Weak IR Bands Research Articles

Fractional order ATR-FTIR differential spectroscopy for detection of weak bands and assessing the radiation modifications in gamma sterilized UHMWPE.

This study presents a new method for identifying radiation modifications in UHMWPE polymer samples. The method involves using a mathematical technique called fractional order differential transformation on IR spectra obtained through ATR-FTIR spectroscopy. This new method was compared to existing techniques such as FTIR, XRD, and DSC, and it was found to be more sensitive and accurate in detecting radiation-induced changes in the polymer. The study focused on identifying changes in weak IR bands in the UHMWPE samples caused by gamma sterilization while simulating IR spectra using different orders of fractional derivatives and compared them to experimental spectra. It was found that applying a lower order of differentiation was more suitable for identifying radiation-induced changes in the UHMWPE samples. Using this method, they were able to identify specific changes in the gamma irradiated structure, such as the splitting of a single absorption peak into a doublet, which was only present in the 50 kGy irradiated sample. The study also used correlation index analysis, principal component analysis, and hierarchy cluster analysis to analyze the simulated and experimental spectra. These techniques allowed to confirm the effectiveness of the fractional order differential transformation method and to identify the specific regions of the IR spectra that were affected by radiation-induced changes in the UHMWPE samples. Overall, this study presents a new method for identifying radiation-induced changes in UHMWPE polymer samples that is more sensitive and accurate than existing techniques. By identifying these changes, researchers can better understand the effects of gamma sterilization on medical equipment and potentially develop new methods for sterilization that do not damage the equipment.

Oxidation of Ethanol in Cu-Faujasites Studied by IR Spectroscopy

In this study, IR studies of the coadsorption of ethanol and CO on Cu+ cations evidenced the transfer of electrons from ethanol to Cu+, which caused the lowering of the frequency of the band attributed to CO bonded to the same Cu+ cation due to the more effective π back donation of d electrons of Cu to antibonding π* orbitals of CO. The reaction of ethanol with acid sites in zeolite HFAU above 370 K produced water and ethane, polymerizing to polyethylene. Ethanol adsorbed on zeolite Cu(2)HFAU containing acid sites and Cu+exch also produced ethene, but in this case, the ethene was bonded to Cu+ and did not polymerize. C=C stretching, which is IR non-active in the free ethene molecule, became IR active, and a weak IR band at 1538 cm−1 was present. The reaction of ethanol above 370 K in Cu(5)NaFAU zeolite (containing small amounts of Cu+exch and bigger amounts of Cu+ox, Cu2+exch and CuO) produced acetaldehyde, which was further oxidized to the acetate species (CH3COO−). As oxygen was not supplied, the donors of oxygen were the Cu species present in our zeolite. The CO and NO adsorption experiments performed in Cu-zeolite before and after ethanol reaction evidenced that both Cu+ox and Cu2+ (Cu2+exch and CuO) were consumed by the ethanol oxidation reaction. The studies of the considered reaction of bulk CuO and Cu2O as well as zeolites, in which the contribution of Cu+ox species was reduced by various treatments, suggest that ethanol was oxidized to acetaldehyde by Cu2+ox (the role of Cu+ox could not be elucidated), but Cu+ox was the oxygen donor in the acetate formation.

ИНСТРУМЕНТАЛЬНЫЕ И МОРФОЛОГИЧЕСКИЕ КРИТЕРИИ ДИАГНОСТИКИ ОПОЯСЫВАЮЩЕГО ГЕРПЕСА

Objective: To assess the instrumental and morphological diagnosis of herpes zoster (HZ). Methods: Instrumental and morphological diagnostics of HZ carried out in 40 patients. The spectra recorded on a standard two-beam IR spectrometer in the frequency range 4000-400 cm-1. Evaluate the results of pathomorphological studies, a computer-aided analysis system for microscopic images, consisting of a light-optical microscope used. Microscopic samples studied under the microscope Olympus CX21 at different magnifications with the Digital Microscope Camera MC-DO 48U (E). Results: Analysis of infrared spectra of blood plasma in HZ patients showed that when IR spectroscopic examination of blood of patients with different forms of HZ observed. A more significant shift of Vmax to the low-frequency region of the band 665 cm-1 observed a significant change in the IR absorption bands lying in the region frequencies of 1800-1200 cm-1, and very weak IR bands with Vmax 1450, 1300 and 1225 cm-1 completely smoothed out. Morphological examination of patients with different forms of HZ in the germ layer of the epidermis determines the phenomena of spongiosis and ballooning (vacuolar) dystrophy, caused by a sharp intracellular oedema and changes in the nuclei. Conclusion: The results of the research showed that both instrumental and morphological diagnostic methods for HZ are technically simple in execution, informative, economic and allow diagnosing all clinical forms of dermatosis in a short time. Keywords: Herpes zoster, instrumental and morphological diagnostics, IR spectrometry.

Interpretation of Nitroindolinospirobenzothiopyran Vibrational Spectra

The structures of four possible stereoisomers of the closed form of photochromic nitroindolinospirobenzothiopyran (NISTP) {1′,3′-dihydro-1′,3′,3′-trimethyl-6-nitrospiro[2H-1-benzothiopyran-2,2′-(2H)-indoline]} were determined by the DFT method. The geometry of the most stable isomer was defined. Nitro-substitution changes mainly the lengths of bonds formed by S and N with spiro-atom Cs. According to the calculations, the CsS bond changes most and lengthens by 0.019 A. It is shown that the S atom has large displacement amplitudes in normal modes assigned to Raman lines at 230, 285, 360, and 575 cm–1 and weak IR bands at 467 and 577 cm–1. Oscillations involving the nitro group are very active in Raman and IR spectra. Their frequencies are slightly lower than similar frequencies of nitrobenzene and nitroindolinospirobenzopyran, indicating a higher degree of vibrational coupling of the NO2 group with the NISTP molecular skeleton.

Structural and spectroscopic studies of two 1,3-benzothiazole tautomers with potential antimicrobial activity in different media. Prediction of their reactivities

In this work, the structural, electronic and vibrational properties of 6-Nitro-1,3-benzothiazole-2(3H)-thione and their 2-thiol tautomer were studied by using density functional theory (DFT) and self consistent reaction force (SCRF) calculations in gas phase and, in formamide, aqueous, DMSO and acetone solutions. The solvation energies were computed taking into account the solvent effects by using the polarized continuum (PCM) and solvation (SM) models. The atomic charges, electrostatic potentials, bond order, energy stabilizations, topological properties were calculated together with the gap energies and some descriptors in order to predict the reactivities and behaviour of both tautomers in the different media. The dipole moment and solvation energy values for both forms show different behaviours with the permittivity values of the solvents. The studies by infrared spectroscopy reveal the presence of both tautomers and of the two dimers of thione in the solid phase, as supported by the weak IR bands at 1702, 1525, 1303 and 1292cm−1 and the shoulder at 915cm−1. Moreover, the strong IR band at 3062cm−1, the bands of the media intensities at 680 and 466cm−1 and, the very weak band at 499cm−1 support the presence of the thione form. The higher electrostatic potentials on the NO2 group of the thiol tautomer and their low electrophilic index show that thiol is better electron donor than thione while, thione has the highest reactivities in all the solvents and in gas phase than thiol. Here, the complete assignments of the normal vibration modes of thione and thiol in gas phase and in the four solvents are reported for the first time.

Vibrational spectroscopic studies, conformations and ab initio calculations of 3,3,3-trifluoropropyltrichlorosilane

Infrared spectra of 3,3,3-trifluoropropyltrichlorosilane (CF 3CH 2CH 2SiCl 3) were obtained in the vapour, amorphous and crystalline solid phases in the range 4000–50 cm −1. Additional spectra in argon matrices at 5.0 K were recorded before and after annealing to 20–36 K. Raman spectra of the compound as a liquid were recorded at various temperatures between 298 and 210 K and spectra of the amorphous and crystalline solids were obtained. The spectra suggested the existence of two conformers ( anti and gauche) in the fluid phases and in the matrix. When the vapour was shock-frozen on a cold finger at 80 K and subsequently annealed to 120–150 K, six weak or very weak Raman bands vanished in the crystal. Similar variations were observed in the corresponding infrared spectra after annealing and four very weak IR bands disappeared after crystallization. From intensity variations between 298 and 210 K of three Raman band pairs an average value Δ conf H° ( gauche–anti) = 6.1 ± 0.5 kJ mol −1 was obtained in the liquid. Annealing experiments indicate that the anti conformer also has a lower energy in the argon matrices. The conformational equilibrium is highly shifted towards anti in the liquid, and the low energy conformer also forms the crystal. The spectra of the abundant anti conformer and the few bands ascribed to the gauche conformer have been interpreted. Ab initio calculations at the HF/6-311G ** and B3LYP/6-311G ** gave optimized geometries, infrared and Raman intensities and vibrational frequencies for the anti and gauche conformers. The conformational energy differences derived were 11.8 and 9.2 kJ mol −1 from the HF and the B3LYP calculations, respectively.

NOx trapping and soot combustion on BaCoO3−y perovskite: LRS and FTIR characterization

The BaCoO3−y perovskite-type mixed oxide is studied for both trapping of NOx and combustion of diesel soot. The starting material consists of a stoichiometric mixture of Ba and Co nitrates. Different crystalline phases are obtained when the solids are calcined at different temperatures (ranging from 400 to 1000°C). After 400°C calcination Ba(NO3)2 and Co3O4 crystalline phases are formed, while after calcination at 700°C the BaCoO3 stoichiometric perovskite is obtained. However, when the temperature is increased to 1000°C, the structure loses oxygen and perovskite BaCoO2.74 is formed. The solids calcined at 700 and 1000°C show high NOx adsorption capacity, the latter being more effective. This solid shows weak IR bands in the 800cm−1 frequency region associated with the perovskite structure. After the catalyst interacts with NOx, new bands associated with bulk nitrates and surface NO3− species are observed. Signals associated with surface N-bounded species of the OBaNO2 type could be masked by the intense Ba(NO3)2 signals. LRS characterization is in agreement with XRD and FTIR results. The Raman signal at 716cm−1 is associated with the BaCoO2.74 structure while a broad signal at 607cm−1 appears in samples containing BaCoO3 and BaCoO2.94 phases. Nitrates formed upon NO+O2 treatments show high thermal stability under He atmosphere up to 490°C. However, reductive treatments either under H2 atmosphere or with soot particles cause decomposition of the nitrates at temperatures lower than 400°C. A reaction scheme is proposed involving the participation of perovskite structures, Co3O4, Ba(NO3)2, BaO and metallic Co particles.The catalyst under study favors the reaction between the soot particles and the trapped NOx species making this system promising for the simultaneous abatement of both contaminants. The addition of K decreases the soot combustion temperature.

Substituent effects on benzdiyne: a density functional theory study.

Density functional theory (DFT) studies were performed to investigate the effect of substituents on the properties of benzdiyne derivatives. Twelve substituted benzdiynes-C(6)X(2), where X = F, Cl, Br, Me, CF(3), CN, OH, NO(2), NH(2), OMe, NMe(2), and Ph-were considered along with the unsubstituted 1,4-benzdiyne. The structures, vibrational frequencies, and IR intensities of these benzdiynes were studied with a popular three-parameter hybrid density functional (B3LYP) combined with the split-valence 6-31G(d) basis set and Dunning's correlation-consistent polarized triple-zeta (cc-pVTZ) basis set. The relative stabilities of the substituted benzdiynes were studied with the help of reaction energies of isodesmic reactions, which showed that the electron-withdrawing groups destabilized the benzdiynes more than they did the corresponding benzenes, whereas the electron-donating groups stabilized the benzdiynes more than they did their benzene counterparts. Correlation analyses revealed that field/inductive effects played a more important role than did resonance effects. The changes in atomic charges and spin populations due to the substituents were also studied. The asymmetric nu(Ctbd1;C) stretching modes obtained were close to the 1500-cm(-)(1) mark. Reinvestigation of the experimental results supported these results; a weak IR band at 1486 cm(-)(1) was assigned to this asymmetric stretching mode in C(6)(CF(3))(2) F. Some other benzdiynes also had large IR intensity values for their asymmetric nu(Ctbd1;C) vibrational modes due to the coupling with other vibrational modes. Heats of formation for the substituted benzdiynes were obtained from the reaction energies calculated at the B3LYP/cc-pVTZ level of theory.

Heat of adsorption of carbon monoxide on a Ru/Al 2O 3 catalyst using adsorption equilibrium conditions at high temperatures

The adsorption of CO on a reduced 3.5%Ru/Al 2O 3 catalyst has been studied by means of FTIR spectroscopy between 298 and 740 K at a constant partial pressure P a=1000 Pa. At 300 K, three adsorbed species were detected on the Ru particles: a linear CO species (strong IR band at 2047 cm −1), a bridged CO species (weak IR band at 1750 cm −1) and a gem-dicarbonyl species (weak IR bands at 2135 and 2080 cm −1). The FTIR spectra show how the coverage θ of the linear CO species evolves with the adsorption temperature T a. This cannot be achieved for the bridged CO species or for the gem-dicarbonyl species due to the weak intensities of their IR bands. At T a>600 K, the curve θ= f( T a) is in very good agreement with Temkin’s adsorption model. Moreover, it is shown that, in the range 300–720 K, the curve agrees well with an adsorption model considering (a) an immobile adsorbed species; and (b) a linear decrease in the heat of adsorption with the increase in θ. This leads for the linear CO species to the heat of adsorption E θ , at various coverages θ: from E 0=175 kJ mol −1 at θ=0 to E 1=115 kJ mol −1 at θ=1. This procedure for the determination of the heat of adsorption of CO on Ru particles is simple (it requires a single isobar) and accurate (≈±5 kJ mol −1). It constitutes a well adapted tool to study the modifications of this parameter with the method of preparation of the catalyst (precursor, support, particle size).

Microstructure of lucite glass-ceramics for dental use

Microstructure of lucite glass-ceramics for dental use was investigated using X-ray diffraction, FT-IR spectroscopy and laser Raman spectroscopy. Main features of the FT-IR and laser Raman spectra were similar to those of silicate glasses containing Al 3+, or other M 3+ (M = metal), as network forming ions. Two weak IR bands at 640 and 543 cm −1 were typical of all lucite-type glass-ceramics and these bands disappeared with the conversion of glass-ceramics into the glass state. The laser Raman spectrum of lucite-type glass showed a broad band with center at ≈ 4600 cm −1 due to fluorescence/luminescence spectral feature with two luminescence sharp peaks at 5037 and 5007 cm −1. The results were compared with those obtained for different silicate glasses.

Oxidation of methylene in low-temperature matrices

The matrix photochemistry of CH3l and its fully deuterated analogue at 4.2 K has been shown to proceed mainly through the intermediacy of methylene. The FTIR spectrum taken after photolysis of CH3l in a nitrogen matrix shows that diazomethane is produced. Furthermore, the nature of the photooxidation products in 16O2- or 18O2-doped argon matrices support mechanisms in which methylene and molecular oxygen react. Weak IR bands which could not be attributed to known oxidation end products or intermediates could be tentatively assigned to dioxirane by comparison with previous ab initio calculations. If this is indeed the case then the appearance of CH2O2 in its cyclic form rather than its open-chain isomer indicates that either: (i) dioxirane is a primary product or (ii) the activation energy barrier between the forms is surmounted by photolysis as observed in other carbonyl oxide systems or (iii) the formaldehyde product is formed in a matrix by the efficient breakdown of peroxymethylene (by analogy with the gas-phase decomposition of CHCIOO, peroxychloromethylene).

Low‐Temperature conformation of Mg2+‐Poly(U) in D2O as revealed by IR and Raman Spectroscopy and by normal‐mode analysis treatment

AbstractInfrared and Raman spectra of the Mg2+ salt of poly(U) in D2O were recorded in the 1600‐1800 cm−1 region and between 1 and 20C. The ir spectra showed a melting curve similar to the uv melting curves with a temperature of transition of about 6.5°C. This spectral change is assumed to be associated with the formation of the secondary structure of Mg2+‐poly(U) in D2O at this temperature. Three double‐helical and two triple‐helical structures were used as inputs to compute the normal modes of vibration. A double‐helical structure was found to give the best agreement with the observations. Knowledge of the C=0 eigenvectors, and of the expression for transition probability from quantum mechanics, was used to explain the so far unanswered question of H. T. Miles [(1964) Proc. Natl. Acad. Sci. USA 51, 1104–1109; (1980) Biomolecular Structure, Conformation, Function and Evolution, Pergamon, Oxford, pp. 251–264] as to why there is an increase in the ir vibrational wave number of a carbonyl band when that group is H‐bonded to another polynucleotide chain in a helix. Such considerations also explain why a predicted band at about 1648 cm−1 is not to be seen in the ir spectra but is present in the Raman spectra. The model incorporating the CO transition dipole‐dipole coupling interaction is able to explain also the observed higher intensity of the higher wave‐number ir band. The experimental results demonstrate that the complete picture of vibrational dynamics of Mg2+‐poly(U) in D2O is obtained only by looking simultaneously at ir and Raman spectra and not at only one of them. Weak ir bands were found to be as useful as the strong ones in understanding structure and vibrational dynamics. On the bases of our ir and Raman spectra, of the normal‐mode analyses, and of the literature data, it is concluded that Mg2+‐poly(U) in D2O is present in a double‐helical structure at temperatures below the temperature of transition, whereby the uracil residues are paired according to arrangement (a) (see Fig. 1). This structure is rodlike and arises by refolding of one poly(U) chain. The computations show that no normal mode is associated with a single CO group vibration; all CO group vibrations are heavily mixed motions of various CO groups.

Spectroscopic and catalytic studies on metal carbonyl clusters supported on Cab-O-Sil: II. Impregnation and decomposition of Ru 3(CO) 12 and the mixture of Ru 3(CO) 12 and Fe 3(CO) 12

The behavior of Ru 3(CO) 12 (I), H 2Ru 3Fe(CO) 12 (II), a 1:1 Ru 3(CO) 12 and Fe 3(CO) 12 mixture (III), RuFe 2(CO) 12 (IV), and Fe 3(CO) 12 (V) deposited on Cab-O-Sil HS-5 has been compared. (III) and (V) have been studied by Mössbauer spectroscopy and by ir-spectroscopy, and (I)-(V) by temperatureprogrammed decomposition (TPDC) and temperature-programmed reduction (TPR). Decomposition, which is faster in hydrogen than in helium or in vacuum, and is reversible below 400 K, is normally faster for (V) than for (I). At low temperature, CO ligands leave the metal carbonyl cluster (MCC) in one step for (V), whereas they are decomposed stepwise via the formation of subcarbonyl species for (I). In this range the formation of Ru 3(CO) 3 species has been verified. On decomposition of (V), there is some CO adsorption, as indicated by ir spectroscopy and low catalytic activity. This increases when decomposition occurs in helium, and is attributed to the smaller particles stabilized by the metal-carbon species, formed from CO during the decomposition. For (I), decomposition results in a slight oxidation, indicated by weak ir bands in the range of 2100–2140 cm −1. Interaction between Fe and Ru in (III) does not occur in the impregnated phase, but develops during the decomposition, which starts with Fe 3(CO) 12 decomposition and thereby influences the decomposition of Ru 3(CO) 12. However, reduction of iron is also facilitated by the presence of ruthenium, as indicated by Mössbauer spectroscopy. The general feature revealed during decomposition in helium, i.e., the increase of surface carbon, is also operative here, and thus the dispersion of the metal is higher than for decomposition in hydrogen. The mechanism of the decomposition is discussed in terms of the formation of subcarbonyl species for Ru-containing samples and the formation of surface carbon is also considered. The mechanism and possible reaction pathways are given.

Consequence of dynamic interaction between two conformers in ground electronic state on ir spectrum

Abstract Supposing the dynamical coupling between conformers caused by torsion vibration around single C-C bond and applying harmonic approximation it was obtain: a explanation of experimentally observed differences between torsion vibration of trans and cis forms of molecule, b/ assignment of experimentally observed very weak ir bands.