A dynamic magic angle spinning NMR study of the local mobility of alanine in an aqueous environment at the inner surface of mesoporous materials.

Dynamic deuterium magic angle spinning NMR has been applied to study the slow motion of small molecules close to a silica surface. In particular, alanine-d(3) molecules dissolved in an aqueous solution were loaded into the pores of the mesoporous materials SBA-15 and MCM-41. Deuterium spectra were measured as a function of the water content of these materials and the temperature. From the analysis of these spectra and the corresponding proton spectra, using a simple molecular exchange model, relatively slow desorption rates of the binding of alanine to the inner pore surface were obtained and were correlated with the low proton concentrations at the pore surfaces.