Line narrowing acidity characterization

Gel-phase NMR spectroscopy is a very convenient technique for the spectroscopic characterization of functionalized solid supports.Optimal conditions for acquiring standard gel-phase NMR spectra from a variety of resins are well-established optimal conditions, i.e. maximum swelling, result in reasonably narrow lines for the pendant groups. This method has the additional advantage of not requiring any special instrumentation besides a conventional FTNMR spectrometer and a conventional probe. In addition to NMR spectroscopy, NMR l and NMRt l spectroscopy can also be used in those cases where fluorine or phosphorous is present in the handle or in the first amino acid. 

The particle beam LC/FT-IR spectrometry interface can also be used for peptide and protein HPLC experiments to provide another degree of structural characterization that is not possible with other detection techniques. Infrared absorption is sensitive to both specific amino acid functionalities and secondary structure. (5, 6) Secondary structure information is contained in the amide I, II, and III absorption bands which arise from delocalized vibrations of the peptide backbone. (7) The amide I band is recognized as the most structurally sensitive of the amide bands. The amide I band in proteins is intrinsically broad as it is composed of multiple underlying absorption bands due to the presence of multiple secondary structure elements. Infrared analysis provides secondary structure details for proteins, while for peptides, residual secondary structure details and amino acid functionalities can be observed. The particle beam (PB) LC/FT-IR spectrometry interface is a low temperature and pressure solvent elimination apparatus which serves to restrict the conformational motions of a protein while in flight. (8,12) The desolvated protein is deposited on an infrared transparent substrate and analyzed with the use of an FT-IR microscope. The PB LC/FT-IR spectrometric technique is an off-line method in that the spectral analysis is conducted after chromatographic analysis. It has been demonstrated that desolvated proteins retain the conformation that they possessed prior to introduction into the PB interface. (8) The ability of the particle beam to determine the conformational state of chromatographically analyzed proteins has recently been demonstrated. (9, 10) As with the ESI interface, the low flow rates required with the use of narrow- or microbore HPLC columns are compatible with the PB interface. 

This made it possible to identify surface hydroxyl groups in zeolites [4,5], characterize Brpnstead acidity [6], porosity, and adsorption sites with adsorbed probe molecules [7-13]. Later on, the adsorbed reaction products were characterized with MAS NMR [14], which provided a stimulus of application of MAS NMR to characterize the chemical reaction occurrence on zeolites [15] with the aim of unraveling the mechanisms of the reactions. Note, however, that researchers sometimes do not have to narrow the NMR signals with MAS to characterize the solids. For example, analysis of the line shape evolution with temperature for wide-line NMR spectra of adsorbates in zeolites affords a valuable information on the adsorbate molecular dynamics [16,17],... 

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