Raman spectroscopy, natural organic

P. Vandenaheele, B. Wohling, L. Moens, H. Edwards, M. De Ren and G. van Hooydonk, Analysis with micro Raman spectroscopy of natural organic binding media and varnishes used in art, Anal. Chim. Acta, 407, 261 274 (2000). 

Many of the characterization techniques described in this chapter require ambient or vacuum conditions, which may or may not be translatable to operational conditions. In situ or in opemndo characterization avoids such issues and can provide insight and information under more realistic conditions. Such approaches are becoming more common in X-ray adsorption spectroscopy (XAS) methods ofXANES and EXAFS, in NMR and in transmission electron microscopy where environmental instruments and cells are becoming common. In situ MAS NMR has been used to characterize reaction intermediates, organic deposits, surface complexes and the nature of transition state and reaction pathways. The formation of alkoxy species on zeolites upon adsorption of olefins or alcohols have been observed by C in situ and ex situ NMR [253]. Sensitivity enhancement techniques play an important role in the progress of this area. In operando infrared and RAMAN is becoming more widely used. In situ RAMAN spectroscopy has been used to online monitor synthesis of zeolites in pressurized reactors [254]. Such techniques will become commonplace. 

A more serious objection is that the evidence for an anhydride intermediate is based upon observation of a transient phase during the hydrolysis of an ester intermediate under cryoenzymological conditions, i.e. at low temperature and in the presence of an organic cosolvent (Makinen et al., 1979). No evidence was obtained by these workers as to the molecular nature of the transient, but subsequently Hoffman et al. (1983) examined the system by multichannel resonance Raman spectroscopy. The characteristic carbonyl stretching frequency of an anhydride should have been detected by their experiments, but was not. Kuo and Makinen (1985), however, re-... 

Cellulose, which Is one of the most abundant organic substances found In nature, has been extensively studied by various techniques such as x-ray scattering, electron microscopy, IR and Raman spectroscopy, NMR spectroscopy etc. However, the crystal structure and noncrystalline state are not yet solved for cotton, ramie, bacterial and valonla celluloses which can be easily obtained in pure form. Cross-polarization/magic angle spinning(CP/MAS) C NMR spectroscopy is a promising new method to study these unsolved problems of cellulose, because this method is very sensitive to local molecular conformations and dynamics. 

The mechanism of the activation of H2O2 by TS-1 and related catalysts has been the subject of much research using spectroscopic and computational techniques. This has centred on the nature of the active site and its mode of reaction with H2O2, solvents and the organic substrates. Work to elucidate the structure of the active site has concentrated on the coordination chemistry of the titanium. X-ray and neutron diffraction studies, coupled with X-ray absorption, infrared and Raman spectroscopies, give evidence that most of the Ti(IV) in calcined TS-1, in the absence of any adsorbate molecules, is in tetrahedral coordination. Upon addition of one molecule of water, one of the Ti-OSi bonds is hydrolysed and the titanium adopts tetrahedral coordination as Ti(0Si)30H. Addition of a further water molecule gives rise to a pentaco-ordinated titanium. ... 

Information on the topology/morphology of MTS mainly comes from XRD patterns, BET isotherms, Al MAS-NMR results. As quoted above, XRD shows that MTS are amorphous in nature, with no short range (atomic) organization. This is elegantly confirmed by Raman spectroscopy [13], which shows the presence of a band at ca. 610 cm , due to cychc trisiloxane structures (three-membered rings), only found with amorphous silicas. 

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