Small-molecule adsorption, spectroscopic studies

Nitrogen dioxide, N02, is a fairly small molecule with an unpaired electron and may be expected to be a selective molecule for electron-deficient or Lewis acid sites. Nevertheless, only very little spectroscopic information on the nature of surface species formed on adsorption of N02 is available. Naccache and Ben Taarit (242) have shown by infrared spectroscopy and ESR that N02 forms Cr+N02+ and Ni+N02+ complexes on chromium and nickel zeolites. Thus, N02 behaves as an electron donor and reducing agent in these zeolites. Boehm (243) has studied the adsorption of N02 on anatase and on tj-A1203, which were pretreated at very low temperatures of only 100°-150°C. At 1380 cm-1, a band which is to be attributed to a free nitrate ion, was observed. Boehm (243) has explained the formation of the nitrate ion by the disproportionation by basic OH ions ... 

J1.3 Surface chemistry on colloidal metals spectroscopic study of adsorption of small molecules... 

The results described in this section show that spectroscopy in the liquid state can be applied to the analysis of both colloidal metal particles and species adsorbed on colloidal metals in a manner reminiscent of the spectroscopic investigations of molecular compounds in solution. There are established infrared and NMR databases from the molecular and solid state literature on which to base analyses of colloid spectra. The NMR data presented suggest that the study of metal particles in the important size range where tranritions from the molecular to the metallic state take place will be greatly facilitated by this method. In addition, the use of NMR in observing the adsorption of small molecules promises to open the way for the development of the surface chemistry of nanoscale colloidal metal particles. 

It is evident that elucidation of the interfacial behavior of proteins is not a simple matter and requires contributions from several disciplines. In recent years considerable progress has been made in applying spectroscopic techniques to proteins in the adsorbed state (e.g., 7,8,9). In such studies a (small) part of the molecule is analyzed in detail. In our laboratory we study protein adsorption from a more classical, colloid-chemical point of view. Arguments are derived from experimental data referring to whole protein molecules or to layers of them. Information is obtained from adsorption isotherms, proton titrations and both electrokinetic and thermochemical measurements. Recently, topical questions such as reversibility of the adsorption process and changes in the protein structure have been considered. This more holistic approach has produced some insights that could not easily be obtained otherwise. 

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