Search results for "Infrared"
showing 10 items of 2110 documents
Crystal structure and IR spectrum of 1-O-α-d-glucopyranosyl-d-mannitol–ethanol (2/1)
1999
Abstract 1- O - α - d -Glucopyranosyl- d -mannitol–ethanol (2/1), (C 12 H 24 O 11 ) 2 –C 2 H 5 OH, crystallizes in the monoclinic space group P2 1 with unit cell dimensions a =11.4230(8) A, b =9.525(4) A, c =15.854(2) A, β =102.751(7)° and V =1682.4(7) A 3 , Z =2, D x =1.45 Mg m −3 , λ (Mo-K α )=0.71069 A, μ=0.128 mm −1 , F (000)=788 and T =293(2) K. The structure was solved by direct methods and refined by least-squares calculations on F 2 to R 1 =0.0371[ I >2 σ ( I )], and 0.0930 (all data, 3542 independent reflections, R int =0.021). There are two molecules of glucopyranosylmannitol (GPM) and one ethanol molecule in the asymmetric unit, and the glucopyranosyl ring adopts a chair conforma…
Various types of polysiloxanes studied by positron annihilation lifetime spectroscopy
2014
Abstract In the work, linear poly(vinylsiloxanes) with regular distributions of vinyl groups along chains, the networks obtained by their hydrosilylation with various hydrogensiloxanes, products of pyrolysis of such networks as well as the networks prepared via reaction of low-molecular siloxanes have been studied by positron anihilation lifetime spectroscopy (PALS). Based on free volume sizes determined by this method, relations between cross-link densities in the investigated systems have been established. They have been compared with the results of swelling experiments conducted in the work and to efficiency of cross-linking reaction evaluated in our previous FTIR investigations of the s…
The infrared and Raman spectra of solid tridehydropeptides : influence of ΔAla and ΔPhe on the spectral profile
2012
Abstract A series of solid tripeptides Boc-Gly-X-Gly-OMe (X = dehydroalanine (ΔAla), dehydrophenylalanine (ΔPhe)) was investigated by Raman scattering and Fourier transform infrared spectra to examine the conformational marker bands of the unsaturated residue. The observed fundamental modes gave us the opportunity to analyze structural features that change due to the substitution of Ala by ΔAla and due to the different spatial arrangement of ΔPhe ( Z and E isomers). In addition, we showed the alteration of the spectral profile when the large size residue (Phe) is introduced into the backbone of the peptide with ΔPhe (in Boc-Gly-Δ (Z) Phe-Phe-OMe). The frequency ranges of interest included t…
The infrared spectrum of CH 3 D between 900 and 3200 cm −1 : extended assignment and modeling
2000
Abstract The high resolution infrared spectrum of CH 3 D in the region from 900 to 3200 cm −1 has been analyzed on the basis of Fourier transform spectra recorded at Kitt Peak and at Giessen. A theoretical model for an effective hamiltonian in terms of irreducible tensor operators recently adapted to symmetric top molecules has been used in order to consider simultaneously all available transitions between the lowest three polyads of the molecule: the Ground State (G.S.), the Triad (three interacting fundamental bands in the 8 μm region) and the Nonad (nine interacting bands in the 4 μm region). A preliminary simultaneous fit of 3467 Triad–G.S., 5208 Nonad–G.S., and 2487 Nonad–Triad (hot ba…
Vibrational spectra and DFT calculations of PPV-oligomers
2003
The first two members of the p-phenylenevinylene- oligomer family (i. e. 1, 4-distyrylbenzene [DSB] and 4, 4'-distyrylstilbene [DSS]) were synthesized and their infrared and Raman spectra recorded and empirically assigned. Molecular geometries were optimized for the planar point group (C2h) by the density functional theory (DFT) method using the B3LYP functional and 6-31G* basis set. Calculations of vibrational spectra, including intensities, were carried out subsequently using the DFT method with the same basis set and linear scaling was applied. Calculated vibrational wavenumbers are in a fair agreement with our own experimental spectra. In order to explore changes in vibrational dynamics…
Direct determination of minerals in human diets by infrared spectroscopy and X-ray fluorescence
2014
The use of near and mid infrared spectroscopy and X-ray fluorescence (XRF) to determine the concentration of mineral elements in Spanish human diets was investigated. Thirty-five commercial baby foods, 6 children fast food menus and 13 university canteen menu samples were analysed by infrared and XRF spectroscopy and spectra evaluated by using reference data obtained by inductively coupled plasma optical emission spectroscopy (ICP-OES). Models for calcium, potassium, iron, magnesium, sodium and zinc determination were built and validated. Spectra were pre-treated by using different pre-processing algorithms (multiplicative scatter correction, standard normal variation, first derivate, ortho…
Atmospheric compensation in Fourier transform infrared (FT-IR) spectra of clinical samples.
2013
A new method is proposed for the elimination of the spectral contribution of two atmospheric gases (CO2 and H2O) in Fourier transform infrared (FT-IR) spectra of clinical samples. The algorithm is based on the measurement of reference spectra of H2O followed by an automatic calculation of the spectral contribution of the above-mentioned gases to the sample spectra. Then this contribution is compensated by spectral subtraction. Attenuated total reflectance FT-IR spectra of serum and urine samples in the presence of atmospheric gases were corrected and compared with spectra obtained with an N2 purge. Visual inspection of the spectra as well as calculated noise levels confirmed that the metho…
The Influence of Alkali Metal Ions in the Chemisorption of CO and CO2on Supported Palladium Catalysts: A Fourier Transform Infrared Spectroscopic Stu…
1996
Two series of palladium-based catalysts were compared on the basis of the adsorption of CO and CO2, monitored by Fourier transform infrared spectroscopy. The first series is represented by a silica-supported palladium catalyst and by some catalysts derived from it by addition of different amounts of sodium ion, 0 ≤ R ≤ 25.6, whereRis the atomic ratio Na/Pd. The second series consists of palladium catalysts supported on “model” and natural pumices. The model pumices, obtained by sol-gel techniques, are silico-aluminates containing variable amounts of sodium so that the corresponding Pd catalysts have anRvalue in the range 0 ≤ R ≤ 6.1. In the Pd/natural pumice catalysts, changes of the atomic…
Oxidomolybdenum(IV), ‐(V), ‐(VI) Complexes with Relevance to Molybdenum Enzymes: Oxygen Atom Transfer, Redox Chemistry and EPR Spectroscopy
2010
The cis-dioxidomolybdenum(VI) complex Mo(NN′)2O2 (1) [(NN′) = N-(4-hydroxyphenyl)-2-pyrrolatocarbaldimine] transfers one oxygen atom to phosphanes PMenPh3–n (n = 0–3) to give quantitatively the respective phosphane oxides OPMenPh3–n (OAT, oxygen atom transfer). The kinetics of these OAT reactions has been investigated spectrophotometrically. When offering excess PMenPh3–n (n = 1–3), oxido(phoshane)molybdenum(IV) complexes Mo(NN′)2O(PMenPh3–n) 5a–5c are isolated and characterized by multinuclear NMR spectroscopy (1H, 13C, 31P, 15N), IR spectroscopy, UV/Vis spectroscopy and mass spectrometry. The redox chemistry of the molybdenum(IV) complexes 5a–5c and of molybdenum(VI) complex 1 has been pr…
Electrosynthesis of Poly(alanine)-Like Peptides in Concentrated Alanine Based Electrolytes, Characterization Coupled to DFT Study and Application to …
2014
The anodic oxidation of concentrated l-alanine on smooth electrodes such as platinum and glassy carbon electrodes was studied. Contrary to the previous studies performed up to now with diluted l-alanine, the electrochemical process generated here results in a completely different situation. The oxidation on smooth platinum was carried out by electrochemical quartz crystal microbalance (EQCM) coupled to cyclic voltammetry technique. The effects of concentration, scan rate, and pH (zwitterion at pH = 6 and alkaline media at pH = 13) on potential values were examined. Glassy carbon and smooth gold electrodes showed the same behavior as on smooth platinum electrode. Spectroscopic analysis such …