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Sample records for absorption circular dichroism

  1. Toroidal circular dichroism

    NASA Astrophysics Data System (ADS)

    Raybould, T. A.; Fedotov, V. A.; Papasimakis, N.; Kuprov, I.; Youngs, I. J.; Chen, W. T.; Tsai, D. P.; Zheludev, N. I.

    2016-07-01

    We demonstrate that the induced toroidal dipole, represented by currents flowing on the surface of a torus, makes a distinct and indispensable contribution to circular dichroism. We show that toroidal circular dichroism supplements the well-known mechanism involving electric dipole and magnetic dipole transitions. We illustrate this with rigorous analysis of the experimentally measured polarization-sensitive transmission spectra of an artificial metamaterial, constructed from elements of toroidal symmetry. We argue that toroidal circular dichroism will be found in large biomolecules with elements of toroidal symmetry and should be taken into account in the interpretation of circular dichroism spectra of organics.

  2. Infrared absorption and vibrational circular dichroism spectra of poly(vinyl ether) containing diastereomeric menthols as pendants

    NASA Astrophysics Data System (ADS)

    McCann, Jennifer L.; Rauk, Arvi; Wieser, Hal

    1997-06-01

    The absorption and vibrational circular dichroism (VCD) spectra in the 1700 to 830 cm -1 region are reported and qualitatively interpreted for poly(vinyl ether) with (+)-menthol (I), (+)-isomenthol (II) and (+)-neomenthol (III) as pendants.

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

    PubMed

    Kamiński, Maciej; Cukras, Janusz; Pecul, Magdalena; Rizzo, Antonio; Coriani, Sonia

    2015-07-15

    We present a computational methodology to calculate the intensity of circular dichroism (CD) in spin-forbidden 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 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 → π* and n ← π* transitions, respectively, in several chiral enones and diketones. Basis set effects in the length and velocity gauge formulations have been explored, and the accuracy achieved when employing approximate (mean-field and effective nuclear charge) spin-orbit operators has been investigated. CPP is shown to be a sensitive probe of the triplet excited state structure. In many cases the sign of the spin-forbidden CD and CPP signals are opposite. For the β,γ-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. PMID:26126575

  4. Temperature-induced structural changes in putidaredoxin: a circular dichroism and UV-VIS absorption study.

    PubMed

    Reipa, Vytas; Holden, Marcia; Mayhew, Martin P; Vilker, Vincent L

    2004-06-01

    Putidaredoxin (Pdx) is an 11,400-Da iron-sulfur protein that sequentially transfers two electrons to the cytochrome P450cam during the enzymatic cycle of the stereospecific camphor hydroxylation. We report two transitions in the Pdx UV-VIS absorption and circular dichroism (CD) temperature dependencies, occurring at 16.3+/-0.5 degrees C and 28.4+/-0.5 degrees C. The 16.3 degrees C transition is attributed to the disruption of the hydrogen bonding of the active center bridging sulfur atom with cysteine 45 and alanine 46. The transition at 28.4 degrees C occurs exclusively in the Pdx(ox) at very nearly the same temperature as the earlier reported biphasicity in the redox potential. The formal potential temperature slope constancy reflects the relative stability of the concentration ratio of both oxidation states. The lower temperature transition affects both Pdx(red) and Pdx(ox) to a comparable extent, and their concentration ratio remains constant. In contrast, the 28.4 degrees C transition preferentially destabilizes Pdx(ox) thereby accelerating the formal potential negative shift and lower redox reaction entropy. There is evidence to suggest that disrupting hydrogen bonding of the iron ligating cysteines 45, 39 with residues threonine 47, serine 44, glycine 41, and serine 42 causes the 28.4 degrees C transition. The sensitivity of the UV-VIS absorption and CD spectroscopy to subtle structural protein backbone transitions is demonstrated. PMID:15158732

  5. Binding of anti-prion agents to glycosaminoglycans: Evidence from electronic absorption and circular dichroism spectroscopy

    SciTech Connect

    Zsila, Ferenc . E-mail: zsferi@chemres.hu; Gedeon, Gabor

    2006-08-11

    The polyanionic glycosaminoglycans (GAGs) are intimately involved in the pathogenesis of protein conformational disorders such as amyloidosis and prion diseases. Several cationic agents are known to exhibit anti-prion activity but their mechanism of action is poorly understood. In this study, UV absorption and circular dichroism (CD) spectroscopic techniques were used to investigate the interaction between heparin and chondroitin-6-sulfate and anti-prion drugs including acridine, quinoline, and phenothiazine derivatives. UV band hypochromism of ({+-})-quinacrine, ({+-})-primaquine, tacrine, quinidine, chlorpromazine, and induced CD spectra of ({+-})-quinacrine upon addition of GAGs provided evidence for the GAG binding of these compounds. The association constants ({approx}10{sup 6}-10{sup 7} M{sup -1}) estimated from the UV titration curves show high-affinity drug-heparin interactions. Ionic strength-dependence of the absorption spectra suggested that the interaction between GAGs and the cationic drugs is principally electrostatic in nature. Drug binding differences of heparin and chondroitin-6-sulfate were attributed to their different negative charge density. These results call the attention to the alteration of GAG-prion/GAG-amyloid interactions by which these compounds might exert their anti-prion/anti-amyloidogenic activities.

  6. Linear-Circular Dichroism of Four-Photon Absorption of Light in Semiconductors with a Complex Valence Band

    NASA Astrophysics Data System (ADS)

    Rasulov, R. Ya.; Rasulov, V. R.; Eshboltaev, I.

    2016-04-01

    Matrix elements of optical transitions occuring between the subbands of the valence band of a p-GaAs type semiconductor are calculated. Transitions associated with the non-simultaneous absorption of single photons and simultaneous absorption of two photons are taken into account. The expressions are obtained for the average values of the square modulus of matrix elements calculated with respect to the solid angle of the wave vector of holes. Linear-circular dichroism of four-photon absorption of light in semiconductors with a complex valence band is theoretically studied.

  7. Nuclear spin circular dichroism

    SciTech Connect

    Vaara, Juha; Rizzo, Antonio; Kauczor, Joanna; Norman, Patrick; Coriani, Sonia

    2014-04-07

    Recent years have witnessed a growing interest in magneto-optic spectroscopy techniques that use nuclear magnetization as the source of the magnetic field. Here we present a formulation of magnetic circular dichroism (CD) due to magnetically polarized nuclei, nuclear spin-induced CD (NSCD), in molecules. The NSCD ellipticity and nuclear spin-induced optical rotation (NSOR) angle correspond to the real and imaginary parts, respectively, of (complex) quadratic response functions involving the dynamic second-order interaction of the electron system with the linearly polarized light beam, as well as the static magnetic hyperfine interaction. Using the complex polarization propagator framework, NSCD and NSOR signals are obtained at frequencies in the vicinity of optical excitations. Hartree-Fock and density-functional theory calculations on relatively small model systems, ethene, benzene, and 1,4-benzoquinone, demonstrate the feasibility of the method for obtaining relatively strong nuclear spin-induced ellipticity and optical rotation signals. Comparison of the proton and carbon-13 signals of ethanol reveals that these resonant phenomena facilitate chemical resolution between non-equivalent nuclei in magneto-optic spectra.

  8. Simulation of Vacuum UV Absorption and Electronic Circular Dichroism Spectra of Methyl Oxirane: The Role of Vibrational Effects.

    PubMed

    Hodecker, Manuel; Biczysko, Malgorzata; Dreuw, Andreas; Barone, Vincenzo

    2016-06-14

    Vibrationally resolved one-photon absorption and electronic circular dichroism spectra of (R)-methyl oxirane were calculated with different electronic and vibronic models selecting, through an analysis of the convergence of the results, the best compromise between reliability and computational cost. Linear-response TD-DFT/CAM-B3LYP/SNST electronic computations in conjunction with the simple vertical gradient vibronic model were chosen and employed for systematic comparison with the available experimental data. Remarkable agreement between simulated and experimental spectra was achieved for both one-photon absorption and circular dichroism concerning peak positions, relative intensities, and general spectral shapes considering the computational efficiency of the chosen theoretical approach. The significant improvement of the results with respect to smearing of vertical electronic transitions by phenomenological Gaussian functions and the possible inclusion of solvent effects by polarizable continuum models at a negligible additional cost paves the route toward the simulation and analysis of spectral shapes of complex molecular systems in their natural environment. PMID:27159495

  9. Compact optical cell system for vacuum ultraviolet absorption and circular dichroism spectroscopy and its application to aqueous solution sample.

    PubMed

    Tanaka, Masahito; Yagi-Watanabe, Kazutoshi; Kaneko, Fusae; Nakagawa, Kazumichi

    2008-09-01

    We have designed a compact optical cell for studying the absorption and circular dichroism (CD) of a solution sample in the vacuum ultraviolet (VUV) region using a temperature control unit. The cell size was 34 mm in diameter and 14 mm in length. Such compactness was obtained by coating the VUV scintillator onto the outside of the back window. Because this scintillator converts the transmitted VUV light to visible light, the outside of this cell is operated under atmospheric pressure. The temperature of the sample solution was maintained in the range of 5 degrees C to 80 degrees C using a temperature control unit with a Peltier thermoelectric element. Changes in the sample temperature were observed by monitoring the absorption intensity of water. Through the study of VUV-CD spectra of ammonium camphor-10-sulfonate aqueous solutions and the transmitted spectrum of an empty cell, it was concluded that this cell unit has sufficient performance for use in VUV spectroscopy. PMID:18473342

  10. X-ray absorption and magnetic circular dichroism studies of Co2FeAl in magnetic tunnel junctions

    SciTech Connect

    Ebke, D.; Kugler, Z.; Thomas, P.; Schebaum, O.; Schafers, M.; Nissen, D.; Schmalhorst, J.; Hutten, A.; Arenholz, E.; Thomas, A.

    2010-01-11

    The bulk magnetic moment and the element specific magnetic moment of Co{sub 2}FeAl thin films were examined as a function of annealing temperature by alternating gradient magnetometer (AGM) and X-ray absorption spectroscopy (XAS)/X-ray magnetic circular dichroism (XMCD), respectively. A high magnetic moment can be achieved for all annealing temperatures and the predicted bulk and interface magnetic moment of about 5 {tilde A}{sub B} are reached via heating. We will also present tunnel magnetoresistance (TMR) values of up to 153% at room temperature and 260% at 13 K for MgO based magnetic tunnel junctions (MTJs) with Co{sub 2}FeAl and Co-Fe electrodes.

  11. Observation of x-ray absorption magnetic circular dichroism in well-characterized iron-cobalt-platinum multilayers

    SciTech Connect

    Jankowski, A.F.; Waddill, G.D.; Tobin, J.G.

    1993-04-01

    Magnetic circular dichroism in the Fe 2p x-ray absorption is observed in multilayers of(Fe9.5{Angstrom}/Pt9.5{Angstrom}){sub 92}. The magnetization and helicity are both in the plane of this multilayer which is prepared by magnetron sputter deposition. This sample is part of a study to examine magnetization in the ternary multilayer system of FeCo/Pt. Lattice and layer pair spacings are measured using x-ray scattering. The atomic concentration profiles of the multilayer films are characterized using Auger electron spectroscopy coupled with depth profiling. Conventional and high resolution transmission electron microscopy are used to examine the thin film, growth morphology and atomic structure.

  12. Femtosecond X-ray magnetic circular dichroism absorption spectroscopy at an X-ray free electron laser.

    PubMed

    Higley, Daniel J; Hirsch, Konstantin; Dakovski, Georgi L; Jal, Emmanuelle; Yuan, Edwin; Liu, Tianmin; Lutman, Alberto A; MacArthur, James P; Arenholz, Elke; Chen, Zhao; Coslovich, Giacomo; Denes, Peter; Granitzka, Patrick W; Hart, Philip; Hoffmann, Matthias C; Joseph, John; Le Guyader, Loïc; Mitra, Ankush; Moeller, Stefan; Ohldag, Hendrik; Seaberg, Matthew; Shafer, Padraic; Stöhr, Joachim; Tsukamoto, Arata; Nuhn, Heinz-Dieter; Reid, Alex H; Dürr, Hermann A; Schlotter, William F

    2016-03-01

    X-ray magnetic circular dichroism spectroscopy using an X-ray free electron laser is demonstrated with spectra over the Fe L(3,2)-edges. The high brightness of the X-ray free electron laser combined with high accuracy detection of incident and transmitted X-rays enables ultrafast X-ray magnetic circular dichroism studies of unprecedented sensitivity. This new capability is applied to a study of all-optical magnetic switching dynamics of Fe and Gd magnetic sublattices in a GdFeCo thin film above its magnetization compensation temperature. PMID:27036761

  13. Femtosecond X-ray magnetic circular dichroism absorption spectroscopy at an X-ray free electron laser

    NASA Astrophysics Data System (ADS)

    Higley, Daniel J.; Hirsch, Konstantin; Dakovski, Georgi L.; Jal, Emmanuelle; Yuan, Edwin; Liu, Tianmin; Lutman, Alberto A.; MacArthur, James P.; Arenholz, Elke; Chen, Zhao; Coslovich, Giacomo; Denes, Peter; Granitzka, Patrick W.; Hart, Philip; Hoffmann, Matthias C.; Joseph, John; Le Guyader, Loïc; Mitra, Ankush; Moeller, Stefan; Ohldag, Hendrik; Seaberg, Matthew; Shafer, Padraic; Stöhr, Joachim; Tsukamoto, Arata; Nuhn, Heinz-Dieter; Reid, Alex H.; Dürr, Hermann A.; Schlotter, William F.

    2016-03-01

    X-ray magnetic circular dichroism spectroscopy using an X-ray free electron laser is demonstrated with spectra over the Fe L3,2-edges. The high brightness of the X-ray free electron laser combined with high accuracy detection of incident and transmitted X-rays enables ultrafast X-ray magnetic circular dichroism studies of unprecedented sensitivity. This new capability is applied to a study of all-optical magnetic switching dynamics of Fe and Gd magnetic sublattices in a GdFeCo thin film above its magnetization compensation temperature.

  14. UV and VUV spectrum of matrix-isolated In: an investigation by absorption, magnetic circular dichroism and emission yield spectroscopy

    NASA Astrophysics Data System (ADS)

    Schroeder, W.; Rotermund, H.-H.; Wiggenhauser, H.; Schrittenlacher, W.; Hormes, J.; Krebs, W.; Laaser, W.

    1986-05-01

    The electronic absorption spectra of In atoms isolated in neon, argon, krypton and xenon matrices have been measured in the energy range between 2.5 and 9.0 eV. This region includes the 5s 25p → 5s 26s and 5s 25p → 5s 25d resonance transitions, higher members of the corresponding s- and d-Rydberg series and the inner shell 5s 25p → 5s5p 2 transitions. A correlation of the absorption spectra with results obtained from magnetic circular dichroism and fluorescence measurements has made it possible to provide a detailed assignment of most of the features in the spectra in spite of the complexities associated with their behavior. For example, the transition to 5s 26s could not be detected in any of the matrices and the 5s 25d configuration was found to be strongly quenched in intensity as compared to the other transitions. In contrast, several Rydberg transitions could be observed for In in Ne. These were satisfactorily interpreted within the Frenkel formalism. Some of these observations have been rationalized by assuming that the average radius of the wavefunction for the excited state is the dominant parameter for the matrix interaction.

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

    NASA Astrophysics Data System (ADS)

    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. Interstellar condensed (icy) amino acids and precursors: theoretical absorption and circular dichroism under UV and soft X-ray irradiation

    NASA Astrophysics Data System (ADS)

    Da Pieve, F.; Avendaño-Franco, G.; De Proft, F.; Geerlings, P.

    2014-05-01

    The photophysics of interstellar ices and condensed molecules adsorbed on grains is of primary importance for studies on the origin of the specific handedness of complex organic molecules delivered to the early Earth and of the homochirality of the building blocks of life. Here, we present quantum mechanical calculations based on time-dependent density functional theory for the absorption and circular dichroism (CD) of isovaline and its chiral precursor 5-ethyl-5-methylhydantoin, both observed in meteoritic findings. The systems are considered in their geometrical conformation as extracted from a full solid (icy) matrix, as a shortcut to understand the behaviour of molecules with fixed orientation, and/or taking into account the full solid matrix. In the context of a possible `condensation-warming plus hydrolysis-recondensation' process, we obtain that: (i) for low-energy excitations, the `condensed' precursor has a stronger CD with respect to the amino acid, suggesting that the handedness of the latter could be biased by asymmetric photolysis of the precursor in cold environments; (ii) enantiomeric excess could in principle be induced more efficiently in both systems for excitation at higher energies (VUV). X-ray absorption near-edge spectroscopy and related CD results could serve as support for future experiments on ionization channels.

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

    SciTech Connect

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

    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.

  18. Method of oriented circular dichroism.

    PubMed Central

    Wu, Y; Huang, H W; Olah, G A

    1990-01-01

    We present a new method for determining the orientation of alpha-helical sections of proteins or peptides in membrane. To apply this method, membranes containing proteins must be prepared in a multilayer array. Circular dichroism (CD) spectra of the multilayer sample are then measured at the normal as well as oblique incident angles with respect to the bilayer planes; we call such spectra oriented circular dichroism (OCD). The procedure of OCD measurement, particularly the ways to avoid the spectral artifacts due to the effects of dielectric interfaces, linear dichroism and birefringence, and the method of data analysis are described in detail. To illustrate the method, we analyze the OCD of alamethicin in diphytanoylphosphatidylcholine multilayers. We conclude unambiguously that the helical section of alamethicin is parallel to the membrane normal when the sample is in the full-hydration state, but the helical section rotates to the plane of membrane when the sample is in a low-hydration state. We also obtained the parallel and perpendicular CD spectra of alpha-helix, and found them to be in agreement with previous theoretical calculations based on the exciton theory. These spectra are useful for analyzing protein orientations in future experiments. Images FIGURE 5 PMID:2344464

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

    NASA Astrophysics Data System (ADS)

    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 0.1absorption 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.

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

    SciTech Connect

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

    2013-11-14

    Tetragonally distorted Mn{sub 3−x}Ga{sub x} thin films with 0.1absorption spectroscopy (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.

  1. Measurement of electron-spin transports in GaAs quantum wells using a transmission-grating-sampled circular dichroism absorption spectroscopy

    SciTech Connect

    Yu, Hua-Liang; Fang, Shaoyin; Wen, Jinhui; Lai, Tianshu

    2014-11-07

    A transmission-grating-sampled circular dichroism absorption spectroscopy (TGS-CDAS) and its theoretical model are developed sensitively to measure decay dynamics of a transient spin grating (TSG). A binary transmission grating with the same period as TSG is set behind TSG. It allows only a same small part of each period in TSG measured by circular dichroism absorption effect of a probe. In this way, the zero average of spin-dependent effects measured over a whole period in TSG is avoided so that TGS-CDAS has a high sensitivity to spin evolution in TSG. Spin transport experiments are performed on GaAs/AlGaAs quantum wells. Experimental results prove the feasibility and reliability of TGS-CDAS.

  2. Measurement of electron-spin transports in GaAs quantum wells using a transmission-grating-sampled circular dichroism absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Yu, Hua-Liang; Fang, Shaoyin; Wen, Jinhui; Lai, Tianshu

    2014-11-01

    A transmission-grating-sampled circular dichroism absorption spectroscopy (TGS-CDAS) and its theoretical model are developed sensitively to measure decay dynamics of a transient spin grating (TSG). A binary transmission grating with the same period as TSG is set behind TSG. It allows only a same small part of each period in TSG measured by circular dichroism absorption effect of a probe. In this way, the zero average of spin-dependent effects measured over a whole period in TSG is avoided so that TGS-CDAS has a high sensitivity to spin evolution in TSG. Spin transport experiments are performed on GaAs/AlGaAs quantum wells. Experimental results prove the feasibility and reliability of TGS-CDAS.

  3. Gauge-Invariant Formulation of Circular Dichroism.

    PubMed

    Raimbault, Nathaniel; de Boeij, Paul L; Romaniello, Pina; Berger, J A

    2016-07-12

    Standard formulations of magnetic response properties, such as circular dichroism spectra, are plagued by gauge dependencies, which can lead to unphysical results. In this work, we present a general gauge-invariant and numerically efficient approach for the calculation of circular dichroism spectra from the current density. First we show that in this formulation the optical rotation tensor, the response function from which circular dichroism spectra can be obtained, is independent of the origin of the coordinate system. We then demonstrate that its trace is independent of the gauge origin of the vector potential. We also show how gauge invariance can be retained in practical calculations with finite basis sets. As an example, we explain how our method can be applied to time-dependent current-density-functional theory. Finally, we report gauge-invariant circular dichroism spectra obtained using the adiabatic local-density approximation. The circular dichroism spectra we thus obtain are in good agreement with experiment. PMID:27295541

  4. Circular dichroism from Fano resonances in planar chiral oligomers

    NASA Astrophysics Data System (ADS)

    Hopkins, Ben; Poddubny, Alexander N.; Miroshnichenko, Andrey E.; Kivshar, Yuri S.

    2015-05-01

    Here we present a general approach for describing the physics of Fano resonances in nanoparticle oligomers. It is shown that the interference of nonorthogonal collective eigenmodes is a sufficient condition to produce Fano resonances. We then show that such nonorthogonality between eigenmodes also permits the existence of a new form circular dichroism in the absorption and scattering cross-sections, even when circular dichroism is forbidden in the extinction cross-section.

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

    SciTech Connect

    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.

  6. Circular dichroism and optical absorption spectra of mononuclear and trinuclear chiral Cu(II) amino-alcohol coordinated compounds: A combined theoretical and experimental study

    NASA Astrophysics Data System (ADS)

    Valencia, Israel; Ávila-Torres, Yenny; Barba-Behrens, Norah; Garzón, Ignacio L.

    2015-04-01

    Studies on the physicochemical properties of biomimetic compounds of multicopper oxidases are fundamental to understand their reaction mechanisms and catalytic behavior. In this work, electronic, optical, and chiroptical properties of copper(II) complexes with amino-alcohol chiral ligands are theoretically studied by means of time-dependent density functional theory. The calculated absorption and circular dichroism spectra are compared with experimental measurements of these spectra for an uncoordinated pseudoephedrine derivative, as well as for the corresponding mononuclear and trinuclear copper(II)-coordinated complexes. This comparison is useful to gain insights into their electronic structure, optical absorption and optical activity. The optical absorption and circular dichroism bands of the pseudoephedrine derivative are located in the UV-region. They are mainly due to transitions originated from n to π anti-bonding orbitals of the alcohol and amino groups, as well as from π bonding to π anti-bonding orbitals of carboxyl and phenyl groups. In the case of the mononuclear and trinuclear compounds, additional signals in the visible spectral region are present. In both systems, the origin of these bands is due to charge transfer from ligand to metal and d-d transitions.

  7. Magnetic circular dichroism in EELS (abstract)

    SciTech Connect

    Harp, G.R.; Farrow, R.F.; Marks, R.F.

    1996-04-01

    We evaluate the possibility of using dichroic electron energy loss spectroscopy (DEELS) as an alternative to x-ray magnetic circular dichroism (XMCD). It is well known that electron energy loss spectroscopy and x-ray absorption spectroscopy are highly analogous, providing similar information. A simple semiclassical model suggests that DEELS might have a magnetic sensitivity similar to that of XMCD. This sensitivity will be reduced, however, by multiple scattering of the probe electron before and after the energy loss event. Thus it is difficult to predict the magnitude of the DEELS effect. Experiments were performed at the {ital L}-edge of polycrystalline Fe, Co, and Ni thin film samples with uniaxial in-plane magnetic anisotropy, prepared {ital in} {ital situ} with a magnetic bias field. Even in those most favorable cases, the DEELS effect is seen to be at least 10 times smaller than similar effects in XMCD. {copyright} {ital 1996 American Institute of Physics.}

  8. Magnetic circular dichroism of peralkylated tetrasilane conformers

    PubMed Central

    Fogarty, Heather A.; Imhof, Roman; Michl, Josef

    2004-01-01

    Magnetic circular dichroism (MCD) of five peralkylated tetrasilanes (1–5) conformationally constrained to angles ranging from nearly 0° to 180° and of the open chain tetrasilane Si4Me10 (6) shows a clear conformational dependence and permits the detection of previously hidden transitions. In the tetrasilane CH2Si4Me8 (1), with the smallest dihedral angle, comparison of MCD with absorption spectra reveals four low-energy electronic transitions. In the tetrasilanes 2–4, three distinct transitions are apparent. In tetrasilanes 5 and 6, MCD reveals the very weak transition that has been predicted to be buried under the first intense peak and to which the anomalous thermochromism of 6 and other short-chain oligosilanes has been attributed. PMID:15249672

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

    SciTech Connect

    Wakabayashi, Masamitsu; Yokojima, Satoshi; Fukaminato, Tuyoshi; Ohtani, Hiroyuki; Nakamura, Shinichiro

    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.

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

    NASA Astrophysics Data System (ADS)

    Wakabayashi, Masamitsu; Yokojima, Satoshi; Fukaminato, Tuyoshi; Ohtani, Hiroyuki; Nakamura, Shinichiro

    2015-04-01

    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.

  11. Electrodynamics of circular dichroism and its application in the construction of a circular polaroid

    NASA Astrophysics Data System (ADS)

    Volobuev, A. N.

    2016-03-01

    Electrodynamic principles of circular dichroism are developed using a concept of conducting circular structures in matter. A simplified representation of material equations for an optically active medium is obtained in the absence of a transition to the complex domain. A dependence of the absorption coefficient of a circular polarization as a component of the linearly polarized radiation on material parameters is found. Such parameters are analyzed to reveal a possibility of construction of a circular polaroid.

  12. Circular dichroism and magnetic circular dichroism of iron-sulfur proteins.

    PubMed

    Stephens, P J; Thomson, A J; Dunn, J B; Keiderling, T A; Rawlings, J; Rao, K K; Hall, D O

    1978-10-31

    Circular dichroism (CD) and magnetic circular dichroism (MCD) spectra are reported for the 2-Fe ferredoxins from Pseudomonas putida and Spirulina maxima, Chromatium HIPIP, the 4-Fe ferredoxin from Bacillus stearothermophilus, and the 8-Fe ferredoxin from Clostridium pasteurianum. The spectral range spans the near-infrared, visible, and near ultraviolet. In all cases except oxidized 2-Fe ferredoxins, electronic absorption is observed continuously from less than 5000 cm-1 to above 30,000 cm-1. The CD spectra of the two 2-Fe ferredoxins are similar. In contrast, the CD of the 4-Fe and 8-Fe proteins, for a given 4-Fe cluster oxidation level, varies considerable with protein. MCD is less sensitive to protein environment than is CD. In the 2-Fe proteins, MCD at 5 T is appreciably smaller than the CD; in the 4-Fe and 8-Fe proteins, MCD and CD are comparable in magnitude. Both CD and MCD are more highly structured than the corresponding absorption spectra. The CD and MCD spectra reported provide a broader base than heretofore available for the characterization of iron-sulfur proteins containing 2-Fe and 4-Fe clusters and for the evaluation of electronic structural models for these clusters. PMID:728385

  13. Retinoic acid binding properties of the lipocalin member beta-lactoglobulin studied by circular dichroism, electronic absorption spectroscopy and molecular modeling methods.

    PubMed

    Zsila, Ferenc; Bikádi, Zsolt; Simonyi, Miklós

    2002-12-01

    Interaction between the Vitamin A derivative all-trans retinoic acid and the lipocalin member bovine beta-lactoglobulin (BLG) was studied by circular dichroism (CD) and electronic absorption spectroscopy at different pH values. In neutral and alkaline solutions achiral retinoic acid forms a non-covalent complex with the protein as indicated by the appearance of a negative Cotton effect around 347 nm associated to the narrowed and red shifted pi-pi(*) absorption band of the ligand. The induced optical activity is attributed to the helical distortion of the conjugated chain caused by the chiral protein binding environment. As the disappearing CD activity showed in the course of CD-pH titration experiment, retinoic acid molecules dissociate from BLG upon acidification but this release is completely reversible as proved by the reconstitution of the CD and absorption spectra after setting the pH back to neutral. This unique behavior of the complex is explained by the conformational change of BLG (Tanford transition) which involves a movement of the EF loop at the entrance of the central cavity from open to closed conformation in the course of pH lowering. From these results it was inferred that retinoic acid binds within the hydrophobic calyx of the beta-barrel. PMID:12429354

  14. Study of the Effect of the Pulse Width of the Excitation Source on the Two-Photon Absorption and Two-Photon Circular Dichroism Spectra of Biaryl Derivatives.

    PubMed

    Vesga, Yuly; Hernandez, Florencio E

    2016-09-01

    Herein we report on the expanded theoretical calculations and the experimental measurements of the two-photon absorption (TPA) and two-photon circular dichroism (TPCD) spectra of a series of optically active biaryl derivatives (R-BINOL, R-VANOL, and R-VAPOL) using femtosecond pulses. The comparative analysis of the experimental TPCD spectra obtained with our tunable amplified femtosecond system with those previously measured in our group on the same series of compounds in the picosecond regime reveals a decrease in the amplitude of the signal and an improvement in matching with the theory in the former. These results can be explained based on the negligible contribution of excited state absorption (ESA) using femtosecond pulses compared to the picosecond regime. We show how ESA affects both the strength of the signal and the shape of the TPA and TPCD spectra. TPA and TPCD spectra were obtained using the double L-scan technique over a broad spectral range (450-750 nm) using 90 fs pulses at 50 Hz repetition rate produced by an amplified femtosecond system. The theoretical calculations were performed using modern analytical response theory within the time-dependent density functional theory (TD-DFT) approach using CAM-B3LYP and 6-311++G(d,p) basis sets. PMID:27525702

  15. Circular dichroism of planar chiral magnetic metamaterials.

    PubMed

    Decker, M; Klein, M W; Wegener, M; Linden, S

    2007-04-01

    We propose, fabricate, and study a double-layer chiral planar metamaterial that exhibits pronounced circular dichroism at near-infrared wavelengths. The antisymmetric oscillation modes of the two coupled layers allow local magnetic-dipole moments and enhanced polarization effects compared with similar single-layer systems where only electric-dipole moments occur. Experiment and rigorous theoretical calculations are in good agreement. PMID:17339960

  16. Local electronic states of Fe{sub 4}N films revealed by x-ray absorption spectroscopy and x-ray magnetic circular dichroism

    SciTech Connect

    Ito, Keita; Toko, Kaoru; Suemasu, Takashi; Takeda, Yukiharu; Saitoh, Yuji; Oguchi, Tamio; Kimura, Akio

    2015-05-21

    We performed x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements at Fe L{sub 2,3} and N K-edges for Fe{sub 4}N epitaxial films grown by molecular beam epitaxy. In order to clarify the element specific local electronic structure of Fe{sub 4}N, we compared experimentally obtained XAS and XMCD spectra with those simulated by a combination of a first-principles calculation and Fermi's golden rule. We revealed that the shoulders observed at Fe L{sub 2,3}-edges in the XAS and XMCD spectra were due to the electric dipole transition from the Fe 2p core-level to the hybridization state generated by σ* anti-bonding between the orbitals of N 2p at the body-centered site and Fe 3d on the face-centered (II) sites. Thus, the observed shoulders were attributed to the local electronic structure of Fe atoms at II sites. As to the N K-edge, the line shape of the obtained spectra was explained by the dipole transition from the N 1s core-level to the hybridization state formed by π* and σ* anti-bondings between the Fe 3d and N 2p orbitals. This hybridization plays an important role in featuring the electronic structures and physical properties of Fe{sub 4}N.

  17. Simulation of magnetic circular dichroism in the electron microscope

    NASA Astrophysics Data System (ADS)

    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).

  18. X-ray magnetic circular dichroism and x-ray absorption spectroscopy of novel magnetic thin films

    SciTech Connect

    Brewer, M.A.; Ju, H.L.; Krishnan, K.M.

    1997-04-01

    The optimization of the magnetic properties of materials for a wide range of applications requires a dynamic iteration between synthesis, property measurements and characterization at appropriate length scales. The authors interest arises both from the increased appreciation of the degree to which magnetic properties can be influenced by tailored microstructures and the ability to characterize them by x-ray scattering/dichroism techniques. Preliminary results of this work at the ALS on `giant` moment in {alpha}{double_prime}-Fe{sub 16}N{sub 2} and `colossal` magnetoresistance in manganite perovskites is presented here. It has recently been claimed that {alpha}{double_prime}-Fe{sub 16}N{sub 2} possesses a giant magnetization of 2.9 T ({approximately}2300 emu/cc) when grown on lattice-matched In{sub 0.2}Ga{sub 0.8}As(001) and Fe/GaAs(001). However, attempts at growth on simpler substrates have resulted in only a modest enhancement in moment and often in multiphase mixtures. Theoretical calculations based on the band structure of Fe{sub 16}N{sub 2} predict values for the magnetization around 2.3 T ({approximately}1780 emu/cc), well below Sugita`s claims, but consistent with the magnetization reported by several other workers. Using appropriate sum rules applied to the integrated MCD spectrum, they hope to determine the magnetic moment of the iron species in the {alpha}{double_prime}-Fe{sub 16}N{sub 2} films and other phases and resolve the orbital and spin contributions to the moment. There is also rapidly growing interest in the `colossal magnetoresistance` effect observed in manganese oxides for both fundamental and commercial applications. To address some of these issues the authors have measured the electron energy loss spectra (EELS) of manganese perovskites at room temperature.

  19. Vibrational absorption and vibrational circular dichroism spectra of leucine in water under different pH conditions: hydrogen-bonding interactions with water.

    PubMed

    Poopari, Mohammad Reza; Zhu, Peiyan; Dezhahang, Zahra; Xu, Yunjie

    2012-11-21

    Vibrational absorption (VA) and vibrational circular dichroism (VCD) spectroscopy have been used to study leucine, a flexible branched-chain amino acid, in aqueous solution. The VA spectra in the range of 1800-1250 cm(-1) of leucine in D(2)O under three representative pHs from strongly acidic (pH = 1), near neutral (pH = 6), to strongly basic (pH = 13), have been measured. The related VCD spectrum has been obtained under near neutral condition. Searches have been carried out to identify the most stable conformers of the Zwitterionic, protonated, and deprotonated forms of leucine in water. The geometry optimization, harmonic frequency calculations, and VA and VCD intensities have been computed at the B3LYP/6-311++G(d,p) level with the implicit polarizable continuum solvation model. While the observed VA spectra under three pHs can be well interpreted with the inclusion of the implicit solvation model, both implicit and explicit solvation models have been found to be crucial for the adequate interpretation of the complex VCD features observed. Molecular dynamics simulations and radial distribution functions have been used to aid the modeling of the leucine-(water)(N) clusters. It has been recognized that the insertion of a water molecule between the COO(-) and NH(3) (+) functional groups in the explicit solvated clusters is critical to reproduce the VCD signatures observed. Furthermore, the inclusion of the implicit bulk water environment has been found to be essential to lock water molecules, which are directly hydrogen bonded to leucine, into the positions expected in solution. The application of the explicit and implicit solvation models simultaneously allows new insights into the hydrogen bonding network surrounding leucine in aqueous solution and the role of the surrounding bulk water in stabilizing such hydrogen-bonding network. PMID:23181307

  20. Vibrational absorption and vibrational circular dichroism spectra of leucine in water under different pH conditions: Hydrogen-bonding interactions with water

    NASA Astrophysics Data System (ADS)

    Poopari, Mohammad Reza; Zhu, Peiyan; Dezhahang, Zahra; Xu, Yunjie

    2012-11-01

    Vibrational absorption (VA) and vibrational circular dichroism (VCD) spectroscopy have been used to study leucine, a flexible branched-chain amino acid, in aqueous solution. The VA spectra in the range of 1800-1250 cm-1 of leucine in D2O under three representative pHs from strongly acidic (pH = 1), near neutral (pH = 6), to strongly basic (pH = 13), have been measured. The related VCD spectrum has been obtained under near neutral condition. Searches have been carried out to identify the most stable conformers of the Zwitterionic, protonated, and deprotonated forms of leucine in water. The geometry optimization, harmonic frequency calculations, and VA and VCD intensities have been computed at the B3LYP/6-311++G(d,p) level with the implicit polarizable continuum solvation model. While the observed VA spectra under three pHs can be well interpreted with the inclusion of the implicit solvation model, both implicit and explicit solvation models have been found to be crucial for the adequate interpretation of the complex VCD features observed. Molecular dynamics simulations and radial distribution functions have been used to aid the modeling of the leucine-(water)N clusters. It has been recognized that the insertion of a water molecule between the COO- and NH3+ functional groups in the explicit solvated clusters is critical to reproduce the VCD signatures observed. Furthermore, the inclusion of the implicit bulk water environment has been found to be essential to lock water molecules, which are directly hydrogen bonded to leucine, into the positions expected in solution. The application of the explicit and implicit solvation models simultaneously allows new insights into the hydrogen bonding network surrounding leucine in aqueous solution and the role of the surrounding bulk water in stabilizing such hydrogen-bonding network.

  1. Electronic circular dichroism behavior of chiral Phthiobuzone

    PubMed Central

    Li, Li; Wang, Lin; Si, Yikang

    2014-01-01

    Phthiobuzone is a bis(thiosemicarbazone) derivative with a single chiral center which has been used as a racemate in the clinical treatment of herpes and trachoma diseases. In this study, its two enantiomers were prepared from chiral amino acids and their absolute configurations were investigated by electronic circular dichroism (ECD) combined with modern quantum-chemical calculations using time-dependent density functional theory. It was found that solvation changed both the conformational distribution and the ECD spectrum of each conformer. The theoretical ECD spectra of the two enantiomers were in good agreement with the experimentally determined spectra of the corresponding isomers in dimethyl sulfoxide. The ECD behavior of the bis(thiosemicarbazone) chromophore in a chiral environment is also discussed. Our results indicate that ECD spectroscopy may be a useful tool for the stereochemical evaluation of chiral drugs. PMID:26579380

  2. Circular dichroism study of the hemocyanin thermostability

    NASA Astrophysics Data System (ADS)

    Nikolova Georgieva, Dessislava; Stoeva, Stanka; Abid Ali, Syed; Abbasi, Atiya; Genov, Nicolay; Voelter, Wolfgang

    1998-05-01

    Circular dichroism spectroscopy is used to investigate the thermostability of six arthropod hemocyanins (Hcs), representatives of the subphyla Crustacea (infraorder Brachyura) and Chelicerate (infraorders Xiphosura and Arachnida), and three molluscan Hcs from gastropod organisms. Melting points ( Tm) are determined from the temperature dependence of ellipticity of dioxygen-binding proteins from Maia squinado, Callinectes sapidus, Carcinus maenas, Limulus polyphemus, Buthus sindicus, Androctonus australis, Megathura crenulata, Haliotis tuberculata, and Rapana thomasiana. Both, arthropod and molluscan Hcs, are thermostable proteins with melting temperatures in the region 68-91°C. Binuclear dioxygen-binding sites contribute significantly to the thermostability and increase the Tm values of the apo-forms by 3-16°C. An elevated thermostability is observed in the case of the Limulus polyphemus Hc. One of the reasons is the high degree of hemocyanin oligomerization.

  3. Circular dichroism spectroscopy of membrane proteins.

    PubMed

    Miles, A J; Wallace, B A

    2016-09-21

    Circular dichroism (CD) spectroscopy is a well-established technique for studying the secondary structures, dynamics, folding pathways, and interactions of soluble proteins, and is complementary to the high resolution but generally static structures produced by X-ray crystallography, NMR spectroscopy, and cryo electron microscopy. CD spectroscopy has special relevance for the study of membrane proteins, which are difficult to crystallise and largely ignored in structural genomics projects. However, the requirement for membrane proteins to be embedded in amphipathic environments such as membranes, lipid vesicles, detergent micelles, bicelles, oriented bilayers, or nanodiscs, in order for them to be soluble or dispersed in solution whilst maintaining their structure and function, necessitates the use of different experimental and analytical approaches than those employed for soluble proteins. This review discusses specialised methods for collecting and analysing membrane protein CD data, highlighting where protocols for soluble and membrane proteins diverge. PMID:27347568

  4. PCDDB: the protein circular dichroism data bank, a repository for circular dichroism spectral and metadata

    PubMed Central

    Whitmore, Lee; Woollett, Benjamin; Miles, Andrew John; Klose, D. P.; Janes, Robert W.; Wallace, B. A.

    2011-01-01

    The Protein Circular Dichroism Data Bank (PCDDB) is a public repository that archives and freely distributes circular dichroism (CD) and synchrotron radiation CD (SRCD) spectral data and their associated experimental metadata. All entries undergo validation and curation procedures to ensure completeness, consistency and quality of the data included. A web-based interface enables users to browse and query sample types, sample conditions, experimental parameters and provides spectra in both graphical display format and as downloadable text files. The entries are linked, when appropriate, to primary sequence (UniProt) and structural (PDB) databases, as well as to secondary databases such as the Enzyme Commission functional classification database and the CATH fold classification database, as well as to literature citations. The PCDDB is available at: http://pcddb.cryst.bbk.ac.uk. PMID:21071417

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

    PubMed Central

    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.

    2015-01-01

    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. PMID:26534992

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

    PubMed

    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. PMID:26534992

  7. Circular dichroism of bradykinin and related peptides

    PubMed Central

    Brady, A. H.; Ryan, J. W.; Stewart, J. M.

    1971-01-01

    1. The circular dichroism of bradykinin and a number of its analogues and homologues was measured over the spectral range 200–300nm. All of the biologically active peptides showed maxima at 220nm and minima at 235nm. The spectra were independent of solvent and temperature. The vibronic transitions of phenylalanyl residues in the 250–280nm range showed no evidence of intra- or inter-molecular interactions. We take this as evidence that bradykinin and its biologically active analogues and homologues exist in solution as disordered chains. 2. None of the analogues with spectra unlike bradykinin possessed biological activity. However, peptides such as retro-bradykinin, des-6-serine-bradykinin, des-1-arginine-bradykinin and des-9-arginine-bradykinin produced spectra like that of bradykinin but were devoid of biological activity. Although we could not identify spectral features that were clearly correlated with biological activity, it appears unlikely that highly ordered peptides of the same amino acid composition as bradykinin would possess bradykinin-like effects. PMID:5117026

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

    NASA Astrophysics Data System (ADS)

    Abbate, Sergio; Longhi, Giovanna; Lebon, France; Tommasini, Matteo

    2012-09-01

    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.

  9. Z-DNA: vacuum ultraviolet circular dichroism

    SciTech Connect

    Sutherland, J.C.; Griffin, K.P.; Keck, P.C.; Takacs, P.Z.

    1981-08-01

    In concentrated salt or ethanolic solutions, the self-complementary copolymer poly(dG-dC)-poly(dG-dC) forms a left-handed double-helical structure that has been termed Z-DNA. The first evidence for this structure came from changes observed in the circular dichroism (CD) spectrum between 230 and 300 nm for low- and high-salt solutions. In 3 M NaCl, the CD spectrum is approximately inverted compared to the B-form spectrum observed in low salt solution. We measured the vacuum ultraviolet CD spectrum of poly(dG-dC)-poly(dG-dC) down to 180 nm under conditions in which the 230- to 300-nm spectrum is inverted. Below 200 nm, where the B form exhibits the large positive peak at 187 nm that is characteristic of right-handed double-helical DNAs, the Z form exhibits a large negative peak at 194 nm and a positive band below 186 nm. Therefore, the Z-form vacuum ultraviolet CD spectrum resembles an inverted and red-shifted B-form spectrum. The magnitudes of the differences observed between the B and Z forms in the CD spectrum below 200 nm are about 10 times greater than those observed between 230 and 300 nm. The vacuum ultraviolet CD spectrum of poly(dG-dC)-poly(dG-dC) is 3 M C/sub 2/O/sub 4/ also is inverted compared to the B-form spectrum; however, between 230 and 300 nm, it is nonconservative with a negative maximum at 290 nm and a weak positive CD signal above 300 nm, presumably reflecting differential light scattering and indicating the existence of molecular aggregates. Our results suggest that the vacuum ultraviolet CD spectrum is sensitive to the handedness of doublehelical DNA structures.

  10. Z-DNA Vacuum ultraviolet circular dichroism

    SciTech Connect

    Sutherland, J.C.; Griffin, K.P.; Keck, P.C.; Takacs, P.Z.

    1981-08-01

    In concentrated salt or ethanolic solutions, the self-complementary copolymer poly(dG-dC).poly(dG-dC) forms a left-handed double-helical structure that has been termed ZDNA. The first evidence for this structure came from changes observed in the circular dichroism (CD) spectrum between 230 and 300 nm for low- and high-salt solutions (Pohl, F.M. and Jovin, T.M. (1972) J. Mol. Biol. 67, 675-696). In 3 M NaCl, the CD spectrum is approximately inverted compared to the B-form spectrum observed in low-salt solution. We measured the vacuum ultraviolet CD spectrum of poly(dG-dC).poly(dG-dC) down to 180 nm under conditions in which the 230 to 300 nm spectrum is inverted. Below 200 nm, where the B form exhibits the large positive peak at 187 nm that is characteristic of right-handed double-helical DNAs, the Z form exhibits a large negative peak at 194 nm and a positive band below 186 nm. Therefore, the Z-form vacuum ultraviolet CD spectrum resembles an inverted and red-shifted B-form spectrum. The magnitudes of the differences observed between the Band Z forms in the CD spectrum below 200 nm are about 10 times greater than those observed between 230 and 300 nm. The vacuum ultraviolet CD spectrum of poly(dG-dC).poly(dG-dC) in 3 M Cs/sub 2/SO/sub 4/ also is inverted compared to the B-form spectrum; however, between 230 and 300 nm, it is nonconservative with a negative maximum at 290 nm and a weak positive CD signal above 300 nm, presumably reflecting differential light scattering and indicating the existence of molecular aggregates. Our results suggest that the vacuum ultraviolet CD spectrum is sensitive to the handedness of double-helical DNA structures.

  11. Circular dichroism of chiral photonic crystal liquid layers with enclosed defect inside

    NASA Astrophysics Data System (ADS)

    Gevorgyan, Ashot; Kocharian, Armen; Vardanyan, Gagik

    2015-03-01

    The photonic crystals of artificial and self-organizing structures with spatial periodic changes in dielectric and magnetic properties have attracted considerable interest recently due to unusual physical properties and wide practical applications. The chiral periodic structure in the scale of optical wavelength gives rise to strong and characteristic circular dichroism responses at visible wavelengths. Here we investigate photonic density, circular dichroism and peculiarities of absorption and emission spectra at various eigen polarizations in multilayered one-dimensional chiral soft matter with two layers of CLCs and an isotropic defect layer inside. The circular dichroism is defined by differences in light energy absorption A=1-(R + T) by the system (R and T are the reflection and transmission coefficients, respectively) and A s , r are the light absorptions, if the incident light has left and right circular polarizations, respectively. This problem can be solved by the modified Ambartsumian's layer addition method. The influence of absorption and gain on the circular dichroism, absorption and emission spectra is established in cholesteric liquid crystal (CLC) cell with an isotropic defect layer inside.

  12. Towards AB Initio Calculation of the Circular Dichroism of Peptides

    NASA Astrophysics Data System (ADS)

    Molteni, E.; Onida, G.; Tiana, G.

    2012-08-01

    In this work we plan to use ab initio spectroscopy calculations to compute circular dichroism (CD) spectra of peptides. CD provides information on protein secondary structure content; peptides, instead, remain difficult to address, due to their tendency to adopt multiple conformations in equilibrium. Therefore peptides are an interesting test-case for ab initio calculation of CD spectra. As a first application, we focus on the (83-92) fragment of HIV-1 protease, which is known to be involved in the folding and dimerization of this protein. As a preliminary step, we performed classical molecular dynamics (MD) simulations, in order to obtain a set of representative conformers of the peptide. Then, on some of the obtained conformations, we calculated absorption spectra at the independent particle, RPA and TDLDA levels, showing the presence of charge transfer excitations, and their influence on spectral features.

  13. Absorption and Circular Dichroism Spectra of La{sub 3}Ga{sub 5}SiO{sub 14} Crystals Doped with Pr{sup 3+}, Ho{sup 3+}, and Er{sup 3+} Ions

    SciTech Connect

    Burkov, V. I.; Lysenko, O. A.; Mill, B. V.

    2010-11-15

    The absorption and circular dichroism (CD) spectra of La{sub 3}Ga{sub 5}SiO{sub 14} langasite crystals doped with Pr{sup 3+}, Ho{sup 3+}, and Er{sup 3+} ions have been studied in the wavelength range of 350-700 nm. The electronic transitions of these ions, which replace La3+ ions in the 3e position with the symmetry 2, are observed in the spectra. All transitions are active in both the absorption and CD spectra. The dipole strengths D{sub om}, rotational strengths R{sub om}, and anisotropy factors g have been calculated for well-resolved bands. Some features are noted for the spectra that were obtained, and their relationship with the structure disorder is considered.

  14. Magnetic x-ray circular dichroism in Fe Co Pt multilayers

    SciTech Connect

    Tobin, J.G.; Jankowski, A.F.; Waddill, G.D.; Sterne, P.A.

    1994-04-01

    Magnetic x-ray circular dichroism in x-ray absorption has been used to investigate the ternary multilayer system, Fe Co Pt. Samples were prepared by planar magnetron sputter deposition and carefully characterized, using a variety of techniques such as grazing-incidence and high-angle x-ray scattering, Auger depth profiling and cross-section transmission electron microscopy. As previously reported, the Fe9.5{Angstrom} Pt9.5{Angstrom} exhibits a large dichroism in the Fe 2p absorption. Interestingly while the Co9.5{Angstrom} Pt9.5{Angstrom} has no measurable dichroism, the Fe4.7{Angstrom} Co4.7{Angstrom} Pt9.5{Angstrom} sample has a dichroism at both the Fe 2p and Co 2p absorption edges. These and other results are compared to slab calculation predictions. Possible explanations are discussed.

  15. Chiral plasmonic DNA nanostructures with switchable circular dichroism

    NASA Astrophysics Data System (ADS)

    Schreiber, Robert; Luong, Ngoc; Fan, Zhiyuan; Kuzyk, Anton; Nickels, Philipp C.; Zhang, Tao; Smith, David M.; Yurke, Bernard; Kuang, Wan; Govorov, Alexander O.; Liedl, Tim

    2013-12-01

    Circular dichroism spectra of naturally occurring molecules and also of synthetic chiral arrangements of plasmonic particles often exhibit characteristic bisignate shapes. Such spectra consist of peaks next to dips (or vice versa) and result from the superposition of signals originating from many individual chiral objects oriented randomly in solution. Here we show that by first aligning and then toggling the orientation of DNA-origami-scaffolded nanoparticle helices attached to a substrate, we are able to reversibly switch the optical response between two distinct circular dichroism spectra corresponding to either perpendicular or parallel helix orientation with respect to the light beam. The observed directional circular dichroism of our switchable plasmonic material is in good agreement with predictions based on dipole approximation theory. Such dynamic metamaterials introduce functionality into soft matter-based optical devices and may enable novel data storage schemes or signal modulators.

  16. The protein circular dichroism data bank, a Web-based site for access to circular dichroism spectroscopic data.

    PubMed

    Whitmore, Lee; Woollett, Benjamin; Miles, Andrew J; Janes, Robert W; Wallace, B A

    2010-10-13

    The Protein Circular Dichroism Data Bank (PCDDB) is a newly released resource for structural biology. It is a web-accessible (http://pcddb.cryst.bbk.ac.uk) data bank for circular dichroism (CD) and synchrotron radiation circular dichroism (SRCD) spectra and their associated experimental and secondary metadata, with links to protein sequence and structure data banks. It is designed to provide a public repository for CD spectroscopic data on macromolecules, to parallel the Protein Data Bank (PDB) for crystallographic, electron microscopic, and nuclear magnetic resonance spectroscopic data. Similarly to the PDB, it includes validation checking procedures to ensure good practice and the integrity of the deposited data. This paper reports on the first public release of the PCDDB, which provides access to spectral data that comprise standard reference datasets. PMID:20947015

  17. Circular Dichroism Method for Heat Capacity Determination of Proteins

    ERIC Educational Resources Information Center

    Jones, Cecil L.; Bailey, Chris; Bheemarti, Kiran Kumar

    2006-01-01

    Circular dichroism spectroscopy was used to measure the thermal unfolding of bovine pancreatic ribonuclease A (RNase A) with various concentrations of guanidine hydrochloride (GuHCl). A red shift in transition midpoint temperatures, T[subscript m], occurred with increasing concentration of the strong protein denaturant. van Hoff enthalpy changes,…

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

    SciTech Connect

    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.

  19. Circular dichroism in the electron microscope: Progress and applications (invited)

    SciTech Connect

    Schattschneider, P.; Loeffler, S.; Ennen, I.; Stoeger-Pollach, M.; Verbeeck, J.

    2010-05-15

    According to theory, x-ray magnetic circular dichroism in a synchrotron is equivalent to energy loss magnetic chiral dichroism (EMCD) in a transmission electron microscope (TEM). After a synopsis of the development of EMCD, the theoretical background is reviewed and recent results are presented, focusing on the study of magnetic nanoparticles for ferrofluids and Heusler alloys for spintronic devices. Simulated maps of the dichroic strength as a function of atom position in the crystal allow evaluating the influence of specimen thickness and sample tilt on the experimental EMCD signal. Finally, the possibility of direct observation of chiral electronic transitions with atomic resolution in a TEM is discussed.

  20. Heparin-induced circular dichroism of an achiral, bicyclic species.

    PubMed

    Stanley, Floyd E; Warner, Andrew M; McWilliams, Kayla M; Stalcup, Apryll M

    2011-01-01

    Antimalarial drugs have shown potential in suppressing the role of glycosaminoglycans (GAGs) in the pathology of prion protein conformational disorders (e.g. "Mad Cow" disease) by competing for sites of electrostatic interaction. In this study, circular dichroism (CD) and UV/Visible (UV/Vis) absorption spectroscopy techniques were used to investigate the interactions between N-methyl-N'-(7-chloro-4-quinolyl)-1,3-diaminopropane (QD), an achiral, bicyclic compound similar to previously investigated antimalarial drugs, and heparin, a complex GAG that is frequently used as a clinical anticoagulant. Relatively intense heparin-induced CD features were observed for QD and were noted to be radically different from previous studies using related chiral drugs, underscoring the importance of the Pfieffer effect on this and similar heparin research. Additionally, the induced CD for QD was observed to be highly dependent upon drug concentration, heparin concentration, system pH, equilibration time, and ionic strength. These results, in connection with recent work, provide new insight into the nature of the association between GAGs and antimalarial species. PMID:21125690

  1. Photoemission and magnetic circular dichroism studies of magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    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.

  2. Stereochemical Study of Sphingosine by Vibrational Circular Dichroism.

    PubMed

    Nakahashi, Atsufumi; C Siddegowda, Ananda Kumar; Hammam, Mostafa A S; Gowda, Siddabasave Gowda B; Murai, Yuta; Monde, Kenji

    2016-05-20

    Vibrational circular dichroism (VCD) was first applied to the stereochemical analysis of sphingosine. VCD patterns derived from the C═C stretch as well as other mid-infrared (IR) regions were practical markers to discriminate all the stereoisomers of intact sphingosine. Glutaraldehyde was found as an excellent derivatizing reagent for sphingosine which improves its solubility in VCD-friendly nonpolar solvents such as chloroform and enhances the VCD intensities by forming a rigid cyclized structure. PMID:27135615

  3. Theoretical analysis of X-ray magnetic circular dichroism at the Yb L2, 3 absorption edges of YbInCu4 in high magnetic fields around the field-induced valence transition

    NASA Astrophysics Data System (ADS)

    Kotani, A.

    2012-01-01

    High-magnetic-field X-ray absorption spectra (XAS) and its X-ray magnetic circular dichroism (XMCD) at the Yb L2, 3 edges of YbInCu4 are calculated around the field-induced valence transition at about 30 T. The calculations are made by using a new theoretical framework with an extended single impurity Anderson model (SIAM) developed recently by the present author. Two parameters in SIAM, the 4 f level and the hybridization strength, are taken as different values in low- and high-magnetic-field phases of the field-induced valence transition. The calculated results are compared with recent experimental data measured by Matsuda et al. by utilizing a miniature pulsed magnet up to 40 T. The field-dependence of the calculated XMCD spectra is explained in detail on the basis of the field-dependence of the Yb 4 f wavefunctions in the ground state. Some possibilities are discussed on the negative XMCD signal observed experimentally at the L2 edge.

  4. Circular Dichroism in the Photoionization of Nanoparticles from Chiral Compounds

    SciTech Connect

    Paul, J.; Doerzbach, A.; Siegmann, K.

    1997-10-01

    The dichroism in photoemission from chiral molecules is observed for the first time. Particles consisting of chiral molecules are suspended in air and irradiated alternately with right and left circularly polarized uv light. We found a polarization dependence in the total photoelectric current. The asymmetries observed are of the order of 10{sup {minus}2} to 10{sup {minus}3} , as expected from perturbation theory, and reverse their sign when the handedness of the molecules is changed. {copyright} {ital 1997} {ital The American Physical Society}

  5. Magnetic circular dichroism study of DABCO in solution

    NASA Astrophysics Data System (ADS)

    Lin, C. T.; Mason, W. R.

    1986-12-01

    Two spectral features are observed for the magnetic circular dichroism (MCD) spectra of 1,4-diazabicyclo-[2.2.2]-octane (DABCO) in solution. First an intense positive A term is revealed in the range of 250-200 nm which provides an unambiguous assignment for a degenerate 1E' state. The energy at which Δɛ M = 0 is found to be sensitive to the solvent used. Second, a negative MCD feature with a minimum at 255.4 nm is observed for DABCO in ethanol, suggesting a 1A 2 state assignment.

  6. Plasmonic nanohelix metamaterials with tailorable giant circular dichroism

    NASA Astrophysics Data System (ADS)

    Gibbs, J. G.; Mark, A. G.; Eslami, S.; Fischer, P.

    2013-11-01

    Plasmonic nanohelix arrays are shown to interact with electromagnetic fields in ways not typically seen with ordinary matter. Chiral metamaterials (CMMs) with feature sizes small with respect to the wavelength of visible light are a promising route to experimentally achieve such phenomena as negative refraction without the need for simultaneously negative ɛ and μ. Here we not only show that giant circular dichroism in the visible is achievable with hexagonally arranged plasmonic nanohelix arrays, but that we can precisely tune the optical activity via morphology and lattice spacing. The discrete dipole approximation is implemented to support experimental data.

  7. Magnetic circular dichroism in the hard X-ray range

    NASA Astrophysics Data System (ADS)

    Rogalev, A.; Wilhelm, F.

    2015-12-01

    An overview of X-ray magnetic circular dichroism (XMCD) spectroscopy in the hard X-ray range is presented. A short historical overview shows how this technique has evolved from the early days of X-ray physics to become a workhorse technique in the modern magnetism research As with all X-ray spectroscopies, XMCD has the advantage of being element specific. Interpretation of the spectra based on magneto-optical sum rules can provide unique information about spin and orbital moment carried by absorbing atom in both amplitude and direction, can infer magnetic interactions from element selective magnetization curves, can allow separation of magnetic and non-magnetic components in heterogeneous systems. The review details the technology currently available for XMCD measurements in the hard X-ray range referring to the ESRF beamline ID12 as an example. The strengths of hard X-ray magnetic circular dichroism technique are illustrated with a wide variety of representative examples, such as actinide based ferromagnets, paramagnetism in metals, pure metallic nanoparticles, exchange spring magnets, half metallic ferromagnets, magnetism at interfaces, and dilute magnetic semiconductors. In this way, we aim to encourage researchers from various scientific communities to consider XMCD as a tool to understanding the electronic and magnetic properties of their samples.

  8. Optical circular dichroism of vacuum-deposited film stacks

    NASA Astrophysics Data System (ADS)

    Fan, B.; Vithana, H. K. M.; Kralik, J. C.; Faris, S. M.

    1998-02-01

    We report on optical circular dichroism of chiral multilayer SiO x films obtained by a novel vacuum deposition technique. The film layers were deposited at an oblique incidence angle to render them optically anisotropic, and were stacked such that the optic axes of the layers spiral in a helical fashion about the substrate normal. The resulting film stacks display both wavelength and polarization selectivity, in analogy with organic cholesteric liquid crystals aligned in the planar texture. Reflectance spectra of two films of opposite chirality are presented. Both film stacks are tuned to reflect in the visible and were prepared using obliquely deposited SiO x. Calculated spectra using a Berreman's 4×4 matrix approach agree well with the experimental findings. It is concluded that vacuum-deposited chiral film stacks hold promise for use as high-efficiency polarizers and other novel optical components.

  9. Supramolecular Chemistry: Induced Circular Dichroism to Study Host-Guest Geometry

    ERIC Educational Resources Information Center

    Mendicuti, Francisco; Gonzalez-Alvarez, Maria Jose

    2010-01-01

    In this laboratory experiment, students obtain information about the structure of a host-guest complex from the interpretation of circular dichroism measurements. The value and sign of the induced circular dichroism (ICD) on an achiral chromophore guest when it complexes with a cyclodextrin can be related to the guest penetration and its…

  10. Instrument for x-ray magnetic circular dichroism measurements at high pressures

    SciTech Connect

    Haskel, D.; Tseng, Y. C.; Lang, J. C.; Sinogeikin, S.

    2007-08-15

    An instrument has been developed for x-ray magnetic circular dichroism (XMCD) measurements at high pressures and low temperatures. This instrument couples a nonmagnetic copper-beryllium diamond anvil cell featuring perforated diamonds with a helium flow cryostat and an electromagnet. The applied pressure can be controlled in situ using a gas membrane and calibrated using Cu K-edge x-ray absorption fine structure measurements. The performance of this instrument was tested by measuring the XMCD spectra of the Gd{sub 5}Si{sub 2}Ge{sub 2} giant magnetocaloric material.

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

    NASA Astrophysics Data System (ADS)

    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 .

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

    SciTech Connect

    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 {phi} 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 {phi} and the helicity of the circularly polarized laser light. For intensities above 5x10{sup 12} W/cm{sup 2} our model predicts a noticeable circular dichroism in the capture probability for slow proton-hydrogen collisions, which persists after averaging over {phi}. 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 {phi}.

  13. Electronic circular dichroism of fluorescent proteins: a computational study.

    PubMed

    Pikulska, Anna; Steindal, Arnfinn Hykkerud; Beerepoot, Maarten T P; Pecul, Magdalena

    2015-02-26

    The electronic circular dichroism (ECD) properties of the green fluorescent protein and other fluorescent proteins have been calculated with density functional theory. The influence of different embedding models on the ECD signal of the chromophore has been investigated by modeling the protein environment by the polarizable continuum model (QM/PCM), by the polarizable embedding model (PE-QM/MM), by treating the minimal environment quantum mechanically at the same footing as the chromophore (QM/QM), and by adding the remaining part of the protein by means of PCM (QM/QM/PCM). The rotatory strength is found to be more sensitive than the oscillatory strength to changes in the geometry of the chromophore and its surroundings and to the type of embedding model used. In general, explicit embedding of the surrounding protein (PE-QM/MM or QM/QM) induces an increase in the rotatory strength of the chromophore. Explicit inclusion of the whole protein through polarizable embedding is found to be an affordable embedding model that gives the correct sign of the rotatory strength for all fluorescent proteins. PCM is useful as a first approximation to protein environment effects, but as a rule seems to underestimate the rotatory strength. PMID:25646666

  14. Optical activity and circular dichroism of plasmonic nanorod assemblies

    NASA Astrophysics Data System (ADS)

    Khosravi Khorashad, Larousse; Liu, Na; Govorov, Alexander O.

    Plasmonic circular dichroism (CD) has offered an efficient spectroscopy method for the electronic, chemical, and structural properties of different types of light active molecules in the subwavelength regime. Among the different chiral geometries of metal nanoparticles utilized by the plasmonic CD spectroscopy, gold nanorods (AuNRs) have shown strong CD signals in the visible frequency range. In this work, we theoretically study the CD signals of AuNR arrangements in order to mimic structures and chemical bonds of chiral biomolecules. In particular, our twisted three-AuNR geometries resemble a molecular structure of tartaric acid. This molecule played an important role in the discovery of chemical chirality. In our study, we show that the strength of CD signals changes dramatically by tuning the interparticle distances and angles. Since the CD signals are typically weak, we develop reliable computational approaches to calculate the plasmonic CD. Manipulating interparticle distances, size, and molecular bond angles result in full control over peak positions, handedness, and positive and negative bands which are observed in the CD spectra. This work has been supported under the grant from Volkswagen Foundation. We also acknowledge the financial support of Condensed Matter and Surface Science program of Ohio University.

  15. Surface plasmon resonance prism coupler for enhanced circular dichroism sensing.

    PubMed

    Phan, Quoc-Hung; Lo, Yu-Lung; Huang, Chih-Ling

    2016-06-13

    A novel method for enhanced circular dichroism (CD) detection is proposed based on a surface plasmon resonance (SPR) prism coupler and a polarization scanning ellipsometry technique. An analytical model is derived to extract the CD and degree of polarization (DOP) properties of optical samples with and without scattering effects, respectively. The validity of the analytical model is confirmed by means of numerical simulations. The simulation results show that the proposed detection method has a sensitivity of 10-5~10-6 RIU (refractive index unit) for refractive indices in the range of 1.32~1.36 and 1.3100~1.3118. The practical feasibility of the proposed method is demonstrated by the experimental results for the sensitivity of the CD with the chlorophyllin samples with/without scattering effect. It is shown that for both types of sample, the extracted CD value increases linearly with the chlorophyll concentration over the considered range. In general, the results obtained in this study show that the measured CD response is highly sensitive to the polarization scanning angle. Consequently, the potential of polarization scanning ellipsometry for high-resolution CD detection is confirmed. PMID:27410300

  16. Circular dichroism study of the carbohydrate-modified opioid peptides

    NASA Astrophysics Data System (ADS)

    Horvat, Štefica; Otvos, Laszlo; Urge, Laszlo; Horvat, Jaroslav; Čudić, Mare; Varga-Defterdarović, Lidija

    1999-09-01

    The conformational preferences of enkephalins and the related glycoconjugates in which free or protected carbohydrate moieties were linked to the opioid peptides through an ether, ester or amide bond were investigated by circular dichroism spectroscopy in water, trifluoroethanol and water-trifluoroethanol mixtures. The analysis of the spectra revealed that the conformation of the enkephalin molecule is very sensitive to slight changes in the peptide structure around the C-terminal region. It was found that the type II β-turn structures are populated in N-terminal tetrapeptide enkephalin fragment, while leucine-enkephalin amide feature a type I (III) β-turn structure in solution. Incorporation of the sugar moiety into opioid peptide compound did not significantly influence the overall conformation of the peptide backbone, although minor intensity changes may reflect shifts in the population of the different turn systems. These small structural alterations can be responsible for the receptor-subtype selectivity of the various carbohydrate-modified enkephalin analogs.

  17. X-ray magnetic circular dichroism imaging with hard X-rays.

    PubMed

    Sato, K; Ueji, Y; Okitsu, K; Matsushita, T; Amemiya, Y

    2001-05-01

    X-ray polarization-contrast images resulting from X-ray magnetic circular dichroism (XMCD) in the hard X-ray region have been successfully recorded for the first time. The apparatus used consisted of an X-ray polarizer, double X-ray phase retarders, and a high-spatial-resolution X-ray charge-coupled-device detector. The sample used was a hexagonal-close-packed cobalt polycrystal foil having a thickness of about 4 microns. The X-ray polarization-contrast image resulting from XMCD was observed at a photon energy of 10 eV above the cobalt K-absorption edge (7709 eV). The observed contrast in the image was reversed by inversion of the magnetic field. Furthermore, the contrast was reversed again at a photon energy of 32 eV above the cobalt K-absorption edge. PMID:11486407

  18. Experimental demonstration of the microscopic origin of circular dichroism in two-dimensional metamaterials

    PubMed Central

    Khanikaev, A. B.; Arju, N.; Fan, Z.; Purtseladze, D.; Lu, F.; Lee, J.; Sarriugarte, P.; Schnell, M.; Hillenbrand, R.; Belkin, M. A.; Shvets, G.

    2016-01-01

    Optical activity and circular dichroism are fascinating physical phenomena originating from the interaction of light with chiral molecules or other nano objects lacking mirror symmetries in three-dimensional (3D) space. While chiral optical properties are weak in most of naturally occurring materials, they can be engineered and significantly enhanced in synthetic optical media known as chiral metamaterials, where the spatial symmetry of their building blocks is broken on a nanoscale. Although originally discovered in 3D structures, circular dichroism can also emerge in a two-dimensional (2D) metasurface. The origin of the resulting circular dichroism is rather subtle, and is related to non-radiative (Ohmic) dissipation of the constituent metamolecules. Because such dissipation occurs on a nanoscale, this effect has never been experimentally probed and visualized. Using a suite of recently developed nanoscale-measurement tools, we establish that the circular dichroism in a nanostructured metasurface occurs due to handedness-dependent Ohmic heating. PMID:27329108

  19. Experimental demonstration of the microscopic origin of circular dichroism in two-dimensional metamaterials.

    PubMed

    Khanikaev, A B; Arju, N; Fan, Z; Purtseladze, D; Lu, F; Lee, J; Sarriugarte, P; Schnell, M; Hillenbrand, R; Belkin, M A; Shvets, G

    2016-01-01

    Optical activity and circular dichroism are fascinating physical phenomena originating from the interaction of light with chiral molecules or other nano objects lacking mirror symmetries in three-dimensional (3D) space. While chiral optical properties are weak in most of naturally occurring materials, they can be engineered and significantly enhanced in synthetic optical media known as chiral metamaterials, where the spatial symmetry of their building blocks is broken on a nanoscale. Although originally discovered in 3D structures, circular dichroism can also emerge in a two-dimensional (2D) metasurface. The origin of the resulting circular dichroism is rather subtle, and is related to non-radiative (Ohmic) dissipation of the constituent metamolecules. Because such dissipation occurs on a nanoscale, this effect has never been experimentally probed and visualized. Using a suite of recently developed nanoscale-measurement tools, we establish that the circular dichroism in a nanostructured metasurface occurs due to handedness-dependent Ohmic heating. PMID:27329108

  20. Irreversible Denaturation of Maltodextrin Glucosidase Studied by Differential Scanning Calorimetry, Circular Dichroism, and Turbidity Measurements

    PubMed Central

    Goyal, Megha; Chaudhuri, Tapan K.; Kuwajima, Kunihiro

    2014-01-01

    Thermal denaturation of Escherichia coli maltodextrin glucosidase was studied by differential scanning calorimetry, circular dichroism (230 nm), and UV-absorption measurements (340 nm), which were respectively used to monitor heat absorption, conformational unfolding, and the production of solution turbidity. The denaturation was irreversible, and the thermal transition recorded at scan rates of 0.5–1.5 K/min was significantly scan-rate dependent, indicating that the thermal denaturation was kinetically controlled. The absence of a protein-concentration effect on the thermal transition indicated that the denaturation was rate-limited by a mono-molecular process. From the analysis of the calorimetric thermograms, a one-step irreversible model well represented the thermal denaturation of the protein. The calorimetrically observed thermal transitions showed excellent coincidence with the turbidity transitions monitored by UV-absorption as well as with the unfolding transitions monitored by circular dichroism. The thermal denaturation of the protein was thus rate-limited by conformational unfolding, which was followed by a rapid irreversible formation of aggregates that produced the solution turbidity. It is thus important to note that the absence of the protein-concentration effect on the irreversible thermal denaturation does not necessarily means the absence of protein aggregation itself. The turbidity measurements together with differential scanning calorimetry in the irreversible thermal denaturation of the protein provided a very effective approach for understanding the mechanisms of the irreversible denaturation. The Arrhenius-equation parameters obtained from analysis of the thermal denaturation were compared with those of other proteins that have been reported to show the one-step irreversible thermal denaturation. Maltodextrin glucosidase had sufficiently high kinetic stability with a half-life of 68 days at a physiological temperature (37°C). PMID

  1. Picosecond circular dichroism spectroscopy: experiment, theory, and applications to protein dynamics

    NASA Astrophysics Data System (ADS)

    Xie, Sunney; Simon, John D.

    1990-05-01

    An experimental technique for measuring time dependent circular dichroism signals with picosecond resolution is described. The details of the experimental apparatus are presented. Theoretical modeling of the detected signal demonstrates that the circular dichroism signal can be isolated from contributions due to pump-induced linear dichroism and linear birefringence effects. The experimental apparatus is used to examine the comformation relaxation in myoglobin following the photoelimination of CO from carbonmonoxymyoglobin. Probing the circular dichroism of the N-band of the herne at 355 nm reveals a relaxation of several hundreds of picosecond, over two orders of magnitude slower than the photo-induced bond cleavage. These results are discussed in terms of the restructuring of the protein following photodissociation.

  2. Characterization of the Cu(Π) and Zn(Π) binding to the Amyloid-β short peptides by both the Extended X-ray Absorption Fine Structure and the Synchrotron Radiation Circular Dichroism spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, Zhiyin; Sun, Shuaishuai; Xu, Jianhua; Zhang, Jing; Huang, Yan; Zhang, Bingbing; Tao, Ye

    2013-04-01

    Alzheimer's disease (AD) is a progressive and devastating neurodegenerative pathology, clinically characterized by dementia, cognitive impairment, personality disorders and memory loss. It is generally accepted that, misfolding of Aβ peptides is the key element in pathogenesis and the secondary structure of Aβ can be changed to major β-strand with reasons unknown yet. Many studies have shown that the misfolding may be linked with some biometals, mainly copper and zinc ions. To characterize interactions of Aβ and metal ions, we utilized both the extended X-ray fine structure spectroscopy (EXAFS) and the synchrotron radiation circular dichroism spectroscopy (SRCD). Aβ (13-22), Aβ (13-21), Aβ (E22G) and Aβ(HH-AA) were selected to study the mechanism of copper and zinc binding to Aβ. We found that Cu interaction with H13 and H14 residues led to the disappearance of the PPΠ, while the Cu binding E22 residue caused a remarkable conformation change to β-sheet enrichment. The Zn ion, in contrast, made little effect on the conformation and it coordinated to only one histidine (H residue) or not.

  3. Vibrational circular dichroism of tetraphenylporphyrin in peptide complexes? A computational study.

    PubMed

    Bour, P; Záruba, K; Urbanová, M; Setnicka, V; Matejka, P; Fiedler, Z; Král, V; Volka, K

    2000-05-01

    The Raman and absorption spectra of tetraphenylporphyrin (TPP) were calculated and compared to experiment. The computation was based on the harmonic molecular force field and electric tensors obtained ab initio at the BPW91/6-31G* level. Good agreement was found between experimental and calculated frequencies and intensities. In order to estimate whether induced optical activity in chiral complexes interferes with the signal of peptide vibrations, the vibrational circular dichroism (VCD) spectra of TPP were simulated. The magnetic field perturbation theory (MFP) and the gauge-invariant atomic orbitals (GIAO) were used for the simulation. Such spectra were compared to theoretical VCD intensities of a model tripeptide as well to experimental spectra of a complex of the peptide and tetrakis(p-sulfonatophenyl)porphyrin (TSPP). No significant contribution to VCD signal from the TPP residue was found in experimental spectra. Thus, possible peptide conformational changes occurring during the complexation can be monitored directly in the amide I frequency region. PMID:10790189

  4. Facility for combined in situ magnetron sputtering and soft x-ray magnetic circular dichroism

    SciTech Connect

    Telling, N. D.; Laan, G. van der; Georgieva, M. T.; Farley, N. R. S.

    2006-07-15

    An ultrahigh vacuum chamber that enables the in situ growth of thin films and multilayers by magnetron sputtering techniques is described. Following film preparation, x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements are performed by utilizing an in vacuum electromagnet. XMCD measurements on sputtered thin films of Fe and Co yield spin and orbital moments that are consistent with those obtained previously on films measured in transmission geometry and grown in situ by evaporation methods. Thin films of FeN prepared by reactive sputtering are also examined and reveal an apparent enhancement in the orbital moment for low N content samples. The advantages of producing samples for in situ XAS and XMCD studies by magnetron sputtering are discussed.

  5. Enantioselective femtosecond laser photoionization spectrometry of limonene using photoelectron circular dichroism.

    PubMed

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

    2015-04-14

    Limonene is ionized by circularly polarized 420 nm femtosecond laser pulses. Ion mass and photoelectron energy spectra identify the dominant (2 + 1) multiphoton ionization mechanism, aided by TDDFT calculations of the Rydberg excitations. Photoelectron circular dichroism measurements on pure enantiomers reveal a chiral asymmetry of ±4 %. PMID:25744283

  6. Interaction of chlorophyll with light: Calculations of absorption spectra and dichroism with a new technique

    NASA Astrophysics Data System (ADS)

    Hamilton, Robert Bryan

    1999-12-01

    The response of a single chlorophyll molecule to light was studied using a semiempirical tight-binding model together with the Peierls substitution. Over a range of wavelengths, the absorption was calculated for unpolarized, linearly polarized, and circularly polarized light. The results are consistent with previous experiments, although detailed comparisons are not possible because the experiments involve chlorophyll molecules in more complicated environments. For unpolarized light, the absorption peaks in the red part of the visible spectrum. There is a secondary shoulder in the blue. For linearly polarized light, the absorption depends on wavelength and the direction of polarization. This can be understood as arising from the joint density of states for transitions at each photon energy, together with matrix-element effects (both of which are included in the present formulation). For circular polarization, the dichroism as a function of wavelength is slightly more subtle, but again can be understood in terms of matrix elements for the states involved in a transition at a given photon energy. We also found that an ``effective helicity'' is useful in understanding the circular dichroism. One advantage of the method used here is that it can be employed for other molecules that are important in photobiology-for example, retinal and melanin.

  7. Four-wave mixing using polarization grating induced thermal grating in liquids exhibiting circular dichroism

    SciTech Connect

    Nunes, J.A.; Tong, W.G.; Chandler, D.W.; Rahn, L.A.

    1995-04-01

    A novel four-wave mixing technique for the detection of circular dichroism in optically active liquid samples is demonstrated. When two cross-polarized laser beams are crossed at a small angle in a circular dichroic liquid a weak thermal grating is produced with a phase depending on the sign of the circular dichroism. The authors show that the polarization of one of the beams can be modified to allow coherent interference with an intensity-grating induced thermal grating. A probe beam scattering from the composite grating results in a signal that reveals the sign and magnitude of the circular dichroism. The use of this technique to optimize the signal-to-noise ratio in the presence of scattered light and laser intensity noise is discussed.

  8. Time Resolved X-ray Magnetic Circular Dichroism at the Linac Coherent Light Source

    NASA Astrophysics Data System (ADS)

    Schlotter, W.; Higley, D.; Jal, E.; Dakovski, G.; Yuan, E.; MacArthur, J.; Lutman, A.; Hirsch, K.; Granitzka, P.; Chen, Z.; Coslovich, G.; Hoffman, M.; Mitra, A.; Reid, A.; Hart, P.; Nuhn, H.-D.; Duerr, H.; Arenholz, E.; Shafer, P.; Dennes, P.; Joseph, J.; Guyader, L.; Tsukamoto, A.

    We demonstrate ultrafast time resolved X-ray Magnetic Circular Dichroism on optically switchable GdFeCo thin film samples. This method extends the element specificity of time resolved x-ray absorption spectroscopy to characterize the evolution of electron spin and orbital angular momenta. These measurements were enabled by a recent upgrade at the Linac Coherent Light Source (LCLS) to generate circularly polarized x-rays. Additionally these measurements were enhanced by new detection systems that benefit all x-ray absorption spectroscopy experiments performed in transmission. Consequently static XMCD data are in excellent agreement with similar measurements at synchrotron light sources. The LCLS is an x-ray free electron laser user facility accessible via a peer-reviewed proposal process. Acknowledgement: The Linac Coherent Light Source (LCLS), SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515.

  9. Analysis of conjugation of chloramphenicol and hemoglobin by fluorescence, circular dichroism and molecular modeling

    NASA Astrophysics Data System (ADS)

    Ding, Fei; Liu, Wei; Sun, Ye; Yang, Xin-Ling; Sun, Ying; Zhang, Li

    2012-01-01

    Chloramphenicol is a low cost, broad spectrum, highly active antibiotic, and widely used in the treatment of serious infections, including typhoid fever and other life-threatening infections of the central nervous system and respiratory tract. The purpose of the present study was to examine the conjugation of chloramphenicol with hemoglobin (Hb) and compared with albumin at molecular level, utilizing fluorescence, UV/vis absorption, circular dichroism (CD) as well as molecular modeling. Fluorescence data indicate that drug bind Hb generate quenching via static mechanism, this corroborates UV/vis absorption measurements that the ground state complex formation with an affinity of 10 4 M -1, and the driving forces in the Hb-drug complex are hydrophilic interactions and hydrogen bonds, as derived from computational model. The accurate binding site of drug has been identified from the analysis of fluorescence and molecular modeling, α1β2 interface of Hb was assigned to possess high-affinity for drug, which located at the β-37 Trp nearby. The structural investigation of the complexed Hb by synchronous fluorescence, UV/vis absorption, and CD observations revealed some degree of Hb structure unfolding upon complexation. Based on molecular modeling, we can draw the conclusion that the binding affinity of drug with albumin is superior, compared with Hb. These phenomena can provide salient information on the absorption, distribution, pharmacology, and toxicity of chloramphenicol and other drugs which have analogous configuration with chloramphenicol.

  10. Vibronic Coupling Explains the Different Shape of Electronic Circular Dichroism and of Circularly Polarized Luminescence Spectra of Hexahelicenes.

    PubMed

    Liu, Yanli; Cerezo, Javier; Mazzeo, Giuseppe; Lin, Na; Zhao, Xian; Longhi, Giovanna; Abbate, Sergio; Santoro, Fabrizio

    2016-06-14

    We present the simulation of the absorption (ABS), electronic circular dichroism (ECD), emission (EMI), and circularly polarized luminescence (CPL) spectra for the weak electronic transition between the ground (S0) and the lowest excited state (S1) of hexahelicene, 2-methylhexahelicene, 2-bromohexahelicene, and 5-azahexahelicene. Vibronic contributions have been computed at zero Kelvin and at room temperature in harmonic approximation including Duschinsky effects and accounting for both Franck-Condon and Herzberg-Teller contributions. Our results nicely capture the effects of the different substituents on the experimental spectra. They also show that HT effects dominate the shape of ECD and CPL spectra where they even induce changes of signs; HT effects are also relevant in ABS and EMI, tuning the relative intensities of the different vibronic bands. HT effects are the main reason for the differences in the line shapes of ABS and ECD and of EMI and CPL spectra and for the mirror-symmetry breaking between ABS and EMI and between ECD and CPL spectra. In order to check the robustness of our results, given also that few examples of calculations of vibronic CPL spectra exist, we adopted both adiabatic and vertical approaches to define the model potential energy surfaces of the (S0) and the (S1) states; moreover we expanded the electric and magnetic dipole transition moments around both the S0 and S1 equilibrium geometries. PMID:27120334

  11. Communication: Broadband and ultrasensitive femtosecond time-resolved circular dichroism spectroscopy.

    PubMed

    Hiramatsu, Kotaro; Nagata, Takashi

    2015-09-28

    We report the development of broadband and sensitive time-resolved circular dichroism (TRCD) spectroscopy by exploiting optical heterodyne detection. Using this method, transient CD signals of submillidegree level can be detected over the spectral range of 415-730 nm. We also demonstrate that the broadband measurement with the aid of singular value decomposition enables the discrimination of genuine TRCD signals from artificial optical-anisotropy, such as linear birefringence and linear dichroism, induced by photoexcitation. PMID:26428989

  12. Recent Theoretical and Experimental Advances in the Electronic Circular Dichroisms of Planar Chiral Cyclophanes

    NASA Astrophysics Data System (ADS)

    Mori, Tadashi; Inoue, Yoshihisa

    The chiroptical properties, such as electronic and vibrational circular dichroism and optical rotation, of planar chiral cyclophanes have attracted much attention in recent years. Although the chemistry of cyclophanes has been extensively explored for more than 60 years, the studies on chiral cyclophanes are rather limited. Experimentally, the use of chiral stationary phases in HPLC becomes more popular and facilitates the enantiomer separation of chiral cyclophanes of interest. Almost all chiral cyclophanes can be readily separated, in analytical and preparative scales, most typically on a Daicel OD type column, which is based on cellulose tris(3,5-dimethylphenylcarbamate). The CD spectra of chiral cyclophanes are unique in their fairly large, significantly coupled Cotton effects observed in all the 1 B b, 1 L a, and 1 L b band regions. Theoretically, the time-dependent density functional theory, or TD-DFT, method becomes a cost-efficient, yet accurate, theoretical method to reproduce the electronic circular dichroisms and the absorption spectra of a variety of cyclophanes. The direct comparison of the experimental CD spectra with the theoretical ones readily leads to the unambiguous assignment of the absolute configuration of cyclophanes. In addition, the analysis of configuration interaction and molecular orbitals allows detailed interpretation of the electronic transitions and Cotton effects in the UV and CD spectra. Through the study of the CD spectra of chiral cyclophanes as model systems, the effects of intra- and intermolecular interactions on the chiroptical properties of molecules can be explored, and the results thus obtained are valuable in comprehensively elucidating the structure-chiroptical property relationship. In this review the recent progress in experimental and theoretical investigations of the electronic CD spectra of chiral cyclophanes is discussed.

  13. Tunable chirality and circular dichroism of a topological insulator with C2v symmetry as a function of Rashba and Dresselhaus parameters

    NASA Astrophysics Data System (ADS)

    Sengupta, Parijat; Bellotti, Enrico

    2016-01-01

    Polarization-sensitive devices rely on meta-materials to exhibit varying degrees of absorption of light of a given handedness. The chiral surface states of a topological insulator selectively absorb right- and left-circularly polarized light in the vicinity of the Dirac cone reaching its maximum of unity at the Γ point. In this letter, we show that a band gap open topological insulator with C2v symmetry, which is represented through a combination of Rashba and Dresselhaus Hamiltonians, alters the preferential absorption of left- and right-circularly polarized light allowing a smooth variation of the circular dichroism. This variation in circular dichroism, in a range of positive and negative values, is shown to be a function of the Rashba and Dresselhaus coupling parameters.

  14. Isotope effect on the circular dichroism spectrum of methyl α-D-glucopyranoside in aqueous solution

    PubMed Central

    Kanematsu, Yusuke; Kamiya, Yukiko; Matsuo, Koichi; Gekko, Kunihiko; Kato, Koichi; Tachikawa, Masanori

    2015-01-01

    H/D isotope effect on the circular dichroism spectrum of methyl α-D-glucopyranoside in aqueous solution has been analyzed by multicomponent density functional theory calculations using the polarizable continuum model. By comparing the computational spectra with the corresponding experimental spectrum obtained with a vacuum-ultraviolet circular dichroism spectrophotometer, it was demonstrated that the isotope effect provides insights not only into the isotopic difference of the intramolecular interactions of the solutes, but also into that of the solute–solvent intermolecular interaction. PMID:26658851

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

    ERIC Educational Resources Information Center

    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…

  16. Remediation of Cr(VI) by biogenic magnetic nanoparticles: An x-ray magnetic circular dichroism study

    SciTech Connect

    Telling, N. D.; Coker, V. S.; Cutting, R. S.; van der Laan, G.; Pearce, C. I.; Pattrick, R. A. D.; Arenholz, E.; Lloyd, J. R.

    2009-09-04

    Biologically synthesized magnetite (Fe{sub 3}O{sub 4}) nanoparticles are studied using x-ray absorption and x-ray magnetic circular dichroism following exposure to hexavalent Cr solution. By examining their magnetic state, Cr cations are shown to exist in trivalent form on octahedral sites within the magnetite spinel surface. The possibility of reducing toxic Cr(VI) into a stable, non-toxic form, such as a Cr{sup 3+}-spinel layer, makes biogenic magnetite nanoparticles an attractive candidate for Cr remediation.

  17. Theoretical Calculation of Electronic Circular Dichroism of a Hexahydroxydiphenoyl-Containing Flavanone Glycoside

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Time-dependent density functional theory (TDDFT) was employed for theoretical calculation of electronic circular dichroism (ECD) of a hexahydroxydiphenoyl (HHDP)-containing flavanone glycoside, mattucinol-7-O-[4'',6''-O-(aS)-hexahydroxydiphenoyl]-ß-d-glucopyranoside (2). It identified the roles of t...

  18. Circular dichroism study on the diastereoselective self-assembly of bacteriochlorophyll cs

    NASA Astrophysics Data System (ADS)

    Balaban, Teodor S.; Holzwarth, Alfred R.; Schaffner, Kurt

    1995-04-01

    Circular dichroism (CD) spectra of self-assembled bacteriochlorophyll cs (BChl cs) aggregates show a pronounced dependency on the solvent, the concentration and on the stereochemistry of the 3 1-hydroxy groups. In n-hexane a psi-type CD is obtained due to the formation of nanostructural aggregates.

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

    ERIC Educational Resources Information Center

    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. Determination of Myoglobin Stability by Circular Dichroism Spectroscopy: Classic and Modern Data Analysis

    ERIC Educational Resources Information Center

    Mehl, Andrew F.; Crawford, Mary A.; Zhang, Lei

    2009-01-01

    Few laboratory procedures describe the use of circular dichroism (CD) at the undergraduate level. To increase the number of laboratory exercises using CD, a thermal denaturation study of myoglobin using CD is described to assess protein stability. Values obtained from a more classic linear data analysis approach are consistent with data analyzed…

  1. EFFECT OF SOLVENT AND TEMPERATURE ON SECONDARY AND TERTIARY STRUCTURE OF ZEIN BY CIRCULAR DICHROISM

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Circular dichroism studies were performed on various samples of commercial zein to determine how the secondary and tertiary structure changes with different solvents, temperatures or pH. It was found that alcoholic solvent type and common denaturants, such as SDS and low amounts of urea, had little...

  2. Magnetic Circular Dichroism Studies XXV. A Preliminary Investigation of Microsomal Cytochromes*

    PubMed Central

    Dolinger, Peter M.; Kielczewski, Michael; Trudell, James R.; Barth, Günter; Linder, Robert E.; Bunnenberg, Edward; Djerassi, Carl

    1974-01-01

    The application of magnetic circular dichroism as an optical probe for simultaneous identification and determination of at least two microsomal cytochromes is demonstrated. The assignments of the bands in the spectra of microsomal suspensions are made from the spectra of soluble preparations of cytochrome P-450 obtained from Pseudomonas putida and of cytochrome b5 obtained from rat livers. PMID:4521811

  3. Generation of circularly polarized radiation from a compact plasma-based extreme ultraviolet light source for tabletop X-ray magnetic circular dichroism studies

    SciTech Connect

    Wilson, Daniel; Rudolf, Denis Juschkin, Larissa; Weier, Christian; Adam, Roman; Schneider, Claus M.; Winkler, Gerrit; Frömter, Robert; Danylyuk, Serhiy; Bergmann, Klaus; Grützmacher, Detlev

    2014-10-15

    Generation of circularly polarized light in the extreme ultraviolet (EUV) spectral region (about 25 eV–250 eV) is highly desirable for applications in spectroscopy and microscopy but very challenging to achieve in a small-scale laboratory. We present a compact apparatus for generation of linearly and circularly polarized EUV radiation from a gas-discharge plasma light source between 50 eV and 70 eV photon energy. In this spectral range, the 3p absorption edges of Fe (54 eV), Co (60 eV), and Ni (67 eV) offer a high magnetic contrast often employed for magneto-optical and electron spectroscopy as well as for magnetic imaging. We simulated and designed an instrument for generation of linearly and circularly polarized EUV radiation and performed polarimetric measurements of the degree of linear and circular polarization. Furthermore, we demonstrate first measurements of the X-ray magnetic circular dichroism at the Co 3p absorption edge with a plasma-based EUV light source. Our approach opens the door for laboratory-based, element-selective spectroscopy of magnetic materials and spectro-microscopy of ferromagnetic domains.

  4. Circular dichroism in a three-dimensional semiconductor chiral photonic crystal

    SciTech Connect

    Takahashi, S.; Ota, Y.; Tatebayashi, J.; Tajiri, T.; Iwamoto, S.; Arakawa, Y.

    2014-08-04

    Circular dichroism covering the telecommunication band is experimentally demonstrated in a semiconductor-based three-dimensional chiral photonic crystal (PhC). We design a rotationally stacked woodpile PhC structure where neighboring layers are rotated by 60° and three layers construct a single helical unit. The mirror-asymmetric PhC made from GaAs with sub-micron periodicity is fabricated by a micro-manipulation technique. Due to the large contrast of refractive indices between GaAs and air, the experimentally obtained circular dichroism extends over a wide wavelength range, with the transmittance of right-handed circularly polarized incident light being 85% and that of left-handed light being 15% at a wavelength of 1.3 μm. The obtained results show good agreement with numerical simulations.

  5. Theory of magnetic circular dichroism of nonresonant x-ray Raman scattering

    NASA Astrophysics Data System (ADS)

    Takahashi, Manabu; Hiraoka, Nozomu

    2015-09-01

    We develop a theory of magnetic circular dichroism (MCD) of hard x-ray Raman scattering (XRS) to analyze the MCD signal at iron L edge from pure ferromagnetic iron. The obtained formula of scattering amplitude has terms corresponding to the charge (Thomson) scattering process, and the orbital and spin scattering processes in the elastic x-ray magnetic scattering. The total scattering intensity is almost independent of incident photon helicity since it is mainly produced by the charge scattering. The weak MCD signals are caused primarily by interference between the charge scattering amplitude and each of the orbital and spin scattering amplitudes. The shape of the MCD spectra depends on angle αM between the wave vector of the incident photon and the magnetization vector. At αM=0∘ , the spin scattering is suppressed so that the MCD spectrum becomes analogous to that observed in the x-ray absorption spectroscopy. At αM=135∘ , the orbital scattering is suppressed, and the spin scattering plays central roles in producing the MCD signal. The magnitude of the MCD signal turns out to be proportional to the spin density of states projected onto the 3 d states in the unoccupied state. Consequently, the value of the integrated MCD signal is proportional to the spin moment in the 3 d states at the scattering site. The calculated MCD spectra with the help of a band structure calculation well reproduce the observed spectra.

  6. UV and circular dichroism thermal lens microscope for integrated chemical systems and HPLC on microchip

    NASA Astrophysics Data System (ADS)

    Mawatari, Kazuma; Kitamori, Takehiko

    2005-09-01

    Thermal lens microscope (TLM) is our original sensitive detector for non-fluorescent molecules in microspace. The principle is based on absorption of light followed by photothermal process. TLM has been successfully applied tosensitive detection on microchip, and TLM enabled various applications combined with microchip technologies. We are now developing HPLC microchips as one of the important separation techniques for analysis and synthesis. For HPLC microchip systems, direct and sensitive UV detection on microchip becomes key technology. Therefore, we extended applicability of TLM from visible to UV light absorbing samples by pulse UV laser excitation (UV-TLM). Quasi- continuous wave (QCW) method was applied for lock-in amplifier detection. By applying UV-TLM for biomolecules separation and detection, about two orders of higher sensitivity was achieved compared with UV spectrophotometer. For synthesis on microchip, recognition and detection of chiral samples become important in pharmaceutical field. Therefore, function of TLM was extended for selective detection of chiral samples by utilizing polarization modulation of excitation beam and resultant circular dichroism of sample (CD-TLM). The chirality of samples was detected selectively on microchip with two orders higher sensitivity than CD spectrophotometer. Finally, we explained the instrumentation using fiber optics and micro lens technology for achieving a miniaturized practical device.

  7. X-ray magnetic circular dichroism of Pseudomonas aeruginosa nickel(II) azurin.

    PubMed

    Funk, Tobias; Kennepohl, Pierre; Di Bilio, Angel J; Wehbi, William A; Young, Anthony T; Friedrich, Stephan; Arenholz, Elke; Gray, Harry B; Cramer, Stephen P

    2004-05-12

    We show that X-ray magnetic circular dichroism (XMCD) can be employed to probe the oxidation states and other electronic structural features of nickel active sites in proteins. As a calibration standard, we have measured XMCD and X-ray absorption (XAS) spectra for the nickel(II) derivative of Pseudomonas aeruginosa azurin (NiAz). Our analysis of these spectra confirms that the electronic ground state of NiAz is high-spin (S = 1); we also find that the L(3)-centroid energy is 853.1(1) eV, the branching ratio is 0.722(4), and the magnetic moment is 1.9(4) mu(B). Density functional theory (DFT) calculations on model NiAz structures establish that orbitals 3d(x2-y2) and 3d(z2) are the two valence holes in the high-spin Ni(II) ground state, and in accord with the experimentally determined orbital magnetic moment, the DFT results also demonstrate that both holes are highly delocalized, with 3d(x2-y2) having much greater ligand character. PMID:15125678

  8. Conformation of membrane-bound proteins revealed by vacuum-ultraviolet circular-dichroism and linear-dichroism spectroscopy.

    PubMed

    Matsuo, Koichi; Maki, Yasuyuki; Namatame, Hirofumi; Taniguchi, Masaki; Gekko, Kunihiko

    2016-03-01

    Knowledge of the conformations of a water-soluble protein bound to a membrane is important for understanding the membrane-interaction mechanisms and the membrane-mediated functions of the protein. In this study we applied vacuum-ultraviolet circular-dichroism (VUVCD) and linear-dichroism (LD) spectroscopy to analyze the conformations of α-lactalbumin (LA), thioredoxin (Trx), and β-lactoglobulin (LG) bound to phosphatidylglycerol liposomes. The VUVCD analysis coupled with a neural-network analysis showed that these three proteins have characteristic helix-rich conformations involving several helical segments, of which two amphiphilic or hydrophobic segments take part in interactions with the liposome. The LD analysis predicted the average orientations of these helix segments on the liposome: two amphiphilic helices parallel to the liposome surface for LA, two hydrophobic helices perpendicular to the liposome surface for Trx, and a hydrophobic helix perpendicular to and an amphiphilic helix parallel to the liposome surface for LG. This sequence-level information about the secondary structures and orientations was used to formulate interaction models of the three proteins at the membrane surface. This study demonstrates the validity of a combination of VUVCD and LD spectroscopy in conformational analyses of membrane-binding proteins, which are difficult targets for X-ray crystallography and nuclear magnetic resonance spectroscopy. PMID:26756612

  9. [Circular dichroism of DNA liquid-crystalline dispersion particles].

    PubMed

    Semenov, S V; Yevdokimov, Yu M

    2015-01-01

    The optical activity of DNA liquid-crystalline dispersions is being investigated based on a theory for absorption of electromagnetic waves by large molecular aggregates. The impact on the dispersions-optical properties, exerted by the interaction between the complexes of nucleic acid molecules and nanoparticles, is being considered. PMID:26016021

  10. Scaling of the L{sub 2,3} circular magnetic x-ray dichroism of Fe nitrides

    SciTech Connect

    Alouani, M. |; Wills, J.M.; Wilkins, J.W.

    1998-04-01

    We have implemented the calculation of the x-ray-absorption cross section for left- and right-circularly polarized x-ray beams within the local-density approximation by means of our all-electron full-relativistic and spin-polarized full-potential linear muffin-tin orbital method. We show that the L{sub 2,3} circular magnetic x-ray dichroism of Fe, Fe{sub 3}N, and Fe{sub 4}N compounds scales to a single curve when divided by the local magnetic moment. Sum rules determine the spin and orbital magnetic moment of iron atoms in these ordered iron nitrides. {copyright} {ital 1998} {ital The American Physical Society}

  11. A broadband silicon quarter-wave retarder for far-infrared spectroscopic circular dichroism

    NASA Astrophysics Data System (ADS)

    Xi, Xiaoxiang; Smith, R. J.; Stanislavchuk, T. N.; Sirenko, A. A.; Gilbert, S. N.; Tu, J. J.; Carr, G. L.

    2014-11-01

    The high brightness, broad spectral coverage and pulsed characteristics of infrared synchrotron radiation enable time-resolved spectroscopy under throughput-limited optical systems, as can occur with the high-field magnet cryostat systems used to study electron dynamics and cyclotron resonance by far-infrared techniques. A natural extension for magnetospectroscopy is to sense circular dichroism, i.e. the difference in a material's optical response for left and right circularly polarized light. A key component for spectroscopic circular dichroism is an achromatic 1 4 wave retarder functioning over the spectral range of interest. We report here the development of an in-line retarder using total internal reflection in high-resistivity silicon. We demonstrate its performance by distinguishing electronic excitations of differing handedness for GaAs in a magnetic field. This 1 4 wave retarder is expected to be useful for far-infrared spectroscopy of circular dichroism in many materials.

  12. First enantioseparation and circular dichroism spectra of Au38 clusters protected by achiral ligands

    PubMed Central

    Dolamic, Igor; Knoppe, Stefan; Dass, Amala; Bürgi, Thomas

    2012-01-01

    Bestowing chirality to metals is central in fields such as heterogeneous catalysis and modern optics. Although the bulk phase of metals is symmetric, their surfaces can become chiral through adsorption of molecules. Interestingly, even achiral molecules can lead to locally chiral, though globally racemic, surfaces. A similar situation can be obtained for metal particles or clusters. Here we report the first separation of the enantiomers of a gold cluster protected by achiral thiolates, Au38(SCH2CH2Ph)24, achieved by chiral high-performance liquid chromatography. The chirality of the nanocluster arises from the chiral arrangement of the thiolates on its surface, forming 'staple motifs'. The enantiomers show mirror-image circular dichroism responses and large anisotropy factors of up to 4×10−3. Comparison with reported circular dichroism spectra of other Au38 clusters reveals that the influence of the ligand on the chiroptical properties is minor. PMID:22531183

  13. Fourier Transform Vibrational Circular Dichroism Of Carbonyl Stretching Modes In N-urethanyl-a-amino acids

    NASA Astrophysics Data System (ADS)

    Chernovitz, Anita C.; Freedman, Teresa B.; Nafie, Laurence A.

    1985-12-01

    The vibrational circular dichroism (VCD) spectra of the N-t-BOC and N-CBZ-derivatives of alanine, proline, phenylalanine and valine in 0.2M CHC13 solutions all exhibit a characteristic, strong bisignate couplet in the carbonyl stretching region. The VCD couplet is interpreted in terms of the coupled oscillation of the urethane and acid carbonyl groups in an intramolecularly hydrogen-bonded structure.

  14. MICROFLUIDIC MIXERS FOR THE INVESTIGATION OF PROTEIN FOLDING USING SYNCHROTRON RADIATION CIRCULAR DICHROISM SPECTROSCOPY

    SciTech Connect

    Kane, A; Hertzog, D; Baumgartel, P; Lengefeld, J; Horsley, D; Schuler, B; Bakajin, O

    2006-03-20

    The purpose of this study is to design, fabricate and optimize microfluidic mixers to investigate the kinetics of protein secondary structure formation with Synchrotron Radiation Circular Dichroism (SRCD) spectroscopy. The mixers are designed to rapidly initiate protein folding reaction through the dilution of denaturant. The devices are fabricated out of fused silica, so that they are transparent in the UV. We present characterization of mixing in the fabricated devices, as well as the initial SRCD data on proteins inside the mixers.

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

    NASA Astrophysics Data System (ADS)

    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.

  16. Circular Dichroism of DNA G-Quadruplexes: Combining Modeling and Spectroscopy To Unravel Complex Structures.

    PubMed

    Gattuso, Hugo; Spinello, Angelo; Terenzi, Alessio; Assfeld, Xavier; Barone, Giampaolo; Monari, Antonio

    2016-03-31

    We report on the comparison between the computational and experimental determination of electronic circular dichroism spectra of different guanine quadruplexes obtained from human telomeric sequences. In particular the difference between parallel, antiparallel, and hybrid structures is evidenced, as well as the induction of transitions between the polymorphs depending on the solution environment. Extensive molecular dynamics simulations (MD) are used to probe the conformational space of the different quadruplexes, and subsequently state-of-the-art hybrid quantum mechanics/molecular mechanics (QM/MM) techniques coupled with excitonic semiempirical Hamiltonian are used to simulate the macromolecular induced circular dichroism. The coupling of spectroscopy and molecular simulation allows an efficient one-to-one mapping between structures and optical properties, offering a way to disentangle the rich, yet complicated, quantity of information embedded in circular dichroism spectra. We show that our methodology is robust and efficient and allows us to take into account subtle conformational changes. As such, it could be used as an efficient tool to investigate structural modification upon DNA/drug interactions. PMID:26943487

  17. Synchrotron Radiation Circular Dichroism (SRCD) Spectroscopy - An Enhanced Method for Examining Protein Conformations and Protein Interactions

    SciTech Connect

    B Wallace; R Janes

    2011-12-31

    CD (circular dichroism) spectroscopy is a well-established technique in structural biology. SRCD (synchrotron radiation circular dichroism) spectroscopy extends the utility and applications of conventional CD spectroscopy (using laboratory-based instruments) because the high flux of a synchrotron enables collection of data at lower wavelengths (resulting in higher information content), detection of spectra with higher signal-to-noise levels and measurements in the presence of absorbing components (buffers, salts, lipids and detergents). SRCD spectroscopy can provide important static and dynamic structural information on proteins in solution, including secondary structures of intact proteins and their domains, protein stability, the differences between wild-type and mutant proteins, the identification of natively disordered regions in proteins, and the dynamic processes of protein folding and membrane insertion and the kinetics of enzyme reactions. It has also been used to effectively study protein interactions, including protein-protein complex formation involving either induced-fit or rigid-body mechanisms, and protein-lipid complexes. A new web-based bioinformatics resource, the Protein Circular Dichroism Data Bank (PCDDB), has been created which enables archiving, access and analyses of CD and SRCD spectra and supporting metadata, now making this information publicly available. To summarize, the developing method of SRCD spectroscopy has the potential for playing an important role in new types of studies of protein conformations and their complexes.

  18. The tuning of light-matter coupling and dichroism in graphene for enhanced absorption: Implications for graphene-based optical absorption devices

    NASA Astrophysics Data System (ADS)

    Rakheja, Shaloo; Sengupta, Parijat

    2016-03-01

    The inter-band optical absorption in graphene characterized by its fine-structure constant has a universal value of 2.3% independent of the material parameters. However, for several graphene-based photonic applications, enhanced optical absorption is highly desired. In this work, we quantify the tunability of optical absorption in graphene via the Fermi level, angle of incidence of the incident polarized light, and the dielectric constants of the surrounding dielectric media in which graphene is embedded. The influence of impurities adsorbed on the surface of graphene on the Lorentzian broadening of the spectral function of the density of states is analytically evaluated within the equilibrium Green’s function formalism. In all the cases, we find that absorption of light graphene embedded in dielectric medium is significantly higher than 2.3%. We also compute the differential absorption of right and left circularly-polarized light in graphene that is uniaxially and optically strained. The preferential absorption or circular dichroism is investigated for armchair and zigzag strain and the interplay of k-space and velocity anisotropy is examined. Finally, we relate circular dichroism to the Berry curvature of gapped graphene and explain the connection to parameters that define the underlying Hamiltonian.

  19. Site-directed circular dichroism of proteins: 1Lb bands of Trp resolve position-specific features in tear lipocalin.

    PubMed

    Gasymov, Oktay K; Abduragimov, Adil R; Glasgow, Ben J

    2008-03-15

    The absorption spectra of N-acetyl-L-tryptophanamide in various solvents were resolved into the sums of the (1)L(a) and (1)L(b) components. The relative intensities of the 0-0 transitions of the (1)L(b) bands correlate linearly with the solvent polarity values (E(T)(N)). A novel strategy that uses a set of the experimental (1)L(b) bands was employed to resolve the near-UV circular dichroism (CD) spectra of tryptophanyl residues. Resolved spectral parameters from the single-tryptophan mutants of tear lipocalin (TL), F99W and Y87W, corroborate the fluorescence and structural data of TL. Analysis of the (1)L(b) bands of the Trp CD spectra in proteins is a valuable tool to obtain the local features. The dimethyl sulfoxide (DMSO)-like (1)L(b) band of Trp CD spectra may be used as a "fingerprint" to identify the tryptophanyl side chains in situations where the benzene rings of Trp have van der Waals interactions with the side chains of its nearest neighbor. In addition, the signs and intensities of the components hold information about the side chain conformations and dynamics in proteins. Combined with Trp mutagenesis, this method, which we call site-directed circular dichroism, is broadly applicable to various proteins to obtain the position-specific data. PMID:18047823

  20. Magnetic circular dichroism and computational study of mononuclear and dinuclear iron(IV) complexes

    PubMed Central

    Xue, Genqiang; Krivokapic, Itana; Petrenko, Taras

    2015-01-01

    High-valent iron(IV)-oxo species are key intermediates in the catalytic cycles of a range of O2-activating iron enzymes. This work presents a detailed study of the electronic structures of mononuclear ([FeIV(O)(L)(NCMe)]2+, 1, L = tris(3,5-dimethyl-4-methoxylpyridyl-2-methyl)amine) and dinuclear ([(L)FeIV(O)(μ-O)FeIV(OH)(L)]3+, 2) iron(IV) complexes using absorption (ABS), magnetic circular dichroism (MCD) spectroscopy and wave-function-based quantum chemical calculations. For complex 1, the experimental MCD spectra at 2–10 K are dominated by a broad positive C-term band between 12000 and 18000 cm−1. As the temperature increases up to ~20 K, this feature is gradually replaced by a derivative-shaped signal. The computed MCD spectra are in excellent agreement with experiment, which reproduce not only the excitation energies and the MCD signs of key transitions but also their temperature-dependent intensity variations. To further corroborate the assignments suggested by the calculations, the individual MCD sign for each transition is independently determined from the corresponding electron donating and accepting orbitals. Thus, unambiguous assignments can be made for the observed transitions in 1. The ABS/MCD data of complex 2 exhibit ten features that are assigned as ligand-field transitions or oxo- or hydroxo-to-metal charge transfer bands, based on MCD/ABS intensity ratios, calculated excitation energies, polarizations, and MCD signs. In comparison with complex 1, the electronic structure of the FeIV=O site is not significantly perturbed by the binding to another iron(IV) center. This may explain the experimental finding that complexes 1 and 2 have similar reactivities toward C-H bond activation and O-atom transfer. PMID:26417426

  1. Angle and temperature dependence of magnetic circular dichroism in core-level photoemission from Gd(0001)

    SciTech Connect

    Denecke, R.; Morais, J.; Ynzunza, R. X.; Menchero, J. G.; Liesegang, J.; Rice, M.; Kortright, J.; Hussain, Z.; Fadley, C. S.

    1997-04-01

    Magnetic dichroism in core-level photoelectron emission from solids represents a promising new element-specific probe of surface and interface atomic structure and magnetic order. One way of measuring such effects is by using photoelectrons excited by circular polarized radiation, thus leading to magnetic circular dichroism (MCD) if the intensity with right-circular polarized (RCP) light is not equal to that with left-circular polarized (LCP) light. The spin-integrated photoelectron intensity in a certain emission direction also in general depends on the direction of the magnetization in a magnetic material. In fact, if the magnetization lies in a surface mirror plane, then inverting its direction can provide a second way of measuring MCD. Purely atomic theoretical models have been successful in explaining many aspects of such data. By varying the emission direction one also probes the geometric structure of the sample. But such MCD in photoelectron angular distributions (MCDAD) then has to be interpreted also in terms of photoelectron diffraction. Measuring the temperature dependence of such MCD effects also provides a useful tool for studying magnetic transition temperatures. The authors have here studied such effects in core-level emission from Gd(0001).

  2. Characterization of intermolecular structure of β(2)-microglobulin core fragments in amyloid fibrils by vacuum-ultraviolet circular dichroism spectroscopy and circular dichroism theory.

    PubMed

    Matsuo, Koichi; Hiramatsu, Hirotsugu; Gekko, Kunihiko; Namatame, Hirofumi; Taniguchi, Masaki; Woody, Robert W

    2014-03-20

    Intermolecular structures are important factors for understanding the conformational properties of amyloid fibrils. In this study, vacuum-ultraviolet circular dichroism (VUVCD) spectroscopy and circular dichroism (CD) theory were used for characterizing the intermolecular structures of β2-microglobulin (β2m) core fragments in the amyloid fibrils. The VUVCD spectra of β2m20-41, β2m21-31, and β2m21-29 fragments in the amyloid fibrils exhibited characteristic features, but they were affected not only by the backbone conformations but also by the aromatic side-chain conformations. To estimate the contributions of aromatic side-chains to the spectra, the theoretical spectra were calculated from the simulated structures of β2m21-29 amyloid fibrils with various types of β-sheet stacking (parallel or antiparallel) using CD theory. We found that the experimental spectrum of β2m21-29 fibrils is largely affected by aromatic-backbone couplings, which are induced by the interaction between transitions within the aromatic and backbone chromophores, and these couplings are sensitive to the type of stacking among the β-sheets of the fibrils. Further theoretical analyses of simulated structures incorporating mutated aromatic residues suggested that the β2m21-29 fibrils are composed of amyloid accumulations in which the parallel β-sheets stack in an antiparallel manner and that the characteristic Phe-Tyr interactions among the β-sheet stacks affect the aromatic-backbone coupling. These findings indicate that the coupling components, which depend on the characteristic intermolecular structures, induce the spectral differences among three fragments in the amyloid fibrils. These advanced spectral analyses using CD theory provide a useful method for characterizing the intermolecular structures of protein and peptide fragment complexes. PMID:24512563

  3. UV-CD12: synchrotron radiation circular dichroism beamline at ANKA

    PubMed Central

    Bürck, Jochen; Roth, Siegmar; Windisch, Dirk; Wadhwani, Parvesh; Moss, David; Ulrich, Anne S.

    2015-01-01

    Synchrotron radiation circular dichroism (SRCD) is a rapidly growing technique for structure analysis of proteins and other chiral biomaterials. UV-CD12 is a high-flux SRCD beamline installed at the ANKA synchrotron, to which it had been transferred after the closure of the SRS Daresbury. The beamline covers an extended vacuum-UV to near-UV spectral range and has been open for users since October 2011. The current end-station allows for temperature-controlled steady-state SRCD spectroscopy, including routine automated thermal scans of microlitre volumes of water-soluble proteins down to 170 nm. It offers an excellent signal-to-noise ratio over the whole accessible spectral range. The technique of oriented circular dichroism (OCD) was recently implemented for determining the membrane alignment of α-helical peptides and proteins in macroscopically oriented lipid bilayers as mimics of cellular membranes. It offers improved spectral quality <200 nm compared with an OCD setup adapted to a bench-top instrument, and accelerated data collection by a factor of ∼3. In addition, it permits investigations of low hydrated protein films down to 130 nm using a rotatable sample cell that avoids linear dichroism artifacts. PMID:25931105

  4. Magnetic circular dichroism of non-local surface lattice resonances in magnetic nanoparticle arrays.

    PubMed

    Kataja, Mikko; Pourjamal, Sara; van Dijken, Sebastiaan

    2016-02-22

    Subwavelength metallic particles support plasmon resonances that allow extreme confinement of light down to the nanoscale. Irradiation with left- and right hand circularly polarized light results in the excitation of circular plasmon modes with opposite helicity. The Lorenz force lifts the degeneracy of the two modes in magnetic nanoparticles. Consequently, the confinement and frequency of localized surface plasmon resonances can be tuned by an external magnetic field. In this paper, we experimentally demonstrate this effect for nickel nanoparticles using magnetic circular dichroism (MCD). Besides, we show that non-local surface lattice resonances in periodic arrays of the same nanoparticles significantly enhance the MCD signal. A numerical model based on the modified long wavelength approximation is used to reproduce the main features in the experimental spectra and provide design rules for large MCD effects in sensing applications. PMID:26907013

  5. Communication: SHG-detected circular dichroism imaging using orthogonal phase-locked laser pulses

    NASA Astrophysics Data System (ADS)

    Jarrett, Jeremy W.; Liu, Xiaoying; Nealey, Paul F.; Vaia, Richard A.; Cerullo, Giulio; Knappenberger, Kenneth L.

    2015-04-01

    We demonstrate a novel method for second harmonic generation-detected circular dichroism (CD) imaging based on the use of phase-locked, temporally delayed femtosecond laser pulses. The polarization state of the fundamental wave was controllably changed over 2π rad by using a birefringent delay line, which provided attosecond inter-pulse delays for orthogonal phase-locked replicas; the achievable phase stability was 14 as. By introducing either a positive or negative delay of ˜667 as, we induced a ±π/2 phase shift between the orthogonally polarized pulses, resulting in left circularly polarized or right circularly polarized light. CD imaging performance using the pulse sequence was compared to results obtained for plasmonic nanoantennas using a rotating quarter-wave plate. The pulse sequence is expected to simplify polarization-resolved optical imaging by reducing experimental artifacts and decreasing image acquisition times. This method can be easily extended to other CD spectroscopy measurements.

  6. Imaging photoelectron circular dichroism of chiral molecules by femtosecond multiphoton coincidence detection

    SciTech Connect

    Lehmann, C. Stefan; Ram, N. Bhargava; Janssen, Maurice H. M.; Powis, Ivan

    2013-12-21

    Here, we provide a detailed account of novel experiments employing electron-ion coincidence imaging to discriminate chiral molecules. The full three-dimensional angular scattering distribution of electrons is measured after photoexcitation with either left or right circular polarized light. The experiment is performed using a simplified photoelectron-photoion coincidence imaging setup employing only a single particle imaging detector. Results are reported applying this technique to enantiomers of the chiral molecule camphor after three-photon ionization by circularly polarized femtosecond laser pulses at 400 nm and 380 nm. The electron-ion coincidence imaging provides the photoelectron spectrum of mass-selected ions that are observed in the time-of-flight mass spectra. The coincident photoelectron spectra of the parent camphor ion and the various fragment ions are the same, so it can be concluded that fragmentation of camphor happens after ionization. We discuss the forward-backward asymmetry in the photoelectron angular distribution which is expressed in Legendre polynomials with moments up to order six. Furthermore, we present a method, similar to one-photon electron circular dichroism, to quantify the strength of the chiral electron asymmetry in a single parameter. The circular dichroism in the photoelectron angular distribution of camphor is measured to be 8% at 400 nm. The electron circular dichroism using femtosecond multiphoton excitation is of opposite sign and about 60% larger than the electron dichroism observed before in near-threshold one-photon ionization with synchrotron excitation. We interpret our multiphoton ionization as being resonant at the two-photon level with the 3s and 3p Rydberg states of camphor. Theoretical calculations are presented that model the photoelectron angular distribution from a prealigned camphor molecule using density functional theory and continuum multiple scattering X alpha photoelectron scattering calculations

  7. Imaging photoelectron circular dichroism of chiral molecules by femtosecond multiphoton coincidence detection

    NASA Astrophysics Data System (ADS)

    Lehmann, C. Stefan; Ram, N. Bhargava; Powis, Ivan; Janssen, Maurice H. M.

    2013-12-01

    Here, we provide a detailed account of novel experiments employing electron-ion coincidence imaging to discriminate chiral molecules. The full three-dimensional angular scattering distribution of electrons is measured after photoexcitation with either left or right circular polarized light. The experiment is performed using a simplified photoelectron-photoion coincidence imaging setup employing only a single particle imaging detector. Results are reported applying this technique to enantiomers of the chiral molecule camphor after three-photon ionization by circularly polarized femtosecond laser pulses at 400 nm and 380 nm. The electron-ion coincidence imaging provides the photoelectron spectrum of mass-selected ions that are observed in the time-of-flight mass spectra. The coincident photoelectron spectra of the parent camphor ion and the various fragment ions are the same, so it can be concluded that fragmentation of camphor happens after ionization. We discuss the forward-backward asymmetry in the photoelectron angular distribution which is expressed in Legendre polynomials with moments up to order six. Furthermore, we present a method, similar to one-photon electron circular dichroism, to quantify the strength of the chiral electron asymmetry in a single parameter. The circular dichroism in the photoelectron angular distribution of camphor is measured to be 8% at 400 nm. The electron circular dichroism using femtosecond multiphoton excitation is of opposite sign and about 60% larger than the electron dichroism observed before in near-threshold one-photon ionization with synchrotron excitation. We interpret our multiphoton ionization as being resonant at the two-photon level with the 3s and 3p Rydberg states of camphor. Theoretical calculations are presented that model the photoelectron angular distribution from a prealigned camphor molecule using density functional theory and continuum multiple scattering X alpha photoelectron scattering calculations

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

    PubMed

    DiLullo, Andrew; Shirato, Nozomi; Cummings, Marvin; Kersell, Heath; Chang, Hao; Rosenmann, Daniel; Miller, Dean; Freeland, John W; Hla, Saw-Wai; Rose, Volker

    2016-03-01

    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 L2,3-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. PMID:26917146

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

    PubMed Central

    DiLullo, Andrew; Shirato, Nozomi; Cummings, Marvin; Kersell, Heath; Chang, Hao; Rosenmann, Daniel; Miller, Dean; Freeland, John W.; Hla, Saw-Wai; Rose, Volker

    2016-01-01

    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 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. PMID:26917146

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

    DOE PAGESBeta

    DiLullo, Andrew; Shirato, Nozomi; Cummings, Marvin; Kersell, Heath; Chang, Hao; Rosenmann, Daniel; Miller, Dean; Freeland, John W.; Hla, Saw -Wai; Rose, Volker

    2016-01-28

    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 FeL2,3-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.

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

    PubMed

    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. PMID:27587106

  12. Magnetic circular x-ray dichroisms of Fe-Ni alloys at K edge.

    SciTech Connect

    Freeman, A. J.; Gofron, K. J.; Kimball, C. W.; Lee, P. L.; Montano, P. A.; Rao, F.; Wang, X.

    1997-04-03

    Magnetic Circular X-ray Dichroism (MCXD) studies at K edges of Fe-Ni alloys reveal changes of the MCXD signal with composition and crystal structure. We observe that the signal at the invar composition is of comparable strength as other compositions. Moreover, the edge position is strongly dependent on lattice constant. First principles calculations demonstrate that the shape and strength of the signal strongly depends on the crystal orientation, composition, and lattice constant. We find direct relation between the MCXD signal and the p DOS. We find that the MCXD at K edge probes the magnetism due to itinerant electrons.

  13. Circular Dichroism studies on the interactions of antimicrobial peptides with bacterial cells

    NASA Astrophysics Data System (ADS)

    Avitabile, Concetta; D'Andrea, Luca Domenico; Romanelli, Alessandra

    2014-03-01

    Studying how antimicrobial peptides interact with bacterial cells is pivotal to understand their mechanism of action. In this paper we explored the use of Circular Dichroism to detect the secondary structure of two antimicrobial peptides, magainin 2 and cecropin A, with E. coli bacterial cells. The results of our studies allow us to gain two important information in the context of antimicrobial peptides- bacterial cells interactions: peptides fold mainly due to interaction with LPS, which is the main component of the Gram negative bacteria outer membrane and the time required for the folding on the bacterial cells depends on the peptide analyzed.

  14. Chiral imaging of collagen by second-harmonic generation circular dichroism

    PubMed Central

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

    2013-01-01

    We provide evidence that the chirality of collagen can give rise to strong second-harmonic generation circular dichroism (SHG-CD) responses in nonlinear microscopy. Although chirality is an intrinsic structural property of collagen, most of the previous studies ignore that property. We demonstrate chiral imaging of individual collagen fibers by using a laser scanning microscope and type-I collagen from pig ligaments. 100% contrast level of SHG-CD is achieved with sub-micrometer spatial resolution. As a new contrast mechanism for imaging chiral structures in bio-tissues, this technique provides information about collagen morphology and three-dimensional orientation of collagen molecules. PMID:23761852

  15. X-ray Magnetic Circular Dichroism Study of La(1 - x)SrxMnO3 Thin Films

    NASA Astrophysics Data System (ADS)

    Kuang, Xilei; Xiao, Zhuyun; Moon, Eun Ju; May, Steven; Keavney, David; Liu, Yaohua; Cheng, X. M.

    2013-03-01

    The perovskite manganite La(1 - x)SrxMnO3 (LSMO) has attracted great attention recently due to its fundamental physics and potential applications in spintronics and data storage. In this work, we report a temperature-dependent x-ray magnetic circular dichroism (XMCD) study of epitaxial LSMO thin films deposited on orthorhombic NdGaO3 (NGO) substrates grown by the molecular beam epitaxy (MBE) method. Small angle x-ray reflectivity and atomic force microscopy (AFM) results confirmed good epitaxial quality. XMCD measurements were performed at beamline 4-ID-C of the Advanced Photon Source at Argonne National Laboratory. XMCD spectra were taken in a 0.5 tesla field at temperatures ranging from 5 K to 180 K after the 0.5 tesla field cool. The total electron yield absorption spectra showed the oxide state characteristics of Mn, and the shapes of the Mn and O dichroism spectra change with temperature. This work is supported by NSF DMR-1053854. Work at Argonne National Laboratory was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract DE-AC02-06CH11357.

  16. X-ray absorption and magnetic circular dichroism of LaCoO3 , La0.7Ce0.3CoO3 , and La0.7Sr0.3CoO3 films: Evidence for cobalt-valence-dependent magnetism

    NASA Astrophysics Data System (ADS)

    Merz, M.; Nagel, P.; Pinta, C.; Samartsev, A.; v. Löhneysen, H.; Wissinger, M.; Uebe, S.; Assmann, A.; Fuchs, D.; Schuppler, S.

    2010-11-01

    Epitaxial thin films of undoped LaCoO3 , of electron-doped La0.7Ce0.3CoO3 , and of hole-doped La0.7Sr0.3CoO3 exhibit ferromagnetic order with a transition temperature TC≈84K , 23 K, and 194 K, respectively. The spin-state structure for these compounds was studied by soft x-ray magnetic circular dichroism and by near-edge x-ray absorption fine structure at the CoL2,3 and OK edges. It turns out that superexchange between Co3+ high-spin and Co3+ low-spin states is responsible for the ferromagnetism in LaCoO3 . For La0.7Ce0.3CoO3 the Co3+ ions are in a low-spin state and the spin and orbital moments are predominantly determined by a Co2+ high-spin configuration. A spin blockade naturally explains the low transition temperature and the insulating characteristics of La0.7Ce0.3CoO3 . For La0.7Sr0.3CoO3 , on the other hand, the magnetic moments in the epitaxial films originate from high-spin Co3+ and high-spin Co4+ states. Ferromagnetism is induced by t2g double exchange between the two high-spin configurations. For all systems, a strong magnetic anisotropy is observed, with the magnetic moments essentially oriented within the film plane.

  17. Irradiation induced ferromagnetism at room temperature in TiO{sub 2} thin films: X-ray magnetic circular dichroism characterizations

    SciTech Connect

    Thakur, Hardeep; Sharma, K. K.; Thakur, P.; Brookes, N. B.; Kumar, Ravi; Singh, A. P.; Kumar, Yogesh; Gautam, S.; Chae, K. H.

    2011-05-09

    We report on the room temperature ferromagnetism in the swift heavy ion (SHI) irradiated TiO{sub 2} thin films by x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) experiments at the O K and Ti L{sub 3,2} absorption edges. The XAS/XMCD measurements provide direct evidence of magnetic polarization of the O 2p and Ti 3d orbitals. The unquenched orbital magnetic moment within the O 2p shell is ferromagnetically coupled to the neighboring Ti moments, which illustrates the intense hybridization of the O 2p and Ti 3d orbitals induced by SHI irradiation.

  18. Photoelectron circular dichroism of the randomly oriented chiral molecules glyceraldehyde and lactic acid

    NASA Astrophysics Data System (ADS)

    Powis, Ivan

    2000-01-01

    The differing interaction of left and right circularly polarized light with chiral molecules is shown to lead to different angular distributions of the photoelectrons created by photoionization of a given enantiomer, even when the target molecules are randomly oriented. Numerical calculations are presented to demonstrate the magnitude of this effect for the C3H6O3 structural isomers lactic acid and glyceraldehyde, including two different conformations of the latter. Circular dichroism in the angular distributions (CDAD) of the valence electrons of these biomolecules is most pronounced close to threshold, but tends to vanish as the electron kinetic energy approaches 20 eV and above. CDAD signals are predicted to range, typically, from 10% to 40% and sometimes to more than 60% of the differential cross section.

  19. Enantiomeric Excess Sensitivity to Below One Percent by Using Femtosecond Photoelectron Circular Dichroism.

    PubMed

    Kastner, Alexander; Lux, Christian; Ring, Tom; Züllighoven, Stefanie; Sarpe, Cristian; Senftleben, Arne; Baumert, Thomas

    2016-04-18

    Photoelectron circular dichroism (PECD) is experimentally investigated with chiral specimens with varying amounts of enantiomeric excess (ee). As a prototype, we measure and analyze the photoelectron angular distribution from randomly oriented fenchone molecules in the gas phase that result from ionization with circularly polarized femtosecond laser pulses. The quantification of these measurements shows a linear dependence with respect to the ee values. In addition, differences in the ee values (denoted as detection limit) of below one percent can be distinguished for nearly enantiopure samples, as well as for almost racemates. In combination with the use of a reference, the assignment of absolute ee values is possible. The present measurement time is a few minutes, but this could be reduced. This table-top laser-based approach should facilitate widespread implementation in chiral analysis. PMID:26836316

  20. Chiral detection in high-performance liquid chromatography by vibrational circular dichroism.

    PubMed

    Tran, C D; Grishko, V I; Huang, G

    1994-09-01

    A novel chiral detector for high-performance liquid chromatography has been developed. This detector is based on the measurement of circular dichroism of chiral effluents in the infrared region, i.e., vibrational circular dichroism (VCD). In this instrument, a solid-state spectral tunable (from 2.4 to 3.5 microns) F-center laser was used as the light source. The linearly polarized laser beam was converted into left circularly polarized light (LCPL) and right circularly polarized light (RCPL) at 42 kHz by means of a photoelastic modulator. The intensity of the LCPL and RCPL transmitted through the sample was measured by a liquid nitrogen cooled indium antimonide detector. Double modulation was employed to reduce the noise associated with the laser beam. Specifically, the linearly polarized laser beam, prior to being converted to CPL, was modulated at 85 Hz by a mechanical chopper. Demodulation and amplification were accomplished with the use of two lock-in amplifiers. In its present configuration, the instrument can be used to measure the VCD of O-H groups. Its sensitivity is so high that it was able, for the first time, to detect chirally (with limits of detection of micrograms) (R)- and (S)-2,2,2-trifluoro-1-(9- anthryl)ethanol and (R)- and (S)-benzoin when these compounds were chromatographically separated from the corresponding racemic mixtures by a Chiralcel-OD column. The main advantage of this chiral detector is, however, its universality; i.e., it can be used to virtually detect any chiral compounds which has O-H group (e.g, aliphatic alcohols such as 2-octanol). PMID:7943734

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

    NASA Astrophysics Data System (ADS)

    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.

  2. Circular Dichroism is Sensitive to Monovalent Cation Binding in Monensin Complexes.

    PubMed

    Nedzhib, Ahmed; Kessler, Jiří; Bouř, Petr; Gyurcsik, Béla; Pantcheva, Ivayla

    2016-05-01

    Monensin is a natural antibiotic that exhibits high affinity to certain metal ions. In order to explore its potential in coordination chemistry, circular dichroism (CD) spectra of monensic acid A (MonH) and its derivatives containing monovalent cations (Li(+) , Na(+) , K(+) , Rb(+) , Ag(+) , and Et4 N(+) ) in methanolic solutions were measured and compared to computational models. Whereas the conventional CD spectroscopy allowed recording of the transitions down to 192 nm, synchrotron radiation circular dichroism (SRCD) revealed other bands in the 178-192 nm wavelength range. CD signs and intensities significantly varied in the studied compounds, in spite of their similar crystal structure. Computational modeling based on the Density Functional Theory (DFT) and continuum solvent model suggests that the solid state monensin structure is largely conserved in the solutions as well. Time-dependent Density Functional Theory (TDDFT) simulations did not allow band-to-band comparison with experimental spectra due to their limited precision, but indicated that the spectral changes were caused by a combination of minor conformational changes upon the monovalent cation binding and a direct involvement of the metal electrons in monensin electronic transitions. Both the experiment and simulations thus show that the CD spectra of monensin complexes are very sensitive to the captured ions and can be used for their discrimination. Chirality 28:420-428, 2016. © 2016 Wiley Periodicals, Inc. PMID:27062535

  3. Giant circular dichroism in extrinsic chiral metamaterials excited by off-normal incident laser beams

    NASA Astrophysics Data System (ADS)

    Feng, C.; Wang, Z. B.; Lee, S.; Jiao, J.; Li, L.

    2012-05-01

    Recently it was shown by experiments that circular dichroism (CD) can be observed in the metamaterials of non-chiral structures when they were subjected to obliquely incident light (E. Plum, et al., Physical Review Letters 102, 113902, 2009). By far, external chirality simulation was only done for a particle array embedded in a homogenous medium (V. Yannopapas, Optics Letters 34, 5, 2009); no attempt has been made on simulating and modelling of circular dichroism in layered metamaterials (e.g., thin film on substrate structure). In this paper, we present the simulation of CD effect in layered external chiral metamaterials using CST software, theoretically investigate this intriguing phenomenon through a frequency domain finite integration technique, and optimize the metamaterial unit cell configurations (size, periodicity and film thickness) to maximize the CD phenomenon in near-infrared spectrum range. We show that the CD effect can be enhanced by five times using an optimized unit cell configuration, which is more than three times higher than the existing maximum theoretical results. The CD generation mechanism was elaborated with the help of induced surface current distributions.

  4. A Solid Phase Vibrational Circular Dichroism Study of Polypeptide-Surfactant Interaction.

    PubMed

    Novotná, Pavlína; Urbanová, Marie

    2015-12-01

    We studied the interaction of poly-l-lysine (PLL) and poly-l-arginine (PLAG) with sodium dodecyl sulfate (SDS) surfactant and the interaction of poly-l-glutamic acid (PLGA) and poly-l-aspartic acid (PLAA) with tetradecyltrimethylammonium bromide (TTAB) surfactant using vibrational circular dichroism (VCD) spectroscopy in the region of C-H stretching vibration and in the Amide I region both in solution and in mulls. A chirality transfer from polypeptides to achiral surfactants was observed in the C-H stretching region, where measurements in solution were impossible. This observation was enabled by a special sample treatment technique using lyophilization and the preparation of mulls. This technique demonstrated itself as an interesting and beneficial tool for VCD measurements. In addition, we observed that SDS changed the secondary structure of PLL to the β-sheet and of PLAG to the α-helix. TTAB disrupted the PLGA and PLAA structure. These results were obtained in the mull but were confirmed by the VCD spectra measured in solution and by electronic circular dichroism. The chirality transfer from the polypeptides to SDS was caused by polypeptides ordered into a specific conformation during the interaction, while in the TTBA system it was induced primarily by the chirality of the amino acid residues. PMID:26413930

  5. Time-resolved magnetic circular dichroism spectroscopy of photolyzed carbonmonoxy cytochrome c oxidase (cytochrome aa3).

    PubMed Central

    Goldbeck, R A; Dawes, T D; Einarsdóttir, O; Woodruff, W H; Kliger, D S

    1991-01-01

    Nanosecond time-resolved magnetic circular dichroism (TRMCD) and time-resolved natural circular dichroism (TRCD) measurements of photolysis products of the CO complex of eukaryotic cytochrome c oxidase (CcO-CO) are presented. TRMCD spectra obtained at 100 ns and 10 microseconds after photolysis are diagnostic of pentacoordinate cytochrome a3Fe2+, as would be expected for simple photodissociation. Other time-resolved spectroscopies (UV-visible and resonance Raman), however, show evidence for unusual Fea3(2+) coordination after CO photolysis (Woodruff, W. H., O. Einarsdóttir, R. B. Dyer, K. A. Bagley, G. Palmer, S. J. Atherton, R. A. Goldbeck, T. D. Dawes, and D. S. Kliger. 1991. Proc. Nat. Acad. Sci. U.S.A. 88:2588-2592). Furthermore, time-resolved IR experiments have shown that photodissociated CO binds to CuB+ prior to recombining with Fea3(2+) (Dyer, R. B., O. Einarsdóttir, P. M. Killough, J. J. López-Garriga, and W. H. Woodruff. 1989. J. Am. Chem. Soc. 111:7657-7659). A model of the CcO-CO photolysis cycle which is consistent with all of the spectroscopic results is presented. A novel feature of this model is the coordination of a ligand endogenous to the protein to the Fe axial site vacated by the photolyzed CO and the simultaneous breaking of the Fe-imidazole(histidine) bond. PMID:1653049

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

    PubMed

    Orlov, Sergey; Goncharova, Iryna; Urbanová, Marie

    2014-05-21

    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. PMID:24589992

  7. Polarization Rotation and Circular Dichroism Near the Potassium D2 Lines

    NASA Astrophysics Data System (ADS)

    Conover, Charles; Thiha, Htet; Dahnke, Jennifer

    2010-03-01

    We have experimentally measured the Faraday rotation and the differential absorption of the two circular polarizations for light tuned near the D2 line in potassium (766.7 nm). In particular we have explored the vapor temperature and magnetic field dependence of the frequency of the zero crossings of the lineshapes from the circular analyzer and the balanced polarimeter used in the measurements. These signals are routinely used as frequency references for laser locking and we discuss the sensitivity to experimental parameters.

  8. Chiral Recognition of 2-Alkylalcohols with Magnetic Circular Dichroism Measurement of Porphyrin J-Aggregate on Silica Gel Plate.

    PubMed

    Watarai, Hitoshi; Kurahashi, Yuriko

    2016-05-01

    Simple chiral recognition method of 2-alkylalcohols on a silica gel plate was proposed by using the induced circular dichroism (ICD) of J-aggregates of diprotonated tetraphenylporphyrin and magnetic circular dichroism (MCD) spectrometry. To the silica gel on a glass slide including a chiral 2-alkylalcohol and 4 M sulfuric acid, the porphyrin in toluene was added and mixed. Then, the glass slide was used for in situ MCD measurement. The observed ICD spectra could recognize well the chirality of the alcohols and the ICD intensity normalized by the MCD intensity of the J-aggregate correlated linearly to the amount of the chiral alcohols in the silica gel. PMID:27074095

  9. Two-photon circular dichroism of molecular structures simulating L-tryptophan residues in proteins with secondary structures

    NASA Astrophysics Data System (ADS)

    Vesga, Yuly; Diaz, Carlos; Higgs, Mary; Hernandez, Florencio E.

    2014-05-01

    Herein, we report on the calculation and the comparative analysis of the theoretical two-photon circular dichroism (TPCD) spectra of L-tryptophan (Trp) residues in proteins with secondary structures (α-helix, β-strand and random coil) conformation, down to the far-UV region (FUV). The examination of the TPCD spectra of the different conformers in each configuration reveals distinctive fingerprints in the FUV, a dark spectral region for electronic circular dichroism (ECD). Our results show the potential of FUV-TPCD to identify and study protein structures in a region never assessed before but filled with important structural information.

  10. Circular Dichroism in Mass Spectrometry: Quantum Chemical Investigations for the Differences between (R)-3-Methylcyclopentanone and Its Cation.

    PubMed

    Kröner, Dominik; Gaebel, Tina

    2015-08-27

    In mass spectrometry enantiomers can be distinguished by multiphoton ionization employing circular polarized laser pulses. The circular dichroism (CD) is detected from the normalized difference in the ion yield after excitation with light of opposite handedness. While there are cases in which fragment and parent ions exhibit the same sign of the CD in the ion yield, several experiments show that they might also differ in sign and magnitude. Supported by experimental observations it has been proposed that the parent ion, once it has been formed, is further excited by the laser, which may result in a change of the CD in the ion yield of the formed fragments compared to the parent ion. To gain a deeper insight in possible excitation pathways we calculated and compared the electronic CD absorption spectra of neutral and cationic (R)-3-methylcyclopentanone, applying density functional theory. In addition, electron wavepacket dynamics were used to compare the CD of one- and two-photon transitions. Our results support the proposed subsequent excitation of the parent ion as a possible origin of the difference of the CD in the ion yield between parent ion and fragments. PMID:26214257

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

    SciTech Connect

    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

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

    SciTech Connect

    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

  13. Transition-density-fragment interaction approach for exciton-coupled circular dichroism spectra

    NASA Astrophysics Data System (ADS)

    Fujimoto, Kazuhiro J.

    2010-09-01

    A transition-density-fragment interaction (TDFI) method for exciton-coupled circular dichroism (ECCD) spectra is proposed. The TDFI method was previously developed for excitation-energy transfer, which led to the successful estimation of the electronic coupling energy between donor and accepter molecules in xanthorhodopsin [K. J. Fujimoto and S. Hayashi, J. Am. Chem. Soc. 131, 14152 (2009)]. In the present study, the TDFI scheme is extended to the ECCD spectral calculation based on the matrix method and is applied to a dimerized retinal (all-trans N-retinylidene-L-alanine Schiff base) chromophore. Compared with the dipole-dipole and transition charge from ESP methods, TDFI has a much improved description of the electronic coupling. In addition, the matrix method combined with TDFI can reduce the computational costs compared with the full quantum-mechanical calculation. These advantages of the present method make it possible to accurately evaluate the CD Cotton effects observed in experiment.

  14. Molecular Design Guidelines for Large Magnetic Circular Dichroism Intensities in Lanthanide Complexes.

    PubMed

    Kitagawa, Yuichi; Wada, Satoshi; Yanagisawa, Kei; Nakanishi, Takayuki; Fushimi, Koji; Hasegawa, Yasuchika

    2016-03-16

    Magneto optical devices based on the Faraday effects of lanthanide ion have attracted much attention. Recently, large Faraday effects were found in nano-sized multinuclear lanthanide complexes. In this study, the Faraday rotation intensities were estimated for lanthanide nitrates [Ln(III) (NO3 )3 ⋅n H2 O: Ln=Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm) and Eu(III) complexes with β-diketone ligands, using magnetic circular dichroism. Eu ions exhibit the largest Faraday rotation intensity for (7) F0 →(5) D1 transitions, and high-symmetry fields around the Eu ions induce larger Faraday effects. The molecular design for the enhancement of Faraday effects in lanthanide complexes is discussed. PMID:26789658

  15. Structural characterization of hydroperoxide lyase in dodecyl maltoside by using circular dichroism.

    PubMed

    Panagakou, I; Touloupakis, E; Ghanotakis, D F

    2013-01-01

    Fatty acid hydroperoxide lyase (HPL) is a membrane protein, member of the lipoxygenase pathway, which holds a central role in plant defense. Green bell pepper fatty acid hydroperoxide lyase, overexpressed in Escherichia coli, was purified and solubilized in two different non ionic detergents, Triton X-100 and dodecyl maltoside (DM). DM is considered to be more useful compared to Triton X-100, as it allows characterization of the protein with spectroscopic techniques, for which Triton X-100 was inapplicable. Circular dichroism demonstrated that HPL's secondary structure in DM consists of 13.53 % α-helix, 32.73 % β-sheet, 21.76 % turn and 31.13 % unordered. PMID:23076732

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

    NASA Astrophysics Data System (ADS)

    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.

  17. Orbital Rashba effect and its detection by circular dichroism angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Park, Jin-Hong; Kim, Choong H.; Rhim, Jun-Won; Han, Jung Hoon

    2012-05-01

    We show, by way of tight-binding and first-principles calculations, that a one-to-one correspondence between an electron's crystal momentum k and nonzero orbital angular momentum (OAM) is a generic feature of surface bands. The OAM forms a chiral structure in momentum space much as its spin counterpart in Rashba model does, as a consequence of the inherent inversion symmetry breaking at the surface but not of spin-orbit interaction. This is the orbital counterpart of conventional Rashba effect and may be called the “orbital Rashba effect.” The circular dichroism (CD) angle-resolved photoemission (ARPES) method is an efficient way to detect this new order, and we derive formulas explicitly relating the CD-ARPES signal to the existence of OAM in the band structure. The cases of degenerate p- and d-orbital bands are considered.

  18. Induced circular dichroism of thioflavin T interacting with acetylcholinesterase: A computational study

    NASA Astrophysics Data System (ADS)

    Rybicka, Anna; Pecul, Magdalena

    2015-12-01

    Induced circular dichroism of thioflavin T (ThT) intercalated in acetylcholinesterase has been modeled by means of density functional theory. ThT in acetylcholinesterase is reported to be flat and thus cannot exhibit induced CD associated with a 'chiral twist' mechanism, i.e. stabilization of one of the enantiomeric forms by a chiral environment. Even so, the presence of aromatic side chains forming the cavity in which ThT is bound is predicted to induce substantial Cotton effect in ThT, of the magnitude comparable to the one predicted to originate from a 'chiral twist' mechanism. The predicted Cotton effect originates mostly from deformation of electron density of ThT by the presence of the aromatic rings, the contribution from crystallization water molecules being one order of magnitude smaller.

  19. Infrared, Raman and ultraviolet with circular dichroism analysis and theoretical calculations of tedizolid

    NASA Astrophysics Data System (ADS)

    Michalska, Katarzyna; Mizera, Mikołaj; Lewandowska, Kornelia; Cielecka-Piontek, Judyta

    2016-07-01

    Tedizolid is the newest antibacterial agent from the oxazolidinone class. For its identification, FT-IR (2000-400 cm-1) and Raman (2000-400 cm-1) analyses were proposed. Studies of the enantiomeric purity of tedizolid were conducted based on ultraviolet-circular dichroism (UV-CD) analysis. Density functional theory (DFT) with the B3LYP hybrid functional and 6-311G(2df,2pd) basis set was used for support of the analysis of the FT-IR and Raman spectra. Theoretical methods made it possible to conduct HOMO and LUMO analysis, which was used to determine the charge transfer for two tedizolid enantiomers. Molecular electrostatic potential maps were calculated with the DFT method for both tedizolid enantiomers. The relationship between the results of ab initio calculations and knowledge about the chemical-biological properties of R- and S-tedizolid enantiomers is also discussed.

  20. Chirality transfer from gold nanocluster to adsorbate evidenced by vibrational circular dichroism

    PubMed Central

    Dolamic, Igor; Varnholt, Birte; Bürgi, Thomas

    2015-01-01

    The transfer of chirality from one set of molecules to another is fundamental for applications in chiral technology and has likely played a crucial role for establishing homochirality on earth. Here we show that an intrinsically chiral gold cluster can transfer its handedness to an achiral molecule adsorbed on its surface. Solutions of chiral Au38(2-PET)24 (2-PET=2-phenylethylthiolate) cluster enantiomers show strong vibrational circular dichroism (VCD) signals in vibrations of the achiral adsorbate. Density functional theory (DFT) calculations reveal that 2-PET molecules adopt a chiral conformation. Chirality transfer from the cluster to the achiral adsorbate is responsible for the preference of one of the two mirror images. Intermolecular interactions between the adsorbed molecules on the crowded cluster surface seem to play a dominant role for the phenomena. Such chirality transfer from metals to adsorbates likely plays an important role in heterogeneous enantioselective catalysis. PMID:25960309

  1. Enhanced circular dichroism based on the dual-chiral metamaterial in terahertz regime

    NASA Astrophysics Data System (ADS)

    Jian, Shao; Jie, Li; Ying-Hua, Wang; Jia-Qi, Li; Zheng-Gao, Dong; Lin, Zhou

    2016-05-01

    The obvious circular dichroism (CD) and optical activity can be obtained based on the chiral metamaterial due to the plasmon-enhanced effect, which is very attractive for future compact devices with enhanced capabilities of light manipulation. In this paper, we propose a dual-chiral metamaterial composed of bilayer asymmetric split ring resonators (ASRR) that are in mirror-symmetry shape. It is demonstrated that the CD can get enhancement in the terahertz regime. Moreover, the CD can be further improved by modulating the asymmetry of ASRR. The enhanced CD effect in the terahertz regime has great potential applications in sensing, biomedical imaging, and molecular recognition. Project supported by the National Natural Science Foundation of China (Grant Nos. 11174051, 11374049, and 11204139), the Natural Science Foundation of Jiangsu Province of China (Grant No. BK20131283), and the Fundamental Research Funds for the Central Universities, China.

  2. Circular dichroism spectroscopy: An efficient approach for the quantitation of ampicillin in presence of cloxacillin.

    PubMed

    Rahman, Nafisur; Khan, Sumaiya

    2016-05-01

    Ampicillin exhibited a negative and a positive cotton effects on the circular dichroism (CD) spectra in the wavelength range of 200-280nm. Cloxacillin showed a positive cotton band peaking at 228nm. Three sensitive, precise and accurate CD spectroscopic methods have been developed for the determination of ampicillin and cloxacillin. Method A was used for the determination of ampicillin in presence of cloxacillin by measuring ellipticity at 206nm. Method B and C were employed to determine ampicillin and cloxacillin based on evaluation of ellipticity at 233nm and 228nm, respectively. Methods A, B and C showed linearity in the concentration range of 10-40μgmL(-1), 5-40μgmL(-1) ampicillin and 10-80μgmL(-1) cloxacillin, respectively. The method A was successfully applied to the determination of ampicillin in commercial dosage forms containing equivalent amount of cloxacillin. PMID:26909703

  3. Strongly tunable circular dichroism in gammadion chiral phase-change metamaterials.

    PubMed

    Cao, Tun; Zhang, Lei; Simpson, Robert E; Wei, Chenwei; Cryan, Martin J

    2013-11-18

    A metal/phase-change material/metal tri-layer planar chiral metamaterial in the shape of a gammadion is numerically modelled. The chiral metamaterial is integrated with Ge2Sb2Te5 phase-change material (PCM) to accomplish a wide tuning range of the circular dichroism (CD) in the mid-infrared wavelength regime. A photothermal model is used to study the temporal variation of the temperature of the Ge2Sb2Te5 layer and to show the potential for fast switching the phase of Ge2Sb2Te5 under a low incident light intensity of 0.016mW/μm2. PMID:24514301

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

    PubMed Central

    Hu, Li; Huang, Yingzhou; 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. PMID:26538460

  5. Ultrafast conformational changes in biomolecules studied by time-resolved circular dichroism

    NASA Astrophysics Data System (ADS)

    Changenet-Barret, P.; Hache, F.

    2015-10-01

    Circular dichroism (CD) is known to be a very sensitive probe of molecular conformation, and it is in particular widely used in biochemistry. Measuring the CD as a function of time is therefore very appealing to access information on the dynamics of conformational changes in molecules or biomolecules. We have implemented such a time-resolved experiments in two complementary configurations: a sub-picosecond pump-probe one and a microsecond detection of CD coupled to a T-jump experiment. We present two experiments based on these techniques: the ultrafast motion of the carbonyl group in the chromophore of the Photoactive Yellow Protein after photoexcitation and the dynamics of thermal denaturation in model peptides.

  6. Dodine as a transparent protein denaturant for circular dichroism and infrared studies.

    PubMed

    Guin, Drishti; Sye, Kori; Dave, Kapil; Gruebele, Martin

    2016-05-01

    The fungicide dodine combines the cooperative denaturation properties of guanidine with the mM denaturation activity of SDS. It was previously tested only on two small model proteins. Here we show that it can be used as a chemical denaturant for phosphoglycerate kinase (PGK), a much larger two-domain enzyme. In addition to its properties as a chemical denaturant, dodine facilitates thermal denaturation of PGK, and we show for the first time that it also facilitates pressure denaturation of a protein. Much higher quality circular dichroism and amide I' infrared spectra of PGK can be obtained in dodine than in guanidine, opening the possibility for use of dodine as a denaturant when UV or IR detection is desirable. One caution is that dodine denaturation, like other detergent-based denaturants, is less reversible than guanidine denaturation. PMID:26941080

  7. Classical Magnetic Dipole Moments for the Simulation of Vibrational Circular Dichroism by ab Initio Molecular Dynamics.

    PubMed

    Thomas, Martin; Kirchner, Barbara

    2016-02-01

    We present a new approach for calculating vibrational circular dichroism spectra by ab initio molecular dynamics. In the context of molecular dynamics, these spectra are given by the Fourier transform of the cross-correlation function of magnetic dipole moment and electric dipole moment. We obtain the magnetic dipole moment from the electric current density according to the classical definition. The electric current density is computed by solving a partial differential equation derived from the continuity equation and the condition that eddy currents should be absent. In combination with a radical Voronoi tessellation, this yields an individual magnetic dipole moment for each molecule in a bulk phase simulation. Using the chiral alcohol 2-butanol as an example, we show that experimental spectra are reproduced very well. Our approach requires knowing only the electron density in each simulation step, and it is not restricted to any particular electronic structure method. PMID:26771403

  8. Circular dichroism spectroscopy: An efficient approach for the quantitation of ampicillin in presence of cloxacillin

    NASA Astrophysics Data System (ADS)

    Rahman, Nafisur; Khan, Sumaiya

    2016-05-01

    Ampicillin exhibited a negative and a positive cotton effects on the circular dichroism (CD) spectra in the wavelength range of 200-280 nm. Cloxacillin showed a positive cotton band peaking at 228 nm. Three sensitive, precise and accurate CD spectroscopic methods have been developed for the determination of ampicillin and cloxacillin. Method A was used for the determination of ampicillin in presence of cloxacillin by measuring ellipticity at 206 nm. Method B and C were employed to determine ampicillin and cloxacillin based on evaluation of ellipticity at 233 nm and 228 nm, respectively. Methods A, B and C showed linearity in the concentration range of 10-40 μg mL- 1, 5-40 μg mL- 1 ampicillin and 10-80 μg mL- 1 cloxacillin, respectively. The method A was successfully applied to the determination of ampicillin in commercial dosage forms containing equivalent amount of cloxacillin.

  9. Reaction monitoring using mid-infrared laser-based vibrational circular dichroism.

    PubMed

    Rüther, Anja; Pfeifer, Marcel; Lórenz-Fonfría, Víctor A; Lüdeke, Steffen

    2014-09-01

    Changes in vibrational circular dichroism (VCD) were recorded on-line during a chemical reaction. The chiral complex nickel-(-)-sparteine chloride was hydrolyzed to free (-)-sparteine base in a biphasic system of sodium hydroxide solution and chloroform (CHCl(3)). Infrared (IR) and VCD spectra were iteratively recorded after pumping a sample from the CHCl(3) phase through a lab-built VCD spectrometer equipped with a tunable mid-IR quantum cascade laser light source, which allows for VCD measurements even in the presence of strongly absorbing backgrounds. Time-dependent VCD spectra were analyzed by singular value decomposition and global exponential fitting. Spectral features corresponding to the complex and free (-)-sparteine could be clearly identified in the fitted amplitude spectrum, which was associated with an exponential decay with an apparent time constant of 127 min (t(½) = 88 min). PMID:24623312

  10. Photoelectron circular dichroism of bicyclic ketones from multiphoton ionization with femtosecond laser pulses.

    PubMed

    Lux, Christian; Wollenhaupt, Matthias; Sarpe, Cristian; Baumert, Thomas

    2015-01-12

    Photoelectron circular dichroism (PECD) is a CD effect up to the ten-percent regime and shows contributions from higher-order Legendre polynomials when multiphoton ionization is compared to single-photon ionization. We give a full account of our experimental methodology for measuring the multiphoton PECD and derive quantitative measures that we apply on camphor, fenchone and norcamphor. Different modulations and amplitudes of the contributing Legendre polynomials are observed despite the similarity in chemical structure. In addition, we study PECD for elliptically polarized light employing tomographic reconstruction methods. Intensity studies reveal dissociative ionization as the origin of the observed PECD effect, whereas ionization of the intermediate resonance is dominating the signal. As a perspective, we suggest to make use of our tomographic data as an experimental basis for a complete photoionization experiment and give a prospect of PECD as an analytic tool. PMID:25492564

  11. Hexamminecobalt(III)-induced condensation of calf thymus DNA: circular dichroism and hydration measurements

    PubMed Central

    Kankia, Besik I.; Buckin, Vitaly; Bloomfield, Victor A.

    2001-01-01

    The interaction of hexamminecobalt(III), Co(NH3)63+, with 160 and 3000–8000 bp length calf thymus DNA has been investigated by circular dichroism, acoustic and densimetric techniques. The acoustic titration curves of 160 bp DNA revealed three stages of interaction: (i) Co(NH3)63+ binding up to the molar ratio [Co(NH3)63+]/[P] = 0.25, prior to DNA condensation; (ii) a condensation process between [Co(NH3)63+]/[P] = 0.25 and 0.30; and (iii) precipitation after [Co(NH3)63+]/[P] = 0.3. In the case of 3000–8000 bp DNA only two processes were observed: (i) binding up to [Co(NH3)63+]/[P] = 0.3; and (ii) precipitation after this point. In agreement with earlier observations, long DNA aggregates without changes in its B-form circular dichroism spectrum, while short DNA demonstrates a positive B→Ψ transition after [Co(NH3)63+]/[P] = 0.25. From ultrasonic and densimetric measurements the effects of Co(NH3)63+ binding on volume and compressibility have been obtained. The binding of Co(NH3)63+ to both short and long DNA is characterized by similar changes in volume and compressibility calculated per mole Co(NH3)63+: ΔV = 9 cm3 mol–1 and Δκ = 33 × 10–4 cm3 mol–1 bar–1. The positive sign of the parameters indicates dehydration, i.e. water release from Co(NH3)63+ and the atomic groups of DNA. This extent of water displacement would be consistent with the formation of two direct, hydrogen bonded contacts between the cation and the phosphates of DNA. PMID:11433025

  12. Characterisation of Conformational and Ligand Binding Properties of Membrane Proteins Using Synchrotron Radiation Circular Dichroism (SRCD).

    PubMed

    Hussain, Rohanah; Siligardi, Giuliano

    2016-01-01

    Membrane proteins are notoriously difficult to crystallise for use in X-ray crystallographic structural determination, or too complex for NMR structural studies. Circular dichroism (CD) is a fast and relatively easy spectroscopic technique to study protein conformational behaviour in solution. The advantage of synchrotron radiation circular dichroism (SRCD) measured with synchrotron beamlines compared to the CD from benchtop instruments is the extended spectral far-UV region that increases the accuracy of secondary structure estimations, in particular under high ionic strength conditions. Membrane proteins are often available in small quantities, and for this SRCD measured at the Diamond B23 beamline has successfully facilitated molecular recognition studies. This was done by probing the local tertiary structure of aromatic amino acid residues upon addition of chiral or non-chiral ligands using long pathlength cells (1-5 cm) of small volume capacity (70 μl-350 μl). In this chapter we describe the use of SRCD to qualitatively and quantitatively screen ligand binding interactions (exemplified by Sbma, Ace1 and FsrC proteins); to distinguish between functionally similar drugs that exhibit different mechanisms of action towards membrane proteins (exemplified by FsrC); and to identify suitable detergent conditions to observe membrane protein-ligand interactions using stabilised proteins (exemplified by inositol transporters) as well as the stability of membrane proteins (exemplified by GalP, Ace1). The importance of the in solution characterisation of the conformational behaviour and ligand binding properties of proteins in both far- andnear-UV regions and the use of high-throughput CD (HT-CD) using 96- and 384-well multiplates to study the folding effects in various protein crystallisation buffers are also discussed. PMID:27553234

  13. Time-Resolved X-Ray Magnetic Circular Dichroism - A Selective Probe of Magnetization Dynamics on Nanosecond Timescales

    NASA Astrophysics Data System (ADS)

    Pizzini, Stefania; Vogel, Jan; Bonfim, Marlio; Fontaine, Alain

    Many synchrotron radiation techniques have been developed in the last 15 years for studying the magnetic properties of thin-film materials. The most attractive properties of synchrotron radiation are its energy tunability and its time structure. The first property allows measurements in resonant conditions at an absorption edge of each of the magnetic elements constituting the probed sample, and the latter allows time-resolved measurements on subnanosecond timescales. In this review, we introduce some of the synchrotron-based techniques used for magnetic investigations. We then describe in detail X-ray magnetic circular dichroism (XMCD) and how time-resolved XMCD studies can be carried out in the pump-probe mode. Finally, we illustrate some applications to magnetization reversal dynamics in spin valves and tunnel junctions, using fast magnetic field pulses applied along the easy magnetization axis of the samples. Thanks to the element-selectivity of X-ray absorption spectroscopy, the magnetization dynamics of the soft (Permalloy) and the hard (cobalt) layers can be studied independently. In the case of spin valves, this allowed us to show that two magnetic layers that are strongly coupled in a static regime can become uncoupled on nanosecond timescales.Present address: Universidade Federal do Paraná, Centro Politécnico CP 19011, Curitiba - PR CEP 81531-990, Brazil

  14. Cadmium binding studies to the earthworm Lumbricus rubellus metallothionein by electrospray mass spectrometry and circular dichroism spectroscopy

    SciTech Connect

    Ngu, Thanh T.; Sturzenbaum, Stephen R.; Stillman, Martin J. . E-mail: Martin.Stillman@uwo.ca

    2006-12-08

    The earthworm Lumbricus rubellus has been found to inhabit cadmium-rich soils and accumulate cadmium within its tissues. Two metallothionein (MT) isoforms (1 and 2) have been identified and cloned from L. rubellus. In this study, we address the metalation status, metal coordination, and structure of recombinant MT-2 from L. rubellus using electrospray ionization mass spectrometry (ESI-MS), UV absorption, and circular dichroism (CD) spectroscopy. This is the first study to show the detailed mass and CD spectral properties for the important cadmium-containing earthworm MT. We report that the 20-cysteine L. rubellus MT-2 binds seven Cd{sup 2+} ions. UV absorption and CD spectroscopy and ESI-MS pH titrations show a distinct biphasic demetalation reaction, which we propose results from the presence of two metal-thiolate binding domains. We propose stoichiometries of Cd{sub 3}Cys{sub 9} and Cd{sub 4}Cys{sub 11} based on the presence of 20 cysteines split into two isolated regions of the sequence with 11 cysteines in the N-terminal and 9 cysteines in the C-terminal. The CD spectrum reported is distinctly different from any other metallothionein known suggesting quite different binding site structure for the peptide.

  15. Structural circular birefringence and dichroism quantified by differential decomposition of spectroscopic transmission Mueller matrices from Cetonia aurata.

    PubMed

    Arwin, H; Mendoza-Galván, A; Magnusson, R; Andersson, A; Landin, J; Järrendahl, K; Garcia-Caurel, E; Ossikovski, R

    2016-07-15

    Transmission Mueller-matrix spectroscopic ellipsometry is applied to the cuticle of the beetle Cetonia aurata in the spectral range 300-1000 nm. The cuticle is optically reciprocal and exhibits circular Bragg filter features for green light. By using differential decomposition of the Mueller matrix, the circular and linear birefringence as well as dichroism of the beetle cuticle are quantified. A maximum value of structural optical activity of 560°/mm is found. PMID:27420518

  16. Magneto-Circular Dichroism Spectra of Cd1-xMnxTe-MnTe Multiple Quantum Well Prepared by Ionized-Cluster Beam Technique

    NASA Astrophysics Data System (ADS)

    Anno, Hiroaki; Koyanagi, Tsuyoshi; Matsubara, Kakuei

    1993-01-01

    Cd1-xMnxTe-MnTe multiple quantum wells were successfully grown on a sapphire (0001) substrate by the ionized-cluster beam deposition technique. In the magneto-circular dichroism spectra, peaks are observed at the energies where shoulders appear in the optical absorption spectra. The peaks shift toward higher energies as the Cd1-xMnxTe well width decreases. The magneto-optical effect is attributed to the Zeeman splitting of mini-band levels due to the spin exchange interaction between Mn2+ magnetic ions and electrons strongly confined in quantum wells.

  17. 4-Arylflavan-3-ols as Proanthocyanidin Models: Absolute Configuration via Density Functional Calculation of Electronic Circular Dichroism

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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...

  18. Estimation of the number of alpha-helical and beta-strand segments in proteins using circular dichroism spectroscopy.

    PubMed Central

    Sreerama, N.; Venyaminov, S. Y.; Woody, R. W.

    1999-01-01

    A simple approach to estimate the number of alpha-helical and beta-strand segments from protein circular dichroism spectra is described. The alpha-helix and beta-sheet conformations in globular protein structures, assigned by DSSP and STRIDE algorithms, were divided into regular and distorted fractions by considering a certain number of terminal residues in a given alpha-helix or beta-strand segment to be distorted. The resulting secondary structure fractions for 29 reference proteins were used in the analyses of circular dichroism spectra by the SELCON method. From the performance indices of the analyses, we determined that, on an average, four residues per alpha-helix and two residues per beta-strand may be considered distorted in proteins. The number of alpha-helical and beta-strand segments and their average length in a given protein were estimated from the fraction of distorted alpha-helix and beta-strand conformations determined from the analysis of circular dichroism spectra. The statistical test for the reference protein set shows the high reliability of such a classification of protein secondary structure. The method was used to analyze the circular dichroism spectra of four additional proteins and the predicted structural characteristics agree with the crystal structure data. PMID:10048330

  19. Circular dichroism in valence photoelectron spectroscopy of free unoriented chiral molecules: Camphor and bromocamphor

    SciTech Connect

    Lischke, T.; Boewering, N.; Schmidtke, B.; Mueller, N.; Khalil, T.; Heinzmann, U.

    2004-08-01

    The circular dichroism in the photoelectron angular distribution was investigated for valence photoionization of randomly oriented pure enantiomers of camphor and bromocamphor molecules using circularly polarized light in the vacuum ultraviolet. The forward-backward electron emission spectra were recorded simultaneously with two spectrometers at several opposite angles relative to the propagation direction of the photon beam and compared for each of the two substances. Measurements were also carried out for reversed light helicity and opposite molecular handedness. For the left- and right-handed enantiomers of both molecules we observed asymmetries of comparable magnitude up to several percent. The measured asymmetry parameters vary strongly for different orbital binding energies and also for the selected photon energies in the valence region. The results for both molecules are compared. They suggest a strong influence of the final states on the asymmetry, depending on the chiral geometry of the molecular electronic structure, as well as a significant dependence on the initial states involved. They also confirm theoretical predictions describing the effect in pure electric-dipole approximation.

  20. The circular dichroism and X-ray diffraction of DNA condensed from ethanolic solutions.

    PubMed Central

    Gray, D M; Edmondson, S P; Lang, D; Vaughan, M

    1979-01-01

    It is known that DNA in aqueous-ethanol solutions undergoes a B to A conformational change between 60% and 80% (w/w) ethanol. We have found that precipitates formed by adding salt to DNA in 60% and 80% ethanolic solutions can be very different. DNA precipitated from 60% ethanol forms a fine condensate that only slowly settles out of suspension and shows a characteristic differential scattering of circularly polarized light at long wavelengths. DNA precipitated from 80% ethanol forms a flocculent aggregate that exhibits the CD spectral features of the A conformation. Data from circular dichroism spectra of natural and synthetic nucleic acids and from X-ray diffraction patterns of the precipitates show that DNA molecules precipitated from 60% and 80% ethanol are, respectively, in the B and A conformation. Therefore, the different secondary conformations of DNA in ethanolic solutions are maintained during precipitation under these conditions. These results are of general importance for the preparation and study of condensed forms of DNA, since a relatively small change in the extent of dehydration can change the secondary conformation of DNA and markedly affect the character of a subsequent precipitate. Images PMID:572544

  1. Band modification in (Ga, Mn)As evidenced by new measurement scheme - photoresistance magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Huang, X. J.; Wang, L. G.; Chen, L.; Zhao, J. H.; Zheng, H. Z.

    2012-11-01

    A new scheme for measuring magneto-optical (MO) effect is developed in the present work, called photoresistance magnetic circular dichroism (PR-MCD). It detects the differential photoresistance of materials between two circularly polarized excitations. That allows us to detect the MO effect induced mainly by interband transitions, as evidenced by the appearance of a clear long wavelength cutoff at 840 nm in PR-MCD spectrum. Our results provide unambiguous evidence that the host semiconductor band structure of (Ga, Mn)As is indeed modified by the strong exchange interactions. It is also found that the interband-induced MO effect decays rather fast with increasing temperatures as compared to MO effects observed in conventional MCD measurements. Moreover, our PR-MCD measurements show interesting feature of diluted magnetic semiconductor Ga1- x Mn x As of a high mole fraction x. PR-MCD signal persists in a reentrant insulating phase at temperatures blow half of Curie temperature (~80 K), and disappears right above it. Such an intrigue feature might be self-consistently explained by recent theory, developed for diluted magnetic semiconductors in the strong correlation regime.

  2. Extrinsic 2D chirality: giant circular conversion dichroism from a metal-dielectric-metal square array

    PubMed Central

    Cao, Tun; Wei, Chenwei; Mao, Libang; Li, Yang

    2014-01-01

    Giant chiroptical responses routinely occur in three dimensional chiral metamaterials (MMs), but their resonance elements with complex subwavelength chiral shapes are challenging to fabricate in the optical region. Here, we propose a new paradigm for obtaining strong circular conversion dichroism (CCD) based on extrinsic 2D chirality in multilayer achiral MMs, showing that giant chiroptical response can be alternatively attained without complex structures. Our structure consists of an array of thin Au squares separated from a continuous Au film by a GaAs dielectric layer, where the Au squares occupy the sites of a rectangular lattice. This structure gives rise to a pronounced extrinsically 2D-chiral effect (CCD) in the mid-infrared (M-IR) region under an oblique incidence, where the 2D-chiral effect is due to the mutual orientation of the Au squares array and the incident light propagation direction; the large magnitude of CCD due to the large difference between left-to-left and right-to-right circularly polarized reflectance conversion efficiencies. PMID:25501766

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

    PubMed Central

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

    2016-01-01

    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. PMID:27220650

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

    PubMed

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

    2016-01-01

    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. PMID:27220650

  6. Suppressed Magnetic Circular Dichroism and Valley-Selective Magnetoabsorption due to the Effective Mass Anisotropy in Bismuth

    NASA Astrophysics Data System (ADS)

    de Visser, Pieter J.; Levallois, Julien; Tran, Michaël K.; Poumirol, Jean-Marie; Nedoliuk, Ievgeniia O.; Teyssier, Jérémie; Uher, Ctirad; van der Marel, Dirk; Kuzmenko, Alexey B.

    2016-07-01

    We measure the far-infrared reflectivity and Kerr angle spectra on a high-quality crystal of pure semimetallic bismuth as a function of magnetic field, from which we extract the conductivity for left- and right-handed circular polarizations. The high spectral resolution allows us to separate the intraband Landau level transitions for electrons and holes. The hole transition exhibits 100% magnetic circular dichroism; it appears only for one polarization as expected for a circular cyclotron orbit. However, the dichroism for electron transitions is reduced to only 13 ±1 %, which is quantitatively explained by the large effective mass anisotropy of the electron pockets of the Fermi surface. This observation is a signature of the mismatch between the metric experienced by the photons and the electrons. It allows for a contactless measurement of the effective mass anisotropy and provides a direction towards valley polarized magnetooptical pumping with elliptically polarized light.

  7. Suppressed Magnetic Circular Dichroism and Valley-Selective Magnetoabsorption due to the Effective Mass Anisotropy in Bismuth.

    PubMed

    de Visser, Pieter J; Levallois, Julien; Tran, Michaël K; Poumirol, Jean-Marie; Nedoliuk, Ievgeniia O; Teyssier, Jérémie; Uher, Ctirad; van der Marel, Dirk; Kuzmenko, Alexey B

    2016-07-01

    We measure the far-infrared reflectivity and Kerr angle spectra on a high-quality crystal of pure semimetallic bismuth as a function of magnetic field, from which we extract the conductivity for left- and right-handed circular polarizations. The high spectral resolution allows us to separate the intraband Landau level transitions for electrons and holes. The hole transition exhibits 100% magnetic circular dichroism; it appears only for one polarization as expected for a circular cyclotron orbit. However, the dichroism for electron transitions is reduced to only 13±1%, which is quantitatively explained by the large effective mass anisotropy of the electron pockets of the Fermi surface. This observation is a signature of the mismatch between the metric experienced by the photons and the electrons. It allows for a contactless measurement of the effective mass anisotropy and provides a direction towards valley polarized magnetooptical pumping with elliptically polarized light. PMID:27419590

  8. Site-directed circular dichroism of proteins: 1Lb bands of Trp resolve position-specific features in tear lipocalin

    PubMed Central

    Gasymov, Oktay K.; Abduragimov, Adil R.; Glasgow, Ben J.

    2008-01-01

    The absorption spectra of N-acetyl-L-tryptophanamide in various solvents were resolved into the sums of the 1La and 1Lb components. The relative intensities of the 0-0 transitions of the 1Lb bands correlate linearly with the solvent polarity values (ETN). A novel strategy, which utilizes a set of the experimental 1Lb bands, was employed to resolve the near-UV CD spectra of tryptophanyl residues. Resolved spectral parameters from the single-tryptophan mutants of tear lipocalin (TL), F99W and Y87W, corroborate the fluorescence as well as structural data of TL. Analysis of the 1Lb bands of the Trp CD spectra in proteins is a valuable tool to obtain the local features. The “DMSO-like” 1Lb band of Trp CD spectra may be used as a “fingerprint” to identify the tryptophanyl side chains in situations where the benzene rings of Trp have van der Waals interactions with the side chains of its nearest neighbor. In addition, the signs and intensities of the components hold information about the side-chain conformations and dynamics in proteins. Combined with Trp mutagenesis, this method we call site-directed circular dichroism is broadly applicable to various proteins to obtain the position-specific data. PMID:18047823

  9. Ground-state wave function of plutonium in PuSb as determined via x-ray magnetic circular dichroism

    DOE PAGESBeta

    Janoschek, M.; Haskel, D.; Fernandez-Rodriguez, J.; van Veenendaal, M.; Rebizant, J.; Lander, G. H.; Zhu, J. -X.; Thompson, J. D.; Bauer, E. D.

    2015-01-14

    Measurements of x-ray magnetic circular dichroism (XMCD) and x-ray absorption near-edge structure (XANES) spectroscopy at the Pu M₄,₅ edges of the ferromagnet PuSb are reported. Using bulk magnetization measurements and a sum rule analysis of the XMCD spectra, we determine the individual orbital [μL = 2.8(1)μB/Pu] and spin moments [μS = –2.0(1)μB/Pu] of the Pu 5f electrons for the first time. Atomic multiplet calculations of the XMCD and XANES spectra reproduce well the experimental data and are consistent with the experimental value of the spin moment. These measurements of Lz and Sz are in excellent agreement with the values thatmore » have been extracted from neutron magnetic form factor measurements, and confirm the local character of the 5f electrons in PuSb. We demonstrate that a split M₅ as well as a narrow M₄ XMCD signal may serve as a signature of 5f electron localization in actinide compounds.« less

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

    NASA Astrophysics Data System (ADS)

    Goings, Joshua J.; Li, Xiaosong

    2016-06-01

    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.

  11. Comparative Analysis of IR and Vibrational Circular Dichroism Spectra for a Series of Camphor-Related Molecules

    NASA Astrophysics Data System (ADS)

    Abbate, Sergio; Burgi, Luigi Filippo; Gangemi, Fabrizio; Gangemi, Roberto; Lebon, France; Longhi, Giovanna; Pultz, Vaughan M.; Lightner, David A.

    2009-09-01

    The absorption spectra and vibrational circular dichroism (VCD) spectra in the mid-IR range 1600-950 cm-1 of 10 camphor-related compounds have been recorded and compared to DFT calculated spectra at the B3PW91/TZ2P level and have been examined together with the corresponding data of the parent molecules. The rigidity of the bridged structure common to all compounds investigated permits (a) identification of three spectroscopic regions in the mid-IR range that can be "used" separately by the interested stereochemist for structural diagnosis and assignment of some major characteristics of the VCD spectra in these regions to what we call "skeletal chiral sense" and (b) recognition of possible conformers for flexible substituent groups, when present. VCD spectra of the 10 molecules have been recorded and analyzed also in the CH-stretching region, 3100-2800 cm-1. Here, we have been able to identify and characterize features of vibrational excitons by comparison of data within the 10-molecule class. To find a theoretical justification of result (a), we have examined the potential energy distribution of the normal modes in the mid-IR range, the partitioning of the calculated rotational strengths in terms of contributions from all couples of internal coordinates, the angle formed by the two vectors, the electric dipole transition moment and the magnetic dipole transition moment, and finally the overlap of normal modes of different molecules. A discussion is provided as to the usability of the introduced algorithms.

  12. Ground-state wave function of plutonium in PuSb as determined via x-ray magnetic circular dichroism

    SciTech Connect

    Janoschek, M.; Haskel, D.; Fernandez-Rodriguez, J.; van Veenendaal, M.; Rebizant, J.; Lander, G. H.; Zhu, J. -X.; Thompson, J. D.; Bauer, E. D.

    2015-01-14

    Measurements of x-ray magnetic circular dichroism (XMCD) and x-ray absorption near-edge structure (XANES) spectroscopy at the Pu M₄,₅ edges of the ferromagnet PuSb are reported. Using bulk magnetization measurements and a sum rule analysis of the XMCD spectra, we determine the individual orbital [μL = 2.8(1)μB/Pu] and spin moments [μS = –2.0(1)μB/Pu] of the Pu 5f electrons for the first time. Atomic multiplet calculations of the XMCD and XANES spectra reproduce well the experimental data and are consistent with the experimental value of the spin moment. These measurements of Lz and Sz are in excellent agreement with the values that have been extracted from neutron magnetic form factor measurements, and confirm the local character of the 5f electrons in PuSb. We demonstrate that a split M₅ as well as a narrow M₄ XMCD signal may serve as a signature of 5f electron localization in actinide compounds.

  13. The Search for Anyon Superconductivity: do High - Superconductors Exhibit a Spontaneous T-Violating Circular Dichroism?

    NASA Astrophysics Data System (ADS)

    Lawrence, Taylor Walton

    The subject of this thesis is an investigation of whether a class of cuprate compounds having superconducting transition temperatures as high as 100 K change the optical properties of reflected light in such a way that would indicate the violation of time-reversal symmetry (T-violation), analogous to that observed in ferromagnets. Such an effect could be interpreted as evidence that anyons are the fundamental microscopic charge carriers responsible for the superconductivity. An "anyon" is a new, fundamental, excitation of a strongly -correlated two-dimensional electron gas which can obey particle-exchange statistics anywhere between the Fermi -Dirac or Bose-Einstein limits. In this thesis, I report on an experiment in which I attempted to reproduce the data originally reported by K. B. Lyons, et al., of AT&T Bell Laboratories. Their data purportedly showed that certain high temperature superconducting compounds exhibit a spontaneous circular dichroism in reflection, below about 200 K. I show a simple extension to their original experiment, which I discovered, that discriminates against an important spurious term, and makes my apparatus exclusively sensitive to T-violating circular dichroism. I found no evidence for a temperature dependent signal in both thin films and an untwinned single crystal of YBa _2Cu_3O _{7-delta} (T_ {rm c} ~ 90 K), to an accuracy approaching 10^{ -6}. However, my data does show a temperature independent "background" signal which is correlated with the optical quality of the sample's surface. I offer a detailed explanation of the origins of this background signal, and show how it can become a temperature dependent signal when there are changes to the surface properties of the sample due to condensation of residual gases in a poor vacuum. Although this experiment shows no evidence for the macroscopic breakdown of time-reversal symmetry, anyons could still be at the heart of high temperature superconductivity, since there are numerous

  14. Circular dichroism spectroscopy of complexes of semiconductor quantum dots with chlorin e6

    NASA Astrophysics Data System (ADS)

    Kundelev, Evgeny V.; Orlova, Anna O.; Maslov, Vladimir G.; Baranov, Alexsander V.; Fedorov, Anatoly V.

    2016-04-01

    Experimental investigation of circular dichroism (CD) spectra of complexes based on ZnS:Mn/ZnS and CdSe/ZnS QDs and chlorin e6 (Ce6) molecules in aqua solutions at different pH level, in methanol and in DMSO were carried out. The changes in CD spectra of Ce6 upon its bonding in complex with semiconductor QDs were analyzed. Application of CD spectroscopy allowed to obtain the CD spectrum of luminescent Ce6 dimer for the first time, and to discover a nonluminescent Ce6 aggregate, preliminary identified as a "tetramer", dissymmetry factor of which is 40 times larger than that for its monomer. The analysis of obtained data showed that in complexes with QDs Ce6 can be either in the monomeric form or in the form of non-luminescent tetramer. The interaction of relatively unstable luminescent Ce6 dimerwith QDs leads to its partial monomerization and formation complexes with chlorin e6 in monomeric form.

  15. Radiation damage to a DNA-binding protein. Combined circular dichroism and molecular dynamics simulation analysis.

    PubMed

    Mazier, S; Villette, S; Goffinont, S; Renouard, S; Maurizot, J C; Genest, D; Spotheim-Maurizot, M

    2008-11-01

    The E. coli lactose operon, the paradigm of gene expression regulation systems, is the best model for studying the effect of radiation on such systems. The operon function requires the binding of a protein, the repressor, to a specific DNA sequence, the operator. We have previously shown that upon irradiation the repressor loses its operator binding ability. The main radiation-induced lesions of the headpiece have been identified by mass spectrometry. All tyrosine residues are oxidized into 3,4-dihydroxyphenylalanine (DOPA). In the present study we report a detailed characterization of the headpiece radiation-induced modification. An original approach combining circular dichroism measurements and the analysis of molecular dynamics simulation of headpieces bearing DOPA-s instead of tyrosines has been applied. The CD measurements reveal an irreversible modification of the headpiece structure and stability. The molecular dynamics simulation shows a loss of stability shown by an increase in internal dynamics and allows the estimation of the modifications due to tyrosine oxidation for each structural element of the protein. The changes in headpiece structure and stability can explain at least in part the radiation-induced loss of binding ability of the repressor to the operator. This conclusion should hold for all proteins containing radiosensitive amino acids in their DNA-binding site. PMID:18959464

  16. Origin-independent two-photon circular dichroism calculations in coupled cluster theory.

    PubMed

    Friese, Daniel H; Hättig, Christof; Rizzo, Antonio

    2016-05-21

    We present the first origin-independent approach for the treatment of two-photon circular dichroism (TPCD) using coupled cluster methods. The approach is assessed concerning its behavior on the choice of the basis set and different coupled cluster methods. We also provide a comparison of results from CC2 with those from density functional theory using the CAM-B3LYP functional. Concerning the basis set we note that in most cases an augmented triple zeta basis or a doubly augmented double zeta basis is needed for reasonably converged results. In the comparison of different coupled cluster methods results from CCSD, CC3 and CC2 have been found to be quite similar in most cases, while CCS results differ remarkably from the results at the higher levels. However, this proof-of-principle study also shows that further benchmarking of DFT and CC2 against accurate coupled cluster reference values (e.g. CCSD or CC3) is needed. PMID:27140590

  17. Giant spin splitting, strong valley selective circular dichroism and valley-spin coupling induced in silicene

    NASA Astrophysics Data System (ADS)

    Qu, Jinfeng; Peng, Xiangyang; Xiao, Di; Zhong, Jianxin

    2016-08-01

    Silicene is a potential candidate for valleytronics. However, in comparison with the transition metal dichalcogenides (TMDs), silicene has a tiny energy gap and zero spin splitting at its Dirac valleys, being unfavorable for valleytronic applications. Based on first principles calculations, we find that by proximity with Bi(111) bilayer, the Dirac valleys of silicene acquire a sizable energy gap and giant spin splittings, which are even larger than the splittings of Mo S2 . Our calculations show that the silicene over Bi layer exhibits a strong valley-contrasting circular dichroism, enabling selective optical pumping of valley carriers. Due to the time reversal symmetry and the breaking of inversion symmetry, the Berry curvatures and the spin splittings are opposite at the K and K' valleys of silicene, and hence the valley and spin are locked and can be simultaneously polarized. In this way, silicene and likely other similar Dirac materials can be comparable to TMDs in valleytronics, which not only adds a new dimension to the properties of silicene but also expands the members of the valleytronic family.

  18. Resolving near-ultraviolet circular dichroism spectra of single trp mutants in tear lipocalin.

    PubMed

    Gasymov, Oktay K; Abduragimov, Adil R; Yusifov, Taleh N; Glasgow, Ben J

    2003-07-15

    Near-ultraviolet circular dichroism (near-UV CD) spectra of tryptophan residues in proteins are complicated because the line shapes are derived from the overlap of both the 1L(a) and the 1L(b) electronic bands that vary independently. Contributing to this complexity, tryptophan near-UV CD spectra differ in the relative amplitude of the 0-0 vibronic band compared to the rest of the 1L(b) spectrum, an inherent feature that may result in poor fitting. To resolve this problem, a computer program that incorporated the separation of the 0-0 transition of 1L(b) component from the rest of the 1L(b) was written in LabVIEW and its amplitude was allowed to vary independently. This method showed dramatically improved fitting of 1L(a) and 1L(b) components in the near-UV CD tryptophan spectra in tear lipocalin mutants featuring low intensity of the 0-0 1L(b) component. Side chain dynamic characteristics (mobility and accessibility to the solvent) identified from different spectroscopic techniques were related to differences in Trp near-UV CD spectra. This method is broadly applicable to different types of Trp near-UV CD spectra. PMID:12814635

  19. Probing tertiary structure of proteins using single Trp mutations with circular dichroism at low temperature.

    PubMed

    Gasymov, Oktay K; Abduragimov, Adil R; Glasgow, Ben J

    2014-01-30

    Trp is the most spectroscopically informative aromatic amino acid of proteins. However, the near-UV circular dichroism (CD) spectrum of Trp is complicated because the intensity and sign of (1)La and (1)Lb bands vary independently. To resolve vibronic structure and gain site-specific information from complex spectra, deconvolution was combined with cooling and site-directed tryptophan substitution. Low temperature near-UV CD was used to probe the local tertiary structure of a loop and α-helix in tear lipocalin. Upon cooling, the enhancement of the intensities of the near-UV CD was not uniform, but depends on the position of Trp in the protein structure. The most enhanced (1)Lb band was observed for Trp at position 124 in the α-helix segment matching the known increased conformational mobility during ligand binding. Some aspects of the CD spectra of W28 and W130 were successfully linked to specific rotamers of Trp previously obtained from fluorescence lifetime measurements. The discussion was based on a framework that the magnitude of the energy differences in local conformations governs the changes in the CD intensities at low temperature. The Trp CD spectral classification of Strickland was modified to facilitate the recognition of pseudo peaks. Near-UV CD spectra harbor abundant information about the conformation of proteins that site directed Trp CD can report. PMID:24404774

  20. Probing Tertiary Structure of Proteins Using Single Trp Mutations with Circular Dichroism at Low Temperature

    PubMed Central

    2015-01-01

    Trp is the most spectroscopically informative aromatic amino acid of proteins. However, the near-UV circular dichroism (CD) spectrum of Trp is complicated because the intensity and sign of 1La and 1Lb bands vary independently. To resolve vibronic structure and gain site-specific information from complex spectra, deconvolution was combined with cooling and site-directed tryptophan substitution. Low temperature near-UV CD was used to probe the local tertiary structure of a loop and α-helix in tear lipocalin. Upon cooling, the enhancement of the intensities of the near-UV CD was not uniform, but depends on the position of Trp in the protein structure. The most enhanced 1Lb band was observed for Trp at position 124 in the α-helix segment matching the known increased conformational mobility during ligand binding. Some aspects of the CD spectra of W28 and W130 were successfully linked to specific rotamers of Trp previously obtained from fluorescence lifetime measurements. The discussion was based on a framework that the magnitude of the energy differences in local conformations governs the changes in the CD intensities at low temperature. The Trp CD spectral classification of Strickland was modified to facilitate the recognition of pseudo peaks. Near-UV CD spectra harbor abundant information about the conformation of proteins that site directed Trp CD can report. PMID:24404774

  1. Numerical study of achiral phase-change metamaterials for ultrafast tuning of giant circular conversion dichroism

    PubMed Central

    Cao, Tun; Wei, Chenwei; Mao, Libang

    2015-01-01

    Control of the polarization of light is highly desirable for detection of material’s chirality since biomolecules have vibrational modes in the optical region. Here, we report an ultrafast tuning of pronounced circular conversion dichroism (CCD) in the mid-infrared (M-IR) region, using an achiral phase change metamaterial (PCMM). Our structure consists of an array of Au squares separated from a continuous Au film by a phase change material (Ge2Sb2Te5) dielectric layer, where the Au square patches occupy the sites of a rectangular lattice. The extrinsically giant 2D chirality appears provided that the rectangular array of the Au squares is illuminated at an oblique incidence, and accomplishes a wide tunable wavelength range between 2664 and 3912 nm in the M-IR regime by switching between the amorphous and crystalline states of the Ge2Sb2Te5. A photothermal model is investigated to study the temporal variation of the temperature of the Ge2Sb2Te5 layer, and shows the advantage of fast transiting the phase of Ge2Sb2Te5 of 3.2 ns under an ultralow incident light intensity of 1.9 μW/μm2. Our design is straightforward to fabricate and will be a promising candidate for controlling electromagnetic (EM) wave in the optical region. PMID:26423517

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

    PubMed

    Uporov, Igor V; Forlemu, Neville Y; Nori, Rahul; Aleksandrov, Tsvetan; Sango, Boris A; Mbote, Yvonne E Bongfen; Pothuganti, Sandeep; Thomasson, Kathryn A

    2015-01-01

    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. PMID:26370961

  3. Structural basis of human erythrocyte glucose transporter function in proteoliposome vesicles: circular dichroism measurements.

    PubMed Central

    Chin, J J; Jung, E K; Chen, V; Jung, C Y

    1987-01-01

    The secondary structural compositions of the human erythrocyte glucose transporter in proteoliposome vesicles were assessed on the basis of circular dichroism (CD) spectra measured in the absence and in the presence of D-glucose or an inhibitor, cytochalasin B. We designed and used a scattered-light-collecting device, which corrects CD spectra for optical artifacts originating from light scattering. Relative contents of eight types of secondary structure were estimated by using basis spectra generated by the eigenvector method based on CD spectra of 15 proteins of known structure. Results indicate that the glucose transporter is composed of approximately 82% alpha-helices, 10% beta-turns, and 8% other random structure, with no beta-strands. In the presence of an excess of D-glucose, the alpha-helical content is reduced by more than 10% and there is a significant increase in the random structure content. Cytochalasin B does not appear to affect the secondary structural composition of the transporter to any significant degree. PMID:3473495

  4. Conformational state of DNA in chromatin subunits. Circular dichroism, melting, and ethidium bromide binding analysis.

    PubMed Central

    Lawrence, J J; Chan, D C; Piette, L H

    1976-01-01

    This study compares some physical properties of DNA in native chromatin and mono-, di-, trinucleosomes obtained after mild micrococcal nuclease digestion. Melting curves and derivatives are shown to be very similar from one sample to another although a shift from 79 to 82 degrees C is observed between the mainly monophasic peak of multimers and chromatin. Careful analysis of the positive band of the circular dichroism spectra shows the appearance of a shoulder at 275nm, the intensity of which increases from the mono- to the di- and trinucleosome. This shoulder is maximum for native chromatin. At the same time binding isotherms of ethidium - bromide are characterized by two highly fluorescent binding sites for all the samples but the product KN of the apparent binding constant of the higher affinity binding sites by the apparent number of those sites increases from the mono- to the di- and trinucleosome. There again the valus is maximum for native chromatin. Such results strongly suggest that the native state of chromatin requires something more than the indefinite repeat of an elementary subunit. Images PMID:1005108

  5. Numerical study of achiral phase-change metamaterials for ultrafast tuning of giant circular conversion dichroism.

    PubMed

    Cao, Tun; Wei, Chenwei; Mao, Libang

    2015-01-01

    Control of the polarization of light is highly desirable for detection of material's chirality since biomolecules have vibrational modes in the optical region. Here, we report an ultrafast tuning of pronounced circular conversion dichroism (CCD) in the mid-infrared (M-IR) region, using an achiral phase change metamaterial (PCMM). Our structure consists of an array of Au squares separated from a continuous Au film by a phase change material (Ge2Sb2Te5) dielectric layer, where the Au square patches occupy the sites of a rectangular lattice. The extrinsically giant 2D chirality appears provided that the rectangular array of the Au squares is illuminated at an oblique incidence, and accomplishes a wide tunable wavelength range between 2664 and 3912 nm in the M-IR regime by switching between the amorphous and crystalline states of the Ge2Sb2Te5. A photothermal model is investigated to study the temporal variation of the temperature of the Ge2Sb2Te5 layer, and shows the advantage of fast transiting the phase of Ge2Sb2Te5 of 3.2 ns under an ultralow incident light intensity of 1.9 μW/μm(2). Our design is straightforward to fabricate and will be a promising candidate for controlling electromagnetic (EM) wave in the optical region. PMID:26423517

  6. Numerical study of achiral phase-change metamaterials for ultrafast tuning of giant circular conversion dichroism

    NASA Astrophysics Data System (ADS)

    Cao, Tun; Wei, Chenwei; Mao, Libang

    2015-10-01

    Control of the polarization of light is highly desirable for detection of material’s chirality since biomolecules have vibrational modes in the optical region. Here, we report an ultrafast tuning of pronounced circular conversion dichroism (CCD) in the mid-infrared (M-IR) region, using an achiral phase change metamaterial (PCMM). Our structure consists of an array of Au squares separated from a continuous Au film by a phase change material (Ge2Sb2Te5) dielectric layer, where the Au square patches occupy the sites of a rectangular lattice. The extrinsically giant 2D chirality appears provided that the rectangular array of the Au squares is illuminated at an oblique incidence, and accomplishes a wide tunable wavelength range between 2664 and 3912 nm in the M-IR regime by switching between the amorphous and crystalline states of the Ge2Sb2Te5. A photothermal model is investigated to study the temporal variation of the temperature of the Ge2Sb2Te5 layer, and shows the advantage of fast transiting the phase of Ge2Sb2Te5 of 3.2 ns under an ultralow incident light intensity of 1.9 μW/μm2. Our design is straightforward to fabricate and will be a promising candidate for controlling electromagnetic (EM) wave in the optical region.

  7. Structural Transition of Bombyx mori Liquid Silk Studied with Vibrational Circular Dichroism Spectroscopy.

    PubMed

    Morisaku, Toshinori; Arai, Sho; Konno, Kohzo; Suzuki, Yu; Asakura, Tetsuo; Yui, Hiroharu

    2015-01-01

    We investigated the structural transition from liquid silk to silk fibers with vibrational circular dichroism spectroscopy. Liquid silk showed a major right-handed optically active band at around 1650 cm(-1) and a minor one at around 1680 cm(-1). The former disappeared over time, while the intensity in the latter increased. With the former wavenumber, liquid silk mainly adopted a random-coil structure. In contrast, the latter may reflect an intermediate structure in the transition. Furthermore, two right-handed bands at around 1630 and 1660 cm(-1) appeared with the disappearance of the major band, and then the wavenumber of the former shifted to around 1620 cm(-1). The shift results from the decrease in the frequency of the CO stretching mode due to the stacking of the β-sheet that comprises fibers. The band at 1660 cm(-1) may reflect another intermediate structure due to its strong correlation with that at 1620 cm(-1) in terms of their temporal change in intensity. PMID:26256598

  8. Solvent-induced conformational changes in cyclic peptides: a vibrational circular dichroism study.

    PubMed

    Merten, Christian; Li, Fee; Bravo-Rodriguez, Kenny; Sanchez-Garcia, Elsa; Xu, Yunjie; Sander, Wolfram

    2014-03-28

    The three-dimensional structure of a peptide is strongly influenced by its solvent environment. In the present study, we study three cyclic tetrapeptides which serve as model peptides for β-turns. They are of the general structure cyclo(Boc-Cys-Pro-X-Cys-OMe) with the amino acid X being either glycine (1), or L- or D-leucine (L- or D-2). Using vibrational circular dichroism (VCD) spectroscopy, we confirm previous NMR results which showed that D-2 adopts predominantly a βII turn structure in apolar and polar solvents. Our results for L-2 indicate a preference for a βI structure over βII. With increasing solvent polarity, the preference for 1 is shifted from βII towards βI. This conformational change goes along with the breaking of an intramolecular hydrogen bond which stabilizes the βII conformation. Instead, a hydrogen bond with a solvent molecule can stabilize the βI turn conformation. PMID:24513908

  9. Magnetic Circular Dichroism Spectroscopy of meso-Tetraphenylporphyrin-Derived Hydroporphyrins and Pyrrole-Modified Porphyrins.

    PubMed

    Rhoda, Hannah M; Akhigbe, Joshua; Ogikubo, Junichi; Sabin, Jared R; Ziegler, Christopher J; Brückner, Christian; Nemykin, Victor N

    2016-07-28

    A large set of free-base and transition-metal 5,10,15,20-tetraphenyl-substituted chlorins, bacteriochlorins, and isobacteriochlorins and their pyrrole-modified analogues were investigated by combined UV-visible spectroscopy, magnetic circular dichroism (MCD), density functional theory (DFT), and time-dependent DFT (TDDFT) approaches and their spectral characteristics were compared to those of the parent compounds, free-base tetraphenylporphyrin 1H2 and chlorin 2H2. It was shown that the nature of the pyrroline substituents in the chlorin derivatives dictates their specific UV-vis and MCD spectroscopic signatures. In all hydroporphyrin-like cases, MCD spectroscopy suggests that the ΔHOMO is smaller than the ΔLUMO for the macrocycle-centered frontier molecular orbitals. DFT and TDDFT calculations were able to explain the large broadening of the UV-vis and MCD spectra of the chlorin diones and their derivatives compared to the other hydroporphyrins and hydroporphyrin analogues. This study contributes to the further understanding of the electronic effects of replacing a pyrrole in porphyrins by pyrrolines or other five-membered heterocycles (oxazoles and imidazoles). PMID:27400337

  10. Applied circular dichroism: a facile spectroscopic tool for configurational assignment and determination of enantiopurity.

    PubMed

    Okuom, Macduff O; Burks, Raychelle; Naylor, Crysta; Holmes, Andrea E

    2015-01-01

    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 (R (2)) 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. PMID:25705549

  11. Electronic Circular Dichroism of [16]Helicene With Simplified TD-DFT: Beyond the Single Structure Approach.

    PubMed

    Bannwarth, Christoph; Seibert, Jakob; Grimme, Stefan

    2016-05-01

    The electronic circular dichroism (ECD) spectrum of the recently synthesized [16]helicene and a derivative comprising two triisopropylsilyloxy protection groups was computed by means of the very efficient simplified time-dependent density functional theory (sTD-DFT) approach. Different from many previous ECD studies of helicenes, nonequilibrium structure effects were accounted for by computing ECD spectra on "snapshots" obtained from a molecular dynamics (MD) simulation including solvent molecules. The trajectories are based on a molecule specific classical potential as obtained from the recently developed quantum chemically derived force field (QMDFF) scheme. The reduced computational cost in the MD simulation due to the use of the QMDFF (compared to ab-initio MD) as well as the sTD-DFT approach make realistic spectral simulations feasible for these compounds that comprise more than 100 atoms. While the ECD spectra of [16]helicene and its derivative computed vertically on the respective gas phase, equilibrium geometries show noticeable differences, these are "washed" out when nonequilibrium structures are taken into account. The computed spectra with two recommended density functionals (ωB97X and BHLYP) and extended basis sets compare very well with the experimental one. In addition we provide an estimate for the missing absolute intensities of the latter. The approach presented here could also be used in future studies to capture nonequilibrium effects, but also to systematically average ECD spectra over different conformations in more flexible molecules. Chirality 28:365-369, 2016. © 2016 Wiley Periodicals, Inc. PMID:27071653

  12. A split beam method for measuring time-resolved circular dichroism

    NASA Astrophysics Data System (ADS)

    Wenzel, Stephan; Buss, Volker

    1997-04-01

    An improvement to the Lewis-Kliger method for measuring transient circular dichroism on the nanosecond time scale is described. The method uses a single-probe beam that is split into two different beams of plane polarized light entering the sample and a retarder from opposite directions in different succession. Rochon polarizers are used as high-quality polarizing beam splitters to select the slow axis component of the emerging elliptical polarized light beams. The intensities of the light beams are determined by an imaging spectrograph coupled to an intensified charge coupled device detector. The split beam method reduces the need for very precise calibration of the central strain plate acting as a retarder and controlling the ellipticity of the probe light. The necessary calculations are simple and can be shown to be equivalent to the formulas derived by Lewis and Kliger. The static CD spectrum of vitamin B12 is presented and compared to a spectrum obtained with a commercial instrument and standard technique. The time resolution of the instrument is demonstrated by observation of photobleaching of carbon monoxy myoglobin from horse heart muscle.

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

    PubMed Central

    Uporov, Igor V.; Forlemu, Neville Y.; Nori, Rahul; Aleksandrov, Tsvetan; Sango, Boris A.; Mbote, Yvonne E. Bongfen; Pothuganti, Sandeep; Thomasson, Kathryn A.

    2015-01-01

    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. PMID:26370961

  14. High Field Magnetic Circular Dichroism in Ferromagnetic InMnSb and InMnAs

    NASA Astrophysics Data System (ADS)

    Meeker, M. A.; Magill, B. A.; Khodaparast, G. A.; Saha, D.; Stanton, C. J.; McGill, S.; Wessels, B. W.

    An understanding of the fundamental interactions in narrow gap ferromagnetic semiconductors such as InMnAs and InMnSb has been developed primarily from static magnetization and electrical transport measurements. In this study, to provide a better understanding of the coupling of the Mn impurities to the conduction and valence bands through the sp-d exchange interactions, we have performed magnetic circular dichroism measurements (MCD) on MOVPE grown InMnAs and InMnSb. In our samples, the Mn content varies from 2% to 10.7% and all the samples have Curie temperatures above 300 K. The samples were photo-excited using a Quartz Tungsten Halogen lamp with energies ranging between 0.92-1.45 eV, and in magnetic fields up to 31 T. The temperatures ranged from 15-190 K. Comparison of the observed MCD with theoretical calculations provides a direct method to probe the band structure including the temperature dependence of the spin-orbit split-off bandgap and g-factors, as well as a means to estimate the sp-d coupling constants. Supported by the AFOSR through grant FA9550-14-1-0376, NSF-Career Award DMR-0846834 , NSF-DMR-60035274 , NSF-DMR-1305666, NSF MRI program (DMR-1229217).

  15. Co-occurrence of circular dichroism and asymmetric transmission in twist nanoslit-nanorod Arrays.

    PubMed

    Wang, Yongkai; Wen, Xiaojing; Qu, Yu; Wang, Li; Wan, Rengang; Zhang, Zhongyue

    2016-07-25

    Circular dichroism (CD) and asymmetric transmission (AT) are important in the field of negative refractive index media and perfect polarization converters. A large difference between T++ and T-- in the transmission matrix T leads to a large CD effect, whereas a large difference between T-+ and T+- leads to a large AT effect. To achieve large CD and AT effects simultaneously, we theoretically analyzed the transmission matrix T and proposed the chiral plasmonic nanostructure of twist nanoslit-nanorod arrays (TNNAs) in this study. Results calculated by the finite element method show that, at around resonant wavelengths, the spectra of T++ and T-- correspondingly present peaks and valleys leading to a large CD effect. Meanwhile one of the spectra for T-+ and T+- presents valleys and another presents peaks leading to a large AT effect. More importantly, the magnitude of CD is equivalent to that of AT. In addition, the CD and AT effects strongly depend on the geometric parameters of TNNAs. Overall, these results are useful for designing chiral plasmonic nanostructures with large CD and AT effects. PMID:27464094

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

    PubMed Central

    Okuom, Macduff O.; Burks, Raychelle; Holmes, Andrea E.

    2015-01-01

    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. PMID:25705549

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

    PubMed

    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. PMID:25802110

  18. Plasmon-Mediated Two-Photon Photoluminescence-Detected Circular Dichroism in Gold Nanosphere Assemblies.

    PubMed

    Jarrett, Jeremy W; Zhao, Tian; Johnson, Jeffrey S; Liu, Xiaoying; Nealey, Paul F; Vaia, Richard A; Knappenberger, Kenneth L

    2016-03-01

    We report plasmon-mediated two-photon photoluminescence (TPPL)-detected circular dichroism (CD) from colloidal metal nanoparticle assemblies. Two classes of solid gold nanosphere (SGN) dimers-heterodimers and homodimers-were examined using polarization-resolved TPPL, second harmonic generation (SHG), and one-photon photoluminescence (OPPL). Unambiguous CD was detected in both the TPPL and SHG signals, and the magnitudes of the CD responses in these measurements showed agreement for individual nanostructures. Heterodimers gave larger CD responses (average TPPL-CDR = 0.62 ± 0.33; average SHG-CDR = 0.51 ± 0.21) than homodimers (average TPPL-CDR = 0.19 ± 0.04; average SHG-CDR = 0.18 ± 0.06). OPPL-CD was not detected for either structure. Analysis of dimer emission properties suggested the CD responses were determined by properties of the one-photon-resonant mode excited by the laser. Average TPPL signals were (4.3 ± 0.6)× larger than those for SHG. Because signal amplitude is a primary determinant for spatial accuracies and precisions obtained from optical microscopy, CD contrast generated from plasmon-mediated TPPL, which we report for the first time, can extend the suite of super-resolution imaging techniques. PMID:26854357

  19. X-ray Magnetic circular dichroism study of hexagonal YbFeO3 thin films

    NASA Astrophysics Data System (ADS)

    Wang, Xiao; Sinha, Kishan; Xu, Xiaoshan; Liu, Yaohua; Keavney, David; Cheng, X. M.

    Multiferroic materials exhibit multiple ferroic orders simultaneously and thus have potential applications in information technology, sensing, and actuation. Hexagonal YbFeO3 is a promising candidate for a multiferroic material with room temperature ferromagnetism because of the expected enhanced Fe moment and higher transition temperature due to the exchange interaction between magnetic Yb and Fe ions. Here we report an x-ray magnetic circular dichroism (XMCD) study of (0001) Hexagonal YbFO3 thin films deposited on (111) yttria-stabilized zirconia substrates via pulsed laser deposition. XMCD spectra for the Fe L2,3 edges and Yb M5 edge were measured with the magnetic field applied parallel to the x-ray propagation direction and 20 degree away from the film normal at beamline 4ID-C of the APS at ANL. Field dependence of the XMCD spectra show that Fe and Yb each has a ferromagnetic ordering at around 6.7 K but with opposite orientations in between. The saturation magnetic moment for Fe is determined by the sum rules to be 0.07 μB / Fe cation at around 6.7 K, about 4 times larger than that in Hexagonal LuFeO3.

  20. B850 pigment-protein complex of Rhodopseudomonas sphaeroides: Extinction coefficients, circular dichroism, and the reversible binding of bacteriochlorophyll

    PubMed Central

    Clayton, Roderick K.; Clayton, Betty J.

    1981-01-01

    Chromatophores of Rhodopseudomonas sphaeroides yield the antenna complex B850 in either of two states, depending on the method of isolation. Methods using dodecyl (= lauryl) dimethylamine oxide yield B850 with an absorption spectrum like that in vivo: the bands at 800 and 850 nm, due to the bacteriochlorophyll (Bchl) components Bchl-800 and Bchl-850, are in ratio A800/A850 = 0.65 ± 0.05. When B850 is isolated by methods using dodecyl sulfate, the Bchl-800 is attenuated or absent. Bchl assays of these materials and of the isolated antenna complex B875 yielded the following extinction coefficients, ±SD, on the basis of the molarity of Bchl: For B875, ε875 = 126 ± 8 mM-1 cm-1. For B850 in the normal (high-Bchl-800) state, ε850 = 132 ± 10 mM-1 cm-1. For the individual components of Bchl in B850, ε850 of Bchl-850 = 184 ± 13 mM-1 cm-1 and ε800 of Bchl-800 = 213 ± 28 mM-1 cm-1. With these coefficients the molecular ratio of Bchl-850 to Bchl-800 equals 1.8 ± 0.4 for B850 in the high-Bchl-800 state. Starting with B850 depleted of Bchl-800, the addition of dodecyldimethylamine oxide restored the 800-nm absorption band. The 850-nm band became shifted toward the blue, narrowed, and slightly attenuated, and its associated circular dichroism became 20% more intense. Free Bchl added with dodecyldimethylamine oxide accelerated the restoration of Bchl-800 and retarded the attenuation of Bchl-850. We conclude that free Bchl can interact reversibly with a binding site for Bchl-800 in the B850 complex, with dodecyl sulfate favoring dissociation and dodecyldimethylamine oxide promoting association. Thus the reversible dissociation of a native chlorophyll-protein complex has now been demonstrated. PMID:16593090

  1. Detailed structural study of β-artemether: Density functional theory (DFT) calculations of Infrared, Raman spectroscopy, and vibrational circular dichroism

    NASA Astrophysics Data System (ADS)

    Wang, Zhiqiang; Chen, Jianchao; Li, Linwei; Zhou, Zhixu; Geng, Yiding; Sun, Tiemin

    2015-10-01

    In this study, the experimental and theoretical studies on the structure of β-artemether are presented. The optimized molecular structure, Mulliken atomic charges, vibrational spectra (IR, Raman and vibrational circular dichroism), and molecular electrostatic potential have been calculated by density functional theory (DFT) using B3LYP method with the 6-311++G (2d, p) basis set. Reliable vibrational assignments for Artemether have been made on the basis of potential energy distribution (PED). The vibrational circular dichroism (VCD) has been explored by ab initio calculations, and then was used to compare with the experimental VCD. The consistence between them confirmed the absolute configuration of Artemether. In addition, HOMO-LUMO of the title compound as well as thermo-dynamical parameters has illustrated the stability of β-artemether.

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

    NASA Astrophysics Data System (ADS)

    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.

  3. Oriented Circular Dichroism: A Method to Characterize Membrane-Active Peptides in Oriented Lipid Bilayers.

    PubMed

    Bürck, Jochen; Wadhwani, Parvesh; Fanghänel, Susanne; Ulrich, Anne S

    2016-02-16

    The structures of membrane-bound polypeptides are intimately related to their functions and may change dramatically with the lipid environment. Circular dichroism (CD) is a rapid analytical method that requires relatively low amounts of material and no labeling. Conventional CD is routinely used to monitor the secondary structure of peptides and proteins in solution, for example, in the presence of ligands and other binding partners. In the case of membrane-active peptides and transmembrane proteins, these measurements can be applied to, and remain limited to, samples containing detergent micelles or small sonicated lipid vesicles. Such traditional CD analysis reveals only secondary structures. With the help of an oriented circular dichroism (OCD) setup, however, based on the preparation of macroscopically oriented lipid bilayers, it is possible to address the membrane alignment of a peptide in addition to its conformation. This approach has been mostly used for α-helical peptides so far, but other structural elements are conceivable as well. OCD analysis relies on Moffitt's theory, which predicts that the electronic transition dipole moments of the backbone amide bonds in helical polypeptides are polarized either parallel or perpendicular to the helix axis. The interaction of the electric field vector of the circularly polarized light with these transitions results in an OCD spectrum of a membrane-bound α-helical peptide, which exhibits a characteristic line shape and reflects the angle between the helix axis and the bilayer normal. For parallel alignment of a peptide helix with respect to the membrane surface (S-state), the corresponding "fingerprint" CD band around 208 nm will exhibit maximum negative amplitude. If the helix changes its alignment via an obliquely tilted (T-state) to a fully inserted transmembrane orientation (I-state), the ellipticity at 208 nm decreases and the value approaches zero due to the decreased interactions between the field and the

  4. Magnetic circular dichroism in the X-ray fluorescence spectra of iron and a glassy-metal iron alloy

    NASA Astrophysics Data System (ADS)

    Hague, C. F.; Mariot, J.-M.

    1995-05-01

    Magnetic circular dichroism (MCD) in the X-ray fluorescence of iron has been examined using white bending magnet radiation at Super-ACO. A new spectrometer fitted with a position sensitive detector provided data with improved statistics compared to earlier results. The origin of a dip observed in the Lα dichroic signal but not in the Lβ dichroic signal is reinterpreted. As a guide to interpretation we have also measured the MCD of glassy FeNiBMo.

  5. Computational Study of the Structure, the Flexibility, and the Electronic Circular Dichroism of Staurosporine - a Powerful Protein Kinase Inhibitor

    NASA Astrophysics Data System (ADS)

    Karabencheva-Christova, Tatyana G.; Singh, Warispreet; Christov, Christo Z.

    2014-07-01

    Staurosporine (STU) is a microbial alkaloid which is an universal kinase inhibitor. In order to understand its mechanism of action it is important to explore its structure-properties relationships. In this paper we provide the results of a computational study of the structure, the chiroptical properties, the conformational flexibility of STU as well as the correlation between the electronic circular dichroism (ECD) spectra and the structure of its complex with anaplastic lymphoma kinase.

  6. A magnetic circular dichroism and optically detected magnetic resonance investigation of Fe2+ and Fe3+ centres in KTaO3

    NASA Astrophysics Data System (ADS)

    Reyher, H. J.; Hausfeld, N.; Pape, M.

    2000-12-01

    A cubic and an axial Fe2+ centre, Fe2+Ta and Fe2+Ta-VO, are found in reduced Fe-doped KTaO3 crystals in conjunction with their trivalent partners. These four defects are characterized by optically detected magnetic resonance (ODMR) via the magnetic circular dichroism (MCD) of the absorption. The g-values are determined by and interpreted using crystal-field terms. For all centres, the optical absorption bands are identified by the tagged-MCD method. The main MCD bands of the divalent ions are attributed to the well known 5T2→{5E} crystal-field transition in the 10 000 cm-1 region. Bands at higher energies are interpreted as intervalence transfer transitions to conduction band-like states.

  7. Pseudo-planar conjugated swastikas metamaterial with giant circular dichroism and negative refraction at near-infrared region

    NASA Astrophysics Data System (ADS)

    Fang, Fang; Gao, Lin; Liao, Honghua

    2016-02-01

    In this paper, a pseudo-planar conjugated swastikas metamaterial (MM) was proposed and investigated numerically at near-infrared region. Numerical results show that the circular dichroism (CD) is more than 25 dB at resonance frequencies. Owing to the stronger chirality, the refractive indices for right-handed and left-handed circularly polarized waves are negative. The surface current distributions are studied to explain mechanism of the chiral behaviors. The pseudo-planar MM is easy to fabricate and thus lead to many applications in photonic devices due to its giant CD effect and negative refraction.

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

    PubMed Central

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

    2016-01-01

    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. PMID:27466066

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

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

    2016-01-01

    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. PMID:27466066

  11. DNA Electronic Circular Dichroism on the Inter-Base Pair Scale: An Experimental-Theoretical Case Study of the AT Homo-Oligonucleotide.

    PubMed

    Di Meo, Florent; Pedersen, Morten N; Rubio-Magnieto, Jenifer; Surin, Mathieu; Linares, Mathieu; Norman, Patrick

    2015-02-01

    A successful elucidation of the near-ultraviolet electronic circular dichroism spectrum of a short double-stranded DNA is reported. Time-dependent density functional theory methods are shown to accurately predict spectra and assign bands on the microscopic base-pair scale, a finding that opens the field for using circular dichroism spectroscopy as a sensitive nanoscale probe of DNA to reveal its complex interactions with the environment. PMID:26261947

  12. X-ray magnetic-circular-dichroism study of Ni/Fe (001) multilayers

    SciTech Connect

    Lin, T.; Schwickert, M.M.; Tomaz, M.A.; Chen, H.; Harp, G.R.

    1999-06-01

    The structure and magnetic properties of Fe/Ni(001) multilayers are studied using x-ray diffraction, magneto-optical Kerr effect magnetometry, and x-ray magnetic circular dichroism. Multilayers are deposited with constant Fe layers (12 {Angstrom}) and wedged Ni layers (0{endash}30 {Angstrom}), repeated 20 times, to explore the magnetic moment and the structure dependence upon thickness of Ni (t{sub Ni}). Up to t{sub Ni}{approx}16 {Angstrom} (11 ML), both the Fe and the Ni have a bct structure, similar to the bulk structure of bcc Fe. The magnetic moments of Ni in the bct region are nearly constant at 0.85{mu}{sub B} for a Ni thickness t{sub Ni} in the range 3 {Angstrom}{lt}t{sub Ni}{lt}16 {Angstrom}. This represents a significant enhancement over the moment in bulk fcc Ni (0.59{mu}B). The Fe/Ni multilayer undergoes a crystalline phase transition between 16 {Angstrom}{lt}t{sub Ni}{lt}23 {Angstrom}, beyond which both the Fe and Ni have an fct structure. In the fct region, the Ni magnetic moment is close to its bulk value and the Fe magnetic moment drops to 1.5{mu}{sub B}, which is {approximately}70{percent} of its bulk value. The crystalline phase transition is also accompanied by a rotation of the magnetic easy axis by 45{degree} in the plane of the film. {copyright} {ital 1999} {ital The American Physical Society}

  13. The secondary structure of echistatin from 1H-NMR, circular-dichroism and Raman spectroscopy.

    PubMed

    Saudek, V; Atkinson, R A; Lepage, P; Pelton, J T

    1991-12-01

    Detailed biophysical studies have been carried out on echistatin, a member of the disintegrin family of small, cysteine-rich, RGD-containing proteins, isolated from the venom of the saw-scaled viper Echis carinatus. Analysis of circular-dichroism spectra indicates that, at 20 degrees C, echistatin contains no alpha-helix but contains mostly beta-turns and beta-sheet. Two isobestic points are observed as the temperature is raised, the conformational changes associated with that observed between 40 degrees C and 72 degrees C being irreversible. Raman spectra also indicate considerable beta-turn and beta-sheet (20%) structure and an absence of alpha-helical structure. Three of the four disulphide bridges are shown to be in an all-gauche conformation, while the fourth adopts a trans-gauche-gauche conformation. The 1H-NMR spectrum of echistatin has been almost fully assigned. A single conformation was observed at 27 degrees C with the four proline residues adopting only the trans conformation. A large number of backbone amide protons were found to exchange slowly, but no segments of the backbone were found to be in either alpha-helical or beta-sheet conformation. A number of turns could be characterised. An irregular beta-hairpin contains the RGD sequence in a mobile loop at its tip. Two of the four disulphide cross-links have been identified from the NMR spectra. The data presented in this paper will serve to define the structure of echistatin more closely in subsequent studies. PMID:1761037

  14. Synchrotron radiation circular dichroism spectroscopy study of recombinant T β4 folding

    NASA Astrophysics Data System (ADS)

    Huang, Yung-Chin; Chu, Hsueh-Liang; Chen, Peng-Jen; Chang, Chia-Ching

    Thymosin beta 4 (T β4) is a 43-amino acid small peptide, has been demonstrated that it can promote cardiac repair, wound repair, tissue protection, and involve in the proliferation of blood cell precursor stem cells of bone marrow. Moreover, T β4 has been identified as a multifunction intrinsically disordered protein, which is lacking the stable tertiary structure. Owing to the small size and disordered character, the T β4 protein degrades rapidly and the storage condition is critical. Therefore, it is not easy to reveal its folding mechanism of native T β4. However, recombinant T β4 protein (rT β4), which fused with a 5-kDa peptide in its amino-terminal, is stable and possesses identical function of T β4. Therefore, rT β4 can be used to study its folding mechanism. By using over-critical folding process, stable folding intermediates of rT β4 can be obtained. Structure analysis of folding intermediates by synchrotron radiation circular dichroism (SRCD) and fluorescence spectroscopies indicate that rT β4 is a random coli major protein and its hydrophobic region becomes compact gradually. Moreover, the rT β4 folding is a two state transition. Thermal denaturation analysis indicates that rT β4 lacks stable tertiary structure. These results indicated that rT β4, similar to T β4, is an intrinsically disordered protein. Research is supported by MOST, Taiwan. MOST 103-2112-M-009-011-MY3. Corresponding author: Chia-Ching Chang; ccchang01@faculty.nctu.edu.tw.

  15. Magnetic circular dichroism spectroscopic characterization of the NOS-like protein from Geobacillus stearothermophilus (gsNOS).

    PubMed

    Kinloch, Ryan D; Sono, Masanori; Sudhamsu, Jawahar; Crane, Brian R; Dawson, John H

    2010-03-01

    Nitric oxide synthase (NOS) catalyzes the NADPH- and O(2)-dependent oxidation of l-arginine (l-Arg) to nitric oxide (NO) and citrulline via an N(G)-hydroxy-l-arginine (NHA) intermediate. Mammalian NOSs have been studied quite extensively; other eukaryotes and some prokaryotes appear to express NOS-like proteins comparable to the oxygenase domain of mammalian NOSs. In this study, a recombinant NOS-like protein from the thermostable bacterium Geobacillus stearothermophilus (gsNOS) has been characterized using magnetic circular dichroism (MCD) and UV-Vis absorption spectroscopic techniques. Spectral comparisons of ligand complexes (with O(2), NO and CO) of substrate-bound (l-Arg or NHA) gsNOS, including the key oxyferrous complex studied at -50 degrees C in cryogenic mixed solvents, with analogous mammalian NOS complexes indicate overall spectroscopic similarities between gsNOS and mammalian NOSs. However, more detailed spectral comparisons reflect subtle structural differences between gsNOS and mammalian NOSs. This may be due to an incomplete tetrahydrobiopterin (BH(4))-binding site and low BH(4)-binding affinity, which may become even lower in the presence of cryosolvent in gsNOS. Although BH(4)-binding may be altered, gsNOS appears to require the pterin for NO production since formation of the stable ferric-NO product complex was only observed when excess BH(4) (>150muM) over gsNOS was present upon single turnover reaction in which O(2) was bubbled into dithionite-reduced NHA-bound protein solution at -35 degrees C or -50 degrees C. PMID:20110129

  16. Zeeman Splitting of Ferromagnetic GaMnAs on InP Observed by Magnetic Circular Dichroism in Reflection Mode

    NASA Astrophysics Data System (ADS)

    Tanaka, H.; Bsatee, M.; Jadwisienczak, W. M.

    2016-08-01

    Systematic investigations of Ga1- x Mn x As grown on InP with different Mn concentrations have been conducted using magnetic circular dichroism (MCD) in reflection mode. The MCD spectrum of Ga0.97Mn0.03As/InP was decomposed into two dispersion curves originating from E 1 and E 1 + Δ1 optical transitions using the energy derivative of a Gaussian function. The Zeeman splitting energy E 1 at the L critical point (0.6 meV) of ferromagnetic Ga0.97Mn0.03As/InP was estimated using a rigid band shift model. Based on the relationship between E 1 and E 0 (Γ critical point) observed in Cd1- x Mn x Te dilute magnetic semiconductor (DMS), the Zeeman splitting energy E 1 (9.6 meV) of ferromagnetic Ga1- x Mn x As/InP was calculated. In addition, it was established that the peaks in the MCD spectra at L critical points shift toward the lower energy side as the Mn concentration is increased, and the observed shift saturates for Mn content of x = 0.001. Furthermore, the measured absorption spectra for Ga1- x Mn x As/InP did not show noticeable peak shifts with increasing Mn content. This suggests that the s, p- d exchange interaction induced in Ga1- x Mn x As/InP has localized nature due to the presence of a Mn rigid sphere of influence.

  17. Relationship between the magnetic moment of Lu and the magnetic behavior of (Y{sub y}Lu{sub 1-y})(Co{sub 1-x}Al{sub x}){sub 2} from x-ray absorption spectroscopy and x-ray magnetic circular dichroism

    SciTech Connect

    Chaboy, J.; Piquer, C.; Laguna-Marco, M. A.; Kawamura, N.; Suzuki, M.; Takagaki, M.

    2007-02-01

    We present an x-ray magnetic circular dichroism (XMCD) study performed at both the Co K edge and the Lu L{sub 2,3} edges on (Y{sub y}Lu{sub 1-y})(Co{sub 1-x}Al{sub x}){sub 2} systems. The XMCD spectra reflect the different magnetic character of these systems, allowing us to monitor the transition from weak to strong ferromagnetism. The XMCD at the Lu L{sub 2,3} edges indicates the existence of an ordered 5d moment at the lutetium sites that is coupled antiparallel to the Co moment. Estimates of the magnetic moment of Lu have been obtained by applying the XMCD sum rules. Our results show that there is a correlation between the Lu 5d-induced magnetic moment and the magnetic character of the (Y{sub y}Lu{sub 1-y})(Co{sub 1-x}Al{sub x}){sub 2} compounds. These results suggest that the developing of the Lu moment plays an important role in reinforcing the magnetic interactions and favoring the ferromagnetic character of the Lu-rich compounds.

  18. Time-resolved x-ray magnetic circular dichroism study of ultrafast demagnetization in a CoPd ferromagnetic film excited by circularly polarized laser pulse

    NASA Astrophysics Data System (ADS)

    López-Flores, Víctor; Arabski, Jacek; Stamm, Christian; Halté, Valérie; Pontius, Niko; Beaurepaire, Eric; Boeglin, Christine

    2012-07-01

    The magnetization dynamics of CoPd films excited by circularly polarized ultrashort laser pulses is studied by time-resolved x-ray magnetic circular dichroism. In those films the ultrafast dynamics measured at the Co-L3 edge is strongly sensitive to the orbital magnetic moment Lz. The amount of angular momentum transferred by the circularly polarized ultrashort laser pulses to the ferromagnetic films is evaluated to ±0.1 ℏ/atom, which is above the detection limit of the experiment. Despite this, no polarization-dependent difference on the magnetization dynamics could be evidenced. These results are explained by ultrafast electronic relaxation mechanisms of the transferred angular momentum, faster than ˜100 fs. This experiment sets the methodology as well as an upper time limit for determination of angular momentum relaxation processes.

  19. Element-resolved orbital polarization in (III,Mn)As ferromagnetic semiconductors from K -edge x-ray magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Wadley, P.; Freeman, A. A.; Edmonds, K. W.; van der Laan, G.; Chauhan, J. S.; Campion, R. P.; Rushforth, A. W.; Gallagher, B. L.; Foxon, C. T.; Wilhelm, F.; Smekhova, A. G.; Rogalev, A.

    2010-06-01

    Using x-ray magnetic circular dichroism (XMCD), we determine the element-specific character and polarization of unoccupied states near the Fermi level in (Ga,Mn)As and (In,Ga,Mn)As thin films. The XMCD at the AsK absorption edge consists of a single peak located on the low-energy side of the edge, which increases with the concentration of ferromagnetic Mn moments. The XMCD at the MnK edge is more detailed and is strongly concentration dependent, which is interpreted as a signature of hole localization for low Mn doping. The results indicate a markedly different character of the polarized holes in low-doped insulating and high-doped metallic films, with a transfer of the hole orbital magnetic moment from Mn to As sites on crossing the metal-insulator transition.

  20. Room-Temperature Ferromagnetism of Cu-Doped ZnO Films Probed by Soft X-Ray Magnetic Circular Dichroism

    SciTech Connect

    Herng, T.S.; Ku, W.; Qi, D.-C.; Berlijn, T.; Yi, J.B.; Yang, K.S.; Dai, Y.; Feng, Y.P.; Santoso, I.; Sanchez-Hanke, C.; Gao, X.Y.; Wee, A.T.S.; Ding, J.; Rusydi, A.

    2010-11-08

    We report direct evidence of room-temperature ferromagnetic ordering in O-deficient ZnO:Cu films by using soft x-ray magnetic circular dichroism and x-ray absorption. Our measurements have revealed unambiguously two distinct features of Cu atoms associated with (i) magnetically ordered Cu ions present only in the oxygen-deficient samples and (ii) magnetically disordered regular Cu{sup 2+} ions present in all the samples. We find that a sufficient amount of both oxygen vacancies (V{sub O}) and Cu impurities is essential to the observed ferromagnetism, and a non-negligible portion of Cu impurities is uninvolved in the magnetic order. Based on first-principles calculations, we propose a microscopic 'indirect double-exchange' model, in which alignments of localized large moments of Cu in the vicinity of the V{sub O} are mediated by the large-sized vacancy orbitals.

  1. Relation between electronic structure and magnetic anisotropy in amorphous TbCo films probed by x-ray magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Ueno, T.; Inami, N.; Sagayama, R.; Wen, Z.; Hayashi, M.; Mitani, S.; Kumai, R.; Ono, K.

    2016-05-01

    Magnetic anisotropy of amorphous TbCo films was investigated by x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD) and synchrotron radiation x-ray diffraction (XRD). The easy magnetization axis was out-of-plane and in-plane for the as-deposited and annealed films, respectively. Remarkable features observed with regard to annealing were a peak-energy shift and increased asymmetry in the Co L 2,3 XMCD spectra and variations of the fine structures in the Tb M 4,5 XMCD spectra. A quantitative analysis of the XMCD results revealed that the Co 3d spin magnetic moment decreased and the orbital magnetic moment increased with annealing. On the other hand, both Tb 4f spin and orbital magnetic moments decreased with annealing. In contrast to the clear change in XAS and XMCD by annealing, no significant change in the amorphous structure was detected by XRD.

  2. Overcoming the existent computational challenges in the ab initio calculations of the two-photon circular dichroism spectra of large molecules using a fragment-recombination approach

    NASA Astrophysics Data System (ADS)

    Diaz, Carlos; Echevarria, Lorenzo; Hernández, Florencio E.

    2013-05-01

    Herein we report on the development of a fragment-recombination approach (FRA) that allows overcoming the computational limitations found in the ab initio calculation of the two-photon circular dichroism (TPCD) spectra of large optically active molecules. Through the comparative analysis of the corresponding theoretical TPCD spectra of the fragments and that of the entire molecule, we prove that TPCD is an additive property. We also demonstrate that the same property apply to two-photon absorption (TPA). TPCD-FRA is expected to find great applications in the structural-analysis of large catalysts and polypeptides due to its reduced computational complexity, cost and time, and to reveal fingerprints in the obscure spectral region between the near and far UV.

  3. Soft x-ray magnetic circular dichroism study of valence and spin states in FeT2O4 (T = V, Cr) spinel oxides

    NASA Astrophysics Data System (ADS)

    Kang, J.-S.; Hwang, Jihoon; Kim, D. H.; Lee, Eunsook; Kim, W. C.; Kim, C. S.; Lee, Han-Koo; Kim, J.-Y.; Han, S. W.; Hong, S. C.; Kim, Bongjae; Min, B. I.

    2013-05-01

    Electronic structures of spinel oxides FeT2O4 (T = V, Cr) have been investigated by employing soft x-ray magnetic circular dichroism (XMCD) and soft x-ray absorption spectroscopy (XAS). XAS reveals that Cr and V ions are trivalent, and that Fe ions are nearly divalent in FeT2O4 (T = V, Cr). Finite XMCD signals are observed in FeV2O4 at T = 80 K, while they are very weak in FeCr2O4. XMCD shows that Fe spins are antiparallel to V and Cr spins, with the V and Cr spins being canted from Fe spins, which suggests a Yafet-Kittel type triangular spin configuration in FeT2O4 (T = V, Cr).

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

    SciTech Connect

    Zamudio-Bayer, V.; Hirsch, K.; Langenberg, A.; Kossick, M.; Ławicki, A.; Lau, J. T.; Terasaki, A.; Issendorff, B. von

    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.

  5. The Role of Heme Chirality in the Circular Dichroism of Heme Proteins

    NASA Astrophysics Data System (ADS)

    Woody, Robert W.; Pescitelli, Gennaro

    2014-07-01

    The rotational strength (R) of the Soret transition in sperm-whale myoglobin (SW Mb), the hemoglobin from Chironomus thummi thummi (CTT Hb), and human hemoglobin (hHb) has been calculated using 20 high-resolution (< 1:5 Å) crystal structures. The intrinsic rotational strength due to heme non-planarity was calculated using π-electron theory and time-dependent density functional theory (TDDFT). Calculations on model protoporphyrins with a planar nucleus and with various torsional angles for the 2- and 4-vinyl substituents showed maximum R of ±0.70 Debye-Bohr magneton (1 DBM = 0.9273 · 10-38 cgs units). Viewing the heme so that the 2- and 4-vinyls are in a counterclockwise relationship, if a vinyl points toward the viewer, it contributes positively to R. Calculations of the intrinsic R for explicit heme geometries of SW Mb, CTT Hb, and hHb gave averages of 0.40±0.09, ±0:44±0.04, and +0.32±0.11 DBM, respectively. Coupling of the Soret transition with aromatic side-chain and peptide backbone transitions was also considered. For SW Mb, the magnitudes of the contributions decreased in the order Rint > Raro > Rpep. For CTT Hb and hHB, the orders were, respectively, Rint > Rpep > Raro and Rint > Raro ≈ Rpep. Human Hb ɑ chains showed the same trend as CTT Hb. Only in the hHb β chains did Raro predominate, with the order Raro > Rint > Rpep. The total predicted Rtot for SW Mb, CTT Hb, and hHb averaged +0.77±0.10 (0.56 - 0.80), -0.37±0.12 (-0.5), and +0.31±0.17 DBM (0.23 - 0.50), respectively. (Values in parentheses are experimental values.) Thus, contrary to the currently accepted view, coupling with aromatic side-chain or peptide transitions is not the dominant factor in the Soret circular dichroism (CD) of these proteins. The Soret CD is dominated by intrinsic CD of the heme chromophore, of which vinyl torsion is the major determinant. This result suggests an explanation for the large effect of heme isomerism on the Soret CD of Mb and Hb. Rotation about the

  6. [Study of the circular dichroism for tribasic complex of amine derivative of beta-cyclodextrindien-Cu2+ -benzoic acid].

    PubMed

    Hu, J; Zhang, H; Shen, B

    1998-02-01

    The circular dichroism spectra of beta-cyclodextrindien, beta-cyclodextrindien-Cu2+ complex, beta-cyclodextrindien-benzoic acid complex, tribasic complex of beta-cyclodextrindien-Cu2+ -benzoic acid were determined by using JASCO J-20C automatic recording spectropolarimeter. The attribution of the bands obtained were made according to the order of orbit energy of Cu2+ complex and benzoic acid, and the coordination structure of tribasic complex of amine derivative of beta-cyclodextrindien-Cu2+ -benzoic acid were decided acording to the structure character of Cu2+ complex and KAJART sector rule of inclusion complex of beta-cyclodextrindien with aromatic compounds. PMID:15810322

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

    SciTech Connect

    Sander, Anke; Christl, Maik; Chiang, Cheng-Tien; Alexe, Marin; Widdra, Wolf

    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.

  8. Induced Circular Dichroism in Phosphine Gold(I) Aryl Acetylide Urea Complexes through Hydrogen-Bonded Chiral Co-Assemblies.

    PubMed

    Dubarle-Offner, Julien; Moussa, Jamal; Amouri, Hani; Jouvelet, Benjamin; Bouteiller, Laurent; Raynal, Matthieu

    2016-03-14

    Phosphine gold(I) aryl acetylide complexes equipped with a central bis(urea) moiety form 1D hydrogen-bonded polymeric assemblies in solution that do not display any optical activity. Chiral co-assemblies are formed by simple addition of an enantiopure (metal-free) complementary monomer. Although exhibiting an intrinsically achiral linear geometry, the gold(I) aryl acetylide fragment is located in the chiral environment displayed by the hydrogen-bonded co-assemblies, as demonstrated by induced circular dichroism (ICD). PMID:26780877

  9. Atomic moments in Mn2CoAl thin films analyzed by X-ray magnetic circular dichroism

    DOE PAGESBeta

    Jamer, M. E.; Assaf, B. A.; Sterbinsky, G. E.; Arena, D. A.; Heiman, D.

    2014-12-05

    Spin gapless semiconductors are known to be strongly affected by structural disorder when grown epitaxially as thin films. The magnetic properties of Mn2CoAl thin films grown on GaAs (001) substrates are investigated here as a function of annealing. This study investigates the atomic-specific magnetic moments of Mn and Co atoms measured through X-ray magnetic circular dichroism as a function of annealing and the consequent structural ordering. Results indicate that the structural distortion mainly affects the Mn atoms as seen by the reduction of the magnetic moment from its predicted value.

  10. Determining the chirality of Weyl fermions from circular dichroism spectra in time-dependent angle-resolved photoemission

    NASA Astrophysics Data System (ADS)

    Yu, Rui; Weng, Hongming; Fang, Zhong; Ding, Hong; Dai, Xi

    2016-05-01

    We show that the intensity of pumped states near Weyl point is different when pumped with left- and right-handed circular-polarized light, which leads to a special circular dichroism (CD) in time-dependent angle-resolved photoemission spectra (ARPES). We derive the expression for the CD of time-dependent ARPES, which is directly related to the chirality of Weyl fermions. Based on the above derivation, we further propose a method to determine the chirality for a given Weyl point from the CD of time-dependent ARPES. The corresponding CD spectra for TaAs has then been calculated from first principles, which can be compared with future experiments.

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

    PubMed

    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. PMID:23702842

  12. A Second Look at Mini-Protein Stability: Analysis of FSD-1 Using Circular Dichroism, Differential Scanning Calorimetry, and Simulations

    PubMed Central

    Feng, Jianwen A.; Kao, Jeff; Marshall, Garland R.

    2009-01-01

    Abstract Mini-proteins that contain <50 amino acids often serve as model systems for studying protein folding because their small size makes long timescale simulations possible. However, not all mini-proteins are created equal. The stability and structure of FSD-1, a 28-residue mini-protein that adopted the ββα zinc-finger motif independent of zinc binding, was investigated using circular dichroism, differential scanning calorimetry, and replica-exchange molecular dynamics. The broad melting transition of FSD-1, similar to that of a helix-to-coil transition, was observed by using circular dichroism, differential scanning calorimetry, and replica-exchange molecular dynamics. The N-terminal β-hairpin was found to be flexible. The FSD-1 apparent melting temperature of 41°C may be a reflection of the melting of its α-helical segment instead of the entire protein. Thus, despite its attractiveness due to small size and purposefully designed helix, sheet, and turn structures, the status of FSD-1 as a model system for studying protein folding should be reconsidered. PMID:19917235

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

    PubMed

    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. PMID:25813022

  14. Combining sequence-based prediction methods and circular dichroism and infrared spectroscopic data to improve protein secondary structure determinations

    PubMed Central

    Lees, Jonathan G; Janes, Robert W

    2008-01-01

    Background A number of sequence-based methods exist for protein secondary structure prediction. Protein secondary structures can also be determined experimentally from circular dichroism, and infrared spectroscopic data using empirical analysis methods. It has been proposed that comparable accuracy can be obtained from sequence-based predictions as from these biophysical measurements. Here we have examined the secondary structure determination accuracies of sequence prediction methods with the empirically determined values from the spectroscopic data on datasets of proteins for which both crystal structures and spectroscopic data are available. Results In this study we show that the sequence prediction methods have accuracies nearly comparable to those of spectroscopic methods. However, we also demonstrate that combining the spectroscopic and sequences techniques produces significant overall improvements in secondary structure determinations. In addition, combining the extra information content available from synchrotron radiation circular dichroism data with sequence methods also shows improvements. Conclusion Combining sequence prediction with experimentally determined spectroscopic methods for protein secondary structure content significantly enhances the accuracy of the overall results obtained. PMID:18197968

  15. Room-temperature photomagnetism in the spinel ferrite (Mn,Zn,Fe)3O4 as seen via soft x-ray magnetic circular dichroism

    SciTech Connect

    Bettinger, J.S.; Piamonteze, C.; Chopdekar, R.V.; Liberati, M.; Arenholz, E.; Suzuki, Y.

    2009-08-01

    We have used X-ray magnetic circular dichroism (XMCD) in conjunction with multiplet simulations to directly probe the origin of photomagnetism in nanocrystalline (Mn,Zn,Fe){sub 3}O{sub 4}. A photomagnetic effect at room temperature has been observed in these films with HeNe illumination. We have verified an intervalence charge transfer among octahedral Fe cations to account for the increase in magnetization observed at and above room temperature in small magnetic fields. Using XMCD, we demonstrate that the dichroism of Fe in octahedral sites increases by 18% at room temperature while the dichroism of Fe in tetrahedral sites does not change.

  16. Laser-driven electron dynamics for circular dichroism in mass spectrometry: from one-photon excitations to multiphoton ionization.

    PubMed

    Kröner, Dominik

    2015-07-15

    The distinction of enantiomers is a key aspect of chemical analysis. In mass spectrometry the distinction of enantiomers has been achieved by ionizing the sample with circularly polarized laser pulses and comparing the ion yields for light of opposite handedness. While resonant excitation conditions are expected to be most efficient, they are not required for the detection of a circular dichroism (CD) in the ion yield. However, the prediction of the size and sign of the circular dichroism becomes challenging if non-resonant multiphoton excitations are used to ionize the sample. Employing femtosecond laser pulses to drive electron wavepacket dynamics based on ab initio calculations, we attempt to reveal underlying mechanisms that determine the CD under non-resonant excitation conditions. Simulations were done for (R)-1,2-propylene oxide, using time-dependent configuration interaction singles with perturbative doubles (TD-CIS(D)) and the aug-cc-pVTZ basis set. Interactions between the electric field and the electric dipole and quadrupole as well as between the magnetic field and the magnetic dipole were explicitly accounted for. The ion yield was determined by treating states above the ionization potential as either stationary or non-stationary with energy-dependent lifetimes based on an approved heuristic approach. The observed population dynamics do not allow for a simple interpretation, because of highly non-linear interactions. Still, the various transition pathways are governed by resonant enantiospecific n-photon excitation, with preferably high transition dipole moments, which eventually dominate the CD in the ionized population. PMID:26151731

  17. Detection of biological particles by the use of circular dichroism measurements improved by scattering theory

    NASA Astrophysics Data System (ADS)

    Rosen, David L.; Pendleton, J. David

    1995-09-01

    Light scattered from optically active spheres was theoretically analyzed for biodetection. The circularly polarized signal of near-forward scattering from circularly dichroic spheres was calculated. Both remote and point biodetection were considered. The analysis included the effect of a circular aperture and beam block at the detector. If the incident light is linearly polarized, a false signal would limit the sensitivity of the biodetector. If the incident light is randomly polarized, shot noise would limit the sensitivity. Suggested improvements to current techniques include a beam block, precise angular measurements, randomly polarized light, index-matching fluid, and larger apertures for large particles.

  18. Electronic structure, noncollinear magnetism, and x-ray magnetic circular dichroism in the Mn3ZnC perovskite

    NASA Astrophysics Data System (ADS)

    Antonov, V. N.; Harmon, B. N.; Yaresko, A. N.; Shpak, A. P.

    2007-04-01

    Mn3ZnC possesses a magnetic phase transition at Tt=233K from a ferromagnetic phase to a ferrimagnetic one with a noncollinear magnetic structure. The transition is accompanied by a structural change from cubic to tetragonal. The experimentally measured x-ray magnetic circular dichroism (XMCD) at the MnK edge shows a drastic change at the magnetic phase transition, which is associated with the appearance of the noncollinear magnetic structure. The electronic structure and XMCD spectra of the Mn3ZnC were investigated theoretically from first principles, using the fully relativistic Dirac linear muffin-tin orbital band-structure method for both the high-temperature cubic and low-temperature tetragonal noncollinear phases. Densities of valence states, spin, and orbital magnetic moments are analyzed and discussed. The origin of the XMCD spectra in the Mn3ZnC compound is examined. The calculated results are compared with the experimental data.

  19. Determination of the composition, encapsulation efficiency and loading capacity in protein drug delivery systems using circular dichroism spectroscopy.

    PubMed

    Peng, Zhili; Li, Shanghao; Han, Xu; Al-Youbi, Abdulrahman O; Bashammakh, Abdulaziz S; El-Shahawi, Mohammad S; Leblanc, Roger M

    2016-09-21

    Peptides and proteins have become very promising drug candidates in recent decades due to their unique properties. However, the application of these drugs has been limited by their high enzymatic susceptibility, low membrane permeability and poor bioavailability when administered orally. Considerable efforts have been made to design and develop drug delivery systems that could transport peptides and proteins to targeted area. Although it is of great importance to determine the composition after loading a drug to the carrier, the ability to do so is significantly limited by current analytical methods. In this letter, five important proteins, α1-antitrypsin, hemoglobin human, human serum albumin, human transferrin and r-globulin were chemically conjugated to two model drug carriers, namely carbon dots and polymer O-(2-carboxyethyl) polyethylene glycol. A simple yet convenient method based on circular dichroism spectroscopy was developed to determine the compositions of the various protein-carrier conjugates. PMID:27590552

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

    SciTech Connect

    Sutherland, J.C.; Polewski, K.; Monteleone, D.C.

    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.

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

    SciTech Connect

    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.

  2. Photoemission Circular Dichroism and Spin Polarization of the Topological Surface States in Ultrathin Bi2Te3 Films.

    PubMed

    Xu, C-Z; Liu, Y; Yukawa, R; Zhang, L-X; Matsuda, I; Miller, T; Chiang, T-C

    2015-07-01

    Circular dichroism (CD) observed by photoemission, being sensitive to the orbital and spin angular momenta of the electronic states, is a powerful probe of the nontrivial surface states of topological insulators, but the experimental results thus far have eluded a comprehensive description. We report a study of Bi2Te3 films with thicknesses ranging from one quintuple layer (two-dimensional limit) to 12 layers (bulk limit) over a wide range of incident photon energy. The data show complex variations in magnitude and sign reversals, which are nevertheless well described by a theoretical calculation including all three photoemission mechanisms: dipole transition, surface photoemission, and spin-orbit coupling. The results establish the nontrivial connection between the spin-orbit texture and CD. PMID:26182112

  3. Thermolysis of (1R,2R)-1,2-dideuteriocyclobutane. An application of vibrational circular dichroism to kinetic analysis

    SciTech Connect

    Chickos, J.S.; Annamalai, A.; Keiderling, T.A.

    1986-07-23

    The relative rates of geometric isomerization to racemization have been studied for the title compound by using a combination of infrared (IR) and vibrational circular dichroism (VCD) spectroscopies, respectively. The results are interpreted with a kinetic and mechanistic scheme which parallels that used by Berson, Pedersen, and Carpenter on a similar study of chiral cyclopropane-d/sub 2/ thermolysis. Relative rates of isomerization to stereomutation of 1.5 +/- 0.4 were obtained which can be interpreted to be consistent with a mechanism best described by random methylene rotation in tetramethylene-d/sub 2/. This is the first application of VCD to kinetic analysis, and the advantages of IR techniques over the more usually employed UV spectroscopies to this type of basic mechanistic problem are illustrated.

  4. Chemistry of porphyrin-appended cellulose strands with a helical structure: spectroscopy, electrochemistry, and in situ circular dichroism spectroelectrochemistry.

    PubMed

    Redl, F X; Lutz, M; Daub, J

    2001-12-17

    Around 100 porphyrin units have been selectively linked at C(6)-O to a cellulose (Avicel). The properties of the metal-free and zincated porphyrin-celluloses 2 and Zn-2 have been determined by optical and electrochemical methods. Circular dichroism indicates a helical arrangement of the porphyrin units and reveals intra-chain coupling reminiscent, in the broadest sense, of strands of nucleic acids. Cyclic voltammetry and spectroelectrochemistry have been used to characterize the radical ions and dianions. The electrochromism of the oxidation of cellulose 2 to porphyrin radical cations of 2 has been employed for both molecular switching and the transduction of an electrochemical input into chiroptical signal expression. PMID:11822435

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

    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. PMID:26882341

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

    PubMed

    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. PMID:26041183

  8. Distinct circular dichroism spectroscopic signatures of polyproline II and unordered secondary structures: Applications in secondary structure analyses

    PubMed Central

    Lopes, Jose L S; Miles, Andrew J; Whitmore, Lee; Wallace, B A

    2014-01-01

    Circular dichroism (CD) spectroscopy is a valuable method for defining canonical secondary structure contents of proteins based on empirically-defined spectroscopic signatures derived from proteins with known three-dimensional structures. Many proteins identified as being “Intrinsically Disordered Proteins” have a significant amount of their structure that is neither sheet, helix, nor turn; this type of structure is often classified by CD as “other”, “random coil”, “unordered”, or “disordered”. However the “other” category can also include polyproline II (PPII)-type structures, whose spectral properties have not been well-distinguished from those of unordered structures. In this study, synchrotron radiation circular dichroism spectroscopy was used to investigate the spectral properties of collagen and polyproline, which both contain PPII-type structures. Their native spectra were compared as representatives of PPII structures. In addition, their spectra before and after treatment with various conditions to produce unfolded or denatured structures were also compared, with the aim of defining the differences between CD spectra of PPII and disordered structures. We conclude that the spectral features of collagen are more appropriate than those of polyproline for use as the representative spectrum for PPII structures present in typical amino acid-containing proteins, and that the single most characteristic spectroscopic feature distinguishing a PPII structure from a disordered structure is the presence of a positive peak around 220nm in the former but not in the latter. These spectra are now available for inclusion in new reference data sets used for CD analyses of the secondary structures of soluble proteins. PMID:25262612

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

    NASA Astrophysics Data System (ADS)

    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.

  10. X-ray magnetic circular dichroism on La2/3Ca1/3Mn0.97Fe0.03O3 thin films

    NASA Astrophysics Data System (ADS)

    Figueroa, Adriana I.; Campillo, Gloria E.; Baker, Alexander A.; Osorio, Jaime A.; Arnache, Oscar L.; van der Laan, Gerrit

    2015-11-01

    The element-selective technique of X-ray magnetic circular dichroism (XMCD) has been used to study the magnetic properties of La2/3Ca1/3Mn0.97Fe0.03O3 (LCMFO) thin films. XMCD measurements below the ferromagnetic ordering temperature at the Mn and Fe L2,3 absorption edges allow the determination of the contributions and relative orientations of the Mn and Fe magnetic moments. A reduction in the Mn L2,3 XMCD signal of the LCMFO sample compared to that for the parent La2/3Ca1/3MnO3 (LCMO) system reveals important modifications in the electronic and magnetic properties with the presence of Fe. The Fe L2,3 X-ray absorption (XAS) for the LCMFO film is characteristic of Fe3+, and the comparison with multiplet calculations shows that the Fe dopants occupy octahedral sites in the crystal, which is consistent with Fe3+ substituting Mn3+ in LCMO. The magnetic moments of Mn and Fe are found to align antiparallel, which suggests the presence of Mn-O-Fe superexchange coupling. This result is consistent with macroscopic magnetometry measurements on the LCMFO system, which show a decrease in saturation magnetization of LCMO with Fe doping.

  11. Circular dichroism of Eu/sup 3 +/ and Nd/sup 3 +/ in a K/sub 3/Nd/sub 2/(NO/sub 3/)/sub 9/ single crystal

    SciTech Connect

    Chatterjee, P.K.; Chowdhury, M.

    1982-06-01

    The low-resolution circular dichroism in (CD) and absorption spectra of doped Nd/sup 3 +/ crystals primarily with a view to verify the expectations regarding low-resolution lanthanide optical activity is presented. In order to compare the CD of the Nd/sup 3 +/ transition, which are commonly considered as electric-dipole allowed, with that of primarily magnetic-dipole-allowed Eu/sup 3 +/ transitions having an identical environment, we have grown and studied a single crystal of K/sub 3/Nd/sub 2/(NO/sub 3/)/sub 9/ with Eu/sup 3 +/ as dopant.

  12. First operation of circular dichroism measurements with periodic photon-helicity switching by a variably polarizing undulator at BL23SU at SPring-8

    NASA Astrophysics Data System (ADS)

    Agui, A.; Yoshigoe, A.; Nakatani, T.; Matsushita, T.; Saitoh, Y.; Yokoya, A.; Tanaka, H.; Miyahara, Y.; Shimada, T.; Takeuchi, M.; Bizen, T.; Sasaki, S.; Takao, M.; Aoyagi, H.; Kudo, T. P.; Satoh, K.; Wu, S.; Hiramatsu, Y.; Ohkuma, H.

    2001-08-01

    This article presents the first operation of the magnetic circular dichroism (MCD) measurement system with periodic photon-helicity switching. The measurements were performed at the newly constructed soft x-ray beamline—BL23SU— at the third-generation synchrotron radiation facility, SPring-8. The monochromator control system was synchronized to the movement of the magnetic row (phase shift) of an APPLE-2 (Sasaki) type variably polarizing undulator. The periodic phase shift of the undulator provided the switching of helicity polarizing soft x rays up to 0.1 Hz. The closed-orbit distortion of the storage ring was controlled to avoid optical axis disturbances at this beamline as well as at other beamlines. The circular dichroism spectra with helicity switching by APPLE-2 show the possibility of high-sensitivity MCD measurements. This method promotes precise MCD measurements and can be a powerful technique to study magnetism as well as dichroism.

  13. Detailed assignment of the magnetic circular dichroism and UV-vis spectra of five-coordinate high-spin ferric [Fe(TPP)(Cl)].

    PubMed

    Paulat, Florian; Lehnert, Nicolai

    2008-06-01

    High-spin (hs) ferric heme centers occur in the catalytic or redox cycles of many metalloproteins and exhibit very complicated magnetic circular dichroism (MCD) and UV-vis absorption spectra. Therefore, detailed assignments of the MCD spectra of these species are missing. In this study, the electronic spectra (MCD and UV-vis) of the five-coordinate hs ferric model complex [Fe(TPP)(Cl)] are analyzed and assigned for the first time. A correlated fit of the absorption and low-temperature MCD spectra of [Fe(TPP)(Cl)] lead to the identification of at least 20 different electronic transitions. The assignments of these spectra are based on the following: (a) variable temperature and variable field saturation data, (b) time-dependent density functional theory calculations, (c) MCD pseudo A-terms, and (d) correlation to resonance Raman (rRaman) data to validate the assignments. From these results, a number of puzzling questions about the electronic spectra of [Fe(TPP)(Cl)] are answered. The Soret band in [Fe(TPP)(Cl)] is split into three components because one of its components is mixed with the porphyrin A2u72-->Eg82/83 (pi-->pi*) transition. The broad, intense absorption feature at higher energy from the Soret band is due to one of the Soret components and a mixed sigma and pi chloro to iron CT transition. The high-temperature MCD data allow for the identification of the Q v band at 20 202 cm(-1), which corresponds to the C-term feature at 20 150 cm(-1). Q is not observed but can be localized by correlation to rRaman data published before. Finally, the low energy absorption band around 650 nm is assigned to two P-->Fe charge transfer transitions, one being the long sought after A1u(HOMO)-->d pi transition. PMID:18438984

  14. Tailoring of the circular dichroism produced by Au covered self-ordered dielectric nanospheres

    NASA Astrophysics Data System (ADS)

    Belardini, A.; Benedetti, A.; Centini, M.; Sibilia, C.; Comoretto, D.; Buatier de Mongeot, F.

    2014-05-01

    Here we show the way to easily tune and engineer the optical response of hybrid structures composed by self ordered dielectric nanospheres partially covered by anisotropic plasmonic structures. The overall structure is a hybrid plasmonic-photonics nanostructure acting as a meta-surface witch morphology allows efficient and versatile light manipulation both for linear polarized and circular polarized fields in the visible and near infrared frequencies.

  15. Solvation dependence observed in the electronic dissymmetry factor spectra: how much information are we missing by analyzing the circular dichroism spectra alone?

    PubMed

    Covington, Cody L; Polavarapu, Prasad L

    2016-05-18

    A study utilizing the newly developed electronic dissymmetry factor (EDF) spectral analysis reveals that for [1,1'-binaphthalene]-2,2'-diol (BN) the experimental EDF spectra show differences due to solvent complexation following the trend in solvent polarity, that are not apparent in the electronic circular dichroism (ECD) or corresponding electronic absorption (EA) spectra. Large experimental EDF spectral magnitudes for BN are seen to peak in regions with no corresponding peaks in the EA spectrum and only a shoulder in the ECD spectrum. This observation indicates that EDF analysis is a new complementary method to conventional ECD analysis of chiral molecules. TD-DFT calculations predict similar EDF peaks as in the experimental EDF spectra, however, the experimentally observed solvation dependent behaviour of the EDF peaks was not reproduced in the calculations. Studies on 6,6'-dibromo-[1,1'-binaphthalene]-2,2'-diol also show similar characteristics in the EDF spectra, though not as pronounced and with different solvent effects. This report thus identifies a new means of chiral molecular structural analysis, hitherto unnoticed, and establishes the use of the dissymmetry factor spectrum as yielding new insight, but at no added cost. PMID:27149694

  16. Determination of the absolute configuration of pentacoordinate chiral phosphorus compounds in solution by using vibrational circular dichroism spectroscopy and density functional theory.

    PubMed

    Yang, Guochun; Xu, Yunjie; Hou, Jianbo; Zhang, Hui; Zhao, Yufen

    2010-02-22

    Vibrational circular dichroism (VCD) spectroscopic measurements and density functional theory (DFT) calculations have been used to obtain the absolute structural information about four sets of diastereomers of pentacoordinate spirophosphoranes derived separately from l- (or d-) valine and l- (or d-) leucine for the first time. Each compound contains three stereogenic centers: one at the phosphorus center and two at the amino acid ligands. Extensive conformational searches for the compounds have been carried out and their vibrational absorption (VA) and VCD spectra have been simulated at the B3LYP/6-311++G** level. Although both VA and VCD spectra are highly sensitive to the structural variation of the apical axis, that is, the O-P-O or N-P-O arrangement, the rotamers generated by the aliphatic amino side chains show little effect on both. The dominant experimental VCD features in the 1100-1500 cm(-1) region were found to be controlled by the chirality at the phosphorus center, whereas those at the C=O stretching region are determined by the chirality of the amino acid ligands. The good agreement between the experimental VA and VCD spectra in CDCl(3) solution and the simulated ones allows us to assign the absolute configurations of these pentacoordinate phosphorus compounds with high confidence. This study shows that the VCD spectroscopy complemented with DFT calculations is a powerful and reliable method for determining the absolute configurations and dominating conformers of synthetic phosphorus coordination complexes in solution. PMID:20077536

  17. Magnetic states of Mn and Co atoms at Co2MnGe/MgO interfaces seen via soft x-ray magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Asakura, D.; Koide, T.; Yamamoto, S.; Tsuchiya, K.; Shioya, T.; Amemiya, K.; Singh, V. R.; Kataoka, T.; Yamazaki, Y.; Sakamoto, Y.; Fujimori, A.; Taira, T.; Yamamoto, M.

    2010-11-01

    The magnetic states of Mn and Co atoms in Co-rich Co2MnGe Heusler alloy thin films facing an MgO barrier were studied by means of soft x-ray magnetic circular dichroism (XMCD). In particular, the Co2MnGe film-thickness dependence of the Mn and Co magnetic moments was investigated. With a decrease in the Co2MnGe film thickness to 1-2 monolayers (MLs), the spin magnetic moment of Mn decreased and the MnL2,3 -edge x-ray absorption spectra (XAS) showed a Mn2+ -like multiplet structure in MnO, in contrast to samples thicker than 4 ML, indicating that the Mn atoms of the 1 and 2 ML samples were oxidized. The Co spin magnetic moment increased slightly with decreasing thickness. A Co2+ -like multiplet structure in CoO was not observed in all the CoL2,3 -edge XAS and XMCD, indicating that, even in the ultrathin samples, the Co atoms were not oxidized, and were more strongly spin polarized than those in the thicker samples. Co spin magnetic moments of 1.40-1.77μB larger than the theoretical value for ideal stoichiometric Co2MnGe (˜1μB) and the Co-rich film composition imply the presence of Co antisites that would lower the spin polarization.

  18. Proximity effects and exchange bias in Co/MnF2(111) heterostructures studied by x-ray magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Suturin, S. M.; Fedorov, V. V.; Banshchikov, A. G.; Baranov, D. A.; Koshmak, K. V.; Torelli, P.; Fujii, J.; Panaccione, G.; Amemiya, K.; Sakamaki, M.; Nakamura, T.; Tabuchi, M.; Pasquali, L.; Sokolov, N. S.

    2013-01-01

    Cobalt nano-structured ultrathin films were grown on orthorhombic MnF2 by molecular beam epitaxy on CaF2 epitaxial layers deposited on Si(111) substrates. The Co film was grown at room temperature. It was found to be polycrystalline, forming nano-islands with height≈diameter≤10 nm. X-ray absorption evidences the chemical stability of the Co/MnF2 interface. Remarkably, x-ray magnetic circular dichroism (XMCD) demonstrates that the Co induces a net magnetization on the Mn ions close to the interface. The magnetic moments of these Mn ions couple antiparallel to the Co and rotate upon field reversal following the magnetization of the Co both below and high above the Néel temperature of MnF2 (TN = 67 K). The density of coupled Mn moments is found to be temperature dependent, with an equivalent thickness of ˜1.5 MnF2 monolayers at 20 K, decreasing to about ˜0.5 ML as the temperature is raised to 300 K. Interestingly, the intensity of the Mn XMCD signal appears to be related to the coercivity of the Co layer. This behavior is interpreted in terms of the competition between thermal fluctuations, exchange coupling between Co and Mn at the interface and, at low temperature, the antiferromagnetic order in MnF2.

  19. Formation and temperature stability of G-quadruplex structures studied by electronic and vibrational circular dichroism spectroscopy combined with ab initio calculations.

    PubMed

    Nový, Jakub; Böhm, Stanislav; Králová, Jarmila; Král, Vladimír; Urbanová, Marie

    2008-02-01

    Variations in the structure of d(GGGA)(5) oligonucleotide in the presence of Li(+), Na(+), and K(+) ions and its temperature stability were studied using electronic and vibrational circular dichroism, IR absorption, and ab initio calculations with the Becke 3-Lee-Yang-Parr functional at the 6-31G** level. The samples were characterized by nondenaturing gel electrophoresis. Oligonucleotide d(GGGA)(5) in the presence of Li(+) forms a nonplanar single tetramer, with angles of 102 degrees and 171 degrees between neighboring guanine bases. This tetramer changes its geometry at temperatures >50 degrees C, but does not form a quadruplex structure. In the presence of Na(+), the d(GGGA)(5) structure was optimized to almost planar tetramers with an angle of 177 degrees between neighboring guanines. The spectral results suggest that it stacks into a quadruplex helical structure. This quadruplex structure decayed to a single tetramer at temperatures >60 degrees C. The Hartree-Fock energies imply that d(GGGA)(5) prefers to form complexes with Na(+) rather than Li(+). The d(GGGA)(5) structure in the presence of monovalent ions is stabilized against thermal denaturation in the order Li(+) < Na(+) < K(+). PMID:17960602

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

    NASA Astrophysics Data System (ADS)

    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.

  1. Ab initio ground state and L{sub 2,3} x-ray magnetic circular dichroism of Mn-based Heusler alloys

    SciTech Connect

    Galanakis, I.; Ostanin, S.; Alouani, M.; Dreysse, H.; Wills, J. M.

    2000-02-01

    Relativistic full-potential calculations within the generalized gradient approximation (GGA) for a series of Mn-based Heusler alloys are presented. Calculated equilibrium lattice parameters deviate less than 1.2% from the experimental values. The main features of a half metallic system are present in the density of states for the PtMnSb and NiMnSb. We predict that PdMnSb shows half metallic character under hydrostatic pressure. The substitution of Sb in PtMnSb by Sn or Te destroys the minority spin band gap. Spin and orbital magnetic moments for all the systems are in good agreement with previous calculations and experimental data. L{sub 2,3} x-ray absorption and x-ray magnetic circular dichroism (XMCD) spectra are calculated for all the five compounds. Pt spectra present big deviations from system to system in the PtMnY (Y=Sn,Sb,Te) compounds while Mn spectra show only small deviations. For all these spectra GGA underestimates the L{sub 3}/L{sub 2} integrated branching ratio and produces a much smaller L{sub 2} peak intensity for the Ni site in NiMnSb. The XMCD sum rules are used to compute the spin and orbital magnetic moments and the results are compared to the direct calculations. (c) 2000 The American Physical Society.

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

    NASA Astrophysics Data System (ADS)

    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

  3. Magnetic and structural properties of Fe/Pd multilayers studied by magnetic x-ray dichroism and x-ray absorption spectroscopy

    SciTech Connect

    Mini, S.M. |; Fullerton, E.E.; Sowers, C.H.; Fontaine, A.; Pizzini, S.; Bommannavar, A.S.; Traverse, A.; Baudelet, F.

    1994-12-01

    The results of magnetic circular x-ray dichroism (MCXD) measurements and extended x-ray absorption fine structure measurements (EXAFS) of the Fe K-edges of textured Fe(110)/Pd(111) multilayers are reported. The EXAFS results indicates that the iron in the system goes from bcc to a more densely packed system as the thickness of the iron layer is decreased. The magnetic properties were measured by SQUID magnetometry from 5-350 K. For all the samples, the saturation magnetization was significantly enhanced over the bulk values indicating the interface Pd atoms are polarized by the Fe layer. The enhancement corresponds to a moment of {approx}2.5{mu}{sub B} per interface Pd atom.

  4. X-ray absorption and x-ray magnetic dichroism study on Ca3CoRhO6 and Ca3FeRhO6

    NASA Astrophysics Data System (ADS)

    Burnus, T.; Hu, Z.; Wu, Hua; Cezar, J. C.; Niitaka, S.; Takagi, H.; Chang, C. F.; Brookes, N. B.; Lin, H.-J.; Jang, L. Y.; Tanaka, A.; Liang, K. S.; Chen, C. T.; Tjeng, L. H.

    2008-05-01

    By using x-ray absorption spectroscopy at the RhL2,3 , CoL2,3 , and FeL2,3 edges, we find a valence state of Co2+/Rh4+ in Ca3CoRhO6 and of Fe3+/Rh3+ in Ca3FeRhO6 . X-ray magnetic circular dichroism spectroscopy at the CoL2,3 edge of Ca3CoRhO6 reveals a giant orbital moment of about 1.7μB , which can be attributed to the occupation of the minority-spin d0d2 orbital state of the high-spin Co2+ (3d7) ions in trigonal prismatic coordination. This active role of the spin-orbit coupling explains the strong magnetocrystalline anisotropy and Ising-type magnetism of Ca3CoRhO6 .

  5. Interaction of water-soluble amino acid Schiff base complexes with bovine serum albumin: fluorescence and circular dichroism studies.

    PubMed

    Gharagozlou, Mehrnaz; Boghaei, Davar M

    2008-12-15

    Fluorescence spectroscopy in combination with circular dichroism (CD) spectroscopy were used to investigate the interaction of water-soluble amino acid Schiff base complexes, [Zn(L1,2)(phen)] where phen is 1,10-phenanthroline and H2L1,2 is amino acid Schiff base ligands, with bovine serum albumin (BSA) under the physiological conditions in phosphate buffer solution adjusted to pH 7.0. The quenching mechanism of fluorescence was suggested as static quenching according to the Stern-Volmer equation. Quenching constants were determined using the Stern-Volmer equation to provide a measure of the binding affinity between amino acid Schiff base complexes and BSA. The thermodynamic parameters DeltaG, DeltaH and DeltaS at different temperatures (298, 310 and 318K) were calculated. The results indicate that the hydrophobic and hydrogen bonding interactions play a major role in [Zn(L1)(phen)]-BSA association, whereas hydrophobic and electrostatic interactions participate a main role in [Zn(L2)(phen)]-BSA binding process. Binding studies concerning the number of binding sites and apparent binding constant Kb were performed by fluorescence quenching method. The distance R between the donor (BSA) and acceptor (amino acid Schiff base complexes) has been obtained utilizing fluorescence resonant energy transfer (FRET). Furthermore, CD spectra were used to investigate the structural changes of the BSA molecule with the addition of amino acid Schiff base complexes. The results indicate that the interaction of amino acid Schiff base complexes with BSA leads to changes in the secondary structure of the protein. Fractional contents of the secondary structure of BSA (f(alpha), f(beta), f(turn) and f(random)) were calculated with and without amino acid Schiff base complexes utilizing circular dichroism spectroscopy. Our results clarified that amino acid Schiff base complexes could bind to BSA and be effectively transported and eliminated in the body, which could be a useful guideline for

  6. Excited electronic states of limonene: A circular dichroism and photoelectron spectroscopy study of d-limonene

    NASA Astrophysics Data System (ADS)

    Brint, P.; Meshulam, Edna; Gedanken, Aharon

    1984-08-01

    The excited states of limonene are discussed in the light of vacuum-UV absorption, VUVCD and photoelectron spectroscopy measurements. Only one π → π* transition arising from the double bond of the ring is observed. The CD sign of the π → π* transition does not obey the octant rule formulated for chiral olefins.

  7. Magnetic circular dichroism spectroscopy of N-confused porphyrin and its ionized forms.

    PubMed

    Ziegler, Christopher J; Erickson, Nathan R; Dahlby, Michael R; Dalby, Michael R; Nemykin, Victor N

    2013-11-14

    N-Confused porphyrin (NCP) and its externally methylated variant (MeNCP) were investigated using UV-vis and magnetic circular dichrosim (MCD) spectroscopies. In addition to evaluating the spectroscopy of the neutral compounds, the acid/base chemistry of these macrocycles was examined by the same methods. NCP exhibits two tautomeric states depending on the polarity of the solvent, and their protonation/deprotonation chemistries also differ depending on solvent polarity. DFT and TDDFT calculations were employed to evaluate the observed spectroscopic changes. Using both experimental and calculated results, we were able to determine the sites of protonation/deprotonation for both tautomeric forms of NCP. Inspection of the MCD Faraday B terms for all of the macrocycles presented in this report showed that the ΔHOMO > ΔLUMO condition is maintained in all cases, and these observations were in good agreement with the DFT calculations. PMID:24131398

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

    SciTech Connect

    Liu, W. Q.; Xu, Y. B. E-mail: rzhang@nju.edu.cn; Song, M. Y.; Lin, J. G.; Maltby, N. J.; Li, S. P.; Samant, M. G.; Parkin, S. S. P.; Bencok, P.; Steadman, Paul; Dobrynin, Alexey; Zhang, R. E-mail: rzhang@nju.edu.cn

    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.

  9. Dependence of magnetic circular dichroism on doping and temperature in In1-xMnxAs epitaxial films

    NASA Astrophysics Data System (ADS)

    Chiu, P. T.; Wessels, B. W.

    2007-10-01

    To elucidate the nature of the exchange interactions in ferromagnetic In1-xMnxAs , the composition and temperature dependencies of the magnetic circular dichroism (MCD) spectrum were investigated. The spectrum is comprised of both a broad transition from 1.6to3.0eV and a negative peak between 2.68 and 2.8eV associated with L -point sp-d transitions. The spectral response of the MCD is strongly temperature dependent. The magnitude of the negative peak and magnetization increases significantly with decreasing temperature for T<150K due to an increase in the sp-d exchange coupling. In contrast, the broad background remains relatively constant over the same temperature range. The difference in the temperature dependence of the two negative background and peak corroborates previous assertions that the two features are due to two distinct transitions. For a series of films ranging from x=0.020to0.063 , the magnitude of the MCD peak and background exhibits a superlinear dependence on Mn concentration at room temperature. The superlinear dependence is attributed to the formation of atomic scale, tetrahedrally coordinated MnAs clusters.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

    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. PMID:27586898

  12. Exciton circular dichroism couplet arising from nitrile-derivatized aromatic residues as a structural probe of proteins.

    PubMed

    Mukherjee, Debopreeti; Gai, Feng

    2016-08-15

    Exciton coupling between two chromophores can produce a circular dichroism (CD) couplet that depends on their separation distance, among other factors. Therefore, exciton CD signals arising from aromatic sidechains, especially those of tryptophan (Trp), have been used in various protein conformational studies. However, the long-wavelength component of the commonly used CD couplet produced by a pair of Trp residues is typically located around 230 nm, thereby overlapping significantly with the protein backbone CD signal. This overlap often prevents a direct and quantitative assessment of the Trp CD couplet in question without further spectral analysis. Here, we show that this inconvenience can be alleviated by using a derivative of Trp, 5-cyanotryptophan (TrpCN), as the chromophore. Specifically, through studying a series of peptides that fold into either α-helical or ß-hairpin conformations, we demonstrate that in comparison with the Trp CD couplet, that arising from two TrpCN residues not only is significantly red-shifted but also becomes more intense due to the larger extinction coefficient of the underlying electronic transition. In addition, we show that a pair of p-cyanophenylalanines (PheCN) or a PheCN-TrpCN pair can also produce a distinct exciton CD couplet that can be useful in monitoring conformational changes in proteins. PMID:27251434

  13. Sub-nanosecond resolution x-ray magnetic circular dichroism photoemission electron microscopy of magnetization processes in a permalloy ring

    NASA Astrophysics Data System (ADS)

    Neeb, D.; Krasyuk, A.; Oelsner, A.; Nepijko, S. A.; Elmers, H. J.; Kuksov, A.; Schneider, C. M.; Schönhense, G.

    2005-04-01

    Fast magnetization processes in a microstructured permalloy ring with 80 µm o.d. and 30 nm thickness have been observed by photoemission electron microscopy exploiting x-ray magnetic circular dichroism as the magnetic contrast mechanism. As a high speed probe we employed synchrotron radiation pulses at the ESRF (Grenoble) operated in 16-bunch mode, yielding photon pulses of 105 ps FWHM with a period of 176 ns. Fast magnetic field pulses have been generated by means of current pulses through coplanar waveguides with the magnetic structure being lithographically prepared on their surface. A stroboscopic pump-probe set-up with a variable time delay between the field pulse and photon pulse allowed us to take snapshots of the dynamic response of the magnetic domain structure. We observed coherent magnetization rotation during the leading edge part of the field pulse, the formation of a characteristic domain pattern ('onion state') in the plateau region of the pulse and the fast formation of a striped domain pattern (incoherent magnetization rotation) during the trailing edge part of the field pulse. A numerical simulation confirmed essential features of the stroboscopic image series.

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

    PubMed

    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. PMID:27070079

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

    PubMed

    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. PMID:26803794

  16. Site-Specific Studies on X-Ray Magnetic Circular Dichroism at Fe K Edge for Transition-Metal Ferrites

    NASA Astrophysics Data System (ADS)

    Matsumoto, Kenji; Saito, Fumikazu; Toyoda, Takeshi; Ohkubo, Koichi; Yamawaki, Koji; Mori, Takeharu; Hirano, Keiichi; Tanaka, Masahiko; Sasaki, Satoshi

    2000-10-01

    Experiments on X-ray magnetic circular dichroism (XMCD) were performed with synchrotron radiation for Zn and Mn-Zn ferrites (normal-spinel structure) and Ni, Co and Cu ferrites and magnetite (inverse-spinel structure). The inverse-spinel ferrites have positive-to-negative dispersion-type XMCD signals in the pre-edge region of the Fe K edge, which originate from Fe3+ ions in the A sites. There are no such signals for normal-spinel ferrites. Two kinds of negative-to-positive dispersion-type XMCD signals were observed in 7.119-7.125 keV and 7.122-7.129 keV regions of the main edge, which are caused by a mixture of Fe3+ and Fe2+ ions of the B sites in magnetite and Fe3+ ions of the B sites in the other inverse-spinel ferrites, respectively. The B-site origin of the XMCD main-edge spectra was also confirmed by observation of X-ray resonant magnetic scattering for the 222 reflection of Ni ferrite.

  17. Induced circular dichroism as a tool to investigate the binding of drugs to carrier proteins: Classic approaches and new trends.

    PubMed

    Tedesco, Daniele; Bertucci, Carlo

    2015-09-10

    Induced circular dichroism (ICD) is a spectroscopic phenomenon that provides versatile and useful methods for characterizing the structural and dynamic properties of the binding of drugs to target proteins. The understanding of biorecognition processes at the molecular level is essential to discover and validate new pharmacological targets, and to design and develop new potent and selective drugs. The present article reviews the main applications of ICD to drug binding studies on serum carrier proteins, going from the classic approaches for the derivation of drug binding parameters and the identification of binding sites, to an overview of the emerging trends for the characterization of binding modes by means of quantum chemical (QC) techniques. The advantages and limits of the ICD methods for the determination of binding parameters are critically reviewed; the capability to investigate the binding interactions of drugs and metabolites to their target proteins is also underlined, as well as the possibility of characterizing the binding sites to obtain a complete picture of the binding mechanism and dynamics. The new applications of ICD methods to identify stereoselective binding modes of drug/protein complexes are then reviewed with relevant examples. The combined application of experimental ICD spectroscopy and QC calculations is shown to identify qualitatively the bound conformations of ligands to target proteins even in the absence of a detailed structure of the binding sites, either obtained from experimental X-ray crystallography and NMR measurements or from computational models of the complex. PMID:25769668

  18. Conformational changes of alamethicin induced by solvent and temperature. A 13C-NMR and circular-dichroism study.

    PubMed

    Jung, G; Dubischar, N

    1975-06-01

    13C nuclear magnetic resonance (NMR) and circular dichroism (CD) have been used for studies on the conformation of alamethicin. The 13C NMR spectrum is assigned with the aid of signals of synthetic partial sequences and selective proton decoupling. The solvent and temperature-dependence of the 13C NMR spectra, T1 measurements and the use of lanthanide-shift reagents allow the differentiation between the amino acids belonging to a rigid alpha-helical portion of the alamethicin sequence and those belonging to a more flexible part. The 13C NMR results are in agreement with results obtained from extended solvent and temperature-dependent CD studies which indicate a highly stabilized nonpolar and intrachenar alpha-helical part. The concentration-dependence of the CD spectrum of alamethicin in a nematic phase revealed aggregation phenomena which might simulate those observed in natural and synthetic membranes. After dissolving alamethicin in aqueous alcohol there is a time-dependence of the ellipticity of the Cotton effects showing a sort of memory effect on the mode of dissolution. Four different conformations can be characterized by CD spectra depending on the solvent and concentration. A model illustrating the dynamic conformations and aggregation phenomena within a membrane is proposed. PMID:1175592

  19. Removal of the free cysteine residue reduces irreversible thermal inactivation of feruloyl esterase: evidence from circular dichroism and fluorescence spectra.

    PubMed

    Li, Jingjing; Zhang, Shuaibing; Yi, Zhuolin; Pei, Xiaoqiong; Wu, Zhongliu

    2015-08-01

    Feruloyl esterase A from Aspergillus niger (AnFaeA) contains three intramolecular disulfide bonds and one free cysteine at position 235. Saturated mutagenesis at Cys235 was carried out to produce five active mutants, all of which displayed unusual thermal inactivation patterns with the most residual activity achieved at 75°C, much higher than the parental AnFaeA. But their optimal reaction temperatures were lower than the parental AnFaeA. Extensive investigation into their free thiol and disulfide bond, circular dichroism spectra and fluorescence spectra revealed that the unfolding of the parental enzyme was irreversible on all the tested conditions, while that of the Cys235 mutants was reversible, and their ability to refold was highly dependent on the denaturing temperature. Mutants denatured at 75°C were able to efficiently reverse the unfolding to regain native structure during the cooling process. This study provided valid evidence that free cysteine substitutions can reduce irreversible thermal inactivation of proteins. PMID:26079173

  20. Magnetic Circular Dichroism (MCD) Studies on MOVPE Grown InMnSb and InMnAs

    NASA Astrophysics Data System (ADS)

    Meeker, M. A.; Magill, B. A.; Khodaparast, G. A.; Saha, D.; Stanton, C. J.; McGill, S.; Wessels, B. W.

    2015-03-01

    Carrier-induced ferromagnetism in magnetic III-V semiconductors has opened up several opportunities for device applications as well as for fundamental studies of a material system in which itinerant carriers interact with the localized spins of magnetic impurities. The origin of the carrier-induced ferromagnetism is still an open and exciting question. In order to understand the hole mediated ferromagnetism, probing the band structure in these material systems is crucial. Here we present magnetic circular dichroism (MCD) studies on MOVPE grown InMnSb and InMnAs, both with Curie temperatures above 300K. The measurements were performed on samples with different Mn contents, with the laser excitation energy tuned from 0.92-1.45eV, and external magnetic fields ranging up to 31 Tesla. The measurements are compared with MCD calculations based on an 8 band Pidgeon-Brown model. Comparison of the experimental results with the theoretical calculations provides a direct method to estimate the sp-d Mn- electron/hole coupling constants. This work was supported by the NSF through Grant: DMR-0846834 Career Award, DMR-1105437, and DMR -1305666. Also supported by the Institute of Critical Technology and Applied Sciences (ICTAS) at Virginia Tech.

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

    SciTech Connect

    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.

  2. A fast but accurate excitonic simulation of the electronic circular dichroism of nucleic acids: how can it be achieved?

    PubMed

    Loco, Daniele; Jurinovich, Sandro; Di Bari, Lorenzo; Mennucci, Benedetta

    2016-01-14

    We present and discuss a simple and fast computational approach to the calculation of electronic circular dichroism spectra of nucleic acids. It is based on a exciton model in which the couplings are obtained in terms of the full transition-charge distributions, as resulting from TDDFT methods applied on the individual nucleobases. We validated the method on two systems, a DNA G-quadruplex and a RNA β-hairpin whose solution structures have been accurately determined by means of NMR. We have shown that the different characteristics of composition and structure of the two systems can lead to quite important differences in the dependence of the accuracy of the simulation on the excitonic parameters. The accurate reproduction of the CD spectra together with their interpretation in terms of the excitonic composition suggest that this method may lend itself as a general computational tool to both predict the spectra of hypothetic structures and define clear relationships between structural and ECD properties. PMID:26646952

  3. The study on the interaction between seryl-histidine dipeptide and proteins by circular dichroism and molecular modeling.

    PubMed

    Zeng, Qing; Yin, Qiang; Zhao, Yufen

    2005-04-01

    The selective cleavage of proteins is very important in key biological processes. Chemical (nonenzymatic) reagents such as cyanogen bromide and transition metal complexes are used extensively with great defects. In this paper, the binding of seryl-histidine dipeptide (abbreviated as SH) with bovine serum albumin (BSA) and lysozyme were investigated by the circular dichroism spectroscopy (CD) at 298K, molecular docking studies and quantum chemical calculations based on the previous results of polyacrylamide gel electrophoresis (PAGE). From the studies of CD, it showed that SH interacted strongly with BSA and lysozyme. The change percentages of the secondary structures of BSA and lysozyme were calculated. The contents of the beta-sheets decreased remarkably. It indicated that the interactions between SH and proteins could break the hydrogen bonds of beta-sheets selectively. The docking studies between SH and BSA showed that the position of the oxygen atom of the hydroxyl group of SH (O(12)) was in favor of a nucleophilic attack on carbon atom of the amide bond of a beta-sheet (C(34)) because the distance between O(12) and C(34) was 3.37A. Natural charges, natural atomic hybrid percentages and square sums of HOMO coefficients calculated by the NBO and population analysis at HF/6-31G* supported the suggested mechanism. And so SH may be an interesting agent for the therapeutic use. PMID:15755667

  4. Dependence of magneto-optical rotatory dispersion and magnetic circular dichroism of deoxy- and methemoglobin on their quaternary structure.

    PubMed

    Sharonov, Y A; Sharonova, N A; Atanasov, B P

    1976-06-15

    Methods of magnetic optical activity, magneto-optical rotatory dispersion (MORD) and magnetic circular dichroism (MCD), were shown to be sensitivie to the quaternary structure of deoxyhemoglobin. The isolated alpha and beta chains, the monomeric hemoglobins (leghemoglobin, fraction III of Chironomus thummi thummi hemoglobin) and hemoglobin in the R state (hemoglobin digested with carboxypeptidases A and B) exhibit in the visible region two MORD minima of equal intensities. In native tetrameric hemoglobins studied (human, horse, porcine, feline, carp, tortoise, frog) the ratio of the intensities of these MORD minima is about 2. The MORD data for deoxy-des Arg-N-ethylsuccinimide-hemoglobin indicate that in solution there is a mixture of the T and R states, the equilibrium between the states being shifted toward the R structure. The identity of the MORD curves for deoxy-bis(N-maleimidoethyl)-ester-hemoglobin and for native deoxyhemoglobin indicates that deoxy-bis(N-maleimidoethyl)ester-hemoglobin has the T structure in solution. Comparison of the MORD curves exhibited by a native methemoglobin, a native metmyoglobin and the modified hemoglobins in the met form in the absence and presence of organic and inorganic phosphates reveals no direct correlation between the MORD changes and methemoglobin quaternary structure. PMID:952896

  5. Circular dichroism studies of the mitochondrial channel, VDAC, from Neurospora crassa.

    PubMed Central

    Shao, L; Kinnally, K W; Mannella, C A

    1996-01-01

    The protein that forms the voltage-gated channel VDAC (or mitochondrial porin) has been purified from Neurospora crassa. At room temperature and pH 7, the circular dichoism (CD) spectrum of VDAC suspended in octyl beta-glucoside is similar to those of bacterial porins, consistent with a high beta-sheet content. When VDAC is reconstituted into phospholipid liposomes at pH 7, a similar CD spectrum is obtained and the liposomes are rendered permeable to sucrose. Heating VDAC in octyl beta-glucoside or in liposomes results in thermal denaturation. The CD spectrum irreversibly changes to one consistent with total loss of beta-sheet content, and VDAC-containing liposomes irreversibly lose sucrose permeability. When VDAC is suspended at room temperature in octyl beta-glucoside at pH < 5 or in sodium dodecyl sulfate at pH 7, its CD spectrum is consistent with partial loss of beta-sheet content. The sucrose permeability of VDAC-containing liposomes is decreased at low pH and restored at pH 7. Similarly, the pH-dependent changes in the CD spectrum of VDAC suspended in octyl beta-glucoside also are reversible. These results suggest that VDAC undergoes a reversible conformational change at low pH involving reduced beta-sheet content and loss of pore-forming activity. Images FIGURE 1 PMID:8842216

  6. Theory of x-ray absorption and linear dichroism at the Ca L23-edge of CaCO3

    NASA Astrophysics Data System (ADS)

    Krüger, Peter; Natoli, Calogero R.

    2016-05-01

    X-ray absorption calculations of Ca L23-edge spectra of calcium carbonate in its two main crystal phases, calcite and aragonite, are reported. The multichannel multiple scattering theory with a correlated particle-hole wave function and a partially screened core-hole potential is used. Very good agreement with experiment for both CaCO3 phases is obtained, while the independent particle approximation completely fails. For aragonite, appreciable linear dichroism is predicted in agreement with recent observations.

  7. Investigation of the complexation between quinidine carbamate and the enantiomers of 3-chloro-1-phenyl-propanol by circular dichroism and UV spectroscopy

    SciTech Connect

    Guiochon, Georges A; Asnin, Leonid

    2006-04-01

    UV and circular dichroism spectroscopic measurements showed that the molecular interactions in hexane/ethyl-acetate solutions between dihydroquinidine tert-butylcarbamate, used as a model for the quinidine carbamate chiral selector (QD), and 3-chloro-1-phenyl-propanol are too weak to affect the corresponding spectra of these compounds. The weak interactions between QD and 3-chloro-1-phenyl-propanol are probably masked by the formation of self-associated dimeric structures in solution.

  8. Interactions of the intact FsrC membrane histidine kinase with its pheromone ligand GBAP revealed through synchrotron radiation circular dichroism.

    PubMed

    Patching, Simon G; Edara, Shalini; Ma, Pikyee; Nakayama, Jiro; Hussain, Rohanah; Siligardi, Giuliano; Phillips-Jones, Mary K

    2012-07-01

    FsrC is the membrane-bound histidine kinase component of the Fsr two-component signal transduction system involved in quorum sensing in the hospital-acquired infection agent Enterococcus faecalis. Synchrotron radiation circular dichroism spectroscopy was used here to study the intact purified protein solubilised in detergent micelles. Conditions required for FsrC stability in detergent were firstly determined and tested by prolonged exposure of stabilised protein to far-ultraviolet radiation. Using stabilised purified protein, far-ultraviolet synchrotron radiation circular dichroism revealed that FsrC is 61% alpha-helical and that it is relatively thermostable, retaining at least 57% secondary structural integrity at 90 degrees C in the presence or absence of gelatinase biosynthesis-activating pheromone (GBAP). Whilst binding of the quorum pheromone ligand GBAP did not significantly affect FsrC secondary structure, near-ultraviolet spectra revealed that the tertiary structure in the regions of the Tyr and Trp residues was significantly affected. Titration experiments revealed a calculated kd value of 2 microM indicative of relatively loose binding ofgelatinase biosynthesis-activating pheromone to FsrC. Although use of synchrotron radiation circular dichroism has been applied to membrane proteins previously, to our knowledge this is the first report of its use to determine a kd value for an intact membrane protein. Based on our findings, we suggest that synchrotron radiation circular dichroism will be a valuable technique for characterising ligand binding by other membrane sensor kinases and indeed other membrane proteins in general. It further provides a valuable screening tool for membrane protein stability under a range of detergent conditions prior to downstream structural methods such as crystallisation and NMR experiments particularly when lower detergent concentrations are used. PMID:22366202

  9. X-ray magnetic circular dichroism measurements using an X-ray phase retarder on the BM25 A-SpLine beamline at the ESRF

    PubMed Central

    Boada, Roberto; Laguna-Marco, María Ángeles; Gallastegui, Jon Ander; Castro, Germán R.; Chaboy, Jesús

    2010-01-01

    Circularly polarized X-rays produced by a diamond X-ray phase retarder of thickness 0.5 mm in the Laue transmission configuration have been used for recording X-ray magnetic circular dichroism (XMCD) on the bending-magnet beamline BM25A (SpLine) at the ESRF. Field reversal and helicity reversal techniques have been used to carry out the measurements. The performance of the experimental set-up has been demonstrated by recording XMCD in the energy range from 7 to 11 keV. PMID:20400827

  10. Circular dichroism and site-directed spin labeling reveal structural and dynamical features of high-pressure states of myoglobin

    PubMed Central

    Lerch, Michael T.; Horwitz, Joseph; McCoy, John; Hubbell, Wayne L.

    2013-01-01

    Excited states of proteins may play important roles in function, yet are difficult to study spectroscopically because of their sparse population. High hydrostatic pressure increases the equilibrium population of excited states, enabling their characterization [Akasaka K (2003) Biochemistry 42:10875–85]. High-pressure site-directed spin-labeling EPR (SDSL-EPR) was developed recently to map the site-specific structure and dynamics of excited states populated by pressure. To monitor global secondary structure content by circular dichroism (CD) at high pressure, a modified optical cell using a custom MgF2 window with a reduced aperture is introduced. Here, a combination of SDSL-EPR and CD is used to map reversible structural transitions in holomyoglobin and apomyoglobin (apoMb) as a function of applied pressure up to 2 kbar. CD shows that the high-pressure excited state of apoMb at pH 6 has helical content identical to that of native apoMb, but reversible changes reflecting the appearance of a conformational ensemble are observed by SDSL-EPR, suggesting a helical topology that fluctuates slowly on the EPR time scale. Although the high-pressure state of apoMb at pH 6 has been referred to as a molten globule, the data presented here reveal significant differences from the well-characterized pH 4.1 molten globule of apoMb. Pressure-populated states of both holomyoglobin and apoMb at pH 4.1 have significantly less helical structure, and for the latter, that may correspond to a transient folding intermediate. PMID:24248390

  11. Surface plasmon resonance and circular dichroism characterization of cucurbitacins binding to serum albumins for early pharmacokinetic profiling.

    PubMed

    Fabini, Edoardo; Fiori, Giovana Maria Lanchoti; Tedesco, Daniele; Lopes, Norberto Peporine; Bertucci, Carlo

    2016-04-15

    Cucurbitacins are a group of tetracyclic triterpenoids, known for centuries for their anti-cancer and anti-inflammatory properties, which are being actively investigated over the past decades in order to elucidate their mechanism of action. In perspective of being used as therapeutic molecules, a pharmacokinetic characterization is crucial to assess the affinity toward blood carrier proteins and extrapolate distribution volumes. Usually, pharmacokinetic data are first collected on animal models and later translated to humans; therefore, an early characterization of the interaction with carrier proteins from different species is highly desirable. In the present study, the interactions of cucurbitacins E and I with human and rat serum albumins (HSA and RSA) were investigated by means of surface plasmon resonance (SPR)-based optical biosensing and circular dichroism (CD) spectroscopy. Active HSA and RSA sensor chip surfaces were prepared through an amine coupling reaction protocol, and the equilibrium dissociation constants (Kd) for the different cucurbitacins-serum albumins complexes were then determined by SPR analysis. Further information on the binding of cucurbitacins to serum albumins was obtained by CD competition experiments with biliverdin, a specific marker binding to subdomain IB of HSA. SPR data unveiled a previously unreported binding event between CucI and HSA; the determined binding affinities of both compounds were slightly higher for RSA with respect to HSA, even though all the compounds can be ranked as high-affinity binders for both carriers. CD analysis showed that the two cucurbitacins modify the binding of biliverdin to serum albumins through opposite allosteric modulation (positive for HSA, negative for RSA), confirming the need for caution in the translation of pharmacokinetic data across species. PMID:26856457

  12. Test of circular dichroism (CD) methods for crambin and CD-assisted secondary structure prediction of its homologous toxins.

    PubMed

    Teeter, M M; Whitlow, M

    1988-01-01

    Methods that analyze protein circular dichroism (CD) spectra for fractions of secondary structure are evaluated for the plant protein crambin, which has a known high-resolution crystal structure. In addition, a two-step secondary structure prediction scheme is presented and used for the toxins homologous to crambin, shown by others to have secondary structures similar to crambin. The test of CD spectral analysis methods with the protein crambin employed two computer programs and several CD basis sets. Crambin's crystal structure, known to 0.945A resolution (Hendrickson, W.A., Teeter, M.M. Nature 290:107-113, 1981), allows accurate evaluation of results. Analysis with the protein spectra basis sets (Provencher, S.W., Glöckner, J. Biochemistry 20:33-37, 1981) as modified (Manavalan, P., Johnson, W.C., Jr. Anal. Biochem. 167:76-85, 1987) agreed most closely with crambin's crystal structure. This method was then applied to the CD spectra of the membrane-active toxins homologous to crambin (alpha 1- and beta-purothionin, phoratoxin A and B, and viscotoxin A3 and B). The new program SEQ (pronounced "seek") was developed to assign the secondary structure along the protein chain in a hierarchical fashion and applied to the plant toxins. The method constrained the secondary structure fractions to those from CD analysis and combined standard statistical methods with amphipathic helix location. Both CD-arrived secondary structure percentages and sequence assignment indicate that the viscotoxins are structurally most similar to crambin. Purothionin's secondary structure was predicted to be fundamentally similar to crambin's with a difference at the start of the first helix. This assignment agreed with Raman and NMR analyses of purothionin and lends validity to the method presented here. Differences from the NMR in the CD secondary structure fraction analysis for phoratoxin suggest interference in the CD from tryptophan residues. PMID:3253736

  13. Circular dichroism and site-directed spin labeling reveal structural and dynamical features of high-pressure states of myoglobin.

    PubMed

    Lerch, Michael T; Horwitz, Joseph; McCoy, John; Hubbell, Wayne L

    2013-12-01

    Excited states of proteins may play important roles in function, yet are difficult to study spectroscopically because of their sparse population. High hydrostatic pressure increases the equilibrium population of excited states, enabling their characterization [Akasaka K (2003) Biochemistry 42:10875-85]. High-pressure site-directed spin-labeling EPR (SDSL-EPR) was developed recently to map the site-specific structure and dynamics of excited states populated by pressure. To monitor global secondary structure content by circular dichroism (CD) at high pressure, a modified optical cell using a custom MgF2 window with a reduced aperture is introduced. Here, a combination of SDSL-EPR and CD is used to map reversible structural transitions in holomyoglobin and apomyoglobin (apoMb) as a function of applied pressure up to 2 kbar. CD shows that the high-pressure excited state of apoMb at pH 6 has helical content identical to that of native apoMb, but reversible changes reflecting the appearance of a conformational ensemble are observed by SDSL-EPR, suggesting a helical topology that fluctuates slowly on the EPR time scale. Although the high-pressure state of apoMb at pH 6 has been referred to as a molten globule, the data presented here reveal significant differences from the well-characterized pH 4.1 molten globule of apoMb. Pressure-populated states of both holomyoglobin and apoMb at pH 4.1 have significantly less helical structure, and for the latter, that may correspond to a transient folding intermediate. PMID:24248390

  14. Electronic circular dichroism of highly conjugated π-systems: breakdown of the Tamm-Dancoff/configuration interaction singles approximation.

    PubMed

    Bannwarth, Christoph; Grimme, Stefan

    2015-04-16

    We show that the electronic circular dichroism (ECD) of delocalized π-systems represents a worst-case scenario for Tamm-Dancoff approximated (TDA) linear response methods. We mainly consider density functional theory (TDA-DFT) variants together with range-separated hybrids, but the conclusions also apply for other functionals as well as the configuration interaction singles (CIS) approaches. We study the effect of the TDA for the computation of ECD spectra in some prototypical extended π-systems. The C76 fullerene, a chiral carbon nanotube fragment, and [11]helicene serve as model systems for inherently chiral, π-chromophores. Solving the full linear response problem is inevitable in order to obtain accurate ECD spectra for these systems. For the C76 fullerene and the nanotube fragment, TDA and CIS approximated methods yield spectra in the origin-independent velocity gauge formalism of incorrect sign which would lead to the assignment of the opposite (wrong) absolute configuration. As a counterexample, we study the ECD of an α-helix polypeptide chain. Here, the lowest-energy transitions are dominated by localized excitations within the individual peptide units, and TDA methods perform satisfactorily. The results may have far-reaching implications for simple semiempirical methods which often employ TDA and CIS for huge molecules. Our recently presented simplified time-dependent DFT approach proves to be an excellent low-cost linear response method which together with range-separated density functionals like ωB97X-D3 produces ECD spectra in very good agreement with experiment. PMID:25798823

  15. Magnetism of an ultrathin Mn film on Co(100) and the effect of oxidation studied by x-ray magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Yonamoto, Yoshiki; Yokoyama, Toshihiko; Amemiya, Kenta; Matsumura, Daiju; Ohta, Toshiaki

    2001-06-01

    The electronic and magnetic structures of a Mn ultrathin film grown on a 3-ML (monolayer) Co film have been investigated during stepwise oxidation by means of O K-, Mn LIII,II-, and Co LIII,II-edge x-ray-absorption spectroscopy and Mn LIII,II-, and Co LIII,II-edge x-ray magnetic circular dichroism (XMCD). Without O2, strong interaction between the Mn and Co 3d orbitals was suggested and Mn-Co ferromagnetic coupling was confirmed. We observed significant suppression of the d hole number and the spin and orbital moments of Co after Mn deposition compared to those before Mn deposition. These findings imply that the Mn d electrons are transferred to the minority-spin levels of Co. At 0.5-L (Langmuir) O2 exposure, the spin and orbital moments of Co do not change noticeably, while the Mn LIII,II-edge XMCD almost completely vanishes. After 5.5-L O2 exposure, an antiparallel spin alignment between Mn and Co was observed. The estimated orbital moments of Mn is reduced from 0.06 (before oxidation) to <0.005μB (after oxidation). It is concluded that unoxidized Mn is in the d5+d6 state while oxidized Mn is in the d5 high-spin state. Such variance of the electron configuration of Mn can explain the unusual magnetic properties. Antiferromagnetic coupling between Co and oxidized Mn may originate from the d5 high-spin configuration of Mn rather than from the superexchange interaction between Mn and Co via the O atom.

  16. Quantitatively analyzing the mechanism of giant circular dichroism in extrinsic plasmonic chiral nanostructures by tracking the interplay of electric and magnetic dipoles

    NASA Astrophysics Data System (ADS)

    Hu, Li; Tian, Xiaorui; Huang, Yingzhou; Fang, Liang; Fang, Yurui

    2016-02-01

    Plasmonic chirality has drawn much attention because of tunable circular dichroism (CD) and the enhancement for chiral molecule signals. Although various mechanisms have been proposed to explain the plasmonic CD, a quantitative explanation like the ab initio mechanism for chiral molecules, is still unavailable. In this study, a mechanism similar to the mechanisms associated with chiral molecules was analyzed. The giant extrinsic circular dichroism of a plasmonic splitting rectangle ring was quantitatively investigated from a theoretical standpoint. The interplay of the electric and magnetic modes of the meta-structure is proposed to explain the giant CD. We analyzed the interplay using both an analytical coupled electric-magnetic dipole model and a finite element method model. The surface charge distributions showed that the circular current yielded by the splitting rectangle ring causes the ring to behave like a magneton at some resonant modes, which then interact with the electric modes, resulting in a mixing of the two types of modes. The strong interplay of the two mode types is primarily responsible for the giant CD. The analysis of the chiral near-field of the structure shows potential applications for chiral molecule sensing.Plasmonic chirality has drawn much attention because of tunable circular dichroism (CD) and the enhancement for chiral molecule signals. Although various mechanisms have been proposed to explain the plasmonic CD, a quantitative explanation like the ab initio mechanism for chiral molecules, is still unavailable. In this study, a mechanism similar to the mechanisms associated with chiral molecules was analyzed. The giant extrinsic circular dichroism of a plasmonic splitting rectangle ring was quantitatively investigated from a theoretical standpoint. The interplay of the electric and magnetic modes of the meta-structure is proposed to explain the giant CD. We analyzed the interplay using both an analytical coupled electric-magnetic dipole

  17. Magnetic circular dichroism spectroscopy.

    PubMed

    Hales, Brian J

    2011-01-01

    Being able to probe the structure and energy levels of metal ions in biological systems is an important goal of bioinorganic scientists. Several of the techniques used rely on the paramagnetic property of certain oxidation states of metal ions. MCD spectroscopy is one of those techniques and represents an effective way of obtaining structure/electronic information of paramagnetic metal ions. The basics of this technique are discussed along with examples of how MCD spectroscopy has been successfully used to elucidate the metal clusters of Nif proteins from nitrogen-fixing bacteria. PMID:21833870

  18. Itinerant Ferromagnetism in the As 4 p Conduction Band of Ba0.6K0.4Mn2As2 Identified by X-Ray Magnetic Circular Dichroism

    NASA Astrophysics Data System (ADS)

    Ueland, B. G.; Pandey, Abhishek; Lee, Y.; Sapkota, A.; Choi, Y.; Haskel, D.; Rosenberg, R. A.; Lang, J. C.; Harmon, B. N.; Johnston, D. C.; Kreyssig, A.; Goldman, A. I.

    2015-05-01

    X-ray magnetic circular dichroism (XMCD) measurements on single-crystal and powder samples of Ba0.6K0.4Mn2As2 show that the ferromagnetism below TC≈100 K arises in the As 4 p conduction band. No XMCD signal is observed at the Mn x-ray absorption edges. Below TC, however, a clear XMCD signal is found at the As K edge which increases with decreasing temperature. The XMCD signal is absent in data taken with the beam directed parallel to the crystallographic c axis indicating that the orbital magnetic moment lies in the basal plane of the tetragonal lattice. These results show that the previously reported itinerant ferromagnetism is associated with the As 4 p conduction band and that distinct local-moment antiferromagnetism and itinerant ferromagnetism with perpendicular easy axes coexist in this compound at low temperature.

  19. Itinerant ferromagnetism in the As 4p conduction band of Ba_{0.6}K_{0.4}Mn_{2}As_{2} identified by X-ray magnetic circular dichroism.

    PubMed

    Ueland, B G; Pandey, Abhishek; Lee, Y; Sapkota, A; Choi, Y; Haskel, D; Rosenberg, R A; Lang, J C; Harmon, B N; Johnston, D C; Kreyssig, A; Goldman, A I

    2015-05-29

    X-ray magnetic circular dichroism (XMCD) measurements on single-crystal and powder samples of Ba_{0.6}K_{0.4}Mn_{2}As_{2} show that the ferromagnetism below T_{C}≈100  K arises in the As 4p conduction band. No XMCD signal is observed at the Mn x-ray absorption edges. Below T_{C}, however, a clear XMCD signal is found at the As K edge which increases with decreasing temperature. The XMCD signal is absent in data taken with the beam directed parallel to the crystallographic c axis indicating that the orbital magnetic moment lies in the basal plane of the tetragonal lattice. These results show that the previously reported itinerant ferromagnetism is associated with the As 4p conduction band and that distinct local-moment antiferromagnetism and itinerant ferromagnetism with perpendicular easy axes coexist in this compound at low temperature. PMID:26066451

  20. 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

    NASA Astrophysics Data System (ADS)

    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.

  1. Itinerant ferromagnetism in the As 4p conduction band of Ba0.6K0.4Mn2As2 identified by x-ray magnetic circular dichroism

    DOE PAGESBeta

    Ueland, B. G.; Pandey, Abhishek; Lee, Y.; Sapkota, A.; Choi, Y.; Haskel, D.; Rosenberg, R. A.; Lang, J. C.; Harmon, B. N.; Johnston, D. C.; et al

    2015-05-27

    In this study, x-ray magnetic circular dichroism (XMCD) measurements on single-crystal and powder samples of Ba0.6K0.4Mn2As2 show that the ferromagnetism below TC ≈ 100 K arises in the As 4p conduction band. No XMCD signal is observed at the Mn x-ray absorption edges. Below TC, however, a clear XMCD signal is found at the As K edge which increases with decreasing temperature. The XMCD signal is absent in data taken with the beam directed parallel to the crystallographic c axis indicating that the orbital magnetic moment lies in the basal plane of the tetragonal lattice. These results show that themore » previously reported itinerant ferromagnetism is associated with the As 4p conduction band and that distinct local-moment antiferromagnetism and itinerant ferromagnetism with perpendicular easy axes coexist in this compound at low temperature.« less

  2. Structural characterization of p53 isoforms due to the polymorphism at codon 72 by mass spectrometry and circular dichroism.

    PubMed

    Naldi, Marina; Pistolozzi, Marco; Bertucci, Carlo; De Simone, Angela; Altilia, Serena; Pierini, Michela; Franceschi, Claudio; Salvioli, Stefano; Andrisano, Vincenza

    2010-10-10

    A common polymorphism at codon 72 of human TP53 gene determines a proline to arginine aminoacidic substitution within the proline-rich domain of p53 protein. The two resulting isoforms (p53P(72) and p53R(72)) are different from a biochemical and biological point of view and many reports suggest that they can modulate individual cancer susceptibility and overall survival. In the attempt to explain the observed biological differences, we characterized the two isoforms by mass spectrometry and circular dichroism (CD) to evaluate the possible alteration in the secondary structure of p53 introduced by this polymorphism. Recombinant human p53R(72) and p53P(72) were produced by using E. coli expression system then purified by chromatography (affinity chromatography and RP-HPLC), and the whole proteins identified by HPLC-ESI-IT and MALDI-TOF analysis. A bottom-up approach, using both MALDI-TOF and HPLC-ESI-QTOF analysis, was then adopted to obtain the sequence information on the two p53 isoforms. To this purpose, peptide maps were obtained by trypsin proteolysis on the two p53 isoforms. The two isoforms proteolytic digests were separated by LC and subsequent mass spectrometry analysis of both entire and fragmented peptides was performed. In particular, precursor peptide ions obtained by ESI were subjected to collision by the triple quadrupole and TOF separation, allowing us to determine the isoforms aminoacidic peptide sequence by peptide ladder sequencing. Because of the presence of arginine, a selective trypsin proteolytic cleavage at R(72), giving rise to two selective shorter peptides, occurred in p53R(72), but was missing in the case of p53P(72) trypsin digest, in which an uncleaved longer peptide was instead identified. Upon primary structure confirmation, the two p53 isoforms were studied by CD in order to investigate the experimental variables, which affect ordered secondary structure adoption. CD analysis indicated that the two isoforms are not structurally

  3. Design and construction of a compact end-station at NSRRC for circular-dichroism spectra in the vacuum-ultraviolet region.

    PubMed

    Liu, Szu Heng; Lin, Yi Hung; Huang, Liang Jen; Luo, Shiang Wen; Tsai, Wan Lin; Chiang, Su Yu; Fung, Hok Sum

    2010-11-01

    A synchrotron-radiation-based circular-dichroism end-station has been implemented at beamline BL04B at the National Synchrotron Radiation Research Center (NSRRC) in Taiwan for biological research. The design and performance of this compact end-station for measuring circular-dichroism spectra in the vacuum-ultraviolet region are described. The linearly polarized light from the beamline is converted to modulated circularly polarized light with a LiF photoelastic modulator to provide a usable wavelength region of 130-330 nm. The light spot at the sample position is 5 mm × 5 mm at a slit width of 300 µm and provides a flux greater than 1 × 10(11) photons s(-1) (0.1% bandwidth)(-1). A vacuum-compatible cell made of two CaF(2) windows has a variable path length from 1.3 µm to 1 mm and a temperature range of 253-363 K. Measured CD spectra of (1S)-(+)-10-camphorsulfonic acid and proteins demonstrated the ability of this system to extend the wavelength down to 172 nm in aqueous solution and 153 nm in hexafluoro-2-propanol. PMID:20975221

  4. Contribution of light scattering to the circular dichroism of deoxyribonucleic acid films, deoxyribonucleic acid-polylysine complexes, and deoxyribonucleic acid particles in ethanolic buffers

    SciTech Connect

    Maestre, M.F.; Reich, C.

    1980-01-01

    The contribution of scattering to the circular dichroism (CD) of DNA films with twisted structures, DNA-polylysine complexes, and condensed DNA aggregates in ethanolic buffers of defined salt concentrations has been studied by the use of novel measuring techniques. These techniques include fluorscat cuvettes, fluorescence-detected circular dichroism (FDCD) methods, backscattering capturing devices, and beam-mounted goniometer detectors. The result of the experimental measurement is that DNA films can be made which have very large ellipticities or CD at sharp specific wavelengths. The sign of these ellipticities is related to the handedness of the twists, with a right-handed twist producing large positive rotations and a left-handed one producing negative rotations. The film shows nodal angles at which the interaction with light is minimal. The scattering patterns of both films, DNA-polylysine particles and DNA-EtOH condensates, show that the main interaction is light scattering produced by a resonance phenomenon similar to that produced in cholestric liquid crystals and twisted-nematic liquid crystals. It is proposed that the so-called psi-type CD spectrum is a manifestation of a side-by-side packing of DNA molecules with a long-range twisting order whose helical parameters match the helical parameter of circularly polarized light at specific resonance or critical wavelengths. Application of the Bragg law for cholesteric liquid crystals gives the periodicity of the long-range ordered structures. 9 figures.

  5. Quantitatively analyzing the mechanism of giant circular dichroism in extrinsic plasmonic chiral nanostructures by tracking the interplay of electric and magnetic dipoles.

    PubMed

    Hu, Li; Tian, Xiaorui; Huang, Yingzhou; Fang, Liang; Fang, Yurui

    2016-02-14

    Plasmonic chirality has drawn much attention because of tunable circular dichroism (CD) and the enhancement for chiral molecule signals. Although various mechanisms have been proposed to explain the plasmonic CD, a quantitative explanation like the ab initio mechanism for chiral molecules, is still unavailable. In this study, a mechanism similar to the mechanisms associated with chiral molecules was analyzed. The giant extrinsic circular dichroism of a plasmonic splitting rectangle ring was quantitatively investigated from a theoretical standpoint. The interplay of the electric and magnetic modes of the meta-structure is proposed to explain the giant CD. We analyzed the interplay using both an analytical coupled electric-magnetic dipole model and a finite element method model. The surface charge distributions showed that the circular current yielded by the splitting rectangle ring causes the ring to behave like a magneton at some resonant modes, which then interact with the electric modes, resulting in a mixing of the two types of modes. The strong interplay of the two mode types is primarily responsible for the giant CD. The analysis of the chiral near-field of the structure shows potential applications for chiral molecule sensing. PMID:26814829

  6. Phase equilibrium in poly(rA).poly(rU) complexes with Cd2+ and Mg2+ ions, studied by ultraviolet, infrared, and vibrational circular dichroism spectroscopy.

    PubMed

    Blagoi, Yurii; Gladchenko, Galina; Nafie, Laurence A; Freedman, Teresa B; Sorokin, Victor; Valeev, Vladimir; He, Yanan

    2005-08-01

    Ultraviolet (UV) and infrared (IR) absorption and vibrational circular dichroism (VCD) spectroscopy were used to study conformational transitions in the double-stranded poly(rA). poly(rU) and its components-single-stranded poly(rA) and poly(rU) in buffer solution (pH 6.5) with 0.1M Na+ and different Mg2+ and Cd2+ (10(-6) to 10(-2) M) concentrations. Transitions were induced by elevated temperature that changed from 10 up to 96 degrees C. IR absorption and VCD spectra in the base-stretching region were obtained for duplex, triplex, and single-stranded forms of poly(rA) . poly(rU) at [Mg2+],[Cd2+]/[P] = 0.3. For single-stranded polynucleotides, the kind of conformational transition (ordering --> disordering --> compaction, aggregation) is conditioned by the dominating type of Me2+-polymer complex that in turn depends on the ion concentration range. The phase diagram obtained for poly(rA) . poly(rU) has a triple point ([Cd2+] approximately 10(-4)M) at which the helix-coil (2 --> 1) transition is replaced with a disproportion transition 2AU --> A2U + poly(rA) (2 --> 3) and the subsequent destruction of the triple helix (3 --> 1). The 2 --> 1 transitions occur in the narrow temperature interval of 2 degrees -5 degrees . Unlike 2 --> 1 and 3 --> 1 melting, the disproportion 2 --> 3 transition is a slightly cooperative one and observed over a wide temperature range. At [Me2+] approximately 10(-3) M, the temperature interval of A2U stability is not less than 20 degrees C. In the case of Cd2+, it increases with the rise of ion concentration due to the decrease of T(m) (2-->3). The T(m) (3-->1) value is practically unchanged up to [Cd2+] approximately 10(-3)M. Differences between diagrams for Mg(2+) and Cd2+ result from the various kinds of ion binding to poly(rA).poly-(rU) and poly(rA). PMID:15892121

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

    SciTech Connect

    Kanai, Shun; Tsujikawa, Masahito; Shirai, Masafumi; Miura, Yoshio; Matsukura, Fumihiro Ohno, Hideo

    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.

  8. Atomic moments in Mn2CoAl thin films analyzed by X-ray magnetic circular dichroism

    SciTech Connect

    Jamer, M. E.; Assaf, B. A.; Sterbinsky, G. E.; Arena, D. A.; Heiman, D.

    2014-12-05

    Spin gapless semiconductors are known to be strongly affected by structural disorder when grown epitaxially as thin films. The magnetic properties of Mn2CoAl thin films grown on GaAs (001) substrates are investigated here as a function of annealing. This study investigates the atomic-specific magnetic moments of Mn and Co atoms measured through X-ray magnetic circular dichroism as a function of annealing and the consequent structural ordering. Results indicate that the structural distortion mainly affects the Mn atoms as seen by the reduction of the magnetic moment from its predicted value.

  9. Strain-induced changes in the electronic structure of MnCr(2)O(4) thin films probed by x-ray magnetic circular dichroism.

    PubMed

    van der Laan, G; Chopdekar, R V; Suzuki, Y; Arenholz, E

    2010-08-01

    We show that the angular dependence of x-ray magnetic circular dichroism (XMCD) is strongly sensitive to strain-induced electronic structure changes in magnetic transition metal oxides. We observe a pronounced dependence of the XMCD spectral shape on the experimental geometry as well as nonvanishing XMCD with distinct spectral features in transverse geometry in compressively strained MnCr(2)O(4) films. The angular dependent XMCD can be described as a sum over an isotropic and anisotropic contribution, the latter linearly proportional to the axial distortion due to strain. The XMCD spectra are well reproduced by atomic multiplet calculations. PMID:20868013

  10. A novel correlation of vibrational circular dichroism spectra with the electronic ground state for Δ-SAPR-8-cesium-tetrakis((+)-heptafluorobutyryl-camphorato)lanthanide(III) complexes.

    PubMed

    Kaizaki, Sumio; Shirotani, Dai; Sato, Hisako

    2013-06-28

    For Δ-SAPR-8-Cs[Ln((+)-hfbc)4]((+)-hfbc = (+)-heptafluoro-butyrylcamphorate; Cs-Ln), the vibrational circular dichroism pattern and intensity of Cs-La, Cs-Nd, Cs-Gd, Cs-Ho, Cs-Er, Cs-Lu and Cs-Sm, Cs-Eu, Cs-Tb, Cs-Dy, Cs-Tm, Cs-Yb, respectively, are correlated with the even and the odd parity of total orbital angular momentum in the ground state terms. PMID:23689479

  11. Photoelectron circular dichroism in the multiphoton ionization by short laser pulses. I. Propagation of single-active-electron wave packets in chiral pseudo-potentials

    SciTech Connect

    Artemyev, Anton N.; Müller, Anne D.; Demekhin, Philipp V.; Hochstuhl, David

    2015-06-28

    A theoretical method to study the angle-resolved multiphoton ionization of polyatomic molecules is developed. It is based on the time-dependent formulation of the Single Center (TDSC) method and consists in the propagation of single-active-electron wave packets in the effective molecular potentials in the presence of intense laser pulses. For this purpose, the time-dependent Schrödinger equation for one electron, moving in a molecular field and interacting with an arbitrary laser pulse, is solved in spherical coordinates by an efficient numerical approach. As a test, the method is applied to the one- and two-photon ionizations of a model methane-like chiral system by circularly polarized short intense high-frequency laser pulses. Thereby, we analyze the photoelectron circular dichroism (PECD) in the momentum distribution. The considered model application illustrates the capability of the TDSC method to study multiphoton PECD in fixed-in-space and randomly oriented chiral molecules.

  12. Fine structures in vibrational circular dichroism spectra of chiral molecules with rotatable hydroxyl groups and their application in the analysis of local intermolecular interactions

    NASA Astrophysics Data System (ADS)

    Konno, Kohzo; Shiina, Isamu; Yui, Hiroharu

    2013-03-01

    The effect of hydroxyl group on vibrational circular dichroism is addressed. (-)-Menthol is investigated as a representative chiral molecule which has been widely used as a chiral starting material. Free rotation of the hydroxyl group in (-)-menthol allows it to exist in various conformations in solution. The variety of conformations inevitably affects local intermolecular interactions and the resultant efficiency of asymmetric syntheses. However, the precise relationship between the conformations and intermolecular interactions arising from rotation of the hydroxyl group has remained an unsolved issue despite the molecule's importance. Here, the conformations and interactions are investigated using vibrational circular dichroism (VCD). VCD is quite sensitive to slight differences in the conformation of chiral molecules and their local environment. We examined various conformers in (-)-menthol and compared the VCD spectrum with that of (-)-menthone. It revealed the rotation of the polar hydroxyl group sensitively affects the VCD activity, resulting in the emergence of various patterns in the corresponding VCD spectra, especially in the wavenumber regions at around 1064 cm-1 and 1254 cm-1. Among these regions, the latter one is further investigated to examine the feasibility of applying the sensitive response to the analysis on the local intermolecular environment. It includes solute-solvent interactions via hydroxyl groups, which is important for biomacromolecule structural stability and efficient stereoselective syntheses. As a consequence, distinctive fine structures in the VCD spectra, including an unpredicted band, are observed when varying temperature and concentration. Their possible assignment is also discussed.

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

    NASA Astrophysics Data System (ADS)

    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.

  14. X-ray magnetic circular dichroism photoemission electron microscopy of focused ion beam-induced magnetic patterns on iron-rhodium surfaces

    NASA Astrophysics Data System (ADS)

    Tohki, Atsushi; Aikoh, Kazuma; Shinoda, Ryoichi; Ohkochi, Takuo; Kotsugi, Masato; Nakamura, Tetsuya; Kinoshita, Toyohiko; Iwase, Akihiro; Matsui, Toshiyuki

    2013-05-01

    Iron-rhodium (FeRh) thin films were irradiated with a 30 keV Ga ion beam using a focused ion beam system to produce micrometer scale ferromagnetic square dot arrays. Two-dimensional magnetic square dot arrays with dimensions of 30 × 30, 10 × 10, and 5 × 5 μm were successfully produced on the FeRh surface, which was confirmed by magnetic force microscopy. The results of photoemission electron microscopy combined with X-ray magnetic circular dichroism revealed that the magnetization of the magnetic square dots could be controlled by changing the amount of irradiation. The magnetic domain structure of the magnetic square dots with sides of 5-30 μm was found to be a single domain structure, which was possibly influenced by the interaction between ferromagnetic and antiferromagnetic interfaces.

  15. Study on ferromagnetic ordering of FeRh thin films induced by energetic heavy ion irradiation by means of X-ray Magnetic Circular Dichroism

    NASA Astrophysics Data System (ADS)

    Aikoh, Kazuma; Tohki, Atsushi; Okuda, Shuichi; Saitoh, Yuichi; Kamiya, Tomihiro; Nakamura, Tetsuya; Kinoshita, Toyohiko; Iwase, Akihiro; Matsui, Toshiyuki

    2013-11-01

    We investigated the ion irradiation induced ferromagnetic state of FeRh thin films with 10 MeV I ion beam by the measurements of a superconducting quantum interference device (SQUID) magnetometer as well as of soft X-ray Magnetic Circular Dichroism (XMCD). It was clearly shown in the magnetization loops by SQUID measurements that the ion irradiation induced the ferromagnetic state in the FeRh thin films even below room temperature. This was also confirmed by the Fe L2,3-edge XMCD measurements for the irradiated FeRh film samples. However, we found that the irradiation ion fluence dependence on the magnetization was totally different between two measurement techniques. We also revealed by XMCD sum rule analysis that the ferromagnetism in the ion irradiated FeRh thin films was mainly dominated by the spin moment.

  16. Common Origin of the Circular-dichroism Pattern in ARPES of SrTiO3 and CuxBi2Se3

    SciTech Connect

    Bell, Christopher

    2011-08-19

    We investigate circular dichroism in the angular distribution (CDAD) of photoelectrons from SrTiO{sub 3}:Nb and Cu{sub x}Bi{sub 2}Se{sub 3} recorded by 7-eV laser ARPES. In addition to the well-known node that occurs in CDAD when the incidence plane matches the mirror plane of the crystal, we show that another type of node occurs when the mirror plane of the crystal is vertical to the incidence plane and the electronic state is two dimensional. The flower-shaped CDAD's occurring around the Fermi level of SrTiO{sub 3}:Nb and around the Dirac point of Cu{sub x}Bi{sub 2}Se{sub 3} are explained on equal footings. A surface-state-to-surface-resonance transition is indicated for the topological state of Cu{sub x}Bi{sub 2}Se{sub 3}.

  17. Studies on the conformational transformations of L-arginine molecule in aqueous solution with temperature changing by circular dichroism spectroscopy and optical rotations

    NASA Astrophysics Data System (ADS)

    Wang, Luning; Zhang, Guanghui; Wang, Xinqiang; Wang, Lei; Liu, Xitao; Jin, Lutong; Xu, Dong

    2012-10-01

    Experimental measurements, including circular dichroism (CD) spectroscopy and optical rotations have been employed to characterize the changing tendency of molecular conformations of the full protonated L-arginine (LA2+) in aqueous solution with the rising of temperature. Calculating methods, including conformational search, molecular structural optimization, CD responses as well as specific rotation calculations have been performed to interpret experimental results. Calculated results, no matter in CD spectra or specific rotations, are consistent with experiments, which strongly certify the transformation of molecular conformations. This successful reproduction of experimental results with molecular simulations in both areas of CD responses and optical rotations is of great significance. More detailed analysis about the relationship between LA2+ molecular structure and the optical activity has been conducted.

  18. End station for nanoscale magnetic materials study: Combination of scanning tunneling microscopy and soft X-ray magnetic circular dichroism spectroscopy

    SciTech Connect

    Ueno, Tetsuro; Sawada, Masahiro; Namatame, Hirofumi; Kishimizu, Yusuke; Kimura, Akio; Taniguchi, Masaki

    2012-12-15

    We have constructed an end station for nanoscale magnetic materials study at the soft X-ray beamline HiSOR BL-14 at Hiroshima Synchrotron Radiation Center. An ultrahigh-vacuum scanning tunneling microscope (STM) was installed for an in situ characterization of nanoscale magnetic materials in combination with soft X-ray magnetic circular dichroism (XMCD) spectroscopy experiment. The STM was connected to the XMCD experimental station via damper bellows to isolate it from environmental vibrations, thus achieving efficient spatial resolution for observing Si(111) surface at atomic resolution. We performed an in situ experiment with STM and XMCD spectroscopy on Co nanoclusters on an Au(111) surface and explored its practical application to investigate magnetic properties for well-characterized nanoscale magnetic materials.

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

    PubMed

    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. PMID:26481381

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

    SciTech Connect

    Robertson, MacCallum J.; Agostino, Christopher J.; N'Diaye, Alpha T.; Chen, Gong; Im, Mi-Young; Fischer, Peter

    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.

  1. Temperature and field-induced magnetization flips in amorphous Er{endash}Fe alloys evidenced by x-ray magnetic circular dichroism

    SciTech Connect

    Garcia, L.M.; Pizzini, S.; Rueff, J.P.; Vogel, J.; Galera, R.M.; Fontaine, A.; Kappler, J.P.; Krill, G.; Goedkoop, J.

    1996-04-01

    Magnetic properties of amorphous Er{sub 1{minus}{ital x}}Fe{sub {ital x}} alloys with {ital x}{approx_equal}0.7 have been studied. Macroscopic characterization has been performed by measuring temperature- and field-dependent magnetization. Applying a magnetic field the compensation temperature first decreases, but increases again at larger fields. This {open_quote}{open_quote}exotic{close_quote}{close_quote} behavior has been interpreted in terms of the sperimagnetic character of both subnetworks. The suggested scheme has been checked by measuring x-ray circular magnetic dichroism at the Er {ital M}{sub 5}-edge. Using this atom-sensitive technique we have been able to detect temperature-induced as well as field-induced flips of the Er-subnetwork with respect to the direction of the applied field. {copyright} {ital 1996 American Institute of Physics.}

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

    NASA Astrophysics Data System (ADS)

    Robertson, MacCallum J.; Agostino, Christopher J.; N'Diaye, Alpha T.; Chen, Gong; Im, Mi-Young; Fischer, Peter

    2015-05-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Scherrer, Arne; Agostini, Federica; Sebastiani, Daniel; Gross, E. K. U.; Vuilleumier, Rodolphe

    2015-08-01

    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.

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

    SciTech Connect

    Scherrer, Arne; Agostini, Federica; Gross, E. K. U.; Sebastiani, Daniel; Vuilleumier, Rodolphe

    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.

  5. Absolute configuration and predominant conformations of a chiral crown ether-based colorimetric sensor: a vibrational circular dichroism spectroscopy and DFT study of chiral recognition.

    PubMed

    Merten, Christian; Hyun, Myung Ho; Xu, Yunjie

    2013-05-01

    In the present work, we report a comprehensive vibrational circular dichroism (VCD) spectroscopic study of a chiral crown ether which features an axial chiral 3.3'-diphenyl-1,1'-binaphthyl group as chiral moiety. By comparing the experimental and calculated VCD spectra, we show that the presumably very flexible crown ether preferably adopts only one ring conformation. Conformational flexibility is observed in the 2,4-dinitrophenyl-diazophenol group, which was previously introduced for colorimetric detection of primary amines and amino alcohols (Cho et al., Chirality 2011;23:349-353). The VCD spectra of the host-guest complexes with phenyl glycinol (PG) and phenyl alaninol have been studied as well. Based on the spectra calculated, it is shown that the diastereomeric complexes in general can be differentiated using VCD spectroscopy. Furthermore, the experimental VCD spectra of the complexes of the host molecule with PG support the above finding. PMID:23620265

  6. Circular-dichroism and electron-microscopy studies of human subcomponent C1q before and after limited proteolysis by pepsin.

    PubMed Central

    Brodsky-Doyle, B; Leonard, K R; Reid, K B

    1976-01-01

    1. A fragment of human subcomponent C1q was prepared by limited proteolysis with pepsin at 37 degrees C for 20 h, and at pH4.4, followed by gel filtration on Sephadex G-200. This fragment was shown to contain all the collagen-like features known to be present in the intact molecule [Reid (1976) Biochem. J. 155, 5-17]. 2. Circular-dichroism studies showed the presence of positive bands at 230 and 223 nm in the intact subcomponent C1q and pepsin fragment respectively, compared with a positive band at 220 nm obtained for lathyritic rat skin collagen. These bands were abolished by collagenase treatment, which suggested that there may some collagen-like triple-helical structure in subcomponent C1q and that this structure resides in the pepsin-resistant portion of the molecule. However, the 230 and 223 nm bands had a substantially lower magnitude than that obtained for the unaggregated single fibres of totally triple-helical collagen. 3. Thermal-transition temperatures obtained for subcomponent C1q, the pepsin fragment and the reduced and alkylated pepsin fragment were 48 degrees, 48 degrees and 39 degrees C respectively, compared with a value of 38 degrees C obtained for lathyritic rat skin collagen. 4. Only the unreduced pepsin fragment regained significant amounts (up to 60%) of collagen-like structure, after heat denaturation and cooling, as estimated by circular-dichroism measurements. 5. Electron-microscopy studies of subcomponent C1q and the collagen-like pepsin-resistant fragment of subcomponent C1q showed that the six peripheral globular regions of the molecule were fragmented by pepsin leaving the six collagen-like connecting strands and fibril-like central portion intact. Images PLATE 1 PLATE 2 PMID:187173

  7. Determination of the absolute configuration of chiral α-aryloxypropanoic acids using vibrational circular dichroism studies: 2-(2-chlorophenoxy) propanoic acid and 2-(3-chlorophenoxy) propanoic acid

    NASA Astrophysics Data System (ADS)

    He, Jiangtao; Polavarapu, Prasad L.

    2005-05-01

    The enantiomers of 2-(2-chlorophenoxy) propanoic acid and 2-(3-chlorophenoxy) propanoic acid were resolved on a chiral HPLC column and investigated using mid-infrared vibrational circular dichroism (VCD). Experimental infrared vibrational absorption and VCD spectra were measured in CDCl 3 solution in the 2000-900 cm -1 region and compared with the ab initio predictions of absorption and VCD spectra. The predicted spectra were obtained with density functional theory using B3LYP/6-31G* basis set for the stable and dominant conformers. But the predicted spectra did not provide unambiguous structural information due to intermolecular hydrogen bonding in solution. To eliminate the hydrogen bonding effects, the acids were converted to the corresponding methyl esters and the experimental absorbance and VCD spectra of methyl esters were measured. B3LYP predicted spectra were also obtained for the stable and dominant conformers of the esters. From a comparison of the experimental VCD spectra of methyl esters with corresponding ab initio predictions, the absolute configurations of esters, and therefore of their parent acids, are unambiguously determined to be (+)-( R).

  8. Photoelectron circular dichroism in the multiphoton ionization by short laser pulses. I. Propagation of single-active-electron wave packets in chiral pseudo-potentials.

    PubMed

    Artemyev, Anton N; Müller, Anne D; Hochstuhl, David; Demekhin, Philipp V

    2015-06-28

    A theoretical method to study the angle-resolved multiphoton ionization of polyatomic molecules is developed. It is based on the time-dependent formulation of the Single Center (TDSC) method and consists in the propagation of single-active-electron wave packets in the effective molecular potentials in the presence of intense laser pulses. For this purpose, the time-dependent Schrödinger equation for one electron, moving in a molecular field and interacting with an arbitrary laser pulse, is solved in spherical coordinates by an efficient numerical approach. As a test, the method is applied to the one- and two-photon ionizations of a model methane-like chiral system by circularly polarized short intense high-frequency laser pulses. Thereby, we analyze the photoelectron circular dichroism (PECD) in the momentum distribution. The considered model application illustrates the capability of the TDSC method to study multiphoton PECD in fixed-in-space and randomly oriented chiral molecules. PMID:26133408

  9. Fluorescence-detected X-ray magnetic circular dichroism of well-defined Mn(II) and Ni(II) doped in MgO crystals: credential evaluation for measurements on biological samples.

    PubMed

    Wang, Hongxin; Bryant, Craig; LeGros, M; Wang, Xin; Cramer, S P

    2012-10-18

    L(2,3)-edge X-ray magnetic circular dichroism (XMCD) spectra have been measured for the well-defined dilute Ni(II) and Mn(II) ions doped into a MgO crystal, with sub-Kelvin dilution refrigerator cooling and 2 T magnetic field magnetization. A 30-element Ge array X-ray detector has been used to measure the XMCD for these dilute ions, whose concentrations are 1400 ppm for Ni(II) and 10,000 ppm for Mn(II). Large XMCD effects have been observed for both Ni(II) and Mn(II), and multiplet simulation described the observed spectra. The fluorescence-detected L-edge absorption spectrum and XMCD of Ni(II) in MgO are comparable with both theoretical calculations and the total electron yield measured ions in similar chemical environments, at least qualitatively validating the use of the sensitive fluorescence detection technique for studying XMCD for dilute 3d metal ions, such as various metalloproteins. Sum rule analyses on the XMCD spectra are also performed. In addition, these XMCD measurements have also been used to obtain the sample's magnetization curve and the beamline's X-ray helicity curve. This study also illustrated that bend magnet beamlines are still useful in examining XMCD on dilute and paramagnetic metal sites. PMID:22650370

  10. {sup 57}Fe Moessbauer and x-ray magnetic circular dichroism study of magnetic compensation of the rare-earth sublattice in Nd{sub 2-x}Ho{sub x}Fe{sub 14}B compounds

    SciTech Connect

    Chaboy, J.; Piquer, C.; Plugaru, N.; Bartolome, F.; Laguna-Marco, M. A.

    2007-10-01

    We present here a study of the magnetic properties of the Nd{sub 2-x}Ho{sub x}Fe{sub 14}B series. The macroscopic properties of these compounds evolve continuously from those of Nd{sub 2}Fe{sub 14}B to those of Ho{sub 2}Fe{sub 14}B as Ho gradually replaces Nd. The system shows a compensation of the rare-earth sublattice magnetization for a critical concentration, x{sub c}=0.55, that is reflected into the anomalous behavior of both macroscopic and microscopic magnetic probes. The combined analysis of magnetization, {sup 57}Fe Moessbauer spectroscopy and Fe K-edge x-ray magnetic circular dichroism (XMCD) measurements suggests that the origin of the anomalous magnetic behavior found at x{sub c}=0.55 is mainly due to the Ho sublattice. Moreover, the analysis of the Fe K-edge XMCD signals reveal the presence of a rare-earth contribution, reflecting the coupling of the rare-earth and Fe magnetic moments, which can lead to the possibility of disentangling the magnetic behavior of both Fe and R atoms using a single absorption edge.

  11. Magnetic structures of FeTiO{sub 3}-Fe{sub 2}O{sub 3} solid solution thin films studied by soft X-ray magnetic circular dichroism and ab initio multiplet calculations

    SciTech Connect

    Hojo, H. E-mail: fujita@dipole7.kuic.kyoto-u.ac.jp; Fujita, K. E-mail: fujita@dipole7.kuic.kyoto-u.ac.jp; Matoba, T.; Tanaka, K.; Ikeno, H.; Mizoguchi, T.; Tanaka, I.; Nakamura, T.; Takeda, Y.; Okane, T.

    2014-03-17

    The solid solutions between ilmenite (FeTiO{sub 3}) and hematite (α-Fe{sub 2}O{sub 3}) have recently attracted considerable attention as a spintronic material due to their interesting magnetic and electrical properties. In this study, the electronic and magnetic structures of epitaxially grown 0.6FeTiO{sub 3}·0.4Fe{sub 2}O{sub 3} solid solution thin films were investigated by combining x-ray absorption near-edge structure (XANES), x-ray magnetic circular dichroism (XMCD) for two different crystallographic projections, and first-principles theoretical calculations. The Fe L-edge XANES and XMCD spectra reveal that Fe is in the mixed-valent Fe{sup 2+}–Fe{sup 3+} states while Fe{sup 2+} ions are mainly responsible for the magnetization. Moreover, the experimental Fe L-edge XANES and XMCD spectra change depending on the incident x-ray directions, and the theoretical spectra explain such spectral features. We also find a large orbital magnetic moment, which can originate the magnetic anisotropy of this system. On the other hand, although the valence state of Ti was interpreted to be 4+ from the Ti L-edge XANES, XMCD signals indicate that some electrons are present in the Ti-3d orbital, which are coupled antiparallel to the magnetic moment of Fe{sup 2+} ions.

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

    SciTech Connect

    Tobin, J.G.; Goodman, K.W.; Schumann, F.O.

    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.

  13. Electrochromism-driven linearly and circularly polarised dichroism of poly(3,4-ethylenedioxythiophene) derivatives with chirality and liquid crystallinity.

    PubMed

    Matsushita, Satoshi; Jeong, Yong Soo; Akagi, Kazuo

    2013-03-01

    This review presents recent advances in the synthesis, electrochemical properties, and optical functions of poly(3,4-ethylenedioxythiophene) (PEDOT) derivatives embodying chirality and liquid crystallinity. Various methods for preparing the optically active and liquid crystalline (LC) PEDOT derivatives, such as (i) the introduction of chiral substituents into polymer side chains, (ii) chemical or electrochemical polymerisation by using lipid assemblies as templates, (iii) electrochemical polymerisation in asymmetric LC reaction fields, and (iv) the addition of a chiral dopant to LC-PEDOT derivatives, are discussed. Throughout the review, linearly and/or circularly dichroic electrochromism, hierarchically controlled spiral structure, and aligned morphology are demonstrated to be promising for the development of multifunctional PEDOT derivatives. PMID:23282471

  14. Magnetic circular dichroism of porphyrins containing M = Ca, Ni, and Zn. A computational study based on time-dependent density functional theory.

    PubMed

    Peralta, G A; Seth, Michael; Ziegler, Tom

    2007-10-29

    A theoretical study is presented on the magnetic circular dichroism (MCD) exhibited by the porphyrin complexes MP (M = Mg,Ni,Zn), MTPP (M = Mg,Ni,Zn), and NiOEP, where P = porphyrin, TPP = tetraphenylporphyrin, and OEP = octaethylporphyrin. The study makes use of a newly implemented method for the calculation of A and B terms from the theory of MCD and is based on time-dependent density functional theory (TD-DFT). It is shown that the MCD spectrum is dominated by a single positive A term in the Q-band region in agreement with experiment where available. The band can be fully explained as the first transition in Gouterman's four-orbital model for the type of porphyrins studied here. For the Soret band, the experimental MCD spectrum appears as a single positive A term. This is also what is found computationally for NiP and NiTPP, where the second transition in Gouterman's four-orbital model give rise to a positive A term. However, for the remaining systems, the simulated MCD spectrum is actually due to two B terms that have the appearance of one positive pseudo A term. The two B terms appear because the second Gouterman state is coupled strongly to a second excited state (b(2u) --> 2e(g)) of nearly the same energy by the external magnetic field. PMID:17914806

  15. Conformation of one- and two-chain high molecular weight urokinase analyzed by small-angle neutron scattering and vacuum ultraviolet circular dichroism

    SciTech Connect

    Mangel, W.F.; Lin, B.H.; Ramakrishnan, V. )

    1991-05-25

    The structures of one- and two-chain high molecular weight human urokinase were analyzed by small-angle neutron scattering and vacuum ultraviolet circular dichroism. Both one- and two-chain high molecular weight urokinases exhibited a radius of gyration of 31 A and a maximum dimension of 90 A. Neither parameter was affected by the presence of lysine sufficient to saturate all the lysine-binding sites in human plasminogen. These physical parameters are consistent with the sedimentation coefficient of high molecular weight urokinase and indicate that both proteins are highly asymmetric. Neither protein contained much alpha-helix or parallel beta-sheet. Most of the secondary structure was in the form of antiparallel beta-sheet and beta-turns, very similar to the secondary structure of plasminogen. The macroscopic kinetic constants, Km and kcat, for the hydrolysis of (pyroGlu-Gly-Arg-NH)2-rhodamine by two-chain high molecular weight urokinase and low molecular weight urokinase which lacks the epidermal growth factor and kringle domains were similar. These structural and kinetic data are consistent with the domains in both forms of urokinase being independent structural and functional units.

  16. Quantitative analysis of magnetic spin and orbital moments from an oxidized iron (1 1 0) surface using electron magnetic circular dichroism

    DOE PAGESBeta

    Thersleff, Thomas; Rusz, Jan; Rubino, Stefano; Hjörvarsson, Björgvin; Ito, Yasuo; J. Zaluzec, Nestor; Leifer, Klaus

    2015-08-17

    Understanding the ramifications of reduced crystalline symmetry on magnetic behavior is a critical step in improving our understanding of nanoscale and interfacial magnetism. However, investigations of such effects are often controversial largely due to the challenges inherent in directly correlating nanoscale stoichiometry and structure to magnetic behavior. Here, we describe how to use Transmission Electron Microscope (TEM) to obtain Electron Magnetic Circular Dichroism (EMCD) signals as a function of scattering angle to locally probe the magnetic behavior of thin oxide layers grown on an Fe (1 1 0) surface. Experiments and simulations both reveal a strong dependence of the magneticmore » orbital to spin ratio on its scattering vector in reciprocal space. We exploit this variation to extract the magnetic properties of the oxide cladding layer, showing that it locally may exhibit an enhanced orbital to spin moment ratio. This finding is supported here by both spatially and angularly resolved EMCD measurements, opening up the way for compelling investigations into how magnetic properties are affected by nanoscale features.« less

  17. Quantitative analysis of magnetic spin and orbital moments from an oxidized iron (1 1 0) surface using electron magnetic circular dichroism

    SciTech Connect

    Thersleff, Thomas; Rusz, Jan; Rubino, Stefano; Hjörvarsson, Björgvin; Ito, Yasuo; J. Zaluzec, Nestor; Leifer, Klaus

    2015-08-17

    Understanding the ramifications of reduced crystalline symmetry on magnetic behavior is a critical step in improving our understanding of nanoscale and interfacial magnetism. However, investigations of such effects are often controversial largely due to the challenges inherent in directly correlating nanoscale stoichiometry and structure to magnetic behavior. Here, we describe how to use Transmission Electron Microscope (TEM) to obtain Electron Magnetic Circular Dichroism (EMCD) signals as a function of scattering angle to locally probe the magnetic behavior of thin oxide layers grown on an Fe (1 1 0) surface. Experiments and simulations both reveal a strong dependence of the magnetic orbital to spin ratio on its scattering vector in reciprocal space. We exploit this variation to extract the magnetic properties of the oxide cladding layer, showing that it locally may exhibit an enhanced orbital to spin moment ratio. This finding is supported here by both spatially and angularly resolved EMCD measurements, opening up the way for compelling investigations into how magnetic properties are affected by nanoscale features.

  18. Interactions of the organogold(III) compound Aubipyc with the copper chaperone Atox1: a joint mass spectrometry and circular dichroism investigation.

    PubMed

    Marzo, Tiziano; Scaletti, Federica; Michelucci, Elena; Gabbiani, Chiara; Pescitelli, Gennaro; Messori, Luigi; Massai, Lara

    2015-12-01

    The so called "copper trafficking system" in mammalian cells is primarily devoted to the regulation of copper transport and homeostasis. This system, now well characterized, consists of a few strictly interconnected proteins that assist copper entrance inside cells and then promote metal transfer and delivery to essential copper-dependent cellular proteins (Boal and Rosenzweig 2009a; Banci et al., Mol Life Sci 67:2563-2589, 2010). Yet, the "copper trafficking system" may also facilitate the entrance inside cells of non-physiological metal species such as clinically established platinum drugs. ESI and MALDI MS methods are exploited here to characterize the interactions occurring between the experimental anticancer organogold(III) drug, Aubipyc, and the copper chaperone Atox1, a key protein of the copper trafficking system. The nature of the adducts that are formed when reacting Aubipyc with Atox1 is elucidated in detail. Characterization of the Aubipyc/Atox1 system is further supported by circular dichroism experiments. Binding competitions with mercury and bismuth ions were also explored. The relevance and the biological implications of the present results are discussed. PMID:26453060

  19. Application of supervised Kohonen map and counter propagation neural network for classification of nucleic acid structures based on their circular dichroism spectra

    NASA Astrophysics Data System (ADS)

    Ghobadi, Mohadeseh Zarei; Kompany-Zareh, Mohsen

    2014-11-01

    One of the most popular instrumental methods to detect the DNA structure is circular dichroism. Specific experimental conditions are required to form different structures of DNA. However, there is the possibility of different structures establishing in the similar circumstance. So, methods development to improve the classification and prediction of structures using their spectra information are needed. To this end, we applied unsupervised (PCA) and supervised (PLS-DA, SKN, and CPNN) approaches to classify CD spectra dataset of different DNA sequences (random coil (ss-DNA), duplex, hairpin, reversed and normal triplex, parallel and antiparallel G-quadruplex, and i-motif). The main part of this work concentrates on the application of artificial neural networks and weight analysis to obtain more classification and prediction accuracy. For this purpose, the trained network was run 10 times, and the average weights were taken. Also, weight analysis was done for the prediction of mixture samples include different structures. The results prove that new method of weights analysis based on SKN and CPNN is useful for classification of complicated data such as different types of DNA structures.

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

    PubMed

    Gu, Zhi-Gang; Bürck, Jochen; Bihlmeier, Angela; Liu, Jinxuan; Shekhah, Osama; Weidler, Peter G; Azucena, Carlos; Wang, Zhengbang; Heissler, Stefan; Gliemann, Hartmut; Klopper, Wim; Ulrich, Anne S; Wöll, Christof

    2014-08-01

    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 [Cu2(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. PMID:24938623

  1. Residual structures in the unfolded state of starch-binding domain of glucoamylase revealed by near-UV circular dichroism and protein engineering techniques.

    PubMed

    Ota, Chiaki; Ikeguchi, Masamichi; Tanaka, Akiyoshi; Hamada, Daizo

    2016-10-01

    Protein folding is a thermodynamic process driven by energy gaps between the native and unfolded states. Although a wealth of information is available on the structure of folded species, there is a paucity of data on unfolded species. Here, we analyzed the structural properties of the unfolded state of the starch-binding domain of glucoamylase from Aspergillus niger (SBD) formed in the presence of guanidinium hydrochloride (GuHCl). Although far-UV CD and intrinsic tryptophan fluorescence spectra as well as small angle X-ray scattering suggested that SBD assumes highly unfolded structures in the presence of GuHCl, near-UV circular dichroism of wild-type SBD suggested the presence of residual structures in the unfolded state. Analyses of the unfolded states of tryptophan mutants (W543L, W563A, W590A and W615L) using Similarity Parameter, a modified version of root mean square deviation as a measure of similarity between two spectra, suggested that W543 and W563 have preferences to form native-like residual structures in the GuHCl-unfolded state. In contrast, W615 was entirely unstructured, while W590 tended to form non-native ordered structures in the unfolded state. These data and the amino acid sequence of SBD suggest that local structural propensities in the unfolded state can be determined by the probability of the presence of hydrophobic or charged residues nearby tryptophan residues. PMID:27164491

  2. Origin of anomalous electronic circular dichroism spectrum of RuPt2(tppz)2Cl2(PF6)4 in acetonitrile.

    PubMed

    Yu, Hua-Gen

    2014-07-24

    We report a theoretical study of the structures, energetics, and electronic spectra of the Pt(II)/Ru(II) mixed-metal complex RuPt2(tppz)2Cl2(PF6)4 (tppz = 2,3,5,6-tetra(2-pyridyl)pyrazine) in acetonitrile. The hybrid B3LYP density functional theory and its TDDFT methods were used with a complete basis set (CBS) extrapolation scheme and a conductor polarizable continuum model (C-PCM) for solvation effects. Results showed that the trinuclear complex has four types of stable conformers and/or enantiomers. They are separated by high barriers owing to the repulsive H/H geometrical constraints in tppz. A strong entropy effect was found for the dissociation of RuPt2(tppz)2Cl2(PF6)n in acetonitrile. The UV-visible and emission spectra of the complex were also simulated. They are in good agreement with experiments. In this work we have largely focused on exploring the origin of anomalous electronic circular dichroism (ECD) spectra of the RuPt2(tppz)2Cl2(PF6)4 complex in acetonitrile. As a result, a new mechanism has been proposed together with a clear illustration by using a physical model. PMID:25026322

  3. Salts employed in hydrophobic interaction chromatography can change protein structure - insights from protein-ligand interaction thermodynamics, circular dichroism spectroscopy and small angle X-ray scattering.

    PubMed

    Komaromy, Andras Z; Kulsing, Chadin; Boysen, Reinhard I; Hearn, Milton T W

    2015-03-01

    Key requirements of protein purification by hydrophobic interaction chromatography (HIC) are preservation of the tertiary/quaternary structure, maintenance of biological function, and separation of the correctly folded protein from its unfolded forms or aggregates. This study examines the relationship between the HIC retention behavior of hen egg white lysozyme (HEWL) in high concentrations of several kosmotropic salts and its conformation, assessed by circular dichroism (CD) spectroscopy. Further, the physicochemical properties of HEWL in the presence of high concentrations of ammonium sulfate, sodium chloride and magnesium chloride were investigated by small angle X-ray scattering (SAXS) at different temperatures. Radii of gyration were extrapolated from Guinier approximations and the indirect transform program GNOM with protein-protein interaction and contrast variation taken into account. A bead model simulation provided information on protein structural changes using ab initio reconstruction with GASBOR. These results correlated to the secondary structure content obtained from CD spectroscopy of HEWL. These changes in SAXS and CD data were consistent with heat capacity ΔCp -values obtained from van't Hoff plot analyses of the retention data. Collectively, these insights enable informed decisions to be made on the choice of chromatographic conditions, leading to improved separation selectivity and opportunities for innovative column-assisted protein refolding methods. PMID:25690783

  4. Mercury-induced DNA polymorphism: Probing the conformation of Hg(II)-DNA via Staphylococcal nuclease digestion and circular dichroism measurements

    SciTech Connect

    Gruenwedel, D.W.; Cruikshank, M.K. )

    1990-02-27

    Exposing native calf thymus DNA to increasing concentrations of Hg(ClO{sub 4}){sub 2} not only produces dramatic changes in its circular dichroism (CD) but results also in the decrease, and ultimate cessation, of endonucleolytic DNA cleavage by staphylococcal nuclease. DNA cleavage proceeds at or near the rates exhibited by untreated DNA. At Hg(II) levels of 0.08 < r < 0.5, the rate of DNA hydrolysis decreases monotonically with increasing Hg(II) concentrations, and at r > 0.4, DNA cleavage ceases. Both the CD changes and the changes in the rate of DNA digestion are totally reversible upon the removal of Hg(II). For comparison purposes, native calf thymus DNA was also treated with methylmercury (CH{sub 3}Hg(II)), an agent known to disrupt the secondary structure of DNA. The treatment yielded single-stranded methylmercurated DNA with preserved right-handed helix screwness. The authors interpret the Hg(II)-induced alterations in the CD of native calf thymus DNA, and the hydrolysis rate changes observed with staphylococcal nuclease, to indicate that Hg(II) either produces in DNA reversible B {leftrightarrow} Z transitions, passing transiently through C-like conformations, or generates non-B-conformational structures of presumably left-handed geometry.

  5. In situ assembly of octahedral Fe(II) complexes for the enantiomeric excess determination of chiral amines using circular dichroism spectroscopy.

    PubMed

    Dragna, Justin M; Pescitelli, Gennaro; Tran, Lee; Lynch, Vincent M; Anslyn, Eric V; Di Bari, Lorenzo

    2012-03-01

    A method for discriminating between α-chiral primary amine enantiomers is reported. The method utilizes circular dichroism (CD) spectroscopy and a sensing ensemble composed of 2-formyl-3-hydroxypyridine (4) and Fe(II)(TfO)(2). Aldehyde 4 reacts rapidly with chiral amines to form chiral imines, which complex Fe(II) to form a series of diastereomeric octahedral complexes that are CD-active in both the UV and visible regions of the spectrum. NMR studies showed that for enantiomerically pure imine complexes, the Δ-fac isomer is preferred. A statistical analysis of the distribution of stereoisomers accurately modeled the calibration curves for enantiomeric excess (ee). CD signals appearing in the UV region were bisignate, and the nulls of the CD signals were coincident with maxima in the UV spectrum, consistent with exciton coupling. Time-dependent density functional theory and semiempirical calculations confirmed that the CD signals in the UV region arise from coupling of the π-π* transitions in the imine chromophores and that they can be used to describe the signs and magnitudes of the curves accurately. The CD signals in the visible region arise from metal-to-ligand charge-transfer bands, and these signals can be used to determine the ee values of chiral amines with an average absolute error of ±5%. Overall, the strategy presented herein represents a facile in situ assembly process that uses commercially available simple reagents to create large optical signals indicative of ee values. PMID:22272943

  6. Applications of circular dichroism (CD) for structural analysis of proteins: qualification of near- and far-UV CD for protein higher order structural analysis.

    PubMed

    Li, Cynthia H; Nguyen, Xichdao; Narhi, Linda; Chemmalil, Letha; Towers, Edward; Muzammil, Salman; Gabrielson, John; Jiang, Yijia

    2011-11-01

    Circular dichroism (CD) spectroscopy is routinely used in the biopharmaceutical industry to study the effects of manufacturing, formulation, and storage conditions on protein conformation and stability, and these results are often included in regulatory filings. In this context, the purpose of CD spectroscopy is often to verify that a change in the formulation or manufacturing process of a product has not produced a change in the conformation of a protein. A comparison of two or more spectra is often required to confirm that the protein's structure has been maintained. Traditionally, such comparisons have been qualitative in nature, based on visually inspecting the overlaid spectra. However, visual assessment is inherently subjective and therefore prone to error. Furthermore, recent requests from regulatory agencies to demonstrate the suitability of the CD spectroscopic method for the purpose of comparing spectra have highlighted the need to appropriately qualify CD spectroscopy for characterization of biopharmaceutical protein products. In this study, we use a numerical spectral comparison approach to establish the precision of the CD spectroscopic method and to demonstrate that it is suitable for protein structural characterization in numerous biopharmaceutical applications. PMID:21732370

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

    SciTech Connect

    France, L.L.; Piatti, P.G.; Newman, J.F.E.; Brown, F. ); Toth, I.; Gibbons, W.A. )

    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.

  8. Quantitative analysis of magnetic spin and orbital moments from an oxidized iron (1 1 0) surface using electron magnetic circular dichroism

    PubMed Central

    Thersleff, Thomas; Rusz, Jan; Rubino, Stefano; Hjörvarsson, Björgvin; Ito, Yasuo; J. Zaluzec, Nestor; Leifer, Klaus

    2015-01-01

    Understanding the ramifications of reduced crystalline symmetry on magnetic behavior is a critical step in improving our understanding of nanoscale and interfacial magnetism. However, investigations of such effects are often controversial largely due to the challenges inherent in directly correlating nanoscale stoichiometry and structure to magnetic behavior. Here, we describe how to use Transmission Electron Microscope (TEM) to obtain Electron Magnetic Circular Dichroism (EMCD) signals as a function of scattering angle to locally probe the magnetic behavior of thin oxide layers grown on an Fe (1 1 0) surface. Experiments and simulations both reveal a strong dependence of the magnetic orbital to spin ratio on its scattering vector in reciprocal space. We exploit this variation to extract the magnetic properties of the oxide cladding layer, showing that it locally may exhibit an enhanced orbital to spin moment ratio. This finding is supported here by both spatially and angularly resolved EMCD measurements, opening up the way for compelling investigations into how magnetic properties are affected by nanoscale features. PMID:26278134

  9. Orbital and spin moments of 5 to 11 nm Fe{sub 3}O{sub 4} nanoparticles measured via x-ray magnetic circular dichroism

    SciTech Connect

    Cai, Y. P.; Chesnel, K. Trevino, M.; Westover, A.; Turley, S.; Harrison, R. G.; Hancock, J. M.; Scherz, A.; Reid, A.; Wu, B.; Graves, C.; Wang, T.; Liu, T.; Dürr, H.

    2014-05-07

    The orbital and spin contributions to the magnetic moment of Fe in Fe{sub 3}O{sub 4} nanoparticles were measured using X-ray magnetic circular dichroism (XMCD). Nanoparticles of different sizes, ranging from 5 to 11 nm, were fabricated via organic methods and their magnetic behavior was characterized by vibrating sample magnetometry (VSM). An XMCD signal was measured for three different samples at 300 K and 80 K. The extracted values for the orbital and spin contributions to the magnetic moment showed a quenching of the orbital moment and a large spin moment. The calculated spin moments appear somewhat reduced compared to the value expected for bulk Fe{sub 3}O{sub 4}. The spin moments measured at 80 K are larger than at 300 K for all the samples, revealing significant thermal fluctuations effects in the nanoparticle assemblies. The measured spin moment is reduced for the smallest nanoparticles, suggesting that the magnetic properties of Fe{sub 3}O{sub 4} nanoparticles could be altered when their size reaches a few nanometers.

  10. K-edge magnetic circular dichroism of O in CO/Ni/Cu(001): Dependence on substrate magnetic anisotropy and its interpretation

    NASA Astrophysics Data System (ADS)

    Yokoyama, Toshihiko; Amemiya, Kenta; Miyachi, Mariko; Yonamoto, Yoshiki; Matsumura, Daiju; Ohta, Toshiaki

    2000-12-01

    O K-edge x-ray magnetic circular dichroism (XMCD) was investigated for molecular CO adsorbed on Ni thin films grown epitaxially on Cu(001). In the case of 10 monolayer (ML) Ni that shows perpendicular magnetic anisotropy (PMA), a relatively strong negative XMCD signal was observed at the O 1s-->CO 2π* transition. Since the CO 2π* orbital is partially filled due to hybridization of Ni 3d levels, this finding implies parallel alignment of the CO 2π* orbital moment with substrate Ni magnetization. The orbital moment is ascribed to the molecular orbital origin that is derived from degeneracy of the two π* orbitals. On the contrary, in the cases of in-plane magnetization of 6 ML and thick (>100 ML) Ni films, the XMCD signal at the CO 2π* resonance was found to be weak and positive. Although the origin of the orbital moment is not yet clear in the in-plane magnetization case, this indicates that the orbital moment shows antiparallel alignment with Ni. The direction of the CO 2π* orbital moment in PMA is interpreted with a framework of chemical bonding between CO and Ni.

  11. Theoretical study of magnetic properties and x-ray magnetic circular dichroism of the ordered Fe{sub 0.5}Pd{sub 0.5} alloy

    SciTech Connect

    Galanakis, I.; Ostanin, S.; Alouani, M.; Dreysse, H.; Wills, J. M.

    2000-01-01

    A detailed theoretical study of magnetic and structural properties of Fe{sub 0.5}Pd{sub 0.5} ordered face-centered tetragonal (fct) alloy, using both the local spin density approximation (LSDA) and the generalized gradient approximation (GGA), is presented. The total energy surface as a function of the lattice parameters a and c shows a long valley where stable structures may exist. Our calculation using the GGA predicts a magnetic phase transition from perpendicular to parallel magnetization as a function of the lattice parameter, whereas LSDA favors always the [001] magnetization axis for all values of the lattice parameters. The spin and orbital magnetic moments and x-ray magnetic circular dichroism spectra are calculated for the easy [001] and the hard [100] magnetization axis and for three sets of experimental lattice parameters, and are compared to the available experimental results on these films. A supercell calculation for a 4 monolayer Fe{sub 0.5}Pd{sub 0.5} thin film produced similar results. While the spin magnetic moments are in fair agreement with experiment, the orbital magnetic moments are considerably underestimated. To improve the agreement with experiment we included an atomic orbital polarization term; however, the computed orbital moments scarcely changed. (c) 2000 The American Physical Society.

  12. A theoretical framework for dichroism and the resonance-enhanced scattering of x-rays by magnetic materials: II. Quadrupolar absorption events

    NASA Astrophysics Data System (ADS)

    Lovesey, Stephen W.

    1996-12-01

    Previous work with the resonant scattering length that is based on an atomic model and dipolar absorption events is extended to encompass quadrupolar absorption events. The scattering length is the common element in calculations of the attenuation coefficient, dichroism and the cross-sections for elastic and inelastic resonance-enhanced scattering of x-rays by magnetic materials. Both jj-coupling and Russell - Saunders coupling schemes for the atomic electrons are utilized; included are tables of relevant Racah unit-tensor operators for the valence shell 0953-8984/8/50/025/img1.

  13. Characterization of the binding of metoprolol tartrate and guaifenesin drugs to human serum albumin and human hemoglobin proteins by fluorescence and circular dichroism spectroscopy.

    PubMed

    Duman, Osman; Tunç, Sibel; Kancı Bozoğlan, Bahar

    2013-07-01

    The interactions of metoprolol tartrate (MPT) and guaifenesin (GF) drugs with human serum albumin (HSA) and human hemoglobin (HMG) proteins at pH 7.4 were studied by fluorescence and circular dichroism (CD) spectroscopy. Drugs quenched the fluorescence spectra of HSA and HMG proteins through a static quenching mechanism. For each protein-drug system, the values of Stern-Volmer quenching constant, bimolecular quenching constant, binding constant and number of binding site on the protein molecules were determined at 288.15, 298.15, 310.15 and 318.15 K. It was found that the binding constants of HSA-MPT and HSA-GF systems were smaller than those of HMG-MPT and HMG-GF systems. For both drugs, the affinity of HMG was much higher than that of HSA. An increase in temperature caused a negative effect on the binding reactions. The number of binding site on blood proteins for MPT and GF drugs was approximately one. Thermodynamic parameters showed that MPT interacted with HSA through electrostatic attraction forces. However, hydrogen bonds and van der Waals forces were the main interaction forces in the formation of HSA-GF, HMG-MPT and HMG-GF complexes. The binding processes between protein and drug molecules were exothermic and spontaneous owing to negative ∆H and ∆G values, respectively. The values of binding distance between protein and drug molecules were calculated from Förster resonance energy transfer theory. It was found from CD analysis that the bindings of MPT and GF drugs to HSA and HMG proteins altered the secondary structure of HSA and HMG proteins. PMID:23471625

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

    NASA Astrophysics Data System (ADS)

    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.

  15. Modulation of the multilamellar membrane organization and of the chiral macrodomains in the diatom Phaeodactylum tricornutum revealed by small-angle neutron scattering and circular dichroism spectroscopy.

    PubMed

    Nagy, Gergely; Szabó, Milán; Unnep, Renáta; Káli, György; Miloslavina, Yuliya; Lambrev, Petar H; Zsiros, Ottó; Porcar, Lionel; Timmins, Peter; Rosta, László; Garab, Győző

    2012-03-01

    Diatoms possess effective photoprotection mechanisms, which may involve reorganizations in the photosynthetic machinery. We have shown earlier, by using circular dichroism (CD) spectroscopy, that in Phaeodactylum tricornutum the pigment-protein complexes are arranged into chiral macrodomains, which have been proposed to be associated with the multilamellar organization of the thylakoid membranes and shown to be capable of undergoing light-induced reversible reorganizations (Szabó et al. Photosynth Res 95:237, 2008). Recently, by using small-angle neutron scattering (SANS) on the same algal cells we have determined the repeat distances and revealed reversible light-induced reorganizations in the lamellar order of thylakoids (Nagy et al. Biochem J 436:225, 2011). In this study, we show that in moderately heat-treated samples, the weakening of the lamellar order is accompanied by the diminishment of the psi-type CD signal associated with the long-range chiral order of the chromophores (psi, polymer or salt-induced). Further, we show that the light-induced reversible increase in the psi-type CD is associated with swelling in the membrane system, with magnitudes larger in high light than in low light. In contrast, shrinkage of the membrane system, induced by sorbitol, brings about a decrease in the psi-type CD signal; this shrinkage also diminishes the non-photochemical quenching capability of the cells. These data shed light on the origin of the psi-type CD signal, and confirm that both CD spectroscopy and SANS provide valuable information on the macro-organization of the thylakoid membranes and their dynamic properties; these parameters are evidently of interest with regard to the photoprotection in whole algal cells. PMID:21986933

  16. Real time observation of proteolysis with Fourier transform infrared (FT-IR) and UV-circular dichroism spectroscopy: Watching a protease eat a protein

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

    Fourier transform infrared (FT-IR)- and UV-circular dichroism (UV-CD) spectroscopy have been used to study real-time proteolytic digestion of β-lactoglobulin (β-LG) and β-casein (β-CN) by trypsin at various substrate/enzyme ratios in D 2O-buffer at 37 °C. Both techniques confirm that protein substrate looses its secondary structure upon conversion to the peptide fragments. This perturbation alters the backbone of the protein chain resulting in conformational changes and degrading of the intact protein. Precisely, the most significant spectral changes which arise from digestion take place in the amide I and amide II regions. The FT-IR spectra for the degraded β-LG show a decrease around 1634 cm -1, suggesting a decrease of β-sheet structure in the course of hydrolysis. Similarly, the intensity around the 1654 cm -1 band decreases for β-CN digested by trypsin, indicating a reduction in the α-helical part. On the other hand, the intensity around ˜1594 cm -1 and ˜1406 cm -1 increases upon enzymatic breakdown of both substrates, suggesting an increase in the antisymmetric and symmetric stretching modes of free carboxylates, respectively, as released digestion products. Observation of further H/D exchange in the course of digestion manifests the structural opening of the buried groups and accessibility to the core of the substrate. On the basis of the UV-CD spectra recorded for β-LG and β-CN digested by trypsin, the unordered structure increases concomitant with a decrease in the remaining structure, thus, revealing breakdown of the intact protein into smaller fragments. This model study in a closed reaction system may serve as a basis for the much more complex digestion processes in an open reaction system such as the stomach.

  17. Controlled cobalt doping in the spinel structure of magnetosome magnetite: new evidences from element- and site-specific X-ray magnetic circular dichroism analyses.

    PubMed

    Li, Jinhua; Menguy, Nicolas; Arrio, Marie-Anne; Sainctavit, Philippe; Juhin, Amélie; Wang, Yinzhao; Chen, Haitao; Bunau, Oana; Otero, Edwige; Ohresser, Philippe; Pan, Yongxin

    2016-08-01

    The biomineralization of magnetite nanocrystals (called magnetosomes) by magnetotactic bacteria (MTB) has attracted intense interest in biology, geology and materials science due to the precise morphology of the particles, the chain-like assembly and their unique magnetic properties. Great efforts have been recently made in producing transition metal-doped magnetosomes with modified magnetic properties for a range of applications. Despite some successful outcomes, the coordination chemistry and magnetism of such metal-doped magnetosomes still remain largely unknown. Here, we present new evidences from X-ray magnetic circular dichroism (XMCD) for element- and site-specific magnetic analyses that cobalt is incorporated in the spinel structure of the magnetosomes within Magnetospirillum magneticum AMB-1 through the replacement of Fe(2+) ions by Co(2+) ions in octahedral (Oh) sites of magnetite. Both XMCD at Fe and Co L2,3 edges, and energy-dispersive X-ray spectroscopy on transmission electron microscopy analyses reveal a heterogeneous distribution of cobalt occurring either in different particles or inside individual particles. Compared with non-doped one, cobalt-doped magnetosome sample has lower Verwey transition temperature and larger magnetic coercivity, related to the amount of doped cobalt. This study also demonstrates that the addition of trace cobalt in the growth medium can significantly improve both the cell growth and the magnetosome formation within M. magneticum AMB-1. Together with the cobalt occupancy within the spinel structure of magnetosomes, this study indicates that MTB may provide a promising biomimetic system for producing chains of metal-doped single-domain magnetite with an appropriate tuning of the magnetic properties for technological and biomedical applications. PMID:27512138

  18. 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

    NASA Astrophysics Data System (ADS)

    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.

  19. Mapping the Anopheles gambiae odorant binding protein 1 (AgamOBP1) using modeling techniques, site directed mutagenesis, circular dichroism and ligand binding assays.

    PubMed

    Rusconi, B; Maranhao, A C; Fuhrer, J P; Krotee, P; Choi, S H; Grun, F; Thireou, T; Dimitratos, S D; Woods, D F; Marinotti, O; Walter, M F; Eliopoulos, E

    2012-08-01

    The major malaria vector in Sub-Saharan Africa is the Anopheles gambiae mosquito. This species is a key target of malaria control measures. Mosquitoes find humans primarily through olfaction, yet the molecular mechanisms associated with host-seeking behavior remain largely unknown. To further understand the functionality of A. gambiae odorant binding protein 1 (AgamOBP1), we combined in silico protein structure modeling and site-directed mutagenesis to generate 16 AgamOBP1 protein analogues containing single point mutations of interest. Circular dichroism (CD) and ligand-binding assays provided data necessary to probe the effects of the point mutations on ligand binding and the overall structure of AgamOBP1. Far-UV CD spectra of mutated AgamOBP1 variants displayed both substantial decreases to ordered α-helix structure (up to22%) and increases to disordered α-helix structure(up to 15%) with only minimal changes in random coil (unordered) structure. In mutations Y54A, Y122A and W114Q, aromatic side chain removal from the binding site significantly reduced N-phenyl-1-naphthylamine binding. Several non-aromatic mutations (L15T, L19T, L58T, L58Y, M84Q, M84K, H111A, Y122A and L124T) elicited changes to protein conformation with subsequent effects on ligand binding. This study provides empirical evidence for the in silico predicted functions of specific amino acids in AgamOBP1 folding and ligand binding characteristics. PMID:22564768

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

    PubMed Central

    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. PMID:24250671

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

    SciTech Connect

    Dinh, Thanh-Chung; Renger, Thomas

    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.

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

    NASA Astrophysics Data System (ADS)

    Dinh, Thanh-Chung; Renger, Thomas

    2015-01-01

    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 Qy transition dipole moments in Chl b homodimers is larger by about 9∘ 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. Combination of chemometrically assisted voltammetry, calorimetry, and circular dichroism as a new method for the study of bioinorganic substances: application to selenocystine metal complexes.

    PubMed

    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. PMID:22015398

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

    PubMed

    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. PMID:27154055

  5. Mimicking the membrane-mediated conformation of dynorphin A-(1-13)-peptide: Circular dichroism and nuclear magnetic resonance studies in methanolic solution

    SciTech Connect

    Lancaster, C.R.D.; Hughes, D.W.; Epand, R.M. ); Mishra, P.K.; Bothner-By, A.A. ); St.Pierre, S.A. )

    1991-05-14

    The structural requirements for the binding of dynorphin to the {kappa}-opioid receptor are of profound clinical interest in the search for a powerful nonaddictive analgesic. These requirements are thought to be met by the membrane-mediated conformation of the opioid peptide dynorphin A-(1-13)-peptide, Tyr{sup 1}-Gly{sup 2}-Gly{sup 3}-Phe{sup 4}-Leu{sup 5}-Arg{sup 6}-Arg{sup 7}-Ile{sup 8}-Arg{sup 9}-Pro{sup 10}-Lys{sup 11}-Leu{sup 12}-Lys{sup 13}. Schwyzer has proposed an essentially {alpha}-helical membrane-mediated conformation of the 13 amino acid peptide. In the present study, circular dichroism (CD) studies on dynorphin A-(1-13)-peptide bound to an anionic phospholipid signified negligible helical content of the peptide. CD studies also demonstrated that the aqueous-membraneous interphase may be mimicked by methanol. The 500- and 620-MHz {sup 1}H nuclear magnetic resonance (NMR) spectra of dynorphin A-(1-13)-peptide in methanolic solution were sequence-specifically assigned with the aid of correlated spectroscopy (COSY), double-quantum filtered phase-sensitive COSY (DQF-COSY), relayed COSY (RELAY), and nuclear Overhauser enhancement spectroscopy (NOESY). 2-D CAMELSPIN/ROESY experiments indicated that at least the part of the molecule from Arg{sup 7} to Arg{sup 9} was in an extended or {beta}-strand conformation, which agreed with deuterium-exchange and temperature-dependence studies of the amide protons and analysis of the vicinal spin-spin coupling constants {sup 3}J{sub HN{alpha}}. The results clearly demonstrated the absence of extensive {alpha}-helix formation. {chi}{sub 1} rotamer analysis of the {sup 3}J{sub {alpha}{beta}} demonstrated no preferred side-chain conformations.

  6. Coordination modes of tyrosinate-ligated catalase-type heme enzymes: magnetic circular dichroism studies of Plexaura homomalla allene oxide synthase, Mycobacterium avium ssp. paratuberculosis protein-2744c, and bovine liver catalase in their ferric and ferrous states.

    PubMed

    Bandara, D M Indika; Sono, Masanori; Bruce, Grant S; Brash, Alan R; Dawson, John H

    2011-12-01

    Bovine liver catalase (BLC), catalase-related allene oxide synthase (cAOS) from Plexaura homomalla, and a recently isolated protein from the cattle pathogen Mycobacterium avium ssp. paratuberculosis (MAP-2744c (MAP)) are all tyrosinate-ligated heme enzymes whose crystal structures have been reported. cAOS and MAP have low (<20%) sequence similarity to, and significantly different catalytic functions from, BLC. cAOS transforms 8R-hydroperoxy-eicosatetraenoic acid to an allene epoxide, whereas the MAP protein is a putative organic peroxide-dependent peroxidase. To elucidate factors influencing the functions of these and related heme proteins, we have investigated the heme iron coordination properties of these tyrosinate-ligated heme enzymes in their ferric and ferrous states using magnetic circular dichroism and UV-visible absorption spectroscopy. The MAP protein shows remarkable spectral similarities to cAOS and BLC in its native Fe(III) state, but clear differences from ferric proximal heme ligand His93Tyr Mb (myoglobin) mutant, which may be attributed to the presence of an Arg(+)-N(ω)-H···¯O-Tyr (proximal heme axial ligand) hydrogen bond in the first three heme proteins. Furthermore, the spectra of Fe(III)-CN¯, Fe(III)-NO, Fe(II)-NO (except for five-coordinate MAP), Fe(II)-CO, and Fe(II)-O(2) states of cAOS and MAP, but not H93Y Mb, are also similar to the corresponding six-coordinate complexes of BLC, suggesting that a tyrosinate (Tyr-O¯) is the heme axial ligand trans to the bound ligands in these complexes. The Arg(+)-N(ω)-H to ¯O-Tyr hydrogen bond would be expected to modulate the donor properties of the proximal tyrosinate oxyanion and, combined with the subtle differences in the catalytic site structures, affect the activities of cAOS, MAP and BLC. PMID:22104301

  7. Coordination modes of tyrosinate-ligated heme enzymes: magnetic circular dichroism studies of Plexaura homomalla allene oxide synthase, Mycobacterium avium ssp. paratuberculosis protein-2744c, and bovine liver catalase in their ferric and ferrous states

    PubMed Central

    Bandara, D. M. Indika; Sono, Masanori; Bruce, Grant S.; Brash, Alan R.; Dawson, John H.

    2012-01-01

    Bovine liver catalase (BLC), catalase-related allene oxide synthase (cAOS) from Plexaura homomalla, and a recently isolated protein from the cattle pathogen Mycobacterium avium ssp. paratuberculosis (MAP-2744c (MAP)) are all tyrosinate-ligated heme enzymes whose crystal structures have been reported. cAOS and MAP have low (< 20%) sequence similarity to, and significantly different catalytic functions from, BLC. cAOS transforms 8R-hydroperoxy-eicosatetraenoic acid to an allene epoxide, whereas the MAP protein is an organic peroxide-dependent peroxidase. To shed light on the functional differences among these three proteins, we have investigated the heme iron coordination properties of these tyrosinate-ligated heme proteins in their ferric and ferrous states using magnetic circular dichroism and UV-visible absorption spectroscopy. The MAP protein shows remarkable spectral similarities to cAOS and BLC in its native Fe(III) state, but clear differences from ferric His93Tyr Mb, which may be attributed to the presence of an Arg+-Nω-H … O-Tyr (proximal heme axial ligand) hydrogen bond in the first three heme proteins. Furthermore, the spectra of Fe(III)-CN−, Fe(III)-NO, Fe(II)-NO (except for five-coordinate MAP), Fe(II)-CO, and Fe(II)-O2 states of cAOS and MAP, but not H93Y Mb, are also similar to the corresponding six-coordinate complexes of BLC, suggesting that a tyrosinate (Tyr-O−) is the heme axial ligand trans to the bound ligands in these complexes. The Arg+-Nω-H to −O-Tyr hydrogen bond would be expected to modulate the donor properties of the proximal tyrosinate oxyanion and, combined with the subtle differences in the catalytic site structures, affect the activities of cAOS, MAP and BLC. PMID:22104301

  8. Elucidating the role of the proximal cysteine hydrogen-bonding network in ferric cytochrome P450cam and corresponding mutants using magnetic circular dichroism spectroscopy.

    PubMed

    Galinato, Mary Grace I; Spolitak, Tatyana; Ballou, David P; Lehnert, Nicolai

    2011-02-15

    Although extensive research has been performed on various cytochrome P450s, especially Cyt P450cam, there is much to be learned about the mechanism of how its functional unit, a heme b ligated by an axial cysteine, is finely tuned for catalysis by its second coordination sphere. Here we study how the hydrogen-bonding network affects the proximal cysteine and the Fe-S(Cys) bond in ferric Cyt P450cam. This is accomplished using low-temperature magnetic circular dichroism (MCD) spectroscopy on wild-type (wt) Cyt P450cam and on the mutants Q360P (pure ferric high-spin at low temperature) and L358P where the "Cys pocket" has been altered (by removing amino acids involved in the hydrogen-bonding network), and Y96W (pure ferric low-spin). The MCD spectrum of Q360P reveals fourteen electronic transitions between 15200 and 31050 cm(-1). Variable-temperature variable-field (VTVH) saturation curves were used to determine the polarizations of these electronic transitions with respect to in-plane (xy) and out-of-plane (z) polarization relative to the heme. The polarizations, oscillator strengths, and TD-DFT calculations were then used to assign the observed electronic transitions. In the lower energy region, prominent bands at 15909 and 16919 cm(-1) correspond to porphyrin (P) → Fe charge transfer (CT) transitions. The band at 17881 cm(-1) has distinct sulfur S(π) → Fe CT contributions. The Q band is observed as a pseudo A-term (derivative shape) at 18604 and 19539 cm(-1). In the case of the Soret band, the negative component of the expected pseudo A-term is split into two features due to mixing with another π → π* and potentially a P → Fe CT excited state. The resulting three features are observed at 23731, 24859, and 25618 cm(-1). Most importantly, the broad, prominent band at 28570 cm(-1) is assigned to the S(σ) → Fe CT transition, whose intensity is generated through a multitude of CT transitions with strong iron character. For wt, Q360P, and L358P, this band

  9. 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

    NASA Astrophysics Data System (ADS)

    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

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

    SciTech Connect

    Singh, V. R.; Verma, V. K.; Ishigami, K.; Shibata, G.; Fujimori, A.; Koide, T.; Miura, Y.; Shirai, M.; Ishikawa, T.; Li, G.-F.; Yamamoto, M.

    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. A theoretical framework for absorption (dichroism) and the resonance-enhanced scattering of x-rays by magnetic materials: I

    NASA Astrophysics Data System (ADS)

    Lovesey, Stephen W.; Balcar, Ewald

    1996-12-01

    The scattering length common to the attenuation coefficient and cross-sections for the resonance-enhanced scattering of x-rays suffers from a dependence on a spectrum of virtual, intermediate states which contain next to no useful information about the environment of the atoms. It is the dependence of the scattering length on intermediate states that sets the x-ray techniques apart from neutron scattering and other techniques which directly probe properties of magnetic materials, and limits the usefulness of physical intuition in the interpretation of empirical x-ray data. As a step toward a legible interpretation, in a language of standard atomic variables, an investigation is reported of a modified scattering length constructed to possess a structure similar to the scattering length for magnetic neutron scattering, namely, it has the mathematical structure of a spherical tensor operator, to which all Racah's methods for electrons in an open valence shell can be applied. In the process of reaching this goal, the influence of the intermediate states on the scattering length is reduced by summing over a limited set of quantum numbers for the intermediate states. Topics covered in the investigation include the attenuation coefficient for x-rays passing through a foil of magnetic material, dichroism, and the cross-sections for resonance-enhanced elastic (Bragg) and inelastic scattering of x-rays by magnetic materials. The treatment of polarization in the primary beam admits states of partial polarization, described by a Stokes vector. Both jj-coupling and Russell - Saunders coupling schemes for the valence states are explored.

  12. Origin of the X-ray magnetic circular dichroism at the L-edges of the rare-earths in RxR(1-x)'Al2 systems.

    PubMed

    Chaboy, Jesús; Laguna-Marco, María Angeles; Piquer, Cristina; Boada, Roberto; Plugaru, Neculai; Maruyama, Hiroshi; Kawamura, Naomi

    2009-05-01

    An X-ray magnetic circular dichroism (XMCD) study performed at the rare-earth L(2,3)-edges in the R(x)R(1-x)'Al(2) compounds is presented. It is shown that both R and R' atoms contribute to the XMCD recorded at the L-edges of the selected rare-earth, either R or R'. The amplitude of the XMCD signal is not directly correlated to the magnetization or to the value of the individual (R, R') magnetic moments, but it is related to the molecular field acting on the rare-earth tuned in the photoabsorption process. This result closes a longstanding study of the origin of the XMCD at the L-edge of the rare-earths in multi-component systems, allowing a full understanding of the exact nature of these signals. PMID:19395807

  13. O K-edge x-ray magnetic circular dichroism of atomic O adsorbed on an ultrathin Co/Cu(100) film: Comparison with molecular CO on Co/Cu(100)

    NASA Astrophysics Data System (ADS)

    Amemiya, Kenta; Yokoyama, Toshihiko; Yonamoto, Yoshiki; Matsumura, Daiju; Ohta, Toshiaki

    2001-10-01

    We observed O K-edge x-ray magnetic circular dichroism (XMCD) of atomic O adsorbed on a fcc Co thin film grown epitaxially on Cu(100). The XMCD of c(2×2)O showed a negative sign at the O1s-->2p transition. The negative sign indicates parallel alignment of the O orbital moment with the substrate magnetization. This finding is in contrast to the CO/Co/Cu(100) case where a positive XMCD was observed at the O1s-->CO2π* transition. A possible explanation for this discrepancy is proposed referring to recent theoretical prediction [Pick et al., Phys. Rev. B 59, 4195 (1999)].

  14. Impact of energy-related pollutants on chromosome structure. Progress report, January 1-December 31, 1980. IQUID COLUMN CHROMATOGRAPHY; ABSORPTION SPECTRA; COMPUTER CODES; DICHROISM; EQUIPMENT INTERFACES; MICROPROCESSORS; SPECTROPHOTOMETERS; ; CARBON 13; COMPLEXES; NUCLEAR MAGNETIC RESONANCE

    SciTech Connect

    Not Available

    1980-01-01

    Methods for rapidly analyzing methylated and ethylated nucleosides and bases by high pressure liquid chromatography were investigated. Deoxyribonucleotides were alkylated with alkyl iodides and dialkyl sulfates. Several unreported products of the reactions of methyl and ethyl iodide in dimethylsulfoxide were found and are being characterized. The Cary 219 UV-Vis spectrophotometer was interfaced to a microcomputer and several utility programs were written. Preliminary absorption and circular dichroism studies of the binding of ethidium to DNA and nucleosome cores showed binding to cores to be quite different from binding to DNA. Free radical and additional reactions of bisulfite with DNA in chromatin were examined. Free radical attack was minimal. Some conversion of cytosine to uracil was noted, but protein crosslinking to DNA was not detected. The first valid natural abundance /sup 13/C nmr spectra of double-stranded DNA and double-stranded DNA complexed with ethidium were obtained. These spectra suggested that DNA undergoes considerable internal motion. The data show that 13-C nmr studies of the conformational and motional properties of native DNA and of complexes of native DNA with small molecules are practical and promising. Studies of subnucleosomes derived from nucleosomes were completed. Based on these studies, a model of the linear arrangement of histone C-terminal and N-terminal chain regions along nucleosome DNA was proposed. The use of staphylococcal protease to probe histone conformations in nucleosomes was explored. Preliminary data indicate that H3 is much more susceptible to protease than other core histones, and is cleaved in its hydrophobic domain. A procedure for fractionating chromatin was alos developed. (ERB)

  15. Itinerant ferromagnetism in the As 4p conduction band of Ba0.6K0.4Mn2As2 identified by x-ray magnetic circular dichroism

    SciTech Connect

    Ueland, B. G.; Pandey, Abhishek; Lee, Y.; Sapkota, A.; Choi, Y.; Haskel, D.; Rosenberg, R. A.; Lang, J. C.; Harmon, B. N.; Johnston, D. C.; Kreyssig, A.; Goldman, A. I.

    2015-05-27

    In this study, x-ray magnetic circular dichroism (XMCD) measurements on single-crystal and powder samples of Ba0.6K0.4Mn2As2 show that the ferromagnetism below TC ≈ 100 K arises in the As 4p conduction band. No XMCD signal is observed at the Mn x-ray absorption edges. Below TC, however, a clear XMCD signal is found at the As K edge which increases with decreasing temperature. The XMCD signal is absent in data taken with the beam directed parallel to the crystallographic c axis indicating that the orbital magnetic moment lies in the basal plane of the tetragonal lattice. These results show that the previously reported itinerant ferromagnetism is associated with the As 4p conduction band and that distinct local-moment antiferromagnetism and itinerant ferromagnetism with perpendicular easy axes coexist in this compound at low temperature.

  16. Circular dichroism of polynucleotides: Interactions of NiCl2 with poly(dA-dT).poly(dA-dT) and poly(dG-dC).poly(dG-dC) in a water-in-oil microemulsion.

    PubMed

    Airoldi, Marta; Gennaro, Giuseppe; Giomini, Marcello; Giuliani, Anna Maria; Giustini, Mauro

    2008-09-01

    The thermal behavior of the synthetic, high molecular weight, double stranded polynucleotides poly(dA-dT).poly(dA-dT) [polyAT] and poly(dG-dC).poly(dG-dC) [polyGC] solubilized in the aqueous core of the quaternary water-in-oil cationic microemulsion CTAB|n-pentanol|n-hexane|water in the presence of increasing amounts of NiCl(2) at several constant ionic strength values (NaCl) has been studied by means of circular dichroism and electronic absorption spectroscopies. In the microemulsive medium, both polynucleotides show temperature-induced modifications that markedly vary with both Ni(II) concentration and ionic strength. An increase of temperature causes denaturation of the polyAT duplex at low nickel concentrations, while more complex CD spectral modifications are observed at higher nickel concentrations and ionic strengths. By contrast, thermal denaturation is never observed for polyGC. At low Ni(II) concentrations, the increase of temperature induces conformational transitions from B-DNA to Z-DNA form, or, more precisely, to left-handed helical structures. In some cases, at higher nickel concentrations, the CD spectra suggest the presence of Z'-type forms of the polynucleotide. PMID:18246552

  17. Plastocyanin conformation: an analysis of its near ultraviolet absorption and circular dichroic spectra

    SciTech Connect

    Draheim, J.E.; Anderson, G.P.; Duane, J.W.; Gross, E.L.

    1986-04-01

    The near-ultraviolet absorption and circular dichroic spectra of plastocyanin are dependent upon the redox state, solution pH, and ammonium sulfate concentration. This dependency was observed in plastocyanin isolated from spinach, poplar, and lettuce. Removal of the copper atom also perturbed the near-ultraviolet spectra. Upon reduction there are increases in both extinction and ellipticity at 252 nm. Further increases at 252 nm were observed upon formation of apo plastocyanin eliminating charge transfer transitions as the cause. The spectral changes in the near-ultraviolet imply a flexible tertiary conformation for plastocyanin. There are at least two charge transfer transitions at approx.295-340 nm. One of these transitions is sensitive to low pH's and is attributed to the His 87 copper ligand. The redox state dependent changes observed in the near-ultraviolet spectra of plastocyanin are attenuated either by decreasing the pH to 5 or by increasing the ammonium sulfate concentration to 2.7 M. This attenuation cannot be easily explained by simple charge screening. Hydrophobic interactions probably play an important role in this phenomenon. The pH and redox state dependent conformational changes may play an important role in regulating electron transport.

  18. Absorption and scattering by bispheres, quadspheres, and circular rings of spheres and their equivalent coated spheres.

    PubMed

    Heng, Ri-Liang; Sy, Ki Cheong; Pilon, Laurent

    2015-01-01

    This study demonstrates that the absorption and scattering cross sections and asymmetry factor of randomly oriented and optically soft bispheres, quadspheres, and circular rings of spheres, with either monodisperse or polydisperse monomers, can be approximated by an equivalent coated sphere with identical volume and average projected area. This approximation could also apply to the angle-dependent scattering matrix elements for monomer size parameter less than 0.1. However, it quickly deteriorated with increasing monomer number and/or size parameter. It was shown to be superior to previously proposed approximations considering a volume equivalent homogeneous sphere and a coated sphere with identical volume and surface area. These results provide a rapid and accurate way of predicting the radiation characteristics of bispheres, quadspheres, and rings of spheres representative of various unicellular and multicellular cyanobacteria considered for producing food supplements, biofuels, and fertilizers. They could also be used in inverse methods for retrieving the monomers' optical properties, morphology, and/or concentration. PMID:26366489

  19. Elucidation of Photoisomerization-Related Structural Changes in an Acrylamide-Bridged Binaphthalene-Diazene Macrocyclic Chiroptical Switch by Experimental Electronic Circular Dichroism Spectra Simulation: Role of Dispersion Corrections.

    PubMed

    Kerner, Lukáš; Kicková, Anna; Filo, Juraj; Kedžuch, Stanislav; Putala, Martin

    2015-08-13

    Nondestructive readout of light-driven molecular memory devices can be achieved by monitoring the alterations in the chiroptical properties of 1,1'-binaphthalene as a conformationally responsive chiral group. In our system, this signaling unit is connected via acrylamide linkers to the receiving diphenyldiazene fragment, which undergoes significant geometrical changes upon (E)/(Z)-photoisomerization. The compound functions as a stable photochromic switch by alternating irradiation at 365/465 nm, with fully reversible modulation of circular dichroism (CD) signal intensity (up to 1:3) and extended thermal stability of the (Z)-isomer. According to molecular modeling, the acrylamide spacers are due to the imposed cyclic strain upon photoisomerization forced to switch amide conformations, which is markedly reflected in the CD spectra, whereas binaphthalene conformational changes are mostly neglected both by theory and by experiment. In CD simulation by TD-DFT, CAM-B3LYP outperforms B3LYP and M06 by means of similarity analysis, whereas the last mentioned functional also delivers satisfactory performance qualitatively. The inclusion of dispersion corrections during geometry optimization was crucial to retain consistency with the measured spectra. By carefully considering all relevant conformations of this 20-membered macrocycle, reasonable agreement with the experiment is reached not only for the CD simulation of the individual conformers but also of the photoisomerization process of their admixture. PMID:26172026

  20. Spin and orbital magnetic moments of Fe and Co in Co/Fe and Fe/Co multilayers on Si from L2,3 edge X-ray Magnetic Circular Dichroism Spectroscopy

    NASA Astrophysics Data System (ADS)

    Vemuru, Krishnamurthy; Rosenberg, Richard; Mankey, Gary

    Nanostructured FeCo thin films are interesting for magnetic recording applications due to their high saturation magnetization, high Curie temperature and low magnetocrystalline anisotropy. It is desirable to know how the magnetism is modified by the nanostructrure. We report Fe L 2 , 3 edge and Co L2 , 3 edge x-ray magnetic circular dichroism (XMCD) investigations of element specific spin and orbital magnetism of Fe and Co in two multilayer samples: (S1) Si/SiO2/[Co 0.8 nm/Fe 1.6 nm]x32/W (2nm) and (S2) Si/SiO2/[Co 1.6 nm/Fe 0.8 nm]x32/W (2nm) thin films at room temperature. Sum rule analysis of XMCD at Fe L2 , 3 edge in sample S1 shows that the orbital moment of Fe is strongly enhanced and the spin moment is strongly reduced as compared to the values found in bulk Fe. Details of sum rule analysis will be presented to compare and contrast spin magnetic moments and orbital magnetic moments of Fe and Co in the two multilayer samples. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

  1. Systematic study on the TD-DFT calculated electronic circular dichroism spectra of chiral aromatic nitro compounds: A comparison of B3LYP and CAM-B3LYP.

    PubMed

    Komjáti, Balázs; Urai, Ákos; Hosztafi, Sándor; Kökösi, József; Kováts, Benjámin; Nagy, József; Horváth, Péter

    2016-02-15

    B3LYP is one of the most widely used functional for the prediction of electronic circular dichroism spectra, however if the studied molecule contains aromatic nitro group computations may fail to produce reliable results. A test set of molecules of known stereochemistry were synthesized to study this phenomenon in detail. Spectra were computed by B3LYP and CAM-B3LYP functionals with 6-311++G(2d,2p) basis set. It was found that the range separated CAM-B3LYP gives better predictions than B3LYP for all test molecules. Fragment population analysis revealed that the nitro groups form highly localized molecule orbitals but the exact composition depends on the functional. CAM-B3LYP allows sufficient spatial overlap between the nitro group and distant parts of the molecule, which is necessary for the accurate description of excited states especially for charge transfer states. This phenomenon and the synthesized test molecules can be used to benchmark theoretical methods as well as to help the development of new functionals intended for spectroscopical studies. PMID:26583523

  2. Measurement of the transmission magnetic circular dichroism of Ga{sub 1−x}Mn{sub x}As epilayers using a built-in p-i-n photodiode

    SciTech Connect

    He, Z. X.; Zheng, H. Z. Wang, H. L.; Zhao, J. H.

    2014-02-28

    By constructing a GaMnAs epilayer/semi-insulating In{sub 0.2}Ga{sub 0.8}As/(001) n{sup +}-GaAs substrate layer structure as a built-in p-i-n photodiode, we developed a scheme for on-chip measurements of transmission magnetic circular dichroism (T-MCD). Both the hysteresis loops in the magnetic field sweeps and the wavelength scans at saturated magnetic fields measured using the new T-MCD scheme, illustrated the same features as those previously measured on the freestanding GaMnAs thin films by conventional T-MCD. Because a large group of epitaxially grown magnetic film/semiconductor heterostructures, such as Fe, NiFe, CoFeAl, and MnGa films on semiconductor substrates, are becoming important new building blocks for semiconductor-based spin field-effect transistor, perpendicular magnetic tunnel junction (p-MTJ) and lateral MTJ devices, the new T-MCD scheme can be applied to tests of their magnetic properties by forming either p-i-n or Schottky photodiodes.

  3. Systematic study on the TD-DFT calculated electronic circular dichroism spectra of chiral aromatic nitro compounds: A comparison of B3LYP and CAM-B3LYP

    NASA Astrophysics Data System (ADS)

    Komjáti, Balázs; Urai, Ákos; Hosztafi, Sándor; Kökösi, József; Kováts, Benjámin; Nagy, József; Horváth, Péter

    2016-02-01

    B3LYP is one of the most widely used functional for the prediction of electronic circular dichroism spectra, however if the studied molecule contains aromatic nitro group computations may fail to produce reliable results. A test set of molecules of known stereochemistry were synthesized to study this phenomenon in detail. Spectra were computed by B3LYP and CAM-B3LYP functionals with 6-311 ++G(2d,2p) basis set. It was found that the range separated CAM-B3LYP gives better predictions than B3LYP for all test molecules. Fragment population analysis revealed that the nitro groups form highly localized molecule orbitals but the exact composition depends on the functional. CAM-B3LYP allows sufficient spatial overlap between the nitro group and distant parts of the molecule, which is necessary for the accurate description of excited states especially for charge transfer states. This phenomenon and the synthesized test molecules can be used to benchmark theoretical methods as well as to help the development of new functionals intended for spectroscopical studies.

  4. Statistical effects in the absorption and optical activity of particulate suspensions.

    PubMed Central

    Bustamante, C; Maestre, M F

    1988-01-01

    The phenomenon of Duysens flattening of the absorption spectra resulting from the inhomogeneous distribution of the chromophores in the solution is analyzed. These inhomogeneities are treated as localized statistical fluctuations in the concentration of the absorbing species, by using the Gaussian distribution. A law of absorbance is obtained, and the effect of light scattering on the flattening is also characterized. The flattening in the circular dichroism spectra of particulate suspensions is then analyzed. It is shown that the degree of flattening of the circular dichroism of a suspension is, in general, different from the corresponding flattening of its absorption spectrum. A quantitative relationship between the two effects is established. PMID:3186738

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

    SciTech Connect

    Ohresser, P. Otero, E.; Choueikani, F.; Chen, K.; Stanescu, S.; Deschamps, F.; Moreno, T.; Polack, F.; Lagarde, B.; Daguerre, J.-P.; Marteau, F.; Scheurer, F.; Joly, L.; Muller, B.; Kappler, J.-P.; Bunau, O.; Sainctavit, Ph.

    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.

  6. A combined magnetic circular dichroism and density functional theory approach for the elucidation of electronic structure and bonding in three- and four-coordinate iron(II)-N-heterocyclic carbene complexes

    PubMed Central

    Fillman, Kathlyn L.; Przyojski, Jacob A.; Al-Afyouni, Malik H.; Tonzetich, Zachary J.

    2014-01-01

    The combination of iron salts and N-heterocyclic carbene (NHC) ligands is a highly effective combination in catalysis, with observed catalytic activities being highly dependent on the nature of the NHC ligand. Detailed spectroscopic and electronic structure studies have been performed on both three- and four-coordinate iron(II)-NHC complexes using a combined magnetic circular dichroism (MCD) and density functional theory (DFT) approach that provide detailed insight into the relative ligation properties of NHCs compared to traditional phosphine and amine ligands as well as the effects of NHC backbone structural variations on iron(II)-NHC bonding. Near-infrared MCD studies indicate that 10Dq(Td) for (NHC)2FeCl2 complexes is intermediate between those for comparable amine and phosphine complexes, demonstrating that such iron(II)-NHC and iron(II)-phosphine complexes are not simply analogues of one another. Theoretical studies including charge decomposition analysis indicate that the NHC ligands are slightly stronger donor ligands than phosphines but also result in significant weakening of the Fe-Cl bonds compared to phosphine and amine ligands. The net result is significant differences in the d orbital energies in four-coordinate (NHC)2FeCl2 complexes relative to the comparable phosphine complexes, where such electronic structure differences are likely a significant contributing factor to the differing catalytic performances observed with these ligands. Furthermore, Mössbauer, MCD and DFT studies of the effects of NHC backbone structure variations (i.e. saturated, unsaturated, chlorinated) on iron-NHC bonding and electronic structure in both three- and four-coordinate iron(II)-NHC complexes indicate only small differences as a function of backbone structure, that are likely amplified at lower oxidation states of iron due to the resulting decrease in the energy separation between the occupied iron d orbitals and the unoccupied NHC π* orbitals. PMID:25621143

  7. 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

    PubMed Central

    Reed, Christopher J.; Bushnell, Sarah; Evilia, Caryn

    2014-01-01

    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. PMID:24594651

  8. Heme Orientation of Cavity Mutant Hemoglobins (His F8 → Gly) in Either α or β Subunits: Circular Dichroism, (1) H NMR, and Resonance Raman Studies.

    PubMed

    Nagai, Masako; Nagai, Yukifumi; Aki, Yayoi; Sakurai, Hiroshi; Mizusawa, Naoki; Ogura, Takashi; Kitagawa, Teizo; Yamamoto, Yasuhiko; Nagatomo, Shigenori

    2016-08-01

    Native human adult hemoglobin (Hb A) has mostly normal orientation of heme, whereas recombinant Hb A (rHb A) expressed in E. coli contains both normal and reversed orientations of heme. Hb A with the normal heme exhibits positive circular dichroism (CD) bands at both the Soret and 260-nm regions, while rHb A with the reversed heme shows a negative Soret and decreased 260-nm CD bands. In order to examine involvement of the proximal histidine (His F8) of either α or β subunits in determining the heme orientation, we prepared two cavity mutant Hbs, rHb(αH87G) and rHb(βH92G), with substitution of glycine for His F8 in the presence of imidazole. CD spectra of both cavity mutant Hbs did not show a negative Soret band, but instead exhibited positive bands with strong intensity at the both Soret and 260-nm regions, suggesting that the reversed heme scarcely exists in the cavity mutant Hbs. We confirmed by (1) H NMR and resonance Raman (RR) spectroscopies that the cavity mutant Hbs have mainly the normal heme orientation in both the mutated and native subunits. These results indicate that the heme Fe-His F8 linkage in both α and β subunits influences the heme orientation, and that the heme orientation of one type of subunit is related to the heme orientation of the complementary subunits to be the same. The present study showed that CD and RR spectroscopies also provided powerful tools for the examination of the heme rotational disorder of Hb A, in addition to the usual (1) H NMR technique. Chirality 28:585-592, 2016. © 2016 Wiley Periodicals, Inc. PMID:27427792

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

    PubMed Central

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

    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. Because of 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. PMID:19416893

  10. Molten globule of bovine alpha-lactalbumin at neutral pH induced by heat, trifluoroethanol, and oleic acid: a comparative analysis by circular dichroism spectroscopy and limited proteolysis.

    PubMed

    Polverino de Laureto, Patrizia; Frare, Erica; Gottardo, Rossella; Fontana, Angelo

    2002-11-15

    The calcium-depleted form of alpha-lactalbumin (alpha-LA) at neutral pH can be induced to adopt a partly folded state or molten globule upon moderate heating, by dissolving the protein in aqueous TFE or by adding oleic acid. This last folding variant of the protein, named HAMLET, can induce apoptosis in tumor cells. The aim of the present work was to unravel from circular dichroism (CD) measurements and proteolysis experiments structural features of the molten globule of apo-alpha-LA at neutral pH. CD spectra revealed that the molten globule of apo-alpha-LA can be obtained upon mild heating at 45 degrees C, as well as at room temperature in the presence of 15% TFE or by adding to the protein solution 7.5 equivalents of oleic acid. Under these various conditions the far- and near-UV CD spectra of apo-alpha-LA are essentially identical to those of the most studied molten globule of alpha-LA at pH 2.0 (A-state). Proteolysis of the 123-residue chain of apo-alpha-LA by proteinase K at 4 degrees C occurs slowly as an all-or-none process leading to small peptides only. At 37 degrees C, proteinase K preferentially cleaves apo-alpha-LA at peptide bonds Ser34-Gly35, Gln39-Ala40, Gln43-Asn44, Phe53-Gln54, and Asn56-Asn57. All these peptide bonds are located at level of the beta-subdomain of the protein (chain region 34-57). Similar sites of preferential cleavage have been observed with the TFE- and oleic acid-induced molten globule of apo-alpha-LA. A protein species given by the N-terminal fragment 1-34 linked via the four disulfide bridges to the C-terminal fragment 54-123 or 57-123 can be isolated from the proteolytic mixture. The results of this study indicate that the same molten globule state of apo-alpha-LA can be obtained at neutral pH under mildly denaturing conditions, as indicated by using a classical spectroscopic technique such as CD and a simple biochemical approach as limited proteolysis. We conclude that the molten globule of alpha-LA maintains a native

  11. Analysis of the major chiral compounds of Artemisia herba-alba essential oils (EOs) using reconstructed vibrational circular dichroism (VCD) spectra: En route to a VCD chiral signature of EOs.

    PubMed

    Said, Mohammed El-Amin; Vanloot, Pierre; Bombarda, Isabelle; Naubron, Jean-Valère; Dahmane, El Montassir; Aamouche, Ahmed; Jean, Marion; Vanthuyne, Nicolas; Dupuy, Nathalie; Roussel, Christian

    2016-01-15

    An unprecedented methodology was developed to simultaneously assign the relative percentages of the major chiral compounds and their prevailing enantiomeric form in crude essential oils (EOs). In a first step the infrared (IR) and vibrational circular dichroism (VCD) spectra of the crude essential oils were recorded and in a second step they were modelized as a linear weighted combination of the IR and VCD spectra of the individual spectra of pure enantiomer of the major chiral compounds present in the EOs. The VCD spectra of enantiomer of known enantiomeric excess shall be recorded if they are not yet available in a library of VCD spectra. For IR, the spectra of pure enantiomer or racemic mixture can be used. The full spectra modelizations were performed using a well known and powerful mathematical model (least square estimation: LSE) which resulted in a weighting of each contributing compound. For VCD modelization, the absolute value of each weighting represented the percentage of the associate compound while the attached sign addressed the correctness of the enantiomeric form used to build the model. As an example, a model built with the non-prevailing enantiomer will show a negative sign of the weighting value. For IR spectra modelization, the absolute value of each weighting represented the percentage of the compounds without of course accounting for the chirality of the prevailing enantiomers. Comparison of the weighting values issuing from IR and VCD spectra modelizations is a valuable source of information: if they are identical, the EOs are composed of nearly pure enantiomers, if they are different the chiral compounds of the EOs are not in an optically pure form. The method was applied on four samples of essential oil of Artemisia herba-alba in which the three major compounds namely (-)-α-thujone, (+)-β-thujone and (-)-camphor were found in different proportions as determined by GC-MS and chiral HPLC using polarimetric detector. In order to validate the

  12. Years of Magnetic X-Ray Dichroism

    NASA Astrophysics Data System (ADS)

    van der Laan, Gerrit

    A historical overview of magnetic x-ray dichroism is presented. I describe the first theoretical and experimental results that have led to the development of this powerful technique for element-specific magnetometry. The theoretical progress of the sum rules is also described, starting with the spinorbit sum rule for the isotropic spectrum which led on to the spin and orbital moment sum rules for x-ray magnetic circular dichroism. The latter has been particularly useful to understand the magnetic anisotropy in thin films and multilayers. Further developments of circular dichroism in (resonant) photoemission and Auger, as well as x-ray detected optical activity, also are summarized. Currently, magnetic x-ray dichroism finds a wide application in x-ray spectroscopy and imaging for the study of magnetic materials and it is considered to be one of the most important discoveries in the field of magnetism in the last few decennia. It is hard to imagine modern research into magnetism without the aid of polarized x-rays.

  13. Circular extinction of plasmonic silver nanocaps and gas sensing.

    PubMed

    Li, Jun; Kotov, Nicholas A

    2016-01-01

    Chiral plasmonic nanostructures exhibit strong rotatory optical activity and are expected to enrich the field of metaoptical materials. Potential applications of chiroplasmonic nanostructures include circular polarizers, optical polarization detectors, asymmetric catalysts, and sensors. However, chiral plasmonic materials require subwavelength structural control and involve laborious chemical or lithographic procedures for their manufacturing. Moreover, strong rotatory activity of subwavelength structures whose chirality was imparted by microfabrication, has been obtained for the red and infrared parts of the spectrum but faces new challenges for the blue and violet spectral ranges even with plasmonic materials with plasmonic bands in the 200-400 nm window. In this study, we address this problem by preparing chiral subwavelength nanostructures by glancing angle sputtering of metallic silver on ZnO nanopillar arrays. Silver deposition in two different planes is a convenient method for preparation of silver chiroplasmonic nanocaps (Ag CPNCs) with controlled asymmetry. Circular dichroism spectroscopy was used to examine the circular extinction for the left-handed nanocaps (L-CPNCs) with understanding that not only circular dichroism but also many other optical effects contribute to the amplitude of these bands. The pillared silver films exhibit circular extinction in the violet area of the electromagnetic spectrum. Partial oxidation of Ag to AgxO causes the absorption and corresponding circular extinction band obtained using a conventional CD spectrometer at 400-525 nm to increase and shift. This optical material may be used to detect oxygen and extends the spectrum of application of chiroplasmonic materials to gas sensing. PMID:26952921

  14. X-Ray Dichroism in Photoelectron Spectroscopy for Direct Element Specific Surface Magnetometry of Nanomagnetic Structures

    NASA Astrophysics Data System (ADS)

    Tobin, James G.

    1997-03-01

    Element specific surface magnetometry remains a central goal of synchrotron radiation based studies of nanomagnetic structures. One appealing possibility is the combination of xray absorption dichroism measurements and the theoretical framework provided by the "sum rules."[1] Unfortunately, sum rule analyses are hampered by several limitations [2], including delocalization of the final state, multi-electronic phenomena and the presence of surface dipoles. An alternative experiment, Magnetic Xray Dichroism in Photoelectron Spectroscopy, holds out promise based upon its elemental specificity, surface sensitivity and high resolution. Computational simulations by Tamura et al [3] demonstrated the relationship between exchange and spin orbit splittings and experimental data of linear and circular dichroisms. Now we [4] 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 [5], 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 [6], 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. [7,8] This work was performed under the auspices of the U.S. Department of Energy by LLNL under contract No. W-7405-ENG-48. 1. B.T. Thole et al, Phys. Rev. Lett. 68,1943 (1992); P. Carra et al. Phys. Rev. Lett. 70, 694 (1993). 2. J.G. Tobin et al Phys. Rev. B 52, 6530 (1995). 3. E. Tamura et al, Phys. Rev. Lett 73, 1533 (1994) 4. J.G. Tobin, K.W. Goodman, F.O. Schumann, R.F. Willis, J

  15. Novel approach for non-invasive glucose sensing using vibrational contrast CD absorption measurements (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Yakovlev, Vladislav V.; Tovar, Carlos; Hokr, Brett; Petrov, Georgi I.

    2016-03-01

    Noninvasive glucose sensing is a Holy Grail of diabetes mellitus management. Unfortunately, despite a number of innovative concepts and a long history of continuous instrumental improvements, the problem remains largely unsolved. Here we propose and experimentally demonstrate the first successful implementation of a novel strategy based on vibrational overtone circular dichroism absorption measurements. Such an approach uses a short-wavelength infrared excitation (1000-2000 nm), which takes the advantage of lower light scattering and intrinsic chemical contrast provided by the chemical structure of D-glucose molecule. We model the propagation of circular polarized light in scattering medium using Monte Carlo simulations to show the feasibility of such approach in turbid medium and demonstrate the proof of principle using optical detection. We also investigate the possibility of using ultrasound detection through circular dichroism absorption measurements to achieve simple and sensitive glucose monitoring.

  16. Temperature-insensitive laser frequency locking near absorption lines

    NASA Astrophysics Data System (ADS)

    Kostinski, Natalie; Olsen, Ben A.; Marsland, Robert; McGuyer, Bart H.; Happer, William

    2011-03-01

    Combined magnetically induced circular dichroism and Faraday rotation of an atomic vapor are used to develop a variant of the dichroic atomic vapor laser lock that eliminates lock sensitivity to temperature fluctuations of the cell. Operating conditions that eliminate first-order sensitivity to temperature fluctuations can be determined by low-frequency temperature modulation. This temperature-insensitive gyrotropic laser lock can be accurately understood with a simple model, that is in excellent agreement with observations in potassium vapor at laser frequencies in a 2 GHz range about the 770.1 nm absorption line. The methods can be readily adapted for other absorption lines.

  17. Temperature-insensitive laser frequency locking near absorption lines

    SciTech Connect

    Kostinski, Natalie; Olsen, Ben A.; Marsland, Robert III; McGuyer, Bart H.; Happer, William

    2011-03-15

    Combined magnetically induced circular dichroism and Faraday rotation of an atomic vapor are used to develop a variant of the dichroic atomic vapor laser lock that eliminates lock sensitivity to temperature fluctuations of the cell. Operating conditions that eliminate first-order sensitivity to temperature fluctuations can be determined by low-frequency temperature modulation. This temperature-insensitive gyrotropic laser lock can be accurately understood with a simple model, that is in excellent agreement with observations in potassium vapor at laser frequencies in a 2 GHz range about the 770.1 nm absorption line. The methods can be readily adapted for other absorption lines.

  18. Magnetic x-ray dichroism in ultrathin epitaxial films

    SciTech Connect

    Tobin, J.G.; Goodman, K.W.; Cummins, T.R.

    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.

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

    PubMed

    Cukras, Janusz; Kauczor, Joanna; Norman, Patrick; Rizzo, Antonio; Rikken, Geert L J A; Coriani, Sonia

    2016-05-21

    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 circular dichroism. The additional information content yielded by the magneto-chiral phenomena, as well as their potential experimental detectability for the selected species, is discussed. PMID:27118603

  20. Applications of soft x-ray magnetic dichroism

    NASA Astrophysics Data System (ADS)

    van der Laan, G.

    2013-04-01

    Applications of x-ray magnetic circular and linear dichroism (XMCD and XMLD) are reviewed in the soft x-ray region, covering the photon energy range 0.4-2 keV, which includes important absorption edges such as the 3d transition metal L2,3 and rare earth M4,5. These techniques enable a broad range of novel and exciting studies such as on the electronic properties and magnetic ordering of novel nanostructured systems. XMCD has a sensitivity better than 0.01 monolayer (at the surface) and due to simple detection methods, such as electron yield and fluorescence yield, it has become a workhorse technique in physics and materials science. It is the only element-specific technique able to distinguish between the spin and orbital parts of the magnetic moments. The applications are vast, e.g., in x-ray holographic imaging, XMCD gives a spatial resolution of tens of nm. While many studies in the past were centered on physics, more recently new applications have emerged in areas such as chemistry, biology and earth and environmental sciences. For instance, XMCD allows the determination of the cation occupations in spinels and other ternary oxides. In scanning transmission x-ray microscopy (STXM), XMCD enables us to map biogenic magnetite redox changes resulting in a surprising degree of variation on the nanoscale. Another recent development is ferromagnetic resonance (FMR) detected by time-resolved XMCD which opens the door to element-, site- and layer-specific dynamical measurements. By exploiting the time structure of the pulsed synchrotron radiation from the storage ring the relative phase of precession in the individual magnetic layers of a multilayer stack can be determined.

  1. Searching for minicharged particles via birefringence, dichroism and Raman spectroscopy of the vacuum polarized by a high-intensity laser wave

    SciTech Connect

    Villalba-Chávez, S. Müller, C.

    2013-12-15

    Absorption and dispersion of probe photons in the field of a high-intensity circularly polarized laser wave are investigated. The optical theorem is applied for determining the absorption coefficients in terms of the imaginary part of the vacuum polarization tensor. Compact expressions for the vacuum refraction indices and the photon absorption coefficients are obtained in various asymptotic regimes of interest. The outcomes of this analysis reveal that, far from the region relatively close to the threshold of the two-photon reaction, the birefringence and dichroism of the vacuum are small and, in some cases, strongly suppressed. On the contrary, in a vicinity of the region in which the photo-production of a pair occurs, these optical properties are manifest with lasers of moderate intensities. We take advantage of such a property in the search of minicharged particles by considering high-precision polarimetric experiments. In addition, Raman-like electromagnetic waves resulting from the inelastic part of the vacuum polarization tensor are suggested as an alternative form for finding exclusion limits on these hypothetical charge carriers. The envisaged parameters of upcoming high-intensity laser facilities are used for establishing upper bounds on the minicharged particles. -- Highlights: •Via dichroism and birefringence of the vacuum by a strong laser wave, minicharged particles can be probed. •The discovery potential is the highest in a vicinity of the first pair production threshold. •As alternative observable, Raman scattered waves are put forward.

  2. Rotation and dichroism associated with microwave propagation in chiral composite samples

    SciTech Connect

    Umari, M.H.; Varadan, V.V.; Varadan, V.K. )

    1991-10-01

    Experimental results are presented on the angle of rotation and the axial ratio (dichroism) associated with the propagation of microwave waves in chiral composite samples (a phenomenon akin to optical rotation and optical dichroism). In the experiments the chiral composite samples tested were made in the form of planar slabs and consisted of low loss dielectric matrix materials in which miniature copper springs of left only, right only, or an equal mixture of left and right handedness were randomly distributed and oriented. The normally incident wave was linearly polarized. In the chiral sample the linearly polarized wave decomposes into left and right circularly polarized waves which propagate with different speeds and different attenuations leading to an elliptically polarized transmitted wave whose orientation (electromagnetic rotation) and axial ratio (dichroism) are proportional to the concentration of springs. Rotation and dichroism are shown to be zero in the equichiral samples. 10 refs.

  3. Dichroism and birefringence of natural violet diamond crystals

    SciTech Connect

    Konstantinova, A. F. Titkov, S. V.; Imangazieva, K. B.; Evdishchenko, E. A.; Sergeev, A. M.; Zudin, N. G.; Orekhova, V. P.

    2006-05-15

    Investigation of the optical properties of natural violet diamonds from the Yakutian kimberlites is performed. A red shift of the absorption edge is revealed in the absorption spectra of these crystals. This shift is indicative of the presence of a high concentration of nitrogen in the diamonds studied. Along with the strong band at 0.550 {mu}m, weaker bands at 0.390, 0.456 and 0.496 {mu}m are revealed. It is shown that violet diamond crystals have birefringence and dichroism of about 10{sup -5} and 10{sup -6}, respectively. When a light beam propagates perpendicularly to colored lamellas, the dichroism is much larger and the birefringence is smaller than in the case where the beam direction is parallel to lamellas.

  4. Microwave Magnetochiral Dichroism in the Chiral-Lattice Magnet Cu2OSeO3

    NASA Astrophysics Data System (ADS)

    Okamura, Y.; Kagawa, F.; Seki, S.; Kubota, M.; Kawasaki, M.; Tokura, Y.

    2015-05-01

    Through broadband microwave spectroscopy in Faraday geometry, we observe distinct absorption spectra accompanying magnetoelectric (ME) resonance for oppositely propagating microwaves, i.e., directional dichroism, in the multiferroic chiral-lattice magnet Cu2OSeO3. The magnitude of the directional dichroism critically depends on the magnetic-field direction. Such behavior is well accounted for by considering the relative direction of the oscillating electric polarizations induced via the ME effect with respect to microwave electric fields. Directional dichroism in a system with an arbitrary form of ME coupling can be also discussed in the same manner.

  5. Microwave Magnetochiral Dichroism in the Chiral-Lattice Magnet Cu_{2}OSeO_{3}.

    PubMed

    Okamura, Y; Kagawa, F; Seki, S; Kubota, M; Kawasaki, M; Tokura, Y

    2015-05-15

    Through broadband microwave spectroscopy in Faraday geometry, we observe distinct absorption spectra accompanying magnetoelectric (ME) resonance for oppositely propagating microwaves, i.e., directional dichroism, in the multiferroic chiral-lattice magnet Cu_{2}OSeO_{3}. The magnitude of the directional dichroism critically depends on the magnetic-field direction. Such behavior is well accounted for by considering the relative direction of the oscillating electric polarizations induced via the ME effect with respect to microwave electric fields. Directional dichroism in a system with an arbitrary form of ME coupling can be also discussed in the same manner. PMID:26024193

  6. Post-Newtonian Expansion of Gravitational Waves from a Particle in Circular Orbits around a Rotating Black Hole: Effects of Black Hole Absorption

    NASA Astrophysics Data System (ADS)

    Tagoshi, H.; Mano, S.; Takasugi, E.

    Gravitational waves from coalescing compact binaries are the most promising candidates which will be able to be detected by the near-future, ground based laser interferometric gravitational wave detectors such as LIGO, VIRGO, TAMA, GEO600 etc. The standard method to calculate inspiraling wave forms from coalescing binaries is the post-Newtonian expansion of the Einstein equations, in which the orbital velocity v of binaries is assumed to be small compared to the speed of light. Then, we calculate the post-Newtonian expansion of the gravitational wave luminosities from a test particle in circular orbit around a rotating black hole. We consider both the gravitational wave at infinity and the black hole absorption of the wave. The calculation is based on the post-Newtonian Techniques for the Teukolsky equation. This calculation is limited to cases when one star is a test particle. However, we can calculate the very high orders of the post-Newtonian expansion in this case. Then these calculation is very helpful for the more general calculations of the post-Newtonian expansion. Using the results, we discuss the convergence property of the post-Newtonian expansion. We also discuss the effects of those high order post-Newtonian effect of gravitational wave emission to the orbital evolution of coalescing compact binaries.

  7. Circular Coinduction

    NASA Technical Reports Server (NTRS)

    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.

  8. Excitation dynamics in Phycoerythrin 545: modeling of steady-state spectra and transient absorption with modified Redfield theory.

    PubMed

    Novoderezhkin, Vladimir I; Doust, Alexander B; Curutchet, Carles; Scholes, Gregory D; van Grondelle, Rienk

    2010-07-21

    We model the spectra and excitation dynamics in the phycobiliprotein antenna complex PE545 isolated from the unicellular photosynthetic cryptophyte algae Rhodomonas CS24. The excitonic couplings between the eight bilins are calculated using the CIS/6-31G method. The site energies are extracted from a simultaneous fit of the absorption, circular dichroism, fluorescence, and excitation anisotropy spectra together with the transient absorption kinetics using the modified Redfield approach. Quantitative fit of the data enables us to assign the eight exciton components of the spectra and build up the energy transfer picture including pathways and timescales of energy relaxation, thus allowing a visualization of excitation dynamics within the complex. PMID:20643051

  9. Circularly Polarized Persistent Room-Temperature Phosphorescence from Metal-Free Chiral Aromatics in Air.

    PubMed

    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. PMID:27058743

  10. Generation of bright phase-matched circularly-polarized extreme ultraviolet high harmonics

    NASA Astrophysics Data System (ADS)

    Kfir, Ofer; Grychtol, Patrik; Turgut, Emrah; Knut, Ronny; Zusin, Dmitriy; Popmintchev, Dimitar; Popmintchev, Tenio; Nembach, Hans; Shaw, Justin M.; Fleischer, Avner; Kapteyn, Henry; Murnane, Margaret; Cohen, Oren

    2015-02-01

    Circularly-polarized extreme ultraviolet and X-ray radiation is useful for analysing the structural, electronic and magnetic properties of materials. To date, such radiation has only been available at large-scale X-ray facilities such as synchrotrons. Here, we demonstrate the first bright, phase-matched, extreme ultraviolet circularly-polarized high harmonics source. The harmonics are emitted when bi-chromatic counter-rotating circularly-polarized laser pulses field-ionize a gas in a hollow-core waveguide. We use this new light source for magnetic circular dichroism measurements at the M-shell absorption edges of Co. We show that phase-matching of circularly-polarized harmonics is unique and robust, producing a photon flux comparable to linearly polarized high harmonic sources. This work represents a critical advance towards the development of table-top systems for element-specific imaging and spectroscopy of multiple elements simultaneously in magnetic and other chiral media with very high spatial and temporal resolution.

  11. Zero-field dichroism in the solar chromosphere.

    PubMed

    Sainz, R Manso; Bueno, J Trujillo

    2003-09-12

    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 and 854.2 nm lines lies in the existence of atomic polarization in their metastable (2)D(3)(/2, 5/2) 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. PMID:14525412

  12. The infrared dichroism of transmembrane helical polypeptides.

    PubMed Central

    Axelsen, P H; Kaufman, B K; McElhaney, R N; Lewis, R N

    1995-01-01

    Polarized attenuated total internal reflectance techniques were applied to study the infrared dichroism of the amide I transition moment in two membrane-bound peptides that are known to form oriented transmembrane helices: gramicidin A in a supported phospholipid monolayer and Ac-Lys2-Leu24-Lys2-amide (L24) in oriented multibilayers. These studies were performed to test the ability of these techniques to determine the orientation of these peptides, to verify the value of optical parameters used to calculate electric field strengths, to examine the common assumptions regarding the amide I transition moment orientation, and to ascertain the effect of surface imperfections on molecular disorder. The two peptides exhibit marked differences in the shape and frequency of their amide I absorption bands. Yet both peptides are highly ordered and oriented with their helical axes perpendicular to the membrane surface. In the alpha-helix formed by L24, there is evidence for a mode with type E1 symmetry contributing to amide I, and the amide I transition moment must be more closely aligned with the peptide C=O (< 34 degrees) than earlier studies have suggested. These results indicate that long-standing assumptions about the orientation of amide I in a peptide require some revision, but that in general, infrared spectroscopy yields reliable information about the orientation of membrane-bound helical peptides. Images FIGURE 1 PMID:8599683

  13. Simulation of circularly polarized luminescence spectra using coupled cluster theory

    SciTech Connect

    McAlexander, Harley R.; Crawford, T. Daniel

    2015-04-21

    We report the first computations of circularly polarized luminescence (CPL) rotatory strengths at the equation-of-motion coupled cluster singles and doubles (EOM-CCSD) level of theory. Using a test set of eight chiral ketones, we compare both dipole and rotatory strengths for absorption (electronic circular dichroism) and emission to the results from time-dependent density-functional theory (TD-DFT) and available experimental data for both valence and Rydberg transitions. For two of the compounds, we obtained optimized geometries of the lowest several excited states using both EOM-CCSD and TD-DFT and determined that structures and EOM-CCSD transition properties obtained with each structure were sufficiently similar that TD-DFT optimizations were acceptable for the remaining test cases. Agreement between EOM-CCSD and the Becke three-parameter exchange function and Lee-Yang-Parr correlation functional (B3LYP) corrected using the Coulomb attenuating method (CAM-B3LYP) is typically good for most of the transitions, though agreement with the uncorrected B3LYP functional is significantly worse for all reported properties. The choice of length vs. velocity representation of the electric dipole operator has little impact on the EOM-CCSD transition strengths for nearly all of the states we examined. For a pair of closely related β, γ-enones, (1R)-7-methylenebicyclo[2.2.1]heptan-2-one and (1S)-2-methylenebicyclo[2.2.1]heptan-7-one, we find that EOM-CCSD and CAM-B3LYP agree with the energetic ordering of the two possible excited-state conformations, resulting in good agreement with experimental rotatory strengths in both absorption and emission, whereas B3LYP yields a qualitatively incorrect result for the CPL signal of (1S)-2-methylenebicyclo[2.2.1]heptan-7-one. Finally, we predict that one of the compounds considered here, trans-bicyclo[3.3.0]octane-3,7-dione, is unique in that it exhibits an achiral ground state and a chiral first excited state, leading to a strong CPL

  14. Circular motion

    NASA Astrophysics Data System (ADS)

    Newton, Isaac; Henry, Richard Conn

    2000-07-01

    An extraordinarily simple and transparent derivation of the formula for the acceleration that occurs in uniform circular motion is presented, and is advocated for use in high school and college freshman physics textbooks.

  15. Pulsed electric linear dichroism of triphenylmethane dyes adsorbed on montmorillonite K10 in aqueous media

    SciTech Connect

    Yamaoka, Kiwamu; Sasai, Ryo

    2000-05-01

    Electric linear dichroism (ELD) spectra of two cationic triphenylmethane dyes, crystal violet (CV) and malachite green (MG), bound to sodium montmorillonite K10 (MK-10) were studied at 20 C in aqueous media at two mixing ratios, D/S, of 0.10 and 0.24 in the 700- to 400 nm wavelength region and in the applied electric field strength range between 0 and 3 kV/cm. The specific parallel and perpendicular dichroism ({Delta}A{sub {parallel}}/A and {Delta}A{sub {perpendicular}}/A) spectra of dye-adsorbed MK-10 suspension were measured at a fixed field strength with an apparatus equipped with a 512-channel photodiode array detector. By changing the field strength over a wide range, a series of the reduced dichroism values of the bound dyes were measured at a fixed wavelength. By fitting these dichroism values to theoretical orientation functions, the intrinsic reduced dichroism ({Delta}A/A){sub int} spectra at the limiting high fields (ELD spectrum) were determined for CV and MG bound to MK-10. No appreciable difference was observed at the two D/S values. The ELD spectra of these bound dyes are undulatory but never constant, throughout their absorption region; thus, the dye plane does not lie flatly either on the surface or between layers of MK-10 particle.

  16. A multichannel magneto-chiral dichroism spectrometer

    NASA Astrophysics Data System (ADS)

    Kopnov, G.; Rikken, G. L. J. A.

    2014-05-01

    In this work, we describe a multichannel magneto-chiral dichroism spectrometer for the visible and near infrared wavelength ranges. The optical signal acquisition is based on commercially available Czerny-Turner spectrograph systems equipped with solid state detector arrays. The signal analysis method is based on post-processing phase sensitive detection, where the optical properties of the sample are modulated by an alternating external magnetic field. As an illustration of the performance of this spectrometer, magneto-chiral dichroism was measured in crystals of α - NiSO4 . 6H2O and good agreement with literature results was obtained.

  17. Octupole Magnet For Soft X Ray Magnetic Dichroism Experiments: Design and Performance

    SciTech Connect

    Arenholz, Elke; Prestemon, Soren O.

    2004-05-12

    An octupole magnet endstation for soft x ray magnetic dichroism measurements has been developed at the Advanced Light Source. The system consists of an eight pole electromagnet that surrounds a small vacuum chamber. The magnet provides fields up to 0.9 T that can be applied in any direction relative to the incoming x ray beam. High precision magnetic circular and linear dichroism spectra can be obtained reversing the magnetic field for each photon energy in an energy scan. Moreover, the field dependence of all components of the magnetization vector can be studied in detail by choosing various angles of x ray incidence while keeping the relative orientation of magnetic field and sample fixed.

  18. Design and performance of an eight pole resistive magnet for softx-ray magnetic dichroism measurements

    SciTech Connect

    Arenholz, Elke; Prestemon, Soren O.

    2005-06-01

    To take full advantage of the strengths of soft x-ray magnetic dichroism (XMD) measurements for the detailed and quantitative characterization of multi-element magnetic materials, we developed an eight pole electromagnet that provides magnetic fields up to 0.9 T in any direction relative to the incoming x-ray beam. The setup allows us to measure magnetic circular and linear dichroism spectra as well as to thoroughly study magnetization reversal processes with very high precision. Design constraints and system optimization for maximum peak field are discussed. The predicted current-field relation is in excellent agreement with experimental findings. A brief discussion of the key technical difficulties in developing a similar superconducting device with peak fields of 5 T and ramping rates suitable for point-by-point full field reversal in an XMD experiment is presented.

  19. Octupole magnet for soft X ray magnetic dichroism experiments: Design and performance

    SciTech Connect

    Arenholz, Elke; Prestemon, Soren O.

    2003-08-24

    An octupole magnet endstation for soft x-ray magnetic dichroism measurements has been developed at the Advanced Light Source. The system consists of an eight pole electromagnet that surrounds a small vacuum chamber. The magnet provides fields up to 0.9 T that can be applied in any direction relative to the incoming x-ray beam. High precision magnetic circular and linear dichroism spectra can be obtained reversing the magnetic field for each photon energy in an energy scan. Moreover, the field dependence of all components of the magnetization vector can be studied in detail by choosing various angles of x-ray incidence while keeping the relative orientation of magnetic field and sample fixed.

  20. Humidity-dependent dynamic infrared linear dichroism study of a poly(ester urethane)

    NASA Astrophysics Data System (ADS)

    Schoonover, Jon R.; Steckle, Warren P., Jr.; Cox, Jonathan D.; Johnston, Cliff T.; Wang, Yanqia; Gillikin, Angela M.; Palmer, Richard A.

    2007-05-01

    Fourier transform infrared techniques, infrared difference spectroscopy and dynamic infrared linear dichroism (DIRLD), have been utilized to explore the effects of humidity and water absorption on a poly(ester urethane). An environmental infrared microbalance cell was used to measure the infrared spectra as a function of humidity and accompanying weight change for the absorption-desorption processes. The infrared difference data indicate that exposure to humidity affects the hydrogen-bonding interactions in the polymer. Dynamic infrared linear dichroism studies in tensile deformation mode as a function of humidity demonstrate how changes in water content affect the orientational response of functional groups. Complex behavior as a function of humidity for functional groups involved in hydrogen bonding indicates that water absorbed by the polymer affects the micro-environments near these functional groups.

  1. Humidity-dependent dynamic infrared linear dichroism study of a poly(ester urethane).

    PubMed

    Schoonover, Jon R; Steckle, Warren P; Cox, Jonathan D; Johnston, Cliff T; Wang, Yanqia; Gillikin, Angela M; Palmer, Richard A

    2007-05-01

    Fourier transform infrared techniques, infrared difference spectroscopy and dynamic infrared linear dichroism (DIRLD), have been utilized to explore the effects of humidity and water absorption on a poly(ester urethane). An environmental infrared microbalance cell was used to measure the infrared spectra as a function of humidity and accompanying weight change for the absorption-desorption processes. The infrared difference data indicate that exposure to humidity affects the hydrogen-bonding interactions in the polymer. Dynamic infrared linear dichroism studies in tensile deformation mode as a function of humidity demonstrate how changes in water content affect the orientational response of functional groups. Complex behavior as a function of humidity for functional groups involved in hydrogen bonding indicates that water absorbed by the polymer affects the micro-environments near these functional groups. PMID:16950649

  2. An investigation of resonant photoemission in Gd with x-ray linear dichroism

    SciTech Connect

    Tobin, J G

    1998-07-01

    The constructive summing of direct and indirect channels above the absorption threshold of a core level can cause a massive increase in the emission cross section, leading to a phenomenon called "resonant photoemission". Using novel magnetic linear dichroism in angular distribution photoelectron spectroscopy experiments and theoretical simulations, we have probed the nature of the resonant photoemission process in Gd metal. It now appears that temporal matching as well as energy matching is a requirement for true resonant photoemission.

  3. Linear Dichroism of Chlorosomes from Chloroflexus Aurantiacus in Compressed Gels and Electric Fields

    PubMed Central

    van Amerongen, H.; Vasmel, H.; van Grondelle, R.

    1988-01-01

    The linear dichroism of chlorosomes from Chloroflexus aurantiacus was measured between 250 and 800 nm. To orient the chlorosomes we used a new way of compressing polyacrylamide gels, where the dimension of the gel along the measuring light-beam is kept constant. The press required for such a way of compressing is relatively easy to construct. A theoretical description is given to interpret the measured linear dichroism in terms of the orientation of the transition moments. The results obtained with the polyacrylamide gels are compared with the linear dichroism measurements for chlorosomes oriented in electric fields. Both the spectral features as well as the absolute size of the linear dichroism signals are in reasonable agreement. We find that the transition moment corresponding to the 741 nm bacteriochlorophyll c (Bchl c) absorption band makes an angle of 20° with the long axis of the chlorosome. For the 461 nm Bchl c band an angle of 30° is found. Both angles are significantly lower than the values reported so far in literature and they imply that Bchl c is highly organized in the chlorosomes. PMID:19431726

  4. Strong magneto-chiral dichroism in a paramagnetic molecular helix observed by hard X-rays

    NASA Astrophysics Data System (ADS)

    Sessoli, Roberta; Boulon, Marie-Emmanuelle; Caneschi, Andrea; Mannini, Matteo; Poggini, Lorenzo; Wilhelm, Fabrice; Rogalev, Andrei

    2015-01-01

    Magneto-chiral dichroism is a non-reciprocal--that is, directional--effect observed in magnetized chiral systems, featuring an unbalanced absorption of unpolarized light depending on the direction of the magnetization. Despite the fundamental interest in a phenomenon breaking both parity and time-reversal symmetries, magneto-chiral dichroism is one of the least investigated aspects of light-matter interaction most likely because of the weakness of the effect in most reported experiments. Here we have exploited the element selectivity of hard X-ray radiation to investigate the magneto-chiral properties of enantiopure crystals of two isostructural molecular helicoidal chains comprising either cobalt(II) or manganese(II) ions. A strong magneto-chiral dichroism, with Kuhn asymmetry of the order of a few per cent, has been observed in the cobalt chains system, whereas it is practically absent for the manganese derivative. The spectral features of the X-ray magneto-chiral dichroism signal differ significantly from the natural and magnetic dichroic contributions and have been rationalized here using the multipolar expansion of matter-radiation interaction.

  5. Magnetic dichroism in angle-resolved hard x-ray photoemission from buried layers

    NASA Astrophysics Data System (ADS)

    Kozina, Xeniya; Fecher, Gerhard H.; Stryganyuk, Gregory; Ouardi, Siham; Balke, Benjamin; Felser, Claudia; Schönhense, Gerd; Ikenaga, Eiji; Sugiyama, Takeharu; Kawamura, Naomi; Suzuki, Motohiro; Taira, Tomoyuki; Uemura, Tetsuya; Yamamoto, Masafumi; Sukegawa, Hiroaki; Wang, Wenhong; Inomata, Koichiro; Kobayashi, Keisuke

    2011-08-01

    This work reports the measurement of magnetic dichroism in angular-resolved photoemission from in-plane magnetized buried thin films. The high bulk sensitivity of hard x-ray photoelectron spectroscopy (HAXPES) in combination with circularly polarized radiation enables the investigation of the magnetic properties of buried layers. HAXPES experiments with an excitation energy of 8 keV were performed on exchange-biased magnetic layers covered by thin oxide films. Two types of structures were investigated with the IrMn exchange-biasing layer either above or below the ferromagnetic layer: one with a CoFe layer on top and another with a Co2FeAl layer buried beneath the IrMn layer. A pronounced magnetic dichroism is found in the Co and Fe 2p states of both materials. The localization of the magnetic moments at the Fe site conditioning the peculiar characteristics of the Co2FeAl Heusler compound, predicted to be a half-metallic ferromagnet, is revealed from the magnetic dichroism detected in the Fe 2p states.

  6. Scanning differential polarization microscope: Its use to image linear and circular differential scattering

    SciTech Connect

    Mickols, W.; Maestre, M.F.

    1988-06-01

    A differential polarization microscope that couples the sensitivity of single-beam measurement of circular dichroism and circular differential scattering with the simultaneous measurement of linear dichroism and linear differential scattering has been developed. The microscope uses a scanning microscope stage and single-point illumination to give the very shallow depth of field found in confocal microscopy. This microscope can operate in the confocal mode as well as in the near confocal condition that can allow one to program the coherence and spatial resolution of the microscope. This microscope has been used to study the change in the structure of chromatin during the development of sperm in Drosophila.

  7. Voltage-controlled magnetic anisotropy in Fe|MgO tunnel junctions studied by x-ray absorption spectroscopy

    SciTech Connect

    Miwa, Shinji Matsuda, Kensho; Tanaka, Kazuhito; Goto, Minori; Suzuki, Yoshishige; Kotani, Yoshinori; Nakamura, Tetsuya

    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.

  8. Note: Derivation of two-photon circular dichroism—Addendum to “Two-photon circular dichroism” [J. Chem. Phys. 62, 1006 (1975)

    SciTech Connect

    Friese, Daniel H.

    2015-09-07

    This addendum shows the detailed derivation of the fundamental equations for two-photon circular dichroism which are given in a very condensed form in the original publication [I. Tinoco, J. Chem. Phys. 62, 1006 (1975)]. In addition, some minor errors are corrected and some of the derivations in the original publication are commented.

  9. X-ray linear dichroism in cubic compounds: The case of Cr3+ in MgAl2O4

    NASA Astrophysics Data System (ADS)

    Juhin, Amélie; Brouder, Christian; Arrio, Marie-Anne; Cabaret, Delphine; Sainctavit, Philippe; Balan, Etienne; Bordage, Amélie; Seitsonen, Ari P.; Calas, Georges; Eeckhout, Sigrid G.; Glatzel, Pieter

    2008-11-01

    The angular dependence (x-ray linear dichroism) of the CrK pre-edge in MgAl2O4:Cr3+ spinel is measured by means of x-ray absorption near-edge structure spectroscopy and compared to calculations based on density functional theory (DFT) and ligand field multiplet (LFM) theory. We also present an efficient method, based on symmetry considerations, to compute the dichroism of the cubic crystal starting from the dichroism of a single substitutional site. DFT shows that the electric dipole transitions do not contribute to the features visible in the pre-edge and provides a clear vision of the assignment of the 1s→3d transitions. However, DFT is unable to reproduce quantitatively the angular dependence of the pre-edge, which is, on the other side, well reproduced by LFM calculations. The most relevant factors determining the dichroism of CrK pre-edge are identified as the site distortion and 3d-3d electronic repulsion. From this combined DFT, LFM approach is concluded that when the pre-edge features are more intense than 4% of the edge jump, pure quadrupole transitions cannot explain alone the origin of the pre-edge. Finally, the shape of the dichroic signal is more sensitive than the isotropic spectrum to the trigonal distortion of the substitutional site. This suggests the possibility to obtain quantitative information on site distortion from the x-ray linear dichroism by performing angular dependent measurements on single crystals.

  10. Spin-Induced Polarizations and Nonreciprocal Directional Dichroism of the Room-Temperature Multiferroic BiFeO3

    DOE PAGESBeta

    Fishman, Randy Scott; Lee, Jun Hee; Bordacs, Sandor; Kezsmarki, Istvan; Nagel, Urmas; Room, Toomas

    2015-09-14

    A microscopic model for the room-temperature multiferroic BiFeO3 that includes two Dzyaloshinskii-Moriya interactions and single-ion anisotropy along the ferroelectric polarization predicts both the zero-field spectroscopic modes as well as their splitting and evolution in a magnetic field. Due to simultaneously broken time-reversal and spatial-inversion symmetries, the absorption of light changes as the magnetic field or the direction of light propagation is reversed. We discuss three physical mechanisms that may contribute to this absorption asymmetry known as directional dichroism: the spin current, magnetostriction, and single-ion anisotropy. We conclude that the directional dichroism in BiFeO3 is dominated by the spin-current polarization andmore » is insensitive to the magnetostriction and easy-axis anisotropy. With three independent spin-current parameters, our model accurately describes the directional dichroism observed for magnetic field along [1, -1, 0]. Since some modes are almost transparent to light traveling in one direction but opaque for light traveling in the opposite direction, BiFeO3 can be used as a room-temperature optical diode at certain frequencies in the GHz to THz range. This work demonstrates that an analysis of the directional dichroism spectra based on an effective spin model supplemented by first-principles calculations can produce a quantitative microscopic theory of the magnetoelectric couplings in multiferroic materials.« less

  11. Instrument for x-ray absorption spectroscopy with in situ electrical control characterizations

    SciTech Connect

    Huang, Chun-Chao; Chang, Shu-Jui; Yang, Chao-Yao; Tseng, Yuan-Chieh; Chou, Hsiung

    2013-12-15

    We report a synchrotron-based setup capable of performing x-ray absorption spectroscopy and x-ray magnetic circular dichroism with simultaneous electrical control characterizations. The setup can enable research concerning electrical transport, element- and orbital-selective magnetization with an in situ fashion. It is a unique approach to the real-time change of spin-polarized electronic state of a material/device exhibiting magneto-electric responses. The performance of the setup was tested by probing the spin-polarized states of cobalt and oxygen of Zn{sub 1-x}Co{sub x}O dilute magnetic semiconductor under applied voltages, both at low (∼20 K) and room temperatures, and signal variations upon the change of applied voltage were clearly detected.

  12. The effect of pea chloroplast alignment and variation of excitation wavelength on the circularly polarized chlorophyll luminescence.

    PubMed

    Barzda, Virginijus; Ionov, Maksim; van Amerongen, Herbert; Gussakovsky, Eugene E; Shahak, Yosepha

    2004-03-01

    Circularly polarized luminescence (CPL) is a powerful technique to study the macroorganization of photosynthetic light-harvesting apparatus in vivo and in vitro. It is particularly useful for monitoring environmental stress induced molecular re-organization of thylakoid membranes in green leaves. The current study focuses on two questions which are important to perform and interpret such experiments: how does CPL depend on the excitation wavelength and how on the orientation of the granal thylakoids. CPL and circular dichroism (CD) of pea chloroplasts were complementarily applied when chloroplasts were either in suspension or trapped in a polyacrylamide gel (PAAG) after alignment in a magnetic field. In contrast to the CD spectrum, the CPL signal was found to be independent of the excitation wavelength in both the Soret and the Qy absorption region for chloroplasts in both suspension and PAAG. The improved resolution of luminescence measurements revealed a relatively small negative CPL band in addition to the previously described large positive band. No effect of photoselection upon excitation on the CPL spectra was detected. The CPL intensity at 690 nm at the edge of the granal thylakoids was found to be higher than at the face of the grana suggesting the CPL anisotropy. PMID:15615047

  13. Non-collinear generation of angularly isolated circularly polarized high harmonics

    NASA Astrophysics Data System (ADS)

    Hickstein, Daniel D.; Dollar, Franklin J.; Grychtol, Patrik; Ellis, Jennifer L.; Knut, Ronny; Hernández-García, Carlos; Zusin, Dmitriy; Gentry, Christian; Shaw, Justin M.; Fan, Tingting; Dorney, Kevin M.; Becker, Andreas; Jaroń-Becker, Agnieszka; Kapteyn, Henry C.; Murnane, Margaret M.; Durfee, Charles G.

    2015-11-01

    We generate angularly isolated beams of circularly polarized extreme ultraviolet light through the first implementation of non-collinear high harmonic generation with circularly polarized driving lasers. This non-collinear technique offers numerous advantages over previous methods, including the generation of higher photon energies, the separation of the harmonics from the pump beam, the production of both left and right circularly polarized harmonics at the same wavelength and the capability of separating the harmonics without using a spectrometer. To confirm the circular polarization of the beams and to demonstrate the practicality of this new light source, we measure the magnetic circular dichroism of a 20 nm iron film. Furthermore, we explain the mechanisms of non-collinear high harmonic generation using analytical descriptions in both the photon and wave models. Advanced numerical simulations indicate that this non-collinear mixing enables the generation of isolated attosecond pulses with circular polarization.

  14. Determination of absolute configuration of natural products: theoretical calculation of electronic circular dichroism as a tool

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Determination of absolute configuration (AC) is one of the most challenging features in the structure elucidation of chiral natural products, especially those with complex structures. With revolutionary advancements in the area of quantum chemical calculations of chiroptical spectroscopy over the pa...

  15. An Extreme Flux Vacuum Ultraviolet/Ultraviolet Beamline For The Measurement Of Biological Circular Dichroism

    SciTech Connect

    Clarke, D.T.; Vasanthi, N.; Shaw, D.; Brown, A.; Todd, B.; Grant, A.F.; Flaherty, J.V.; Mullacrane, I.D.; Miller, M.J.; Bowler, M.A.; Jones, G.R.; Mythen, C.

    2004-05-12

    A new extreme flux vacuum ultraviolet bending magnet beamline (CD12) has been commission at the SRS, Daresbury. The beamline has met all of its designed performance parameters and these are detailed. The clear advantages of SRCD over CD undertaken on conventional instruments are discussed and examples of its capabilities in terms of measurement precision and enhanced signal-to-noise for both steady-state CD and time-resolved CD are given.

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

    ERIC Educational Resources Information Center

    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…

  17. Induced birefringence and dichroism in azo polymers. Comparison between amorphous and liquid crystalline polymers

    SciTech Connect

    Natansohn, A.; Brown, D.; Rochon, P.

    1993-12-31

    Macroscopic order can be induced in amorphous high-Tg azo polymers (usually containing electron-donor - electron-acceptor substituted azobenzene moieties) by exposure to polarized light. The phenomenon is based on a series of trans-cis-trans isomerization cycles and the induced birefringence is typically of 2x10{sup {minus}2}. The ordered domains can be returned to randomness ({open_quotes}erased{close_quotes}) using circularly polarized light. This paper will present a comparison between amorphous and liquid crystalline azo polymers. The most significant difference between these two types of polymers is that any other type of concert with the azo moiety. Consequently the dichroism and birefringence induced in the liquid crystalline polymers can be one order of magnitude higher than in the amorphous polymers. At the same time, however, the time required to achieve saturation also increases by at least one order of magnitude.

  18. Achieving atomic resolution magnetic dichroism by controlling the phase symmetry of an electron probe

    DOE PAGESBeta

    Rusz, Jan; Idrobo, Juan -Carlos; Bhowmick, Somnath

    2014-09-30

    The calculations presented here reveal that an electron probe carrying orbital angular momentum is just a particular case of a wider class of electron beams that can be used to measure electron magnetic circular dichroism (EMCD) with atomic resolution. It is possible to obtain an EMCD signal with atomic resolution by simply breaking the symmetry of the electron probe phase front using the aberration-corrected optics of a scanning transmission electron microscope. The probe’s required phase distribution depends on the sample’s magnetic symmetry and crystal structure. The calculations indicate that EMCD signals that use the electron probe’s phase are as strongmore » as those obtained by nanodiffraction methods.« less

  19. Achieving atomic resolution magnetic dichroism by controlling the phase symmetry of an electron probe

    SciTech Connect

    Rusz, Jan; Idrobo, Juan -Carlos; Bhowmick, Somnath

    2014-09-30

    The calculations presented here reveal that an electron probe carrying orbital angular momentum is just a particular case of a wider class of electron beams that can be used to measure electron magnetic circular dichroism (EMCD) with atomic resolution. It is possible to obtain an EMCD signal with atomic resolution by simply breaking the symmetry of the electron probe phase front using the aberration-corrected optics of a scanning transmission electron microscope. The probe’s required phase distribution depends on the sample’s magnetic symmetry and crystal structure. The calculations indicate that EMCD signals that use the electron probe’s phase are as strong as those obtained by nanodiffraction methods.

  20. Broadening and shifting of the methanol 119 {mu}m gain line of linear and circular polarization by collision with chiral molecules

    SciTech Connect

    J.S. Bakos; G. Djotyan; Zsuzsa Soerlei; J. Szigeti; D. K. Mansfield; J. Sarkozi

    2000-06-21

    Evidence of circular dichroism has been observed in the spectral properties of a gas of left-right symmetric molecules. This dichroism comes about as the result of collisions of the symmetric molecules with left-right asymmetric molecules introduced as a buffer gas. In this sense, the dichroism can be said to have been transferred from the chiral buffer molecules to the symmetric, non-chiral molecules of the background vapor. This transferred dichroism appears as broadening in the gain line of the symmetric molecule which is asymmetric with respect to the right or left handedness of a circularly polarized probe. The broadening of the 119 {mu}m line of the methanol molecule was observed using infrared-far infrared double resonance spectroscopy.

  1. Polarization dependent two-photon absorption spectroscopy on a naturally occurring biomarker (curcumin) in solution: A theoretical-experimental study

    NASA Astrophysics Data System (ADS)

    Tiburcio-Moreno, Jose A.; Alvarado-Gil, J. J.; Diaz, Carlos; Echevarria, Lorenzo; Hernández, Florencio E.

    2013-09-01

    We report on the theoretical-experimental analysis of the two-photon absorption (TPA) and two-photon circular-linear dichroism (TPCLD) spectra of (1E,6E)-1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione (curcumin) in Tetrahydrofuran (THF) solution. The measurement of the full TPA spectrum of this molecule reveals a maximum TPA cross-section at 740 nm, i.e. more than 10 times larger than the maximum reported in the literature at 800 nm for the application of curcumin in bioimaging. The TPCLD spectrum exposes the symmetry of the main excited-states involved in the two-photon excitation process. TD-DFT calculations support the experimental results. These outcomes are expected to expand the application of natural-occurring dyes in bioimaging.

  2. Characterization of Circular RNAs.

    PubMed

    Zhang, Yang; Yang, Li; Chen, Ling-Ling

    2016-01-01

    Accumulated lines of evidence reveal that a large number of circular RNAs are produced in transcriptomes from fruit fly to mouse and human. Unlike linear RNAs shaped with 5' cap and 3' tail, circular RNAs are characterized by covalently closed loop structures without open terminals, thus requiring specific treatments for their identification and validation. Here, we describe a detailed pipeline for the characterization of circular RNAs. It has been successfully applied to the study of circular intronic RNAs derived from intron lariats (ciRNAs) and circular RNAs produced from back spliced exons (circRNAs) in human. PMID:26721494

  3. Home Sewage Disposal. Special Circular 212.

    ERIC Educational Resources Information Center

    Wooding, N. Henry

    This circular provides current information for homeowners who must repair or replace existing on-lot sewage disposal systems. Site requirements, characteristics and preparation are outlined for a variety of alternatives such as elevated sand mounds, sand-lined beds and trenches, and oversized absorption area. Diagrams indicating construction…

  4. A circular polarimeter for the Cosmic Microwave Background

    SciTech Connect

    Giovannini, Massimo

    2010-08-01

    A primordial degree of circular polarization of the Cosmic Microwave Background is not observationally excluded. The hypothesis of primordial dichroism can be quantitatively falsified if the plasma is magnetized prior to photon decoupling since the initial V-mode polarization affects the evolution of the temperature fluctuations as well as the equations for the linear polarization. The observed values of the temperature and polarization angular power spectra are used to infer constraints on the amplitude and on the spectral slope of the primordial V-mode. Prior to photon decoupling magnetic fields play the role of polarimeters insofar as they unveil the circular dichroism by coupling the V-mode power spectrum to the remaining brightness perturbations. Conversely, for angular scales ranging between 4 deg and 10 deg the joined bounds on the magnitude of circular polarization and on the magnetic field intensity suggest that direct limits on the V-mode power spectrum in the range of 0.01 mK could directly rule out pre-decoupling magnetic fields in the range of 10–100 nG. The frequency dependence of the signal is located, for the present purposes, in the GHz range.

  5. K-edge x-ray dichroism investigation of Fe1-xCoxSi: Experimental evidence for spin polarization crossover

    NASA Astrophysics Data System (ADS)

    Hearne, G. R.; Diguet, G.; Baudelet, F.; Itié, J.-P.; Manyala, N.

    2015-04-01

    Both Fe and Co K-edge x-ray magnetic circular dichroism (XMCD) have been employed as element-specific probes of the magnetic moments in the composition series of the disordered ferromagnet Fe1-xCoxSi (for x=0.2, 0.3, 0.4, 0.5). A definitive single peaked XMCD profile occurs for all compositions at both Fe and Co K-edges. The Fe 4p orbital moment, deduced from the integral of the XMCD signal, has a steep dependence on x at low doping levels and evolves to a different (weaker) dependence at x≥0.3, similar to the behavior of the magnetization in the Co composition range studied here. It is systematically higher, by at least a factor of two, than the corresponding Co orbital moment for most of the composition series. Fine structure beyond the K-edge absorption (limited range EXAFS) suggests that the local order (atomic environment) is very similar across the series, from the perspective of both the Fe and Co absorbing atom. The variation in the XMCD integral across the Co composition range has two regimes, that which occurs below x=0.3 and then evolves to different behavior at higher doping levels. This is more conspicuously present in the Fe contribution. This is rationalized as the evolution from a half-metallic ferromagnet at low Co doping to that of a strong ferromagnet at x>0.3 and as such, spin polarization crossover occurs. The Fermi level is tuned from the majority spin band for x<0.3 where a strongly polarized majority spin electron gas prevails, to a regime where minority spin carriers dominate at higher doping. The evolution of the Fe-derived spin polarized (3d) bands, indirectly probed here via the 4p states, is the primary determinant of the doping dependence of the magnetism in this alloy series.

  6. Dynamics of photoinduced dichroism and birefringence in optically thick azopolymers

    SciTech Connect

    Ponomarev, Yu V; Ivanov, Yu V; Rumyantsev, Yu A; Gromchenko, A A

    2009-01-31

    Dynamics of photoinduced dichroism and birefringence have been studied experimentally and theoretically (with the help of the Dumont model) by using some comb-shaped azopolymers. It is shown that the dynamics of trans-isomer concentration and their angular distribution anisotropy can be restored from the experimentally found dichroism dynamics, with the concentration and anisotropy being averaged over the thickness for optically thick samples. At the initial stage of photoinduced anisotropy when the active role of the polymer matrix can be neglected, the experimental time dependence of dichroism is shown to comply well with the Dumont model even if the orientation memory is neglected, provided that only a part of trans-isomers participates in trans-isomerisation. (nonlinear optical phenomena)

  7. Strong magneto-chiral dichroism in a paramagnetic molecular helix observed by hard X-ray

    PubMed Central

    Sessoli, Roberta; Boulon, Marie-Emmanuelle; Caneschi, Andrea; Mannini, Matteo; Poggini, Lorenzo; Wilhelm, Fabrice; Rogalev, Andrei

    2014-01-01

    Magneto-chiral dichroism (MχD) is a non-reciprocal, i. e. directional, effect observed in magnetised chiral systems featuring an unbalanced absorption of unpolarised light depending on the direction of the magnetisation. Despite the fundamental interest in a phenomenon breaking both parity and time reversal symmetries, MχD is one of the least investigated aspects of light-matter interaction because of the weakness of the effect in most reported experiments. Here we have exploited the element selectivity of hard X-ray radiation to investigate the magneto-chiral properties of enentiopure crsytals of two isostructural molecular helicoidal chains comprising Cobalt(II) and Manganese (II) ions, respectively. A strong magneto-chiral dichroism, with Kuhn asymmetry of the order of a few percent, has been observed in the Cobalt chain system, while it is practically absent for the Manganese derivative. The spectral features of the XMχD signal differ significantly from the natural and magnetic dichroic contributions and have been here rationalized using the simple multipolar expansion of matter-radiation interaction. PMID:25729401

  8. Spin-Induced Polarizations and Nonreciprocal Directional Dichroism of the Room-Temperature Multiferroic BiFeO3

    SciTech Connect

    Fishman, Randy Scott; Lee, Jun Hee; Bordacs, Sandor; Kezsmarki, Istvan; Nagel, Urmas; Room, Toomas

    2015-09-14

    A microscopic model for the room-temperature multiferroic BiFeO3 that includes two Dzyaloshinskii-Moriya interactions and single-ion anisotropy along the ferroelectric polarization predicts both the zero-field spectroscopic modes as well as their splitting and evolution in a magnetic field. Due to simultaneously broken time-reversal and spatial-inversion symmetries, the absorption of light changes as the magnetic field or the direction of light propagation is reversed. We discuss three physical mechanisms that may contribute to this absorption asymmetry known as directional dichroism: the spin current, magnetostriction, and single-ion anisotropy. We conclude that the directional dichroism in BiFeO3 is dominated by the spin-current polarization and is insensitive to the magnetostriction and easy-axis anisotropy. With three independent spin-current parameters, our model accurately describes the directional dichroism observed for magnetic field along [1, -1, 0]. Since some modes are almost transparent to light traveling in one direction but opaque for light traveling in the opposite direction, BiFeO3 can be used as a room-temperature optical diode at certain frequencies in the GHz to THz range. This work demonstrates that an analysis of the directional dichroism spectra based on an effective spin model supplemented by first-principles calculations can produce a quantitative microscopic theory of the magnetoelectric couplings in multiferroic materials.

  9. Correlated visible-light absorption and intrinsic magnetism of SrTiO3 due to oxygen deficiency: bulk or surface effect?

    PubMed

    Choi, Heechae; Song, Jin Dong; Lee, Kwang-Ryeol; Kim, Seungchul

    2015-04-20

    The visible-light absorption and luminescence of wide band gap (3.25 eV) strontium titanate (SrTiO3) are well-known, in many cases, to originate from the existence of natural oxygen deficiency in the material. In this study based on density functional theory (DFT) calculations, we provide, to the best of our knowledge, the first report indicating that oxygen vacancies in the bulk and on the surfaces of SrTiO3 (STO) play different roles in the optical and magnetic properties. We found that the doubly charged state of oxygen vacancy (VO(2+)) is dominant in bulk SrTiO3 and does not contribute to the sub-band gap photoexcitation or intrinsic magnetism of STO. Neutral oxygen vacancies (VO(0)) on (001) surfaces terminated with both TiO2 and SrO layers induce magnetic moments, which are dependent on the charged state of VO. The calculated absorption spectra for the (001) surfaces exhibit mid-infrared absorption (<0.5 eV) and sub-band gap absorption (2.5-3.1 eV) due to oxygen vacancies. In particular, VO(0) on the TiO2-terminated surface has a relatively low formation energy and magnetic moments, which can explain the recently observed spin-dependent photon absorptions of STO in a magnetic circular dichroism measurement [Rice, W. D.; et al. Nat. Mater.13, 481, 2014]. PMID:25815532

  10. 2. Northwest circular bastion, seen from edge of southwest circular ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. Northwest circular bastion, seen from edge of southwest circular bastion wall. Metal roof beams extend up to form peak. World War II gun installation at right. - Fort Hamilton, Northwest Circular Bastion, Rose Island, Newport, Newport County, RI

  11. Linear dichroism and resonant photoemission in Gd 011

    SciTech Connect

    Mishra, S.R.; Cummins, T.R.; Gammon, W.J.; van der Laan, G.; Goodman, K.W.; Tobin, J.G.

    1998-05-13

    Magnetic Linear Dichroism in Angular Distributions (MLDAD) from Photoelectron Emission was used to probe the nature of Resonant Photoemission. Gd 5p and Gd 4f emission were investigated. Using novel theoretical simulations, we were able to show that temporal matching is a requirement for ``True`` Resonant Photoemission, where the Resonant Photoemission retains the characteristics of Photoelectron Emission.

  12. Dichroism for orbital angular momentum using parametric amplification

    NASA Astrophysics Data System (ADS)

    Lowney, J.; Roger, T.; Faccio, D.; Wright, E. M.

    2014-11-01

    We theoretically analyze parametric amplification as a means to produce dichroism based on the orbital angular momentum (OAM) of an incident signal field. The nonlinear interaction is shown to provide differential gain between signal states of differing OAM, the peak gain occurring at half the OAM of the pump field.

  13. The high-field magnet endstation for X-ray magnetic dichroism experiments at ESRF soft X-ray beamline ID32.

    PubMed

    Kummer, K; Fondacaro, A; Jimenez, E; Velez-Fort, E; Amorese, A; Aspbury, M; Yakhou-Harris, F; van der Linden, P; Brookes, N B

    2016-03-01

    A new high-field magnet endstation for X-ray magnetic dichroism experiments has been installed and commissioned at the ESRF soft X-ray beamline ID32. The magnet consists of two split-pairs of superconducting coils which can generate up to 9 T along the beam and up to 4 T orthogonal to the beam. It is connected to a cluster of ultra-high-vacuum chambers that offer a comprehensive set of surface preparation and characterization techniques. The endstation and the beam properties have been designed to provide optimum experimental conditions for X-ray magnetic linear and circular dichroism experiments in the soft X-ray range between 400 and 1600 eV photon energy. User operation started in November 2014. PMID:26917134

  14. Applications of circularly polarized photons at the ALS with a bend magnet source

    SciTech Connect

    Not Available

    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.

  15. Circular polarization sensitive absorbers based on graphene

    PubMed Central

    Yang, Kunpeng; Wang, Min; Pu, Mingbo; Wu, Xiaoyu; Gao, Hui; Hu, Chenggang; Luo, Xiangang

    2016-01-01

    It is well known that the polarization of a linearly polarized (LP) light would rotate after passing through a single layer graphene under the bias of a perpendicular magnetostatic field. Here we show that a corresponding phase shift could be expected for circularly polarized (CP) light, which can be engineered to design the circular polarization sensitive devices. We theoretically validate that an ultrathin graphene-based absorber with the thickness about λ/76 can be obtained, which shows efficient absorption >90% within incident angles of ±80°. The angle-independent phase shift produced by the graphene is responsible for the nearly omnidirectional absorber. Furthermore, a broadband absorber in frequencies ranging from 2.343 to 5.885 THz with absorption over 90% is designed by engineering the dispersion of graphene. PMID:27034257

  16. Circular polarization sensitive absorbers based on graphene

    NASA Astrophysics Data System (ADS)

    Yang, Kunpeng; Wang, Min; Pu, Mingbo; Wu, Xiaoyu; Gao, Hui; Hu, Chenggang; Luo, Xiangang

    2016-04-01

    It is well known that the polarization of a linearly polarized (LP) light would rotate after passing through a single layer graphene under the bias of a perpendicular magnetostatic field. Here we show that a corresponding phase shift could be expected for circularly polarized (CP) light, which can be engineered to design the circular polarization sensitive devices. We theoretically validate that an ultrathin graphene-based absorber with the thickness about λ/76 can be obtained, which shows efficient absorption >90% within incident angles of ±80°. The angle-independent phase shift produced by the graphene is responsible for the nearly omnidirectional absorber. Furthermore, a broadband absorber in frequencies ranging from 2.343 to 5.885 THz with absorption over 90% is designed by engineering the dispersion of graphene.

  17. Squaring a Circular Segment

    ERIC Educational Resources Information Center

    Gordon, Russell

    2008-01-01

    Consider a circular segment (the smaller portion of a circle cut off by one of its chords) with chord length c and height h (the greatest distance from a point on the arc of the circle to the chord). Is there a simple formula involving c and h that can be used to closely approximate the area of this circular segment? Ancient Chinese and Egyptian…

  18. Tunable circular patch antennas

    NASA Astrophysics Data System (ADS)

    Lan, G.-L.; Sengupta, D. L.

    1985-10-01

    A method to control the resonant or operating frequencies of circular patch antennas has been investigated experimentally and theoretically. It consists of the placement of passive metallic or tuning posts at approximate locations within the input region of the antenna. Comparison of measured and analytical results seems to establish the validity of a theoretical model proposed to determine the input performance of such circular patch antennas.

  19. Circular Intensity Differential Scattering of chiral molecules

    SciTech Connect

    Bustamante, C.J.

    1980-12-01

    In this thesis a theory of the Circular Intensity Differential Scattering (CIDS) of chiral molecules as modelled by a helix oriented with respect to the direction of incidence of light is presented. It is shown that a necessary condition for the existence of CIDS is the presence of an asymmetric polarizability in the scatterer. The polarizability of the scatterer is assumed generally complex, so that both refractive and absorptive phenomena are taken into account.

  20. DESIRS: a state-of-the-art VUV beamline featuring high resolution and variable polarization for spectroscopy and dichroism at SOLEIL.

    PubMed

    Nahon, Laurent; de Oliveira, Nelson; Garcia, Gustavo A; Gil, Jean-François; Pilette, Bertrand; Marcouillé, Olivier; Lagarde, Bruno; Polack, François

    2012-07-01

    DESIRS is a new undulator-based VUV beamline on the 2.75 GeV storage ring SOLEIL (France) optimized for gas-phase studies of molecular and electronic structures, reactivity and polarization-dependent photodynamics on model or actual systems encountered in the universe, atmosphere and biosphere. It is equipped with two dedicated endstations: a VUV Fourier-transform spectrometer (FTS) for ultra-high-resolution absorption spectroscopy (resolving power up to 10(6)) and an electron/ion imaging coincidence spectrometer. The photon characteristics necessary to fulfill its scientific mission are: high flux in the 5-40 eV range, high spectral purity, high resolution, and variable and well calibrated polarizations. The photon source is a 10 m-long pure electromagnetic variable-polarization undulator producing light from the very near UV up to 40 eV on the fundamental emission with tailored elliptical polarization allowing fully calibrated quasi-perfect horizontal, vertical and circular polarizations, as measured with an in situ VUV polarimeter with absolute polarization rates close to unity, to be obtained at the sample location. The optical design includes a beam waist allowing the implementation of a gas filter to suppress the undulator high harmonics. This harmonic-free radiation can be steered toward the FTS for absorption experiments, or go through a highly efficient pre-focusing optical system, based on a toroidal mirror and a reflective corrector plate similar to a Schmidt plate. The synchrotron radiation then enters a 6.65 m Eagle off-plane normal-incidence monochromator equipped with four gratings with different groove densities, from 200 to 4300 lines mm(-1), allowing the flux-to-resolution trade-off to be smoothly adjusted. The measured ultimate instrumental resolving powers are 124000 (174 µeV) around 21 eV and 250000 (54 µeV) around 13 eV, while the typical measured flux is in the 10(10)-10(11) photons s(-1) range in a 1

  1. FAST TRACK COMMUNICATION: Generalized geometrical model for photoionization of polarized atoms: II. Magnetic dichroism in the 3p photoemission from the K 3p64s 2S1/2 ground state

    NASA Astrophysics Data System (ADS)

    Grum-Grzhimailo, A. N.; Cubaynes, D.; Heinecke, E.; Hoffmann, P.; Zimmermann, P.; Meyer, M.

    2010-10-01

    The generalized geometrical model for photoionization from polarized atoms is extended to include mixing of configurations in the initial atomic and/or the final photoion states. The theoretical results for angle-resolved linear and circular magnetic dichroism are in good agreement with new high-resolution photoelectron data for 3p-1 photoionization of potassium atoms polarized in the K 3p64s 2S1/2 ground state by laser optical pumping.

  2. Circular free-electron laser

    DOEpatents

    Brau, Charles A.; Kurnit, Norman A.; Cooper, Richard K.

    1984-01-01

    A high efficiency, free electron laser utilizing a circular relativistic electron beam accelerator and a circular whispering mode optical waveguide for guiding optical energy in a circular path in the circular relativistic electron beam accelerator such that the circular relativistic electron beam and the optical energy are spatially contiguous in a resonant condition for free electron laser operation. Both a betatron and synchrotron are disclosed for use in the present invention. A free electron laser wiggler is disposed around the circular relativistic electron beam accelerator for generating a periodic magnetic field to transform energy from the circular relativistic electron beam to optical energy.

  3. Spectral broadening of interacting pigments: polarized absorption by photosynthetic proteins.

    PubMed Central

    Somsen, O J; van Grondelle, R; van Amerongen, H

    1996-01-01

    Excitonic interaction between pigment molecules is largely responsible for the static and dynamic spectroscopic properties of photosynthetic pigment-proteins. This paper provides a new description of its effect on polarized absorption spectroscopy, in particular on circular dichroism (CD). We investigate excitonic spectra of finite width and use "spectral moments" to compare 1) inhomogeneously broadened excitonic spectra, 2) spectra that are (homogeneously broadened by vibrations or electron-phonon interaction, and 3) spectra that are simulated by applying convolution after the interaction has been evaluated. Two cases are distinguished. If the excitonic splitting is smaller than the width of the interacting absorption bands, the broadening of the excitonic spectrum can be approximated by a convolution approach, although a correction is necessary for CD spectra. If the excitonic splitting exceeds the bandwidth, the well-known exchange narrowing occurs. We demonstrate that this is accompanied by redistribution of dipole strength and spectral shifts. The magnitude of a CD spectrum is conveniently expressed by its first spectral moment. As will be shown, this is independent of spectral broadening as well as dispersive shifts induced by pigment-protein interactions. Consequently, it provides a simple tool to relate the experimental CD spectrum of a pigment complex to the excitonic interactions from which it originates. To illustrate the potential of the presented framework, the spectroscopy of the LH2 pigment-protein complex from purple bacteria is analyzed and compared for dimer-like and ring-like structures. Furthermore, it is demonstrated that the variability of the CD of chlorosomes from green bacteria can be explained by small changes in the structure of their cylindrical bacteriochlorophyll c subunits. Images FIGURE 3 FIGURE 4 PMID:8889168

  4. Compact waveguide circular polarizer

    DOEpatents

    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.

  5. Macroorganization of Chlorophyll a/b light-harvesting complex in thylakoids and aggregates: information from circular differential scattering

    SciTech Connect

    Garab, G.; Faludi-Daniel, A.; Sutherland, J.C.; Hind, G.

    1988-04-05

    Circular dichroism (CD) and magnetic circular dichroism (MCD) spectra were recorded for spinach thylakoids and for isolated, aggregated chlorophyll a/b light-harvesting pigment-protein complex, in random and magnetically aligned states of orientation at room and low temperatures. The shape and magnitude of the CD signal of most bands strongly depended on the orientation of the thylakoid membranes or the aggregated pigment-protein complex. In both thylakoids and aggregated light-harvesting complexes, however, the MCD spectra of the two different orientations were almost identical. Random and magnetically aligned samples exhibited anomalous, large CD signals outside the bands of pigment absorbance. Lack of similarity between the corresponding MCD and CD spectra showed that the large CD signals are not produced as a distortion of CD of absorbance by light scattering. Instead, these anomalous spectral features are believed to originate in differential selective scattering of circularly polarized light. The results lead to the conclusion that the light-harvesting pigment-protein complex in thylakoid grana forms a helical macroarray with dimensions commensurate with the wavelengths of the anomalous circular dichroism signals. A hypothesis is put forward suggesting a role for these macrodomains in granal organization.

  6. Energy-loss magnetic chiral dichroism study of epitaxial MnAs film on GaAs(001)

    SciTech Connect

    Fu, X.; Warot-Fonrose, B.; Arras, R.; Serin, V.; Demaille, D.; Eddrief, M.; Etgens, V.

    2015-08-10

    The room-temperature ferromagnetic behavior of MnAs/GaAs(001) thin film has been locally explored by Transmission Electron Microscope (TEM). We first differentiated hexagonal α-MnAs and quasi-hexagonal β-MnAs which are very similar in atomic structure by electron diffraction. Local magnetic moment information of the identified α-MnAs was extracted from manganese-L{sub 2,3} edges using Energy-loss Magnetic Circular Dichroism technique and the ratio of orbital to spin magnetic moment was measured. In this experiment, atomic structure identification, chemical analysis, and magnetic moment measurement were simultaneously achieved at high spatial resolution in TEM, thus providing a potential method for in-situ study of local properties of multiphase magnetic materials.

  7. Thermochromic properties of the ferroelectric ?-doped ?: study of the temperature-induced dichroism

    NASA Astrophysics Data System (ADS)

    Valiente, Rafael; Rodríguez, Fernando

    1999-03-01

    A new thermochromic material formed by doping 0953-8984/11/12/014/img3 into the ferroelectric 0953-8984/11/12/014/img4 crystal is presented. The change of colour from green (room temperature) to red (low temperature) under polarized light observation is accompanied by a strong temperature-induced dichroism at low temperature. The origin of these phenomena is investigated through the polarized charge transfer spectra associated with 0953-8984/11/12/014/img3 complexes formed in the title compound, and their dependence on temperature in the 10-300 K range. Attention is paid to correlating the optical spectra with the local structure around 0953-8984/11/12/014/img3. The results are compared with those obtained in the tribromide 0953-8984/11/12/014/img7 and 0953-8984/11/12/014/img8, and the tetrabromide 0953-8984/11/12/014/img9 and 0953-8984/11/12/014/img10 crystals, where 0953-8984/11/12/014/img3 forms 0953-8984/11/12/014/img12 complexes of nearly 0953-8984/11/12/014/img13 symmetry, and tetrahedral distorted 0953-8984/11/12/014/img14 complexes of 0953-8984/11/12/014/img15 symmetry, respectively. An interesting feature is the presence of a strongly polarized absorption band at 15 800 0953-8984/11/12/014/img16 in 0953-8984/11/12/014/img17, which is responsible for the observed dichroism and thermochromism. The existence of this band is associated with the formation of highly distorted 0953-8984/11/12/014/img14 complexes in the monoclinic 0953-8984/11/12/014/img19 host crystal. The enhancement of dichroism exhibited by this crystal with decreasing temperature is noteworthy. The analysis of the spectra reveals that this unusual thermal behaviour can be explained in terms of thermally activated reorientations rather than structural changes of the 0953-8984/11/12/014/img3 complex.

  8. Non-reciprocal directional dichroism in the AFM phase of BiFeO3 at THz frequencies

    NASA Astrophysics Data System (ADS)

    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).

  9. Wiimote Experiments: Circular Motion

    ERIC Educational Resources Information Center

    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…

  10. Copyright Basics. Circular 1.

    ERIC Educational Resources Information Center

    Library of Congress, Washington, DC. Copyright Office.

    This circular answers some of the questions that are frequently asked about copyright, a form of protection provided by the laws of the United States to authors of "original works of authorship" including library, dramatic musical, artistic, and certain other intellectual works. The Copyright Act of 1976 (title 17 of the United States Code), which…

  11. Wiimote Experiments: Circular Motion

    NASA Astrophysics Data System (ADS)

    Kouh, Minjoon; Holz, Danielle; Kawam, Alae; Lamont, Mary

    2013-03-01

    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 bicycle wheel.

  12. Configuration of singular optical cones in gyrotropic crystals with dichroism

    SciTech Connect

    Merkulov, V. S.

    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.

  13. Light absorption dichroism and magnetic configuration of weakly ferromagnetic CoCO 3

    NASA Astrophysics Data System (ADS)

    Litvinenko, Yu. G.; Verdyan, A. I.; Shapiro, V. V.

    1980-01-01

    Investigation of light interaction with magnetically ordered crystals [1] revealed a correlation between certain spectral characteristics of a crystal on the one hand and its magnetic properties on the other.

  14. Circular inferences in schizophrenia.

    PubMed

    Jardri, Renaud; Denève, Sophie

    2013-11-01

    A considerable number of recent experimental and computational studies suggest that subtle impairments of excitatory to inhibitory balance or regulation are involved in many neurological and psychiatric conditions. The current paper aims to relate, specifically and quantitatively, excitatory to inhibitory imbalance with psychotic symptoms in schizophrenia. Considering that the brain constructs hierarchical causal models of the external world, we show that the failure to maintain the excitatory to inhibitory balance results in hallucinations as well as in the formation and subsequent consolidation of delusional beliefs. Indeed, the consequence of excitatory to inhibitory imbalance in a hierarchical neural network is equated to a pathological form of causal inference called 'circular belief propagation'. In circular belief propagation, bottom-up sensory information and top-down predictions are reverberated, i.e. prior beliefs are misinterpreted as sensory observations and vice versa. As a result, these predictions are counted multiple times. Circular inference explains the emergence of erroneous percepts, the patient's overconfidence when facing probabilistic choices, the learning of 'unshakable' causal relationships between unrelated events and a paradoxical immunity to perceptual illusions, which are all known to be associated with schizophrenia. PMID:24065721

  15. Switchable circular beam deflectors

    NASA Astrophysics Data System (ADS)

    Shang, Xiaobing; Joshi, Pankaj; Tan, Jin-Yi; De Smet, Jelle; Cuypers, Dieter; Baghdasaryan, Tigran; Vervaeke, Michael; Thienpont, Hugo; De Smet, Herbert

    2016-04-01

    In this work, we report two types of electrically tunable photonic devices with circularly symmetric polarization independent beam steering performance (beam condensing resp. beam broadening). The devices consist of circular micro grating structures combined with nematic liquid crystal (LC) layers with anti-parallel alignment. A single beam deflector converts a polarized and monochromatic green laser beam (λ =543.5 nm) into a diffraction pattern, with the peak intensity appearing at the third order when 0~{{V}\\text{pp}} is applied and at the zeroth order (no deflection) for voltages above 30~{{V}\\text{pp}} . Depending on the shape of the grating structure (non-inverted or inverted), the deflection is inwards or outwards. Both grating types can be made starting from the same diamond-tooled master mold. A polarized white light beam is symmetrically condensed resp. broadened over 2° in the off state and is passed through unchanged in the on state. By stacking two such devices with mutually orthogonal LC alignment layers, polarization independent switchable circular beam deflectors are realized with a high transmittance (>80%), and with the same beam steering performance as the polarization dependent single devices.

  16. N-single-helix photonic-metamaterial based broadband optical range circular polarizer by induced phase lags between helices.

    PubMed

    Behera, Saraswati; Joseph, Joby

    2015-02-10

    In this work, we have designed a photonic-metamaterial based broadband circular polarizer using N=4 phase-lagged aluminum single helices arranged in a square array as a unit cell. The effect of phase differences between the helices in an array on the optical performance of the structure is studied, and a comparative study is done with that of multi-intertwined helices. It is observed that the proposed metamaterial structure shows circular polarization sensitivity over a broad optical wavelength range (≈450-900  nm), with improved optical performance in average extinction ratio and broad positive circular dichroism in comparison to multiple intertwined helices. The induced phase lag between the helices in a square-array based unit cell reduces the linear birefringence and leads to the recovery of circular space symmetry in the structure. PMID:25968042

  17. Rectenna composed of a circular microstrip antenna

    SciTech Connect

    Itoh, K.; Ohgane, T.; Ogawa, Y.

    1986-01-01

    One of the big problems in the SPS system is reradiation of the harmonic waves generated by the rectifying diode. The authors proposed the use of a circular microstrip antenna (CMSA), since the CMSA has no higher resonance-harmonic of integer multiple of the dominant resonance frequency. However, characteristics of a large rectenna array of CMSA's have not been clarified. This paper is concerned with the absorption efficiency of the rectenna composed of the CMSA. The efficiency is estimated explicitly using an infinite array model. The results show that the absorption efficiency of the infinite rectenna array composed of the CMSA is 100%. Also, this paper considers the effect of the losses of the composed of the CMSA is 100%. Also, this paper considers the effect of the losses of the CMSA. 4 references, 4 figures.

  18. Fluorescence Linear Dichroism Imaging for Quantifying Membrane Order

    PubMed Central

    Benninger, Richard K.P.

    2014-01-01

    The plasma membrane of a cell is an ordered environment, giving rise to anisotropic orientations and restricted motion of constituent lipids and proteins. The membrane environment is also dynamic and heterogeneous, which is important for the regulation of membrane-localized signaling. A number of fluorescent microscopy approaches enable the membrane order to be quantified with high spatial and temporal resolution. A polarization-resolved fluorescence method, termed fluorescent linear dichroism (fLD) imaging, can quantify the orientation of membrane bound fluorophores which allows spatially resolved measurement of membrane order and sub-resolution membrane topology (ruffling). Here we describe the detailed methods for performing fLD imaging in biological membrane environments such as the plasma membrane of living cells. This includes the preparation of the sample with appropriate fluorescent dyes, the requirements of the microscope system, the data collection protocol, and post-acquisition image processing, analysis, and interpretation. PMID:25331136

  19. Spin exchange interaction in quasi-1D Cu-phthalocyanine crystalline thin film measured by Magnetic Circular Dichroism (MCD) spectroscopy

    NASA Astrophysics Data System (ADS)

    Pan, Zhenwen; Rawat, Naveen; Lamarche, Cody; Tokumoto, Takahisa; Wetherby, Anthony; Waterman, Rory; Headrick, Randy; McGill, Steve; Furis, Madalina

    2012-02-01

    Highly-oriented Cu-phthalocyanine (PC) pen-written crystalline thin films can be viewed as quasi-1D spin 1/2 magnetic chains. In order to reveal the nature of spin exchange between localized S=1/2 Cu spins, MCD spectroscopy was performed on films with millimeter-sized grains fabricated from a soluble CuPc derivative in magnetic fields up to 10 Tesla at temperatures ranging from 0.4 K to 77K. At T<2K and B<4T the MCD associated with transitions between Q-band π electron states exhibits a non-linear temperature-dependent Brillouin-like increase with magnetic field. For B>4T the MCD evolves linearly with magnetic field, as expected from diamagnetic carbon-based systems. Theoretical modelingootnotetextW. Wu et. al.,PRB 84,024427(2011) of electronic structure and exchange interactions in this system predicts an indirect exchange mechanism mediated by delocalized ligand states. Our MCD measurements identified the states responsible for this exchange.

  20. The structure of Escherichia coli heat-stable enterotoxin b by nuclear magnetic resonance and circular dichroism.

    PubMed Central

    Sukumar, M.; Rizo, J.; Wall, M.; Dreyfus, L. A.; Kupersztoch, Y. M.; Gierasch, L. M.

    1995-01-01

    The heat-stable enterotoxin b (STb) is secreted by enterotoxigenic Escherichia coli that cause secretory diarrhea in animals and humans. It is a 48-amino acid peptide containing two disulfide bridges, between residues 10 and 48 and 21 and 36, which are crucial for its biological activity. Here, we report the solution structure of STb determined by two- and three-dimensional NMR methods. Approximate interproton distances derived from NOE data were used to construct structures of STb using distance-geometry and simulated annealing procedures. The NMR-derived structure shows that STb is helical between residues 10 and 22 and residues 38 and 44. The helical structure in the region 10-22 is amphipathic and exposes several polar residues to the solvent, some of which have been shown to be important in determining the toxicity of STb. The hydrophobic residues on the opposite face of this helix make contacts with the hydrophobic residues of the C-terminal helix. The loop region between residues 21 and 36 has another cluster of hydrophobic residues and exposes Arg 29 and Asp 30, which have been shown to be important for intestinal secretory activity. CD studies show that reduction of disulfide bridges results in a dramatic loss of structure, which correlates with loss of function. Reduced STb adopts a predominantly random-coil conformation. Chromatographic measurements of concentrations of native, fully reduced, and single-disulfide species in equilibrium mixtures of STb in redox buffers indicate that the formation of the two disulfide bonds in STb is only moderately cooperative. Similar measurements in the presence of 8 M urea suggest that the native secondary structure significantly stabilizes the disulfide bonds. PMID:8528070