D-GLUCOSAMINE SORPTION ON Cu(II)-MONTMORILLONITE AS THE PROTONATED A N D NEUTRAL SPECIES

-The adsorption of D-glucosamine (2-amino-2-deoxy-D-glucose) in the protonated or neutral form on homoionic Cu2+-bentonite was investigated by infrared (IR) and electron spin resonance (ESR) spectroscopy and chemical analyses of solution. The results show that the interaction of the glucosamine hydrochloride with the clay complexed a small fraction of interlayer metal ions with neutral amino sugar molecules. In contrast, the adsorption of free glucosamine was much more favorable and resulted in interlayer copper(II) complexes, mainly those in which the ligand was coordinated through amino and deprotonated hydroxyl groups. Part of the amino sugar molecules, however, were transformed into glucosammonium, replacing copper as the saturating ion. Key Words--Adsorption, Copper, D-glucosamine, Eleclron spin resonance, Infrared spectroscopy, Montmorillonite, Protonation. I N T R O D U C T I O N The amino sugars glucosamine and galactosamine are important constituents of the soil nitrogen pool (Parsons, 1981; Stevenson, 1982). An accumulation of these compounds has been observed in the smallest particle-size fraction of soil (Benzing-Purdie, 1984), and strong acid hydrolysis has been required for their release, indicating a close physical association of these compounds with clays (Belluomini et al., 1986). A study aimed at understanding the adsorption ofglucosamine hydrochloride on Caand Na-montmoril lonite has indicated that the charged sugar was adsorbed by a cation-exchange mechanism (Parfitt, 1972). On the other hand, amino sugars are known to be very effective ligands for metal chelation (Micera et al., 1985; Lerivrey et al., 1986). To obtain greater insight into the interactions which take place between amino sugars and clays in soil, this study of the glucosamine-Cu 2+montmoriUonite system was undertaken. The adsorption of this amino sugar, in either the charged or neutral form, from aqueous solutions was examined by chemical analyses and spectroscopy.