Infrared Spectra of α-Alanine Adsorbed on Cu-Montmorillonite

Infrared spectroscopy has presented an effective tool for determining the structures of compounds adsorbed on clays. Cloos et al. have investigated the infrared spectra of amino acids such as glycine, glycylglycine, and β-alanine adsorbed on sodium-, calcium-, and hydrogen-montmorillonite, and determined that the protonated cation was the dominant adsorbed species. In this investigation, we have analyzed the infrared spectra of α-alanine adsorbed on copper-montmorillonite prepared at several different pH's to determine the types of complexes that are formed in the interlamellar spaces. Cu2+ ions readily form complexes with α-alanine in aqueous solution and, therefore, similar adsorbed species should be observed on montmorillonite. The infrared spectra of related complexes in crystals and solutions have been used to identify the adsorbed species, and to make empirical band assignments.