Geochemical characterization of organic ligands for copper(II) in different molecular size fractions in Lake Biwa, Japan

In a previous study, we reported the isolation of organic ligands for copper(II), their mass distribution and fluorescence properties in different molecular size fractions of the waters in Lake Biwa by immobilized metal ion affinity chromatography (IMAC) and three dimensional excitation/emission matrix spectroscopy (3DEEM) (Wu, F., Tanoue, E., 2001. Molecular mass distributions and fluorescence characteristics of organic ligands for copper (II) in Lake Biwa, Japan. Org. Geochem. 32, 11–20). In this continuous study, geochemical properties of these isolated ligand fractions were characterized in terms of binding complexation, functional groups and amino acid composition. The results show that two ligand classes (L1 and L2) were recovered from all molecular size ligand fractions, L1 with a conditional stability constant (LogK′CuL) of 7.82–9.56, and L2 with a LogK′CuL value of 7.05–8.78. The stronger ligands with protein-like fluorescence were of recent biogenic origin, and the weaker ligands with humic-like fluorescence were related to refractory humic substances. Functional groups responsible for the fluorescence in the ligand fractions are also discussed. The results presented here would have significance for understanding the nature of natural organic ligands and their biogeochemical role in aquatic systems.