Science.gov

Sample records for absorption linear dichroism

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

    PubMed Central

    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 spectra of the polynucleotides were compared with previously measured solution spectra. The good agreement between calculated and measured polynucleotide spectra indicates, for the first time, that the DeVoe theory is a useful means of calculating the VCD and IR absorption spectra of polynucleotides. For the first time, calculated DeVoe theory VCD and IR absorption spectra of oriented polynucleotides are presented. The calculated VCD spectra for the oriented polynucleotides are used to predict the spectra for such measurements made in the future. The calculated IR spectra for the oriented polynucleotides are useful in interpreting the linear dichroism of the polynucleotides. PMID:9199798

  2. Three-photon circular dichroism: towards a generalization of chiroptical non-linear light absorption.

    PubMed

    Friese, Daniel H; Ruud, Kenneth

    2016-02-07

    We present the theory of three-photon circular dichroism (3PCD), a novel non-linear chiroptical property not yet described in the literature. We derive the observable absorption cross section including the orientational average of the necessary seventh-rank tensors and provide origin-independent expressions for 3PCD using either a velocity-gauge treatment of the electric dipole operator or a length-gauge formulation using London atomic orbitals. We present the first numerical results for hydrogen peroxide, 3-methylcyclopentanone (MCP) and 4-helicene, including also a study of the origin dependence and basis set convergence of 3PCD. We find that for the 3PCD-brightest low-lying Rydberg state of hydrogen peroxide, the dichroism is extremely basis set dependent, with basis set convergence not being reached before a sextuple-zeta basis is used, whereas for the MCP and 4-helicene molecules, the basis set dependence is more moderate and at the triple-zeta level the 3PCD contributions are more or less converged irrespective of whether the considered states are Rydberg states or not. The character of the 3PCD-brightest states in MCP is characterized by a fairly large charge-transfer character from the carbonyl group to the ring system. In general, the quadrupole contributions to 3PCD are found to be very small.

  3. Absorption linear dichroism measured directly on a single light-harvesting system: the role of disorder in chlorosomes of green photosynthetic bacteria.

    PubMed

    Furumaki, Shu; Vacha, Frantisek; Habuchi, Satoshi; Tsukatani, Yusuke; Bryant, Donald A; Vacha, Martin

    2011-05-04

    Chlorosomes are light-harvesting antennae of photosynthetic bacteria containing large numbers of self-aggregated bacteriochlorophyll (BChl) molecules. They have developed unique photophysical properties that enable them to absorb light and transfer the excitation energy with very high efficiency. However, the molecular-level organization, that produces the photophysical properties of BChl molecules in the aggregates, is still not fully understood. One of the reasons is heterogeneity in the chlorosome structure which gives rise to a hierarchy of structural and energy disorder. In this report, we for the first time directly measure absorption linear dichroism (LD) on individual, isolated chlorosomes. Together with fluorescence-detected three-dimensional LD, these experiments reveal a large amount of disorder on the single-chlorosome level in the form of distributions of LD observables in chlorosomes from wild-type bacterium Chlorobaculum tepidum . Fluorescence spectral parameters, such as peak wavelength and bandwidth, are measures of the aggregate excitonic properties. These parameters obtained on individual chlorosomes are uncorrelated with the observed LD distributions and indicate that the observed disorder is due to inner structural disorder along the chlorosome long axis. The excitonic disorder that is also present is not manifested in the LD distributions. Limiting values of the LD parameter distributions, which are relatively free of the effect of structural disorder, define a range of angles at which the excitonic dipole moment is oriented with respect to the surface of the two-dimensional aggregate of BChl molecules. Experiments on chlorosomes of a triple mutant of Chlorobaculum tepidum show that the mutant chlorosomes have significantly less inner structural disorder and higher symmetry, compatible with a model of well-ordered concentric cylinders. Different values of the transition dipole moment orientations are consistent with a different molecular level

  4. Investigation of magneto-induced linear dichroism of magnetic fluid.

    PubMed

    Du, Bobo; Yang, Dexing; Bai, Yang; Yuan, Yuan; Mao, Dong; Zhang, Wending; She, Xiaoyang

    2017-01-20

    A fiber-optic component is fabricated with etched fiber coated by magnetic fluid (MF) for its evanescent field to be modulated by the MF. The magneto-induced linear dichroism of the MF is investigated under different temperatures with the component. The experimental results show that the MF possesses weak linear dichroism (maximum of 2.37% at 25°C) caused by its sparse magneto-induced chains. Considering the relationships between the linear dichroisms and temperature, there is a transition point of magnetic field at ∼4  mT. Up to ∼4  mT, the linear dichroisms decrease with the temperature; however, for higher magnetic field strengths, the linear dichroisms increase with the temperature. Interestingly, a small initial linear dichroism (up to 0.255% at 5°C) without magnetic field is also observed.

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

    SciTech Connect

    Tobin, J.G.; Goodman, K.W.; Mankey, G.J.; Willis, R.F.; Denlinger, J.D.; Rotenberg, E.; Warwick, A.

    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.

  6. Circular Dichroism Microscopy Free from Commingling Linear Dichroism via Discretely Modulated Circular Polarization

    PubMed Central

    Narushima, Tetsuya; Okamoto, Hiromi

    2016-01-01

    In this work, we developed a circular dichroism (CD) imaging microscope with a device to suppress the commingling of linear birefringence (LB) and linear dichroism (LD) signals. CD signals are, in principle, free from the commingling influence of LD and LB if the sample is illuminated with pure circularly polarized light, with no linear polarization contribution. Based on this idea, we here propose a novel circular polarization modulation method to suppress the contribution of linear polarization, which enables high-sensitivity CD detection (10−4 level in optical density unit or mdeg level in ellipticity) for microscopic imaging at a nearly diffraction limited spatial resolution (sub-μm level). The highly sensitive, diffraction-limited local CD detection will make direct analyses of chiral structures and spatial mappings of optical activity feasible for μm- to sub-μm-sized materials and may yield a number of applications as a unique optical imaging method. PMID:27761022

  7. A combination spectrophotometer for measuring electronic absorption, natural circular dichroism, and magnetic circular dichroism spectra

    NASA Astrophysics Data System (ADS)

    Policke, Timothy A.; Schreiner, Anton F.; Trexler, Jack W.; Knopp, James A.

    1990-08-01

    The design, construction, and evaluation of a combination spectrometer for measuring electronic absorption (EA), natural circular dichroism (CD), and magnetic circular dichroism (MCD) are described. Around the optical components of a JASCO ORD/UV-5 spectropolarimeter, a new EA/CD/MCD instrument was built with the realized intentions of increasing sensitivity and upgrading the analog tube type circuitry to a solid-state digitally, computer-controlled spectrophotometer. It is a flexible, dynamic, and user-controllable system, interfaced to an Apple II Plus computer, for studying instrument and signal parameters. The monochromator (M), photoelastic modulator (PEM), photomultiplier tube applied voltage (PMHV), and photomultiplier tube dc output current (PMdc) are under complete and independent software control. Our system has two unique aspects for obtaining the circular dichroism. First, the ac signal is measured with a voltage-to-frequency (V/f) converter; and, second, both the ac and the dc are independently recorded and their ratio is digitally calculated. This design has several advantages which include the elimination of voltage divider integrated circuits or division electronics, a wide dynamic range, a greater precision of ac values at low percentages of full scale, and the capability of continuous integration over long time periods. Also, both types of spectra, EA and CD or MCD, are obtained from the current output of the PM. This paper not only describes the design of the instrument for obtaining the two types of spectra but also compares four methods of obtaining the circular dichroism. Sensitivities of ˜1×10-7ΔA units are achievable as determined by measuring CD spectra of the well-known enantiomer (+)-[Co(en)3]3+.

  8. Pulsed electric linear dichroism of triphenylmethane dyes adsorbed on montmorillonite K10 in aqueous media

    SciTech Connect

    Yamaoka, Kiwamu; Sasai, Ryo

    2000-05-01

    Electric linear dichroism (ELD) spectra of two cationic triphenylmethane dyes, crystal violet (CV) and malachite green (MG), bound to sodium montmorillonite K10 (MK-10) were studied at 20 C in aqueous media at two mixing ratios, D/S, of 0.10 and 0.24 in the 700- to 400 nm wavelength region and in the applied electric field strength range between 0 and 3 kV/cm. The specific parallel and perpendicular dichroism ({Delta}A{sub {parallel}}/A and {Delta}A{sub {perpendicular}}/A) spectra of dye-adsorbed MK-10 suspension were measured at a fixed field strength with an apparatus equipped with a 512-channel photodiode array detector. By changing the field strength over a wide range, a series of the reduced dichroism values of the bound dyes were measured at a fixed wavelength. By fitting these dichroism values to theoretical orientation functions, the intrinsic reduced dichroism ({Delta}A/A){sub int} spectra at the limiting high fields (ELD spectrum) were determined for CV and MG bound to MK-10. No appreciable difference was observed at the two D/S values. The ELD spectra of these bound dyes are undulatory but never constant, throughout their absorption region; thus, the dye plane does not lie flatly either on the surface or between layers of MK-10 particle.

  9. Linear dichroism, produced by thermo-electric alignment of silver nanoparticles on the surface of ion-exchanged glass

    NASA Astrophysics Data System (ADS)

    Nahal, Arashmid; Shapoori, Kiyanoosh

    2009-06-01

    A heated Ag +-doped glass is subjected to an external constant uniform electric field ( Eo > 250 V/cm) parallel to its surface. Absorption spectra studies by linear polarized light imply the induction of a linear dichroism in the samples, after the above-mentioned thermo-electrical process. It is found that the increase in the temperature (400 °C ≤ T ≤ 600 °C), results in the formation of neutral silver multimers and clusters on the samples. Dichroism is the result of simultaneous application of the steady uniform electric field and heating. That is, the process aligns the produced silver nanoparticles along the applied electric field ( Eo) during the aggregation of silver nano-clusters via dipole-dipole interaction, leading to the formation of chain-like conductive structures.

  10. Linear Dichroism and Orientation of the Phycomyces Photopigment

    PubMed Central

    Jesaitis, A. J.

    1974-01-01

    The greater sensitivity of a cylindrical Phycomyces sporangiophore to blue light polarized transversely rather than longitudinally is a consequence of the dichroism and orientation of the receptor pigment. The abilities of wild type and several carotene mutants to distinguish between the two directions of polarization are the same. The E-vector angle for maximum response relative to the transverse direction is 42 ± 4° at 280 nm, 7° ± 3° at 456 nm, and 7° ± 8° at 486 nm. The in vivo attenuation of polarized light at these wavelengths is very small. The polarized light effect in Phycomyces cannot arise from reflections at the cell surface or from differential attenuations due to internal screening or scattering. PMID:4810207

  11. Transition-moment directions of selected carbocyanines from emission anisotropy and linear dichroism measurements in uniaxially stretched polymer films

    NASA Astrophysics Data System (ADS)

    Synak, Anna; Bojarski, Piotr

    2005-12-01

    Based on the Kawski-Gryczyński method the values of angle between absorption and fluorescence transition moments of carbocyanines are given. This method is applied to the linear molecules: 3,3'-diethylthiacyanine iodide (DTTHCI), diethyloxacarbocyanine iodide (DOCI), 3,3'-diethyl-9-methylthiacarbocyanine iodide (MDTCI), diethylthiacarbocyanine iodide (DTCI) and 3,3'-diethyloxadicarbocyanine iodide (DODCI). Similarly located transition moments polarized approximately along the long axis of DTTHCI, DOCI, MDTCI, DTCI and DODCI are responsible for absorption and fluorescence ( β ⩽ 10°), when exciting in the long wavelength absorption band. The results are compared with relevant data obtained from linear dichroism measurements, energy migration data in partly ordered films and general Perrin formula.

  12. Magnetic x-ray linear dichroism in the photoelectron spectroscopy of ultrathin magnetic alloy films

    NASA Astrophysics Data System (ADS)

    Tobin, J. G.; Goodman, K. W.; Mankey, G. J.; Willis, R. F.; Denlinger, J. D.; Rotenberg, E.; Warwick, A.

    1996-04-01

    The magnetic structure of nanoscale alloy films has been probed using the magnetic x-ray linear dichroism in photoelectron spectroscopy. FeNi and CoFe epitaxial films were grown on Cu(001), in situ and using molecular beam epitaxy techniques. The magnetic x-ray linear dichroism measurements were made at the Spectromicroscopy Facility of the Third Generation Advanced Light Source. Because soft x-rays were used to generate photoemission from the 3p core levels, both elemental selectivity and magnetic sensitivity were achieved simultaneously.

  13. Electronic states of the fluorophore 9,10-bis(phenylethynyl)anthracene (BPEA). A synchrotron radiation linear dichroism investigation

    NASA Astrophysics Data System (ADS)

    Thulstrup, Peter W.; Jones, Nykola C.; Hoffmann, Søren V.; Spanget-Larsen, Jens

    2013-02-01

    The electronic transitions of 9,10-bis(phenylethynyl)anthracene (BPEA) were investigated by synchrotron radiation linear dichroism (SRLD) spectroscopy in the range 20 000-58 000 cm-1 (500-170 nm) on molecular samples aligned in stretched polyethylene. The investigation was supported by variable temperature spectroscopy and by quantum chemical calculations in the LCOAO and TD-DFT models. The combined experimental and theoretical evidence leads to characterization of several previously unobserved transitions and provides a revised polarization analysis of the visible absorption band of BPEA.

  14. Magnetic x-ray linear dichroism of ultrathin Fe-Ni alloy films

    SciTech Connect

    Schumann, F.O.; Willis, R.F.; Goodman, K.W.

    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.

  15. Subpicosecond UV spectroscopy of carbonmonoxy-myoglobin: absorption and circular dichroism studies.

    PubMed

    Dartigalongue, Thibault; Niezborala, Claire; Hache, François

    2007-04-07

    A thorough absorption and circular dichroism study is performed in carbonmonoxy-myoglobin with a sub-picosecond visible pump, ultraviolet probe experiment. Differential absorption in the 220-360 nm range shows that the time-resolved response mainly comes from the heme and that aromatic amino acids do not contribute significantly. Time-resolved CD at 260 nm shows no dynamics and confirms this result. On the contrary, a strong CD dynamics is observed at 230 nm. This signal could originate from transient deformation of the alpha-helices in the protein.

  16. Magnetic x-ray linear dichroism in resonant and non-resonant Gd 4f photoemission

    SciTech Connect

    Mishra, S.; Gammon, W.J.; Pappas, D.P.

    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.

  17. Kondo screening and beyond: An x-ray absorption and dichroism study of CePt5/Pt(111 )

    NASA Astrophysics Data System (ADS)

    Praetorius, C.; Fauth, K.

    2017-03-01

    We use x-ray absorption spectroscopy as well as its linear and circular magnetic dichroisms to characterize relevant interactions and energy scales in the surface intermetallic CePt5/Pt(111 ). The experiments provide insight into crystal field splitting, effective paramagnetic moments, their Kondo screening and mutual interactions, and thus into many aspects which typically determine the low-temperature behavior of correlated rare-earth compounds. Exploiting the tunability of Ce valence through the thickness-dependent epitaxial strain at the CePt5/Pt(111 ) interface, we are able to systematically investigate the impact of hybridization strength on these interactions. Considerable Kondo screening is indeed observed at all CePt5 thicknesses, and found to be strongest in case of strongest hybridization. While the magnetic response is commensurate with an impurity Kondo scale of TK≳102 K for specimen temperatures T ≳30 K, this is no longer the case at lower temperature. Its detailed study by x-ray circular magnetic dichroism (XMCD) at one specific thickness of CePt5 reveals an anomaly of the susceptibility at T*≈25 K instead, which we tentatively associate with the onset of lattice coherence. At lowest temperature we observe paramagnetic saturation with a small Ce 4 f saturation magnetization. Within the framework of itinerant 4 f electrons, saturation is due to a field-induced Lifshitz transition involving a very heavy band with correspondingly small degeneracy temperature of TF≈7 K. This small energy scale results in the persistence of Curie-Weiss behavior across the entire range of experimentally accessible temperatures (T ≳2 K). Our work highlights the potential of magnetic circular dichroism studies in particular for Kondo and heavy-fermion materials, which so far has remained largely unexplored.

  18. Computational study of the one- and two-photon absorption and circular dichroism of (L)-tryptophan.

    PubMed

    Guillaume, Maxime; Ruud, Kenneth; Rizzo, Antonio; Monti, Susanna; Lin, Zijing; Xu, Xuee

    2010-05-20

    A density functional theory (DFT) study of the one- and two-photon absorption and circular dichroism spectra of (l)-tryptophan in water is presented. The effects on the simulated spectra of conformational averaging, of solvent as described by the polarizable continuum model (PCM), and of the choice of exchange-correlation (XC) functional are analyzed. Conformational Maxwell-Boltzmann (MB) averaging is carried out at room temperature in the gas phase using the ten lowest-energy conformers in the gas phase, whereas in the solvent, the nine lowest zwitterionic conformers are determined in combination with a PCM continuum model and employed in the calculations. One- and two-photon absorption and circular dichroism spectra are calculated using time-dependent DFT with both the B3LYP and CAM-B3LYP XC functionals, including the 15 lowest excited electronic states in each case. The spectra are shown to be strongly influenced by all parameters of our computational models. Changing the XC functional yields large changes not only in the excitation energies but also in the transition dipole moments and the rotational strengths of each excited state. The inclusion of the effect of water solvation also yields different response properties for each excited state, as well as different ground-state equilibrium geometries for the gas and solvated phases. MB weights change significantly from the gas to the solvated phase, making the effect of conformational averaging strongly phase dependent. The study of all these effects highlights the importance of an accurate and reliable treatment of both ground and excited states when aiming at predicting experimental one- or two-photon spectra. However, the comparison between the MB weighted spectra and experiment for the linear spectroscopies turns out to be rather satisfactory, showing that our approach can yield at least information on the major features of the spectra.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    SciTech Connect

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

    2006-08-11

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

  1. Studying metal ion-protein interactions: electronic absorption, circular dichroism, and electron paramagnetic resonance.

    PubMed

    Quintanar, Liliana; Rivillas-Acevedo, Lina

    2013-01-01

    Metal ions play a wide range of important functional roles in biology, and they often serve as cofactors in enzymes. Some of the metal ions that are essential for life are strongly associated with proteins, forming obligate metalloproteins, while others may bind to proteins with relatively low affinity. The spectroscopic tools presented in this chapter are suitable to study metal ion-protein interactions. Metal sites in proteins are usually low symmetry centers that differentially absorb left and right circularly polarized light. The combination of electronic absorption and circular dichroism (CD) in the UV-visible region allows the characterization of electronic transitions associated with the metal-protein complex, yielding information on the geometry and nature of the metal-ligand interactions. For paramagnetic metal centers in proteins, electron paramagnetic resonance (EPR) is a powerful tool that provides information on the chemical environment around the unpaired electron(s), as it relates to the electronic structure and geometry of the metal-protein complex. EPR can also probe interactions between the electron spin and nuclear spins in the vicinity, yielding valuable information on some metal-ligand interactions. This chapter describes each spectroscopic technique and it provides the necessary information to design and implement the study of metal ion-protein interactions by electronic absorption, CD, and EPR.

  2. In situ azimuthal rotation device for linear dichroism measurements in scanning transmission x-ray microscopy

    NASA Astrophysics Data System (ADS)

    Hernández-Cruz, D.; Hitchcock, A. P.; Tyliszczak, T.; Rousseau, M.-E.; Pézolet, M.

    2007-03-01

    A novel miniature rotation device used in conjunction with a scanning transmission x-ray microscope is described. It provides convenient in situ sample rotation to enable measurements of linear dichroism at high spatial resolution. The design, fabrication, and mechanical characterization are presented. This device has been used to generate quantitative maps of the spatial distribution of the orientation of proteins in several different spider and silkworm silks. Specifically, quantitative maps of the dichroic signal at the C 1s→π*amide transition in longitudinal sections of the silk fibers give information about the spatial orientation, degree of alignment, and spatial distribution of protein peptide bonds. A new approach for analyzing the dichroic signal to extract orientation distributions, in addition to magnitudes of aligned components, is presented and illustrated with results from Nephila clavipes dragline spider silk measured using the in situ rotation device.

  3. Probing the structure of long DNA molecules in solution using synchrotron radiation linear dichroism.

    PubMed

    Rittman, Martyn; Hoffmann, Søren V; Gilroy, Emma; Hicks, Matthew R; Finkenstadt, Bärbel; Rodger, Alison

    2012-01-07

    Linear dichroism (LD), a spectroscopic method for aligned samples, has been used with a synchrotron radiation source to reveal insights into the structure and stability of DNA with increasing salt concentrations (thus stabilizing the base pairing) and increasing temperature while remaining below the melting point (thus destabilizing the base pairing). Measurements have been made from 350 nm to 182 nm, and the spectral changes observed quantified using a Bayesian Markov chain Monte Carlo (MCMC) algorithm, which uses statistical methods to fit to experimental data. Based on literature H-D exchange experiments, we surmise that the cause of the spectral variations is the induction of transient single stranding of tracts in the DNA polymer, particularly those with significant content of the weaker AT base pairs. More detailed analysis of the LD data will require better nucleotide transition polarization assignments.

  4. Linear dichroism amplification: Adapting a long-known technique for ultrasensitive femtosecond IR spectroscopy

    SciTech Connect

    Rehault, Julien; Helbing, Jan; Zanirato, Vinicio; Olivucci, Massimo

    2011-03-28

    We demonstrate strong amplification of polarization-sensitive transient IR signals using a pseudo-null crossed polarizer technique first proposed by Keston and Lospalluto [Fed. Proc. 10, 207 (1951)] and applied for nanosecond flash photolysis in the visible by Che et al. [Chem. Phys. Lett. 224, 145 (1994)]. We adapted the technique to ultrafast pulsed laser spectroscopy in the infrared using photoelastic modulators, which allow us to measure amplified linear dichroism at kilohertz repetition rates. The method was applied to a photoswitch of the N-alkylated Schiff base family in order to demonstrate its potential of strongly enhancing sensitivity and signal to noise in ultrafast transient IR experiments, to simplify spectra and to determine intramolecular transition dipole orientations.

  5. Experimental study of linear magnetic dichroism in photoionization satellite transitions of atomic rubidium

    SciTech Connect

    Jaenkaelae, K.; Alagia, M.; Feyer, V.; Richter, R.; Prince, K. C.

    2011-11-15

    Laser orientation in the initial state has been used to study the properties of satellite transitions in inner-shell photoionization of rubidium atoms. The linear magnetic dichroism in the angular distribution (LMDAD) has been utilized to probe the continuum waves of orbital angular momentum conserving monopole, and angular momentum changing conjugate satellites, accompanying the 4p ionization of atomic Rb. We show experimentally that LMDAD of both types of satellite transitions is nonzero and that LMDAD of monopole satellites, measured as a function of photon energy, mimics the LMDAD of direct photoionization, whereas the LMDAD of conjugate transitions deviates drastically from that trend. The results indicate that conjugate transitions cannot be described theoretically without explicit inclusion of electron-electron interaction. The present data can thus be used as a very precise test of current models for photoionization.

  6. Absorption dichroism of monolayer 1T‧-MoTe2 in visible range

    NASA Astrophysics Data System (ADS)

    Han, Gang Hee; Keum, Dong Hoon; Zhao, Jiong; Shin, Bong Gyu; Song, Seunghyun; Bae, Jung Jun; Lee, Jubok; Kim, Jung Ho; Kim, Hyun; Moon, Byoung Hee; Lee, Young Hee

    2016-09-01

    Among various transition metal dichalcogenides, MoTe2 has drawn attention due to its capability of robust phase engineering between semiconducting (2H) and semi-metallic distorted octahedral (1T‧) phase. In particular, 1T‧-MoTe2 has been predicted to have intriguing physics such as quantum spin Hall insulator, large magnetoresistance, and superconductivity. Recent progress showed weak antilocalization behavior in 1T‧-MoTe2 which is the one of representative characteristics in topological insulator. Here, we grow centimeter-scale monolayer 1T‧-MoTe2 on SiO2/Si substrate via chemical vapordeposition and demonstrate dichroism in visible range. Ribbon-like 1T‧-MoTe2 flakes were initially nucleated randomly on SiO2 substrate and at a later stage merged to form a continuous monolayer film over the entire substrate. Each flake revealed one dimensional Mo-Mo dimerization feature and anisotropic absorption behavior in visible range (400-600 nm). This allowed us to detect the grain boundary due to stark contrast difference among flakes in different orientations.

  7. Linear Dichroism of Cyanine Dyes in Stretched Polyvinyl Alcohol Films: A Physical Chemistry Laboratory Experiment.

    ERIC Educational Resources Information Center

    Natarajan, L. V.; And Others

    1983-01-01

    Provides background information, procedures, and results of an undergraduate physical chemistry experiment on the polarization of absorption spectra of cyanine dyes in stretched polyvinyl alcohol films. The experiment gives a simple demonstration of the concept of linear dichromism and the validity of the TEM method used in the analyses. (JN)

  8. Combined SERS and flow linear dichroism approach to monitoring the interaction of pharmaceuticals with their target

    NASA Astrophysics Data System (ADS)

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

    1999-04-01

    Surface-Enhanced Raman Scattering (SERS) spectroscopy and Flow Linear Dichroism (FLD) technique have been employed to study the anticancer agent fagaronine and its derivative ethoxidine - double inhibitors of DNA topoisomerases I and II. Cooperative use of two methods permitted (i) to determine the molecular determinants of the drug-DNA interactions; (ii) to monitor in real time the process of topo I inhibition by these anticancer agents. FLD technique allowed us to identify the mode of drug interactions with the DNA as a 'major groove intercalation' and to determine orientation of the drugs chromophores within the complexes. Using SERS spectroscopy we have determined the drugs molecular determinants interacting with the DNA. FLD was also used for real time monitoring of the process of sc DNA relaxation by topo I and of inhibition of relaxation with the pharmaceuticals. Ethoxidine was found to exhibit the same activity of inhibition of sc DNA relaxation as fagaronine at the 10-fold less concentration. The proposed SERS-FLD combined approach demonstrates the new perspectives for screening new pharmaceuticals due to its relative simplicity and low expense, high sensitivity and selectivity, and, finally, possibility of real-time monitoring of the structure-function correlation within the series of drug derivatives.

  9. Theory of Kerr and Faraday rotations and linear dichroism in Topological Weyl Semimetals.

    PubMed

    Kargarian, Mehdi; Randeria, Mohit; Trivedi, Nandini

    2015-08-03

    We consider the electromagnetic response of a topological Weyl semimetal (TWS) with a pair of Weyl nodes in the bulk and corresponding Fermi arcs in the surface Brillouin zone. We compute the frequency-dependent complex conductivities σαβ(ω) and also take into account the modification of Maxwell equations by the topological θ-term to obtain the Kerr and Faraday rotations in a variety of geometries. For TWS films thinner than the wavelength, the Kerr and Faraday rotations, determined by the separation between Weyl nodes, are significantly larger than in topological insulators. In thicker films, the Kerr and Faraday angles can be enhanced by choice of film thickness and substrate refractive index. We show that, for radiation incident on a surface with Fermi arcs, there is no Kerr or Faraday rotation but the electric field develops a longitudinal component inside the TWS, and there is linear dichroism signal. Our results have implications for probing the TWS phase in various experimental systems.

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

    NASA Astrophysics Data System (ADS)

    Rakheja, Shaloo; Sengupta, Parijat

    2016-03-01

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

  11. Oxidized polyethylene films for orienting polar molecules for linear dichroism spectroscopy.

    PubMed

    Razmkhah, Kasra; Chmel, Nikola Paul; Gibson, Matthew I; Rodger, Alison

    2014-03-21

    Stretched polyethylene (PE) films have been used to orient small molecules for decades by depositing solutions on their surface and allowing the solvent to evaporate leaving the analyte absorbed on the polymer film. However, the non-polar hydrophobic nature of PE is an obstacle to aligning polar molecules and biological samples. In this work PE film was treated with oxygen plasma in order to increase surface hydrophilicity. Different treatment conditions were evaluated using contact angle measurement and X-ray photoelectron spectroscopy. Treated PE (PE(OX)) films are shown to be able to align molecules of different polarities including progesterone, 1-pyrenecarboxaldehyde, 4',6-diamidino-2-phenylindole (DAPI) and anthracene. The degree of alignment of each molecule was studied by running series of linear dichroism (LD) experiments and the polarizations of electronic transition moments were determined. For the first time optimal conditions (such as stretching factor and concentration of the sample) for stretched film LD were determined. PE(OX) aligning ability was compared to that of normal PE films. Progesterone showed a slightly better alignment on PE(OX) than PE. 1-Pyrenecarboxaldehyde oriented differently on the two different films which enabled transition moment assignment for this low symmetry molecule. DAPI (which does not align on PE) aligned well on PE(OX) and enabled us to obtain better LD data than had previously been collected with polyvinyl alcohol. Anthracene alignment and formation of dimers and higher order structures were studied in much more detail than previously possible, showing a variety of assemblies on PE and PE(OX) films.

  12. The use of linear dichroism in forensic fibre examinations--part 6. Validation and practical aspects of MSP-PPL.

    PubMed

    De Wael, K; Lepot, L; Lunstroot, K

    2012-12-01

    This paper summarizes the results of previous work on the microscopic observation of linear dichroism found in dyed fibres (polyesters, polyamides, wool, silk, cotton, viscose, acrylics and acetates) and in pigmented fibres as well as the measurements on these fibre classes using microspectrophotometry with plane polarized light (MSP-PPL). The validation of this method is discussed and a practical tool is proposed for comparing fibre traces with control fibres. The limitations and strengths of this method are also revised.

  13. Flexible bent rod model with a saturating induced dipole moment to study the electric linear dichroism of DNA fragments

    NASA Astrophysics Data System (ADS)

    Bertolotto, Jorge A.; Umazano, Juan P.

    2016-06-01

    In the present work we make a theoretical study of the steady state electric linear dichroism of DNA fragments in aqueous solution. The here developed theoretical approach considers a flexible bent rod model with a saturating induced dipole moment. The electric polarizability tensor of bent DNA fragments is calculated considering a phenomenological model which theoretical and experimental backgroung is presented here. The model has into account the electric polarizability longitudinal and transversal to the macroion. Molecular flexibility is described using an elastic potential. We consider DNA fragments originally bent with bending fluctuations around an average bending angle. The induced dipole moment is supposed constant once the electric field strength grows up at critical value. To calculate the reduced electric linear dichroism we determine the optical factor considering the basis of the bent DNA perpendicular to the molecular axis. The orientational distribution function has into account the anisotropic electric properties and the molecule flexibility. We applied the present theoretical background to fit electric dichroism experimental data of DNA fragments reported in the bibliography in a wide range of molecular weight and electric field. From these fits, values of DNA physical properties are estimated. We compare and discuss the results here obtained with the theoretical and experimental data presented by other authors. The original contributions of this work are: the inclusion of the transversal electric polarizability saturating with the electric field, the description of the electric properties with an electric polarizability tensor dependant on the bending angle and the use of an arc model originally bent.

  14. Mn L3,2 X-ray absorption and magnetic circular dichroism inferromagnetic Ga1-xMnxP

    SciTech Connect

    Stone, P.R.; Scarpulla, M.A.; Farshchi, R.; Sharp, I.D.; Haller,E.E.; Dubon, O.D.; Yu, K.M.; Beeman, J.W.; Arenholz, E.; Denlinger, J.D.; Ohldag, H.

    2006-03-25

    We have measured the X-ray absorption and X-ray magnetic circular dichroism (XMCD) at the Mn L{sub 3,2} edges in ferromagnetic Ga{sub 1-x}Mn{sub x}P for 0.018 {le} x {le} 0.042. Large XMCD asymmetries at the L{sub 3} edge indicate significant spin-polarization of the density of states at the Fermi energy. The temperature dependence of the XMCD and moment per Mn of 2.67 {+-} 0.45 {mu}{sub B} calculated using sum rules are consistent with magnetometry values. The spectral shapes of the X-ray absorption and XMCD are nearly identical with those for Ga{sub 1-x}Mn{sub x}As indicating that the hybridization of Mn d and anion p states is similar in the two materials.

  15. Excited-state absorption and circular dichroism of ruthenium(II) tris(phenanthroline) in the ultraviolet region.

    PubMed

    Niezborala, Claire; Hache, François

    2007-08-16

    Excitation of ruthenium(II) tris(phenanthroline) in the visible region results in the tranfer of an electron from the central atom toward one of the ligands. To probe this excited state, we have performed pump-induced absorption and circular dichroism in the ultraviolet wavelengths, in the intraligand pi-pi* transition region. On top of the bleaching of the ground state transitions, new structures appear in the absorption and CD spectra. Thanks to a classical calculation based on the polarizability theory, we can interpret these features as the result of a strong reduction of the excitonic coupling due to a blue shift of the pi-pi* transition in the reduced ligand accompanied by the onset of new excited-state transitions.

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

    SciTech Connect

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

    2015-12-14

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

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

    SciTech Connect

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

    2010-01-11

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

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

    SciTech Connect

    Apitz, D.; Bertram, R.P.; Benter, N.; Buse, K.; Hieringer, W.; Andreasen, J.W.; Nielsen, M.M.; Johansen, P.M.

    2005-09-01

    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 calculated and displayed for several poling temperatures and chromophore concentrations. The influence of dipole-dipole interaction on the overall polymer dynamics is discussed. The first order parameter, and therefore the Pockels effect, peaks for a poling temperature of around 10 deg. C above the glass transition. The decrease of the Pockels effect above this temperature region is triggered by a head-to-tail chromophore orientation, i.e., a transition to a microcrystalline phase, increasing the second order parameter. Comparison of the experimentally observed absorption spectra and those obtained by 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.

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

    SciTech Connect

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

    2015-01-14

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  1. Infrared linear dichroism as a tool to monitor antitumor drug-induced changes of the conformational flexibility of biopolymers

    NASA Astrophysics Data System (ADS)

    Fritzsche, H.

    1990-03-01

    Conformational changes of biopolymers are often a prerequisite for their biological functioning. Drugs are able to induce restrictions of the conformational flexibility of their biopolymer targets. We studied oriented films of DNA complexed with drugs of potential antitumor activity. The infrared linear dichroism reflects quantitatively the extent of restriction, in this case the repression of the conformational transition of DNA from the B to the A form which is driven by the water activity. The investigated drugs show very different capabilities to restrict the B-A transition of DNA. Strong effects have been found with several nonintercalating as well as intercalating antitumor antibiotics which "freeze" 10-24 DNA base pairs per drug molecule which is up to 2.5 turns of the double helix. The results contribute to a rationale drug design as well as to a better understanding of their antitumor action on the molecular level.

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

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

    Tetragonally distorted Mn3-xGax thin films with 0.1absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD). A highly textured L10 crystal structure of the Mn-Ga films was verified by X-ray diffraction measurements. For samples with e-beam evaporated MgO barrier no evidence for Mn-O was found whereas in samples with magnetron sputtered MgO, Mn-O was detected, even for the thickest interlayer thickness. Both XAS and XMCD measurements showed an increasing interfacial Mn-O amount with decreasing CoFeB interlayer thickness. Additional element specific full hysteresis loops determined an out-of-plane magnetization axis for the Mn and Co, respectively.

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

    SciTech Connect

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

    2013-11-14

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

  4. The association of defensin HNP-2 with negatively charged membranes: A combined fluorescence and linear dichroism study.

    PubMed

    Pridmore, Catherine J; Rodger, Alison; Sanderson, John M

    2016-04-01

    The association of defensin HNP-2 with negatively charged membranes has been studied using a new approach that combines fluorescence and linear dichroism (LD) spectroscopies with simulated LD spectra in order to characterise the binding kinetics and bound configurations of the peptide. Binding to membranes composed of mixtures of diacylglycerophosphocholines (PC) with either diacylglycerophosphoglycerol (PG) or diacylglycerophosphoserine (PS) was conducted at lipid:peptide ratios that yielded binding, but not membrane fusion. HNP-2 association with membranes under these conditions was a 2 stage-process, with both stages exhibiting first order kinetics. The fast initial step, with a half-life of < 1 min, was followed by a slower step with a half-life of > 3 min. Conversion between the states was estimated to have an enthalpy of activation of approximately 10 kJ mol(-1) and an entropy of activation of -0.2 kJ K mol(-1). LD spectra corresponding to each of the membrane bound states were generated by non-linear regression using a standard kinetic model. These spectra are interpreted in comparison with spectra calculated using the program Dichrocalc and reveal that the peptide associates with membranes in a small number of stable configurations. All of these configurations have a significant proportion of β-sheet structure residing in the plane of the membrane. Two configurations support structures previously proposed for defensins in membranes.

  5. Z-form DNA specific binding geometry of Zn(II) meso-tetrakis(N-methylpyridinium-4-yl)porphyrin probed by linear dichroism spectroscopy.

    PubMed

    Gong, Lindan; Jang, Yoon Jung; Kim, Jinheung; Kim, Seog K

    2012-08-16

    Zn(II) meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (ZnTMPyP) produced a unique linear dichroism (LD) spectrum when forming a complex with Z-form poly[d(G-C)(2)]. The spectrum was characterized by a large positive wavelength-dependent LD signal in the Soret absorption region. The magnitudes of LD in both the DNA and Soret band increased as the [porphyrin]/[DNA base] ratio increased and were larger by 20-40 times compared to the negative LD of the ZnTMPyP bound to B-form poly[d(G-C)(2)] and poly[d(A-T)(2)]. The angles calculated from LD were respectively 49° and 42° for B(x) and B(y) transitions of the porphyrin with respect to the local helix axis of Z-form poly[d(G-C)(2)]. The appearance of the unique LD spectrum for the Z-form poly[d(G-C)(2)] complex was accompanied by a bisignate circular dichroism spectrum in the Soret region, whose magnitude was proportional to the square of the porphyrin concentration, suggesting a stacking interaction between Z-form poly[d(G-C)(2)]-bound ZnTMPyP with other bound ZnTMPyP. From these observations, a conceivable binding mode of ZnTMPyP to Z-form poly[d(G-C)(2)] complex was proposed, in which ZnTMPyP binds at the major groove or across the groove. In contrast with Z-form poly[d(G-C)(2)], ZnTMPyP binds to poly[d(A-T)(2)] in a monomeric manner with the angles of 57° and 59° for the two porphyrin's transition moments with respect to the local polynucleotide helix axis. The polarized spectral properties of ZnTMPyP bound to B-form poly[d(G-C)(2)] coincide with the intercalated nonmetallic TMPyP, namely, a negative CD signal in the Soret band and a negative wavelength-dependent reduced LD signal, with a magnitude larger than that in the DNA absorption region in spite of its axial ligands.

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

    PubMed

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

    2013-09-01

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

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

    PubMed

    Lundahl, P Johan; Kitts, Catherine C; Nordén, Bengt

    2011-08-21

    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.

  8. Theory and experiment of linear and nonlinear optical media and waveguides with anisotropy and dichroism

    NASA Astrophysics Data System (ADS)

    Purvinis, Georgeanne M.

    Organic crystals and certain polymer films, such as ionically self-assembled monolayer (ISAM) films, are lossy and anisotropic. These materials may have a large chi(2) nonlinear response, and thus are conceivably capable of efficient second order processes. Anomalous dispersion phase-matched second harmonic generation (ADPM-SHG) in organic media is a second order wavelength conversion process that phase matches like-order modes in a waveguide (ex: TM0o → TM02o ), thus maximizing the overlap integral. Demonstration of ADPM-SHG in economical and easily fabricated polymer ISAM film is the ultimate experimental goal of this research. In order to achieve demonstration of ADPM-SHG in an ISAM film, both theoretical and material research contributions are accomplished. The predominant analysis approaches in literature are based on the finite element method, which is approximate and computationally intensive, thus prohibiting arbitrary crystallographic media orientations in devices. This restricted treatment in the literature may be insufficient with ISAM films, as SHG occurs in a spectral region of residual absorption, the film is uniaxial, and the optic axis may not be aligned the waveguide coordinate system. Thus, the theory objectives of the dissertation research are: (1) develop an exact solution for finding the polarization states in lossy anisotropic media using a new complex orthogonal similarity transformation with the complex symmetric impermeability tensor, (2) develop a rigorous transverse resonance analysis to find the eigenmodes of general lossy anisotropic planar waveguides with arbitrary principal axes orientations, and (3) integrate the results of steps 1--2 to determine the conversion efficiency of an ISAM planar waveguide using ADPM-SHG, thus illustrating the importance of the dissertation research by highlighting the errors resulting in algorithms published in other works. Experimentally, the dissertation focuses on designing anionic and cationic

  9. An analysis of the x-ray linear dichroism spectrum for NiO thin films grown on vicinal Ag(001)

    SciTech Connect

    Wu, Y.Z.; Zhao, Y.; Arenholz, E.; Young, A.T.; Sinkovic, B.; Qiu, Z.Q.

    2008-05-10

    Antiferromagnetic (AFM) NiO thin films are grown epitaxially on vicinal Ag(118) substrate and investigated by x-ray linear dichroism (XLD). We find that the NiO AFM spin exhibits an in-plane spin reorientation transition from parallel to perpendicular to the step edges with increasing the NiO film thickness. In addition to the conventional L{sub 2} adsorption edge, x-ray linear dichroism (XLD) effect at the Ni L{sub 3} adsorption edge is also measured and analyzed. The result identifies a small energy shift of the L{sub 3} peak. Temperature-dependent measurement confirms that the observed XLD effect in this system at the normal incidence of the x-rays originates entirely from the NiO magnetic ordering.

  10. Electronic ground states of Fe2(+) and Co2(+) as determined by x-ray absorption and x-ray magnetic circular dichroism spectroscopy.

    PubMed

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

    2015-12-28

    The (6)Π electronic ground state of the Co2 (+) 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)Φ, (8)Φ, and (8)Γ, for the electronic ground state of Fe2 (+) have been identified. These states carry sizable 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 transition elements cannot generally be assumed to be connected by a one-electron process.

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

    SciTech Connect

    Tobin, J.G.; Goodman, K.W.; Schumann, F.O.

    1997-04-01

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

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

    PubMed

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

    2015-08-06

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

  13. Interaction between adenovirus DNA-binding protein and single-stranded polynucleotides studied by circular dichroism and ultraviolet absorption.

    PubMed

    van Amerongen, H; van Grondelle, R; van der Vliet, P C

    1987-07-28

    The adenovirus DNA-binding protein (AdDBP) is a multifunctional protein required for viral DNA replication and control of transcription. We have studied the binding of AdDBP to single-stranded M13 DNA and to the homopolynucleotides poly(rA), poly(dA), and poly(dT) by means of circular dichroism (CD) and optical density (OD) measurements. The binding to all these polynucleotides was strong and nearly stoichiometric. Titration experiments showed that the size of the binding site is 9-11 nucleotides long for M13 DNA, poly(dA), and poly(rA). A higher value (15.0 +/- 0.8) was found for poly(dT). Pronounced changes in the circular dichroism and optical density spectra were observed upon binding of AdDBP. In general, both the positive peak around 260-270 nm and the negative peak around 240-250 nm in the CD spectra decreased in intensity, and a shift of the crossover point to longer wavelengths was found. The OD spectra observed upon binding of AdDBP are remarkably similar to those obtained with prokaryotic helix-destabilizing proteins like bacteriophage T4 gene 32 protein and fd gene 5 protein. The data can best be interpreted by assuming that the AdDBP-polynucleotide complex has a regular, rigid, and extended configuration that satifies two criteria: (1) a considerable tilt of the bases in combination with (2) a small rotation per base and/or a shift of the bases closer to the helix axis.

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

    SciTech Connect

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

    1994-12-01

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

  15. Rhenocene: Magnetic circular dichroism and laser-induced fluorescence in nitrogen matrices

    NASA Astrophysics Data System (ADS)

    Cox, P. Anthony; Grebenik, Peter; Perutz, Robin N.; Graham, Robin G.; Grinter, Roger

    1984-07-01

    Rhenocene generated in nitrogen matrices by photolysis of Re(η-C 5H 5) 2H, shows an intense, structured progression in magnetic circular dichroism. The non-linear magnetic field and temperature dependence of the dichroism indicate a 2E 2g(= 5/2) ground state. Lazer-induced fluorescence is used to establish the (0.0) component of the absorption band and to derive the energies of three totally symmetric vibrational fundamentals.

  16. Orientation-dependent x-ray Raman scattering from cubic crystals: Natural linear dichroism in MnO and CeO2

    NASA Astrophysics Data System (ADS)

    Gordon, R. A.; Haverkort, M. W.; Gupta, Subhra Sen; Sawatzky, G. A.

    2009-11-01

    Information on valence orbitals and electronic interactions in single crystal systems can be obtained through orientation-dependent x-ray measurements, but this can be problematic for a cubic system. Polarisation-dependent x-ray absorption measurements are common, but are dominated by dipole transitions which, for a cubic system, are isotropic even though a cubic system is not. Many edges, particularly for transition metals, do have electric quadrupole features that could lead to dichroism but proximity to the dipole transition can make interpretation challenging. X-ray Raman Spectroscopy (XRS) can also be used to perform orientation-dependent near-edge measurements - not only dependent on the direction of the momentum transfer but also its magnitude, q. Previous XRS measurements on polycrystalline materials revealed that multipole (higher order than dipole) transitions are readily observable in the pre-threshold region of rare earth N4,5 edges, actually replacing the dipole at high-q. We have extended these studies to examine orientation-dependent XRS for CeO2 and MnO single crystals, as prototype systems for theoretical treatment. Dichroism is observed at both the Ce N4,5 and Mn M2,3 edges in these cubic materials.

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

    SciTech Connect

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

    1997-04-01

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

  18. Investigation of the optical-absorption bands of Nb4+ and Ti3+ in lithium niobate using magnetic circular dichroism and optically detected magnetic-resonance techniques

    NASA Astrophysics Data System (ADS)

    Reyher, H.-J.; Schulz, R.; Thiemann, O.

    1994-08-01

    The magnetic circular dichroism (MCD) of the absorption of Nb4+Li and Ti3+Li centers in LiNbO3 has been selectively measured by applying optically detected magnetic resonance. The attribution of a well-known broad and unstructured absorption band peaking at 1.6 eV to the Nb4+Li bound small polaron is now unambiguously confirmed. In the MCD spectrum of the isoelectronic Ti3+Li center, bands show up, which closely resemble the MCD bands at 1.6 eV of this bound small polaron. This striking similarity is explained by a cluster model, representing both defects. Either TiLi or NbLi is at the center of this cluster. In both cases, the small polaron is bound to the cluster, and its MCD bands correspond to intervalence transfer transitions within the constituents of the cluster. A study of the spin-orbit coupling of the molecular orbitals of the cluster allows one to analyze the structure of the MCD bands at 2.9 eV of Ti3+Li have no counterpart in the Nb4+Li spectrum. These bands are assigned to transitions to excited states, which are specific to the impurity and are related to the 10Dq transitions known for the crystal field states of a d1 ion.

  19. X-ray natural linear dichroism of graphitic materials across the carbon K-edge: Correction for perturbing high-order harmonics

    NASA Astrophysics Data System (ADS)

    Jansing, C.; Mertins, H. C.; Gaupp, A.; Sokolov, A.; Gilbert, M. C.; Wahab, H.; Timmers, H.

    2016-05-01

    Reflectivity measurements on graphitic materials such as graphene at energies across the carbon K-edge are frustrated by significant intensity loss due to adventitious carbon on beamline mirrors. Such intensity reduction enhances effects due to perturbing high-order harmonics in the beam. These effects distort the actual structure of the reflectance curve. In order to overcome this limitation, a correction technique has been developed and demonstrated first with measurements for highly ordered pyrolytic graphite. The same approach may be applied to other graphitic materials such as graphene and it may be used with other synchrotron beamlines. The fraction of high-order harmonics was determined by passing the incident beam through a 87 nm thin silicon nitride absorber that can be well modeled. Using the corrected measurements the x-ray natural linear dichroism of the sample has been determined.

  20. Local electronic states of Fe4N films revealed by x-ray absorption spectroscopy and x-ray magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    We performed x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements at Fe L2,3 and N K-edges for Fe4N epitaxial films grown by molecular beam epitaxy. In order to clarify the element specific local electronic structure of Fe4N, 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 L2,3-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 Fe4N.

  1. Theoretical calculations of infrared absorption, vibrational circular dichroism, and two-dimensional vibrational spectra of acetylproline in liquids water and chloroform.

    PubMed

    Hahn, Seungsoo; Lee, Hochan; Cho, Minhaeng

    2004-07-22

    Infrared absorption, vibrational circular dichroism, and two-dimensional infrared pump-probe and photon echo spectra of acetylproline solutions are theoretically calculated and directly compared with experiments. In order to quantitatively determine interpeptide interaction-induced amide I mode frequency shifts, high-level quantum chemistry calculations were performed. The solvatochromic amide I mode frequency shift and fluctuation were taken into account by carrying out molecular dynamics simulations of acetylproline dissolved in liquids water and chloroform and by using the extrapolation method developed recently. We first studied correlation time scales of the two amide I vibrational frequency fluctuations, cross correlation between the two fluctuating local mode frequencies, ensemble averaged conformations of the acetylproline molecule in liquids water and chloroform. The corresponding conformations of the acetylproline in liquids water and chloroform are close to the ideal 3(10) helix and the C(7) structure, respectively. A few methods proposed to determine the angle between the two transition dipoles associated with the amide I vibrations were tested and their limitations are discussed.

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

    SciTech Connect

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

    2015-05-21

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

  3. Comparative Study of Optical Absorption and Circular Dichroism of Bacteriochlorophyll Oligomers in Triton X-100, the Antenna Pigment B850, and the Primary Donor p-860 of Photosynthetic Bacteria Indicates that All are Similar Dimers of Bacteriochlorophyll a

    NASA Astrophysics Data System (ADS)

    Scherz, A.; Rosenbach-Belkin, V.

    1989-03-01

    Dimers of bacteriochlorophyll a (Bchla) with optical absorption maximum at 853 nm and a nonconservative circular dichroism spectrum are formed in a solution of formamide/water that contains micelles of Triton X-100. The apparent equilibrium constant and the corresponding Gibbs energy change for the Bchl self-organization are 4.9 × 106 M-1 and -9.2 kcal/mol, respectively. The experimental absorption and circular dichroism spectra of the in vitro Bchl dimer (termed Bchl-853) are similar to the spectra of the bacterial light-harvesting complex B850 and the primary electron donor P-860 and probably point to a common structural motif. Indeed, simulation of the dimers' spectra (optical absorption and circular dichroism), achieved by using an extended version of the exciton theory, suggests the same geometry as recently elucidated for P-860 by x-ray diffraction crystallography. The proposed geometry is predicted to have the minimum energy in the gas phase. In conclusion, the spectral properties of the bathochromically shifted forms of Bchla are likely a result of strong dipolar interactions in self-organized structures of Bchls.

  4. Impact of energy-related pollutants on chromosome structure. Progress report, January 1-December 31, 1980. IQUID COLUMN CHROMATOGRAPHY; ABSORPTION SPECTRA; COMPUTER CODES; DICHROISM; EQUIPMENT INTERFACES; MICROPROCESSORS; SPECTROPHOTOMETERS; ; CARBON 13; COMPLEXES; NUCLEAR MAGNETIC RESONANCE

    SciTech Connect

    Not Available

    1980-01-01

    Methods for rapidly analyzing methylated and ethylated nucleosides and bases by high pressure liquid chromatography were investigated. Deoxyribonucleotides were alkylated with alkyl iodides and dialkyl sulfates. Several unreported products of the reactions of methyl and ethyl iodide in dimethylsulfoxide were found and are being characterized. The Cary 219 UV-Vis spectrophotometer was interfaced to a microcomputer and several utility programs were written. Preliminary absorption and circular dichroism studies of the binding of ethidium to DNA and nucleosome cores showed binding to cores to be quite different from binding to DNA. Free radical and additional reactions of bisulfite with DNA in chromatin were examined. Free radical attack was minimal. Some conversion of cytosine to uracil was noted, but protein crosslinking to DNA was not detected. The first valid natural abundance /sup 13/C nmr spectra of double-stranded DNA and double-stranded DNA complexed with ethidium were obtained. These spectra suggested that DNA undergoes considerable internal motion. The data show that 13-C nmr studies of the conformational and motional properties of native DNA and of complexes of native DNA with small molecules are practical and promising. Studies of subnucleosomes derived from nucleosomes were completed. Based on these studies, a model of the linear arrangement of histone C-terminal and N-terminal chain regions along nucleosome DNA was proposed. The use of staphylococcal protease to probe histone conformations in nucleosomes was explored. Preliminary data indicate that H3 is much more susceptible to protease than other core histones, and is cleaved in its hydrophobic domain. A procedure for fractionating chromatin was alos developed. (ERB)

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

    SciTech Connect

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

    2015-04-21

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

  6. Dichroism in Helicoidal Crystals.

    PubMed

    Cui, Xiaoyan; Nichols, Shane M; Arteaga, Oriol; Freudenthal, John; Paula, Froilanny; Shtukenberg, Alexander G; Kahr, Bart

    2016-09-21

    Accounting for the interactions of light with heterogeneous, anisotropic, absorbing, optically active media is part of the characterization of complex, transparent materials. Stained biological structures in thin tissue sections share many of these features, but systematic optical analyses beyond the employ of the simple petrographic microscopes have not be established. Here, this accounting is made for polycrystalline, spherulitic bundles of twisted d-mannitol lamellae grown from melts containing light-absorbing molecules. It has long been known that a significant percentage of molecular crystals readily grow as helicoidal ribbons with mesoscale pitches, but a general appreciation of the commonality of these non-classical crystal forms has been lost. Helicoidal crystal twisting was typically assayed by analyzing refractivity modulation in the petrographic microscope. However, by growing twisted crystals from melts in the presence of dissolved, light-absorbing molecules, crystal twisting can be assayed by analyzing the dichroism, both linear and circular. The term "helicoidal dichroism" is used here to describe the optical consequences of anisotropic absorbers precessing around radii of twisted crystalline fibrils or lamellae. d-Mannitol twists in two polymorphic forms, α and δ. The two polymorphs, when grown from supercooled melts in the presence of a variety of histochemical stains and textile dyes, are strongly dichroic in linearly polarized white light. The bis-azo dye Chicago sky blue is modeled because it is most absorbing when parallel and perpendicular to the radial axes in the respective spherulitic polymorphs. Optical properties were measured using Mueller matrix imaging polarimetry and simulated by taking into account the microstructure of the lamellae. The optical analysis of the dyed, patterned polycrystals clarifies aspects of the mesostructure that can be difficult to extract from bundles of tightly packed fibrils.

  7. Zero-field dichroism in the solar chromosphere.

    PubMed

    Sainz, R Manso; Bueno, J Trujillo

    2003-09-12

    We explain the linear polarization of the Ca ii infrared triplet observed close to the edge of the solar disk. In particular, we demonstrate that the physical origin of the enigmatic polarizations of the 866.2 and 854.2 nm lines lies in the existence of atomic polarization in their metastable (2)D(3)(/2, 5/2) lower levels, which produces differential absorption of polarization components (dichroism). To this end, we have solved the problem of the generation and transfer of polarized radiation by taking fully into account all the relevant optical pumping mechanisms in multilevel atomic models. We argue that "zero-field" dichroism may be of great diagnostic value in astrophysics.

  8. Itinerant and localized magnetic moments in ferrimagnetic Mn{sub 2}CoGa thin films identified with x-ray magnetic linear dichroism: experiment and ab initio theory

    SciTech Connect

    Meinert, M.; Schmalhorst, J; Klewe, C.; Reiss, G.; Arenholz, E.; Bohnert, T.; Nielsch, K.

    2011-08-08

    Epitaxial thin films of the half-metallic X{sub a}-compound Mn{sub 2}CoGa (Hg{sub 2}CuTi prototype) were prepared by dc magnetron co-sputtering with different heat treatments on MgO (001) substrates. High-quality lms with a bulk magnetization of 1.95(5) {mu}{sub }B per unit cell were obtained. The average Mn magnetic moment and the Co moment are parallel, in agreement with theory. The x-ray magnetic circular dichroism spectra agree with calculations based on density functional theory and reveal the antiparallel alignment of the two inequivalent Mn moments. X-ray magnetic linear dichroism allows to distinguish between itinerant and localized Mn moments. It is shown that one of the two Mn moments has localized character, whereas the other Mn moment and the Co moment are itinerant.

  9. Toroidal circular dichroism

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  10. Dynamic perturbation effects upon the circular dichroism intensity induced in an aggregate of dye chromophores bound to biopolymers

    NASA Astrophysics Data System (ADS)

    Kamiya, Mamoru

    1980-11-01

    The dynamic perturbation effects of polarizable monomer perturbers upon the circular dichroism intensity arising from absorption transitions of an arbitrary aggregate of dye chromophores bound to a large host polymer are formulated using the linear response theory in the decorrelation approximation, where the interchromophoric retardation phase factors are eliminated by a first-order Taylor expansion which is compatible with the use of the retarded helix selection rules in the long-wavelength approximation. A space-averaged and closed-form formulation of the non-conservative circular dichroism intensity which is perturbed by intensity with the outside perturber transitions is derived in the limit of the weak dynamic perturbation where perturber—perturber interactions are negligible. The relevant formulation is applied in order to investigate the intercalation model dependence of the non-conservative circular dichroism intensity induced at the visible absorption band of proflavine molecules intercalated in either poly(A—T) or poly(G—C).

  11. Nuclear spin circular dichroism

    SciTech Connect

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

    2014-04-07

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

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

    SciTech Connect

    Dinh, Thanh-Chung; Renger, Thomas

    2015-01-21

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

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

    NASA Astrophysics Data System (ADS)

    Dinh, Thanh-Chung; Renger, Thomas

    2015-01-01

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

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

    PubMed

    Dinh, Thanh-Chung; Renger, Thomas

    2015-01-21

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

  15. DEIMOS: a beamline dedicated to dichroism measurements in the 350-2500 eV energy range.

    PubMed

    Ohresser, P; Otero, E; Choueikani, F; Chen, K; Stanescu, S; Deschamps, F; Moreno, T; Polack, F; Lagarde, B; Daguerre, J-P; Marteau, F; Scheurer, F; Joly, L; Kappler, J-P; Muller, B; Bunau, O; Sainctavit, Ph

    2014-01-01

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

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

    SciTech Connect

    Ohresser, P. Otero, E.; Choueikani, F.; Chen, K.; Stanescu, S.; Deschamps, F.; Moreno, T.; Polack, F.; Lagarde, B.; Daguerre, J.-P.; Marteau, F.; Scheurer, F.; Joly, L.; Muller, B.; Kappler, J.-P.; Bunau, O.; Sainctavit, Ph.

    2014-01-15

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

  17. Efficient Algorithms for Estimating the Absorption Spectrum within Linear Response TDDFT

    SciTech Connect

    Brabec, Jiri; Lin, Lin; Shao, Meiyue; Govind, Niranjan; Yang, Chao; Saad, Yousef; Ng, Esmond

    2015-10-06

    We present two iterative algorithms for approximating the absorption spectrum of molecules within linear response of time-dependent density functional theory (TDDFT) framework. These methods do not attempt to compute eigenvalues or eigenvectors of the linear response matrix. They are designed to approximate the absorption spectrum as a function directly. They take advantage of the special structure of the linear response matrix. Neither method requires the linear response matrix to be constructed explicitly. They only require a procedure that performs the multiplication of the linear response matrix with a vector. These methods can also be easily modified to efficiently estimate the density of states (DOS) of the linear response matrix without computing the eigenvalues of this matrix. We show by computational experiments that the methods proposed in this paper can be much more efficient than methods that are based on the exact diagonalization of the linear response matrix. We show that they can also be more efficient than real-time TDDFT simulations. We compare the pros and cons of these methods in terms of their accuracy as well as their computational and storage cost.

  18. X-ray magnetic circular dichroism measured at the Fe K-edge with a reduced intrinsic broadening: x-ray absorption spectroscopy versus resonant inelastic x-ray scattering measurements

    NASA Astrophysics Data System (ADS)

    Juhin, Amélie; Sainctavit, Philippe; Ollefs, Katharina; Sikora, Marcin; Filipponi, Adriano; Glatzel, Pieter; Wilhelm, Fabrice; Rogalev, Andrei

    2016-12-01

    X-ray magnetic circular dichroism is measured at the Fe K pre-edge in yttrium iron garnet using two different procedures that allow reducing the intrinsic broadening due to the 1s corehole lifetime. First, deconvolution of XMCD data measured in total fluorescence yield (TFY) with an extremely high signal-to-noise ratio enables a factor of 2.4 to be gained in the XMCD intensity. Ligand field multiplet calculations performed with different values of intrinsic broadening show that deconvolving such high quality XMCD data is similar to reducing the lifetime broadening from a 1s corehole to a 2p corehole. Second, MCD is measured by resonant inelastic x-ray scattering spectroscopy as a function of incident energy and emission energy. Selection of a fixed emission energy, instead of using the TFY, allows enhancing the MCD intensity up to a factor of  ∼4.7. However, this significantly changes the spectral shape of the XMCD signal, which cannot be interpreted any more as an absorption spectrum.

  19. Characterization of absorption and non-linear effects in infrasound propagation using an augmented Burgers' equation

    NASA Astrophysics Data System (ADS)

    Sabatini, R.; Bailly, C.; Marsden, O.; Gainville, O.

    2016-12-01

    The long-range atmospheric propagation of explosion-like waves of frequency in the infrasound range is investigated using non-linear ray theory. Simulations are performed for sources of increasing amplitude on rays up to the lower thermosphere and for distances of hundreds of kilometres. A study of the attenuation of the waveforms observed at ground level induced by both the classical mechanisms and the vibrational relaxation of the molecules comprising the atmospheric gas is carried out. The relative importance of classical absorption and vibrational relaxation along the typical atmospheric propagation trajectories is assessed. Non-linear effects are highlighted as well and particular emphasis is placed on their strong interaction with absorption phenomena. A detailed description of the propagation model and of the numerical algorithm used in this work is first reported. Results are then discussed and the importance of the different mechanisms is clarified.

  20. Dynamics of microwave absorption by a plasma near a linear focal point

    NASA Astrophysics Data System (ADS)

    Arkhipenko, V. I.; Budnikov, V. N.; Gusakov, E. Z.; Kiselevskii, L. I.; Romanchuk, I. A.; Simonchik, L. V.

    1984-11-01

    The absorption of 2.35-GHz microwave radiation in an Ar plasma in a magnetic field near a focal point at which it is transformed linearly into plasma waves is investigated experimentally in the Granit plasma apparatus (Arkhipenko et al., 1981). Operating parameters include plasma density at the microwave input point 10 to the 12th/cu cm, density at the focal point 7 x 10 to the 10th/cu cm, Ar pressure 16 mtorr, and longitudinal magnetic-field strength 3 kOe. The absorption is found to follow linear theory at microwave power less than 20 mW, remaining concentrated near the focus, while at higher powers the absorption region migrates toward the beam source (by about 1 cm at t = 3 microsec), with simultaneous onset of 2-3-MHz oscillation of the reflected signal (revealing parametric instability at the focus) and further shifting of the absorption region at t greater than 3 microsec (forming a plasma burnthrough channel).

  1. Multiple ligand-binding properties of the lipocalin member chicken alpha1-acid glycoprotein studied by circular dichroism and electronic absorption spectroscopy: the essential role of the conserved tryptophan residue.

    PubMed

    Zsila, Ferenc; Matsunaga, Hisami; Bikádi, Zsolt; Haginaka, Jun

    2006-08-01

    Multiple ligand-binding properties of the 30-kDa chicken alpha(1)-acid glycoprotein (cAGP), a member of the lipocalin protein family, were investigated for the first time by using circular dichroism (CD) and UV/Vis absorption spectroscopy methods. By measuring induced CD (ICD) spectra, high-affinity binding (K(a) approximately 10(5)-10(6) M(-1)) of several drugs, dyes and natural compounds to cAGP was demonstrated including antimalarial agents (quinacrine, primaquine), phenotiazines (chlorpromazine, methylene blue), propranolol, non-steroidal antiinflammatory drugs (ketoprofen, diclofenac), tamoxifen, diazepam, tacrine, dicoumarol, cationic dyes (auramine O, thioflavine T, ethidium bromide), benzo[a]pyrene, L-thyroxine, bile pigments (bilirubin, biliverdin), alkaloids (piperine, aristolochic acid), saturated and unsaturated fatty acids. Analysis of the extrinsic CD spectra with the study of the covalently modified protein and CD displacement experiments revealed that a single Trp26 residue of cAGP conserved in the whole lipocalin family is part of the binding site, and it is essentially involved in the ligand-binding process via pi-pi stacking interaction resulting in the appearance of strong induced CD bands due to the non-degenerate intermolecular exciton coupling between the pi-pi* transitions of the stacked indole ring-ligand chromophore. The finding that cAGP is able to accommodate a broad spectrum of ligands belonging to different chemical classes suggests that its core beta-barrel cavity is unusually wide containing overlapping sub-sites. Significance of these new data in understanding of the ligand-binding properties of other lipocalins, especially that of human AGP, and potential practical applications are briefly discussed. Overall, cAGP serves as a simple, ultimate model to extend our knowledge on ligand-binding properties of lipocalins and to study the role of tryptophan residues in molecular recognition processes.

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

    SciTech Connect

    SUTHERLAND,J.C.

    2002-01-19

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

  3. Comparison of Monte-Carlo Ion Cyclotron Heating Model with Full-Wave Linear Absorption Model

    NASA Astrophysics Data System (ADS)

    Choi, M.; Chan, V. S.; Berry, L. A.; Jaeger, E. F.; Green, D.; Bonoli, P.; Wright, J.

    2009-05-01

    To fully account for the wave-particle interaction physics in ion-cyclotron resonant frequency heating experiments, the 5-D Monte-Carlo code ORBIT-RF is being coupled with the 2-D full wave code AORSA to iteratively evolve ion distribution in x-v space that is used to update the dielectric tensor in AORSA for evaluating the full-wave fields. It is demonstrated that using the full-wave fields from a Maxwellian dielectric tensor in AORSA and confining the resonant ions to their initial orbits in ORBIT-RF, ORBIT-RF largely reproduces the AORSA linear wave absorption profiles for fundamental and higher harmonic ICRF heating. An exception is an observed inward shift of the ORBIT-RF absorption peak for high harmonics near the magnetic-axis compared with that of AORSA, which can be attributed to a finite orbit width effect. Analysis of power absorption in velocity space confirms that significant power is absorbed by energetic particles with their banana tips at resonance locations.

  4. Specific absorption rate calculations of magnetite, using a modified linear response model for applications in magnetic hyperthermia

    SciTech Connect

    Hernández S, A. E-mail: meduardo2001@hotmail.com; Cano, M. E. E-mail: meduardo2001@hotmail.com; Torres-Arenas, J.

    2014-11-07

    Currently the absorption of electromagnetic radiation by magnetic nanoparticles is studied for biomedical applications of cancer thermotherapy. Several experiments are conduced following the framework of the Rosensweig model, in order to estimate their specific absorption rate. Nevertheless, this linear approximation involves strong simplifications which constrain their accuracy and validity range. The main aim of this work is to incorporate the deviation of the sphericity assumption in particles shapes, to improve the determination of their specific absorption rate. The correction to the effective particles volume is computed as a measure of the apparent amount of magnetic material, interacting with the external AC magnetic field. Preliminary results using the physical properties of Fe3O4 nanoparticles, exhibit an important correction in their estimated specific absorption rate, as a function of the apparent mean particles radius. Indeed, we have observed using a small deviation (6% of the apparent radius), up to 40% of the predicted specific absorption rate by the Rosensweig linear approximation.

  5. Microscopic Modeling of Intersubband Optical Processes in Type II Semiconductor Quantum Wells: Linear Absorption

    NASA Technical Reports Server (NTRS)

    Li, Jian-Zhong; Kolokolov, Kanstantin I.; Ning, Cun-Zheng

    2003-01-01

    Linear absorption spectra arising from intersubband transitions in semiconductor quantum well heterostructures are analyzed using quantum kinetic theory by treating correlations to the first order within Hartree-Fock approximation. The resulting intersubband semiconductor Bloch equations take into account extrinsic dephasing contributions, carrier-longitudinal optical phonon interaction and carrier-interface roughness interaction which is considered with Ando s theory. As input for resonance lineshape calculation, a spurious-states-free 8-band kp Hamiltonian is used, in conjunction with the envelop function approximation, to compute self-consistently the energy subband structure of electrons in type II InAs/AlSb single quantum well structures. We demonstrate the interplay of nonparabolicity and many-body effects in the mid-infrared frequency range for such heterostructures.

  6. Analysis of Pu Isotopes in Melted Fuel by Neutron Resonance Transmission: Examination by Linear Absorption Model

    NASA Astrophysics Data System (ADS)

    Kitatani, F.; Harada, H.; Takamine, J.; Kureta, M.; Seya, M.

    2014-04-01

    We have been studying the feasibility of neutron resonance transmission analysis (NRTA) for quantifying nuclear materials (Pu/U isotopes) in particle-like debris of melted fuel for nuclear material accountability and safeguards. The achievable measurement accuracy of NRTA was examined using a linear absorption model for the sample which contain substances other than nuclear fuel materials, such as boron and iron. The impurities (boron and iron etc.) in melted fuel are from the support structure and criticality control materials of the reactor core, and should be included to study the feasibility of NRTA for actual application. Neutron transmission spectra were calculated using the total neutron cross-sections in JENDL-4.0. The transmission spectra together with their uncertainties were evaluated. The study showed quantitatively that the statistical uncertainty in the determination of atomic number density of each isotope depends on the impurity density in the sample. The optimal thickness of the sample was determined for various impurity densities.

  7. A comparison study of linear reconstruction techniques for diffuse optical tomographic imaging of absorption coefficient

    NASA Astrophysics Data System (ADS)

    Gaudette, Richard J.; Brooks, Dana H.; Di Marzio, Charles A.; Kilmer, Misha E.; Miller, Eric L.; Gaudette, Thomas; Boas, David A.

    2000-04-01

    We compare, through simulations, the performance of four linear algorithms for diffuse optical tomographic reconstruction of the three-dimensional distribution of absorption coefficient within a highly scattering medium using the diffuse photon density wave approximation. The simulation geometry consisted of a coplanar array of sources and detectors at the boundary of a half-space medium. The forward solution matrix is both underdetermined, because we estimate many more absorption coefficient voxels than we have measurements, and ill-conditioned, due to the ill-posedness of the inverse problem. We compare two algebraic techniques, ART and SIRT, and two subspace techniques, the truncated SVD and CG algorithms. We compare three-dimensional reconstructions with two-dimensional reconstructions which assume all inhomogeneities are confined to a known horizontal slab, and we consider two `object-based' error metrics in addition to mean square reconstruction error. We include a comparison using simulated data generated using a different FDFD method with the same inversion algorithms to indicate how our conclusions are affected in a somewhat more realistic scenario. Our results show that the subspace techniques are superior to the algebraic techniques in localization of inhomogeneities and estimation of their amplitude, that two-dimensional reconstructions are sensitive to underestimation of the object depth, and that an error measure based on a location parameter can be a useful complement to mean squared error.

  8. Efficient Algorithms for Estimating the Absorption Spectrum within Linear Response TDDFT.

    PubMed

    Brabec, Jiri; Lin, Lin; Shao, Meiyue; Govind, Niranjan; Yang, Chao; Saad, Yousef; Ng, Esmond G

    2015-11-10

    We present a special symmetric Lanczos algorithm and a kernel polynomial method (KPM) for approximating the absorption spectrum of molecules within the linear response time-dependent density functional theory (TDDFT) framework in the product form. In contrast to existing algorithms, the new algorithms are based on reformulating the original non-Hermitian eigenvalue problem as a product eigenvalue problem and the observation that the product eigenvalue problem is self-adjoint with respect to an appropriately chosen inner product. This allows a simple symmetric Lanczos algorithm to be used to compute the desired absorption spectrum. The use of a symmetric Lanczos algorithm only requires half of the memory compared with the nonsymmetric variant of the Lanczos algorithm. The symmetric Lanczos algorithm is also numerically more stable than the nonsymmetric version. The KPM algorithm is also presented as a low-memory alternative to the Lanczos approach, but the algorithm may require more matrix-vector multiplications in practice. We discuss the pros and cons of these methods in terms of their accuracy as well as their computational and storage cost. Applications to a set of small and medium-sized molecules are also presented.

  9. Propagation of ultrashort laser pulses in water: linear absorption and onset of nonlinear spectral transformation.

    PubMed

    Sokolov, Alexei V; Naveira, Lucas M; Poudel, Milan P; Strohaber, James; Trendafilova, Cynthia S; Buck, William C; Wang, Jieyu; Strycker, Benjamin D; Wang, Chao; Schuessler, Hans; Kolomenskii, Alexandre; Kattawar, George W

    2010-01-20

    We study propagation of short laser pulses through water and use a spectral hole filling technique to essentially perform a sensitive balanced comparison of absorption coefficients for pulses of different duration. This study is motivated by an alleged violation of the Bouguer-Lambert-Beer law at low light intensities, where the pulse propagation is expected to be linear, and by a possible observation of femtosecond optical precursors in water. We find that at low intensities, absorption of laser light is determined solely by its spectrum and does not directly depend on the pulse duration, in agreement with our earlier work and in contradiction to some work of others. However, as the laser fluence is increased, interaction of light with water becomes nonlinear, causing energy exchange among the pulse's spectral components and resulting in peak-intensity dependent (and therefore pulse-duration dependent) transmission. For 30 fs pulses at 800 nm center wavelength, we determine the onset of nonlinear propagation effects to occur at a peak value of about 0.12 mJ/cm(2) of input laser energy fluence.

  10. The formation of linear aggregates in magnetic hyperthermia: implications on specific absorption rate and magnetic anisotropy.

    PubMed

    Saville, Steven L; Qi, Bin; Baker, Jonathon; Stone, Roland; Camley, Robert E; Livesey, Karen L; Ye, Longfei; Crawford, Thomas M; Mefford, O Thompson

    2014-06-15

    The design and application of magnetic nanoparticles for use as magnetic hyperthermia agents has garnered increasing interest over the past several years. When designing these systems, the fundamentals of particle design play a key role in the observed specific absorption rate (SAR). This includes the particle's core size, polymer brush length, and colloidal arrangement. While the role of particle core size on the observed SAR has been significantly reported, the role of the polymer brush length has not attracted as much attention. It has recently been reported that for some suspensions linear aggregates form in the presence of an applied external magnetic field, i.e. chains of magnetic particles. The formation of these chains may have the potential for a dramatic impact on the biomedical application of these materials, specifically the efficiency of the particles to transfer magnetic energy to the surrounding cells. In this study we demonstrate the dependence of SAR on magnetite nanoparticle core size and brush length as well as observe the formation of magnetically induced colloidal arrangements. Colloidally stable magnetic nanoparticles were demonstrated to form linear aggregates in an alternating magnetic field. The length and distribution of the aggregates were dependent upon the stabilizing polymer molecular weight. As the molecular weight of the stabilizing layer increased, the magnetic interparticle interactions decreased therefore limiting chain formation. In addition, theoretical calculations demonstrated that interparticle spacing has a significant impact on the magnetic behavior of these materials. This work has several implications for the design of nanoparticle and magnetic hyperthermia systems, while improving understanding of how colloidal arrangement affects SAR.

  11. Collision-induced absorption in mixtures of symmetrical linear and tetrahedral molecules - Methane-nitrogen

    NASA Technical Reports Server (NTRS)

    Birnbaum, G.; Borysow, A.; Buechele, A.

    1993-01-01

    The far infrared absorption of a CH4-N2 mixture was measured at 297, 195, and 162 K from 30 to 650/cm. The spectral invariants gamma1 and alpha1, proportional, respectively, to the zeroth and first spectral moments, due to bimolecular collisions between CH4 and N2 were obtained from these data and compared with theoretical values. The theory for collision-induced dipoles between a tetrahedral and a diatomic or symmetrical linear molecule includes contributions not previously considered. Whereas the theoretical values of gamma1 are only somewhat greater than experiment at all temperatures, the theoretical values of alpha1 are significantly lower than the experimental values. From the theoretical spectral moments for the various induced dipole components, the parameters of the BC shape were computed, and theoretical spectra were constructed. Good agreement was obtained at the lower frequencies, but with increasing frequencies the theoretical spectra were increasingly less intense than the experimental spectra. Although the accuracy of the theoretical results may suffer from the lack of a reliable potential function, it does not appear that this high frequency discrepancy can be removed by any conceivable modification in the potential.

  12. Linear absorption coefficient of beryllium in the 50-300-A wavelength range. [bandpass filter materials for ultraviolet astronomy instrumentation

    NASA Technical Reports Server (NTRS)

    Barstow, M. A.; Lewis, M.; Petre, R.

    1983-01-01

    Transmittances of thin-film filters fabricated for an extreme-UV astronomy sounding-rocket experiment yield values for the linear absorption coefficient of beryllium in the 50-300-A wavelength range, in which previous measurements are sparse. The inferred values are consistent with the lowest data previously published and may have important consequences for extreme-UV astronomers.

  13. Compact characterization of liquid absorption and emission spectra using linear variable filters integrated with a CMOS imaging camera

    PubMed Central

    Wan, Yuhang; Carlson, John A.; Kesler, Benjamin A.; Peng, Wang; Su, Patrick; Al-Mulla, Saoud A.; Lim, Sung Jun; Smith, Andrew M.; Dallesasse, John M.; Cunningham, Brian T.

    2016-01-01

    A compact analysis platform for detecting liquid absorption and emission spectra using a set of optical linear variable filters atop a CMOS image sensor is presented. The working spectral range of the analysis platform can be extended without a reduction in spectral resolution by utilizing multiple linear variable filters with different wavelength ranges on the same CMOS sensor. With optical setup reconfiguration, its capability to measure both absorption and fluorescence emission is demonstrated. Quantitative detection of fluorescence emission down to 0.28 nM for quantum dot dispersions and 32 ng/mL for near-infrared dyes has been demonstrated on a single platform over a wide spectral range, as well as an absorption-based water quality test, showing the versatility of the system across liquid solutions for different emission and absorption bands. Comparison with a commercially available portable spectrometer and an optical spectrum analyzer shows our system has an improved signal-to-noise ratio and acceptable spectral resolution for discrimination of emission spectra, and characterization of colored liquid’s absorption characteristics generated by common biomolecular assays. This simple, compact, and versatile analysis platform demonstrates a path towards an integrated optical device that can be utilized for a wide variety of applications in point-of-use testing and point-of-care diagnostics. PMID:27389070

  14. Compact characterization of liquid absorption and emission spectra using linear variable filters integrated with a CMOS imaging camera

    NASA Astrophysics Data System (ADS)

    Wan, Yuhang; Carlson, John A.; Kesler, Benjamin A.; Peng, Wang; Su, Patrick; Al-Mulla, Saoud A.; Lim, Sung Jun; Smith, Andrew M.; Dallesasse, John M.; Cunningham, Brian T.

    2016-07-01

    A compact analysis platform for detecting liquid absorption and emission spectra using a set of optical linear variable filters atop a CMOS image sensor is presented. The working spectral range of the analysis platform can be extended without a reduction in spectral resolution by utilizing multiple linear variable filters with different wavelength ranges on the same CMOS sensor. With optical setup reconfiguration, its capability to measure both absorption and fluorescence emission is demonstrated. Quantitative detection of fluorescence emission down to 0.28 nM for quantum dot dispersions and 32 ng/mL for near-infrared dyes has been demonstrated on a single platform over a wide spectral range, as well as an absorption-based water quality test, showing the versatility of the system across liquid solutions for different emission and absorption bands. Comparison with a commercially available portable spectrometer and an optical spectrum analyzer shows our system has an improved signal-to-noise ratio and acceptable spectral resolution for discrimination of emission spectra, and characterization of colored liquid’s absorption characteristics generated by common biomolecular assays. This simple, compact, and versatile analysis platform demonstrates a path towards an integrated optical device that can be utilized for a wide variety of applications in point-of-use testing and point-of-care diagnostics.

  15. Photoelectron circular dichroism of isopropanolamine

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

  16. Electromagnetic particle simulation of the effect of toroidicity on linear mode conversion and absorption of lower hybrid waves

    NASA Astrophysics Data System (ADS)

    Bao, J.; Lin, Z.; Kuley, A.; Wang, Z. X.

    2016-06-01

    Effects of toroidicity on linear mode conversion and absorption of lower hybrid (LH) waves in fusion plasmas have been studied using electromagnetic particle simulation. The simulation confirms that the toroidicity induces an upshift of parallel refractive index when LH waves propagate from the tokamak edge toward the core, which affects the radial position for the mode conversion between slow and fast LH waves. Furthermore, moving LH antenna launch position from low field side toward high field side leads to a larger upshift of the parallel refractive index, which helps the slow LH wave penetration into the tokamak core. The broadening of the poloidal spectrum of the wave-packet due to wave diffraction is also verified in the simulation. Both the upshift and broadening effects of the parallel spectrum of the wave-packet modify the parallel phase velocity and thus the linear absorption of LH waves by electron Landau resonance.

  17. Quantum-cascade laser-based vibrational circular dichroism.

    PubMed

    Lüdeke, Steffen; Pfeifer, Marcel; Fischer, Peer

    2011-04-20

    Vibrational circular dichroism (VCD) spectra were recorded with a tunable external-cavity quantum-cascade laser (QCL). In comparison with standard thermal light sources in the IR, QCLs provide orders of magnitude more power and are therefore promising for VCD studies in strongly absorbing solvents. The brightness of this novel light source is demonstrated with VCD and IR absorption measurements of a number of compounds, including proline in water.

  18. Characterization of Photon-Counting Detector Responsivity for Non-Linear Two-Photon Absorption Process

    NASA Technical Reports Server (NTRS)

    Sburlan, S. E.; Farr, W. H.

    2011-01-01

    Sub-band absorption at 1550 nm has been demonstrated and characterized on silicon Geiger mode detectors which normally would be expected to have no response at this wavelength. We compare responsivity measurements to singlephoton absorption for wavelengths slightly above the bandgap wavelength of silicon (approx. 1100 microns). One application for this low efficiency sub-band absorption is in deep space optical communication systems where it is desirable to track a 1030 nm uplink beacon on the same flight terminal detector array that monitors a 1550 nm downlink signal for pointingcontrol. The currently observed absorption at 1550 nm provides 60-70 dB of isolation compared to the response at 1064 nm, which is desirable to avoid saturation of the detector by scattered light from the downlink laser.

  19. Thermal lens-circular dichroism detector for high-performance liquid chromatography.

    PubMed

    Xu, M R; Tran, C D

    1990-11-15

    A novel and ultrasensitive chiral detector for high-performance liquid chromatography has been developed. This detector is based on the measurement of circular dichroism of chiral effluents by the thermal lens effect. In this instrument, the chromatographic effluent was sequentially excited by left circularly polarized laser light (LCPL) and right circularly polarized laser light (RCPL); both of these excitation beams were derived from the same argon ion laser whose linearly polarized output was transformed into circularly polarized light by means of a Pockels cell. The heat generated as a consequence of the sample absorption of the LCPL and RCPL was measured by the probe laser beam collinearly overlapping with the two excitation beams. A lock-in amplifier was used to measure the thermal lens-circular dichroism (TL-CD) signal which corresponds to the difference in the thermal lens signals produced by the LCPL and RCPL excitation beams. In addition to its high sensitivity, the advantages of this TL-CD chiral detector include its ability to provide, directly and in real time, information on the chirality (i.e., circular dichroism) and optical purity of chiral samples. A detection limit of 7.2 ng was achieved for (-)-tris(ethylenediamine)cobalt(III) (k' = 0.45) as well as for the (+)-tris(ethylenediamine)cobalt(III) (k' = 1.40) when these two enantiomers were chromatographically separated from the corresponding racemic mixture through the use of bis(mu-d-tartrato)diantiomonate(III) ion pair reversed-phase chromatography. This limit of detection was found by using a 10-microL flow cell and having 5-mm path length and 6-mW excitation laser beam (lambda = 514.5 nm) modulated at 2 Hz.

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  1. Chromophores and Materials for Temporal and Frequency Agile Non-Linear Absorption

    DTIC Science & Technology

    2014-05-31

    is related to the proposed new research, we explored the effects of stereochemistry on the photophysics, 2PA absorption and nanosecond NLA...600 nm. This result reveals how subtle aspects such as stereochemistry (and symmetry) can influence the 2PA and the NLA response to longer pulses

  2. Electric field effect on the nonlinear and linear intersubband absorption spectra in CdTe/ZnTe spherical quantum dot

    NASA Astrophysics Data System (ADS)

    Kostić, Radmila; Stojanović, Dušanka

    2012-01-01

    Linear and nonlinear absorption spectra of neutral (D0) hydrogenic impurity located at the center of the CdTe/ZnTe spherical quantum dot (QD) were investigated after assuming a spherically symmetric confining potential of finite depth. Calculations were performed under the effective mass approximation on the basis of exact solution of the Schrödinger and Poisson equations. Eigenfunctions were expressed in terms of the Whittaker and Coulomb wave functions. Results for D0 impurity energies of ground 1s, and excited 2p, 3d, and 2s states strongly depend on QD radius if it does not exceed a few effective Bohr radius. Wave functions and Stark shift energy levels in external electric field were determined from a variational-calculus approach for states labeled m=0. The absorption spectra for intersubband transitions were found to depend strongly on the QD radius. Whether or not the impurity is present, the peak energy of absorption decreases with increasing QD radius. An external electric field increases the transition energy but does not significantly change absorption characteristics.

  3. Self-Focusing of Quadruple Gaussian Laser Beam in an Inhomogenous Magnetized Plasma with Ponderomotive Non-Linearity: Effect of Linear Absorption

    NASA Astrophysics Data System (ADS)

    Aggarwal, Munish; Vij, Shivani; Kant, Niti

    2015-11-01

    The propagation of quadruple Gaussian laser beam in a plasma characterized by axial inhomogeneity and nonlinearity due to ponderomotive force in the paraxial ray approximation is investigated. An appropriate expression for the nonlinear dielectric constant has been developed in the presence of external magnetic field, with linear absorption and due to saturation effects for arbitrary large intensity. The effects of different types of plasma axial inhomogeneities on self-focusing of laser beam have been studied with the typical laser and plasma parameters. Self-focusing of quadruple Gaussian laser beam in the presence of externally applied magnetic field and saturating parameter is found significantly improved in the case of extraordinary mode. Our results reveal that initially converging beam shows oscillatory convergence whereas initially diverging beam shows oscillatory divergence. The beam is more focussed at lower intensity in both cases viz. extraordinary and ordinary mode.

  4. Applications of soft x-ray magnetic dichroism

    NASA Astrophysics Data System (ADS)

    van der Laan, G.

    2013-04-01

    Applications of x-ray magnetic circular and linear dichroism (XMCD and XMLD) are reviewed in the soft x-ray region, covering the photon energy range 0.4-2 keV, which includes important absorption edges such as the 3d transition metal L2,3 and rare earth M4,5. These techniques enable a broad range of novel and exciting studies such as on the electronic properties and magnetic ordering of novel nanostructured systems. XMCD has a sensitivity better than 0.01 monolayer (at the surface) and due to simple detection methods, such as electron yield and fluorescence yield, it has become a workhorse technique in physics and materials science. It is the only element-specific technique able to distinguish between the spin and orbital parts of the magnetic moments. The applications are vast, e.g., in x-ray holographic imaging, XMCD gives a spatial resolution of tens of nm. While many studies in the past were centered on physics, more recently new applications have emerged in areas such as chemistry, biology and earth and environmental sciences. For instance, XMCD allows the determination of the cation occupations in spinels and other ternary oxides. In scanning transmission x-ray microscopy (STXM), XMCD enables us to map biogenic magnetite redox changes resulting in a surprising degree of variation on the nanoscale. Another recent development is ferromagnetic resonance (FMR) detected by time-resolved XMCD which opens the door to element-, site- and layer-specific dynamical measurements. By exploiting the time structure of the pulsed synchrotron radiation from the storage ring the relative phase of precession in the individual magnetic layers of a multilayer stack can be determined.

  5. Rotation and dichroism associated with microwave propagation in chiral composite samples

    SciTech Connect

    Umari, M.H.; Varadan, V.V.; Varadan, V.K. )

    1991-10-01

    Experimental results are presented on the angle of rotation and the axial ratio (dichroism) associated with the propagation of microwave waves in chiral composite samples (a phenomenon akin to optical rotation and optical dichroism). In the experiments the chiral composite samples tested were made in the form of planar slabs and consisted of low loss dielectric matrix materials in which miniature copper springs of left only, right only, or an equal mixture of left and right handedness were randomly distributed and oriented. The normally incident wave was linearly polarized. In the chiral sample the linearly polarized wave decomposes into left and right circularly polarized waves which propagate with different speeds and different attenuations leading to an elliptically polarized transmitted wave whose orientation (electromagnetic rotation) and axial ratio (dichroism) are proportional to the concentration of springs. Rotation and dichroism are shown to be zero in the equichiral samples. 10 refs.

  6. Excited-state symmetry breaking of linear quadrupolar chromophores: A transient absorption study

    NASA Astrophysics Data System (ADS)

    Dozova, Nadia; Ventelon, Lionel; Clermont, Guillaume; Blanchard-Desce, Mireille; Plaza, Pascal

    2016-11-01

    The photophysical properties of two highly symmetrical quadrupolar chromophores were studied by both steady-state and transient absorption spectroscopy. Their excited-state behavior is dominated by the solvent-induced Stokes shift of the stimulated-emission band. The origin of this shift is attributed to symmetry breaking that confers a non-vanishing dipole moment to the excited state of both compounds. This dipole moment is large and constant in DMSO, whereas symmetry breaking appears significantly slower and leading to smaller excited-state dipole in toluene. Time-dependant increase of the excited-state dipole moment induced by weak solvation is proposed to explain the results in toluene.

  7. Influence of the light propagation models on a linearized photoacoustic image reconstruction of the light absorption coefficient

    NASA Astrophysics Data System (ADS)

    Okawa, Shinpei; Hirasawa, Takeshi; Kushibiki, Toshihiro; Ishihara, Miya

    2015-03-01

    Quantification of the optical properties of the tissues and blood by noninvasive photoacoustic (PA) imaging may provide useful information for screening and early diagnosis of diseases. Linearized 2D image reconstruction algorithm based on PA wave equation and the photon diffusion equation (PDE) can reconstruct the image with computational cost smaller than a method based on 3D radiative transfer equation. However, the reconstructed image is affected by the differences between the actual and assumed light propagations. A quantitative capability of a linearized 2D image reconstruction was investigated and discussed by the numerical simulations and the phantom experiment in this study. The numerical simulations with the 3D Monte Carlo (MC) simulation and the 2D finite element calculation of the PDE were carried out. The phantom experiment was also conducted. In the phantom experiment, the PA pressures were acquired by a probe which had an optical fiber for illumination and the ring shaped P(VDF-TrFE) ultrasound transducer. The measured object was made of Intralipid and Indocyanine green. In the numerical simulations, it was shown that the linearized image reconstruction method recovered the absorption coefficients with alleviating the dependency of the PA amplitude on the depth of the photon absorber. The linearized image reconstruction method worked effectively under the light propagation calculated by 3D MC simulation, although some errors occurred. The phantom experiments validated the result of the numerical simulations.

  8. Electromagnetic particle simulation of the effect of toroidicity on linear mode conversion and absorption of lower hybrid waves

    NASA Astrophysics Data System (ADS)

    Bao, Jian; Lin, Zhihong; Kuley, Animesh; Wang, Zhixuan

    2016-10-01

    Effects of toroidicity on linear mode conversion and absorption of lower hybrid (LH) waves in tokamak have been studied by electromagnetic particle simulation using GTC. The simulation confirms that the toroidicity induces an upshift of parallel refractive index when LH waves propagate from the tokamak edge toward the core, which affects the radial position for the mode conversion between slow and fast LH waves. Furthermore, moving LH antenna launch position from low field side toward high field side leads to a larger upshift of the parallel refractive index, which helps the slow LH wave penetration into the tokamak core. The broadening of the poloidal spectrum of the wave-packet due to wave diffraction is also verified in the simulation. Both the upshift and broadening effects of the parallel spectrum of the wave-packet modify the parallel phase velocity and thus the linear absorption of LH waves by electron Landau resonance. In the nonlinear electromagnetic simulation, nonlinear wave trapping of electrons is verified and a plasma current is nonlinearly driven. Preliminary results of the nonlinear parametric decay of LH waves will be presented.

  9. The infrared dichroism of transmembrane helical polypeptides.

    PubMed Central

    Axelsen, P H; Kaufman, B K; McElhaney, R N; Lewis, R N

    1995-01-01

    Polarized attenuated total internal reflectance techniques were applied to study the infrared dichroism of the amide I transition moment in two membrane-bound peptides that are known to form oriented transmembrane helices: gramicidin A in a supported phospholipid monolayer and Ac-Lys2-Leu24-Lys2-amide (L24) in oriented multibilayers. These studies were performed to test the ability of these techniques to determine the orientation of these peptides, to verify the value of optical parameters used to calculate electric field strengths, to examine the common assumptions regarding the amide I transition moment orientation, and to ascertain the effect of surface imperfections on molecular disorder. The two peptides exhibit marked differences in the shape and frequency of their amide I absorption bands. Yet both peptides are highly ordered and oriented with their helical axes perpendicular to the membrane surface. In the alpha-helix formed by L24, there is evidence for a mode with type E1 symmetry contributing to amide I, and the amide I transition moment must be more closely aligned with the peptide C=O (< 34 degrees) than earlier studies have suggested. These results indicate that long-standing assumptions about the orientation of amide I in a peptide require some revision, but that in general, infrared spectroscopy yields reliable information about the orientation of membrane-bound helical peptides. Images FIGURE 1 PMID:8599683

  10. Quantification and parametrization of non-linearity effects by higher-order sensitivity terms in scattered light differential optical absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Puķīte, Jānis; Wagner, Thomas

    2016-05-01

    We address the application of differential optical absorption spectroscopy (DOAS) of scattered light observations in the presence of strong absorbers (in particular ozone), for which the absorption optical depth is a non-linear function of the trace gas concentration. This is the case because Beer-Lambert law generally does not hold for scattered light measurements due to many light paths contributing to the measurement. While in many cases linear approximation can be made, for scenarios with strong absorptions non-linear effects cannot always be neglected. This is especially the case for observation geometries, for which the light contributing to the measurement is crossing the atmosphere under spatially well-separated paths differing strongly in length and location, like in limb geometry. In these cases, often full retrieval algorithms are applied to address the non-linearities, requiring iterative forward modelling of absorption spectra involving time-consuming wavelength-by-wavelength radiative transfer modelling. In this study, we propose to describe the non-linear effects by additional sensitivity parameters that can be used e.g. to build up a lookup table. Together with widely used box air mass factors (effective light paths) describing the linear response to the increase in the trace gas amount, the higher-order sensitivity parameters eliminate the need for repeating the radiative transfer modelling when modifying the absorption scenario even in the presence of a strong absorption background. While the higher-order absorption structures can be described as separate fit parameters in the spectral analysis (so-called DOAS fit), in practice their quantitative evaluation requires good measurement quality (typically better than that available from current measurements). Therefore, we introduce an iterative retrieval algorithm correcting for the higher-order absorption structures not yet considered in the DOAS fit as well as the absorption dependence on

  11. Magnetic x-ray dichroism in ultrathin epitaxial films

    SciTech Connect

    Tobin, J.G.; Goodman, K.W.; Cummins, T.R.

    1997-04-01

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

  12. Absorption spectra of adenocarcinoma and squamous cell carcinoma cervical tissues

    NASA Astrophysics Data System (ADS)

    Ivashko, Pavlo; Peresunko, Olexander; Zelinska, Natalia; Alonova, Marina

    2014-08-01

    We studied a methods of assessment of a connective tissue of cervix in terms of specific volume of fibrous component and an optical density of staining of connective tissue fibers in the stroma of squamous cancer and cervix adenocarcinoma. An absorption spectra of blood plasma of the patients suffering from squamous cancer and cervix adenocarcinoma both before the surgery and in postsurgical periods were obtained. Linear dichroism measurements transmittance in polarized light at different orientations of the polarization plane relative to the direction of the dominant orientation in the structure of the sample of biotissues of stroma of squamous cancer and cervix adenocarcinoma were carried. Results of the investigation of the tumor tissues showed that the magnitude of the linear dichroism Δ is insignificant in the researched spectral range λ=280-840 nm and specific regularities in its change observed short-wave ranges.

  13. Effect of the concentration of magnetic grains on the linear-optical-absorption coefficient of ferrofluid-doped lyotropic mesophases: deviation from the Beer-Lambert law.

    PubMed

    Cuppo, F L S; Gómez, S L; Figueiredo Neto, A M

    2004-04-01

    In this paper is reported a systematic experimental study of the linear-optical-absorption coefficient of ferrofluid-doped isotropic lyotropic mixtures as a function of the magnetic-grains concentration. The linear optical absorption of ferrolyomesophases increases in a nonlinear manner with the concentration of magnetic grains, deviating from the usual Beer-Lambert law. This behavior is associated to the presence of correlated micelles in the mixture which favors the formation of small-scale aggregates of magnetic grains (dimers), which have a higher absorption coefficient with respect to that of isolated grains. We propose that the indirect heating of the micelles via the ferrofluid grains (hyperthermia) could account for this nonlinear increase of the linear-optical-absorption coefficient as a function of the grains concentration.

  14. Electronic absorption and resonance Raman spectra of large linear carbon clusters isolated in solid argon.

    PubMed

    Szczepanski, J; Fuller, J; Ekern, S; Vala, M

    2001-03-15

    Neutral and anionic carbon clusters have been generated via a laser-induced graphite-based plasma and deposited in a solid argon matrix. Anionic clusters were formed from neutral clusters by using crossed electron/carbon cluster beams. Thermal annealing (to 36 K) resulted in the aggregation of the smaller carbon species, leading to the formation of long chain neutral and anionic clusters. Spectroscopic measurements in the ultraviolet, visible, near-infrared and infrared regions revealed a series of bands attributable to a homologous set of odd-numbered C5-C29 neutral clusters and even-numbered C6(-)-C36- anionic clusters. Good agreement is found for the band positions of carbon chains containing odd C15-C21 neutrals and even C6(-)-C22- anions, with species previously identified by Maier and coworkers using mass selection or laser vaporization, followed by neon matrix isolation. Resonance Raman frequencies for the neutral C17, C21 and C23 species are shown to be consistent with the above attributions. Density functional theory calculations agree well with the observed bands. It is found that certain low frequency Raman stretching frequencies decrease in a predictable way with increasing chain length. Comparison of the 0(0)0 absorption transitions of the even C18(-)-C36- anionic clusters with the 'unidentified' infrared (UIR) interstellar emission bands suggests that the electronic emission from specific long chain carbon anions may contribute to the some of the UIR bands.

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

    PubMed

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

    2014-03-01

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

  16. Circular dichroism and magnetic circular dichroism of reduced molybdenum-iron protein of Azotobacter vinelandii nitrogenase.

    PubMed

    Stephens, P J; McKenna, C E; McKenna, M C; Nguyen, H T; Devlin, F

    1981-05-12

    Studies of the circular dichroism (CD) and magnetic circular dichroism (MCD) of the dithionite-reduced molybdenum-iron protein of Azotobacter vinelandii nitrogenase (Av1) are reported. CD and MCD are measurable at room temperature across a wide spectral range, from the near-UV to the near-IR. The visible-near-UV CD is insignificantly affected by moderate variations in pH, temperature, ionic strength, and buffer, providing evidence against conformational change in the range studied. Mg2+ and ATP also cause no observable change in the visible-near-UV CD. Both CD and MCD in the visible-near-UV are unaffected by 30% inactivation by O2. However, the CD and MCD spectra of uncrystallized Av1 differ very significantly from those of crystallized Av1; in particular, the MCD spectrum is very sensitive to the presence of heme impurities. The identicality in both CD and MCD spectra of the reduced molybdenum-iron proteins from Azotobacter vinelandii and Klebsiella pneumoniae shows that these proteins contain metal clusters, identical in number, structure, and protein environment. While the absorption, CD, and MCD spectra of reduced Av1 are typical in many respects of simpler iron-sulfur proteins and are most similar to the [Fe4S4(SR)4]3- clusters found in reduced bacterial ferredoxins, significant differences exist. It is concluded, therefore, that the clusters present are not identical with those previously characterized, a conclusion earlier arrived at from electron paramagnetic resonance, Mössbauer, and EXAFS spectroscopies.

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

    NASA Astrophysics Data System (ADS)

    Gevorgyan, Ashot; Kocharian, Armen; Vardanyan, Gagik

    2015-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

  19. Spectroscopic determination of leaf biochemistry using band-depth analysis of absorption features and stepwise multiple linear regression

    USGS Publications Warehouse

    Kokaly, R.F.; Clark, R.N.

    1999-01-01

    We develop a new method for estimating the biochemistry of plant material using spectroscopy. Normalized band depths calculated from the continuum-removed reflectance spectra of dried and ground leaves were used to estimate their concentrations of nitrogen, lignin, and cellulose. Stepwise multiple linear regression was used to select wavelengths in the broad absorption features centered at 1.73 ??m, 2.10 ??m, and 2.30 ??m that were highly correlated with the chemistry of samples from eastern U.S. forests. Band depths of absorption features at these wavelengths were found to also be highly correlated with the chemistry of four other sites. A subset of data from the eastern U.S. forest sites was used to derive linear equations that were applied to the remaining data to successfully estimate their nitrogen, lignin, and cellulose concentrations. Correlations were highest for nitrogen (R2 from 0.75 to 0.94). The consistent results indicate the possibility of establishing a single equation capable of estimating the chemical concentrations in a wide variety of species from the reflectance spectra of dried leaves. The extension of this method to remote sensing was investigated. The effects of leaf water content, sensor signal-to-noise and bandpass, atmospheric effects, and background soil exposure were examined. Leaf water was found to be the greatest challenge to extending this empirical method to the analysis of fresh whole leaves and complete vegetation canopies. The influence of leaf water on reflectance spectra must be removed to within 10%. Other effects were reduced by continuum removal and normalization of band depths. If the effects of leaf water can be compensated for, it might be possible to extend this method to remote sensing data acquired by imaging spectrometers to give estimates of nitrogen, lignin, and cellulose concentrations over large areas for use in ecosystem studies.We develop a new method for estimating the biochemistry of plant material using

  20. Propagation of femtosecond laser pulses through water in the linear absorption regime.

    PubMed

    Naveira, Lucas M; Strycker, Benjamin D; Wang, Jieyu; Ariunbold, Gombojav O; Sokolov, Alexei V; Kattawar, George W

    2009-04-01

    We investigate the controversy regarding violations of the Bouguer-Lambert-Beer (BLB) law for ultrashort laser pulses propagating through water. By working at sufficiently low incident laser intensities, we make sure that any nonlinear component in the response of the medium is negligible. We measure the transmitted power and spectrum as functions of water cell length in an effort to confirm or disprove alleged deviations from the BLB law. We perform experiments at two different laser pulse repetition rates and explore the dependence of transmission on pulse duration. Specifically, we vary the laser pulse duration either by cutting its spectrum while keeping the pulse shape near transform-limited or by adjusting the pulses chirp while keeping the spectral intensities fixed. Over a wide range of parameters, we find no deviations from the BLB law and conclude that recent claims of BLB law violations are inconsistent with our experimental data. We present a simple linear theory (based on the BLB law) for propagation of ultrashort laser pulses through an absorbing medium and find our experimental results to be in excellent agreement with this theory.

  1. Dichroism measurements in forensic fibre examination. Part 4-dyed acrylic and acetate fibres.

    PubMed

    De Wael, K

    2012-06-01

    A number of dyed acrylic and acetate fibre samples were examined with plane polarized light on their dichroic behavior by optical light microscopy (OLM) and microspectrophotometry with plane polarized light (MSP-PPL). It was found that most of these low birefringent fibres possess weak dichroic effects that are very hard to observe with microscopy. However, using MSP-PPL, the linear dichroism could be measured. A comparison between the dichroic effects found for the same disperse dyes on triacetate (TrAc), diacetate (Ac), polyester (PES) and polyamide (PA) shows that the linear dichroism follows the order: PA>PES >TrAc, Ac.

  2. Configuration of singular optical cones in gyrotropic crystals with dichroism

    SciTech Connect

    Merkulov, V. S.

    2015-02-15

    Optical conic singularities in crystals with linear dichroism and natural optical activity at the point of intersection of dispersion curves for the main refractive indices are considered. The possible existence of singularities like a nodal point, tangency point, triple point, and cusps of the first and second order is demonstrated. Forty-nine different types of irreducible fourth-order optical cones obtained by sequential bifurcations of eight main singular cones are established. The classification is based on the concept of roughness of systems depending on parameters.

  3. Dichroism measurements in forensic fibre examination. Part 2 - dyed polyamide, wool and silk fibres.

    PubMed

    De Wael, K; Vanden Driessche, T

    2011-12-01

    A number of dyed polyamide, wool and silk samples were examined with plane polarized light on their dichroic behavior by optical light microscopy (OLM) and microspectrophotometry with plane polarized light (MSP-PPL). It was found that most of these acid dyed peptidic fibres possess dichroism, but these are weaker than the effects previously described for polyester fibres. The small effects may be not observed, especially for wool, but these can be measured using MSP-PPL. In the three peptidic fibre classes, for the first time, a so called "inverse dichroism" is observed which appears in the absorption spectra as a hyperchromic effect.

  4. Effect of size and indium-composition on linear and nonlinear optical absorption of InGaN/GaN lens-shaped quantum dot

    NASA Astrophysics Data System (ADS)

    Ahmed, S. Jbara; Zulkafli, Othaman; M, A. Saeed

    2016-05-01

    Based on the Schrödinger equation for envelope function in the effective mass approximation, linear and nonlinear optical absorption coefficients in a multi-subband lens quantum dot are investigated. The effects of quantum dot size on the interband and intraband transitions energy are also analyzed. The finite element method is used to calculate the eigenvalues and eigenfunctions. Strain and In-mole-fraction effects are also studied, and the results reveal that with the decrease of the In-mole fraction, the amplitudes of linear and nonlinear absorption coefficients increase. The present computed results show that the absorption coefficients of transitions between the first excited states are stronger than those of the ground states. In addition, it has been found that the quantum dot size affects the amplitudes and peak positions of linear and nonlinear absorption coefficients while the incident optical intensity strongly affects the nonlinear absorption coefficients. Project supported by the Ministry of Higher Education and Scientific Research in Iraq, Ibnu Sina Institute and Physics Department of Universiti Teknologi Malaysia (UTM RUG Vote No. 06-H14).

  5. Magnetic circular dichroism in the ion yield of polarized chromium atoms at the 2p edge

    SciTech Connect

    Pruemper, G.; Viefhaus, J.; Becker, U.; Kroeger, S.; Mueller, R.; Zimmermann, P.; Martins, M.

    2003-09-01

    The effect of magnetic dichroism in the partial and total ion yield of chromium, i.e., the absorption of polarized chromium vapor was observed in the gas phase. The measurements were performed at the 2p edge and at photon energies above the 2p edge. The structure of the dichroism at the 2p edge can be understood by including the coupling of the 2p hole with the 3d and 4s shells. Our experimental results for the dichroism at the 2p edge are similar to results of solid-state experiments. Implications for the sum rules used as a standard tool to calculate the spin and orbital momentum are discussed.

  6. Supercontinuum of a 3.9 -μ m filament in air: Formation of a two-octave plateau and nonlinearly enhanced linear absorption

    NASA Astrophysics Data System (ADS)

    Panov, Nikolay A.; Shipilo, Daniil E.; Andreeva, Vera A.; Kosareva, Olga G.; Saletsky, Alexander M.; Xu, Huailiang; Polynkin, Pavel

    2016-10-01

    Through numerical simulations we reveal the scenario of 3.9 -μ m filament spectrum enrichment in the atmosphere in the cases of linear and circular polarization of the incident pulse. The discrete spectrum of odd harmonics transforms into the two-octave plateau in the case of linear polarization. In contrast, in the case of circular polarization of the incident pulse, the harmonic-free flat supercontinuum appears with the plasma onset, reaching the tenth harmonic of the input radiation. We identify the energy balance specific to the filamentation near 4 μ m : the absorption on CO2 lines in the atmosphere is accelerated by the self-phase modulation in the Kerr nonlinearity early before the plasma channel is formed. This nonlinearly enhanced linear absorption overwhelms the plasma losses and conversion of the input pulse energy to the higher harmonics as well as the plateau.

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

    ERIC Educational Resources Information Center

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

    2009-01-01

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

  8. Complex polarization propagator calculations of magnetic circular dichroism spectra

    NASA Astrophysics Data System (ADS)

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

    2008-03-01

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

  9. A mixed quantum-classical description of pheophorbide a linear absorption spectra: Quantum-corrections of the Qy- and Qx-absorption vibrational satellites

    NASA Astrophysics Data System (ADS)

    Megow, Jörg; Kulesza, Alexander; May, Volkhard

    2016-01-01

    The ground-state classical path approximation is utilized to compute molecular absorption spectra in a mixed quantum-classical frame. To improve the description for high-frequency vibrational satellites, related quantum correction factors are introduced. The improved method is demonstrated for the Qy- and Qx-bands of pheophorbide a.

  10. Linear Dichroism Characteristics of Ethidium and Proflavine Supercoiled DNA Complexes

    DTIC Science & Technology

    1990-01-01

    of Ethidium-and Proflavine -Supercoi led DNA Complexes CHARLES E. SWENBERG, 1 SUSAN E. CARBERRV, 2 * and NICHOLAS E. GEACINTOV’ SRadliationl Biochenitr...drug were stained with EB, photographed under uv light, molecules, EB and proflavine (PF) (Figure 1), and the bands were quantitated by densitometry

  11. Measurement of dichroism in aligned molecules

    NASA Astrophysics Data System (ADS)

    Lavorel, B.; Babilotte, Ph.; Karras, G.; Billard, F.; Hertz, E.; Faucher, O.

    2016-10-01

    We present dichroism measurements in molecules prealigned with a short and intense laser pulse, using a balanced detection and a pump-probe scheme. The birefringence signal is recorded under the same irradiation conditions along with the dichroism one. Our results show that the dichroism signal is of comparable order of magnitude as the one originating from birefringence and reflects the degree of alignment. The balanced detection scheme directly provides an heterodyne signal for both birefringence and dichroism. Experiments are first conducted in air and then in pure nitrogen and carbon dioxide gases. A general approach allows us to explain the temporal shape of the dichroic response and to extract the imaginary part of the polarizability anisotropy. Furthermore, a simple model invoking the finite response time of the molecule to the probe excitation provides a complementary perspective. Using this model, the phase shift between the oscillations of the probe electric field and the induced polarization can be estimated. We find that the phase shift corresponds to a time delay of about 130 as (10-18s) in both molecules. Calculation of the energy flow between the probe field and the molecules taking into account the phase shift is compared to the experimental data.

  12. All-dielectric metasurface circular dichroism waveplate.

    PubMed

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

    2017-01-31

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

  13. All-dielectric metasurface circular dichroism waveplate

    PubMed Central

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

    2017-01-01

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

  14. All-dielectric metasurface circular dichroism waveplate

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

  15. Flow dichroism in critical colloidal fluids

    SciTech Connect

    Lenstra, T. A. J.; Dhont, J. K. G.

    2001-06-01

    Due to long-range correlations and slow dynamics of concentration fluctuations in the vicinity of the gas-liquid critical point, shear flow is very effective in distorting the microstructure of near-critical fluids. The anisotropic nature of the shear-field renders the microstructure highly anisotropic, leading to dichroism. Experiments on the dichroic behavior can thus be used to test theoretical predictions on microstructural order under shear flow conditions. We performed both static and dynamic dichroism and turbidity measurements on a colloid-polymer mixture, existing of silica spheres (radius 51 nm) and polydimethylsiloxane polymer (molar weight 204 kg/mol). Sufficiently far away from the critical point, in the mean-field region, the experimental data are in good agreement with theory. Very close to the critical point, beyond mean field, for which no theory exists yet, an unexpected decrease of dichroism on approach of the critical point is observed. Moreover, we do not observe critical slowing down of shear-induced dichroism, right up to the critical point, in contrast to the turbidity.

  16. Comparison of absorption spectra of adenocarcinoma and squamous cell carcinoma cervical tissue

    NASA Astrophysics Data System (ADS)

    Peresunko, O. P.; Zelinska, N. V.; Prydij, O. G.; Zymnyakov, D. A.; Ushakova, O. V.

    2013-12-01

    We studied a methods of assessment of a connective tissue of cervix in terms of specific volume of fibrous component and an optical density of staining of connective tissue fibers in the stroma of squamous cancer and cervix adenocarcinoma. An absorption spectra of blood plasma of the patients suffering from squamous cancer and cervix adenocarcinoma both before the surgery and in postsurgical periods were obtained. Linear dichroism measurements transmittance in polarized light at different orientations of the polarization plane relative to the direction of the dominant orientation in the structure of the sample of biotissues of stroma of squamous cancer and cervix adenocarcinoma were carried. Results of the investigation of the tumor tissues showed that the magnitude of the linear dichroism Δ is insignificant in the researched spectral range λ=280-840 nm and specific regularities in its change observed short-wave ranges.

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

    PubMed

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

    2014-10-01

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

  18. Biological Sensing with Terahertz Circular Dichroism Spectroscopy

    DTIC Science & Technology

    2005-05-31

    S.J. and Plaxco, K.W. (2003) “Terahertz circular dichroism spectroscopy: a potential approach to unbiased, in situ life detection.” Astrobiology , 3...detection.” Astrobiology , 3, 489-504 Xu, J., Ramian, G.J., Galan, J.F., Savvidis, P.G., Scopatz, A.M., Birge, R.R., Allen, S.J. and Plaxco, K.W. (2004

  19. DISCO synchrotron-radiation circular-dichroism endstation at SOLEIL.

    PubMed

    Réfrégiers, Matthieu; Wien, Frank; Ta, Ha Phuong; Premvardhan, Lavanya; Bac, Stéphane; Jamme, Frederic; Rouam, Valerie; Lagarde, Bruno; Polack, François; Giorgetta, Jean Luc; Ricaud, Jean Paul; Bordessoule, Michel; Giuliani, Alexandre

    2012-09-01

    The new synchrotron-radiation circular-dichroism (SRCD) endstation on the UV-visible synchrotron beamline DISCO has been commissioned at the SOLEIL synchrotron. The design has been focused on preservation of a high degree of linear polarization at high flux and moderate resolving power covering the vacuum ultraviolet to visible spectral range (125-600 nm). The beam dimensions have been set to 4 mm × 4 mm at 1 nm bandwidth for lower sample degradation. The nitrogen-purged sample chamber fits three types of sample holders accommodating conventional round cell mounting, automated rotation of the samples, as well as a microfluidic set-up. Automated temperature-controlled data collection on microvolumes is now available to the biology and chemistry communities. Macromolecules including membrane proteins, soluble proteins, bio-nanotubes, sugars, DNA and RNAs are now routinely investigated.

  20. Strong magneto-chiral dichroism in a paramagnetic molecular helix observed by hard X-rays

    NASA Astrophysics Data System (ADS)

    Sessoli, Roberta; Boulon, Marie-Emmanuelle; Caneschi, Andrea; Mannini, Matteo; Poggini, Lorenzo; Wilhelm, Fabrice; Rogalev, Andrei

    2015-01-01

    Magneto-chiral dichroism is a non-reciprocal--that is, directional--effect observed in magnetized chiral systems, featuring an unbalanced absorption of unpolarized light depending on the direction of the magnetization. Despite the fundamental interest in a phenomenon breaking both parity and time-reversal symmetries, magneto-chiral dichroism is one of the least investigated aspects of light-matter interaction most likely because of the weakness of the effect in most reported experiments. Here we have exploited the element selectivity of hard X-ray radiation to investigate the magneto-chiral properties of enantiopure crystals of two isostructural molecular helicoidal chains comprising either cobalt(II) or manganese(II) ions. A strong magneto-chiral dichroism, with Kuhn asymmetry of the order of a few per cent, has been observed in the cobalt chains system, whereas it is practically absent for the manganese derivative. The spectral features of the X-ray magneto-chiral dichroism signal differ significantly from the natural and magnetic dichroic contributions and have been rationalized here using the multipolar expansion of matter-radiation interaction.

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

    SciTech Connect

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

    2014-10-15

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

  2. Nanosecond T-jump experiment in poly(glutamic acid): a circular dichroism study.

    PubMed

    Mendonça, Lucille; Hache, François

    2012-01-01

    Poly(glutamic acid) has been studied with a nanosecond T-jump experiment. A new experimental set-up based on the frequency-quadrupling of an 82 MHz Titanium-Sapphire laser allows rapid CD measurements to be performed. Combining time-resolved absorption and circular dichroism at 204 and 220 nm, we are able to measure precisely the unfolding relaxation time as well as the helical fraction evolution. We show that only CD at 220 nm is relevant to observe the unfolding of an alpha helix whereas no change is observed for CD at 204 nm. Conversely, both absorptions yield information on the dynamics of the process.

  3. Vibrational absorption spectra from vibrational coupled cluster damped linear response functions calculated using an asymmetric Lanczos algorithm

    NASA Astrophysics Data System (ADS)

    Thomsen, Bo; Hansen, Mikkel Bo; Seidler, Peter; Christiansen, Ove

    2012-03-01

    We report the theory and implementation of vibrational coupled cluster (VCC) damped response functions. From the imaginary part of the damped VCC response function the absorption as function of frequency can be obtained, requiring formally the solution of the now complex VCC response equations. The absorption spectrum can in this formulation be seen as a matrix function of the characteristic VCC Jacobian response matrix. The asymmetric matrix version of the Lanczos method is used to generate a tridiagonal representation of the VCC response Jacobian. Solving the complex response equations in the relevant Lanczos space provides a method for calculating the VCC damped response functions and thereby subsequently the absorption spectra. The convergence behaviour of the algorithm is discussed theoretically and tested for different levels of completeness of the VCC expansion. Comparison is made with results from the recently reported [P. Seidler, M. B. Hansen, W. Györffy, D. Toffoli, and O. Christiansen, J. Chem. Phys. 132, 164105 (2010)] vibrational configuration interaction damped response function calculated using a symmetric Lanczos algorithm. Calculations of IR spectra of oxazole, cyclopropene, and uracil illustrate the usefulness of the new VCC based method.

  4. Vibrational absorption spectra from vibrational coupled cluster damped linear response functions calculated using an asymmetric Lanczos algorithm.

    PubMed

    Thomsen, Bo; Hansen, Mikkel Bo; Seidler, Peter; Christiansen, Ove

    2012-03-28

    We report the theory and implementation of vibrational coupled cluster (VCC) damped response functions. From the imaginary part of the damped VCC response function the absorption as function of frequency can be obtained, requiring formally the solution of the now complex VCC response equations. The absorption spectrum can in this formulation be seen as a matrix function of the characteristic VCC Jacobian response matrix. The asymmetric matrix version of the Lanczos method is used to generate a tridiagonal representation of the VCC response Jacobian. Solving the complex response equations in the relevant Lanczos space provides a method for calculating the VCC damped response functions and thereby subsequently the absorption spectra. The convergence behaviour of the algorithm is discussed theoretically and tested for different levels of completeness of the VCC expansion. Comparison is made with results from the recently reported [P. Seidler, M. B. Hansen, W. Györffy, D. Toffoli, and O. Christiansen, J. Chem. Phys. 132, 164105 (2010)] vibrational configuration interaction damped response function calculated using a symmetric Lanczos algorithm. Calculations of IR spectra of oxazole, cyclopropene, and uracil illustrate the usefulness of the new VCC based method.

  5. Calculation of the circular dichroism spectra of carbon monoxy- and deoxy myoglobin: interpretation of a time-resolved circular dichroism experiment.

    PubMed

    Dartigalongue, Thibault; Hache, François

    2005-11-08

    A calculation of the circular dichroism (CD) spectra of carbon monoxy- and deoxy myoglobin is carried out in relation with a time-resolved CD experiment. The calculation is based on the polarizability theory and the parameters are adjusted to fit the experimental absorption and CD spectra. By performing the calculation for intermediate configurations of the protein, we are able to propose an explanation of the CD structure observed on a sub-100 ps time scale. The role of the proximal histidine is, in particular, clearly demonstrated in the first step of the myoglobin relaxation from its liganded to it deliganded form.

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

    NASA Astrophysics Data System (ADS)

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

    2011-08-01

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

  7. Characterization of Co distribution in ZnO by x-ray magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Zhang, Y.; Wang, Z.; Cao, J. X.

    2013-05-01

    We analyze the electronic and magnetic properties of the various atomic arrangements of Zn1-xCoxO with x = 10% using K-edge x-ray absorption and magnetic circular dichroism spectra from both measurements and first principle calculations. Significantly, the K-edge spectroscopic features of Co are highly sensitive to the local atomic arrangement, and thus can be used as a powerful tool to investigate structural properties of dilute magnetic semiconductors. We clearly showed that defects such as interstitial Co and O vacancy near to substitutional Co are present in the 10% Co doped ZnO sample. The magnetic ordering of ZnO-based diluted magnetic semiconductors is strongly correlated with the presence of oxygen vacancies. Finally, we elucidated the origin of the X-ray magnetic circular dichroism signals.

  8. Donor impurity-related linear and nonlinear intraband optical absorption coefficients in quantum ring: effects of applied electric field and hydrostatic pressure

    PubMed Central

    2012-01-01

    The linear and nonlinear intraband optical absorption coefficients in GaAs three-dimensional single quantum rings are investigated. Taking into account the combined effects of hydrostatic pressure and electric field, applied along the growth direction of the heterostructure, the energies of the ground and first excited states of a donor impurity have been found using the effective mass approximation and a variational method. The energies of these states are examined as functions of the dimensions of the structure, electric field, and hydrostatic pressure. We have also investigated the dependencies of the linear, nonlinear, and total optical absorption coefficients as a function of incident photon energy for several configurations of the system. It is found that the variation of distinct sizes of the structure leads to either a redshift and/or a blueshift of the resonant peaks of the intraband optical spectrum. In addition, we have found that the application of an electric field leads to a redshift, whereas the influence of hydrostatic pressure leads to a blueshift (in the case of on-ring-center donor impurity position) of the resonant peaks of the intraband optical spectrum. PMID:23021497

  9. Photoelectron circular dichroism in different ionization regimes

    NASA Astrophysics Data System (ADS)

    Wollenhaupt, Matthias

    2016-12-01

    Photoelectron circular dichroism (PECD) describes an asymmetry in the photoelectron angular distribution (PAD) from photoionization of randomly oriented enantiomers with circularly polarized light. Baulieu et al present a comprehensive set of measured PADs from multiphoton ionization of limonene and fenchone in different ionization regimes (multiphoton and tunneling) and analyze the resulting PECD (Baulieu et al 2016 New J. Phys. 18 102002). From their observations the authors conclude that the PECD is universal in the sense that the molecular chirality is encoded in the PAD independent of the ionization regime. The analysis is supplemented by a classical model based on electron scattering in a chiral potential. The paper presents beautiful data and is an important step towards a more complete physical picture of PECD. The results and their interpretation stimulate the ongoing vivid debate on the role of resonances in multiphoton PECD.

  10. Circular dichroism of erythrocyte membrane glycoproteins.

    PubMed

    Decker, R V; Carraway, K L

    1975-03-28

    The circular dichroism spectra were obtained for purified equine, human and bovine membrane glycoproteins, which have 40, 55 and 70% carbohydrate, respectively. The spectra in aqueous buffer show similar shapes, maxima and minima but somewhat different peak amplitudes. Analysis of the spectra indicated that the glycoproteins can be pictured as existing primarily in an unordered form in dilute aqueous buffer with small amounts of alpha-helix (13-23%) present. In 2-chloroethanol, a helix-promoting solvent, the amount of alpha-helix is increased to 60-70%. The glycoproteins underwent denaturation in guanidine hydrochloride, although evidence of some residual structure did remain. The spectra of the glycoproteins change relatively little on going from aqueous buffer to dodecylsulfate solutions. Removal of 60% of the sialic acid does not induce significant conformational alterations. The anomalous behavior of the glycoproteins during molecular weight determinations does not appear to be related primarily to conformational restrictions on the polypeptide chain.

  11. Optical properties and circular dichroism of chiral metal nanoparticles

    NASA Astrophysics Data System (ADS)

    Fan, Zhiyuan; Govorov, Alexander; OU Team

    2013-03-01

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

  12. Structural, thermal, linear and nonlinear optical studies of an organic optical limiter based on reverse saturable absorption

    NASA Astrophysics Data System (ADS)

    Menezes, Anthoni Praveen; Raghavendra, S.; Jayarama, A.; Sarveshwara, H. P.; Dharmaprakash, S. M.

    2016-09-01

    A new derivative of chalcone, 3-(4-bromophenyl)-1-(pyridin-4-yl) prop-2-en-1-one (4BP4AP), crystallizing in centrosymmetric structure has been synthesized using the Claisen-Schmidt condensation reaction method. The FTIR and FT-Raman spectral studies were carried out on 4BP4AP for structural conformation. The single crystals were grown using slow evaporation solution growth technique. The single crystal XRD of the crystal shows that the crystal system of 4BP4AP is triclinic with space group P-1. Scanning electron microscope images enunciate the surface smoothness and the two dimensional growth mechanisms in the crystal. The crystal is transparent in the entire visible region as indicated by the UV-VIS-NIR spectrum. The thermal stability and phase transition of the compound was studied by thermogravimetric and differential scanning calorimetric analysis and found to be stable up to 200 °C. By performing the open aperture z-scan experiment, nonlinear absorption and optical limiting behavior of the crystal were studied. The crystal can be used for optoelectronic application due to its excellent photo-physical properties.

  13. Elimination of artifacts derived from the residual birefringence of a phase modulator for circular dichroism by retardation domain analysis.

    PubMed

    Satozono, Hiroshi

    2015-04-01

    It is well known that various artifacts interfere with circular dichroism (CD) measurement using the polarization modulation technique. In this report, we propose a simple analysis method for eliminating the artifacts derived from the residual birefringence of a phase modulator. We consider the origin of the artifacts and find that those in CD can be distinguished by analyzing signals as a function of the retardation of the phase modulator using a Mueller matrix method. We experimentally obtain pure CD from a sample with CD and linear dichroism by applying retardation domain analysis.

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

    PubMed

    Goings, Joshua J; Li, Xiaosong

    2016-06-21

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

  15. Spin-induced polarizations and nonreciprocal directional dichroism of the room-temperature multiferroic BiFeO3

    NASA Astrophysics Data System (ADS)

    Fishman, Randy S.; Lee, Jun Hee; Bordács, Sándor; Kézsmárki, István; Nagel, Urmas; Rõõm, Toomas

    2015-09-01

    A microscopic model for the room-temperature multiferroic BiFeO3 that includes two Dzyaloshinskii-Moriya interactions and single-ion anisotropy along the ferroelectric polarization predicts both the zero-field spectroscopic modes as well as their splitting and evolution in a magnetic field. Due to simultaneously broken time-reversal and spatial-inversion symmetries, the absorption of light changes as the magnetic field or the direction of light propagation is reversed. We discuss three physical mechanisms that may contribute to this absorption asymmetry known as nonreciprocal directional dichroism: the spin current, magnetostriction, and single-ion anisotropy. We conclude that the nonreciprocal directional dichroism in BiFeO3 is dominated by the spin-current polarization and is insensitive to the magnetostriction and easy-axis anisotropy. With three independent spin-current parameters, our model accurately describes the nonreciprocal directional dichroism observed for magnetic field along [1 ,-1 ,0 ] . Since some modes are almost transparent to light traveling in one direction but opaque for light traveling in the opposite direction, BiFeO3 behaves as a room-temperature optical diode at certain frequencies in the gigahertz to terahertz range. Our work demonstrates that an analysis of the nonreciprocal directional dichroism spectra based on an effective spin model supplemented by first-principles calculations can produce a quantitative microscopic theory of the magnetoelectric couplings in multiferroic materials.

  16. Spin-Induced Polarizations and Nonreciprocal Directional Dichroism of the Room-Temperature Multiferroic BiFeO3

    DOE PAGES

    Fishman, Randy Scott; Lee, Jun Hee; Bordacs, Sandor; ...

    2015-09-14

    A microscopic model for the room-temperature multiferroic BiFeO3 that includes two Dzyaloshinskii-Moriya interactions and single-ion anisotropy along the ferroelectric polarization predicts both the zero-field spectroscopic modes as well as their splitting and evolution in a magnetic field. Due to simultaneously broken time-reversal and spatial-inversion symmetries, the absorption of light changes as the magnetic field or the direction of light propagation is reversed. We discuss three physical mechanisms that may contribute to this absorption asymmetry known as directional dichroism: the spin current, magnetostriction, and single-ion anisotropy. We conclude that the directional dichroism in BiFeO3 is dominated by the spin-current polarization andmore » is insensitive to the magnetostriction and easy-axis anisotropy. With three independent spin-current parameters, our model accurately describes the directional dichroism observed for magnetic field along [1, -1, 0]. Since some modes are almost transparent to light traveling in one direction but opaque for light traveling in the opposite direction, BiFeO3 can be used as a room-temperature optical diode at certain frequencies in the GHz to THz range. This work demonstrates that an analysis of the directional dichroism spectra based on an effective spin model supplemented by first-principles calculations can produce a quantitative microscopic theory of the magnetoelectric couplings in multiferroic materials.« less

  17. Photoemission and magnetic circular dichroism studies of magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Fujimori, Atsushi

    2005-03-01

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

  18. Magnetic circular dichroism for surface and thin film magnetism

    NASA Astrophysics Data System (ADS)

    Yokoyama, Toshihiko; Nakagawa, Takeshi; Takagi, Yasumasa

    The technical development of the characterization of magnetic thin films is an urgent subject especially for further improvement of high-density and high-speed recording media. This article focuses attention on the fundamental methodology and recent exploitations of various magnetic circular dichroism (MCD) techniques. First, basic theories and experimental methods of the magneto-optical Kerr effect (MOKE) and X-ray magnetic circular dichroism (XMCD) are described. MOKE is a conventional but usually the most useful method to characterize macroscopic magnetization of metal thin films using visible lasers. Moreover, recent development of MOKE allows one to perform optical microscopic and ultrafast time resolved investigations. XMCD has now become a mature technique by virtue of the developments of soft and hard X-ray synchrotron radiation sources. Since XMCD is based on core absorption spectroscopy, the technique provides information on element specific magnetization. Using the so-called sum rules, one can determine the microscopic spin and orbital magnetic moments. The experimental method and an example using a superconducting magnet system combined with a liquid helium sample cryostat are described. Moreover, by combining XMCD with photoelectron emission microscopy (PEEM), one can perform spatiotemporal measurements, whose spatial resolution reaches several tens of nanometres. Magnetization induced second harmonic generation (MSHG) is also described. This is a unique technique for its inherently high sensitivity to surfaces and interfaces since MSHG is inhibited in the bulk of centrosymmetric crystals. The drastic polarization dependence of MSHG based on the selection rules is also discussed. As a last method addressed in this article, the threshold photoemission MCD technique is reviewed. The technique has recently been proposed and has demonstrated the possibility of an ultrafast spatiotemporal method by combining PEEM. Applications of these various MCD families

  19. Determination of the quasi-TE mode (in-plane) graphene linear absorption coefficient via integration with silicon-on-insulator racetrack cavity resonators.

    PubMed

    Crowe, Iain F; Clark, Nicholas; Hussein, Siham; Towlson, Brian; Whittaker, Eric; Milosevic, Milan M; Gardes, Frederic Y; Mashanovich, Goran Z; Halsall, Matthew P; Vijayaraghaven, Aravind

    2014-07-28

    We examine the near-IR light-matter interaction for graphene integrated cavity ring resonators based on silicon-on-insulator (SOI) race-track waveguides. Fitting of the cavity resonances from quasi-TE mode transmission spectra reveal the real part of the effective refractive index for graphene, n(eff) = 2.23 ± 0.02 and linear absorption coefficient, α(gTE) = 0.11 ± 0.01dBμm(-1). The evanescent nature of the guided mode coupling to graphene at resonance depends strongly on the height of the graphene above the cavity, which places limits on the cavity length for optical sensing applications.

  20. Contribution of the transition moments, form of the absorption band, exciton, and the correlation effects in the linear and nonlinear optical properties of conjugated polymers

    NASA Astrophysics Data System (ADS)

    Díaz-Ponce, Javier Alejandro

    2017-04-01

    This work compares the linear and nonlinear optical properties of polyenes and polyenynes. The simulation was made for finite and infinite conjugation of conjugated polymers, such as polyacetylene, β-carotene, bis (p-toluene sulfonate) (PTS) polyenyne, and a short conjugated polyenyne poly-2,6-decadyin-1,6-ylene azelate (PHDAz). The resonance energy and degree of conjugation are determined by fitting the linear absorption spectra. These parameters are then used for calculating the two photon and third-order nonlinear optical properties. The contribution of the transition moment, the form of the absorption band, the exciton, and phonons in the optical properties are determined. The difference of the experimental values is assigned to correlation effects. We found that the exciton, the correlation effects, and the conduction band are more important in the optical properties of polyenynes than of polyenes. In this way, the dependence of the optical properties of polyenynes on the conduction band makes it possible to increase their nonlinear optical properties by interaction with photons (θ ≈ 0). The dependence of the optical properties on the conduction band also produces that the finiteness of the conjugation strongly decreases the optical properties of polyenynes in relation to polyenes with similar conjugation. On the other hand, the phonons are more important in the optical properties of polyenes than of polyenynes. Consequently, the band is indirect for the studied polyenes and direct for the polyenynes. Therefore, the nonlinear optical properties in the resonance frequency of polyenyne PTS are higher than those for polyacetylene. We also found that asymmetric oscillations of χ(3) in the Brillouin zone increases the χ(3) final value in polyenynes. In addition, we found a change of sign of the wave function coefficients by the Peierls distortion of polyenes to become polyenynes, but this change of sign does not affect the optical properties. As a corollary

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

    SciTech Connect

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

    2007-08-15

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

  2. A magnetizing system for dichroism measurements in soft x-ray emission excited by synchrotron radiation

    SciTech Connect

    Dallera, C.; Ghiringhelli, G.; Braicovich, L.

    1996-02-01

    We present the design and performance of a magnetic circuit suitable for magnetizing solid samples in the measurements of soft x-ray emission dichroism excited by synchrotron radiation. The system allows a variety of samples to be magnetized and satisfies the rather stringent geometrical constraints due to the need for minimizing the effect of photon self-absorption by the sample. The magnetic circuit is ultrahigh vacuum compatible, can reach about 2800 G, and allows fine adjustment of sample position. {copyright} {ital 1996 American Institute of Physics.}

  3. Dichroism measurements in forensic fibre examination Part 1--Dyed polyester fibres.

    PubMed

    De Wael, K; Vanden Driessche, T

    2011-06-01

    One hundred and twenty dyed polyester samples were examined with plane polarized light on their dichroic behaviour by optical light microscopy (OLM) and microspectrophotometry in the visible range (MSP Vis). It was found that most of these disperse dyed polyester fibres possess a strong dichroism, which fall into two broad categories. Either a decrease of intensity (hypochromic effect) or a change of hue (hypsochromic or bathochromic shift of absorption bands) is noted. These dichroic effects are related to the orientation of the dye structure with respect to the polymer chains.

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

    NASA Astrophysics Data System (ADS)

    Shvets, Gennady B.

    2016-09-01

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

  5. Effects of temperature dependent conductivity and absorptive/generative heat transfer on MHD three dimensional flow of Williamson fluid due to bidirectional non-linear stretching surface

    NASA Astrophysics Data System (ADS)

    Bilal, S.; Khalil-ur-Rehman; Malik, M. Y.; Hussain, Arif; Khan, Mair

    Present work is communicated to identify characteristics of magnetohydrodynamic (MHD) three dimensional boundary layer flow of Williamson fluid confined by a bidirectional stretched surface. Conductivity of working fluid is assumed to be temperature dependent. Generative/absorptive heat transfer is also taken into account. Mathematical model is formulated in the form of partial expressions and then transmuted into ordinary differential equations with the help of newfangled set of similarity transformations. The resulting non-linear differential system of equations is solved numerically with the aid of Runge-Kutta algorithm supported by shooting method. Flow features are exemplified quantitatively through graphs. Scintillating results for friction factor and convective heat transfer are computed and scrutinized tabularly. Furthermore, the accuracy of present results is tested with existing literature and we found an excellent agreement. It is inferred that velocity along x-direction mounts whereas along y-direction depreciates for incrementing values of stretching ratio parameter. Moreover, it is also elucidated that non-linearity index tends to decrement the velocity and thermal distributions of fluid flow.

  6. On the existence of Jones birefringence and Jones dichroism.

    PubMed

    Arteaga, Oriol

    2010-05-01

    We claim that the so-called Jones birefringence and Jones dichroism effects, understood as new optical phenomena of difficult experimental observation, cannot be deduced from Jones publications and were proposed due to a misinterpretation of his original work.

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

    PubMed Central

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

    2015-01-01

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

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

    PubMed

    Hussain, Rohanah; Jávorfi, Tamás; Siligardi, Giuliano

    2012-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-09-01

    Apomorphine is a chiral drug molecule; notwithstanding its extraordinary importance, little attention has been paid to the characterization of its chiroptical properties. Here we report on its electronic circular dichroism (ECD) spectra, recorded in methanol and water, and vibrational circular dichroism (VCD) in methanol and dimethyl sulfoxide (DMSO) solutions. Density functional theory (DFT) calculations have allowed us to interpret the spectra and to evaluate the role of possible conformations, charge-states and interactions with counter ions.

  10. Z-DNA: vacuum ultraviolet circular dichroism

    SciTech Connect

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

    1981-08-01

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

  11. Z-DNA Vacuum ultraviolet circular dichroism

    SciTech Connect

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

    1981-08-01

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

  12. Induced circular dichroism of polyoxometalates via electrostatic encapsulation with chiral organic cations.

    PubMed

    Wang, Yizhan; Shi, Lei; Yang, Yang; Li, Bao; Wu, Lixin

    2014-09-21

    To explore the principle of chiral induction in inorganic clusters, chiral organic cations with two stereocenters, R- and S-BPEA, are used to encapsulate a series of polyoxometalates (POMs) bearing different structures and transition absorption bands in aqueous solution, constructing a series of chiral supramolecular complexes. Due to the induction of chiral organic cations, POMs possessing both chiral and achiral structures show an induced circular dichroism (ICD) effect. ICD signals in the absorption bands corresponding to ligand to metal charge transfer (LMCT) transitions, d-d transitions and intervalence charge transfer (IVCT) transitions are observed for different complexes. Moreover, the ICD of the POMs exhibits a direct correlation with the degree of POM distortion and the distance between the chiral center and the POM surface. The encapsulation of POMs with chiral organic cations via electrostatic interactions provides a facile and effective method for constructing optically pure POM-based materials.

  13. Circular dichroism of a finite number of identical chromophores in a helical arrangement.

    PubMed

    Dick, Bernhard

    2011-06-06

    Compact expressions to calculate the transition energies, absorption line strengths, and rotational line strengths of circular dichroism for the excitonic states in a helical arrangement of N identical chromophores are presented. The absorption spectrum A(ν) and the CD spectrum C(ν) are given in terms of the same function G(ν,α) as A(ν) = a(1)G(ν,0) + a(2)G(ν,α), C(ν) = (s(1) - s(2))G(ν,α) + s(3)(d/dα)G(ν,α). The function G(ν,α) depends only on the helical angle α and the number N of interacting chromophores. An analytical expression can be given when only next-neighbor interactions are considered. All other structural parameters of the system (e.g. orientation of transition dipoles and the translation vector of the helix) enter only into the prefactors a(j) and s(j).

  14. Conformational changes in photoexcited (R)-(+)-1,1'-bi-2-naphthol studied by time-resolved circular dichroism.

    PubMed

    Niezborala, Claire; Hache, François

    2008-09-24

    Conformational changes following photoexcitation of ( R)-(+)-1,1'-bi-2-naphthol are studied with a time-resolved circular dichroism (CD) experiment. Two wavelengths are investigated. For lambda = 237 nm, we observe a bleaching of the ground-state absorption and a transient CD structure. Thanks to a coupled-oscillator calculation, we can attribute this effect to a decrease of the dihedral angle. For lambda = 245 nm, excited-state absorption and CD are observed. All these effects are solvent-dependent. In particular, it is shown that dynamics is slower in a protic solvent, which is attributed to hydrogen-bonding of the hydroxy groups with the solvent.

  15. Circular dichroism and magnetic circular dichroism of Azotobacter vinelandii ferredoxin I.

    PubMed

    Stephens, P J; Jensen, G M; Devlin, F J; Morgan, T V; Stout, C D; Martin, A E; Burgess, B K

    1991-04-02

    Room temperature circular dichroism (CD) and low temperature magnetic circular dichroism (MCD) spectra of air-oxidized and dithionite-reduced Azotobacter vinelandii ferredoxin I (FdI), a [( 4Fe-4S]2+/1+, [3Fe-4S]1+/0) protein, are reported. Unlike the CD of oxidized FdI, the CD of dithionite-reduced FdI exhibits significant pH dependence, consistent with protonation-deprotonation at or near the cluster reduced: the [3Fe-4S] cluster. The MCD of reduced FdI, which originates in the paramagnetic reduced [3Fe-4S]0 cluster, is also pH-dependent. Detailed studies of the field dependence and temperature dependence of the MCD of oxidized and reduced FdI, in the latter case at pH 6.0 and 8.3, are reported. The low-field temperature dependence of the MCD of oxidized FdI, which originates in the paramagnetic oxidized [3Fe-4S]1+ cluster, establishes the absence of a significant population of excited electronic states of this cluster up to 60 K. The low-field temperature dependence of the MCD of reduced FdI establishes that the ground-state manifold of the reduced [3Fe-4S]0 cluster possesses S greater than or equal to 2 at both pH 6.0 and 8.3. Analysis, assuming S = 2 and an axial zero-field splitting Hamiltonian, leads to D = -2.0 and -3.5 cm-1 at pH 6.0 and 8.3, respectively. The site of the (de)protonation affecting the spectroscopic properties of the [3Fe-4S] cluster remains unknown.

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

    SciTech Connect

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

    2011-06-12

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

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

    SciTech Connect

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

    2012-03-01

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

  18. X-ray absorption near edge structure/electron energy loss near edge structure calculation using the supercell orthogonalized linear combination of atomic orbitals method

    NASA Astrophysics Data System (ADS)

    Ching, Wai-Yim; Rulis, Paul

    2009-03-01

    Over the last eight years, a large number of x-ray absorption near edge structure (XANES) and/or electron energy loss near edge structure (ELNES) spectroscopic calculations for complex oxides and nitrides have been performed using the supercell-OLCAO (orthogonalized linear combination of atomic orbitals) method, obtaining results in very good agreement with experiments. The method takes into account the core-hole effect and includes the dipole matrix elements calculated from ab initio wavefunctions. In this paper, we describe the method in considerable detail, emphasizing the special advantages of this method for large complex systems. Selected results are reviewed and several hitherto unpublished results are also presented. These include the Y K edge of Y ions segregated to the core of a Σ31 grain boundary in alumina, O K edges of water molecules, C K edges in different types of single walled carbon nanotubes, and the Co K edge in the cyanocobalamin (vitamin B12) molecule. On the basis of these results, it is argued that the interpretation of specific features of the calculated XANES/ELNES edges is not simple for complex material systems because of the delocalized nature of the conduction band states. The long-standing notion of the 'fingerprinting' technique for spectral interpretation of experimental data is not tenable. A better approach is to fully characterize the structure under study, using either crystalline data or accurate ab initio modeling. Comparison between calculated XANES/ELNES spectra and available measurements enables us to ascertain the validity of the modeled structure. For complex crystals or structures, it is necessary to use the weighted sum of the spectra from structurally nonequivalent sites for comparison with the measured data. Future application of the supercell-OLCAO method to complex biomolecular systems is also discussed.

  19. Giant local circular dichroism within an asymmetric plasmonic nanoparticle trimer.

    PubMed

    Wang, Hancong; Li, Zhipeng; Zhang, Han; Wang, Peijie; Wen, Shuangchun

    2015-02-03

    We investigated the near-field response in silver nanoparticle aggregates to the excitation of circular polarized light. In a right-angle trimer system, the local field intensity excited by right-hand circularly polarized light is almost one thousand times larger than the left-hand case. By analyzing the polarization and phase of the local field in plasmonic hotspots, we found this local circular dichroism is originated from the near-field interference excited by orthogonal polarized incident lights. The local circular dichroism can be tuned by the rotation of the third particle, the interparticle distance, and the dielectric environment. This phenomenon could also widely exist in more complicated nanoaggregates. These findings would benefit for resolving light handedness, and enhancing circular dichroism and optical activity.

  20. Strong magneto-chiral dichroism in a paramagnetic molecular helix observed by hard X-ray

    PubMed Central

    Sessoli, Roberta; Boulon, Marie-Emmanuelle; Caneschi, Andrea; Mannini, Matteo; Poggini, Lorenzo; Wilhelm, Fabrice; Rogalev, Andrei

    2014-01-01

    Magneto-chiral dichroism (MχD) is a non-reciprocal, i. e. directional, effect observed in magnetised chiral systems featuring an unbalanced absorption of unpolarised light depending on the direction of the magnetisation. Despite the fundamental interest in a phenomenon breaking both parity and time reversal symmetries, MχD is one of the least investigated aspects of light-matter interaction because of the weakness of the effect in most reported experiments. Here we have exploited the element selectivity of hard X-ray radiation to investigate the magneto-chiral properties of enentiopure crsytals of two isostructural molecular helicoidal chains comprising Cobalt(II) and Manganese (II) ions, respectively. A strong magneto-chiral dichroism, with Kuhn asymmetry of the order of a few percent, has been observed in the Cobalt chain system, while it is practically absent for the Manganese derivative. The spectral features of the XMχD signal differ significantly from the natural and magnetic dichroic contributions and have been here rationalized using the simple multipolar expansion of matter-radiation interaction. PMID:25729401

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

    PubMed

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

    2015-11-17

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

  2. Synchrotron radiation circular dichroism spectroscopy applied to metmyoglobin and a 4-alpha-helix bundle carboprotein.

    PubMed

    Thulstrup, Peter W; Brask, Jesper; Jensen, Knud J; Larsen, Erik

    2005-05-01

    The novel technique, synchrotron radiation-based circular dichroism (SR-CD), has been applied to the study of metmyoglobin and a carboprotein (carbohydrate-based peptide with protein tertiary structure) with 4-alpha-helix bundle structure, as well as a carbopeptide (carbohydrate-based peptide) with a truncated peptide sequence. The use of synchroton radiation (SR) enabled circular dichroism (CD) measurements in the vacuum ultraviolet (VUV) down to 168 nm in D(2)O and 160 nm in 2,2,2-trifluoroethanol (TFE). The band shape in the CD spectra in the low wavelength region was studied, comparing samples with two types of alpha-helical tertiary structure, namely the globin fold and the 4-alpha-helix bundle motif. No significant differences were found between the CD spectra of the alpha-helical samples (metmyoglobin and carboprotein) in D(2)O solution. The use of 2,2,2-TFE (TFE) as solvent clearly alters the VUV CD but the two samples have very similar CD spectra. The solvent-induced denaturing of metmyoglobin in TFE was observed using absorption and CD spectroscopy of the Soret band, with results indicating heme release. The VUV spectrum of TFE-denatured metmyoglobin exhibits dramatic differences in comparison with previous studies of the native enzyme in aqueous solution. The implications of this observation are discussed.

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

    PubMed Central

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

    2015-01-01

    We demonstrate, to our knowledge, the first bright circularly polarized high-harmonic beams in the soft X-ray region of the electromagnetic spectrum, and use them to implement X-ray magnetic circular dichroism measurements in a tabletop-scale setup. Using counterrotating circularly polarized laser fields at 1.3 and 0.79 µm, we generate circularly polarized harmonics with photon energies exceeding 160 eV. The harmonic spectra emerge as a sequence of closely spaced pairs of left and right circularly polarized peaks, with energies determined by conservation of energy and spin angular momentum. We explain the single-atom and macroscopic physics by identifying the dominant electron quantum trajectories and optimal phase-matching conditions. The first advanced phase-matched propagation simulations for circularly polarized harmonics reveal the influence of the finite phase-matching temporal window on the spectrum, as well as the unique polarization-shaped attosecond pulse train. Finally, we use, to our knowledge, the first tabletop X-ray magnetic circular dichroism measurements at the N4,5 absorption edges of Gd to validate the high degree of circularity, brightness, and stability of this light source. These results demonstrate the feasibility of manipulating the polarization, spectrum, and temporal shape of high harmonics in the soft X-ray region by manipulating the driving laser waveform. PMID:26534992

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

    NASA Astrophysics Data System (ADS)

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

    2012-01-01

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

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

    SciTech Connect

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

    1980-04-01

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

  6. Circular Dichroism Method for Heat Capacity Determination of Proteins

    ERIC Educational Resources Information Center

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

    2006-01-01

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

  7. Magneto-chiral dichroism measurements using a pulsed electromagnet

    NASA Astrophysics Data System (ADS)

    Hattori, Shingo; Yamamoto, Yusuke; Miyatake, Tomohiro; Ishii, Kazuyuki

    2017-04-01

    A system for measuring magneto-chiral dichroism (MChD) under strong magnetic fields using a pulsed electromagnet was constructed. We succeeded in observing a relatively intense MChD signal for chiral J-aggregates of a zinc chlorin at 5 T using this measurement system. This study will be useful for observing weak MChD signals of various organic molecules.

  8. Non-linear absorption of 1.3-μm wavelength femtosecond laser pulses focused inside semiconductors: Finite difference time domain-two temperature model combined computational study

    NASA Astrophysics Data System (ADS)

    Bogatyrev, I. B.; Grojo, D.; Delaporte, P.; Leyder, S.; Sentis, M.; Marine, W.; Itina, T. E.

    2011-11-01

    We present a theoretical model, which describes local energy deposition inside IR-transparent silicon and gallium arsenide with focused 1.3-μm wavelength femtosecond laser pulses. Our work relies on the ionization rate equation and two temperature model (TTM), as we simulate the non-linear propagation of focused femtosecond light pulses by using a 3D finite difference time domain method. We find a strong absorption dependence on the initial free electron density (doping concentration) that evidences the role of avalanche ionization. Despite an influence of Kerr-type self-focusing at intensity required for non-linear absorption, we show the laser energy deposition remains confined when the focus position is moved down to 1-mm below the surface. Our simulation results are in agreement with the degree of control observed in a simple model experiment.

  9. Spin-Induced Polarizations and Nonreciprocal Directional Dichroism of the Room-Temperature Multiferroic BiFeO3

    SciTech Connect

    Fishman, Randy Scott; Lee, Jun Hee; Bordacs, Sandor; Kezsmarki, Istvan; Nagel, Urmas; Room, Toomas

    2015-09-14

    A microscopic model for the room-temperature multiferroic BiFeO3 that includes two Dzyaloshinskii-Moriya interactions and single-ion anisotropy along the ferroelectric polarization predicts both the zero-field spectroscopic modes as well as their splitting and evolution in a magnetic field. Due to simultaneously broken time-reversal and spatial-inversion symmetries, the absorption of light changes as the magnetic field or the direction of light propagation is reversed. We discuss three physical mechanisms that may contribute to this absorption asymmetry known as directional dichroism: the spin current, magnetostriction, and single-ion anisotropy. We conclude that the directional dichroism in BiFeO3 is dominated by the spin-current polarization and is insensitive to the magnetostriction and easy-axis anisotropy. With three independent spin-current parameters, our model accurately describes the directional dichroism observed for magnetic field along [1, -1, 0]. Since some modes are almost transparent to light traveling in one direction but opaque for light traveling in the opposite direction, BiFeO3 can be used as a room-temperature optical diode at certain frequencies in the GHz to THz range. This work demonstrates that an analysis of the directional dichroism spectra based on an effective spin model supplemented by first-principles calculations can produce a quantitative microscopic theory of the magnetoelectric couplings in multiferroic materials.

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

    SciTech Connect

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

    2006-07-15

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

  11. X-ray magnetic dichroism in (Zn,Mn)O diluted magnetic semiconductors: First-principles calculations

    NASA Astrophysics Data System (ADS)

    Antonov, V. N.; Bekenov, L. V.; Mazur, D. V.; Germash, L. P.

    2012-06-01

    The electronic structure of (Zn,Mn)O diluted magnetic semiconductors was investigated theoretically from first principles by using the fully-relativistic Dirac linear muffin-tin orbital band structure method with the local spin-density approximation (LSDA) and the LSDA+ U approach. The X-ray magnetic circular dichroism (XMCD) spectra at the Mn, Zn, and O K and Mn L 2,3 edges were investigated theoretically from first principles. The origin of the XMCD spectra in these compounds was examined. The effect of oxygen vacancy atoms was found to be crucial for the X-ray magnetic dichroism at the Mn L 2,3 edges. The calculated results are compared with available experimental data.

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

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

    NASA Astrophysics Data System (ADS)

    Rizzo, Antonio; Lin, Na; Ruud, Kenneth

    2008-04-01

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

  14. PCDDB: new developments at the Protein Circular Dichroism Data Bank.

    PubMed

    Whitmore, Lee; Miles, Andrew John; Mavridis, Lazaros; Janes, Robert W; Wallace, B A

    2017-01-04

    The Protein Circular Dichroism Data Bank (PCDDB) has been in operation for more than 5 years as a public repository for archiving circular dichroism spectroscopic data and associated bioinformatics and experimental metadata. Since its inception, many improvements and new developments have been made in data display, searching algorithms, data formats, data content, auxillary information, and validation techniques, as well as, of course, an increase in the number of holdings. It provides a site (http://pcddb.cryst.bbk.ac.uk) for authors to deposit experimental data as well as detailed information on methods and calculations associated with published work. It also includes links for each entry to bioinformatics databases. The data are freely available to accessors either as single files or as complete data bank downloads. The PCDDB has found broad usage by the structural biology, bioinformatics, analytical and pharmaceutical communities, and has formed the basis for new software and methods developments.

  15. PCDDB: new developments at the Protein Circular Dichroism Data Bank

    PubMed Central

    Whitmore, Lee; Miles, Andrew John; Mavridis, Lazaros; Janes, Robert W.; Wallace, B.A.

    2017-01-01

    The Protein Circular Dichroism Data Bank (PCDDB) has been in operation for more than 5 years as a public repository for archiving circular dichroism spectroscopic data and associated bioinformatics and experimental metadata. Since its inception, many improvements and new developments have been made in data display, searching algorithms, data formats, data content, auxillary information, and validation techniques, as well as, of course, an increase in the number of holdings. It provides a site (http://pcddb.cryst.bbk.ac.uk) for authors to deposit experimental data as well as detailed information on methods and calculations associated with published work. It also includes links for each entry to bioinformatics databases. The data are freely available to accessors either as single files or as complete data bank downloads. The PCDDB has found broad usage by the structural biology, bioinformatics, analytical and pharmaceutical communities, and has formed the basis for new software and methods developments. PMID:27613420

  16. Circular dichroism in biological photonic crystals and cubic chiral nets.

    PubMed

    Saba, M; Thiel, M; Turner, M D; Hyde, S T; Gu, M; Grosse-Brauckmann, K; Neshev, D N; Mecke, K; Schröder-Turk, G E

    2011-03-11

    Nature provides impressive examples of chiral photonic crystals, with the notable example of the cubic so-called srs network (the label for the chiral degree-three network modeled on SrSi2) or gyroid structure realized in wing scales of several butterfly species. By a circular polarization analysis of the band structure of such networks, we demonstrate strong circular dichroism effects: The butterfly srs microstructure, of cubic I4(1)32 symmetry, shows significant circular dichroism for blue to ultraviolet light, that warrants a search for biological receptors sensitive to circular polarization. A derived synthetic structure based on four like-handed silicon srs nets exhibits a large circular polarization stop band of a width exceeding 30%. These findings offer design principles for chiral photonic devices.

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

    PubMed

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

    2013-11-14

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

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

    NASA Astrophysics Data System (ADS)

    Rahman, Nafisur; Khan, Sumaiya

    2016-05-01

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

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

    PubMed

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

    2016-04-18

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

  20. Vibrational circular dichroism in general anisotropic thin solid films: measurement and theoretical approach.

    PubMed

    Buffeteau, Thierry; Lagugné-Labarthet, François; Sourisseau, Claude

    2005-06-01

    In this study, the measurement of the true vibrational circular dichroism (VCD) spectrum is considered from an experimental and theoretical approach for any general anisotropic thin solid sample exhibiting linear as well as circular birefringence (LB, CB) and dichroism (LD, CD) properties. For this purpose, we have made use of a simple model alpha-helix polypeptide, namely, the poly(gamma-benzyl-L-glutamate) or PBLG, reference sample possessing a well-known VCD spectrum and giving rise to slightly oriented films by deposition onto a solid substrate. Also, we have used a different Fourier transform infrared modulation of polarization (PM-FTIR) optical setup with two-channel electronic processing in order to record the PM-VLD and PM-VCD spectra for various sample orientations in its film plane. All the corresponding general relations of the expected intensities in these experiments and the related properly designed calibration measurements were established using the Stokes-Mueller formalism; in addition, the residual birefringence of the optical setup and the transmittance anisotropy of the detector were estimated. From a comparative study of the results obtained in solution and in the solid state, we then propose a simple new experimental procedure to extract the true VCD spectrum of an oriented PBLG thin film: its consists of calculating the half-sum of two spectra recorded at theta and at theta +/- 90 degrees sample orientations. Moreover, the complete linear and circular birefringence and dichroism properties of the ordered PBLG thin film are estimated in the amide I and amide II vibrational regions. This allows us to establish for any sample orientation various theoretical simulations of the VCD spectra that agree nicely with the observed experimental results; this confirms that the measurement of LD and LB is in this case a prerequisite in simulating the true VCD spectrum of a partly oriented anisotropic sample. This validates our combined experimental and

  1. Circular Dichroism of Carotenoids in Bacterial Light-Harvesting Complexes: Experiments and Modeling

    PubMed Central

    Georgakopoulou, S.; van Grondelle, R.; van der Zwan, G.

    2004-01-01

    In this work we investigate the origin and characteristics of the circular dichroism (CD) spectrum of rhodopin glucoside and lycopene in the light-harvesting 2 complex of Rhodopseudomonas acidophila and Rhodospirillum molischianum, respectively. We successfully model their absorption and CD spectra based on the high-resolution structures. We assume that these spectra originate from seven interacting transition dipole moments: the first corresponds to the 0-0 transition of the carotenoid, whereas the remaining six represent higher vibronic components of the S2 state. From the absorption spectra we get an estimate of the Franck-Condon factors of these transitions. Furthermore, we investigate the broadening mechanisms that lead to the final shape of the spectra and get an insight into the interaction energy between carotenoids. Finally, we examine the consequences of rotations of the carotenoid transition dipole moment and of deformations in the light-harvesting 2 complex rings. Comparison of the modeled carotenoid spectra with modeled spectra of the bacteriochlorophyll QY region leads to a refinement of the modeling procedure and an improvement of all calculated results. We therefore propose that the combined carotenoid and bacteriochlorophyll CD can be used as an accurate reflection of the overall structure of the light-harvesting complexes. PMID:15326029

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

    NASA Astrophysics Data System (ADS)

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

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

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

    NASA Astrophysics Data System (ADS)

    Matei, Iulia; Ionescu, Sorana; Hillebrand, Mihaela

    2012-10-01

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

  4. Non-reciprocal directional dichroism in the AFM phase of BiFeO3 at THz frequencies

    NASA Astrophysics Data System (ADS)

    Nagel, Urmas; Rõõm, T.; Farkas, D.; Szaller, D.; Bordács, S.; Kézsmárki, I.; Engelkamp, H.; Ozaki, Y.; Tomiaki, Y.; Ito, T.; Fishman, Randy S.

    We did THz absorption spectroscopy of BiFeO3 single crystals in the AFM phase, where the spin cycloid is destroyed in magnetic fields between 18 T and 32 T in Voigt geometry at 1.6 K. If B0 ∥ [ 1 1 0 ] , we see strong directional dichroism (DD) of absorption of the magnon mode with light propagating along the direction of the ferroelectric polarization k ∥ P ∥ [ 111 ] and eω ∥ [ 1 1 0 ] , bω ∥ [ 1 1 2 ] . The sign of DD can be reversed (i) by reversing the direction of B0 or (ii) by flipping the sample, thus reversing the propagation direction of light. The observed effect is caused by the strong magneto-electric coupling in the collinear AFM phase. Research sponsored by the Estonian Ministry of Education and Research (IUT23-3).

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

    SciTech Connect

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

    1997-10-01

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

  6. Fourier transform vibrational circular dichroism of small pharmaceutical molecules

    NASA Astrophysics Data System (ADS)

    Long, Fujin; Freedman, Teresa B.; Nafie, Laurence A.

    1998-06-01

    Fourier transform vibrational circular dichroism (FT-VCD) spectra of the small pharmaceutical molecules propanolol, ibuprofen and naproxen have been measured in the hydrogen stretching and mid-infrared regions to obtain information on solution conformation and to identify markers for absolute configuration determination. Ab initio molecular orbital calculations of low energy conformations, vibrational frequencies and VCD intensities for fragments of the drugs were utilized in interpreting the spectra. Features characteristic of five conformers of propranolol were identified. The weak positive CH stretching VCD signal in ibuprofen and naproxen is characteristic of the S-configuration of the chiral center common to these two analgesics.

  7. Dichroism measurements in forensic fibre examination: part 5-pigmented fibres.

    PubMed

    De Wael, K; Lepot, L

    2012-09-01

    A number of pigmented fibre samples were examined with plane polarized light on their dichroic behaviour by optical light microscopy (OLM) and microspectrophotometry with plane polarized light (MSP-PPL). It was found that about half of the samples show a strong dichroic effect and another 20% have a weak dichroism. Both regular (80%) and inversed dichroic effects (20%) occur. The dichroic characteristics of pigmented fibres can be compared to these of sheet polarizers. It is suggested that the dichroic behaviour of pigmented fibres depends strongly on the crystal structure (shape of the pigment grains) and the draw ratio (orientation of the polymer chains).

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

    PubMed

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

    2011-04-01

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

  9. Direct determination of polymyxin B sulfate using resonance Rayleigh scattering and resonance non-linear scattering methods with hexatungstate.

    PubMed

    Kong, Ling; Liu, Zhongfang; Liu, Shaopu; Wu, Limin; Tian, Fengling

    2014-02-01

    At pH 1.3-1.6, tungstate WO4(2-) , can be converted to hexatungstate W6 O19(2-) , which can react with positively charged polymyxin B sulfate (PMB) to result in enhancement of resonance Rayleigh scattering (RRS) and resonance non-linear scattering, including second order scattering and frequency doubling scattering. Linear relationships can be established between enhanced scattering intensity and PMB concentration. The detection limits (3σ) were 5.5 ng/mL (RRS), 10.1 ng/mL (second order scattering) and 34.6 ng/mL (frequency doubling scattering). The optimum reaction conditions, influencing factors and related analytical properties were tested. The interaction mechanism was investigated via absorption spectrum, circular dichroism spectra and atomic force microscopy imaging. The basis of scattering enhancement is discussed. PMB in eardrops, human serum and urine, were quantified satisfactorily by RRS.

  10. Conditions for instantaneous support shrinking and sharp estimates for the support of the solution of the Cauchy problem for a doubly non-linear parabolic equation with absorption

    SciTech Connect

    Degtyarev, S P

    2008-04-30

    Instantaneous support shrinking is studied for a doubly non-linear degenerate parabolic equation in the case of slow diffusion when, in general, the Cauchy initial data are Radon measures. For a non-negative solution, a necessary and sufficient condition for instantaneous support shrinking is obtained in terms of the local behaviour of the mass of the initial data. In the same terms, estimates are obtained for the size of the support, that are sharp with respect to order. Bibliography: 24 titles.

  11. Thermal behavior of long wavelength absorption transitions in Spirulina platensis photosystem I trimers.

    PubMed Central

    Cometta, A; Zucchelli, G; Karapetyan, N V; Engelmann, E; Garlaschi, F M; Jennings, R C

    2000-01-01

    In photosystem I trimers of Spirulina platensis a major long wavelength transition is irreversibly bleached by illumination with high-intensity white light. The photobleaching hole, identified by both absorption and circular dichroism spectroscopies, is interpreted as the inhomogeneously broadened Q(y) transition of a chlorophyll form that absorbs maximally near 709 nm at room temperature. Analysis of the mean square deviation of the photobleaching hole between 80 and 300 K, in the linear electron-phonon frame, indicates that the optical reorganization energy is 52 cm(-1), four times greater than that for the bulk, short-wavelength-absorbing chlorophylls, and the inhomogenous site distribution bandwidth is close to 150 cm(-1). The room temperature bandwidth, close to 18.5 nm, is dominated by thermal (homogeneous) broadening. Photobleaching induces correlated circular dichroism changes, of opposite sign, at 709 and 670 nm, which suggests that the long wavelength transition may be a low energy excitonic band, in agreement with its high reorganization energy. Clear identification of the 709-nm spectral form was used in developing a Gaussian description of the long wavelength absorption tail by analyzing the changing band shape during photobleaching using a global decomposition procedure. Additional absorption states near 720, 733, and 743 nm were thus identified. The lowest energy state at 743 nm is present in substoichiometric levels at room temperature and its presence was confirmed by fluorescence spectroscopy. This state displays an unusual increase in intensity upon lowering the temperature, which is successfully described by assuming the presence of low-lying, thermally populated states. PMID:11106627

  12. Light absorption dichroism and magnetic configuration of weakly ferromagnetic CoCO 3

    NASA Astrophysics Data System (ADS)

    Litvinenko, Yu. G.; Verdyan, A. I.; Shapiro, V. V.

    1980-01-01

    Investigation of light interaction with magnetically ordered crystals [1] revealed a correlation between certain spectral characteristics of a crystal on the one hand and its magnetic properties on the other.

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

    NASA Astrophysics Data System (ADS)

    Rogalev, A.; Wilhelm, F.

    2015-12-01

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

  14. Enzymatic assay of beta-lactamase using circular dichroism spectropolarimetry.

    PubMed

    Long, D M

    1997-05-01

    A method for measuring the rates of enzymatic hydrolysis of beta-lactam antibiotics based on circular dichroism spectropolarimetry is described. Unhydrolyzed beta-lactam antibiotics have high molar ellipticities, but the hydrolyzed compounds are circular dichroism (CD) inactive in the case of penams or have significantly different CD spectra in the case of cephems. By measuring CD at constant wavelength as a function of time for reaction mixtures containing beta-lactamase and beta-lactam antibiotics, rates of hydrolysis and steady-state enzyme kinetic constants can be derived. The method was applied to measurement of a wide range of enzymatic reaction constants for wild-type and four mutant RTEM-1 beta-lactamases. Compared to the commonly employed assay based on ultraviolet spectroscopy, the new method offers several advantages. These include the ability to measure larger enzymatic Michaelis-Menten constants, less interference from high concentrations of beta-lactamase, higher sensitivity, and potentially less interference from other uv-absorbing components of complex reaction mixtures.

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

    PubMed

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

    2010-09-01

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

  16. Energy transfer among CP29 chlorophylls: calculated Förster rates and experimental transient absorption at room temperature.

    PubMed Central

    Cinque, G; Croce, R; Holzwarth, A; Bassi, R

    2000-01-01

    The energy transfer rates between chlorophylls in the light harvesting complex CP29 of higher plants at room temperature were calculated ab initio according to the Förster mechanism (Förster T. 1948, Ann. Physik. 2:55-67). Recently, the transition moment orientation of CP29 chlorophylls was determined by differential linear dichroism and absorption spectroscopy of wild-type versus mutant proteins in which single chromophores were missing (Simonetto R., Crimi M., Sandonà D., Croce R., Cinque G., Breton J., and Bassi R. 1999. Biochemistry. 38:12974-12983). In this way the Q(y) transition energy and chlorophyll a/b affinity of each binding site was obtained and their characteristics supported by reconstruction of steady-state linear dichroism and absorption spectra at room temperature. In this study, the spectral form of individual chlorophyll a and b ligands within the protein environment was experimentally determined, and their extinction coefficients were also used to evaluate the absolute overlap integral between donors and acceptors employing the Stepanov relation for both the emission spectrum and the Stokes shift. This information was used to calculate the time-dependent excitation redistribution among CP29 chlorophylls on solving numerically the Pauli master equation of the complex: transient absorption measurements in the (sub)picosecond time scale were simulated and compared to pump-and-probe experimental data in the Q(y) region on the native CP29 at room temperature upon selective excitation of chlorophylls b at 640 or 650 nm. The kinetic model indicates a bidirectional excitation transfer over all CP29 chlorophylls a species, which is particularly rapid between the pure sites A1-A2 and A4-A5. Chlorophylls b in mixed sites act mostly as energy donors for chlorophylls a, whereas site B5 shows high and bidirectional coupling independent of the pigment hosted. PMID:11023879

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

    SciTech Connect

    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.

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

    PubMed

    Tedsana, Wimonsiri; Tuntulani, Thawatchai; Ngeontae, Wittaya

    2015-03-31

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

  19. Theoretical Prediction of Vibrational Circular Dichroism of Hexoses in Linear Form

    DTIC Science & Technology

    1992-06-01

    A . L . Lehninger , Biochemistry, Worth Publishers, New...IL)p I *G(/f)>]g (6) N 0 =Zke8p (7) = <( a *CIiGQ)/aX..) L I (a8*G(FZ,,HO)/aHP)H..O> (8) 10\\0 -(i /4hc)7,Xp.,(Zke)Rj. (9) where A = the nuclear geometry...J. Chem. Phys. 90, 3204-13 (1989). 8. P. L . Polavarapu, B. A . Hess, Jr., L . J. Schaad, D. 0. Henderson, L . P. Fontana, H. E. Smith, L . A . Nafie, T.

  20. Near-field Raman dichroism of azo-polymers exposed to nanoscale dc electrical and optical poling.

    PubMed

    Kharintsev, Sergey S; Fishman, Alexandr I; Saikin, Semion K; Kazarian, Sergei G

    2016-12-01

    Azobenzene-functionalized polymer films are functional materials, where the (planar vs. homeotropic) orientation of azo-dyes can be used for storing data. In order to characterize the nanoscale 3D orientation of the pigments in sub-10 nm thick polymer films we use two complementary techniques: polarization-controlled tip-enhanced Raman scattering (TERS) microscopy and contact scanning capacity microscopy. We demonstrate that the homeotropic and planar orientations of the azo-dyes are produced by applying a local dc electrical field and a resonant longitudinal optical near-field, respectively. For a non-destructive probe of the azo-dye orientation we apply a non-resonant optical near-field and compare the intensities of the Raman-active vibrational modes. We show that near-field Raman dichroism, a characteristic similar to the absorption dichroism used in far-field optics, can be a quantitative indicator of the 3D molecular orientation of the azo-dye at the nanoscale. This study directly benefits the further development of photochromic near-field optical memory that can lead to ultrahigh density information storage.

  1. Molecular magnetic dichroism in spectra of white dwarfs.

    PubMed

    Berdyugina, S V; Berdyugin, A V; Piirola, V

    2007-08-31

    We present novel calculations of the magnetic dichroism appearing in molecular bands in the presence of a strong magnetic field, which perturbs the internal structure of the molecule and results in net polarization due to the Paschen-Back effect. Based on that, we analyze new spectropolarimetric observations of the cool magnetic helium-rich white dwarf G99-37, which shows strongly polarized molecular bands in its spectrum. In addition to previously known molecular bands of the C2 Swan and CH A-X systems, we find a firm evidence for the violet CH B-X bands at 390 nm and C2 Deslandres-d'Azambuja bands at 360 nm. Combining the polarimetric observations with our model calculations, we deduce a dipole magnetic field of 7.5+/-0.5 MG with the positive pole pointing towards the Earth. We conclude that the developed technique is an excellent tool for studying magnetic fields on cool magnetic stars.

  2. Circular dichroism study of chiral biomolecules conjugated with silver nanoparticles

    NASA Astrophysics Data System (ADS)

    Li, Taihua; Park, Hyun Gyu; Lee, Hee-Seung; Choi, Seong-Ho

    2004-10-01

    Chiral biomolecules conjugated with silver nanoparticles were investigated by circular dichroism (CD) spectroscopy. Silver nanoparticles were prepared by the citrate reduction method and were characterized by UV spectroscopy and TEM. Conjugation of thiol group-containing biomolecules, such as cysteine, glutathione and penicillamine, with silver nanoparticles resulted in the generation of new characteristic CD signals in the region of 240-400 nm, whereas no CD signal changes were found with lysine or glutamine. Association through hydrogen bonding among the biomolecules is considered to be essential for CD signal generation, which was confirmed by experiment with cysteine methyl ester. Interestingly, Au nanoparticles were not found to generate CD signals in the wavelength region tested, indicating that this phenomenon is a unique feature of silver nanoparticles, distinguished from gold nanoparticles.

  3. A novel computational method for comparing vibrational circular dichroism spectra.

    PubMed

    Shen, Jian; Zhu, Chengyue; Reiling, Stephan; Vaz, Roy

    2010-08-01

    A novel method, SimIR/VCD, for comparing experimental and calculated VCD (vibrational circular dichroism) spectra is developed, based on newly defined spectra similarities. With computationally optimized frequency scaling and shifting, a calculated spectrum can be easily identified to match an observed spectrum, which leads to an unbiased molecular chirality assignment. The time-consuming manual band-fitting work is greatly reduced. With (1S)-(-)-alpha-pinene as an example, it demonstrates that the calculated VCD similarity is correlated with VCD spectra matching quality and has enough sensitivity to identify variations in the spectra. The study also compares spectra calculated using different DFT methods and basis sets. Using this method should facilitate the spectra matching, reduce human error and provide a confidence measure in the chiral assignment using VCD spectroscopy.

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

    ERIC Educational Resources Information Center

    Mendicuti, Francisco; Gonzalez-Alvarez, Maria Jose

    2010-01-01

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

  5. Orientation of nucleosomes and linker DNA in calf thymus chromatin determined by photochemical dichroism

    NASA Astrophysics Data System (ADS)

    Mitra, Sekhar; Sen, Dipankar; Crothers, Donald M.

    1984-03-01

    The dichroism for photochemical attachment of a psoralen derivative to Mg2+ -stabilized chromatin fibres is used to deduce the orientation of nucleosomal disks and linker DNA in the 30-nm fibre. The new technique of photochemical electric dichroism should have general applicability to problems of nucleic acid organization in cellular subunits and viruses.

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

    NASA Astrophysics Data System (ADS)

    Tardif, Samuel; Titov, Andrey; Arras, Emmanuel; Slipukhina, Ivetta; Hlil, El-Kébir; Cherifi, Salia; Joly, Yves; Jamet, Matthieu; Barski, André; Cibert, Joël; Kulatov, Erkin; Uspenskii, Yurii A.; Pochet, Pascal

    2014-03-01

    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.

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

    PubMed

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

    2003-05-05

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

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

    NASA Astrophysics Data System (ADS)

    Mawatari, Kazuma; Kitamori, Takehiko

    2005-09-01

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

  9. Linear and nonlinear optical absorption coefficients and refractive index changes in GaN/Al{sub x}Ga{sub (1−x)}N double quantum wells operating at 1.55 μm

    SciTech Connect

    Dakhlaoui, Hassen

    2015-04-07

    In the present paper, the linear and nonlinear optical absorption coefficients and refractive index changes between the ground and the first excited states in double GaN/Al{sub x}Ga{sub (1−x)}N quantum wells are studied theoretically. The electronic energy levels and their corresponding wave functions are obtained by solving Schrödinger-Poisson equations self-consistently within the effective mass approximation. The obtained results show that the optical absorption coefficients and refractive index changes can be red- and blue-shifted through varying the left quantum well width and the aluminum concentration x{sub b2} of the central barrier, respectively. These structural parameters are found to present optimum values for carrying out the transition of 0.8 eV (1.55 μm). Furthermore, we show that the desired transition can also be achieved by replacing the GaN in the left quantum well with Al{sub y}Ga{sub (1−y)}N and by varying the aluminum concentration y{sub Al}. The obtained results give a new degree of freedom in optoelectronic device applications such as optical fiber telecommunications operating at (1.55 μm)

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

    NASA Astrophysics Data System (ADS)

    Fujimoto, Kazuhiro J.; Balashov, Sergei P.

    2017-03-01

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

  11. Measurement of c-axis angular orientation in calcite (CaCO3) nanocrystals using X-ray absorption spectroscopy

    PubMed Central

    Gilbert, P. U. P. A.; Young, Anthony; Coppersmith, Susan N.

    2011-01-01

    We demonstrate that the ability to manipulate the polarization of synchrotron radiation can be exploited to enhance the capabilities of X-ray absorption near-edge structure (XANES) spectroscopy, to include linear dichroism effects. By acquiring spectra at the same photon energies but different polarizations, and using a photoelectron emission spectromicroscope (PEEM), one can quantitatively determine the angular orientation of micro- and nanocrystals with a spatial resolution down to 10 nm. XANES-PEEM instruments are already present at most synchrotrons, hence these methods are readily available. The methods are demonstrated here on geologic calcite (CaCO3) and used to investigate the prismatic layer of a mollusk shell, Pinctada fucata. These XANES-PEEM data reveal multiply oriented nanocrystals within calcite prisms, previously thought to be monocrystalline. The subdivision into multiply oriented nanocrystals, spread by more than 50°, may explain the excellent mechanical properties of the prismatic layer, known for decades but never explained. PMID:21693647

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

    DOE PAGES

    DiLullo, Andrew; Shirato, Nozomi; Cummings, Marvin; ...

    2016-01-28

    Localized spectroscopy with simultaneous topographic, elemental and magnetic information is presented. A synchrotron X-ray scanning tunneling microscope has been employed for the local study of the X-ray magnetic circular dichroism at the FeL2,3-edges of a thin iron film grown on Cu(111). Polarization-dependent X-ray absorption spectra have been obtained through a tunneling smart tip that serves as a photoelectron detector. In contrast to conventional spin-polarized scanning tunneling microscopy, X-ray excitations provide magnetic contrast even with a non-magnetic tip. Intensity variations in the photoexcited tip current point to chemical variations within a single magnetic Fe domain.

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

    SciTech Connect

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

    2016-01-28

    Localized spectroscopy with simultaneous topographic, elemental and magnetic information is presented. A synchrotron X-ray scanning tunneling microscope has been employed for the local study of the X-ray magnetic circular dichroism at the FeL2,3-edges of a thin iron film grown on Cu(111). Polarization-dependent X-ray absorption spectra have been obtained through a tunneling smart tip that serves as a photoelectron detector. In contrast to conventional spin-polarized scanning tunneling microscopy, X-ray excitations provide magnetic contrast even with a non-magnetic tip. Intensity variations in the photoexcited tip current point to chemical variations within a single magnetic Fe domain.

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

    PubMed

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

    2016-03-01

    Localized spectroscopy with simultaneous topographic, elemental and magnetic information is presented. A synchrotron X-ray scanning tunneling microscope has been employed for the local study of the X-ray magnetic circular dichroism at the Fe L2,3-edges of a thin iron film grown on Cu(111). Polarization-dependent X-ray absorption spectra have been obtained through a tunneling smart tip that serves as a photoelectron detector. In contrast to conventional spin-polarized scanning tunneling microscopy, X-ray excitations provide magnetic contrast even with a non-magnetic tip. Intensity variations in the photoexcited tip current point to chemical variations within a single magnetic Fe domain.

  15. The high-field magnet endstation for X-ray magnetic dichroism experiments at ESRF soft X-ray beamline ID32

    PubMed Central

    Kummer, K.; Fondacaro, A.; Jimenez, E.; Velez-Fort, E.; Amorese, A.; Aspbury, M.; Yakhou-Harris, F.; van der Linden, P.; Brookes, N. B.

    2016-01-01

    A new high-field magnet endstation for X-ray magnetic dichroism experiments has been installed and commissioned at the ESRF soft X-ray beamline ID32. The magnet consists of two split-pairs of superconducting coils which can generate up to 9 T along the beam and up to 4 T orthogonal to the beam. It is connected to a cluster of ultra-high-vacuum chambers that offer a comprehensive set of surface preparation and characterization techniques. The endstation and the beam properties have been designed to provide optimum experimental conditions for X-ray magnetic linear and circular dichroism experiments in the soft X-ray range between 400 and 1600 eV photon energy. User operation started in November 2014. PMID:26917134

  16. Structure vs. excitonic transitions in self-assembled porphyrin nanotubes and their effect on light absorption and scattering.

    PubMed

    Arteaga, Oriol; Canillas, Adolf; El-Hachemi, Zoubir; Crusats, Joaquim; Ribó, Josep M

    2015-12-28

    The optical properties of diprotonated meso-tetrakis(4-sulphonatophenyl)porphyrin (TPPS(4)) J-aggregates of elongated thin particles (nanotubes in solution and ribbons when deposited on solid interfaces) are studied by different polarimetric techniques. The selective light extinction in these structures, which depends on the alignment of the nanoparticle with respect to the polarization of light, is contributed by excitonic absorption bands and by resonance light scattering. The optical response as a function of the polarization of light is complex because, although the quasi-one-dimensional structure confines the local fields along the nanotube axis, there are two orthogonal excitonic bands, of H- and J-character, that can work in favor of or against the field confinement. Results suggest that resonance light scattering is the dominant effect in solid state preparations, i.e. in collective groups (bundles) of ribbons but in diluted solutions, i.e. with isolated nanotubes, the absorption at the excitonic transitions remains dominant and linear dichroism spectra can be a direct probe of the exciton orientations. Therefore, by analyzing scattering and absorption data we can determine the alignment of the excitonic bands within the nanoparticle, i.e. of the orientation of the basic 2D porphyrin architecture in the nanoparticle. This is a necessary first step for understanding the directions of energy transport, charge polarization and non-linear optical properties in these materials.

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

    PubMed

    Miyake, Hiroyuki; Terada, Keiko; Tsukube, Hiroshi

    2014-06-01

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

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

    PubMed

    Ngamdee, Kessarin; Puangmali, Theerapong; Tuntulani, Thawatchai; Ngeontae, Wittaya

    2015-10-22

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

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

    PubMed

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

    2007-09-01

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

  20. Optical activity and circular dichroism of plasmonic nanorod assemblies

    NASA Astrophysics Data System (ADS)

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

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

  1. Theoretical UV circular dichroism of aliphatic cyclic dipeptides.

    PubMed

    Carlson, Kristine L; Lowe, Stephen L; Hoffmann, Mark R; Thomasson, Kathryn A

    2005-06-23

    Four cyclic dipeptides (piperazine-2,5-diones), cyclo(L-Pro-Gly), cyclo(L-Pro-L-Leu), cyclo(L-Ala-L-Ala), and cyclo(L-Pro-L-Ala), were modeled from crystal structure data. Conformations resulting from energy minimization using molecular mechanics were compared with traditional ab initio and density functional theory geometric optimizations for each dipeptide. In all computational cases, the gas phase was assumed. The pi-pi transition feature of the UV circular dichroic (CD) spectra was predicted for each peptide structure via the classical dipole interaction model. The dipole interaction model predicted CD spectra that qualitatively agreed with experiment when MP2 or DFT geometries were used. By coupling MP2 or DFT geometric optimizations with the classical physics method of the dipole interaction model, significantly better CD spectra were calculated than those using geometries obtained by molecular mechanics. Thus, one can couple quantum mechanical geometries with a classical physics model for calculation of circular dichroism.

  2. Structures of plant viruses from vibrational circular dichroism.

    PubMed

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

    2005-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1999-09-01

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

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

    PubMed Central

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

    2016-01-01

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

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

    SciTech Connect

    Loeffler, W.; Woerdman, J. P.; Broer, D. J.

    2011-06-15

    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.

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

    NASA Astrophysics Data System (ADS)

    Orlov, Sergey; Goncharova, Iryna; Urbanová, Marie

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

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

    PubMed

    Orlov, Sergey; Goncharova, Iryna; Urbanová, Marie

    2014-05-21

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

  8. Applications of the Cartesian coordinate tensor transfer technique in the simulations of vibrational circular dichroism spectra of oligonucleotides.

    PubMed

    Andrushchenko, Valery; Bouř, Petr

    2010-01-01

    The application of the Cartesian coordinate tensor transfer (CCT) technique for simulations of the IR absorption and vibrational circular dichroism (VCD) spectra of relatively large nucleic acid fragments is demonstrated on several case studies. The approach is based on direct ab initio calculations of atomic tensors, determining molecular properties, for relatively small fragments, and subsequent transfer of these tensors to the larger systems in Cartesian coordinates. This procedure enables precise computations of vibrational spectra for large biomolecular systems, currently with up to several thousands of atoms. The versatile ability of the CCT methods is emphasized on the examples of VCD and IR absorption spectra calculations for B- and Z-forms of DNA, single-, double-, and triple-stranded RNA helices and DNA structures with different base content and sequences. The development and recent improvements of the methodology are followed, including utilization of the constrained normal mode optimization (NMO) strategy and combined quantum mechanics and molecular dynamics simulations. Advantages, drawbacks, and recommendations for future improvements of the CCT method as applied to nucleic acid spectra calculations are discussed.

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

    SciTech Connect

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

    2006-12-08

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

  10. Magnetic circular dichroism investigation on chromophores in reaction centers of photosystem I and II of green plant photosynthesis

    NASA Astrophysics Data System (ADS)

    Nozawa, Tsunenori; Kobayashi, Masayuki; Wang, Zheng-Yu; Itoh, Shigeru; Iwaki, Masayo; Mimuro, Mamoru; Satoh, Kimiyuki

    1995-01-01

    Magnetic circular dichroism (MCD) of chlorophylls (Chl) in P700-enriched (12 Chl/P700) photosystem (PS) I particles and D1-D2-cyt b559 (PSII reaction center) particles isolated from spinach are measured in the wavelength region between 450 and 750 nm. The relative magnitude of MCD to absorption intensity ([MCD]/[Abs]) is found to be a good measure to estimate the interaction of chromophores (dimer or monomer). The difference spectrum between reduced and oxidized state for the 12 Chl/P700 particles can be interpreted to be composed of a positive MCD from P700 and a negative MCD for P700 +. MCD signals for the primary acceptor Chl a monomer (A 0) and the reduced cytochrome f are also observed. The MCD signal from pheophytin a in the PSII reaction center is remarkably in the Qx, region as strong as the signal from the reaction center chlorophylls (P680 and accessory) and other attached chlorophylls. Based on the data, the MCD bands, as well as the absorption bands in the Qy region, are deconvoluted into the contribution from reaction center chlorophylls and the other chlorophylls. The [MCD]/[Abs] ratio of P680 or P700 is small and similar to that of special pair bacteriochlorophylls in the reaction center of purple bacteria, indicating the specific feature of MCD signals that originate from a dimer-type interaction.

  11. Transient absorption spectroscopy of laser shocked explosives

    SciTech Connect

    Mcgrane, Shawn D; Dang, Nhan C; Whitley, Von H; Bolome, Cindy A; Moore, D S

    2010-01-01

    Transient absorption spectra from 390-890 nm of laser shocked RDX, PETN, sapphire, and polyvinylnitrate (PVN) at sub-nanosecond time scales are reported. RDX shows a nearly linear increase in absorption with time after shock at {approx}23 GPa. PETN is similar, but with smaller total absorption. A broad visible absorption in sapphire begins nearly immediately upon shock loading but does not build over time. PVN exhibits thin film interference in the absorption spectra along with increased absorption with time. The absorptions in RDX and PETN are suggested to originate in chemical reactions happening on picosecond time scales at these shock stresses, although further diagnostics are required to prove this interpretation.

  12. Steady-state and transient polarized absorption spectroscopy of photosystem I complexes from the cyanobacteria Arthrospira platensis and Thermosynechococcus elongatus.

    PubMed

    Schlodder, Eberhard; Shubin, Vladimir V; El-Mohsnawy, Eithar; Roegner, Matthias; Karapetyan, Navassard V

    2007-06-01

    Core antenna and reaction centre of photosystem I (PS I) complexes from the cyanobacteria Arthrospira platensis and Thermosynechococcus elongatus have been characterized by steady-state polarized absorption spectroscopy, including linear dichroism (LD) and circular dichroism (CD). CD spectra and the second derivatives of measured 77 K CD spectra reveal the spectral components found in the polarized absorption spectra indicating the excitonic origin of the spectral forms of chlorophyll in the PS I complexes. The CD bands at 669-670(+), 673(+), 680(-), 683-685(-), 696-697(-), and 711(-) nm are a common feature of used PSI complexes. The 77 K CD spectra of the trimeric PS I complexes exhibit also low amplitude components around 736 nm for A. platensis and 720 nm for T. elongatus attributed to red-most chlorophylls. The LD measurements indicate that the transition dipole moments of the red-most states are oriented parallel to the membrane plane. The formation of P700(+)A(1)(-) or (3)P700 was monitored by time-resolved difference absorbance and LD spectroscopy to elucidate the spectral properties of the PS I reaction centre. The difference spectra give strong evidence for the delocalization of the excited singlet states in the reaction centre. Therefore, P700 cannot be considered as a dimer but should be regarded as a multimer of the six nearly equally coupled reaction centre chlorophylls in accordance with structure-based calculations. On the basis of the results presented in this work and earlier work in the literature it is concluded that the triplet state is localized most likely on P(A), whereas the cation is localized most likely on P(B).

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

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

    PubMed Central

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

    2016-01-01

    Experimental band structure analyses of single-walled carbon nanotubes have not yet been reported, to the best of our knowledge, except for a limited number of reports using scanning tunnelling spectroscopy. Here we demonstrate the experimental determination of the excitonic band structures of single-chirality single-walled carbon nanotubes using their circular dichroism spectra. In this analysis, we use gel column chromatography combining overloading selective adsorption with stepwise elution to separate 12 different single-chirality enantiomers. Our samples show higher circular dichroism intensities than the highest values reported in previous works, indicating their high enantiomeric purity. Excitonic band structure analysis is performed by assigning all observed Eii and Eij optical transitions in the circular dichroism spectra. The results reproduce the asymmetric structures of the valence and conduction bands predicted by density functional theory. Finally, we demonstrate that an extended empirical formula can estimate Eij optical transition energies for any (n,m) species. PMID:27703139

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

    SciTech Connect

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

    1995-04-01

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

  16. Acid-Base Titration of (S)-Aspartic Acid: A Circular Dichroism Spectrophotometry Experiment

    NASA Astrophysics Data System (ADS)

    Cavaleiro, Ana M. V.; Pedrosa de Jesus, Júlio D.

    2000-09-01

    The magnitude of the circular dichroism of (S)-aspartic acid in aqueous solutions at a fixed wavelength varies with the addition of strong base. This laboratory experiment consists of the circular dichroism spectrophotometric acid-base titration of (S)-aspartic acid in dilute aqueous solutions, and the use of the resulting data to determine the ionization constant of the protonated amino group. The work familiarizes students with circular dichroism and illustrates the possibility of performing titrations using a less usual instrumental method of following the course of a reaction. It shows the use of a chiroptical property in the determination of the concentration in solution of an optically active molecule, and exemplifies the use of a spectrophotometric titration in the determination of an ionization constant.

  17. Amide I vibrational circular dichroism of dipeptide: Conformation dependence and fragment analysis

    NASA Astrophysics Data System (ADS)

    Choi, Jun-Ho; Cho, Minhaeng

    2004-03-01

    The amide I vibrational circular dichroic response of alanine dipeptide analog (ADA) was theoretically investigated and the density functional theory calculation and fragment analysis results are presented. A variety of vibrational spectroscopic properties, local and normal mode frequencies, coupling constant, dipole, and rotational strengths, are calculated by varying two dihedral angles determining the three-dimensional ADA conformation. Considering two monopeptide fragments separately, we show that the amide I vibrational circular dichroism of the ADA can be quantitatively predicted. For several representative conformations of the model ADA, vibrational circular dichroism spectra are calculated by using both the density functional theory calculation and fragment analysis methods.

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

    PubMed

    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.

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

    PubMed Central

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Dixit, Anant; Alouani, M.

    2016-10-01

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

  1. PERITONEAL ABSORPTION

    PubMed Central

    Hahn, P. F.; Miller, L. L.; Robscheit-Robbins, F. S.; Bale, W. F.; Whipple, G. H.

    1944-01-01

    The absorption of red cells from the normal peritoneum of the dog can be demonstrated by means of red cells labeled with radio-iron incorporated in the hemoglobin of these red cells. Absorption in normal dogs runs from 20 to 100 per cent of the amount given within 24 hours. Dogs rendered anemic by bleeding absorb red cells a little less rapidly—ranging from 5 to 80 per cent of the injected red cells. Doubly depleted dogs (anemic and hypoproteinemic) absorb even less in the three experiments recorded. This peritoneal absorption varies widely in different dogs and even in the same dog at different times. We do not know the factors responsible for these variations but there is no question about active peritoneal absorption. The intact red cells pass readily from the peritoneal cavity into lymph spaces in diaphragm and other areas of the peritoneum. The red cells move along the lymphatics and through the lymph glands with little or no phagocytosis and eventually into the large veins through the thoracic ducts. PMID:19871404

  2. Nutrient absorption.

    PubMed

    Rubin, Deborah C

    2004-03-01

    Our understanding of nutrient absorption continues to grow, from the development of unique animal models and from studies in which cutting-edge molecular and cellular biologic approaches have been used to analyze the structure and function of relevant molecules. Studies of the molecular genetics of inherited disorders have also provided many new insights into these processes. A major advance in lipid absorption has been the cloning and characterization of several intestinal acyl CoA:monoacylglycerol acyltransferases; these may provide new targets for antiobesity drug therapy. Studies of intestinal cholesterol absorption and reverse cholesterol transport have encouraged the development of novel potential treatments for hyperlipidemia. Observations in genetically modified mice and in humans with mutations in glucose transporter 2 suggest the importance of a separate microsomal membrane transport pathway for glucose transport. The study of iron metabolism has advanced greatly with the identification of the hemochromatosis gene and the continued examination of the genetic regulation of iron absorptive pathways. Several human thiamine transporters have been identified, and their specific roles in different tissues are being explored.

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

    ERIC Educational Resources Information Center

    Abriata, Luciano A.

    2011-01-01

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

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

    SciTech Connect

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

    2015-01-14

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

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

    DOE PAGES

    Janoschek, M.; Haskel, D.; Fernandez-Rodriguez, J.; ...

    2015-01-14

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

  7. Circular dichroism of two conformations of poly[d(G-C)] induced by low pH.

    PubMed Central

    Antao, V P; Gray, C W; Gray, D M; Ratliff, R L

    1986-01-01

    Circular dichroism (CD) and UV absorption data showed that poly[d(G-C)] (at 0.09M NaCl, 0.01M Na+ (phosphate), 20 degrees C) underwent two conformational transitions upon lowering of the pH by the addition of HCl. The first transition was complete at about pH 3.0. The second transition was complete upon lowering the pH to 2.6 or upon raising the temperature, at pH 3.0, to about 40 degrees C. There was no indication of denaturation during either transition. The CD spectrum for the second acid conformation had large CD bands including a positive one at 288nm, a characteristic associated with C X C+ base-pairs. Electron microscopy showed no significant formation of condensed supramolecular aggregates corresponding to the first or second acid forms of poly[d(G-C)]. On the basis of spectral data, electron microscopy, and proton-uptake measurements, we propose models for the secondary structures that poly[d(G-C)] adopts in its two acid conformations. PMID:3808946

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

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

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

    ERIC Educational Resources Information Center

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

    2005-01-01

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

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

    PubMed

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

    2006-06-01

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

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  12. NIR-VCD, vibrational circular dichroism in the near-infrared: experiments, theory and calculations.

    PubMed

    Abbate, Sergio; Castiglioni, Ettore; Gangemi, Fabrizio; Gangemi, Roberto; Longhi, Giovanna

    2009-01-01

    The first well documented experiments of Near Infrared Vibrational Circular Dichroism (NIR-VCD) were performed around 1975. We review the thirty year history of NIR-VCD, encompassing both instrumental development and theoretical/computational methods that allow interpretation of experimental spectra, harvesting useful structural information therefrom. We hope to stimulate interest in this still scarcely explored spectroscopy of chiral molecules.

  13. Existence of orbital order and its fluctuation in superconducting Ba(Fe(1-x)Co(x))2As2 single crystals revealed by x-ray absorption spectroscopy.

    PubMed

    Kim, Y K; Jung, W S; Han, G R; Choi, K-Y; Chen, C-C; Devereaux, T P; Chainani, A; Miyawaki, J; Takata, Y; Tanaka, Y; Oura, M; Shin, S; Singh, A P; Lee, H G; Kim, J-Y; Kim, C

    2013-11-22

    We performed temperature dependent x-ray linear dichroism (XLD) experiments on an iron pnictide system, Ba(Fe(1-x)Co(x))2As2 with x=0.00, 0.05, 0.08, and 0.10 to experimentally verify the existence of orbital ordering (OO). Substantial XLD was observed in polarization dependent x-ray absorption spectra of Fe L edges. By exploiting the difference in the temperature dependent behaviors, OO, and structure contributions to XLD could be clearly separated. The observed OO signal indicates different occupation numbers for d(yz) and d(zx) orbitals and supports the existence of ferro-OO. The results are also consistent with the theoretical prediction. Moreover, we find substantial OO signal well above the structural and magnetic transition temperatures, which suggests the existence of strong OO fluctuations up to high temperatures.

  14. Polarized x-ray-absorption spectroscopy of the uranyl ion: Comparison of experiment and theory

    SciTech Connect

    Hudson, E.A.; Allen, P.G.; Terminello, L.J.; Denecke, M.A.; Reich, T.

    1996-07-01

    The x-ray linear dichroism of the uranyl ion (UO{sub 2}{sup 2+}) in uranium {ital L}{sub 3}-edge extended x-ray-absorption fine structure (EXAFS), and {ital L}{sub 1}- and {ital L}{sub 3}-edge x-ray-absorption near-edge structure (XANES), has been investigated both by experiment and theory. A striking polarization dependence is observed in the experimental XANES and EXAFS for an oriented single crystal of uranyl acetate dihydrate [UO{sub 2}(CH{sub 3}CO{sub 2}){sub 2}{center_dot}2H{sub 2}O], with the x-ray polarization vector aligned either parallel or perpendicular to the bond axis of the linear uranyl cation (O-U-O). Single-crystal results are compared to experimental spectra for a polycrystalline uranyl acetate sample and to calculations using the {ital ab} {ital initio} multiple-scattering (MS) code FEFF 6. Theoretical XANES spectra for uranyl fluoride (UO{sub 2}F{sub 2}) reproduce all the features of the measured uranyl acetate spectra. By identifying scattering paths which contribute to individual features in the calculated spectrum, a detailed understanding of the {ital L}{sub 1}-edge XANES is obtained. MS paths within the uranyl cation have a notable influence upon the XANES. The measured {ital L}{sub 3}-edge EXAFS is also influenced by MS, especially when the x-ray polarization is parallel to the uranyl species. These MS contributions are extracted from the total EXAFS and compared to calculations. The best agreement with the isolated MS signal is obtained by using nonoverlapped muffin-tin spheres in the FEFF 6 calculation. This contrasts the {ital L}{sub 1}-edge XANES calculations, in which overlapping was required for the best agreement with experiment. {copyright} {ital 1996 The American Physical Society.}

  15. Linear Accelerators

    NASA Astrophysics Data System (ADS)

    Sidorin, Anatoly

    2010-01-01

    In linear accelerators the particles are accelerated by either electrostatic fields or oscillating Radio Frequency (RF) fields. Accordingly the linear accelerators are divided in three large groups: electrostatic, induction and RF accelerators. Overview of the different types of accelerators is given. Stability of longitudinal and transverse motion in the RF linear accelerators is briefly discussed. The methods of beam focusing in linacs are described.

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

    SciTech Connect

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

    2010-11-08

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

  17. Specific features of the circular dichroism of a chiral photonic crystal with a defect layer inside in the presence of a gain

    NASA Astrophysics Data System (ADS)

    Gevorgyan, A. H.

    2017-01-01

    The specific features of the circular dichroism (CD) spectra of a cholesteric liquid crystal (CLC) layer with a defect layer inside in the presence of gain have been investigated. The features of the dependence of CD on the parameter characterizing the gain on the defect mode are analyzed for two cases: (i) gain is present in the defect layer and is absent in the CLC sublayers and (ii) gain is absent in the defect layer but is present in the CLC sublayers. It is shown that these dependences significantly differ in the two aforementioned cases. The dependences of the reflection, transmission, and absorption on the defect mode on the gain parameter have been investigated for incident light with both circular polarizations.

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

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

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

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

    SciTech Connect

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

    2015-06-21

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

  20. Quantum absorption refrigerator.

    PubMed

    Levy, Amikam; Kosloff, Ronnie

    2012-02-17

    A quantum absorption refrigerator driven by noise is studied with the purpose of determining the limitations of cooling to absolute zero. The model consists of a working medium coupled simultaneously to hot, cold, and noise baths. Explicit expressions for the cooling power are obtained for Gaussian and Poisson white noise. The quantum model is consistent with the first and second laws of thermodynamics. The third law is quantified; the cooling power J(c) vanishes as J(c) ∝ T(c)(α), when T(c)→0, where α=d+1 for dissipation by emission and absorption of quanta described by a linear coupling to a thermal bosonic field, where d is the dimension of the bath.

  1. Acoustic absorption by sunspots

    NASA Technical Reports Server (NTRS)

    Braun, D. C.; Labonte, B. J.; Duvall, T. L., Jr.

    1987-01-01

    The paper presents the initial results of a series of observations designed to probe the nature of sunspots by detecting their influence on high-degree p-mode oscillations in the surrounding photosphere. The analysis decomposes the observed oscillations into radially propagating waves described by Hankel functions in a cylindrical coordinate system centered on the sunspot. From measurements of the differences in power between waves traveling outward and inward, it is demonstrated that sunspots appear to absorb as much as 50 percent of the incoming acoustic waves. It is found that for all three sunspots observed, the amount of absorption increases linearly with horizontal wavenumber. The effect is present in p-mode oscillations with wavelengths both significantly larger and smaller than the diameter of the sunspot umbrae. Actual absorption of acoustic energy of the magnitude observed may produce measurable decreases in the power and lifetimes of high-degree p-mode oscillations during periods of high solar activity.

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

    PubMed

    Bannwarth, Christoph; Grimme, Stefan

    2015-04-16

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Salluzzo, Marco; CNR-SPIN Team

    2014-03-01

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

  5. Nuclear-Spin-Induced Circular Dichroism in the Infrared Region for Liquids.

    PubMed

    Chen, Fang; Yao, Guo-hua; Zhang, Zhen-lin; Liu, Fan-chen; Chen, Dong-ming

    2015-06-22

    Recently, the nuclear-spin-induced optical rotation (NSOR) and circular dichroism (NSCD) for liquids were discovered and extensively studied and developed. However, so far, nuclear-spin-induced magnetic circular dichroism in the IR region (IR-NSCD) has not been explored, even though all polyatomic molecules exhibit extensive IR spectra. Herein, IR-NSCD is proposed and discussed theoretically. The results indicate that in favorable conditions the IR-NSCD angle may be much larger than the NSOR angle in the UV/Vis region due to a vibrational resonance effect and can be measurable by using the NSOR experiment scheme. IR-NSCD can automatically combine and give NMR spectra and IRCD spectra of the nuclear spin prepolarized samples in liquids, which, in principle, could be developed to become a unique, novel analytical tool.

  6. Multiphoton ionization and circular dichroism: new experimental approach and application to natural products.

    PubMed

    Logé, Christoph; Boesl, Ulrich

    2011-07-11

    Enantio-sensitive laser mass spectrometry is the combination of multiphoton ionization by circularly polarized laser light with mass spectrometric detection of ions. The method has been developed as a tool for the fast investigation of chiral molecules in sample mixtures without any preceding separation and offers many new experimental possibilities. The main difficulties of the detection of circular dichroism in this way arise from systematic and statistical deviations. Herein, we report the newest approach to overcome these problems using a so-called twin-peak ion source, back-reflection of the laser light, and reference substances. By these means, the detection limit for circular dichroism can be lowered from the percent to the per-mill range. The capabilities of the new setup are demonstrated by the investigation of several natural products.

  7. ValiDichro: a website for validating and quality control of protein circular dichroism spectra

    PubMed Central

    Woollett, Benjamin; Whitmore, Lee; Janes, Robert W.; Wallace, B. A.

    2013-01-01

    Circular dichroism (CD) spectroscopy is widely used in structural biology as a technique for examining the structure, folding and conformational changes of proteins. A new server, ValiDichro, has been developed for checking the quality and validity of CD spectral data and metadata, both as an aid to data collection and processing and as a validation procedure for spectra to be included in publications. ValiDichro currently includes 25 tests for data completeness, consistency and quality. For each test that is done, not only is a validation report produced, but the user is also provided with suggestions for correcting or improving the data. The ValiDichro server is freely available at http://valispec.cryst.bbk.ac.uk/circularDichroism/ValiDichro/upload.html. PMID:23625965

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

    NASA Astrophysics Data System (ADS)

    Shcherbin, Dmitry; Ruud, Kenneth

    2008-06-01

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

  9. Chiral optical fields: a unified formulation of helicity scattered from particles and dichroism enhancement.

    PubMed

    Nieto-Vesperinas, Manuel

    2017-03-28

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

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

    SciTech Connect

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

    2014-08-04

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

  11. Time-resolved circular dichroism in carbonmonoxy-myoglobin: the central role of the proximal histidine.

    PubMed

    Dartigalongue, Thibault; Hache, François

    2006-05-05

    A calculation of the circular dichroism (CD) spectra of carbonmonoxy- and deoxy-myoglobin is carried out in relation to a time-resolved CD experiment. This calculation allows us to assign a dominant role to the proximal histidine in the definition of the electronic normal modes and to interpret the transient CD structure observed in a strain of the proximal histidine. This strain builds up in 10 ps and relaxes in 50 ps as the protein evolves towards its deoxy form.

  12. Reversible binding of ethacrynic acid to human serum albumin: difference circular dichroism study.

    PubMed

    Bertucci, C; Nanni, B; Salvadori, P

    1999-01-01

    The reversible binding of ethacrynic acid was characterized by a difference circular dichroism method. A 2/1 stoichiometry was determined for the [drug]/[HSA] (human serum albumin) complex. The reversible binding of ethacrynic acid to HSA determines direct competition with ligands that selectivity bind to site II and to the fatty acid site. Furthermore, indirect competition was shown for ligands for site I (anti-cooperative) and to site III (cooperative).

  13. Circular dichroism spectroscopy study of crystalline-to-amorphous transformation in chiral platinum(II) complexes.

    PubMed

    Zhang, Xiao-Peng; Wu, Tao; Liu, Jian; Zhao, Jin-Cheng; Li, Cheng-Hui; You, Xiao-Zeng

    2013-07-01

    Two couples of enantiomeric platinum(II) complexes: Pt(L1a )Cl (1a), Pt(L1b )Cl (1b) and Pt(L1a )(C ≡ C - Ph) (2a), Pt(L1b )(C ≡ C - Ph) (2b) (L1a  = (+)-1,3-di-(2-(4,5-pinene)pyridyl)benzene, L1b  = (-)-1,3-di-(2-(4,5-pinene)pyridyl)benzene) were synthesized and characterized. Their absolute configurations were determined by single crystal X-ray diffraction and further verified by circular dichroism (CD) spectra (including electronic circular dichroism [ECD] and vibrational circular dichroism [VCD]). These complexes show interesting mechanoluminescence and/or vapoluminescence due to crystalline-to-amorphous transformation. The crystalline solids, grinding-induced amorphous powders, and vapor-induced amorphous powders of complexes 2a and 2b were comparatively investigated by solid-state ECD and VCD spectra. The transformation from crystalline solids to amorphous powders was accompanied by significant variances of the spectral feature in both ECD and VCD spectra.

  14. ABSORPTION ANALYZER

    DOEpatents

    Brooksbank, W.A. Jr.; Leddicotte, G.W.; Strain, J.E.; Hendon, H.H. Jr.

    1961-11-14

    A means was developed for continuously computing and indicating the isotopic assay of a process solution and for automatically controlling the process output of isotope separation equipment to provide a continuous output of the desired isotopic ratio. A counter tube is surrounded with a sample to be analyzed so that the tube is exactly in the center of the sample. A source of fast neutrons is provided and is spaced from the sample. The neutrons from the source are thermalized by causing them to pass through a neutron moderator, and the neutrons are allowed to diffuse radially through the sample to actuate the counter. A reference counter in a known sample of pure solvent is also actuated by the thermal neutrons from the neutron source. The number of neutrons which actuate the detectors is a function of a concentration of the elements in solution and their neutron absorption cross sections. The pulses produced by the detectors responsive to each neu tron passing therethrough are amplified and counted. The respective times required to accumulate a selected number of counts are measured by associated timing devices. The concentration of a particular element in solution may be determined by utilizing the following relation: T2/Ti = BCR, where B is a constant proportional to the absorption cross sections, T2 is the time of count collection for the unknown solution, Ti is the time of count collection for the pure solvent, R is the isotopic ratlo, and C is the molar concentration of the element to be determined. Knowing the slope constant B for any element and when the chemical concentration is known, the isotopic concentration may be readily determined, and conversely when the isotopic ratio is known, the chemical concentrations may be determined. (AEC)

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

    PubMed

    Pipolo, Silvio; Percudani, Riccardo; Cammi, Roberto

    2016-04-14

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

  16. Simulated IR, isotropic and anisotropic Raman, and vibrational circular dichroism amide I band profiles of stacked β-sheets.

    PubMed

    Schweitzer-Stenner, Reinhard

    2012-04-12

    The amide I mode is a highly structure sensitive vibration of polypeptides that gives rise to a very strong band in IR absorption and a moderate band in Raman spectra. Many theoretical simulations of IR-band profiles have been undertaken thus far in order to expand the usability of amide I for the structure analysis of peptides and proteins. These simulations have thus far focused on the IR band profiles and to a limited extent on calculating the corresponding vibrational circular dichroism (VCD) signal. In this paper, we use excitonic coupling theory to simulate the IR, isotropic Raman, anisotropic Raman, and VCD band profiles of amide I of parallel and antiparallel β-sheets as well as of two layers of stacked β-sheets with antiparallel and parallel orientations of the respective sheets. Our calculations reveal anisotropic Raman and to a lesser extent VCD amide I profiles rather than the corresponding IR profile as suitable tools to discriminate between parallel and antiparallel β-sheets. Stacking has a very limited influence on the Raman and IR band profiles, but enhance the VCD signal, the sign of which allows one to discriminate between parallel and antiparallel orientations of stacked sheets. Helical twisting and bending of parallel β-sheets give rise to a very enhanced positive couplet, in agreement with the recent work of Schweitzer-Stenner and Measey (J. Am. Chem. Soc., 2011, 133, 1066). Stochastic uncorrelated inhomogeneity of individual peptide groups causes significant asymmetric broadening of Raman bands and, to a lesser extent, of IR bands and reduces the VCD-couplet of stacked β-sheets.

  17. Terahertz Circular Dichroism Spectroscopy: A Potential Approach to the In Situ Detection of Life's Metabolic and Genetic Machinery

    NASA Astrophysics Data System (ADS)

    Xu, Jing; Ramian, Gerald J.; Galan, Jhenny F.; Savvidis, Pavlos G.; Scopatz, Anthony Michael; Birge, Robert R.; Allen, S. James; Plaxco, Kevin W.

    2003-11-01

    We propose a terahertz (far-infrared) circular dichroism-based life-detection technology that may provide a universal and unequivocal spectroscopic signature of living systems regardless of their genesis. We argue that, irrespective of the specifics of their chemistry, all life forms will employ well-structured, chiral, stereochemically pure macromolecules (>500 atoms) as the catalysts with which they perform their metabolic and replicative functions. We also argue that nearly all such macromolecules will absorb strongly at terahertz frequencies and exhibit significant circular dichroism, and that this circular dichroism unambiguously distinguishes biological from abiological materials. Lastly, we describe several approaches to the fabrication of a terahertz circular dichroism spectrometer and provide preliminary experimental indications of their feasibility. Because terahertz circular dichroism signals arise from the molecular machinery necessary to carry out life's metabolic and genetic processes, this life-detection method differs fundamentally from more well-established approaches based on the detection of isotopic fractionation, "signature" carbon compounds, disequilibria, or other by-products of metabolism. Moreover, terahertz circular dichroism spectroscopy detects this machinery in a manner that makes few, if any, assumptions as to its chemical nature or the processes that it performs.

  18. Novel approach for non-invasive glucose sensing using vibrational contrast CD absorption measurements (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Yakovlev, Vladislav V.; Tovar, Carlos; Hokr, Brett; Petrov, Georgi I.

    2016-03-01

    Noninvasive glucose sensing is a Holy Grail of diabetes mellitus management. Unfortunately, despite a number of innovative concepts and a long history of continuous instrumental improvements, the problem remains largely unsolved. Here we propose and experimentally demonstrate the first successful implementation of a novel strategy based on vibrational overtone circular dichroism absorption measurements. Such an approach uses a short-wavelength infrared excitation (1000-2000 nm), which takes the advantage of lower light scattering and intrinsic chemical contrast provided by the chemical structure of D-glucose molecule. We model the propagation of circular polarized light in scattering medium using Monte Carlo simulations to show the feasibility of such approach in turbid medium and demonstrate the proof of principle using optical detection. We also investigate the possibility of using ultrasound detection through circular dichroism absorption measurements to achieve simple and sensitive glucose monitoring.

  19. LINEAR ACCELERATOR

    DOEpatents

    Christofilos, N.C.; Polk, I.J.

    1959-02-17

    Improvements in linear particle accelerators are described. A drift tube system for a linear ion accelerator reduces gap capacity between adjacent drift tube ends. This is accomplished by reducing the ratio of the diameter of the drift tube to the diameter of the resonant cavity. Concentration of magnetic field intensity at the longitudinal midpoint of the external sunface of each drift tube is reduced by increasing the external drift tube diameter at the longitudinal center region.

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

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

  1. Circular dichroism and thermal denaturation studies of subnucleosomes and their relationships to nucleosome structure

    SciTech Connect

    Mencke, A.J.; Rill, R.L.

    1982-01-01

    Chicken erythrocyte chromatin moderately digested with micrococcal nuclease yields several species of nucleosomes and subnucleosomes that are resolved by electrophoresis in the presence of 3 M urea. This report compares the circulr dichroism spectra, thermal denaturation, and certain other properties of chromatosomes (trimmed nucleosomes cores, and four subnucleosomes. One subnucleosome is a partial core lacking an H2a-H2b pair and 40-50 DNA base pairs(bp) from one end. The stoichiometries of the other subnucleosomes, which contain homotypic histones associated with short DNA fragments, are (H3)(H4)/70-80 bp, (H1)/60-70 bp, and (H2a)(H2b)/50-60 bp. The latter subnucleosomes originate from the ends of nucleosome cores. All properties of partial and whole nucleosome cores were nearly identical, indicating that the terminal H2a-H2b pairs do not make binding contacts with the residual core DNA or histones that are critical to the conformation of the remaining core structure. Analyses of histone contributions of the far-UV circular dichroism of subnucleosomes showed that H2a-H2b pairs and H3-H4 pairs in nucleosomes are both nearly 50% ..cap alpha.. helical and that their helix contents do not depend on the nucleosome integrity. These and other results suggest that homotypic histone pairs and the DNA they tightly bind define quasi-independent conformational subdomains within nucleosomes. H3-H4 pairs stabilized and reduced the 275-nm circular dichroism intensity of short DNA fragments much more effectively than H2a-H2b pairs. In addition, H3-H4 pairs stabilized considerably more DNA than predicted for simple electrostatic interactions. H1 also thermally stabilized less effectively than H3-H4 pairs, and modestly increased the 275-nm CD intensity relative to protein-free DNA.

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

    PubMed

    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.

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

    SciTech Connect

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

    1997-04-03

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

  4. Measurement of circular dichroism dynamics in a nanosecond temperature-jump experiment.

    PubMed

    Khuc, Mai-Thu; Mendonça, Lucille; Sharma, Sapna; Solinas, Xavier; Volk, Martin; Hache, François

    2011-05-01

    The use of a fast temperature jump (T-jump) is a very powerful experiment aiming at studying protein denaturation dynamics. However, probing the secondary structure is a difficult challenge and rarely yields quantitative values. We present the technical implementation of far-UV circular dichroism in a nanosecond T-jump experiment and show that this experiment allows us to follow quantitatively the change in the helical fraction of a poly(glutamic acid) peptide during its thermal denaturation with 12 ns time resolution.

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

    PubMed Central

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

    2013-01-01

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

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

    PubMed

    Reiter, Kevin; Kühn, Michael; Weigend, Florian

    2017-02-07

    We present an implementation of vibrational circular dichroism (VCD) spectra in TURBOMOLE. We mainly followed the route proposed by Cheeseman [Chem. Phys. Lett. 252, 211 (1996)] and extended the modules for calculating the magnetic response and vibrational frequencies accordingly. The implementation allows for gauge origin invariant employment of effective core potentials, as demonstrated for Co(ppy)3, ppy = 2-Phenylpyridine. In this way, scalar relativistic effects are covered and heavy elements can be treated. Further, with the present implementation molecular symmetry may be efficiently exploited, which makes the calculation of large (symmetric) systems feasible. The calculation of the VCD spectrum of icosahedral C620(2+) is shown as an illustrative application.

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

    PubMed

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

    2013-09-20

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

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

    PubMed

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

    2013-06-01

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

  10. Dichroism measurements in forensic fibre examination. Part 3 - dyed cotton and viscose fibres.

    PubMed

    De Wael, K; Lepot, L

    2011-12-01

    A number of dyed cellulosic fibres were examined with plane polarized light on their dichroic behavior by microscopy and microspectrophotometry (MSP-PPL). Significant dichroic effects (mostly hypochromic effects and hypsochromic bands shifts) were reported. The effect is related to the chemical structure: some dye structures always possess dichroism (azo, stilbene, thiazole and oxazine), some dyes demonstrate sometimes dichroic effects (anthraquinoid, indigoid) while other structures never demonstrate dichroic effects (sulphur, diphenylmethanes, triarylmethanes, phthalocyanines). In some cases a different dichroic behavior was found for the same dyes applied on cotton and on viscose.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    Reiter, Kevin; Kühn, Michael; Weigend, Florian

    2017-02-01

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

  13. Theoretical study of the X-ray natural circular dichroism of some crystalline amino acids

    NASA Astrophysics Data System (ADS)

    Takahashi, Osamu; Kimoto, Mai; Pettersson, Lars G. M.

    2015-04-01

    X-ray natural circular dichroism (XNCD) spectra of alanine and serine were calculated at the C, N, and O K-edges within the framework of density functional theory. Basis set and gauge dependence of D-alanine were examined as a test case. XNCD spectra of crystalline D-alanine and L-serine were obtained using cluster models of increasing size. The absolute intensities of the XNCD spectra were found to be reduced in the solid phase compared to the gas phase monomers, suggesting that a monomer model is not necessarily a good representation of the solid phase.

  14. Two-photon absorption in arsenic sulfide glasses

    NASA Astrophysics Data System (ADS)

    Chunaev, D. S.; Snopatin, G. E.; Plotnichenko, V. G.; Karasik, A. Ya.

    2016-10-01

    The two-photon absorption coefficient of 1047-{\\text{nm}} light in {\\text{As}}35{\\text{S}}65 chalcogenide glass has been measured. CW probe radiation has been used to observe the linear absorption in glass induced by two-photon excitation. The induced absorption lifetime was found to be ∼ 2 {\\text{ms}}.

  15. Stereoselective bile pigment binding to polypeptides and albumins: a circular dichroism study.

    PubMed

    Goncharova, Iryna; Urbanová, Marie

    2008-12-01

    Stereoselective recognition of bilirubin and biliverdin by poly(L-lysine) (PLL), poly(D-lysine) (PDL), and poly(L-arginine) (PLA) and their micelles with dodecanoate ions (C(12)) at different pH has been studied using a combination of vibrational and electronic circular dichroism. Biliverdin has been found to be more sensitive to pH in its complexes with the polypeptides. In acidic media in the complexes with PLL-C(12) and PDL-C(12) the conformation becomes more closed than the characteristic one found at physiological pH. Partial flattening and chiral self-association of bilirubin molecules takes place at higher concentrations with PLL and PDL. For both pigments, inversions of the ECD signals are observed in the systems with PLA at pH > or = 8.5. This study was carried out in order to clarify the role of Lys and Arg residues in pigment binding to serum albumin. The circular dichroism spectra obtained for bilirubin bound to different mammalian serum albumins have been compared with the homology within the IIA principal ligand-binding structural domains. Analysis suggests that the chiroptical properties of the pigment in the complexes with serum albumins depend on the location of Lys and/or Arg at positions 222 and 199 in the binding site.

  16. Advantages of synchrotron radiation circular dichroism spectroscopy to study intrinsically disordered proteins.

    PubMed

    Kumagai, Patricia S; DeMarco, Ricardo; Lopes, Jose L S

    2017-03-03

    The unordered secondary structural content of an intrinsically disordered protein (IDP) is susceptible to conformational changes induced by many different external factors, such as the presence of organic solvents, removal of water, changes in temperature, binding to partner molecules, and interaction with lipids and/or other ligands. In order to characterize the high-flexibility nature of an IDP, circular dichroism (CD) spectroscopy is a particularly useful method due to its capability of monitoring both subtle and remarkable changes in different environments, relative ease in obtaining measurements, the small amount of sample required, and the capability for sample recovery (sample not damaged) and others. Using synchrotron radiation as the light source for CD spectroscopy represents the state-of-the-art version of this technique with feasibility of accessing the lower wavelength UV region, and therefore presenting a series of advantages over conventional circular dichroism (cCD) to monitor a protein conformational behavior, check protein stability, detect ligand binding, and many others. In this paper, we have performed a comparative study using cCD and SRCD methods for investigating the secondary structure and the conformational behavior of natively unfolded proteins: MEG-14 and soybean trypsin inhibitor. We show that the SRCD technique greatly improves the analysis and accuracy of the studies on the conformations of IDPs.

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

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

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

  18. Synergistic gel formation of xyloglucan/gellan mixtures as sudied by rheology, DSC, and circular dichroism.

    PubMed

    Nitta, Yoko; Kim, Bo S; Nishinari, Katsuyoshi; Shirakawa, Mayumi; Yamatoya, Kazuhiko; Oomoto, Toshio; Asai, Iwao

    2003-01-01

    The gelation behavior of mixtures of tamarind seed xyloglucan (TSX) and sodium form gellan (Na-G) was investigated. The storage and loss shear moduli, G' and G'', of the mixtures showed that a thermoreversible gel was obtained although each polysaccharide alone did not form a gel at experimental conditions. The viscoelastic behavior of the mixtures showed a gel formation of TSX and Na-G induced by synergistic interaction. This synergistic interaction was also revealed by differential scanning calorimetry (DSC) and circular dichroism. Although TSX alone did not show any peak in DSC curves, mixtures with only a small amount of Na-G, which by itself did not show any peak, showed a single peak. With increasing Na-G content, another peak began to appear at the same temperature at which a peak of Na-G alone appeared. Thermally induced changes in circular dichroism of the mixtures were different from those expected from the individual behavior of TSX and Na-G.

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

    NASA Astrophysics Data System (ADS)

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

    2012-05-01

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

  20. A sensitive method based on fluorescence-detected circular dichroism for protein local structure analysis.

    PubMed

    Nehira, Tatsuo; Ishihara, Kaoru; Matsuo, Koichi; Izumi, Shunsuke; Yamazaki, Takeshi; Ishida, Atsuhiko

    2012-11-15

    We report an improved fluorescence-detected circular dichroism (FDCD)-based analytical method that is useful for probing protein three-dimensional structures. The method uses a novel FDCD device with an ellipsoidal mirror that functions on a standard circular dichroism (CD) spectrometer and eliminates all artifacts. Our experiments demonstrated three important findings. First, the method is applicable to any proteins either by using intrinsic fluorescence derived from tryptophan residues or by introducing a fluorescent label onto nonfluorescent proteins. Second, by using intrinsic fluorescence, FDCD spectroscopy can detect a structural change in the tertiary structure of metmyoglobin due to stepwise denaturation on a change in pH. Such changes could not be detected by conventional CD spectroscopy. Third, based on the typical advantages of fluorescence-based analyses, FDCD measurements enable observation of only the target proteins in a solution even in the presence of other peptides. Using our ellipsoidal mirror FDCD device, we could observe structural changes of fluorescently labeled calmodulin on binding with Ca(2+) and/or interacting with binding peptides. Because FDCD appears to reflect the protein's local structure around the fluorophore, it may provide a useful means for "pinpoint analysis" of protein structures.

  1. Secondary-structure analysis of denatured proteins by vacuum-ultraviolet circular dichroism spectroscopy.

    PubMed

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

    2007-06-01

    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 proteins exhibited characteristic VUVCD spectra that reflected a considerable amount of residual secondary structures. The contents of alpha-helices, beta-strands, turns, poly-L-proline type II (PPII), and unordered structures were estimated for each denatured state of the three proteins using the SELCON3 program with Protein Data Bank data and the VUVCD spectra of 31 reference proteins reported in our previous study. Based on these contents, the characteristics of the four types of denaturation were discussed for each protein. In all types of denaturation, a decrease in alpha-helices was accompanied by increases in beta-strands, PPII, and unordered structures. About 20% beta-strands were present even in the proteins fully unfolded by GdnHCl in which beta-sheets should be broken. From these results, we propose that denatured proteins constitute an ensemble of residual alpha-helices and beta-sheets, partly unfolded (or distorted) alpha-helices and beta-strands, PPII, and unordered structures.

  2. Conformational structure of bombesin as studied by vibrational and circular dichroism spectroscopy.

    PubMed

    Carmona, P; Lasagabaster, A; Molina, M

    1995-01-19

    Raman and Fourier transform infrared (FTIR) spectroscopies and circular dichroism (CD) have been applied to investigate the secondary structure of bombesin in the solid state and in phosphate buffer solution (pH 3.8). At concentrations around 10(-5) M, circular dichroism reveals that bombesin exists as an irregular or disordered conformation. However, the secondary structure of the peptide appears to be a mixture of disordered structure and intermolecular beta-sheets in 0.01 M sodium phosphate buffer when the peptide concentrations are higher than around 6.5 mM. The tendency of bombesin to form aggregated beta-sheet species seems to be originated mainly in the sequence of the residues 7-14, as supported by the Raman spectra and beta-sheet propensities (P beta) of the amino-acid residues. It is the hydrophobic force of this amino-acid sequence, and not a salt bridge effect, that is the factor responsible for the formation of peptide aggregates.

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

    PubMed

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

    2013-04-01

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

  4. Light-driven linear helical supramolecular polymer formed by molecular-recognition-directed self-assembly of bis(p-sulfonatocalix[4]arene) and pseudorotaxane.

    PubMed

    Sun, Ruyi; Xue, Chenming; Ma, Xiang; Gao, Min; Tian, He; Li, Quan

    2013-04-24

    A light-driven, linear, chiral supramolecular polymer was constructed in water by host-guest molecular recognition between bis(p-sulfonatocalix[4]arene) and the α-cyclodextrin-based pseudo[3]rotaxane containing axially chiral 1,1'-binaphthyl and photoresponsive azobenzene moieties. The successful supramolecular polymerization by non-covalent host-guest molecular recognition was confirmed by (1)H NMR spectroscopy and dynamic light scattering (DLS) measurements, and its photoresponsive behavior was investigated by UV-vis absorption spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The chirality of this supramolecular polymer was confirmed by circular dichroism spectroscopy. The dramatic morphology change of this chiral polymer driven by light was observed in SEM, AFM and TEM images. More interestingly, dynamically self-assembled, light-driven, single-helical linear supramolecular polymer molecules with lengths of hundreds of nanometers to micrometers in water were directly observed in their native state using cryo-TEM measurements. The observation of considerably lengthy individual supramolecular polymer molecules indicates that the molecular self-assembly in water by non-covalent host-guest molecular recognition is sufficiently strong to form the supramolecular polymer. Moreover, preliminary molecular modeling was performed to substantiate this interesting photoresponsive supramolecular structure.

  5. LINEAR ACCELERATOR

    DOEpatents

    Colgate, S.A.

    1958-05-27

    An improvement is presented in linear accelerators for charged particles with respect to the stable focusing of the particle beam. The improvement consists of providing a radial electric field transverse to the accelerating electric fields and angularly introducing the beam of particles in the field. The results of the foregoing is to achieve a beam which spirals about the axis of the acceleration path. The combination of the electric fields and angular motion of the particles cooperate to provide a stable and focused particle beam.

  6. Theory of Monte Carlo simulations of the magnetic circular dichroism spectra of alkali metal/rare gas systems

    NASA Astrophysics Data System (ADS)

    Kenney, John W.; Boatz, Jerry A.; Terrill Vosbein, Heidi A.

    The history of magnetic circular dichroism (MCD) spectroscopy in the study of alkali metal/rare gas (M/Rg) cryogenic systems is reviewed in the context of developing a better understanding of alkali metal/hydrogen systems of current interest to the U.S. Air Force as enhanced-performance cryogenic rocket propellants. A new theory for simulating the MCD spectra of M/Rg systems is presented together with a careful discussion of the theory's implicit and explicit approximations and their implications. This theory uses a classical Monte Carlo (MC) simulation scheme to model the perturbing effects of the Rg environment on the 2S → 2P MCD-active transition of the M atom. The theory sets up the MC-MCD simulation as a 6 × 6 matrix eigenvalue/eigenvector problem in the 2P manifold in which are included the effects of M-Rg interactions, metal atom spin-orbit coupling in the 2P manifold, magnetic Zeeman perturbations of the 2S and 2P manifolds, Boltzmann temperature factors, and electric dipole transition moment integrals for left circularly polarized (LCP) and right circularly polarized (RCP) light. The theory may be applied to any type of trapping site of the host M in the guest Rg matrix; a single atom substitutional metal atom trapping site (one host Rg atom is replaced by one guest M atom) is modeled in this study for M = Na and Rg = Ar. Two temperature factors are used in these simulations; a lattice temperature to model the mobility of the Rg lattice and a magnetic temperature to model Boltzmann factors in the 2S ground manifold. The 6 × 6 eigenvalue/eigenvector problem is solved for a number of randomly generated and suitably averaged Rg configurations to yield the simulated MC-MCD spectrum for the single substitutional Na/Ar system. The MC-MCD simulations of Na/Ar give the characteristic triplet MCD spectrum with the correct Boltzmann temperature dependence. The simulated MC-MCD spectrum correctly inverts when the direction of the applied magnetic field is

  7. Linear Clouds

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Context image for PIA03667 Linear Clouds

    These clouds are located near the edge of the south polar region. The cloud tops are the puffy white features in the bottom half of the image.

    Image information: VIS instrument. Latitude -80.1N, Longitude 52.1E. 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

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

    DOE PAGES

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

    2014-09-30

    The calculations presented here reveal that an electron probe carrying orbital angular momentum is just a particular case of a wider class of electron beams that can be used to measure electron magnetic circular dichroism (EMCD) with atomic resolution. It is possible to obtain an EMCD signal with atomic resolution by simply breaking the symmetry of the electron probe phase front using the aberration-corrected optics of a scanning transmission electron microscope. The probe’s required phase distribution depends on the sample’s magnetic symmetry and crystal structure. The calculations indicate that EMCD signals that use the electron probe’s phase are as strongmore » as those obtained by nanodiffraction methods.« less

  9. Conformational Effects on the Circular Dichroism of Human Carbonic Anhydrase II: A Multilevel Computational Study

    PubMed Central

    Karabencheva-Christova, Tatyana G.; Carlsson, Uno; Balali-Mood, Kia; Black, Gary W.; Christov, Christo Z.

    2013-01-01

    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. PMID:23526922

  10. Rotationally Resolved Magnetic Vibrational Circular Dichroism of Hydrogen Chloride and Deuterium Chloride

    NASA Astrophysics Data System (ADS)

    Tam, C. N.; Keiderling, T. A.

    1993-02-01

    The magnetic vibrational circular dichroism (MVCD) spectra of HCI and DCI are presented. The average rotational g-value of H35Cl in the first excited vibrational states was determined to be 0.45 l and 0.449 for the P and R branches, respectively, using moment analysis of the MVCD bandshapes. In addition, the gJ-values of H37Cl, D35Cl, and D37Cl were measured for the first time. Within our experimental error, the gJ-values obtained were consistent with the accepted gJ-values for the ground state of H35Cl and with theoretically calculated gJ-values for the other isotopomers. The results show that MVCD can provide an alternative method to microwave spectroscopy or molecular beam magnetic resonance spectroscopy for determining rotational g-values.

  11. Vitamin E Circular Dichroism Studies: Insights into Conformational Changes Induced by the Solvent's Polarity.

    PubMed

    Marquardt, Drew; Van Oosten, Brad J; Ghelfi, Mikel; Atkinson, Jeffrey; Harroun, Thad A

    2016-12-14

    We used circular dichroism (CD) to study differences in CD spectra between α-, δ-, and methylated-α-tocopherol in solvents with different polarities. CD spectra of the different tocopherol structures differ from each other in intensity and peak locations, which can be attributed to chromanol substitution and the ability to form hydrogen bonds. In addition, each structure was examined in different polarity solvents using the Reichardt index-a measure of the solvent's ionizing ability, and a direct measurement of solvent-solute interactions. Differences across solvents indicate that hydrogen bonding is a key contributor to CD spectra at 200 nm. These results are a first step in examining the hydrogen bonding abilities of vitamin E in a lipid bilayer.

  12. Strong intermolecular exciton couplings in solid-state circular dichroism of aryl benzyl sulfoxides.

    PubMed

    Padula, Daniele; Di Pietro, Sebastiano; Capozzi, Maria Annunziata M; Cardellicchio, Cosimo; Pescitelli, Gennaro

    2014-09-01

    A series of 13 enantiopure aryl benzyl sulfoxides () with different substituents on the two aromatic rings has been previously analyzed by means of electronic circular dichroism (CD) spectroscopy. Most of these compounds are crystalline and their X-ray structure is established. For almost one-half of the series, CD spectra measured in the solid state were quite different from those in acetonitrile solution. We demonstrate that the difference is due to strong exciton couplings between molecules packed closely together in the crystal. The computational approach consists of time-dependent density functional theory (TDDFT) calculations run on "dimers" composed of nearest neighbors found in the lattice. Solid-state CD spectra are well reproduced by the average of all possible pairwise terms. The relation between the crystal space group and conformation, and the appearance of solid-state CD spectra, is also discussed.

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

    PubMed

    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.

  14. Development of a universal ellipsoidal mirror device for fluorescence detected circular dichroism: elimination of polarization artifacts.

    PubMed

    Nehira, Tatsuo; Tanaka, Katsunori; Takakuwa, Takashi; Ohshima, Chie; Masago, Hisashi; Pescitelli, Gennaro; Wada, Akio; Berova, Nina

    2005-01-01

    We have developed an ellipsoidal mirror fluorescence detected circular dichroism (FDCD) device with enhanced detection sensitivity that eliminates the polarization artifact; this is applicable to samples with strongly polarized fluorescence. The device, JASCO FDCD465, has an ellipsoidal mirror structure with a framework consisting of three mirrors (one elliptical and two plane mirrors) that maximally collects light in the FDCD. All assemblies on the device including the ellipsoidal mirror, cylindrical cell, and photomultiplier tube (PMT) are aligned on the chamber-fitting sample mount as an attachment compatible with a standard CD spectropolarimeter. The new FDCD465 device eliminates the polarization artifact caused by anisotropic distribution of the emitted light. It represents a convenient, reliable, and sensitive FDCD attachment to the JASCO J-800 CD spectrometer series that can be used under both isotropic and photoselected conditions.

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

    SciTech Connect

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

    2014-09-30

    The calculations presented here reveal that an electron probe carrying orbital angular momentum is just a particular case of a wider class of electron beams that can be used to measure electron magnetic circular dichroism (EMCD) with atomic resolution. It is possible to obtain an EMCD signal with atomic resolution by simply breaking the symmetry of the electron probe phase front using the aberration-corrected optics of a scanning transmission electron microscope. The probe’s required phase distribution depends on the sample’s magnetic symmetry and crystal structure. The calculations indicate that EMCD signals that use the electron probe’s phase are as strong as those obtained by nanodiffraction methods.

  16. Circular dichroism of stem bromelain: a third spectral class within the family of cysteine proteinases.

    PubMed Central

    Arroyo-Reyna, A; Hernandez-Arana, A; Arreguin-Espinosa, R

    1994-01-01

    Two forms of stem bromelain (EC 3.4.22.4) were isolated from commercial, crude and chromatographically purified preparations of the enzyme by means of gel-filtration and cation-exchange liquid chromatography. These forms possess nearly identical secondary and tertiary structures, as judged from their circular dichroism (c.d.) spectra. The spectral characteristics of stem bromelain suggest that this enzyme belongs to the alpha + beta protein class, as other cysteine proteinases do. In agreement with these results, quantitative estimation of secondary structures yielded amounts similar to those for papain and proteinase omega. However, the bromelain c.d. curve is clearly distinguishable from those reported for papain and proteinase omega, on one hand, and that of chymopapain, on the other. Thus, it is apparent that there are at least three types of c.d. spectra associated with the family of cysteine proteinases. PMID:8198520

  17. Microfluidic mixers for the investigation of rapid protein folding kinetics using synchrotron radiation circular dichroism spectroscopy.

    PubMed

    Kane, Avinash S; Hoffmann, Armin; Baumgärtel, Peter; Seckler, Robert; Reichardt, Gerd; Horsley, David A; Schuler, Benjamin; Bakajin, Olgica

    2008-12-15

    We have developed a microfluidic mixer optimized for rapid measurements of protein folding kinetics using synchrotron radiation circular dichroism (SRCD) spectroscopy. The combination of fabrication in fused silica and synchrotron radiation allows measurements at wavelengths below 220 nm, the typical limit of commercial instrumentation. At these wavelengths, the discrimination between the different types of protein secondary structure increases sharply. The device was optimized for rapid mixing at moderate sample consumption by employing a serpentine channel design, resulting in a dead time of less than 200 micros. Here, we discuss the design and fabrication of the mixer and quantify the mixing efficiency using wide-field and confocal epi-fluorescence microscopy. We demonstrate the performance of the device in SRCD measurements of the folding kinetics of cytochrome c, a small, fast-folding protein. Our results show that the combination of SRCD with microfluidic mixing opens new possibilities for investigating rapid conformational changes in biological macromolecules that have previously been inaccessible.

  18. A simple method for correction of circular dichroism spectra obtained from membrane-containing samples.

    PubMed

    Chakraborty, Hirak; Lentz, Barry R

    2012-02-07

    Circular dichroism (CD) spectroscopy is an important technique in structural biology for examining folding and conformational changes of proteins in solution. However, the use of CD spectroscopy in a membrane medium (and also in a nonhomogeneous medium) is limited by (i) high light scattering and (ii) differential scattering of incident left and right circularly polarized light, especially at shorter wavelengths (<200 nm). We report a novel methodology for estimating the distortion of CD spectra caused by light scattering for membrane-bound peptides and proteins. The method is applied to three proteins with very different secondary structures to illustrate the limits of its capabilities when calibrated with a simple soluble peptide ([Ac]ANLKALEAQKQKEQRQAAEELANAK[OH], standard peptide) with a balanced secondary structure. The method with this calibration standard was quite successful in estimating α-helix but more limited when it comes to proteins with very high β-sheet or β-turn content.

  19. Vacuum-ultraviolet circular dichroism reveals DNA duplex formation between short strands of adenine and thymine.

    PubMed

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

    2012-11-21

    Absorbance spectroscopy is used extensively to tell when two DNA single strands come together and form a double strand. Here we show that circular dichroism in the vacuum ultraviolet region provides an even stronger indication for duplex formation in the case of short strands of adenine and thymine (4 to 16 bases in each strand). Indeed, our results show that a strong positive CD band appears at 179 nm when double strands are formed. Melting experiments were done in aqueous solution with and without added Na(+) counter ions. With additional salt present a huge increase in the 179 nm CD band was observed when lowering the temperature. A 179 nm CD marker band for duplex formation can be used to measure the kinetics for the association of two single strands. Such experiments rely on large changes at one particular wavelength since it is too time-consuming to record a full-wavelength spectrum.

  20. Universality of photoelectron circular dichroism in the photoionization of chiral molecules

    NASA Astrophysics Data System (ADS)

    Beaulieu, S.; Ferré, A.; Géneaux, R.; Canonge, R.; Descamps, D.; Fabre, B.; Fedorov, N.; Légaré, F.; Petit, S.; Ruchon, T.; Blanchet, V.; Mairesse, Y.; Pons, B.

    2016-10-01

    Photoionization of chiral molecules by circularly polarized radiation gives rise to a strong forward/backward asymmetry in the photoelectron angular distribution, referred to as photoelectron circular dichroism (PECD). Here we show that PECD is a universal effect that reveals the inherent chirality of the target in all ionization regimes: single photon, multiphoton, above-threshold and tunnel ionization. These different regimes provide complementary spectroscopic information at electronic and vibrational levels. The universality of the PECD can be understood in terms of a classical picture of the ionizing process, in which electron scattering on the chiral potential under the influence of a circularly polarized electric field results in a strong forward/backward asymmetry.

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

    PubMed Central

    Dolamic, Igor; Varnholt, Birte; Bürgi, Thomas

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

    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.

  3. Vitamin E Circular Dichroism Studies: Insights into Conformational Changes Induced by the Solvent’s Polarity

    PubMed Central

    Marquardt, Drew; Van Oosten, Brad J.; Ghelfi, Mikel; Atkinson, Jeffrey; Harroun, Thad A.

    2016-01-01

    We used circular dichroism (CD) to study differences in CD spectra between α-, δ-, and methylated-α-tocopherol in solvents with different polarities. CD spectra of the different tocopherol structures differ from each other in intensity and peak locations, which can be attributed to chromanol substitution and the ability to form hydrogen bonds. In addition, each structure was examined in different polarity solvents using the Reichardt index—a measure of the solvent’s ionizing ability, and a direct measurement of solvent–solute interactions. Differences across solvents indicate that hydrogen bonding is a key contributor to CD spectra at 200 nm. These results are a first step in examining the hydrogen bonding abilities of vitamin E in a lipid bilayer. PMID:27983631

  4. Chiral Orbital Angular Momentum and Circular Dichroism ARPES in p- and d-orbital Bands

    NASA Astrophysics Data System (ADS)

    Park, Jin-Hong; Han, Jung Hoon

    2012-02-01

    We derive explicit formulas relating the circular dichroism angle-resolved photoemission (CD-ARPES) signal to the existence of nonzero chiral orbital angular momentum (OAM) in the band structure. The existence of nonzero chiral OAM is a generic feature of surface states that break inversion symmetry, as pointed out in several recent articles [1-3]. We propose that CD-ARPES setup is an effective probe of the OAM of quasi-particles occupying the surface states. Explicit formulas for the p- and d-orbital bands are derived to show that the CD-ARPES signal is proportional to the OAM in the momentum space.[4pt] [1] S. R. Park, C. H. Kim, J. Yu, J. H. Han and C. Kim, Phys. Rev. Lett. 107, 156803 (2011).[0pt] [2] S. R. Park et al., arXiv:1103.0805 (2011).[0pt] [3] Choong H. Kim et al., arXiv:1107.3285 (2011).

  5. Rashba splitting in an image potential state investigated by circular dichroism two-photon photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Nakazawa, T.; Takagi, N.; Kawai, Maki; Ishida, H.; Arafune, R.

    2016-09-01

    We have explored the band splitting and spin texture of the image potential state (IPS) on Au(001) derived from the Rashba-type spin-orbit interaction (SOI) by using angle-resolved bichromatic two-photon photoemission (2PPE) spectroscopy in combination with circular dichroism (CD). The Rashba parameter for the first (n =1 ) IPS is determined to be 48-20+8meV Å , which is consistent with the spin-polarized band structure calculated from the embedded Green's function technique for semi-infinite crystals. The present results demonstrate that bichromatic CD-2PPE spectroscopy is powerful for mapping the spin-polarized unoccupied band structures originating from SOIs in various classes of condensed matter.

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

    PubMed Central

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

    2015-01-01

    In this work, the circular dichroisms (CD) of nanorice heterodimers consisting of two parallel arranged nanorices with the same size but different materials are investigated theoretically. Symmetry-breaking is introduced by using different materials and oblique incidence to achieve strong CD at the vicinity of Fano resonance peaks. We demonstrate that all Au-Ag heterodimers exhibit multipolar Fano resonances and strong CD effect. A simple quantitative analysis shows that the structure with larger Fano asymmetry factor has stronger CD. The intensity and peak positions of the CD effect can be flexibly tuned in a large range by changing particle size, shape, the inter-particle distance and surroundings. Furthermore, CD spectra exhibit high sensitivity to ambient medium in visible and near infrared regions. Our results here are beneficial for the design and application of high sensitive CD sensors and other related fields. PMID:26538460

  7. Spin polarization and magnetic dichroism in core-level photoemission from ferromagnets

    SciTech Connect

    Menchero, Jose Gabriel

    1997-05-01

    In this thesis we present a theoretical investigation of angle- and spin-resolved core-level photoemission from ferromagnetic Fe and Ni. We also consider magneto-dichroic effects due to reversal of the photon helicity or reversal of the sample magnetization direction. In chapter 1, we provide a brief outline of the history of photoemission, and show how it has played an important role in the development of modern physics. We then review the basic elements of the theory of core-level photoemission, and discuss the validity of the some of the commonly-used approximations. In chapter 2, we present a one-electron theory to calculate spin- and angle-resolved photoemission spectra for an arbitrary photon polarization. The Hamiltonian includes both spin-orbit and exchange interactions. As test cases for the theory, we calculate the spin polarization and magnetic dichroism for the Fe 2p core level, and find that agreement with experiment is very good.

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

    PubMed

    Zsila, F; Hollósi, M; Gergely, A

    2000-11-01

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

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

    PubMed

    Campbell, Kirby R; Campagnola, Paul J

    2017-03-02

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

  10. First-principles approach to the dynamic magnetoelectric couplings for the non-reciprocal directional dichroism in BiFeO3

    DOE PAGES

    Kezsmarki, I.; Fishman, Randy Scott

    2016-04-18

    Due to the complicated magnetic and crystallographic structures of BiFeO3, its magnetoelectric (ME) couplings and microscopic model Hamiltonian remain poorly understood. By employing a firstprinciples approach, we uncover all possibleMEcouplings associated with the spin-current (SC) and exchange-striction (ES) polarizations, and construct an appropriate Hamiltonian for the long-range spin-cycloid in BiFeO3. First-principles calculations are used to understand the microscopic origins of theMEcouplings.Wefind that inversion symmetries broken by ferroelectric and antiferroelectric distortions induce the SC and the ES polarizations, which cooperatively produce the dynamicME effects in BiFeO3. A model motivated by first principles reproduces the absorption difference of counter-propagating light beams calledmore » non-reciprocal directional dichroism. The current paper focuses on the spin-driven (SD) polarizations produced by a dynamic electric field, i.e. the dynamic MEcouplings. Due to the inertial properties of Fe, the dynamic SD polarizations differ significantly from the static SD polarizations. Our systematic approach can be generally applied to any multiferroic material, laying the foundation for revealing hiddenMEcouplings on the atomic scale and for exploiting opticalMEeffects in the next generation of technological devices such as optical diodes.« less

  11. First-principles approach to the dynamic magnetoelectric couplings for the non-reciprocal directional dichroism in BiFeO3

    SciTech Connect

    Kezsmarki, I.; Fishman, Randy Scott

    2016-04-18

    Due to the complicated magnetic and crystallographic structures of BiFeO3, its magnetoelectric (ME) couplings and microscopic model Hamiltonian remain poorly understood. By employing a firstprinciples approach, we uncover all possibleMEcouplings associated with the spin-current (SC) and exchange-striction (ES) polarizations, and construct an appropriate Hamiltonian for the long-range spin-cycloid in BiFeO3. First-principles calculations are used to understand the microscopic origins of theMEcouplings.Wefind that inversion symmetries broken by ferroelectric and antiferroelectric distortions induce the SC and the ES polarizations, which cooperatively produce the dynamicME effects in BiFeO3. A model motivated by first principles reproduces the absorption difference of counter-propagating light beams called non-reciprocal directional dichroism. The current paper focuses on the spin-driven (SD) polarizations produced by a dynamic electric field, i.e. the dynamic MEcouplings. Due to the inertial properties of Fe, the dynamic SD polarizations differ significantly from the static SD polarizations. Our systematic approach can be generally applied to any multiferroic material, laying the foundation for revealing hiddenMEcouplings on the atomic scale and for exploiting opticalMEeffects in the next generation of technological devices such as optical diodes.

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

    SciTech Connect

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

    2000-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  14. X-ray magnetic circular dichroism and photoemission studies of ferromagnetism in CaMn1-xRuxO3 thin films

    NASA Astrophysics Data System (ADS)

    Terai, K.; Yoshii, K.; Takeda, Y.; Fujimori, S. I.; Saitoh, Y.; Ohwada, K.; Inami, T.; Okane, T.; Arita, M.; Shimada, K.; Namatame, H.; Taniguchi, M.; Kobayashi, K.; Kobayashi, M.; Fujimori, A.

    2008-03-01

    We have studied the electronic and magnetic properties of epitaxially grown CaMn1-xRuxO3 thin films (x=1.0,0.75,0.5) by soft x-ray absorption, soft x-ray magnetic circular dichroism (XMCD), and hard x-ray photoemission spectroscopy (HXPES) measurements. The XMCD studies indicated that the spin moments of Mn and Ru are aligned in opposite directions. The valence-band HXPES spectra revealed that the Ru4d t2g states around the Fermi level and the Mn3d t2g up-spin states centered ˜2eV below it showed systematic concentration dependences. From these results, we propose that the localized Mn3d t2g states and the itinerant Ru4d t2g band are antiferromagnetically coupled and give rise to the ferromagnetic ordering, which is in analogy to the mechanism proposed for double perovskite oxides, such as Sr2FeMoO6 .

  15. Effects of electron configuration and coordination number on the vibrational circular dichroism spectra of metal complexes of trans-1,2-diaminocyclohexane.

    PubMed

    Merten, Christian; Hiller, Kaitlynd; Xu, Yunjie

    2012-10-05

    Transition metal complexes of ethylenediamine have attracted significant interest as prototype systems for a range of studies related to their chiroptical properties. In order to better elucidate the effects of different central metal ions and also different coordination numbers on the vibrational circular dichroism (VCD) spectra, trans-1,2-diamino cyclohexane (chxn) was chosen as the chiral ligands in the current report. In this case the conformation of the diamino ligand is predetermined by its absolute configuration and the transition from the λ- to the δ-form that can occur in the case of ethylenediamine is no longer possible. The fingerprint region of the vibrational absorption and VCD spectra of three transition metal complexes of chxn have been analysed in detail. For the tris chelate complexes Ni(chxn)(3)(2+) and Cu(chxn)(3)(2+), selective enhancement of some VCD bands in the otherwise almost identical spectra has been observed and explained in terms of a ring current mechanism and of a different number of unpaired electrons of the metal centers. The comparison of the VCD spectra of Cu(chxn)(3)(2+) and Cu(chxn)(2)(2+) reveals the effects of coordination number that manifest as an inversion of the strong bisignate VCD pattern of the NH(2) scissor vibrational modes. This leads to the conclusion that this region can be used to extract information about the ligand environment and the chirality of the metal center.

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

    PubMed

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

    2011-09-22

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

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  18. Theory of graphene saturable absorption

    NASA Astrophysics Data System (ADS)

    Marini, A.; Cox, J. D.; García de Abajo, F. J.

    2017-03-01

    Saturable absorption is a nonperturbative nonlinear optical phenomenon that plays a pivotal role in the generation of ultrafast light pulses. Here we show that this effect emerges in graphene at unprecedentedly low light intensities, thus opening avenues to new nonlinear physics and applications in optical technology. Specifically, we theoretically investigate saturable absorption in extended graphene by developing a semianalytical nonperturbative single-particle approach, describing electron dynamics in the atomically-thin material using the two-dimensional Dirac equation for massless Dirac fermions, which is recast in the form of generalized Bloch equations. By solving the electron dynamics nonperturbatively, we account for both interband and intraband contributions to the intensity-dependent saturated conductivity and conclude that the former dominates regardless of the intrinsic doping state of the material. We obtain results in qualitative agreement with atomistic quantum-mechanical simulations of graphene nanoribbons including electron-electron interactions, finite-size, and higher-band effects. Remarkably, such effects are found to affect mainly the linear absorption, while the predicted saturation intensities are in good quantitative agreement in the limit of extended graphene. Additionally, we find that the modulation depth of saturable absorption in graphene can be electrically manipulated through an externally applied gate voltage. Our results are relevant for the development of graphene-based optoelectronic devices, as well as for applications in mode-locking and random lasers.

  19. Slow light and saturable absorption

    NASA Astrophysics Data System (ADS)

    Selden, A. C.

    2009-06-01

    Quantitative analysis of slow light experiments utilising coherent population oscillation (CPO) in a range of saturably absorbing media, including ruby and alexandrite, Er3+:Y2SiO5, bacteriorhodopsin, semiconductor quantum devices and erbium-doped optical fibres, shows that the observations may be more simply interpreted as saturable absorption phenomena. A basic two-level model of a saturable absorber displays all the effects normally associated with slow light, namely phase shift and modulation gain of the transmitted signal, hole burning in the modulation frequency spectrum and power broadening of the spectral hole, each arising from the finite response time of the non-linear absorption. Only where hole-burning in the optical spectrum is observed (using independent pump and probe beams), or pulse delays exceeding the limits set by saturable absorption are obtained, can reasonable confidence be placed in the observation of slow light in such experiments. Superluminal (“fast light”) phenomena in media with reverse saturable absorption (RSA) may be similarly explained.

  20. Perpendicular magnetic anisotropy and the reorientation transition of the magnetization in CeH2/Fe multilayers probed by x-ray magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Arend, M.; Felsch, W.; Krill, G.; Delobbe, A.; Baudelet, F.; Dartyge, E.; Kappler, J.-P.; Finazzi, M.; San Miguel-Fuster, A.; Pizzini, S.; Fontaine, A.

    1999-02-01

    The transition of the magnetization of multilayers [CeH2(x Å)/Fe(16 Å)]×n, x=10, 16, 25, from planar to perpendicular orientation at low temperatures is explained on a microscopic basis by performing angle- and temperature-dependent measurements of x-ray magnetic circular dichroism at the 2p absorption edge of Fe and at the 2p and 3d absorption edges of Ce. The 3d orbital magnetic moment in the Fe sublayers is considerably enhanced with respect to bulk bcc Fe and distinctly larger parallel to the layer normal than perpendicular to it. The Ce 4f states in these structures are well localized. The 4f magnetic moment is oriented along the layer normal due to a strong single-ion anisotropy resulting from crystal-field effects. The spin-split 3d states of Fe induce magnetic order on the Ce 5d states via hybridization and spin-orbit coupling, even on ions more distant from the interface. By intra-atomic 5d-4f exchange coupling the 4f states become magnetically polarized, with increasing strength toward low temperature. Together with the 5d-mediated 4f-3d coupling and the crystal-field induced single-ion 4f anisotropy this leads to a perpendicular orientation of the Fe 3d moment at low temperature. Hence the Ce 4f states are the motor of the reorientation transition of the multilayer magnetization. The 4f-5d exchange interaction in the hydrided Ce sublayers affects dramatically the spectral shape of the dichroic Ce 5d spectra and, at low temperature, the ratio of the integrated signals at the L2 and L3 edges.

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

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

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

    DOE PAGES

    Ueland, B. G.; Pandey, Abhishek; Lee, Y.; ...

    2015-05-27

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

  3. X-ray absorption spectroscopy to analyze nuclear geometry and electronic structure of biological metal centers--potential and questions examined with special focus on the tetra-nuclear manganese complex of oxygenic photosynthesis.

    PubMed

    Dau, Holger; Liebisch, Peter; Haumann, Michael

    2003-07-01

    X-ray absorption spectroscopy (XAS) has become a prominent tool for the element-specific analysis of transition metals at the catalytic center of metalloenzymes. In the present study the information content of X-ray spectra with respect to the nuclear geometry and, in particular, to the electronic structure of the protein-bound metal ions is explored using the manganese complex of photosystem II (PSIII) as a model system. The EXAFS range carries direct information on the number and distances of ligands as well as on the chemical type of the ligand donor function. For first-sphere ligands and second-sphere metals (in multinuclear complexes), the determination of precise distances is mostly straightforward, whereas the determination of coordination numbers clearly requires more effort. The EXAFS section starts with an exemplifying discussion of a PSII spectrum data set with focus on the coordination number problem. Subsequently, the method of linear dichroism EXAFS spectroscopy is introduced and it is shown how the EXAFS data leads to an atomic resolution model for the tetra-manganese complex of PSII. In the XANES section the following aspects are considered: (1) Alternative approaches are evaluated for determination of the metal-oxidation state by comparison with a series of model compounds. (2) The interpretation of XANES spectra in terms of molecular orbitals (MOs) is approached by comparative multiple-scattering calculations and MO calculations. (3) The underlying reasons for the oxidation-state dependence of the XANES spectra are explored. Furthermore, the potential of modern XANES theory is demonstrated by presenting first simulations of the dichroism in the XANES spectra of the PSII manganese complex.

  4. UV-visible microscope spectrophotometric polarization and dichroism with increased discrimination power in forensic analysis

    NASA Astrophysics Data System (ADS)

    Purcell, Dale Kevin

    Microanalysis of transfer (Trace) evidence is the application of a microscope and microscopical techniques for the collection, observation, documentation, examination, identification, and discrimination of micrometer sized particles or domains. Microscope spectrophotometry is the union of microscopy and spectroscopy for microanalysis. Analytical microspectroscopy is the science of studying the emission, reflection, transmission, and absorption of electromagnetic radiation to determine the structure or chemical composition of microscopic-size materials. Microscope spectrophotometry instrument designs have evolved from monochromatic illumination which transmitted through the microscope and sample and then is detected by a photometer detector (photomultiplier tube) to systems in which broad-band (white light) illumination falls incident upon a sample followed by a non-scanning grating spectrometer equipped with a solid-state multi-element detector. Most of these small modern spectrometers are configured with either silicon based charged-couple device detectors (200-950 nm) or InGaAs based diode array detectors (850-2300 nm) with computerized data acquisition and signal processing being common. A focus of this research was to evaluate the performance characteristics of various modern forensic (UV-Vis) microscope photometer systems as well as review early model instrumental designs. An important focus of this research was to efficiently measure ultraviolet-visible spectra of microscopically small specimens for classification, differentiation, and possibly individualization. The first stage of the project consisted of the preparation of microscope slides containing neutral density filter reference materials, molecular fluorescence reference materials, and dichroic reference materials. Upon completion of these standard slide preparations analysis began with measurements in order to evaluate figures of merit for comparison of the instruments investigated. The figures of

  5. Atmospheric absorption cell characterization

    NASA Astrophysics Data System (ADS)

    1982-06-01

    The measurement capability of the Avionics Laboratory IR Facility was used to evaluate an absorption cell that will be used to simulate atmospheric absorption over horizontal paths of 1 - 10 km in length. Band models were used to characterize the transmittance of carbon dioxide (CO2), nitrogen (N2), and nitrous oxide (N2O) in the cell. The measured transmittance was compared to the calculated values. Nitrous oxide is important in the 4 - 4.5 micron range in shaping the weak line absorption of carbon dioxide. The absorption cell is adequate for simulating atmospheric absorption over these paths.

  6. On the linear and non-linear electronic spectroscopy of chlorophylls: a computational study.

    PubMed

    Graczyk, Alicja; Żurek, Justyna M; Paterson, Martin J

    2014-01-01

    A theoretical analysis of linear and non-linear (two-photon absorption) electronic spectroscopy of all known porphyrinic pigments has been performed using linear and quadratic density functional response theory, with the long-range corrected CAM-B3LYP functional. We found that higher Soret transitions often contain non-Gouterman contributions and that each chlorophyll has the possibility for resonance enhanced TPA in the Soret region, although there is also significant TPA in the Q region.

  7. Excitation dynamics in Phycoerythrin 545: modeling of steady-state spectra and transient absorption with modified Redfield theory.

    PubMed

    Novoderezhkin, Vladimir I; Doust, Alexander B; Curutchet, Carles; Scholes, Gregory D; van Grondelle, Rienk

    2010-07-21

    We model the spectra and excitation dynamics in the phycobiliprotein antenna complex PE545 isolated from the unicellular photosynthetic cryptophyte algae Rhodomonas CS24. The excitonic couplings between the eight bilins are calculated using the CIS/6-31G method. The site energies are extracted from a simultaneous fit of the absorption, circular dichroism, fluorescence, and excitation anisotropy spectra together with the transient absorption kinetics using the modified Redfield approach. Quantitative fit of the data enables us to assign the eight exciton components of the spectra and build up the energy transfer picture including pathways and timescales of energy relaxation, thus allowing a visualization of excitation dynamics within the complex.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

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

    2015-11-01

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

  10. Ligand Induced Circular Dichroism and Circularly Polarized Luminescence in CdSe Quantum Dots

    PubMed Central

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

    2014-01-01

    Chiral thiol capping ligands L- and D-cysteines induced modular chiroptical properties in achiral cadmium selenide quantum dots (CdSe QDs). Cys-CdSe prepared from achiral oleic acid capped CdSe by post-synthetic ligand exchange displayed size-dependent electronic circular dichroism (CD) and circularly polarized luminescence (CPL). Opposite CPL signals were measured for the CdSe QDs capped with D- and L-cysteine. The CD profile and CD anisotropy varied with size of CdSe nanocrystals with largest anisotropy observed for CdSe nanoparticles of 4.4 nm. Magic angle spinning solid state NMR (MAS ssNMR) experiments suggested bidentate interaction between cysteine and the surface of CdSe. Density functional theory (DFT) calculations verified that attachment of L- and D-cysteine to the surface of model (CdSe)13 nanoclusters induces measurable opposite CD signals for the exitonic band of the nanocluster. The chirality was induced by the hybridization of highest occupied CdSe molecular orbitals with those of the chiral ligand. PMID:24200288

  11. Thermal unfolding of the N-terminal region of p53 monitored by circular dichroism spectroscopy.

    PubMed

    Schaub, Leasha J; Campbell, James C; Whitten, Steven T

    2012-11-01

    It has been estimated that 30% of eukaryotic protein and 70% of transcription factors are intrinsically disordered (ID). The biochemical significance of proteins that lack stable tertiary structure, however, is not clearly understood, largely owing to an inability to assign well-defined structures to specific biological tasks. In an attempt to investigate the structural character of ID protein, we have measured the circular dichroism spectrum of the N-terminal region of p53 over a range of temperatures and solution conditions. p53 is a well-studied transcription factor that has a proline-rich N-terminal ID region containing two activation domains. High proline content is a property commonly associated with ID, and thus p53 may be a good model system for investigating the biochemical importance of ID. The spectra presented here suggest that the N-terminal region of p53 may adopt an ordered structure under physiological conditions and that this structure can be thermally unfolded in an apparent two-state manner. The midpoint temperature for this thermal unfolding of the N-terminal region of p53 was at the near-physiological temperature of 39°C, suggesting the possibility of a physiological role for the observed structural equilibrium.

  12. Nuclear magnetic resonance and circular dichroism study of metastin (Kisspeptin-54) structure in solution.

    PubMed

    Shin, Ronald; Welch, Danny R; Mishra, Vinod K; Nash, Kevin T; Hurst, Douglas R; Rama Krishna, N

    2009-01-01

    KISS1 was first discovered as a metastasis suppressor, but also plays crucial roles in the onset of puberty. The KISS1 gene encodes a secreted protein of 145 amino acids that exhibits no sequence similarity with any known proteins. KISS1 protein is proteolytically processed to generate a number of so-called kisspeptins (KP), the most well characterized is known as KP-54 or metastin. KP-54 is carboxy-terminally amidated and binds to and activates the KISS1 receptor (KISS1R). The current studies were undertaken in order to determine structure of KP-54 using nuclear magnetic resonance and circular dichroism. KP-54 is mostly disordered both in water and in trifluoroethanol/water mixed solvent, with no structural motifs. In sodium dodecyl sulfate micelles, KP-54 remains mostly disordered except for a small increase in helical propensity (from 3.7% in water to 9.9% in micelles). Despite this apparent lack of structure, KP-54 is biologically active. The intrinsic disorder of KP-54 may confer advantages in its ability to recognize and bind a wide range of target proteins.

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

    PubMed

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

    2014-04-01

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

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

    PubMed

    Štěpánek, Petr; Bouř, Petr

    2013-07-05

    Magnetic circular dichroism (MCD) spectroscopy has been established as a convenient method to study electronic structure, in particular for small symmetric organic molecules. Newer applications on more complex systems are additionally stimulated by the latest availability of precise quantum-chemical techniques for the spectral simulations. In this work, a sum over states (SOS) summation is reexamined as an alternative to the derivative techniques for the MCD modeling. Unlike in previous works, the excited electronic states are calculated by the time-dependent density functional theory (TDDFT). A gradient formulation of the MCD intensities is also proposed, less dependent on the origin choice than the standard expressions. The dependencies of the results on the basis set, number of electronic states, and coordinate origin are tested on model examples, including large symmetric molecules with degenerate electronic states. The results suggest that the SOS/TDDFT approach is a viable and accurate technique for spectral simulation. It may even considerably reduce the computational time, if compared with the traditional MCD computational procedures based on the response theory.

  15. Ultrafast carbonyl motion of the photoactive yellow protein chromophore probed by femtosecond circular dichroism.

    PubMed

    Mendonça, Lucille; Hache, François; Changenet-Barret, Pascale; Plaza, Pascal; Chosrowjan, Haik; Taniguchi, Seiji; Imamoto, Yasushi

    2013-10-02

    Motions of the trans-p-coumaric acid carbonyl group following the photoexcitation of the R52Q mutant of photoactive yellow protein (PYP) are investigated, for the first time, by ultrafast time-resolved circular dichroism (TRCD) spectroscopy. TRCD is monitored in the near-ultraviolet, over a time scale of 10 ps. Immediately after excitation, TRCD is found to exhibit a large negative peak, which decays within a few picoseconds. A quantitative analysis of the signals shows that, upon excitation, the carbonyl group undergoes a fast (≪0.8 ps) and unidirectional flipping motion in the excited state with an angle of ca. 17-53°. For the subset of proteins that do not enter the signaling photocycle, TRCD provides strong evidence that the carbonyl group moves back to its initial position, leading to the formation of a nonreactive ground-state intermediate of trans conformation. The initial ground state is then restored within ca. 3 ps. Comparative study of R52Q and wild-type PYP provides direct evidence that the absence of Arg52 has no effect on the conformational changes of the chromophore during those steps.

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

    NASA Astrophysics Data System (ADS)

    Wenzel, Stephan; Buss, Volker

    1997-04-01

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

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

    PubMed

    Jin, Xue; Jiang, Jian; Liu, Minghua

    2016-12-27

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

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

    SciTech Connect

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

    2004-08-01

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

  19. Detection of electron magnetic circular dichroism signals under zone axial diffraction geometry.

    PubMed

    Song, Dongsheng; Rusz, Jan; Cai, Jianwang; Zhu, Jing

    2016-10-01

    EMCD (electron magnetic circular dichroism) technique provides us a new opportunity to explore magnetic properties in the transmission electron microscope. However, specific diffraction geometry is the major limitation. Only the two-beam and three-beam case are demonstrated in the experiments until now. Here, we present the more general case of zone axial (ZA) diffraction geometry through which the EMCD signals can be detected even with the very strong sensitivity to dynamical diffraction conditions. Our detailed calculations and well-controlled diffraction conditions lead to experiments in agreement with theory. The effect of dynamical diffraction conditions on EMCD signals are discussed both in theory and experiments. Moreover, with the detailed analysis of dynamical diffraction effects, we experimentally obtain the separate EMCD signals for each crystallographic site in Y3Fe5O12, which is also applicable for other materials and cannot be achieved by site-specific EMCD and XMCD technique directly. Our work extends application of more general diffraction geometries and will further promote the development of EMCD technique.

  20. Probing the Interaction of Quantum Dots with Chiral Capping Molecules Using Circular Dichroism Spectroscopy

    PubMed Central

    2016-01-01

    Circular dichroism (CD) induced at exciton transitions by chiral ligands attached to single component and core/shell colloidal quantum dots (QDs) was used to study the interactions between QDs and their capping ligands. Analysis of the CD line shapes of CdSe and CdS QDs capped with l-cysteine reveals that all of the features in the complex spectra can be assigned to the different excitonic transitions. It is shown that each transition is accompanied by a derivative line shape in the CD response, indicating that the chiral ligand can split the exciton level into two new sublevels, with opposite angular momentum, even in the absence of an external magnetic field. The role of electrons and holes in this effect could be separated by experiments on various types of core/shell QDs, and it was concluded that the induced CD is likely related to interactions of the highest occupied molecular orbitals of the ligands with the holes. Hence, CD was useful for the analysis of hole level–ligand interactions in quantum semiconductor heterostructures, with promising outlook toward better general understanding the properties of the surface of such systems. PMID:27960517

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

    PubMed Central

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

    2015-01-01

    The dipole interaction model is a classical electromagnetic theory for calculating circular dichroism (CD) resulting from the π-π* transitions of amides. The theoretical model, pioneered by J. Applequist, is assembled into a package, DInaMo, written in Fortran allowing for treatment of proteins. DInaMo reads Protein Data Bank formatted files of structures generated by molecular mechanics or reconstructed secondary structures. Crystal structures cannot be used directly with DInaMo; they either need to be rebuilt with idealized bond angles and lengths, or they need to be energy minimized to adjust bond lengths and bond angles because it is common for crystal structure geometries to have slightly short bond lengths, and DInaMo is sensitive to this. DInaMo reduces all the amide chromophores to points with anisotropic polarizability and all nonchromophoric aliphatic atoms including hydrogens to points with isotropic polarizability; all other atoms are ignored. By determining the interactions among the chromophoric and nonchromophoric parts of the molecule using empirically derived polarizabilities, the rotational and dipole strengths are determined leading to the calculation of CD. Furthermore, ignoring hydrogens bound to methyl groups is initially explored and proves to be a good approximation. Theoretical calculations on 24 proteins agree with experiment showing bands with similar morphology and maxima. PMID:26370961

  2. Multiple site-specific infrared dichroism of CD3-zeta, a transmembrane helix bundle.

    PubMed

    Torres, Jaume; Briggs, John A G; Arkin, Isaiah T

    2002-02-15

    The structure of the transmembrane domain of CD3-zeta a component of the T-cell receptor involved in signal transduction, has been studied in its native state (a lipid bilayer) by multiple site-specific infrared dichroism. For the first time, the transmembrane domain has been labelled at multiple positions along the sequence, representing a total of 11 samples, each labelled at a different residue with an isotopically modified carbonyl group, (13)C [double bond] (18)O. A strategy is outlined that, based on the above data, can yield the rotational orientation and the local helix tilt for each labelled residue, giving a detailed description of helix geometry. The results obtained indicate that the transmembrane segment is in an alpha-helical conformation throughout, with an average helix tilt of 12 degrees. The N-terminal side of the helix is more tilted than the C-terminal. In an accompanying paper we describe the implementation of the infrared data in a model-building study of the CD3-zeta transmembrane complex. The model obtained is entirely consistent with results based on evolutionary conservation data. Taken together, this study represents the first step towards elucidation of the backbone structure of a transmembrane alpha-helical bundle by infrared spectroscopy.

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

    PubMed

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

    1990-01-01

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

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

    PubMed Central

    Gopal, Ramamourthy; Park, Jin Soon; Seo, Chang Ho; Park, Yoonkyung

    2012-01-01

    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 (KW)4 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. PMID:22489150

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  7. Circular dichroism spectroscopy of chlorin e6 and its complexes with quantum dots in different media

    NASA Astrophysics Data System (ADS)

    Kundelev, E. V.; Orlova, A. O.; Maslov, V. G.; Baranov, A. V.; Fedorov, A. V.

    2017-01-01

    The circular dichroism (CD) spectra of chlorin e6 and its complexes with ZnS:Mn/ZnS and CdSe/ZnS quantum dots (QDs) in aqueous solutions with different pH, in methanol, and in dimethyl sulfoxide (DMSO) have been experimentally investigated. The changes in the CD spectra of free chlorin e6 caused by its complexing with semiconductor QDs are analyzed. The application of CD spectroscopy made it possible to record for the first time the CD spectrum of luminescent dimer of chlorin e6 and reveal a nonluminescent aggregate of chlorin e6 (interpreted preliminary as a "tetramer"), the anisotropy factor of which exceeds that of its monomer by a factor of 40. An analysis of the experimental data shows that chlorin e6 in a complex with QDs can be either in the monomeric form or in the form of a nonluminescent "tetramer." The interaction with a relatively low-stable luminescent dimer of chlorin e6 with QDs leads to its partial monomerization and formation of complexes where chlorin e6 is in the monomeric form.

  8. Comparison of vibrational circular dichroism instruments: development of a new dispersive VCD.

    PubMed

    Lakhani, Ahmed; Malon, Petr; Keiderling, Timothy A

    2009-07-01

    A dispersive vibrational circular dichroism (VCD) instrument has been designed and optimized for the measurement of mid-infrared (MIR) bands such as the amide I and amide II vibrational modes of peptides and proteins. The major design considerations were to construct a compact VCD instrument for biological molecules, to increase signal-to-noise (S/N) ratio, to simultaneously collect and digitize the sample transmission and polarization modulation signals, and to digitally ratio them to yield a VCD spectrum. These were realized by assembling new components using design factors adapted from previous VCD instruments. A collection of spectra for peptides and proteins having different dominant secondary structures (alpha-helix, beta-sheet, and random coil) measured for identical samples under the same conditions showed that the new instrument had substantially improved S/N as compared with our previous dispersive VCD instrument. These instruments both provide protein VCD for the amide I that are comparable to or somewhat better than those measurable with commercial Fourier transform (FT) VCD instruments if just the amide I band in the spectra is obtained at modest resolution (8 cm(-1)) with the same total data collection time on each type of instrument.

  9. The determination of the absolute configurations of chiral molecules using vibrational circular dichroism (VCD) spectroscopy.

    PubMed

    Stephens, Philip J; Devlin, Frank J; Pan, Jian-Jung

    2008-05-15

    The vibrational circular dichroism (VCD) spectra of the two enantiomers of a chiral molecule are of equal magnitude and opposite sign: i.e. mirror-image enantiomers give mirror-image VCD spectra. In principle, the absolute configuration (AC) of a chiral molecule can therefore be determined from its VCD spectrum. In practice, the determination of the AC of a chiral molecule from its experimental VCD spectrum requires a methodology which reliably predicts the VCD spectra of its enantiomers. The only reliable methodology developed to date uses the Stephens quantum-mechanical theory of the rotational strengths of fundamental vibrational transitions, developed in the early 1980s, implemented using ab initio density functional theory in the GAUSSIAN program in the mid 1990s. This methodology has by now been widely used in determining ACs from experimental VCD spectra. In this article we discuss the protocol for determining the ACs of chiral molecules with optimum reliability and its implementation for a variety of molecules, including the D3 symmetry perhydrotriphenylene, a thiazino-oxadiazolone recently shown to be a highly active calcium entry channel blocker, the alkaloid natural products schizozygine, iso-schizogaline, and iso-schizogamine, and the iridoid natural products plumericin, iso-plumericin, and prismatomerin. The power of VCD spectroscopy in determining ACs, even for large organic molecules and for substantially conformationally-flexible organic molecules is clearly documented.

  10. Fluorescence and Circular Dichroism Spectroscopy of Cytochrome c in Alkylammonium Formate Ionic Liquids

    PubMed Central

    Wei, Wenjun; Danielson, Neil D.

    2012-01-01

    The structural stability of cytochrome c has been studied in alkylammonium formate (AAF) ionic liquids such as methylammonium formate (MAF) and ethylammonium formate (EAF) by fluorescence and circular dichroism (CD) spectroscopy. At room temperature, the native structure of cytochrome c is maintained in relatively high ionic liquid concentrations (50%–70% AAF/water or AAF/phosphate buffer pH 7.0) in contrast to denaturation of cytochrome c in similar solutions of methanol or acetonitrile, with water or buffer co-solvents. Fluorescence and CD spectra indicate the conformation of cytochrome c is maintained in 20% AAF-80% water from 30 – 50 °C. No such temperature stability is found in 80% AAF-20% water. About one third of the enzyme activity of cytochrome c in 80% AAF-20% water can be maintained as compared to phosphate buffer and this is greater than the activities measured in corresponding methanol and acetonitrile aqueous solutions. This biophysical study shows that AAFs have potential application as organic solvent replacements at moderate temperature in the mobile phase for the separation of proteins in their native form by reversed phase liquid chromatography. PMID:21210672

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

    PubMed

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

    2015-09-07

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

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

    PubMed Central

    Cao, Tun; Wei, Chenwei; Mao, Libang

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  14. Optical Dichroism in Fibers of Aligned SWNT Inferred from Polarized Raman Spectroscopy

    NASA Astrophysics Data System (ADS)

    Alldredge, J. W.; Gommans, H. H.; Tashiro, H.; Park, J.; Magnuson, J.; Rinzler, A. G.

    2000-03-01

    To probe the 1D nature of single wall carbon nanotubes (SWNT) in bulk samples we devised a method for generating fibers of aligned SWNT. We measured polarization dependent Raman spectra on the oriented fibers to verify mode assignments appearing in the literature. Surprisingly, ALL the Raman line intensities are observed to decrease in EQUAL amounts for 647.1 nm laser excitation polarized perpendicular to the fiber axis versus that polarized parallel to the fiber axis. We attribute this anisotropy to a consequence of the 1D nature of the nanotubes. The strong Raman signal from SWNT has been ascribed to resonance Raman scattering with optical transitions between van Hove singularities in the 1D density of states. When the excitation is polarized along the nanotube axis it excites transitions between these singularities in the (metallic) nanotubes of the sample. For the polarization perpendicular to the nanotube axis, evidently no such optical transitions (resonant with our laser) are available, yielding the uniformly smaller Raman signal. The fibers thus exhibit optical dichroism. This effect frustrates the use of polarized Raman spectroscopy for identification of vibration mode symmetries, however the Raman polarization ratio provides a convenient measure of the degree of SWNT alignment in the fibers .

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

    PubMed Central

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

    2016-01-01

    Circular Dichroism data are often decomposed into their constituent spectra to quantify the secondary structure of peptides or proteins but the estimation of the secondary structure content fails when light scattering leads to spectral distortion. If peptide-induced liposome self-association occurs, subtracting control curves cannot correct for this. We show that if the cause of the light scattering is independent from the peptide structural changes, the CD spectra can be corrected using principal component analysis (PCA). The light scattering itself is analysed and found to be in good agreement with backscattering experiments. This method therefore allows to simultaneously follow structural changes related to peptide-liposome binding as well as peptide induced liposome self-association. We apply this method to study the structural changes and liposome binding of vectofusin-1, a transduction enhancing peptide used in lentivirus based gene therapy. Vectofusin-1 binds to POPC/POPS liposomes, causing a reversal of the negative liposome charge at high peptide concentrations. When the peptide charges exactly neutralise the lipid charges on both leaflets reversible liposome self-association occurs. These results are in good agreement with biological observations and provide further insight into the conditions required for efficent transduction enhancement. PMID:28004740

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

    PubMed

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

    2010-01-01

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

  17. Magnetic Circular Dichroism of X-Ray Emission for Gadolinium in 4d-4f Excitation Region

    NASA Astrophysics Data System (ADS)

    Takayama, Yasuhiro; Shinoda, Motoki; Obu, Kenji; Lee, Chol; Shiozawa, Hidetsugu; Hirose, Masaaki; Ishii, Hiroyoshi; Miyahara, Tsuneaki; Okamoto, Jun

    2002-01-01

    We have measured magnetic circular dichroism of x-ray emission spectra (XES) for gadolinium in the 4d-4f excitation region. At a pre-threshold excitation energy, a large magnetic circular dichroism (MCD) signal appeared in a Raman scattering and the dramatic dependence of the MCD spectra on the excitation energy was observed. Theoretical calculation shows that the magnetic moment estimated with total photoelectron yield (TEY) spectra was much smaller than that with the emission spectra. This indicates that the MCD for the TEY reflects the magnetic state on the surface whereas the MCD for the XES reflects that in the bulk. We also observed the MCD spectra for total photon yield (TPY) and found the great difference of the MCD spectra for the TEY and TPY.

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  20. Synchrotron Radiation Circular Dichroism (SRCD) Spectroscopy: An Emerging Method in Structural Biology for Examining Protein Conformations and Protein Interactions

    SciTech Connect

    Wallace, B.A.; Sutherland, J.; Gekko, K.; Hoffmann, S. V.; Lin, Y.-H.; Tao, Y.; Wien, F.; Janes, R. W.

    2011-09-01

    Circular dichroism (CD) spectroscopy is a well-established technique in structural biology. The use of synchrotron radiation as an intense light source for these measurements extends the applications possible using lab-based instruments. In recent years, there has been a major growth in synchrotron radiation circular dichroism (SRCD) beamlines worldwide, including ones at the NSLS, ISA, SRS, HiSOR, BSRF, NSRRC, SOLEIL, Diamond, TERAS, BESSYII, and ANKA synchrotrons. Through the coordinated efforts of beamline scientists and users at these sites, important proof-of-principle studies have been done enabling the method to be developed for novel and productive studies on biological systems. This paper describes the characteristics of SRCD beamlines and some of the new types of applications that have been undertaken using these beamlines.

  1. New synchrotron radiation circular dichroism end-station on DISCO beamline at SOLEIL synchrotron for biomolecular analysis.

    PubMed

    Miron, Simona; Réfregiers, Matthieu; Gilles, Anne-Marie; Maurizot, Jean-Claude

    2005-08-05

    The novel Synchrotron Radiation Circular Dichroism (SRCD) technique is becoming a new tool of investigation for the molecular structures of biomolecules, like proteins, carbohydrates or others bio-materials. Here, we describe the characteristics of a new experimental end-station for circular dichroism studies, in construction on DISCO beamline at SOLEIL synchrotron (Saint-Aubin, France). This experimental end-station will be an open facility for the community of researchers in structural biology. In order to show the kind of information accessible with this type of technique, we give an example: the conformational study of the galactose mutarotase from Escherichia coli, an enzyme involved in the galactose metabolism. This study was made using an operational SRCD station available at SRS (Daresbury Laboratory, UK).

  2. Light Scattering and Absorption Studies of Sickle Cell Hemoglobin

    NASA Astrophysics Data System (ADS)

    Kim-Shapiro, Daniel

    1997-11-01

    exponentially. The length of this delay time depends on the concentration of deoxy-HbS. The kinetics of polymerization was described by a novel double nucleation mechanism. These light scattering studies led to the understanding that many cells could travel through oxygen deficient tissue without sickling due to the delay time in polymerization. Some treatment strategies involve prolonging the delay time. Less work has been done in trying to understand polymer melting. Such investigations are important in order to determine whether polymers that reach the lungs melt before they enter the oxygen deficient tissues. I have initially addressed this problem by exploring the kinetics of oxygen binding to the polymers. These studies were conducted using time-resolved linear dichroism following laser photolysis. Preliminary studies in my laboratory indicate that polymer melting is slow enough to be an important consideration in understanding sickle cell disease. One of the most common therapies for sickle cell disease that is currently used involves administering the drug, hydroxyurea. The mechanism by which this drug benefits patients is not fully understood. One of its mechanisms (as determined by light scattering and absorption studies) involves increasing the delay time for polymerization.

  3. [Oligonucleotides and their analogs. II. Spectra of the circular dichroism of dinucleoside phosphate analogs containing 4-thiouracil].

    PubMed

    Kritsyn, A M; Mikhaĭlov, S N; Stepanov, S V; Florent'ev, V L

    1978-01-01

    The dinucleoside phosphates analogues APpSU, SUPpA and UPpSU have been synthesised by direct thionation of DNP analogues, containing cytosine. The structure of compounds prepared was proved by UV- and PMR-spectra. The CD spectra of the DNP analogues were examined. It has been demonstrated that the "induced" dichroism contribution in the Cotton-effect of DNP was substantial in the case of stacking conformations and negligible for unstacking conformations.

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

  5. Anomalous absorption of laser light on ion acoustic fluctuations

    NASA Astrophysics Data System (ADS)

    Rozmus, Wojciech; Bychenkov, Valery Yu.

    2016-10-01

    Theory of laser light absorption due to ion acoustic turbulence (IAT) is discussed in high Z plasmas where ion acoustic waves are weakly damped. Our theory applies to the whole density range from underdense to critical density plasmas. It includes an absorption rate for the resonance anomalous absorption due to linear conversion of electromagnetic waves into electron plasma oscillations by the IAT near the critical density in addition to the absorption coefficient due to enhanced effective electron collisionality. IAT is driven by large electron heat flux through the return current instability. Stationary spectra of IAT are given by weak plasma turbulence theory and applied in description of the anomalous absorption in the inertial confinement fusion plasmas at the gold walls of a hohlraum. This absorption is anisotropic in nature due to IAT angular anisotropy and differs for p- and s-polarization of the laser radiation. Possible experiments which could identify the resonance anomalous absorption in a laser heated plasma are discussed.

  6. Vibrational circular dichroism (VCD), VCD exciton coupling, and X-ray determination of the absolute configuration of an α,β-unsaturated germacranolide.

    PubMed

    Sánchez-Castellanos, Mariano; Bucio, María A; Hernández-Barragán, Angelina; Joseph-Nathan, Pedro; Cuevas, Gabriel; Quijano, Leovigildo

    2015-03-01

    The absolute configuration of was deduced by vibrational circular dichroism together with the evaluation of the Flack and Hooft X-ray parameters. Vibrational circular dichroism exciton coupling, using the carbonyl group signals, confirmed the absolute configuration of . In addition, sodium borohydride reduction of the 11,13-double bond of 6-epi-desacetyllaurenobiolide () yields an almost equimolecular mixture of C11 epimers, while reduction of the same double bond of 6-epi-laurenobiolide () provided almost exclusively the (11S) diastereoisomer .

  7. Electronic circular dichroism of the chiral rigid tricyclic dilactam with nonplanar tertiary amide groups.

    PubMed

    Pazderková, Markéta; Profant, Václav; Seidlerová, Beata; Dlouhá, Helena; Hodačová, Jana; Jávorfi, Tamás; Siligardi, Giuliano; Baumruk, Vladimír; Bednárová, Lucie; Maloň, Petr

    2014-09-25

    Electronic circular dichroism (ECD) of the spirocyclic dilactam 5,8-diazatricyclo[6,3,0,0(1,5)]undecane-4,9-dione has been measured in the extended wavelength range (170-260 nm) utilizing far-UV CD instrumentation including synchrotron radiation light source. The data of this model of two nonplanar tertiary amide groups interacting within the rigid chiral environment provided new information particularly about the shorter wavelength π-π* transition region below 190 nm. The interpretation using TDDFT calculations confirmed that effects of amide nonplanarity follow our previous observations on monolactams as far as amide n-π* transitions are concerned. ECD band in the n-π* transition region of the nonplanar diamide exhibits an identical bathochromic shift and its sign remains tied to the sense of nonplanar deformation in the same way. As far as n-π* transitions are concerned amide nonplanarity acts as a local phenomenon independently reflecting sum properties of single amide groups. On the other hand, CD bands associated with π-π* transitions (found between ∼170 to 210 nm) form an exciton-like couplet with the sign pattern determined by mutual orientation of the associated electric transition moments. This sign pattern follows predictions pertaining to a coupled oscillator. The influence of amide nonplanarity on π-π* transitions is only minor and concentrates into the shorter wavelength lobe of the π-π* couplet. The detailed analysis of experimental ECD with the aid of TDDFT calculations shows that there is only little interaction between effects of inherent chirality caused by nonplanarity of amide groups and amide-amide coupling. Consequently these two effects can be studied nearly independently using ECD. In addition, the calculations indicate that participation of other type of transitions (n-σ*, π-σ* or Rydberg type transitions) is only minor and is concentrated below 180 nm.

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

    NASA Astrophysics Data System (ADS)

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

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

  9. Magnetic circular dichroism of symmetry and spin forbidden transitions of high-spin metal ions

    NASA Astrophysics Data System (ADS)

    Oganesyan, Vasily S.; Thomson, Andrew J.

    2000-09-01

    Recently we have developed a general method of analyzing magnetic circular dichroism (MCD) spectra and magnetization curves of high-spin metal ions for spin-allowed transitions [Oganesyan et al., J. Chem. Phys. 110, 762 (1999)]. In the present article this approach is extended to cover the cases of spin- and symmetry-forbidden transitions. At high ligand fields many low-energy ligand field transitions become spin-forbidden. Extraction of information content about the electronic structure of the ground state can be obtained through the analysis and correlation of the positions, signs, and intensities of the MCD bands and magnetization curves of these transitions. The casting of the theory in terms of the irreducible tensor method allows full advantage to be taken of any symmetry elements and simplifies multielectron calculations. The theory is valid over the entire range of magnetic field strength and, therefore, allows the information content of spectra over the full field and temperature range to be exploited. The method is applied to the analysis of the recorded MCD spectra and magnetization curves of the lowest energy spin-forbidden ligand field transitions of pseudo-tetrahedral high-spin Fe(III), S=5/2, in the protein rubredoxin from Methanobacterium thermoautotrophicum (strain Marburg). The predicted signs, intensities, and magnetization curves for these transitions are in excellent agreement with experimental data. We also show that when the anisotropy of the ground state is larger than the Zeeman splitting the MCD of both spin-forbidden and allowed transitions can become comparable in magnitude. Hence caution is needed in order to avoid the misinterpretation of experimental results.

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

    PubMed

    Pistolozzi, Marco; Bertucci, Carlo

    2008-03-01

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

  11. Ultracentrifuge and circular dichroism studies of folding equilibria in a retro GCN4-like leucine zipper.

    PubMed Central

    Holtzer, M E; Braswell, E; Angeletti, R H; Mints, L; Zhu, D; Holtzer, A

    2000-01-01

    Equilibrium ultracentrifuge and circular dichroism (CD) studies of a retropeptide of a GCN4-like leucine zipper in neutral saline buffer are reported as functions of temperature. Ultracentrifuge results indicate the presence of three oligomeric species: monomer, dimer, and tetramer, in quantifiable amounts, and the data provide values for the standard DeltaG, DeltaH, and DeltaS for interconversion. CD at 222 nm displays the strong concentration dependence characteristic of dissociative unfolding, but also shows a helicity far below that of the parent propeptide. Remarkably enough, the CD at 222 nm shows an extremum in the region between 0 and 20 degrees C. At higher T, the usual cooperative unfolding is observed. Comparable data are presented for a mutant retropeptide, in which a single asparagine residue is restored to the characteristic heptad position it occupies in the propeptide. The mutant shows marked differences from its unmutated relative in both thermodynamic properties and CD, although the oligomeric ensemble also comprises monomers, dimers, and tetramers. The mutant is closer in helicity to the parent propeptide but is less stable. These findings do not support either of the extant views on retropeptides. The behavior seen is consistent neither with the view that retropeptides should have the same structure as propeptides nor with the view that they should have the same structure but opposite chirality. The simultaneous availability of oligomeric population data and CD allows the latter to be dissected into individual contributions from monomers, dimers, and tetramers. This dissection yields explanations for the observed extrema in curves of CD (222 nm) versus T and reveals that the dimer population in both retropeptides undergoes "cold denaturation." PMID:10733982

  12. First-principles approach to the dynamic magnetoelectric couplings for the non-reciprocal directional dichroism in BiFeO3

    NASA Astrophysics Data System (ADS)

    Lee, Jun Hee; Kézsmáki, István; Fishman, Randy S.

    2016-04-01

    Due to the complicated magnetic and crystallographic structures of BiFeO3, its magnetoelectric (ME) couplings and microscopic model Hamiltonian remain poorly understood. By employing a first-principles approach, we uncover all possible ME couplings associated with the spin-current (SC) and exchange-striction (ES) polarizations, and construct an appropriate Hamiltonian for the long-range spin-cycloid in BiFeO3. First-principles calculations are used to understand the microscopic origins of the ME couplings. We find that inversion symmetries broken by ferroelectric and antiferroelectric distortions induce the SC and the ES polarizations, which cooperatively produce the dynamic ME effects in BiFeO3. A model motivated by first principles reproduces the absorption difference of counter-propagating light beams called non-reciprocal directional dichroism. The current paper focuses on the spin-driven (SD) polarizations produced by a dynamic electric field, i.e. the dynamic ME couplings. Due to the inertial properties of Fe, the dynamic SD polarizations differ significantly from the static SD polarizations. Our systematic approach can be generally applied to any multiferroic material, laying the foundation for revealing hidden ME couplings on the atomic scale and for exploiting optical ME effects in the next generation of technological devices such as optical diodes. This manuscript has been written by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the US Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan.

  13. Microscopic Theory and Simulation of Quantum-Well Intersubband Absorption

    NASA Technical Reports Server (NTRS)

    Li, Jianzhong; Ning, C. Z.

    2004-01-01

    We study the linear intersubband absorption spectra of a 15 nm InAs quantum well using the intersubband semiconductor Bloch equations with a three-subband model and a constant dephasing rate. We demonstrate the evolution of intersubband absorption spectral line shape as a function of temperature and electron density. Through a detailed examination of various contributions, such as the phase space filling effects, the Coulomb many-body effects and the non-parabolicity effect, we illuminate the underlying physics that shapes the spectra. Keywords: Intersubband transition, linear absorption, semiconductor heterostructure, InAs quantum well

  14. Solar absorption surface panel

    DOEpatents

    Santala, Teuvo J.

    1978-01-01

    A composite metal of aluminum and nickel is used to form an economical solar absorption surface for a collector plate wherein an intermetallic compound of the aluminum and nickel provides a surface morphology with high absorptance and relatively low infrared emittance along with good durability.

  15. Rectal absorption of propylthiouracil.

    PubMed

    Bartle, W R; Walker, S E; Silverberg, J D

    1988-06-01

    The rectal absorption of propylthiouracil (PTU) was studied and compared to oral absorption in normal volunteers. Plasma levels of PTU after administration of suppositories of PTU base and PTU diethanolamine were significantly lower compared to the oral route. Elevated plasma reverse T3 levels were demonstrated after each treatment, however, suggesting a desirable therapeutic effect at this dosage level for all preparations.

  16. Petawatt laser absorption bounded

    PubMed Central

    Levy, Matthew C.; Wilks, Scott C.; Tabak, Max; Libby, Stephen B.; Baring, Matthew G.

    2014-01-01

    The interaction of petawatt (1015 W) lasers with solid matter forms the basis for advanced scientific applications such as table-top particle accelerators, ultrafast imaging systems and laser fusion. Key metrics for these applications relate to absorption, yet conditions in this regime are so nonlinear that it is often impossible to know the fraction of absorbed light f, and even the range of f is unknown. Here using a relativistic Rankine-Hugoniot-like analysis, we show for the first time that f exhibits a theoretical maximum and minimum. These bounds constrain nonlinear absorption mechanisms across the petawatt regime, forbidding high absorption values at low laser power and low absorption values at high laser power. For applications needing to circumvent the absorption bounds, these results will accelerate a shift from solid targets, towards structured and multilayer targets, and lead the development of new materials. PMID:24938656

  17. Temporal evolutional absorption behaviors of graphene under Landau quantization

    NASA Astrophysics Data System (ADS)

    Hamedi, H. R.; Sahrai, M.

    2017-02-01

    We investigate the evolutional absorption behaviors of Landau-quantized graphene structure based on the transient solution to the density matrix equations of the motion. The impact of various system parameters on temporal evolution of probe absorption is studied. In addition, the required times for switching the high-absorption case to the zero-absorption (transparency) of a probe field is discussed. Due to unusual optical and electronic characteristics of graphene resulting from linear, massless dispersion of electrons near the Dirac point and the chiral character of electron states, our study may have potential applications in telecommunication, biomedicine, and optical information processing and may cause significant impact on technological applications.

  18. Quasar Absorption Studies

    NASA Technical Reports Server (NTRS)

    Mushotzky, Richard (Technical Monitor); Elvis, Martin

    2004-01-01

    The aim of the proposal is to investigate the absorption properties of a sample of inter-mediate redshift quasars. The main goals of the project are: Measure the redshift and the column density of the X-ray absorbers; test the correlation between absorption and redshift suggested by ROSAT and ASCA data; constrain the absorber ionization status and metallicity; constrain the absorber dust content and composition through the comparison between the amount of X-ray absorption and optical dust extinction. Unanticipated low energy cut-offs where discovered in ROSAT spectra of quasars and confirmed by ASCA, BeppoSAX and Chandra. In most cases it was not possible to constrain adequately the redshift of the absorber from the X-ray data alone. Two possibilities remain open: a) absorption at the quasar redshift; and b) intervening absorption. The evidences in favour of intrinsic absorption are all indirect. Sensitive XMM observations can discriminate between these different scenarios. If the absorption is at the quasar redshift we can study whether the quasar environment evolves with the Cosmic time.

  19. DESIRS: a state-of-the-art VUV beamline featuring high resolution and variable polarization for spectroscopy and dichroism at SOLEIL.

    PubMed

    Nahon, Laurent; de Oliveira, Nelson; Garcia, Gustavo A; Gil, Jean-François; Pilette, Bertrand; Marcouillé, Olivier; Lagarde, Bruno; Polack, François

    2012-07-01

    DESIRS is a new undulator-based VUV beamline on the 2.75 GeV storage ring SOLEIL (France) optimized for gas-phase studies of molecular and electronic structures, reactivity and polarization-dependent photodynamics on model or actual systems encountered in the universe, atmosphere and biosphere. It is equipped with two dedicated endstations: a VUV Fourier-transform spectrometer (FTS) for ultra-high-resolution absorption spectroscopy (resolving power up to 10(6)) and an electron/ion imaging coincidence spectrometer. The photon characteristics necessary to fulfill its scientific mission are: high flux in the 5-40 eV range, high spectral purity, high resolution, and variable and well calibrated polarizations. The photon source is a 10 m-long pure electromagnetic variable-polarization undulator producing light from the very near UV up to 40 eV on the fundamental emission with tailored elliptical polarization allowing fully calibrated quasi-perfect horizontal, vertical and circular polarizations, as measured with an in situ VUV polarimeter with absolute polarization rates close to unity, to be obtained at the sample location. The optical design includes a beam waist allowing the implementation of a gas filter to suppress the undulator high harmonics. This harmonic-free radiation can be steered toward the FTS for absorption experiments, or go through a highly efficient pre-focusing optical system, based on a toroidal mirror and a reflective corrector plate similar to a Schmidt plate. The synchrotron radiation then enters a 6.65 m Eagle off-plane normal-incidence monochromator equipped with four gratings with different groove densities, from 200 to 4300 lines mm(-1), allowing the flux-to-resolution trade-off to be smoothly adjusted. The measured ultimate instrumental resolving powers are 124000 (174 µeV) around 21 eV and 250000 (54 µeV) around 13 eV, while the typical measured flux is in the 10(10)-10(11) photons s(-1) range in a 1

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

    PubMed

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

    2017-02-13

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

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

    NASA Astrophysics Data System (ADS)

    Woody, Robert W.; Pescitelli, Gennaro

    2014-07-01

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

  2. Freeze-Quench Magnetic Circular Dichroism Spectroscopic Study of the "Very Rapid" Intermediate in Xanthine Oxidase.

    PubMed

    Jones, Robert M.; Inscore, Frank E.; Hille, Russ; Kirk, Martin L.

    1999-11-01

    Freeze-quench magnetic circular dichroism spectroscopy (MCD) has been used to trap and study the excited-state electronic structure of the Mo(V) active site in a xanthine oxidase intermediate generated with substoichiometric concentrations of the slow substrate 2-hydroxy-6-methylpurine. EPR spectroscopy has shown that the intermediate observed in the MCD experiment is the "very rapid" intermediate, which lies on the main catalytic pathway. The low-energy (< approximately 30 000 cm(-1)) C-term MCD of this intermediate is remarkably similar to that of the model compound LMoO(bdt) (L = hydrotris(3,5-dimethyl-1-pyrazolyl)borate; bdt = 1,2-benzenedithiolate), and the MCD bands have been assigned as dithiolate S(ip) --> Mo d(xy) and S(op) --> Mo d(xz,yz) LMCT transitions. These transitions result from a coordination geometry of the intermediate where the Mo=O bond is oriented cis to the ene-1,2-dithiolate of the pyranopterin. Since X-ray crystallography has indicated that a terminal sulfido ligand is oriented cis to the ene-1,2-dithiolate in oxidized xanthine oxidase related Desulfovibrio gigas aldehyde oxidoreductase, we have suggested that a conformational change occurs upon substrate binding. The substrate-mediated conformational change is extremely significant with respect to electron-transfer regeneration of the active site, as covalent interactions between the redox-active Mo d(xy) orbital and the S(ip) orbitals of the ene-1,2-dithiolate are maximized when the oxo ligand is oriented cis to the dithiolate plane. This underlies the importance of the ene-1,2-dithiolate portion of the pyranopterin in providing an efficient superexchange pathway for electron transfer. The results of this study indicate that electron-transfer regeneration of the active site may be gated by the orientation of the Mo=O bond relative to the ene-1,2-dithiolate chelate. Poor overlap between the Mo d(xy) orbital and the S(ip) orbitals of the dithiolate in the oxidized enzyme geometry may

  3. Rotational averaging of multiphoton absorption cross sections

    NASA Astrophysics Data System (ADS)

    Friese, Daniel H.; Beerepoot, Maarten T. P.; Ruud, Kenneth

    2014-11-01

    Rotational averaging of tensors is a crucial step in the calculation of molecular properties in isotropic media. We present a scheme for the rotational averaging of multiphoton absorption cross sections. We extend existing literature on rotational averaging to even-rank tensors of arbitrary order and derive equations that require only the number of photons as input. In particular, we derive the first explicit expressions for the rotational average of five-, six-, and seven-photon absorption cross sections. This work is one of the required steps in making the calculation of these higher-order absorption properties possible. The results can be applied to any even-rank tensor provided linearly polarized light is used.

  4. Rotational averaging of multiphoton absorption cross sections.

    PubMed

    Friese, Daniel H; Beerepoot, Maarten T P; Ruud, Kenneth

    2014-11-28

    Rotational averaging of tensors is a crucial step in the calculation of molecular properties in isotropic media. We present a scheme for the rotational averaging of multiphoton absorption cross sections. We extend existing literature on rotational averaging to even-rank tensors of arbitrary order and derive equations that require only the number of photons as input. In particular, we derive the first explicit expressions for the rotational average of five-, six-, and seven-photon absorption cross sections. This work is one of the required steps in making the calculation of these higher-order absorption properties possible. The results can be applied to any even-rank tensor provided linearly polarized light is used.

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

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

    PubMed Central

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

    2016-01-01

    Magnetic recording using circularly polarised femto-second laser pulses is an emerging technology that would allow write speeds much faster than existing field driven methods. However, the mechanism that drives the magnetisation switching in ferromagnets is unclear. Recent theories suggest that the interaction of the light with the magnetised media induces an opto-magnetic field within the media, known as the inverse Faraday effect. Here we show that an alternative mechanism, driven by thermal excitation over the anisotropy energy barrier and a difference in the energy absorption depending on polarisation, can create a net magnetisation over a series of laser pulses in an ensemble of single domain grains. Only a small difference in the absorption is required to reach magnetisation levels observed experimentally and the model does not preclude the role of the inverse Faraday effect but removes the necessity that the opto-magnetic field is 10 s of Tesla in strength. PMID:27466066

  7. Absorption heat pump system

    DOEpatents

    Grossman, G.

    1982-06-16

    The efficiency of an absorption heat pump system is improved by conducting liquid from a second stage evaporator thereof to an auxiliary heat exchanger positioned downstream of a primary heat exchanger in the desorber of the system.

  8. Compounds affecting cholesterol absorption

    NASA Technical Reports Server (NTRS)

    Hua, Duy H. (Inventor); Koo, Sung I. (Inventor); Noh, Sang K. (Inventor)

    2004-01-01

    A class of novel compounds is described for use in affecting lymphatic absorption of cholesterol. Compounds of particular interest are defined by Formula I: ##STR1## or a pharmaceutically acceptable salt thereof.

  9. Soliton absorption spectroscopy

    PubMed Central

    Kalashnikov, V. L.; Sorokin, E.

    2010-01-01

    We analyze optical soliton propagation in the presence of weak absorption lines with much narrower linewidths as compared to the soliton spectrum width using the novel perturbation analysis technique based on an integral representation in the spectral domain. The stable soliton acquires spectral modulation that follows the associated index of refraction of the absorber. The model can be applied to ordinary soliton propagation and to an absorber inside a passively modelocked laser. In the latter case, a comparison with water vapor absorption in a femtosecond Cr:ZnSe laser yields a very good agreement with experiment. Compared to the conventional absorption measurement in a cell of the same length, the signal is increased by an order of magnitude. The obtained analytical expressions allow further improving of the sensitivity and spectroscopic accuracy making the soliton absorption spectroscopy a promising novel measurement technique. PMID:21151755

  10. Absorption heat pump system

    DOEpatents

    Grossman, Gershon

    1984-01-01

    The efficiency of an absorption heat pump system is improved by conducting liquid from a second stage evaporator thereof to an auxiliary heat exchanger positioned downstream of a primary heat exchanger in the desorber of the system.

  11. QED-driven laser absorption

    NASA Astrophysics Data System (ADS)

    Levy, Matthew; Blackburn, T.; Ratan, N.; Sadler, J.; Ridgers, C.; Kasim, M.; Ceurvorst, L.; Holloway, J.; Baring, M.; Bell, A.; Glenzer, S.; Gregori, G.; Ilderton, A.; Marklund, M.; Tabak, M.; Wilks, S.; Norreys, P.

    2016-10-01

    Absorption covers the physical processes which convert intense photon flux into energetic particles when a high-power laser (I >1018 W cm-2 where I is intensity at 1 μm wavelength) illuminates optically-thick matter. It underpins important applications of petawatt laser systems today, e.g., in isochoric heating of materials. Next-generation lasers such as ELI are anticipated to produce quantum electrodynamical (QED) bursts of γ-rays and anti-matter via the multiphoton Breit-Wheeler process which could enable scaled laboratory probes, e.g., of black hole winds. Here, applying strong-field QED to advances in plasma kinematic theory, we present a model elucidating absorption limited only by an avalanche of self-created electron-positron pairs at ultra-high-field. The model, confirmed by multidimensional QED-PIC simulations, works over six orders of magnitude in optical intensity and reveals this cascade is initiated at 1.8 x 1025 W cm-2 using a realistic linearly-polarized laser pulse. Here the laser couples its energy into highly-collimated electrons, ions, γ-rays, and positrons at 12%, 6%, 58% and 13% efficiency, respectively. We remark on attributes of the QED plasma state and possible applications.

  12. Optical absorption measurement system

    DOEpatents

    Draggoo, Vaughn G.; Morton, Richard G.; Sawicki, Richard H.; Bissinger, Horst D.

    1989-01-01

    The system of the present invention contemplates a non-intrusive method for measuring the temperature rise of optical elements under high laser power optical loading to determine the absorption coefficient. The method comprises irradiating the optical element with a high average power laser beam, viewing the optical element with an infrared camera to determine the temperature across the optical element and calculating the absorption of the optical element from the temperature.

  13. Solar selective absorption coatings

    DOEpatents

    Mahoney, Alan R.; Reed, Scott T.; Ashley, Carol S.; Martinez, F. Edward

    2003-10-14

    A new class of solar selective absorption coatings are disclosed. These coatings comprise a structured metallic overlayer such that the overlayer has a sub-micron structure designed to efficiently absorb solar radiation, while retaining low thermal emissivity for infrared thermal radiation. A sol-gel layer protects the structured metallic overlayer from mechanical, thermal, and environmental degradation. Processes for producing such solar selective absorption coatings are also disclosed.

  14. Solar selective absorption coatings

    DOEpatents

    Mahoney, Alan R.; Reed, Scott T.; Ashley, Carol S.; Martinez, F. Edward

    2004-08-31

    A new class of solar selective absorption coatings are disclosed. These coatings comprise a structured metallic overlayer such that the overlayer has a sub-micron structure designed to efficiently absorb solar radiation, while retaining low thermal emissivity for infrared thermal radiation. A sol-gel layer protects the structured metallic overlayer from mechanical, thermal, and environmental degradation. Processes for producing such solar selective absorption coatings are also disclosed.

  15. Intranasal absorption of oxymorphone.

    PubMed

    Hussain, M A; Aungst, B J

    1997-08-01

    The nasal bioavailability of oxymorphone HCI was determined. Rats were surgically prepared to isolate the nasal cavity, into which a solution of oxymorphone was administered. A reference group of rats was administered oxymorphone HCl intravenously. Plasma oxymorphone concentrations were determined by HPLC. Nasal absorption was rapid, nasal bioavailability was 43%, and the iv and nasal elimination profiles were similar. Oxymorphone HCI appears to have the solubility, potency, and absorption properties required for efficient nasal delivery, which is an alternative to injections.

  16. [Conformation study of cyclic adenosine-3',5'-monophosphate and some of its derivatives by means of circular dichroism].

    PubMed

    Tunitskaia, V L; Guliaev, N N; Poletaev, A I; Severin, E S

    1977-04-01

    Circular dichroism spectra of adenosine and cyclic adenosine-3',5'-monophosphate (cAMP) and their derivatives, having different substituents in 8-position of heterocycle, are studied, cAMP is suggested to have preferable anti-conformation in the solution, while its derivatives with substituents in 8-position of purine base are preferable in sin-conformation. An exception is 8-(beta aminoethylamine-)cAMP, which has an anti-conformation within pH range from 4.5 to 9.5. This is probably due to the formation of intra-molecular ionic bond between cyclophosphate group and aliphatic amino group of 8-position substituent.

  17. X-ray magnetic circular dichroism of CeFe2 by resonant inelastic x-ray scattering

    NASA Astrophysics Data System (ADS)

    Jaouen, N.; Chiuzbăian, S. G.; Hague, C. F.; Delaunay, R.; Baumier, C.; Lüning, J.; Rogalev, A.; Schmerber, G.; Kappler, J.-P.

    2010-05-01

    We have measured the CeL x-ray magnetic circular dichroism (XMCD) in ferromagnetic CeFe2 using the partial fluorescence yield given by the Ce2p3d resonant inelastic x-ray scattering (RIXS) spectrum. The lifetime broadening of the 3d core hole is four times smaller than that of the Ce2p core hole providing improved resolution over earlier experiments. Clear evidence for a 4f2 , 4f1 , 4f0 strongly mixed-valent ground state is observed confirming, by and large, impurity Anderson model predictions which take into account the RIXS XMCD geometrical dependence.

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

    NASA Astrophysics Data System (ADS)

    Baǧda, Efkan; Baǧda, Esra; Yabaş, Ebru

    2017-01-01

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

  19. Planar chiral metamaterial design utilizing metal-silicides for giant circular dichroism and polarization rotation in the infrared region

    NASA Astrophysics Data System (ADS)

    Yan, Bo; Zhong, Kesong; Ma, Hongfeng; Li, Yun; Sui, Chenghua; Wang, Juanzhuan; Shi, Yi

    2017-01-01

    A planar chiral metamaterial (PCMM) comprizing double-layer sandwich structure utilizing metal-silicides in the shape of windmill is proposed in the infrared region (IR). Giant circular dichroism (CD) and polarization rotation are observed simultaneously. Furthermore, the effect of Drude model parameters (ωp,ωτ) of metal-silicides on CD and optical activity are also investigated. The results show that CD and optical activity reach maximum if ωp and ωτ are in the distribution of narrow trumpet shape.

  20. Determination of the absolute configuration of the natural product Klaivanolide via density functional calculations of vibrational circular dichroism (VCD).

    PubMed

    Devlin, Frank J; Stephens, Philip J; Figadère, Bruno

    2009-01-01

    The absolute configuration (AC) of the antiprotozoal lactone, Klaivanolide, 1, from Uvaria klaineana, has been determined using Vibrational Circular Dichroism (VCD) spectroscopy. The experimental VCD spectrum of the (+) enantiomer of 1 was measured. To analyze the AC of (+)-1, the conformationally-averaged VCD spectrum of 7-S-1 was calculated using density functional theory (DFT) and the GAUSSIAN 03 program. The B3PW91/TZ2P conformationally-averaged VCD spectrum of 7-S-1 proves that the AC of 1 is 7-S-(+).

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

    DOE PAGES

    Jamer, M. E.; Assaf, B. A.; Sterbinsky, G. E.; ...

    2014-12-05

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

  3. Optimized absorption imaging of mesoscopic atomic clouds

    NASA Astrophysics Data System (ADS)

    Muessel, Wolfgang; Strobel, Helmut; Joos, Maxime; Nicklas, Eike; Stroescu, Ion; Tomkovič, Jiří; Hume, David B.; Oberthaler, Markus K.

    2013-10-01

    We report on the optimization of high-intensity absorption imaging for small Bose-Einstein condensates. The imaging calibration exploits the linear scaling of the quantum projection noise with the mean number of atoms for a coherent spin state. After optimization for atomic clouds containing up to 300 atoms, we find an atom number resolution of atoms, mainly limited by photon shot noise and radiation pressure.

  4. Ab Initio Study of the Electric Dipole Transition Moment for the Electronic X to C Transition in Acetylene: Theoretical Predictions of the Absorption and Magnetic Circular Dichroism Intensities

    DTIC Science & Technology

    1990-12-01

    Electronic Structure Theory, Modem Theoretical Chemistry III. H. F. Schaefer III (ed.), New York: Plenum Press, 1977. Gedanken, A ., and 0. Schnepp. "The...Reserve Univ. Div. of Aerospace Sciences ATfN: J. lien Cleveland, OH 44135 Cornell University Department of Chemistry A TfN: T . A . Cool Baker...Laboratory Ithaca, NY 14853 University of Delaware A 1TN: T. Brill Chemistry Department Newark, DE 19711 1 University of Florida Dept. of

  5. Seven-effect absorption refrigeration

    DOEpatents

    DeVault, R.C.; Biermann, W.J.

    1989-05-09

    A seven-effect absorption refrigeration cycle is disclosed utilizing three absorption circuits. In addition, a heat exchanger is used for heating the generator of the low absorption circuit with heat rejected from the condenser and absorber of the medium absorption circuit. A heat exchanger is also provided for heating the generator of the medium absorption circuit with heat rejected from the condenser and absorber of the high absorption circuit. If desired, another heat exchanger can also be provided for heating the evaporator of the high absorption circuit with rejected heat from either the condenser or absorber of the low absorption circuit. 1 fig.

  6. Seven-effect absorption refrigeration

    DOEpatents

    DeVault, Robert C.; Biermann, Wendell J.

    1989-01-01

    A seven-effect absorption refrigeration cycle is disclosed utilizing three absorption circuits. In addition, a heat exchanger is used for heating the generator of the low absorption circuit with heat rejected from the condenser and absorber of the medium absorption circuit. A heat exchanger is also provided for heating the generator of the medium absorption circuit with heat rejected from the condenser and absorber of the high absorption circuit. If desired, another heat exchanger can also be provided for heating the evaporator of the high absorption circuit with rejected heat from either the condenser or absorber of the low absorption circuit.

  7. Effects of dispersion and absorption in resonant Bragg diffraction of x-rays.

    PubMed

    Lovesey, S W; Scagnoli, V; Dobrynin, A N; Joly, Y; Collins, S P

    2014-03-26

    Resonant diffraction of x-rays by crystals with anisotropic optical properties is investigated theoretically, to assess how the intensity of a Bragg spot is influenced by effects related to dispersion (birefringence) and absorption (dichroism). Starting from an exact but opaque expression, simple analytic results are found to expose how intensity depends on dispersion and absorption in the primary and secondary beams and, also, the azimuthal angle (rotation of the crystal about the Bragg wavevector). If not the full story for a given application, our results are more than adequate to explore consequences of dispersion and absorption in the intensity of a Bragg spot. Results are evaluated for antiferromagnetic copper oxide, and low quartz. For CuO, one of our results reproduces all salient features of a previously published simulation of the azimuthal-angle dependence of a magnetic Bragg peak. It is transparent in our analytic result that dispersion and absorption effects alone cannot reproduce published experimental data. Available data for the azimuthal-angle dependence of space-group forbidden reflections (0,0, l), with l ≠ 3n, of low quartz depart from symmetry imposed by the triad axis of rotation symmetry. The observed asymmetry can be induced by dispersion and absorption even though absorption coefficients are constant, independent of the azimuthal angle, in this class of reflections.

  8. Linear theory of a cold bounded plasma

    NASA Astrophysics Data System (ADS)

    Gradov, O. M.; Stenflo, L.

    1983-02-01

    The linear dispersive properties of the electron surface waves of a bounded plasma are considered by means of the cold fluid theory. Wave dissipation due to resonant absorption as well as leaking processes are discussed. A general method is introduced to describe the eigenmodes of a plasma with arbitrary boundary shape. A hydrodynamic fluctuation theory, which can be useful for plasma diagnostics, is also presented. By means of the eigenmode theory we then discuss total absorption of plasma radiation as well as superreflectivity processes.

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

    PubMed Central

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

    2016-01-01

    Circularly polarized laser sources with small footprints and high efficiencies can possess advanced functionalities in optical communication and biophotonic integrated systems. However, the conventional lasers with additional circular-polarization converters are bulky and hardly compatible with nanophotonic circuits, and most active chiral plasmonic nanostructures nowadays exhibit broadband emission and low circular dichroism. In this work, with spirals of gallium nitride (GaN) nanowires (NWRs) covered by a metal layer, we demonstrated an ultrasmall semiconductor laser capable of emitting circularly-polarized photons. The left- and right-hand spiral metal nanowire cavities with varied periods were designed at ultraviolet wavelengths to achieve the high quality factor circular dichroism metastructures. The dissymmetry factors characterizing the degrees of circular polarizations of the left- and right-hand chiral lasers were 1.4 and −1.6 (±2 if perfectly circular polarized), respectively. The results show that the chiral cavities with only 5 spiral periods can achieve lasing signals with the high degrees of circular polarizations. PMID:27220650

  10. Probing early events in ferrous cytochrome c folding with time-resolved natural and magnetic circular dichroism spectroscopies.

    PubMed

    Chen, Eefei; Goldbeck, Robert A; Kliger, David S

    2009-10-01

    In a 1998 collaboration with Tony Fink, we coupled nanosecond circular dichroism methods (TRCD) with a CO-photolysis system for quickly triggering folding in cytochrome c (cyt c) in order to make the first time-resolved far-UV CD measurement of early secondary structure formation in a protein. The small signal observed in that initial study, approximately 10% of native helicity, became the seed for increasingly robust results from subsequent studies bringing additional natural and magnetic circular polarization dichroism and optical rotatory dispersion detection methods (e.g., TRORD, TRMCD, and TRMORD), coupled to fast photolysis and photoreduction triggers, to the study of early folding events. Nanosecond polarization methods are reviewed here in the context of the range of initiation methods and structure-sensitive probes currently available for fast folding studies. We also review the impact of experimental results from fast polarization studies on questions in folding dynamics such as the possibility of multiple folding pathways implied by energy landscape models, the sequence dependence of ultrafast helix formation, and the simultaneity of chain collapse and secondary structure formation implicit in molten globule models for kinetic folding intermediates.

  11. Folding-unfolding of goat alpha-lactalbumin studied by stopped-flow circular dichroism and molecular dynamics simulations.

    PubMed

    Yoda, T; Saito, M; Arai, M; Horii, K; Tsumoto, K; Matsushima, M; Kumagai, I; Kuwajima, K

    2001-01-01

    Folding reaction of goat alpha-lactalbumin has been studied by stopped-flow circular dichroism and molecular dynamics simulations. The effects of four single mutations and a double mutation on the stability of the protein under a native condition were studied. The mutations were introduced into residues located at a hydrophobic core in the alpha-domain of the molecule. Here we show that an amino acid substitution (T29I) increases the native-state stability of goat alpha-lactalbumin against the guanidine hydrochloride-induced unfolding by 3.5 kcal/mol. Kinetic refolding and unfolding of wild-type and mutant goat alpha-lactalbumin measured by stopped-flow circular dichroism showed that the local structure around the Thr29 side chain was not constructed in the transition state of the folding reaction. To characterize the local structural change around the Thr29 side chain to an atomic level of resolution, we performed high-temperature (at 400 K and 600 K) molecular dynamics simulations and studied the structural change at an initial stage of unfolding observed in the simulation trajectories. The Thr29 portion of the molecule experienced structural disruption accompanied with the loss of inter-residue contacts and with the water molecule penetration in the 400-K simulation as well as in four of the six 600-K simulations. Disruption of the N-terminal portion was also observed and was consistent with the results of kinetic refolding/unfolding experiments shown in our previous report.

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

    PubMed

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

    2016-05-25

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

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

    NASA Astrophysics Data System (ADS)

    Shih, Min-Hsiung

    2016-09-01

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

  14. Experimental study of NIR absorption due to Nb4+ polarons in pure and Cr- or Ce-doped SBN crystals

    NASA Astrophysics Data System (ADS)

    Gao, Ming; Kapphan, S.; Porcher, S.; Pankrath, R.

    1999-06-01

    A broad absorption band around 0.72 eV, assigned to the absorption of Nb4+ polarons, is observed in strontium barium niobate (SBN) crystals (nominally pure or Cr- or Ce-doped) either under illumination at low temperature or after a previous reduction treatment. The absorption spectra of Nb4+ polarons at low temperature show considerable dichroism, which in reduced SBN crystals exists even far above room temperature. The peak position of the Nb4+ polaron absorption in reduced SBN crystals shifts to higher energies with decreasing temperature. The dependence on light intensity and temperature of the Nb4+ polaron absorption during the build-up process under illumination and the decay process after the illumination is switched off are investigated in detail. Compared with pure SBN, doping with Ce or Cr creates additional absorption bands in the visible (2.6 eV) and red (1.9 eV for Cr doping) spectral regions. Illumination in these absorption bands at low temperature gives rise to strong Nb4+ polaron absorption in the NIR (0.72 eV), giving evidence of the enhanced sensitivity even in the red spectral region for SBN:Cr. The light-induced charge transfer process and formation of Nb4+ polarons in SBN are briefly discussed.

  15. Absorption heat pump system

    DOEpatents

    Grossman, Gershon; Perez-Blanco, Horacio

    1984-01-01

    An improvement in an absorption heat pump cycle is obtained by adding adiabatic absorption and desorption steps to the absorber and desorber of the system. The adiabatic processes make it possible to obtain the highest temperature in the absorber before any heat is removed from it and the lowest temperature in the desorber before heat is added to it, allowing for efficient utilization of the thermodynamic availability of the heat supply stream. The improved system can operate with a larger difference between high and low working fluid concentrations, less circulation losses, and more efficient heat exchange than a conventional system.

  16. Absorption Heat Pump Cycles

    NASA Astrophysics Data System (ADS)

    Kunugi, Yoshifumi; Kashiwagi, Takao

    Various advanced absorption cycles are studied, developed and invented. In this paper, their cycles are classified and arranged using the three categories: effect, stage and loop, then an outline of the cycles are explained on the Duehring diagram. Their cycles include high COP cycles for refrigerations and heat pumps, high temperature lift cycles for heat transformer, absorption-compression hybrid cycles and heat pump transformer cycle. The highest COPi is attained by the seven effect cycle. In addition, the cycles for low temperature are invented and explained. Furthermore the power generation • refrigeration cycles are illustrated.

  17. The search for circular dichroism in high-Tc superconductors (abstract)

    NASA Astrophysics Data System (ADS)

    Lyons, K. B.; Kwo, J.; Dillon, J. F., Jr.; Espinosa, G. P.; McGlashan-Powell, M.; Ramirez, A. P.; Schneemeyer, L. F.

    1991-04-01

    Stimulated by recent predictions of broken time reversal symmetry in cuprate superconductors, we have carried out a study of the polar Kerr ellipticity (the ellipticity of normally reflected light with the incident beam linearly polarized) for various cuprate materials, both superconducting and nonsuperconducting. The technique used employs a rotating half-wave retardation plate in order to discriminate against linear polarization effects. The results reveal a signature of a nonzero polar Kerr ellipticity which appears on cooling near 200 K in a variety of superconducting materials, and which is not observed in the corresponding insulating compounds. In this talk, in addition to summarizing these results, we plan to discuss the measurement technique itself in some detail. Measurements on both thin films and bulk samples will be discussed, together with a variety of tests on unrelated materials, which serve to eliminate various possible experimental artifacts.

  18. Inferring surface solar absorption from broadband satellite measurements

    NASA Technical Reports Server (NTRS)

    Cess, Robert D.; Vulis, Inna L.

    1989-01-01

    An atmospheric solar radiation model and surface albedo models that include wavelength dependence and surface anisotropy are combined to study the possibility of inferring the surface solar absorption from satellite measurements. The model includes ocean, desert, pasture land, savannah, and bog surface categories. Problems associated with converting narrowband measurements to broadband quantities are discussed, suggesting that it would be easier to infer surface solar absorption from broadband measurements directly. The practice of adopting a linear relationship between planetary and surface albedo to estimate surface albedos from satellite measurements is examined, showing that the linear conversion between broadband planetary and surface albedos is strongly dependent on vegetation type. It is suggested that there is a linear slope-offset relationship between surface and surface-atmosphere solar absorption.

  19. Ultraviolet absorption spectra of metalorganic molecules diluted in hydrogen gas

    NASA Astrophysics Data System (ADS)

    Itoh, Hideo; Watanabe, Masanobu; Mukai, Seiji; Yajima, Hiroyoshi

    1988-12-01

    Ultraviolet absorption spectra of trimethyl gallium, triethyl gallium, and trimethyl aluminum diluted in hydrogen gas were measured as a function of the wavelength (185-350 nm) and the concentration of the molecules (4.8×10 -6 -1.6×10 -4 mol/liter). Their absorbances changed linearly with the concentration of the molecules, which allowed us to calculate the molar absorption coefficients of the molecules on the basis of the Beer-Lambert law.

  20. Two-Phonon Absorption

    ERIC Educational Resources Information Center

    Hamilton, M. W.

    2007-01-01

    A nonlinear aspect of the acousto-optic interaction that is analogous to multi-photon absorption is discussed. An experiment is described in which the second-order acousto-optically scattered intensity is measured and found to scale with the square of the acoustic intensity. This experiment using a commercially available acousto-optic modulator is…

  1. Linear integrated circuits

    NASA Astrophysics Data System (ADS)

    Young, T.

    This book is intended to be used as a textbook in a one-semester course at a variety of levels. Because of self-study features incorporated, it may also be used by practicing electronic engineers as a formal and thorough introduction to the subject. The distinction between linear and digital integrated circuits is discussed, taking into account digital and linear signal characteristics, linear and digital integrated circuit characteristics, the definitions for linear and digital circuits, applications of digital and linear integrated circuits, aspects of fabrication, packaging, and classification and numbering. Operational amplifiers are considered along with linear integrated circuit (LIC) power requirements and power supplies, voltage and current regulators, linear amplifiers, linear integrated circuit oscillators, wave-shaping circuits, active filters, DA and AD converters, demodulators, comparators, instrument amplifiers, current difference amplifiers, analog circuits and devices, and aspects of troubleshooting.

  2. A linear programming manual

    NASA Technical Reports Server (NTRS)

    Tuey, R. C.

    1972-01-01

    Computer solutions of linear programming problems are outlined. Information covers vector spaces, convex sets, and matrix algebra elements for solving simultaneous linear equations. Dual problems, reduced cost analysis, ranges, and error analysis are illustrated.

  3. Linear Accelerator (LINAC)

    MedlinePlus

    ... equipment? How is safety ensured? What is this equipment used for? A linear accelerator (LINAC) is the ... Therapy (SBRT) . top of page How does the equipment work? The linear accelerator uses microwave technology (similar ...

  4. Aerosol Angstrom Absorption Coefficient Comparisons during MILAGRO.

    NASA Astrophysics Data System (ADS)

    Marley, N. A.; Marchany-Rivera, A.; Kelley, K. L.; Mangu, A.; Gaffney, J. S.

    2007-12-01

    Measurements of aerosol absorption were obtained as part of the MAX-Mex component of the MILAGRO field campaign at site T0 (Instituto Mexicano de Petroleo in Mexico City) by using a 7-channel aethalometer (Thermo- Anderson) during the month of March, 2006. The absorption measurements obtained in the field at 370, 470, 520, 590, 660, 880, and 950 nm were used to determine the aerosol Angstrom absorption exponents by linear regression. Since, unlike other absorbing aerosol species (e.g. humic like substances, nitrated PAHs), black carbon absorption is relatively constant from the ultraviolet to the infrared with an Angstrom absorption exponent of -1 (1), a comparison of the Angstrom exponents can indicate the presence of aerosol components with an enhanced UV absorption over that expected from BC content alone. The Angstrom exponents determined from the aerosol absorption measurements obtained in the field varied from - 0.7 to - 1.3 during the study and was generally lower in the afternoon than the morning hours, indicating an increase in secondary aerosol formation and photochemically generated UV absorbing species in the afternoon. Twelve-hour integrated samples of fine atmospheric aerosols (<0.1micron) were also collected at site T0 and T1 (Universidad Technologica de Tecamac, State of Mexico) from 5 am to 5 pm (day) and from 5 pm to 5 am (night) during the month of March 2006. Samples were collected on quartz fiber filters with high volume impactor samplers. Continuous absorption spectra of these aerosol samples have been obtained in the laboratory from 280 to 900nm with the use of an integrating sphere coupled to a UV spectrometer (Beckman DU with a Labsphere accessory). The integrating sphere allows the detector to collect and spatially integrate the total radiant flux reflected from the sample and therefore allows for the measurement of absorption on highly reflective or diffusely scattering samples. These continuous spectra have also been used to obtain the

  5. IR Linearity Monitor

    NASA Astrophysics Data System (ADS)

    Hilbert, Bryan

    2012-10-01

    These observations will be used to monitor the signal non-linearity of the IR channel, as well as to update the IR channel non-linearity calibration reference file. The non-linearity behavior of each pixel in the detector will be investigated through the use of full frame and subarray flat fields, while the photometric behavior of point sources will be studied using observations of 47 Tuc. This is a continuation of the Cycle 19 non-linearity monitor, program 12696.

  6. IR linearity monitor

    NASA Astrophysics Data System (ADS)

    Hilbert, Bryan

    2013-10-01

    These observations will be used to monitor the signal non-linearity of the IR channel, as well as to update the IR channel non-linearity calibration reference file. The non-linearity behavior of each pixel in the detector will be investigated through the use of full frame and subarray flat fields, while the photometric behavior of point sources will be studied using observations of 47 Tuc. This is a continuation of the Cycle 20 non-linearity monitor, program 13079.

  7. Linear-Algebra Programs

    NASA Technical Reports Server (NTRS)

    Lawson, C. L.; Krogh, F. T.; Gold, S. S.; Kincaid, D. R.; Sullivan, J.; Williams, E.; Hanson, R. J.; Haskell, K.; Dongarra, J.; Moler, C. B.

    1982-01-01

    The Basic Linear Algebra Subprograms (BLAS) library is a collection of 38 FORTRAN-callable routines for performing basic operations of numerical linear algebra. BLAS library is portable and efficient source of basic operations for designers of programs involving linear algebriac computations. BLAS library is supplied in portable FORTRAN and Assembler code versions for IBM 370, UNIVAC 1100 and CDC 6000 series computers.

  8. Model Building Using Linear Free Energy Relationship Parameters-Eliminating Calibration Curves for Optical Analysis of Enantiomeric Excess.

    PubMed

    Lin, Chung-Yon; Lim, Stephanie; Anslyn, Eric V

    2016-07-06

    Linear free energy relationship (LFER) parameters are routinely used to parametrize physicochemical effects while investigating reaction mechanisms. In this Communication, we describe an alternate application for LFERs: training sets for model building in an analytical application. In this study, the sterics, quantified by Charton parameters (Δv), of nine secondary chiral alcohol analytes were correlated to the circular dichroism output from a chiral alcohol optical sensor. To test the validity of the model, the correlative linear model was applied to determine the enantiomeric excess of samples of two alcohols without a priori knowledge of a calibration curve. The error in this method was comparable to those of previous experimental methods (<5%).

  9. Mid-infrared FEL absorption spectra

    NASA Astrophysics Data System (ADS)

    Kozub, John A.; Feng, Bibo; Gabella, William E.

    2002-04-01

    The Vanderbilt Mark III FEL is a tunable source of high- intensity coherent mid-infrared radiation occurring as a train of picosecond pulses spaced 350ps apart. The laser beam is transported to each laboratory under vacuum, but is typically transmitted through some distance of atmosphere before reaching the target. Losses due to absorption by water vapor and CO2 can be large, and since the bandwidth of the FEL is several percent of the wavelength, the spectrum can be altered by atmospheric absorptions. In order to provide an accurate representation of the laser spectrum delivered to the target, and to investigate any non-linear effects associated with transport of the FEL beam, we have recorded the spectrum of the FEL output using a vacuum spectrometer positioned after measured lengths of atmosphere. The spectrometer is equipped with a linear pyroelectric array which provides the laser spectrum for each pulse. Absorption coefficients are being measured for laboratory air, averaged over the bandwidth of the FEL. The high peak powers of this Fel have induced damage in common infrared-transparent materials; we are also measuring damage thresholds for several materials at various wavelengths.

  10. Intestinal absorption of biotin in the rat

    SciTech Connect

    Bowman, B.B.; Selhub, J.; Rosenberg, I.H.

    1986-07-01

    We examined the absorption of biotin using the in vivo intestinal loop technique. Jejunal segments from male rats were filled with solutions containing (/sup 3/H)biotin and (/sup 14/C)inulin in Krebs-Ringer phosphate buffer, pH 6.5. Absorption was determined on the basis of luminal tritium disappearance after correction for inulin recovery. At biotin concentrations of 0.1 and 5.0 microM, luminal biotin disappearance was linear for at least 10 min. At biotin concentrations ranging from 2.3 nM to 75 microM, 10-28% of the administered dose was absorbed in 10 min. The concentration dependence of luminal biotin disappearance is consistent with the presence of both saturable and nonsaturable (linear) components of biotin uptake, with estimated Km = 9.6 microM and Jmax = 75.2 pmol/(2.5 cm loop X min). The rate constant for nonsaturable uptake is 3.1 pmol/(2.5 cm loop X min X microM). We conclude that at biotin concentrations less than 5 microM, biotin absorption proceeds largely by the saturable process, whereas at concentrations above 25 microM, nonsaturable uptake predominates. Additional studies demonstrated significantly less biotin uptake in the ileum than in the jejunum, a finding in agreement with previous in vitro studies.

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

    NASA Astrophysics Data System (ADS)

    Rosen, David L.; Pendleton, J. David

    1995-09-01

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

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

    SciTech Connect

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

    1998-01-23

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

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

    SciTech Connect

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

    2009-11-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

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

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

    SciTech Connect

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

    1986-07-23

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

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

    PubMed

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

    2016-01-14

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

  17. Conformational dependence of the circular dichroism spectra of single amino acids from plane-waves-based density functional theory calculations.

    PubMed

    Molteni, E; Onida, G; Tiana, G

    2015-04-09

    We study the conformational dependence of circular dichroism (CD) spectra of amino acid molecules by means of an efficient ab initio DFT approach which is free from the typical gauge invariance issues arising with the use of localized basis sets and/or real-space grids. We analyze the dependence of the chiroptical spectra on the backbone dihedrals in the specific case of alanine and consider the role of side chain degrees of freedom at the examples of leucine, phenylalanine, and serine, whose side chains have different physicochemical properties. The results allow one to identify the most diagnostic regions of the CD spectra and to critically compare the conformations which match the experimental CD data with conformations extracted from the rotamer library. The inclusion of a solvation shell of explicit water molecules and its effect on the CD spectrum are analyzed at the example of alanine.

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

    PubMed

    Norman, Patrick; Linares, Mathieu

    2014-09-01

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

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

    PubMed Central

    2016-01-01

    Unravelling the main initial dynamics responsible for chiral recognition is a key step in the understanding of many biological processes. However, this challenging task requires a sensitive enantiospecific probe to investigate molecular dynamics on their natural femtosecond time scale. Here we show that, in the gas phase, the ultrafast relaxation dynamics of photoexcited chiral molecules can be tracked by recording time-resolved photoelectron circular dichroism (TR-PECD) resulting from the photoionization by a circularly polarized probe pulse. A large forward–backward asymmetry along the probe propagation axis is observed in the photoelectron angular distribution. Its evolution with pump–probe delay reveals ultrafast dynamics that are inaccessible in the angle-integrated photoelectron spectrum or via the usual electron emission anisotropy parameter (β). PECD, which originates from the electron scattering in the chiral molecular potential, appears as a new sensitive observable for ultrafast molecular dynamics in chiral systems. PMID:27786493

  20. Structure and conformational stability of the enzyme I of Streptomyces coelicolor explored by FTIR and circular dichroism.

    PubMed

    Hurtado-Gómez, Estefanía; Barrera, Francisco N; Neira, José L

    2005-04-01

    The bacterial phosphoenolpyruvate (PEP): sugar phosphotransferase system (PTS), formed by a cascade of several proteins, couples the translocation and phosphorylation of specific sugars across cell membranes. The structure and thermal stability of the first protein (enzyme I, EI) of the PTS in Streptomyces coelicolor is studied by using far-UV circular dichroism (CD) and Fourier transform infrared spectroscopy (FTIR) at pH 7.0. The deconvolution of FTIR spectra indicates that the protein is mainly composed by a 35% of alpha-helical structure and 30% of beta-sheet. The thermal denaturation curves, as followed by both techniques, show only a midpoint at 330 K. This thermal denaturation behaviour is different to that observed in other members of the EI family.

  1. Absolute Configuration Assignment of 3',4'-di-O-acylkhellactones Using Vibrational Circular Dichroism Exciton Chirality.

    PubMed

    Buendía-Trujillo, Abigail I; Torrres-Valencia, J Martín; Joseph-Nathan, Pedro; Burgueño-Tapia, Eleuterio

    2015-06-01

    The 3'R,4'R absolute configuration (AC) of the angular-type pyranocoumarins (-)-3',4'-di-O-acetylkhellactone (2), (-)-4'-O-acetyl-3'-O-angeloylkhellactone (3), (+)-3'-O-acetyl-4'-O-isobutyroylkhellactone (4), and (-)-3'-O-angeloyl-4'-O-senecioylkhellactone (5), isolated from the aerial parts of Prionosciadium thapsoides, was assigned by vibrational circular dichroism exciton chirality (VCDEC), and confirmed by comparison of their VCD frequencies with those calculated using DFT at the B3LYP/DGDZVP level. This again reveals that AC assignments based on optical rotation data are not very confident. Evaluation of Flack and Hooft parameters obtained after single-crystal X-ray diffraction analysis of 3, independently confirmed this AC.

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

    PubMed

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

    2006-09-01

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

  3. Soft x-ray magnetic circular dichroism of L21-type Co2FeGa Heusler alloy

    NASA Astrophysics Data System (ADS)

    Umetsu, R. Y.; Nakamura, T.; Kobayashi, K.; Kainuma, R.; Sakuma, A.; Fukamichi, K.; Ishida, K.

    2010-03-01

    Spin and orbital magnetic moments of the L21-type Co2FeGa Heusler alloy have been investigated using x-ray magnetic circular dichroism spectra in the soft x-ray region. From the spectra of the L2,3-edge of Co and Fe, the ratios of the orbital magnetic moment to the spin magnetic moment Morb/Mspin are estimated to be 0.06 for Co and 0.02 for Fe, in agreement with the available theoretical values. The orbital magnetic moments of these two elements are small in line with theoretical results, reflecting the high symmetry of the L21-type crystal structure. Furthermore, it has been confirmed that the magnetic moment of Ga is induced in the present alloy.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

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

    SciTech Connect

    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.

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

    PubMed

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

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-11-01

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

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

    PubMed

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

    2014-12-01

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

  9. 69. INTERIOR VIEW OF THE ABSORPTION TOWER BUILDING, ABSORPTION TOWER ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    69. INTERIOR VIEW OF THE ABSORPTION TOWER BUILDING, ABSORPTION TOWER UNDER CONSTRUCTION. (DATE UNKNOWN). - United States Nitrate Plant No. 2, Reservation Road, Muscle Shoals, Muscle Shoals, Colbert County, AL

  10. Effect of nonlinear absorption on electric field applied lead chloride by Z-scan technique

    SciTech Connect

    Rejeena, I.; Lillibai,; Nampoori, V. P. N.; Radhakrishnan, P.; Rahimkutty, M. H.

    2014-10-15

    The preparation, spectral response and optical nonlinearity of gel grown lead chloride single crystals subjected to electric field of 20V using parallel plate arrangements have been investigated. Optical band gap of the samples were determined using linear absorption spectra. Open aperture z-scan was employed for the determination of nonlinear absorption coefficient of PbCl{sub 2} solution. The normalized transmittance curve exhibits a valley shows reverse saturable absorption. The non linear absorption at different input fluences were recorded using a single Gaussian laser beam in tight focus geometry. The RSA nature of the sample makes it suitable for optical limiting applications.

  11. Magnetic structures of FeTiO{sub 3}-Fe{sub 2}O{sub 3} solid solution thin films studied by soft X-ray magnetic circular dichroism and ab initio multiplet calculations

    SciTech Connect

    Hojo, H. E-mail: fujita@dipole7.kuic.kyoto-u.ac.jp; Fujita, K. E-mail: fujita@dipole7.kuic.kyoto-u.ac.jp; Matoba, T.; Tanaka, K.; Ikeno, H.; Mizoguchi, T.; Tanaka, I.; Nakamura, T.; Takeda, Y.; Okane, T.

    2014-03-17

    The solid solutions between ilmenite (FeTiO{sub 3}) and hematite (α-Fe{sub 2}O{sub 3}) have recently attracted considerable attention as a spintronic material due to their interesting magnetic and electrical properties. In this study, the electronic and magnetic structures of epitaxially grown 0.6FeTiO{sub 3}·0.4Fe{sub 2}O{sub 3} solid solution thin films were investigated by combining x-ray absorption near-edge structure (XANES), x-ray magnetic circular dichroism (XMCD) for two different crystallographic projections, and first-principles theoretical calculations. The Fe L-edge XANES and XMCD spectra reveal that Fe is in the mixed-valent Fe{sup 2+}–Fe{sup 3+} states while Fe{sup 2+} ions are mainly responsible for the magnetization. Moreover, the experimental Fe L-edge XANES and XMCD spectra change depending on the incident x-ray directions, and the theoretical spectra explain such spectral features. We also find a large orbital magnetic moment, which can originate the magnetic anisotropy of this system. On the other hand, although the valence state of Ti was interpreted to be 4+ from the Ti L-edge XANES, XMCD signals indicate that some electrons are present in the Ti-3d orbital, which are coupled antiparallel to the magnetic moment of Fe{sup 2+} ions.

  12. {sup 57}Fe Moessbauer and x-ray magnetic circular dichroism study of magnetic compensation of the rare-earth sublattice in Nd{sub 2-x}Ho{sub x}Fe{sub 14}B compounds

    SciTech Connect

    Chaboy, J.; Piquer, C.; Plugaru, N.; Bartolome, F.; Laguna-Marco, M. A.

    2007-10-01

    We present here a study of the magnetic properties of the Nd{sub 2-x}Ho{sub x}Fe{sub 14}B series. The macroscopic properties of these compounds evolve continuously from those of Nd{sub 2}Fe{sub 14}B to those of Ho{sub 2}Fe{sub 14}B as Ho gradually replaces Nd. The system shows a compensation of the rare-earth sublattice magnetization for a critical concentration, x{sub c}=0.55, that is reflected into the anomalous behavior of both macroscopic and microscopic magnetic probes. The combined analysis of magnetization, {sup 57}Fe Moessbauer spectroscopy and Fe K-edge x-ray magnetic circular dichroism (XMCD) measurements suggests that the origin of the anomalous magnetic behavior found at x{sub c}=0.55 is mainly due to the Ho sublattice. Moreover, the analysis of the Fe K-edge XMCD signals reveal the presence of a rare-earth contribution, reflecting the coupling of the rare-earth and Fe magnetic moments, which can lead to the possibility of disentangling the magnetic behavior of both Fe and R atoms using a single absorption edge.

  13. Anisotropy in the thermal hysteresis of resistivity and charge density wave nature of single crystal SrFeO3-δ: X-ray absorption and photoemission studies.

    PubMed

    Hsieh, S H; Solanki, R S; Wang, Y F; Shao, Y C; Lee, S H; Yao, C H; Du, C H; Wang, H T; Chiou, J W; Chin, Y Y; Tsai, H M; Chen, J-L; Pao, C W; Cheng, C-M; Chen, W-C; Lin, H J; Lee, J F; Chou, F C; Pong, W F

    2017-12-01

    The local electronic and atomic structures of the high-quality single crystal of SrFeO3-δ (δ~0.19) were studied using temperature-dependent x-ray absorption and valence-band photoemission spectroscopy (VB-PES) to investigate the origin of anisotropic resistivity in the ab-plane and along the c-axis close to the region of thermal hysteresis (near temperature for susceptibility maximum, Tm~78 K). All experiments herein were conducted during warming and cooling processes. The Fe L 3,2-edge X-ray linear dichroism results show that during cooling from room temperature to below the transition temperature, the unoccupied Fe 3d e g states remain in persistently out-of-plane 3d 3z(2)-r(2) orbitals. In contrast, in the warming process below the transition temperature, they change from 3d 3z(2)-r(2) to in-plane 3d x(2)-y(2) orbitals. The nearest-neighbor (NN) Fe-O bond lengths also exhibit anisotropic behavior in the ab-plane and along the c-axis below Tm. The anisotropic NN Fe-O bond lengths and Debye-Waller factors stabilize the in-plane Fe 3d x(2)-y(2) and out-of-plane 3d 3z(2)-r(2) orbitals during warming and cooling, respectively. Additionally, a VB-PES study further confirms that a relative band gap opens at low temperature in both the ab-plane and along the c-axis, providing the clear evidence of the charge-density-wave nature of SrFeO3-δ (δ~0.19) single crystal.

  14. Bioacoustic Absorption Spectroscopy

    DTIC Science & Technology

    2016-06-07

    seas in co-operation with fisheries biologists. The first planned experiment will be in the seas off California in co-operation with the Southwest... Fisheries Science Center of NOAA’s National Marine Fisheries Service. These experiments will be designed to investigate the “signatures” of the two major...formulating environmental adaptation strategies for tactical sonars. Fisheries applications: These results suggest that bioacoustic absorptivity can be used to

  15. Vehicular impact absorption system

    NASA Technical Reports Server (NTRS)

    Knoell, A. C.; Wilson, A. H. (Inventor)

    1978-01-01

    An improved vehicular impact absorption system characterized by a plurality of aligned crash cushions of substantially cubic configuration is described. Each consists of a plurality of voided aluminum beverage cans arranged in substantial parallelism within a plurality of superimposed tiers and a covering envelope formed of metal hardware cloth. A plurality of cables is extended through the cushions in substantial parallelism with an axis of alignment for the cushions adapted to be anchored at each of the opposite end thereof.

  16. Hydrogen Absorption by Niobium.

    DTIC Science & Technology

    1982-04-13

    incorporate an independent means for ascertaining surface cleanliness (e.g. AES). The form of the absorption curve in Fig. 7 appears to agree with that...very interesting study and is well within the capabilities of the systen designed, if the surface cleanliness can be assured. Wire specimens have a...assessing surface cleanliness would be an important supporting technique for understanding the results of these measurements. The simple kinetic

  17. Relic Neutrino Absorption Spectroscopy

    SciTech Connect

    Eberle, b

    2004-01-28

    Resonant annihilation of extremely high-energy cosmic neutrinos on big-bang relic anti-neutrinos (and vice versa) into Z-bosons leads to sizable absorption dips in the neutrino flux to be observed at Earth. The high-energy edges of these dips are fixed, via the resonance energies, by the neutrino masses alone. Their depths are determined by the cosmic neutrino background density, by the cosmological parameters determining the expansion rate of the universe, and by the large redshift history of the cosmic neutrino sources. We investigate the possibility of determining the existence of the cosmic neutrino background within the next decade from a measurement of these absorption dips in the neutrino flux. As a by-product, we study the prospects to infer the absolute neutrino mass scale. We find that, with the presently planned neutrino detectors (ANITA, Auger, EUSO, OWL, RICE, and SalSA) operating in the relevant energy regime above 10{sup 21} eV, relic neutrino absorption spectroscopy becomes a realistic possibility. It requires, however, the existence of extremely powerful neutrino sources, which should be opaque to nucleons and high-energy photons to evade present constraints. Furthermore, the neutrino mass spectrum must be quasi-degenerate to optimize the dip, which implies m{sub {nu}} 0.1 eV for the lightest neutrino. With a second generation of neutrino detectors, these demanding requirements can be relaxed considerably.

  18. Absorption lineshapes of molecular aggregates revisited

    SciTech Connect

    Gelzinis, Andrius; Valkunas, Leonas; Abramavicius, Darius

    2015-04-21

    Linear absorption is the most basic optical spectroscopy technique that provides information about the electronic and vibrational degrees of freedom of molecular systems. In simulations of absorption lineshapes, often diagonal fluctuations are included using the cumulant expansion, and the off-diagonal fluctuations are accounted for either perturbatively, or phenomenologically. The accuracy of these methods is limited and their range of validity is still questionable. In this work, a systematic study of several such methods is presented by comparing the lineshapes with exact results. It is demonstrated that a non-Markovian theory for off-diagonal fluctuations, termed complex time dependent Redfield theory, gives good agreement with exact lineshapes over a wide parameter range. This theory is also computationally efficient. On the other hand, accounting for the off-diagonal fluctuations using the modified Redfield lifetimes was found to be inaccurate.

  19. Corrosion Problems in Absorption Chillers

    ERIC Educational Resources Information Center

    Stetson, Bruce

    1978-01-01

    Absorption chillers use a lithium bromide solution as the medium of absorption and water as the refrigerant. Discussed are corrosion and related problems, tests and remedies, and cleaning procedures. (Author/MLF)

  20. Linear collider: a preview

    SciTech Connect

    Wiedemann, H.

    1981-11-01

    Since no linear colliders have been built yet it is difficult to know at what energy the linear cost scaling of linear colliders drops below the quadratic scaling of storage rings. There is, however, no doubt that a linear collider facility for a center of mass energy above say 500 GeV is significantly cheaper than an equivalent storage ring. In order to make the linear collider principle feasible at very high energies a number of problems have to be solved. There are two kinds of problems: one which is related to the feasibility of the principle and the other kind of problems is associated with minimizing the cost of constructing and operating such a facility. This lecture series describes the problems and possible solutions. Since the real test of a principle requires the construction of a prototype I will in the last chapter describe the SLC project at the Stanford Linear Accelerator Center.