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PubMed1992

Observation of the FeIV=O stretching Raman band for a thiolate-ligated heme protein. Compound I of chloroperoxidase.

The FeIV=O stretching vibration has never been identified for a cysteine-coordinated heme enzyme. In this study, resonance Raman and visible absorption spectra were observed simultaneously for transient species in the catalytic reaction of chloroperoxidase with hydrogen peroxide by using our original apparatus for mixed-flow and Raman/absorption simultaneous measurements. For the first intermediate, the FeIV=O stretching Raman band was observed at 790 cm-1, which shifted to 756 cm-1 with the 18O derivative, but the v4 band was too weak to be identified. This suggested the formation of an oxoferryl porphyrin pi cation radical. The second intermediate gave an intense v4 band at 1,372 cm-1 but no oxygen isotope-sensitive Raman band, suggesting oxygen exchange with bulk water.

Chloride Peroxidase↗

PubMed2005

In-line monitoring of partial and overall solid concentration during solvent-mediated phase transition using Raman spectroscopy.

A calibration strategy for the continuous monitoring of solvent-mediated phase transition was developed using in situ Raman spectroscopy. Citric acid which exhibits enantiotropy during its anhydrous/monohydrate phase transition was selected as a model organic product. Using 25 samples in suspension, specific calibration of the spectral data was obtained for estimating in-line both the overall solid concentration in suspension and the composition of the solid phase. In addition to such key-measurements, reliable estimates of supersaturation were computed in-line from the mass balance of the solute. In order to validate the technique, anhydrous to monohydrate phase transition experiments were performed in suspensions at 15 degrees C and the kinetic process involved was monitored. Despite the use of various solid concentrations and reactor configurations, both the reproducibility and the reliability of the in situ Raman measurements are shown to be satisfactory.

Calibration↗

PubMed2005

FT-Raman and FTIR spectra, assignments and ab initio calculations of 2-aminobenzyl alcohol.

The Fourier transform Raman and Fourier transform infrared spectra of 2-aminobenzyl alcohol (2ABA) were recorded in the solid phase. Geometry optimizations were done with out any constraint and harmonic vibrational wave numbers and several thermodynamic parameters were calculated for the minimum energy conformer at ab initio and DFT levels invoking 6-31g** and 6-311+g(2d, p) basis sets and the results were compared with the experimental values. With the help of three specific scaling procedures, the observed vibrational wavenumbers in FTIR and FT-Raman spectra were analyzed and assigned to different normal modes of the molecule. Most of the modes have wavenumbers in the expected range and the error obtained was in general very low. The appropriate theoretical spectrograms for the Raman and IR spectra of 2ABA were also constructed.

Benzyl Alcohols↗

PubMed2005

Raman spectroscopic study of the hydrotalcite desautelsite Mg6Mn2CO3(OH)16 x 4H2O.

The structure of the hydrotalcite desautelsite Mg6Mn2CO3(OH)16.4H2O has been studied by a combination of Raman and infrared spectroscopy. Three intense Raman bands are observed at 1086, 1062 and 1055 cm(-1). A model based upon the observation of three CO3 stretching vibrations is presented. The CO3 anion may be (a) non-hydrogen bonded, (b) hydrogen bonded to the interlayer water and (c) hydrogen bonded to the brucite-like hydroxyl surface. Two intense bands at 3646 and 3608 cm(-1) are attributed to MgOH and MnOH stretching vibrations. Infrared bands at 3476, 3333, 3165 and 2991 cm(-1) are assigned to water stretching bands. Raman spectroscopy has proven a powerful tool for the study of hydrotalcite minerals.

Aluminum Hydroxide↗

PubMed2005

Stand-off Raman detection using dispersive and tunable filter based systems.

Small, transportable Raman systems are being developed for stand-off Raman measurements at intermediate ranges (e.g. <20 m) for planetary measurements. Four variations of stand-off Raman systems are described that use a small telescope for light collection that is either fiber-optic or lens-coupled to a detection system. The performance of an acousto-optic tunable filter for wavelength selection and spectral imaging is tested by comparing signal-to-noise ratio and throughput to similar measurements using a conventional spectrograph, and by measuring a variety of organic and inorganic mineral samples at distances up to 15 m. We also determine optimal ICCD gate widths for acquiring remote Raman spectra under high ambient light conditions.

Filtration↗

PubMed2003

Raman-spectral depolarisation ratios of ions in concentrated aqueous solution. The next-to-negligible effect of highly asymmetric ion surroundings on the symmetry properties of polarisability changes during vibrations of symmetric ions. Ammonium sulphate and tetramethylammonium bromide.

Depolarisation ratios rho have been measured for the Raman spectra of solutions of composition (NH4)2 SO4*11H2O and (CH3)4NBr*29D2O. Even though the former's vibration spectrum shows clear evidence of lowered ion symmetries (presence of nu1 of SO4(2-) in the IR spectrum, IR versus R nu(max) shifts for nu3 and nu4 of SO4(2-) and nu4 of NH4+) nu1 of SO4(2-) has (apparent) rho of only 0.014, while nu2, nu3 and nu4 of SO4(2-) and nu4 (probably also nu2) of NH4+ have rho in the range 0.73-0.77; within the experimental error and base line uncertainty the latter are equal to 0.75, i.e. to rho(max) with the geometry of the optics used. For (CH3)4NBr symmetric N+-C stretching has rho 0.012; all-in-phase C-H stretching and four overtones in Fermi resonance with it have rho in the range 0.02-0.035, but the deviation from zero here is in part due to underlying or overlapping depolarised bands. The sufficiently well isolated antisymmetric CH stretching and degenerate CH bending bands again have rho in the range 0.74-0.76. These results show that the selection rules in respect of rho, which apply strictly only to isolated molecules, are for practical purposes still valid for molecules in strongly symmetry-distorting external environments in the liquid phase. More specifically: (A) During vibrations in which quasi-spherical intramolecular symmetry is retained, the externally caused aspherical component of the polarizability ellipsoid does not change aspherically to a sufficient extent for an appreciably intense anisotropic Raman band to appear. (B) During intramolecularly anti-symmetric vibrations of symmetric molecules, the portion of the externally caused distortion of the polarizability ellipsoid that fails to cancel over a whole vibration period is not large enough to give rise to an appreciably intense isotropic component of the Raman band. This means in practice rho for these Raman bands is still rho(max), even for concentrated aqueous solutions.

Ammonium Sulfate↗

PubMed2004

Surface-enhanced Raman scattering and micro-Raman imaging of Langmuir-Blodgett films of rhodium phthalocyanine.

Rhodium phthalocyanine (RhPc) was synthesized and ultra thin Langmuir-Blodgett (LB) films of RhPc were successfully fabricated. The LB film characterization was carried out using both UV-vis absorption spectra and Raman scattering. The Raman spectroscopy was carried out using 633 and 780 nm laser lines. LB films were deposited onto Ag nanoparticles to achieve the surface-enhanced pre-resonance Raman scattering (pre-SERRS) and surface-enhanced Raman scattering (SERS) for both laser lines, respectively, which allowed the characterization of the RhPc ultra thin films. The morphology of the LB RhPc neat film is extracted from micro-Raman imaging.

Electromagnetic Phenomena↗

PubMed2004

Synthetic deuterated erythrite--a vibrational spectroscopic study.

A comparison of deuterated and non-deuterated erythrite has been made using a combination of infrared and Raman spectroscopy. Infrared spectrum shows bands at 3442, 3358, 3194 and 3039 cm(-1). The band at 3442 cm(-1) is attributed to weakly hydrogen bonded water and the band at 3039 cm(-1) to strongly hydrogen bonded water. Deuteration results in the observation of OD bands at 2563, 2407 and 2279 cm(-1). The ratio of these bands change with deuteration. Deuteration shows that the strongly hydrogen bonded water is replaced in preference to the weakly hydrogen bonded water. Three HOH bending modes are observed at 1686, 1633, 1572 and DOD bending modes at 1236, 1203 and 1176 cm(-1). Deuteration causes the loss of intensity of the bands at 841, 710 and 561 cm(-1) and new bands are observed at 692, 648 and 617 cm(-1). These three bands are attributed to the water librational modes. Deuteration results in an additional Raman band at 809 cm(-1) with increasing intensity with extent of deuteration. Deuteration results in the shift of Raman bands to lower wavenumbers.

Cobalt↗

PubMed2005

Effect of sample and substrate electric properties on the electric field enhancement at the apex of SPM nanotips.

Finite element (FE) models were built to define the optimal experimental conditions for tip-enhanced Raman spectroscopy (TERS) of thin samples. TERS experimental conditions were mimicked by including in the FE models dielectric or metallic substrates with thin dielectric samples and by considering the wavelength dependence of the dielectric properties for the metallic materials. Electromagnetic coupling between the substrate/sample and the SPM tips led to dramatic changes of both the spatial distribution and magnitude of the scattered electric field which depended on the substrate dielectric permittivity and excitation wavelength. Raman scattering as high as 10(8) with a spatial resolution of approximately 8 nm was estimated for gold SPM tips and gold substrate when excitation is performed at 532 nm (near-resonance wavelength). For dielectric samples (approximately 4 nm thick), the enhancement of Raman scattering intensity is estimated at approximately 10(5); this does not depend significantly on the sample dielectric permittivity for dielectric samples. These results suggest that TERS experimental conditions should be estimated and optimized for every individual application considering the geometric factors and electric properties of the materials involved. Such optimizations could enlarge the range of applications for TERS to samples eliciting weaker intrinsic Raman scattering, such as biological samples.

Algorithms↗

PubMed2006

Time-domain calculations of the polarized Raman spectra, the transient infrared absorption anisotropy, and the extent of delocalization of the OH stretching mode of liquid water.

The polarized Raman spectrum and the time dependence of the transient infrared (TRIR) absorption anisotropy are calculated for the OH stretching mode of liquid water (neat liquid H2O) by using time-domain formulations, which include the effects of both the diagonal frequency modulations (of individual oscillators) induced by the interactions between the dipole derivatives and the intermolecular electric field, and the off-diagonal (intermolecular) vibrational coupling described by the transition dipole coupling (TDC) mechanism. The IR spectrum of neat liquid H2O and the TRIR anisotropy of a liquid mixture of H2O/HDO/D2O are also calculated. It is shown that the calculated features of these optical signals, including the temperature dependence of the polarized Raman and IR spectra, are in reasonable agreement with the experimental results, indicating that the frequency separation between the isotropic and anisotropic components of the polarized Raman spectrum and the rapid decay (approximately 0.1 ps) of the TRIR anisotropy of the OH stretching mode of neat liquid H2O are mainly controlled by the resonant intermolecular vibrational coupling described by the TDC mechanism. Comparing with the time evolution of vibrational excitations, it is suggested that the TRIR anisotropy decays in the time needed for the initially localized vibrational excitations to delocalize over a few oscillators. It is also shown that the enhancement of the dipole derivatives by the interactions with surrounding molecules is an important factor in generating the spectral profiles of the OH stretching Raman band. The time-domain behavior of the molecular motions that affect the spectroscopic features is discussed.

Algorithms↗

PubMed2006

Right bipyramids of silver: a new shape derived from single twinned seeds.

Silver nanoparticles with a single (111) twin were selectively nucleated and grown for the first time to produce right bipyramids 75-150 nm in edge length. Key to the production of single twinned seeds was the addition of NaBr to a polyol synthesis in which AgNO3 is reduced by ethylene glycol in the presence of poly(vinyl pyrrolidone). Examination of nanoparticles at different stages of the reaction with electron microscopy revealed that the spherical, single twinned seeds grew to become right bipyramids through enlargement of their (100) facets. The UV-vis-NIR spectrum exhibited by right bipyramids is distinct from that of any other silver nanostructure, and their sharp corners make these new nanoparticles especially promising for enhancement of Raman scattering.

Crystallization↗

PubMed1976

Coherent anti-Stokes Raman scattering (CARS) spectra, with resonance enhancement, of cytochrome c and vitamin B12 in dilute aqueous solution.

Coherent anti-Stokes Raman scattering (CARS) spectra have been obtained for ferrocytochrome c and cyano cobalamin in aqueous solution at millimolar concentrations, using a pair of tunable dye lasers pumped by a pulsed nitrogen laser. Resonance enhancement was obtained by tuning the omega1 laser to the visible absorption bands of the samples. The spectral features correspond to those observed in the conventional resonance Raman spectra. It appears that CARS spectroscopy, with its advantageous fluorescence rejection, can be usefully applied to biological samples by exploiting resonance enhancement. While the background scattering from water is 10 times higher than that of benzene and other aromatic solvents, it is actually at the low end of the scale for most liquids. The anomalously low background of aromatic liquids is thought to result from competition by the unusually efficient stimulated Raman scattering which they display. Off-resonance spectra for both cobalamin and cytochrome c contain negative peaks, i.e., absorption bands in the background. These are interpreted as inverse Raman processes induced by the omega1 photons in the presence of the continuum provided by the background scattering. While both CARS and the inverse Raman effect are subject to resonance enhancement, the wavelength dependence of CARS is evidently steeper.

Cytochrome c Group↗

PubMed1993

Far-infrared study of the vibrational modes of 5'-GMP gels and crystals of Na+ and K+.

Five Far-Infrared (50-600 cm-1) spectra are presented: the sodium and potassium salts of 5' Guanosine Monophosphate (GMP), each salt in both the gel and crystal conformations, and poly(rG). Measurements were performed at a sample temperature of 10 K under vacuum with a liquid He-cooled bolometer. The spectra were fit with Lorentzians and assignments are suggested. There are noteworthy differences in oscillator strengths and frequencies of the bands between all spectra. We report the tentative observation of a 100 cm-1 mode which is in the neighborhood of a mode observed by Raman spectroscopy in solution (1) and dried gels (2).

Crystallization↗

PubMed2004

Raman spectroscopy of fullerenes and fullerene-nanotube composites.

The discovery of fullerenes in 1985 opened a completely new field of materials research. Together with the single-wall carbon nanotubes (SWCNTs) discovered later, these curved carbon networks are a playground for pure as well as applied science. We present a review of Raman spectroscopy of fullerenes, SWCNTs and composite materials. Beginning with pristine C(60), we discuss intercalated C(60) compounds and polymerized C(60), as well as higher and endohedral fullerenes. Concerning SWCNTs, we show how the diameter distribution can be obtained from the Raman spectra and how doping modifies the spectra. Finally, the Raman response of C(60) encapsulated into SWCNTs (C(60) peapods) is discussed.

Carbon↗

PubMed1990

Ultraviolet resonance Raman spectroscopy of bacteriorhodopsin.

Ultraviolet resonance Raman spectra of bacteriorhodopsin have been obtained using 229 nm excitation from a hydrogen-shifted neodymium yttrium aluminum garnet (Nd: YAG) laser. High signal-to-noise spectra are observed exhibiting vibrational bands at 762, 877, 1011, 1175, 1356, 1552 and 1617 cm-1 which are assigned to scattering from tryptophan and tyrosine side chains. This demonstrates the feasibility of using UV resonance Raman spectroscopy to monitor aromatic amino acid structural changes during the bacteriorhodopsin photocycle.

Bacteriorhodopsins↗

PubMed2006

Quantitative mapping of the orientation of fibroin beta-sheets in B. mori cocoon fibers by scanning transmission X-ray microscopy.

The spatial distribution of the linear dichroic signal associated with aligned beta-sheets in a microtomed section of a Bombyx mori cocoon silk fiber was derived from scanning transmission X-ray microscopy (STXM). The intense C 1s --> pi(amide) peak at 288.25 eV was found to have negligible dichroic signal in transverse sections but a large dichroic signal in longitudinal sections. This is consistent with other measurements of the orientation of the aligned beta-sheets in silk fibers, in particular with those obtained by polarized Raman microspectroscopy to which our results are compared. When the dichroic signal strength is mapped at better than 100 nm spatial resolution, microscopic variations are found. Although the magnitude of the dichroic signal changes over a fine spatial scale, the direction of the maximum signal at any position does not change. We interpret the spatial variation of the intensity of the dichroic signal as a map of the quality of local orientation of the beta-sheets in the fiber. At sufficiently high magnification and resolution, this technique should image individual beta-sheet crystallites, although the present implementation does not achieve that. A map of the orientation parameter P(2) is derived. The average value of P(2) (-0.20 +/- 0.04) from STXM is smaller than that derived from the analysis of the amide I band in polarized Raman spectra (-0.41 +/- 0.03). This deviation is attributed to the fact that the STXM results also include the signal from unaligned regions of the protein.

Animals↗

PubMed2003

Effects of modification of molecular structure on Raman spectral depolarization ratios: aqueous betaine (CH3)3NCH2CO229D2O versus (CH3)4NBr29D2O.

Replacement of a CH in (CH3)4N+ by a CO2- group raises rho from 0.012 to 0.034 for symmetric N-C stretching and from ca. 0.026 to 0.031 for all-in-phase methyl C-H stretching. rho for antisymmetric C-H stretching and CH3 bending remains in the 0.73-0.75 range. No significant effect on rho attributable to the failure of solvation sheath symmetry to match the symmetry of the solute molecule is seen either near rho=0 or near p=3/4. The drastic change in charge distribution on going from cation to zwitterion, too, does not cause a major change near rho=0. Corroborative evidence of weakness of interaction between most surrounding D2O molecules and the Me3N+ portion of the zwitterion, derived from the O-D stretching region of the Raman spectrum, and implying the absence of symmetry in the solvation sheath, is discussed in Appendix A.

Betaine↗

PubMed2005

[Raman spectroscopic analysis of dissolution and phase transformation of chloropinnoite in the boric acid aqueous solution].

Raman spectroscopy of dissolution and transformation of chloropinnoite in 4.5% (w.t.%) boric acid aqueous solution at 30 degrees C has been recorded. The Raman spectra of kinetics process have been obtained. The phase transformation product is kurnakovite (2MgO x 3B2O3 x 15H2O). The main polyborate anions and their interaction in aqueous solution have been proposed according to the Raman spectrum. Some assignments were tentatively given and the relations between the existing forms of polyborate anions and the crystallizing solid phases have been gained. A mechanisms of dissolution and crystallization reactions and the formation condition of kurnakovite in Qinghai-Tibet plateau were proposed and discussed.

Anions↗