科研之友
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摘要
The adsorption of glycine on a well-characterized silica surface was investigated at the molecular level by means of solid-state C-13 and N-15 NMR spectroscopy, combined with macroscopic level information such as adsorption isotherms, pH dependence, or TGA. At least three different forms of glycine were observed and could be distinguished on the basis of their NMR properties: two bulk crystalline forms (alpha- and beta-glycine, both containing the amino acid in the zwitterionic form) and a molecularly adsorbed glycine species. The latter is formed by adsorption of zwitterionic glycine to the silica surface through the formation of cooperative hydrogen-bond networks in a kind of molecular recognition phenomenon, yielding a glycine/surface adduct. In addition, crystallites of metastable beta-glycine nucleate at the silica/solution interface already during the initial adsorption, in a phenomenon of surface-induced precipitation. On gamma-alumina, glycine does not form well-defined adducts but may coordinate the Al3 ions upon thermal activation.
- 出版日期2009-10-22
