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Sample records for circular dichroism measurement

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

    Energy Technology Data Exchange (ETDEWEB)

    SUTHERLAND,J.C.

    2002-01-19

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

  2. Toroidal circular dichroism

    Science.gov (United States)

    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.

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

    OpenAIRE

    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 ...

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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.

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

    KAUST Repository

    Furumaki, Shu

    2012-12-06

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

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

    OpenAIRE

    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(NH...

  8. Gauge-Invariant Formulation of Circular Dichroism.

    Science.gov (United States)

    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

  9. Angle-resolved x-ray circular and magnetic circular dichroisms: Definitions and applications

    OpenAIRE

    Tong, DSY; X Guo; Tobin, JG; Waddill, GD

    1996-01-01

    We introduce definitions of angle-resolved x-ray circular dichroism (ARXCD) and magnetic x-ray circular dichroism (ARMXCD). As defined, the much larger effect of circular dichroism (ARXCD) is separated from the smaller magnetic (ARMXCD) effect. In all materials, ARXCD is zero along mirror planes while nonzero elsewhere. ARMXCD is nonzero only in magnetic materials. The measurement and analysis of ARMXCD allow element specific surface magnetism and surface structure as well as their inter-rela...

  10. Exciton circular dichroism in channelrhodopsin.

    Science.gov (United States)

    Pescitelli, Gennaro; Kato, Hideaki E; Oishi, Satomi; Ito, Jumpei; Maturana, Andrés Daniel; Nureki, Osamu; Woody, Robert W

    2014-10-16

    Channelrhodopsins (ChRs) are of great interest currently because of their important applications in optogenetics, the photostimulation of neurons. The absorption and circular dichroism (CD) spectra of C1C2, a chimera of ChR1 and ChR2 of Chlamydomonas reinhardtii, have been studied experimentally and theoretically. The visible absorption spectrum of C1C2 shows vibronic fine structure in the 470 nm band, consistent with the relatively nonpolar binding site. The CD spectrum has a negative band at 492 nm (Δε(max) = -6.17 M(-1) cm(-1)) and a positive band at 434 nm (Δε(max) = +6.65 M(-1) cm(-1)), indicating exciton coupling within the C1C2 dimer. Time-dependent density functional theory (TDDFT) calculations are reported for three models of the C1C2 chromophore: (1) the isolated protonated retinal Schiff base (retPSB); (2) an ion pair, including the retPSB chromophore, two carboxylate side chains (Asp 292, Glu 162), modeled by acetate, and a water molecule; and (3) a hybrid quantum mechanical/molecular mechanical (QM/MM) model depicting the binding pocket, in which the QM part consists of the same ion pair as that in (2) and the MM part consists of the protein residues surrounding the ion pair within 10 Å. For each of these models, the CD of both the monomer and the dimer was calculated with TDDFT. For the dimer, DeVoe polarizability theory and exciton calculations were also performed. The exciton calculations were supplemented by calculations of the coupling of the retinal transition with aromatic and peptide group transitions. For the dimer, all three methods and three models give a long-wavelength C2-axis-polarized band, negative in CD, and a short-wavelength band polarized perpendicular to the C2 axis with positive CD, differing in wavelength by 1-5 nm. Only the retPSB model gives an exciton couplet that agrees qualitatively with experiment. The other two models give a predominantly or solely positive band. We further analyze an N-terminal truncated mutant

  11. Nuclear spin circular dichroism in fullerenes

    Czech Academy of Sciences Publication Activity Database

    Straka, Michal

    Brno : Masaryk University Press, 2015 - (Sklenář, V.). s. 153 ISBN 978-80-210-7890-1. [EUROMAR 2015. 05.07.2015-10.07.2015, Praha] R&D Projects: GA ČR(CZ) GA14-03564S Institutional support: RVO:61388963 Keywords : nuclear spin circular dichroism * fullerenes Subject RIV: CF - Physical ; Theoretical Chemistry

  12. Vibrational circular dichroism of nucleic acids

    Czech Academy of Sciences Publication Activity Database

    Andrushchenko, Valery; Wieser, H.; Bouř, Petr

    Brescia, 2009. s. 60-60. [International Conference on Circular Dichroism /12./. Interdisciplinary Symposium on Biological Chirality /5./. 30.08.2009-04.09.2009, Brescia] Institutional research plan: CEZ:AV0Z40550506 Keywords : VCD * G-quadruplex Subject RIV: CF - Physical ; Theoretical Chemistry

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

    CERN Document Server

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

    2016-01-01

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

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

    International Nuclear Information System (INIS)

    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

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

    Science.gov (United States)

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-04-21

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

  17. Circular Dichroism Method for Heat Capacity Determination of Proteins

    Science.gov (United States)

    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. Porphyrin Protonation Studied by Magnetic Circular Dichroism

    Czech Academy of Sciences Publication Activity Database

    Štěpánek, Petr; Andrushchenko, Valery; Ruud, K.; Bouř, Petr

    2012-01-01

    Roč. 116, č. 1 (2012), s. 778-783. ISSN 1089-5639 R&D Projects: GA ČR GAP208/11/0105; GA ČR GA203/09/2037; GA ČR GAP208/10/0559; GA MŠk(CZ) LH11033 Institutional research plan: CEZ:AV0Z40550506 Keywords : magnetic circular dichroism (MCD) * TPPS * spectra simulations * porphyrin protonation Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.771, year: 2012

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

    Science.gov (United States)

    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…

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

    International Nuclear Information System (INIS)

    The experimental set-up at SpLine (BM25A, ESRF) to measure XMCD by using a diamond X-ray phase retarder to obtain circularly polarized X-rays is described. 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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2012-09-11

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

  2. Transient vibrational circular dichroism spectrometer: technical development

    Directory of Open Access Journals (Sweden)

    Helbing J.

    2010-06-01

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

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

    Science.gov (United States)

    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.

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

    CERN Document Server

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

    2016-01-01

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

  5. Circular dichroism from Fano resonances in planar chiral oligomers

    Science.gov (United States)

    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.

  6. Nuclear spin circular dichroism in fullerenes: a computational study

    Czech Academy of Sciences Publication Activity Database

    Straka, Michal; Štěpánek, Petr; Coriani, S.; Vaara, J.

    2014-01-01

    Roč. 50, č. 96 (2014), s. 15228-15231. ISSN 1359-7345 R&D Projects: GA ČR(CZ) GA14-03564S Grant ostatní: GA MŠk(CZ) ED3.2.00/08.0144 Institutional support: RVO:61388963 Keywords : nuclear spin circular dichroism * fullerenes * C60 * C70 * density functional calculations * magnetic circular dichroism Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 6.834, year: 2014

  7. Circular dichroism in XUV + IR multiphoton ionization of atoms

    International Nuclear Information System (INIS)

    Circular dichroism (CD) is theoretically considered for two-colour multiphoton ionization of arbitrary atomic subshells. In particular, p-subshell ionization is analysed and compared with s-subshell ionization. Simple analytical expressions for the CD are obtained for both s- and p-subshell ionization. The calculations performed for Ne(2p) ionization by an extreme ultraviolet pulse in the presence of an infrared laser pulse show that the CD in this case is appreciably larger than in previously discussed s-shell ionization. It makes this case favourable for applications as a sensitive tool for measuring the helicity of short-wavelength free-electron laser beams. (paper)

  8. Secondary-Structure Analysis of Denatured Proteins by Vacuum-Ultraviolet Circular Dichroism Spectroscopy

    OpenAIRE

    Matsuo, Koichi; Sakurada, Yoshie; Yonehara, Ryuta; Kataoka, Mikio; Gekko, Kunihiko

    2007-01-01

    To elucidate the structure of denatured proteins, we measured the vacuum-ultraviolet circular dichroism (VUVCD) spectra from 260 to 172 nm of three proteins (metmyoglobin, staphylococcal nuclease, and thioredoxin) in the native and the acid-, cold-, and heat-denatured states, using a synchrotron-radiation VUVCD spectrophotometer. The circular dichroism spectra of proteins fully unfolded by guanidine hydrochloride (GdnHCl) were also measured down to 197 nm for comparison. These denatured prote...

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

    International Nuclear Information System (INIS)

    Full text: We investigated the effects of a strong circularly polarized 1064 nm laser field on electron capture and emission in slow (keV) proton-hydrogen collisions within a reduced-dimensionality model of the scattering system in which both the motion of the active electron and the laser electric field vector are confined to the scattering plane. During the collision, the proton is assumed to move on a straight-line trajectory with impact parameter b. The rotating laser electric field breaks the azimuthal symmetry, and the projectile either follows the rotating laser field ('co-rotating' collisions) or moves against the rotating electric field ('counter-rotating' collisions). By solving the time-dependent Schroedinger equation, we examined the probabilities for electron capture and ionization as a function of laser intensity, impact parameter, and the laser phase 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 the helicity of the circularly polarized laser light. For intensities above 2x1012 W/cm2, our model predicts a noticeable circular dichroism in the capture probability. Interestingly, this dichroism persists after averaging over . 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. For a fixed impact parameter, the capture probability as a function of φ shows large amplitude oscillations and differs from the field-free results most strikingly at φ = 0o and 180o. It displays a strong dichroism effect, i.e., a substantial difference in the electron capture probability for co-rotating as compared to counter-rotating collisions. Ionization

  10. Circular dichroism readout of sugar recognition in the cleft of a fused-pyridine receptor

    OpenAIRE

    Tamaru, Shun-ichi; Shinkai, Seiji; Khasanov, Alisher B.; Bell, Thomas W.

    2002-01-01

    Dicarboxamide host 2 forms 1:1 complexes with n-octyl pyranosides derived from d-glucose, d-mannose, d-galactose, d-fucose, d-lyxose, and d-arabinose. Association constants (Ka) in the range of 77–940 M−1 were measured in chloroform by means of induced circular dichroism and fluorescence spectroscopy. Variations in Ka values correspond qualitatively to expected differences in hydrogen-bonding abilities of guest hydroxyl groups. Induced circular dichroism effects for...

  11. Circular dichroism of cholesteric polymers and the orbital angular momentum of light

    International Nuclear Information System (INIS)

    We explore experimentally if light's orbital angular momentum (OAM) interacts with chiral nematic polymer films. Specifically, we measure the circular dichroism of such a material using light beams with different OAM. We investigate the case of strongly focused, nonparaxial light beams, where the spatial and polarization degrees of freedom are coupled. Within the experimental accuracy, we cannot find any influence of the OAM on the circular dichroism of cholesteric polymers.

  12. Calculation of magnetic circular dichroism of rare-earth elements

    International Nuclear Information System (INIS)

    We present atomic calculations for the magnetic circular dichroism (MCD) in the 4d→4f excitation region of Eu, Gd, Tb, Dy, and Ho metal. The spectral shapes at T=0 K for non-polarized, right and left circularly polarized light, and their difference spectra are given. The interference effect between the 4d→4f excitation followed by 4d-4f4f super-Coster-Kronig decay process and the 4f→εg direct excitation process, which is known as the Fano effect, is considered in the calculations. The result reproduces the overall features of recently measured experiments. It is essential to consider the Fano effect for the understanding of the heavy rare-earth 4d→4f absorption and their MCD. (author)

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

    Science.gov (United States)

    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

  14. A new multichannel detector for proteomics studies and circular dichroism

    International Nuclear Information System (INIS)

    The conventional instrument for the measurement of Circular Dichroism (CD) comprises of a single anode photomultiplier tube (PMT) detector connected to a 'lock-in' amplifier. This requires the sequential scanning across the wavelength spectrum, making it a useful method for structure determination but not for time-resolved measurements and the observation of structural changes. In this paper, we report on our progress to develop a novel system based on a semiconductor linear array detector that will overcome the limitations of the conventional systems and will allow for the observation of dynamic phenomena to the time limits imposed by the technique itself, i.e. 20 μs with conventional light modulation methods. Our final aim is to develop an instrument that will enable the simultaneous measurement of both spectroscopic and time resolved CD by the realisation of energy-dispersive experiments (EDE-CD)

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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

  17. Monitoring of Porphyrin Protonation by the Magnetic Circular Dichroism

    Czech Academy of Sciences Publication Activity Database

    Štěpánek, Petr; Bouř, Petr

    Oxford : Diamond, 2011. s. 21-21. [CD 2011. The International Conference on Chiroptical Spectroscopy /13./. 24.07.2011-28.07.2011, Oxford] Grant ostatní: 7th European Community Framework Program(XE) 230955 Institutional research plan: CEZ:AV0Z40550506 Keywords : porphyrin * magnetic circular dichroism * DFT calculation Subject RIV: CF - Physical ; Theoretical Chemistry

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

    Institute of Scientific and Technical Information of China (English)

    Jing CAO; Hua-Jie YIN; Rui SONG

    2013-01-01

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

  19. Detection of magnetic circular dichroism using a transmission electron microscoe

    Czech Academy of Sciences Publication Activity Database

    Schattschneider, P.; Rubino, S.; Hébert, C.; Rusz, Ján; Kuneš, Jan; Novák, Pavel; Carlino, E.; Fabrizioli, M.; Panaccione, G.; Rossi, G.

    2006-01-01

    Roč. 441, - (2006), s. 486-488. ISSN 0028-0836 Grant ostatní: CHIRALTEM (NEST-2003-1 Adventure)(XE) STREP 508971 Institutional research plan: CEZ:AV0Z10100521 Keywords : magnetism * circular dichroism * electron microscope Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 26.681, year: 2006

  20. Vibrational circular dichroism spectroscopy study of paroxetine and femoxetine precursors

    Czech Academy of Sciences Publication Activity Database

    Urbanová, M.; Setnička, V.; Bouř, Petr; Navrátilová, H.; Volka, K.

    2002-01-01

    Roč. 67, - (2002), s. 298-301. ISSN 0006-3525 R&D Projects: GA AV ČR IAA4055104 Institutional research plan: CEZ:AV0Z4055905 Keywords : vibrational circular dichroism Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.372, year: 2002

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

    DEFF Research Database (Denmark)

    Pedersen, Jesper Goor; Mortensen, Asger

    2007-01-01

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

  2. On the analysis of membrane protein circular dichroism spectra

    OpenAIRE

    Sreerama, Narasimha; Woody, Robert W.

    2004-01-01

    Analysis of circular dichroism spectra of proteins provides information about protein secondary structure. Analytical methods developed for such an analysis use structures and spectra of a set of reference proteins. The reference protein sets currently in use include soluble proteins with a wide range of secondary structures, and perform quite well in analyzing CD spectra of soluble proteins. The utility of soluble protein reference sets in analyzing membrane protein CD spectra, however, has ...

  3. Amplifying vibrational circular dichroism by manipulation of the electronic manifold.

    Science.gov (United States)

    Domingos, Sérgio R; Panman, Matthijs R; Bakker, Bert H; Hartl, Frantisek; Buma, Wybren J; Woutersen, Sander

    2012-01-11

    Vibrational circular dichroism is a powerful technique to study the stereochemistry of chiral molecules, but often suffers from small signal intensities. Electrochemical modulation of the energies of the electronically excited state manifold is now demonstrated to lead to an order of magnitude enhancement of the differential absorption. Quantum-chemical calculations show that increased mixing between ground and excited states is at the origin of this amplification. PMID:22002107

  4. Magnetic Circular Dichroism of Porphyrin Lanthanide M3+ Complexes

    Czech Academy of Sciences Publication Activity Database

    Andrushchenko, Valery; Padula, Daniele; Zhivotova, E.; Yamamoto, S.; Bouř, Petr

    2014-01-01

    Roč. 26, č. 10 (2014), s. 655-662. ISSN 0899-0042 R&D Projects: GA ČR GA13-03978S; GA ČR GAP208/11/0105; GA MŠk(CZ) LH11033 Grant ostatní: GA AV ČR(CZ) M200550902 Institutional support: RVO:61388963 Keywords : magnetic circular dichroism * lanthanides * porphyrin complexes * density functional theory * sum over state computations Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.886, year: 2014

  5. Vibrational Circular Dichroism Studies of Biological Macromolecules and their Complexes

    Czech Academy of Sciences Publication Activity Database

    Polyanichko, A. M.; Andrushchenko, Valery; Bouř, Petr; Wieser, H.

    Hauppauge, NY : Nova Science Publishers, Inc, 2012 - (Rodgers, D.), s. 67-126 ISBN 978-1-61122-522-8 R&D Projects: GA ČR GAP208/10/0559; GA AV ČR IAA400550702 Grant ostatní: AV ČR(CZ) M200550902 Institutional research plan: CEZ:AV0Z40550506 Keywords : vibrational circular dichroism (VCD) * proteins * nucleic acids * peptides * spectra simulations Subject RIV: CF - Physical ; Theoretical Chemistry https://www.novapublishers.com/catalog/ product _info.php? product s_id=32793

  6. Plasmonic nanohelix metamaterials with tailorable giant circular dichroism

    Science.gov (United States)

    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. Detecting Chiral Orbital Angular Momentum by Circular Dichroism ARPES

    OpenAIRE

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

    2011-01-01

    We show, by way of tight-binding and first-principles calculations, that a one-to-one correspondence between electron's crystal momentum k and non-zero 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. Circular dichroism (CD) angle-resolved photoemission (ARPES) e...

  8. Stereochemical analysis of glycerophospholipids by vibrational circular dichroism.

    Science.gov (United States)

    Taniguchi, Tohru; Manai, Daisuke; Shibata, Masataka; Itabashi, Yutaka; Monde, Kenji

    2015-09-30

    The stereochemistry of glycerophospholipids (GPLs) has been of interest for its roles in the evolution of life and in their biological activity. However, because of their structural complexity, no convenient method to determine their configuration has been reported. In this work, through the first systematic application of vibrational circular dichroism (VCD) spectroscopy to various diacylated GPLs, we have revealed that their chirality can be assigned by the sign of a VCD exciton couplet generated by the interaction of two carbonyl groups. This paper also presents spectroscopic evidence for the stereochemistry of GPLs isolated from bacteria, eukaryotes, and mitochondria. PMID:26379046

  9. Vacuum-ultraviolet circular dichroism spectrophotometer using synchrotron radiation

    International Nuclear Information System (INIS)

    Full text: Circular dichroism (CD) spectroscopy is powerful for analyzing the structure of optically active materials such as biopolymers. However, no commercial CD spectrophotometer is capable of measuring the CD in the vacuum ultraviolet (VUV) region below 190 nm because of technical difficulties involved in the light source, optical device, and sample cell. CD measurements extended to the VUV region can provide more detailed and new information on the structure of biopolymers based on the higher energy transition of chromophores such as hydroxyl and acetal groups. We have constructed a VUVCD spectrophotometer to measure the CD spectra of biomaterials in aqueous solutions in the 310-140 nm wavelength region under a high vacuum, using a small-scale SR source (0.7 GeV) at Hiroshima Synchrotron Radiation Center (HiSOR). All optical devices of the spectrophotometer were set up under a high vacuum (10-6 Torr), to avoid the absorption of light by air and water vapor. The SR light is separated into two orthogonal linearly polarized light beams by a linear polarizer and then modulated to circularly polarized light at 50 kHz by a photo-elastic modulator (PEM). In order to control PEM accurately and to stabilize the lock-in amplifier under a high vacuum, we used the optical servo-control system. Also, an assembled-type MgF2 cell with a temperature-control unit was constructed using a Peltier thermoelectric element. Its path length can be adjusted by various Tefron spacers in the range from 1.3 to 50 μm and its temperature can be controlled within an accuracy of ± 1 deg C in the range from -30 to 70 deg C. The performance of the spectrophotometer and MgF2 cell constructed was tested by monitoring the CD spectra of ammonium d-camphor-10-sulfonate (ACS), D- and L-isomers of amino acids. These obtained results demonstrate that the optical system and the sample cell constructed normally operate under a high vacuum to provide useful information on the structure analysis of

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

    NARCIS (Netherlands)

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

    1992-01-01

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

  11. Optical circular dichroism of vacuum-deposited film stacks

    Science.gov (United States)

    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.

  12. Vibrational and Electronic Circular Dichroism Monitoring of Copper(II) Coordination with a Chiral Ligand

    Czech Academy of Sciences Publication Activity Database

    Wu, T.; Zhang, X. P.; Li, C. H.; Bouř, Petr; Li, Y. Z.; You, X. Z.

    2012-01-01

    Roč. 24, č. 6 (2012), s. 451-458. ISSN 0899-0042 R&D Projects: GA ČR GAP208/11/0105 Institutional research plan: CEZ:AV0Z40550506 Keywords : circular dichroism * vibrational circular dichroism * coordination compounds * density functional theory computations Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.718, year: 2012

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

    International Nuclear Information System (INIS)

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

  14. Nucleic acid vibrational circular dichroism, absorption, and linear dichroism spectra. I. A DeVoe theory approach.

    OpenAIRE

    Self, B D; Moore, D S

    1997-01-01

    Infrared (IR) vibrational circular dichroism (VCD), absorption, and linear dichroism (LD) spectra of four homopolyribonucleotides, poly(rA), poly(rG), poly(rC), and poly(rU), have been calculated, in the 1750-1550 cm-1 spectral region, using the DeVoe polarizability theory. A newly derived algorithm, which approximates the Hilbert transform of imaginaries to reals, was used in the calculations to obtain real parts of oscillator polarizabilities associated with each normal mode. The calculated...

  15. High-Flux Beamline for Ultraviolet and Vacuum-Ultraviolet Circular Dichroism at NSRL

    International Nuclear Information System (INIS)

    This paper describes the commissioning and characterization of an NSRL bending magnet beamline constructed for the measurement of vacuum-ultraviolet circular dichroism on biological and other materials. The beamline provides high fluxes of ultraviolet and vacuum-ultraviolet radiation, which is converted into plane polarized light using a polarizer and subsequently converted into circularly polarized light using a photoelastic modulator with a switching frequency of 50 kHz. The beamline has the best wavelength resolution of 0.3 nm and stray light levels better than 0.03%. Example spectra of (1s)-(+)-10-camphorsulphonic acid (CSA) and myoglobin are given

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  17. Optical activity and circular dichroism of plasmonic nanorod assemblies

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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

  19. Angular momentum-induced circular dichroism in non-chiral nanostructures

    CERN Document Server

    Zambrana-Puyalto, Xavier; Molina-Terriza, Gabriel

    2014-01-01

    Circular dichroism (CD), i.e. the differential response of a system to left and right circularly polarized light, is one of the only techniques capable of providing morphological information of certain samples. In biology, for instance, CD spectroscopy is widely used to study the structure of proteins. More recently, it has also been used to characterize metamaterials and plasmonic structures. Typically, CD can only be observed in chiral objects. Here, we present experimental results showing that a non-chiral sample such as a sub-wavelength circular nano-aperture can produce giant CD when a vortex beam is used to excite it. These measurements can be understood by studying the symmetries of the sample and the total angular momentum that vortex beams carry. Our results show that CD can provide a wealth of information about the sample when combined with the control of the total angular momentum of the input field.

  20. Effects of symmetry on circular and linear magnetic dichroism in angle-resolved photoemission spectra of Gd/Y (0001) and Fe-Ni//Cu (001)

    Energy Technology Data Exchange (ETDEWEB)

    Goodman, K.W.; Tobin, J.G.; Schumann, F.O. [Pennsylvania State Univ., University Park, PA (United States); Willis, R.F. [Pennsylvania State Univ., University Park, PA (United States); Gammon, J.W. [Virginia Commonwealth Univ., Richmond, VA (United States); Pappas, D.P. [Virginia Commonwealth Univ., Richmond, VA (United States); Kortright, J.B. [Lawrence Berkeley National Lab., CA (United States); Denlinger, J.D. [Lawrence Berkeley National Lab., CA (United States); Rotenberg, E. [Lawrence Berkeley National Lab., CA (United States); Warwick, A. [Lawrence Berkeley National Lab., CA (United States); Smith, N.V. [Lawrence Berkeley National Lab., CA (United States)

    1997-03-26

    We have observed circular and linear magnetic dichroism in angle- resolved photoemission spectra of 50-monolayer Gd film grown on Y(0001) and 6-monolayer Fe-Ni alloy films grown on Cu(001). The 4f level of Gd and the Fe 3p level of the Fe-Ni alloy were measured. A different geometry was used for the magnetic circular dichroism than was used to measure the magnetic linear dichroism. The geometries were chosen so that the shape of the magnetic circular dichroism is predicted to be equal to the shape of the magnetic linear dichroism for four-fold symmetric Fe-Ni/Cu(001) but not for three-fold symmetric Gd/Y(0001). Experimental results are presented. In this paper we examine the effect of symmetry (experimental geometry and sample geometry) on magnetic linear and circular dichroism in angle- resolved photoemission. In particular we chose separate geometries for measuring magnetic circular and magnetic linear dichroism. The geometries were chosen such that samples with four-fold symmetry about the sample normal may have magnetic circular and magnetic linear dichroism of the same shape. But samples with three-fold symmetry should not exhibit circular and magnetic linear dichroism of the same shape. The samples studied are three-fold symmetric Gd films grown on Y(0001) and four-fold symmetric Fe-Ni alloy grown on Cu(001). After presenting the methods of the experiment, we briefly review parts of a model of magnetic dichroism developed by Venus and coworkers and our specialization and extension of it, particularly for FeNi/Cu(001). We then show the results of our measurements.

  1. Nucleic acid vibrational circular dichroism, absorption, and linear dichroism spectra. II. A DeVoe theory approach.

    OpenAIRE

    Self, B D; Moore, D S

    1998-01-01

    The DeVoe polarizability theory is used to calculate vibrational circular dichroism (VCD) and infrared (IR) absorption spectra of four polyribonucleotides: poly(rA) x poly(rU), poly(rU) x poly(rA) x poly(rU), poly(rG) x poly(rC), and poly(rC+) x poly(rI) x poly(rC). This is the first report on the use of the DeVoe theory to calculate VCD, oriented VCD, IR absorption, and IR linear dichroism (LD) spectra of double- and triple-stranded polyribonucleotides. Results are reported for DeVoe theory ...

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

    Energy Technology Data Exchange (ETDEWEB)

    Lehmann, C. Stefan; Ram, N. Bhargava; Janssen, Maurice H. M., E-mail: m.h.m.janssen@vu.nl [LaserLaB Amsterdam, VU University Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam (Netherlands); Powis, Ivan [School of Chemistry, University of Nottingham, Nottingham NG7 2RD (United Kingdom)

    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

  3. Chiroptical studies on brevianamide B: vibrational and electronic circular dichroism confronted

    OpenAIRE

    Bultinck, Patrick; Cherblanc, Fanny L.; Fuchter, Matthew J.; Herrebout, Wouter A; Lo, Ya-Pei; Rzepa, Henry S; Siligardi, Giuliano; Weimar, Marko

    2015-01-01

    Chiroptical spectroscopy, such as electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) are highly sensitive techniques to probe molecular conformation, configuration, solvation and aggregation. Here we report the application of these techniques to study the fungal metabolite brevianamide B. Comparison of the experimental ECD and VCD spectra with the density functional theory (DFT) simulated counterparts establishes that VCD is the more reliable technique to assign abso...

  4. Magnetic circular X-ray dichroism in amorphous Fe-RE alloys

    International Nuclear Information System (INIS)

    Magnetic circular X-ray dichroism and X-ray absorption near-edge structures were measured at the rare-earth (RE) L3,2 edges in amorphous Fe-RE alloys (RE=Pr, Sm, Gd, Tb and Dy). The Gd 5d spin and orbital moments in the amorphous 80 at% Fe-Gd alloy are evaluated to be about 0.39μB and -0.02μB per atom at room temperature using the sum rules. ((orig.))

  5. X-ray magnetic circular dichroism in (Ge,Mn) compounds: Experiments and modeling

    International Nuclear Information System (INIS)

    X-ray absorption (XAS) and x-ray magnetic circular dichroism (XMCD) spectra at the L2,3 edges of Mn in (Ge,Mn) compounds have been measured and are compared to the results of first principles calculation. Early ab initio studies show that the Density Functional Theory (DFT) can very well describe the valence band electronic properties but fails to reproduce a characteristic change of sign in the L3 XMCD spectrum of Mn in Ge3Mn5, which is observed in experiments. In this work we demonstrate that this disagreement is partially related to an underestimation of the exchange splitting of Mn 2p core states within the local density approximation. It is shown that the change in sign experimentally observed is reproduced if the exchange splitting is accurately calculated within the Hartree–Fock approximation, while the final states can be still described by the DFT. This approach is further used to calculate the XMCD in different (Ge,Mn) compounds. It demonstrates that the agreement between experimental and theoretical spectra can be improved by combining state of the art calculations for the core and valence states respectively. - Highlights: • X-ray absorption and magnetic circular dichroism spectra are measured and compared to first principles calculations in (Ge,Mn) compounds. • Standard density functional theory fails in properly describing peculiar features observed in the experiment. • A new approach to calculate theoretical X-ray absorption and magnetic circular dichroism spectra is proposed. • Improved modeling of the core levels splitting using the Hartree–Fock approximation allows for a better matching with the experiment. • This new method could be generalized to any 3d metallic-like system

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

    Science.gov (United States)

    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

  7. The design and commissioning of the vacuum-ultraviolet circular dichroism facility at NSRL

    International Nuclear Information System (INIS)

    This paper describes the design and commissioning of the vacuum-ultraviolet circular dichroism facility at NSRL. At 0.5nm resolution, the normal incident beamline can provide ultraviolet and vacuum-ultraviolet radiation at fluxes higher than 1012ph/s, which is converted into the plane polarized light using a polarizer and subsequently converted into the circularly polarized light using a photoelastic modulator with a switching frequency of 50 kHz. Example spectra of (1s)-(+)-10-camphorsulphonic acid (CSA) and myoglobin are given. Normally, the measurable wavelength range is 178--300 nm. But the short wavelength limit can be shifted to 140nm by using special solvent and short light-pass sample cell. (authors)

  8. Extreme optical activity and circular dichroism of chiral metal hole arrays

    CERN Document Server

    Gorkunov, M V; Artemov, V V; Rogov, O Y; Yudin, S G

    2014-01-01

    We report extremely strong optical activity and circular dichroism exhibited by subwavelength arrays of four-start-screw holes fabricated with one-pass focused ion beam milling of freely suspended silver films. Having the fourth order rotational symmetry, the structures exhibit the polarization rotation up to 90 degrees and peaks of full circular dichroism and operate as circular polarizers within certain ranges of wavelengths in the visible. We discuss the observations on the basis of general principles (symmetry, reciprocity and reversibility) and conclude that the extreme optical chirality is determined by the chiral localized plasmonic resonances.

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

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

    2013-08-01

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

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

    International Nuclear Information System (INIS)

    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

  12. Estimation of protein secondary structure from synchrotron radiation circular dichroism (SRCD) spectroscopy with five methods

    International Nuclear Information System (INIS)

    To study the nanosafety issues, we integrate several different techniques including nuclear techniques such as nuclear analytical method, synchrotron radiation analyses, biological techniques, and nanotechniques, etc., applying to explore interactions of nanoparticles on the protein and DNA. Circular dichroism (CD) is a measure of the difference in absorption of left- and right- polarized light as it passes through an optically active or chiral sample. Optical activity arises due to the influence of neighbouring groups on the electronic structure of a chromophore involved in an electronic transition. Electronic transitions span a large wavelength range, including the near UV (from 300 to 250 nm), the far UV (from 250 to 190 nm) and the VUV (from 190 to 178 nm). CD has found its principal application in studies of protein secondary structures (α-helical, β-strand, β-turn, and Unordered) because the shape of a CD spectrum is related to the geometry of the polypeptide backbone. The data in the region around 190 nm are potentially very valuable as they can provide information on sheet and aperiodic structures, and helix effects dominate the higher-wavelength data. Generally, conventional CD (CCD) instruments can detect transitions in the 300-200 nm, but the signals in the VUV region go beyond the CCD research. Using the synchrotron radiation circular dichroisrn (SRCD) with a vacuum environment instrument, the data in the VUV region can be obtained. Five methods (CONTINLL, SELCON3, CDSSTR, VARSLC, and K2D) based on deferent arithmetic, models and reference protein. databases are used to analyze the circular dichroism spectra. CONTINLL, SELCON3, CDSSTR, and VARSLC methods are the development of SVD algorithm in different sides; otherwise K2D is one of a few neural network programmes. In order to establish perfect experiment and data-analysis system for circular dichroism spectraphotometer of Beijing Synchrotron Radiation Facility (BEPC), comparison and estimation of

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

    International Nuclear Information System (INIS)

    UV-CD12 at ANKA and its current end-station are described, with a standard module for vacuum-UV synchrotron radiation circular dichroism of bio-macromolecules in the liquid state, and a unique module for macroscopically oriented lipid membranes (oriented circular dichroism). 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

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

    Energy Technology Data Exchange (ETDEWEB)

    Bürck, Jochen, E-mail: jochen.buerck@kit.edu; Roth, Siegmar; Windisch, Dirk; Wadhwani, Parvesh; Moss, David [Karlsruhe Institute of Technology (KIT), POB 3640, D-76021 Karlsruhe (Germany); Ulrich, Anne S., E-mail: jochen.buerck@kit.edu [Karlsruhe Institute of Technology (KIT), POB 3640, D-76021 Karlsruhe (Germany); Karlsruhe Institute of Technology (KIT), Fritz-Haber-Weg 6, D-76131 Karlsruhe (Germany)

    2015-04-11

    UV-CD12 at ANKA and its current end-station are described, with a standard module for vacuum-UV synchrotron radiation circular dichroism of bio-macromolecules in the liquid state, and a unique module for macroscopically oriented lipid membranes (oriented circular dichroism). 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.

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

    CERN Document Server

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

    2014-01-01

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

  16. Surface plasmon resonance coupled circular dichroism of DNA–gold nanorods assembly

    International Nuclear Information System (INIS)

    Linker mediated self-assembly of gold nanoparticles is emerging as an interesting strategy for construction of hybrid nanoscale systems with enhanced plasmonic circular dichroism (PCD) signals. Herein, gold nanorods were assembled via DNA linker to investigate the possibility of signal enhancement. Assemblies were characterized by UV–visible, fluorescence, dynamic light scattering and circular dichroism (CD) spectroscopy. Hybridization of complementary strands resulted in PCD signal enhancement, which was further monitored by the increase of real time PicoGreen fluorescence intensity. Impressively, such changes in the real time fluorescence and plasmonic CD responses could be used as a new detection method for ultrasensitive sensors. (paper)

  17. Vibrational Circular Dichroism (VCD) Reveals Subtle Conformational Aspects and Intermolecular Interactions in the Carnitine Family.

    Science.gov (United States)

    Mazzeo, Giuseppe; Abbate, Sergio; Longhi, Giovanna; Castiglioni, Ettore; Villani, Claudio

    2015-12-01

    Vibrational circular dichroism spectra (VCD) in the mid-IR region and electronic circular dichroism (ECD) spectra for three carnitine derivatives in the form of hydrochloride salts were recorded in deuterated methanol solutions. Density Functional Theory calculations help one to understand the significance of the observed VCD bands. VCD and ECD spectra are informative about the absolute configuration of the molecule, but VCD data reveal also some conformational aspects in the N,N,N-trimethyl moiety and inform us about intermolecular interactions gained from the carbonyl stretching region for the acyl substituted carnitines. PMID:26447810

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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.

  20. Magneto-optical measurement of spin-lattice relaxation time in KBr and in the Na and Cs halogenetes and Co++ ion magnetic circular dichroism study in KCl

    International Nuclear Information System (INIS)

    A magnetic circular dicroism spectrometer is described, which was used in the following experiments: 1) The spin-lattice relaxation time (T1) for F centers in NaCl, NaBr, CsBr and CsCl, at 1,80K in magnetic fields up to 15000Gs is described. The suitability of the theory of ref. (08) to explain the differences observed for halides of differents alkali ions as well as for different structures is verified proves that the hyperfine interaction is the most important mechanism for this kind of centers. It is also verified that, for temperatures between 60K and 150K, T1 experimental values fits the theory of ref. (21) reasonably well, for F centers in KBr. This theory us an extension of that of ref. (8). 2) The MCD spectra for KCl:Co++ and Caf2:Co++ in different magnetic fields up to 56KGs, and in temperature range between 1,80K and 4,20K is obtained. The results are consistent with the assumption that Co++ centers are intersticial in KCl lattice

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

    OpenAIRE

    Lees Jonathan G; Janes Robert W

    2008-01-01

    Abstract 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 method...

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  4. Synthesis and structural study of sugar derivatives of oligopyrroles using circular dichroism

    Czech Academy of Sciences Publication Activity Database

    Štěpánek, P.; Kaminský, Jakub; Šimák, Ondřej; Drašar, P.

    2012-01-01

    Roč. 106, - (2012), s1354-s1354. ISSN 0009-2770. [EuCheMS Chemistry Congress /4./. 26.08.2012-30.08.2012, Prague] Institutional research plan: CEZ:AV0Z40550506 Keywords : circular dichroism * C-Glycosides * supramolecular chemistry Subject RIV: CC - Organic Chemistry

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

    Directory of Open Access Journals (Sweden)

    H.H. Klump

    2010-01-01

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

  6. DNA electronic circular dichroism on the inter-base pair scale

    DEFF Research Database (Denmark)

    Di Meo, Florent; Nørby, Morten Steen; Rubio-Magnieto, Jenifer;

    2015-01-01

    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...

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

    Science.gov (United States)

    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…

  8. RNA structural forms studied by vibrational circular dichroism: Ab initio interpretation of the spectra

    Czech Academy of Sciences Publication Activity Database

    Andrushchenko, V.; Wieser, H.; Bouř, Petr

    2004-01-01

    Roč. 108, - (2004), s. 3899-3911. ISSN 1089-5647 R&D Projects: GA AV ČR IAA4055104; GA ČR GA203/01/0031 Institutional research plan: CEZ:AV0Z4055905 Keywords : vibrational circular dichroism * RNA Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.679, year: 2003

  9. Comparison of Vibrational Circular Dichroism Instruments: Development of a New Dispersive VCD

    Czech Academy of Sciences Publication Activity Database

    Lakhani, A.; Maloň, Petr; Keiderling, T. A.

    2009-01-01

    Roč. 63, č. 7 (2009), s. 775-785. ISSN 0003-7028 Institutional research plan: CEZ:AV0Z40550506 Keywords : vibrational circular dichroism * VCD * dispersive infrared spectroscopy * peptides Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.564, year: 2009

  10. Conformational flexibility of Corey lactone derivatives indicated by absorption and vibrational circular dichroism spectra

    Czech Academy of Sciences Publication Activity Database

    Tománková, Z.; Setnička, V.; Urbanová, M.; Matějka, P.; Král, V.; Volka, K.; Bouř, Petr

    2004-01-01

    Roč. 69, č. 1 (2004), s. 26-32. ISSN 0022-3263 R&D Projects: GA AV ČR IAA4055104; GA ČR GA203/01/0031 Institutional research plan: CEZ:AV0Z4055905 Keywords : vibrational circular dichroism * lactone Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.462, year: 2004

  11. Vibrational circular dichroism of nucleic acids: Combination of theory and experiment

    Czech Academy of Sciences Publication Activity Database

    Andrushchenko, Valery; Wieser, H.; Bouř, Petr

    Pisa : -, 2012. s. 46-46. [CECAM 2012. International Conference on Vibrational Optical Activity: Interplay of Theory and Experiment /3./. 23.09.2012-27.09.2012, Pisa] Institutional support: RVO:61388963 Keywords : vibrational circular dichroism * VCD spectroscopy Subject RIV: CF - Physical ; Theoretical Chemistry

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

    DEFF Research Database (Denmark)

    Lassen, Peter Rygaard

    2006-01-01

    Chiral molecules, i.e., molecules with handedness, are essential to biology, because most amino acids and sugars are chiral. A pair of molecules which are mirror images of each other have identical physical properties, but they differ in their interaction with other chiral molecules. This is the...... cornerstone of biological specificity. Chiral molecules also interact differently with different polarization states of electromagnetic radiation, because the absorption coefficient depends on the state of polarization. This is called dichroism and gives rise to several spectroscopic techniques targeting...... compounds of pharmaceutical interest. Others are transition metal complexes relevant for the search for parity-violation effects in vibrational spectroscopy (rhenium complexes), for asymmetric catalysis (Schiff-base complexes), or as model systems for metal centres in biology (Schiff-bases and heme...

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

    CERN Document Server

    Takahashi, S; Ota, Y; Tatebayashi, J; Iwamoto, S; Arakawa, Y

    2014-01-01

    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 degrees 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 1300 nm. The obtained results show good agreement with numerical simulations.

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

    International Nuclear Information System (INIS)

    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

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

    Science.gov (United States)

    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

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

    OpenAIRE

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

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

    OpenAIRE

    Li Hu; Yingzhou Huang; Liang Fang; Guo Chen; Hua Wei; Yurui Fang

    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 la...

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

    CERN Document Server

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

    2016-01-01

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

  19. Emerging Magneto-Optic Spectroscopy: Nuclear Spin-Induced Circular Dichroism in Fullerenes

    Czech Academy of Sciences Publication Activity Database

    Štěpánek, Petr; Vaara, J.; Coriani, S.; Straka, Michal

    Opole: -, 2014. P11. [MMNB 2014. Polish-Taiwanese Conference. From Molecular Modeling to Nano- and Biotechnology. 04.09.2014-06.09.2014, Opole] R&D Projects: GA ČR(CZ) GA14-03564S; GA ČR GA13-03978S Institutional support: RVO:61388963 Keywords : nuclear spin circular dichroism * fullerene * nuclei-specific signal Subject RIV: CF - Physical ; Theoretical Chemistry

  20. Circular magnetic dichroism of the Fa center adsorption in KCl doped with Li and Na

    International Nuclear Information System (INIS)

    The spin-orbit structure of FA in KCl:Li and KCl:Na have been studied by means of the magnetic circular dichroism. Due to their C4V, symmetry the FA centers have two different spin-orbit parameters, Δ* and Δ*, which only in the KCl:Li case follow the relation: Δ* F A centers have been determined using the method of moment

  1. Circular dichroism spectra of langasite family crystals in the range of electronic transitions of structure defects

    International Nuclear Information System (INIS)

    The absorption and circular dichroism spectra of langasite family crystals are studied. Wide bands in the range of 285-500 nm that are related to the structure lattice defects are found. For all the crystals, these bands are in approximately the same spectral region, have identical structures, and can be attributed to one type of defects formed by cation vacancies and excess oxygen atoms in the optically active positions.

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

    OpenAIRE

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

    2013-01-01

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

  3. Elucidating the backbone conformation of photoswitchable foldamers using vibrational circular dichroism

    OpenAIRE

    Domingos, S.R.; Roeters, S.J.; Amirjalayer, S.; Yu, Z.L.; Hecht, S; Woutersen, S.

    2013-01-01

    The backbone conformation of amphiphilic oligo(azobenzene) foldamers is investigated using vibrational circular dichroism (VCD) spectroscopy on a mode involving the stretching of the N=N bonds in the backbone. From denaturation experiments, we find that the VCD response in the helical conformation arises mainly from through-space interaction between the N=N-stretch transition-dipole moments, so that the coupled-oscillator model can be used to predict the VCD spectrum associated with a particu...

  4. Vibrational circular dichroism of 1,1'-binaphthyl derivatives: experimental and theoretical study

    Czech Academy of Sciences Publication Activity Database

    Setnička, V.; Urbanová, M.; Bouř, Petr; Král, V.; Volka, K.

    2001-01-01

    Roč. 105, - (2001), s. 8931-8938. ISSN 1089-5639 R&D Projects: GA ČR GA203/97/P002; GA ČR GA203/01/0031; GA AV ČR IAA4055104 Institutional research plan: CEZ:AV0Z4055905 Keywords : vibrational circular dichroism Subject RIV: CE - Biochemistry Impact factor: 2.630, year: 2001

  5. Circular Dichroism Enhancement in Large DNA Aggregates Simulated by a generalized oscillator model

    Czech Academy of Sciences Publication Activity Database

    Andrushchenko, Valery; Bouř, Petr

    2008-01-01

    Roč. 29, č. 16 (2008), s. 2693-2703. ISSN 0192-8651 R&D Projects: GA ČR GA203/06/0420; GA ČR GA202/07/0732; GA AV ČR IAA400550702 Institutional research plan: CEZ:AV0Z40550506 Keywords : DNA * circular dichroism * oscillator model Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.390, year: 2008

  6. A critical assessment of possible pitfalls in absolute configuration assignment using Vibrational Circular Dichroism

    OpenAIRE

    Debie, Elke

    2009-01-01

    Vibrational Circular Dichroism (VCD) is no longuer a curious novelty in the field of molecular spectroscopy as VCD spectrometers are commercially available as well as the algorithms to calculate the spectra, which are implemented in various software packages. This makes VCD routinely applicable for the determination of absolute configurations. The VCD technique is gaining interest in mainly pharmaceutical industry and the technique also has been accepted by regulatory agencies (e.g. FDA) as a...

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

    Science.gov (United States)

    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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2005-04-01

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

  9. Theoretical computations of vibrational circular dichroism (VCD) and IR spectra of oligonucleotides and comparison with experimental results

    Czech Academy of Sciences Publication Activity Database

    Andrushchenko, V.; Wieser, H.; Bouř, Petr

    Toronto, 2002. s. 77. [International Symposium on Bioorganic Chemistry /6./. 11.08.2002-14.08.2002, Toronto] Institutional research plan: CEZ:AV0Z4055905 Keywords : vibrational circular dichroism Subject RIV: CE - Biochemistry

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

    International Nuclear Information System (INIS)

    Here we present several low energy conformers of Leu-enkephalin (LeuE) calculated with the density functional theory using the Becke 3LYP hybrid functional and the 6-31G* basis set. The structures, conformational energies, vibrational frequencies, vibrational absorption (VA) intensities, vibrational circular dichroism (VCD) intensities and Raman scattering intensities are reported for the conformers of LeuE which are expected to be populated at room temperature. The species of LeuE present in non-polar solvents is the neutral non-ionic species with the NH2 and CO2H groups, in contrast to the zwitterionic neutral species with the NH3+ and CO2- groups which predominates in aqueous solution and in the crystal. All of our attempts to find the zwitterionic species in the isolated state failed, with the result that a hydrogen atom from the positively charged N-terminus ammonium group transferred either to one of the oxygens of the carboxylate group of the C-terminus or to the oxygen of the amide group of one of the other residues. Hence we conclude that the zwitterionic species of LeuE is not stable in the isolated state. Spectral simulations of the species expected to be found in the isolated state can be compared to the measured VA, VCD and Raman spectra of LeuE in non-polar solvents to identify which conformer or conformers of LeuE are present in these media. Characteristic features in the VCD spectra are more sensitive to conformational changes than those in either the VA or Raman spectra, similar to the characteristic features in electronic circular dichroism spectra with respect to those in the UV-vis electronic absorption spectra. Finally, we have also attempted to stabilize the zwitterionic species by treating the aqueous environment by using a continuum solvent approach, the Onsager model. Here we found that the zwitterionic species is now stable. The neutral species in an aqueous environment was also modelled by the continuum solvent approaches to determine the

  11. Magnetic Circular Dichroism spectroscopy in epitaxial La0.7Sr0.3MnO3 thin films

    OpenAIRE

    Nath, T. K.; Neal, J. R.; G A Gehring

    2008-01-01

    Magneto optic measurements are a very powerful tool for investigating the polarization of a conduction band as a function of temperature and are used here to study the polarization of the mobile electrons in 50nm LSMO (x=0.3) strained thin films grown epitaxially on single crystalline (001) LaAlO3 (LAO) and (001) lattice matched substrate (LSAT). The magnetic circular dichroism (MCD) has been investigated in magnetic fields up to 0.5 T and over a temperature range (10 to 450 K). The MCD spect...

  12. Magnetic exchange coupling in 3d-4f molecular nanomagnets investigated by X-ray magnetic circular dichroism

    International Nuclear Information System (INIS)

    Full text: Single-molecule magnets are exchange-coupled spin clusters showing slow relaxation of magnetization. In recent years, efforts have been intensified to increase the magnetization reversal barrier and thus enhance relaxation times by combining rare earth ions with transition-metal ions. Rare-earth ions exhibit very large magnetic anisotropies due to their strong spin-orbit coupling and their mostly unquenched orbital momentum. In this contribution we use X-ray magnetic circular dichroism to observe element-specific magnetization curves. In conjunction with SQUID magnetization and susceptibility measurements, we are able to obtain information about the magnetic coupling between 3d and 4f ions. (author)

  13. X-ray magnetic circular dichroism study of Re 5d magnetism in Sr2CrReO6

    OpenAIRE

    Majewski, P.; Gepraegs, S.; Sanganas, O.; Opel, M.; Gross, R.; Wilhelm, F; Rogalev, A.; Alff, L.

    2006-01-01

    We have measured Re 5d spin and orbital magnetic moments in the ferrimagnetic double perovskite Sr2CrReO6 by X-ray magnetic circular dichroism at the L_{2,3} edges. In fair agreement with recent band-structure calculations [Vaitheeswaran et. al., Ref 1], at the Re site a large 5d spin magnetic moment of -0.68 mu_B and a considerable orbital moment of +0.25 mu_B have been detected. We found that the Curie temperature of the double perovskites A2BB'O6 scales with the spin magnetic moment of the...

  14. Vibrational circular dichroism of A-, B-, and Z-form nucleic acids in the PO2-stretching region.

    OpenAIRE

    Wang, L.; Yang, L; Keiderling, T A

    1994-01-01

    Vibrational circular dichroism (VCD) spectra were measured for H2O solutions of several natural and model DNAs (single and double strands, oligomers and polymers) in the B-form, poly(dG-dC)-poly(dG-dC) in the Z-form, and various duplex RNAs in an A-form over the PO2-stretching region. Only the symmetric PO2 stretch at approximately 1075 cm-1 yields a significant intensity VCD signal. Differences of the PO2-stretching VCD spectra found for these conformational types are consistent with the spe...

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

    DEFF Research Database (Denmark)

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

    2009-01-01

    A detailed study of the magnetic circular dichroism (MCD) spectra of weakly exchange coupled transition metal heterodimers is reported. The systems consist of three isostructural complexes of the type [LM(III)(PyA)(3)M(II)](ClO4)(2) where L represents 1,4,7-trimethyl-1,4,7-triazacyclonanane and Py......A- is the monoanion of pyridine-2-aldoxime. The trivalent metal ion M(III) is either diamagnetic Ga(III) or paramagnetic Cr(III) (S-Cr = 3/2). The divalent metal ion M(II) is either diamagnetic Zn(II) or paramagnetic Ni(II) (S-Ni = 1). The three systems 1 (CrZn), 2 (GaNi) and 3 (CrNi) have been...... structurally and magnetically characterized through magnetic susceptibility measurements. For I the zero-field splitting is D = 0.6 cm(-1) while for 2 the value D = 3.5 cm(-1) was found. These values have been fixed in analyzing 3 which was found to be characterized by an antiferromagnetic interaction Of J(CrNi...

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

    Science.gov (United States)

    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

  17. Magnetic Circular Dichroism in Resonant Raman Scattering in the Perpendicular Geometry at the L edge of 3d Transition Metal Systems

    International Nuclear Information System (INIS)

    We measured circular dichroism in resonant x-ray scattering 3dn→2p53dn+1→3s13dn+1 with incidence perpendicular to the magnetization where the absorption dichroism vanishes. The advantages of photon scattering over other techniques make it possible to study a wide range of materials. The Ni L3 dichroism in NiFe2O 4 is (28±5)% in agreement with a localized model. In the metal Co the dichroism is reduced to (10.4±1)% (L3) and (6.8±1.5)% (7.5 eV above L3 ), indicating a large sensitivity to the nature of the valence states despite the fact that this spectroscopy is based on inner shell transitions. copyright 1999 The American Physical Society

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

    DEFF Research Database (Denmark)

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

    2015-01-01

    We present a computational methodology to calculate the intensity of circular dichroism (CD) in spinforbidden absorption and of circularly polarized phosphorescence (CPP) signals, a manifestation of the optical activity of the triplet–singlet transitions in chiral compounds. The protocol is based...... 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 b,g-enones under investigation, where there are two minima on the lowest triplet excited state potential energy surface, each minimum exhibits a CPP signal of a different sign....

  19. Vibrational circular dichroism and chiroptical properties of chiral Ir(iii) luminescent complexes.

    Science.gov (United States)

    Mazzeo, Giuseppe; Fusè, Marco; Longhi, Giovanna; Rimoldi, Isabella; Cesarotti, Edoardo; Crispini, Alessandra; Abbate, Sergio

    2016-01-21

    The octahedral ionic Ir(iii) complex with a dual stereogenic centre of general formula Δ,Λ-(R,S)-[(ppy)2Ir(Me-Campy)]X, where ppy = 2-phenylpyridine and Me-Campy = 2-methyl-5,6,7,8-tetrahydroquinolin-8-amine, and the complex Λ-(R,S)-[(ppy)2Ir(H-Campy)]X, where ppy = 2-phenylpyridine, H-Campy = 8-amino-5,6,7,8-tetrahydroquinolines and X(-) = Cl(-) as a counterion in both cases, have been characterized by vibrational circular dichroism (VCD), which turns out to be efficacious in diastereomeric discrimination. Moreover, the single crystal X-ray structure of the complex Δ-(R)-[(ppy)2Ir(Me-Campy)]Cl is reported here. Density functional theory (DFT) calculations allow us to conclude that the most important doublet feature in the VCD spectra is associated with a clear vibrational exciton structure located on the two dissymmetrically disposed phenylpyridine ligands. The features in the VCD spectra associated with the (R) or (S)-central chirality configuration are identified and commented on. DFT calculations provide also the interpretation of electronic circular dichroism (ECD) spectra. Finally, circularly polarized luminescence (CPL) spectra are presented as an additional chiroptical characterization of these luminescent iridium complexes. PMID:26647994

  20. Circularity-Measuring System

    Science.gov (United States)

    WHIPPO. WALTER B.; Rohrkaste, G. R.; Miller, John E.

    1989-01-01

    Shape gauge and associated computer constitute system measuring deviations of large cylinders from roundness. Shaped and held somewhat like crossbow, measures relative locations of three points on surface of large, round object. By making connected series of measurements around periphery technician using gauge determines deviation of object from perfect circularity. Used to measure straightness, roundness, or complicated shapes of such large geometrical objects as surfaces of aircraft and hulls of ships.

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

    Science.gov (United States)

    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

  2. Study on interactions between nanoparticles and DNA by synchrotron radiation circular dichroism (SRCD)

    International Nuclear Information System (INIS)

    Fullerenic derivatives have attracted considerable attention, in particular, in the field of biomedical applications. Due to the unique structure, fullerenes exhibit intriguing biological activities. In solution, fullerenic derivatives exist as nanoparticles because of the molecular interactions. But how nanoparticles act with the biological molecules, this is an important issue that direct influences any of the biomedical applications in practice. Here we investigate how nanoparticles induce the conformational transition of the protein and DNA by the synchrotron radiation circular dichroism (SRCD). Circular dichroism (CD) is now widely used to study biological systems. Its spectral studies in the far UV region (180 nm - 250 nm) can probe the secondary structures of proteins, and in the near UV region(∼250 and ∼350) can monitor the side chain tertiary structures of proteins. Using circular dichroism spectraphotometer of Beijing Synchrotron Radiation Facility (BEPC), as well as some proteins' secondary structures, we successfully obtained the information of the changes in the secondary structures of DNA after interactions with Gd doped C82(OH)x nanoparticles. The results revealed that manufactured Gd doped C82(OH)x nanoparticles induced conformational changes in proteins and DNA at a very low concentration. Furthermore, the nanoparticle-induced structural changes depend on the percentage of the secondary structures (a-helical, β-strand, β-turn, and unordered) of DNA. These observations provide us with important information that how Gd doped C82(OH)x nanoparticles act on the biological system at the molecular level, and are helpful for understanding biomedical functions as well as the nanosafety issue of these nanoparticles.

  3. Computation of magnetic circular dichroism by sum-over-states summations

    Czech Academy of Sciences Publication Activity Database

    Štěpánek, Petr; Bouř, Petr

    2013-01-01

    Roč. 34, č. 18 (2013), s. 1531-1539. ISSN 0192-8651 R&D Projects: GA ČR GAP208/11/0105; GA MŠk(CZ) LH11033; GA ČR GA13-03978S Grant ostatní: AV ČR(CZ) M200551205 Institutional support: RVO:61388963 Keywords : time-dependent * density functional theory * sum over states * spectroscopy * magnetic circular dichroism * origin dependence Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.601, year: 2013

  4. Beta sheets with a twist: the conformation of helical polyisocyanopeptides determined by using vibrational circular dichroism.

    Science.gov (United States)

    Schwartz, Erik; Liégeois, Vincent; Koepf, Matthieu; Bodis, Pavol; Cornelissen, Jeroen J L M; Brocorens, Patrick; Beljonne, David; Nolte, Roeland J M; Rowan, Alan E; Woutersen, Sander; Champagne, Benoît

    2013-09-23

    Detailed information on the architecture of polyisocyanopeptides based on vibrational circular dichroism (VCD) spectroscopy in combination with DFT calculations is presented. It is demonstrated that the screw sense of the helical polyisocyanides can be determined directly from the C=N-stretch vibrational region of the VCD spectrum. Analysis of the VCD signals associated with the amide I and amide II modes provides detailed information on the peptide side-chain arrangement in the polymer and indicates the presence of a helical β-sheet architecture, in which the dihedral angles are slightly different to those of natural β-sheet helices. PMID:23939984

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

    DEFF Research Database (Denmark)

    Jalkanen, Karl J.

    2003-01-01

    Here we present several low energy conformers of Leu-enkephalin (LeuE) calculated with the density functional theory using the Becke 3LYP hybrid functional and the 6-31G* basis set. The structures, conformational energies, vibrational frequencies, vibrational absorption (VA) intensities......, vibrational circular dichroism (VCD) intensities and Raman scattering intensities are reported for the conformers of LeuE which are expected to be populated at room temperature. The species of LeuE-present in non-polar solvents is the neutral non-ionic species with the NH2 and CO2H groups, in contrast to the...

  6. The connection between robustness angles and dissymmetry factors in vibrational circular dichroism spectra

    Science.gov (United States)

    Longhi, Giovanna; Tommasini, Matteo; Abbate, Sergio; Polavarapu, Prasad L.

    2015-10-01

    To analyze vibrational circular dichroism (VCD) spectra the angle between the electric and magnetic dipole transition moments was introduced as robustness index. We demonstrate that VCD for each normal mode can be made robust by a suitable translation of the coordinate system origin to a robust point. Normal modes differ in how VCD band robustness varies under translations from these respective robust points. It is shown that variation in robustness of a VCD band depends on a parameter inversely proportional to the dissymmetry factor g. Thus, robustness varies slowly for VCD bands with large dissymmetry factors and vice versa.

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

    Science.gov (United States)

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

    2016-01-01

    Elucidation of absolute configuration of chiral molecules including structurally complex natural products remains a challenging problem in organic chemistry. A reliable method for assigning the absolute stereostructure is to combine the experimental circular dichroism (CD) techniques such as electronic and vibrational CD (ECD and VCD), with quantum mechanics (QM) ECD and VCD calculations. The traditional QM methods as well as their continuing developments make them more applicable with accuracy. Taking some chiral natural products with diverse conformations as examples, this review describes the basic concepts and new developments of QM approaches for ECD and VCD calculations in solution and solid states. PMID:26880597

  8. Vibrational Circular Dichroism: Recent Advances for the Assignment of the Absolute Configuration of Natural Products.

    Science.gov (United States)

    Burgueño-Tapia, Eleuterio; Joseph-Nathan, Pedro

    2015-10-01

    Vibrational circular dichroism (VCD) emerged during the last decade as a reliable tool for the absolute configuration (AC) determination of organic compounds. The principles, instrumentation, and methodology applied prior to early 2013 were recently reviewed by us. Since VCD is a very dynamic field, the aim of this review is to update VCD advances for the AC assignment of terpenoids, aromatic compounds, alkaloids, and other natural products for the 2013-2014 period, when VCD was applied to the AC assignment of some 70 natural products. In addition, although discovered in 2012, a brief introduction to the VCD exciton coupling approach and its applications in natural products AC assignment is presented. PMID:26669125

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

    Directory of Open Access Journals (Sweden)

    Lees Jonathan G

    2008-01-01

    Full Text Available Abstract 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.

  10. X-ray magnetic circular dichroism strongly influenced by non-magnetic cover layers

    Energy Technology Data Exchange (ETDEWEB)

    Zafar, K.; Audehm, P.; Schütz, G. [Max-Planck-Institute for Intelligent Systems (Former Metals Research), Stuttgart 70569 (Germany); Goering, E., E-mail: goering@is.mpg.de [Max-Planck-Institute for Intelligent Systems (Former Metals Research), Stuttgart 70569 (Germany); Pathak, M.; Chetry, K.B.; LeClair, P.R.; Gupta, A. [MINT Center, University of Alabama, Tuscaloosa, AL 35487 (United States)

    2013-12-15

    Highlights: •Energy filtering gives much larger sampling depth and escape length as expected. •XMCD sum rules could be dramatically altered by this effect. •Strong enhanced effective escape length for buried layers. •A “universal curve” model gives semi quantitative understanding. •Buried layers are more sensitive to self-absorption phenomena. -- Abstract: Total electron yield (TEY) is the dominating measurement mode in soft X-ray absorption spectroscopy (XAS), where the sampling depth is generally assumed to be quite small and constant, and the related self-absorption or saturation phenomena are about to be negligible at normal incidence conditions. From the OK edge to CrL{sub 2,3} edge XAS ratio we determined a strong change in the effective electron escape length between an uncovered and a RuO{sub 2} covered CrO{sub 2} sample. This effect has been explained by a simple electron energy filtering model, providing a semi quantitative description. In addition, this simple model can quantitatively describe the unexpected reduced and positive CrL{sub 2,3} X-ray magnetic circular dichroism (XMCD) signal of a RuO{sub 2}/CrO{sub 2} bilayer, while previous results have identified a clear negative Cr magnetization at the RuO{sub 2}/CrO{sub 2} interface. In our case this escape length enhancement has strong impact on the XMCD sum rule results and in general it provides much deeper sampling depth, but also larger self-absorption or saturation effects.

  11. A Reference Database for Circular Dichroism Spectroscopy Covering Fold and Secondary Structure Space

    International Nuclear Information System (INIS)

    Circular Dichroism (CD) spectroscopy is a long-established technique for studying protein secondary structures in solution. Empirical analyses of CD data rely on the availability of reference datasets comprised of far-UV CD spectra of proteins whose crystal structures have been determined. This article reports on the creation of a new reference dataset which effectively covers both secondary structure and fold space, and uses the higher information content available in synchrotron radiation circular dichroism (SRCD) spectra to more accurately predict secondary structure than has been possible with existing reference datasets. It also examines the effects of wavelength range, structural redundancy and different means of categorizing secondary structures on the accuracy of the analyses. In addition, it describes a novel use of hierarchical cluster analyses to identify protein relatedness based on spectral properties alone. The databases are shown to be applicable in both conventional CD and SRCD spectroscopic analyses of proteins. Hence, by combining new bioinformatics and biophysical methods, a database has been produced that should have wide applicability as a tool for structural molecular biology

  12. Vibrational Circular Dichroism Spectra for Large Molecules through Molecules-in-Molecules Fragment-Based Approach.

    Science.gov (United States)

    Jose, K V Jovan; Beckett, Daniel; Raghavachari, Krishnan

    2015-09-01

    We present the first implementation of the vibrational circular dichroism (VCD) spectrum of large molecules through the Molecules-in-Molecules (MIM) fragment-based method. An efficient projection of the relevant higher energy derivatives from smaller fragments to the parent molecule enables the extension of the MIM method for the evaluation of VCD spectra (MIM-VCD). The overlapping primary subsystems in this work are constructed from interacting fragments using a number-based scheme and the dangling bonds are saturated with link hydrogen atoms. Independent fragment calculations are performed to evaluate the energies, Hessian matrix, atomic polar tensor (APT), and the atomic axial tensor (AAT). Subsequently, the link atom tensor components are projected back onto the corresponding host and supporting atoms through the Jacobian projection method, as in the ONIOM approach. In the two-layer model, the long-range interactions between fragments are accounted for using a less computationally intensive lower level of theory. The performance of the MIM model is calibrated on the d- and l-enantiomers of 10 carbohydrate benchmark molecules, with strong intramolecular interactions. The vibrational frequencies and VCD intensities are accurately reproduced relative to the full, unfragmented, results for these systems. In addition, the MIM-VCD method is employed to predict the VCD spectra of perhydrotriphenylene and cryptophane-A, yielding spectra in agreement with experiment. The accuracy and performance of the benchmark systems validate the MIM-VCD model for exploring vibrational circular dichroism spectra of large molecules. PMID:26575919

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2009-11-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2009-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2004-09-15

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

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

    Science.gov (United States)

    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

  17. Energy-dispersive phase plate for magnetic circular dichroism experiments in the X-ray range

    International Nuclear Information System (INIS)

    A 220 diamond phase plate was combined with an energy-dispersive absorption spectrometer to convert linearly polarized X-rays into circularly polarized photons and to detect circular magnetic X-ray dichroism (CMXD) from ferromagnetic samples. In these experiments, carried out at LURE, the energy-dispersive spectrometer was equipped with a bent Si (311) polychromator and vertically collimating slits accepting essentially a linearly polarized incident beam. The quarter-wave plate was operated in the Bragg geometry but well outside the range of quasi total reflection, with the consequence that the forward-diffracted beam was circularly polarized with a polarization rate approaching 80% over the whole energy bandpass of the polychromator. CMXD spectra of GdFe2 and GdCo2 intermetallic compounds were recorded at ca 7.2 keV near the Gd LIII absorption edge: they are essentially identical to the spectra commonly recorded with elliptically polarized X-ray photons collected out of the orbit plane of the storage ring. It is suggested that the energy-dispersive phase plate will be very useful to detect CMXD spectra with energy-dispersive spectrometers exploiting the well collimated linearly polarized emission of standard undulators installed on the storage rings of the third generation. (orig.)

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

    Science.gov (United States)

    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

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

    CERN Document Server

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

    2015-01-01

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

  20. Magnetocrystalline anisotropy in FePd alloys studied using transverse X-ray magnetic circular dichroism

    International Nuclear Information System (INIS)

    The structural and magnetic properties of Fe0.5Pd0.5 alloys have been correlated using X-ray diffraction (XD), vibrating sample magnetometry (VSM) and transverse X-ray magnetic circular dichroism (TXMCD) at the Pd L2,3 edges. XD indicates that codeposition of Fe and Pd, at elevated temperatures (350 deg. C), results in a well-ordered L10 phase which exhibits perpendicular magnetic anisotropy (PMA). On the other hand, codeposition at room temperature results in a disordered phase with in-plane easy-axis of magnetization. By codepositing at intermediate temperatures, a series of alloys has been produced with varying degree of compositional order. The TXMCD results show that increased compositional ordering leads to an increased orbital moment anisotropy favouring PMA. The magnetocrystalline anisotropy energy resulting from the orbital anisotropy is compared to VSM results

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

    CERN Document Server

    Ganesan, Aravindhan; Wang, Feng

    2013-01-01

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

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

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

    1999-05-01

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

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

    Science.gov (United States)

    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.

  5. Nitrogen K-edge soft X-ray natural circular dichroism of histidine thin film

    International Nuclear Information System (INIS)

    We report preliminary natural circular dichroism (NCD) spectra of amino acids, Land D-histidine, thin films in the nitrogen K-edge energy region. NCD peaks were observed at 399.9 eV and were assigned to the 1s → π* transition of the nitrogen atoms in imidazole ring. Imidazole ring is positioned at the side chain distant from the asymmetric carbon. This result suggests that NCD spectroscopy in the soft X-ray region can selectively pick up the information on local structure around specific atoms, regardless of the position of atoms in molecules. It is interesting in view of application of NCD spectroscopy in the soft X-ray region to investigation of protein structures.

  6. 5f-hybridization in URhAl studied by X-ray magnetic circular dichroism

    International Nuclear Information System (INIS)

    We report X-ray magnetic circular dichroism experiments performed at the U-M4,5 edges of an URhAl single crystal. Thanks to the sum-rules, we derive an orbital moment on the uranium atoms equal to (1.63±0.14)μB. The comparison of the shape of the M5 dichroic signal with pure J multiplet calculations shows effects due to 5f-hybridization. However, we found that the contribution of the magnetic dipole term left angle TZ right angle to the effective spin moment left angle SZeff right angle =(SZ right angle +3 left angle TZ right angle) is non negligible. These results indicate an higher localization of the 5f-orbitals with respect to other itinerant ferromagnetic actinides compounds such as UFe2 or UNi2. (orig.)

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

    CERN Document Server

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

    2016-01-01

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

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

    Directory of Open Access Journals (Sweden)

    Tatyana G Karabencheva-Christova

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

  9. Elucidating the backbone conformation of photoswitchable foldamers using vibrational circular dichroism.

    Science.gov (United States)

    Domingos, Sérgio R; Roeters, Steven J; Amirjalayer, Saeed; Yu, Zhilin; Hecht, Stefan; Woutersen, Sander

    2013-10-28

    The backbone conformation of amphiphilic oligo(azobenzene) foldamers is investigated using vibrational circular dichroism (VCD) spectroscopy on a mode involving the stretching of the N=N bonds in the backbone. From denaturation experiments, we find that the VCD response in the helical conformation arises mainly from through-space interaction between the N=N-stretch transition-dipole moments, so that the coupled-oscillator model can be used to predict the VCD spectrum associated with a particular conformation. Using this approach, we elucidate the origin of the VCD signals in the folded conformation, and can assign the observed partial loss of VCD signals upon photo-induced unfolding to specific conformational changes. Our results show that the N=N-stretch VCD response provides an excellent probe of the helical conformation of the N=N bonds in this type of switchable molecular system. PMID:24018416

  10. Switchable amplification of vibrational circular dichroism as a probe of local chiral structure.

    Science.gov (United States)

    Domingos, Sérgio R; Sanders, Hans J; Hartl, František; Buma, Wybren J; Woutersen, Sander

    2014-12-15

    A new method to detect the vibrational circular dichroism (VCD) of a localized part of a chiral molecular system is reported. A local VCD amplifier was implemented, and the distance dependence of the amplification was investigated in a series of peptides. The results indicate a characteristic distance of 2.0±0.3 bonds, which suggests that the amplification is a localized phenomenon. The amplifier can be covalently coupled to a specific part of a molecule, and can be switched ON and OFF electrochemically. By subtracting the VCD spectra obtained when the amplifier is in the ON and OFF states, the VCD of the local environment of the amplifier can be separated from the total VCD spectrum. Switchable local VCD amplification thus makes it possible to "zoom in" on a specific part of a chiral molecule. PMID:25212702

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    Sato, Hisako; Yajima, Tomoko; Yamagishi, Akihiko

    2016-05-01

    Vibrational circular dichroism (VCD) spectroscopy was applied to gelation by a chiral low-molecular mass weight gelator, N,N'-diperfluoroalkanoyl-1,2-trans-diaminocyclohexane. Attention was focused on the winding effects of (-CF2 )n chains on the gelating ability. For this purpose, a series of gelators were synthesized with perfluoroalkyl chains of different length (n = 6-8). When gelation was studied using acetonitrile as a solvent, the fibrils took different morphologies, depending on the chain length: twisted saddle-like ribbon or helical ribbon from fibril (n = 6) and a helical ribbon from platelet (n = 8). The signs of VCD peaks assigned to the couplet of C=O stretching and to the C-F stretching were also dependent on n, indicating that a gelator molecule changed conformation on elongating perfluoroalkyl chains. A model is proposed for the aggregation modes in fibrils. Chirality 28:361-364, 2016. © 2016 Wiley Periodicals, Inc. PMID:26992437

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

    Science.gov (United States)

    Dolamic, Igor; Varnholt, Birte; Bürgi, Thomas

    2015-05-01

    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.

  15. Enhanced sensitivity to conformation in various proteins. Vibrational circular dichroism results

    International Nuclear Information System (INIS)

    Vibrational circular dichroism (VCD) spectra of several globular proteins dissolved in D2O are presented and compared to conventional UV-CD results. It can be seen that, for the alpha, beta, and alpha + beta categories of Levitt and Chothia, VCD evidences much larger band shape variations, including sign alteration, than does UV-CD. A direct parallel is seen between the VCD of the alpha-helix found in model polypeptides and the amide I' VCD of myoglobin. Since all structural aspects of the protein contribute to the VCD on a roughly equal footing, a similar correlation of the chymotrypsin amide I' VCD with that of beta-sheet models is not as clear. In addition, the VCD of random-coil-type proteins is found to be clearly related to VCD results from random-coil polypeptides. Finally, simulations are presented to postulate the expected VCD for protein structures having conformations that lie between the limiting cases discussed here

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

    Science.gov (United States)

    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.

  17. Gigantic transverse x-ray magnetic circular dichroism in ultrathin Co in Au/Co/Au(001)

    International Nuclear Information System (INIS)

    Transverse-geometry x-ray magnetic circular dichroism (TXMCD) measurements on Au/Co-staircase/Au(001) reveal the orbital origin of intrinsic in-plane magnetic anisotropy A gigantic TXMCD was successfully observed at the Co L3,2 edges for Co thickness (tC0) in the 2-monolayer regime. A TXMCD-sum-rule analysis shows a remarkable enhancement of an orbital-moment anisotropy (Δmorb) and of an in-plane magnetic dipole moment (m||T). Both Δmorb and m||T exhibit close similarity in tCo dependence, reflecting the in-plane magnetic anisotropy These observations evidence that extremely strong, intrinsic, in-plane magnetic anisotropy originates from the anisotropic orbital part of the wave function, dominating the dipole-dipole-interaction-derived, extrinsic, in-plane magnetic anisotropy.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1998-01-23

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

  19. 4-Arylflavan-3-ols as Proanthocyanidin Models: Absolute Configuration via Density Functional Calculation of Electronic Circular Dichroism

    Science.gov (United States)

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

  20. Synthesis and vibrational circular dichroism of enantiopure chiral oxorhenium(V) complexes containing the hydrotris(1-pyrazolyl)borate ligand

    DEFF Research Database (Denmark)

    Lassen, Peter Rygaard

    2006-01-01

    The infrared and vibrational circular dichroism (VCD) spectra of six chiral oxorhenium(V) complexes, bearing a hydrotris(1-pyrazolyl)borate (Tp) ligand, have been investigated. These complexes are promising candidates for observation of parity violation (symmetry breaking due to the weak nuclear ...

  1. Theoretical computations of vibrational circular dichroism (VCD) and IR spectra of oligonucleotides and comparison with experimental results

    Czech Academy of Sciences Publication Activity Database

    Andrushchenko, V.; Wieser, H.; Bouř, Petr

    Lille : Université des Sciences et Technologies de Lille, 2002. s. 112. [European Congress on Molecular Spectroscopy /26./. 01.09.2002-06.09.2002, Villeneuve d'Ascq] Institutional research plan: CEZ:AV0Z4055905 Keywords : vibrational circular dichroism Subject RIV: CF - Physical ; Theoretical Chemistry

  2. (3 R ,4 S )-4-(4-fluorophenyl)-3-hydroxymethyl-1-methylpiperidine: conformation and structure monitoring by vibrational circular dichroism

    Czech Academy of Sciences Publication Activity Database

    Bouř, Petr; Navrátilová, H.; Setnička, V.; Urbanová, M.; Volka, K.

    2002-01-01

    Roč. 67, č. 1 (2002), s. 161-168. ISSN 0022-3263 R&D Projects: GA AV ČR IAA4055104; GA ČR GA203/01/0031 Institutional research plan: CEZ:AV0Z4055905 Keywords : vibrational circular dichroism Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.217, year: 2002

  3. Hydrogen bonding to carbonyl oxygen of nitrogen-pyramidalized amide - detection of pyramidalization direction preference by vibrational circular dichroism spectroscopy.

    Science.gov (United States)

    Wang, Siyuan; Taniguchi, Tohru; Monde, Kenji; Kawahata, Masatoshi; Yamaguchi, Kentaro; Otani, Yuko; Ohwada, Tomohiko

    2016-03-01

    Nitrogen-pyramidalization of amide increases electron density on nitrogen and decreases that on carbonyl oxygen. We identified hydrogen-bonding to carbonyl of nitrogen-pyramidalized bicyclic β-proline derivatives by crystallography, and by NMR and vibrational circular dichroism (VCD) spectroscopy in solution. Such hydrogen-bonding can switch the preferred nitrogen-pyramidalization direction, as detected by VCD spectroscopy. PMID:26889607

  4. B-Z conformational transition of DNA monitored by vibrational circular dichroism. Ab initio interpretation of the experiment

    Czech Academy of Sciences Publication Activity Database

    Andrushchenko, V.; Wieser, H.; Bouř, Petr

    2002-01-01

    Roč. 106, - (2002), s. 12623-12634. ISSN 1089-5647 R&D Projects: GA ČR GA203/01/0031; GA AV ČR IAA4055104 Institutional research plan: CEZ:AV0Z4055905 Keywords : vibrational circular dichroism Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.611, year: 2002

  5. Vibrational circular dichroism spectroscopy as a tool to study DNA structural changes: Experimental and computional approaches (Lecture)

    Czech Academy of Sciences Publication Activity Database

    Andrushchenko, Valery; Wieser, H.; Bouř, Petr

    Kharkiv : Institute of Radiophysics and Electronics NASU, 2007, 28/145. [Kharkiv Young Scientist Conference on Radiophysics and Electronics /7./. Kharkiv (UA), 12.12.2007-14.12.2007] Institutional research plan: CEZ:AV0Z40550506 Keywords : vibrational circular dichroism * DNA * RNA Subject RIV: CF - Physical ; Theoretical Chemistry www.ire.kharkov.ua/ysc

  6. TD-DFT Modeling of the Circular Dichroism for a Tryptophan Zipper Peptide with Coupled Aromatic Residues

    Czech Academy of Sciences Publication Activity Database

    Roy, A.; Bouř, Petr; Keiderling, T. A.

    2009-01-01

    Roč. 21, S1 (2009), E163-E171. ISSN 0899-0042 R&D Projects: GA ČR GA202/07/0732; GA AV ČR IAA400550702 Institutional research plan: CEZ:AV0Z40550506 Keywords : tryptophan * circular dichroism * TDDFT Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.677, year: 2009

  7. Circular and elliptical dichroism effects in two-photon disintegration of atoms and molecules

    International Nuclear Information System (INIS)

    Full text: Compact convenient for the analysis expressions for the cross sections considerably simplify studying the interaction of electromagnetic radiation with atomic systems and allow us to discover some fine effects. In the present paper on the basis of the general symmetry considerations taking only into account the dipole approximation and without any other approximations used in atomic calculations we derive the compact invariant expressions for the angular distribution of photoelectrons escaping from atoms or molecules in the process of two-photon ionization and for the angular distribution of fragments forming under two-photon two-particle dissociation of molecules. The dependence on all geometric parameters - the unit vector p determining the direction of photoelectron (photofragments in the case of dissociation) motion, k specifying the direction of propagation for the electromagnetic radiation and the unit complex vector e specifying polarization of the radiation - is completely separated in the angular distributions in the form of scalar and triple scalar products of the vectors. The information of the intrinsic structure of the atomic system is included in few constant dynamic parameters of the system that can independently be calculated using the well-known approximations. In case of atoms and optically inactive molecules the angular distributions contain the term linear in the pseudoscalar degree of circular polarization of the electromagnetic radiation ξik · (e x e*): ξaRe[k · (p x e)(p · e*)], where a is a scalar dynamic parameter of the atomic system. The term leads to the interesting effect of elliptical dichroism in the angular distribution of photoelectrons (photo-fragments of the molecule): under elliptical polarization of the radiation, 0 1ξk · p + b2ξk · p(|p · e|2 - 1/5), where b1 and b2 are the pseudoscalar dynamic parameters of the chiral molecule. The terms (2) do not vanish in case of circular polarization and, therefore

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

    Science.gov (United States)

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

    2016-05-01

    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.

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

    Science.gov (United States)

    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

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

    Directory of Open Access Journals (Sweden)

    Macduff O. Okuom

    2015-01-01

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

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

    International Nuclear Information System (INIS)

    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 (∼106-107 M-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

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

    Science.gov (United States)

    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.

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

    Directory of Open Access Journals (Sweden)

    Yoonkyung Park

    2012-03-01

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

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

    Science.gov (United States)

    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

  15. pH titration monitored by quantum cascade laser-based vibrational circular dichroism.

    Science.gov (United States)

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

    2014-04-10

    Vibrational circular dichroism (VCD) spectra of aqueous solutions of proline were recorded in the course of titrations from basic to acidic pH using a spectrometer equipped with a quantum cascade laser (QCL) as an infrared light source in the spectral range from 1320 to 1220 cm(-1). The pH-dependent spectra were analyzed by singular value decomposition and global fitting of a two-pK Henderson-Hasselbalch model. The analysis delivered relative fractions of the three different protonation species. Their agreement with the relative fractions obtained from performing the same analysis on pH-dependent Fourier transform infrared (FT-IR) and QCL-IR spectra validates the quantitative results from QCL-VCD. Global fitting of the pH-dependent VCD spectra of L-proline allowed for extraction of pure spectra corresponding to anionic, zwitterionic, and cationic L-proline. From a static experiment, only pure spectra of the zwitterion would be accessible in a straightforward way. A comparison to VCD spectra calculated for all three species led to assignment of vibrational modes that are characteristic for the respective protonation states. The study demonstrates the applicability of QCL-VCD both for quantitative evaluation and for qualitative interpretation of dynamic processes in aqueous solutions. PMID:24655319

  16. Magnetic properties of Fe nanoclusters on Cu(111) studied with X-ray magnetic circular dichroism

    Energy Technology Data Exchange (ETDEWEB)

    Fauth, Kai [Physikalisches Institut, Universitaet Wuerzburg (Germany); MPI for Metals Research, Stuttgart (Germany); Ballentine, Greg E. [MPI for Metals Research, Stuttgart (Germany); Praetorius, Christian [Physikalisches Institut, Universitaet Wuerzburg (Germany); Kleibert, Armin; Wilken, Norman; Voitkans, Andris; Meiwes-Broer, Karl-Heinz [Institute of Physics, University of Rostock (Germany)

    2010-05-15

    The magnetisation and magnetic response of Fe nanoclusters are studied by temperature and density dependent in situ X-ray magnetic circular dichroism after deposition onto Cu(111). The nanoclusters possess enhanced spin magnetic moments at low temperature, whereas no enhancement is found for the orbital moments. The analysis of magnetisation curves and the temperature dependent remnant magnetisation reveals that the individual magnetic anisotropy energies are distributed over a wide range of values, ranging from below to far above the value of bulk {alpha}-Fe. As a result, ferromagnetic response is obtained at ambient temperature, even though the nanocluster densities range well below percolation threshold. At higher cluster densities agglomeration and substrate mediated interaction increase the mean blocking temperature in the particle ensemble. The observed macroscopic magnetic in-plane anisotropy derives from the average dipolar interactions between the nanoclusters. Single particle properties, substrate mediated coupling and dipolar interactions thus independently contribute to magnetic characteristics on equal footing. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    Ganesan, Aravindhan; Brunger, Michael J.; Wang, Feng

    2013-11-01

    Vibrational optical activity (VOA) spectra, such as vibrational circular dichroism (VCD) and Raman optical activity (ROA) spectra, of aliphatic amino acids are simulated using density functional theory (DFT) methods in both gas phase (neutral form) and solution (zwitterionic form), together with their respective infrared (IR) and Raman spectra of the amino acids. The DFT models, which are validated by excellent agreements with the available experimental Raman and ROA spectra of alanine in solution, are employed to study other aliphatic amino acids. The inferred (IR) intensive region (below 2000 cm-1) reveals the signature of alkyl side chains, whereas the Raman intensive region (above 3000 cm-1) contains the information of the functional groups in the amino acids. Furthermore, the chiral carbons of the amino acids (except for glycine) dominate the VCD and ROA spectra in the gas phase, but the methyl group vibrations produce stronger VCD and ROA signals in solution. The C-H related asymmetric vibrations dominate the VOA spectra (i.e., VCD and ROA) > 3000 cm-1 reflecting the side chain structures of the amino acids. Finally the carboxyl and the C(2)H modes of aliphatic amino acids, together with the side chain vibrations, are very active in the VCD/IR and ROA/Raman spectra, which makes such the vibrational spectroscopic methods a very attractive means to study biomolecules.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-08-15

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

  20. X-ray magnetic circular dichroism at the U M4,5 absorption edges of UFe2

    International Nuclear Information System (INIS)

    We present an x-ray magnetic circular dichroism study performed at the U M4,5 edges on UFe2, a ferromagnet with almost itinerant 5f electrons. The analysis of the branching ratio of the U M4,5 edges confirms the fact that the occupation number of the 5f states in UFe2 is lower than in other compounds where the f electrons are more localized. Magnetic circular dichroism effects are observed consistently with the presence of an orbital 5f magnetic moment which aligns parallel to the total magnetic moment. In agreement with a polarized neutron study, we find a nearly perfect cancellation of the U-5f spin and orbital magnetic moments, which results in a vanishing small total U-5f magnetic moment. Results are discussed in comparison with atomic multiplet calculations. copyright 1997 The American Physical Society

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

    Science.gov (United States)

    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. Elucidating the Structure of Chiral Molecules by using Amplified Vibrational Circular Dichroism: From Theory to Experimental Realization.

    Science.gov (United States)

    Domingos, Sérgio R; Hartl, František; Buma, Wybren Jan; Woutersen, Sander

    2015-11-16

    Recent experimental observations of enhanced vibrational circular dichroism (VCD) in molecular systems with low-lying electronically excited states suggest interesting new applications of VCD spectroscopy. The theory describing VCD enhancement through vibronic coupling schemes was derived by Nafie in 1983, but only recently experimental evidence of VCD amplification has demonstrated the extent to which this effect can be exploited as a structure elucidation tool to probe local structure. In this Concept paper, we give an overview of the physics behind vibrational circular dichroism, in particular the equations governing the VCD amplification effect, and review the latest experimental developments with a prospective view on the application of amplified VCD to locally probe biomolecular structure. PMID:26289778

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-03-02

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

  4. Feedback control system for soft X-ray magnetic circular dichroism experimental station based on LabVIEW

    International Nuclear Information System (INIS)

    A feedback control system was developed for soft X-ray magnetic circular dichroism experimental station based on LabVIEW. By implementing the system, the stability of current through the sample was improved to provide a good criterion for absorption spectrum analysis. The friendly user interface, flexible interface instruction and strong data storage function are also important for National Synchrotron Radiation Laboratory which is open to users from all over the country. (authors)

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

    Science.gov (United States)

    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. Protein-containing PEGylated cubosomic particles: freeze-fracture electron microscopy and synchrotron radiation circular dichroism study

    Czech Academy of Sciences Publication Activity Database

    Angelov, Borislav; Angelova, A.; Papahadjopoulos-Sternberg, B.; Hoffmann, S. V.; Nicolas, V.; Lesieur, S.

    2012-01-01

    Roč. 116, č. 26 (2012), s. 7676-7686. ISSN 1520-6106 R&D Projects: GA ČR GAP208/10/1600 Institutional research plan: CEZ:AV0Z40500505 Institutional support: RVO:61389013 Keywords : freeze-fracture electron microscopy * synchrotron radiation circular dichroism * SAXS Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.607, year: 2012

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

    OpenAIRE

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

    2000-01-01

    Understanding the detailed mechanism of protein folding requires dynamic, site-specific stereochemical information. The short time response of vibrational spectroscopies allows evaluation of the distribution of populations in rapid equilibrium as the peptide unfolds. Spectral shifts associated with isotopic labels along with local stereochemical sensitivity of vibrational circular dichroism (VCD) allow determination of the segment sequence of unfolding. For a series of alanine-rich peptides t...

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

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

    2016-05-01

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

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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

  12. Origin-Independent Sum Over States Simulations of Magnetic and Electronic Circular Dichroism Spectra via the Localized Orbital/Local Origin Method

    Czech Academy of Sciences Publication Activity Database

    Štěpánek, Petr; Bouř, Petr

    2015-01-01

    Roč. 36, č. 10 (2015), s. 723-730. ISSN 0192-8651 R&D Projects: GA ČR GA13-03978S; GA ČR GAP208/11/0105 Grant ostatní: GA AV ČR(CZ) M200551205 Institutional support: RVO:61388963 Keywords : density functional theory * electronic circular dichroism * magnetic circular dichroism * origin-dependence Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.589, year: 2014

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

    Science.gov (United States)

    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

  14. Circular dichroism and polarized fluorescence characteristics of blue-green algal allophycocyanins

    Energy Technology Data Exchange (ETDEWEB)

    Canaani, O.D.; Gantt, E.

    1980-06-24

    Allophycocyanin, the terminal pigment in the phycobiliprotein transfer sequence, isolated from dissociated phycobilisomes of Nostoc sp., was fractionated on calcium phosphate columns into four spectral forms: APC I, II, III, and B. These forms had distinctive isoelectric points of 5.15, 4.68, 4.82, and 4.98, respectively. The APC forms differed in their secondary structure as suggested by the varying percentages of their ..cap alpha.. helix and ..beta..-pleated sheets. APC II and III are short-emitting forms with a fluorescence maximum at 660 nm, while APC I and B are long-emitting forms with a maximum at 681 nm. The maximum of APC I and B at -196/sup 0/C in 0.1 M phosphate and 20% glycerol shifted to 688 nm. Fluorescence polarization spectra suggest that there are at least two groups of chromophores responsible for the absorption of APC I and similarly of APC B. In APC II and III, the fluorescence was mostly depolarized. Circular dichroism revealed extensive positive and negative ellipticity band multiplicities in the chromophore absorption region of APC I and B, but not in APC II and III. Two main CD extrema in APC B, a negative band and a positive band, are probably the result of exciton coupling of phycocyanobilin chromophores absorbing at longer wavelength. In APC I three different peaks are revealed in the absorption spectrum and four ellipticity bands in the CD spectrum at -196/sup 0/C. These can best be explained as being due to the combined interactions of the chromophore with the protein and exciton coupling between chromophores.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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

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

    International Nuclear Information System (INIS)

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Tietze, Thomas Hermann

    2014-12-15

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

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

    International Nuclear Information System (INIS)

    Interface perpendicular magnetic anisotropy (PMA) in ultrathin Fe/MgO (001) has been investigated using angular-dependent x-ray magnetic circular dichroism (XMCD). We found that anisotropic orbital magnetic moments deduced from the analysis of XMCD contribute to the large PMA energies, whose values depend on the annealing temperature. The large PMA energies determined from magnetization measurements are related to those estimated from the XMCD and the anisotropic orbital magnetic moments through the spin-orbit interaction. The enhancement of anisotropic orbital magnetic moments can be explained mainly by the hybridization between the Fe 3dz2 and O 2pz states.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-09-22

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

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

    International Nuclear Information System (INIS)

    We study the spin and orbital magnetic moments in Ta/Co0.4Fe0.4B0.2/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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-12-01

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

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

    Science.gov (United States)

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

    2016-04-22

    Five Chinese herbal medicines--matrine, oxymatrine, sophoridine, artemisinin, and dihydroartemisinin--were investigated using vibrational circular dichroism (VCD) experiments and density functional theory calculations to extract their stereochemical information. The three matrine-type alkaloids are available from the dry roots of Sophora flavescens and have long been used in various traditional Chinese herbal medicines to combat diseases such as cancer and cardiac arrhythmia. Artemisinin and the related dihydroartemisinin, discovered in 1979 by Professor Youyou Tu, a 2015 Nobel laureate in medicine, are effective drugs for the treatment of malaria. The VCD measurements were carried out in CDCl3 and DMSO-d6, two solvents with different dielectric constants and hydrogen-bonding characteristics. A "clusters-in-a-liquid" approach was used to model both explicit and implicit solvent effects. The studies show that effectively accounting for solvent effects is critical to using IR and VCD spectroscopy to provide unique spectroscopic features to differentiate the potential stereoisomers of these Chinese herbal medicines. PMID:27070079

  4. Electronic structure and x-ray magnetic circular dichroism in (Ge,MnTe diluted magnetic semiconductors

    Directory of Open Access Journals (Sweden)

    V.N. Antonov

    2010-01-01

    Full Text Available The electronic structure of the (Ge,MnTe diluted magnetic semiconductors was investigated theoretically from first principles, using the fully relativistic Dirac linear muffin-tin orbital (LMTO band structure method. The electronic structure is obtained with the local spin-density approximation (LSDA as well as the LSDA+U method. The x-ray magnetic circular dichroism (XMCD spectra of (Ge,MnTe DMSs at the Mn L2,3 edges are investigated theoretically from first principles. The origin of the XMCD spectra in the compound is examined. The calculated results are compared with available experimental data.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-12-14

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

  6. Helical nature of poly(dI-dC).poly(dI-dC). Vibrational circular dichroism results.

    OpenAIRE

    Wang, L.; Keiderling, T A

    1993-01-01

    Poly(dI-dC).poly(dI-dC) was studied using vibrational circular dichroism and IR spectroscopy in both the base deformation C = O and symmetric PO2- stretching regions. VCD spectra of this duplex under low salt conditions are consistent with its having a B-form structure. Addition of 5 M NaCl leads to relatively uniform VCD intensity loss which is consistent with loss of helical structure rather than formation of an intermediate state between the B and Z forms. This duplex polymer under high sa...

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

    CERN Document Server

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

    2016-01-01

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

  8. Study on ferromagnetic ordering of FeRh thin films induced by energetic heavy ion irradiation by means of X-ray Magnetic Circular Dichroism

    Science.gov (United States)

    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.

  9. Study on ferromagnetic ordering of FeRh thin films induced by energetic heavy ion irradiation by means of X-ray Magnetic Circular Dichroism

    Energy Technology Data Exchange (ETDEWEB)

    Aikoh, Kazuma; Tohki, Atsushi [Department of Materials Science, Osaka Prefecture University, Sakai, Osaka 599-8531 (Japan); Okuda, Shuichi [Radiation Research Center, Osaka Prefecture University, Sakai, Osaka 599-8570 (Japan); Saitoh, Yuichi; Kamiya, Tomihiro [Takasaki Advanced Radiation Research Institute, Japan Atomic Energy Agency, Takasaki, Gumma 370-1292 (Japan); Nakamura, Tetsuya [Japan Synchrotron Radiation Research Institute, SPring-8, Sayo, Hyogo 679-5198 (Japan); Kinoshita, Toyohiko [Japan Synchrotron Radiation Research Institute, SPring-8, Sayo, Hyogo 679-5198 (Japan); CREST-JST, Kawaguchi, Saitama 332-0012 (Japan); Iwase, Akihiro [Department of Materials Science, Osaka Prefecture University, Sakai, Osaka 599-8531 (Japan); Matsui, Toshiyuki, E-mail: t-matsui@21c.osakafu-u.ac.jp [Research Organization of the 21st Century, Osaka Prefecture University, Sakai, Osaka 599-8531 (Japan)

    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 L{sub 2,3}-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.

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

    Science.gov (United States)

    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

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

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

    Science.gov (United States)

    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

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

    International Nuclear Information System (INIS)

    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.

  14. TD-DFT Investigation of the Magnetic Circular Dichroism Spectra of Some Purine and Pyrimidine Bases of Nucleic Acids

    DEFF Research Database (Denmark)

    Fahleson, Tobias; Kauczor, Joanna; Norman, Patrick;

    2015-01-01

    We present a computational study of the magnetic circular dichroism (MCD) spectra in the 200–300 nm wavelength region of purine and its derivative hypoxanthine, as well as of the pyrimidine bases of nucleic acids uracil, thymine, and cytosine, using the B3LYP and CAM–B3LYP functionals. Solvent...... effects are investigated within the polarizable continuum model and by inclusion of explicit water molecules. In general, the computed spectra are found to be in good agreement with the experimental ones, apart from some overall blue shifts. Both the pseudo-A term shape of the MCD spectra of the purines...... and the B term shape of the spectra of pyrimidine bases are reproduced. Our calculations also correctly reproduce the reversed phase of the MCD bands in purine compared to that of its derivatives present in nucleic acids. Solvent effects are sizable and system specific, but they do not in general...

  15. Development of a depth-resolved x-ray magnetic circular dichroism: application to Fe/Cu(100) ultrathin films

    International Nuclear Information System (INIS)

    A depth-resolved technique is applied in the x-ray magnetic circular dichroism (XMCD) method by controlling the probing depth of the electron yield XMCD spectra. The usefulness of this technique is demonstrated for the study of magnetic structures of 4 and 8 ML Fe films grown on Cu(100), which are known to exhibit peculiar magnetic depth profiles. It was directly shown that the 4 ML film is uniformly magnetized, while the magnetic moment is localized at the surface in the case of the 8 ML film. The XMCD spectrum for each layer of the 4 ML film was separately extracted. All the extracted spectra were almost identical to each other, confirming the ferromagnetic coupling over the whole film. As for the 8 ML film, it was suggested that the surface two layers are ferromagnetically coupled, while the inner layers are in a spin density wave state with a wavenumber q=2π/2.4d

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2012-06-05

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

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

    Science.gov (United States)

    Kosaka, Tomoyo; Inoue, Yoshihisa; Mori, Tadashi

    2016-03-01

    Hexaarylbenzenes (HABs) have greatly attracted much attention due to their unique propeller-shaped structure and potential application in materials science, such as liquid crystals, molecular capsules/rotors, redox materials, nonlinear optical materials, as well as molecular wires. Less attention has however been paid to their propeller chirality. By introducing small point-chiral group(s) at the periphery of HABs, propeller chirality was effectively induced, provoking strong Cotton effects in the circular dichroism (CD) spectrum. Temperature and solvent polarity manipulate the dynamics of propeller inversion in solution. As such, whizzing toroids become more substantial in polar solvents and at an elevated temperature, where radial aromatic rings (propeller blades) prefer orthogonal alignment against the central benzene ring (C6 core), maximizing toroidal interactions. PMID:26882341

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

    International Nuclear Information System (INIS)

    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-d2 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-d2. 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

  1. First principles structures and circular dichroism spectra for the close-packed and the 7/2 motif of collagen

    CERN Document Server

    Jalkanen, Karl J; Knapp-Mohammady, Michaela; Bohr, Jakob

    2012-01-01

    The recently proposed close-packed motif for collagen is investigated using first principles semi-empirical wave function theory and Kohn-Sham density functional theory. Under these refinements the close-packed motif is shown to be stable. For the case of the 7/2 motif a similar stability exists. The electronic circular dichroism of the close-packed model has a significant negative bias and a large signal. An interesting feature of the close-packed structure is the existence of a central channel. Simulations show that, if hydrogen atoms are placed in the cavity, a chain of molecular hydrogens is formed suggesting a possible biological function for molecular hydrogen.

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

    Science.gov (United States)

    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.

  3. A circular dichroism sensor for Ni2+ and Co2+ based on L-cysteine capped cadmium sulfide quantum dots

    International Nuclear Information System (INIS)

    Highlights: • Demonstrated a new efficient sensor platform based quantum dots. • Used chiral quantum dots as CD sensor for the detection of heavy metal ions for the first time. • The proposed CD sensor showed highest selectivity towards Ni2+ and Co2+. • Low detection limits of 7.33 μM and 1.13 μM for Ni2+ and Co2+, respectively. • Can be used in real water samples comparing with ICP-OES. - Abstract: A new circular dichroism sensor for detecting Ni2+ and Co2+ 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 Ni2+ or Co2+. 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 Ni2+ and Co2+. On the other hand, other studied cations did not alter the original CD spectrum. Moreover, when increasing the concentration of Ni2+ or Co2+, the intensity of the CD spectrum linearly increased as a function of concentration and could be useful for the quantitative analysis. The proposed CD sensor showed linear working concentration ranges of 10–60 μM and 4–80 μM with low detection limits of 7.33 μM and 1.13 μM for the detection of Ni2+ and Co2+, 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 Ni2+ and Co2+ in real water samples, and the results agreed well with the analysis using the standard ICP-OES

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

    Science.gov (United States)

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

    2015-10-01

    The stereochemistry of two 6, 9-oxygen bridge dibenzocyclooctadiene lignans from Kadsura coccinea, are difficult to separate and very unstable. The present study was designed to develop a high-performance liquid chromatography using circular dichroism detection for the analysis of the stereochemistry. A new 6, 9-oxygen bridge dibenzocyclooctadiene lignans named Kadsulignan Q was firstly found with an S-biphenyl configuration. The other compound was identified as Kadsulignan L with an R- biphenyl configuration. In order to obtain kinetic data on their reversible interconversion, the stability was measured at different deuterated solvents such as deuterated methanol, deuterated chloroform and deuterated dimethylsulfoxide. The lignans were more unstable and converted more easily in deuterated methanol than in deuterated chloroform and deuterated dimethylsulfoxide. PMID:26481381

  5. Electronic structure, magnetic ordering and X-ray magnetic circular dichroism in La1-xPrxCo2P2 phosphides

    Directory of Open Access Journals (Sweden)

    L.V. Bekenov

    2015-09-01

    Full Text Available The electronic structure and magnetic ordering in La1-xPrxCo2P2 (x=0, 0.25, and 1 phosphides have been studied theoretically using the fully relativistic spin-polarized Dirac linear muffin-tin orbital (LMTO band-structure method. The X-ray absorption and X-ray magnetic circular dichroism spectra at the Co L2,3 and Pr M4,5 edges have been investigated theoretically within the framework of the LSDA+U method. The core-hole effect in the final state as well as the effects of the electric quadrupole E2 and magnetic dipole M1 transitions have been investigated. Good agreement with experimental measurements has been found.

  6. Structures, vibrational absorption and vibrational circular dichroism spectra of L-alanine in aqueous solution: a density functional theory and RHF study

    DEFF Research Database (Denmark)

    Frimand, Kenneth; Bohr, Henrik; Jalkanen, Karl J.; Suhai, S.

    A detailed comparative study of structures, vibrational absorption (VA) and vibrational circular dichroism (VCD) spectra has been carried out for the zwitterionic structure of the amino acid L-alanine. Theoretically determined structures necessary for deriving VA and VCD spectra were calculated...... water molecules and a dielectric media through the Onsager model and only this combination gave excellent comparison to experimental VA and VCD spectra. Two dominant conformers with different backbone configurations are identified, and the inclusion of solvent effects clearly favours one of the...... conformers. The calculated VA and VCD spectra of this conformer are in better agreement with experimentally measured VA and VCD spectra previously reported. (C) 2000 Elsevier Science B.V. All rights reserved....

  7. Effects of fluorination on iridium(III) complex phosphorescence: magnetic circular dichroism and relativistic time-dependent density functional theory.

    Science.gov (United States)

    Smith, A R G; Riley, M J; Burn, P L; Gentle, I R; Lo, S-C; Powell, B J

    2012-03-01

    We use a combination of low temperature, high field magnetic circular dichroism, absorption, and emission spectroscopy with relativistic time-dependent density functional calculations to reveal a subtle interplay between the effects of chemical substitution and spin-orbit coupling (SOC) in a family of iridium(III) complexes. Fluorination at the ortho and para positions of the phenyl group of fac-tris(1-methyl-5-phenyl-3-n-propyl-[1,2,4]triazolyl)iridium(III) cause changes that are independent of whether the other position is fluorinated or protonated. This is demonstrated by a simple linear relationship found for a range of measured and calculated properties of these complexes. Further, we show that the phosphorescent radiative rate, k(r), is determined by the degree to which SOC is able to hybridize T(1) to S(3) and that k(r) is proportional to the inverse fourth power of the energy gap between these excitations. We show that fluorination in the para position leads to a much larger increase of the energy gap than fluorination at the ortho position. Theory is used to trace this back to the fact that fluorination at the para position increases the difference in electron density between the phenyl and triazolyl groups, which distorts the complex further from octahedral symmetry, and increases the energy separation between the highest occupied molecular orbital (HOMO) and the HOMO-1. This provides a new design criterion for phosphorescent iridium(III) complexes for organic optoelectronic applications. In contrast, the nonradiative rate is greatly enhanced by fluorination at the ortho position. This may be connected to a significant redistribution of spectral weight. We also show that the lowest energy excitation, 1A, has almost no oscillator strength; therefore, the second lowest excitation, 2E, is the dominant emissive state at room temperature. Nevertheless the mirror image rule between absorption and emission is obeyed, as 2E is responsible for both absorption and

  8. Simulations of Vibrational Circular Dichroism (VCD) and IR absorption spectra of several nucleic acid octamers. Comparison of calculated and experimental spectra

    Czech Academy of Sciences Publication Activity Database

    Andrushchenko, V.; Bouř, Petr; Wieser, H.

    Lugano : ETH, 2002. s. PC443. [WAT '02. World Congress of Theoretically Oriented Chemists /6./. 04.08.2002-09.08.2002, Lugano] Institutional research plan: CEZ:AV0Z4055905 Keywords : vibrational circular dichroism Subject RIV: CF - Physical ; Theoretical Chemistry

  9. Vibrational circular dichroism (VCD) and IR spectroscopic study of DNA structural changes induced by metal ions and drugs. Experimental results and theoretical simulations

    Czech Academy of Sciences Publication Activity Database

    Andrushchenko, V.; Sande van de, J. H.; Bouř, Petr; Wieser, H.

    Lille : Université des Sciences et Technologies de Lille, 2002. s. 13. [European Congress on Molecular Spectroscopy /26./. 01.09.2002-06.09.2002, Villeneuve d'Ascq] Institutional research plan: CEZ:AV0Z4055905 Keywords : vibrational circular dichroism Subject RIV: CF - Physical ; Theoretical Chemistry

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

    Science.gov (United States)

    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. Resonant photoemission and magnetic x-ray circular dichroism in the M shell of ultrathin films of Fe

    International Nuclear Information System (INIS)

    Using magnetic ultra thin films (2--4 ml) of Fe on Cu(001) and bulk-like Fe, the Fe3p and Fe3s core states have been investigated with resonant photoemission and core-level photoemission, including, magnetic x-ray circular dichroism (MXCD) experiments. The resonant photoemission experiment has been done in fine steps over a wide photon energy range (hν = 695 eV - 715 eV), to probe the parentage of various spectral structures. The onset of secondary channels at the L3(hν = 707 eV) and L2(hν = 72O eV) edges will be analyzed in light of results from bulk Ni. The MXCD photoelectron spectroscopy of the Fe3p exhibits a 0.2 eV shift with circular polarization variation. The previously observed split peak structure in the Fe3s will be discussed with regard to the new resonant photoemission results. The resonant photoemission results will also be put into the context of our MXCD absorption results for monolayer and multilayers of Fe

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

    Science.gov (United States)

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

    2016-01-01

    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

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

    Science.gov (United States)

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

    2016-04-01

    An efficient and rapid process for isoquercitrin production by hesperidinase-catalyzed hydrolysis of rutin was successfully developed under microwave irradiation detecting the affinity by circular dichroism (CD) and surface plasmon resonance (SPR) spectroscopy. A maximum isoquercitrin yield of 91.5±2.7% was obtained in 10min with the conditions of 10g/L hesperidinase, 2g/L rutin, 30°C and microwave power density 88.9W/L. Enzymatic reaction rate and Vm/Km in the microwave reactor were 6.34-fold higher than in a continuous flow microreactor and 1.24-fold higher than in a biphasic system. CD and SPR analysis results also showed that hesperidinase has a better selectivity and affinity (3.3-fold than in a batch reactor) to generate isoquercitrin under microwave irradiation. Microwave irradiation greatly improved the reaction efficiency and productivity, leading to a more positive economical assessment. The binding affinity indicates the presence of strong multivalent interactions between rutin and hesperidinase under microwave irradiation. PMID:26803794

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-05-07

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

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

    Science.gov (United States)

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

    2015-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-01-14

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

  17. Studying the magnetic anisotropy in CuFeO2 by x-ray magnetic circular dichroism

    International Nuclear Information System (INIS)

    Full text: The compound CuFeO2 has a delafossite structure where triangular layers of magnetic Fe3+ are separated by non-magnetic Cu1+ and O2- layers. CuFeO2 orders in a collinear four sublattice structure below TN2=11K. Moreover, associated with TN2 is a first order structural transition from hexagonal to orthorhombic. The explanation for the collinear magnetic structure remains unclear for CuFeO2, since it requires a 2D Ising model type, which is difficult to conciliate with the spherical Fe3+ ion. However, structural distortions around the Fe3+ ion and/or charge transfer could lead to a non-zero orbital magnetic moment. This might explain the puzzling strong magnetic anisotropy in CuFeO2. We present x-ray magnetic circular dichroism (XMCD) data extracting separately the orbital and spin moments of the Fe3+ ions. These results are discussed in the context to the observed magnetic anisotropy. (author)

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

    Science.gov (United States)

    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 Tconstant 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.

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

    Science.gov (United States)

    Goings, Joshua J.; Li, Xiaosong

    2016-06-01

    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.

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

    Science.gov (United States)

    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.

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

    Directory of Open Access Journals (Sweden)

    Genet H. Zemede

    2012-08-01

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

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

    Science.gov (United States)

    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

  3. Determination of the Absolute Configurations Using Exciton Chirality Method for Vibrational Circular Dichroism: Right Answers for the Wrong Reasons?

    Science.gov (United States)

    Covington, Cody L; Nicu, Valentin P; Polavarapu, Prasad L

    2015-10-22

    Quantum chemical (QC) predictions of vibrational circular dichroism (VCD) spectra for the keto form of 3-benzoylcamphor and conformationally flexible diacetates of spiroindicumide A and B are presented. The exciton chirality (EC) model has been briefly reviewed, and a procedure to evaluate the relevance of the EC model has been presented. The QC results are compared with literature experimental VCD spectra as well as with those obtained using the EC model for VCD. These comparisons reveal that the EC contributions to bisignate VCD couplets associated with the C═O stretching vibrations of benzoylcamphor, spiroindicumide A diacetate, and spiroindicumide B diacetate are only ∼30%, ∼3%, and ∼15%, respectively. With such meager EC contributions, the correct absolute configurations (ACs) suggested in the literature for spiroindicumide A diacetate and spiroindicumide B diacetate molecules using the EC concepts can be considered fortuitous. The possibilities for obtaining wrong AC predictions using the EC concepts for VCD are identified, and guidelines for the future use of this model are presented. PMID:26401833

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

    Science.gov (United States)

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

    2015-12-15

    Dimethyl sulfoxide (DMSO) induced destabilization of insulin fibrils has been previously studied by Fourier transform infrared spectroscopy and interpreted in terms of secondary structural changes. The variation of this process for fibrils with different types of higher-order morphological structures remained unclear. Here, we utilize vibrational circular dichroism (VCD), which has been reported to provide a useful biophysical probe of the supramolecular chirality of amyloid fibrils, to characterize changes in the macroscopic chirality following DMSO-induced disassembly for two types of insulin fibrils formed under different conditions, at different reduced pH values with and without added salt and agitation. We confirm that very high concentrations of DMSO can disaggregate both types of insulin fibrils, which initially maintained a β-sheet conformation and eventually changed their secondary structure to a disordered form. The two types responded to varying concentrations of DMSO, and disaggregation followed different mechanisms. Interconversion of specific insulin fibril morphological types also occurred during the destabilization process as monitored by VCD. With transmission electron microscopy, we were able to correlate the changes in VCD sign patterns to alteration of morphology of the insulin fibrils. PMID:26582046

  5. Interplay of Exciton Coupling and Large-Amplitude Motions in the Vibrational Circular Dichroism Spectrum of Dehydroquinidine.

    Science.gov (United States)

    Nicu, Valentin P; Domingos, Sérgio R; Strudwick, Benjamin H; Brouwer, Albert M; Buma, Wybren J

    2016-01-11

    A detailed analysis of the computed structure, energies, vibrational absorption (VA) and circular dichroism (VCD) spectra of 30 low-energy conformers of dehydroquinidine reveals the existence of families of pseudo-conformers, the structures of which differ mostly in the orientation of a single O-H bond. The pseudo-conformers in a family are separated by very small energy barriers (i.e., 1.0 kcal mol(-1) or smaller) and have very different VCD spectra. First, we demonstrate the unreliable character of the Boltzmann factors predicted with DFT. Then, we show that the large differences observed between the VCD spectra of the pseudo-conformers in a family are caused by large-amplitude motions involving the O-H bond, which trigger the appearance/disappearance of strong VCD exciton-coupling bands in the fingerprint region. This interplay between exciton coupling and large-amplitude-motion phenomena demonstrates that when dealing with flexible molecules with polar bonds, vibrational averaging of VCD spectra should not be neglected. In this regard, the dehydroquinidine molecule considered here is expected to be a typical example and not the exception to the rule. PMID:26611817

  6. Multi-frame acquisition scheme for efficient energy-dispersive X-ray magnetic circular dichroism in pulsed high magnetic fields at the Fe K-edge

    International Nuclear Information System (INIS)

    A multi-frame acquisition scheme for efficient energy-dispersive X-ray magnetic circular dichroism at the Fe K-edge is presented. Using a fast silicon strip detector, a multi-frame acquisition scheme was implemented to perform energy-dispersive X-ray magnetic circular dichroism at the iron K-edge in pulsed high magnetic fields. The acquisition scheme makes use of the entire field pulse. The quality of the signal obtained from samples of ferrimagnetic erbium iron garnet allows for quantitative evaluation of the signal amplitude. Below the compensation point, two successive field-induced phase transitions and the reversal of the net magnetization of the iron sublattices in the intermediate phase were observed

  7. An optically transparent thin-layer electrochemical cell for the study of vibrational circular dichroism of chiral redox-active molecules.

    Science.gov (United States)

    Domingos, Sérgio R; Luyten, Henk; van Anrooij, Fred; Sanders, Hans J; Bakker, Bert H; Buma, Wybren J; Hartl, František; Woutersen, Sander

    2013-03-01

    An optically transparent thin-layer electrochemical (OTTLE) cell with a locally extended optical path has been developed in order to perform vibrational circular dichroism (VCD) spectroscopy on chiral molecules prepared in specific oxidation states by means of electrochemical reduction or oxidation. The new design of the electrochemical cell successfully addresses the technical challenges involved in achieving sufficient infrared absorption. The VCD-OTTLE cell proves to be a valuable tool for the investigation of chiral redox-active molecules. PMID:23556803

  8. An optically transparent thin-layer electrochemical cell for the study of vibrational circular dichroism of chiral redox-active molecules

    Science.gov (United States)

    Domingos, Sérgio R.; Luyten, Henk; van Anrooij, Fred; Sanders, Hans J.; Bakker, Bert H.; Buma, Wybren J.; Hartl, František; Woutersen, Sander

    2013-03-01

    An optically transparent thin-layer electrochemical (OTTLE) cell with a locally extended optical path has been developed in order to perform vibrational circular dichroism (VCD) spectroscopy on chiral molecules prepared in specific oxidation states by means of electrochemical reduction or oxidation. The new design of the electrochemical cell successfully addresses the technical challenges involved in achieving sufficient infrared absorption. The VCD-OTTLE cell proves to be a valuable tool for the investigation of chiral redox-active molecules.

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

    OpenAIRE

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

    2008-01-01

    We describe the implementation of the rotational strengths for vibrational circular dichroism (VCD) in the Slater-type orbital based Amsterdam Density Functional (ADF) package. We show that our implementation, which makes use of analytical derivative techniques and London atomic orbitals, yields origin independent rotational strengths. The basis set dependence in the particular case of Slater-type basis functions is also discussed. It turns out that the triple zeta STO basis sets with one set...

  10. Tight beta-turns in peptides. DFT-based study of infrared absorption and vibrational circular dichroism for various conformers including solvent effects

    Czech Academy of Sciences Publication Activity Database

    Kim, J.; Kapitán, Josef; Lakhani, A.; Bouř, Petr; Keiderling, T. A.

    2008-01-01

    Roč. 119, 1/3 (2008), s. 81-97. ISSN 1432-881X R&D Projects: GA ČR GA203/06/0420 Grant ostatní: NSF(US) CHE03-16014 Institutional research plan: CEZ:AV0Z40550506 Keywords : peptide beta-turn * density functional theory * infrared absorption * vibrational circular dichroism Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.370, year: 2008

  11. Conformational studies of the smallest structural motifs of DNA detectable via vibrational circular dichroism: cytidylyl-(3'-5')-guanosine and guanylyl-(3'-5')-cytidine.

    OpenAIRE

    Birke, S S; Diem, M.

    1995-01-01

    The infrared absorption and vibrational circular dichroism (VCD) spectra of buffered aqueous solutions of cytidylyl-(3'-5')-guanosine (5'(CG)3') and guanylyl-(3'-5')-cytidine (5'(GC)3') are reported. Under low ionic strength conditions, these dinucleotides exhibit VCD features that can be predicted qualitatively from structural data of (CG)2 and (GC)2 sequences of poly(dG-dC).poly(dG-dC), using the exciton model for infrared VCD intensities.

  12. Changes in beta-lactoglobulin conformation at the oil/water interface of emulsions studied by synchrotron radiation circular dichroism spectroscopy.

    Science.gov (United States)

    Zhai, Jiali; Miles, Andrew J; Pattenden, Leonard Keith; Lee, Tzong-Hsien; Augustin, Mary Ann; Wallace, B A; Aguilar, Marie-Isabel; Wooster, Tim J

    2010-08-01

    The structure of proteins at interfaces is a key factor determining the stability as well as organoleptic properties of food emulsions. While it is widely believed that proteins undergo conformational changes at interfaces, the measurement of these structural changes remains a significant challenge. In this study, the conformational changes of beta-lactoglobulin (beta-Lg) upon adsorption to the interface of hexadecane oil-in-water emulsions were investigated using synchrotron radiation circular dichroism (SRCD) spectroscopy. Far-UV SRCD spectra showed that adsorption of beta-Lg to the O/W interface caused a significant increase in non-native alpha-helix structure, accompanied by a concomitant loss of beta-sheet structure. Near-UV SRCD spectra revealed that a considerable disruption of beta-Lg tertiary structure occurred upon adsorption. Moreover, heat-induced changes to the non-native beta-Lg conformation at the oil/water interface were very small compared to the dramatic loss of beta-Lg secondary structure that occurred during heating in solution, suggesting that the interface has a stabilizing effect on the structure of non-native beta-Lg. Overall, our findings provide insight into the conformational behavior of proteins at oil/water interfaces and demonstrate the applicability of SRCD spectroscopy for measuring the conformation of adsorbed proteins in optically turbid emulsions. PMID:20690721

  13. Laser-induced generation and quenching of magnetization on FeRh investigated with time-resolved X-ray magnetic circular dichroism

    Energy Technology Data Exchange (ETDEWEB)

    Radu, Ilie [Regensburg University, Regensburg (Germany); BESSY GmbH, Berlin (Germany); Stamm, Christian; Pontius, Niko; Kachel, Torsten; Duerr, Hermann [BESSY GmbH, Berlin (Germany); Ramm, Paul; Back, Christian [Regensburg University, Regensburg (Germany); Thiele, Jan-Ulrich [Hitachi Global Storage, San Jose, CA (United States)

    2009-07-01

    Upon heating, the equiatomic FeRh alloy exhibits a first-order magnetic phase transition from the antiferromagnetic (AFM) to the ferromagnetic (FM) state around room temperature. Here, we study the fs laser-induced AFM-FM phase transition as well as the transition from FM towards the paramagnetic state by employing the time-resolved X-ray magnetic circular dichroism. Both Fe and Rh elements show a gradual growth of the magnetic moment within 200 ps after laser excitation. Temperature-dependent data, measured at intermediate temperatures between AFM and FM state, provide evidence for the rapid nucleation and subsequent slow expansion of the FM regions within an AFM matrix. Once in the FM state, FeRh can be optically demagnetized on a few ps time scale (limited by the X-ray probing pulse). Further time-resolved magneto-optics measurements done in the visible spectral range reveal a demagnetization time constant of 200 fs. For the photo-induced demagnetization process we consider a mechanism that follows the transient electronic structure of the system.

  14. Conformational requirement of signal sequences functioning in yeast: Circular dichroism and 1H nuclear magnetic resonance studies of synthetic peptides

    International Nuclear Information System (INIS)

    Recently, the authors have designed a series of simplified artificial signal sequences and have shown that a proline residue in the signal sequence plays an important role in the secretion of human lysozyme in yeast, presumably by altering the conformation of the signal sequence. To elucidate the conformational requirement of the signal sequence in more detail, functional and nonfunctional signal sequences connected to the N-terminal five residues of mature human lysozyme were chemically synthesized and their conformations in a lipophilic environment analyzed by circular dichroism (CD) and 1H nuclear magnetic resonance (NMR) spectroscopy. The helix content of the peptides, including functional (L8, CL10) and nonfunctional (L8PL, L8PG, L8PL2) signal sequences, was estimated from CD spectra to be 40-50% and 60-70%, respectively, indicating that the helical structure is more abundant in the nonfunctional signal sequences. Two-dimensional NMR analyses in 50% TFE/H2O revealed that each peptide adopted a helical conformation throughout the sequence except for a few residues at the N- and C-termini. Furthermore, H-D exchange experiments indicated that the helical structure of the C-terminal region of the functional signal sequences (L8 and CL10) was less stable than that of the nonfunctional signal sequences (L8PL and L8PL2). On the basis of these results, a model was developed in which the functional signal sequence is inserted in the membrane with a helical conformation and the C-terminal helix unraveled in an extended conformational form through an interaction with the signal peptidase

  15. Theory of circular dichroism of nanomaterials comprising chiral molecules and nanocrystals: plasmon enhancement, dipole interactions, and dielectric effects.

    Science.gov (United States)

    Govorov, Alexander O; Fan, Zhiyuan; Hernandez, Pedro; Slocik, Joseph M; Naik, Rajesh R

    2010-04-14

    Our calculations show that a nonchiral nanocrystal is able to dramatically change the circular dichroism (CD) of a chiral molecule when the nanocrystal and molecule form a complex and couple via dipole and multipole Coulomb interactions. Plasmon resonances of metal nanocrystals in the nanocrystal-molecule complex result in both the resonant enhancement of CD signals of molecules and the appearance of new spectral structures. Two mechanisms, in which a nanocrystal can influence the CD effect, have been identified. The first mechanism is the plasmon-induced change in the electromagnetic field inside the chiral molecule. The second is the optical absorption of the nanocrystal-molecule complex due to the chiral currents inside the metal nanocrystal induced by the dipole of the chiral molecule. The first mechanism creates a change in the angle between the effective electric and magnetic dipoles of the molecule. This mechanism can lead to symmetry breaking and to a plasmon-induced CD signal of the nonchiral molecule. Both mechanisms create interesting Fano-like shapes in the CD spectra. Importantly, the second mechanism gives the main contribution to the CD signal at the plasmon frequency when the absorption band of the chiral molecule is far from the plasmon resonance. This may happen in many cases since many biomolecules are optically active in the UV range, whereas plasmon resonances in commonly used nanometals are found at longer wavelengths. As concrete examples, the paper describes alpha-helix and calixarene ligand molecules coupled with metal nanocrystals. The above results are also applied to complexes incorporating semiconductor nanocrystals. The results obtained here can be used to design a variety of hybrid nanostructures with enhanced and tailored optical chirality in the visible wavelength range. PMID:20184381

  16. Ag(I)-mediated homo and hetero pairs of guanosine and cytidine: Monitoring by circular dichroism spectroscopy

    Science.gov (United States)

    Goncharova, Iryna

    2014-01-01

    Ag(I)-containing compounds are attractive as antibacterial and antifungal agents. The renewed interest in the application of silver(I) compounds has led to the need for detailed knowledge of the mechanism of their action. One of the possible ways is the coordination of Ag(I) to G-C pairs of DNA, where Ag+ ions form Ag(I)-mediated base pairs and inhibit the transcription. Herein, a systematic chiroptical study on silver(I)-mediated homo and mixed pairs of the C-G complementary-base derivatives cytidine(C) and 5‧-guanosine monophosphate(G) in water is presented. Ag(I)-mediated homo and hetero pairs of G and C and their self-assembled species were studied under two pH levels (7.0 and 10.0) by vibrational (VCD) and electronic circular dichroism(ECD). VCD was used for the first time in this field and showed itself to be a powerful method for obtaining specific structural information in solution. Based on results of the VCD experiments, the different geometries of the homo pairs were proposed under pH 7.0 and 10.0. ECD was used as a diagnostic tool to characterize the studied systems and as a contact point between the previously defined structures of the metal or proton mediated pairs of nucleobases and the systems studied here. On the basis of the obtained data, the formation of the self-assembled species of cytidine with a structure similar to the i-motif structure in DNA was proposed at pH 10.0.

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

    DEFF Research Database (Denmark)

    Jalkanen, Karl J.

    2003-01-01

    can be compared to the measured VA, VCD and Raman spectra of LeuE in non-polar solvents to identify which conformer or conformers of LeuE are present in these media. Characteristic features in the VCD spectra are more sensitive to conformational changes than those in either the VA or Raman spectra...... species is higher than neutral species, in contradiction to experiment. Hence the use of explicit water molecules plus either this or another continuum model to treat the bulk water environment is necessary to make the zwitterionic species more stable than the neutral species. We are pursuing explicit...

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

    Energy Technology Data Exchange (ETDEWEB)

    Ito, Keita, E-mail: keita.ito.729@gmail.com [Institute of Applied Physics, Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8573 (Japan); Department of Electronic Engineering, Graduate School of Engineering, Tohoku University, Sendai 980-8579 (Japan); Japan Society for the Promotion of Science (JSPS), Chiyoda, Tokyo 102-0083 (Japan); Toko, Kaoru; Suemasu, Takashi [Institute of Applied Physics, Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8573 (Japan); Takeda, Yukiharu; Saitoh, Yuji [Condensed Matter Science Division, Japan Atomic Energy Agency (JAEA), Sayo, Hyogo 679-5148 (Japan); Oguchi, Tamio [The Institute of Scientific and Industrial Research (ISIR), Osaka University, Ibaraki, Osaka 567-0047 (Japan); Kimura, Akio [Graduate School of Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 (Japan)

    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.

  19. Photo-induced magnetization dynamics of FeRh thin films investigated by time-resolved X-ray magnetic circular dichroism

    Energy Technology Data Exchange (ETDEWEB)

    Radu, Ilie [Institut fuer Experimentelle Physik, Universitaet Regensburg (Germany); BESSY GmbH, Berlin (Germany); Stamm, Christian; Kachel, Torsten; Pontius, Niko; Duerr, Hermann [BESSY GmbH, Berlin (Germany); Ramm, Paul; Back, Christian [Institut fuer Experimentelle Physik, Universitaet Regensburg (Germany); Thiele, Jan [Hitachi GST, San Jose Research Center (United States)

    2008-07-01

    For close to equiatomic composition the FeRh alloy undergoes a first-order phase transition from the antiferromagnetic (AFM) to ferromagnetic (FM) state upon heating above room temperature. We trigger the magnetic phase transition by femtosecond laser excitation and study the subsequent dynamics of the Fe and Rh magnetic moments in an element specific manner using X-ray magnetic circular dichroism (XMCD) as a probing tool. For both elements we observe a gradual growth of ferromagnetic ordering that takes place on a 200 ps time scale after optical excitation. On the other hand, once in the FM state, FeRh can be demagnetized on a few picoseconds time interval, the observed dynamics being limited by the width of the X-ray probing pulse (here 10 ps). By comparison to the demagnetization dynamics measured on Ni under similar conditions, we retrieve the lower limit of the demagnetization process that evolves on a sub-picosecond time scale. Hence, the AFM-FM phase transition in conjunction with time-resolved XMCD allow us to study at a microscopic level the elementary processes involved in the magnetization growth, demagnetization and re-magnetization phenomena.

  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

    Science.gov (United States)

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

    2016-05-01

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

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

    Science.gov (United States)

    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

  2. Photoelectron circular dichroism in the multiphoton ionization by short laser pulses. I. Propagation of single-active-electron wave packets in chiral pseudo-potentials

    International Nuclear Information System (INIS)

    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

  3. Mapping the Anopheles gambiae odorant binding protein 1 (AgamOBP1) using modeling techniques, site directed mutagenesis, circular dichroism and ligand binding assays.

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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.

  5. Electronic and magnetic properties of off-stoichiometric Co2MnβSi/MgO interfaces studied by x-ray magnetic circular dichroism

    International Nuclear Information System (INIS)

    We have studied the electronic and magnetic states of Co and Mn atoms at the interface of the Co2MnβSi (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, mspin(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, mspin(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 CoMn 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

  6. Fine structures in vibrational circular dichroism spectra of chiral molecules with rotatable hydroxyl groups and their application in the analysis of local intermolecular interactions

    Science.gov (United States)

    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.

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

    Science.gov (United States)

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

    2013-09-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-06-21

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

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

    International Nuclear Information System (INIS)

    The electronic structure and magnetic moments of free Mn2+ and Mn3+ 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 μB are created by 3d5(6S) 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 μB for Mn2+ and 16 μB for Mn3+, with no contribution of orbital angular momentum

  10. 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

    Science.gov (United States)

    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.

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

    International Nuclear Information System (INIS)

    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

  12. Investigating orbital magnetic moments in spinel-type MnV2O4 using X-ray magnetic circular dichroism

    International Nuclear Information System (INIS)

    Element-specific magnetic structures, particularly orbital magnetic moments, of spinel-type MnV2O4 were investigated using X-ray magnetic circular dichroism (XMCD). X-ray absorption and XMCD spectra clearly reveal that the Mn2+ (d5) and V3+ (d2) states are coupled antiferromagnetically. Analyses of XMCD spectra using magneto optical sum rules revealed that small but finite orbital magnetic moments remain in both V and Mn 3d states, which accounts for the antiferro-type orbital ordering in the V sites of MnV2O4 with coexisting complex and real orbital states. Additionally, the Cr doping effect in MnV2O4 was examined. The XMCD spectra of Cr3+ (d3) L-edges exhibited the substitution of Cr ions to the V sites ferromagnetically, with low conductivity through the suppression of the orbital ordering. (author)

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-05-07

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

  14. X-ray magnetic circular dichroism photoemission electron microscopy of focused ion beam-induced magnetic patterns on iron–rhodium surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Tohki, Atsushi; Aikoh, Kazuma; Shinoda, Ryoichi [Department of Materials Science, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531 (Japan); Ohkochi, Takuo [Japan Synchrotron Radiation Research Institute, SPring-8, Sayo, Hyogo 679-5198 (Japan); Kotsugi, Masato [Japan Synchrotron Radiation Research Institute, SPring-8, Sayo, Hyogo 679-5198 (Japan); CREST-JST, Kawaguchi, Saitama 332-0012 (Japan); Nakamura, Tetsuya [Japan Synchrotron Radiation Research Institute, SPring-8, Sayo, Hyogo 679-5198 (Japan); Kinoshita, Toyohiko [Japan Synchrotron Radiation Research Institute, SPring-8, Sayo, Hyogo 679-5198 (Japan); CREST-JST, Kawaguchi, Saitama 332-0012 (Japan); Iwase, Akihiro [Department of Materials Science, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531 (Japan); Matsui, Toshiyuki, E-mail: t-matsui@21c.osakafu-u.ac.jp [Research Organization for the 21st Century, Osaka Prefecture University, 1-1 Gakuen-cho, Sakai, Osaka 599-8531 (Japan)

    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. X-ray magnetic circular dichroism photoemission electron microscopy of focused ion beam-induced magnetic patterns on iron-rhodium surfaces

    Science.gov (United States)

    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.

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

    International Nuclear Information System (INIS)

    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

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

    Science.gov (United States)

    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.

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

    CERN Document Server

    Scherrer, Arne; Sebastiani, Daniel; Gross, E K U; Vuilleumier, Rodolphe

    2015-01-01

    The nuclear velocity perturbation current-density 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, similarly 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 strength, 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.

  19. Direct Observation of High-Spin States in Manganese Dimer and Trimer Cations by X-ray Magnetic Circular Dichroism Spectroscopy in an Ion Trap

    CERN Document Server

    Zamudio-Bayer, Vicente; Langenberg, Andreas; Kossick, Martin; Ławicki, Arkadiusz; Terasaki, Akira; von Issendorff, Bernd; Lau, J Tobias

    2015-01-01

    The electronic structure and magnetic moments of free Mn$_2^+$ and Mn$_3^+$ 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 show directly that localized magnetic moments of 5 $\\mu_B$ are created by $3d^5 (^6\\mathrm{S})$ states at each ionic core, which are coupled in parallel 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 orbital with an unpaired spin. This leads to total magnetic moments of 11 $\\mu_B$ for Mn$_2^+$ and 16 $\\mu_B$ for Mn$_3^+$, with no contribution of orbital angular momentum.

  20. Band intensities in the circular dichroism and absorption spectra and the states of d ions in absorbing media: I. Octahedrally coordinated positions of d ions

    International Nuclear Information System (INIS)

    The factors affecting the band intensity in circular dichroism (CD) and absorption spectra (selection rules, point group of structural position, and the electron density of the ground state of octahedrally coordinated d ion in absorbing medium) are considered. The intensities of CD and absorption bands are calculated and compared with the experimental data. It is shown that the differences in the spatial inversion of the electric- and magnetic-dipole moment transformations lead to a more rigorous validity of the symmetry selection rules and increase the resolution of peaks and transparency window of medium absorption in CD spectra (in contrast to absorption ones). Some criteria for estimating the valence and structural states of d ions are formulated.

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

    Science.gov (United States)

    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.

  2. Electronic structure and x-ray magnetic circular dichroism in YbAgCu4 and YbInCu4

    Energy Technology Data Exchange (ETDEWEB)

    Antonov, VN; Bekenov, LV; Antropov, VP

    2014-04-08

    X-ray absorption and magnetic circular dichroism spectra at the L-3 edge of Yb have been studied theoretically in the mixed-valent compounds YbAgCu4 and YbInCu4 using the fully relativistic Dirac linear muffin-tin orbital band structure method. The effect of the spin-orbit (SO) interaction and Coulomb repulsion U on the electronic structure of YbAgCu4 and YbInCu4 is examined in the frame of the local spin-density approximation (LSDA)+SO+U method. The core-hole effect in the final states as well as the effect of the electric quadrupole E-2 and magnetic dipole M-1 transitions have been investigated. The calculated results are compared with available experimental data.

  3. Electronic structure and x-ray magnetic circular dichroism in YbAgCu4 and YbInCu4

    Energy Technology Data Exchange (ETDEWEB)

    Antonov, V N; Bekenov, L V; Antropov, V P

    2014-04-01

    X-ray absorption and magnetic circular dichroism spectra at the L3 edge of Yb have been studied theoretically in the mixed-valent compounds YbAgCu4 and YbInCu4 using the fully relativistic Dirac linear muffin-tin orbital band structure method. The effect of the spin-orbit (SO) interaction and Coulomb repulsion U on the electronic structure of YbAgCu4 and YbInCu4 is examined in the frame of the local spin-density approximation (LSDA)+SO+U method. The core-hole effect in the final states as well as the effect of the electric quadrupole E2 and magnetic dipole M1 transitions have been investigated. The calculated results are compared with available experimental data.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-08-21

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

  5. 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.

    Science.gov (United States)

    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

  6. Study on the interaction of phthalate esters to human serum albumin by steady-state and time-resolved fluorescence and circular dichroism spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Xie, Xiaoyun [National Key Laboratory of Organic Chemistry, Lanzhou University, Lanzhou 730000 (China); College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000 (China); Wang, Zhaowei [College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000 (China); Zhou, Ximin; Wang, Xiaoru [National Key Laboratory of Organic Chemistry, Lanzhou University, Lanzhou 730000 (China); Chen, Xingguo, E-mail: chenxg@lzu.edu.cn [National Key Laboratory of Organic Chemistry, Lanzhou University, Lanzhou 730000 (China); Department of Chemistry, Lanzhou University, Lanzhou 730000 (China)

    2011-09-15

    Highlights: {center_dot} Molecular docking revealed PAEs to be located in the hydrophobic pocket of HSA. {center_dot} HSA-DMP had one class of binding sites while HSA-BBP and HSA-DEHP had two types. {center_dot} Hydrophobic and hydrogen interactions dominated in the association of HSA-PAEs. {center_dot} The lifetime of Trp residue of HSA decreased after the addition of PAEs. {center_dot} The presences of PAEs could alter the second structure of HSA. - Abstract: Phthalate esters (PAEs) are globally pervasive contaminants that are considered to be endocrine disruptor chemicals and toxic environmental priority pollutants. In this paper, the interactions between PAEs and human serum albumin (HSA) were examined by molecular modelling, steady state and time-resolved fluorescence, ultraviolet-visible spectroscopy (UV-vis) and circular dichroism spectroscopy (CD). The association constants between PAEs and HSA were determined using the Stern-Volmer and Scatchard equations. The binding of dimethyl phthalate (DMP) to HSA has a single class of binding site and its binding constants (K) are 4.08 x 10{sup 3}, 3.97 x 10{sup 3}, 3.45 x 10{sup 3}, and 3.20 x 10{sup 3} L mol{sup -1} at 289, 296, 303, and 310 K, respectively. The Stern-Volmer and Scatchard plots both had two regression curves for HSA-butylbenzyl phthalate (BBP) and HSA-di-2-ethylhexyl phthalate (DEHP), which indicated that these bindings were via two types of binding sites: the numbers of binding site for the first type were lower than for the second type. The binding constants of the first type binding site were higher than those of the second type binding site at corresponding temperatures, the results suggesting that the first type of binding site had high affinity and the second binding site involved other sites with lower binding affinity and selectivity. The thermodynamic parameters of the binding reactions ({Delta}G{sup o}, {Delta}H{sup o} and {Delta}S{sup o}) were measured, and they indicated the presences

  7. Study on the interaction of phthalate esters to human serum albumin by steady-state and time-resolved fluorescence and circular dichroism spectroscopy

    International Nuclear Information System (INIS)

    Highlights: · Molecular docking revealed PAEs to be located in the hydrophobic pocket of HSA. · HSA-DMP had one class of binding sites while HSA-BBP and HSA-DEHP had two types. · Hydrophobic and hydrogen interactions dominated in the association of HSA-PAEs. · The lifetime of Trp residue of HSA decreased after the addition of PAEs. · The presences of PAEs could alter the second structure of HSA. - Abstract: Phthalate esters (PAEs) are globally pervasive contaminants that are considered to be endocrine disruptor chemicals and toxic environmental priority pollutants. In this paper, the interactions between PAEs and human serum albumin (HSA) were examined by molecular modelling, steady state and time-resolved fluorescence, ultraviolet-visible spectroscopy (UV-vis) and circular dichroism spectroscopy (CD). The association constants between PAEs and HSA were determined using the Stern-Volmer and Scatchard equations. The binding of dimethyl phthalate (DMP) to HSA has a single class of binding site and its binding constants (K) are 4.08 x 103, 3.97 x 103, 3.45 x 103, and 3.20 x 103 L mol-1 at 289, 296, 303, and 310 K, respectively. The Stern-Volmer and Scatchard plots both had two regression curves for HSA-butylbenzyl phthalate (BBP) and HSA-di-2-ethylhexyl phthalate (DEHP), which indicated that these bindings were via two types of binding sites: the numbers of binding site for the first type were lower than for the second type. The binding constants of the first type binding site were higher than those of the second type binding site at corresponding temperatures, the results suggesting that the first type of binding site had high affinity and the second binding site involved other sites with lower binding affinity and selectivity. The thermodynamic parameters of the binding reactions (ΔGo, ΔHo and ΔSo) were measured, and they indicated the presences of hydrophobic forces and hydrogen interactions in the PAEs-HSA interactions, which agreed well with the results

  8. Photoelectron circular dichroism in the multiphoton ionization by short laser pulses. I. Propagation of single-active-electron wave packets in chiral pseudo-potentials.

    Science.gov (United States)

    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. Applications of X-ray magnetic dichroism in spintronics

    International Nuclear Information System (INIS)

    The advantages of X-ray magnetic circular dichroism and X-ray magnetic linear dichroism are reviewed. With some typical examples we will show that the techniques based on synchrotron facilities have many advantages, such as elemental specification, high sensitivity, nanometer space resolution, picosecond time resolution, and the capability to measure both ferromagnetic and anti-ferromagnetic properties. These techniques are thus very powerful tools in the study of spintronics and its device applications. (author)

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-03-31

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

  11. 3D measurement using circular gratings

    Science.gov (United States)

    Harding, Kevin

    2013-09-01

    3D measurement using methods of structured light are well known in the industry. Most such systems use some variation of straight lines, either as simple lines or with some form of encoding. This geometry assumes the lines will be projected from one side and viewed from another to generate the profile information. But what about applications where a wide triangulation angle may not be practical, particularly at longer standoff distances. This paper explores the use of circular grating patterns projected from a center point to achieve 3D information. Originally suggested by John Caulfield around 1990, the method had some interesting potential, particularly if combined with alternate means of measurement from traditional triangulation including depth from focus methods. The possible advantages of a central reference point in the projected pattern may offer some different capabilities not as easily attained with a linear grating pattern. This paper will explore the pros and cons of the method and present some examples of possible applications.

  12. Linear birefringence and dichroism measurement in oil-based Fe3O4 magnetic nanoparticles

    Science.gov (United States)

    Lin, Jing-Fung; Wang, Chia-Hung; Lee, Meng-Zhe

    2013-04-01

    To prepare dispersed Fe3O4 magnetic nanoparticles (MNPs), we adopt a co-precipitation method and consider surfactant amount, stirring speed, dispersion mode, and molar ratio of Fe3+/Fe2+. Via transmission electronic microscopy and X-ray diffractometry, we characterize the dispersibility and size of the products and determine the appropriate values of experimental parameters. The stirring speed is 1000 rpm in titration. There is simultaneous ultrasonic vibration and mechanical stirring in the titration and surface coating processes. The surfactant amount of oleic acid is 1.2 ml for molar ratios of Fe3+/Fe2+ as 1.7:1, 1.8:1, and 1.9:1. The average diameters of these Fe3O4 MNPs are 11 nm, and the ratios of saturation magnetization for these MNPs to that of bulk magnetite range from 45% to 65%, with remanent magnetization close to zero and low coercivity. Above all, the linear birefringence and dichroism measurements of the kerosene-based ferrofluid (FF) samples are investigated by a Stokes polarimeter. The influences of particle size distribution and magnetization in the birefringence and dichroism measurements of FFs are discussed.

  13. Method of Gaussian quadrature in the calculation of optical absorption and magnetic circular dichroism spectra of s2 ions in alkali halide crystals: application to KBr:In+

    International Nuclear Information System (INIS)

    The problem of calculating the lineshape functon for optical absorption and magnetic circular dichroism due to ionic impurities with the ns2 outer electron configuraton, incorporated substitutionally in alkali halide crystals, has been reformulated. The complete energy matrix has been diagonalized directly. Integration over the interaction mode coordinates of E sub(g) and T sub(2g) symmetry has been carried out numerically using Gaussian quadrature formulae; the interaction with the A sub(1g) mode has been taken into account by the usual convolution procedure. The method has been applied to KBr:In+. The calculated lineshape functions for optical absorption at temperatures ranging from 4 to 300 K and, for MCD at 5 K, are in good agreement with the experimentally determined lineshapes. Moreover, the theory accounts very well for the observed variation of the effective g tensor for the A band with temperature. The calculated values for the moments of the absorption and MCD lineshape functions are in reasonably satisfactory agreement with those deduced from the observed spectra. (author)

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

    Science.gov (United States)

    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.

  15. Applications of circular dichroism (CD) for structural analysis of proteins: qualification of near- and far-UV CD for protein higher order structural analysis.

    Science.gov (United States)

    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

  16. Solvent effects on the absorption, circular dichroism and Raman spectroscopy of meso-tetrakis [3-methoxy-4-(N-carbazyl)n-hexyloxyphenyl] porphyrin in water-THF solution

    Science.gov (United States)

    Wang, Xueli; Lu, Ming; Huo, Cheng; Li, Hongjing; Wang, Yue; Li, Zhengqiang

    2009-08-01

    Solutions of meso-tetrakis [3-methoxy-4-(N-carbazyl)n-hexyloxyphenyl] porphyrin (4C6-TPP) in a water-organic mixture (tetrahydrofuran, THF) generate aggregates with absorption spectra characterized by broader red shifts of the Soret band relative to the monomeric porphyrin band. For the aggregated form several phenyl modes enhance and some modes weaken, the ν 2, ν 3 and ν 11 bands in the Raman spectra are slightly downshifted compared with the monomeric form. These data suggest that the phenyl groups of 4C6-TPP in the aggregate rotate to an orientation more coplanar with the porphyrin core. The increased conjugation of the meso-phenyl rings with the porphyrin core brings about the red shift of the Soret band. The circular dichroism (CD) band of the aggregate undergoes some changes with time, as indicated by the transition from a negative band to no signal resulted from the rotation of phenyl groups. All of the results imply that the location of the phenyl groups plays a key role in the determination of the morphology of the aggregate.

  17. Magnetic circular dichroism of porphyrins containing M = Ca, Ni, and Zn. A computational study based on time-dependent density functional theory.

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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. Application of supervised Kohonen map and counter propagation neural network for classification of nucleic acid structures based on their circular dichroism spectra

    Science.gov (United States)

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

    Science.gov (United States)

    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

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

    KAUST Repository

    Gu, Zhigang

    2014-06-17

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

  2. Effect of urea on bovine serum albumin in aqueous and reverse micelle environments investigated by small angle X-ray scattering, fluorescence and circular dichroism

    International Nuclear Information System (INIS)

    The influence that urea has on the conformation of water-soluble globular protein, bovine serum albumin (BSA), exposed directly to the aqueous solution as compared to the condition where the macromolecule is confined in the Aerosol-OT (AOT - sodium bis-2-ethylhexyl sulfosuccinate)/n-hexane/water reverse micelle (RM) is addressed. Small angle X-ray scattering (SAXS), tryptophan (Trp) fluorescence emission and circular dichroism (CD) spectra of aqueous BSA solution in the absence and in the presence of urea (3M and 5M) confirm the known denaturing effect of urea in proteins. The loss of the globular native structure is observed by the increase in the protein maximum dimension and gyration radius, through the Trp emission increase and maximum red-shift as well as the decrease in helix content. In RMs, the Trp fluorescence and CD spectra show that BSA is mainly located in its interfacial region independently of the micellar size. Addition of urea in this BSA/RM system also causes changes in the Trp fluorescence (emission decrease and maximum red-shift) and in the BSA CD spectra (decrease in helix content), which are compatible with the denaturation of the protein and Trp exposition to a more apolar environment in the RM. The fact that urea causes changes in the protein structure when it is located in the interfacial region (evidenced by CD) is interpreted as an indication that the direct interaction of urea with the protein is the major factor to explain its denaturing effect. (author)

  3. Mulliken population analysis of X-ray magnetic circular dichroism in uranium monochalcogenides. Examination of sum rules by fully relativistic full-potential LCAO method

    International Nuclear Information System (INIS)

    We study the X-ray magnetic circular dichroism (XMCD) spectra at the U M4,5 and N4,5 edges of uranium monochalcogenides, UX where X=S, Se, and Te, examining the applicability of the XMCD sum rules to UX by the fully relativistic full-potential linear-combination-of-atomic-orbitals (LCAO) method based on the density functional theory. To extract the transitions relevant to the sum-rule analysis, we employ the Mulliken population analysis (MPA). Using the MPA, the orbital sum rule is found to be valid to 10-20% for the M4,5 edges and valid to 5-15% for the N4,5 edges. On the other hand, the spin sum rule is found to be valid to 10-20% for the M4,5 edges whereas valid to 30-35% for the N4,5 edges. Furthermore, it is found that the calculated XMCD spectra are consistent with a recent experimental observation that the intensity of the N4,5 XMCD signal is comparable to that of the M4,5 XMCD signal although contradicting a previous theoretical prediction that the XMCD intensity at the N4,5 edges is one order of magnitude smaller than that at the M4,5 edges. (author)

  4. 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

    Science.gov (United States)

    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).

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-04-01

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

  6. Photoinduced Circular Anisotropy in Side-Chain Azobenzene Polyesters

    DEFF Research Database (Denmark)

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

    1997-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-01-21

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

  8. The influence of carbon nanotubes on enzyme activity and structure: investigation of different immobilization procedures through enzyme kinetics and circular dichroism studies

    International Nuclear Information System (INIS)

    In the last decade, many environmental organizations have devoted their efforts to identifying renewable biosystems, which could provide sustainable fuels and thus enhance energy security. Amidst the myriad of possibilities, some biofuels make use of different types of waste biomasses, and enzymes are often employed to hydrolyze these biomasses and produce sugars that will be subsequently converted into ethanol. In this project, we aimed to bridge nanotechnology and biofuel production: here we report on the activity and structure of the enzyme amyloglucosidase (AMG), physically adsorbed or covalently immobilized onto single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs). In fact, carbon nanotubes (CNTs) present several properties that render them ideal support systems, without the diffusion limitations displayed by porous material and with the advantage of being further functionalizable at their surface. Chemical ligation was achieved both on oxidized nanotubes (via carbodiimide chemistry), as well as on amino-functionalized nanotubes (via periodate-oxidized AMG). Results showed that AMG retained a certain percentage of its specific activity for all enzyme-carbon nanotubes complexes prepared, with the physically adsorbed samples displaying better catalytic efficiency than the covalently immobilized samples. Analysis of the enzyme's structure through circular dichroism (CD) spectroscopy revealed significant structural changes in all samples, the degree of change being consistent with the activity profiles. This study proves that AMG interacts differently with carbon nanotubes depending on the method employed. Due to the higher activity reported by the enzyme physically adsorbed onto CNTs, these samples demonstrated a vast potential for further development. At the same time, the possibility of inducing magnetic properties into CNTs offers the opportunity to easily separate them from the original solution. Hence, substances to which they

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

    International Nuclear Information System (INIS)

    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

  10. The influence of carbon nanotubes on enzyme activity and structure: investigation of different immobilization procedures through enzyme kinetics and circular dichroism studies

    Energy Technology Data Exchange (ETDEWEB)

    Cang-Rong, Jason Teng; Pastorin, Giorgia [Department of Pharmacy, National University of Singapore, 117543 (Singapore)], E-mail: jasonteng@nus.edu.sg, E-mail: phapg@nus.edu.sg

    2009-06-24

    In the last decade, many environmental organizations have devoted their efforts to identifying renewable biosystems, which could provide sustainable fuels and thus enhance energy security. Amidst the myriad of possibilities, some biofuels make use of different types of waste biomasses, and enzymes are often employed to hydrolyze these biomasses and produce sugars that will be subsequently converted into ethanol. In this project, we aimed to bridge nanotechnology and biofuel production: here we report on the activity and structure of the enzyme amyloglucosidase (AMG), physically adsorbed or covalently immobilized onto single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs). In fact, carbon nanotubes (CNTs) present several properties that render them ideal support systems, without the diffusion limitations displayed by porous material and with the advantage of being further functionalizable at their surface. Chemical ligation was achieved both on oxidized nanotubes (via carbodiimide chemistry), as well as on amino-functionalized nanotubes (via periodate-oxidized AMG). Results showed that AMG retained a certain percentage of its specific activity for all enzyme-carbon nanotubes complexes prepared, with the physically adsorbed samples displaying better catalytic efficiency than the covalently immobilized samples. Analysis of the enzyme's structure through circular dichroism (CD) spectroscopy revealed significant structural changes in all samples, the degree of change being consistent with the activity profiles. This study proves that AMG interacts differently with carbon nanotubes depending on the method employed. Due to the higher activity reported by the enzyme physically adsorbed onto CNTs, these samples demonstrated a vast potential for further development. At the same time, the possibility of inducing magnetic properties into CNTs offers the opportunity to easily separate them from the original solution. Hence, substances to which

  11. Characterization of the binding of metoprolol tartrate and guaifenesin drugs to human serum albumin and human hemoglobin proteins by fluorescence and circular dichroism spectroscopy.

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

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

    1999-04-01

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

  14. Controlled cobalt doping in the spinel structure of magnetosome magnetite: new evidences from element- and site-specific X-ray magnetic circular dichroism analyses.

    Science.gov (United States)

    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

  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.

    Science.gov (United States)

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

    Science.gov (United States)

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

    2016-02-01

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

  17. Deflection gating for time-resolved x-ray magnetic circular dichroism-photoemission electron microscopy using synchrotron radiation.

    Science.gov (United States)

    Wiemann, C; Kaiser, A M; Cramm, S; Schneider, C M

    2012-06-01

    In this paper, we present a newly developed gating technique for a time-resolving photoemission microscope. The technique makes use of an electrostatic deflector within the microscope's electron optical system for fast switching between two electron-optical paths, one of which is used for imaging, while the other is blocked by an aperture stop. The system can be operated with a switching time of 20 ns and shows superior dark current rejection. We report on the application of this new gating technique to exploit the time structure in the injection bunch pattern of the synchrotron radiation source BESSY II at Helmholtz-Zentrum Berlin for time-resolved measurements in the picosecond regime. PMID:22755633

  18. Electronic states of magnetic refrigerator materials Mn{sub 0.9}Fe{sub 1.1}P{sub 0.55}As{sub 0.45} using soft x-ray magnetic circular dichroism

    Energy Technology Data Exchange (ETDEWEB)

    Takeda, Y; Okane, T; Ohkochi, T; Fujimori, S-I; Saitoh, Y; Yamagami, H [Japan Atomic Energy Agency, Synchrotron Radiation Research Center SPring-8, Kouto, Sayo, Hyogo 679-5148 (Japan); Yabuta, H; Takabatake, T, E-mail: ytakeda@spring8.or.j [Department of Quantum Matter, Graduate School of Advanced Sciences of Matter, Hiroshima University, Kagamiyama, Higashi-Hiroshima 739-8530 (Japan)

    2010-01-15

    The system of MnFeP{sub 1-x}As{sub x} is a candidate of a magnetic refrigerator material. We have investigated the temperature (T)- and magnetic field (H)-dependence of the magnetic properties of the Mn and Fe ions for Mn{sub 0.9}Fe{sub 1.1}P{sub 0.55}As{sub 0.45} using a soft x-ray magnetic circular dichroism (XMCD) in the regions of the Mn and Fe L{sub 2,3} absorption edges. In the ferromagnetic states, the magnetic moments of the Mn and Fe ions turn to the same direction. It is considered that the Mn ions are close to divalent (Mn{sup 2+}) states and that the Fe ions are a mixture of trivalent (Fe{sup 3+}) and divalent (Fe{sup 2+}) states. However, we deduce that the ferromagnetic properties of the Fe ions are mainly derived from the Fe{sup 2+} states. Using the XMCD sum rules, we have found that the magnitude of the magnetic moment of the Mn ions is larger than that of the Fe ions. The paramagnetic to ferromagnetic transitions are clearly observed by the T- and H- dependent XMCD measurements. Since the shapes of the spectra don't change in all experiment conditions, the electronic configurations of the Mn and Fe ions are not changed by the PM-FM transition.

  19. Elucidating the role of the proximal cysteine hydrogen-bonding network in ferric cytochrome P450cam and corresponding mutants using magnetic circular dichroism spectroscopy.

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    Valencia Navarro, Laura N.

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

  2. Circular dichroism and UV melting studies on formation of an intramolecular triplex containing parallel T*A:T and G*G:C triplets: netropsin complexation with the triplex.

    OpenAIRE

    Gondeau, C.; Maurizot, J C; Durand, M

    1998-01-01

    We have used circular dichroism and UV absorption spectroscopy to characterize the formation and melting behaviour of an intramolecular DNA triple helix containing parallel T*A:T and G*G:C triplets. Our approach to induce and to stabilize a parallel triplex involves the oligonucleotide 5'-d(G4A4G4[T4]C4T4C4-[T4]G4T4G4) ([T4] represents a stretch of four thymine residues). In a 10 mM sodium cacodylate, 0.2 mM disodium EDTA (pH 7) buffer, we have shown the following significant results. (i) Whi...

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

    CERN Document Server

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

    2015-01-01

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

  4. Contactless Measurement of Angular Velocity using Circularly Polarized Antennas

    OpenAIRE

    Sipal, Vit; Narbudowicz, Adam; Ammann, Max

    2014-01-01

    An innovative method to measure the angular velocity using circularly polarized antennas is proposed. Due to the properties of circular polarization, the angular velocity is frequency modulated (FM) on a wireless carrier. This enables a low-cost precise continuous measurement of angular velocity using a standard FM demodulator. The hardware can be easily adapted for both high and low angular velocity values. The precise alignment angle between the antennas can be determined if the initial ant...

  5. Time-dependent density functional theory applied to ligand-field excitations and their circular dichroism in some transition metal complexes

    International Nuclear Information System (INIS)

    Graphical abstract: Ligand-field (LF) transitions in [Co(en)3]3+ and [Rh(en)3]2+ and the low-energy part of the electronic circular dichroism (CD) spectrum of [Fe(phen)3]2+ are investigated with time-dependent density functional theory (TDDFT). There is a strong functional dependence for [Co(en)3]3+ and [Fe(phen)3]2+. ΔSCF methods reproduce the ligand-field singlet excitation energies of [Co(en)3]3+ and [Rh(en)3]2+ well. For the LF transitions of [Co(en)3]3+ TDDFT with a hybrid functional with around 25correction/Coulomb attenuation offers little improvement for the LF transitions in [Co(en)3]3+ because the occupied and unoccupied orbitals involved are in close spatial proximity. Highlights: ► TDDFT Ligand-field (LF) excitations in 3d metal complexes are functional dependent. ► Study of Co(en)3(3+) links sensitivity to correlation/self-interaction balance. ► Correlation effects on the LF spectra are very large. ► Range separated functionals offer limited improvement due to spatial proximity of orbitals. - Abstract: Ligand-field transitions in [Co(en)3]3+ and [Rh(en)3]3+ as well as the low-energy part of the electronic spectrum of [Fe(phen)3]2+ are investigated with time-dependent density functional theory (TDDFT). There is a strong functional dependence for [Co(en)3]3+ and [Fe(phen)3]2+. ΔSCF methods reproduce the ligand-field singlet excitation energies of [Co(en)3]3+ and [Rh(en)3]3+ very well. The case of [Co(en)3]3+ is analyzed in some detail, in particular regarding the possibility of applying a charge-transfer (CT) correction [M.E. Casida, F. Gutierrez, J. Guan, F.-X. Gadea, D.R. Salahub, J.-P. Daudey, J. Chem. Phys. 113 (2000) 7062]. A simple CT correction would not be sufficient, but the magnitude of the charge transfer correction term in comparison with the calculated excitation energy appears to be indicative of self-interaction problems in the ground state electronic structure and in the calculated excitation energies. For the ligand

  6. Method for measuring optical fiber core no-circularity

    Science.gov (United States)

    Xiao, Shao-rong; Zhang, Xian-ling; Mao, Xiao-li

    2007-12-01

    Tops of optical fiber are polished to be detectable, the tops come into plane, which are perpendicular to fiber axis. A cirque pattern is formed on the out top of fiber by skew rays in the fiber. The pattern is shot with a digital camera. A bitmap format cirque pattern is obtained. The inside and outside boundaries are taken out with digital image processing method. Three different pels on the boundaries are picked out to define a circle at every space. The maximum and the minimum diameter are picked out from many circles acquired to calculate the fiber core no-circularity in according to definition. A quartz fiber core no-circularity was measured, with numerical aperture 0.22, and diameter 100 micron. When the optical fiber was placed straight, periphery of the pattern on the out top appear regular denotation, the core no-circularity is less than 4.0%. But the fiber is made into a spiral cord in diameter 20cm, the periphery of the pattern is smooth, measured the no-circularity is about 1.7%, the result is identical to which obtained by microscope measurement. The result indicates that no-circularity measured is almost independent of wavelength of laser with modes being disturbed.

  7. A Circular Statistical Method for Extracting Rotation Measures

    Indian Academy of Sciences (India)

    S. Sarala; Pankaj Jain

    2002-03-01

    We propose a new method for the extraction of Rotation Measures from spectral polarization data. The method is based on maximum likelihood analysis and takes into account the circular nature of the polarization data. The method is unbiased and statistically more efficient than the standard 2 procedure.

  8. Circular polarization measurements with a Ge(Li) detector

    DEFF Research Database (Denmark)

    Kopecký, J.; Warming, Inge Elisabeth

    1969-01-01

    This paper presents the results obtained in measurements of the degree of circular polarization of gamma transitions to bound states of 33S, 36Cl, 49Ti, 56Mn, 57Fe, 60Co and 64Cu following the capture of polarized thermal neutrons. Spin values have been determined on the basis of these results....

  9. Linear birefringence and dichroism measurement in oil-based Fe{sub 3}O{sub 4} magnetic nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Jing-Fung, E-mail: jacklin@cc.feu.edu.tw [Graduate School of Computer Application Engineering, Far East University, Tainan 74448, Taiwan (China); Wang, Chia-Hung [Department of Automation and Control Engineering, Far East University, Tainan 74448, Taiwan (China); Lee, Meng-Zhe [Graduate School of Computer Application Engineering, Far East University, Tainan 74448, Taiwan (China)

    2013-04-15

    To prepare dispersed Fe{sub 3}O{sub 4} magnetic nanoparticles (MNPs), we adopt a co-precipitation method and consider surfactant amount, stirring speed, dispersion mode, and molar ratio of Fe{sup 3+}/Fe{sup 2+}. Via transmission electronic microscopy and X-ray diffractometry, we characterize the dispersibility and size of the products and determine the appropriate values of experimental parameters. The stirring speed is 1000 rpm in titration. There is simultaneous ultrasonic vibration and mechanical stirring in the titration and surface coating processes. The surfactant amount of oleic acid is 1.2 ml for molar ratios of Fe{sup 3+}/Fe{sup 2+} as 1.7:1, 1.8:1, and 1.9:1. The average diameters of these Fe{sub 3}O{sub 4} MNPs are 11 nm, and the ratios of saturation magnetization for these MNPs to that of bulk magnetite range from 45% to 65%, with remanent magnetization close to zero and low coercivity. Above all, the linear birefringence and dichroism measurements of the kerosene-based ferrofluid (FF) samples are investigated by a Stokes polarimeter. The influences of particle size distribution and magnetization in the birefringence and dichroism measurements of FFs are discussed. - Highlights: ► Dispersed Fe{sub 3}O{sub 4} magnetic nanoparticles (MNPs) are produced by a co-precipitation method. ► Simultaneous ultrasonic vibration and mechanical stirring are used in titration and coating. ► Diameters of Fe{sub 3}O{sub 4} MNPs are determined as 11 nm with maximum magnetization as 54.27 emu/g. ► Birefringence and dichroism of ferrofluids are obtained by a Stokes polarimeter successfully.

  10. Circular Hough Transform and Local Circularity Measure for Weight Estimation of a Graph-Cut based Wood Stack Measurement

    DEFF Research Database (Denmark)

    Galsgaard, Bo; Lundtoft, Dennis Holm; Nikolov, Ivan Adriyanov;

    2015-01-01

    difficult task. Graph-cut has shown to be good enough for such a segmentation. However, it is hard to find proper graph weights. This is exactly the contribution of this paper to propose a method for setting the weights of the graph. To do so, we use Circular Hough Transform (CHT) for obtaining information...... about the foreand background regions of a stack image, and then use this together with a Local Circularity Measure (LCM) to modify the weights of the graph to segment the wood logs from the rest of the image. We further improve the segmentation by separating overlapping logs. These segmented wood logs...

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

    DEFF Research Database (Denmark)

    Naydenova, I.; Nikolova, L.; Todorov, T.; Andruzzi, F.; Hvilsted, Søren; Ramanujam, P.S.

    1997-01-01

    We investigate light propagation through materials with both linear and circular anisotropy and find the relation of the amplitude and polarization transfer functions to the four anisotropic characteristics: linear circular birefringence, and linear and circular dichroism. We determine these four...... characteristics of anisotropic samples by measuring the output intensity and polarization corresponding to different input polarization azimuths and fitting the theoretical and experimental results. In our experiments we have used films of side-chain azobenzene polyesters in which optical anisotropy had been...

  12. Higgs Measurement at e+e- Circular Colliders

    CERN Document Server

    Ruan, M

    2014-01-01

    Now that the mass of the Higgs boson is known, circular electron positron colliders, able to measure the properties of these particles with high accuracy, are receiving considerable attention. Design studies have been launched (i) at CERN with the Future Circular Colliders (FCC), of which an e+e- collider is a potential first step (FCC-ee, formerly caller TLEP) and (ii) in China with the Circular Electron Positron Collider (CEPC). Hosted in a tunnel of at least 50 km (CEPC) or 80-100 km (FCC), both projects can deliver very high luminosity from the Z peak to HZ threshold (CEPC) and even to the top pair threshold and above (FCC-ee). At the ZH production optimum, around 240 GeV, the FCC-ee (CEPC) will be able to deliver 10 (5) ab-1 integrated luminosity in 5 (10) years with 4 (2) interaction points: hence to produce millions of Higgs bosons through the Higgsstrahlung process and vector boson fusion processes. This sample opens the possibility of subper-cent precision absolute measurements of the Higgs boson cou...

  13. The Primordial Inflation Polarization Explorer: Science from Circular Polarization Measurements

    Science.gov (United States)

    Switzer, Eric; Ade, P.; Benford, D. J.; Bennett, C. L.; Chuss, D. T.; Dotson, J. L.; Eimer, J.; Fixsen, D. J.; Halpern, M.; Hinshaw, G. F.; Irwin, K.; Jhabvala, C.; Johnson, B.; Kogut, A. J.; Lazear, J.; Mirel, P.; Moseley, S. H.; Staguhn, J.; Tucker, C. E.; Weston, A.; Wollack, E.

    2014-01-01

    The Primordial Inflation Polarization Explorer (PIPER) is a balloon-borne CMB polarimeter designed to constrain the B-mode signature of cosmological inflation. Sequential one-day flights from Northern- and Southern- Hemisphere sites will yield maps of Stokes I, Q, U and V at 200, 270, 350 and 600 GHz over 85% of the sky. The full optical path is cooled to 1.5 K by liquid helium in the ARCADE bucket dewar, and a variable-delay polarization modulator (VPM) at the front of the optics modulates the polarization response. Independent Q and U cameras each have two 32x40 Transition Edge Sensor array receivers. In addition to its primary inflationary science goal, PIPER will also measure the circular (Stokes V) polarization to a depth similar to that of the primary linear polarization. The circular polarization has received relatively little attention in large-area surveys, with constraints from the 1980’s and recent results by the Milan Polarimeter. Astrophysical circular polarization is generally tied to the presence of magnetic fields, either in relativistic plasmas or Zeeman splitting of resonances. These effects are thought to be undetectable at PIPER's frequencies and resolution, despite the depth. The expectation of a null result makes the deep Stokes V map a good cross-check for experimental systematics. More fundamentally, the fact that the sky is expected to be dark in Stokes V makes it a sector sensitive to processes such as Lorentz-violating terms in the standard model or magnetic fields in the CMB era.

  14. 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

    Science.gov (United States)

    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.

  15. 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

    International Nuclear Information System (INIS)

    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.

  16. Systematic study on the TD-DFT calculated electronic circular dichroism spectra of chiral aromatic nitro compounds: A comparison of B3LYP and CAM-B3LYP

    Science.gov (United States)

    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.

  17. 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

    Science.gov (United States)

    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.

  18. Magnetic structures of FeTiO3-Fe2O3 solid solution thin films studied by soft X-ray magnetic circular dichroism and ab initio multiplet calculations

    International Nuclear Information System (INIS)

    The solid solutions between ilmenite (FeTiO3) and hematite (α-Fe2O3) 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 0.6FeTiO3·0.4Fe2O3 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 Fe2+–Fe3+ states while Fe2+ 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 Fe2+ ions

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

    Indian Academy of Sciences (India)

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

    2002-05-01

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

  20. Cluster model calculation for X-ray magnetic circular dichroism at rare-earth (R) L sub 2 sub , sub 3 absorption edges in R sub 2 Fe sub 1 sub 4 B

    CERN Document Server

    Asakura, K; Harada, I; Ogasawara, H; Fukui, K; Kotani, A

    2002-01-01

    X-ray magnetic circular dichroism (MCD) at the L sub 2 sub , sub 3 absorption edges for the entire series of rare-earth (RE) elements in R sub 2 Fe sub 1 sub 4 B (R=RE) is studied based on a cluster model including 10 RE and 16 Fe atoms. The cluster model takes into account band effects of RE 5d states, to which the electric dipole transition occurs from the core 2p states, as well as spin polarization of the 5d states due to the interatomic hybridization with the spin polarized Fe 3d states. We also take into account spin and orbital polarization of the 5d states due to the 5d-4f intra-atomic exchange interaction, and the 2p to 4f quadrupole transition. The calculated results are in satisfactory agreement with experimental ones, suggesting that the cluster model calculation provides a new method to calculate quantitatively MCD spectra of RE systems with complicated atomic arrangements. (author)

  1. A new highly adaptable design of shear-flow device for orientation of macromolecules for Linear Dichroism (LD) measurement

    KAUST Repository

    Lundahl, P. Johan

    2011-01-01

    This article presents a new design of flow-orientation device for the study of bio-macromolecules, including DNA and protein complexes, as well as aggregates such as amyloid fibrils and liposome membranes, using Linear Dichroism (LD) spectroscopy. The design provides a number of technical advantages that should make the device inexpensive to manufacture, easier to use and more reliable than existing techniques. The degree of orientation achieved is of the same order of magnitude as that of the commonly used concentric cylinders Couette flow cell, however, since the device exploits a set of flat strain-free quartz plates, a number of problems associated with refraction and birefringence of light are eliminated, increasing the sensitivity and accuracy of measurement. The device provides similar shear rates to those of the Couette cell but is superior in that the shear rate is constant across the gap. Other major advantages of the design is the possibility to change parts and vary sample volume and path length easily and at a low cost. © 2011 The Royal Society of Chemistry.

  2. The PVLAS experiment: measuring vacuum magnetic birefringence and dichroism with a birefringent Fabry-Perot cavity

    Energy Technology Data Exchange (ETDEWEB)

    Della Valle, Federico; Milotti, Edoardo [INFN, Trieste (Italy); Universita di Trieste, Dipt. di Fisica, Trieste (Italy); Ejlli, Aldo; Messineo, Giuseppe; Zavattini, Guido [INFN, Ferrara (Italy); Universita di Ferrara, Dipt. di Fisica e Scienze della Terra, Ferrara (Italy); Gastaldi, Ugo [INFN, Ferrara (Italy); Pengo, Ruggero; Ruoso, Giuseppe [INFN, Lab. Nazionale di Legnaro, Legnaro (Italy)

    2016-01-15

    Vacuum magnetic birefringence was predicted long time ago and is still lacking a direct experimental confirmation. Several experimental efforts are striving to reach this goal, and the sequence of results promises a success in the next few years. This measurement generally is accompanied by the search for hypothetical light particles that couple to two photons. The PVLAS experiment employs a sensitive polarimeter based on a high finesse Fabry-Perot cavity. In this paper we report on the latest experimental results of this experiment. The data are analysed taking into account the intrinsic birefringence of the dielectric mirrors of the cavity. Besides a new limit on the vacuum magnetic birefringence, the measurements also allow the model-independent exclusion of new regions in the parameter space of axion-like and milli-charged particles. In particular, these last limits hold also for all types of neutrinos, resulting in a laboratory limit on their charge. (orig.)

  3. Measuring the Innermost Stable Circular Orbits of Supermassive Black Holes

    Science.gov (United States)

    Zalesky, L.; Chartas, G.

    2016-06-01

    We present a promising new technique (g-distribution method) for measuring the innermost stable circular orbit (ISCO), the inclination angle (i), and the spin of a supermassive black hole. The g-distribution method involves measurements of the distribution of the energy shifts of the relativistic iron line emitted from the accretion disk of a supermassive black hole that is microlensed by stars in a foreground galaxy and a comparison of the measured g-distribution with microlensing caustic simulations. The method has been applied to the gravitationally lensed quasars RX J1131-1231 (z_{s} = 0.658, z_{l} = 0.295), QJ 0158-4325 (z_{s} = 1.29, z_{l} = 0.317), and SDSS 1004+4112 (z_{s} = 1.73, z_{l} = 0.68). For RX J1131-1231 our initial results indicate an ISCO radius of < 5 gravitational radii and i < 65 degrees. Further monitoring of lensed quasars will provide tighter constraints on their inclination angles, ISCO radii, and spins.

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

    Directory of Open Access Journals (Sweden)

    Christopher J Reed

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

  5. Angle measurement error and compensation for decentration rotation of circular gratings

    Institute of Scientific and Technical Information of China (English)

    CHEN Xi-jun; WANG Zhen-huan; ZENG Qing-shuang

    2010-01-01

    As the geometric center of circular grating does not coincide with the rotation center,the angle measurement error of circular grating is analyzed.Based on the moire fringe equations in decentration condition,the mathematical model of angle measurement error is derived.It is concluded that the deeentration between the centre of circular grating and the center of revolving shaft leads to the first-harmonic error of angle measurement.The correctness of the result is proved by experimental data.The method of error compensation is presented,and the angle measurement accuracy of the circular grating is effectively improved by the error compensation.

  6. Mapping the Anopheles gambiae Odorant Binding Protein 1 (AgamOBP1) using modeling techniques, site directed mutagenesis, circular dichroism and ligand binding assays

    OpenAIRE

    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.

    2012-01-01

    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 c...

  7. Changes in the Molar Ellipticities of HEWL Observed by Circular Dichroism and Quantitated by Time Resolved Fluorescence Anisotropy Under Crystallizing Conditions

    Science.gov (United States)

    Sumida, John

    2002-01-01

    Fluid models for simple colloids predict that as the protein concentration is increased, crystallization should occur at some sufficiently high concentration regardless of the strength of attraction. However, empirical measurements do not fully support this assertion. Measurements of the second virial coefficient (B22) indicate that protein crystallization occurs only over a discrete range of solution parameters. Furthermore, observations of a strong correlation between protein solubility and B22, has led to an ongoing debate regarding the relationship between the two. Experimental work in our lab, using Hen Egg White Lysozyme (HEWL), previously revealed that the rotational anisotropy of the protein under crystallizing conditions changes systematically with pH, ionic strength and temperature. These observations are now supported by recent work revealing that small changes in the molar ellipticity also occur systematically with changes in ionic strength and temperature. This work demonstrates that under crystallization conditions, the protein native state is characterized by a conformational heterogeneity that may prove fundamental to the relationship between protein crystallization and protein solubility.

  8. A study of magnetic properties of hard and soft magnetic materials by Lorentz transmission electron microscopy and magnetic x-ray circular dichroism

    CERN Document Server

    Pickford, R A

    2001-01-01

    iron spin and orbital magnetic moments were found to decrease with increasing iron content. In collaboration with CEA Saclay, Paris, a set of cobalt elements were patterned by electron beam lithography. The elements were designed to isolate domain walls and to monitor their movement in an applied field. The shape anisotropy of the element was found to be too large for the insitu magnetic field to flip the magnetisation. The domain walls found in the as received magnetic state were associated with defects in the structure of the element. The magnetisation process was compared to micromagnetic simulations, A further study of magnetic elements was made to study the competition of anisotropy in patterned cobalt dots. The shape anisotropy was calculated and the crystalline anisotropy of the cobalt film was measured. The dots (rectangles) were patterned so that the shape anisotropy was comparable to the crystalline anisotropy of the cobalt. The dots were patterned at 45 degrees to the crystalline anisotropy. This t...

  9. Characterization of the 1st and 2nd EF-hands of NADPH oxidase 5 by fluorescence, isothermal titration calorimetry, and circular dichroism

    Directory of Open Access Journals (Sweden)

    Wei Chin-Chuan

    2012-04-01

    Full Text Available Abstract Background Superoxide generated by non-phagocytic NADPH oxidases (NOXs is of growing importance for physiology and pathobiology. The calcium binding domain (CaBD of NOX5 contains four EF-hands, each binding one calcium ion. To better understand the metal binding properties of the 1st and 2nd EF-hands, we characterized the N-terminal half of CaBD (NCaBD and its calcium-binding knockout mutants. Results The isothermal titration calorimetry measurement for NCaBD reveals that the calcium binding of two EF-hands are loosely associated with each other and can be treated as independent binding events. However, the Ca2+ binding studies on NCaBD(E31Q and NCaBD(E63Q showed their binding constants to be 6.5 × 105 and 5.0 × 102 M-1 with ΔHs of -14 and -4 kJ/mol, respectively, suggesting that intrinsic calcium binding for the 1st non-canonical EF-hand is largely enhanced by the binding of Ca2+ to the 2nd canonical EF-hand. The fluorescence quenching and CD spectra support a conformational change upon Ca2+ binding, which changes Trp residues toward a more non-polar and exposed environment and also increases its α-helix secondary structure content. All measurements exclude Mg2+-binding in NCaBD. Conclusions We demonstrated that the 1st non-canonical EF-hand of NOX5 has very weak Ca2+ binding affinity compared with the 2nd canonical EF-hand. Both EF-hands interact with each other in a cooperative manner to enhance their Ca2+ binding affinity. Our characterization reveals that the two EF-hands in the N-terminal NOX5 are Ca2+ specific. Graphical abstract

  10. Contribution to the study of TRH (thyrotropin-releasing hormone) conformation using circular dichroism. Physico-chemical studies, radioactive labelling and biological applications

    International Nuclear Information System (INIS)

    In an attempt to reach a better understanding at the molecular level of phenomena connected with the action of TRF the conformation and radioactive labelling of this hormone were investigated. The specific detection of a hormone at its action site is only possible if labelled substances of very high specific activity are used. TRF was tritium labelled by three methods: direct catalytic exchange; catalytic dehalogenation of mono- and di-iodo TRF; catalytic denitrogenation of mono-azo-TRF. Whatever the method used the tritiated TRF has a very high specific activity and keeps all its biological properties. Biological activity measurements carried out on labelled TRF, in vivo in rats and in vitro on a TRF-sensitive prolactine cell clone, are described. TRF tritiated by the above methods is shown to have the same biological activity as standard TRF. Some results are given concerning the application of labelled TRF to research on the hormone action mechanism. The tritiated TRF distribution kinetics were examined in vivo and in vitro. The kinetics of hormone fixation on the antehypophysary tissue match those of in vivo release of the plasma thyreotropic hormone, confirming the relationships between the hormone fixation on its target tissue and its biological effect. Finally an outline is given of work on the interaction of tritiated TRF with prolactine cell receptors and on the penetration of intact tritiated TRF into these cells. In addition the radioimmunological analysis of TRF was developed by the use of 125I-mono-iodo-TRF at high specific activity (above 2000 Ci/mmole)

  11. Formation of local native-like tertiary structures in the slow refolding reaction of human carbonic anhydrase II as monitored by circular dichroism on tryptophan mutants.

    Science.gov (United States)

    Andersson, D; Freskgård, P O; Jonsson, B H; Carlsson, U

    1997-04-15

    In the present study, near-UV CD kinetic measurements on mutants, in which one Trp residue had been replaced, were performed to probe the development of asymmetric environments around specific Trp residues during the refolding of human carbonic anhydrase II (HCAII). In addition, the formation of the active site was probed by the binding of a fluorescent sulfonamide inhibitor. The development of the individual Trp CD spectra during refolding was obtained by subtracting the CD spectrum of the mutant lacking one Trp from that of HCAII at different time points. The same method was used for the particular Trp residues to obtain the kinetic CD traces monitored at a specific wavelength (270 nm). Trp residues 16, 97, and 245 were analyzed. Trp16 probes the N-terminal domain (amino acid residues 1-25), and this part is forming its tertiary structure slower than the major domain (amino acid residues 26-260) of the protein molecule, which contains the active site and a dominating beta-sheet. An essentially native structure of the major domain seems to act as a template for the correct folding of the N terminus. Trp97 is located in a hydrophobic cluster comprising beta-strands 3-5 in the protein core. Previously, we have shown that this region is remarkably stable and compact, and stopped-flow fluorescence data indicate that Trp97 is buried in an apolar compact cluster within a few milliseconds [Svensson, M., Jonasson, P., Freskgård, P.-O., Jonsson, B.-H., Lindgren, M., Martensson, L.-G., Gentile, M., Bóren, K., & Carlsson, U. (1995) Biochemistry 34, 8606-8620; Jonasson, P., Aronsson, G., Carlsson, U., & Jonsson, B.-H. (1997) Biochemistry 36 (in press)]. Here it is shown that the development of the native tertiary structure at Trp97 occurs in the minute time domain. Trp245 is located in a long loop between the N-terminal domain and the core structure. Although this Trp has attained native-like fluorescence properties within the dead time of the CD experiment, it assumes a

  12. Achieving atomic resolution magnetic dichroism by controlling the phase symmetry of an electron probe

    OpenAIRE

    Rusz, Jan; Idrobo, Juan-Carlos; Bhowmick, Somnath

    2014-01-01

    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 distribution using the aberration-corrected optics of an scanning transmission electron microscope. The required phase di...

  13. 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.

    Science.gov (United States)

    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

  14. Years of Magnetic X-Ray Dichroism

    Science.gov (United States)

    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.

  15. Stability, failure, and measurements of boreholes and other circular openings

    International Nuclear Information System (INIS)

    This report provides the reader with an update on the understanding of the stability and instability of circular openings excavated in rock formations. During the past decade, there has been a flurry of activity in this area, mainly spirited by the emergence of new challenges in the oil and gas industry. Detailed tests were conducted in many laboratories throughout the world under controlled conditions. New findings were substantiated by careful field observations, and new analytical methodologies were developed to explain some of the observed mechanisms. This report begins by clarifying that a failure criterion is a relative notion and exists as a function of the individual application. The concept of abnormal stability is then introduced, after which all potential failure are reviewed in chronological order. The report describes the influence of temporary supports during excavation, the stabilizing effect of the end face, delayed instabilities due to time-dependent effects, and long-term stability conditions. The report clearly outlines unusual and/or unexplainable phenomena requiring additional research. The observational evidence given in this report demonstrates the inadequacy of strictly elastic considerations. The report clearly shows the similarities observed in large circular excavations compared to small diameter boreholes. Whenever possible, it attempts to bridge the gap between various disciplines by discussing the findings of typical failures

  16. Mechanical design and analysis of an eight-pole superconducting vector magnet for soft x-ray magnetic dichroism measurements

    Energy Technology Data Exchange (ETDEWEB)

    Arbelaez, D.; Black, A.; Prestemon, S.O.; Wang, S.; Chen, J.; Arenholz, E.

    2010-01-13

    An eight-pole superconducting magnet is being developed for soft x-ray magnetic dichroism (XMD) experiments at the Advanced Light Source, Lawrence Berkley National Laboratory (LBNL). Eight conical Nb{sub 3}Sn coils with Holmium poles are arranged in octahedral symmetry to form four dipole pairs that provide magnetic fields of up to 5 T in any direction relative to the incoming x-ray beam. The dimensions of the magnet yoke as well as pole taper, diameter, and length were optimized for maximum peak field in the magnet center using the software package TOSCA. The structural analysis of the magnet is performed using ANSYS with the coil properties derived using a numerical homogenization scheme. It is found that the use of orthotropic material properties for the coil has an important influence in the design of the magnet.

  17. A new method to measure circular runout of end-milling spindle based on cutting mark

    Science.gov (United States)

    Zhou, Jianlai; Liu, Shuchun

    2008-12-01

    A practical method is introduced to measure the circular runout of a end-milling spindle system at high speed rotations without the need of a reference sphere. A workpiece is held on a linear slide which moves along the axial direction of the spindle. The spindle is then programmed to run at a specific speed. A very sharp edge cutter must be used and the depth of cut will be very shallow in order to keep the cutting force very small. The workpiece is then fed into the end mill in order to make a cutting mark of teens μm in depth. The cutting marks are circular, and their diameters are related to the circular runout of the spindle system. The cutting mark that is generated at a specific speed is expected to contain information about the spindle circular runout at this speed. In practice the cutting marks are not perfectly circular. Therefore, a best-fit circle of a cutting mark is needed to determine its diameter. A high-resolution edge detector machine is used for this purpose. Quantitative precision analysis was carried out to confirm the accuracy and repeatability of this new measurement technique. It is demonstrated that this technique for the measurement of spindle circular runout is an effective tool in verifying the actual running accuracy of spindles at their actual operating speeds and can be accomplished without the need for a reference sphere.

  18. An iterative neighborhood search approach for minimum zone circularity evaluation from coordinate measuring machine data

    International Nuclear Information System (INIS)

    An iterative neighborhood search approach (INSA) was proposed to precisely evaluate the circularity error under minimum zone conditions without directly solving nonlinear equations from coordinate measurement machine (CMM) data. The method starts with calculating the initial location and radius of an initial circular search scope. The location is the center of the circle based on an approximate least-squares method of all measurement data points uniformly sampled around the circle, and the radius is the circularity error value by using the approximate center as the datum center of two concentric circles enclosing all measurement data points. Then the circular search scope was divided according to some concentric circles and radials with some radius and angle step lengths. Intersections of the circles and radials were candidate centers for circularity evaluation under the minimum zone criteria. An optimal center with minimum circularity error value was picked out as a new location of the search scope. The distance from the old location was the radius of the new search scope. Further it was divided and the intersections were evaluated until the optimal solution was met. Some examples in the literature were used to verify the validity of this method. The results are the same as or better than those minimum zone solutions adopted from previous work, and computation time is no more than 0.07 s implementing on an IBM ThinkPad R40 laptop for all examples. The computation and comparison show that the proposed INSA is a precise, fast, convergent and simple approach which solved circularity evaluation problems effectively. (technical design note)

  19. Measurement and analysis of typical motion error traces from a circular test

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The circular test provides a rapid and efficient way of measuring the contouring accuracy of a machine tool.To get the actual point coordinate in the work plane,an improved measurement instrument - a new ball bar test system - is presented in this paper to identify both the radial error and the rotation angle error when the machine is manipulated to move in circular traces.Based on the measured circular error,a combination of Fourier components is chosen to represent the systematic form error that fluctuates in the radial direction.The typical motion errors represented by the corresponding Fourier components can thus be identified.The values for machine compensation can be calculated and adjusted until the desired results are achieved.

  20. A study on flow characteristics with ultrasonic forcing in a coaxial circular pipe by PIV measurement

    Energy Technology Data Exchange (ETDEWEB)

    Koo, J.H.; Park, Y.H.; Choi, W.C.; Song, M.G. [Gyeongsang National University Graduate School, Jinju (Korea); Ju, E.S. [Gyeongsang National University, Jinju (Korea)

    2000-11-01

    An experiment on the enhancement of turbulent flow with ultrasonic forcing was carried out by using PIV measurement in a coaxial circular pipe which could offer characteristics of the turbulence flow plentifully through its jet. A large transparent acryl tank and a coaxial circular pipe nozzle were made for the above research. City water of 25 deg.C was selected as an experimental liquid and the front flow field of the coaxial circular pipe was divided vertically as 3 measuring regions to observe characteristics of flow phenomena. Characteristics of fluid flow such as velocity vector distribution, kinetic energy, turbulent intensity and etc. were visualized, observed, examined and considered at 5 kinds of Re No. such as Re=1 X 10{sup 3}, 2 X 10{sup 3}, 3 X 10{sup 3}, 5 X 10{sup 3}, 1 X 10{sup 4}. In result it was proved that ultrasonic vibration affected the enhancement of turbulent flow. (author). 12 refs., 6 figs.

  1. Circularity measuring system: A shape gauge designed especially for use on large objects

    Science.gov (United States)

    Rohrkaste, G. R.

    1990-01-01

    The Circularity Measuring System (CMS) was developed to make an in-situ determination of shape similarity for selected fit large cylinders (RSRM segments). It does this to a repeatable accuracy of 0.10 mm (0.004 inch). This is less that the goal of 0.07 mm (0.003 inch), but was determined adequate because of the addition of an assembly aid that increased the entry chamfer of the clevis side of the joint. The usefulness of the CMS is demonstrated by the application to measurements other than its specified design purpose, such as submarine hull circularity, SRM mid-case circularity, as well as circularity of interfacing SRM tooling, specifically the rounding devices and horizontal disassembly devices. Commercialization of the tool is being pursued, since it is an enhancement of metrology technology for circularity determination. The most accurate in-situ technology it replaces is determined from a template. The CMS is an improvement in accuracy and operation.

  2. Ultrasound Tomography in Circular Measurement Configuration using Nonlinear Reconstruction Method

    Directory of Open Access Journals (Sweden)

    Tran Quang-Huy

    2015-12-01

    Full Text Available Ultrasound tomography offers the potential for detecting of very small tumors whose sizes are smaller than the wavelength of the incident pressure wave without ionizing radiation. Based on inverse scattering technique, this imaging modality uses some material properties such as sound contrast and attenuation in order to detect small objects. One of the most commonly used methods in ultrasound tomography is the Distorted Born Iterative Method (DBIM. The compressed sensing technique was applied in the DBIM as a promising approach for the image reconstruction quality improvement. Nevertheless, the random measurement configuration of transducers in this method is very difficult to set up in practice. Therefore, in this paper, we take advantages of simpler sparse uniform measurement configuration set-up of transducers and high-quality image reconstruction of 1 non-linear regularization in sparse scattering domain. The simulation results demonstrate the high performance of the proposed approach in terms of tremendously reduced total runtime and normalized error.

  3. Polarization measurement and vertical aperture optimization for obtaining circularly polarized bend-magnet radiation

    Energy Technology Data Exchange (ETDEWEB)

    Kortright, J.B.; Rice, M.; Hussain, Z. [Lawrence Berkeley National Lab., CA (United States)] [and others

    1997-04-01

    Growing interest in utilizing circular polarization prompted the design of bend-magnet beamline 9.3.2 at the Advanced Light Source, covering the 30-1500 eV spectral region, to include vertical aperturing capabilities for optimizing the collection of circular polarization above and below the orbit plane. After commissioning and early use of the beamline, a multilayer polarimeter was used to characterize the polarization state of the beam as a function of vertical aperture position. This report partially summarizes the polarimetry measurements and compares results with theoretical calculations intended to simulate experimental conditions.

  4. Constraining ALPs with linear and circular polarisation measurements of quasar light

    Energy Technology Data Exchange (ETDEWEB)

    Payez, Alexandre [Liege Univ. (Belgium). IFPA Group; Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)

    2013-09-15

    We discuss the constraints derived on the mixing of photons with light pseudoscalars using the distributions of good-quality linear and circular polarisation measurements of light from the least polarised classes of quasars. We also provide the dependence of our limit on the average electron density in the local supercluster for nearly massless particles.

  5. Vortex magnetic structure in circularly magnetized microwires as deduced from magneto-optical Kerr measurements

    KAUST Repository

    Ivanov, Yurii P.

    2014-02-14

    The magneto-optic Kerr effect has been employed to determine the magnetization process and estimate the domain structure of microwires with circular magnetic anisotropy. The diameter of microwires was 8 μm, and pieces 2 cm long were selected for measurements. The analysis of the local surface longitudinal and transverse hysteresis loops has allowed us to deduce a vortex magnetic structure with axial core and circular external shell. Moreover, a bamboo-like surface domain structure is confirmed with wave length of around 10 to 15 μm and alternating chirality in adjacent circular domains. The width of the domain wall is estimated to be less than 3 μm. Finally, closure domain structures with significant helical magnetization component are observed extending up to around 1000 μm from the end of the microwire.

  6. First measurement of the circular beam asymmetry in the gamma p --> pi0 eta p reaction

    OpenAIRE

    Kashevarov, V. L.; Fix, A.; Aguar-Bartolomé, P.; Akasoy, L. K.; Annand, J. R. M.; Arends, H.J.(Institut für Kernphysik, University of Mainz, Mainz, D-55099, Germany); Bantawa, K.(Kent State University, Kent, OH, 44242, USA); Beck, R.; Bekrenev, V.; H. Berghäuser; Braghieri, A.; Branford, D.; Briscoe, W. J.; Brudvik, J.; Cherepnya, S.

    2010-01-01

    The circular photon asymmetry for pi0 eta photoproduction on the proton was measured for the first time at the tagged photon facility of the MAMI C accelerator using the Crystal Ball/TAPS photon spectrometer. The experimental results are interpreted within a phenomenological isobar model that confirms the dominant role of the Delta(1700)D33 resonance. The measured asymmetry allows us to identify small contributions from positive-parity resonances via interference terms with the dominant D33 a...

  7. Comparative study of electrostatic sensors with circular and probe electrodes for velocity measurement of pulverised coal

    Institute of Scientific and Technical Information of China (English)

    Shao Jiaqing; Krabicka Jan; Yah Yong

    2007-01-01

    This paper presents recent progress on the velocity measurement of pulverised coal in pneumatic pipelines using electrostatic sensors in combination with correlation signal processing techniques. A comparative study of electrostatic sensors with circular and probe electrodes was conducted on a 94 mm bore horizontal pipeline in a 4 MW furnace. The advantages and limitations of both sensors are discussed. Experimental results demonstrate that both sensors are capable of providing pulverised coal velocity measurement with excellent repeatability and dynamic response.

  8. Linear and Chiral Dichroism in the Electron Microscope

    CERN Document Server

    Schattschneider, Peter

    2012-01-01

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

  9. A Protocol for the Creation of Useful Geometric Shape Metrics Illustrated with a Newly Derived Geometric Measure of Leaf Circularity

    Directory of Open Access Journals (Sweden)

    Jonathan D. Krieger

    2014-08-01

    Full Text Available Premise of the study: I present a protocol for creating geometric leaf shape metrics to facilitate widespread application of geometric morphometric methods to leaf shape measurement. Methods and Results: To quantify circularity, I created a novel shape metric in the form of the vector between a circle and a line, termed geometric circularity. Using leaves from 17 fern taxa, I performed a coordinate-point eigenshape analysis to empirically identify patterns of shape covariation. I then compared the geometric circularity metric to the empirically derived shape space and the standard metric, circularity shape factor. Conclusions: The geometric circularity metric was consistent with empirical patterns of shape covariation and appeared more biologically meaningful than the standard approach, the circularity shape factor. The protocol described here has the potential to make geometric morphometrics more accessible to plant biologists by generalizing the approach to developing synthetic shape metrics based on classic, qualitative shape descriptors.

  10. Talbot interferometer with circular gratings for the measurement of temperature in axisymmetric gaseous flames.

    Science.gov (United States)

    Shakher, C; Daniel, A J

    1994-09-01

    A detailed study for measuring the temperature distribution in axisymmetric flames by using a Talbot interferometer with circular gratings is presented. We increased the sensitivity of the interferometer by optimizing the pitch of the grating and the Talbot plane. We compare the experimental results with the values that were measured with a thermocouple to an accuracy of ±0.2% of full scale ±4 digits. Good agreement is seen between the temperatures measured by use of a thermocouple and those measured by use of Talbot interferometry. PMID:20936022

  11. Transmitting Antenna with Dual Circular Polarization for Indoor Antenna Measurement Range

    OpenAIRE

    Mrnka, M.; Vélim, J.

    2015-01-01

    The presented paper describes design of an original transmitting antenna for specific indoor far-field measurement range. The antenna is able to generate both senses of the circular polarization with high polarization purity by using stepped septum polarizer inside a waveguide. Very high suppression of the side lobes is achieved by utilization of the higher order modes in the aperture of the final horn antenna which is directly connected to the septum polarizer. The antenna was simulated and ...

  12. Magnetic dichroism in angle-resolved hard x-ray photoemission from buried layers

    Science.gov (United States)

    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.

  13. Correlation of magnetic dichroism in x-ray absorption and photoelectron emission using ultrathin magnetic alloy films

    Energy Technology Data Exchange (ETDEWEB)

    Tobin, J.G.; Goodman, K.W. [Lawrence Livermore National Lab., CA (United States); Mankey, G.J.; Willis, R.F. [Pennsylvania State Univ., University Park, PA (United States). Dept. of Physics; Denlinger, J.D.; Rotenberg, E.; Warwick, A. [Lawrence Berkeley Lab., CA (United States)

    1996-04-01

    We have begun a program to characterize magnetic alloy overlays using both magnetic x-ray circular dichroism (MXCD) and magnetic x-ray linear dichroism (MXLD). This will allow a direct comparison of MXCD-absorption and MXLD-photoelectron emission. First results from the Advanced Light Source will be presented.

  14. Magnetic x-ray dichroism in ultrathin epitaxial films

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-04-01

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

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

    Science.gov (United States)

    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

  16. A new vision for the measure of circularity using a certain representation space

    International Nuclear Information System (INIS)

    Detecting and characterizing families of plane circles is a fundamental concern in image processing. Many methods have been developed for these purposes, often on ad hoc bases, for example in the context of metrology. This paper is based on the consideration of circles as topological points in a certain 3D representation space (RS). Instead of the natural RS with (a,b,R) coordinates, (a, b) for the center and R for the radius of the circle, another RS, denoted Σ, is studied, with the third coordinate changed from R to c with c = a2 + b2 - R2. Z is connected with Voronoi closest et farthest point diagrams and their 'lifted' version. Moreover, Σ possesses a canonical measure, introduced by Stoka. This paper is focused on families of circles S(P,Q) constrained to have two fixed sets of internal (Pi) and external (Qj) points, representable as polyhedra in Σ. The Stoka measure of these polyhedra is shown to be an adequate measure of circularity expressed by a simple formula. The power of this approach is shown on two applications : circularity assessment as used in metrology, and Fillmore formula. This approach has several ramifications, for example in Hyperbolic Geometry.

  17. Development of a Tonometric Sensor with a Decoupled Circular Array for Precisely Measuring Radial Artery Pulse

    Science.gov (United States)

    Jun, Min-Ho; Kim, Young-Min; Bae, Jang-Han; Jung, Chang Jin; Cho, Jung-Hee; Jeon, Young Ju

    2016-01-01

    The radial artery pulse is one of the major diagnostic indices used clinically in both Eastern and Western medicine. One of the prominent methods for measuring the radial artery pulse is the piezoresistive sensor array. Independence among channels and an appropriate sensor arrangement are important for effectively assessing the spatial-temporal information of the pulse. This study developed a circular-type seven-channel piezoresistive sensor array using face-down bonding (FDB) as one of the sensor combination methods. The three-layered housing structure that included independent pressure sensor units using the FDB method not only enabled elimination of the crosstalk among channels, but also allowed various array patterns to be created for effective pulse measurement. The sensors were arranged in a circular-type arrangement such that they could estimate the direction of the radial artery and precisely measure the pulse wave. The performance of the fabricated sensor array was validated by evaluating the sensor sensitivity per channel, and the possibility of estimating the blood vessel direction was demonstrated through a radial artery pulse simulator. We expect the proposed sensor to allow accurate extraction of the pulse indices for pulse diagnosis. PMID:27240363

  18. Magnetic dichroism in the one-electron atom

    International Nuclear Information System (INIS)

    The difference in absorption rate of right or left circularly polarized x-rays by magnetic materials is known as magnetic dichroism and is a well established method of investigating the magnetic properties of materials on a microscopic level. In this paper we illustrate this effect with a study of magnetic dichroism in the one-electron atom. The standard relativistic one-electron atom is solved. First-order perturbation theory is used to calculate eigenfunctions in an applied constant magnetic field. These eigenfunctions are used in a golden rule calculation of the absorption rate for right and left circularly polarized light as a function of applied field. All calculations have been done analytically. The difference in absorption rates for right and left circularly polarized light for 1s to 2p1/2 is of opposite sign to the difference for 1s to 2p3/2. We comment on the significance of these results in the interpretation of dichroism experiments on magnetic materials. (author)

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

    DEFF Research Database (Denmark)

    Cukras, Janusz; Kauczor, Joanna; Norman, Patrick;

    2016-01-01

    A computational protocol for magneto-chiral dichroism and magneto-chiral birefringence dispersion is presented within the framework of damped response theory, also known as complex polarization propagator theory, at the level of time-dependent Hartree–Fock and time-dependent density functional th...... 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....

  20. Applications of circularly polarized photons at the ALS with a bend magnet source

    Energy Technology Data Exchange (ETDEWEB)

    1992-02-01

    The purpose of this workshop is to focus attention on, and to stimulate the scientific exploitation of, the natural polarization properties of bend-magnet synchrotron radiation at the ALS -- for research in biology, materials science, physics, and chemistry. The topics include: The Advanced Light Source; Magnetic Circular Dichroism and Differential Scattering on Biomolecules; Tests of Fundamental Symmetries; High {Tc} Superconductivity; Photoemission from Magnetic and Non-magnetic Solids; Studies of Highly Correlated Systems; and Instrumentation for Photon Transport and Polarization Measurements.

  1. Applications of circularly polarized photons at the ALS with a bend magnet source

    International Nuclear Information System (INIS)

    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

  2. Polarization measurement and vertical aperture optimization for obtaining circularly polarized bend-magnet radiation

    International Nuclear Information System (INIS)

    Using multilayer linear polarizers, we have characterized the polarization state of radiation from bend-magnet beamline 9.3.2 at the Advanced Light Source as a function of vertical opening angle at photon energies of 367 and 722 eV. Both a fine slit and a coarse semi-aperture were stepped across the beam to accept different portions of the vertical radiation fan. Polarimetry yields the degree of linear polarization directly and the degree of circular polarization indirectly assuming an immeasurably small amount of unpolarized radiation based on the close agreement of the theoretical and experimental results for linear polarization. The results are in good agreement with theoretical calculations, with departures from theory resulting from uncertainty in the effective aperture of the measured beam. The narrow 0.037-mrad aperture on the orbit plane transmits a beam whose degree of linear polarization exceeds 0.99 at these energies. The wide semi-aperture blocking the beam from above and below transmits a beam with a maximum figure of merit, given by the square root of flux times the degree of circular polarization, when the aperture edge is on the orbit plane thus blocking only half of the total available flux. copyright 1996 American Institute of Physics

  3. Polarization measurement and vertical aperture optimization for obtaining circularly polarized bend-magnet radiation

    International Nuclear Information System (INIS)

    Using multilayer linear polarizers, we have studied the polarization state of radiation from bend magnet beamline 9.3.2 at Advanced Light Source as function of vertical oping angle at photon energies 367 and 722 eV. Both a fine slit and a coarse semi-aperture were stepped across the beam to accept different parts of the vertical radiation fan. Polarimetry yields the degree of linear polarization directly and the degree of circular polarization indirectly assuming an immeasurably small amount of unpolarized radiation based on close agreement of theory and experiment for linear polarization. Results are in good agreement with theoretical calculations, with departures from theory owing to uncertainty in effective aperture of the measured beam. The narrow 0.037 mrad aperture on the orbit plane transmits a beam whose degree of linear polarization exceeds 0.99 at these energies. The wide semi-aperture blocking the beam from above and below transmits a beam with a max figure of merit, given by the square root of flux times degree of circular polarization, when the aperture edge is on the orbit plane thus blocking only half of the total available flux

  4. Measurements of radon concentration (circular DGS/VS5 no.99 289 from May 20, 1999 - public health)

    International Nuclear Information System (INIS)

    This regulatory text is a complement to the circular no 99-46 from January 27, 1999 concerning the measurements of radon concentration inside public buildings. It precise the sanitary rules and interpretation procedure concerning the radon measurements performed inside public buildings: campaign of measurements, expert appraisement, localization of the rooms with the highest concentration and evaluation of the technical solutions. (J.S.)

  5. Investigation of chromophore-chromophore interaction by electro-optic measurements, linear dichroism, x-ray scattering, and density-functional calculations

    DEFF Research Database (Denmark)

    Apitz, Dirk; Bertram, R.P.; Benter, N.;

    2005-01-01

    Free-beam interferometry and angle-resolved absorption spectra are used to investigate the linear electro-optic coefficients and the linear dichroism in photoaddressable bis-azo copolymer thin films. From the first- and second order parameters deduced, the chromophore orientation distribution is ...... density-functional calculations support the picture of differently aligned bis-azo dye molecules in a trans,trans configuration. Complementary wide-angle x-ray scattering is recorded to confirm the various kinds of ordering in samples poled at different temperatures....

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

    Science.gov (United States)

    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.

  7. X-ray linear dichroism dependence on ferroelectric polarization

    International Nuclear Information System (INIS)

    X-ray absorption spectroscopy and photoemission electron microscopy are techniques commonly used to determine the magnetic properties of thin films, crystals, and heterostructures. Recently, these methods have been used in the study of magnetoelectrics and multiferroics. The analysis of such materials has been compromised by the presence of multiple order parameters and the lack of information on how to separate these coupled properties. In this work, we shed light on the manifestation of dichroism from ferroelectric polarization and atomic structure using photoemission electron microscopy and x-ray absorption spectroscopy. Linear dichroism arising from the ferroelectric order in the PbZr0.2Ti0.8O3 thin films was studied as a function of incident x-ray polarization and geometry to unambiguously determine the angular dependence of the ferroelectric contribution to the dichroism. These measurements allow us to examine the contribution of surface charges and ferroelectric polarization as potential mechanisms for linear dichroism. The x-ray linear dichroism from ferroelectric order revealed an angular dependence based on the angle between the ferroelectric polarization direction and the x-ray polarization axis, allowing a formula for linear dichroism in ferroelectric samples to be defined. (paper)

  8. Miniature magnetic bottle confined by circularly polarized laser light and measurements of the inverse Faraday effect in plasmas

    International Nuclear Information System (INIS)

    A new concept of hot plasma confinement in a miniature magnetic bottle induced by circularly polarized laser light is suggested. Magnetic fields generated by circularly polarized laser light may be of the order of megagauss, depending on the laser intensity. In this configuration the circularly polarized light is used to obtain confinement of a plasma contained in a good conductor vessel. The confinement in this scheme is supported by the magnetic forces. The Lawson criterion for a DT plasma might be achieved for number density n = 5*1021 cm-3 and confinement time τ= 20 ns. The laser and plasma parameters required to obtain an energetic gain are calculated. Experiments and preliminary calculations were performed to study the feasibility of the above scheme. Measurements of the axial magnetic field induced by circularly polarized laser light, the so called inverse Faraday effect, and of the absorption of circularly polarized laser light in plasma, are reported. The experiments were performed with a circularly polarized Nd:YAG laser, having a wavelength of 1.06 τm and a pulse duration of 7 ns, in a range of irradiances from 109 to 1014 W/cm2. Axial magnetic fields from 500 Gauss to 2 megagauss were measured. Up to 5*1013 W/cm3 the results are in agreement with a nonlinear model of the inverse Faraday effect dominated by the ponderomotive force. For the laser irradiance studied here, 9*1013 - 2.5*1014 W/cm2, the absorption of circularly polarized light was 14% higher relative to the absorption of linear polarized light

  9. Diet quality of supermarket sales circulars measured by the Healthy Eating Index-2010

    Science.gov (United States)

    The purpose of this study was to determine how closely the contents of weekly supermarket sales circulars conform to current dietary guidance and how closely the diet quality of those foods compare to that of the U.S. population’s intakes. Food and beverage items (n = 9,151) in 52 weekly circulars ...

  10. Administrative Circulars

    CERN Multimedia

    Département des Ressources humaines

    2004-01-01

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

  11. Cyanobacterial phycobilisomes: Selective dissociation monitored by fluorescence and circular dichroism

    OpenAIRE

    Rigbi, Meir; Rosinski, Joanne; Siegelman, Harold W.; Sutherland, John Clark

    1980-01-01

    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°C, as indicated by a blue shift in fluorescence emission, and i...

  12. Nuclear spin-induced circular dichroism in fullerene compounds

    Czech Academy of Sciences Publication Activity Database

    Štěpánek, Petr; Vaara, J.; Coriani, S.; Straka, Michal

    Brno : Masaryk University, 2014 - (Novotný, J.; Foroutan -Nejad, C.; Marek, R.). C2 ISBN 978-80-86441-45-0. [NMR Valtice. Central European NMR Meeting /29./. 27.4.-30.4.2014, Valtice] Institutional support: RVO:61388963 Keywords : NSCD * fullerenes Subject RIV: CF - Physical ; Theoretical Chemistry

  13. Magnetic circular dichroism of chlorofullerenes: Experimental and computational study

    Czech Academy of Sciences Publication Activity Database

    Štěpánek, Petr; Straka, Michal; Šebestík, Jaroslav; Bouř, Petr

    2016-01-01

    Roč. 647, Mar (2016), s. 117-121. ISSN 0009-2614 R&D Projects: GA ČR GA13-03978S; GA ČR(CZ) GA14-03564S Institutional support: RVO:61388963 Keywords : spectra * MCD * transitions Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.897, year: 2014

  14. Spectroscopic Detection of DNA Quadruplexes by Vibrational Circular Dichroism

    Czech Academy of Sciences Publication Activity Database

    Andrushchenko, Valery; Tsankov, D.; Krasteva, M.; Wieser, H.; Bouř, Petr

    2011-01-01

    Roč. 133, č. 38 (2011), s. 15055-15064. ISSN 0002-7863 R&D Projects: GA ČR GAP208/10/0559; GA ČR GAP208/11/0105; GA MŠk(CZ) LH11033 Grant ostatní: AV ČR(CZ) M200550902 Institutional research plan: CEZ:AV0Z40550506 Keywords : nucleic acids * VCD * DFT computations * DNA quadruplexes Subject RIV: CC - Organic Chemistry Impact factor: 9.907, year: 2011

  15. Conformational analysis of cationic sequential oligopeptides using circular dichroism spectroscopy

    Czech Academy of Sciences Publication Activity Database

    Setnička, V.; Hlaváček, Jan; Urbanová, M.

    Naples : Universita di Napoli, 2006, s. 138-139. [Naples workshop on bioactive peptides /10./. Naples (IT), 11.06.2006-14.06.2006] R&D Projects: GA ČR(CZ) GP203/06/P371 Institutional research plan: CEZ:AV0Z40550506 Keywords : sequential oligopeptides * conformation * IR spectroscopy * VCD spectroscopy Subject RIV: CC - Organic Chemistry

  16. Detection and Measurement of Parsec-Scale Circular Polarization in Four AGN

    CERN Document Server

    Homan, D C

    1999-01-01

    We present five epochs of 15 GHz VLBA observations of 13 AGN. These observations were specially calibrated to detect parsec scale circular polarization and our calibration techniques are discussed and analyzed in detail. We obtained reliable detections of parsec scale circular polarization in the radio jets of 4 AGN: 3C84, PKS 0528+134, 3C273, and 3C279. For each of these objects our detections are at the level of ~ 0.3-1% local fractional circular polarization. Our observations are consistent across multiple epochs (and different calibration techniques) in the sign and magnitude of the circular polarization observed. 3C273 and 3C279 both undergo core outbursts during our observations and changes in the circular polarization of both sources are correlated with these outbursts. In general, we observe the circular polarization to be nearly coincident with the strong VLBI cores of these objects; however, in 3C84 the circular polarization is located a full milli-arcsecond south of the source peak, and in the 1996...

  17. Detection and Measurement of Parsec-Scale Circular Polarization in Four AGN

    OpenAIRE

    Homan, D. C.; Wardle, J. F. C.

    2000-01-01

    We present five epochs of 15 GHz VLBA observations of 13 AGN. These observations were specially calibrated to detect parsec scale circular polarization and our calibration techniques are discussed and analyzed in detail. We obtained reliable detections of parsec scale circular polarization in the radio jets of 4 AGN: 3C84, PKS 0528+134, 3C273, and 3C279. For each of these objects our detections are at the level of ~ 0.3-1% local fractional circular polarization. Our observations are consisten...

  18. Two-dimensional flow of foam around a circular obstacle: local measurements of elasticity, plasticity and flow

    OpenAIRE

    Dollet, Benjamin; Graner, Francois

    2006-01-01

    We investigate the two-dimensional flow of a liquid foam around circular obstacles by measuring all the local fields necessary to describe this flow: velocity, pressure, bubble deformations and rearrangements. We show how our experimental setup, a quasi-2D "liquid pool" system, is adapted to the determination of these fields: the velocity and bubble deformations are easy to measure from 2D movies, and the pressure can be measured by exploiting a specific feature of this system, a 2D effective...

  19. 3D UTD Modeling of a Measured Antenna Disturbed by a Dielectric Circular Cylinder in WBAN Context

    OpenAIRE

    Plouhinec, Eric; Uguen, Bernard; Mhedhbi, Meriem; Avrillon, Stéphane

    2014-01-01

    This paper describes a work realized for On-Body antennas characterization: the 3D deterministic modeling of a measured antenna disturbed by a dielectric circular cylinder of finite length. This prediction model is based on the ray-tracing technique for the electromagnetic wave paths search and the Uniform Theory of Diffraction (UTD) for the modeling of the electromagnetic waves interactions with the cylinder. After a detailed description, the model is validated in 3D with measurements made f...

  20. Studies and measurements of linear coupling and nonlinearities in hadron circular accelerators

    International Nuclear Information System (INIS)

    In this thesis a beam-based method has been developed to measure the strength and the polarity of corrector magnets (skew quadrupoles and sextupoles) in circular accelerators. The algorithm is based on the harmonic analysis (via FFT) of beam position monitor (BPM) data taken turn by turn from an accelerator in operation. It has been shown that, from the differences of the spectral line amplitudes between two consecutive BPMs, both the strength and the polarity of non-linear elements placed in between can be measured. The method has been successfully tested using existing BPM data from the SPS of CERN. A second beam-based method has been studied for a fast measurement and correction of betatron coupling driven by skew quadrupole field errors and tilted focusing quadrupoles. In this thesis it has been shown how the correction for minimizing the coupling stop band C can be performed in a single machine cycle from the harmonic analysis of multi-BPM data. The method has been successfully applied to RHIC. A third theoretical achievement is a new description of the betatron motion close to the difference resonance in presence of linear coupling. New formulae describing the exchange of RMS resonances have been derived here making use of Lie algebra providing a better description of the emittance behavior. A new way to decouple the equations of motion and explicit expressions for the individual single particle invariants have been found. For the first time emittance exchange studies have been carried out in the SIS-18 of GSI. Applications of this manipulation are: emittance equilibration under consideration for future operations of the SIS-18 as booster for the SIS-100; emittance transfer during multi-turn injection to improve the efficiency and to protect the injection septum in high intensity operations, by shifting part of the horizontal emittance into the vertical plane. Multi-particle simulations with 2D PIC space-charge solver have been run to infer heuristic scaling

  1. Studies and measurements of linear coupling and nonlinearities in hadron circular accelerators

    Energy Technology Data Exchange (ETDEWEB)

    Franchi, A.

    2006-07-01

    In this thesis a beam-based method has been developed to measure the strength and the polarity of corrector magnets (skew quadrupoles and sextupoles) in circular accelerators. The algorithm is based on the harmonic analysis (via FFT) of beam position monitor (BPM) data taken turn by turn from an accelerator in operation. It has been shown that, from the differences of the spectral line amplitudes between two consecutive BPMs, both the strength and the polarity of non-linear elements placed in between can be measured. The method has been successfully tested using existing BPM data from the SPS of CERN. A second beam-based method has been studied for a fast measurement and correction of betatron coupling driven by skew quadrupole field errors and tilted focusing quadrupoles. In this thesis it has been shown how the correction for minimizing the coupling stop band C can be performed in a single machine cycle from the harmonic analysis of multi-BPM data. The method has been successfully applied to RHIC. A third theoretical achievement is a new description of the betatron motion close to the difference resonance in presence of linear coupling. New formulae describing the exchange of RMS resonances have been derived here making use of Lie algebra providing a better description of the emittance behavior. A new way to decouple the equations of motion and explicit expressions for the individual single particle invariants have been found. For the first time emittance exchange studies have been carried out in the SIS-18 of GSI. Applications of this manipulation are: emittance equilibration under consideration for future operations of the SIS-18 as booster for the SIS-100; emittance transfer during multi-turn injection to improve the efficiency and to protect the injection septum in high intensity operations, by shifting part of the horizontal emittance into the vertical plane. Multi-particle simulations with 2D PIC space-charge solver have been run to infer heuristic scaling

  2. Temperature-field measurements of a premixed butane/air circular impinging-flame using reference-beam interferometry

    International Nuclear Information System (INIS)

    Reference-beam interferometry (RBI) was applied to study the axisymmetric temperature fields of a small-scale, low Reynolds-number, low-pressure and fuel-rich premixed butane/air circular-flame jet, when it was impinging vertically upwards onto a horizontal copper plate. By maintaining a Reynolds number, Re, of 500 and an equivalence ratio, φ, of 1.8, interferograms of the impinging-flame jet were obtained for various nozzle-to-plate-distances. Temperature fields of the flame were then determined using the inverse Abel transformation from the obtained interferograms. Temperatures at several locations were measured experimentally with a T-type thermocouple: they were used as a reference to help in the determination as well as the validation. In the present study, a non-contact method has been successfully developed to measure the temperature fields of a circular impinging gas-fired flame jet

  3. 圆二色谱研究胶原模拟多肽三螺旋结构及其热稳定性%Study of Collagen Mimetic Peptide’s Triple-Helix Structure and Its Thermostability by Circular Dichroism

    Institute of Scientific and Technical Information of China (English)

    张之宝; 王静洁; 陈晖娟; 熊青青; 刘玲蓉; 张其清

    2014-01-01

    In the present study ,the authors explore the triple-helix conformation and thermal stability of collagen mimetic pep-tides (CMPs) as a function of peptide sequence and/or chain length by circular dichroism (CD) .Five CMPs were designed and synthetized varying the number of POG triplets or incorporating an integrin α2β1 binding motif Gly-Phe-Hyp-Gly-Glu-Arg (GFOGER) .CD spectroscopy from 260 to 190 nm was recorded to confirm the existence of triple-helix conformation at room temperature ,while thermal melting and thermal annealing of triple-helix (thermal unfolding and refolding of triple-helix ,respec-tively) was characterized by monitoring ellipticity at 225 nm as a function of temperature .The results demonstrated that all the CMPs adopted triple-helix conformation ,and the thermal stability of the CMPs was enhanced with increasing the number of POG triplets .In contrast to natural collagen ,the thermal denaturation processes of CMPs were reversible ,i .e .the triple-helix unfol-ded upon heating while refolded upon cooling .Meanwhile ,the phenomenon of “hysteresis” was observed by comparing melting and thermal curves .These findings add new insights to the mechanisms of collagen and CMPs assembly ,as well as provide an alternative approach to the fabrication of artificial collagen-likes biomaterials .%胶原是广泛研究和应用的生物材料,具有独特的三螺旋结构,此结构与其生物学性能密切相关。以胶原模拟多肽(collagen mimetic peptide ,CM P)作为胶原的模型分子,通过圆二色谱研究了CM P的三螺旋结构、热稳定性等随序列或长度的改变所发生的规律性变化。根据形成胶原三螺旋结构的重复序列(POG )n及胶原上α2β1整合素识别位点序列GFOGER设计五种不同序列或长度的CM P ,采用圆二色谱表征了CM P的三螺旋结构,并通过检测CM P的程序升温变性和程序降温复性过程中圆二色谱的变化,研究了CM P三螺旋结

  4. Thoughts on measuring particle's circular polarization variation with respect to the reaction plane in relativistic heavy-ion collisions

    CERN Document Server

    Tang, A H

    2016-01-01

    The EM field pattern created by spectators in relativistic heavy-ion collisions plants a seed of positive (negative) magnetic helicity in the hemisphere above (below) the reaction plane. Owing to the chiral anomaly, the magnetic helicity interacts with the fermionic helicity of the collision system, and causes photons emitted in upper- and lower-hemispheres to have different preferences in the circular polarization. In this paper, we lay down a procedure to measure the variation of the circular polarization w.r.t the reaction plane in relativistic heavy-ion collisions for massless photons, as well as similar polarization patterns for vector mesons decaying into two daughters. We propose to study the yield differentially and compare the yield between upper- and lower-hemispheres in order to identify and quantify such effects.

  5. Energy-loss magnetic chiral dichroism study of epitaxial MnAs film on GaAs(001)

    International Nuclear Information System (INIS)

    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-L2,3 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

  6. Stress Measurement around a Circular Role in a Cantilever Beam under Bending Moment Using Strain Gage and Reflective Photoelasticity

    International Nuclear Information System (INIS)

    It is necessary to study on the stress concentration experimentally, which is the main reason to avoid mechanical dilapidation and failure, when designing a mechanical structure. Stress concentration factor of a specimen of cantilever beam with a circular hole in the center was measured using both strain gage and photoelastic methods in this paper. In strain-gage measurement, three strain gages along the line near a hole of the specimen were installed and maximum strain was extrapolated from three measurements. In photoelastic measurement, two methods were employed. First, the Babinet-Soleil compensation method was used to measure the maximum strain. Secondly, photoelastic 4-step phase shilling method was applied to observe the strain distribution around the hole. Measurements obtained by different experiments were comparable within the range of experimental error

  7. Standard Test Method for Measuring Heat Flux Using a Copper-Constantan Circular Foil, Heat-Flux Transducer

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2007-01-01

    1.1 This test method describes the measurement of radiative heat flux using a transducer whose sensing element (1,2 ) is a thin circular metal foil. These sensors are often called Gardon Gauges. 1.2 The values stated in SI units are to be regarded as the standard. The values stated in parentheses are provided for information only. 1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

  8. Information Circulars

    International Nuclear Information System (INIS)

    Information circulars are published from time to time under the symbol INFCIRC/. . . . for the purpose of bringing matters of general interest to the attention of all Members of the Agency. A list of the circulars which were of current interest on 15 January 1969 is given below, followed by an index to their subject matter. Other circulars can be traced by reference to earlier issues of the present document.

  9. Measuring field multipoles in accelerator magnets with small-apertures by an oscillating wire moved on a circular trajectory

    International Nuclear Information System (INIS)

    A method based on an oscillating wire for measuring the field quality in accelerator magnets with small apertures of the order of 10 mm is proposed. The wire is positioned step-by-step on the generators of a cylindrical domain inside the magnet aperture, i.e. its end-points at the stages are moved on a circular trajectory. The amplitudes of the wire's forced oscillations are measured and related to field harmonics by a suitable analytical model. In this paper, the analytical model, the measurement procedure, and the measurement system architecture of the oscillating wire method are presented. The method is validated by comparison with the standard rotating-coil system. A case study on small-aperture, permanent-magnet quadrupoles constructed for the Linac4 injector at CERN is illustrated.

  10. Circular intensity differential scattering (CIDS) measurements in the soft x-ray region of the spectrum (@16 eV to 500 eV)

    Energy Technology Data Exchange (ETDEWEB)

    Maestre, M.F. (Lawrence Berkeley Lab., CA (United States)); Bustamante, C. (Oregon Univ., Eugene, OR (United States). Dept. of Chemistry); Snyder, P. (Florida Atlantic Univ., Boca Raton, FL (United States). Dept. of Chemistry); Rowe, E.; Hansen, R. (Wisconsin Univ., Stoughton, WI (United States). Synchrotron Radiation Center)

    1991-03-01

    We propose the use of recently developed techniques of circular intensity differential scattering (CIDS), as extended to the soft x-ray region of the spectrum (16 eV to 500 eV), to study the higher order organization of the eukaryotic chromosome. CIDS is the difference in scattering power of an object when illuminated by right circularly polarized vs. left circularly polarized electromagnetic radiation of arbitrary wavelength. CIDS has been shown to be a very sensitive measure of the helical organization of the scattering object eg. the eukaryotic chromosome. Preliminary results of measurements of samples of bacteriophages and octopus sperm done at SRC, Wisconsin, show the technique to be very sensitive to the dimensional parameters of the particles interrogated by circularly polarized light. 7 refs., 5 figs.

  11. Error analysis of linear optics measurements via turn-by-turn beam position data in circular accelerators

    CERN Document Server

    Franchi, Andrea

    2016-01-01

    Many advanced techniques have been developed, tested and implemented in the last decades in almost all circular accelerators across the world to measure the linear optics. However, the greater availability and accuracy of beam diagnostics and the ever better correction of linear magnetic lattice imperfections (beta beating at 1% level and coupling at 0.1%) are reaching what seems to be the intrinsic accuracy and precision of different measurement techniques. This paper aims to highlight and quantify, when possible, the limitations of one standard method, the harmonic analysis of turn-by-turn beam position data. To this end, new analytic formulas for the evaluation of lattice parameters modified by focusing errors are derived. The unexpected conclusion of this study is that for the ESRF storage ring (and possibly for any third generation light source operating at ultra-low coupling and with similar diagnostics), measurement and correction of linear optics via orbit beam position data are to be preferred to the...

  12. Information circulars

    International Nuclear Information System (INIS)

    Information circulars are published from time to time under the symbol INFCIRC/... for the purpose of bringing matters of general interest to the attention of all Members of the Agency. The present revision contains INFCIRCs published up to mid-August 1994. A complete numerical list of information circulars is reproduced with their titles in the Annex

  13. Information circulars

    International Nuclear Information System (INIS)

    The document summarizes the Information Circulars published by the IAEA for the purpose of bringing matters of general interest to the attention of all Members of the Agency. This revision contains INFCIRCs published up to mid-August 1992. A complete numerical lift of Information Circulars with their titles is reproduced in an Annex

  14. Information circulars

    International Nuclear Information System (INIS)

    The document summarizes the Information Circulars published by the IAEA for the purpose of bringing matters of general interest to the attention of all Member States. This revision contains INFCIRCs published up to the end of May 1999, grouped by field of activity. A complete list of information circulars in numerical order is given in an annex

  15. Information Circulars

    International Nuclear Information System (INIS)

    Information circulars are published from time to time under the symbol INFCIRC/. for the purpose of bringing matters of general interest to the attention of all Members of the Agency. A list of the circulars that were current on 31 December 1964 is given, followed by an index to their subject matter.

  16. Information circulars

    International Nuclear Information System (INIS)

    The document summarizes the Information Circulars published by the IAEA for the purpose of bringing matters of general interest to the attention of all Member States. This revision contains INFCIRCs published up to February 1997, grouped by field of activity. A complete list of information circulars in numerical order is given in an annex

  17. Information circulars

    International Nuclear Information System (INIS)

    Information circulars are published from time to time under the symbol INFCIRC/... for the purpose of bringing matters of general interest to the attention of all Members of the Agency. The present revision contains INFCIRCs published up to the end of April 2002. A complete numerical list of information circulars is reproduced with their titles in the Annex

  18. A protocol for the creation of useful geometric shape metrics illustrated with a newly derived geometric measure of leaf circularity 1

    OpenAIRE

    Jonathan D. Krieger

    2014-01-01

    • Premise of the study: I present a protocol for creating geometric leaf shape metrics to facilitate widespread application of geometric morphometric methods to leaf shape measurement. • Methods and Results: To quantify circularity, I created a novel shape metric in the form of the vector between a circle and a line, termed geometric circularity. Using leaves from 17 fern taxa, I performed a coordinate-point eigenshape analysis to empirically identify patterns of shape covariation. I then com...

  19. Circular polarisation measurements of the Lα cascade radiation for the 32Dj states of atomic hydrogen, excited by electron impact

    International Nuclear Information System (INIS)

    Measurements are reported for the circular polarisation of the Lα radiation arising from the cascade of the 32Dj states of atomic hydrogen to the 22Pj states detected in coincidence with electrons with n = 3 energy loss. Data for the atomic orientation parameter L perpendicular are presented at incident electron energies of 54.4 and 100 eV and at scattering angles θe of 200 and 250. These data, together with previous measurements for this transition, constitute a determination of the complete parameter set {γ, P1, ρ00, L perpendicular} for 32Dj excitations in this dynamic range. Calculations for P3 and L perpendicular using distorted-wave approximation theory are also performed. The theoretical results are presented and compared with the experimental data. (author)

  20. A simple Fourier transform-based reconstruction formula for photoacoustic computed tomography with a circular or spherical measurement geometry

    CERN Document Server

    Wang, Kun

    2012-01-01

    Photoacoustic computed tomography (PACT), also known as optoacoustic tomography, is an emerging imaging modality that has great potential for a wide range of biomedical imaging applications. In this Note, we derive a hybrid reconstruction formula that is mathematically exact and operates on a data function that is expressed in the temporal frequency and spatial domains. This formula explicitly reveals new insights into how the spatial frequency components of the sought-after object function are determined by the temporal frequency components of the data function measured with a circular or spherical measurement geometry in two- and three-dimensional implementations of PACT, respectively. The structure of the reconstruction formula is surprisingly simple compared with existing Fourier-domain reconstruction formulae. It also yields a straightforward numerical implementation that is robust and two orders of magnitude more computationally efficient than filtered backprojection algorithms.

  1. Error analysis of rigid body posture measurement system based on circular feature points

    Science.gov (United States)

    Huo, Ju; Cui, Jishan; Yang, Ning

    2015-02-01

    For monocular vision pose parameters determine the problem, feature-based target feature points on the plane quadrilateral, an improved two-stage iterative algorithm is proposed to improve the optimization of rigid body posture measurement calculating model. Monocular vision rigid body posture measurement system is designed; experimentally in each coordinate system determined coordinate a unified method to unify the each feature point measure coordinates; theoretical analysis sources of error from rigid body posture measurement system simulation experiments. Combined with the actual experimental analysis system under the condition of simulation error of pose accuracy of measurement, gives the comprehensive error of measurement system, for improving measurement precision of certain theoretical guiding significance.

  2. Circular statistics in R

    CERN Document Server

    Pewsey, Arthur; Ruxton, Graeme D

    2013-01-01

    Circular Statistics in R provides the most comprehensive guide to the analysis of circular data in over a decade. Circular data arise in many scientific contexts whether it be angular directions such as: observed compass directions of departure of radio-collared migratory birds from a release point; bond angles measured in different molecules; wind directions at different times of year at a wind farm; direction of stress-fractures in concretebridge supports; longitudes of earthquake epicentres or seasonal and daily activity patterns, for example: data on the times of day at which animals are c

  3. Circular Updates

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Circular Updates are periodic sequentially numbered instructions to debriefing staff and observers informing them of changes or additions to scientific and specimen...

  4. Analysis of the circular track experiment measuring the one-way speed of light

    OpenAIRE

    Philip, Evan John

    2012-01-01

    All experiments attempting to verify the invariance of speed of light directly are based on two-way speed measurement. The challenge in one-way speed measurement, the requirement of spatially separated synchronised clocks, can be possibly circumvented by measuring the speed of light travelling in a closed path. An apparent violation of the invariance principle has been recently reported in the first experiment attempting to measure the one-way speed of light utilising this concept. This exper...

  5. Information circulars

    International Nuclear Information System (INIS)

    The document summarizes the information circulars published by the IAEA for the purpose of bringing matters of general interest to the attention of all Members of the Agency. In the main body of the document only those documents which are regarded as likely to be of current interest are listed. A complete numerical list of information circulars with their titles is reproduced in the Annex

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

    International Nuclear Information System (INIS)

    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 ∼2.5μB per interface Pd atom

  7. Circular resistor networks for electrical impedance tomography with partial boundary measurements

    International Nuclear Information System (INIS)

    We introduce an algorithm for the numerical solution of electrical impedance tomography (EIT) in two dimensions, with partial boundary measurements. The algorithm is an extension of the one in Borcea et al (2008 Inverse Problems 24 035013 (31pp)) and Vasquez (2006 PhD Thesis Rice University, Houston, TX, USA) for EIT with full boundary measurements. It is based on resistor networks that arise in finite volume discretizations of the elliptic partial differential equation for the potential on so-called optimal grids that are computed as part of the problem. The grids are adaptively refined near the boundary, where we measure and expect better resolution of the images. They can be used very efficiently in inversion, by defining a reconstruction mapping that is an approximate inverse of the forward map, and acts therefore as a preconditioner in any iterative scheme that solves the inverse problem via optimization. The main result in this paper is the construction of optimal grids for EIT with partial measurements by extremal quasiconformal (Teichmüller) transformations of the optimal grids for EIT with full boundary measurements. We present the algorithm for computing the reconstruction mapping on such grids, and we illustrate its performance with numerical simulations. The results show an interesting trade-off between the resolution of the reconstruction in the domain of the solution and distortions due to artificial anisotropy induced by the distribution of the measurement points on the accessible boundary

  8. Novel approach for non-invasive glucose sensing using vibrational contrast CD absorption measurements (Conference Presentation)

    Science.gov (United States)

    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.

  9. Operational Circulars

    CERN Document Server

    2003-01-01

    Operational Circular N° 4 - April 2003 Conditions for use by members of the CERN personnel of vehicles belonging to or rented by CERN - This circular has been drawn up. Operational Circular N° 5 - October 2000 Use of CERN computing facilities - Further details on the personal use of CERN computing facilities Operational Circular N° 5 and its Subsidiary Rules http://cern.ch/ComputingRules defines the rules for the use of CERN computing facilities. One of the basic principles governing such use is that it must come within the professional duties of the user concerned, as defined by the user's divisional hierarchy. However, personal use of the computing facilities is tolerated or allowed provided : a) It is in compliance with Operational Circular N° 5 and not detrimental to official duties, including those of other users; b) the frequency and duration is limited and there is a negligible use of CERN resources; c) it does not constitute a political, commercial and/or profit-making activity; d) it is not...

  10. Enhancing the circular waveguide microresonator temperature measurement sensitivity and accuracy by using liquid crystal gap filling

    OpenAIRE

    Goncharenko, Igor; Marciniak, Marian

    2014-01-01

    We consider the design methods and principles of operation of a fast-response integrated optical sensor for temperature measurement. The sensitive element consists of a microring resonator based on the double-slot waveguide made from Si3N4 and coated on a SiO2 buffer layer, which is disposed on a silicon substrate. The nematic 5CB liquid crystal (LC) fills the slots of the ring waveguide. The sensor uses only the optical radiation, and the electrical current is not supplied to the measured ma...

  11. An evaluation of effective radiuses of bulk-wave ultrasonic transducers as circular piston sources for accurate velocity measurements.

    Science.gov (United States)

    Arakawa, Mototaka; Kushibiki, Jun-ichi; Aoki, Naoya

    2004-05-01

    The effective radius of a bulk-wave ultrasonic transducer as a circular piston source, fabricated on one end of a synthetic silica (SiO2) glass buffer rod, was evaluated for accurate velocity measurements of dispersive specimens over a wide frequency range. The effective radius was determined by comparing measured and calculated phase variations due to diffraction in an ultrasonic transmission line of the SiO2 buffer rod/water-couplant/SiO2 standard specimen, using radio-frequency (RF) tone burst ultrasonic waves. Fourteen devices with different device parameters were evaluated. The velocities of the nondispersive standard specimen (C-7940) were found to be 5934.10 +/- 0.35 m/s at 70 to 290 MHz, after diffraction correction using the nominal radius (0.75 mm) for an ultrasonic device with an operating center frequency of about 400 MHz. Corrected velocities were more accurately found to be 5934.15 +/- 0.03 m/s by using the effective radius (0.780 mm) for the diffraction correction. Bulk-wave ultrasonic devices calibrated by this experimental procedure enable conducting extremely accurate velocity dispersion measurements. PMID:15217227

  12. Modeling and measurements of circular and trapezoidal shape HTS coils for electrical machines applications

    International Nuclear Information System (INIS)

    Axial Flux Electrical Machines (AFEM) with good power-to-weight and diameter-to-length ratio and high efficiency are very attractive for most industrial and power applications. Investigations with both theoretical and experimental methods of ac losses are important for a reliable prediction of dissipation mechanisms in AFEM. In this paper, simulated and measured results for both critical current (Ic) and transport current losses (Ploss), obtained on HTS coils, are reported. To investigate shape effects, double pancake coils with variable turns and shapes have been manufacted. Commercial grade ReBa2Cu3O7−x (Re = Y or rare earths, ReBCO) tape and epoxy resin has been used for coil winding. A magneto-static 2D finite element model (FEM) for the coils cross section, and a lumped model for AC losses estimations, have been implemented. The agreement among measured and simulated results are satisfactory.

  13. Thomson scattering measurements in non-circular tokamak TNT-A

    International Nuclear Information System (INIS)

    A highly-sensitive, low-noise Thomson scattering apparatus has been developed. Measurements of electron densities of less than 1 x 1018 m-3 were performed using GaAs(Cs) photomultipliers with a quantum efficiency of over 10%, a light guide system with a high transmittance and a 6 J ruby laser. Detecting the scattered light with longer wavelength than that of the ruby laser protects the signal from disturbance by plasma light, especially by the H sub(α) line. The time evolutions of the electron temperature and the density profiles of the elongated plasma in the noncircular tokamak TNT-A are presented in this paper. (author)

  14. Information circulars

    International Nuclear Information System (INIS)

    The document summarizes the Information Circulars published by the IAEA under the symbol INFCIRC/ for the purpose of bringing matters of general interest to the attention of all Members of the Agency. A complete list of INFCIRCs in numerical order with their titles is given in the Annex

  15. Measurement of developing turbulent flow in a U-bend of circular cross-section

    International Nuclear Information System (INIS)

    Hot-wire measurements of the full mapping of the velocity and Reynolds stress components are reported for developing turbulent flow in a strongly curved 180 deg pipe and its tangents. A slanted wire is rotated into 6 orientations and the voltage outputs from wires are combined to obtain the mean velocity and Reynolds stress components. The strength of secondary flow reaches up to the 28% of bulk mean velocity. The strong counter-rotating vortex pair induced by the transverse pressure gradient and centrifugal force imbalance grows up to θ = 67.5 .deg. into the bend. But the vortex pair breaks down into two cell pattern after θ=90 .deg. Core vortex formation and reversal of secondary flow direction along the bend symmetry plane is cleanly found in the secondary vector plot. At θ=67.5 .deg. and θ = 90 .deg. into bend a large 'trough' develops in the longitudinal velocity toward the inside of the bend due to the breakdown of secondary flow. In the bend, the mean longitudinal velocity component changes little after θ=90 .deg., but secondary flow never achieves fully-developed state. Similar behaviors are observed in the radial and circumferential stresses

  16. ADMINISTRATIVE CIRCULARS

    CERN Multimedia

    Division des ressources humaines

    2000-01-01

    N° 2 (Rev. 1) - March 2000Guidelines and procedures concerning recruitment and probation period of staff membersN° 9 (Rev. 2) - March 2000Staff members contractsN° 16 (Rev. 2) - January 2000TrainingN° 30 (Rev. 1) - January 2000Indemnities and reimbursements upon taking up appointment and termination of contractN° 32 - February 2000Principles and procedures governing complaints of harassmentThese circular have been amended (No 2, N° 9, N° 16 and N° 30) or drawn up (N° 32).Copies are available in the Divisional Secretariats.Note:\tAdministrative and operational circulars, as well as the lists of those in force, are available for consultation in the server SRV4_Home in the Appletalk zone NOVELL (as GUEST or using your Novell username and password), volume PE Division Data Disk.The Word files are available in the folder COM, folder Public, folder ADM.CIRC.docHuman Resources DivisionTel. 74128

  17. Compact motorized circular wheel of polarization optics for ultra-broadband polarization state generation

    Science.gov (United States)

    Weng, Chun-Jen; Liu, Da-Ren; Hsu, Ken-Yuh; Chen, Yung-Fu

    2012-10-01

    This study proposes an innovative optical mechanism with a miniature motorized circular wheel for polarization optics for an ultra-broadband polarization state generator. The proposed apparatus can be suitable for a polarimetric microspectrophotometer for measurements of micro optics and metamaterials with circular dichroism and linear dichroism. Different types of micro optics have their own wavelength dependence, meaning different curves in the broadband range of light. This study presents an ultra-broadband platform for measuring and identifying micro optics such as chiral metamaterials, plasmonics, micro polarizers, and patterned retarders. The key component of a polarimetric microspectrophotometer is a polarization state generator (PSG). A simple PSG consists of a polarizer and a waveplate. An arbitrary polarization state can be created by rotating either the polarizer or the waveplate. Sheet polarizers and achromatic waveplates have a limited bandwidth range. For the ultra-broadband measurement range of 400 nm to 1700 nm, the PSG needs at least three sheet polarizers and three achromatic waveplates: 400 nm-700 nm, 700 nm-1000 nm, and 1000 nm-1700 nm. This optical mechanism, which consists of only one control motor and two high precision unidirectional bearings, includes several polarizers and waveplates arranged in a matrix on a circular wheel. This apparatus can shift one of the polarizers and waveplates to a predetermined position and rotate all the polarizers to change the polarization status. An ultra-broadband polarimetric microspectrophotometer with a compact motorized wheel is an advanced polarization optical instrument for research on chiral metamaterials, plasmonics, micro polarization optics, green optics, and bio optics.

  18. Magnetic x-ray linear dichroism of ultrathin Fe-Ni alloy films

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-04-01

    The authors have studied the magnetic structure of ultrathin Fe-Ni alloy films as a function of Fe concentration by measuring the linear dichroism of the 3p-core levels in angle-resolved photoemission spectroscopy. The alloy films, grown by molecular-beam epitaxy on Cu(001) surfaces, were fcc and approximately four monolayers thick. The intensity of the Fe dichroism varied with Fe concentration, with larger dichroisms at lower Fe concentrations. The implication of these results to an ultrathin film analogue of the bulk Invar effect in Fe-Ni alloys will be discussed. These measurements were performed at the Spectromicroscopy Facility (Beamline 7.0.1) of the Advanced Light Source.

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

    CERN Document Server

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

    2009-01-01

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

  20. Circular extinction of plasmonic silver nanocaps and gas sensing.

    Science.gov (United States)

    Li, Jun; Kotov, Nicholas A

    2016-04-12

    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

  1. Measurement of the circular polarization of radio sources at frequencies of 0.63, 1.4, 5.0 and 8.9 GHz

    International Nuclear Information System (INIS)

    Circular polarization measurements were made with the Parkes 64 m telescope on 66 mainly extragalactic sources, 33 of which were studied at two or more frequencies. Circular polarization was definitely found in the eight quasistellar sources PKS0237-23, 0537-441, 1127-14, 1226+02 (3C273), 1253-05 (3C279), 2134+004, 2145+06 and 2345-16, as it was measured at the 4sigma level or higher in at least two observing sessions. For all eight sources the total power spectrum shows the effects of self-absorption. For none of the eight is there evidence of a reversal of the sense of polarization with frequency. For several of the sources of the degree of circular polarization changed by a factor >2 between observing sessions, while any accompanying change in total flux density was <20%. Instrumental effects are discussed in some detail. Fluctuations due to system noise provide the main limitation, but for strong sources uncertainties in the determination of the zero of polarization are important. (author)

  2. A chemical deposition method to prepare circular planar 147Pm sources for the measurement of particulate emission in air

    International Nuclear Information System (INIS)

    This paper describes a method for preparing a circular planar source of 17 mm diameter containing approximately 400 kBq of 147Pm employing a wet chemical deposition technique to be used in dust monitors. This manuscript described the overall process concept and experimental procedure. The technical feasibility, efficiency of the process and product quality has been evaluated. The quality of the prepared source in terms of nonleachability, uniform distribution of activity and stability, which are necessary attributes of a radioactive source were evaluated and found to be satisfactory. - Highlights: • Preparation of circular planar 147Pm source for dust monitors. • Evaluation of efficiency of the process and product quality. • Quality evaluation of the sources

  3. Circular polarization measurements of Lyman-α radiation from the decay of the 22Pj states of hydrogen excited by 54.4 eV electrons

    International Nuclear Information System (INIS)

    New coincidence measurements are reported for the circular polarization of Lyman-α radiation resulting from the decay of 22Pj states excited by electron impact at an incident energy of 54.4 eV in a range of scattering angles from 5o ≤ θe ≤ 40o. The data were obtained using a recently developed efficient polarization analyser for this spectral line and the statistical significance of the data is much better than for previously reported measurements. The data are analysed to yield values for the coherence parameter P+ and show that spin exchange interactions play a significant, if unexpected, role in the dynamic range investigated. (author)

  4. Study of Flowrate Measurement Characteristics of a Circular Cylinder with a Slit%带狭缝圆柱钝体流量测量特性研究

    Institute of Scientific and Technical Information of China (English)

    王慧; 黄咏梅

    2013-01-01

    The flowrate characteristics of vortex flowmeter is closely related to the size and geometry shape of vortex bluff body. A new kind of circular cylinder with a slit structure is proposed and applied to vortex flowmeter. Theoretical analysis shows that the slit can be regarded as a feedback channel, which can effectively accelerate vortex shedding and increase vortex intensity. Experiments were carried out in a water pipe with a diameter of 50 mm. Vortex signals produced by circular cylinder with a slit and trapezoidal cylinder respectively at different flowrate were collected. This paper mainly focuses on analyzing the low flowrate measurement performance of circular cylinder with a slit. Experimental results show that compared with trapezoidal cylinder circular cylinder with a slit possesses following characteristics:vortex signal intensity is stronger, signal-to-noise ratio is higher, the Reynolds number of measurement range can be as low as 9. 5í103 and linearity of Strouhal number is better as well. Theoretical analysis and experimental results manifest that circular cylinder with a slit possesses good flowrate meas-urement features and can be applied to vortex flowmeter successfully.%涡街流量计的流量特性与旋涡发生体的形状和几何尺寸密切相关,提出了一种新型的带狭缝圆柱发生体结构并应用于涡街流量计。理论分析表明狭缝可以看作是一个反馈通道,可有效加快旋涡脱落并增强旋涡强度。在内径为50 mm的管道中进行实验,采集不同流量下带狭缝圆柱与梯形柱绕流产生的涡街信号,重点讨论带狭缝圆柱的小流量测量性能。实验表明,与梯形柱相比,带狭缝圆柱涡街信号更强,信噪比高,雷诺数测量范围可低至9.5×103,斯特劳哈尔数线性度更好。理论分析与实验结果表明,带狭缝圆柱具有较好的流量测量特性,可应用于涡街流量计。

  5. Note: Derivation of two-photon circular dichroism—Addendum to “Two-photon circular dichroism” [J. Chem. Phys. 62, 1006 (1975)

    Energy Technology Data Exchange (ETDEWEB)

    Friese, Daniel H., E-mail: daniel.h.friese@uit.no [Department of Chemistry, Centre for Theoretical and Computational Chemistry CTCC, University of Tromsø, N-9037 Tromsø (Norway)

    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.

  6. Measurements of Thermal Effects on Acoustic Screech in a Choked Circular Jet Emanating from a Sharp-Edged Orifice

    Science.gov (United States)

    Kandula, Max

    2012-01-01

    Experiments are performed in a 24.4 mm diameter choked circular hot and cold jets issuing from a sharp-edged orifice at a fully expanded jet Mach number of 1.85. The stagnation temperature of the hot and the cold jets are 319 K and 299 K respectively. The results suggest that temperature effects on the screech amplitude and frequency are manifested for the fundamental, with a reduced amplitude and increased frequency for hot jet relative to the cold jet. Temperature effects on the second harmonic are also observed.

  7. Circular polarization measurements of Lyman-α radiation from the decay of the 2Pj states of hydrogen excited by 54.4 eV electrons

    International Nuclear Information System (INIS)

    Corrigendum: The set of three equations (5a), (5b) and (5c) given in the above paper are correct only for the restricted set of coordinates reported in this experiment. They lead to the correct form of the circular polarization parameter P-bar3 which is given in equation (6), but again only for the set of angles used in this experiment. The general expressions relating the reduced Stokes parameters P-bari to the normalized Stokes parameters si measured for radiation propagating in a direction determined by the set of polar angles (θn, φn) defined in the natural frame are given. (author)

  8. X-ray magnetic dichroism in (Zn,Mn)O diluted magnetic semiconductors: first-principles calculations

    Energy Technology Data Exchange (ETDEWEB)

    Antonov, V. N. [Max-Planck-Institut fur Festkorperforschung, Stuttgart (Germany); Institute of Metal Physics, Kiev (Ukraine); Bekenov, L. V.; Mazur, D. V. [Institute of Metal Physics, Kiev (Ukraine); Germash, L. P. [National Technical University of Ukraine, Kiev (Ukraine)

    2012-06-15

    The electronic structure of (Zn,Mn)O diluted magnetic semiconductors was investigated theoretically from first principles by using the fully-relativistic Dirac linear muffin-tin orbital band structure method with the local spin-density approximation (LSDA) and the LSDA+U approach. The X-ray magnetic circular dichroism (XMCD) spectra at the Mn, Zn, and O K and Mn L{sub 2,3} edges were investigated theoretically from first principles. The origin of the XMCD spectra in these compounds was examined. The effect of oxygen vacancy atoms was found to be crucial for the X-ray magnetic dichroism at the Mn L{sub 2,3} edges. The calculated results are compared with available experimental data.

  9. A solid-state dedicated circularly polarized luminescence spectrophotometer: Development and application

    Science.gov (United States)

    Harada, Takunori; Hayakawa, Hiroshi; Watanabe, Masayuki; Takamoto, Makoto

    2016-07-01

    A new solid-state dedicated circularly polarized luminescence (CPL) instrument (CPL-200CD) was successfully developed for measuring true CPL spectra for optically anisotropic samples on the basis of the Stokes-Mueller matrix approach. Electric components newly installed in the CPL-200CD include a pulse motor-driven sample rotation holder and a 100 kHz lock-in amplifier to achieve the linearly polarized luminescence measurement, which is essential for obtaining the true CPL signal for optically anisotropic samples. An acquisition approach devised for solid-state CPL analysis reduces the measurement times for a data set by ca. 98% compared with the time required in our previous method. As a result, the developed approach is very effective for samples susceptible to light-induced degradation. The theory and implementation of the method are described, and examples of its application to a CPL sample with macroscopic anisotropies are provided. An important advantage of the developed instrument is its ability to obtain molecular information for both excited and ground states because circular dichroism measurements can be performed by switching the monochromatic light to white light without rearrangement of the sample.

  10. Circularity and Lambda Abstraction

    DEFF Research Database (Denmark)

    Danvy, Olivier; Thiemann, Peter; Zerny, Ian

    2013-01-01

    In this tribute to Doaitse Swierstra, we present the rst transformation between lazy circular programs a la Bird and strict cir- cular programs a la Pettorossi. Circular programs a la Bird rely on lazy recursive binding: they involve circular unknowns and make sense equa- tionally. Circular...... unknowns from what is done to them, which we lambda-abstract with functions. The circular unknowns then become dead variables, which we eliminate. The result is a strict circu- lar program a la Pettorossi. This transformation is reversible: given a strict circular program a la Pettorossi, we introduce...

  11. Transfer of Frequency-Dependent Polarizabilities: A Tool To Simulate Absorption and Circular Dichroism Molecular Spectra

    Czech Academy of Sciences Publication Activity Database

    Kessler, Jiří; Bouř, Petr

    2015-01-01

    Roč. 11, č. 5 (2015), s. 2210-2220. ISSN 1549-9618 R&D Projects: GA ČR GAP208/11/0105; GA ČR GA13-03978S; GA ČR GA15-09072S Grant ostatní: GA AV ČR(CZ) M200551205; GA MŠk(CZ) ED3.2.00/08.0144; GA MŠk(CZ) LM2010005 Institutional support: RVO:61388963 Keywords : Raman optical activity * density functional theory * charge-transfer transitions Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 5.498, year: 2014

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

    DEFF Research Database (Denmark)

    Lassen, Peter Rygaard

    2005-01-01

    enables establishment of the absolute configuration of (-)-hinokiresinol, which is concluded to be S. A total synthesis and resolution of hinokiresinol has been performed to resolve the conflicting reports of the coupling constant of the vinylic protons of the disubstituted double bond in this molecule...

  13. Electronic Circular Dichroism of the Chiral Rigid Tricyclic Dilactam with Nonplanar Tertiary Amide Groups

    Czech Academy of Sciences Publication Activity Database

    Pazderková, Markéta; Profant, V.; Seidlerová, Beata; Dlouhá, Helena; Hodačová, J.; Javorfi, T.; Siligardi, G.; Baumruk, V.; Bednárová, Lucie; Maloň, P.

    2014-01-01

    Roč. 118, č. 38 (2014), s. 11100-11108. ISSN 1520-6106 R&D Projects: GA ČR GAP205/10/1276 Institutional support: RVO:61388963 Keywords : Gaussian basis sets * correlated molecular calculations * density functional calculations Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.302, year: 2014

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

    DEFF Research Database (Denmark)

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

    2008-01-01

    between two different types of protein fibrils, highlighting that bona fide fibrils formed by lysozyme are structurally more similar to the nonclassical fibrillar aggregates formed by the SerADan peptide than with the amyloid formed by alpha-synuclein. Thus, despite the lack of direct structural...

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

    Science.gov (United States)

    Geiger, H. Cristina; Donohoe, James S.

    2012-01-01

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

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

    Institute of Scientific and Technical Information of China (English)

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

    2009-01-01

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

  17. Tunable circular dichroism due to the chiral anomaly in Weyl semimetals

    OpenAIRE

    Hosur, Pavan; Qi, Xiao-Liang

    2014-01-01

    Weyl semimetals are a three dimensional gapless topological phase in which bands intersect at arbitrary points -- the Weyl nodes -- in the Brillouin zone. These points carry a topological quantum number known as the \\emph{chirality} and always appear in pairs of opposite chiralities. The notion of chirality leads to anomalous non-conservation of chiral charge, known as the \\emph{chiral anomaly}, according to which charge can be pumped between Weyl nodes of opposite chiralities by an electroma...

  18. Molecular photoionisation using synchrotron radiation. Photoelectron photoion coincidence and circular dichroism

    CERN Document Server

    Garcia-Macias, G A

    2002-01-01

    The first ionisation potential of the CF sub 3 radical has been determined in this work from the appearance potential of the CF sub 3 sup + fragment, formed in the photofragmentation of CF sub 3 Br. In obtaining this value special care has been taken in removing the contributions from second order light and internal energy of the fragmenting parent ion. The resulting ionisation potential was found to be in very good agreement with a number of recent theoretical calculations. The valence photoelectron spectra of three monoterpenes such as limonene, carvone and camphor have been recorded along with their mass spectra taken in coincidence with energy selected photoelectrons, providing information about state selected parent ion fragmentation channels. A new photoelectron spectrometer based on the Alien box design has been studied by ray-tracing simulations. It will include a two dimensional position sensitive detector system consisting in two micro channel plates in a chevron stack and a delay-line anode to enco...

  19. Amplified vibrational circular dichroism as a probe of local biomolecular structure.

    Science.gov (United States)

    Domingos, Sérgio R; Huerta-Viga, Adriana; Baij, Lambert; Amirjalayer, Saeed; Dunnebier, Dorien A E; Walters, Annemarie J C; Finger, Markus; Nafie, Laurence A; de Bruin, Bas; Buma, Wybren Jan; Woutersen, Sander

    2014-03-01

    We show that the VCD signal intensities of amino acids and oligopeptides can be enhanced by up to 2 orders of magnitude by coupling them to a paramagnetic metal ion. If the redox state of the metal ion is changed from paramagnetic to diamagnetic the VCD amplification vanishes completely. From this observation and from complementary quantum-chemical calculations we conclude that the observed VCD amplification finds its origin in vibronic coupling with low-lying electronic states. We find that the enhancement factor is strongly mode dependent and that it is determined by the distance between the oscillator and the paramagnetic metal ion. This localized character of the VCD amplification provides a unique tool to specifically probe the local structure surrounding a paramagnetic ion and to zoom in on such local structure within larger biomolecular systems. PMID:24506134

  20. X-ray magnetic circular dichroism experiments and theory of transuranium Laves phase compounds

    Czech Academy of Sciences Publication Activity Database

    Wilhelm, F.; Eloirdi, R.; Rusz, Ján; Springell, R.; Colineau, E.; Griveau, J.C.; Oppeneer, P. M.; Caciuffo, R.; Rogalev, A.; Lander, G.H.

    2013-01-01

    Roč. 88, č. 2 (2013), "024424-1"-"024424-14". ISSN 1098-0121 Institutional support: RVO:68378271 Keywords : electronic -structure * uranium-compounds * self-absorption * moments Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.664, year: 2013

  1. Circular dichroism in hydrogen multiphoton ionization by a bichromatic field of frequencies {omega} and 3{omega}

    Energy Technology Data Exchange (ETDEWEB)

    Fifirig, Magda [Department of Chemistry, University of Bucharest, Bucharest (Romania); Cionga, Aurelia [Institute of Space Sciences, Bucharest-Magurele (Romania)

    2002-02-28

    The dichroic effects in the multiphoton ionization of the ground state hydrogen atom by a coherent superposition of a laser beam and its third harmonic, are studied via perturbative calculations. The final state of the photoelectrons, which has the energy E=E{sub 1}+3(h/2{pi}){omega} (E{sub 1} the ground state energy and {omega} the laser frequency), is reached by two interfering quantum paths: (a) absorption of one harmonic photon and (b) absorption of three laser photons. In the chosen regime of field intensities, the radiative corrections to the absorption of one harmonic photon may be disregarded. Our numerical results illustrate the influence of the laser frequency, of the relative intensity and of the harmonic phase upon the dichroic signal. (author)

  2. Anharmonic Effects on Vibrational Spectra Intensities: Infrared, Raman, Vibrational Circular Dichroism, and Raman Optical Activity.

    Science.gov (United States)

    Bloino, Julien; Biczysko, Malgorzata; Barone, Vincenzo

    2015-12-10

    The aim of this paper is 2-fold. First, we want to report the extension of our virtual multifrequency spectrometer (VMS) to anharmonic intensities for Raman optical activity (ROA) with the full inclusion of first- and second-order resonances for both frequencies and intensities in the framework of the generalized second-order vibrational perturbation theory (GVPT2) for all kinds of vibrational spectroscopies. Then, from a more general point of view, we want to present and validate the performance of VMS for the parallel analysis of different vibrational spectra for medium-sized molecules (IR, Raman, VCD, ROA) including both mechanical and electric/magnetic anharmonicity. For the well-known methyloxirane benchmark, careful selection of density functional, basis set, and resonance thresholds permitted us to reach qualitative and quantitative agreement between experimental and computed band positions and shapes. Next, the whole series of halogenated azetidinones is analyzed, showing that it is now possible to interpret different spectra in terms of mass, electronegativity, polarizability, and hindrance variation between closely related substituents, chiral spectroscopies being particular effective in this connection. PMID:26580121

  3. Development of methodology to assign absolute configurations using vibrational circular dichroism

    OpenAIRE

    Kuppens, T

    2006-01-01

    De kennis van de 3D structuur van actieve bestanddelen van chirale medicijnen is zeer belangrijk, aangezien stereo-isomeren dikwijls een verschillende activiteit vertonen. Er zijn meerdere technieken beschikbaar om deze Absolute Configuratie te bepalen (eenkristal x-straal diffractie bijv.). Een nieuwe methode die sterk in opmars is en heel wat voordelen biedt is gebaseerd op het vibrationeel circulair dichroïsme (VCD). Het VCD fenomeen is een gevolg van de optische activiteit van een medium ...

  4. Towards the Limits of Vibrational Circular Dichroism Spectroscopy: VCD Spectra of Some Alkyl Vinylethers.

    Science.gov (United States)

    Zinna, Francesco; Pescitelli, Gennaro

    2016-02-01

    Three alkyl vinylethers from our collection of chiral samples were investigated through VCD spectroscopy, in combination with Density Functional Theory (DFT) calculations. Despite the simplicity of the compounds, reproducing all the spectral features is an involved task, since the many significantly populated conformers contribute to the total VCD spectrum with bands which often have opposite signatures. Nevertheless, we show that certain bands can be satisfactorily reproduced by calculation and therefore they may be employed for the determination of absolute configuration in these and similar compounds, for which no simple alternative method is available. Chirality 28:143-146, 2016. © 2015 Wiley Periodicals, Inc. PMID:26634887

  5. Conformational properties of chiral tobacco alkaloids by DFT calculations and vibrational circular dichroism: (-)-S-anabasine.

    Science.gov (United States)

    Rodríguez Ortega, P G; Montejo, M; Márquez, F; López González, J J

    2015-07-01

    A thorough DFT and MM study of the conformational landscape, molecular and electronic structures of (-)-S-anabasine is reported aimed to reveal the mechanism controlling its conformational preference. Although the conformational flexibility and diversity of this system is quite extensive, only two structures are populated both in gas-phase and solution (CCl4 and DMSO). NBO-aided electronic structure analyses performed for the eight conformers representing minima in the potential energy surface of (-)-S-anabasine indicate that both steric and electrostatic factors are determinant in the conformational distribution of the sample in gas phase. Nonetheless, hyperconjugative effects are the key force tipping the balance in the conformational equilibrium between the two main rotamers. Increasing the polarity of the medium (using the IEF-PCM formalism) barely affect the conformational energy profile, although a slight increase in the theoretical population of those structures more affected by electrostatic interactions is predicted. The validity of the theoretical models and calculated conformers populations are endorsed by the accurate reproduction of the IR and VCD spectra (recorded in pure liquid and in CCl4 solution) of the sample (that have been firstly recorded and assigned in the present work) which are consistent with the occurrence of a 2:1 conformational ratio. PMID:26059478

  6. Vibrational circular dichroism study of isotropic and liquid crystalline phases formed by guanine quadruplexes

    Czech Academy of Sciences Publication Activity Database

    Andrushchenko, Valery; Tsankov, D.; Krasteva, M.; Wieser, H.; Bouř, Petr

    2012-01-01

    Roč. 19, č. 1 (2012), s. 3-3. ISSN 1210-8529. [10th Discussions in Structural Molecular Biology. 22.03.2012-24.03.2012, Nové Hrady] R&D Projects: GA ČR GAP208/10/0559; GA ČR GAP208/11/0105 Grant ostatní: AV ČR M200550902 Institutional research plan: CEZ:AV0Z40550506 Keywords : G-quadruplexes * DNA * liquid crystals * VCD spectroscopy Subject RIV: CF - Physical ; Theoretical Chemistry

  7. Optically induced dichroism of Z2-centers in LiF : Mg, Ti (TLD-100)

    International Nuclear Information System (INIS)

    Crystals of γ-irradiated TLD-100 are bleached at 313 nm at 77 K with light polarized in one selected direction, and then with light polarized at 900 from the initial direction. Dichroism is induced in the Z2 center by bleaching with polarized light. The decrease in absorbance is always larger when measured with light polarized in the same direction as the bleaching light. There is an increase in absorbance at 313 nm after the second bleach when the measuring light is polarized perpendicular to the bleaching light. The results are observed in all four directions: [001], [010], [011], and [011]. A second defect center, which adsorbs at 313 nm, is proposed to explain the observed dichroism. (author)

  8. Circular-rubbing Manipulation

    Institute of Scientific and Technical Information of China (English)

    SHEN Guo-quan; XIAO Yuan-chun

    2003-01-01

    @@ "Mo" literally means "rubbing between two things"and "eliminating". Circular-rubbing is one of the earliest manipulations used in clinical practice. Circular-rubbing differs from pressing actually. Pressing is a static manipulation and acts to inhibit motion; circular-rubbing is a movable manipulation and serves to eliminate stationary. Circular-rubbing can be performed by either the palm or the finger.

  9. Light Flux Density Threshold at Which Protein Denaturation is Induced by Synchrotron Radiation Circula Dichroism Beamlines

    International Nuclear Information System (INIS)

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

  10. Broadening and shifting of the methanol 119 μm gain line of linear and circular polarization by collision with chiral molecules

    International Nuclear Information System (INIS)

    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 μm line of the methanol molecule was observed using infrared-far infrared double resonance spectroscopy

  11. Orientation of gramicidin A transmembrane channel. Infrared dichroism study of gramicidin in vesicles.

    OpenAIRE

    Nabedryk, E.; Gingold, M P; Breton, J

    1982-01-01

    Polarized infrared spectroscopy has been used to investigate the orientation of gramicidin A incorporated in dimyristoylphosphatidylcholine liposomes. Dichroism measurements of the major lipid (C = O ester, PO2-, CH2) and peptide (amide A, I, II) bands were performed on liposomes (with or without gramicidin) oriented by air-drying. The mean orientation of the lipid groups and of the pi LD helix chain in the gramicidin has been determined. It can be inferred from infrared frequencies of gramic...

  12. Magnetic x-ray linear dichroism in resonant and non-resonant Gd 4f photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Mishra, S.; Gammon, W.J.; Pappas, D.P. [Virginia Commonwealth Univ., Richmond, VA (United States)] [and others

    1997-04-01

    The enhancement of the magnetic linear dichroism in resonant 4f photoemission (MLDRPE) is studied from a 50 monolayer film of Gd/Y(0001). The ALS at beamline 7.0.1 provided the source of linearly polarized x-rays used in this study. The polarized light was incident at an angle of 30 degrees relative to the film plane, and the sample magnetization was perpendicular to the photon polarization. The linear dichroism of the 4f core levels is measured as the photon energy is tuned through the 4d-4f resonance. The authors find that the MLDRPE asymmetry is strongest at the resonance. Near the threshold the asymmetry has several features which are out of phase with the fine structure of the total yield.

  13. Inductive Sensor for Lightning Current Measurement, Fitted in Aircraft Windows-Part I: Analysis for a Circular Window

    Czech Academy of Sciences Publication Activity Database

    van Deursen, A.P.J.; Stelmashuk, Vitaliy

    2011-01-01

    Roč. 11, č. 1 (2011), s. 199-204. ISSN 1530-437X Institutional research plan: CEZ:AV0Z20430508 Keywords : Lightning * inductive sensor * aircraft * window * viewport Subject RIV: JB - Sensors, Measurment, Regulation Impact factor: 1.520, year: 2011

  14. Vitrified chiral-nematic liquid crystalline films for selective reflection and circular polarization

    Energy Technology Data Exchange (ETDEWEB)

    Katsis, D.; Chen, P.H.M.; Mastrangelo, J.C.; Chen, S.H. [Univ. of Rochester, NY (United States); Blanton, T.N. [Eastman Kodak Co., Rochester, NY (United States)

    1999-06-01

    Nematic and left-handed chiral-nematic liquid crystals comprising methoxybiphenylbenzoate and (S)-(-)-1-phenylethylamine pendants to a cyclohexane core were synthesized and characterized. Although pristine samples were found to be polycrystalline, thermal quenching following heating to and annealing at elevated temperatures permitted the molecular orders characteristic of liquid crystalline mesomorphism to be frozen in the glassy state. Left at room temperature for 6 months, the vitrified liquid crystalline films showed no evidence of recrystallization. An orientational order parameter of 0.65 was determined with linear dichroism of a vitrified nematic film doped with Exalite 428 at a mole fraction of 0.0025. Birefringence dispersion of a blank vitrified nematic film was determined using a phase-difference method complemented by Abbe refractometry. A series of vitrified chiral-nematic films were prepared to demonstrate selective reflection and circular polarization with a spectral region tunable from blue to the infrared region by varying the chemical composition. The experimentally measured circular polarization spectra were found to agree with the Good-Karali theory in which all four system parameters were determined a priori: optical birefringence, average refractive index, selective reflection wavelength, and film thickness.

  15. Circular polarisation measurements of the L sub. alpha. cascade radiation for the 3 sup 2 D sub j states of atomic hydrogen, excited by electron impact

    Energy Technology Data Exchange (ETDEWEB)

    Farrell, D.; Slevin, J. (Saint Patrick' s Coll., Maynooth (Ireland)); Chwirot, S. (Uniwersytet Mikolaja Kopernika, Torun (Poland). Inst. Fizyki); Srivastava, R. (Roorkee Univ. (India). Dept. of Physics)

    1990-01-28

    Measurements are reported for the circular polarisation of the L{sub {alpha}} radiation arising from the cascade of the 3{sup 2}D{sub j} states of atomic hydrogen to the 2{sup 2}P{sub j} states detected in coincidence with electrons with n = 3 energy loss. Data for the atomic orientation parameter L {sub perpendicular} are presented at incident electron energies of 54.4 and 100 eV and at scattering angles {theta}{sub e} of 20{sup 0} and 25{sup 0}. These data, together with previous measurements for this transition, constitute a determination of the complete parameter set {l brace}{gamma}, P{sub 1}, {rho}{sub 00}, L {sub perpendicular}{r brace} for 3{sup 2}D{sub j} excitations in this dynamic range. Calculations for P{sub 3} and L {sub perpendicular} using distorted-wave approximation theory are also performed. The theoretical results are presented and compared with the experimental data. (author).

  16. Results of stretched wire field integral measurements on the mini-undulator magnet - comparison of results obtained from circular and translational motion of the integrating wire

    International Nuclear Information System (INIS)

    Measurements of the multipole content of the Mini-Undulator magnet have been made with two different integrating wire techniques. Both measurements used 43 strand Litz wire stretched along the length of the magnet within the magnet gap. In the first technique, the wire motion was purely translational, while in the second technique the wire was moved along a circular path. The induced voltage in the Litz wire was input into a Walker integrator, and the integrator output was analyzed as a function of wire position for determination of the multipole content of the magnetic field. The mini-undulator magnet is a 10 period, 80 mm per period hybrid insertion device. For all the data contained herein the magnet gap was set at 49 mm. In the mini-undulator magnet, the iron poles are 18mm x 32mm x 86 mm, and the Samarium Cobalt permanent magnet blocks are 22mm x 21mm x 110mm. For this magnet, which is a shortened prototype for the NSLS Soft X-Ray Undulator Magnet, the undulator parameter K = 0.934 B (Tesla)λ(cm), and B(tesla) = 0.534/sinh(πGap/λ). At a gap of 49 mm, the magnetic field is 1590 Gauss

  17. Measurements of true polymer melt temperature in a circular cross-sectional duct by moving temperature sensor

    Directory of Open Access Journals (Sweden)

    Patcharaphun,S.

    2002-01-01

    Full Text Available The objective of this research was to design and develop an experimental apparatus and a temperature sensor in order to measure true melt temperature rise due to the shear heating during the flow. The designed apparatus featured two different forms, one being the polymer melt flowing past the stationary sensor (so-called moving piston, and the other being the sensor moving along the stationary polymer melt (so-called moving sensor. By subtracting the temperature data obtained by moving sensor from those obtained by moving piston the true melt temperature rise could be yielded. The temperature data were collected using a high-speed data logger and a computer. The effects of melt/piston velocity, initial melts temperature and various types of polymer melts used were of interest in this work. It was found that the experimental apparatus designed and used in this work was very effective and gave reasonably accurate

  18. PUBLICATION OF ADMINISTRATIVE CIRCULAR

    CERN Multimedia

    HR Department

    2008-01-01

    ADMINISTRATIVE CIRCULAR NO. 23 (REV. 2) – SPECIAL WORKING HOURS Administrative Circular No. 23 (Rev. 2) entitled "Special working hours", approved following discussion in the Standing Concertation Committee meeting of 9 December 2008, will be available on the intranet site of the Human Resources Department as from 19 December 2008: http://cern.ch/hr-docs/admincirc/admincirc.asp It cancels and replaces Administrative Circular No. 23 (Rev. 1) entitled "Stand-by duty" of April 1988. A "Frequently Asked Questions" information document on special working hours will also be available on this site. Paper copies of this circular will shortly be available in departmental secretariats. Human Resources Department Tel. 78003

  19. Publication of administrative circular

    CERN Multimedia

    HR Department

    2009-01-01

    ADMINISTRATIVE CIRCULAR NO. 23 (REV. 2) – SPECIAL WORKING HOURS Administrative Circular No. 23 (Rev. 2) entitled "Special working hours", approved following discussion in the Standing Concertation Committee on 9 December 2008, will be available on the intranet site of the Human Resources Department as from 19 December 2008: http://cern.ch/hr-docs/admincirc/admincirc.asp It cancels and replaces Administrative Circular No. 23 (Rev. 1) entitled "Stand-by duty" of April 1988. A "Frequently Asked Questions" information document on special working hours will also be available on this site. Paper copies of this circular will shortly be available in Departmental Secretariats. Human Resources Department Tel. 78003

  20. Circular Dichrosim in Photoionization of H2 and D2

    International Nuclear Information System (INIS)

    In this work, circular dichroism in H2 (D2) photoionization is studied in detail. We have selected several photon energies for a case study: 19 eV for which only direct ionization to the 1sσg ionization channel is present, 27 eV where autoionization of Q11Σ+u doubly excited states takes place, and 32.5 eV for which autoionization from Q1 and doubly excited states and direct ionization to 1sσg and 2pσu channels strongly interfere. The latter case shows clear evidence of different behavior of the photoionization against radiation helicity.

  1. The Circular Camera Movement

    DEFF Research Database (Denmark)

    Hansen, Lennard Højbjerg

    2014-01-01

    It has been an accepted precept in film theory that specific stylistic features do not express specific content. Nevertheless, it is possible to find many examples in the history of film in which stylistic features do express specific content: for instance, the circular camera movement is used...... circular camera movement. Keywords: embodied perception, embodied style, explicit narration, interpretation, style pattern, television style...

  2. Perfect Circular Dichroic Metamirrors

    CERN Document Server

    Wang, Zuojia; Liu, Yongmin

    2015-01-01

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

  3. Dichroism for Orbital Angular Momentum using Stimulated Parametric Down Conversion

    CERN Document Server

    Lowney, Joseph; Faccio, Daniele; Wright, Ewan M

    2014-01-01

    We theoretically analyze stimulated parametric down conversion 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.

  4. Boundaries for efficient use of electron vortex beams to measure magnetic properties

    Czech Academy of Sciences Publication Activity Database

    Rusz, Ján; Bhowmick, S.

    2013-01-01

    Roč. 111, č. 10 (2013), "105504-1"-"105504-5". ISSN 0031-9007 Institutional support: RVO:68378271 Keywords : orbital angular - momentum * circular-dichroism * chiral dichroism * microscope * resolution Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 7.728, year: 2013

  5. Circular polarization memory in polydisperse scattering media

    CERN Document Server

    Macdonald, Callum M; Meglinski, Igor

    2015-01-01

    We investigate the survival of circularly polarized light in random scattering media. The surprising persistence of this form of polarization has a known dependence on the size and refractive index of scattering particles, however a general description regarding polydisperse media is lacking. Through analysis of Mie theory, we present a means of calculating the magnitude of circular polarization memory in complex media, with total generality in the distribution of particle sizes and refractive indices. Quantification of this memory effect enables an alternate pathway towards recovering particle size distribution, based on measurements of diffusing circularly polarized light.

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

    Science.gov (United States)

    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.

  7. Photoionization of epichlorohydrin enantiomers and clusters studied with circularly polarized vacuum ultraviolet radiation.

    Science.gov (United States)

    Daly, Steven; Powis, Ivan; Garcia, Gustavo A; Soldi-Lose, Héloïse; Nahon, Laurent

    2011-02-14

    The photoionization of enantiomerically pure epichlorohydrin (C(3)H(5)OCl) has been studied using linearly and circularly polarized vacuum ultraviolet synchrotron radiation. The threshold photoelectron spectrum was recorded and the first three bands assigned using molecular orbital calculations for the expected conformers, although uncertain experimental conformer populations and an anticipated breakdown in Koopmans' theorem leave some ambiguity. Measurements of the photoelectron circular dichroism (PECD) were obtained across a range of photon energies for each of these bands, using electron velocity map imaging to record the angular distributions, during which a record PECD chiral asymmetry factor of 32% was observed. A comparison with calculated PECD curves clarifies the assignment achieved using ionization energies alone and further suggests a likely relative population of the conformers. Threshold photoelectron-photoion coincidence methods were used to study the ionic fragmentation of epichlorohydrin. Fragment ion appearance energies show nonstatistical behavior with clear indications that the cationic epoxide ring is unstable and lower energy decay channels proceeding via ring breaking are generally open. Extensive neutral homochiral clusters of epichlorohydrin may be formed in supersonic molecular beam expansions seeded in Ar. Electron angular distribution measurements made in coincidence with dimer and trimer ions are used to effect an examination of the PECD associated with ionization of size-selected neutral cluster species, and these results differ clearly from PECD of the neutral monomer. The shifted ionization thresholds of the n-mers (n = 2, ..., 7) are shown to follow a simple linear relationship, but under intense beam expansion conditions the monomer deviates from this relationship, and the monomer electron spectra tail to below the expected monomer adiabatic ionization potential (IP). PECD measurements made in coincidence with monomer ions obtained

  8. The effect of pea chloroplast alignment and variation of excitation wavelength on the circularly polarized chlorophyll luminescence.

    Science.gov (United States)

    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

  9. Electric dichroism transients of aqueous solutions of DNA

    Energy Technology Data Exchange (ETDEWEB)

    Bertolotto, J A; Corral, G M; Farias de La Torre, E M; Roston, G B [Department of Physics, Faculty of Natural Sciences, National University of La Pampa, Santa Rosa, La Pampa (Argentina)

    2010-12-15

    In this work we develop a theory of reduced electric linear dichroism transients of DNA fragments in aqueous solution. The DNA fragments are modelled as rigid 'bent-rod molecules' (BRM) with the following physical parameters: electric charge, electric polarizability tensors and hydrodynamical ones, and the average transition probability tensor per molecule. In order to study the growth and decay of electric dichroism transients, the orientational distribution function of the molecules is needed. This function is obtained by solving the time-dependent Fokker-Planck equation in the presence of a low electric field E, using a perturbation method and the Fourier method with time-dependent coefficients. In our calculations the origin of the coordinate system is the mass centre of the BRM. With respect to this centre, the electric dipole moment of the molecule is zero. The developed theory adequately explains the experimental results. We show that the theoretical approach used in this work is equivalent to the one applied in the Brownian dynamics simulation work performed by Porschke and co-workers. We also analyse the effect of a possible electric dipole moment on the transients of the reduced electric linear dichroism in DNA bent fragments.

  10. Compact waveguide circular polarizer

    Energy Technology Data Exchange (ETDEWEB)

    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.

  11. A general way for quantitative magnetic measurement by transmitted electrons.

    Science.gov (United States)

    Song, Dongsheng; Li, Gen; Cai, Jianwang; Zhu, Jing

    2016-01-01

    EMCD (electron magnetic circular dichroism) technique opens a new door to explore magnetic properties by transmitted electrons. The recently developed site-specific EMCD technique makes it possible to obtain rich magnetic information from the Fe atoms sited at nonequivalent crystallographic planes in NiFe2O4, however it is based on a critical demand for the crystallographic structure of the testing sample. Here, we have further improved and tested the method for quantitative site-specific magnetic measurement applicable for more complex crystallographic structure by using the effective dynamical diffraction effects (general routine for selecting proper diffraction conditions, making use of the asymmetry of dynamical diffraction for design of experimental geometry and quantitative measurement, etc), and taken yttrium iron garnet (Y3Fe5O12, YIG) with more complex crystallographic structure as an example to demonstrate its applicability. As a result, the intrinsic magnetic circular dichroism signals, spin and orbital magnetic moment of iron with site-specific are quantitatively determined. The method will further promote the development of quantitative magnetic measurement with high spatial resolution by transmitted electrons. PMID:26726959

  12. Live cell linear dichroism imaging reveals extensive membrane ruffling within the docking structure of natural killer cell immune synapses

    DEFF Research Database (Denmark)

    Benninger, Richard K P; Vanherberghen, Bruno; Young, Stephen;

    2009-01-01

    We have applied fluorescence imaging of two-photon linear dichroism to measure the subresolution organization of the cell membrane during formation of the activating (cytolytic) natural killer (NK) cell immune synapse (IS). This approach revealed that the NK cell plasma membrane is convoluted into...... absent from the center of the mature synapse. Understanding the role of such extensive membrane ruffling in the assembly of cytolytic synapses is an intriguing new goal....

  13. Nanoconfined circular and linear DNA - equilibrium conformations and unfolding kinetics

    CERN Document Server

    Alizadehheidari, M; Noble, C; Reiter-Schad, M; Nyberg, L K; Fritzsche, J; Mehlig, B; Tegenfeldt, J O; Ambjörnsson, T; Persson, F; Westerlund, F

    2016-01-01

    Studies of circular DNA confined to nanofluidic channels are relevant both from a fundamental polymer-physics perspective and due to the importance of circular DNA molecules in vivo. We here observe the unfolding of DNA from the circular to linear configuration as a light-induced double strand break occurs, characterize the dynamics, and compare the equilibrium conformational statistics of linear and circular configurations. This is important because it allows us to determine to which extent existing statistical theories describe the extension of confined circular DNA. We find that the ratio of the extensions of confined linear and circular DNA configurations increases as the buffer concentration decreases. The experimental results fall between theoretical predictions for the extended de Gennes regime at weaker confinement and the Odijk regime at stronger confinement. We show that it is possible to directly distinguish between circular and linear DNA molecules by measuring the emission intensity from the DNA....

  14. Wiimote Experiments: Circular Motion

    Science.gov (United States)

    Kouh, Minjoon; Holz, Danielle; Kawam, Alae; Lamont, Mary

    2013-01-01

    The advent of new sensor technologies can provide new ways of exploring fundamental physics. In this paper, we show how a Wiimote, which is a handheld remote controller for the Nintendo Wii video game system with an accelerometer, can be used to study the dynamics of circular motion with a very simple setup such as an old record player or a…

  15. Magnetic measurements with atomic-plane resolution.

    Science.gov (United States)

    Rusz, Ján; Muto, Shunsuke; Spiegelberg, Jakob; Adam, Roman; Tatsumi, Kazuyoshi; Bürgler, Daniel E; Oppeneer, Peter M; Schneider, Claus M

    2016-01-01

    Rapid development of magnetic nanotechnologies calls for experimental techniques capable of providing magnetic information with subnanometre spatial resolution. Available probes of magnetism either detect only surface properties, such as spin-polarized scanning tunnelling microscopy, magnetic force microscopy or spin-polarized low-energy electron microscopy, or they are bulk probes with limited spatial resolution or quantitativeness, such as X-ray magnetic circular dichroism or classical electron magnetic circular dichroism (EMCD). Atomic resolution EMCD methods have been proposed, although not yet experimentally realized. Here, we demonstrate an EMCD technique with an atomic size electron probe utilizing a probe-corrected scanning transmission electron microscope in its standard operation mode. The crucial element of the method is a ramp in the phase of the electron beam wavefunction, introduced by a controlled beam displacement. We detect EMCD signals with atomic-plane resolution, thereby bringing near-atomic resolution magnetic circular dichroism spectroscopy to hundreds of laboratories worldwide. PMID:27578421

  16. Orientational dependence of linear dichroism exemplified by dyed spherulites.

    Science.gov (United States)

    Benedict, Jason B; Freudenthal, John H; Hollis, Eva; Kahr, Bart

    2008-08-13

    D-sorbitol forms so-called spherulites from under-cooled melts. These polycrystalline formations have optically uniaxial radii. Melts pressed between glasses crystallize as plane sections of spheres. Dyes that are soluble in molten sorbitol become oriented as the crystallization front passes through the melt so as to form disks with large linear dichroism in the absorption bands of the dyes. The dyeing of spherulites is thus a general method of solute alignment. The linear optical properties of sorbitol spherulites containing the azo dye amaranth were analyzed in detail so as to correct a persistent confusion in the literature regarding the orientational dependence of linear dichroism. In cases involving thin film dichroism of multilayered samples requiring many corrections of intensity data in non-normal incidence, some authors have taken transmittance and others absorbance as having a cosine-squared angular dependence on the plane of the electric vector of linearly polarized light. Plane sections of doped spherulites present all orientations of an electric dipole oscillator in spatially localized region in normal incidence. As such, the samples described herein are ideally suited to resolving this confusion. Images of transmittance of dyed spherulites in polarized light were recorded with a CCD camera and simulated under the assumption that both absorbance and transmittance show a cosine-squared angular dependence but with respect to different angles. Transmittance with a cosine-squared dependence follows azimuthal rotations of the spherulite radii around the wave vector, while absorbance with a cosine-squared dependence follows rotations about axes perpendicular to the wave vector, natural consequences of the properties of the optical indicatrix that are often overlooked. Spherulites obviate the substantial experimental complexities that are engendered in non-normal incidence by sample reorientation. Thus, the principles of anisotropic absorption are given in a

  17. Linear birefringence and dichroism in citric acid coated Fe{sub 3}O{sub 4} magnetic nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Jing-Fung, E-mail: jacklin@cc.feu.edu.tw [Graduate School of Computer Application Engineering, Far East University, No. 49, Zhonghua Road, Xinshi District, Tainan, Taiwan, ROC (China); Tsai, Chun-Chin [Department of Optoelectronic Engineering, Far East University, No. 49, Zhonghua Road, Xinshi District, Tainan, Taiwan, ROC (China); Lee, Meng-Zhe [Graduate School of Computer Application Engineering, Far East University, No. 49, Zhonghua Road, Xinshi District, Tainan, Taiwan, ROC (China)

    2014-12-15

    To prepare highly dispersed water-based Fe{sub 3}O{sub 4} magnetic nanoparticles (MNPs), we adopted the co-precipitation method and used citric acid (CA) as the surfactant. Via transmission electronic microscopy, dynamic light scattering, and X-ray diffractometry, we characterized the dispersibility and size of the products. Through two single-parameter experiments, including the pH value of suspension and the action of double centrifugations, the appropriate parameters' values were determined. Further, to produce CA coated MNPs with good magneto-optical properties as high retardance and low dichroism, the orthogonal design method was used to find the optimal parameters' values, including pH value of suspension after coating was 5, molar ratio of CA to Fe{sub 3}O{sub 4} MNPs was 0.06, volume of CA was 40 ml, and coating temperature was 70 °C. Above all, the linear birefringence and dichroism of the best CA coated ferrofluid we produced were measured by a Stokes polarimeter as 23.6294° and 0.3411 under 64.5 mT, respectively. Thus, the biomedical applications could be performed hereafter. - Highlights: • We examine pH changes about retardance/dichroism of citric acid coated ferrofluid. • We examine centrifugal action about dispersity of citric acid coated ferrofluid. • Dispersity of coated suspensions with different pH is investigated by DLS results. • Optimum combination and influence sequence obtained by Taguchi method is found. • Molar ratio of CA to Fe{sub 3}O{sub 4} deeply influences the retardance and dichroism of FFs.

  18. Circular arc structures

    KAUST Repository

    Bo, Pengbo

    2011-07-01

    The most important guiding principle in computational methods for freeform architecture is the balance between cost efficiency on the one hand, and adherence to the design intent on the other. Key issues are the simplicity of supporting and connecting elements as well as repetition of costly parts. This paper proposes so-called circular arc structures as a means to faithfully realize freeform designs without giving up smooth appearance. In contrast to non-smooth meshes with straight edges where geometric complexity is concentrated in the nodes, we stay with smooth surfaces and rather distribute complexity in a uniform way by allowing edges in the shape of circular arcs. We are able to achieve the simplest possible shape of nodes without interfering with known panel optimization algorithms. We study remarkable special cases of circular arc structures which possess simple supporting elements or repetitive edges, we present the first global approximation method for principal patches, and we show an extension to volumetric structures for truly threedimensional designs. © 2011 ACM.

  19. Switchable circular beam deflectors

    Science.gov (United States)

    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.

  20. Recollision with circular polarization

    Science.gov (United States)

    Mauger, Francois; Kamor, Adam; Bandrauk, Andre; Chandre, Cristel; Uzer, Turgay

    2013-05-01

    Since its identification in the 90s, the recollision scenario has revealed to be very helpful in explaining many phenomena in atomic and molecular systems subjected to strong and short laser pulses, and it is now at the core of the strong field physics and attosecond science. For linearly polarized laser fields, the recollision scenario has been able to explain nonsequential double ionization (NSDI), high harmonic generation (HHG) and laser induced diffraction (LIED), just to cite them. The same scenario also predicts the absence of recollision when the field is circularly polarized, therefore leading to the absence of NSDI, HHG or LIED. Recently, the influence of the ellipticity of the laser has drawn an increasing level of interest in the strong field community as it is seen as a way to control the electronic dynamics and, for instance, HHG. Using classical models, the common belief of the absence of recollision with circularly polarized laser fields has been proven wrong. In my talk I will present classical and quantum evidence of the presence of recollision with circular polarization. I will discuss the conditions under which such recollisions happen and what they imply.