IR and Raman spectral and X-ray structural studies of polymorphic forms of sulfamethoxazole

The crystal structure of the polymorphic form III (hemihydrate) of sulfamethoxazole (SMZ) was determined to exist in both the E- and Z-forms by X-ray analysis and was compared with the polymorphic forms I and II which are known to exist in the E-form. IR spectra of I–III and their corresponding forms I_D–III_D which contain the deuterated amino and amido groups and D₂O and Raman spectra of I–III have been measured. For I–III, assignment of the stretching vibration [ν(NH) and ν(CH)] bands of amino and amido groups and the CH bond of the isoxazole ring involved in the inter-molecular hydrogen bonds has been proposed based on consideration of the IR and Raman spectra and the results of X-ray analysis. A relationship was established between the relative intensity and wavenumbers for the ν(CH) band in the inter-molecular C(sp²)H⋯X hydrogen bond of the E-form.     

Steam reforming of toluene as model of tar compound over Mo catalysts derived from hydrotalcites

This study evaluated the catalytic activity of Mo catalysts derived from hydrotalcite-like compounds for steam reforming of toluene as a model compound for tar. The catalysts with 1.5, 3 and 4.5 Mo loadings (wt%), denoted as Mo_1.5MgAl, Mo₃MgAl and Mo_4.5MgAl respectively, were prepared by coprecipitation and characterized by BET, XRD, SEM, TEM, FT-IR and UV–VIS. The results showed that toluene conversion increased with increasing molybdenum content. The hydrogen amount depended on two factors: the presence of molybdate species on the surface and the presence of aluminum cations in tetrahedral sites (Mo₃MgAl), with molybdenum influence being more pronounced. The H₂/CO ratio decreased at increasing temperature while, the H₂/CO₂ ratio increased proportionally with temperature. Mo_1.5MgAl catalyst was more selective for CO₂ and H₂, while, Mo₃MgAl and Mo_4.5MgAl were more selective for CO and H₂.     

High-temperature transformations of Cu-rich hydrotalcites

CuM(II)Al ternary hydrotalcites (M(II) = Ni, Co and Mg) with a (Cu+M(II))/Al atomic ratio of 3.0 and Cu/M(II) atomic ratio of 5.0 were synthesized by coprecipitation under low supersaturation. Powder X-ray diffraction of the as-synthesized samples showed a pattern characteristic of hydrotalcite-like (HT-like) structure (JCPDS: 41-1428). Thermal analyses of these samples showed four stages of weight loss/heat change when recorded in nitrogen. Analysis of the evolved gases characterized the nature of these transformations. The thermoanalytical effects differed significantly especially for the high-temperature transformations, when the treatment was performed in oxygen. In situ powder X-ray diffraction of the samples was carried out to elucidate the phase evolution of these compounds. Surprisingly formation of CuO was noted at temperatures around 200°C well below the destruction of the layered network. The nature of the resulting phases varied with both the nature of the co-bivalent metal ion and the heating atmosphere. FT-IR spectroscopy confirmed the retention of carbonate ions at higher temperatures (above 700°C), although the concentration of carbonate anion (most likely unidentate) varied with the calcination temperature. The crystallinity of CuO increased significantly above 600°C, probably through dissociation of copper oxycarbonate. Significant differences in the thermal transformation temperatures (for the third and the fourth transformations) of these samples containing different co-bivalent metal ions were not observed. This suggests that an association of the co-bivalent metal ions and/or trivalent metal ion in this phase is unlikely. A plausible thermal evolution scheme of these hydrotalcites is proposed.     

Quantum-chemical calculations of the IR absorption spectra of modified polytetrafluoroethylene forms

DFT(B3LYP) (basis set 6–31 + G(d)) and HF (basis set 6–31G) calculations were performed to determine the geometric structure and vibrational spectra of the C_nF_2n and C_nF_2n O molecules (n = 3–13). The IR spectra of chain C_nF_2n O molecules with the terminal carbonyl group (-COF) were found to contain a band at 1885 cm^?1. The C=C and C=O stretching vibrations of the-CF=CF₂ and COF terminal groups were independent, and there was no mutual influence of their frequencies starting with the seven-fragment molecule. In the presence of chain branching, the sensitivity of the ν(C=C) and ν(C=O) frequencies in the olefin and carbonyl groups depended on where branching occurred. The chain configuration was found to be energetically favorable compared with branched structures.     

Aqueous-phase catalytic hydrogenation of furfural to cyclopentanol over Cu-Mg-Al hydrotalcites derived catalysts: Model reaction for upgrading of bio-oil

A series of Cu-Mg-Al hydrotalcites derived oxides with a (Cu+Mg)/Al mole ratio of 3 and varied Cu/Mg mole ratio (from 0.07 to 0.30) were prepared by co-precipitation and calcination methods, then they were introduced to the hydrogenation of furfural in aqueous-phase. Effects of Cu/Mg mole ratio, reaction temperature, initial hydrogen pressure, reaction time and catalyst amount on the conversion rate of furfural as well as the selectivity toward desired product cyclopentanol were systematically investigated. The conversion of furfural over calcined hydrotalcite catalyst with a Cu/Mg mole ratio of 0.2 was up to 98.5% when the reaction was carried out under 140 °C and the initial hydrogen pressure of 4 MPa for 10 h, while the selectivity toward cyclopentanol was up to 94.8%. The catalysts were characterized by XRD and SEM. XRD diffraction of all the samples showed characteristic pattern of hydrotalcite with varied peak intensity as a result of different Cu content. The catalytic activity was improved gradually with the increase of Cu component in the hydrotalcite.     

First structural evidence of actinide-nitrite coordination

The first nitrite complex of actinide metal, {C(NH 2)3}2[NpO 2(NO 2)(Pic)2], was synthesized, and its crystal structure was determined using X-ray diffractometry and confirmed by NIR and IR spectroscopies. Main crystallographic data: space group P1, triclinic, a = 8.9329(1) A, b = 11.6669(2) A, c = 11.6698(2) A, alpha = 68.080(1) degrees, beta = 88.213(1) degrees, gamma = 73.254(1) degrees, V = 1076.45(3) A (3), and Z = 2.     

Catalytic applications of hydrotalcite-like materials and their derived forms

Hydrotalcite-like (HT-like) materials have been studied extensively in the last three decades. Although these materials initially perceived as potential anion exchangers, unrelenting efforts have also been attempted to use them as catalytic materials or as catalytic supports. There are varied ways by which one can use them for catalysis viz.; 1. Use them in as-synthesized form 2. Use them after calcining where the structural integrity of layered lattice is lost 3. Use the interlayer as functional spaces with moieties of catalytic interest 4. Use them after destruction or delamination and restructuring and 5. Use them as support or matrix. In this review, we are reporting the catalytic applications of HT-like materials and their derived forms carried out in our research group for the last 15 years in these various ways, covering reactions such as nitrous oxide decomposition, selective oxidation of organic compounds of industrial relevance and base-catalyzed isomerization of chemicals of perfumery interest. Although this review primarily focuses on our work, wherever applicable, related or relevant works from other groups are also presented to bestow comprehensiveness.     

Surface modification of oxidic nanoparticles using 3-methacryloxypropyltrimethoxysilane

Tin oxide, antimony-doped tin oxide (ATO), and silica nanosized particles in aqueous dispersion were reacted with various amounts of 3-methacryloxypropyltrimethoxysilane (MPS). The kinetics were followed by 29Si NMR and the products were analyzed by FTIR and 29Si NMR. The kinetic experiments on ATO and silica revealed that the hydrolysis is the rate-determining step in these reactions. The reaction of MPS with the particles is favored over the homocondensation of MPS. Quantitative analysis using FTIR revealed that the amount of MPS grafted onto the tin oxide and silica particles is limited to the amount needed to fill one monolayer. For ATO the maximum amount of grafted MPS was only 50-70% of the amount that is needed for a closed monolayer. The MPS molecules are for the most part oriented parallel to the oxide surface, and a hydrogen bond between the MPS-carbonyl and the oxide is formed.     

Molecular oxidic phases of diluted silica supported vanadia

Different surface phases of silica supported vanadia catalysts have been characterized by static adsorption, reduction, and reoxidation experiments under vacuum conditions. The obvious mobility of vanadium involved in some preparation steps gives rise to a diversification of initial precursor phases as a function of pretreatment conditions and SiOH concentration.

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SiO₂ , . , , SiOH.

     

IR study of adsorbed piperidine dehydrogenation on oxidic or sulfided Ni?W/Al2O3 catalysts

IR spectroscopy has been used to follow the transformation at different temperatures of piperidine chemisorbed on oxidic or sulfided Ni–W/Al₂O₃ catalysts. Formation of an intermediate species, possibly tetrahydropyridine, and pyridine is evidenced. Their formation temperature on the sulfided samples accounts for the catalyst activity in pyridine hydrogenation under H₂ pressure.

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- , Ni–W/Al₂O₃, . , , . .

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This work was supported by the Groupement scientifique Hydrotraitement catalytique (CNRS-IFP, TOTAL. ELF).     

Identifying structural distortion in doped VO2 with IR spectroscopy

Doping VO(2) with tungsten can lower the metal-insulator transition (MIT) temperature and thus provide a controlled means for tailoring the MIT properties of VO(2) materials. Here, infrared spectroscopy has been employed as a tool for identifying structural changes in doped VO(2) as a way of lowering the MIT temperature.     

Probing the differential effects of infrared light sources IR1072 and IR880 on human lymphocytes: evidence of selective cytoprotection by IR1072

Light therapy, both laser and LED, have been shown to provide clinical benefit in many therapeutic arenas. The effects of IR1072 and IR880 were investigated, using a range of single and multiple irradiation protocols, for their effect on freshly prepared human lymphocytes stimulated with phytohemagglutinin. Viable cell numbers remained significantly higher after irradiation with IR1072 and were significantly lower after IR880 irradiation compared to untreated controls, following a daily single irradiation over a 5-day period. Cell numbers were significantly higher after pre-treatment with IR1072 and exposure to UVA, compared to cells treated with UVA only. Cells irradiated twice on Day 3 post-harvest with various wavebands confirm on Day 5, an increase in % cell viability after IR1072, and IR1072 alternating with IR1268 irradiation, and a decrease in % cell viability after IR880 irradiation alone. Further, wavebands tested displayed no significant differences compared to the control. Cells were collected after exposure on Days 3 and 5 with IR1072 and IR880 treatments and protein levels were compared using quantitative immunoblotting probed with an anti-iNOS antibody. Following IR1072, but not IR880, treatment there was a 4.9+/-2.1-fold higher iNOS protein expression in treated cells compared to the control on Day 5 post-treatment.     

Urea method for the synthesis of hydrotalcites

Mg-Al, Zn-Al and Ni-Al hydrotalcite-like compounds with high crystallinity were synthesized by using the decomposing property of urea at high temperature. The crystallinity and the regularly of the samples were much preferable to those synthesized by other methods. This revised version was published online in June 2006 with corrections to the Cover Date.     

Structure and base properties of calcined hydrotalcites

Five hydrotalcites with Mg/Al molar ratio range of 3-15 were prepared. The structure and basicity of Mg-Al mixed oxides (Mg(Al)O) transformed from hydrotalcites were investigated by TPD, XPS, XRD, FT-IR and NMR techniques. The results of elemental analysis and XPS indicate that Al is enriched in the surface regions of Mg(Al)0, and its amount increases with the Mg/Al molar ratio and the calcination temperature. 27Al-MAS-NMR results show that Al exists in two chemical environments: tetrahedral aluminium (Al(t)) and octahedral aluminium (Al(o)) in Mg(Al)O. The amount of Al(t) increases with the Mg/Al molar ratio and the calcination temperature. It is assumed that Al(t) may be mainly from the surface Al. Temperature-programmed desorption (TPD) of CO2 shows that the number of basic sites of Mg(Al)O samples increases with the Mg/Al molar ratio, and the maximum number of basic sites is obtained for hydrotalcite calcined at 773 K. Infrared spectra of adsorbed CO2 and B(OCH3)3 reveal that there are two kinds of     

Sorption of 2,4-dichlorophenol on modified hydrotalcites

The adsorption of anionic surfactants (sodium dodecyl sulfate (SDS) and sodium bis[2-ethylhexil]sulfosuccinate (AOT)) on hydrotalcite (HT) and the adsorption of 2,4-dichlorophenol (DCP) on HT and its modified forms from aqueous solutions was studied. The modification was carried out by calcinations (heat treatment) and hydrophobization using different anionic surfactants. The anionic surfactant isotherms were of the H-type. It was assumed that first the ion exchange mechanism takes place until approximately the anion exchange capacity of HT is reached and hereafter, the hydrophobic mechanism occurs forming surfactant bilayers. While the DCP adsorption was very poor on HT, significant uptake of DCP took place on calcined HT which was attributed to the simultaneously occurring rehydration and adsorption during the reconstruction of the layered structure. On anionic surfactant-HT complexes (“organo-hydrotalcites”) DCP was considerably adsolubilized in the anionic surfactant layers intercalated in HT. The AOT–HT complex appeared the more effective adsorbents for DCP.     

The luminescence of some oxidic bismuth and lead compounds

The luminescence properties of the bismuth compounds Bi₂Ge₃O₉, Bi₁₂MO₂₀ (M = Ge, Ti), and Bi₂Al₄O₉ and of the lead compounds PbGe₃O₇ and PbM₂O₄ (M = Al, Ga) are reported and discussed. Bi₁₂MO₂₀ and probably PbGe₃O₇ show semiconductor-type luminescence. For Bi₁₂MO₂₀ blue and red emission bands are reported which both are ascribed to radiative recombination at (deep) defect centre levels in the band gap. The blue emission originates probably from surface defects. The other compounds show broad emission and excitation bands with large Stokes shifts. The transitions occur on one and the same Bi³⁺(Pb²⁺) ion. From decay time measurements it is found that the energy difference between the two lowest excited levels is very small for all compounds. The large Stokes shifts and small trap depths are discussed in terms of the asymmetrical coordination of the 6s² ions in the compounds under discussion. It is concluded that asymmetrically surrounded Bi³⁺ ions give rise to luminescence which is characterized by a broad emission band which shows a very large Stokes shift (?2 eV).     

Microwave-assisted homogeneous precipitation of hydrotalcites by urea hydrolysis

The use of urea as a precipitating agent in the synthesis of Ni-Al and Zn-Al layered double hydroxides having a hydrotalcite-like structure via a microwave-hydrothermal method is reported. For comparison purposes, the samples were also prepared by a conventional hydrothermal method. Ni-Al compounds with the hydrotalcite-like structure were obtained in shorter periods of time by the microwave method than by the conventional method, whereas when zinc cations were involved, no successful synthesis was achieved regardless of the method used. In order to find the best synthesis conditions for the Ni-Al solids, samples were submitted to microwave-hydrothermal treatment at different temperatures for increasing periods of time, and the structural, thermal, and textural properties of the synthesized materials were evaluated. All of the solids were fully characterized by chemical elemental analysis, powder X-ray diffraction (PXRD), FT-IR spectroscopy, and transmission and scanning electron microscopy as well as by N 2 adsorption/desorption at -196 degrees C for assessment of specific surface area and porosity. The PXRD patterns showed that the layered structure appeared after merely 10 min when the synthesis was carried out at 125 degrees C; however, the FT-IR spectra showed the presence of some cyanate groups that were formed during urea hydrolysis and were quite difficult to remove completely. When the conventional hydrothermal treatment was used, longer periods of time were required in order to develop the hydrotalcite-like structure, but increasing the aging time improved the crystallinity of the compounds and yielded large particles.     

In situ synthesis of surfactant/silane-modified hydrotalcites

In this study, anionic surfactant and silane-modified hydrotalcites were synthesized through a soft chemical in situ method. The resulting materials were characterized using X-ray diffraction (XRD), high-resolution thermogravimetric analysis (HRTG), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and N2 adsorption-desorption. The Mg-Al hydrotalcite (LDH) and the only surfactant-modified hydrotalcite (LDH-2) display similar XRD patterns while both surfactant and silane-modified hydrotalcite (LDH-3) show two distinct series of reflections, corresponding to hydrotalcite and smectite-like materials, respectively. The smectite-like materials show a series of regular (001) reflections with d 001=12.58 A. Further supporting evidence was obtained from FTIR and TG, for example, the vibration at 1198 cm(-1) corresponds to SiOSi-stretching mode and the mass loss at ca. 861 degrees C to dehydroxylation. In LDH-2, the loaded surfactants are located in both the interlayer space and the interparticle pores with a "house of cards" structure as supported by FTIR, TG, and N2 adsorption-desorption isotherms. Both electron microscopy (SEM and TEM) micrographs and N2 adsorption-desorption isotherms show that in situ modification with surfactant and silane has a significant influence on the morphology and porous parameters of the resulting hydrotalcite materials.     

Evaluation of the relationship between spectral and structural similarity in IR spectroscopy

Representation of a structural formula of a compound as a complete set of nonisomorphic k-vertex (2 ≤k≤7) connected fragments is used to evaluate the structural similarity of compounds. The spectra and structures of spectrally or structurally alike compounds are compared statistically using a database containing 32,000 IR spectra and structures. This study reveals some tendencies typical for both full IR spectra and their abbreviated versions represented by sets of most characteristic peaks. Applicability of IR databases to spectrum simulation for compounds with a specified structure is justified statistically. A method is proposed for evaluating the efficiency of a search algorithm selecting structural analogs of the compound from an IR database according to the query spectrum. Translated fromZhurnal Strukturnoi Khimii, Vol. 41, No. 2, pp. 379–390, March–April, 2000.