chiroptical properties well into the X-ray regime.

  10. Vibrational circular dichroism from ab initio molecular dynamics and nuclear velocity perturbation theory in the liquid phase

    Science.gov (United States)

    Scherrer, Arne; Vuilleumier, Rodolphe; Sebastiani, Daniel

    2016-08-01

    We report the first fully ab initio calculation of dynamical vibrational circular dichroism spectra in the liquid phase using nuclear velocity perturbation theory (NVPT) derived electronic currents. Our approach is rigorous and general and thus capable of treating weak interactions of chiral molecules as, e.g., chirality transfer from a chiral molecule to an achiral solvent. We use an implementation of the NVPT that is projected along the dynamics to obtain the current and magnetic dipole moments required for accurate intensities. The gauge problem in the liquid phase is resolved in a twofold approach. The electronic expectation values are evaluated in a distributed origin gauge, employing maximally localized Wannier orbitals. In a second step, the gauge invariant spectrum is obtained in terms of a scaled molecular moments, which allows to systematically include solvent effects while keeping a significant signal-to-noise ratio. We give a thorough analysis and discussion of this choice of gauge for the liquid phase. At low temperatures, we recover the established double harmonic approximation. The methodology is applied to chiral molecules ((S)-d2-oxirane and (R)-propylene-oxide) in the gas phase and in solution. We find an excellent agreement with the theoretical and experimental references, including the emergence of signals due to chirality transfer from the solute to the (achiral) solvent.

  11. Co K-edge magnetic circular dichroism across the spin state transition in LaCoO3 single crystal

    Science.gov (United States)

    Efimov, V.; Ignatov, A.; Troyanchuk, I. O.; Sikolenko, V. V.; Rogalev, A.; Wilhelm, F.; Efimova, E.; Tiutiunnikov, S. I.; Karpinsky, D.; Kriventsov, V.; Yakimchuk, E.; Molodtsov, S.; Sainctavit, P.; Prabhakaran, D.

    2016-05-01

    We report on Co K-edge x-ray magnetic circular dichroism (XMCD) measurements of LaCoO3 single crystal in temperature range from 5 to 300 K and external magnetic field of 17 T. The response consists of pre-edge (at 7712 eV) and bi-polar peak (up at 7727, down at 7731 eV) with amplitudes, respectively, less than 10-3 and 10-2 of the Co K-edge jump. Using the sum rule the orbital magnetic moment of 4p Co is evaluated. Its temperature dependence reaches a maximum of (2.7 ± 0.9) x10-3 μB at 120 K, following the trend for the total magnetic moment on the Co obtained from the superconducting quantum interference device measurements. However, on warming from 25 to 120 K, the orbital magnetic moment of the 4p Co doubles while total magnetic moment of Co increases 10 times. First principle calculations are in order to relate the Co K-edge XMCD results to the orbital and spin moment of 3d Co.

  12. Dumbbell-type fullerene-steroid hybrids: a join experimental and theoretical investigation for conformational, configurational, and circular dichroism assignments.

    Science.gov (United States)

    Ruíz, Alberto; Morera-Boado, Cercis; Almagro, Luis; Coro, Julieta; Maroto, Enrique E; Herranz, María Ángeles; Filippone, Salvatore; Molero, Dolores; Martínez-Álvarez, Roberto; Garcia de la Vega, José M; Suárez, Margarita; Martín, Nazario

    2014-04-18

    New [60]fullerene-steroid conjugates (4-6) have been synthesized by 1,3-dipolar cycloaddition and Bingel-Hirsch cyclopropanation reactions from suitably functionalized epiandrosterone and [60]fullerene. Since a new stereocenter is created in the formation of the Prato monoaduct, two different diastereomers were isolated by HPLC (4, 5) whose absolute configurations were assigned according to the highly reliable "sector rule" on fullerenes. A further reaction of the malonate-containing diastereomer 5 with a second C60 molecule has afforded dumbbell fullerene 6 in which the two fullerene units are covalently connected through an epiandrosterone moiety. The new compounds have been spectroscopically characterized and their redox potentials, determined by cyclic voltametry, reveal three reversible reduction waves for hybrids 4 and 5, whereas these signals are split in dumbbell 6. Theoretical calculations at semiempirical (AM1) and single point B3LYP/6-31G(d) levels have predicted the most stable conformations for the hybrid compounds (4-6), showing the importance of the chlorine atom on the D ring of the steroid. Furthermore, TDDFT calculations have allowed assignments of the experimentally determined circular dichroism (CD) of the [60]fullerene-steroid hybrids based on the sign and position of the Cotton effects, despite the exceptionally large systems under study.

  13. X-ray magnetic circular dichroism study of epitaxial magnetite ultrathin film on MgO(100)

    Energy Technology Data Exchange (ETDEWEB)

    Liu, W. Q.; Xu, Y. B., E-mail: yongbing.xu@york.ac.uk, E-mail: rzhang@nju.edu.cn [York-Nanjing International Center for Spintronics (YNICS), School of Electronics Science and Engineering, Nanjing University, Nanjing 210093 (China); Spintronics and Nanodevice Laboratory, Department of Electronics, University of York, York YO10 5DD (United Kingdom); Song, M. Y.; Lin, J. G. [Center for Condensed Matter Sciences, National Taiwan University, Taipei 106, Taiwan (China); Maltby, N. J.; Li, S. P. [Spintronics and Nanodevice Laboratory, Department of Electronics, University of York, York YO10 5DD (United Kingdom); Samant, M. G.; Parkin, S. S. P. [IBM Research Division, Almaden Research Center, San Jose, California 95120 (United States); Bencok, P.; Steadman, Paul; Dobrynin, Alexey [Diamond Light Source, Didcot OX11 0DE (United Kingdom); Zhang, R., E-mail: yongbing.xu@york.ac.uk, E-mail: rzhang@nju.edu.cn [York-Nanjing International Center for Spintronics (YNICS), School of Electronics Science and Engineering, Nanjing University, Nanjing 210093 (China)

    2015-05-07

    The spin and orbital magnetic moments of the Fe{sub 3}O{sub 4} epitaxial ultrathin film synthesized by plasma assisted simultaneous oxidization on MgO(100) have been studied with X-ray magnetic circular dichroism. The ultrathin film retains a rather large total magnetic moment, i.e., (2.73 ± 0.15) μ{sub B}/f.u., which is ∼70% of that for the bulk-like Fe{sub 3}O{sub 4}. A significant unquenched orbital moment up to 0.54 ± 0.05 μ{sub B}/f.u. was observed, which could come from the symmetry breaking at the Fe{sub 3}O{sub 4}/MgO interface. Such sizable orbital moment will add capacities to the Fe{sub 3}O{sub 4}-based spintronics devices in the magnetization reversal by the electric field.

  14. Unraveling the thermodynamics and kinetics of RNA assembly: surface plasmon resonance, isothermal titration calorimetry, and circular dichroism.

    Science.gov (United States)

    Hoogstraten, Charles G; Sumita, Minako; White, Neil A

    2014-01-01

    The mechanisms and driving forces of the assembly of RNA tertiary structure are a topic of much current interest. In several systems, including our own work in the docking transition of the hairpin ribozyme, intramolecular RNA tertiary folding has been converted into an intermolecular binding event, allowing the full power of contemporary biophysical techniques to be brought to bear on the analysis. We review the use of three such methods: circular dichroism to isolate the binding of multivalent cations coupled to tertiary assembly, surface plasmon resonance to determine the rates of association and dissociation, and isothermal titration calorimetry to dissect the thermodynamic contributions to RNA assembly events. We pay particular attention to practical aspects of these studies, such as careful preparation of samples with fixed free concentrations of cations in order to avoid errors due to ion depletion effects that are common in RNA systems. Examples of applications from our own work with the hairpin ribozyme are shown. Distinctions among the data handling procedures for the various techniques used and solution conditions encountered are also discussed.

  15. Validation of a method using an achiral liquid chromatography sorbent and a circular dichroism detector. Analysis of the efaroxan enantiomers.

    Science.gov (United States)

    Lorin, Marie; Delépée, Raphaël; Ribet, Jean-Paul; Morin, Philippe

    2007-02-01

    The known HPLC method using an achiral C8 silica sorbent and a circular dichroism (CD) detector for the determination of efaroxan enantiomeric excess has been validated. After optimization of the mobile phase, the enantiomers were detected at 278 nm offering maximum ellipticity between two optically active forms. The calibration curve of the anisotropy factor (g) versus the enantiomeric excess was linear with a correlation coefficient (r2) of 0.9985. The accuracy of the method was assessed by comparing the enantiomeric excess obtained by measuring the g factor (C8 column, CD and UV detections) with those determined by enantioselective HPLC (Chiralpak AD-H column, UV detection). Statistical tests (level of confidence of 95%) were assessed to compare the two orthogonal methods. The straight line gave a correlation coefficient of 0.9995, an intercept not significantly different from zero (0.0549) and a slope of 1.026. The precision evaluated on retention time (RSDmethod has the advantages of being fast and precise without using expensive chiral column. Non-enantioselective HPLC-CD was suitable for the simultaneous determination of the optical and chemical purity of efaroxan.

  16. Multireference ab initio studies of zero-field splitting and magnetic circular dichroism spectra of tetrahedral Co(II) complexes.

    Science.gov (United States)

    Sundararajan, Mahesh; Ganyushin, Dmitry; Ye, Shengfa; Neese, Frank

    2009-08-14

    A newly developed multireference (MR) ab initio method for the calculation of magnetic circular dichroism (MCD) spectra was calibrated through the calculation of the ground- and excited state properties of seven high-spin (S = 3/2) Co(II) complexes. The MCD spectra were computed by the explicit treatment of spin-orbit coupled (SOC) and spin-spin coupled (SSC) N-electron states. For the complexes studied in this work, we found that the SOC is more important than the SSC for determining the ground state zero field splitting (ZFS). Our computed ZFS parameter D for the [Co(PPh(3))(2)Cl(2)] model complex is -17.6 cm(-1), which is reasonably close to the experimental value of -14.8 cm(-1). Generally, the computed absorption and MCD spectra are in fair agreement with experiment for all investigated complexes. Thus, reliable electronic structure and spectroscopic predictions for medium sized transition metal complexes are feasible on the basis of this methodology. This characterizes the presented method as a promising tool for MCD spectra interpretations of transition metal complexes in a variety of areas of chemistry and biology.

  17. Complexation behavior of gelatin with amphiphilic drug imipramine hydrochloride as studied by conductimetry, surface tensiometry and circular dichroism studies.

    Science.gov (United States)

    Ali, Mohd Sajid; Anjum, Kahkashan; Khan, Javed M; Khan, Rizwan H; Kabir-ud-Din

    2011-01-01

    Herein we report our studies carried out on the interaction between IMP and gelatin in aqueous medium at 25°C using conductimetry, surface tensiometry and circular dichroism (CD) techniques. Both surface tensiometry and conductimetry results indicate that the drug interacts with the gelatin in a surfactant-like manner, i.e., both critical aggregation (cac) and polymer saturation points (psp) were observed. The interaction starts with the formation of a highly surface-active complex as revealed by the lowering of surface tension on the addition of drug to the macromolecule. The decrease in cac on increasing gelatin concentration is an indication of the strong interaction between gelatin and IMP. However, at low concentration of gelatin the interaction was not much strong as exposed by surface tension study, i.e., the cac was not very clear (as with higher gelatin concentrations). As usual, the psp increased on increasing the gelatin concentration and was always higher than the critical micelle concentration of the drug in pure aqueous medium. Using CD measurements the influence of IMP on the secondary structure of gelatin in aqueous solutions was also investigated. CD studies (performed at very low drug concentrations) illustrated that the random coil content of gelatin increases with increasing drug concentration. Free energies of aggregation (ΔG(agg)) and micellization (ΔG(mic)) were computed with the help of degrees of micelle ionization obtained from the specific conductivity - [IMP] plots.

  18. Determining the polarization state of an extreme ultraviolet free-electron laser beam using atomic circular dichroism.

    Science.gov (United States)

    Mazza, T; Ilchen, M; Rafipoor, A J; Callegari, C; Finetti, P; Plekan, O; Prince, K C; Richter, R; Danailov, M B; Demidovich, A; De Ninno, G; Grazioli, C; Ivanov, R; Mahne, N; Raimondi, L; Svetina, C; Avaldi, L; Bolognesi, P; Coreno, M; O'Keeffe, P; Di Fraia, M; Devetta, M; Ovcharenko, Y; Möller, Th; Lyamayev, V; Stienkemeier, F; Düsterer, S; Ueda, K; Costello, J T; Kazansky, A K; Kabachnik, N M; Meyer, M

    2014-04-16

    Ultrafast extreme ultraviolet and X-ray free-electron lasers are set to revolutionize many domains such as bio-photonics and materials science, in a manner similar to optical lasers over the past two decades. Although their number will grow steadily over the coming decade, their complete characterization remains an elusive goal. This represents a significant barrier to their wider adoption and hence to the full realization of their potential in modern photon sciences. Although a great deal of progress has been made on temporal characterization and wavefront measurements at ultrahigh extreme ultraviolet and X-ray intensities, only few, if any progress on accurately measuring other key parameters such as the state of polarization has emerged. Here we show that by combining ultra-short extreme ultraviolet free electron laser pulses from FERMI with near-infrared laser pulses, we can accurately measure the polarization state of a free electron laser beam in an elegant, non-invasive and straightforward manner using circular dichroism.

  19. Vibrational circular dichroism from ab initio molecular dynamics and nuclear velocity perturbation theory in the liquid phase.

    Science.gov (United States)

    Scherrer, Arne; Vuilleumier, Rodolphe; Sebastiani, Daniel

    2016-08-28

    We report the first fully ab initio calculation of dynamical vibrational circular dichroism spectra in the liquid phase using nuclear velocity perturbation theory (NVPT) derived electronic currents. Our approach is rigorous and general and thus capable of treating weak interactions of chiral molecules as, e.g., chirality transfer from a chiral molecule to an achiral solvent. We use an implementation of the NVPT that is projected along the dynamics to obtain the current and magnetic dipole moments required for accurate intensities. The gauge problem in the liquid phase is resolved in a twofold approach. The electronic expectation values are evaluated in a distributed origin gauge, employing maximally localized Wannier orbitals. In a second step, the gauge invariant spectrum is obtained in terms of a scaled molecular moments, which allows to systematically include solvent effects while keeping a significant signal-to-noise ratio. We give a thorough analysis and discussion of this choice of gauge for the liquid phase. At low temperatures, we recover the established double harmonic approximation. The methodology is applied to chiral molecules ((S)-d2-oxirane and (R)-propylene-oxide) in the gas phase and in solution. We find an excellent agreement with the theoretical and experimental references, including the emergence of signals due to chirality transfer from the solute to the (achiral) solvent.

  20. Microscopic Magnetic Properties of the Itinerant Metamagnet UCoAl by X-ray Magnetic Circular Dichroism

    Science.gov (United States)

    Combier, Tristan; Palacio-Morales, Alexandra; Sanchez, Jean-Pierre; Wilhelm, Fabrice; Pourret, Alexandre; Brison, Jean-Pascal; Aoki, Dai; Rogalev, Andrei

    2017-02-01

    The itinerant metamagnet UCoAl has been investigated by high field X-ray magnetic circular dichroism (XMCD) at the U M4,5 and Co K edges. The orbital and spin moments of U at 2.1 K for H || c applied below and above the first order metamagnetic transition field (HM) have been determined. The magnetism of UCoAl is dominated by the U moment. There is no evidence for any change of the orbital to spin moment ratio (˜-2.05) across HM and within the ferromagnetic phase up to 17 T. The possibility of a Fermi surface reconstruction at HM remains an open option. XMCD at the Co K-edge reveals the presence of a small Co 4p-orbital moment parallel to the macroscopic magnetization. In addition, the Co 3d-moment is estimated to be at most 0.1 μB at 17 T. The similar field dependence of the U and Co magnetizations indicates that the Co moment is induced by the U moment.

  1. X-ray magnetic circular dichroism: Orbital and spin moments of iron single-crystal thin film deposited on MgO substrate

    Institute of Scientific and Technical Information of China (English)

    LI Honghong; WANG Jie; LI Ruipeng; GUO Yuxian; WANG Feng; HU Zhiwei

    2005-01-01

    X-ray magnetic circular dichroism in absorption of the single-crystal iron layer deposited epitaxially on MgO substrate is studied. Spin and orbital moment, 0.069 and 2.33 -B, respectively, are calculated in terms of the XMCD sum rules. Our results are accordant to those published. Experiments show that the orbital moment would be decreased to that in bulk materials as iron film is thinned down, but spin moment changes little.

  2. A combined binding mechanism of nonionic ethoxylated surfactants to bovine serum albumin revealed by fluorescence and circular dichroism.

    Science.gov (United States)

    Iovescu, Alina; Băran, Adriana; Stîngă, Gabriela; Cantemir-Leontieş, Anca Ruxandra; Maxim, Monica Elisabeta; Anghel, Dan Florin

    2015-12-01

    The study systematically investigates aqueous mixtures of fixed bovine serum albumin (BSA) and various ethoxylated nonionic surfactants belonging to a homologous series or not. Mono-disperse tetra-(C12E4), hexa-(C12E6) and octa-ethyleneglycol mono-n-dodecyl ether (C12E8), and poly-disperse eicosa-ethyleneglycol mono-n-tetradecyl ether (C14EO20) are respectively employed. Fluorescence and circular dichroism measurements are performed at surfactant/protein molar ratios (rm)s lower and higher than one. We aim to get new insights into the binding mechanism of these species and to differentiate among the interaction abilities of these surfactants. The relative magnitude of the binding thermodynamic parameters by fluorescence, and the increase of α-helix prove that hydrogen bonding drives the interaction next to the hydrophobic attraction. C12En (n=4,6,8) develop more H bonds with the albumin than C14EO20 owing to a zigzag conformation of their short ethyleneoxide chains. Among the homologous surfactants, C12E6 has a slightly stronger interaction with BSA due to a maximal number of H bonds at a minimal hindering. Static fluorescence and dynamic fluorescence indicate an inter-conversion between the tryptophan (Trp) rotamers which happens around the surfactants critical micellar concentration. For C14EO20, the meander conformation of the polar group determines a less evident conversion of the Trp rotamers and smaller α-helix rise. Binding isotherms of the homologous surfactants and the fluorescence quenching mechanism by C12E6 are also provided.

  3. Expedient synthesis of novel pregnane-NSAIDs prodrugs, XRD, stereochemistry of their C-20 derivatives by circular dichroism, conformational analysis, their DFT and TD-DFT studies

    Science.gov (United States)

    Singh, Ranvijay Pratap; Sharma, Sonia; Kant, Rajni; Amandeep; Singh, Praveer; Sethi, Arun

    2016-02-01

    Four novel pregnane-NSAIDs prodrugs 3β-(2-(6-methoxynaphthalene-2yl) propionoxy)-16α-methoxy-pregn-5-ene-20-one (3), 16α-methoxy-pregn-5-ene-20-one-3yl-2(4-iso butyl phenyl) propanoate (4), 3β-(2-(6-methoxynaphthalene-2yl) propionoxy) 20-hydroxy-16α-methoxy-pregn-5-ene (5) and 20-hydroxy-16α-methoxy-pregn-5-ene-20-one-3yl-2(4-iso butyl phenyl) propanoate (6) have been synthesized. They were analyzed experimentally by spectroscopic techniques like 1H, 13C NMR, FT-IR, UV-visible spectroscopy, mass spectrometry and correlated by theoretical calculations. The structure and conformations of 3 was established by single crystal X-ray diffraction, which crystallized in orthorhombic form having P212121 space group. Absolute configuration of C-20 hydroxy derivatives 5 and 6 was established by circular dichroism (CD) analysis. Conformational analysis of 5 was carried out to determine the most stable conformation. The electronic properties, such as frontier orbitals, band gap energies, oscillator strength and wavelength have been calculated using time dependent density functional theory (TD-DFT). The vibrational wavenumbers have been calculated using DFT method and assigned with the help of potential energy distribution (PED). Global and local reactivity descriptors have been computed to predict reactivity and reactive sites in the molecule. First hyperpolarizability (β0) of synthesized compounds has been computed to evaluate non-linear optical (NLO) response. Molecular electrostatic potential (MEP) for synthesized compounds have also been determined to check their electrophilic or nucleophilic reactivity as well as reaction path.

  4. Studying the Stability of S-Layer Protein of Lactobacillus Acidophilus ATCC 4356 in Simulated Gastrointestinal Fluids Using SDS-PAGE and Circular Dichroism.

    Science.gov (United States)

    Eslami, Neda; Kermanshahi, Rouha Kasra; Erfan, Mohammad

    2013-01-01

    Crystalline arrays of proteinaceous subunits forming surface layers (S-layers) are now recognized as one of the most common outermost cell envelope components of prokaryotic organisms. The surface layer protein of Lactobacillus acidophilus ATCC4356 is composed of a single species of protein of apparent molecular weight of 43-46 KDa. Considering the Lactobacillus acidophilus ATCC4356 having the S-layer is stable in harsh gastrointestinal (GI) conditions, a protective role against destructive GI factors which has been proposed for these nanostructures. It opens interesting perspectives in the using and development of this S-layer as a protective coat for oral administration of unstable drug nanocarriers. To achieve this goal, it is necessary to study the in-vitro stability of the S-layers in the simulated gastrointestinal fluids (SGIF). This study was planned to evaluate the in-vitro stability of the extracted S-layer protein of Lactobacillus acidophilus ATCC4356 in SGIF using it as a protective coat in oral drug delivery. Sodium dodecyl sulfate gel electrophoresis (SDS-PAGE) and circular dichroism (CD) spectroscopy were used to study the stability of the S-layer protein incubated in SGIF. Both the SDS-PAGE and CD spectra results showed that Lactobacillus acidophilus ATCC4356 S-layer protein is stable in simulated gastric fluid (SGF) with pH = 2 up to 5 min. It is stable in SGF pH = 3.2 and above it, with and without pepsin. It is also stable in all the simulated intestinal fluids. This S-layer is also stable in all of the simulated intestinal fluids.

  5. Combination of chemometrically assisted voltammetry, calorimetry, and circular dichroism as a new method for the study of bioinorganic substances: application to selenocystine metal complexes.

    Science.gov (United States)

    Gusmão, Rui; Prohens, Rafel; Díaz-Cruz, José Manuel; Ariño, Cristina; Esteban, Miquel

    2012-02-01

    Selenium-containing compounds play an important role in antioxidant defense systems, binding to toxic metals, preventing their uptake into cells, and thus protecting cells from metal-induced formation of reactive oxygen species. Here, we present a proposal for a relatively new method as a complement to the more usual methods used in selenium studies. A systematic study of the metal-binding properties of selenocystine (SeCyst) in the presence of divalent metal cations (Cd, Co, Hg, Ni, and Zn) is reported. Isothermal titration calorimetry provides thermodynamic parameters of the systems. Titrations produced curves that could be fit reasonably well to the one set of sites model. The data clearly demonstrate that one M(2+) binds one SeCyst molecule, and the stable M(SeCyst) complex is formed under these conditions. The order of the SeCyst binding constant for the metal ions is Hg(2+) > Cd(2+) ~ Zn(2+) > Ni(2+)> Co(2+). Cadmium ion was selected as a modulator for the behavior of SeCyst in the presence of a nonessential metal, and zinc was selected for the case of an essential element. These interactions of SeCyst with Cd(2+) and Zn(2+), either individually or combined, were studied in aqueous buffered solutions at physiological pH by differential pulse polarography and circular dichroism spectroscopy. Furthermore, recently developed chemometric tools were applied to differential pulse polarography data obtained in mixtures of SeCyst and glutathione in the presence of Cd(2+) at physiological pH.

  6. Circular Dichroism in the 3d and 4d Core Photoabsorption for Ferromagnetic Ce Compounds —Interplay of Hybridization, Spin Orbit Interaction and Crystal Field—

    Science.gov (United States)

    Jo, Takeo; Imada, Shin

    1990-04-01

    The Ce 3d- and 4d-core photoabsorption spectra (3d XAS and 4d XAS) of ferromagnetic mixed valent Ce compounds are calculated on the basis of the impurity Anderson model. The model takes into account the Coulomb interaction producing multiplet structures, the spin-orbit interaction, the crystal field effect and the molecular field acting on the 4f spin. The calculation shows a strong circular dichroism even for the Ce magnetic moment of ˜0.5 μB. The dichroism is furthermore shown to be a powerful method to measure the spin and orbital contributions to the 4f moment. On the basis of the calculation, the 4f magnetic state of the ferromagnet CeRh3B2 is discussed.

  7. Lanthanide tris(β-diketonates) as useful probes for chirality determination of biological amino alcohols in vibrational circular dichroism: ligand to ligand chirality transfer in lanthanide coordination sphere.

    Science.gov (United States)

    Miyake, Hiroyuki; Terada, Keiko; Tsukube, Hiroshi

    2014-06-01

    A series of lanthanide tris(β-diketonates) functioned as useful chirality probes in the vibrational circular dichroism (VCD) characterization of biological amino alcohols. Various chiral amino alcohols induced intense VCD signals upon ternary complexation with racemic lanthanide tris(β-diketonates). The VCD signals observed around 1500 cm(-1) (β-diketonate IR absorption region) correlated well with the stereochemistry and enantiomeric purity of the targeted amino alcohol, while the corresponding monoalcohol, monoamine, and diol substrates induced very weak VCD signals. The high-coordination number and dynamic property of the lanthanide complex offer an effective chirality VCD probing of biological substrates.

  8. Magnetic anisotropy in Ta/CoFeB/MgO investigated by x-ray magnetic circular dichroism and first-principles calculation

    Energy Technology Data Exchange (ETDEWEB)

    Kanai, Shun [Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Tsujikawa, Masahito; Shirai, Masafumi [Center for Spintronics Integrated Systems, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Miura, Yoshio [Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Department of Electronics and Information Science, Kyoto Institute of Technology, Kyoto (Japan); Matsukura, Fumihiro, E-mail: f-matsu@wpi-aimr.tohoku.ac.jp; Ohno, Hideo [Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); WPI-Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan)

    2014-12-01

    We study the spin and orbital magnetic moments in Ta/Co{sub 0.4}Fe{sub 0.4}B{sub 0.2}/MgO by x-ray magnetic circular dichroism measurements as well as first-principles calculations, in order to clarify the origin of the perpendicular magnetic anisotropy. Both experimental and theoretical results show that orbital magnetic moment of Fe is more anisotropic than that of Co with respect to the magnetization direction. The anisotropy is larger for thinner CoFeB, indicating that Fe atoms at the interface with MgO contribute more than Co to the observed perpendicular magnetic anisotropy.

  9. Perpendicular magnetic anisotropy at the interface between ultrathin Fe film and MgO studied by angular-dependent x-ray magnetic circular dichroism

    Energy Technology Data Exchange (ETDEWEB)

    Okabayashi, J. [Research Center for Spectrochemistry, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan); Koo, J. W.; Mitani, S. [National Institute for Materials Science (NIMS), Tsukuba 305-0047 (Japan); Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8577 (Japan); Sukegawa, H. [National Institute for Materials Science (NIMS), Tsukuba 305-0047 (Japan); Takagi, Y.; Yokoyama, T. [Institute of Molecular Science, Okazaki, Aichi 444-8585 (Japan)

    2014-09-22

    Interface perpendicular magnetic anisotropy (PMA) in ultrathin Fe/MgO (001) has been investigated using angular-dependent x-ray magnetic circular dichroism (XMCD). We found that anisotropic orbital magnetic moments deduced from the analysis of XMCD contribute to the large PMA energies, whose values depend on the annealing temperature. The large PMA energies determined from magnetization measurements are related to those estimated from the XMCD and the anisotropic orbital magnetic moments through the spin-orbit interaction. The enhancement of anisotropic orbital magnetic moments can be explained mainly by the hybridization between the Fe 3d{sub z}{sup 2} and O 2p{sub z} states.

  10. Large anisotropic Fe orbital moments in perpendicularly magnetized Co2FeAl Heusler alloy thin films revealed by angular-dependent x-ray magnetic circular dichroism

    Science.gov (United States)

    Okabayashi, Jun; Sukegawa, Hiroaki; Wen, Zhenchao; Inomata, Koichiro; Mitani, Seiji

    2013-09-01

    Perpendicular magnetic anisotropy (PMA) in Heusler alloy Co2FeAl thin films sharing an interface with a MgO layer is investigated by angular-dependent x-ray magnetic circular dichroism. Orbital and spin magnetic moments are deduced separately for Fe and Co 3d electrons. In addition, the PMA energies are estimated using the orbital magnetic moments parallel and perpendicular to the film surfaces. We found that PMA in Co2FeAl is determined mainly by the contribution of Fe atoms with large orbital magnetic moments, which are enhanced at the interface between Co2FeAl and MgO. Furthermore, element specific magnetization curves of Fe and Co are found to be similar, suggesting the existence of ferromagnetic coupling between Fe and Co PMA directions.

  11. A high-performance liquid chromatography with circular dichroism detector for determination of stereochemistry of 6, 9-oxygen bridge dibenzocyclooctadiene lignans from kadsura coccinea.

    Science.gov (United States)

    Zhu, Hui; Xu, Liang; Yang, Shi-Lin; Li, He-Ran

    2015-10-01

    The stereochemistry of two 6, 9-oxygen bridge dibenzocyclooctadiene lignans from Kadsura coccinea, are difficult to separate and very unstable. The present study was designed to develop a high-performance liquid chromatography using circular dichroism detection for the analysis of the stereochemistry. A new 6, 9-oxygen bridge dibenzocyclooctadiene lignans named Kadsulignan Q was firstly found with an S-biphenyl configuration. The other compound was identified as Kadsulignan L with an R- biphenyl configuration. In order to obtain kinetic data on their reversible interconversion, the stability was measured at different deuterated solvents such as deuterated methanol, deuterated chloroform and deuterated dimethylsulfoxide. The lignans were more unstable and converted more easily in deuterated methanol than in deuterated chloroform and deuterated dimethylsulfoxide.

  12. Soft x-ray magnetic circular dichroism of L2{sub 1}-type Co{sub 2}FeGa Heusler alloy

    Energy Technology Data Exchange (ETDEWEB)

    Umetsu, R Y; Kainuma, R; Fukamichi, K [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Sendai 980-8577 (Japan); Nakamura, T [JASRI/SPring-8, 1-1-1 Kouto, Sayo, Hyogo 679-5198 (Japan); Kobayashi, K; Ishida, K [Department of Materials Science, Graduate School of Engineering, Tohoku University, 6-6-02 Aoba, Sendai 980-8579 (Japan); Sakuma, A, E-mail: rie@tagen.tohoku.ac.j [Department of Applied Physics, Graduate School of Engineering, Tohoku University, 6-6-08 Aoba, Sendai 980-8579 (Japan)

    2010-03-17

    Spin and orbital magnetic moments of the L2{sub 1}-type Co{sub 2}FeGa Heusler alloy have been investigated using x-ray magnetic circular dichroism spectra in the soft x-ray region. From the spectra of the L{sub 2,3}-edge of Co and Fe, the ratios of the orbital magnetic moment to the spin magnetic moment M{sub orb}/M{sub spin} are estimated to be 0.06 for Co and 0.02 for Fe, in agreement with the available theoretical values. The orbital magnetic moments of these two elements are small in line with theoretical results, reflecting the high symmetry of the L2{sub 1}-type crystal structure. Furthermore, it has been confirmed that the magnetic moment of Ga is induced in the present alloy.

  13. Quantitative x-ray magnetic circular dichroism mapping with high spatial resolution full-field magnetic transmission soft x-ray spectro-microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Robertson, MacCallum J. [Center for X-ray Optics, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Physics Department, University of California, Berkeley, California 94720 (United States); Agostino, Christopher J. [Physics Department, University of California, Berkeley, California 94720 (United States); National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); N' Diaye, Alpha T. [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Chen, Gong [National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Im, Mi-Young [Center for X-ray Optics, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Department of Emerging Materials Science, Daegu Gyeongbuk Institute of Science and Technology, Daegu 711-873 (Korea, Republic of); Fischer, Peter, E-mail: PJFischer@lbl.gov [Center for X-ray Optics, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Physics Department, University of California, Santa Cruz, California 94056 (United States)

    2015-05-07

    The spectroscopic analysis of X-ray magnetic circular dichroism (XMCD), which serves as strong and element-specific magnetic contrast in full-field magnetic transmission soft x-ray microscopy, is shown to provide information on the local distribution of spin (S) and orbital (L) magnetic moments down to a spatial resolution of 25 nm limited by the x-ray optics used in the x-ray microscope. The spatially resolved L/S ratio observed in a multilayered (Co 0.3 nm/Pt 0.5 nm) × 30 thin film exhibiting a strong perpendicular magnetic anisotropy decreases significantly in the vicinity of domain walls, indicating a non-uniform spin configuration in the vertical profile of a domain wall across the thin film. Quantitative XMCD mapping with x-ray spectro-microscopy will become an important characterization tool for systems with topological or engineered magnetization inhomogeneities.

  14. Ga+ ion irradiation-induced changes in magnetic anisotropy of a Pt/Co/Pt thin film studied by X-ray magnetic circular dichroism

    Directory of Open Access Journals (Sweden)

    Liedke M. O.

    2013-01-01

    Full Text Available Ga+ ion irradiation-induced changes in magnetic anisotropy of a Pt/Co/Pt ultrathin film are investigated by means of the X-ray magnetic circular dichroism (XMCD technique. A large difference in the Co orbital moment is observed between out-of-plane and in-plane directions of the film at moderate Ga+ fluences of ~1-2×1014 ions/cm2, which corresponds to the perpendicular magnetic anisotropy (PMA, while further increased fluences reduce the orbital moment difference, resulting in in-plane magnetization. In contrast, at much higher Ga+ fluences of ~5×1015 ions/cm2, at which PMA is observed again, no significant difference is found in the orbital moment of Co between out-of-plane and in-plane directions. Different origins are thus suggested for the appearance of PMA induced by the irradiation between moderate and high Ga+ fluences.

  15. Nuclear velocity perturbation theory for vibrational circular dichroism: An approach based on the exact factorization of the electron-nuclear wave function

    Energy Technology Data Exchange (ETDEWEB)

    Scherrer, Arne [Martin-Luther-University Halle-Wittenberg, von-Danckelmann-Platz 4, D-06120 Halle (Germany); UMR 8640 ENS-CNRS-UPMC, Département de Chimie, 24 rue Lhomond, École Normale Supérieure, 75005 Paris (France); UPMC Université Paris 06, 4, Place Jussieu, 75005 Paris (France); Agostini, Federica; Gross, E. K. U. [Max-Planck-Institute of Microstructure Physics, Weinberg 2, D-06120 Halle (Germany); Sebastiani, Daniel [Martin-Luther-University Halle-Wittenberg, von-Danckelmann-Platz 4, D-06120 Halle (Germany); Vuilleumier, Rodolphe [UMR 8640 ENS-CNRS-UPMC, Département de Chimie, 24 rue Lhomond, École Normale Supérieure, 75005 Paris (France); UPMC Université Paris 06, 4, Place Jussieu, 75005 Paris (France)

    2015-08-21

    The nuclear velocity perturbation theory (NVPT) for vibrational circular dichroism (VCD) is derived from the exact factorization of the electron-nuclear wave function. This new formalism offers an exact starting point to include correction terms to the Born-Oppenheimer (BO) form of the molecular wave function, similar to the complete-adiabatic approximation. The corrections depend on a small parameter that, in a classical treatment of the nuclei, is identified as the nuclear velocity. Apart from proposing a rigorous basis for the NVPT, we show that the rotational strengths, related to the intensity of the VCD signal, contain a new contribution beyond-BO that can be evaluated with the NVPT and that only arises when the exact factorization approach is employed. Numerical results are presented for chiral and non-chiral systems to test the validity of the approach.

  16. Valence-state Model of Strain-dependent Mn L2,3 X-ray Magnetic Circular Dichroism from Ferromagnetic Semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    van der Laan, G.; Edmonds, K. W.; Arenholz, E.; Farley, N. R. S.; Gallagher, B. L.

    2010-03-30

    We present a valence-state model to explain the characteristics of a recently observed pre-edge feature in Mn L{sub 3} x-ray magnetic circular dichroism (XMCD) of ferromagnetic (Ga,Mn)As and (Al,Ga,Mn)As thin films. The prepeak XMCD shows a uniaxial anisotropy, contrary to the cubic symmetry of the main structures induced by the crystalline electric field. Reversing the strain in the host lattice reverses the sign of the uniaxial anisotropy. With increasing carrier localization, the prepeak height increases, indicating an increasing 3d character of the hybridized holes. Hence, the feature is ascribed to transitions from the Mn 2p core level to unoccupied p-d hybridized valence states. The characteristics of the prepeak are readily reproduced by the model calculation taking into account the symmetry of the strain-, spin-orbit-, and exchange-split valence states around the zone center.

  17. A vibrational circular dichroism approach to the determination of the absolute configurations of flavorous 5-substituted-2(5H)-furanones.

    Science.gov (United States)

    Nakahashi, Atsufumi; Yaguchi, Yoshihiro; Miura, Nobuaki; Emura, Makoto; Monde, Kenji

    2011-04-25

    Sotolon (1) and maple furanone (2) are naturally occurring chiral furanones. These 5-substituted-2(5H)-furanones are industrially significant aroma compounds due to their characteristic organoleptic properties and extraordinarily low odor thresholds. Each enantiomer of 1 and 2 was successfully obtained by preparative enantioselective supercritical fluid chromatography. The absolute configuration of 1 was confirmed as (R)-(-)-1 and (S)-(+)-1 by adopting the vibrational circular dichroism (VCD) approach. The absolute configuration of 2, which has remained ambiguous since its discovery in 1957, was determined as (R)-(+)-2 and (S)-(-)-2 for the first time by the VCD technique. Surprisingly, the signs of the optical rotation of 2 are opposite of those of 1 regardless of their identical absolute configurations. This observation emphasizes the risk in absolute configurational assignments based on comparison of optical rotation signs of similar structures. Odor evaluation of the enantiomers of 2 revealed different odor intensities.

  18. Angle-resolved soft X-ray magnetic circular dichroism in a monatomic Fe layer facing an MgO(0 0 1) tunnel barrier

    Energy Technology Data Exchange (ETDEWEB)

    Mamiya, K. [Photon Factory, Institute of Materials Structure Science (IMSS), High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan); Koide, T. [Photon Factory, Institute of Materials Structure Science (IMSS), High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan)]. E-mail: tsuneharu.koide@kek.jp; Ishida, Y. [Department of Complexity Science and Engineering, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan); Osafune, Y. [Department of Complexity Science and Engineering, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan); Fujimori, A. [Department of Complexity Science and Engineering, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan); Suzuki, Y. [Graduate School of Engineering Science, Osaka University, 1-3 Toyonaka, Osaka 560-8531 (Japan); NanoElectronics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Katayama, T. [NanoElectronics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Yuasa, S. [NanoElectronics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan)

    2006-11-15

    The electronic and magnetic states of a monatomic Fe(0 0 1) layer directly facing an MgO(0 0 1) tunnel barrier were studied by angle-resolved X-ray magnetic circular dichroism (XMCD) at the Fe L {sub 2,3} edges in the longitudinal (L) and transverse (T) arrangements. A strong XMCD reveals no oxidation of the 1-ML Fe, showing its crucial role in giant tunnel magnetoresistance effects in Fe/MgO/Fe magnetic tunnel junctions. Sum-rule analyses of the angle-resolved XMCD give values of a spin moment, in-plane and out-of-plane orbital and magnetic dipole moments. Argument is given on their physical implication.

  19. Determination of the absolute configuration of perylene quinone-derived mycotoxins by measurement and calculation of electronic circular dichroism spectra and specific rotations.

    Science.gov (United States)

    Podlech, Joachim; Fleck, Stefanie C; Metzler, Manfred; Bürck, Jochen; Ulrich, Anne S

    2014-09-01

    Altertoxins I-III, alterlosins I and II, alteichin (alterperylenol), stemphyltoxins I-IV, stemphyperylenol, stemphytriol, 7-epi-8-hydroxyaltertoxin I, and 6-epi-stemphytriol are mycotoxins derived from perylene quinone, for which the absolute configuration was not known. Electronic circular dichroism (ECD) spectra were calculated for these compounds and compared with measured spectra of altertoxins I-III, alteichin, and stemphyltoxin III and with reported Cotton effects. Specific rotations were calculated and compared with reported specific rotations. The absolute configuration of all the toxins, except for stemphyltoxin IV, could thus be determined. The validity of the assignment was high whenever reported ECD data were available for comparison, and the validity was lower when the assignment was based only on the comparison of calculated and reported specific rotations. ECD spectra are intrinsically different for toxins with a biphenyl substructure and for toxins derived from dihydroanthracene.

  20. Temperature and magnetic field dependence of the soft X-ray magnetic circular dichroism intensity for the Mn-L3 edge of MnFeP0.78Ge0.22

    NARCIS (Netherlands)

    Tsunekawa, M.; Imada, S.; Matsumoto, A.; Yamasaki, A.; Suga, S.; Schmid, B.; Higashimichi, H.; Hattori, Y.; Nakamura, T.; Brück, E.

    2007-01-01

    Soft X-ray magnetic circular dichroism (XMCD) measurements were performed at the L3 edge of manganese for MnFeP0.78Ge0.22 at 290 and 279 K. Temperature and magnetic field dependence of the XMCD intensity was clearly observed, which is consistent with that of the magnetization measurements as reporte

  1. Vacuum-Ultraviolet Circular Dichroism Spectra of Escherichia coli Dihydrofolate Reductase and Its Mutants: Contributions of Phenylalanine and Tyrosine Side Chains and Exciton Coupling of Two Tryptophan Side Chains.

    Science.gov (United States)

    Ohmae, Eiji; Tanaka, Suguru; Miyashita, Yurina; Katayanagi, Katsuo; Matsuo, Koichi

    2015-10-15

    Vacuum-ultraviolet (VUV) circular dichroism (CD) spectroscopy has recently been used for secondary structure analysis of proteins; however, the contribution of aromatic side chains to protein VUV CD spectra is unresolved. In this report, VUV CD spectra of 10 Escherichia coli dihydrofolate reductase (DHFR) mutants, in which each phenylalanine or tyrosine residue was mutated to leucine, were measured down to 175 nm at 25 °C and pH 8.0 to elucidate the contributions of these aromatic side chains to the high-energy transitions of peptide bonds. The VUV CD spectra of these mutants were different from the spectrum of the wild-type protein, indicating that the contribution of the phenylalanine and tyrosine side chains of DHFR extends to the VUV region. Furthermore, the VUV CD spectrum and the folate- or NADP(+)-induced spectral change of F103L mutant DHFR indicated a modification and regeneration of exciton coupling between the Trp47 and Trp74 side chains, respectively, suggesting that exciton coupling may also contribute to the CD spectrum of DHFR in the VUV region. These results should be useful for theoretically characterizing the contribution of aromatic side chains to protein CD spectra, leading to the improvement of protein secondary-structure analysis by VUV CD spectroscopy.

  2. Stereochemistry and solid-state circular dichroism spectroscopy of eight-coordinate chiral lanthanide complexes

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Eight-coordinate chiral lanthanide complexes [Eu(dbm)3LRR](1),[Eu(dbm)3LSS](2) and [Tb(dbm)3LRR](3)(LRR/LSS =(-)-/(+)-4,5-pineno-2,2’-bipyridine,Hdbm = dibenzoylmethane) were synthesized stereoselectively,which were characterized by UV-vis,CD spectra and X-ray single-crystal diffraction.The mirrorimage structure features of complexes 1 and 2 were obtained by combination of the solid-state CD spectra and the crystal structure analysis.After further comparison with the solid-state CD spectra of six-coordinate and seven-coordinate metal complexes containing β-diketone ligands,the CD spectraabsolute configuration correlation rule for the eight-coordinate β-diketonate lanthanide complexes was proposed through the exciton chirality method for the first time.The △ or Λ absolute configurations of complexes 1―3 with the distorted square antiprism geometry were confirmed by the X-ray single-crystal analysis.

  3. Stereochemistry and solid-state circular dichroism spectroscopy of eight-coordinate chiral lanthanide complexes

    Institute of Scientific and Technical Information of China (English)

    ZHOU Nan; WAN ShiGang; ZHAO Jian; LIN YiJi; XUAN WeiMin; FANG XueMing; ZHANG Hui

    2009-01-01

    Eight-coordinate chiral lanthanide complexes[Eu(dbm)_3L~(RR)](1),[Eu(dbm)_3L~(SS)](2) and[Tb(dbm)_3L~(RR)](3)(L~(RR)/L~(SS)=(-)-1(+)-4,5-pineno-2,2'-bipyridine,Hdbm=dibenzoylmethane) were synthesized stereoselectively,which were characterized by UV-vis,CD spectra and X-ray single-crystal diffraction.The mirrorimage structure features of complexes 1 and 2 were obtained by combination of the solid-state CD spectra and the crystal structure analysis.After further comparison with the solid-state CD spectra of six-coordinate and seven-coordinate metal complexes containing β-diketone ligands,the CD spectraabsolute configuration correlation rule for the eight-coordinate β-diketonate lanthanide complexes was proposed through the exciton chirality method for the first time.The △ or Λ absolute configurations of complexes 1-3 with the distorted square antiprism geometry were confirmed by the X-ray single-crystal analysis.

  4. Green Oxidation of Menthol Enantiomers and Analysis by Circular Dichroism Spectroscopy: An Advanced Organic Chemistry Laboratory

    Science.gov (United States)

    Geiger, H. Cristina; Donohoe, James S.

    2012-01-01

    Green chemistry addresses environmental concerns associated with chemical processes and increases awareness of possible harmful effects of chemical reagents. Efficient reactions that eliminate or reduce the use of organic solvents or toxic reagents are increasingly available. A two-week experiment is reported that entails the calcium hypochlorite…

  5. Electronic structure and x-ray magnetic circular dichroism in A2FeReO6 (A =Ca ,Sr ,andBa ) oxides

    Science.gov (United States)

    Antonov, V. N.; Bekenov, L. V.; Ernst, A.

    2016-07-01

    A systematic electronic structure study of A2FeReO6 (A =Ba ,Sr ,andCa ) has been performed by employing the local-spin-density approximation (LSDA) and LSDA +U methods using the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. We investigated the effects of the subtle interplay between spin-orbit coupling, electron correlations, and lattice distortion on the electronic structure of double perovskites. Ca2FeReO6 has a large distortion in the Fe-O-Re bond, and the electronic structure is mainly determined by electron correlations and lattice distortion. In the Ba -Sr -Ca row, the correlation effects at the Fe site are increased. The correlations at the Re site are small in the Ba- and Sr-based compounds but significant in Ca2FeReO6 . Ca2FeReO6 behaves like an insulator only if considered with a relatively large value of Coulomb repulsion Ueff=2.3 eV at the Re site in addition to Ueff=3.1 eV at the Fe site. Ca2FeReO6 possesses a phase transition at 140 K where the metal-insulator transition (MIT) occurs between metallic high-temperature and insulating low-temperature phases. The spin and orbital magnetic moments are linear functions of temperature before and after the MIT but change abruptly at the point of the phase transition. From theoretically calculated magnetocrystalline anisotropy energy (MAE), we found that the easy axis of magnetization for the low-temperature phase is along the b direction, in agreement with experimental data. We found that the major contribution to the MAE is due to the orbital magnetic anisotropy at the Re site. X-ray-absorption spectra and x-ray magnetic circular dichroism at the Re, Fe, and Ba L2 ,3 and Fe, Ca, and O K edges were investigated theoretically in the frame of the LSDA +U method. A qualitative explanation of the x-ray magnetic circular dichroism spectra shape is provided by an analysis of the corresponding selection rules, orbital character, and occupation numbers of individual orbitals

  6. A circular dichroism sensor for Ni{sup 2+} and Co{sup 2+} based on L-cysteine capped cadmium sulfide quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Tedsana, Wimonsiri [Materials Chemistry Research Center, Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Khon Kaen University, Khon Kaen 40002 (Thailand); Tuntulani, Thawatchai [Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330 (Thailand); Ngeontae, Wittaya, E-mail: wittayange@kku.ac.th [Materials Chemistry Research Center, Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Khon Kaen University, Khon Kaen 40002 (Thailand)

    2015-03-31

    Highlights: • Demonstrated a new efficient sensor platform based quantum dots. • Used chiral quantum dots as CD sensor for the detection of heavy metal ions for the first time. • The proposed CD sensor showed highest selectivity towards Ni{sup 2+} and Co{sup 2+}. • Low detection limits of 7.33 μM and 1.13 μM for Ni{sup 2+} and Co{sup 2+}, respectively. • Can be used in real water samples comparing with ICP-OES. - Abstract: A new circular dichroism sensor for detecting Ni{sup 2+} and Co{sup 2+} was proposed for the first time using chiral chelating quantum dots. The detection principle was based on changing of circular dichroism signals of the chiral quantum dots when forming a chiral complex with Ni{sup 2+} or Co{sup 2+}. L-Cysteine capped cadmium sulfide quantum dots (L-Cyst-CdS QDs) were proposed as a chiral probe. The CD spectrum of L-Cyst-CdS QDs was significantly changed in the presence of Ni{sup 2+} and Co{sup 2+}. On the other hand, other studied cations did not alter the original CD spectrum. Moreover, when increasing the concentration of Ni{sup 2+} or Co{sup 2+}, the intensity of the CD spectrum linearly increased as a function of concentration and could be useful for the quantitative analysis. The proposed CD sensor showed linear working concentration ranges of 10–60 μM and 4–80 μM with low detection limits of 7.33 μM and 1.13 μM for the detection of Ni{sup 2+} and Co{sup 2+}, respectively. Parameters possibly affected the detection sensitivity such as solution pH and incubation time were studied and optimized. The proposed sensor was applied to detect Ni{sup 2+} and Co{sup 2+} in real water samples, and the results agreed well with the analysis using the standard ICP-OES.

  7. Direct surface magnetometry with photoemission magnetic x-ray dichroism

    Energy Technology Data Exchange (ETDEWEB)

    Tobin, J.G.; Goodman, K.W. [Lawrence Berkeley National Lab., CA (United States); Schumann, F.O. [Pennsylvania State Univ., University Park, PA (United States)] [and others

    1997-04-01

    Element specific surface magnetometry remains a central goal of synchrotron radiation based studies of nanomagnetic structures. One appealing possibility is the combination of x-ray absorption dichroism measurements and the theoretical framework provided by the {open_quotes}sum rules.{close_quotes} Unfortunately, sum rule analysis are hampered by several limitations including delocalization of the final state, multi-electronic phenomena and the presence of surface dipoles. An alternative experiment, Magnetic X-Ray Dichroism in Photoelectron Spectroscopy, holds out promise based upon its elemental specificity, surface sensitivity and high resolution. Computational simulations by Tamura et al. demonstrated the relationship between exchange and spin orbit splittings and experimental data of linear and circular dichroisms. Now the authors have developed an analytical framework which allows for the direct extraction of core level exchange splittings from circular and linear dichroic photoemission data. By extending a model initially proposed by Venus, it is possible to show a linear relation between normalized dichroism peaks in the experimental data and the underlying exchange splitting. Since it is reasonable to expect that exchange splittings and magnetic moments track together, this measurement thus becomes a powerful new tool for direct surface magnetometry, without recourse to time consuming and difficult spectral simulations. The theoretical derivation will be supported by high resolution linear and circular dichroism data collected at the Spectromicroscopy Facility of the Advanced Light Source.

  8. Wavelength-Dependent Second Harmonic Generation Circular Dichroism for Differentiation of Col I and Col III Isoforms in Stromal Models of Ovarian Cancer Based on Intrinsic Chirality Differences.

    Science.gov (United States)

    Campbell, Kirby R; Campagnola, Paul J

    2017-03-02

    Extensive remodeling of the extracellular matrix (ECM) occurs in many epithelial cancers. For example, in ovarian cancer, upregulation of collagen isoform type III has been linked to invasive forms of the disease, and this change may be a potential biomarker. To examine this possibility, we implemented wavelength-dependent second harmonic generation circular dichroism (SHG-CD) imaging microscopy to quantitatively determine changes in chirality in ECM models comprised of different Col I/Col III composition. In these models, Col III was varied between 0 and 40%, and we found increasing Col III results in reduced net chirality, consistent with structural biology studies of Col I and III in tissues where the isoforms comingle in the same fibrils. We further examined the wavelength dependence of the SHG-CD to both optimize the response and gain insight into the underlying mechanism. We found using shorter SHG excitation wavelengths resulted in increased SHG-CD sensitivity, where this is consistent with the electric-dipole-coupled oscillator model suggested previously for the nonlinear chirality response from thin films. Moreover, the sensitivity is further consistent with the wavelength dependency of SHG intensity fit to a two-state model of the two-photon absorption in collagen. We also provide experimental calibration protocols to implement the SHG-CD modality on a laser scanning microscope. We last suggest that the technique has broad applicability in probing a wide range of diseased states with changes in collagen molecular structure.

  9. Measuring magnetisation reversal in micron-sized Nd2Fe14B single crystals by microbeam x-ray magnetic circular dichroism

    Science.gov (United States)

    Sugawara, Akira; Ueda, Kazuhiro; Nakayama, T.; Lee, N.; Yamamoto, H.

    2016-10-01

    Magnetisation reversal of micron-sized Nd2Fe14B single crystals with magnetisation as weak as 10-9 emu (1 µm size) was studied. Single-crystal specimens (cylinders with diameter and height of 1 to 6 µm) were prepared by focused-ion beam so that both the magnetic easy and hard axes were included in the basal plane. Their magnetic hysteresis loops were measured when they were rotated with respect to the cylindrical axis by using microbeam hard-x-ray magnetic circular dichroism (XMCD) under transmission geometry. It was found that coercivity is inversely proportional to the cosine of the angle between the magnetocrystalline easy axis and magnetic-field direction and that the magnetisation reversal is dominated by domain-wall pinning in two different modes. One is related to penetration of the reversed domain nucleated in a subsurface soft layer into the bulk hard phase, of which the hysteresis loops exhibit a single-stage abrupt jump in magnetization. The other mode is pinning of the walls within the bulk grain, of which the hysteresis loops exhibit a plateau. The multi-domain structure associated with the pinning was confirmed by XMCD mapping. The proposed method fills the gap between conventional bulk magnetic measurement and submicron-scale electrical-transport measurement for nanofabricated thin films and/or fine particles. It is expected to provide new insights into elemental magnetisation processes in micron-scale regions.

  10. Influence of bovine serum albumin on the secondary structure of interferon alpha 2b as determined by far UV circular dichroism spectropolarimetry.

    Science.gov (United States)

    Johnston, Michael J W; Nemr, Kayla; Hefford, Mary A

    2010-03-01

    Many therapeutic biologics are formulated with excipients, including the protein excipient human serum albumin (HSA), to increase stability and prevent protein aggregation and adsorption onto glass vials. One biologic formulated with albumin is interferon alpha-2b (IFN alpha-2b). As is the case with other therapeutic biologics, the increased structural complexity of IFN alpha-2b compared to a small molecule drug requires that both the correct chemical structure (amino acid sequence) and also the correct secondary and tertiary structures (3 dimensional fold) be verified to assure safety and efficacy. Although numerous techniques are available to assess a biologic's primary, secondary and tertiary structures, difficulties arise when assessing higher order structure in the presence of protein excipients. In these studies far UV circular dichroism spectropolarimetry (far UV-CD) was used to determine the secondary structure of IFN alpha-2b in the presence of a protein excipient (bovine serum albumin, BSA). We demonstrated that the secondary structure of IFN alpha-2b remains mostly unchanged at a variety of BSA to IFN alpha-2b protein ratios. A significant difference in alpha helix and beta sheet content was noted when the BSA to IFN alpha-2b ratio was 5:1 (w/w), suggesting a potential conformational change in IFN alpha-2b secondary structure when BSA is in molar excess.

  11. Oriented circular dichroism analysis of chiral surface-anchored metal-organic frameworks grown by liquid-phase epitaxy and upon loading with chiral guest compounds

    KAUST Repository

    Gu, Zhigang

    2014-06-17

    Oriented circular dichroism (OCD) is explored and successfully applied to investigate chiral surface-anchored metal-organic frameworks (SURMOFs) based on camphoric acid (D- and Lcam) with the composition [Cu2(Dcam) 2x(Lcam)2-2x(dabco)]n (dabco=1,4-diazabicyclo- [2.2.2]-octane). The three-dimensional chiral SURMOFs with high-quality orientation were grown on quartz glass plates by using a layer-by-layer liquid-phase epitaxy method. The growth orientation, as determined by X-ray diffraction (XRD), could be switched between the [001] and [110] direction by using either OH- or COOH-terminated substrates. These SURMOFs were characterized by using OCD, which confirmed the ratio as well as the orientation of the enantiomeric linker molecules. Theoretical computations demonstrate that the OCD band intensities of the enantiopure [Cu2(Dcam)2(dabco)] n grown in different orientations are a direct result of the anisotropic nature of the chiral SURMOFs. Finally, the enantiopure [Cu 2(Dcam)2(dabco)]n and [Cu2(Lcam) 2(dabco)]n SURMOFs were loaded with the two chiral forms of ethyl lactate [(+)-ethyl-D-lactate and (-)-ethyl-L-lactate)]. An enantioselective enrichment of >60 % was observed by OCD when the chiral host scaffold was loaded from the racemic mixture. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Near-ultraviolet tyrosyl circular dichroism of pig insulin monomers, dimers, and hexamers. Dipole-dipole coupling calculations in the monopole approximation.

    Science.gov (United States)

    Strickland, E H; Mercola, D

    1976-08-24

    The tyrosyl circular dichroism (CD) has been calculated using the conformation of pig insulin observed in rhombohedral crystals containing 2 zinc atoms per hexamer. These calculations predict that the tyrosyl CD at 275 nm will be enhanced disproportionally as monomers interact to form dimers and as dimers interact to form hexamers. This enhanced tyrosyl CD (delta epsilon per 5800 molecular weight) results from new coupling interactions generated in the regions of contact between monomers and between dimers. These calculations illustrate that a large CD enhancement may accompany aggregation even in the absence of a conformation change in eith monomer. The tyrosyl CD intensities calculated for monomers, dimers, and hexamers of 2-zinc pig insulin are compatible with the experimentally observed CD spectra which are enhanced about fourfold in the hexamer compared with the monomer. Zinc ions and other metals do not contribute directly to the tyrosyl CD but only influence the optical properties by promoting the hexameric state. The relation of the integrity of the molecule to dimer formation and the biological activity of the molecules are discussed. The largest calculated contributions to tryosyl CD arise from interactions with far-ultraviolet transitions of neighboring aromatic groups. In the hexamer, about half of the tyrosyl CD intensity is calculated to arise from Tyr-A14.

  13. Circular dichroism, molecular modeling, and serology indicate that the structural basis of antigenic variation in foot-and-mouth disease virus is [alpha]-helix formation

    Energy Technology Data Exchange (ETDEWEB)

    France, L.L.; Piatti, P.G.; Newman, J.F.E.; Brown, F. (Plum Island Animal Disease Center, Greenport, NY (United States)); Toth, I.; Gibbons, W.A. (Univ. of London (United Kingdom))

    1994-08-30

    Seven antigenic variants obtained from a single field isolate of foot-and-mouth disease virus, serotype A12, differ only at residues 148 and 153 in the immunodominant loop of viral protein VP1. Synthetic peptides corresponding to the region 141-160 are highly immunogenic. UV circular dichroism shows that (i) in aqueous solution of the peptides are nearly identical, but in 100% trifluoroethanol they display helix-forming properties which correlate well with their serological crossreactivities for anti-peptide sera, and (ii) these properties are insensitive to substitutions at position 153, except for proline, but are highly sensitive to substitutions at position 148. This pattern can be explained by the effects of these substitutions on the amphiphilic character and positions of helices postulated in the region 146-156. Molecular models indicate that residues 147, 148, 150, 151, 153-155, and 157 are most likely to interact with residues of the antibody paratopes. The data are consistent with the existence of an inverse [gamma]-turn around Pro-153, and a [beta]-turn at the cell-attachment site at residues 145-147. 31 refs., 5 figs.

  14. Interaction of bovine serum albumin (BSA) with novel gemini surfactants studied by synchrotron radiation scattering (SR-SAXS), circular dichroism (CD), and nuclear magnetic resonance (NMR).

    Science.gov (United States)

    Gospodarczyk, W; Szutkowski, K; Kozak, M

    2014-07-24

    The interaction of three dicationic (gemini) surfactants-3,3'-[1,6-(2,5-dioxahexane)]bis(1-dodecylimidazolium) chloride (oxyC2), 3,3'-[1,16-(2,15-dioxahexadecane)]bis(1-dodecylimidazolium) chloride (oxyC12), and 1,4-bis(butane)imidazole-1-yl-3-dodecylimidazolium chloride (C4)--with bovine serum albumin (BSA) has been studied by the use of small-angle X-ray scattering (SAXS), circular dichroism (CD), and (1)H nuclear magnetic resonance diffusometry. The results of CD studies show that the conformation of BSA was changed dramatically in the presence of all studied surfactants. The greater decrease (from 56 to 24%) in the α-helical structure of BSA was observed for oxyC2 surfactant. The radii of gyration estimated from SAXS data varied between 3 and 26 nm for the BSA/oxyC2 and BSA/oxyC12 systems. The hydrodynamic radius of the BSA/surfactant system estimated from NMR diffusometry varies between 5 and 11 nm for BSA/oxyC2 and 5 and 8 nm for BSA/oxyC12.

  15. First principle simulation of the temperature dependent magnetic circular dichroism of a trinuclear copper complex in the presence of zero field splitting.

    Science.gov (United States)

    Zhekova, Hristina R; Seth, Michael; Ziegler, Tom

    2011-09-22

    We present a test of a recently developed density functional theory (DFT) based methodology for the calculation of magnetic circular dichroism (MCD) spectra in the presence of zero-field splitting (ZFS). The absorption and MCD spectra of the trinuclear copper complex μ(3)O ([Cu(3)(L)(μ(3)-O)](4+)), which models the native intermediate produced in the catalytic cycle of the multicopper oxidases, have been simulated from first principle within the framework of adiabatic time dependent density functional theory. The effects of the ZFS of the quartet (4)A(2) ground state on the theoretical MCD spectrum of μ(3)O have been analyzed. The simulated spectra are consistent with the experimental ones. The theoretical assignments of the MCD spectra are based on direct simulation as well as a detailed analysis of the molecular orbitals in μ(3)O. Some of the assignments differ from those given in previous studies. The ZFS effects in the presence of a strong external magnetic field (7 T) prove negligible. The change of the sign of the ZFS changes systematically the intensity of the MCD bands of the z-polarized excitations. The effect of the ZFS on the x,y-polarized excitations is not uniform.

  16. Ab initio calculations of X-ray magnetic circular dichroism spectra within the projector augmented wave method: An implementation into the VASP code

    Science.gov (United States)

    Dixit, Anant; Alouani, M.

    2016-10-01

    X-ray absorption and X-ray magnetic circular dichroism (XMCD) are very powerful tools for probing the orbital and spin moments of each atomic species orbital of magnetic materials. In this work, we present the implementation of a module for computing the X-ray absorption and XMCD spectra into the VASP code. We provide a derivation of the absorption cross-section in the electric dipole approximation. The matrix elements, which make up the X-ray absorption cross-section for a given polarization of light, are then computed using either the momentum operator p or the position operator r, within the projector augmented wave method. The core electrons are described using the relativistic basis-set whereas for the valence electrons, the spin-orbit coupling is added perturbatively to the semi-relativistic Hamiltonian. We show that both the p and the r implementations lead to the same results. The results for the K-edge and L23-edges of bcc-iron are then computed and compared to experiment.

  17. Probing chiral solute-water hydrogen bonding networks by chirality transfer effects: A vibrational circular dichroism study of glycidol in water

    Science.gov (United States)

    Yang, Guochun; Xu, Yunjie

    2009-04-01

    Vibrational absorption (VA) and vibrational circular dichroism (VCD) spectra of (S)-(-)-glycidol were measured in water with a concentration of 6.0M in the 1000-1750 cm-1 region. Prominent and complex VCD spectral features were detected at the water bending vibrational region. Our experimental results show that water molecules can become optically active through hydrogen bonding interactions with glycidol molecules. To model the glycidol-water hydrogen bonding network in the solution, molecular dynamics simulations using the AMBER9 suite of programs were carried out. Altogether, 34 conformers of the small glycidol-(water)N clusters with N =1, 2, 3, and 4 were considered. Geometry optimizations, harmonic frequency calculations, and the VA and VCD intensity predictions of these small glycidol-water clusters were performed at the B3LYP/6-311++G(d,p) level of theory using the GAUSSIAN 03 program package. Strong cooperative hydrogen bonding effects were detected in the larger glycidol-(water)N clusters. The population weighted VA and VCD spectra of each N group of glycidol (water)N=1,2,3,4 were used to produce the simulated VA and VCD spectra, which are in good agreement with the experimental VA and VCD spectra. The study shows that all these clusters make important contributions to the observed spectra and are the most important species in the aqueous solution with complicated equilibriums among them.

  18. Molecular and vibrational structure of diphenylether and its 4,4' -dibromo derivative. Infrared linear dichroism spectroscopy and density functional theory calculations

    DEFF Research Database (Denmark)

    Eriksen, Troels K; Karlsen, Eva; Spanget-Larsen, Jens

    2015-01-01

    The title compounds were investigated by means of Linear Dichroism (LD) IR spectroscopy on samples partially aligned in uniaxially stretched low-density polyethylene and by density functional theory calculations. Satisfactory overall agreement between observed and calculated vibrational wavenumbe...... and IR intensities are obtained, allowing a fairly detailed assignment of the observed transitions in terms of individual nuclear motions....

  19. Linear and Chiral Dichroism in the Electron Microscope

    CERN Document Server

    Schattschneider, Peter

    2012-01-01

    The growing interest in the miniaturization of magnetic storage media and the quest for novel spintronics applications rely on element specific detection of spin and orbital magnetic moments in a solid. The most sophisticated technique to reach this aim has been XMCD (X-ray magnetic circular dichroism), largely used in synchrotron beam lines. The spatial resolution limit of this technique is of the order of 20 - 50 nm. This poses a sensible limit for the study of nanostructured devices. This book describes EMCD (energy loss magnetic chiral dichroism), a phenomenon in energy loss spectroscopy d

  20. Room temperature observation by X-ray magnetic circular dichroism of the orbital momentum enhancement of Co nanoclusters grown on Au(110)

    Energy Technology Data Exchange (ETDEWEB)

    Roa, Daniel Bretas; Reis, Diogo Duarte; Coelho Neto, Paula Mariel; Simoes, Wendell; Siervo, Abner de; Magalhaes-Paniago, Rogerio [Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG (Brazil)

    2012-07-01

    Full text: Increase in magnetic storage capabilities inevitably requires miniaturization of magnetic bits. Two solutions for this problem have been proposed: the assembly of magnetic vortexes, where the competition between exchange and dipolar interactions stabilizes a specific magnetic configuration and the modification of magnetic properties of nanoclusters due to change in structural properties, leading to an enhancement of their orbital momentum, especially in 3D transition metals. Since nanoclusters inevitable exhibit superparamagnetism, the determination of the orbital momentum of nanoclusters suffers from the need of high magnetic fields and extremely low temperatures. Therefore, even the search for enhanced magnetic materials is jeopardized by this limitation. In the present work, we have grown cobalt nanoclusters on Au(110) by electron beam deposition under ultra-high vacuum conditions. Scanning tunneling microscopy and low energy electron diffraction confirmed the preparation of a clean Au surface as well as the formation of pure Co nanoclusters in the range of the equivalent of 1-4 monolayers. The magnetization of Cobalt clusters was confirmed by X-ray Magnetic Circular Dichroism (XMCD) measured at the new PGM beamline at the Brazilian Synchrotron Radiation Laboratory (LNLS). A reasonably low magnetic field (1.1 Tesla) was used and the measurements were done at room temperature. By fixing the spin momentum and determining the average angle between the incident X-ray photon and the total magnetic moment, we clearly observe the enhancement of Co orbital momentum as coverage decreases down to approximately 1.5 monolayers. The procedure of determination of the orbital momentum a low magnetic fields will be discussed in detail. (author)

  1. Raman, SERS, and induced circular dichroism techniques as a probe of pharmaceuticals in their interactions with the human serum albumin and p-glycoprotein

    Science.gov (United States)

    Fleury, Fabrice; Ianoul, Anatoli I.; Baggetto, Loris; Jardillier, Jean-Claude; Alix, Alain J.; Nabiev, Igor R.

    1999-04-01

    Camptothecin (CPT) derivatives are the well known inhibitors of the human DNA topoisomerase (topo) I. Two of them, irinotecan and topotecan, are just in the clinics; 9-amino- CPT is on the stage II of clinical trials, and the active search for new derivatives is now in progress. Stability of the CPT derivatives on their way to the target and resistance of cancer cells to these drugs present the crucial problem of the chemotherapy. Human serum albumin (HSA) is the mediator of transport and metabolism of numerous pharmaceuticals in the blood and P-glycoprotein (P- gp) plays a crucial role of the mediator of the multidrug resistance (MDR) of the cancer cells. This paper present the result of analysis of molecular interactions of some drugs of CPT family with the HSA and P-gp. Induced circular dichroism (CD) and Raman techniques have been applied for monitoring molecular interaction of drugs with HSA as well as to identify the conformational transition of the protein induced by the drug binding. Drug molecular determinants responsible for interaction have been identified and their binding sites within the HSA have been localized. New cancer cells lines exhibiting an extremely high level of MDR resistance have been established and were shown to contain the P-gp overproduced in the quantities of 35 percent from the all membrane proteins. The membrane fractions of these cells with the controls presented by the membranes of the parental membrane proteins. The membrane fractions of these cells with the controls presented by the membranes of the parental sensitive cells may be used as a model system for spectroscopic analysis of the specific pharmaceuticals/P-gp interactions.

  2. Towards an exact theory of linear absorbance and circular dichroism of pigment-protein complexes: Importance of non-secular contributions

    Energy Technology Data Exchange (ETDEWEB)

    Dinh, Thanh-Chung; Renger, Thomas, E-mail: thomas.renger@jku.at [Institut für Theoretische Physik, Johannes Kepler University Linz, Altenberger Str. 69, 4040 Linz (Austria)

    2015-01-21

    A challenge for the theory of optical spectra of pigment-protein complexes is the equal strength of the pigment-pigment and the pigment-protein couplings. Treating both on an equal footing so far can only be managed by numerically costly approaches. Here, we exploit recent results on a normal mode analysis derived spectral density that revealed the dominance of the diagonal matrix elements of the exciton-vibrational coupling in the exciton state representation. We use a cumulant expansion technique that treats the diagonal parts exactly, includes an infinite summation of the off-diagonal parts in secular and Markov approximations, and provides a systematic perturbative way to include non-secular and non-Markov corrections. The theory is applied to a model dimer and to chlorophyll (Chl) a and Chl b homodimers of the reconstituted water-soluble chlorophyll-binding protein (WSCP) from cauliflower. The model calculations reveal that the non-secular/non-Markov effects redistribute oscillator strength from the strong to the weak exciton transition in absorbance and they diminish the rotational strength of the exciton transitions in circular dichroism. The magnitude of these corrections is in a few percent range of the overall signal, providing a quantitative explanation of the success of time-local convolution-less density matrix theory applied earlier. A close examination of the optical spectra of Chl a and Chl b homodimers in WSCP suggests that the opening angle between Q{sub y} transition dipole moments in Chl b homodimers is larger by about 9{sup ∘} than for Chl a homodimers for which a crystal structure of a related WSCP complex exists. It remains to be investigated whether this change is due to a different mutual geometry of the pigments or due to the different electronic structures of Chl a and Chl b.

  3. Kramers-Kronig transformation of experimental electronic circular dichroism: application to the analysis of optical rotatory dispersion in dimethyl-L-tartrate.

    Science.gov (United States)

    Polavarapu, Prasad L; Petrovic, Ana G; Zhang, Peng

    2006-09-01

    When a limited region of the experimental electronic circular dichroism (ECD) spectrum is subjected to Kramers-Kronig (KK) transformation, the resulting optical rotatory dispersion (ORD) may or may not reproduce the experimentally measured ORD in the long-wavelength nonresonant region. If the KK transform of experimentally measured ECD in a limited wavelength region reproduces the experimentally measured ORD in the long-wavelength nonresonant region, then that observation indicates that the ORD in the long-wavelength nonresonant region should be satisfactorily predicted from the correspondingly limited number of electronic transitions in a reliable quantum mechanical calculation. On the other hand, if the KK transform of experimentally measured ECD in a limited region does not reproduce the experimentally measured ORD in the long-wavelength nonresonant region, then it should be possible to identify the ECD bands in the shorter wavelength region that are responsible for the differences between experimentally observed ORD and KK-transformed ECD. This approach helps to identify the role of ECD associated with higher energy-excited states in the nature of ORD in the long-wavelength nonresonant region. These concepts are demonstrated here by measuring the experimental ECD and ORD for dimethyl-L-tartrate in different solvents. While ECD spectra of dimethyl-L-tartrate in different solvents show little variation, ORD spectra in the long-wavelength nonresonant region show marked solvent dependence. These observations are explained using the difference between experimental ORD and KK-transformed ECD. Quantum mechanical predictions of ECD and ORD are also presented for isolated (R, R)-dimethyl tartrate at the B3LYP/aug-cc-pVDZ level.

  4. Infrared, vibrational circular dichroism, and Raman spectral simulations for β-sheet structures with various isotopic labels, interstrand, and stacking arrangements using density functional theory.

    Science.gov (United States)

    Welch, William R W; Kubelka, Jan; Keiderling, Timothy A

    2013-09-12

    Infrared (IR), Raman, and vibrational circular dichroism (VCD) spectral variations for different β-sheet structures were studied using simulations based on density functional theory (DFT) force field and intensity computations. The DFT vibrational parameters were obtained for β-sheet fragments containing nine-amides and constrained to a variety of conformations and strand arrangements. These were subsequently transferred onto corresponding larger β-sheet models, normally consisting of five strands with ten amides each, for spectral simulations. Further extension to fibril models composed of multiple stacked β-sheets was achieved by combining the transfer of DFT parameters for each sheet with dipole coupling methods for interactions between sheets. IR spectra of the amide I show different splitting patterns for parallel and antiparallel β-sheets, and their VCD, in the absence of intersheet stacking, have distinct sign variations. Isotopic labeling by (13)C of selected residues yields spectral shifts and intensity changes uniquely sensitive to relative alignment of strands (registry) for antiparallel sheets. Stacking of multiple planar sheets maintains the qualitative spectral character of the single sheet but evidences some reduction in the exciton splitting of the amide I mode. Rotating sheets with respect to each other leads to a significant VCD enhancement, whose sign pattern and intensity is dependent on the handedness and degree of rotation. For twisted β-sheets, a significant VCD enhancement is computed even for sheets stacked with either the same or opposite alignments and the inter-sheet rotation, depending on the sense, can either further increase or weaken the enhanced VCD intensity. In twisted, stacked structures (without rotation), similar VCD amide I patterns (positive couplets) are predicted for both parallel and antiparallel sheets, but different IR intensity distributions still enable their differentiation. Our simulation results prove useful

  5. Magnetic x-ray dichroism in ultrathin epitaxial films

    Energy Technology Data Exchange (ETDEWEB)

    Tobin, J.G.; Goodman, K.W. [Lawrence Berkeley National Lab., CA (United States); Cummins, T.R. [Univ. of Missouri, Rolla, MO (United States)] [and others

    1997-04-01

    The authors have used Magnetic X-ray Linear Dichroism (MXLD) and Magnetic X-ray Circular Dichroism (MXCD) to study the magnetic properties of epitaxial overlayers in an elementally specific fashion. Both MXLD and MXCD Photoelectron Spectroscopy were performed in a high resolution mode at the Spectromicroscopy Facility of the ALS. Circular Polarization was obtained via the utilization of a novel phase retarder (soft x-ray quarter wave plate) based upon transmission through a multilayer film. The samples were low temperature Fe overlayers, magnetic alloy films of NiFe and CoNi, and Gd grown on Y. The authors results include a direct comparison of high resolution angle resolved Photoelectron Spectroscopy performed in MXLD and MXCD modes as well as structural studies with photoelectron diffraction.

  6. Theoretical analysis of the unusual vicinal effects on electronic circular dichroism spectra of cobalt(III) complexes with ED3A-type and related ligands

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yuekui; Zhang, Chunxia [Shanxi Univ., Taiyuan, Shanxi (China). Key Laboratory of Chemical Biology and Molecular Engineering

    2014-07-15

    To investigate the origin of unusual N-vicinal effects, the geometries of the two series of cobalt(III) complexes, [Co(ED3A-type)(X)]{sup -} (X = CN{sup -}, NO{sub 2}{sup -}) and [Co(EDDS-type)]{sup -}, with the pentadentate ethylenediamine-N, N, N'-triacetate (ED3A), hexadentate (S,S)-ethylenediamine-N, N'-dissuccinate (EDDS), and their N-alkyl-substituted ligands in aqueous solution have been optimized at the DFT/B3P86/6-311++G(2d,p) level of theory. Based on the optimized geometries, the excitation energies and rotational strengths have been calculated using the time dependent density functional theory (TDDFT) method with the same functional and basis set. The optimized geometries and calculated electronic circular dichroism (ECD) curves are in good agreement with the observed ones. Based on this agreement, the characteristics of usual and unusual N-vicinal effects as well as the related chiral stereochemistry phenomena have been discussed. To reveal the origin of the unusual N-vicinal effects, a novel calculation scheme has been proposed, which permits efficiently assessing the contribution of the octahedral core to the optical activities of the chelates. The results show that the substituent effects and conformational relaxation effects make opposite contributions to the overall N-vicinal effects with the former being dominant. The unusual N-vicinal effects originate from the negligible chirality of the octahedral core in the unsubstituted [Co(ED3A)(X)]{sup -} chelates. For this reason, their optical activity is dominated by the asymmetric nitrogens and behaves different from the normal cases. The unusual vicinal effects observed in the N-alkyl-substituted ED3A-type chelates reflect an increase in the contribution of the octahedral core to their optical activity, which recovers the ECD spectra from the special cases to the normal ones.These findings provide some insight into the unusual N-vicinal effects as well as the chiroptical properties of the

  7. Extending students' practice of metacognitive regulation strategies in the undergraduate chemistry laboratory and investigation of Pb2+ binding to calmodulin with circular dichroism and molecular dynamics modeling

    Science.gov (United States)

    Valencia Navarro, Laura N.

    The following dissertation was composed of two projects in chemistry education and benchwork/computational biochemistry. The chemistry education research explored students' practice of metacognitive strategies while solving open-ended laboratory problems when engaged in an instructional environment, the Science Writing Heuristic (SWH), that was characterized as supporting metacognitive regulation strategy use. Through in-depth interviews with students, results demonstrated that students in the SWH environment, compared to non-SWH students, used metacognitive strategies to a greater degree and to a greater depth when solving open-ended laboratory problems. As students engaged in higher levels of metacognitive regulation, their elective use of peers became a prominent path for supporting the practice of metacognitive strategies. Students claimed that the structure of the SWH weekly laboratory experiments improved their ability to solve open-ended lab problems. This research not only provided a lens into students' descriptions of their regulation strategy practices in the laboratory, but it also supported that the way that a laboratory environment is arranged can affect these regulation strategy practices and their transfer to new situations. In the biochemical study on the binding of Pb2+ to calmodulin (CaM), data was acquired via circular dichroism (CD) and molecular dynamics modeling. CD signal data indicated a unique signal from Pb-CaM and a significantly smaller ratio theta208/theta222 for Pb-CaM than Ca-CaM. An analysis of secondary structure content indicated that alpha-helical structure decreased and random coil structure increased when CaM was saturated with Pb2+ compared to Ca2+ saturated CaM. A molecular dynamics simulation of Pb2+ binding to CaM showed that Pb2+ ions bound to sites outside of the known canonical binding sites including the linker region, and indicated change in secondary structure. These results support the theory of opportunistic binding

  8. Structure of human Rad51 protein filament from molecular modeling and site-specific linear dichroism spectroscopy

    KAUST Repository

    Reymer, A.

    2009-07-08

    To get mechanistic insight into the DNA strand-exchange reaction of homologous recombination, we solved a filament structure of a human Rad51 protein, combining molecular modeling with experimental data. We build our structure on reported structures for central and N-terminal parts of pure (uncomplexed) Rad51 protein by aid of linear dichroism spectroscopy, providing angular orientations of substituted tyrosine residues of Rad51-dsDNA filaments in solution. The structure, validated by comparison with an electron microscopy density map and results from mutation analysis, is proposed to represent an active solution structure of the nucleo-protein complex. An inhomogeneously stretched double-stranded DNA fitted into the filament emphasizes the strategic positioning of 2 putative DNA-binding loops in a way that allows us speculate about their possibly distinct roles in nucleo-protein filament assembly and DNA strand-exchange reaction. The model suggests that the extension of a single-stranded DNA molecule upon binding of Rad51 is ensured by intercalation of Tyr-232 of the L1 loop, which might act as a docking tool, aligning protein monomers along the DNA strand upon filament assembly. Arg-235, also sitting on L1, is in the right position to make electrostatic contact with the phosphate backbone of the other DNA strand. The L2 loop position and its more ordered compact conformation makes us propose that this loop has another role, as a binding site for an incoming double-stranded DNA. Our filament structure and spectroscopic approach open the possibility of analyzing details along the multistep path of the strand-exchange reaction.

  9. Application of magnetically-perturbed time-dependent density functional theory to magnetic circular dichroism. IV. The influence of zero-field splitting on the spectra of S > 1/2 molecules

    Energy Technology Data Exchange (ETDEWEB)

    Seth, Michael, E-mail: mseth@ucalgary.ca [Department of Chemistry, University of Calgary, University Drive 2500, Calgary, AB T2N-1N4 (Canada); Ziegler, Tom, E-mail: ziegler@ucalgary.ca [Department of Chemistry, University of Calgary, University Drive 2500, Calgary, AB T2N-1N4 (Canada)

    2012-02-20

    The theory of calculating magnetic circular dichroism in the presence of zero-field splitting is presented and illustrated with applications to small and medium-sized systems. Highlights: Black-Right-Pointing-Pointer ZFS and MCD calculated with DFT are combined. Black-Right-Pointing-Pointer Influence of ZFS on the MCD spectra of group 15 hydrides analyzed. Black-Right-Pointing-Pointer Absorption and MCD spectra of Fe-EDTA-peroxide complex calculated. Black-Right-Pointing-Pointer ZFS does not appear to influence MCD spectra qualitatively. Black-Right-Pointing-Pointer Quantitative effects are present and difficult to model. - Abstract: An implementation into the ADF program of a method for calculating zero-field splitting (ZFS) of molecules with spin degenerate ground states and S > 1/2 is reported. ZFS can influence temperature-dependent magnetic circular dichroism (MCD) intensity. Previously published equations for the calculation of MCD with time-dependent density functional theory are modified to take zero-field splitting into account. The MCD spectra of the group 15 hydrides and the complex formed from iron (III), ethylenediaminetetraacetate and peroxide, [Fe(III)(EDTA)O{sub 2}]{sup 3-} are simulated. These spectra are analyzed with particular reference to the influence of ZFS on the MCD intensity.

  10. Electronic and magnetic properties of off-stoichiometric Co{sub 2}Mn{sub β}Si/MgO interfaces studied by x-ray magnetic circular dichroism

    Energy Technology Data Exchange (ETDEWEB)

    Singh, V. R.; Verma, V. K.; Ishigami, K.; Shibata, G.; Fujimori, A., E-mail: fujimori@wyvern.phys.s.u-tokyo.ac.jp [Department of Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan); Koide, T. [Photon Factory, IMSS, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801 (Japan); Miura, Y.; Shirai, M. [Research Institute of Electrical Communication, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577 (Japan); Ishikawa, T.; Li, G.-F.; Yamamoto, M. [Division of Electronics for Informatics, Hokkaido University, Sapporo 060-0814 (Japan)

    2015-05-28

    We have studied the electronic and magnetic states of Co and Mn atoms at the interface of the Co{sub 2}Mn{sub β}Si (CMS)/MgO (β = 0.69, 0.99, 1.15, and 1.29) magnetic tunnel junction (MTJ) by means of x-ray magnetic circular dichroism. In particular, the Mn composition (β) dependences of the Mn and Co magnetic moments were investigated. The experimental spin magnetic moments of Mn, m{sub spin}(Mn), derived from x-ray magnetic circular dichroism weakly decreased with increasing Mn composition β in going from Mn-deficient to Mn-rich CMS films. This behavior was explained by first-principles calculations based on the antisite-based site-specific formula unit (SSFU) composition model, which assumes the formation of only antisite defect, not vacancies, to accommodate off-stoichiometry. Furthermore, the experimental spin magnetic moments of Co, m{sub spin}(Co), also weakly decreased with increasing Mn composition. This behavior was consistently explained by the antisite-based SSFU model, in particular, by the decrease in the concentration of Co{sub Mn} antisites detrimental to the half-metallicity of CMS with increasing β. This finding is consistent with the higher tunnel magnetoresistance ratios which have been observed for CMS/MgO/CMS MTJs with Mn-rich CMS electrodes.

  11. UV-Vis spectroscopy of tyrosine side-groups in studies of protein structure. Part 2: selected applications.

    Science.gov (United States)

    Antosiewicz, Jan M; Shugar, David

    In Part 2 we discuss application of several different types of UV-Vis spectroscopy, such as normal, difference, and second-derivative UV absorption spectroscopy, fluorescence spectroscopy, linear and circular dichroism spectroscopy, and Raman spectroscopy, of the side-chain of tyrosine residues in different molecular environments. We review the ways these spectroscopies can be used to probe complex protein structures.

  12. Stereospecific ligands and their complexes. Part XIX. Synthesis, characterization, circular dichroism and antimicrobial activity of oxalato and malonato-(S,S)-ethylenediamine-N,N‧-di-2-(3-methyl)butanoato-chromate(III) complexes

    Science.gov (United States)

    Ilić, Dragoslav; Jevtić, Verica V.; Radojević, Ivana D.; Vasić, Sava M.; Stefanović, Olgica D.; Čomić, Ljiljana R.; Vasojević, Miorad M.; Jelić, Miodrag Ž.; Koval'chuk, Tatyana V.; Loginova, Natalia V.; Trifunović, Srećko R.

    2013-10-01

    The s-cis-[Cr(S,S-eddv)L]-complexes (1,2) (S,S-eddv = (S,S)-ethylenediamine-N,N‧-di-2-(3-methyl)butanoato ion; L = oxalate or malonate ion) were prepared. The complexes were purified by ion-exchange chromatography. The geometry of the complexes has been supposed on the basis of the infrared and electronic absorption spectra, and the absolute configurations of the isolated s-cis-[Cr(S,S-eddv)L]-complexes have been predicted on the basis of their circular dichroism (CD) spectra. Also, the results of thermal decomposition have been discussed. Antimicrobial activity of the prepared complexes (1-4) was investigated against 28 species of microorganisms. Testing was performed by microdilution method and minimum inhibitory concentrations (MIC) and minimum microbicidal concentration (MMC) have been determined. Complexes demonstrated in generally low antibacterial and antifungal activity.

  13. X-ray absorption spectroscopy and magnetic circular dichroism studies of L10-Mn-Ga thin films

    OpenAIRE

    Glas, M; Sterwerf, C.; Schmalhorst, J.M.; Ebke, D.; Jenkins, C.; Arenholz, E.; Reiss, G.

    2013-01-01

    Tetragonally distorted \\(\\rm{Mn}_{3-x}\\rm{Ga}_x\\) thin films with \\(0.1< x < 2\\) show a strong perpendicular magnetic anisotropy and low magnetization and thus have the potential to serve as electrodes in spin transfer torque magnetic random access memory. Because a direct capping of these films with MgO is problematic due to oxide formation, we examined the influence of a CoFeB interlayer, and of two different deposition methods for the MgO barrier on the formation of interfacial MnO for \\(\\...

  14. The vibrational structure of (E,E’)-1,4-diphenyl-1,3-butadiene. Linear dichroism FTIR spectroscopy and quantum chemical calculations

    DEFF Research Database (Denmark)

    Hansen, Bjarke Knud Vilster; Møller, Søren; Spanget-Larsen, Jens

    2006-01-01

    The title compound (DPB) was investigated by FTIR spectroscopy in liquid solutions and by FTIR linear dichroism (LD) measurements on samples aligned in stretched polyethylene. The LD data provided experimental assignments of molecular transition moment directions and vibrational symmetries for more...... than 40 vibrational transitions. The observed IR wavenumbers, relative intensities, and polarization directions were generally well reproduced by the results of a harmonic analysis based on B3LYP/cc-pVTZ density functional theory (DFT). The combined experimental and theoretical results led to proposal...... of a nearly complete assignment of the IR active fundamentals of DPB, involving reassignment of a number of transitions. In addition, previously published Raman spectra of DPB were well predicted by the B3LYP/cc-pVTZ calculations....

  15. UV-Vis spectroscopy of tyrosine side-groups in studies of protein structure. Part 1: basic principles and properties of tyrosine chromophore.

    Science.gov (United States)

    Antosiewicz, Jan M; Shugar, David

    Spectroscopic properties of tyrosine residues may be employed in structural studies of proteins. Here we discuss several different types of UV-Vis spectroscopy, like normal, difference and second-derivative UV absorption spectroscopy, fluorescence spectroscopy, linear and circular dichroism spectroscopy, and Raman spectroscopy, and corresponding optical properties of the tyrosine chromophore, phenol, which are used to study protein structure.

  16. Calculation of parity violating effects in the 6/sup 2/P/sub 1/2/-7/sup 2/P/sub 1/2/ forbidden M1 transition in thallium. [E1 amplitude, circular dichroism, parity violation, hyperfine structure

    Energy Technology Data Exchange (ETDEWEB)

    Neuffer, D.B.

    1977-05-01

    Calculations are presented of the E1 amplitude expected in forbidden M1 transitions of Tl and Cs if parity is violated in the neutral weak e-N interaction, as proposed in a number of gauge models, including that of Weinberg and Salam. Valence electron wave functions are generated as numerical solutions to the Dirac equation in a modified Tietz central potential. These wave functions are used to calculate allowed E1 transition rates, hfs splittings, and Stark E1 transition ampitudes. These results are compared with experiment and the agreement is generally good. The relativistic Tl 6/sup 2/P/sub 1/2/-7/sup 2/P/sub 1/2/ M1 transition amplitude M is also calculated, and corrections due to interconfiguration interaction, Breit interaction, and hfs mixing are included. The parity violating E1 amplitude E/sub PV/ is calculated and a value for the circular dichroism in the Weinberg model delta = -2.6 x 10/sup -3/ is obtained. Parity violating effects in other Tl transitions are discussed. Contributions to the M1 amplitude for the forbidden Cs 6/sup 2/S/sub 1/2/-7/sup 2/S/sub 1/2/ and 6/sup 2/S/sub 1/2/-8/sup 2/S/sub 1/2/ transitions and to the Cs 6/sup 2/S/sub 1/2/ g-factor anomaly from relativistic effects, Breit interaction, interconfiguration interaction, and hfs mixing are calculated, and it is found that this current theoretical description is not entirely adequate. The parity violating E1 amplitude E/sub PV/ for the 6S/sub 1/2/-7/sup 2/S/sub 1/2/ and 6S/sub 1/2/-8/sup 2/S/sub 1/2/ transitions is evaluated. With a measured value M/sub expt/ and the Weinberg value Q/sub W/ = -99, a circular dichroism delta = 1.64 x 10/sup -4/ for the 6/sup 2/S/sub 1/2/-7/sup 2/S/sub 1/2/ transition is found.

  17. DEIMOS: A beamline dedicated to dichroism measurements in the 350–2500 eV energy range

    Energy Technology Data Exchange (ETDEWEB)

    Ohresser, P., E-mail: philippe.ohresser@synchrotron-soleil.fr; Otero, E.; Choueikani, F.; Chen, K.; Stanescu, S.; Deschamps, F.; Moreno, T.; Polack, F.; Lagarde, B.; Daguerre, J.-P.; Marteau, F. [Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin - BP 48, 91192 Gif-sur-Yvette (France); Scheurer, F.; Joly, L.; Muller, B. [Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504 UdS-CNRS, 67034 Strasbourg Cedex 2 (France); Kappler, J.-P. [Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin - BP 48, 91192 Gif-sur-Yvette (France); Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504 UdS-CNRS, 67034 Strasbourg Cedex 2 (France); Bunau, O.; Sainctavit, Ph. [Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin - BP 48, 91192 Gif-sur-Yvette (France); Institut de Minéralogie et de Physique des Milieux Condensés, CNRS UMR 7590, Université Pierre et Marie Curie, 75252 Paris Cedex 5 (France)

    2014-01-15

    The DEIMOS (Dichroism Experimental Installation for Magneto-Optical Spectroscopy) beamline was part of the second phase of the beamline development at French Synchrotron SOLEIL (Source Optimisée de Lumière à Energie Intermédiaire du LURE) and opened to users in March 2011. It delivers polarized soft x-rays to perform x-ray absorption spectroscopy, x-ray magnetic circular dichroism, and x-ray linear dichroism in the energy range 350–2500 eV. The beamline has been optimized for stability and reproducibility in terms of photon flux and photon energy. The main end-station consists in a cryo-magnet with 2 split coils providing a 7 T magnetic field along the beam or 2 T perpendicular to the beam with a controllable temperature on the sample from 370 K down to 1.5 K.

  18. Electronic states of magnetic refrigerator materials Mn0.9Fe1.1P0.55As0.45 using soft x-ray magnetic circular dichroism

    Science.gov (United States)

    Takeda, Y.; Okane, T.; Ohkochi, T.; Fujimori, S.-i.; Saitoh, Y.; Yamagami, H.; Yabuta, H.; Takabatake, T.

    2010-01-01

    The system of MnFeP1-xAsx is a candidate of a magnetic refrigerator material. We have investigated the temperature (T)- and magnetic field (H)-dependence of the magnetic properties of the Mn and Fe ions for Mn0.9Fe1.1P0.55As0.45 using a soft x-ray magnetic circular dichroism (XMCD) in the regions of the Mn and Fe L2,3 absorption edges. In the ferromagnetic states, the magnetic moments of the Mn and Fe ions turn to the same direction. It is considered that the Mn ions are close to divalent (Mn2+) states and that the Fe ions are a mixture of trivalent (Fe3+) and divalent (Fe2+) states. However, we deduce that the ferromagnetic properties of the Fe ions are mainly derived from the Fe2+ states. Using the XMCD sum rules, we have found that the magnitude of the magnetic moment of the Mn ions is larger than that of the Fe ions. The paramagnetic to ferromagnetic transitions are clearly observed by the T- and H- dependent XMCD measurements. Scince the shapes of the spectra don't change in all experiment conditions, the electronic configurations of the Mn and Fe ions are not changed by the PM-FM transition.

  19. X-ray magnetic circular dichroism at IrL2,3 edges in Fe100-Ir and Co100-Ir alloys: Magnetism of 5d electronic states

    Indian Academy of Sciences (India)

    V V Krishnamurthy; M Suzuki; N Kawamura; T Ishikawa

    2002-05-01

    The formation of induced 5 magnetic moment on Ir in Fe100-Ir (=3, 10 and 17) and Co100-Ir (=5, 17, 25 and 32) alloys has been investigated by X-ray magnetic circular dichroism (XMCD) at Ir L2,3 absorption edges. Sum rule analysis of the XMCD data show that the orbital moment of Ir is in the range of -0.071(2)B to -0.030(1)B in Fe–Ir alloys and -0.067(2)B to 0.024(1)B in Co–Ir alloys. We find that the total moment of Ir in Fe–Ir alloys is approximately 1/5 of the total 3 moment on Fe at all the three compositions. In contrast, the total moment on Ir in Co–Ir alloys varies between 1/6 to 1/16 of the 3 moment on cobalt. The observed trends of Ir moments and the role of interatomic exchange interactions in 5 moment formation are discussed.

  20. Photo-physics study of an hydroxy-quinoline derivative as inhibitor of Pim-1 kinase: ultraviolet-visible linear dichroism spectroscopy and quantum chemical calculations.

    Science.gov (United States)

    Lamhasni, T; Ait Lyazidi, S; Hnach, M; Haddad, M; Desmaële, D; Spanget-Larsen, J; Nguyen, D D; Ducasse, L

    2013-09-01

    The photophysical properties of the antiviral 7-nicotinoyl-styrylquinoline (MB96) were investigated by means of UV-Vis linear dichroism (LD) spectroscopy on molecular samples aligned in stretched polyvinylalcohol (PVA), supported by time dependent density functional theory (TD-DFT) calculations. Experimentally, the directions of the transitions moments with respect to the long axis of the molecule were deduced from the orientation K factors, determined by means of "trial-and-error" procedure. The absorption spectrum presents two parts. The main transition in the lowest energy part, observed around 365 nm and showing the highest K value 0.8, is longitudinally in-plane polarized. The highest energy part which is extended between 230 and 320 nm, large, diffuse, and of weak intensity, shows estimated K values between 0.2 and 0.5. This complex structure is transversally polarized with some contamination by the longitudinal character of the first strong band. The TD-DFT results agree fairly well with the LD measurements.

  1. Detection of circular polarization in light scattered from photosynthetic microbes

    CERN Document Server

    Sparks, William B; Germer, Thomas A; Chen, Feng; DasSarma, Shiladitya; DasSarma, Priya; Robb, Frank T; Manset, Nadine; Kolokolova, Ludmilla; Reid, Neill; Macchetto, F Duccio; Martin, William; 10.1073/pnas.0810215106

    2009-01-01

    The identification of a universal biosignature that could be sensed remotely is critical to the prospects for success in the search for life elsewhere in the universe. A candidate universal biosignature is homochirality, which is likely to be a generic property of all biochemical life. Due to the optical activity of chiral molecules, it has been hypothesized that this unique characteristic may provide a suitable remote sensing probe using circular polarization spectroscopy. Here, we report the detection of circular polarization in light scattered by photosynthetic microbes. We show that the circular polarization appears to arise from circular dichroism of the strong electronic transitions of photosynthetic absorption bands. We conclude that circular polarization spectroscopy could provide a powerful remote sensing technique for generic life searches.

  2. Secondary structure of the intact H+,K+ -ATPase and of its membrane-embedded region. An attenuated total reflection infrared spectroscopy, circular dichroism and Raman spectroscopy study

    NARCIS (Netherlands)

    Raussens, V.; Jongh, H. de; Pézolet, M.; Ruysschaert, J.-M.; Goormaghtigh, E.

    1998-01-01

    Models of P-type ATPase predict that membrane-embedded fragments represent about 20% of the protein and adopt an all-α-helical structure. While this prediction was confirmed for the Ca2+ -ATPase [Corbalan-Garcia, S., Teruel, J., Villalain, J. and Gomez-Fernandez, J. (1994) Biochemistry 33, 8247-8254

  3. Dichroism in the photoionisation of atoms at XUV free-electron lasers

    Energy Technology Data Exchange (ETDEWEB)

    Mazza, T., E-mail: tommaso.mazza@xfel.eu [European XFEL GmbH, Albert-Einstein-Ring 19, D-22761 Hamburg (Germany); Gryzlova, E.V.; Grum-Grzhimailo, A.N. [Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Moscow 119991 (Russian Federation); Kazansky, A.K. [Departamento de Fisica de Materiales, UPV/EHU, E-20018 San Sebastian/Donostia (Spain); IKERBASQUE, Basque Foundation for Science, E-48011 Bilbao (Spain); Donostia International Physics Center (DIPC), E-20018 San Sebastian/Donostia (Spain); Kabachnik, N.M. [European XFEL GmbH, Albert-Einstein-Ring 19, D-22761 Hamburg (Germany); Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Moscow 119991 (Russian Federation); Donostia International Physics Center (DIPC), E-20018 San Sebastian/Donostia (Spain); Meyer, M., E-mail: michael.meyer@xfel.eu [European XFEL GmbH, Albert-Einstein-Ring 19, D-22761 Hamburg (Germany)

    2015-10-15

    Highlights: • We studied 2-color photoionization of He by angle-resolved electron spectroscopy. • Beta-parameters contain information about the symmetry of outgoing electron waves. • Experiments are compared to strong field approximation and perturbation theory. • 2-Photon measurements can be used to characterize FEL radiation properties. • Non-dipole contributions are predicted to produce new features in the dichroism. - Abstract: Two-color photoionization of atomic He has been investigated by angle-integrated and angle-resolved electron spectroscopy. The combined action of intense radiation pulses from the XUV free-electron laser (FEL), FERMI or FLASH, and a synchronized optical laser on the target atom gives rise to a rich sideband structure in the photoemission spectrum. Measurements of the angular distribution parameters and the determination of the circular and linear dichroism for the two-color photoionization enable a detailed analysis of the symmetry of the outgoing electron waves and of the dynamics underlying the multi-photon processes. The experimental results are in excellent agreement with theoretical results obtained using perturbation theory (low intensity regime) and the strong field approximation. For the particular case of two-photon ionization the measurements represent an ideal tool for characterizing certain FEL parameters, here for example the degree and the sign of circular polarization. Finally, new features of the dichroism are theoretically predicted originating from the non-dipole contribution into the photoionization amplitudes.

  4. 基于手性金纳米粒子圆二色光谱法识别与检测银离子%Recognition and Detection of Silver Ion by Circular Dichroism Spectrum Based on Chiral Gold Nanoparticles

    Institute of Scientific and Technical Information of China (English)

    韦克毅; 王猛; 杜宇; 蔡波; 江云宝

    2016-01-01

    In this work,chiral gold particles with optical activity can be obtained by a facile liquid phase method.The textural proper-ties of the as-prepared samples were characterized by high resolution transmission electron microscopy,circular dichroism spectrum and absorption spectrum.The results show that the average particle size for the production is 3.6 nm and silver ion can be selectively recognized from 1 3 kinds of metal ions in 1 2 min with universal recurrence.We also established the standard curve for detecting silver ion.This study demonstrates that the linear range for this curve is 0.2-30μmol/L,the linearly dependent coefficient is 0.995(n=15),which supplies a simple new environmentally friendly method for quickly detecting and recognizing silver ion in environmental water samples with high precision.%采用液相制备方法获得具有光学活性的手性金纳米粒子,通过吸收光谱和圆二色光谱及高分辨透射电镜对手性金纳米粒子进行表征.利用圆二色光谱法建立手性金纳米粒子对 Ag+选择性识别方法,结果表明手性金纳米粒子对Ag+响应时间仅需12 min,手性金纳米粒子能够从13种常见金属离子中选择性识别 Ag+,并对多种常见金属离子具有较好的抗干扰能力,检测灵敏度高并且具有良好的重现性.所建立标准曲线线性范围为0.2~30μmol/L,线性相关系数R2=0.995(n=15),Ag+的检测限为0.2μmol/L;为环境水样中 Ag+的识别和检测提供了一种简单、精确、快速、环境友好的新方法.

  5. Polarimetric investigation of materials with both linear and circular anisotropy

    DEFF Research Database (Denmark)

    Naydenova, I.; Nikolova, L.; Todorov, T.;

    1997-01-01

    We investigate light propagation through materials with both linear and circular anisotropy and find the relation of the amplitude and polarization transfer functions to the four anisotropic characteristics: linear circular birefringence, and linear and circular dichroism. We determine these four...

  6. Ⅱ型胶原蛋白的热稳定性、圆二色性和红外光谱研究%Studies on thermostability, circular dichroism and Infrared spectral characteristics of type Ⅱ collagen

    Institute of Scientific and Technical Information of China (English)

    宋瑞瑞; 包斌; 卜永士; 王永先; 陈丽娟; 吴文惠

    2013-01-01

    目的 以蓝鲨Ⅱ型胶原蛋白为材料,分析Ⅱ型胶原蛋白的热稳定性、圆二色性和红外光谱特性.方法 采用限制性酶解法分离蓝鲨软骨Ⅱ型胶原蛋白,通过SDS-PAGE、DSC、CD、IR分析Ⅱ型胶原蛋白的相对分子质量、热变性温度、二级结构特征和红外光谱特征.结果 蓝鲨Ⅱ型胶原蛋白是由相对分子质量为130 kDa的α1链构成;蓝鲨Ⅱ型胶原蛋白的热变性温度为40.5℃,[Na+]和[H+]改变了胶原蛋白的热稳定性;蓝鲨Ⅱ型胶原蛋白在3411、3008、1648、1549 cm-1有红外特征性吸收峰;蓝鲨Ⅱ型胶原蛋白以β-折叠为主,占主链的36.9%,接近于全β型三级结构,[H+]将改变Ⅱ型胶原蛋白的二级结构元件构成,使其β-折叠消失,出现少量的α-螺旋,Ⅱ型胶原蛋白肽链转变成无规卷曲.结论 蓝鲨Ⅱ型胶原蛋白是典型的纤维状蛋白质,具有作为生物功能物质的优良生物化学特性.%Objective To study the thermostability, circular dichroism and infrared spectral characteristics of type Ⅱ collagen purified from cartilage of Prionace glauca. Methods The digestion of pepsin was applied to extract type Ⅱ collagen from Prionace glauca cartilage. SDS-PAGE 、 DSC 、 CD and IR were used to analyze type Ⅱ collagen relative molecular mass、thermal denaturation temperature、secondary structure and infrared spectral characteristics respectively. Results The type Ⅱ collagen from Prionace glauca was composed of al chains with relative molecular mass 130kDa. The thermal denaturation temperature of Prionace glauca type Ⅱ collagen was 40. 5 ℃ , and [Na+] and [H+] could alter its thermostability. IR analysis indicated that the characteristic absorption peaks of Prionace glauca type Ⅱ collagen were at 3411、3008、1648 and 1549cm-1. β-sheet was the main secondary structure of Prionace glauca type Ⅱ collagen, and its ratio was 36. 9%, which was close to all-β-type tertiary structure. [H+] could

  7. Measuring spin diffusion of electrons in bulk n-GaAs using circularly dichromatic absorption difference spectroscopy of spin gratings

    Science.gov (United States)

    Yu, Hua-Liang; Zhang, Xiu-Min; Wang, Peng-Fei; Ni, Hai-Qiao; Niu, Zhi-Chuan; Lai, Tianshu

    2009-05-01

    Circular dichromatic absorption difference spectroscopy is developed to measure the spin diffusion dynamics of electrons in bulk n-GaAs. This spectroscopy has higher detection sensitivity over homodyne detection of spin-grating-diffracted signal. A model to describe circular dichromatic absorption difference signal is derived and used to fit experimental signal to retrieve decaying rate of spin gratings. A spin diffusion constant of Ds=201±25 cm2/s for bulk n-GaAs has been measured at room temperature using this technique and is close to electron diffusion constant (Dc), which is much different from the case in GaAs quantum wells where Ds is markedly less than Dc.

  8. Acquisition of pro-oxidant activity of fALS-linked SOD1 mutants as revealed using circular dichroism and UV-resonance Raman spectroscopy

    Science.gov (United States)

    Fujimaki, Nobuhiro; Nishiya, Ken; Miura, Takashi; Nakabayashi, Takakazu

    2016-11-01

    The acquisition of pro-oxidant activity of the mutated form of human Cu, Zn-superoxide dismutase (SOD1) has been investigated to clarify the relationship between mutations in SOD1 and the pathogenesis of amyotrophic lateral sclerosis (ALS). Ala4 → Val (A4V) and Gly93 → Ala (G93A) mutants, which are representative ALS-linked SOD1 mutants, have been found to exhibit both the denaturation and the gain of pro-oxidant activity after incubation in the apo-form at a physiological condition of 37 °C and pH 7.4 and the rebinding of Cu2+. These characteristics are similar to those previously reported for the His43 → Arg (H43R) mutant. UV-resonance Raman spectra indicated that the coordination structure of the Cu-binding site catalyzing the oxidation reaction is the same among the denatured A4V, G93A, and H43R. Since wild-type SOD1 does not exhibit the denaturation in its apo-form at 37 °C and pH 7.4, the instability of the protein structure due to mutation can be considered as a significant factor that induces the denaturation and the subsequent pro-oxidant activity.

  9. Vibrational circular dichroism spectroscopy of a spin-triplet bis-(biuretato) cobaltate(III) coordination compound with low-lying electronic transitions

    DEFF Research Database (Denmark)

    Johannessen, Christian; Thulstrup, Peter W.

    2007-01-01

    of (6S, 7S)-1,3,5,8,10,12-hexaaza-2,4,9,11-tetraoxo-6,7-diphenyl-dodecanato(4-) cobaltate( III) in DMSO solution and in potassium bromide pellets. The chiral anion exhibits an unusual geometry for cobalt( III), being four-coordinate, planar, and paramagnetic with an intermediate spin state....... The spectroscopic results were compared to measurements performed on the free ligand and to theoretical calculations using density functional theory (B3LYP/TZVP). The results of the VCD analysis of the coordination compound identified an electronic, dipole-forbidden, magnetic dipole-allowed low-lying d-d transition...

  10. Transfer of chirality from adsorbed chiral molecules to the substrates highlighted by circular dichroism in angle-resolved valence photoelectron spectroscopy

    DEFF Research Database (Denmark)

    Contini, G.; Turchini, S.; Sanna, Simone

    2012-01-01

    Studies of self-assembled chiral molecules on achiral metallic surfaces have mostly focused on the determination of the geometry of adsorbates and their electronic structure. The aim of this paper is to provide direct information on the chirality character of the system and on the chirality trans...

  11. Theory for magnetic linear dichroism of electronic transitions between twofold-degenerate molecular spin levels

    Science.gov (United States)

    Bominaar, Emile L.; Achim, Catalina; Peterson, Jim

    1998-07-01

    Magnetic linear dichroism (MLD) spectroscopy is a relatively new technique which previously has been almost exclusively applied to atoms. These investigations have revealed that the study of MLD, in conjunction with electronic absorption and magnetic circular dichroism (MCD) spectroscopies, provides significant additional information concerning the electronic structure of atoms. More recent measurements have indicated that MLD is also observable from transition ions in inorganic compounds and metalloproteins. While the theory for atomic MLD has been worked out in considerable detail during the last two decades, an MLD theory of practical utility for the analysis of the spectra derived from the majority of paramagnetic molecules is not available. In the present contribution, the MLD of an electric-dipole-allowed transition between twofold-degenerate molecular spin levels is analyzed, assuming nonsaturating conditions. As for atomic systems, it is found that the MLD of a single molecule is dominated by the term G0. However, this term vanishes in the powder average evaluated for a randomly oriented ensemble of molecules, leading to a drastic reduction of the MLD differential absorption for systems with spin S=1/2 compared to that observed for systems with higher ground-state spin. It is found that MLD and MCD spectroscopies on solution samples have complementary spin-state specific sensitivities which suggest that the two methods can be used to selectively probe the individual metal sites in multicenter metalloprotein assemblies.

  12. Exciton Coupling in Circular Dichroic Spectroscopy as a Tool for Establishing the Absolute Configuration of alpha,beta-Unsaturated Esters of Allylic Alcohols

    DEFF Research Database (Denmark)

    Lauridsen, A.; Cornett, Claus; Christensen, S. B.

    1991-01-01

    alpha-beta-Unsaturated esters of allylic alcohols have been shown to exhibit exciton coupling by circular dichroic spectroscopy. This coupling permits the establishment of the absolute configuration. The method was used to prove the absolute configuration at C-2 of archangelolide. Detailed NMR sp...

  13. Measurements of linear and circular birefringence in metals by femtosecond optical pump-probe spectroscopy

    CERN Document Server

    Wilks, R

    2002-01-01

    Optically induced transient linear and circular birefringence has been studied in three different materials: ferromagnetic Ni, semiconducting GaAs and the non-magnetic metal Al. A pump-probe experiment with sub-ps resolution was set up for this purpose. The time-resolved reflectivity, rotation and ellipticity of the reflected probe beam were recorded after pumping with light of variable helicity. In the Ni sample an ultrafast demagnetisation effect was observed and the variation of the rotation and ellipticity on sub-picosecond time scales was compared. Rotation and ellipticity were found to have a similar time dependence. In GaAs, optical orientation of spin was achieved and the subsequent spin relaxation was measured for different pump powers. Fitting of the optical rotation data has revealed the power dependence of the various decay constants. In the Al sample a small signal was observed that decays on ps time scales. This was attributed to a linear birefringence effect resulting from a cubic optical nonli...

  14. Characterization of magnetic domain walls using electron magnetic chiral dichroism

    Directory of Open Access Journals (Sweden)

    Ren Chao Che, Chong Yun Liang, Xiang He, Hai Hua Liu and Xiao Feng Duan

    2011-01-01

    Full Text Available Domain walls and spin states of permalloy were investigated by electron magnetic chiral dichroism (EMCD technique in Lorentz imaging mode using a JEM-2100F transmission electron microscope. EMCD signals from both Fe and Ni L3,2 edges were detected from the Bloch lines but not from the adjacent main wall. The magnetic polarity orientation of the circular Bloch line is opposite to that of the cross Bloch line. The orientations of Fe and Ni spins are parallel rather than antiparallel, both at the cross Bloch line and circular Bloch line.

  15. Expression, Purification, and Monitoring of Conformational Changes of hCB2 TMH67H8 in Different Membrane-Mimetic Lipid Mixtures Using Circular Dichroism and NMR Techniques

    Directory of Open Access Journals (Sweden)

    Elvis K. Tiburu

    2017-02-01

    Full Text Available This work was intended to develop self-assembly lipids for incorporating G-protein coupled receptors (GPCRs in order to improve the success rate for nuclear magnetic resonance spectroscopy (NMR structural elucidation. We hereby report the expression and purification of uniformly 15N-labeled human cannabinoid receptor-2 domain in insect cell media. The domain was refolded by screening several membrane mimetic environments. Different q ratios of isotropic bicelles were screened for solubilizing transmembrane helix 6, 7 and 8 (TMH67H8. As the concentration of dimyristoylphosphocholine (DMPC was increased such that the q ratio was between 0.16 and 0.42, there was less crowding in the cross peaks with increasing q ratio. In bicelles of q = 0.42, the maximum number of cross peaks were obtained and the cross peaks were uniformly dispersed. The receptor domain in bicelles beyond q = 0.42 resulted in peak crowding. These studies demonstrate that GPCRs folding especially in bicelles is protein-specific and requires the right mix of the longer chain and shorter chain lipids to provide the right environment for proper folding. These findings will allow further development of novel membrane mimetics to provide greater diversity of lipid mixtures than those currently being employed for GPCR stability and folding, which are critical for both X-ray and NMR studies of GPCRs.

  16. A complex-polarization-propagator protocol for magneto-chiral axial dichroism and birefringence dispersion

    DEFF Research Database (Denmark)

    Cukras, Janusz; Kauczor, Joanna; Norman, Patrick

    2016-01-01

    A computational protocol for magneto-chiral dichroism and magneto-chiral birefringence dispersion is presented within the framework of damped response theory, also known as complex polarization propagator theory, at the level of time-dependent Hartree–Fock and time-dependent density functional...... theory. Magneto-chiral dichroism and magneto-chiral birefringence spectra in the (resonant) frequency region below the first ionization threshold of R-methyloxirane and L-alanine are presented and compared with the corresponding results obtained for both the electronic circular dichroism and the magnetic...

  17. Photoinduced Circular Anisotropy in Side-Chain Azobenzene Polyesters

    DEFF Research Database (Denmark)

    Nikolova, L.; Todorov, T.; Ivanov, M.;

    1997-01-01

    We report for the first time the inducing of large circular anisotropy in previously unoriented films of side-chain azobenzene polyesters on illumination with circularly polarized light at a wavelength of 488 nm. The circular dichroism and optical activity are measured simultaneously in real time...

  18. Reload Purified Melittin and Lactoferrin on Perfluorooctyl Bromide Nanoparticles (PFOB-Nps and Examine the Distribution of Particle Size, Zeta Potential and Confirmation of Their Accession on the Nanoparticles Via Tryptophan Fluorescence and Circular Dichroism (CD and its Anti-Cancer Effects on Human Breast Cancer Cell Line MCF7

    Directory of Open Access Journals (Sweden)

    Hadis Rahmani Incheh Keykanlu

    2016-12-01

    Full Text Available Acording to the prevalence of cancer in today's societies, it is too important to find new drugs for that treatment. Cationic antimicrobial peptides that are able to eliminate a wide range of bacteria, fungi, parasites, viruses and unicellular, are natural anti-cancer agents. In the present study, the effect of cationic peptides of bee venom Melittin (ML and Lactoferrin (LF of camel milk which was loaded on the Perfluorooctyl Bromide (PFOB nanoparticles, were examined on MCF7 cells. Nanoparticles using oil in water emulsion was prepared by ultra-thoracic and ultrasonic. Then ML and LF were separately added to the nanoparticles then incorporation of them were confirmed by tryptophan fluorescence and circular dichroism (CD spectra. The mean diameter of the nanoparticles did not change after addition of ML and LF (~100 nm, but as expected, the zeta potential of the nanoparticles with increasing of ML and LF concentrations to the preformed nanoparticles increased from -18.43(without ML and LF to +21.61(LF 110.66µg/ml and +20.93(ML 0.1µg/ml and +23.75(LF 110.66µg/ml and ML 0.1µg/ml. By using of scanning electron microscopy (SEM, the morphology and structure of nanoparticles was investigated, homogeneity and uniformity during processing and loading of ML and LF was observed. Effectiveness of nanoparticles loaded on cancer cells was performed with MTT test. The results showed that ML and LF had a positive effect on cancer cell death. Percent of cell death was higher when ML and LF was loaded on nanoparticles. With increase of ML and LF concentration loading on nanoparticles, increases cancer cell death. Minitab software was used to analyze some data.

  19. A circular dichroism study of undegraded human ceruloplasmin.

    Science.gov (United States)

    Noyer, M; Putnam, F W

    1981-06-09

    The CD spectrum of human ceruloplasmin (Cp) has been studied between pH 6.90 and 12.00 in the far-ultraviolet, near-ultraviolet, and visible light regions. The spectrum in the far-ultraviolet region showed that undegraded holo and apo single-chain ceruloplasmin and a cleaved ceruloplasmin preparation have a low content of alpha helix but a high content of beta and unordered structure. A conformational transition accompanied by a decrease in beta and an increase in unordered structure occurred at pH 11.10 for intact ceruloplasmin. This transition probably involved the ionization of buried tyrosines, as shown by the increase of a near-ultraviolet band at 250 nm. The copper atoms may contribute to the stability of the native structure since the conformational transition occurred at a low pH value (10.50) in the case of apoceruloplasmin. The apo-Cp also presented a more intense CD band at 292 nm, suggesting the presence of tryptophan(s) near the environment of copper(s) in the molecule where no tyrosine residue seems to be involved. The spectrum between 320 and 700 nm of intact and cleaved Cp was resolved into six Gaussian bands which were assigned to type-1 copper atoms. Important changes in only two of these bands upon pH increase (bands III at 541 nm and VII at 322 nm) confirmed the nonequivalence of the two blue coppers in human ceruloplasmin.

  20. Administrative Circulars

    CERN Multimedia

    Département des Ressources humaines

    2004-01-01

    Administrative Circular N° 2 (Rev. 2) - May 2004 Guidelines and procedures concerning recruitment and probation period of staff members This circular has been revised. It cancels and replaces Administrative Circular N° 2 (Rev. 1) - March 2000. Administrative Circular N° 9 (Rev. 3) - May 2004 Staff members contracts This circular has been revised. It cancels and replaces Administrative Circular N° 9 (Rev. 2) - March 2000. Administrative Circular N° 26 (Rev. 4) - May 2004 Procedure governing the career evolution of staff members This circular has also been revised. It Administrative Circulars Administrative Circular N° 26 (Rev. 3) - December 2001 and brings up to date the French version (Rev. 4) published on the HR Department Web site in January 2004. Operational Circular N° 7 - May 2004 Work from home This circular has been drawn up. Operational Circular N° 8 - May 2004 Dealing with alcohol-related problems...

  1. Circular Coinduction

    Science.gov (United States)

    Rosu, Grigore; Goguen, Joseph; Norvig, Peter (Technical Monitor)

    2001-01-01

    Circular coinduction is a technique for behavioral reasoning that extends cobasis coinduction to specifications with circularities. Because behavioral satisfaction is not recursively enumerable, no algorithm can work for every behavioral statement. However. algorithms using circular coinduction can prove every practical behavioral result that we know. This paper proves the correctness of circular coinduction and some consequences.

  2. Characterization of amino acids using Raman spectroscopy

    Science.gov (United States)

    Jenkins, Amanda L.; Larsen, Richard A.; Williams, Timothy B.

    2005-05-01

    A key process in the development of new drugs is elucidation of the interaction between the drug molecule and the target protein. Such knowledge then makes it possible to make systematic structural modifications of the drug molecule to optimize the interaction. Many analytical techniques can be applied to proteins in solution such as circular dichroism, ultraviolet, and fluorescence spectroscopy but these all have limitations. In this paper, we investigate the feasibility of using relatively simple, visible light Raman spectroscopic methods to investigate amino acids and related biopolymers.

  3. Electronic and vibrational spectroscopy of the cytochrome c:cytochrome c oxidase complexes from bovine and Paracoccus denitrificans.

    OpenAIRE

    Lynch, S. R.; Copeland, R. A.

    1992-01-01

    The 1:1 complex between horse heart cytochrome c and bovine cytochrome c oxidase, and between yeast cytochrome c and Paracoccus denitrificans cytochrome c oxidase have been studied by a combination of second derivative absorption, circular dichroism (CD), and resonance Raman spectroscopy. The second derivative absorption and CD spectra reveal changes in the electronic transitions of cytochrome a upon complex formation. These results could reflect changes in ground state heme structure or chan...

  4. Perfect Circular Dichroic Metamirrors

    CERN Document Server

    Wang, Zuojia; Liu, Yongmin

    2015-01-01

    In nature, the beetle Chrysina gloriosa derives its iridescence by selectively reflecting left-handed circularly polarized light only. Here, for the first time, we introduce and demonstrate the optical analogue based on an ultrathin metamaterial, which we term circular dichroic metamirror. A general method to design the circular dichroic metasmirror is presented under the framework of Jones calculus. It is analytically shown that the metamirror can be realized by two layers of anisotropic metamaterial structures, in order to satisfy the required simultaneous breakings of n-fold rotational (n>2) and mirror symmetries. We design an infrared metamirror, which shows perfect reflectance for left-handed circularly polarized light without reversing its handedness, while almost completely absorbs right-handed circularly polarized light. These findings offer new methodology to realize novel chiral optical devices for a variety of applications, including polarimetric imaging, molecular spectroscopy, as well as quantum ...

  5. Chiral optical fields: A unified formulation of helicity scattered from particles and dichroism enhancement

    CERN Document Server

    Nieto-Vesperinas, Manuel

    2016-01-01

    We establish a general unified formulation which, using the optical theorem of electromagnetic helicity, shows that dichorism is a phenomenon arising in any scattering -or diffraction- process, elastic or not, of chiral electromagnetic fields by objects either chiral or achiral. It is shown how this approach paves the way to overcoming well-known limitations of standard circular dichroism, like its weak signal or the difficulties of using it with magnetodielectric particles. Based on the angular spectrum representation of optical fields with only right circular or left circular plane waves, we introduce beams with transverse elliptic polarization and posessing a longitudinal component. Then our formulation for general optical fields shows how to enhance the helicity, (and therefore the dichroism signal), versus the energy of the light scattered or emitted by a particle, or viceversa.

  6. 黄曲霉毒素解毒酶在大肠杆菌中的可溶性表达、纯化及其圆二色谱分析%Soluble Expression, Purification of Recombinant Aflatoxin-detoxifizyme in E.coli and Analysis of Circular Dichroism Spectrum

    Institute of Scientific and Technical Information of China (English)

    胡熔; 刘大岭; 谢春芳; 姚冬生

    2011-01-01

    Objective : To expresss and purify the aflatoxin-detoxifizyme( ADTZ) in E. coli. and to study the biological activities and secondary structure of rADTZ. Methods and Results: the mature peptide of ADTZ was subcloned into pMAL-c2x vector to construct the prokaryotic expression plasmid. The recombinant plasmid was transformed into Rosetta( DE3) and the soluble fusion protein MBP-ADTZ was highly induced by IPTG. The expression level was approximately 50% of the total bacterial protein. The pure fusion protein was got from the cell lysate by amylose affinity chromatography. 42kDa MBP and 76kDa rADTZ were gained via digestion of fusion protein by Factor Xa, and pure rADTZ was obtained by Hydrophobic interaction chromatography ( HIC ).Biological activities of rADTZ had been examined and results showed that the protein had AFB1-detoxifying activity with the specific activity of 136U/mg. Circular dichroism spectra analysis revealed that rADTZ was composed of 43.3% of α-helix, 31. 1% of β-sheet, 10.5% of β-turn and 15. 1% of random coil. Conclusion:Purified rADTZ protein with AFB1-detoxifying activity was obtained and that laid the foundation for exploration of the relationship between the structure and function of rADTZ.%目的:应用原核表达系统对黄曲霉毒素解毒酶(aflatoxin-detoxifizyme,ADTZ)进行高效可溶表达和纯化,并对其进行生物学活性与二级结构分析.方法与结果:亚克隆ADTZ的成熟肽,并构建与pMAL-c2x的重组质粒,转化大肠杆菌Rosetta(DE3),IPTG诱导实现了MBP_ADTZ融合蛋白的高效可溶表达,其表达量约占总蛋白的50%.经Amylose亲和层析、Factor Xa酶切和疏水层析后得到高纯度的rADTZ蛋白.生物学活性分析表明rADTZ蛋白具有降解AFB的酶活性,酶比活为136U/rag.圆二色光谱对rADTZ蛋白二级结构的分析结果为:а-螺旋为43.3%、β-折叠为31.1%、β-转角为10.5%和无规则卷曲为15.1%.结论:用大肠杆菌成功表达并得到高纯度有

  7. Surface spin-polarized currents generated in topological insulators by circularly polarized synchrotron radiation and their photoelectron spectroscopy indication

    Science.gov (United States)

    Shikin, A. M.; Klimovskikh, I. I.; Filyanina, M. V.; Rybkina, A. A.; Pudikov, D. A.; Kokh, K. A.; Tereshchenko, O. E.

    2016-08-01

    A new method for generating spin-polarized currents in topological insulators has been proposed and investigated. The method is associated with the spin-dependent asymmetry of the generation of holes at the Fermi level for branches of topological surface states with the opposite spin orientation under the circularly polarized synchrotron radiation. The result of the generation of holes is the formation of compensating spin-polarized currents, the value of which is determined by the concentration of the generated holes and depends on the specific features of the electronic and spin structures of the system. The indicator of the formed spin-polarized current can be a shift of the Fermi edge in the photoelectron spectra upon photoexcitation by synchrotron radiation with the opposite circular polarization. The topological insulators with different stoichiometric compositions (Bi1.5Sb0.5Te1.8Se1.2 and PbBi2Se2Te2) have been investigated. It has been found that there is a correlation in the shifts and generated spin-polarized currents with the specific features of the electronic spin structure. Investigations of the graphene/Pt(111) system have demonstrated the possibility of using this method for other systems with a spin-polarized electronic structure.

  8. Chiroptical Spectroscopy

    Science.gov (United States)

    Gurst, Jerome E.

    1995-09-01

    A brief review of the literature, and Chemical and Engineering News in particular, reveals that the determination and use of optical activity is of increasing importance in today's commercial and research laboratories. The classical technique is to measure [alpha]D using a manual or recording polarimeter to provide a single value, the specific rotation at 589 nm. A spectropolarimeter can be used to determine optical activity through the UV-Visible spectrum (Optical Rotatory Dispersion [ORD]). At wavelengths far removed from electronic absorption bands, optical activity arises from circular birefringence, or the difference in the refractive index for left- and right-circularly polarized light; i.e., nL - nR does not equal zero for chiral materials. If the optical activity is measured through an absorption band, complex behavior is observed (a Cotton Effect curve). At an absorption band, chiral materials exhibit circular dichroism (CD), or a difference in the absorption of left- and right-circularly polarized light; epsilon L minus epsilon R does not equal zero. If the spectropolarimeter is set for the measurement of CD spectra, one observes what appears to be a UV-Vis spectrum except that some absorption bands are positive while others may be negative. Just as enantiomers have specific rotations that are equal and opposite at 589 nm (sodium D line), rotations are equal and opposite at all wavelengths, and CD measurements are equal and opposite at all wavelengths. Figure 1 shows the ORD curves for the enantiomeric carvones while Figure 2 contains the CD curves. The enantiomer of carvone that has the positive [alpha]D is obtained from caraway seeds and is known to have the S-configuration while the R-enantiomer is found in spearmint oil. Figure 1. ORD of S-(+)- and R-(-)-carvones Figure 2. CD of S-(+)- and R-(-)-carvones While little can be done to correlate stereochemistry with [alpha]D values, chiroptical spectroscopy (ORD and/or CD) often can be used to assign

  9. Comprehensive Chiroptical Spectroscopy, Applications in Stereochemical Analysis of Synthetic Compounds, Natural Products, and Biomolecules

    CERN Document Server

    Berova, Nina; Nakanishi, Koji; Woody, Robert W

    2012-01-01

    This book provides an introduction to the important methods of chiroptical spectroscopy in general, and circular dichroism (CD) in particular, which are increasingly important in all areas of chemistry, biochemistry, and structural biology. The book can be used as a text for undergraduate and graduate students and as a reference for researchers in academia and industry. Experimental methods and instrumentation are described with topics ranging from the most widely used methods (electronic and vibrational CD) to frontier areas such as nonlinear spectroscopy and photoelectron CD,

  10. Comprehensive chiroptical spectroscopy, instrumentation, methodologies, and theoretical simulations

    CERN Document Server

    Berova, Nina; Nakanishi, Koji

    2011-01-01

    This book provides an introduction to the important methods of chiroptical spectroscopy in general, and circular dichroism (CD) in particular, which are increasingly important in all areas of chemistry, biochemistry, and structural biology. The book can be used as a text for undergraduate and graduate students and as a reference for researchers in academia and industry, with or without the companion volume in this set. Experimental methods and instrumentation are described with topics ranging from the most widely used methods (electronic and vibrational CD) to frontier areas such as nonlinear

  11. Circular Updates

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Circular Updates are periodic sequentially numbered instructions to debriefing staff and observers informing them of changes or additions to scientific and specimen...

  12. Operational Circulars

    CERN Multimedia

    2003-01-01

    Operational Circular N° 4 - April 2003 Conditions for use by members of the CERN personnel of vehicles belonging to or rented by CERN - This circular has been drawn up. Operational Circular N° 5 - October 2000 Use of CERN computing facilities - Further details on the personal use of CERN computing facilities Operational Circular N° 5 and its Subsidiary Rules http://cern.ch/ComputingRules defines the rules for the use of CERN computing facilities. One of the basic principles governing such use is that it must come within the professional duties of the user concerned, as defined by the user's divisional hierarchy. However, personal use of the computing facilities is tolerated or allowed provided : a) It is in compliance with Operational Circular N° 5 and not detrimental to official duties, including those of other users; b) the frequency and duration is limited and there is a negligible use of CERN resources; c) it does not constitute a political, commercial and/or profit-making activity; d) it is not...

  13. Magnetic x-ray linear dichroism of ultrathin Fe-Ni alloy films

    Energy Technology Data Exchange (ETDEWEB)

    Schumann, F.O.; Willis, R.F. [Pennsylvania State Univ., University Park, PA (United States); Goodman, K.W. [Lawrence Berkeley National Lab., CA (United States)] [and others

    1997-04-01

    The authors have studied the magnetic structure of ultrathin Fe-Ni alloy films as a function of Fe concentration by measuring the linear dichroism of the 3p-core levels in angle-resolved photoemission spectroscopy. The alloy films, grown by molecular-beam epitaxy on Cu(001) surfaces, were fcc and approximately four monolayers thick. The intensity of the Fe dichroism varied with Fe concentration, with larger dichroisms at lower Fe concentrations. The implication of these results to an ultrathin film analogue of the bulk Invar effect in Fe-Ni alloys will be discussed. These measurements were performed at the Spectromicroscopy Facility (Beamline 7.0.1) of the Advanced Light Source.

  14. 含有碘代酪氨酸的铜(Ⅱ)三元混配配合物的圆二色光谱研究——碘对甲状腺激素生物活性的结构作用探索%Circular Dichroism Study on Ternary Copper(Ⅱ) Complexes with Diiodotyrosinate-An Approach for Structural Effects of Iodines on Biological Activation of Thyroid Hormones

    Institute of Scientific and Technical Information of China (English)

    刘晓瀛; 张锋

    2001-01-01

    Absorption and circular dichroism (CD) spectra of the ternary copper(Ⅱ) complexes with 3-iodo-L-tyrosine (L-Ityr),L-tyrosine (L-Tyr),or L-homoserine (L-Hser) and amino acids L-AA,where AA represents arginine (Arg),lysine (Lys),asparagine (Asn),glutamine (Gln),or alanine (Ala),have been determined in the d-d region in various ionic strength ( I = 1.0 or 0.1 mol/L KNO3) and solvents (H2O,50% ethanol-H2O,or 50% dioxane-H2O).CD spectra for all the ternary complexes exhibit a maximum at 587~627 nm,and the △ε for Cu(L-Ityr) (L-Arg) and Cu(L-Ityr) (L-Lys) are abnormally negative (-0.479~-0.884).The △ε for Cu(L-Ityr) (L-AA) is obviously more negative than that for Cu(L-Tyr)(L-AA).The possible ligand-ligand interactions in these ternary complexes were discussed,and a structural effect of iodine on the interaction was emphasized.%用圆二色光谱法研究了铜(Ⅱ)与3-碘基-L-酪氨酸(L-Ityr),L-酪氨酸(L-Tyr),或L-高丝氨酸(L-Hser)和L-AA(AA代表精氨酸(Arg),赖氨酸(Lys),天冬酰胺(Asn),谷氨酰胺(Gln),或丙氨酸(Ala)三元混配配合物体系在不同离子强度(I=1.0或0.1mol/L KNO3)和溶剂环境(水,50%(v/v)乙醇-水或50%(v/v)二氧六环-水)条件下配体间相互作用.全部混配配合物体系的圆二色光谱在587~627nm范围均有负的极大吸收,且Cu(L-Ityr)L-Arg)和Cu(L-Ityr)(L-Lys)体系的△ε异常负(-0.479~-0.884);Cu(L-Ityr)(L-AA)体系的△ε明显比Cu(L-Tyr)(L-AA)负.讨论了这些混配配合物中配体间相互作用的规律和碘的结构效应.

  15. Characterization of linear forms of the circular enterocin AS-48 obtained by limited proteolysis

    NARCIS (Netherlands)

    Montalbán-López, Manuel; Spolaore, Barbara; Pinato, Odra; Martínez-Bueno, Manuel; Valdivia, Eva; Maqueda, Mercedes; Fontana, Angelo

    2008-01-01

    AS-48 is a 70-residue circular peptide from Enterococcus faecalis with a broad antibacterial activity. Here, we produced by limited proteolysis a protein species carrying a single nicking and fragments of 55 and 38 residues. Nicked AS-48 showed a lower helicity by far-ultraviolet circular dichroism

  16. Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Hellman, Hal

    1968-01-01

    This booklet discusses spectroscopy, the study of absorption of radiation by matter, including X-ray, gamma-ray, microwave, mass spectroscopy, as well as others. Spectroscopy has produced more fundamental information to the study of the detailed structure of matter than any other tools.

  17. ADMINISTRATIVE CIRCULARS

    CERN Multimedia

    Division des ressources humaines

    2000-01-01

    N° 2 (Rev. 1) - March 2000Guidelines and procedures concerning recruitment and probation period of staff membersN° 9 (Rev. 2) - March 2000Staff members contractsN° 16 (Rev. 2) - January 2000TrainingN° 30 (Rev. 1) - January 2000Indemnities and reimbursements upon taking up appointment and termination of contractN° 32 - February 2000Principles and procedures governing complaints of harassmentThese circular have been amended (No 2, N° 9, N° 16 and N° 30) or drawn up (N° 32).Copies are available in the Divisional Secretariats.Note:\tAdministrative and operational circulars, as well as the lists of those in force, are available for consultation in the server SRV4_Home in the Appletalk zone NOVELL (as GUEST or using your Novell username and password), volume PE Division Data Disk.The Word files are available in the folder COM, folder Public, folder ADM.CIRC.docHuman Resources DivisionTel. 74128

  18. Spectroscopy

    CERN Document Server

    Walker, S

    1976-01-01

    The three volumes of Spectroscopy constitute the one comprehensive text available on the principles, practice and applications of spectroscopy. By giving full accounts of those spectroscopic techniques only recently introduced into student courses - such as Mössbauer spectroscopy and photoelectron spectroscopy - in addition to those techniques long recognised as being essential in chemistry teaching - sucha as e.s.r. and infrared spectroscopy - the book caters for the complete requirements of undergraduate students and at the same time provides a sound introduction to special topics for graduate students.

  19. Polyproline II structure in proteins: identification by chiroptical spectroscopies, stability, and functions.

    Science.gov (United States)

    Bochicchio, Brigida; Tamburro, Antonio Mario

    2002-11-01

    In the last years polyproline II (PPII) structure has been demonstrated to be essential to biological activities such as signal transduction, transcription, cell motility, and immune response. The polyproline left-handed helical structure was nearly unknown until now and often confused with unordered, disordered, irregular, unstructured, extended, or random coil conformations because it is neither alpha-helical nor beta-turn nor beta-sheet, i.e., a classical structure. In spite of the regularity of the PPII structure and, more precisely, its well-defined dihedral angle values, a typical feature of PPII structure is the absence of any intramolecular hydrogen bonds that renders the PPII structure indistinguishable from an irregular backbone structure by (1)H-NMR spectroscopy. The only way to unambiguously reveal PPII structure in solution is to use spectroscopies based on optical activity, such as circular dichroism (CD), vibrational circular dichroism (VCD), and Raman optical activity (ROA). Herein we focus on the identification of PPII structure by CD, widely considered to be the most reliable methodology. Then we report on VCD and ROA spectroscopies as tools in the identification of PPII structure. A third section is dedicated to the analysis of the stabilization of PPII conformation in aqueous solution. Finally, the significance of PPII in self-assembly processes, in elasticity of elastomeric proteins, and in proteins-(peptides) proteins molecular recognition processes are considered.

  20. Protein folding and misfolding shining light by infrared spectroscopy

    CERN Document Server

    Fabian, Heinz

    2012-01-01

    Infrared spectroscopy is a new and innovative technology to study protein folding/misfolding events in the broad arsenal of techniques conventionally used in this field. The progress in understanding protein folding and misfolding is primarily due to the development of biophysical methods which permit to probe conformational changes with high kinetic and structural resolution. The most commonly used approaches rely on rapid mixing methods to initiate the folding event via a sudden change in solvent conditions. Traditionally, techniques such as fluorescence, circular dichroism or visible absorption are applied to probe the process. In contrast to these techniques, infrared spectroscopy came into play only very recently, and the progress made in this field up to date which now permits to probe folding events over the time scale from picoseconds to minutes has not yet been discussed in a book. The aim of this book is to provide an overview of the developments as seen by some of the main contributors to the field...

  1. Electronic states of the fluorophore 9,10-bis(phenylethynyl)anthracene (BPEA). A synchrotron radiation linear dichroism investigation

    DEFF Research Database (Denmark)

    Thulstrup, Peter Waaben; Jones, Nykola; Hoffmann, Søren Vrønning

    2013-01-01

    The electronic transitions of 9,10-bis(phenylethynyl)anthracene (BPEA) were investigated by synchrotron radiation linear dichroism (SRLD) spectroscopy in the range 20000–58000 cm1 (500–170 nm) on molecular samples aligned in stretched polyethylene. The investigation was supported by variable...

  2. Circular causality.

    Science.gov (United States)

    Thomas, R

    2006-07-01

    The problem of disentangling complex dynamic systems is addressed, especially with a view to identifying those variables that take part in the essential qualitative behaviour of systems. The author presents a series of reflections about the methods of formalisation together with the principles that govern the global operation of systems. In particular, a section on circuits, nuclei, and circular causality and a rather detailed description of the analytic use of the generalised asynchronous logical description, together with a brief description of its synthetic use (OreverseO logic). Some basic rules are recalled, such as the fact that a positive circuit is a necessary condition of multistationarity. Also, the interest of considering as a model, rather than a well-defined set of differential equations, a variety of systems that differ from each other only by the values of constant terms is emphasised. All these systems have a common Jacobian matrix and for all of them phase space has exactly the same structure. It means that all can be partitioned in the same way as regards the signs of the eigenvalues and thus as regards the precise nature of any steady states that might be present. Which steady states are actually present, depends on the values of terms of order zero in the ordinary differential equations (ODEs), and it is easy to find for which values of these terms a given point in phase space is steady. Models can be synthesised first at the level of the circuits involved in the Jacobian matrix (that determines which types and numbers of steady states are consistent with the model), then only at the level of terms of order zero in the ODE's (that determines which of the steady states actually exist), hence the title 'Circular casuality'.

  3. Spectroscopy

    DEFF Research Database (Denmark)

    Berg, Rolf W.

    This introductory booklet covers the basics of molecular spectroscopy, infrared and Raman methods, instrumental considerations, symmetry analysis of molecules, group theory and selection rules, as well as assignments of fundamental vibrational modes in molecules.......This introductory booklet covers the basics of molecular spectroscopy, infrared and Raman methods, instrumental considerations, symmetry analysis of molecules, group theory and selection rules, as well as assignments of fundamental vibrational modes in molecules....

  4. In situ protein secondary structure determination in ice: Raman spectroscopy-based process analytical tool for frozen storage of biopharmaceuticals.

    Science.gov (United States)

    Roessl, Ulrich; Leitgeb, Stefan; Pieters, Sigrid; De Beer, Thomas; Nidetzky, Bernd

    2014-08-01

    A Raman spectroscopy-based method for in situ monitoring of secondary structural composition of proteins during frozen and thawed storage was developed. A set of reference proteins with different α-helix and β-sheet compositions was used for calibration and validation in a chemometric approach. Reference secondary structures were quantified with circular dichroism spectroscopy in the liquid state. Partial least squares regression models were established that enable estimation of secondary structure content from Raman spectra. Quantitative secondary structure determination in ice was accomplished for the first time and correlation with existing (qualitative) protein structural data from the frozen state was achieved. The method can be used in the presence of common stabilizing agents and is applicable in an industrial freezer setup. Raman spectroscopy represents a powerful, noninvasive, and flexibly applicable tool for protein stability monitoring during frozen storage.

  5. X-ray magnetic dichroism in (Zn,Mn)O diluted magnetic semiconductors: First-principles calculations

    Science.gov (United States)

    Antonov, V. N.; Bekenov, L. V.; Mazur, D. V.; Germash, L. P.

    2012-06-01

    The electronic structure of (Zn,Mn)O diluted magnetic semiconductors was investigated theoretically from first principles by using the fully-relativistic Dirac linear muffin-tin orbital band structure method with the local spin-density approximation (LSDA) and the LSDA+ U approach. The X-ray magnetic circular dichroism (XMCD) spectra at the Mn, Zn, and O K and Mn L 2,3 edges were investigated theoretically from first principles. The origin of the XMCD spectra in these compounds was examined. The effect of oxygen vacancy atoms was found to be crucial for the X-ray magnetic dichroism at the Mn L 2,3 edges. The calculated results are compared with available experimental data.

  6. Chiroptical Spectroscopy in the Vapor Phase

    Science.gov (United States)

    Lahiri, Priyanka; Long, Benjamin D.; Wiberg, Kenneth B.; Vaccaro, Patrick H.

    2011-06-01

    Electromagnetic radiation propagating through an isotropic chiral medium experiences a complex index of refraction that differs in both real (in-phase) and imaginary (in-quadrature) parts for the right-circular and left-circular polarization states that define the helicity basis. The resulting phenomena of circular birefringence (CB) and circular dichroism (CD) lead to observable effects in the form of dispersive rotation and absorptive elliptization for an impinging beam of plane-polarized light, which commonly are measured under conditions of nonresonant and resonant excitation, respectively. This talk will discuss ongoing efforts designed to elucidate the provenance of electronic optical activity under complementary solvated and isolated conditions, with the latter vapor-phase work made possible by our continuing development of Cavity Ring-Down Polarimetry (CRDP). Molecules of interest include the rigid bicyclic ketone (1R,4R)-norbornenone, where the spatial arrangement of distal alkene and carbonyl moeities gives rise to extraordinarily large specific rotation (CB) parameters that are predicted incongruously by different quantum-chemical methods; the monoterpene constitutional isomers (S)-2-carene and (S)-3-carene, which display surprisingly distinct chiroptical properties; and conjugated ketones such as (S)-verbenone, where CD probes of weak π*←n absorption bands have been performed at vibronic resolution. The disparate nature of gas-phase and condensed-phase optical activity will be highlighted, with complementary ab initio calculations serving to elucidate the structural, chemical, and electronic origins of observed behavior. T. Müller, K. B. Wiberg, P. H. Vaccaro, J. R. Cheeseman, and M. J. Frisch, J. Opt. Soc. Am. B 19, 125 (2002) P. H. Vaccaro, ``Chapter 1.II.10: Optical Rotation and Intrinsic Optical Activity'' in Comprehensive Chiroptical Spectroscopy, N. Berova, P. L. Polavarapu, K. Nakanishi, and R. W. Woody, eds. (John Wiley and Sons, Inc

  7. Spectroscopy reveals that ethyl esters interact with proteins in wine.

    Science.gov (United States)

    Di Gaspero, Mattia; Ruzza, Paolo; Hussain, Rohanah; Vincenzi, Simone; Biondi, Barbara; Gazzola, Diana; Siligardi, Giuliano; Curioni, Andrea

    2017-02-15

    Impairment of wine aroma after vinification is frequently associated to bentonite treatments and this can be the result of protein removal, as recently demonstrated for ethyl esters. To evaluate the existence of an interaction between wine proteins and ethyl esters, the effects induced by these fermentative aroma compounds on the secondary structure and stability of VVTL1, a Thaumatin-like protein purified from wine, was analyzed by Synchrotron Radiation Circular Dichroism (SRCD) spectroscopy. The secondary structure of wine VVTL1 was not strongly affected by the presence of selected ethyl esters. In contrast, VVTL1 stability was slightly increased by the addition of ethyl-octanoate, -decanoate and -dodecanoate, but decreased by ethyl-hexanoate. This indicates the existence of an interaction between VVTL1 and at least some aroma compounds produced during fermentation. The data suggest that proteins removal from wine by bentonite can result in indirect removal of at least some aroma compounds associated with them.

  8. Spectroscopy Investigation on Conformational Transition of Tea Glycoconjugate from Green Tea

    Institute of Scientific and Technical Information of China (English)

    CHEN,Hai-Xia(陈海霞); ZHANG,Min(张民); XIE,Bi-Jun(谢笔钧)

    2004-01-01

    The conformational transition of a new glycoconjugate,tea glycoconjugate(TGC),was investigated by spectroscopy techniques including circular dichroism(CD)and ultraviolet(UV)spectroscopy.The solution behaviors of TGC inthe mediums of different temperature,pH value,and ions were compared.Results showed that the native conformation of TGC was partially ordered.The CD value and UV absorbance of TGC altered with the change of pH value,temperature,the addition of ions,and also accompanied order-disorder transition.Especially the conditions with temperature higher than the glasstransition temperature(Tg=62℃),higher pH value orlower pH value will have the most impact on the conformation of TGC,which will destroy the hydrogen bonds between the TGC molecules.The results indicated that the outside factors playimportant roles onthe stability of the conformation of TGC.

  9. Synchrotron radiation linear dichroism (SRLD) investigation of the electronictransitions of quinizarin, chrysazin, and anthrarufin

    DEFF Research Database (Denmark)

    Nguyen, Duy Duc; Jones, Nykola C.; Hoffmann, Søren Vrønning;

    2010-01-01

    The electronic transitions of the three , (alpha), (alphaPrime) -dihydroxy derivatives of anthraquinone, 1,4-dihydroxy-, 1,8-dihydroxy-, and 1,5-dihydroxy-9,10-anthraquinone (quinizarin, chrysazin, and anthrarufin), were investigated by synchrotron radiation linear dichroism (SRLD) spectroscopy...... the investigated region (15,000-58,000cm-1), essentially similar wavenumbers, intensities, and transition moment directions were determined for chrysazin and anthrarufin, while the spectrum of quinizarin deviated significantly. The results of time-dependent density functional theory (TD-DFT) calculations were...

  10. Circular dichroism in hydrogen multiphoton ionization by a bichromatic field of frequencies {omega} and 3{omega}

    Energy Technology Data Exchange (ETDEWEB)

    Fifirig, Magda [Department of Chemistry, University of Bucharest, Bucharest (Romania); Cionga, Aurelia [Institute of Space Sciences, Bucharest-Magurele (Romania)

    2002-02-28

    The dichroic effects in the multiphoton ionization of the ground state hydrogen atom by a coherent superposition of a laser beam and its third harmonic, are studied via perturbative calculations. The final state of the photoelectrons, which has the energy E=E{sub 1}+3(h/2{pi}){omega} (E{sub 1} the ground state energy and {omega} the laser frequency), is reached by two interfering quantum paths: (a) absorption of one harmonic photon and (b) absorption of three laser photons. In the chosen regime of field intensities, the radiative corrections to the absorption of one harmonic photon may be disregarded. Our numerical results illustrate the influence of the laser frequency, of the relative intensity and of the harmonic phase upon the dichroic signal. (author)

  11. Hydroxypyridyl Imines: Enhancing Chromatographic Separation and Stereochemical Analysis of Chiral Amines via Circular Dichroism.

    Science.gov (United States)

    Joyce, Leo A; Regalado, Erik L; Welch, Christopher J

    2016-09-16

    Imine-bond formation between chiral amines and commercially available 3-hydroxypyridine-2-carboxaldehyde (HCA) was exploited for rapid determination of stereochemical composition. Chiral supercritical fluid chromatography (SFC) screening of the derivatized imine compounds led to the elucidation of multiple combinations of mobile and stationary phases that gave resolution of all members of a series of chiral amines. The first eluting enantiomer was generally the derivative of the (R)-amine enantiomer across the series that was studied, indicating that the imine formed from the (S)-amine has more favorable interaction with the chiral stationary phase of the column. These conditions were then applied to more challenging compounds, namely amino alcohols and diastereomers possessing more than one stereocenter. The approach was utilized to monitor stereoselective biocatalytic transamination and assign the absolute configuration of the enantiomeric products. Finally, hydrolysis of the imine bond of the derivative was shown to generate enantiopure amine starting materials without racemization. This further highlights the value of this approach for creating readily reversed derivatives that enhance chromatographic separation and aid in the determination of absolute configuration.

  12. Magnetic circular dichroism in real-time time-dependent density functional theory

    CERN Document Server

    Lee, K -M; Bertsch, G F

    2010-01-01

    We apply the adiabatic time-dependent density functional theory to magnetic ci the real-space, real-time computational method. The standard formulas for the MCD response and its A and B terms are derived from the observables in the time-dependent wave function. We find the real time method is well suited for calculating the overall spectrum, particularly at higher excitation energies where individual excited states are numerous and overlapping. The MCD sum rules are derived and interpreted in the real-time formalism; we find that they are very useful for normalization purposes and assessing the accuracy of the theory. The method is applied to MCD spectrum of C-60 using the adiabatic energy functional from the local density approximation. The theory correctly predicts the signs of the A and B terms for the lowest allowed excitations. However, the magnitudes of the terms only show qualitative agreement with experiment.

  13. Circular dichroism anisotrophy of DNA with different modifications at N7 of guanine.

    Science.gov (United States)

    Zavriev, S K; Minchenkova, L E; Vorlícková, M; Kolchinsky, A M; Volkenstein, M V; Ivanov, V I

    1979-09-27

    The complexex DNA-Ag1+, DNA-Cu1+, protonated DNA and DNA methylated at N7 of guanine were oriented by pumping the solutions through a multicapillary cell in the direction of a light beam. The CD components along the DNA axis, delta epsilon parallel, and normal to it, 2 delta epsilon perpendicular, were calculated from the CD spectra of the oriented samples by the method of Chung and Holzwarth, (1975) J. Mol. Biol. 92, 449--466. It was shown that in most cases, except that of the protonated DNA, the degree of orientation was only slightly less than that for pure DNA. This demonstrated the absence of aggregation and of appreciable denaturation. In all cases the modifications of DNA give rise to a negative component 2 delta epsilon perpendicular, whose magnitude increased as the extent of modification increased. From both the CD spectra of non-oriented samples and the absorption spectra, an inference is drawn that Ag1+ and Cu1+ are attached to the same site as CH3 groups i.e., to the N7 atom of guanine. Proton transfer along the H-bond from the N1 atom of G to the N3 atom of the complementary cytosine is suggested to be a result of the modifications, although the case of H+-DNA may differ from the others. Based on the CD spectra for the anisotropic components, delta epsilon parallel and 2 delta epsilon perpendicular, it is proposed that ligand binding is accompanied by winding of the DNA helix.

  14. The search for circular dichroism in high-Tc superconductors (abstract)

    Science.gov (United States)

    Lyons, K. B.; Kwo, J.; Dillon, J. F., Jr.; Espinosa, G. P.; McGlashan-Powell, M.; Ramirez, A. P.; Schneemeyer, L. F.

    1991-04-01

    Stimulated by recent predictions of broken time reversal symmetry in cuprate superconductors, we have carried out a study of the polar Kerr ellipticity (the ellipticity of normally reflected light with the incident beam linearly polarized) for various cuprate materials, both superconducting and nonsuperconducting. The technique used employs a rotating half-wave retardation plate in order to discriminate against linear polarization effects. The results reveal a signature of a nonzero polar Kerr ellipticity which appears on cooling near 200 K in a variety of superconducting materials, and which is not observed in the corresponding insulating compounds. In this talk, in addition to summarizing these results, we plan to discuss the measurement technique itself in some detail. Measurements on both thin films and bulk samples will be discussed, together with a variety of tests on unrelated materials, which serve to eliminate various possible experimental artifacts.

  15. Molecular photoionisation using synchrotron radiation. Photoelectron photoion coincidence and circular dichroism

    CERN Document Server

    Garcia-Macias, G A

    2002-01-01

    The first ionisation potential of the CF sub 3 radical has been determined in this work from the appearance potential of the CF sub 3 sup + fragment, formed in the photofragmentation of CF sub 3 Br. In obtaining this value special care has been taken in removing the contributions from second order light and internal energy of the fragmenting parent ion. The resulting ionisation potential was found to be in very good agreement with a number of recent theoretical calculations. The valence photoelectron spectra of three monoterpenes such as limonene, carvone and camphor have been recorded along with their mass spectra taken in coincidence with energy selected photoelectrons, providing information about state selected parent ion fragmentation channels. A new photoelectron spectrometer based on the Alien box design has been studied by ray-tracing simulations. It will include a two dimensional position sensitive detector system consisting in two micro channel plates in a chevron stack and a delay-line anode to enco...

  16. On the existence of Jones birefringence and Jones dichroism.

    Science.gov (United States)

    Arteaga, Oriol

    2010-05-01

    We claim that the so-called Jones birefringence and Jones dichroism effects, understood as new optical phenomena of difficult experimental observation, cannot be deduced from Jones publications and were proposed due to a misinterpretation of his original work.

  17. Circular polarisation in AGN

    NARCIS (Netherlands)

    Macquart, JP

    2002-01-01

    We discuss the constraints that recent observations place on circular polarisation in AGN. In many sources the circular polarisation is variable on short timescales, indicating that it originates in compact regions of the sources. The best prospects for gleaning further information about circular po

  18. Coherence specific signal detection via chiral pump-probe spectroscopy.

    Science.gov (United States)

    Holdaway, David I H; Collini, Elisabetta; Olaya-Castro, Alexandra

    2016-05-21

    We examine transient circular dichroism (TRCD) spectroscopy as a technique to investigate signatures of exciton coherence dynamics under the influence of structured vibrational environments. We consider a pump-probe configuration with a linearly polarized pump and a circularly polarized probe, with a variable angle θ between the two directions of propagation. In our theoretical formalism the signal is decomposed in chiral and achiral doorway and window functions. Using this formalism, we show that the chiral doorway component, which beats during the population time, can be isolated by comparing signals with different values of θ. As in the majority of time-resolved pump-probe spectroscopy, the overall TRCD response shows signatures of both excited and ground state dynamics. However, we demonstrate that the chiral doorway function has only a weak ground state contribution, which can generally be neglected if an impulsive pump pulse is used. These findings suggest that the pump-probe configuration of optical TRCD in the impulsive limit has the potential to unambiguously probe quantum coherence beating in the excited state. We present numerical results for theoretical signals in an example dimer system.

  19. Voltage-controlled magnetic anisotropy in Fe|MgO tunnel junctions studied by x-ray absorption spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Miwa, Shinji, E-mail: miwa@mp.es.osaka-u.ac.jp; Matsuda, Kensho; Tanaka, Kazuhito; Goto, Minori; Suzuki, Yoshishige [Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531 (Japan); Kotani, Yoshinori; Nakamura, Tetsuya [Japan Synchrotron Radiation Research Institute/SPring-8, Sayo, Hyogo 679-5198 (Japan)

    2015-10-19

    In this study, voltage-controlled magnetic anisotropy (VCMA) in Fe|MgO tunnel junctions was investigated via the magneto-optical Kerr effect, soft x-ray absorption spectroscopy, and magnetic circular dichroism spectroscopy. The Fe|MgO tunnel junctions showed enhanced perpendicular magnetic anisotropy under external negative voltage, which induced charge depletion at the Fe|MgO interface. Despite the application of voltages of opposite polarity, no trace of chemical reaction such as a redox reaction attributed to O{sup 2−} migration was detected in the x-ray absorption spectra of the Fe. The VCMA reported in the Fe|MgO-based magnetic tunnel junctions must therefore originate from phenomena associated with the purely electric effect, that is, surface electron doping and/or redistribution induced by an external electric field.

  20. Binding between bixin and whey protein at pH 7.4 studied by spectroscopy and isothermal titration calorimetry.

    Science.gov (United States)

    Zhang, Yue; Zhong, Qixin

    2012-02-22

    Bixin is the major coloring component of annatto used in manufacturing colored cheeses, but its presence in liquid whey causes undesirable quality of the recovered whey protein ingredients. The objective of this work was to study molecular binding between bixin and three major whey proteins (β-lactoglobulin, α-lactalbumin, and bovine serum albumin) at pH 7.4 using UV-vis absorption spectroscopy, fluorescence spectroscopy, isothermal titration calorimetry, and circular dichroism. These complementary techniques illustrated that the binding is a spontaneous complexation process mainly driven by hydrophobic interactions. The complexation is favored at a lower temperature and a higher ionic strength. At a lower temperature, the binding is entropy-driven, while it changes to an enthalpy-driven process at higher temperatures. The binding also increases the percentage of unordered secondary structures of proteins. Findings from this work can be used to develop whey protein recovery processes for minimizing residual annatto content in whey protein ingredients.

  1. Kinetic flow dichroism study of conformational changes in supercoiled DNA induced by ethidium bromide and noncovalent and covalent binding of benz[a]pyrene diol epoxide.

    Science.gov (United States)

    Yoshida, H; Swenberg, C E; Geacintov, N E

    1987-03-10

    The dynamic conformational changes due to the noncovalent intercalative binding of ethidium bromide and racemic trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE), and the covalent binding of BPDE to supercoiled phi X174 DNA, have been studied by gel electrophoresis and a novel application of a kinetic flow linear dichroism technique. The magnitude of the linear dichroism (delta A) of the DNA oriented in the flow gradient is sensitive to the hydrodynamic shape of the DNA molecule which is affected by the binding of the drug or the carcinogen BPDE. While the linear dichroism of ethidium bromide supercoiled DNA is time independent, the delta A spectra of BPDE-DNA reaction mixtures vary on time scales of minutes, which correspond to the reaction rate constant of BPDE to form 7,8,9,10-tetrahydroxytetrahydrobenzo[a]pyrene hydrolysis products and covalent DNA adducts. The rapid noncovalent intercalation of BPDE causes an initial large increase in delta A (up to 250%, corresponding to the dichroism observed with relaxed circular DNA), followed by a slower decrease in the linear dichroism signal. This decrease in delta A is attributed to the removal of intercalated diol epoxide molecules and the resulting reversible increase in the number of superhelical turns. The kinetic flow dichroism spectra indicate that the noncovalent BPDE-DNA complexes are intercalative in nature, while the covalent adducts are characterized by a very different conformation in which the long axes of the pyrenyl residues are oriented at a large angle with respect to the average orientation of the planes of the DNA bases.(ABSTRACT TRUNCATED AT 250 WORDS)

  2. Zero-Field Dichroism in the Solar Chromosphere

    CERN Document Server

    Sainz, R M

    2003-01-01

    We explain the linear polarization of the Ca II infrared triplet observed close to the edge of the solar disk. In particular, we demonstrate that the physical origin of the enigmatic polarizations of the 866.2 nm and 854.2 nm lines lies in the existence of atomic polarization in their metastable lower levels, which produces differential absorption of polarization components (dichroism). To this end, we have solved the problem of the generation and transfer of polarized radiation by taking fully into account all the relevant optical pumping mechanisms in multilevel atomic models. We argue that `zero-field' dichroism may be of great diagnostic value in astrophysics.

  3. Strong Trinucleotide Circular Codes

    Directory of Open Access Journals (Sweden)

    Christian J. Michel

    2011-01-01

    Full Text Available Recently, we identified a hierarchy relation between trinucleotide comma-free codes and trinucleotide circular codes (see our previous works. Here, we extend our hierarchy with two new classes of codes, called DLD and LDL codes, which are stronger than the comma-free codes. We also prove that no circular code with 20 trinucleotides is a DLD code and that a circular code with 20 trinucleotides is comma-free if and only if it is a LDL code. Finally, we point out the possible role of the symmetric group ∑4 in the mathematical study of trinucleotide circular codes.

  4. Publication of administrative circular

    CERN Multimedia

    HR Department

    2009-01-01

    ADMINISTRATIVE CIRCULAR NO. 23 (REV. 2) – SPECIAL WORKING HOURS Administrative Circular No. 23 (Rev. 2) entitled "Special working hours", approved following discussion in the Standing Concertation Committee on 9 December 2008, will be available on the intranet site of the Human Resources Department as from 19 December 2008: http://cern.ch/hr-docs/admincirc/admincirc.asp It cancels and replaces Administrative Circular No. 23 (Rev. 1) entitled "Stand-by duty" of April 1988. A "Frequently Asked Questions" information document on special working hours will also be available on this site. Paper copies of this circular will shortly be available in Departmental Secretariats. Human Resources Department Tel. 78003

  5. PUBLICATION OF ADMINISTRATIVE CIRCULAR

    CERN Multimedia

    HR Department

    2008-01-01

    ADMINISTRATIVE CIRCULAR NO. 23 (REV. 2) – SPECIAL WORKING HOURS Administrative Circular No. 23 (Rev. 2) entitled "Special working hours", approved following discussion in the Standing Concertation Committee meeting of 9 December 2008, will be available on the intranet site of the Human Resources Department as from 19 December 2008: http://cern.ch/hr-docs/admincirc/admincirc.asp It cancels and replaces Administrative Circular No. 23 (Rev. 1) entitled "Stand-by duty" of April 1988. A "Frequently Asked Questions" information document on special working hours will also be available on this site. Paper copies of this circular will shortly be available in departmental secretariats. Human Resources Department Tel. 78003

  6. Binding of chrysoidine to catalase: spectroscopy, isothermal titration calorimetry and molecular docking studies.

    Science.gov (United States)

    Yang, Bingjun; Hao, Fang; Li, Jiarong; Chen, Dongliang; Liu, Rutao

    2013-11-01

    Chrysoidine is an industrial azo dye and the presence of chrysoidine in water and food has become an environmental concern due to its negative effects on human beings. In this work, the interactions between chrysoidine and bovine liver catalase (BLC) were explored. Obvious loss in catalytic activity was observed after incubation of BLC with chrysoidine, and the inhibition effect of BLC was found to be of the non-competitive type. No profound conformational change of BLC occurs in the presence of chrysoidine as revealed by UV-vis absorption, circular dichroism and fluorescence spectroscopy studies. Isothermal titration calorimetry results indicate that catalase has two sets of binding sites for chrysoidine. Further, molecular docking simulations show that chrysoidine is located within the bottleneck in the main channel of the substrate to the active site of BLC, which explain the activity inhibition of BLC by chrysoidine.

  7. Structure and Absolute Configuration of Ginkgolide B Characterized by IR- and VCD Spectroscopy

    DEFF Research Database (Denmark)

    Andersen, Niels Højmark; Christensen, N.J.; Lassen, Peter Rygaard

    2010-01-01

    Experimental and calculated (B3LYP/6-31G(d)) vibrational Circular dichroism (VCD) and IR spectra are compared, illustrating that the structure and absolute configuration of ginkgolide B (GB) may be characterized directly in solution. A conformational search for GB using MacroModel and subsequent......, displaying different intramolecular hydrogen bonding. Differences between measured and calculated IR and VCD spectra for GB at certain wavenumbers are rationalized in terms of interactions with solvent, intermolecular GB-GB interactions, and the potential presence of more than one conformer....... This is the first detailed investigation of the spectroscopic fingerprint region (850-1300 cm(-1)) of the natural product GB employing infrared absorption and VCD spectroscopy. Chirality 22:217-223, 2010....

  8. Circularity and Lambda Abstraction

    DEFF Research Database (Denmark)

    Danvy, Olivier; Thiemann, Peter; Zerny, Ian

    2013-01-01

    circular unknowns as dead variables, and we apply the functions to them. The result is a lazy circular program a la Bird. We illustrate the two transformations by mapping an algebraic construct to an isomorphic one with new leaves, reading a binary number as sug- gested by Knuth, and backpatching...

  9. [Application and development of spectroscopy methodologies in the study on non-covalent interactions].

    Science.gov (United States)

    Li, Rui; Dai, Ben-Cai; Zhao, Yong-De; Lu, Kui

    2009-01-01

    Spectrophotometric method is widely used in the structure determination of biologic macromolecules and non-covalent interactions study for its convenience and speed. In the present paper, spectroscopy methodologies in the study of non-covalent interactions between small-molecule and biomacromolecule is comprehensively reviewed with 25 references. This review article focuses on the applications and development of common spectroscopy methodologies in the study of non-covalent interactions between small molecule and biomacromolecule,including the UV, fluorescence, CD, IR, Raman, resonance light scattering technique and SPR. The advantages and disadvantages of spectroscopy methodologies are also described. UV-Vis absorption spectrum (UV) method is widely used in the study of non-covalent interactions for its convenience and speed. The binding site number, the apparent binding constant and the interaction mode of non-covalent interactions can be obtained by fluorescence spectrum method. Circular dichroism (CD) method is effective way in the study of non-covalent interactions measure. Spectroscopy information about protein secondary structure and conformation can be acquired by infrared spectrometry (IR) method. Raman spectroscopy method is a better way to investigate the conformation change in macromolecules in solution. Non-covalent interactions can be measured by surface plasma resonance (SPR) method under the natural active condition. X-ray diffraction analysis method is better for non-covalent interactions research, but it is difficult to cultivate crystalline complex.

  10. Circular-Arc Cartograms

    CERN Document Server

    Kämper, Jan-Hinrich; Nöllenburg, Martin

    2011-01-01

    We present a new circular-arc cartogram model in which countries are drawn with circular arcs instead of straight-line segments. Given a geographic map and values associated with each country in the map, the cartogram is a new map in which the areas of the countries represent the corresponding values. In the circular-arc cartogram model straight-line segments can be replaced with circular arcs in order to achieve the desired areas, while the corners of the polygons defining each country remain fixed. The countries in circular-arc cartograms have the aesthetically pleasing appearance of clouds or snowflakes, depending on whether their edges are bent outwards or inwards. This makes is easy to determine whether a country has grown or shrunk, just by its overall shape. We show that determining whether a given map and area-values can be realized with a circular-arc cartogram is an NP-hard problem. Next we describe a heuristic method for constructing circular-arc cartograms, which uses a max-flow computation on the...

  11. Building a Circular Future

    DEFF Research Database (Denmark)

    Merrild, Heidi; Guldager Jensen, Kasper; Sommer, John

    2016-01-01

    of the circular strategies is not only in the future. Increased flexibility, optimized operation and maintenance, as well as a healthier building, is low-hanging fruit that can be harvested today. The project’s principles can be implemented in industrialized construction in a large scale today. That is proven......Natural resources are scarce and construction accounts for 40 percent of the material and energy consumption in Europe. This means that a switch to a circular future is necessary. ’Building a Circular Future’ maps out where we are, where we are going, and what is needed for this conversion to take...

  12. Circular statistics in R

    CERN Document Server

    Pewsey, Arthur; Ruxton, Graeme D

    2013-01-01

    Circular Statistics in R provides the most comprehensive guide to the analysis of circular data in over a decade. Circular data arise in many scientific contexts whether it be angular directions such as: observed compass directions of departure of radio-collared migratory birds from a release point; bond angles measured in different molecules; wind directions at different times of year at a wind farm; direction of stress-fractures in concretebridge supports; longitudes of earthquake epicentres or seasonal and daily activity patterns, for example: data on the times of day at which animals are c

  13. External cavity-quantum cascade laser infrared spectroscopy for secondary structure analysis of proteins at low concentrations

    Science.gov (United States)

    Schwaighofer, Andreas; Alcaráz, Mirta R.; Araman, Can; Goicoechea, Héctor; Lendl, Bernhard

    2016-09-01

    Fourier transform infrared (FTIR) and circular dichroism (CD) spectroscopy are analytical techniques employed for the analysis of protein secondary structure. The use of CD spectroscopy is limited to low protein concentrations (5 mg ml-1). Here we introduce a quantum cascade laser (QCL)-based IR transmission setup for analysis of protein and polypeptide secondary structure at concentrations as low as 0.25 mg ml-1 in deuterated buffer solution. We present dynamic QCL-IR spectra of the temperature-induced α-helix to β-sheet transition of poly-L-lysine. The concentration dependence of the α-β transition temperature between 0.25 and 10 mg ml-1 was investigated by QCL-IR, FTIR and CD spectroscopy. By using QCL-IR spectroscopy it is possible to perform IR spectroscopic analysis in the same concentration range as CD spectroscopy, thus enabling a combined analysis of biomolecules secondary structure by CD and IR spectroscopy.

  14. Circularly symmetric light scattering from nanoplasmonic spirals.

    Science.gov (United States)

    Trevino, Jacob; Cao, Hui; Dal Negro, Luca

    2011-05-11

    In this paper, we combine experimental dark-field imaging, scattering, and fluorescence spectroscopy with rigorous electrodynamics calculations in order to investigate light scattering from planar arrays of Au nanoparticles arranged in aperiodic spirals with diffuse, circularly symmetric Fourier space. In particular, by studying the three main types of Vogel's spirals fabricated by electron-beam lithography on quartz substrates, we demonstrate polarization-insensitive planar light diffraction in the visible spectral range. Moreover, by combining dark-field imaging with analytical multiparticle calculations in the framework of the generalized Mie theory, we show that plasmonic spirals support distinctive structural resonances with circular symmetry carrying orbital angular momentum. The engineering of light scattering phenomena in deterministic structures with circular Fourier space provides a novel strategy for the realization of optical devices that fully leverage on enhanced, polarization-insensitive light-matter coupling over planar surfaces, such as thin-film plasmonic solar cells, plasmonic polarization devices, and optical biosensors.

  15. Administrative & Operational Circulars - Reminder

    CERN Multimedia

    HR Department

    2011-01-01

    All Administrative and Operational Circulars are available on the intranet site of the Human Resources Department at the following address: http://cern.ch/hr-docs/admincirc/admincirc.asp Department Head Office  

  16. Applications of circularly polarized photons at the ALS with a bend magnet source

    Energy Technology Data Exchange (ETDEWEB)

    1992-02-01

    The purpose of this workshop is to focus attention on, and to stimulate the scientific exploitation of, the natural polarization properties of bend-magnet synchrotron radiation at the ALS -- for research in biology, materials science, physics, and chemistry. The topics include: The Advanced Light Source; Magnetic Circular Dichroism and Differential Scattering on Biomolecules; Tests of Fundamental Symmetries; High {Tc} Superconductivity; Photoemission from Magnetic and Non-magnetic Solids; Studies of Highly Correlated Systems; and Instrumentation for Photon Transport and Polarization Measurements.

  17. Structure–Activity Relationship Study of Selective Excitatory Amino Acid Transporter Subtype 1 (EAAT1) Inhibitor 2-Amino-4-(4-methoxyphenyl)-7-(naphthalen-1-yl)-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile (UCPH-101) and Absolute Configurational Assignment Using Infrared and Vibrational Circular Dichroism Spectroscopy in Combination with ab Initio Hartree–Fock Calculations

    DEFF Research Database (Denmark)

    Huynh, Tri H.V.; Shim, Irene; Bohr, Henrik;

    2012-01-01

    in rodents, respectively. In this paper, we present the design, synthesis, and pharmacological evaluation of seven 7-N-substituted analogues of UCPH-101/102. Analogue 9 inhibited EAAT1 in the micromolar range (IC50 value 20 μM), whereas analogues 8 and 10 were inactive (IC50 values >100 μ......M). The diastereomeric pairs 11a/11b and 12a/12b were separated by HPLC and the absolute configuration assigned by VCD technique in combination with ab initio Hartree–Fock calculations. Analogues 11a (RS-isomer) and 12b (RR-isomer) inhibited EAAT1 (IC50 values 5.5 and 3.8 μM, respectively), whereas analogues 11b (SS......-isomer) and 12a (SR-isomer) failed to inhibit EAAT1 uptake (IC50 values >300 μM)....

  18. Circular words and applications

    Directory of Open Access Journals (Sweden)

    Benoît Rittaud

    2011-08-01

    Full Text Available We define the notion of circular words, then consider on such words a constraint derived from the Fibonacci condition. We give several results on the structure of these circular words, then mention possible applications to various situations: periodic expansion of numbers in numeration systems, "gcd-property" of integer sequences, partition of the prefix of the fixed point of the Fibonacci substitution, spanning trees of a wheel. Eventually, we mention some open questions.

  19. The Circular Camera Movement

    DEFF Research Database (Denmark)

    Hansen, Lennard Højbjerg

    2014-01-01

    It has been an accepted precept in film theory that specific stylistic features do not express specific content. Nevertheless, it is possible to find many examples in the history of film in which stylistic features do express specific content: for instance, the circular camera movement is used...... such as the circular camera movement. Keywords: embodied perception, embodied style, explicit narration, interpretation, style pattern, television style...

  20. A chiral rhenium complex with predicted high parity violation effects: synthesis, stereochemical characterization by VCD spectroscopy and quantum chemical calculations

    CERN Document Server

    Saleh, Nidal; Roisnel, Thierry; Guy, Laure; Bast, Radovan; Saue, Trond; Darquié, Benoît; Crassous, Jeanne

    2015-01-01

    With their rich electronic, vibrational, rotational and hyperfine structure, molecular systems have the potential to play a decisive role in precision tests of fundamental physics. For example, electroweak nuclear interactions should cause small energy differences between the two enantiomers of chiral molecules, a signature of parity symmetry breaking. Enantioenriched oxorhenium(VII) complexes S-(-)- and R-(+)-3 bearing a chiral 2-methyl-1-thio-propanol ligand have been prepared as potential candidates for probing molecular parity violation effects via high resolution laser spectroscopy of the Re=O stretching. Although the rhenium atom is not a stereogenic centre in itself, experimental vibrational circular dichroism (VCD) spectra revealed a surrounding chiral environment, evidenced by the Re=O bond stretching mode signal. The calculated VCD spectrum of the R enantiomer confirmed the position of the sulfur atom cis to the methyl, as observed in the solid-state X-ray crystallographic structure, and showed the ...

  1. Fe3S4 and Fe3O4 magnetic nanocrystals: magneto-optical and Mössbauer spectroscopy study

    Science.gov (United States)

    Lin, C.-R.; Tseng, Y.-T.; Ovchinnikov, S. G.; Ivantsov, R. D.; Edelman, I. S.; Fedorov, A. S.; Kuzubov, A. A.; Fedorov, D. A.; Starchikov, S. S.; Lyubutin, I. S.

    2014-04-01

    Iron oxide magnetite (Fe3O4) should be a reasonable analog for conception and understanding of the magnetic properties of iron sulfide greigite (Fe3S4)—one of the most required magnetic materials having numerous applications but being far from the complete understanding now. We present here a comparative study of the Mössbauer effect (ME) and the magnetic circular dichroism (MCD) spectroscopy of Fe3O4 and Fe3S4 nanoparticles. The ME spectrum parameters of Fe3S4 are shown to distinguish strongly from that of Fe3O4, and the MCD spectrum shapes are shown to be absolutely different for two compounds. To clarify the origin of the Fe3S4 MCD spectrum we have performed ab initio band structure calculations and identified the MCD spectrum features with the transitions between calculated energy states.

  2. Multiband Circular Polarizer Based on Fission Transmission of Linearly Polarized Wave for X-Band Applications

    Directory of Open Access Journals (Sweden)

    Farman Ali Mangi

    2016-01-01

    Full Text Available A multiband circular polarizer based on fission transmission of linearly polarized wave for x-band application is proposed, which is constructed of 2 × 2 metallic strips array. The linear-to-circular polarization conversion is obtained by decomposing the linearly incident x-polarized wave into two orthogonal vector components of equal amplitude and 90° phase difference between them. The innovative approach of “fission transmission of linear-to-circular polarized wave” is firstly introduced to obtain giant circular dichroism based on decomposition of orthogonal vector components through the structure. It means that the incident linearly polarized wave is converted into two orthogonal components through lower printed metallic strips layer and two transmitted waves impinge on the upper printed strips layer to convert into four orthogonal vector components at the end of structure. This projection and transmission sequence of orthogonal components sustain the chain transmission of electromagnetic wave and can achieve giant circular dichroism. Theoretical analysis and microwave experiments are presented to validate the performance of the structure. The measured results are in good agreement with simulation results. In addition, the proposed circular polarizer exhibits the optimal performance with respect to the normal incidence. The right handed circularly polarized wave is emitted ranging from 10.08 GHz to 10.53 GHz and 10.78 GHz to 11.12 GHz, while the left handed circular polarized wave is excited at 10.54 GHz–10.70 GHz and 11.13 GHz–11.14 GHz, respectively.

  3. Compact waveguide circular polarizer

    Science.gov (United States)

    Tantawi, Sami G.

    2016-08-16

    A multi-port waveguide is provided having a rectangular waveguide that includes a Y-shape structure with first top arm having a first rectangular waveguide port, a second top arm with second rectangular waveguide port, and a base arm with a third rectangular waveguide port for supporting a TE.sub.10 mode and a TE.sub.20 mode, where the end of the third rectangular waveguide port includes rounded edges that are parallel to a z-axis of the waveguide, a circular waveguide having a circular waveguide port for supporting a left hand and a right hand circular polarization TE.sub.11 mode and is coupled to a base arm broad wall, and a matching feature disposed on the base arm broad wall opposite of the circular waveguide for terminating the third rectangular waveguide port, where the first rectangular waveguide port, the second rectangular waveguide port and the circular waveguide port are capable of supporting 4-modes of operation.

  4. Circular Fibonacci gratings.

    Science.gov (United States)

    Gao, Nan; Zhang, Yuchao; Xie, Changqing

    2011-11-01

    We introduce circular Fibonacci gratings (CFGs) that combine the concept of circular gratings and Fibonacci structures. Theoretical analysis shows that the diffraction pattern of CFGs is composed of fractal distributions of impulse rings. Numerical simulations are performed with two-dimensional fast Fourier transform to reveal the fractal behavior of the diffraction rings. Experimental results are also presented and agree well with the numerical results. The fractal nature of the diffraction field should be of great theoretical interest, and shows potential to be further developed into practical applications, such as in laser measurement with wideband illumination.

  5. Around the circular law

    CERN Document Server

    Bordenave, Charles

    2011-01-01

    These expository notes are centered around the circular law theorem, which states that the empirical spectral distribution of a n \\times n random matrix with i.i.d. entries of variance 1/n tends to the uniform law on the unit disc of the complex plane as the dimension n tends to infinity. This phenomenon is the non-Hermitian counterpart of the semi circular limit for Wigner random Hermitian matrices, and the quarter circular limit for Marchenko-Pastur random covariance matrices. We present a proof in a Gaussian case, due to Silverstein, based on a formula by Ginibre, and a proof of the universal case by revisiting the approach of Tao and Vu, based on the Hermitization of Girko, the logarithmic potential, and the control of the small singular values. Beyond the finite variance model, we also consider the case where the entries have heavy tails, by using the objective method of Aldous and Steele borrowed from randomized combinatorial optimization. The limiting law is then no longer the circular law and is relat...

  6. Radical Circular Economy

    NARCIS (Netherlands)

    Prins, M.; Mohammadi, S.; Slob, N.

    2015-01-01

    Recently the Circular Economy (CE) concept has gained momentum in the Netherlands, propounding that environmental impact reduction can provide a significant positive economical impulse. The government, larger parts of the industry as a whole, as well as the construction industry, has warmly received

  7. Wiimote Experiments: Circular Motion

    Science.gov (United States)

    Kouh, Minjoon; Holz, Danielle; Kawam, Alae; Lamont, Mary

    2013-01-01

    The advent of new sensor technologies can provide new ways of exploring fundamental physics. In this paper, we show how a Wiimote, which is a handheld remote controller for the Nintendo Wii video game system with an accelerometer, can be used to study the dynamics of circular motion with a very simple setup such as an old record player or a…

  8. Configuration of singular optical cones in gyrotropic crystals with dichroism

    Energy Technology Data Exchange (ETDEWEB)

    Merkulov, V. S., E-mail: merkul@physics.by [National Academy of Sciences of Belarus, Material Science Applied Research Center (Belarus)

    2015-02-15

    Optical conic singularities in crystals with linear dichroism and natural optical activity at the point of intersection of dispersion curves for the main refractive indices are considered. The possible existence of singularities like a nodal point, tangency point, triple point, and cusps of the first and second order is demonstrated. Forty-nine different types of irreducible fourth-order optical cones obtained by sequential bifurcations of eight main singular cones are established. The classification is based on the concept of roughness of systems depending on parameters.

  9. Transposable elements and circular DNAs

    KAUST Repository

    Mourier, Tobias

    2016-09-26

    Circular DNAs are extra-chromosomal fragments that become circularized by genomic recombination events. We have recently shown that yeast LTR elements generate circular DNAs through recombination events between their flanking long terminal repeats (LTRs). Similarly, circular DNAs can be generated by recombination between LTRs residing at different genomic loci, in which case the circular DNA will contain the intervening sequence. In yeast, this can result in gene copy number variations when circles contain genes and origins of replication. Here, I speculate on the potential and implications of circular DNAs generated through recombination between human transposable elements.

  10. Combined SERS and flow linear dichroism approach to monitoring the interaction of pharmaceuticals with their target

    Science.gov (United States)

    Ianoul, Anatoli I.; Fleury, Fabrice; Duval, Olivier; Jardillier, Jean-Claude; Alix, Alain J.; Nabiev, Igor R.

    1999-04-01

    Surface-Enhanced Raman Scattering (SERS) spectroscopy and Flow Linear Dichroism (FLD) technique have been employed to study the anticancer agent fagaronine and its derivative ethoxidine - double inhibitors of DNA topoisomerases I and II. Cooperative use of two methods permitted (i) to determine the molecular determinants of the drug-DNA interactions; (ii) to monitor in real time the process of topo I inhibition by these anticancer agents. FLD technique allowed us to identify the mode of drug interactions with the DNA as a 'major groove intercalation' and to determine orientation of the drugs chromophores within the complexes. Using SERS spectroscopy we have determined the drugs molecular determinants interacting with the DNA. FLD was also used for real time monitoring of the process of sc DNA relaxation by topo I and of inhibition of relaxation with the pharmaceuticals. Ethoxidine was found to exhibit the same activity of inhibition of sc DNA relaxation as fagaronine at the 10-fold less concentration. The proposed SERS-FLD combined approach demonstrates the new perspectives for screening new pharmaceuticals due to its relative simplicity and low expense, high sensitivity and selectivity, and, finally, possibility of real-time monitoring of the structure-function correlation within the series of drug derivatives.

  11. Kappa Coefficients for Circular Classifications

    NARCIS (Netherlands)

    Warrens, Matthijs J.; Pratiwi, Bunga C.

    2016-01-01

    Circular classifications are classification scales with categories that exhibit a certain periodicity. Since linear scales have endpoints, the standard weighted kappas used for linear scales are not appropriate for analyzing agreement between two circular classifications. A family of kappa coefficie

  12. Broadband spectroscopy with external cavity quantum cascade lasers beyond conventional absorption measurements.

    Science.gov (United States)

    Lambrecht, Armin; Pfeifer, Marcel; Konz, Werner; Herbst, Johannes; Axtmann, Felix

    2014-05-07

    Laser spectroscopy is a powerful tool for analyzing small molecules, i.e. in the gas phase. In the mid-infrared spectral region quantum cascade lasers (QCLs) have been established as the most frequently used laser radiation source. Spectroscopy of larger molecules in the gas phase, of complex mixtures, and analysis in the liquid phase requires a broader tuning range and is thus still the domain of Fourier transform infrared (FTIR) spectroscopy. However, the development of tunable external cavity (EC) QCLs is starting to change this situation. The main advantage of QCLs is their high spectral emission power that is enhanced by a factor of 10(4) compared with thermal light sources. Obviously, transmission measurements with EC-QCLs in strongly absorbing samples are feasible, which can hardly be measured by FTIR due to detector noise limitations. We show that the high power of EC-QCLs facilitates spectroscopy beyond simple absorption measurements. Starting from QCL experiments with liquid samples, we show results of fiber evanescent field analysis (FEFA) to detect pesticides in drinking water. FEFA is a special case of attenuated total reflection spectroscopy. Furthermore, powerful CW EC-QCLs enable fast vibrational circular dichroism (VCD) spectroscopy of chiral molecules in the liquid phase - a technique which is very time consuming with standard FTIR equipment. We present results obtained for the chiral compound 1,1'-bi-2-naphthol (BINOL). Finally, powerful CW EC-QCLs enable the application of laser photothermal emission spectroscopy (LPTES). We demonstrate this for a narrowband and broadband absorber in the gas phase. All three techniques have great potential for MIR process analytical applications.

  13. Spectroscopy and computational studies on the interaction of octyl, dodecyl, and hexadecyl derivatives of anionic and cationic surfactants with adenosine deaminase.

    Science.gov (United States)

    Ajloo, Davood; Mahmoodabadi, Najmeh; Ghadamgahi, Maryam; Saboury, Ali Akbar

    2016-07-01

    Effects of sodium (octyl, dodecyl, hexadecyl) sulfate and their cationic analogous on the structure of adenosine deaminase (ADA) were investigated by fluorescence and circular dichroism spectroscopy as well as molecular dynamics simulation and docking calculation. Root-mean-square derivations, radius of gyration, solvent accessible surface area, and radial distribution function were obtained. The results showed that anionic and cationic surfactants reduce protein stability. Cationic surfactants have more effect on the ADA structure in comparison with anionic surfactants. More concentration and longer surfactants are parallel to higher denaturation. Furthermore, aggregation in the presence of anionic surfactants is more than cationic surfactants. Docking data showed that longer surfactants have more interaction energy and smaller ones bound to the active site.

  14. Structural determination of molecular stereochemistry using VCD spectroscopy and a conformational code: absolute configuration and solution conformation of a chiral liquid pesticide, (R)-(+)-malathion.

    Science.gov (United States)

    Izumi, Hiroshi; Ogata, Atsushi; Nafie, Laurence A; Dukor, Rina K

    2009-01-01

    The absolute configuration and solution conformation of (R)-(+)-malathion were determined by using vibrational circular dichroism spectroscopy and a fragment-conformational search with a recently published conformational code. The determination of molecular stereochemistry was carried out without a conformational search using molecular mechanics calculations. Density functional theory calculations of the fragments of (R)-malathion, ethyl propionate, (R)-ethyl 2-(methylthio)propanoate, (R)-diethyl 2-(methylthio)succinate, and O,O,S-trimethyl phosphorodithioate were carried out, and the principal conformational features of the fragments were profiled. This fragment-conformational search reduces the time needed for the selection of the predominant conformations for (R)-malathion and significantly improves the accuracy of the determination of absolute configuration.

  15. Rashba splitting and dichroism of surface states in Bi/Ag surface alloy

    Energy Technology Data Exchange (ETDEWEB)

    Bian, Guang; Miller, T. [Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, IL 61801-3080 (United States); Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, 104 South Goodwin Avenue, Urbana, IL 61801-2902 (United States); Chiang, T.-C., E-mail: tcchiang@illinois.edu [Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, IL 61801-3080 (United States); Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, 104 South Goodwin Avenue, Urbana, IL 61801-2902 (United States)

    2015-05-15

    The Rashba effect plays an important role in various spin-related phenomena in two-dimensional electronic systems. In this work we present a theoretical analysis of the Rashba effect both analytically and numerically for the prototypical Rashba system Bi/Ag surface alloy, which shows a giant Rashba spin splitting. The results reveal the critical influence of atomic spin-orbit coupling and structural inversion asymmetry. In addition, we demonstrate a theoretical route to interpret the prominent circular dichroic patterns observed by angle-resolved photoemission spectroscopy in this system. The results reveal a close connection between the experimentally observed dichroic patterns and the Rashba spin texture.

  16. Spectroscopy, calorimetry and molecular simulation studies on the interaction of catalase with copper ion.

    Science.gov (United States)

    Hao, Fang; Jing, Mingyang; Zhao, Xingchen; Liu, Rutao

    2015-02-01

    In this research, the binding mechanism of Cu(2+) to bovine liver catalase (BLC) was studied by fluorescence spectroscopy, ultraviolet-visible (UV-vis) absorption spectroscopy, circular dichroism (CD) spectroscopy, isothermal titration calorimetry (ITC) and molecular docking methods. The cellar experiment was firstly carried out to investigate the inhibition effect of catalase. During the fluorescence quenching study, after correcting the inner filter effect (IFE), the fluorescence of BLC was found to be quenched by Cu(2+). The quenching mechanism was determined by fluorescence lifetime measurement, and was confirmed to be the dynamic mode. The secondary structure content of BLC was changed by the addition of Cu(2+), as revealed by UV-vis absorption and CD spectra, which further induces the decrease in BLC activity. Molecular simulation study indicates that Cu(2+) is located between two β-sheets and two random coils of BLC near to the heme group, and interacts with His 74 and Ser 113 residues near a hydrophilic area. The decrease of α-helix and the binding of His 74 are considered to be the major reason for the inhibition of BLC activity caused by Cu(2+). The ITC results indicate that the binding stoichiometry of Cu(2+) to catalase is 11.4. Moreover, the binding of Cu(2+) to BLC destroyed H-bonds, which was confirmed by the CD result.

  17. Circular arc structures

    KAUST Repository

    Bo, Pengbo

    2011-07-01

    The most important guiding principle in computational methods for freeform architecture is the balance between cost efficiency on the one hand, and adherence to the design intent on the other. Key issues are the simplicity of supporting and connecting elements as well as repetition of costly parts. This paper proposes so-called circular arc structures as a means to faithfully realize freeform designs without giving up smooth appearance. In contrast to non-smooth meshes with straight edges where geometric complexity is concentrated in the nodes, we stay with smooth surfaces and rather distribute complexity in a uniform way by allowing edges in the shape of circular arcs. We are able to achieve the simplest possible shape of nodes without interfering with known panel optimization algorithms. We study remarkable special cases of circular arc structures which possess simple supporting elements or repetitive edges, we present the first global approximation method for principal patches, and we show an extension to volumetric structures for truly threedimensional designs. © 2011 ACM.

  18. Insights into the binding of the drugs diclofenac sodium and cefotaxime sodium to serum albumin: calorimetry and spectroscopy.

    Science.gov (United States)

    Sharma, Ruchika; Choudhary, Sinjan; Kishore, Nand

    2012-08-15

    Understanding physical chemistry underlying drug-protein interactions is essential to devise guidelines for the synthesis of target oriented drugs. Binding of a non-steroidal anti-inflammatory drug, diclofenac sodium (DCF) and an antibiotic drug, cefotaxime sodium (CFT) belonging to the family of cephalosporins with bovine serum albumin (BSA) has been examined using a combination of isothermal titration calorimetry (ITC), differential scanning calorimetry (DSC), steady state and time resolved fluorescence and circular dichroism spectroscopies. Binding affinity of both DCF and CFT with BSA is observed to be of the order of 10(4)M(-1), with the binding profiles fitting well to the single set of binding site model. The disagreement between calorimetric and van't Hoff enthalpies indicates non-adherence to a two-state binding process which could be attributed to changes in the conformation of the protein upon ligand binding as well as with increase in the temperature. Circular dichroism and the fluorescence results, however, do not show any major conformational changes upon binding of these drugs to BSA, and hence the discrepancy could be due to temperature induced conformational changes in the protein. The results of ionic strength dependence and binding in the presence of anionic, cationic and non-ionic surfactants indicate, involvement of more that a single type of interaction in the binding process. The ITC results for the binding of these drugs to BSA in presence of each other indicate that the binding sites for the two drugs are different, and therefore binding of one is not influenced by the other. The DSC results provide quantitative information on the effect of these drugs on the stability of serum albumin. The combined calorimetric and spectroscopic approach has provided a detailed analysis including thermodynamics of the binding of DCF and CFT with BSA qualitatively and quantitatively.

  19. Probing the structure of glucan lyases – the lytic members of GH31 - by sequence analysis, circular dichroism and proteolysis

    DEFF Research Database (Denmark)

    Ernst, Heidi; Lo Leggio, Leila; Yu, Shukun

    2005-01-01

    Glucan lyase (GL) is a polysaccharide lyase with unique characteristics. It is involved in an alternative pathway for the degradation of alpha-glucans, the anhydrofructose pathway. Sequence similarity suggests that this lytic enzyme belongs to glycoside hydrolase family 31, for which until very r...

  20. Basic amphipathic model peptides: Structural investigations in solution, studied by circular dichroism, fluorescence, analytical ultracentrifugation and molecular modelling

    Science.gov (United States)

    Mangavel, C.; Sy, D.; Reynaud, J. A.

    1999-05-01

    A twenty amino acid residue long amphipathic peptide made of ten leucine and ten lysine residues and four derivatives, in which a tryptophan, as a fluorescent probe, is substituted for a leucine, are studied. The peptides in water are mainly in an unordered conformation (~90%), and undergo a two state reversible transition upon heating, leading to a partially helical conformation (cold denaturation). Time resolved fluorescence results show that fluorescence decay for the four Trp containing peptides is best described by triple fluorescence decay kinetics. In TFE/water mixture, peptides adopt a single α-helix conformation but the Leu-Trp9 substitution leads to an effective helix destabilizing effect. In salted media, the peptides are fully helical and present a great tendency to self associate by bringing the hydrophobic faces of helices into close contact. This proceeds in non-cooperative multisteps leading to the formation of α helix aggregates with various degrees of complexation. Using modelling, the relative hydrophobic surface areas accessible to water molecules in n-mer structures are calculated and discussed. Nous avons étudié un peptide amphipathique composé de dix lysine et dix leucine, ainsi que quatre dérivés comportant un résidu tryptophane pour les études par fluorescence. Dans l'eau, les peptides ne sont pas structurés (~90%), et se structurent partiellement en hélice α par chauffage (dénaturation froide). Les mesures de déclin de fluorescence font apparaître une cinétique à trois temps de vie. Dans un mélange eau/TFE, les peptides adoptent une conformation en hélice α, mais la substitution Leu-Trp9 possède un effet déstabilisant. En mileu salin, les peptides sont totalement hélicoïdaux et ont tendance à s'agréger de façon à regrouper leur face hydrophobe. Ce processus se fait en plusieurs étapes avec des agrégats de taille variable. L'existence de tels agrégats est discutée sur la base de la modélisation moléculaire complétée par des calculs d'accessibilité des surfaces hydrophobes.

  1. A circular dichroism study of ethidium bromide binding to Z-DNA induced by dinuclear platinum complexes.

    Science.gov (United States)

    Wu, P K; Kharatishvili, M; Qu, Y; Farrell, N

    1996-07-01

    Dinuclear bis(platinum) complexes have been shown previously to induce the B-->Z transition in synthetic DNAs (Nucleic Acids Res. 7, 1697-1703, J. Inorganic Biochem. 54, 207-220). In this paper, the reversibility of the Z conformation back to the B form was assessed by treatment of the induced Z form in poly(dG-dC).poly(dG-dC) with ethidium bromide (Etd). Z-DNA induced by the tetra-amine cations [{Pt(NH3)3}2(H2N(CH2)nNH2)]4+, which are capable of only electrostatic interactions with the polynucleotide, was readily reversible. The spectroscopic data mirrored that of ethidium bromide/poly(dG-dC).poly(dG-dC) in the presence of 4.4 M NaCl. In contrast, Z-DNA induced by the bifunctional complexes [{trans-PtCl(NH3)2}2(H2N(CH2)nNH2)]2+ did not produce spectra typical of Etd intercalation and reversal to B-form DNA. The original Z-form CD spectra of DNA treated with the bifunctional complexes could be reobtained following removal of Etd by extensive dialysis. The bifunctional complexes are very effective interstrand cross-linking agents. The data suggest that interstrand cross-linking by dinuclear complexes can stabilize or "lock" the Z-conformation prohibiting its reversal to the B-form. The implications for the biological activity of the dinuclear complexes are briefly discussed.

  2. Antennas on circular cylinders

    DEFF Research Database (Denmark)

    Knudsen, H. L.

    1959-01-01

    antenna in a circular cylinder. By a procedure similar to the one used by Silver and Saunders, expressions have been derived for the field radiated from an arbitrary surface current distribution on a cylinder surface coaxial with a perfectly conducting cylinder. The cases where the space between the two...... cylindrical surfaces have the sane characteristic constants and different constants are treated separately. Extensive numerical computations of the field radiated from the slot antennas described here are being carried out, but no numerical results are yet available...

  3. Circularly polarized antennas

    CERN Document Server

    Gao, Steven; Zhu, Fuguo

    2013-01-01

    This book presents a comprehensive insight into the design techniques for different types of CP antenna elements and arrays In this book, the authors address a broad range of topics on circularly polarized (CP) antennas. Firstly, it introduces to the reader basic principles, design techniques and characteristics of various types of CP antennas, such as CP patch antennas, CP helix antennas, quadrifilar helix antennas (QHA), printed quadrifilar helix antennas (PQHA), spiral antenna, CP slot antennas, CP dielectric resonator antennas, loop antennas, crossed dipoles, monopoles and CP horns. Adva

  4. Magneto-optical spectroscopy of (Ga,Mn)N epilayers

    Science.gov (United States)

    Marcet, S.; Ferrand, D.; Halley, D.; Kuroda, S.; Mariette, H.; Gheeraert, E.; Teran, F. J.; Sadowski, M. L.; Galera, R. M.; Cibert, J.

    2006-09-01

    We report on the magneto-optical spectroscopy and cathodoluminescence of a set of wurtzite (Ga,Mn)N epilayers with a low Mn content, grown by molecular-beam epitaxy. The sharpness of the absorption lines associated with the Mn3+ internal transitions allows a precise study of its Zeeman effect in both Faraday and Voigt configurations. We obtain a good agreement if we assume a dynamical Jahn-Teller effect in the 3d4 configuration of Mn, and we determine the parameters of the effective Hamiltonians describing the T25 and E5 levels, and those of the spin Hamiltonian in the ground spin multiplet, from which the magnetization of the isolated ion can be calculated. On layers grown on transparent substrates, transmission close to the band gap, and the associated magnetic circular dichroism, reveal the presence of the giant Zeeman effect resulting from exchange interactions between the Mn3+ ions and the carriers. The spin-hole interaction is found to be ferromagnetic.

  5. Itinerant and localized magnetic moments in ferrimagnetic Mn{sub 2}CoGa thin films identified with x-ray magnetic linear dichroism: experiment and ab initio theory

    Energy Technology Data Exchange (ETDEWEB)

    Meinert, M.; Schmalhorst, J; Klewe, C.; Reiss, G.; Arenholz, E.; Bohnert, T.; Nielsch, K.

    2011-08-08

    Epitaxial thin films of the half-metallic X{sub a}-compound Mn{sub 2}CoGa (Hg{sub 2}CuTi prototype) were prepared by dc magnetron co-sputtering with different heat treatments on MgO (001) substrates. High-quality lms with a bulk magnetization of 1.95(5) {mu}{sub }B per unit cell were obtained. The average Mn magnetic moment and the Co moment are parallel, in agreement with theory. The x-ray magnetic circular dichroism spectra agree with calculations based on density functional theory and reveal the antiparallel alignment of the two inequivalent Mn moments. X-ray magnetic linear dichroism allows to distinguish between itinerant and localized Mn moments. It is shown that one of the two Mn moments has localized character, whereas the other Mn moment and the Co moment are itinerant.

  6. Non-reciprocal directional dichroism in the AFM phase of BiFeO3 at THz frequencies

    Science.gov (United States)

    Nagel, Urmas; Rõõm, T.; Farkas, D.; Szaller, D.; Bordács, S.; Kézsmárki, I.; Engelkamp, H.; Ozaki, Y.; Tomiaki, Y.; Ito, T.; Fishman, Randy S.

    We did THz absorption spectroscopy of BiFeO3 single crystals in the AFM phase, where the spin cycloid is destroyed in magnetic fields between 18 T and 32 T in Voigt geometry at 1.6 K. If B0 ∥ [ 1 1 0 ] , we see strong directional dichroism (DD) of absorption of the magnon mode with light propagating along the direction of the ferroelectric polarization k ∥ P ∥ [ 111 ] and eω ∥ [ 1 1 0 ] , bω ∥ [ 1 1 2 ] . The sign of DD can be reversed (i) by reversing the direction of B0 or (ii) by flipping the sample, thus reversing the propagation direction of light. The observed effect is caused by the strong magneto-electric coupling in the collinear AFM phase. Research sponsored by the Estonian Ministry of Education and Research (IUT23-3).

  7. Operational circular No. 1 (Rev. 1) – Operational circulars

    CERN Multimedia

    HR Department

    2011-01-01

    Operational Circular No. 1 (Rev. 1) is applicable to members of the personnel and other persons concerned. Operational Circular No. 1 (Rev. 1) entitled "Operational circulars", approved following discussion at the Standing Concertation Committee meeting on 4 May 2011, is available on the intranet site of the Human Resources Department: https://hr-docs.web.cern.ch/hr-docs/opcirc/opcirc.asp It cancels and replaces Operational Circular No. 1 entitled "Operational Circulars” of December 1996. This new version clarifies, in particular, that operational circulars do not necessarily arise from the Staff Rules and Regulations, and the functional titles have been updated to bring them into line with the current CERN organigram. Department Head Office  

  8. Circularly Polarized MHOHG with Bichromatic Circularly Polarized Laser Pulses

    Science.gov (United States)

    Bandrauk, Andre D.; Mauger, Francois; Uzer, Turgay

    2016-05-01

    Circularly polarized MHOHG-Molecular High Order Harmonic Generation is shown to occur efficiently with intense ultrashort bichromatic circularly polarized pulses due to frequent electron-parent -ion recollision with co-or counter-rotating incident circular pulses as predicted in 1995. We show in this context that molecules offer a very robust and efficient frameworkfor the production of circularly polarized harmonics for the generation of single circularly polarized ``attosecond'' pulses. The efficiency of such new MHOHG is shown to depend on the compatibility of the symmetry of the molecular medium with the net electric field generated by the combination of the laser pulses.Using a time-dependent symmetry analysis with concrete examples such as H 2 + vs H 3 + we show how all the features(harmonic order and ∧ polarization) of MHOHG can be explained and predicted.

  9. Molecular Magnetic Dichroism in Spectra of White Dwarfs

    Science.gov (United States)

    Berdyugina, S. V.; Berdyugin, A. V.; Piirola, V.

    2007-08-01

    We present novel calculations of the magnetic dichroism appearing in molecular bands in the presence of a strong magnetic field, which perturbs the internal structure of the molecule and results in net polarization due to the Paschen-Back effect. Based on that, we analyze new spectropolarimetric observations of the cool magnetic helium-rich white dwarf G99-37, which shows strongly polarized molecular bands in its spectrum. In addition to previously known molecular bands of the C2 Swan and CH A-X systems, we find a firm evidence for the violet CH B-X bands at 390 nm and C2 Deslandres-d’Azambuja bands at 360 nm. Combining the polarimetric observations with our model calculations, we deduce a dipole magnetic field of 7.5±0.5MG with the positive pole pointing towards the Earth. We conclude that the developed technique is an excellent tool for studying magnetic fields on cool magnetic stars.

  10. Structural study of human growth hormone-releasing factor fragment (1?29) by vibrational spectroscopy

    Science.gov (United States)

    Carmona, P.; Molina, M.; Lasagabaster, A.

    1995-05-01

    The conformational structure of fragment 1-29 of human growth hormone releasing factor, hGHRF (1-29), in aqueous solution and in the solid state is investigated by infrared and Raman spectroscopy. The polypeptide backbone is found to be unordered in the solid state. However, the spectra of the peptide prepared as 5% (w/w) aqueous solutions show that approximately 28% of the peptide is involved in intermolecular β-sheet aggregation. The remainder of the peptide exists largely as disordered and β-sheet conformations with a small portion of α-helices. Tyrosine residues are found to be exposed to the solvent. The secondary structures are quantitatively examined through infrared spectroscopy, the conformational percentages being near those obtained by HONDAet al. [ Biopolymers31, 869 (1991)] using circular dichroism. The fast hydrogen/deuterium exchange in peptide groups and the absence of any NMR sign indicative of ordered structure [ G. M. CLOREet al., J. Molec. Biol.191, 553 (1986)] support that the solution conformations of the non-aggregated peptide interconvert in dynamic equilibrium. Some physiological advantages that may derive from this conformational flexibility are also discussed

  11. Aptamer-based biosensor for label-free detection of ethanolamine by electrochemical impedance spectroscopy.

    Science.gov (United States)

    Liang, Gang; Man, Yan; Jin, Xinxin; Pan, Ligang; Liu, Xinhui

    2016-09-14

    A label-free sensing assay for ethanolamine (EA) detection based on G-quadruplex-EA binding interaction is presented by using G-rich aptamer DNA (Ap-DNA) and electrochemical impedance spectroscopy (EIS). The presence of K(+) induces the Ap-DNA to form a K(+)-stabilized G-quadruplex structure which provides binding sites for EA. The sensing mechanism was further confirmed by circular dichroism (CD) spectroscopy and EIS measurement. As a result, the charge transfer resistance (RCT) is strongly increased as demonstrated by using the ferro/ferricyanide ([Fe(CN)6](3-/4-)) as a redox probe. Under the optimized conditions, a linear relationship between ΔRCT and EA concentration was obtained over the range of 0.16 nM and 16 nM EA, with a detection limit of 0.08 nM. Interference by other selected chemicals with similar structure was negligible. Analytical results of EA spiked into tap water and serum by the sensor suggested the assay could be successfully applied to real sample analysis. With the advantages of high sensitivity, selectivity and simple sensor construction, this method is potentially suitable for the on-site monitoring of EA contamination.

  12. A Physico-Chemical Study of Some Areas of Fundamental Significance to Biophysics

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Devendra; McGlynn, S. P.

    1999-04-01

    This report covers: Radiation Signatures; Electronic Structure of Steroids, Vitamins, and others; Laser Optogalvanic Effect; Vacuum Ultraviolet Spectroscopy, including Electron Scattering, Photochemistry, and Magnetic Circular Dichroism; and Ozone.

  13. Circular chemiresistors for microchemical sensors

    Science.gov (United States)

    Ho, Clifford K.

    2007-03-13

    A circular chemiresistor for use in microchemical sensors. A pair of electrodes is fabricated on an electrically insulating substrate. The pattern of electrodes is arranged in a circle-filling geometry, such as a concentric, dual-track spiral design, or a circular interdigitated design. A drop of a chemically sensitive polymer (i.e., chemiresistive ink) is deposited on the insulating substrate on the electrodes, which spreads out into a thin, circular disk contacting the pair of electrodes. This circularly-shaped electrode geometry maximizes the contact area between the pair of electrodes and the polymer deposit, which provides a lower and more stable baseline resistance than with linear-trace designs. The circularly-shaped electrode pattern also serves to minimize batch-to-batch variations in the baseline resistance due to non-uniform distributions of conductive particles in the chemiresistive polymer film.

  14. Optically active mixed phthalocyaninato-porphyrinato rare-earth double-decker complexes: synthesis, spectroscopy, and solvent-dependent molecular conformations.

    Science.gov (United States)

    Zhang, Xiaomei; Muranaka, Atsuya; Lv, Wei; Zhang, Yuexing; Bian, Yongzhong; Jiang, Jianzhuang; Kobayashi, Nagao

    2008-01-01

    Reaction between the optically active metal-free phthalocyanine with a pi system with noncentrosymmetrical C(2) [corrected] symmetry ((S)- and (R)-H(2){Pc(OBNP)(2)}; OBNP=binaphthylphthalocyanine) and half-sandwich complexes [M(III)(acac)(TClPP)] (M=Y, Eu; TClPP=meso-tetrakis(4-chlorophenyl)porphyrinate; acac=acetylacetonate), which were generated in situ from [M(acac)(3)].n H(2)O and H(2)(TClPP) in n-octanol at reflux, provided the first optically active protonated mixed phthalocyaninato-porphyrinato rare-earth double-decker complexes [M(III)H{Pc(OBNP)(2)}(TClPP)] (M=Y, Eu) in good yield. In addition to electronic absorption spectroscopy and magnetic circular dichroism results, circular dichroism shows different spectroscopic features of these mixed-ring rare-earth double-decker compounds in different solvents, such as DMF and CHCl(3), which was well-reproduced on the basis of time-dependent density functional theory calculation results for the yttrium species (S)-[Y(III){Pc(OBNP)(2)}(Por)](-) (Por=porphyrinate, which is obtained by removing the four chlorophenyl groups from the TClPP ligand) in terms of the change in the rotation angle between the two macrocyclic ligands in the double-decker molecules. These results revealed the solvent-dependent nature of the molecular conformation of mixed-ring rare-earth double-decker complexes, which suggests a new way of tuning the optical and the electrochemical properties of sandwich-type bis(tetrapyrrole)-metal double-decker complexes in solution by changing the solvent.

  15. Circularly Polarized Persistent Room-Temperature Phosphorescence from Metal-Free Chiral Aromatics in Air.

    Science.gov (United States)

    Hirata, Shuzo; Vacha, Martin

    2016-04-21

    Circularly polarized room-temperature phosphorescence (RTP) with persistent emission characteristics was observed from metal-free chiral binaphthyl structures. Enantiomers of the binaphthyl compounds doped into an amorphous hydroxylated steroid matrix produced blue fluorescence and yellow persistent RTP in air. The lifetime and quantum yield of the yellow persistent RTP were 0.67 s and 2.3%, respectively. The dissymmetry factors of circular dichroism (CD) in the first absorption band, circularly polarized fluorescence (CPF), and circularly polarized persistent RTP were |1.1 × 10(-3)|, |4.5 × 10(-4)|, and |2.3 × 10(-3)|, respectively. A comparison between the experimental data and calculations by time-dependent density functional theory for transient CD spectra confirmed that the binaphthyl conformations in the lowest singlet excited state (S1) and the lowest triplet state (T1) were different. The large difference in the dissymmetry factors for the CPF and the circularly polarized persistent RTP was likely caused by this conformational change between S1 and T1.

  16. Towards Future Circular Colliders

    CERN Document Server

    AUTHOR|(CDS)2108454; Zimmermann, Frank

    2016-01-01

    The Large Hadron Collider (LHC) at CERN presently provides proton-proton collisions at a centre-of-mass (c.m.) energy of 13 TeV. The LHC design was started more than 30 years ago, and its physics programme will extend through the second half of the 2030’s. The global Future Circular Collider (FCC) study is now preparing for a post-LHC project. The FCC study focuses on the design of a 100-TeV hadron collider (FCC-hh) in a new ∼100 km tunnel. It also includes the design of a high-luminosity electron-positron collider (FCC-ee) as a potential intermediate step, and a lepton-hadron collider option (FCC-he). The scope of the FCC study comprises accelerators, technology, infrastructure, detectors, physics, concepts for worldwide data services, international governance models, and implementation scenarios. Among the FCC core technologies figure 16-T dipole magnets, based on $Nb_3Sn$ superconductor, for the FCC-hh hadron collider, and a highly efficient superconducting radiofrequency system for the FCC-ee lepton c...

  17. Future Circular Colliders

    CERN Document Server

    AUTHOR|(CDS)2108454; Zimmermann, Frank

    2015-01-01

    In response to a request from the 2013 Update of the European Strategy for Particle Physics, the global Future Circular Collider (FCC) study is preparing the foundation for a next-generation large-scale accelerator infrastructure in the heart of Europe. The FCC study focuses on the design of a 100-TeV hadron collider (FCC-hh), to be accommodated in a new ∼100 km tunnel near Geneva. It also includes the design of a high-luminosity electron-positron collider (FCC-ee), which could be installed in the same tunnel as a potential intermediate step, and a lepton-hadron collider option (FCC-he). The scope of the FCC study comprises accelerators, technology, infrastructure, detectors, physics, concepts for worldwide data services, international governance models, and implementation scenarios. Among the FCC core technologies figure 16-T dipole magnets, based on Nb3Sn superconductor, for the FCC-hh hadron collider, and a highly efficient superconducting radiofrequency system for the FCC-ee lepton collider. The interna...

  18. Future Circular Colliders

    CERN Document Server

    AUTHOR|(CDS)2108454; Zimmermann, Frank

    2015-01-01

    In response to a request from the 2013 Update of the European Strategy for Particle Physics, the global Future Circular Collider (FCC) study is preparing the foundation for a next-generation large-scale accelerator infrastructure in the heart of Europe. The FCC study focuses on the design of a 100-TeV hadron collider (FCC-hh), to be accommodated in a new ∼100 km tunnel near Geneva. It also includes the design of a high-luminosity electron-positron collider (FCC-ee), which could be installed in the same tunnel as a potential intermediate step, and a lepton-hadron collider option (FCC-he). The scope of the FCC study comprises accelerators, technology, infrastructure, detector, physics, concepts for worldwide data services, international governance models, and implementation scenarios. Among the FCC core technologies figure 16-T dipole magnets, based on Nb3Sn superconductor, for the FCC-hh hadron collider, and a highly efficient superconducting radiofrequency system for the FCC-ee lepton collider. The internat...

  19. Structural investigation of proapoptotic peptide by CD and NMR spectroscopy.

    Science.gov (United States)

    Pulsinelli, Emy; Vasile, Francesca; Vergani, Laura; Parodi, Silvio; Nicolini, Claudio

    2003-12-01

    We have performed a systematic investigation of the structural features of the peptides Int (a sequence able to cross cell membranes) and Int-H1(S6A,F8A) (which shows interesting antitumoral properties). After screening in aqueous solution at different ionic strength and pH values, we analyzed the structures of the peptides in different water/trifluoroethanol mixtures by Circular Dichroism and Nuclear Magnetic Resonance techniques.

  20. Digitalizing the Circular Economy

    Science.gov (United States)

    Reuter, Markus A.

    2016-12-01

    Metallurgy is a key enabler of a circular economy (CE), its digitalization is the metallurgical Internet of Things (m-IoT). In short: Metallurgy is at the heart of a CE, as metals all have strong intrinsic recycling potentials. Process metallurgy, as a key enabler for a CE, will help much to deliver its goals. The first-principles models of process engineering help quantify the resource efficiency (RE) of the CE system, connecting all stakeholders via digitalization. This provides well-argued and first-principles environmental information to empower a tax paying consumer society, policy, legislators, and environmentalists. It provides the details of capital expenditure and operational expenditure estimates. Through this path, the opportunities and limits of a CE, recycling, and its technology can be estimated. The true boundaries of sustainability can be determined in addition to the techno-economic evaluation of RE. The integration of metallurgical reactor technology and systems digitally, not only on one site but linking different sites globally via hardware, is the basis for describing CE systems as dynamic feedback control loops, i.e., the m-IoT. It is the linkage of the global carrier metallurgical processing system infrastructure that maximizes the recovery of all minor and technology elements in its associated refining metallurgical infrastructure. This will be illustrated through the following: (1) System optimization models for multimetal metallurgical processing. These map large-scale m-IoT systems linked to computer-aided design tools of the original equipment manufacturers and then establish a recycling index through the quantification of RE. (2) Reactor optimization and industrial system solutions to realize the "CE (within a) Corporation—CEC," realizing the CE of society. (3) Real-time measurement of ore and scrap properties in intelligent plant structures, linked to the modeling, simulation, and optimization of industrial extractive process

  1. Towards future circular colliders

    Science.gov (United States)

    Benedikt, Michael; Zimmermann, Frank

    2016-09-01

    The Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) presently provides proton-proton collisions at a center-of-mass (c.m.) energy of 13 TeV. The LHC design was started more than 30 years ago, and its physics program will extend through the second half of the 2030's. The global Future Circular Collider (FCC) study is now preparing for a post-LHC project. The FCC study focuses on the design of a 100-TeV hadron collider (FCC-hh) in a new ˜100 km tunnel. It also includes the design of a high-luminosity electron-positron collider (FCCee) as a potential intermediate step, and a lepton-hadron collider option (FCC-he). The scope of the FCC study comprises accelerators, technology, infrastructure, detectors, physics, concepts for worldwide data services, international governance models, and implementation scenarios. Among the FCC core technologies figure 16-T dipole magnets, based on Nb3 S n superconductor, for the FCC-hh hadron collider, and a highly-efficient superconducting radiofrequency system for the FCC-ee lepton collider. Following the FCC concept, the Institute of High Energy Physics (IHEP) in Beijing has initiated a parallel design study for an e + e - Higgs factory in China (CEPC), which is to be succeeded by a high-energy hadron collider (SPPC). At present a tunnel circumference of 54 km and a hadron collider c.m. energy of about 70 TeV are being considered. After a brief look at the LHC, this article reports the motivation and the present status of the FCC study, some of the primary design challenges and R&D subjects, as well as the emerging global collaboration.

  2. Circular spectropolarimetric sensing of chiral photosystems in decaying leaves

    Science.gov (United States)

    Patty, C. H. Lucas; Visser, Luuk J. J.; Ariese, Freek; Buma, Wybren Jan; Sparks, William B.; van Spanning, Rob J. M.; Röling, Wilfred F. M.; Snik, Frans

    2017-03-01

    Circular polarization spectroscopy has proven to be an indispensable tool in photosynthesis research and (bio)molecular research in general. Oxygenic photosystems typically display an asymmetric Cotton effect around the chlorophyll absorbance maximum with a signal ≤ 1 % . In vegetation, these signals are the direct result of the chirality of the supramolecular aggregates. The circular polarization is thus directly influenced by the composition and architecture of the photosynthetic macrodomains, and is thereby linked to photosynthetic functioning. Although ordinarily measured only on a molecular level, we have developed a new spectropolarimetric instrument, TreePol, that allows for both laboratory and in-the-field measurements. Through spectral multiplexing, TreePol is capable of fast measurements with a sensitivity of ∼ 1 *10-4 and is therefore suitable of non-destructively probing the molecular architecture of whole plant leaves. We have measured the chiroptical evolution of Hedera helix leaves for a period of 22 days. Spectrally resolved circular polarization measurements (450-900 nm) on whole leaves in transmission exhibit a strong decrease in the polarization signal over time after plucking, which we accredit to the deterioration of chiral macro-aggregates. Chlorophyll a levels measured over the same period by means of UV-vis absorption and fluorescence spectroscopy showed a much smaller decrease. With these results we are able to distinguish healthy from deteriorating leaves. Hereby we indicate the potency of circular polarization spectroscopy on whole and intact leaves as a nondestructive tool for structural and plant stress assessment. Additionally, we underline the establishment of circular polarization signals as remotely accessible means of detecting the presence of extraterrestrial life.

  3. Explicit Consideration of Water Molecules to Study Vibrational Circular DICHROÎSM of Monosaccharide's

    Science.gov (United States)

    Moussi, Sofiane; Ouamerali, Ourida

    2014-06-01

    Carbohydrates have multiples roles in biological systems. It has been found that the glycoside bond is fundamentally important in many aspects of chemistry and biology and forms the basis of carbohydrate chemistry. That means the stereochemical information, namely, glycosidic linkages α or β, gives an significant features of the carbohydrate glycosidation position of the glycosylic acceptor. For these reasons, much effort was made for the synthesis and analysis of the glycoside bond. Vibrational circular dichroism VCD has some advantages over conventional electronic circular dichroism (ECD) due to the applicability to all organic molecules and the reliability of ab initio quantum calculation. However, for a molecule with many chiral centers such as carbohydrates, determination of the absolute configuration tends to be difficult because the information from each stereochemical center is mixed and averaged over the spectrum. In the CH stretching region, only two VCD studies on carbohydrates have been reported and spectra--structure correlation, as determined for the glycoside band, remains to be investigated. T. Taniguchi and collaborators report that methyl glycosides exhibit a characteristic VCD peak, the sign of which solely reflects the C-1 absolute configuration. This work is a theoretical contribution to study the behaviour of VCD spectrum's of the monosaccharides when the water molecules are taken explicitly. This study is focused on six different monosaccharides in theirs absolute configuration R and S. We used the method of density functional theory DFT by means of the B3LYP hybrid functional and 6-31G * basis set.

  4. Enantioselective silver nanoclusters: Preparation, characterization and photoluminescence spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Farrag, Mostafa, E-mail: mostafafarrag@aun.edu.eg

    2016-09-01

    Herein, we report a new wet-synthesis method to separate some water-soluble chiral silver nanoclusters with high yield. The cluster material was obtained by the reduction of silver nitrate with NaBH{sub 4} in the presence of three ligands L-penicillamine (L-pen), D-penicillamine (D-pen) and racemic mixture of penicillamine (rac-pen), functioning as capping ligand. For characterizing all silver cluster samples, the particle size was assessed by transmission electron microscopy (TEM) and powder X-ray diffraction (XRD) and their average chemical formula was determined from thermogravimetric analysis (TGA) and elemental analysis (EA). The particles sizes of all three clusters are 2.1 ± 0.2 nm. The optical properties of the samples were studied by four different methods: UV-vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), photoluminescence spectroscopy (PL) and circular dichroism (CD) spectroscopy. The spectra are dominated by the typical and intense plasmon peak at 486 nm accompanied by a small shoulder at 540 nm. Infrared spectroscopy was measured for the free ligand and protected silver nanoclusters, where the disappearance of the S-H vibrational band (2535–2570 cm{sup −1}) in the silver nanoclusters confirmed anchoring of ligand to the cluster surface through the sulfur atom. PL studies yielded the fluorescent properties of the samples. The main focus of this work, however, lies in the chirality of the particles. For all silver clusters CD spectra were recorded. While for clusters capped with one of the two enantiomers (D- or L-form) typical CD spectra were observed, no significant signals were detected for a racemic ligand mixture. Furthermore, silver clusters show quite large asymmetry factors (up to 3 × 10{sup −4}) in comparison to most other ligand protected clusters. These large factors and bands in the visible range of the spectrum suggest a strong chiral induction from the ligand to the metal core. Textural features of the

  5. A polarized Infrared Spectroscopy Studies of Waterborne Polyurethane Orientation

    Institute of Scientific and Technical Information of China (English)

    Jin Guangkui; Cui Liyan; Yao Hongwei

    2015-01-01

    In this article,we prepare waterborne polyurethane(WPU)by polycarbonate diol,polyoxytetramethylene,dimethylol propionic acid and isophorone diisocyanate.We studied the stretch-oriented behavior of waterborne polyurethane films by universal tensile testing machine and FT-IR. And we analyzed the behavior of polyurethane orientation by infrared dichroism spectroscopy.

  6. A configurational and conformational study of aframodial and its diasteriomers via experimental and theoretical VA and VCD spectroscopies

    DEFF Research Database (Denmark)

    Jalkanen, Karl J.; Gale, J.D.; Lassen, Peter Rygaard;

    2008-01-01

    In this work we present the experimental and theoretical vibrational absorption (VA) and the theoretical vibrational circular dichroism (VCD) spectra for aframodial. In addition, we present the theoretical VA and VCD spectra for the diasteriomers of aframodial. Aframodial has four chiral centers ...

  7. Novel type of red-shifted chlorophyll a antenna complex from Chromera velia: II. Biochemistry and spectroscopy.

    Science.gov (United States)

    Bína, David; Gardian, Zdenko; Herbstová, Miroslava; Kotabová, Eva; Koník, Peter; Litvín, Radek; Prášil, Ondřej; Tichý, Josef; Vácha, František

    2014-06-01

    A novel chlorophyll a containing pigment-protein complex expressed by cells of Chromera velia adapted to growth under red/far-red illumination [1]. Purification of the complex was achieved by means of anion-exchange chromatography and gel-filtration. The antenna is shown to be an aggregate of ~20kDa proteins of the light-harvesting complex (LHC) family, unstable in the isolated form. The complex possesses an absorption maximum at 705nm at room temperature in addition to the main chlorophyll a maximum at 677nm producing the major emission band at 714nm at room temperature. The far-red absorption is shown to be the property of the isolated aggregate in the intact form and lost upon dissociation. The purified complex was further characterized by circular dichroism spectroscopy and fluorescence spectroscopy. This work thus identified the third different class of antenna complex in C. velia after the recently described FCP-like and LHCr-like antennas. Possible candidates for red antennas are identified in other taxonomic groups, such as eustigmatophytes and the relevance of the present results to other known examples of red-shifted antenna from other organisms is discussed. This work appears to be the first successful isolation of a chlorophyll a-based far-red antenna complex absorbing above 700nm unrelated to LHCI.

  8. The interaction of 2-mercaptobenzimidazole with human serum albumin as determined by spectroscopy, atomic force microscopy and molecular modeling.

    Science.gov (United States)

    Li, Yuqin; Jia, Baoxiu; Wang, Hao; Li, Nana; Chen, Gaopan; Lin, Yuejuan; Gao, Wenhua

    2013-04-01

    The interaction of 2-mercaptobenzimidazole (MBI) with human serum albumin (HSA) was studied in vitro by equilibrium dialysis under normal physiological conditions. This study used fluorescence, ultraviolet-visible spectroscopy (UV-vis), Fourier transform infrared (FT-IR), circular dichroism (CD) and Raman spectroscopy, atomic force microscopy (AFM) and molecular modeling techniques. Association constants, the number of binding sites and basic thermodynamic parameters were used to investigate the quenching mechanism. Based on the fluorescence resonance energy transfer, the distance between the HSA and MBI was 2.495 nm. The ΔG(0), ΔH(0), and ΔS(0) values across temperature indicated that the hydrophobic interaction was the predominant binding Force. The UV, FT-IR, CD and Raman spectra confirmed that the HSA secondary structure was altered in the presence of MBI. In addition, the molecular modeling showed that the MBI-HSA complex was stabilized by hydrophobic forces, which resulted from amino acid residues. The AFM results revealed that the individual HSA molecule dimensions were larger after interaction with MBI. Overall, this study suggested a method for characterizing the weak intermolecular interaction. In addition, this method is potentially useful for elucidating the toxigenicity of MBI when it is combined with the biomolecular function effect, transmembrane transport, toxicological testing and other experiments.

  9. Implementing circularity using partial evaluation

    DEFF Research Database (Denmark)

    Lawall, Julia Laetitia

    2001-01-01

    of an imperative C-like language, by extending the language with a new construct, persistent variables. We show that an extension of partial evaluation can eliminate persistent variables, producing a staged C program. This approach has been implemented in the Tempo specializer for C programs, and has proven useful......Complex data dependencies can often be expressed concisely by defining a variable in terms of part of its own value. Such a circular reference can be naturally expressed in a lazy functional language or in an attribute grammar. In this paper, we consider circular references in the context...

  10. Circular threshold quantum secret sharing

    Institute of Scientific and Technical Information of China (English)

    Yang Yu-Guang; Wen Qiao-Yan

    2008-01-01

    This paper proposes a circular threshold quantum secret sharing (TQSS) scheme with polarized single photons.A polarized single photon sequence runs circularly among any t or more of n parties and any t or more of n parties can reconstruct the secret key when they collaborate.It shows that entanglement is not necessary for quantum secret sharing.Moreover,the theoretic efficiency is improved to approach 100% as the single photons carrying the secret key are deterministically forwarded among any t or more of n parties,and each photon can carry one bit of information without quantum storage.This protocol is feasible with current technology.

  11. Synthesis of chiral polyaniline films via chemical vapor phase polymerization

    DEFF Research Database (Denmark)

    Chen, J.; Winther-Jensen, B.; Pornputtkul, Y.;

    2006-01-01

    methods, such as cyclic voltammetry (CV), UV- vis spectroscopy, four- point probe conductivity measurement, Raman spectroscopy, circular dichroism spectroscopy, and scanning electron microscopy. The polyaniline films grown by this method not only showed high electrochemical activity, supported by CV...

  12. Comparative Studies of Interactions between Fluorodihydroquinazolin Derivatives and Human Serum Albumin with Fluorescence Spectroscopy

    Directory of Open Access Journals (Sweden)

    Yi Wang

    2016-10-01

    Full Text Available In the present study, 3-(fluorobenzylideneamino-6-chloro-1-(3,3-dimethylbutanoyl-phenyl-2,3-dihydroquinazolin-4(1H-one (FDQL derivatives have been designed and synthesized to study the interaction between fluorine substituted dihydroquinazoline derivatives with human serum albumin (HSA using fluorescence, circular dichroism and Fourier transform infrared spectroscopy. The results indicated that the FDQL could bind to HSA, induce conformation and the secondary structure changes of HSA, and quench the intrinsic fluorescence of HSA through a static quenching mechanism. The thermodynamic parameters, ΔH, ΔS, and ΔG, calculated at different temperatures, revealed that the binding was through spontaneous and hydrophobic forces and thus played major roles in the association. Based on the number of binding sites, it was considered that one molecule of FDQL could bind to a single site of HSA. Site marker competition experiments indicated that the reactive site of HSA to FDQL mainly located in site II (subdomain IIIA. The substitution by fluorine in the benzene ring could increase the interactions between FDQL and HSA to some extent in the proper temperature range through hydrophobic effect, and the substitution at meta-position enhanced the affinity greater than that at para- and ortho-positions.

  13. Binding of Ru(terpyridine)(pyridine)dipyridophenazine to DNA studied with polarized spectroscopy and calorimetry.

    Science.gov (United States)

    Mårtensson, Anna K F; Lincoln, Per

    2015-02-28

    Linear and circular dichroism (LD and CD) spectroscopy as well as isothermal titration calorimetry (ITC) have been used to investigate the interaction of Ru(tpy)(py)dppz(2+) (tpy = 2,2':6',2''-terpyridyl; py = pyridine; dppz = dipyrido[3,2-a:2'3'-c]phenazine) with DNA, providing detailed information about the DNA binding thermodynamics and binding geometry of the metal complex. Flow LD, CD and isotropic absorption indicate that Ru(tpy)(py)dppz(2+) bind to DNA from the minor groove with the dppz ligand intercalated between base pairs, very similar to its chiral structural isomers Δ- and Λ-Ru(bpy)2dppz(2+) (bpy = 2,2'-bipyridine). A simple cooperative binding model with one binding geometry provide an excellent fit for calorimetric and absorption titration data. The values of the neighbor interaction thermodynamic parameters for Ru(tpy)(py)dppz(2+) suggest that complexes bound contiguously prefer to have their tpy ligands oriented towards the same strand.

  14. Insights into Hydrocarbon-rich Environments from Studies of Protein Dynamics, Thermodynamics, and Spectroscopy

    Science.gov (United States)

    Magyar, J. S.; Asous, N. K.; Barth, S. J.; Benzik, E.; Chou, J.; Dalchand, N.; Gallagher, G. E.; Montero, K. S.; Lone, S. K.; Salerno, G. J.

    2015-12-01

    Extraordinary amounts of information are now available from genomic and metagenomic analyses of a wide variety of environments of geological and biological interest. Using such genomic information as a starting point, we are interested in looking at microbial systems at the molecular level, using the tools and approaches of inorganic chemistry, physical chemistry, and molecular biology. From these studies, spanning the molecular to the global, we gain insights into relationships between microbial life and the geochemical environment in which it lives. In our work to date, we have focused on hydrocarbon-rich environments, including the La Brea Tar Pits and the Gulf of Mexico. Starting from genomic information, we have identified proteins of interest, cloned synthetic genes into E. coli, overexpressed and purified the proteins, and characterized them by UV-visible absorption, circular dichroism, and NMR spectroscopies; X-ray crystallography; and electrochemistry. Using as examples our recent studies of a metal-uptake protein from a methanogenic archaeon native to the La Brea Tar Pits, and of electron-transfer and hydrocarbon-degrading proteins from cold marine ecosystems, we describe how new combinations of genomics, molecular biology, and bioinorganic chemistry can provide novel insights into geobiological processes.

  15. Single-molecule spectroscopy of the temperature-induced collapse of unfolded proteins.

    Science.gov (United States)

    Nettels, Daniel; Müller-Späth, Sonja; Küster, Frank; Hofmann, Hagen; Haenni, Dominik; Rüegger, Stefan; Reymond, Luc; Hoffmann, Armin; Kubelka, Jan; Heinz, Benjamin; Gast, Klaus; Best, Robert B; Schuler, Benjamin

    2009-12-01

    We used single-molecule FRET in combination with other biophysical methods and molecular simulations to investigate the effect of temperature on the dimensions of unfolded proteins. With single-molecule FRET, this question can be addressed even under near-native conditions, where most molecules are folded, allowing us to probe a wide range of denaturant concentrations and temperatures. We find a compaction of the unfolded state of a small cold shock protein with increasing temperature in both the presence and the absence of denaturant, with good agreement between the results from single-molecule FRET and dynamic light scattering. Although dissociation of denaturant from the polypeptide chain with increasing temperature accounts for part of the compaction, the results indicate an important role for additional temperature-dependent interactions within the unfolded chain. The observation of a collapse of a similar extent in the extremely hydrophilic, intrinsically disordered protein prothymosin alpha suggests that the hydrophobic effect is not the sole source of the underlying interactions. Circular dichroism spectroscopy and replica exchange molecular dynamics simulations in explicit water show changes in secondary structure content with increasing temperature and suggest a contribution of intramolecular hydrogen bonding to unfolded state collapse.

  16. Correlation spectroscopy and molecular dynamics simulations to study the structural features of proteins.

    Directory of Open Access Journals (Sweden)

    Antonio Varriale

    Full Text Available In this work, we used a combination of fluorescence correlation spectroscopy (FCS and molecular dynamics (MD simulation methodologies to acquire structural information on pH-induced unfolding of the maltotriose-binding protein from Thermus thermophilus (MalE2. FCS has emerged as a powerful technique for characterizing the dynamics of molecules and it is, in fact, used to study molecular diffusion on timescale of microsecond and longer. Our results showed that keeping temperature constant, the protein diffusion coefficient decreased from 84±4 µm(2/s to 44±3 µm(2/s when pH was changed from 7.0 to 4.0. An even more marked decrease of the MalE2 diffusion coefficient (31±3 µm(2/s was registered when pH was raised from 7.0 to 10.0. According to the size of MalE2 (a monomeric protein with a molecular weight of 43 kDa as well as of its globular native shape, the values of 44 µm(2/s and 31 µm(2/s could be ascribed to deformations of the protein structure, which enhances its propensity to form aggregates at extreme pH values. The obtained fluorescence correlation data, corroborated by circular dichroism, fluorescence emission and light-scattering experiments, are discussed together with the MD simulations results.

  17. Enzyme stability, thermodynamics and secondary structures of α-amylase as probed by the CD spectroscopy.

    Science.gov (United States)

    Kikani, B A; Singh, S P

    2015-11-01

    An amylase of a thermophilic bacterium, Bacillus sp. TSSC-3 (GenBank Number, EU710557) isolated from the Tulsi Shyam hot spring reservoir (Gujarat, India) was purified to the homogeneity in a single step on phenyl sepharose 6FF. The molecular weight of the enzyme was 25kD, while the temperature and pH optima for the enzyme catalysis were 80°C and 7, respectively. The purified enzyme was highly thermostable with broad pH stability and displayed remarkable resistance against surfactants, chelators, urea, guanidine HCl and various solvents as well. The stability and changes in the secondary structure of the enzyme under various extreme conditions were determined by the circular dichroism (CD) spectroscopy. The stability trends and the changes in the α-helices and β-sheets were analyzed by Mean Residual Ellipticity (MRE) and K2D3. The CD data confirmed the structural stability of the enzyme under various harsh conditions, yet it indicated reduced α-helix content and increased β-sheets upon denaturation. The thermodynamic parameters; deactivation rate constant, half-life, changes in entropy, enthalpy, activation energy and Gibb's free energy indicated that the enzyme-substrate reactions were highly stable. The overall profile of the enzyme: high thermostability, alkalitolerance, calcium independent nature, dextrose equivalent values and resistance against chemical denaturants, solvents and surfactants suggest its commercial applications.

  18. Circular polarization observed in bioluminescence

    NARCIS (Netherlands)

    Wijnberg, Hans; Meijer, E.W.; Hummelen, J.C.; Dekkers, H.P.J.M.; Schippers, P.H.; Carlson, A.D.

    1980-01-01

    While investigating circular polarization in luminescence, and having found it in chemiluminescence, we have studied bioluminescence because it is such a widespread and dramatic natural phenomenon. We report here that left and right lanterns of live larvae of the fireflies, Photuris lucicrescens and

  19. Circular polarization in relativistic jets

    NARCIS (Netherlands)

    Macquart, JP

    2003-01-01

    Circular polarization is observed in some relativistic jet sources at radio wavelengths. It is largely associated with activity in the cores of the radio sources, is highly variable, and is strongest during ejection episodes. VLBI imaging and interstellar scintillation arguments show that the degree

  20. Class IIc or Circular Bacteriocins

    Science.gov (United States)

    Martin-Visscher, Leah A.; van Belkum, Marco J.; Vederas, John C.

    The circular bacteriocins produced by Gram-positive bacteria represent a diverse class of antimicrobial peptides. These bacteriocins display enhanced stability compared to linear bacteriocins, which arises from their characteristic circular backbone. Currently, eight unique circular bacteriocins have been identified, and analysis of their gene clusters indicates that they likely utilize complex mechanisms for maturation and secretion, as well as for immunity. These bacteriocins target the cytoplasmic membrane of sensitive cells, leading to pore formation that results in loss of ions, dissipation of membrane potential, and ultimately, cell death. Structural studies suggest that despite variation in their sequences, most of these bacteriocins likely adopt a common three-dimensional architecture, consisting of four or five tightly packed helices encompassing a hydrophobic core. There are many mysteries surrounding the biosynthesis of these peptides, particularly in regard to the mechanism by which they are cyclized. Elucidation of such a mechanism may provide exciting new approaches to the bioengineering of new, stable, and antimicrobially active circular peptides.

  1. Probing the magnetic moments of [Mn{sup III}{sub 6}Cr{sup III}]{sup 3+} single-molecule magnets—A cross comparison of XMCD and spin-resolved electron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Helmstedt, Andreas, E-mail: helmstedt.andreas@gmail.com [Faculty of Physics, Bielefeld University, Universitätsstr. 25, 33615 Bielefeld (Germany); Dohmeier, Niklas; Müller, Norbert; Gryzia, Aaron; Brechling, Armin; Heinzmann, Ulrich [Faculty of Physics, Bielefeld University, Universitätsstr. 25, 33615 Bielefeld (Germany); Hoeke, Veronika; Krickemeyer, Erich; Glaser, Thorsten [Faculty of Chemistry, Bielefeld University, Universitätsstr. 25, 33615 Bielefeld (Germany); Leicht, Philipp; Fonin, Mikhail [Fachbereich Physik, Universität Konstanz, Universitätsstr. 10, 78457 Konstanz (Germany); Tietze, Thomas [Max Planck Institute for Intelligent Systems, Heisenbergstr. 3, 70569 Stuttgart (Germany); Joly, Loïc [Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504, CNRS-Université de Strasbourg, BP 43, 23 rue du Loess, F-67034 Strasbourg Cedex 2 (France); Kuepper, Karsten [Institut für Festkörperphysik, Universität Ulm, 89069 Ulm (Germany)

    2015-01-15

    Highlights: • [Mn{sup III}{sub 6}Cr{sup III}]{sup 3+} single-molecule magnets are investigated. • XMCD and spin-resolved electron spectroscopy (SPES) results are compared. • A simple sum rule evaluation is performed for comparison. • Differences between SPES and XMCD results are discussed. • Influences of the magnetic field on the Mn L edge absorption are observed. - Abstract: Single-molecule magnets (SMM) of the [Mn{sup III}{sub 6}Cr{sup III}]{sup 3+} structural type prepared on Si and gold-coated glass substrates have been investigated by spin-resolved electron spectroscopy (SPES) and X-ray magnetic circular dichroism (XMCD) at the Mn L{sub 3,2} edge and in addition by XMCD at the Cr L{sub 3,2} edge using synchrotron radiation. Differences between the two methods are discussed. Despite its severe limitations for 3d transition metals, a spin sum rule evaluation is nevertheless performed for the Mn{sup III} centres in the [Mn{sup III}{sub 6}Cr{sup III}]{sup 3+} SMM to provide a simple means of comparing XMCD and spin-resolved electron spectroscopy results.

  2. Magnetic dichroism and spin structure of antiferromagnetic NiO(001) films

    NARCIS (Netherlands)

    Altieri, S; Finazzi, M; Hsieh, HH; Lin, HJ; Chen, CT; Hibma, T; Valeri, S; Sawatzky, GA

    2003-01-01

    We find that Ni L-2 edge x-ray magnetic linear dichroism is fully reversed for NiO(001) films on materials with reversed lattice mismatch. We relate this phenomenon to a preferential stabilization of magnetic S domains with main spin component either in or out of the plane, via dipolar interactions.

  3. SPIN POLARIZATION AND MAGNETIC DICHROISM IN PHOTOEMISSION FROM CORE AND VALENCE STATES IN LOCALIZED MAGNETIC SYSTEMS

    NARCIS (Netherlands)

    THOLE, BT; VANDERLAAN, G

    1991-01-01

    Using group theory we derive a general model for spin polarization and magnetic dichroism in photo-emission in the presence of atomic interactions between the hole created and the valence holes. We predict strong effects in the photoemission from core levels and localized valence levels of transitio

  4. Combination of UV-vis spectroscopy and chemometrics to understand protein-nanomaterial conjugate: a case study on human serum albumin and gold nanoparticles.

    Science.gov (United States)

    Wang, Yong; Ni, Yongnian

    2014-02-01

    Study of the interactions between proteins and nanomaterials is of great importance for understanding of protein nanoconjugate. In this work, we choose human serum albumin (HSA) and citrate-capped gold nanoparticles (AuNPs) as a model of protein and nanomaterial, and combine UV-vis spectroscopy with multivariate curve resolution by an alternating least squares (MCR-ALS) algorithm to present a new and efficient method for comparatively comprehensive study of evolution of protein nanoconjugate. UV-vis spectroscopy coupled with MCR-ALS allows qualitative and quantitative extraction of the distribution diagrams, spectra and kinetic profiles of absorbing pure species (AuNPs and AuNPs-HSA conjugate are herein identified) and undetectable species (HSA) from spectral data. The response profiles recovered are converted into the desired thermodynamic, kinetic and structural parameters describing the protein nanoconjugate evolution. Analysis of these parameters for the system gives evidence that HSA molecules are very likely to be attached to AuNPs surface predominantly as a flat monolayer to form a stable AuNPs-HSA conjugate with a core-shell structure, and the binding process takes place mainly through electrostatic and hydrogen-bond interactions between the positively amino acid residues of HSA and the negatively carboxyl group of citrate on AuNPs surface. The results obtained are verified by transmission electron microscopy, zeta potential, circular dichroism spectroscopy and Fourier transform infrared spectroscopy, showing the potential of UV-vis spectroscopy for study of evolution of protein nanoconjugate. In parallel, concentration evolutions of pure species resolved by MCR-ALS are used to construct a sensitive spectroscopic biosensor for HSA with a linear range from 1.8 nM to 28.1 nM and a detection limit of 0.8 nM.

  5. A new highly adaptable design of shear-flow device for orientation of macromolecules for Linear Dichroism (LD) measurement

    KAUST Repository

    Lundahl, P. Johan

    2011-01-01

    This article presents a new design of flow-orientation device for the study of bio-macromolecules, including DNA and protein complexes, as well as aggregates such as amyloid fibrils and liposome membranes, using Linear Dichroism (LD) spectroscopy. The design provides a number of technical advantages that should make the device inexpensive to manufacture, easier to use and more reliable than existing techniques. The degree of orientation achieved is of the same order of magnitude as that of the commonly used concentric cylinders Couette flow cell, however, since the device exploits a set of flat strain-free quartz plates, a number of problems associated with refraction and birefringence of light are eliminated, increasing the sensitivity and accuracy of measurement. The device provides similar shear rates to those of the Couette cell but is superior in that the shear rate is constant across the gap. Other major advantages of the design is the possibility to change parts and vary sample volume and path length easily and at a low cost. © 2011 The Royal Society of Chemistry.

  6. Control of a Circular Jet

    CERN Document Server

    Gohil, Trushar B; Muralidhar, K

    2010-01-01

    The present study report direct numerical simulation (DNS) of a circular jet and the effect of a large scale perturbation at the jet inlet. The perturbation is used to control the jet for increased spreading. Dual-mode perturbation is obtained by combining an axisymmetric excitation with the helical. In the fluid dynamics videos, an active control of the circular jet at a Reynolds number of 2000 for various frequency ratios (both integer and non-integer) has been demonstrated. When the frequency ratio is fixed to 2, bifurcation of the jet on a plane is evident. However, for a non-integer frequency ratio, the axisymmetric jet is seen to bloom in all directions.

  7. Insights into circular RNA biology

    DEFF Research Database (Denmark)

    Ebbesen, Karoline K; Hansen, Thomas B; Kjems, Jørgen

    2016-01-01

    Circular RNAs (circRNAs) are a novel class of non-coding RNA characterized by a covalently closed-loop structure generated through a special type of alternative splicing termed backsplicing. CircRNAs are emerging as a heterogeneous class of molecules involved in modulating gene expression by regu...... and lastly, an outlook with a focus on unanswered questions regarding circRNA biology will be included....

  8. Granger causality for circular variables

    Energy Technology Data Exchange (ETDEWEB)

    Angelini, Leonardo; Pellicoro, Mario [Istituto Nazionale di Fisica Nucleare, Sezione di Bari (Italy); Dipartimento di Fisica, University of Bari (Italy); Stramaglia, Sebastiano, E-mail: sebastiano.stramaglia@ba.infn.i [Istituto Nazionale di Fisica Nucleare, Sezione di Bari (Italy); Dipartimento di Fisica, University of Bari (Italy)

    2009-06-29

    In this Letter we discuss the use of Granger causality to the analyze systems of coupled circular variables, by modifying a recently proposed method for multivariate analysis of causality. We show the application of the proposed approach on several Kuramoto systems, in particular one living on networks built by preferential attachment and a model for the transition from deeply to lightly anaesthetized states. Granger causalities describe the flow of information among variables.

  9. Capacitance of circular patch resonator

    Energy Technology Data Exchange (ETDEWEB)

    Miano, G.; Verolino, L. [Dip. di Ingegneria Elettrica, Ist. Nazionale di Fisica Nucleare, Naples (Italy); Panariello, G. [Dip. di Ingegneria Elettronica, Naples (Italy); Vaccaro, V.G. [Ist. Nazionale di Fisica Nucleare, Naples (Italy). Dipt. di Scienze Fisiche

    1995-11-01

    In this paper the capacitance of the circular microstrip patch resonator is computed. It is shown that the electrostatic problem can be formulated as a system of dual integral equations, and the most interesting techniques of solutions of these systems are reviewed. Some useful approximated formulas for the capacitance are derived and plots of the capacitance are finally given in a wide range of dielectric constants.

  10. Circular Polarization in Pulsar Integrated Profiles: Updates

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    We update the systematic studies of circular polarization in integrated pulse profiles by Han et al. Data of circular polarization profiles are compiled. Sense reversals can occur in core or cone components, or near the intersection between components. The correlation between the sense of circular polarization and the sense of position angle variation for conal-double pulsars is confirmed with a much large database. Circular polarization of some pulsars has clear changes with frequency.Circular polarization of millisecond pulsars is marginally different from that of normal pulsars.

  11. Two-Photon Polarization Dependent Spectroscopy in Chirality: A Novel Experimental-Theoretical Approach to Study Optically Active Systems

    Directory of Open Access Journals (Sweden)

    Florencio E. Hernández

    2011-04-01

    Full Text Available Many phenomena, including life itself and its biochemical foundations are fundamentally rooted in chirality. Combinatorial methodologies for catalyst discovery and optimization remain an invaluable tool for gaining access to enantiomerically pure compounds in the development of pharmaceuticals, agrochemicals, and flavors. Some exotic metamaterials exhibiting negative refractive index at optical frequencies are based on chiral structures. Chiroptical activity is commonly quantified in terms of circular dichroism (CD and optical rotatory dispersion (ORD. However, the linear nature of these effects limits their application in the far and near-UV region in highly absorbing and scattering biological systems. In order to surmount this barrier, in recent years we made important advancements on a novel non linear, low-scatter, long-wavelength CD approach called two-photon absorption circular dichroism (TPACD. Herein we present a descriptive analysis of the optics principles behind the experimental measurement of TPACD, i.e., the double L-scan technique, and its significance using pulsed lasers. We also make an instructive examination and discuss the reliability of our theoretical-computational approach, which uses modern analytical response theory, within a Time-Dependent Density Functional Theory (TD-DFT approach. In order to illustrate the potential of this novel spectroscopic tool, we first present the experimental and theoretical results obtained in C2-symmetric, axially chiral R-(+-1,1'-bi(2-naphthol, R-BINOL, a molecule studied at the beginning of our investigation in this field. Next, we reveal some preliminary results obtained for (R-3,3′-diphenyl-2,2′-bi-1-naphthol, R-VANOL, and (R-2,2′-diphenyl-3,3′-(4-biphenanthrol, R-VAPOL. This family of optically active compounds has been proven to be a suitable model for the structure-property relationship study of TPACD, because its members are highly conjugated yet photo-stable, and easily

  12. Two-photon polarization dependent spectroscopy in chirality: a novel experimental-theoretical approach to study optically active systems.

    Science.gov (United States)

    Hernández, Florencio E; Rizzo, Antonio

    2011-04-18

    Many phenomena, including life itself and its biochemical foundations are fundamentally rooted in chirality. Combinatorial methodologies for catalyst discovery and optimization remain an invaluable tool for gaining access to enantiomerically pure compounds in the development of pharmaceuticals, agrochemicals, and flavors. Some exotic metamaterials exhibiting negative refractive index at optical frequencies are based on chiral structures. Chiroptical activity is commonly quantified in terms of circular dichroism (CD) and optical rotatory dispersion (ORD). However, the linear nature of these effects limits their application in the far and near-UV region in highly absorbing and scattering biological systems. In order to surmount this barrier, in recent years we made important advancements on a novel non linear, low-scatter, long-wavelength CD approach called two-photon absorption circular dichroism (TPACD). Herein we present a descriptive analysis of the optics principles behind the experimental measurement of TPACD, i.e., the double L-scan technique, and its significance using pulsed lasers. We also make an instructive examination and discuss the reliability of our theoretical-computational approach, which uses modern analytical response theory, within a Time-Dependent Density Functional Theory (TD-DFT) approach. In order to illustrate the potential of this novel spectroscopic tool, we first present the experimental and theoretical results obtained in C(2)-symmetric, axially chiral R-(+)-1,1'-bi(2-naphthol), R-BINOL, a molecule studied at the beginning of our investigation in this field. Next, we reveal some preliminary results obtained for (R)-3,3'-diphenyl-2,2'-bi-1-naphthol, R-VANOL, and (R)-2,2'-diphenyl-3,3'-(4-biphenanthrol), R-VAPOL. This family of optically active compounds has been proven to be a suitable model for the structure-property relationship study of TPACD, because its members are highly conjugated yet photo-stable, and easily derivatized at the 5

  13. Investigation on interaction of DNA and several cationic surfactants with different head groups by spectroscopy, gel electrophoresis and viscosity technologies.

    Science.gov (United States)

    Guo, Qing; Zhang, Zhaohong; Song, Youtao; Liu, Shuo; Gao, Wei; Qiao, Heng; Guo, Lili; Wang, Jun

    2017-02-01

    In this study, the interaction between DNA and several cationic surfactants with different head groups such as ethyl hexadecyl dimethyl ammonium bromide (EHDAB), hexadecyl dimethyl benzyl ammonium chloride (HDBAC), and cetyl pyridinium bromide (CPB) were investigated by UV-vis absorption, fluorescence and circular dichroism (CD) spectroscopy, gel electrophoresis, and viscosity technologies. The results show that these cationic surfactants can interact with DNA and major binding modes are electrostatic and hydrophobic. Also, CPB and HDBAC molecules interact with DNA by partial intercalation, and CPB has slightly stronger intercalation than HDBAC, while EHDAB interacts with DNA by non-intercalation. The different head groups of the surfactant molecules can influence the interaction strength. CPB has the stronger interaction with DNA than the others. Moreover, surfactant concentration, the ratio of DNA and fluorescence probe, ionic strength can influence the interaction. The surfactants may interact with DNA by the competition reactions with BR for DNA-BR. The increase of ionic strength may favor the surface binding between DNA and surfactants to some extent. This work provides deep mechanistic insight on the toxicity of cationic surfactants with different head groups to DNA molecules.

  14. Temperature-dependent structural change of D-penicillamine-capped chiral gold nanoparticles investigated by infrared spectroscopy

    Science.gov (United States)

    Ock, Kwang-Su; Dembereldorj, Uuriintuya; Park, Jin; Ganbold, Erdene-Ochir; Kim, Semi; Shin, Hang-Cheol; Joo, Sang-Woo

    2013-02-01

    The structure and stability of D-penicillamine-capped gold nanoparticles (D-Pen Au NPs) were studied using spectroscopic tools. The synthesis of D-Pen Au NPs was examined using high-resolution transmission electron microscopy (HR-TEM), UV-vis absorption spectroscopy, and circular dichroism (CD). Temperature-dependent reversible structural changes of D-Pen Au NPs were observed using infrared spectroscopic tools. The three thiol, carboxyl, and amino binding groups of D-Pen were presumed to interact with Au NP surfaces on the basis of the infrared spectral features. D-Pen appeared to form quite a stable structure and desorb at a high temperature above 453 K on Au NPs. Our deconvolution analysis indicated the νs(COO-) and νas(COO-) carboxylate bands at ˜1392 and ˜1560 cm-1 appeared to be weakened, whereas the amino band at ˜1595 cm-1 remained strong in increasing the temperature from 293 to 373 K. On the other hand, the intensities of the zwitter ionic bands at ˜999, ˜1117, and ˜1631 cm-1 for NH3+ appeared to decrease presumably due to the deprotonation process at 373 K. Our infrared spectroscopic study suggests that the deprotonated amino groups bind stronger, whereas the intra-carboxylate bonds become weaker as the temperature increase. Such structural changes of D-Pen Au NPs appeared to be reversible between 293 and 373 K.

  15. Structural stability of soybean (Glycine max) α-amylase: properties of the unfolding transition studied with fluorescence and CD spectroscopy.

    Science.gov (United States)

    Kumari, Arpana; Rosenkranz, Tobias; Fitter, Jörg; Kayastha, Arvind M

    2011-03-01

    Stability and unfolding of mammalian and microbial α-amylases have been intensively investigated. However, there is only limited information available on the structural stability of plant α-amylases, namely of the two isoenzymes from barley AMY1 and AMY2, of the α-amylase from mung bean (Vigna radiata), and of the α-amylase from malted sorghum (Sorghum bicolor). We report here the stability of soyabean α-amylase (GMA), against elevated temperatures and chemical denaturants (GndHCl) by employing circular dichroism and fluorescence spectroscopy. Since it is well-known that calcium ions play a crucial role for enzymatic activity and stability of a-amylases, we performed our studies with calcium bound and calcium free GMA. The thermal unfolding transition temperature decreased from 72°C for calcium saturated samples to 57°C for the case of calcium depleted GMA. Similarly, the GndHCl transition concentration was lowered from 0.70 M for calcium bound GMA to 0.41 M in the absence of calcium. Thermal unfolding of GMA irreversible due to aggregation of the unfolded state. GMA unfolded in 6 M GndHCl shows high degree of reversibility after diluting the unfolded enzyme in native buffer containing 7 M glycerol. Furthermore, the refolded enzyme showed 93% of activity.

  16. Linear dichroism and optical anisotropy of silver nanoprisms in polymer films

    Science.gov (United States)

    Requena, S.; Doan, H.; Raut, S.; D'Achille, A.; Gryczynski, Z.; Gryczynski, I.; Strzhemechny, Y. M.

    2016-08-01

    We present optical studies of two different size distributions of silver triangular nanoprisms, one with a dipole resonance at 520 nm and the other with a dipole resonance at 650 nm, placed in different media. Significant wavelength-dependent depolarization of scattered light from the silver nanoprisms suspended in water indicates strong interference of multiple surface plasmon resonant modes in the same particle. We use this depolarization as a probe of light scattering by the nanoprisms in a lipid solution due to the rejection of a polarized background scattering. Also, the silver nanoprisms were embedded in a polyvinyl alcohol polymer matrix and oriented by stretching the polymer/nanoprism nanocomposite films. We observe significantly increased linear dichroism in the region associated with the plasmonic in-plane dipole mode upon stretching. Additionally, there is a weaker linear dichroism in the region associated with out-of-plane modes, which vanish in the extinction spectrum of the stretched nanocomposite film.

  17. Magnetic x-ray linear dichroism in resonant and non-resonant Gd 4f photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Mishra, S.; Gammon, W.J.; Pappas, D.P. [Virginia Commonwealth Univ., Richmond, VA (United States)] [and others

    1997-04-01

    The enhancement of the magnetic linear dichroism in resonant 4f photoemission (MLDRPE) is studied from a 50 monolayer film of Gd/Y(0001). The ALS at beamline 7.0.1 provided the source of linearly polarized x-rays used in this study. The polarized light was incident at an angle of 30 degrees relative to the film plane, and the sample magnetization was perpendicular to the photon polarization. The linear dichroism of the 4f core levels is measured as the photon energy is tuned through the 4d-4f resonance. The authors find that the MLDRPE asymmetry is strongest at the resonance. Near the threshold the asymmetry has several features which are out of phase with the fine structure of the total yield.

  18. Boxicity of Circular Arc Graphs

    OpenAIRE

    Bhowmick, Diptendu; Chandran, L. Sunil

    2008-01-01

    A $k$-dimensional box is the cartesian product $R_1 \\times R_2 \\times ... \\times R_k$ where each $R_i$ is a closed interval on the real line. The {\\it boxicity} of a graph $G$, denoted as $box(G)$, is the minimum integer $k$ such that $G$ can be represented as the intersection graph of a collection of $k$-dimensional boxes: that is two vertices are adjacent if and only if their corresponding boxes intersect. A circular arc graph is a graph that can be represented as the intersection graph of ...

  19. Deterministic Circular Self Test Path

    Institute of Scientific and Technical Information of China (English)

    WEN Ke; HU Yu; LI Xiaowei

    2007-01-01

    Circular self test path (CSTP) is an attractive technique for testing digital integrated circuits(IC) in the nanometer era, because it can easily provide at-speed test with small test data volume and short test application time. However, CSTP cannot reliably attain high fault coverage because of difficulty of testing random-pattern-resistant faults. This paper presents a deterministic CSTP (DCSTP) structure that consists of a DCSTP chain and jumping logic, to attain high fault coverage with low area overhead. Experimental results on ISCAS'89 benchmarks show that 100% fault coverage can be obtained with low area overhead and CPU time, especially for large circuits.

  20. Encryption using circular harmonic key

    OpenAIRE

    Jorge Enrique Rueda-Parada

    2015-01-01

    En este trabajo presento un estudio sobre la varianza a la rota ción de la llave del procesador de encriptación basado en la tr ansformada de Fourier. Determiné que la llave en coordenadas rectangulares pe rmite un nivel de tolerancia inferior a 0.2 grados de rotación de la llave en el proceso de decriptación. Entonces la solución es construir la llave en coordenadas polares, por medio de una expansión en armónicos circulares. De esta manera, el umbral de tolerancia a um...

  1. Attenuation in Superconducting Circular Waveguides

    Directory of Open Access Journals (Sweden)

    K. H. Yeap

    2016-09-01

    Full Text Available We present an analysis on wave propagation in superconducting circular waveguides. In order to account for the presence of quasiparticles in the intragap states of a superconductor, we employ the characteristic equation derived from the extended Mattis-Bardeen theory to compute the values of the complex conductivity. To calculate the attenuation in a circular waveguide, the tangential fields at the boundary of the wall are first matched with the electrical properties (which includes the complex conductivity of the wall material. The matching of fields with the electrical properties results in a set of transcendental equations which is able to accurately describe the propagation constant of the fields. Our results show that although the attenuation in the superconducting waveguide above cutoff (but below the gap frequency is finite, it is considerably lower than that in a normal waveguide. Above the gap frequency, however, the attenuation in the superconducting waveguide increases sharply. The attenuation eventually surpasses that in a normal waveguide. As frequency increases above the gap frequency, Cooper pairs break into quasiparticles. Hence, we attribute the sharp rise in attenuation to the increase in random collision of the quasiparticles with the lattice structure.

  2. First observation of spin dichroism with deuterons up to 20 MeV in a carbon target

    CERN Document Server

    Baryshevsky, V; Engels, R; Rathmann, F; Seyfarth, H; Ströher, H; Ullrich, T; D"uweke, C; Emmerich, R; Imig, A; Ley, J; Schieck, H P; Schulze, R; Tenckhoff, G; Weske, C; Mikirtytchiants, M; Vasilev, A

    2005-01-01

    The first observation of the phenomenom of deuteron spin dichroism in the energy region of 6-20 MeV is described. Experimental values of this effect for deuterons after passage of an unpolarized carbon target are reported.

  3. Total positive curvature of circular DNA

    DEFF Research Database (Denmark)

    Bohr, Jakob; Olsen, Kasper Wibeck

    2013-01-01

    molecules, e.g., plasmids, it is shown to have implications for the total positive curvature integral. For small circular micro-DNAs it follows as a consequence of Fenchel's inequality that there must exist a minimum length for the circular plasmids to be double stranded. It also follows that all circular...... micro-DNAs longer than the minimum length must be concave, a result that is consistent with typical atomic force microscopy images of plasmids. Predictions for the total positive curvature of circular micro-DNAs are given as a function of length, and comparisons with circular DNAs from the literature......The properties of double-stranded DNA and other chiral molecules depend on the local geometry, i.e., on curvature and torsion, yet the paths of closed chain molecules are globally restricted by topology. When both of these characteristics are to be incorporated in the description of circular chain...

  4. Thematic Minireview Series on Circular Proteins

    OpenAIRE

    Craik, David J.; Allewell, Norma M.

    2012-01-01

    Circular proteins have now been discovered in all kingdoms of life and are characterized by their exceptional stability and the diversity of their biological activities, primarily in the realm of host defense functions. This thematic minireview series provides an overview of the distribution, evolution, activities, and biological synthesis of circular proteins. It also reviews approaches that biological chemists are taking to develop synthetic methods for making circular proteins in the labor...

  5. Determining Molecular Orientations in Disordered Materials from X-ray Linear Dichroism at the Iodine L1-Edge.

    Science.gov (United States)

    Palmer, Benjamin A; Collins, Stephen P; Hulliger, Jürg; Hughes, Colan E; Harris, Kenneth D M

    2016-12-21

    To demonstrate that measurements of X-ray linear dichroism are effective for determining bond orientations in disordered materials, we report the first observation of X-ray linear dichroism at the iodine L1-edge. The iodine-containing molecular solid studied in this work was the inclusion compound containing 4,4'-diiodobiphenyl guest molecules in the perhydrotriphenylene host structure. In this material, the guest substructure does not exhibit three-dimensional ordering, and thus diffraction-based techniques do not provide insights on the orientational properties of the guest molecules. Iodine L1-edge X-ray absorption spectra, recorded as a function of orientation of a single crystal of the material, exhibit significant dichroism (whereas no dichroism is observed at the iodine L2- and L3-edges). From quantitative analysis of the X-ray dichroism, the orientational properties of the C-I bonds within this material are established. The results pave the way for applying X-ray dichroism to determine molecular orientational properties of other materials, especially for partially ordered materials such as liquid crystals, confined liquids, and disordered crystalline phases, for which diffraction techniques may not be applicable.

  6. Theoretical investigation on single-molecule chiroptical spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Wakabayashi, M. [Tokyo Institute of Technology, School and Graduate School of Bioscience and Biotechnology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa (Japan); Yokojima, S. [Tokyo University of Pharmacy and Life Sciences, 1423-1 Horinouchi, Hachiouji-shi, Tokyo (Japan); Fukaminato, T. [Research Institute for Electronic Science, Hokkaido University, N20, W10, Kita-ku, Sapporo 001-0020 (Japan); Ogata, K.; Nakamura, S. [Research Cluster for Innovation, Nakamura Lab, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan)

    2013-12-10

    Some experimental results of chiroptical response of single molecule have already reported. In those experiments, dissymmetry parameter, g was used as an indicator of the relative circular dichroism intensity. The parameter for individual molecules was measured. For the purpose of giving an interpretation or explanation to the experimental result, the dissymmetry parameter is formulated on the basis of Fermi’s golden rule. Subsequently, the value of individual molecules is evaluated as a function of the direction of light propagation to the orientationary fixed molecules. The ground and excited wavefunction of electrons in the molecule and transition moments needed are culculated using the density functional theory.

  7. Nanofocusing in circular sector-like nanoantennas

    DEFF Research Database (Denmark)

    Zenin, Volodymyr; Pors, Anders Lambertus; Han, Zhanghua;

    2014-01-01

    a concentric circular line of phase contrast, demonstrating resonant excitation of a standing wave of counter-propagating surface plasmons, travelling between a tip and opposite circular edge of the antenna. Transmission spectra obtained in the range 900 - 2100 nm are in good agreement with numerical...

  8. Exon circularization in mammalian nuclear extracts.

    Science.gov (United States)

    Pasman, Z; Been, M D; Garcia-Blanco, M A

    1996-06-01

    Correct ligation of exons in pre-mRNA splicing requires splice site juxtaposition (splice site pairing), usually involving a 5' splice site and a downstream 3' splice site. Splicing of a 5' splice site to an upstream 3' splice site, however, is predicted to result in a circular RNA. This mode of splice site pairing across the axon has been hypothesized to account for rare RNAs containing scrambled exons (Nigro JM et al., 1991, Celt 64:607-613; Cocquerelle C et al., 1992, EMBO J 11:1 095-1098). Additionally, this mode of splice site pairing has been postulated to explain the formation of SRY circular transcripts in mouse testis (Capel B et al., 1993, Celt 73:1019- 1030). Here we show that splice site pairing across the exon can result in exon circularization in vitro. These results indicate that spliceosome-mediated axon circularization indeed can account for the formation of scrambled exons and circular RNAs. Exon circularization efficiency decreased dramatically as the length of the exon was increased from 95 nt to 274 nt. Circularization of this longer exon was restored, however, when intronic complementary sequences were included in the RNA substrate. These complementary sequences could form a stem that served to bring the splice sites into proximity and thereby promote splice site pairing. Therefore, the splicing of this structured RNA recapitulated SRY-like exon circularization in vitro.

  9. 21 CFR 606.122 - Instruction circular.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 7 2010-04-01 2010-04-01 false Instruction circular. 606.122 Section 606.122 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) BIOLOGICS CURRENT GOOD MANUFACTURING PRACTICE FOR BLOOD AND BLOOD COMPONENTS Finished Product Control § 606.122 Instruction circular. An instruction...

  10. CIRCULAR ECONOMY IN ROMANIA WITHIN EUROPEAN CONTEXT

    Directory of Open Access Journals (Sweden)

    Cornelia Marcela Danu

    2015-07-01

    Full Text Available In the present paper we have approached some conceptual and coordinated marks of the societal reality connected to the circular economy. Generated by „the limits of certainty” regarding the future of the world business, the operationalization of the circular economy has become a part of the EU strategies and started the various stages of implementation as an active process in all countries. We have highlighted the opportunities and the risks related to the circular economy, the European dimension and, in particular, the Romanian one of this process, the role of the triad: consumer-company-natural environment, while implementing the circular economy. Circular economy is both a new approach of the societal life, based on changing the mentalities of the individuals having the role of decision makers at the company level and public administration and the decision makers – consumers, as well as a policy meant to be made operational across all entities: governmental, entrepreneurial, individually – human.

  11. Circular motion in NUT space-time

    CERN Document Server

    Jefremov, Paul

    2016-01-01

    We consider circular motion in the NUT (Newman-Unti-Tamburino) space-time. Among other things, we determine the location of circular time-like geodesic orbits, in particular of the innermost stable circular orbit (ISCO) and of the marginally bound circular orbit. Moreover, we discuss the von Zeipel cylinders with respect to the stationary observers and with respect to the Zero Angular Momentum Observers (ZAMOs). We also investigate the relation of von Zeipel cylinders to inertial forces, in particular in the ultra-relativistic limit. Finally, we generalise the construction of thick accretion tori ("Polish doughnuts") which are well known on the Schwarzschild or Kerr background to the case of the NUT metric. We argue that, in principle, a NUT source could be distinguished from a Schwarzschild or Kerr source by observing the features of circular matter flows in its neighbourhood.

  12. Preparation of circular Rydberg states in helium using the crossed fields method

    CERN Document Server

    Zhelyazkova, V

    2016-01-01

    Helium atoms have been prepared in the circular $|n=55,\\ell=54,m_{\\ell}=+54\\rangle$ Rydberg state using the crossed electric and magnetic fields method. The atoms, initially travelling in pulsed supersonic beams, were photoexcited from the metastable $1s2s\\,^3S_1$ level to the outermost, $m_{\\ell}=0$ Rydberg-Stark state with $n=55$ in the presence of a strong electric field and weak perpendicular magnetic field. Following excitation, the electric field was adiabatically switched off causing the atoms to evolve into the circular state with $m_{\\ell}=+54$ defined with respect to the magnetic field quantization axis. The circular states were detected by ramped electric field ionization along the magnetic field axis. The dependence of the circular state production efficiency on the strength of the excitation electric field, and the electric-field switch-off time was studied, and microwave spectroscopy of the circular-to-circular $|55,54,+54\\rangle\\rightarrow|56,55,+55\\rangle$ transition at $\\sim38.5$~GHz was perf...

  13. Preparation of circular Rydberg states in helium using the crossed-fields method

    Science.gov (United States)

    Zhelyazkova, V.; Hogan, S. D.

    2016-08-01

    Helium atoms have been prepared in the circular |n =55 ,ℓ =54 , mℓ=+54 > Rydberg state using the crossed electric and magnetic fields method. The atoms, initially traveling in pulsed supersonic beams, were photoexcited from the metastable 1 s 2 s S31 level to the outermost, mℓ=0 Rydberg-Stark state with n =55 in the presence of a strong electric field and weak perpendicular magnetic field. Following excitation, the electric field was adiabatically switched off causing the atoms to evolve into the circular state with mℓ=+54 defined with respect to the magnetic-field quantization axis. The circular states were detected by ramped electric-field ionization along the magnetic-field axis. The dependence of the circular state production efficiency on the strength of the excitation electric field, and the electric-field switch-off time was studied, and microwave spectroscopy of the circular-to-circular |55 ,54 ,+54 >→|56 ,55 ,+55 > transition at ˜38.5 GHz was performed.

  14. Inversed linear dichroism in F K-edge NEXAFS spectra of fluorinated planar aromatic molecules

    DEFF Research Database (Denmark)

    de Oteyza, D. G.; Sakko, A.; El-Sayed, A.;

    2012-01-01

    orbitals with significant density of states on the fluorine atoms show different symmetry from those mainly located on C and N atoms. As a result, the angle-dependent linear dichroism in NEXAFS F K-edge spectra is inversed with respect to that in the C and N K-edges. In addition, the significant overlap...... in energy of π* and σ* orbitals throughout the F K-edge spectrum hampers its use for analysis of molecular orientations from angle-dependent NEXAFS measurements....

  15. Vibrational analysis of various irotopes of L-alanyl-L-alanine in aqueous solution: Vibrational Absorption (VA), Vibrational Circular Dichroism (VCD), Raman and Raman Optical Activity (ROA) Spectra

    DEFF Research Database (Denmark)

    Jalkanen, Karl J.; Nieminen, R.M.; Knapp-Mohammady, M.;

    2003-01-01

    . DFT Becke3LYP/6-31G* theory has been used to determine the geometry, Hessian, atomic polar tensors (APT), and atomic axial tensors (AAT), and the electric dipole-electric dipole polarizability derivatives (EDEDPD), which are required for us to simulate the VA, VCD, and Raman spectra. The electric...... dipole-magnetic dipole polarizability derivatives (EDMDPD) and the electric dipole-electric cluadrapole polarizability derivatives (EDEQPD) have been calculated at the RHF/6-31G* level of theory, The VA, VCD, Raman, and ROA spectral simulations for the various isotoporners are compared...

  16. Vibrational circular dichroism analysis reveals a conformational change of the baccatin III ring of paclitaxel: visualization of conformations using a new code for structure-activity relationships.

    Science.gov (United States)

    Izumi, Hiroshi; Ogata, Atsushi; Nafie, Laurence A; Dukor, Rina K

    2008-03-21

    The comparison between measured and conformer-weighted calculated VCD spectra of the baccatin III ring of paclitaxel and visualization of the conformations using the new code for structure-activity relationships are reported for the first time. The VCD spectrum of paclitaxel closely resembles that of the baccatin III ring. The large characteristic nuCO VCD bands with bisignate signs (1732 cm-1, Deltaepsilon = -1.6 x 10(-1); 1715 cm(-1), Deltaepsilon = 2.4 x 10(-1)) strongly reflect the structural property of the family of conformations bacc-ABC32F defined using the new code. The comparison with the conformation of the baccatin III core in the electron micrograph of the crystal structure of tubulin-paclitaxel (1JFF) suggests a conformational change of paclitaxel corresponding to a switch through the binding with beta-tublin and the intermolecular interactions involving the hydroxyl group (D) and carbonyl of acetoxy group (E). The representation of conformational codes allows complicated conformations to be very easily compared and facilitates future computational analyses such as those for the large-molecule calculations as well as genome analysis.

  17. A study of magnetic properties of hard and soft magnetic materials by Lorentz transmission electron microscopy and magnetic x-ray circular dichroism

    CERN Document Server

    Pickford, R A

    2001-01-01

    iron spin and orbital magnetic moments were found to decrease with increasing iron content. In collaboration with CEA Saclay, Paris, a set of cobalt elements were patterned by electron beam lithography. The elements were designed to isolate domain walls and to monitor their movement in an applied field. The shape anisotropy of the element was found to be too large for the insitu magnetic field to flip the magnetisation. The domain walls found in the as received magnetic state were associated with defects in the structure of the element. The magnetisation process was compared to micromagnetic simulations, A further study of magnetic elements was made to study the competition of anisotropy in patterned cobalt dots. The shape anisotropy was calculated and the crystalline anisotropy of the cobalt film was measured. The dots (rectangles) were patterned so that the shape anisotropy was comparable to the crystalline anisotropy of the cobalt. The dots were patterned at 45 degrees to the crystalline anisotropy. This t...

  18. Structures, vibrational absorption and vibrational circular dichroism spectra of L-alanine in aqueous solution: a density functional theory and RHF study

    DEFF Research Database (Denmark)

    Frimand, Kenneth; Bohr, Henrik; Jalkanen, Karl J.;

    2000-01-01

    at the density functional theory level using the B3LYP functional with the 6-31G* basis set. The Hessians and atomic polar tensors and atomic axial tensors were all calculated at the B3LYP/6-31G* level of theory. An important result is the method of treating solvent effects by both adding explicit water....... The calculated VA and VCD spectra of this conformer are in better agreement with experimentally measured VA and VCD spectra previously reported. (C) 2000 Elsevier Science B.V. All rights reserved....

  19. A new approach to determine the stereospecificity in lipase catalysed hydrolysis using circular dichroism (CD): lipases produce optically active diglycerides from achiral triglycerides.

    Science.gov (United States)

    Uzawa, H; Nishida, Y; Ohrui, H; Meguro, H

    1990-04-30

    We describe a sensitive CD method for determining the stereospecificity in lipase (E.C.3.1.1.3) catalysed hydrolysis of triacyl glycerols into diacyl glycerols. The diglycerols were converted to chiral tert-butyldimethylsilylated 1,2- or 2,3-di-O-benzoyl-sn-glycerol (5 or 5'), and their CD was measured. This approach showed for the first time that lipases produce optically active diacyl glycerides from achiral tripalmitin and tribenzoyl glyceride with a variable extent of enantioselectivity depending on the acyl groups and the enzymes.

  20. Circular Dichroism and Fluorescence Spectroscopic Study of RNA-protein Folding Patterns in Human hnRNP A3 and Their Implications in Human Autoimmune Diseases

    Institute of Scientific and Technical Information of China (English)

    E.SüLEYMANO(G)LU

    2004-01-01

    In human cells, the heterogeneous nuclear ribonucleoproteins (hnRNP) are represented by a group of polypeptides, with various molecular properties, comprizing the most abundant constituents of the cell nucleus. Autoantibodies to hnRNPs have been reported in patients suffering from different rheumatic dieseases since 1980s. Experimental evidence indicates that hnRNP complexes undergo substantial structural changes during mRNA formation and export. However, how this contributes to disease development still has to be elucidated. Here some preliminary physicochemical features of RNA-protein folding and stability patterns of newly characterized hnRNP A3 with further functional implications in development of systemic human autoimmune states are reported.

  1. Characterization of the 1st and 2nd EF-hands of NADPH oxidase 5 by fluorescence, isothermal titration calorimetry, and circular dichroism

    Directory of Open Access Journals (Sweden)

    Wei Chin-Chuan

    2012-04-01

    Full Text Available Abstract Background Superoxide generated by non-phagocytic NADPH oxidases (NOXs is of growing importance for physiology and pathobiology. The calcium binding domain (CaBD of NOX5 contains four EF-hands, each binding one calcium ion. To better understand the metal binding properties of the 1st and 2nd EF-hands, we characterized the N-terminal half of CaBD (NCaBD and its calcium-binding knockout mutants. Results The isothermal titration calorimetry measurement for NCaBD reveals that the calcium binding of two EF-hands are loosely associated with each other and can be treated as independent binding events. However, the Ca2+ binding studies on NCaBD(E31Q and NCaBD(E63Q showed their binding constants to be 6.5 × 105 and 5.0 × 102 M-1 with ΔHs of -14 and -4 kJ/mol, respectively, suggesting that intrinsic calcium binding for the 1st non-canonical EF-hand is largely enhanced by the binding of Ca2+ to the 2nd canonical EF-hand. The fluorescence quenching and CD spectra support a conformational change upon Ca2+ binding, which changes Trp residues toward a more non-polar and exposed environment and also increases its α-helix secondary structure content. All measurements exclude Mg2+-binding in NCaBD. Conclusions We demonstrated that the 1st non-canonical EF-hand of NOX5 has very weak Ca2+ binding affinity compared with the 2nd canonical EF-hand. Both EF-hands interact with each other in a cooperative manner to enhance their Ca2+ binding affinity. Our characterization reveals that the two EF-hands in the N-terminal NOX5 are Ca2+ specific. Graphical abstract

  2. LDA+DMFT calculations of X-ray absorption and x-ray circular dichroism spectra: Role of valence-band correlations

    Energy Technology Data Exchange (ETDEWEB)

    Sipr, Ondrej; Simunek, Antonin [Institute of Physics AS CR, Cukrovarnicka 10, Prague (Czech Republic); Minar, Jan; Ebert, Hubert [Universitaet Muenchen (Germany)

    2010-07-01

    L{sub 2,3}-edge XAS and XMCD spectra of 3d elements are calculated via a self-consistent LDA+DMFT method (including thus valence-band correlations). It is found that the asymmetry of the calculated XAS white lines increases upon inclusion of the correlations for Fe and Co but not for Ni. The change in the height of the L{sub 3} and L{sub 2} peaks in the XMCD spectra is in a good agreement with the change of the orbital magnetic moment caused by adding the valence-band correlations. As a whole, adding valence-band correlations improves the agreement between the theory and experiment but visible differences still remain. Therefore, a core hole is additionally accounted for via the final state approximation and the impact of such a procedure is assessed.

  3. (E)-4-methyl-1-tributylstannyl-oct-1-en-6-yn-3-ol: circular dichroism measurement and determination of the absolute configuration by quantum-chemical CD calculations

    Energy Technology Data Exchange (ETDEWEB)

    Voloshina, E.N.; Raabe, G.; Fleischhauer, J.; Kramp, G.J.; Gais, H.J. [Rheinisch-Westfaelische Technische Hochschule Aachen (Germany). Inst. fuer Organische Chemie

    2004-07-01

    The chiroptical properties of the diastereomeric alcohols (E)-(3S,4S)-4-methyl-1-tributylstannyl-oct-1-en-6-yn-3-ol ((S,S)-3) and (E)-(3R,4S)-4-methyl-1-tributylstannyl-oct-1-en-6-yn-3-ols ((R,S)-3) have been studied experimentally as well as by quantum-chemical calculations. The structures of 20 conformers of each isomer, which were found to represent local minima at the MNDO level, have been optimized with density functional theory (DFT). Based on these geometries the excitation energies and oscillator as well as rotational strengths have been calculated using a time-dependent DFT (TDDFT) method. The CD spectra of the compounds were then obtained as superposition of Boltzmann-weighted spectra for each of the structures. By comparison of the calculated and the experimental CD spectra the absolute configurations have been assigned to the investigated compounds. (orig.)

  4. (E)-4-Methyl-1-tributylstannyl-oct-1-en-6-yn-3-ol: Circular Dichroism Measurement and Determination of the Absolute Configuration by Quantum-chemical CD Calculations

    Science.gov (United States)

    Voloshina, E. N.; Raabe, G.; Fleischhauer, J.; Kramp, G. J.; Gais, H.-J.

    2004-03-01

    The chiroptical properties of the diastereomeric alcohols (E)-(3S,4S)-4-methyl-1-tributylstannyloct- 1-en-6-yn-3-ol ((S,S)-) and (E)-(3R,4S)-4-methyl-1-tributylstannyl-oct-1-en-6-yn-3-ols ((R,S)- 3) have been studied experimentally as well as by quantum-chemical calculations. The structures of 20 conformers of each isomer, which were found to represent local minima at the MNDO level, have been optimized with density functional theory (DFT). Based on these geometries the excitation energies and oscillator as well as rotational strengths have been calculated using a time-dependent DFT (TDDFT) method. The CD spectra of the compounds were then obtained as superposition of Boltzmann-weighted spectra for each of the structures. By comparison of the calculated and the experimental CD spectra the absolute configurations have been assigned to the investigated compounds.

  5. A solid-state dedicated circularly polarized luminescence spectrophotometer: Development and application

    Science.gov (United States)

    Harada, Takunori; Hayakawa, Hiroshi; Watanabe, Masayuki; Takamoto, Makoto

    2016-07-01

    A new solid-state dedicated circularly polarized luminescence (CPL) instrument (CPL-200CD) was successfully developed for measuring true CPL spectra for optically anisotropic samples on the basis of the Stokes-Mueller matrix approach. Electric components newly installed in the CPL-200CD include a pulse motor-driven sample rotation holder and a 100 kHz lock-in amplifier to achieve the linearly polarized luminescence measurement, which is essential for obtaining the true CPL signal for optically anisotropic samples. An acquisition approach devised for solid-state CPL analysis reduces the measurement times for a data set by ca. 98% compared with the time required in our previous method. As a result, the developed approach is very effective for samples susceptible to light-induced degradation. The theory and implementation of the method are described, and examples of its application to a CPL sample with macroscopic anisotropies are provided. An important advantage of the developed instrument is its ability to obtain molecular information for both excited and ground states because circular dichroism measurements can be performed by switching the monochromatic light to white light without rearrangement of the sample.

  6. Towards circularly polarized (sub-) femtosecond XUV pulses for ultrafast pump-probe experiments

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, Juergen; Chew, Soo Hoon; Kranjec, Mihael; Kleineberg, Ulf [LMU Muenchen, Physik-Department, Garching (Germany); Guggenmos, Alexander; Hofstetter, Michael [MPQ fuer Quantenoptik, Garching (Germany)

    2012-07-01

    Circularly polarized (CP) XUV radiation has been demonstrated to be a useful probe for the experimental investigation of electronic effects in magnetic materials such as magnetic circular dichroism, spin-polarized photoemission, magneto-optical Kerr-effect and others. On the laboratory scale, High Harmonic (HH) gas jet sources which inherently provide coherent and ultrashort linearly polarized XUV pulses in the sub-fs domain, suitable to study ultrafast dynamics, have emerged. In our setup we aim at incorporating in-house fabricated broadband transmission multilayer phase shifters into a laser driven 10kHz repetition rate HH Source in the 50-70eV photon energy range. To our knowledge only little investigation on such polarizers intended for use in HH radiation has been made so far. We examine our phase shifters regarding tunability of energy range, phase retardation, transmission efficiency and spectral bandwidth. For this purpose we use a home-made XUV flat-field spectrometer and a multilayer mirror based polarization analyzer. Combining the expected CP pulses with our TOF-PEEM and ARPES spectrometer will pave the way towards time resolved measurements of exchange-coupled electron dynamics.

  7. Vitrified chiral-nematic liquid crystalline films for selective reflection and circular polarization

    Energy Technology Data Exchange (ETDEWEB)

    Katsis, D.; Chen, P.H.M.; Mastrangelo, J.C.; Chen, S.H. [Univ. of Rochester, NY (United States); Blanton, T.N. [Eastman Kodak Co., Rochester, NY (United States)

    1999-06-01

    Nematic and left-handed chiral-nematic liquid crystals comprising methoxybiphenylbenzoate and (S)-(-)-1-phenylethylamine pendants to a cyclohexane core were synthesized and characterized. Although pristine samples were found to be polycrystalline, thermal quenching following heating to and annealing at elevated temperatures permitted the molecular orders characteristic of liquid crystalline mesomorphism to be frozen in the glassy state. Left at room temperature for 6 months, the vitrified liquid crystalline films showed no evidence of recrystallization. An orientational order parameter of 0.65 was determined with linear dichroism of a vitrified nematic film doped with Exalite 428 at a mole fraction of 0.0025. Birefringence dispersion of a blank vitrified nematic film was determined using a phase-difference method complemented by Abbe refractometry. A series of vitrified chiral-nematic films were prepared to demonstrate selective reflection and circular polarization with a spectral region tunable from blue to the infrared region by varying the chemical composition. The experimentally measured circular polarization spectra were found to agree with the Good-Karali theory in which all four system parameters were determined a priori: optical birefringence, average refractive index, selective reflection wavelength, and film thickness.

  8. Band structure of Heusler compounds studied by photoemission and tunneling spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Arbelo Jorge, Elena

    2011-07-01

    Heusler compounds are key materials for spintronic applications. They have attracted a lot of interest due to their half-metallic properties predicted by band structure calculations. The aim of this work is to evaluate experimentally the validity of the predictions of half metallicity by band structure calculations for two specific Heusler compounds, Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} and Co{sub 2}MnGa. Two different spectroscopy methods for the analysis of the electronic properties were used: Angular Resolved Ultraviolet Photoemission Spectroscopy (ARUPS) and Tunneling Spectroscopy. Heusler compounds are prepared as thin films by RF-sputtering in an ultra high vacuum system. For the characterization of the samples, bulk and surface crystallographic and magnetic properties of Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} and Co{sub 2}MnGa are studied. X-ray and electron diffraction reveal a bulk and surface crossover between two different types of sublattice order (from B2 to L2{sub 1}) with increasing annealing temperature. X-ray magnetic circular dichroism results show that the magnetic properties in the surface and bulk are identical, although the magnetic moments obtained are 5 % below from the theoretically predicted. By ARUPS evidence for the validity of the predicted total bulk density of states (DOS) was demonstrated for both Heusler compounds. Additional ARUPS intensity contributions close to the Fermi energy indicates the presence of a specific surface DOS. Moreover, it is demonstrated that the crystallographic order, controlled by annealing, plays an important role on broadening effects of DOS features. Improving order resulted in better defined ARUPS features. Tunneling magnetoresistance measurements of Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} and Co{sub 2}MnGa based MTJ's result in a Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} spin polarization of 44 %, which is the highest experimentally obtained value for this compound, although it is lower than the 100 % predicted. For Co

  9. Modelling the circular polarisation of Earth-like exoplanets: constraints on detecting homochirality

    Science.gov (United States)

    Hogenboom, Michael; Stam, Daphne; Rossi, Loic; Snik, Frans

    2016-04-01

    polarisation signals for both spatially resolved and spatially unresolved planets, using various atmospheric and surface properties and across a range of phase angles. As a test, the calculated degree of circular polarisation resulting from the multiple scattering of light in an atmosphere with varying properties was compared with results presented by Kawata te{circatmos} and was found to be in agreement. Initial modelling of the atmospheric scattering of light by a planetary disk has shown a presence of degree of circular polarisation in the order of 10-4. This represents a static case with one cloudy hemisphere, one cloudless hemisphere and a Lambertian surface. Results containing varied patchy cloud patterns shall also be presented in a bid to reflect the random nature of planetary cloud cover. We will also present the calculated degree of circular polarisation of planets with various cloud coverage and a circularly polarising surface in order to discover the influence of organisms on the numerical results. {1} {hansen} J. E. {Hansen} and L. D. {Travis}. {Light scattering in planetary atmospheres}. {Space Science Reviews}, 16:527-610, October 1974. {circplanets} J. C. {Kemp} and R. D. {Wolstencroft}. {Circular Polarization: Jupiter and Other Planets}. {Nature}, 232:165-168, July 1971. {chiralbailey} J. {Bailey}. {Circular Polarization and the Origin of Biomolecular Homochirality}. In G. {Lemarchand} and K. {Meech}, editors, {Bioastronomy 99}, volume 213 of {Astronomical Society of the Pacific Conference Series}, 2000. {circpolchar} L. {Nagdimunov}, L. {Kolokolova}, and D. {Mackowski}. {Characterization and remote sensing of biological particles using circular polarization}. {Journal of Quantitative Spectroscopy and Radiative Transfer}, 131:59-65, December 2013. dehaan} J. F. {de Haan}, P. B. {Bosma}, and J. W. {Hovenier}. {The adding method for multiple scattering calculations of polarized light}. {Astronomy and Astrophysics}, 183:371-391, September 1987. {circatmos} Y

  10. Encryption using circular harmonic key

    Directory of Open Access Journals (Sweden)

    Jorge Enrique Rueda-Parada

    2015-01-01

    Full Text Available En este trabajo presento un estudio sobre la varianza a la rota ción de la llave del procesador de encriptación basado en la tr ansformada de Fourier. Determiné que la llave en coordenadas rectangulares pe rmite un nivel de tolerancia inferior a 0.2 grados de rotación de la llave en el proceso de decriptación. Entonces la solución es construir la llave en coordenadas polares, por medio de una expansión en armónicos circulares. De esta manera, el umbral de tolerancia a umenta aproximadamente hasta 40 grados de rotación de la llave en el proceso de decriptación. Esta solución es un valor agregado par a el procesador de encriptación óptico. He desarrollado una her ramienta computacional para las simulaciones y resultados obtenidos en e ste estudio.

  11. Process engineering in circular economy

    Institute of Scientific and Technical Information of China (English)

    Lothar Reh

    2013-01-01

    Driven by increasing global population and by growing demand for individual wealth,the consumption of energy and raw materials as well as the steadily growing CO2 concentration in atmosphere pose great challenges to process engineering.This complex multi-scale discipline deals with the transformation of mass by energy to manifold products in different industrial fields under economical and ecological sustainable conditions.In growing circular economy,process engineering increasingly plays an important role in recovering valuable components from very diffuse material flows leaving the user stocks following widely variable time periods of use.As well it is engaged in thermal recovery of energy therefrom and in environmentally safe disposal of residual solid wastes whose recovery economically is not feasible.An efficient recovery of materials and energy following the laws of entropy is a must.A complex network of mass,energy,transportation and information flows has to be regarded with growing traded quantities of used goods even on global level.Important constraints in time,however,exist for a necessary realization of innovative new processes and communal mobility and industrial infrastructure on medium and large scale.Based on reasonable long term and highly reliable statistics from industrial organizations representing steel and paper industry,some limits and trends of possible developments in processing of those industries with long recycling experience will be discussed.

  12. Uniformity Tests in Circular Data: Review

    Directory of Open Access Journals (Sweden)

    Ismet DOGAN

    2015-10-01

    Full Text Available Circular data are a large class of directional data, which are interest in many fields. Examples include phenomena that are periodic in time, including those dependent on hours of the day (hospital visits, times of birth, etc. or days of the year (unemployment or sales variations. The elementary but also fundamental property of circular data is that the beginning and end of the scale coincide: for example, 0° = 360°. An immediate implication is that the arithmetic mean is likely to be a poor summary: the mean of 1° and 359° cannot sensibly be 180°. The solution is use the vector mean direction as circular mean. The statistical analysis of angular or circular data differs from the analysis of linear data. Unlike linear distributions, which are often two-tailed and infinite, circular distributions exhibit finite closure because a circular data set comes back on itself, and therefore, 0° and 360° are actually the same point on a circle. Circular statistics is concerned mainly with observations which are unit vectors in the plane. Thus the sample space is typically a circle or a sphere, so that standart methods for analysing univariate or multivariate measurement data can?t be used. Special circular methods are required take into account the structure of these sample spaces. In most circular statistical analyses, the null hypothesis is a uniform distribution in which all directions occur with equal probability. In this study, eight different testing methods improved for uniformity in angular data have been introduced and these methods were compared with each other by using the information obtained from the literature.

  13. Q & A Experiment to Search for Vacuum Dichroism, Pseudoscalar-Photon Interaction and Millicharged Fermions

    CERN Document Server

    Chen, S J; Ni, W T; Chen, Sheng-Jui; Mei, Hsien-Hao; Ni, Wei-Tou

    2006-01-01

    A number of experiments are underway to detect vacuum birefringence and dichroism -- PVLAS, Q & A, and BMV. Recently, PVLAS experiment has observed optical rotation in vacuum by a magnetic field (vacuum dichroism). Theoretical interpretations of this result include a possible pseudoscalar-photon interaction and the existence of millicharged fermions. Here, we report the progress and first results of Q & A (QED [quantum electrodynamics] and Axion) experiment proposed and started in 1994. A 3.5-m high-finesse (around 30,000) Fabry-Perot prototype detector extendable to 7-m has been built and tested. We use X-pendulums and automatic control schemes developed by the gravitational-wave detection community for mirror suspension and cavity control. To polarize the vacuum, we use a 2.3-T dipole permanent magnet, with 27-mm-diameter clear borehole and 0.6-m field length,. In the experiment, the magnet is rotated at 5-10 rev/s to generate time-dependent polarization signal with twice the rotation frequency. Our...

  14. Electronic states of model hydrocarbon chromophores investigated by Synchrotron Radiation Linear Dichroism (SRLD) spectroscopy on aligned samples

    DEFF Research Database (Denmark)

    Nguyen, Duy Duc; Hoffmann, Søren Vrønning; Jones, Nykola;

    2010-01-01

    , differently polarized absorption bands, and to symmetry assignments of the observed molecular states. This information is highly useful in the study of molecular symmetry and reactivity. Partially aligned molecular samples may be produced in a simple fashion by the use of stretched polymers as anisotropic...

  15. Circular polarization memory in polydisperse scattering media

    CERN Document Server

    Macdonald, Callum M; Meglinski, Igor

    2015-01-01

    We investigate the survival of circularly polarized light in random scattering media. The surprising persistence of this form of polarization has a known dependence on the size and refractive index of scattering particles, however a general description regarding polydisperse media is lacking. Through analysis of Mie theory, we present a means of calculating the magnitude of circular polarization memory in complex media, with total generality in the distribution of particle sizes and refractive indices. Quantification of this memory effect enables an alternate pathway towards recovering particle size distribution, based on measurements of diffusing circularly polarized light.

  16. Peptides as Model Systems for the Unfolded State of Proteins Explored By Vibrational Spectroscopy

    Science.gov (United States)

    Schweitzer-Stenner, Reinhard; Measey, Thomas; Hagarman, Andrew

    2008-11-01

    Unfolded proteins are generally thought to be structurally random with a minimum of non-local interactions. This concept implies that with the exception of glycine and proline the conformational propensities of amino acid residues in polypeptides should be comparable in that they all sample the statistically allowed region of the Ramachandran plot. However, over the last ten years experimental and computational evidence has emerged for the notion that the conformational space of residues might be more restricted than predicted by random or statistical coil models. We have developed several algorithms which can be used to simulate the amide I band profile of the IR, isotropic Raman, anisotropic Raman and Vibrational Circular Dichroism (VCD) spectra of polypeptides based on assumed ensembles of side chain conformations. The simulations are generally restricted by 3JcαHNH coupling constants obtained from NMR spectroscopy. A comparison with experimental results reveals that e.g. alanine has a clear preference for the so called polyproline II (PPII) conformation in short peptides. The situation becomes more complex if longer polyalanines are doped with negatively charged residues. For the so-called XAO-peptide (X2A7O2, X: diaminobutyric acid, O;ornithine) we found a more compact structure owing to multiple turn conformations sampled by the X2A7 interfaces. For Salmon Calcitonin, a 32-residue hormone, we identified a mixture of PPII, β-strand and helical conformations. Currently, we are in the process of investigating short GxG (x; different natural amino acid residues) peptides in terms of conformational distributions obtained from coil libraries. This will enable us obtain the conformational preferences of amino acid residues in the absence of nearest neighbor interactions.

  17. Polarisation vision: beetles see circularly polarised light.

    Science.gov (United States)

    Warrant, Eric J

    2010-07-27

    It has long been known that the iridescent cuticle of many scarab beetles reflects circularly polarised light. It now turns out that scarabs can also see this light, potentially using it as a covert visual signal.

  18. NMFS Scientific Publications Office: Legacy Series: Circulars

    Science.gov (United States)

    ... Research related to the case for abstention, ... The Colorado River-Matagorda Bay study, by Charles H. Koski, p. 70-74; Movement of water masses ... Circular 191. Extent of acid mine pollution ...

  19. Unleashing the Power of the Circular Economy

    Energy Technology Data Exchange (ETDEWEB)

    Kok, L.; Wurpel, G.; Ten Wolde, A. [IMSA Amsterdam, Amsterdam (Netherlands)

    2013-04-15

    The concept of circular economy is an economic and industrial system that focuses on the reusability of products and raw materials, reduces value destruction in the overall system and aims at value creation within each tier of the system. This report for Circle Economy (CE) outlines the general direction and concrete steps that must be taken to accomplish a breakthrough to a circular economy. It also provides a knowledge base behind the concept, connecting it to sustainability.

  20. A Conceptual Framework for Circular Design

    Directory of Open Access Journals (Sweden)

    Mariale Moreno

    2016-09-01

    Full Text Available Design has been recognised in the literature as a catalyst to move away from the traditional model of take-make-dispose to achieve a more restorative, regenerative and circular economy. As such, for a circular economy to thrive, products need to be designed for closed loops, as well as be adapted to generate revenues. This should not only be at the point of purchase, but also during use, and be supported by low-cost return chains and reprocessing structures, as well as effective policy and regulation. To date, most academic and grey literature on the circular economy has focused primarily on the development of new business models, with some of the latter studies addressing design strategies for a circular economy, specifically in the area of resource cycles and design for product life extension. However, these studies primarily consider a limited spectrum of the technical and biological cycles where materials are recovered and restored and nutrients (e.g., materials, energy, water are regenerated. This provides little guidance or clarity for designers wishing to design for new circular business models in practice. As such, this paper aims to address this gap by systematically analysing previous literature on Design for Sustainability (DfX (e.g., design for resource conservation, design for slowing resource loops and whole systems design and links these approaches to the current literature on circular business models. A conceptual framework is developed for circular economy design strategies. From this conceptual framework, recommendations are made to enable designers to fully consider the holistic implications for design within a circular economy.

  1. Construction of Circular Economy Industrial System

    Institute of Scientific and Technical Information of China (English)

    Cao Man; Ye Wenhu

    2007-01-01

    It is difficult to realize the transformation from traditional economy industrial system to circular economy industrial system.Regarding primary raw materials as the indicators,the industrial system has been specified according to the divergence among the indicators and the circular utilization modes.In comparison with the association among industrial systems,the relationship among industrial sub-systems is named as industrial cross-linking in this paper.The industrial system which could completely utilize and recycle the indicators should be increased and strengthened,and the circular economy industrial system with complete industrial association and industrial cross-linking should also be constructed.Taking the development of circular agricultural system basing on the traditional agricultural system as an example,the traditional agricultural products are regarded as the indicators which have been divided into foodstuff and crop straws which are used to produce food and articlesfor use,like fertilizer,energy and papers etc.The way to construct the circular agricultural industrial system is to increase the industrial systems that could utilize the products generated from crop straws,feces and other castoffs and transform the wastewater and other trucks into environmental friendly products.It has also been pointed out that the construction of circular economy industrial system is conducive to the foundation of circular industrial economics and the establishment of the construction layout of circular economy and the application schemes.Suggestions to the theoretical and practical work of the next step have also been brought forward in this paper.

  2. Laminar circular hydraulic jumps without separation

    Science.gov (United States)

    Dasgupta, Ratul; Tomar, Gaurav; Govindarajan, Rama

    2009-11-01

    The traditional inviscid criterion for the occurrence of a planar, standing hydraulic jump is to have the Froude number decrease downstream and go through a value of 1 at some location. Here, upstream propagating, small-amplitude, long, non-dispersive gravity waves are trapped, and non-linear steepening is said to result in a near-discontinuous height profile, but it is not clear how. Such a condition on the Froude number is shown in the present axisymmetric Navier-Stokes computations to hold for a circular jump as well. The relevance of non-linear steepening to a circular jump is therefore a question we wish to answer. In circular jumps, moreover, a region of recirculation is usually observed underneath the jump, underlining the importance of viscosity in this process. This led Tani (J. Phys. Soc. Japan, 1949) to hypothesise that boundary-layer separation was the cause of the circular jump. This hypothesis has been debated extensively and the possibility of circular jumps without separation hinted at. In our simulations, we are able to obtain circular hydraulic jumps without any flow separation. This, and the necessity or otherwise of viscosity in jump formation will be discussed.

  3. PLANAR MOTION OF A SLIGHTLY DISTORTED CIRCULAR CYLINDER AROUND ANOTHER CIRCULAR ONE

    Institute of Scientific and Technical Information of China (English)

    SUN Ren; CHWANG Allen T.

    2004-01-01

    Accurate prediction of the motion of a body moving around another one in an unbounded fluid and determi-nation of the hydrodynamic interaction between them are im-portant in the coastal and offshore engineering. For two-dimensional cases, most of the previous studies were focused on the interaction between circular cylinders without considering the non-circular situation. To break through the limitation of"circular" bodies, in the present paper the boundary perturbation method was employed to investigate the motion of a slightly distorted circular cylinder around a circular one. An approximate complex velocity potential in terms of double infinite series expanded at two singular points was derived using the method of continued fractions. The hydrodynamic interaction between two cylinders was computed by solving the dynamical equations of motion. In a relative coordinate system moving with the uniform stream, the kinetic energy of the fluid was expressed as a function of fifteen added masses. Approximate analytical solutions of added masses in the series form were obtained and applied to determine the trajectories of the slightly distorted circular cylinder around a fixed circular one. Numerical results show that the presence of the circular cylinder affects the planar motion of the slightly distorted cirular cylinder and the initial configuration of the slightly distorted circular cylinder has a decisive influence on the development of its rotational motion.

  4. Theoretical Simulations and Ultrafast Pump-probe Spectroscopy Experiments in Pigment-protein Photosynthetic Complexes

    Energy Technology Data Exchange (ETDEWEB)

    Buck, D.R.

    2000-09-12

    Theoretical simulations and ultrafast pump-probe laser spectroscopy experiments were used to study photosynthetic pigment-protein complexes and antennae found in green sulfur bacteria such as Prosthecochloris aestuarii, Chloroflexus aurantiacus, and Chlorobium tepidum. The work focused on understanding structure-function relationships in energy transfer processes in these complexes through experiments and trying to model that data as we tested our theoretical assumptions with calculations. Theoretical exciton calculations on tubular pigment aggregates yield electronic absorption spectra that are superimpositions of linear J-aggregate spectra. The electronic spectroscopy of BChl c/d/e antennae in light harvesting chlorosomes from Chloroflexus aurantiacus differs considerably from J-aggregate spectra. Strong symmetry breaking is needed if we hope to simulate the absorption spectra of the BChl c antenna. The theory for simulating absorption difference spectra in strongly coupled photosynthetic antenna is described, first for a relatively simple heterodimer, then for the general N-pigment system. The theory is applied to the Fenna-Matthews-Olson (FMO) BChl a protein trimers from Prosthecochloris aestuarii and then compared with experimental low-temperature absorption difference spectra of FMO trimers from Chlorobium tepidum. Circular dichroism spectra of the FMO trimer are unusually sensitive to diagonal energy disorder. Substantial differences occur between CD spectra in exciton simulations performed with and without realistic inhomogeneous distribution functions for the input pigment diagonal energies. Anisotropic absorption difference spectroscopy measurements are less consistent with 21-pigment trimer simulations than 7-pigment monomer simulations which assume that the laser-prepared states are localized within a subunit of the trimer. Experimental anisotropies from real samples likely arise from statistical averaging over states with diagonal energies shifted by

  5. Theoretical Simulations and Ultrafast Pump-probe Spectroscopy Experiments in Pigment-protein Photosynthetic Complexes

    Energy Technology Data Exchange (ETDEWEB)

    Buck, D. R. [Iowa State Univ., Ames, IA (United States)

    2000-09-12

    Theoretical simulations and ultrafast pump-probe laser spectroscopy experiments were used to study photosynthetic pigment-protein complexes and antennae found in green sulfur bacteria such as Prosthecochloris aestuarii, Chloroflexus aurantiacus, and Chlorobium tepidum. The work focused on understanding structure-function relationships in energy transfer processes in these complexes through experiments and trying to model that data as we tested our theoretical assumptions with calculations. Theoretical exciton calculations on tubular pigment aggregates yield electronic absorption spectra that are superimpositions of linear J-aggregate spectra. The electronic spectroscopy of BChl c/d/e antennae in light harvesting chlorosomes from Chloroflexus aurantiacus differs considerably from J-aggregate spectra. Strong symmetry breaking is needed if we hope to simulate the absorption spectra of the BChl c antenna. The theory for simulating absorption difference spectra in strongly coupled photosynthetic antenna is described, first for a relatively simple heterodimer, then for the general N-pigment system. The theory is applied to the Fenna-Matthews-Olson (FMO) BChl a protein trimers from Prosthecochloris aestuarii and then compared with experimental low-temperature absorption difference spectra of FMO trimers from Chlorobium tepidum. Circular dichroism spectra of the FMO trimer are unusually sensitive to diagonal energy disorder. Substantial differences occur between CD spectra in exciton simulations performed with and without realistic inhomogeneous distribution functions for the input pigment diagonal energies. Anisotropic absorption difference spectroscopy measurements are less consistent with 21-pigment trimer simulations than 7-pigment monomer simulations which assume that the laser-prepared states are localized within a subunit of the trimer. Experimental anisotropies from real samples likely arise from statistical averaging over states with diagonal energies shifted by

  6. In situ azimuthal rotation device for linear dichroism measurements in scanning transmission x-ray microscopy

    Science.gov (United States)

    Hernández-Cruz, D.; Hitchcock, A. P.; Tyliszczak, T.; Rousseau, M.-E.; Pézolet, M.

    2007-03-01

    A novel miniature rotation device used in conjunction with a scanning transmission x-ray microscope is described. It provides convenient in situ sample rotation to enable measurements of linear dichroism at high spatial resolution. The design, fabrication, and mechanical characterization are presented. This device has been used to generate quantitative maps of the spatial distribution of the orientation of proteins in several different spider and silkworm silks. Specifically, quantitative maps of the dichroic signal at the C 1s→π*amide transition in longitudinal sections of the silk fibers give information about the spatial orientation, degree of alignment, and spatial distribution of protein peptide bonds. A new approach for analyzing the dichroic signal to extract orientation distributions, in addition to magnitudes of aligned components, is presented and illustrated with results from Nephila clavipes dragline spider silk measured using the in situ rotation device.

  7. Dichroism, chirality, and polarization eigenstates in Babinet nanoslot-dimer membrane metamaterials

    DEFF Research Database (Denmark)

    Zhukovsky, Sergei; Chigrin, Dmitry N.; Kremers, Christian;

    2013-01-01

    We present a detailed theoretical description of the optical properties of planar metamaterials comprising a metal membrane patterned with openings (microslots) arranged in closely located couples (dimers). Using the covariant coupled-dipole approach, the effective material tensors of such a meta......We present a detailed theoretical description of the optical properties of planar metamaterials comprising a metal membrane patterned with openings (microslots) arranged in closely located couples (dimers). Using the covariant coupled-dipole approach, the effective material tensors...... of such a metamaterial are recovered, and contributions responsible for elliptical dichroism and optical activity are identified. Polarization conversion properties of II-shaped and V-shaped dimers are determined and explained in terms of elliptically polarized eigenmodes of the metamaterial. Good agreement with direct...

  8. Spin polarization and magnetic dichroism in core-level photoemission from ferromagnets

    Energy Technology Data Exchange (ETDEWEB)

    Menchero, Jose Gabriel [Univ. of California, Berkeley, CA (United States). Dept. of Physics

    1997-05-01

    In this thesis we present a theoretical investigation of angle- and spin-resolved core-level photoemission from ferromagnetic Fe and Ni. We also consider magneto-dichroic effects due to reversal of the photon helicity or reversal of the sample magnetization direction. In chapter 1, we provide a brief outline of the history of photoemission, and show how it has played an important role in the development of modern physics. We then review the basic elements of the theory of core-level photoemission, and discuss the validity of the some of the commonly-used approximations. In chapter 2, we present a one-electron theory to calculate spin- and angle-resolved photoemission spectra for an arbitrary photon polarization. The Hamiltonian includes both spin-orbit and exchange interactions. As test cases for the theory, we calculate the spin polarization and magnetic dichroism for the Fe 2p core level, and find that agreement with experiment is very good.

  9. Terahertz spectroscopy

    DEFF Research Database (Denmark)

    Jepsen, Peter Uhd

    2009-01-01

    In this presentation I will review methods for spectroscopy in the THz range, with special emphasis on the practical implementation of the technique known ad THz time-domain spectroscopy (THz-TDS). THz-TDS has revived the old field of far-infrared spectroscopy, and enabled a wealth of new...

  10. OPERATIONAL CIRCULAR NO 6 - JUNE 2001 'CERN SCIENTIFIC DOCUMENTS'

    CERN Multimedia

    Human Resources Division

    2001-01-01

    This new operational circular has been drawn up. It cancels and replaces Administrative Circular N° 29 entitled "Principles and procedures governing CERN publications and reports and other publications arising from CERN work". Copies are available from Divisional Secretariats. Note : Administrative and operational circulars, as well as the lists of those in force, are available for consultation on WWW : ADMINISTRATIVE CIRCULARSOPERATIONAL CIRCULARS

  11. Calculations of magnetic x-ray dichroism in the 3d absorption spectra of rare-earth compounds

    NARCIS (Netherlands)

    GOEDKOOP, JB; THOLE, BT; VANDERLAAN, G; SAWATZKY, GA; DEGROOT, FMF; FUGGLE, JC; de Groot, Frank

    1988-01-01

    We present atomic calculations for the recently discovered magnetic x-ray dichroism (MXD) displayed by the 3d x-ray-absorption spectra of rare-earth compounds. The spectral shapes expected at T=0 K for linear polarization parallel and normal to the local magnetic field is given, together with the te

  12. Researches on Relationship between Circular Agriculture and Industrial Diversity

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    First, this paper establishes the conceptual model of circular agriculture, conducts systematic analysis on the circular agriculture on the basis of conceptual model, and discusses the characteristics of closeness and openness of circular agriculture and relationship between closeness and openness of circular agriculture. Second, this paper introduces the industrial diversity related to circular agriculture, defines the concept of industry and the concept of industries related to agriculture, and illustrates the related industries that are conducive to circular agriculture and the related industries that are not conducive to circular agriculture. Finally, this paper analyzes the mutual relationship between circular agriculture and industrial diversity as follows: in the system of circular agriculture, the industrial diversity can transform the wastes in upstream industries into resources in downstream industries; the industrial diversity creates possibility for recycling of agricultural byproducts; the industrial diversity is conducive to the diversification of industries related to circular agriculture.

  13. Circular design - A manual on how to integrate circular design in buildings

    NARCIS (Netherlands)

    Mac-lean, M.; Van Splunter, M.; Sun, X.

    2014-01-01

    This "designers' manual" is made during the TIDO-course AR0531 Innovation and Sustainability Circular design is based on two sustainability concepts: Cradle to Cradle® and circular economy. The former is more dogmatic and specific for the manufacturing and design industry, while the latter presents

  14. Environmental issues elimination through circular economy

    Science.gov (United States)

    Špirková, M.; Pokorná, E.; Šujanová, J.; Samáková, J.

    2016-04-01

    Environmental efforts of European Union are currently going towards circular economy. Tools like Extended Producer Responsibility and Eco-design were established. The circular economy deals with resources availability issue on one hand and waste management on the other hand. There are few pioneering companies all over the world with some kind of circular economy practice. Generally the concept is not very wide-spread. The paper aims to evaluate possibility of transition towards circular economy in Slovak industrial companies. They need to have an active approach to material treatment of their products after usage stage. Innovation is another important pre-condition for the transition. Main problem of current cradle to grave system is landfilling of valuable materials after one cycle of usage. Their potential value for next manufacturing cycles is lost. Companies may do not see connection between waste management and material resource prices and volatility of supplies. Municipalities are responsible for municipal waste collection and treatment in Slovakia. The circular economy operates by cradle to cradle principle. Company manages material flow until the material comes back to the beginning of manufacturing process by itself or by another partners. Stable material supplies with quite low costs are provided this way. It is necessary to deal with environmental problems in phase of product design. Questionnaire survey results show on one hand low involvement of industrial companies in waste management area, however on the other hand they are open to environmental innovations in future.

  15. A COMPACT CIRCULARLY POLARIZED SLOTTED MICROSTRIP ANTENNA

    Directory of Open Access Journals (Sweden)

    V. Jebaraj

    2014-12-01

    Full Text Available Slot antennas are often used at UHF and microwave frequencies. In slot antenna for RFID reader applications the frequency ranges from 902-923MHz to achieve circular polarization. The shapes and size of the slot, as well as the driving frequency, determine the radiation distribution pattern. The proposed compact size circularly polarized slotted microstrip antenna are summarized with design rules. The circularly polarized radiation in square patch antenna can be obtained by perturbation technique with different shapes of slot in the orthogonal direction. A single feed configuration based symmetric slotted microstrip antenna is adapted to realize the compact circularly polarized microstrip antennas. Based on the perimeter, the size of the slot on microstrip slot antenna are studied and compared. The Operating frequency of the antenna is 912MHz that can be tuned by varying the perimeter of the slot while the keeping the circularly polarized radiation unchanged. The schematic and layout are configured by using Advanced Design System (ADS. Return loss, Resonant Frequency, Axial Ratio (AR, and Gain were determined for the proposed system using ADS. A measured 3dB Axial Ratio (AR bandwidth around 6MHz with 16MHz impedance bandwidth has been achieved for the antenna on a RO3004C substrate with dielectric constant 3.38.

  16. Circular and Elliptic Submerged Impinging Water Jets

    Science.gov (United States)

    Claudey, Eric; Benedicto, Olivier; Ravier, Emmanuel; Gutmark, Ephraim

    1999-11-01

    Experiments and CFD have been performed to study circular and elliptic jets in a submerged water jet facility. The tests included discharge coefficient measurement to evaluate pressure losses encountered in noncircular nozzles compared to circular ones. Three-dimensional pressure mappings on the impingement surface and PIV measurement of the jet mean and turbulent velocity have been performed at different compound impingement angles relative to the impingement surface and at different stand-off distances. The objective was to investigate the effect of the non-circular geometry on the flow field and on the impact region. The tests were performed in a close loop system in which the water was pumped through the nozzles into a clear Plexiglas tank. The Reynolds numbers were typically in the range of 250000. Discharge coefficients of the elliptic nozzle was somewhat lower than that of the circular jet but spreading rate and turbulence level were higher. Pressure mapping showed that the nozzle exit geometry had an effect on the pressure distribution in the impact region and that high-pressure zones were generated at specific impact points. PIV measurements showed that for a same total exit area, the elliptic jets affected a surface area that is 8the equivalent circular. The turbulence level in the elliptic jet tripled due to the nozzle design. Results of the CFD model were in good agreement with the experimental data.

  17. A broadband, circular-polarization selective surface

    Science.gov (United States)

    Momeni Hasan Abadi, Seyed Mohamad Amin; Behdad, Nader

    2016-06-01

    We introduce a new technique for designing wideband circular-polarization selective surfaces (CPSSs) based on anisotropic miniaturized element frequency selective surfaces. The proposed structure is a combination of two linear-to-circular polarization converters sandwiching a linear polarizer. This CPSS consists of a number of metallic layers separated from each other by thin dielectric substrates. The metallic layers are in the form of two-dimensional arrays of subwavelength capacitive patches and inductive wire grids with asymmetric dimensions and a wire grid polarizer with sub-wavelength period. The proposed device is designed to offer a wideband circular-polarization selection capability allowing waves with left-hand circular polarization to pass through while rejecting those having right-hand circular polarization. A synthesis procedure is developed that can be used to design the proposed CPSS based on its desired band of operation. Using this procedure, a prototype of the proposed CPSS operating in the 12-18 GHz is designed. Full-wave electromagnetic simulations are used to predict the response of this structure. These simulation results confirm the validity of the proposed design concept and synthesis procedure and show that proposed CPSS operates within a fractional bandwidth of 40% with a co-polarization transmission discrimination of more than 15 dB. Furthermore, the proposed design is shown to be capable of providing an extremely wide field of view of ±60°.

  18. Liquid chromatography with mass spectrometry enantioseparation of pomalidomide on cyclodextrin-bonded chiral stationary phases and the elucidation of the chiral recognition mechanisms by NMR spectroscopy and molecular modeling.

    Science.gov (United States)

    Szabó, Zoltán-István; Szőcs, Levente; Horváth, Péter; Komjáti, Balázs; Nagy, József; Jánoska, Ádám; Muntean, Daniela-Lucia; Noszál, Béla; Tóth, Gergő

    2016-08-01

    A sensitive and validated liquid chromatography with mass spectrometry method was developed for the enantioseparation of the racemic mixture of pomalidomide, a novel, second-generation immunomodulatory drug, using β-cyclodextrin-bonded stationary phases. Four cyclodextrin columns (β-, hydroxypropyl-β-, carboxymethyl-β-, and sulfobutyl-β-cyclodextrin) were screened and the effects of eluent composition, flow rate, temperature, and organic modifier on enantioseparation were studied. Optimized parameters, offering baseline separation (resolution = 2.70 ± 0.02) were the following: β-cyclodextrin stationary phase, thermostatted at 15°C, and mobile phase consisting of methanol/0.1% acetic acid 10:90 v/v, delivered with 0.8 mL/min flow rate. For the optimized parameter at multiple reaction monitoring mode 274.1-201.0 transition with 20 eV collision energy and 100 V fragmentor voltage the limit of detection and limit of quantitation were 0.75 and 2.00 ng/mL, respectively. Since enantiopure standards were not available, elution order was determined upon comparison of the circular dichroism signals of the separated pomalidomide enantiomers with that of enantiopure thalidomide. The mechanisms underlying the chiral discrimination between the enantiomers were also investigated. Pomalidomide-β-cyclodextrin inclusion complex was characterized using nuclear magnetic resonance spectroscopy and molecular modeling. The thermodynamic aspects of chiral separation were also studied.

  19. Determination of the cation site distribution of the spinel in multiferroic CoFe{sub 2}O{sub 4}/BaTiO{sub 3} layers by X-ray photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Aghavnian, T. [CEA/Saclay, DSM/IRAMIS/SPEC, CNRS UMR 3680, F-91191 Gif-sur-Yvette (France); Synchrotron SOLEIL, L’Orme des Merisiers Saint-Aubin, F-91192 Gif-sur-Yvette (France); Moussy, J.-B.; Stanescu, D. [CEA/Saclay, DSM/IRAMIS/SPEC, CNRS UMR 3680, F-91191 Gif-sur-Yvette (France); Belkhou, R. [Synchrotron SOLEIL, L’Orme des Merisiers Saint-Aubin, F-91192 Gif-sur-Yvette (France); Jedrecy, N. [Sorbonne Universités, UPMC Univ Paris 06, UMR 7588, INSP, F-75005 Paris (France); Magnan, H. [CEA/Saclay, DSM/IRAMIS/SPEC, CNRS UMR 3680, F-91191 Gif-sur-Yvette (France); Ohresser, P. [Synchrotron SOLEIL, L’Orme des Merisiers Saint-Aubin, F-91192 Gif-sur-Yvette (France); Arrio, M.-A.; Sainctavit, Ph. [IMPMC, F-75015 Paris (France); Barbier, A., E-mail: abarbier@cea.fr [CEA/Saclay, DSM/IRAMIS/SPEC, CNRS UMR 3680, F-91191 Gif-sur-Yvette (France)

    2015-07-15

    Highlights: • We grow epitaxial and well characterized CoFe{sub 2}O{sub 4}/BaTiO{sub 3} thin films. • We studied the spinel cation site distribution in CoFe{sub 2}O{sub 4}/BaTiO{sub 3} thin films. • We quantitatively determine the spinel inversion parameter by XMCD and XPS. • We propose a reproducible XPS fit method based on physical principles. - Abstract: The properties of CoFe{sub 2}O{sub 4}/BaTiO{sub 3} artificial multiferroic multilayers strongly depend on the crystalline structure, the stoichiometry and the cation distribution between octahedral (Oh) and tetrahedral (Td) sites (inversion factor). In the present study, we have investigated epitaxial CoFe{sub 2}O{sub 4} layers grown on BaTiO{sub 3}, with different Co/Fe ratios. We determined the cation distribution in our samples by X-ray magnetic circular dichroism (XMCD), a well accepted method to do so, and by X-ray photoelectron spectroscopy (XPS), using a fitting method based on physical considerations. We observed that our XPS approach converged on results consistent with XMCD measurements made on the same samples. Thus, within a careful decomposition based on individual chemical environments it is shown that XPS is fully able to determine the actual inversion factor.

  20. Site-specific thermodynamic stability and unfolding of a de novo designed protein structural motif mapped by 13C isotopically edited IR spectroscopy.

    Science.gov (United States)

    Kubelka, Ginka S; Kubelka, Jan

    2014-04-23

    The mechanism of protein folding remains poorly understood, in part due to limited experimental information available about partially folded states. Isotopically edited infrared (IR) spectroscopy has emerged as a promising method for studying protein structural changes with site-specific resolution, but its full potential to systematically probe folding at multiple protein sites has not yet been realized. We have used (13)C isotopically edited IR spectroscopy to investigate the site-specific thermal unfolding at seven different locations in the de novo designed helix-turn-helix protein αtα. As one of the few stable helix-turn-helix motifs, αtα is an excellent model for studying the roles of secondary and tertiary interactions in folding. Circular dichroism (CD) experiments on the full αtα motif and its two peptide fragments show that interhelical tertiary contacts are critical for stabilization of the secondary structure. The site-specific thermal unfolding probed by (13)C isotopically edited IR is likewise consistent with primarily tertiary stabilization of the local structure. The least thermally stable part of the αtα motif is near the turn where the interhelical contacts are rather loose, while the motif's center with best established core packing has the highest stability. Similar correlation between the local thermal stability and tertiary contacts was found previously for a naturally occurring helix-turn-helix motif. These results underline the importance of native-like tertiary stabilizing interactions in folding, in agreement with recent state-of-the art folding simulations as well as simplified, native-centric models.