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Vibrational Modes (vibrational + mode)
Kinds of Vibrational Modes Selected AbstractsAb initio Calculations of Raman, IR-Active Vibrational Modes in Isotopically Modified B12 Icosahedral Clusters.CHEMINFORM, Issue 46 2006Naoyuki Nogi Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Vibrational modes in a square cross-section InAs/InP nanowire superlatticePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2010Seiji Mizuno Abstract We study theoretically the phonon modes in a square cross-section nanowire superlattice (NWSL) consisting of InAs and InP. The phonon modes in the NWSL composed of cubic materials are classified into five types, i.e., A1, A2, B1, B2, and E modes. We calculate the dispersion relations of each phonon mode and corresponding displacement fields for this NWSL. The A1, A2, B1, B2, and E modes have features of dilatational, torsional, stretching, shear, and flexural modes, respectively. We examine the effects of both the superlattice modulation along the wire axis and lateral confinement of phonons. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A VCD robust mode analysis of induced chirality: The case of pulegone in chloroform,CHIRALITY, Issue 1E 2009Valentin Paul Nicu Abstract Vibrational modes in an achiral molecule may acquire rotational strength by complexation to a chiral molecule, as happens for achiral solvent molecules complexed to a chiral solute. We investigate this transfer of chirality in vibrational circular dichroism for the pulegone molecule in CDCl3 solvent from the point of view of the robustness concept introduced recently. It turns out that the transfer of chirality yields nonrobust modes, which means that, although they are observed in vibrational circular dichroism (VCD) experiments, the sign of these modes cannot be predicted reliably with standard (Density Functional Theory) VCD calculations. This limits the usefulness of the induced chirality phenomenon for obtaining information on the intermolecular interactions that give rise to it. Chirality 21:E287,E297, 2009. © 2010 Wiley-Liss, Inc. [source] Explicitly correlated SCF study of anharmonic vibrations in (H2O)2INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4-5 2002Donald D. Shillady Abstract Modeling solvation in high-pressure liquid chromatography (HPLC) requires calculation of anharmonic vibrational frequencies of solvent clusters for a statistical partition function. An efficient computational method that includes electron correlation is highly desirable for large clusters. A modified version of the "soft Coulomb hole" method of Chakravorty and Clementi has recently been implemented in a Gaussian-lobe-orbital (GLO) program (PCLOBE) to include explicit electron,electron correlation in molecules. The soft Coulomb hole is based on a modified form of Coulomb's law: An algorithm has been developed to obtain the parameter "w" from a polynomial in the effective scaling of each primitive Gaussian orbital relative to the best single Gaussian of the H1s orbital. This method yields over 90% of the correlation energy for molecules of low symmetry for which the original formula of Chakravorty and Clementi does not apply. In this work, all the vibrations of the water dimer are treated anharmonically. A quartic perturbation of the harmonic vibrational modes is constrained to be equal to the exact Morse potential eigenvalue based on a three-point fit. This work evaluates the usefulness of fitting a Morse potential to a hydrogen bond vibrational mode and finds it to be slightly better than using MP2 vibrational analysis for this important dimer. A three-point estimate of the depth, De, of a Morse potential leads to a correction formula for anharmonicity in terms of the perturbed harmonic frequency: When scaled by 0.9141, the harmonic Morse method leads to essentially the same results as scaling the BPW91 local density method by 0.9827. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 [source] Molecular structural analysis of noncarious cervical sclerotic dentin using Raman spectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2009Changqi Xu Abstract Molecular structure of the sclerotic dentin in noncarious cervical lesions (NCCLs) including both the inorganic phase and organic phase was investigated using Raman spectroscopy. It was found that NCCL sclerotic dentin was hypermineralized with the mineral/matrix ratios 2,3 times higher than those of normal dentin, which was caused by both the increase of mineral content and decrease of organic matrix (collagen) content in the sclerotic dentin. For the inorganic phase, the phosphate band (PO43,, ,1, symmetric stretching vibrational mode) in NCCL sclerotic dentin was shifted from 960 to 963 cm,1, and the width of this band was decreased from 16.4 to 10.4 cm,1, indicating that the degree of mineral crystallinity in NCCL sclerotic dentin was higher than that of normal dentin. In addition, the carbonate content in the mineral of NCCL sclerotic dentin was less than that of normal dentin. As compared to the inorganic phase, the changes within the organic phase were not dramatic. However, the changes in collagen cross-link density along with other spectral changes were still detectable. There was a noteworthy reduction in the ratio of nonreducible to reducible cross-links in the NCCL sclerotic dentin, indicating that cross-link breaks occurred in the collagen matrix of the lesions. Copyright © 2009 John Wiley & Sons, Ltd. [source] Functional mapping of carious enamel in human teeth with Raman microspectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 5 2008H. Kinoshita Abstract We employed Raman microspectroscopy to measure the Raman spectra of phosphate in sound and carious tooth substance. The peak intensity at 960 cm,1 of the phosphate (PO43,) symmetric stretching vibrational mode (,1) in sound enamel was stronger than that of sound dentin, which indicated that sound enamel contained more phosphate than sound dentin. Furthermore, the element analysis of phosphate in sound teeth substance, measured using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectroscope (EDX), gave similar results to those of the Raman measurement. In addition, the border between sound enamel and dentin was clearly demonstrated by mapping the image of the Raman spectrum of phosphate. The mapping image of phosphate in the carious enamel region revealed a heterogeneous low Raman spectrum intensity of phosphate in the area surrounding carious enamel; this finding indicates that phosphate had dissolved from the tooth substance in such areas. In contrast with the decrease in the Raman spectrum intensity of phosphate, the intensity of amide I increased mainly in the low-phosphate area. Although it remains very difficult to clinically identify the accurate border between sound and carious tooth substance, this distinction may be enabled by using the Raman spectrum of carious tooth substance. Copyright © 2008 John Wiley & Sons, Ltd. [source] Adsorption of 4,4,-thiobisbenzenethiol on silver surfaces: surface-enhanced Raman scattering studyJOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2008Yuling Wang Abstract Adsorption of 4,4,-thiobisbenzenethiol (4,4,-TBBT) on a colloidal silver surface and a roughened silver electrode surface was investigated by means of surface-enhanced Raman scattering (SERS) for the first time, which indicates that 4,4,-TBBT is chemisorbed on the colloidal silver surface as dithiolates by losing two H-atoms of the SH bond, while as monothiolates on the roughened silver electrode. The different orientations of the molecules on both silver surfaces indicate the different adsorption behaviors of 4,4,-TBBT in the two systems. It is inferred from the SERS signal that the two aromatic rings in 4,4,-TBBT molecule are parallel to the colloidal silver surface as seen from the disappearance of ,CH band (3054 cm,1), which is a vibrational mode to be used to determine the orientation of a molecule on metals according to the surface selection rule, while on the roughened silver electrode surface they are tilted to the surface as seen from the enhanced signal of ,CH. The orientation of the C-S bond is tilted with respect to the silver surface in both cases as inferred from the strong enhancement of the ,CS. SERS spectra of 4,4,-TBBT on the roughened silver electrode with different applied potentials reveal that the enhancement of 4,4,-TBBT on the roughened silver electrode surface may be related to the chemical mechanism (CM). More importantly, the adsorption of 4,4,-TBBT on the silver electrode is expected to be useful to covalently adsorb metal nanoparticles through the free SH bond to form two- or three- dimensional nanostructures. Copyright © 2007 John Wiley & Sons, Ltd. [source] Applicability of laser-induced Raman microscopy for in situ monitoring of imine formation in a glass microfluidic chipJOURNAL OF RAMAN SPECTROSCOPY, Issue 10 2003Moonkwon Lee Abstract Laser-induced Raman microscopy has been used to illustrate its applicability for the in situ monitoring of imine formation reaction in a glass microfluidic chip. In order to monitor the diffusion process in a micro channel, the Raman spectra were measured at various points along the channel with a constant flow rate of 2.7 µl min,1. Time-dependent Raman spectra were also measured without flow in order to monitor the variation of Raman peaks to a complete conversion. The disappearance of the CO stretching peak at 1700 cm,1 of the reactant, benzaldehyde, and the appearance of the Raman peak for the product, an imine, at 1628 cm,1 were successfully monitored. In addition, the intensity increases of three phenyl stretching modes in the 1550,1630 cm,1 region were also observed. The increase in Raman intensity for this vibrational mode is caused by an effective ,-electron conjugation between two phenyl rings through the ,CN,bridging group of the product. Laser-induced Raman microscopy enables us to monitor in situ product formation and to obtain detailed structural information in a glass microfluidic chip. Copyright © 2003 John Wiley & Sons, Ltd. [source] Analysis of Raman modes in Mn-doped ZnO nanocrystalsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2009Shuxia Guo Abstract Mn-doped ZnO was synthesized using a co-precipitation technique. X-ray diffraction (XRD) measurements and photoluminescence (PL) spectra show that Mn ions are doped into the lattice positions of ZnO. The modes at 202, 330, and 437,cm,1 in the Raman spectrum are assigned as 2E2 (low), E2 (high),E2 (low), and E2 (high) modes of ZnO base, respectively. The mode at 528,cm,1 is ascribed to a local vibrational mode related to Mn. The mode at 580,cm,1 should be an intrinsic mode of ZnO and assigned to E1 longitudinal optical (LO). Its reinforcement should result from a combination of resonance at the excitation wavelength and impurity-induced scattering. [source] Uniaxial stress study of the Cu,H complex in ZnOPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2006E. V. Lavrov The cover picture of the current issue refers to the article by Lavrov and Weber which was selected as Editor's Choice [1]. The picture shows a microscopic model of the Cu,H complex investigated in the paper. The complex consists of a substitutional Cu atom at the Zn site with an H atom located between nearby O and Cu in the basal plane of the ZnO lattice. The atoms are shown in different colors: yellow for copper, red for hydrogen, cyan for oxygen, and grey for zinc. Hydrogen forms a strong bond with the O atom which gives rise to a local vibrational mode at 3192 cm,1 investigated in the paper under uniaxial stress. The c -axis is parallel to the Cu,O bond pointing to the top of the figure. The authors work at the Institute of Applied Physics/Semiconductor Physics, TU Dresden, Germany. [source] Light-induced neutralization of hydrogen shallow donors in zinc oxidePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2006N. H. Nickel Abstract Infrared absorption measurements of the O,H shallow donor complex in zinc oxide show that its vibrational mode is very sensitive to sub band-gap illumination. Upon illumination the intensity of the O,H vibrational line exhibits a pronounced decrease. This effect is completely reversible. Annealing the specimens at temperatures above 30 K restores the O,H vibrational line. The decrease and increase of the O,H absorption line is caused by a change of the infrared effective charge due to neutralization and ionization, respectively, of H shallow donors. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Quasi-localized low-frequency vibrational modes of disordered solids: Study by single-molecule spectroscopyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 15 2004A. V. Naumov Editor's Choice of this issue of physica status solidi (b) is the article [1] by Andrei V. Naumov et al. This paper is Part II (Part I see [2]) of a study on elementary excitations in glasses, presented at the 11th International Conference on Phonon Scattering in Condensed Matter, St. Petersburg, 25,30 July 2004. For his outstanding talk, Naumov received the new physica status solidi Young Researcher Award which was bestowed for the first time at this conference. The cover picture is a sketch of a glass with a single impurity molecule and one hypothetical quasi-localized vibrational mode. The broadening and shift of the chromophore spectral line are caused by the interaction with this mode. Andrei V. Naumov is senior scientific researcher and deputy head of the Molecular Spectroscopy Department of the Institute of Spectroscopy, Troitsk. His main research interests are experimental and theoretical studies of low-temperature dynamics of amorphous solids (glasses, polymers etc.) via high resolution laser selective spectroscopy techniques. The second Editor's Choice is an article by E. A. Eliseev and M. D. Glinchuk [3]. Eugene A. Eliseev is scientific researcher at the Frantsevich Institute for Problems of Materials Science of the Ukrainian National Academy of Sciences, Kiev. His research areas are the theory of size and correlation effects in ferroelectric materials as well as modelling of disordered ferroelectrics properties. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Defect-impurity interactions in irradiated tin-doped Cz-Si crystalsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2003L. I. Khirunenko Abstract Results of a combined infrared absorption (IR) and deep-level transient spectroscopy (DLTS) study of defects induced by irradiation with fast electrons in Sn-doped Czochralski-grown Si crystals are reported. Tin atoms were found to interact effectively with vacancy as well as with interstitial-type radiation-induced defects. Manifestations of stable tin-vacancy and tin-interstitial carbon atom complexes were observed in DLTS and IR absorption spectra. Defect transformations upon heat-treatments of the irradiated samples were studied. Tin atoms were found to be effective traps for mobile vacancy,oxygen (V,O) complexes. A local vibrational mode of a Sn,V,O complex has been identified. [source] Dimerization of CO2 at High Pressure and TemperatureCHEMPHYSCHEM, Issue 9 2005Francesco Tassone Dr. Two,s company: Constant-pressure ab initio molecular dynamics simulations reveal the reaction of two CO2 molecules to form the metastable C2O4 species (see picture) in high-temperature (4000 K) and high-pressure (,20 GPa) liquid CO2. The dimer exhibits a unique Raman-active vibrational mode, which is characteristic for this molecule and consistent with experimental observations. [source] Observation and characterization of a specific vibrational circular dichroism band in phenyl glycosides,CHIRALITY, Issue 3-4 2008Tohru Taniguchi Abstract Application of vibrational circular dichroism (VCD) spectroscopy to structural analysis of carbohydrates has recently progressed. However, few studies on glycoconjugates VCD have thus far been reported, despite the fact that naturally occurring carbohydrates exist as various glycoconjugates. To further explore the application of the VCD technique, we have measured a series of aromatic glycosides and found that axial aromatic glycosides exhibited a negative band at around 1230 cm,1 while equatorial ones showed flat features in this region. This is the first structure,spectra relationship on glycoconjugate VCD that distinguishes the stereochemistry of the sugar anomers. Several model compounds were prepared and their vibrational properties calculated by using the density functional theory (DFT) method, which assigned the vibrational mode of this band based on the stretching motion of the glycosidic oxygen and aromatic carbon. This concept that aglycan parts can reflect stereochemical information of sugar moieties may encourage further VCD studies on glycoconjugates to realize practical structural analysis of carbohydrates. Chirality, 2008. © 2007 Wiley-Liss, Inc. [source] Probing the access of protons to the K pathway in the Paracoccus denitrificans cytochrome c oxidaseFEBS JOURNAL, Issue 2 2005Oliver-M. In recent studies on heme-copper oxidases a particular glutamate residue in subunit II has been suggested to constitute the entry point of the so-called K pathway. In contrast, mutations of this residue (E78II) in the Paracoccus denitrificans cytochrome c oxidase do not affect its catalytic activity at all (E78IIQ) or reduce it to about 50% (E78IIA); in the latter case, the mutation causes no drastic decrease in heme a3 reduction kinetics under anaerobic conditions, when compared to typical K pathway mutants. Moreover, both mutant enzymes retain full proton-pumping competence. While oxidized-minus-reduced Fourier-transform infrared difference spectroscopy demonstrates that E78II is indeed addressed by the redox state of the enzyme, absence of variations in the spectral range characteristic for protonated aspartic and glutamic acids at ,,1760 to 1710 cm,1 excludes the protonation of E78II in the course of the redox reaction in the studied pH range, although shifts of vibrational modes at 1570 and 1400 cm,1 reflect the reorganization of its deprotonated side chain at pH values greater than 4.8. We therefore conclude that protons do not enter the K channel via E78II in the Paracoccus enzyme. [source] Study of Cation Ordering in Ba(Yb1/2Ta1/2)O3 by X-Ray Diffraction and Raman SpectroscopyINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2008Dibyaranjan Rout The complex perovskite Ba(Yb1/2Ta1/2)O3 has been prepared by the two-stage solid-state reaction method. Rietveld' refinement analysis indicates cubic perovskite phase with space group . The 1:1 cation ordering at the B-site is revealed by the presence of (111) superlattice reflection in the X-ray diffraction pattern and further evidenced by the presence of A1g and F2g vibrational modes in the Raman spectra. The dielectric constant is measured to be 29.1, the product of quality factor and resonant frequency (Q×f) is found to be 32,000 GHz and the temperature coefficient of resonant frequency (,f) is 135 (ppm/°C) in the temperature range 30,70°C. [source] Theoretical studies on the mechanism and kinetics of the reaction of F atom with NCO radicalINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 2 2003Zheng-Yu Zhou The reaction of a F atom with an NCO radical was studied at 6-311+g* level, using DFT methods. All geometries, vibrational frequencies, and energies of different stationary points were calculated by HF, UMP2, and DFT methods, and the results agreed with the experimental values. The vibrational frequencies and vibrational modes of the reactant, intermediates, transition states, and products were calculated and the changes of these frequencies and modes were analyzed. Simultaneously, the vibrational modes of various species were assigned. The relationship and the change among these confirmed the mechanism of the reaction and the process of electron transfer. The major channel for the reaction was found to be the cis-channel. At the same time the rate constant was estimated. A new method of analyzing reaction mechanism is also presented. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 52,60, 2003 [source] Revealing the Electron,Phonon Coupling in a Conjugated Polymer by Single-Molecule Spectroscopy,ADVANCED MATERIALS, Issue 15 2007R. Hildner Electron,phonon coupling in a ,-conjugated polymer is revealed by single-molecule spectroscopy in combination with statistical pattern recognition techniques. The technique allows to reveal the phonon-side band in the spectra of methyl-substituted ladder-type poly(para-phenylene) (see figure). For this polymer a weak electron,phonon coupling strength is found at low temperatures. The distribution of the phonon frequencies provides strong evidence that the low-energy vibrational modes, which couple to the electronic transitions, stem from vibrations of the host matrix. [source] Explicitly correlated SCF study of anharmonic vibrations in (H2O)2INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4-5 2002Donald D. Shillady Abstract Modeling solvation in high-pressure liquid chromatography (HPLC) requires calculation of anharmonic vibrational frequencies of solvent clusters for a statistical partition function. An efficient computational method that includes electron correlation is highly desirable for large clusters. A modified version of the "soft Coulomb hole" method of Chakravorty and Clementi has recently been implemented in a Gaussian-lobe-orbital (GLO) program (PCLOBE) to include explicit electron,electron correlation in molecules. The soft Coulomb hole is based on a modified form of Coulomb's law: An algorithm has been developed to obtain the parameter "w" from a polynomial in the effective scaling of each primitive Gaussian orbital relative to the best single Gaussian of the H1s orbital. This method yields over 90% of the correlation energy for molecules of low symmetry for which the original formula of Chakravorty and Clementi does not apply. In this work, all the vibrations of the water dimer are treated anharmonically. A quartic perturbation of the harmonic vibrational modes is constrained to be equal to the exact Morse potential eigenvalue based on a three-point fit. This work evaluates the usefulness of fitting a Morse potential to a hydrogen bond vibrational mode and finds it to be slightly better than using MP2 vibrational analysis for this important dimer. A three-point estimate of the depth, De, of a Morse potential leads to a correction formula for anharmonicity in terms of the perturbed harmonic frequency: When scaled by 0.9141, the harmonic Morse method leads to essentially the same results as scaling the BPW91 local density method by 0.9827. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 [source] Thermodynamic calculations for molecules with asymmetric internal rotors.JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2008Abstract The thermodynamic properties of three halocarbon molecules relevant in atmospheric and public health applications are presented from ab initio calculations. Our technique makes use of a reaction path-like Hamiltonian to couple all the vibrational modes to a large-amplitude torsion for 1,2-difluoroethane, 1,2-dichloroethane, and 1,2-dibromoethane, each of which possesses a heavy asymmetric rotor. Optimized ab initio energies and Hessians were calculated at the CCSD(T) and MP2 levels of theory, respectively. In addition, to investigate the contribution of electronically excited states to thermodynamic properties, several excited singlet and triplet states for each of the halocarbons were computed at the CASSCF/MRCI level. Using the resulting potentials and projected frequencies, the couplings of all the vibrational modes to the large-amplitude torsion are calculated using the new STAR-P 2.4.0 software platform that automatically parallelizes our codes with distributed memory via a familiar MATLAB interface. Utilizing the efficient parallelization scheme of STAR-P, we obtain thermodynamic properties for each of the halocarbons, with temperatures ranging from 298.15 to 1000 K. We propose that the free energies, entropies, and heat capacities obtained from our methods be used to supplement theoretical and experimental values found in current thermodynamic tables. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008 [source] Formation of 8-nitroguanine and 8-oxoguanine due to reactions of peroxynitrite with guanineJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 8 2007N. R. Jena Abstract Reactions of peroxynitrite with guanine were investigated using density functional theory (B3LYP) employing 6-31G** and AUG-cc-pVDZ basis sets. Single point energy calculations were performed at the MP2/AUG-cc-pVDZ level. Genuineness of the calculated transition states (TS) was tested by visually examining the vibrational modes corresponding to the imaginary vibrational frequencies and applying the criterion that the TS properly connected the reactant and product complexes (PC). Genuineness of all the calculated TS was further ensured by intrinsic reaction coordinate (IRC) calculations. Effects of aqueous media were investigated by solvating all the species involved in the reactions using the polarizable continuum model (PCM). The calculations reveal that the most stable nitro-product complex involving the anion of 8-nitroguanine and a water molecule i.e. 8NO2G, + H2O can be formed according to one reaction mechanism while there are two possible reaction mechanisms for the formation of the oxo-product complex involving 8-oxoguanine and anion of the NO2 group i.e. 8OG + NO2,. The calculated relative stabilities of the PC, barrier energies of the reactions and the corresponding enthalpy changes suggest that formation of the complex 8OG + NO2, would be somewhat preferred over that of the complex 8NO2G, + H2O. The possible biological implications of this result are discussed. © 2007 Wiley Periodicals, Inc. J Comput Chem 2007 [source] Wavelet transform analysis of ab initio molecular dynamics simulation: Application to core-excitation dynamics of BF3JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2007Takao Otsuka Abstract We propose a novel analysis method of ab initio molecular dynamics (AIMD) simulation using a continuous wavelet transform (c-WT) technique. The c-WT technique, one of the time-frequency signal analysis methods, provides a clear view of the dynamical information in time developments. Combined with the auto-correlation function of velocity by AIMD simulation, c-WT analysis enables us to well understand dynamical distribution, such as the vibrational properties following a change of electronic structure in a molecular system. As a practical application, AIMD simulation of core-excited BF3 (B1s , 2a) is illustrated. AIMD simulation leads to the change of vibrational motion as well as structural deformation by core-excitation. The c-WT analysis clarifies the relationship between structural deformation and the related significant vibrational modes in core-excitation within 50 fs. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [source] Infrared laser desorption and ionization of polypeptides from a polyacrylamide gelJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 3 2002Michelle Baltz-Knorr Abstract We observed direct desorption and ionization of angiotensin II and bovine insulin from a frozen polyacrylamide gel without the addition of an exogenous matrix, using picosecond pulses from a tunable, mid-infrared free-electron laser tuned to strong absorption bands of the gel. At 5.7, 5.9, 6.1 and 6.3 µm we were able to desorb and ionize both analyte molecules, with the strongest analyte signal generated at 5.9 µm. However, no analyte signal was observed at 5.5 µm. Consistent with a previous report, we did not observe ions of either polypeptide at 2.9 µm, in spite of strong overall absorption. We discuss the implications of this wavelength-dependent ionization, including possible ablation mechanisms and energy partitioning between competing vibrational modes. Copyright © 2002 John Wiley & Sons, Ltd. [source] Noncontact photo-acoustic defect detection in drug tabletsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2007Ivin Varghese Abstract Quality assurance monitoring is of great importance in the pharmaceutical industry for the reason that if defects such as coating layer irregularities, internal cracks, and delamination are present in a drug tablet, the desired dose delivery and bioavailability can be compromised. The U.S. Food and Drug Administration (FDA) established the Process Analytical Technology (PAT) initiative, in order to ensure efficient quality monitoring at each stage of the manufacturing process by the integration of analysis systems into the evaluation procedure. Improving consistency and predictability of tablet action by improving quality and uniformity of tablet coatings as well as ensuring core integrity is required. An ideal technique for quality monitoring would be noninvasive, nondestructive, have a short measurement time, intrinsically safe, and relatively inexpensive. In the proposed acoustic system, a pulsed laser is utilized to generate noncontact mechanical excitations and interferometric detection of transient vibrations of the drug tablets is employed for sensing. Two novel methods to excite vibrational modes in drug tablets are developed and employed: (i) a vibration plate excited by a pulsed-laser and (ii) pulsed laser-induced plasma generated shockwave expansion. Damage in coat and/or core of a tablet weakens its mechanical stiffness and, consequently, affects its acoustic response to an external dynamic force field. From the analysis of frequency spectra and the time,frequency spectrograms obtained under both mechanisms, it can be concluded that defective tablets can be effectively differentiated from the defect-free ones and the proposed proof-of-concept techniques have potential to provide a technology platform to be used in the greater PAT effort. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96:2125,2133, 2007 [source] Raman and surface-enhanced Raman spectroscopic studies of the 15-mer DNA thrombin-binding aptamerJOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2010Cynthia V. Pagba Abstract Aptamers are single-stranded oligonucleotides that selectively bind to their target molecules owing to their ability to form secondary structures and shapes. The 15-mer (5,-GGTTGGTGTGGTTGG-3,) DNA thrombin-binding aptamer (TBA) binds to thrombin following the formation of a quadruplex structure via the Hoogsten-type G,G interactions. In the present study, Raman and SERS spectra of TBA and thiolated TBA (used to facilitate covalent bonding to metal nanoparticle) in different conditions are investigated. The spectra of the two analogs exhibit vibrations, such as the C8N7H2 deformation band at ,1480 cm,1 of the guanine tetrad, that are characteristic of the quadruplex structure in the presence of K+ ions or at low temperature. Interestingly, SERS spectra of the two analogs differ markedly from their respective normal Raman spectra, possibly due to changes in the conformation of the aptamer upon binding, as well as to the specific interaction of individual vibrational modes with the metal surface. In addition, the SERS spectra of the thiolated aptamer show significant changes with different concentrations, which may be due to different orientation of the molecule with respect to the metal surface. This study provides useful information for the development of label-free aptamer-based SERS sensors and assays. Copyright © 2009 John Wiley & Sons, Ltd. [source] Characterisation of FXTAS related isolated intranuclear protein inclusions using laser tweezers Raman spectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 1 2010Tobias J. Moritz Abstract We report the analysis of the vibrational modes of intranuclear protein inclusions isolated from the brain of human subjects with the Fragile X-associated tremor/ataxia syndrome (FXTAS). In this preliminary study, Raman spectra of optically trapped inclusions were measured and analysed to determine protein composition and structure. Our main findings are as follows: (1) The spectra of protein inclusions are characteristic of H2A and H2B histones, which correlate with previous mass spectrometry (MS) studies; (2) Tyrosine is present in its OH form and exposed at the protein surface; (3) Zn and to a lesser extent Cu bound to histidine side chains are detected in the inclusions; (4) The tryptophan side-chain torsion angle is calculated to be 102°; (5) Several potential spectroscopic markers for the inclusions of FXTAS are identified. These results show the capability of using laser tweezers Raman spectroscopy to identify protein inclusions in a non-perturbative way and to gain further insight into the pathogenesis and progression of FXTAS in human subjects and in experimental models of this disorder. Copyright © 2009 John Wiley & Sons, Ltd. [source] Flexibility of paramagnetic (d1) organometallic dithiolene complex [Cp2Mo(dmit)]+, studied by Raman spectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2009Roman, wietlik Abstract We report on the experimental and theoretical studies of the flexible organometallic complex Cp2Mo(dmit) which often exhibits a folding in the solid state. Raman spectra of charge-transfer salts formed by Cp2Mo(dmit) with various anions (Br,, BF4,, PF6,, SbF6,, ReO(dmit)2,, TCNQF4,) were measured at room temperature using red (632.8 nm) and near-infrared (780 nm) excitations. The influence of the folding of the MoS2C2 metallacycle in [Cp2Mo(dmit)]+, cation on the Raman spectra was investigated. Due to folding of [Cp2Mo(dmit)]+,, the bands related to the CC and some CS stretching vibrations shift toward lower wavenumbers by about 0.5,0.6 cm,1deg,1. The bond lengths, charge distribution on atoms, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies, and dipole moments for neutral and ionized complex with various folding angles were calculated by density functional theory (DFT) methods. Additionally, the normal vibrational modes and theoretical Raman spectra were calculated and compared with experimental data. Our results indicate that vibrational spectroscopy can be applied for investigation of complex deformations in the solid state. Copyright © 2009 John Wiley & Sons, Ltd. [source] Identification and characterisation of the E951 artificial food sweetener by vibrational spectroscopy and theoretical modellingJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2009Niculina Peica Abstract Aspartame (E951), a very well-known dipeptide sweetener, approximately 150,200 times sweeter than sugar, is widely used in a variety of applications, especially in soft drinks. A drawback of E951 is its relatively low stability at high pH values and at high temperatures, thereby limiting its use. The changes observed in the very strong bands from the 1600,1300 cm,1 spectral region, characteristic to the ,(CO) mode coupled with the NH bending mode, allows to establish the species present in the Raman and SERS solutions at different concentrations and pH values. More exactly, a molecule protonation at the amino group was detected on going from basic to acidic pH values. The DFT calculated geometry, harmonic vibrational modes and Raman scattering activities of E951 were in good agreement with the experimental data and helped establish its SERS behaviour on silver surfaces. According to the DFT calculations performed, E951 can give rise to an intramolecular hydrogen bonding network, with lengths in the same range as the hydrogen bonds in the peptide unit moieties. Copyright © 2009 John Wiley & Sons, Ltd. [source] Study of the vibrational spectra of (CH3)3GeCl from experimental and DFT calculationsJOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2009María Lorena Roldán Abstract New infrared (for gas and liquid phase) and Raman (for liquid) spectra were measured for the chlorotrimethylgermane to obtain a complete assignment of its fundamental modes. The measurement of the low-temperature infrared spectrum together with the application of Fourier self-deconvolution to the Raman spectra resolves the CH vibrational modes into their components. The Rauhut and Pulay scaled quantum mechanical (SQM) force field methodology and the wavenumber-linear scaling (WLS) method were used to predict the vibrational spectra as a guide to the assignment of the fundamental bands. A quantum mechanical analysis was carried out to obtain the harmonic force field. Copyright © 2009 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||