Fluorescence properties of organic ligands for copper(II) in Lake Biwa and its rivers.

Abstract

Organic ligands for copper(II) were isolated from lake waters in Lake Biwa and its river waters by immobilized metal ion affinity chromatography (IMAC), and were characterized by three-dimensional excitation/emission matrix spectroscopy (3DEEM) and fluorescence quenching titration. The results show that the contribution of total organic ligands was 0.63-4.68% of the bulk dissolved organic matter (DOM), in terms of UV absorbance, in lake and river waters. Three characteristic excitation/emission (Ex/Em) fluorescence peaks were identified in organic ligands from both lake and river waters, at Ex/Em 310-330/ 374-434 nm (Peak A), 250/414-454 nm (Peak B), and 260-270/306-330 nm (Peak C). Peaks A and B were referred to as humic-like fluorescence, Peak C as protein-like fluorescence. All Ex/Em maxima of organic ligands in lake waters were shifted towards shorter wavelength, and the fluorescence intensities were higher than those in river waters. The results of fluorescence quenching titration show that the IMAC ligands were weak ligands, with conditional stability constants (logK' C u L ) around 7.27 for river ligands, and 7.84-9.23 for lake ligands. The differences of fluorescence properties indicate the variability of fluorescent ligands between river terrestrial and lake aquatic environments.