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Infrared Study (infrared + study)
Selected AbstractsInfrared Study of Intercomponent Interactions in a Switchable Hydrogen-Bonded RotaxaneCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2008Dhiredj Abstract The macrocycle in rotaxane 1 is preferentially hydrogen bonded to the succinamide station in the neutral form, but can be moved to the naphthalimide station by one-electron reduction of the latter. The hydrogen bonding between the amide NH groups of the macrocycle and the CO groups in the binding stations in the thread was studied with IR spectroscopy in different solvents in both states. In addition, the solvent effect on the vibrational frequencies was analyzed; a correlation with the solvent acceptor number (AN) was observed. The conformational switching upon reduction could be detected by monitoring the hydrogen-bond-induced shifts of the ,(CO) frequencies of the CO groups of the succinamide and the reduced naphthalimide stations. The macrocycle was found to shield the encapsulated station from the solvent: wavenumbers of ,(CO) bands of the CO groups residing inside the macrocycle cavity remain unaffected by the solvent polarity. [source] Real-time Fourier transform infrared study of the free-radical ultraviolet-induced polymerization of a hybrid sol,gel.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2003Abstract Free-radical photocurable hybrid sol,gel materials have gained special interest during the last decades. Compared to thermally processed materials, they present the advantages of fast curing, low energy consumption, and spatiotemporal control of the reaction. Although comprehension of the photochemical step is fundamental, little is known about the characteristic of photochemistry in this kind of material. Real-time Fourier transform infrared spectroscopy was used to study the photopolymerization of a hybrid sol,gel upon ultraviolet irradiation. Various photoinitiator systems were tested for their efficiency in inducing the polymerization of pendant polymerizable moieties anchored on a partially condensed silicate network. The presence of O2 and the nature of the polymerizable function were shown to be crucial factors in the photoinduced process. The effects of the photoinitiator concentration and light intensity were also studied. These results were explained in terms of classical kinetic models developed for all-organic photopolymers to point out the distinctive aspects related to the use of photoinitiated polymerization in hybrid sol,gel materials. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 831,840, 2003 [source] Real-time Fourier transform infrared study of free-radical UV-induced polymerization of hybrid sol,gel.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2003Abstract Free-radical photocurable hybrid sol,gel materials have gained special interest. They are becoming more and more widely used for applications in coatings, optics, sensors, catalysis, and so forth. The photochemical step is a fundamental step in the elaboration of this kind of hybrid sol,gel. However, little is known about the specifics of the photochemistry in this material. The relation between the organic and the inorganic part is investigated. Hydrolysis and condensation reactions were characterized by 29Si NMR. A precise description of the material before irradiation is of paramount importance to understand photoinduced phenomena. Real-time Fourier transform infrared spectroscopy was used to examine the photopolymerization of hybrid sol,gel under UV irradiation. UV photopolymerization occurred efficiently in hybrid sol,gel although inhibition of free-radical polymerization by molecular oxygen was pronounced. Important structural modifications during irradiation were also measured. They concern both inorganic and organic parts of the hybrid material. The condensation state of the silicate network was of crucial importance. The presence of the silicate backbone did not limit the final conversion ratio. On the contrary, photopolymerization occurred more efficiently for systems with a higher degree of condensation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 716,724, 2003 [source] Raman and Fourier transform infrared study of phytol effects on saturated and unsaturated lipid multibilayersJOURNAL OF RAMAN SPECTROSCOPY, Issue 1 2003M. Picquart Abstract The effects of phytol on DPPC and OPPC multilayers were investigated using FT-IR and Raman spectroscopy. The results were compared with those obtained with ,-tocopherol (,-T) and ,-tocopherol acetate (,-TA). The chain packing was analyzed using Raman intensity ratios measured in the CH2 stretching region, whereas the number of gauche bonds introduced by phytol was estimated by the measure of the FT-IR absorbance of the CH2 wagging progression modes. It is shown that the chain packing is reduced and that gauche rotamer formation is promoted by phytol in the gel phase. Phytol has a very similar effect on the acyl chains of DPPC to ,-T but does not have the same impact on the CO stretching vibrations of this lipid. The results indicate that phytol perturbs the interfacial region of DPPC causing dehydration or a conformational modification of the ester groups. Furthermore, the modification of the OPPC chain order induced by phytol is slightly different with respect to ,-T. It is concluded that (1) a hydrogen bond between the hydroxyl group of ,-T and the phospholipid carbonyl groups may not necessarily be associated with the stabilization of the membrane, (2) the studied phytyl compounds may be located more or less close to the membrane interface, (3) the presence of the chromanol ring may strongly influence the location of vitamin E within the membrane and, consequently, its capacity to catch free radicals and (4) the hydroxyl group, chroman moiety and phytyl chain all play a crucial role that determines the effects of ,-T on lipid acyl chains and its location within membranes, which in turn can affect its biological function. Copyright © 2002 John Wiley & Sons, Ltd. [source] | ||||||||||