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Vibrational Bands (vibrational + bands)
Selected AbstractsThe analysis of pH-dependent protonated conformers of 1-hydroxyethylidene-1,1-diphosphonic acid by means of FT-Raman spectroscopy, multivariate curve resolution and DFT modellingJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2009Werner Barnard Abstract 1-Hydroxyethylidene-1,1-diphosphonic acid (HEDP) solutions in the pH range 0.98,13.00 were analysed using FT-Raman spectroscopy and 31P and 23Na NMR spectroscopy. Vibrational bands for different protonated species were observed in the Raman spectra, whereas only a single NMR signal that shifted with pH was observed for all samples over the entire pH range. No significant shift in the 23Na NMR signal was observed, confirming that formation of Na+(aq) complexes did not take place; hence, no interference with the different protonated forms of HEDP occurred. Vibrational bands were assigned using density functional theory(DFT)-calculated spectra of the most likely conformers in solution. Multivariate curve resolution was performed on the Raman spectra in the region containing the PO stretching vibrations to determine the number of protonated species formed over the entire pH range. Chemometric analysis compares very favourably with the experimental species distribution diagram which was generated using the reported log KH values. Copyright © 2009 John Wiley & Sons, Ltd. [source] Global Minimum-Energy Structure and Spectroscopic Properties of I2.,,n,H2O Clusters: A Monte Carlo Simulated Annealing StudyCHEMPHYSCHEM, Issue 1 2010Arup Kumar Pathak Abstract The vibrational (IR and Raman) and photoelectron spectral properties of hydrated iodine-dimer radical-anion clusters, I2.,,n,H2O (n=1,10), are presented. Several initial guess structures are considered for each size of cluster to locate the global minimum-energy structure by applying a Monte Carlo simulated annealing procedure including spin,orbit interaction. In the Raman spectrum, hydration reduces the intensity of the II stretching band but enhances the intensity of the OH stretching band of water. Raman spectra of more highly hydrated clusters appear to be simpler than the corresponding IR spectra. Vibrational bands due to simultaneous stretching vibrations of OH bonds in a cyclic water network are observed for I2.,,n,H2O clusters with n,3. The vertical detachment energy (VDE) profile shows stepwise saturation that indicates closing of the geometrical shell in the hydrated clusters on addition of every four water molecules. The calculated VDE of finite-size small hydrated clusters is extrapolated to evaluate the bulk VDE value of I2., in aqueous solution as 7.6 eV at the CCSD(T) level of theory. Structure and spectroscopic properties of these hydrated clusters are compared with those of hydrated clusters of Cl2., and Br2.,. [source] Polarized Raman microspectroscopy on intact human hairJOURNAL OF BIOPHOTONICS, Issue 5 2008K. R. Ackermann Abstract Polarization-resolved Raman microspectroscopy with near-infrared laser excitation was applied to intact human hair in order to non-invasively investigate the conformation and orientation of the polypeptide chains. By varying the orientation of the hair shaft relative to the polarization directions of the laser/analyzer, a set of four polarized Raman spectra is obtained; this allows to simultaneously determine both the secondary structure of hair proteins and the orientation of the polypeptide strands relative to the axis of the hair shaft. For the amide I band, results from a quantitative analysis of the polarized Raman spectra are compared with theoretically expected values for fibers with uniaxial symmetry. Based on the polarization behavior of the amide I band and further vibrational bands, a partial ordering of ,-helical polypeptide strands parallel to the hair shaft can be concluded. We suggest that this microspectroscopic approach may be used for human hair diagnostics by detecting structural or orientational alterations of keratins. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Screening Tablets for DOB Using Surface-Enhanced Raman Spectroscopy,JOURNAL OF FORENSIC SCIENCES, Issue 5 2007Steven E. J. Bell Ph.D. Abstract:, 2,5,-Dimethoxy-4-bromoamphetamine (DOB) is of particular interest among the various "ecstasy" variants because there is an unusually long delay between consumption and effect, which dramatically increases the danger of accidental overdose in users. Screening for DOB in tablets is problematic because it is pharmacologically active at 0.2,3 mg, which is c. 50 times less than 3,4-methylenedioxy-N-methylamphetamine (MDMA) and makes it more difficult to detect in seized tablets using conventional spot tests. The normal Raman spectra of seized DOB tablets are dominated by the bands of the excipient with no evidence of the drug component. Here we report the first use of on-tablet surface-enhanced Raman spectroscopy (SERS) to enhance the signal from a low concentration drug. Raman studies (785-nm excitation) were carried on series of model DOB/lactose tablets (total mass c. 400 mg) containing between 1 mg and 15 ,g of DOB and on seized DOB tablets. To generate surface-enhanced spectra, 5 ,L of centrifuged silver colloid was dispensed onto the upper surface of the tablets, followed by 5 ,L of 1.0 mol/dm3 NaCl. The probe laser was directed onto the treated area and spectra accumulated for c. 20 sec (10 sec × 2). It was found that the enhancement of the DOB component in the model tablets containing 1 mg DOB/tablet and in the seized tablets tested was so large that their spectra were completely dominated by the vibrational bands of DOB with little or no contribution from the unenhanced lactose excipient. Indeed, the most intense DOB band was visible even in tablets containing just 15 ,g of the drug. On-tablet surface-enhanced Raman spectroscopy is a simple method to distinguish between low dose DOB tablets and those with no active constituent. The fact that unique spectra are obtained allows identification of the drug while the lack of sample preparation and short signal accumulation times mean that the entire test can be carried out in <1 min. [source] Synthesis and vibrational analysis of N-(2,-Furyl)-ImidazoleJOURNAL OF RAMAN SPECTROSCOPY, Issue 8 2009A. E. Ledesma Abstract The N-(2,-furyl)-imidazole (1) has been prepared and characterized using infrared, Raman and multidimensional nuclear magnetic resonance spectroscopies. Theoretical calculations have been carried out by employing the Density Functional Theory (DFT) method, in order to optimize the geometry of their two conformers in the gas phase and to support the assignments of the vibrational bands of 1 to their normal modes. For a complete assignment of the compound, DFT calculations were combined with Scaled Quamtum Mecanic Force Field (SQMFF) methodology in order to fit the theoretical wavenumber values to the experimental one. Furthermore, Natural Bond Orbital (NBO) and topological properties by Atoms In Molecules (AIM) calculations were performed to analyze the nature and magnitude of the intramolecular interactions. The result reveals that two conformers are expected in liquid phase. Copyright © 2009 John Wiley & Sons, Ltd. [source] Vibrational spectroscopy investigation using density functional theory on 7-chloro-3-methyl-2H-1,2,4- benzothiadiazine 1,1-dioxideJOURNAL OF RAMAN SPECTROSCOPY, Issue 6 2009S. Seshadri Abstract The solid phase Fourier transform infrared (FTIR) and Fourier transform (FT) Raman spectral analysis of 7-chloro-3-methyl-2H-1,2,4-benzothiadiazine 1,1-dioxide (diazoxide), an antihypertensive agent was carried out along with density functional computations. The optimized geometry, wavenumber and intensity of the vibrational bands of diazoxide were obtained by DFT-B3LYP level of theory with complete relaxation in the potential energy surface using 6-31G(d,p) basis set. A complete vibrational assignment aided by the theoretical harmonic frequency analysis has been proposed. The harmonic vibrational wavenumbers calculated have been compared with experimental FTIR and FT Raman spectra. The observed and the calculated wavenumbers are found to be in good agreement. The experimental spectra coincide satisfactorily with those of calculated spectra. Copyright © 2009 John Wiley & Sons, Ltd. [source] Identification of chemical species of fluorescein isothiocyanate isomer,I (FITC) monolayers on platinum by doubly resonant sum-frequency generation spectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2008Toshiki Maeda Abstract Doubly resonant sum-frequency generation (DR-SFG) spectroscopy of fluorescein-4-isothiocyanate isomer-I (FITC) monolayers on platinum was performed. Vibrational spectra of the monolayers for the IR wavenumber of 1750,1450 cm,1 were measured with visible probes ranging from 431 to 582 nm. Two vibrational bands at 1643 and 1610 cm,1 were observed, and their DR-SFG excitation profiles displayed different shapes. By rinsing the monolayers with an alkaline solution, the smaller wavenumber band disappeared and the larger wavenumber band gained intensity. On the basis of the spectral response to the rinsing, we concluded that the FITC molecules existed on platinum as deprotonated and protonated forms; the former corresponds to the 1643 cm,1 band and the latter to the 1610 cm,1 band. The deprotonated form was assigned to an anionic surface species, and the protonated form to a neutral surface species by comparing the DR-SFG excitation profiles with electronic absorption spectra of the protolytic forms of fluorescein in an aqueous solution (Sjöback R et al., Spectrochimica Acta A 1995; 51: L7,L21). The results demonstrate that the measurement of DR-SFG excitation profiles is a useful technique to identify chemical species of monolayers on metal surfaces. Copyright © 2008 John Wiley & Sons, Ltd. [source] Adsorption of pyridine, ,-picoline and isonicotinonitrile on Ag colloidal particles studied by surface-enhanced Raman scattering spectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2005Tomoe Osaki Abstract The surface-enhanced Raman scattering (SERS) spectra of pyridine and related compounds, ,-picoline and isonicotinonitrile, in Ag colloids were studied. Electron diffraction measurement indicated that the Ag colloidal particles are composed of Ag crystals. Models for the molecules adsorbed on Ag particles were proposed and the optimized geometries of the models were determined through calculations of the stabilization energies due to adsorption made for the models with Gaussian 98 using the Hartree,Fock theory with the 3,21G basis set. The normal vibrations of the molecules adsorbed on Ag particles were calculated using the optimized models and assignments of the vibrational bands of the SERS spectra were made. On the basis of the results obtained, it was concluded that (1) pyridine and related compounds are adsorbed on Ag particles through NAg bonds and (2) the N atoms of the molecules are bound to the pointed ends of the surface of Ag particles on adsorption. Copyright © 2004 John Wiley & Sons, Ltd. [source] Surface-enhanced Raman scattering of 4,4,-dicyanobiphenyl on gold and silver nanoparticle surfacesJOURNAL OF RAMAN SPECTROSCOPY, Issue 6 2002Chung-ro Lee The adsorption behavior of 4,4,-dicyanobiphenyl (DCBP) on Ag and Au nanoparticle surfaces was studied by surface-enhanced Raman scattering (SERS). The absence of the ring CH band denoted a flat orientation of the biphenyl ring on Ag and Au. The red shift of the ,8a band indicated a direct ring ,-orbital interaction with the surfaces. The two benzene rings of DCBP appeared to lie on the same plane with a ,-type interaction upon adsorption on the surfaces. The ,(CN) bands were blue shifted in the Ag and Au SERS spectra by 2 and 22 cm,1, respectively from the ordinary Raman spectrum. The orientation of DCBP on the Ag and Au surfaces was analyzed by the relative enhancement factors of the vibrational bands based on the electromagnetic SERS selection rule. Copyright © 2002 John Wiley & Sons, Ltd. [source] Dispersing silicon nanoparticles in a stirred media mill , investigating the evolution of morphology, structure and oxide formationPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2007A. Reindl Abstract Silicon nanoparticles were dispersed for 24 hours in 1-butanol using a stirred media mill. Via this process intrinsically stable suspensions (in regard to aggregation) of Si nanoparticles were produced after 6 hours of dispersing. The evolution of morphology, particle size and structure was investigated by dynamic light scattering, X-ray diffraction, Raman spectroscopy and high resolution transmission electron microscopy as a function of dispersing time. The average crystallite size decreased from about 18 nm down to about 10 nm within 24 hours of milling as determined by X-ray diffraction and Raman scattering measurements. In addition careful analysis of the Raman spectra revealed a decrease of the crystalline volume fraction from 75% down to 24% and a corresponding increase of the amorphous phase. The microstructural development with varying crystallite size and crystalline volume fraction was directly confirmed by transmission electron microscopy measurements. Elemental analysis showed an increase of oxygen content that was directly proportional to the increase in specific surface area of the silicon nanoparticles during the dispersing process. The surface chemistry of the Si nanoparticles was analyzed by diffuse reflectance infrared Fourier transform spectroscopy that indicated vibrational bands of HSi,Si3,xOx, SiOx, and residual 1-butanol. The final product of the dispersing process seems to be a two-phase mixture of amorphous Si and Si nanocrystallites covered with SiOx on the surface. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Infrared reflectivity spectra of thin porous aluminum oxide filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2009Vladimir A. Yakovlev Abstract Angular dependencies of infrared (50,7500 cm,1) reflectivity spectra of thin porous aluminum oxide films on aluminum had been measured. These spectra show vibrational bands and strong interference bands allowing film thickness and dielectric function calculation. Angular dependencies of interference bands give thicknesses and refractive indices of the films. The refractive indices decrease and hence the film porosities increase with the thickness. The dispersion analysis of the reflectivity spectra below 2000 cm,1 allows us to obtain the film dielectric functions in the fundamental vibrations region. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Vibrational polaritons in thin oxide and nitride filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2008V. A. Yakovlev Abstract Angular dependencies of infrared reflectivity spectra of thin silicon oxinitride amorphous films on silicon and porous aluminum oxide films on aluminum had been measured. These spectra show vibrational bands and strong interference bands allowing film thickness and dielectric function calculation and providing useful information on the bonding structure of the coatings. Angular dependencies of these bands give the dispersion of vibrational and interference polariton modes in the films. The intersection of vibrational and interference polaritons has been observed for silicon oxinitride film. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Hydroxil ions in scheelite type molybdates and tungstatesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007L. Kovács Abstract The presence of hydroxil ions has been detected for the first time in as-grown scheelite type crystals. A number of stretching vibrational bands were observed in PbMoO4 and BaWO4 crystals at 8 K, while only very weak OH, absorption was found in CaMoO4, SrMoO4 and SrWO4 in the 3200,3600 cm,1 wavenumber range. The anharmonicity of the stretching modes for all bands in PbMoO4 and BaWO4 was found to be in agreement with that observed in other oxides. The model of weak coupling to a single phonon band was used to interpret the temperature dependence of the OH, band positions and halfwidths. Strong polarization dependence was observed for the OH, vibrations in both crystals indicating that the O,H dipoles incorporate the lattice along different O,O bonds. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Hydration of polysaccharide hyaluronan observed by IR spectrometry.BIOPOLYMERS, Issue 1 2003Abstract This article is the first one in a series dedicated to the study of hyaluronan as observed by IR spectrometry. The goal is to determine its hydration mechanism and the structural changes this mechanism implies. Hyaluronan is a natural polysaccharide that is widely used in biomedical applications and cosmetics. Its macroscopic properties are significantly dependent on its degree of hydration. In this article we record the IR spectrum of a several micron thick dried film and deduce that four or five residual H2O molecules remain around each disaccharide repeat unit in the dried film. We then compare the spectra of sodium hyaluronan and its acid form to assign vibrational bands linked to the carboxylate group. We proceed with a qualitative analysis of the spectral changes induced by changes of temperature and hygroscopicity, two independent parameters that act by modifying the hydrogen bond network of the sample. This enables us to assign most of the vibrational bands of the hydrophilic groups and to distinguish the bands that are due to these hydrophilic groups when they are or are not hydrogen bonded. It constitutes a prerequisite for the quantitative analysis of hydration spectra that will be described in the following articles of this series. © 2002 Wiley Periodicals, Inc. Biopolymers (Biospectroscopy) 72: 10,20, 2003 [source] Properties of Ionic Liquid Confined in Porous Silica MatrixCHEMPHYSCHEM, Issue 9 2010Manish Pratap Singh Abstract Porous silica matrices of different pore sizes with confined ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) [BMIM] [PF6] were prepared by sol-gel technique using a tetraethyl orthosilicate (TEOS) precursor with an aim to study the changes in physico-chemical properties of ionic liquid on confinement. It is found that on confinement 1) melting point decreases, 2) fluorescence spectra shows a red shift and 3) the vibrational bands are affected particularly those of imadazolium ring, which interacts more with the walls of the silica matrix. Preliminary theoretical calculations suggest that SiO2 matrix interact more with the heterocyclic group of [BMIM] cation than the tail alkyl chain end group resulting in significant changes in the aromatic vibrations. [source] IR and Raman Vibrational Assignments for Metal-free Phthalocyanine from Density Functional B3LYP/6-31G(d) MethodCHINESE JOURNAL OF CHEMISTRY, Issue 4 2004Xian-Xi Zhang Abstract Vibrational (IR and Raman) spectra for the metal-free phthalocyanine (H2Pc) have been comparatively investigated through experimental and theoretical methods. The frequencies and intensities were calculated at density functional B3LYP level using the 6-31G(d) basis set. The calculated vibrational frequencies were scaled by the factor 0.9613 and compared with the experimental result. In the IR spectrum, the characteristic IR band at 1008 cm,1 is interpreted as C,N (pyrrole) in-plane bending vibration, in contrast with the traditional assigned N,H in-plane or out-of-plane bending vibration. The band at 874 cm,1 is attributed to the isoindole deformation and aza vibration. In the Raman spectrum, the bands at 540. 566, 1310, 1340, 1425, 1448 and 1618 cm,1 are also re-interpreted. Assignments of vibrational bands in the IR and Raman spectra are given based on density functional calculations for the first time. The present work provides valuable information to the traditional empirical assignment and will be helpful for further investigation of the vibration spectra of phthalocyanine analogues and their metal complexes. [source] | |||||||||||||