Infrared spectroscopy background spectrum

The secondary structure of proteins may also be assessed using vibrational spectroscopy, fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy both provide information on the secondary structure of proteins. The bulk of the literature using vibrational spectroscopy to study protein structure has involved the use of FTIR. Water produces vibrational bands that interfere with the bands associated with proteins. For this reason, most of the FTIR literature focuses on the use of this technique to assess structure in the solid state or in the presence of non-aqueous environments. Recently, differential FTIR has been used in which a water background is subtracted from the FTIR spectrum. This workaround is limited to solutions containing relatively high protein concentrations. 

Infrared spectroscopy has been the most useful method, especially when the attached species incorporate carbonyl ligands. FT analysis is useful for substractlng the background spectrum of the support and for allowing identification of species present in low concentrations. Membrane supports about 10 ym thick, described above, are optimal. Many examples are given in the literature (27), and the technique has been used to characterize working catalysts in the presence of vapor- and liquid-phase reactants. 

In the case of an unknown chemical, or where resonance overlap occurs, it may be necessary to call upon the full arsenal of NMR methods. To confirm a heteronuclear coupling, the normal H NMR spectrum is compared with 1H 19F and/or XH 31 P NMR spectra. After this, and, in particular, where a strong background is present, the various 2-D NMR spectra are recorded. Homonuclear chemical shift correlation experiments such as COSY and TOCSY (or some of their variants) provide information on coupled protons, even networks of protons (1), while the inverse detected heteronuclear correlation experiments such as HMQC and HMQC/TOCSY provide similar information but only for protons coupling to heteronuclei, for example, the pairs 1H-31P and - C. Although interpretation of these data provides abundant information on the molecular structure, the results obtained with other analytical or spectrometric techniques must be taken into account as well. The various methods of MS and gas chromatography/Fourier transform infrared (GC/FTIR) spectroscopy supply complementary information to fully resolve or confirm the structure. Unambiguous identification of an unknown chemical requires consistent results from all spectrometric techniques employed. 

INS spectroscopy has been applied to characterising hydroxo and aquo components of oxide catalysts and adsorbed hydrogenous reactant molecules and intermediates. The INS spectra are complementary to infrared and Raman spectra, which have been used widely in the study of oxide catalysts. In an INS spectrum background scattering from an oxide is weak and can be subtracted from the spectrum the lower energy region (below 600 cm" ) is readily accessible. For an introduction to industrial applications of oxide catalysts see [91]. 

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