Structure and Bonding of Cu(II)–Glutamate Complexes at the g-Al2O3–Water Interface

N t e The composition and mode of attachment of Cu(II) complexes t the g-Al2O3–water interface in suspensions containing a simple mino acid (glutamate) were characterized with EXAFS and TIR spectroscopies. The spectroscopic results indicate that two ypes of Cu(II)–glutamate–alumina interactions are primarily reponsible for Cu(II) and glutamate uptake between pH 4 and 9. In cidic suspensions of alumina, glutamate forms a bridge between u(II) ions and the (hydr)oxide surface (Type B complex). In this ype B surface complex, Cu(II) is bonded to amino acid headroups (i.e., 1H3NCHRCOO ) of two glutamate molecules. Specroscopic and ionic strength dependent uptake results are comined to propose that the nonbonded side chain carboxylate roups of this complex are attracted to the oxide surface through ong-range forces, leading to enhanced Cu(II) uptake relative to he glutamate-free system. In alkaline suspensions the relative mount of surface-bound Cu(II) complexed by glutamate dereases, and a direct Cu(II)–surface bond becomes the dominant ode of attachment (Type A complex). These surface complexes iffer markedly from the species found in the alumina-free Cu(II)– lutamate aqueous system under similar solution conditions, here Cu(H2O)6 21 and Cu(glutamate)2 22 are the dominant species n acidic and alkaline solutions, respectively. Based on these specroscopic results, surface complexation reactions are proposed for he Cu(II) and glutamate ternary interactions with the alumina urface in this system. Similarities between the results of this study nd Cu(II) uptake behavior and complexation in the presence of atural organic material (NOM) indicate that Cu(II)–glutamate nteractions mimic those in more complex Cu(II)–NOM–mineral– ater systems. © 1999 Academic Press