XANES study of Cu2+-binding sites in aquatic humic substances

The structure and composition of the inner shell df copper (II) complexes w ith aquatic humic substances (HS) were studied by X-ray absorption near-edg e structure (XANES) spectroscopy. The interpretation of the XANES data was based on FEFF8 code real-space multiple-scattering calculations for the pro totype [CU(H2O)(6)](2+) complex. These calculations reproduced the tetragon al distortion of the CuO6 octahedron representing the inner shell. They als o demonstrated the polarization nature of this effect's manifestations ("sp litting" of the derivative) in XANES. The extension of this interpretation to the Cu-HS system confirmed suppression of the tetragonal distortion of t he inner shell in these species established by independent EXAFS experiment s. XANES measurements for Cu/C ratios varying from 0.0005 to 0.03 demonstra ted the nonuniform nature of copper binding sites. Experiments with Cu-ethy lenediamine and Cu-glycine model systems and FEFF8 calculations indicated t hat for low copper concentrations (Cu/C < 0.005) nitrogen-containing functi onal groups dissimilar to those of amino acids are likely to be engaged in the complexation.