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′ CuL ) 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. a significant role in the mobilization and transport of nutrients and pollutants (As, Zn, Cd, Pb, and Ce), and soil weathering in terrestrial ecosystems (Tegen and Dorr, 1996;Li and Shuman, 1997;Kalbitz and Wennrich, 1998). However, most previous studies have only provided concentrations and conditional stability constants of organic ligands, the fundamentals pertaining to the properties of organic ligands are poorly understood since they have never been isolated (Gordon et al., 1996; Tanoue, 1996, 1998).Immobilized metal ion affinity chromatography (IMAC) has been successfully applied to isolate organic ligands for copper(II) from estuarine, coastal and oceanic waters (Gordon, 1992; Gordon INTRODUCTIONNaturally occurring organic ligands have been extensively studied in terms of metal speciation in aquatic environments during the past decades (Tanoue and Midorikawa, 1995). In oceanic waters, copper speciation is controlled by complexation with organic ligands (Donat and Bruland, 1995). In freshwaters, there are at least three ligand classes with logK values ranging from 15 to 8.6 (Xue and Sunda, 1997), which may control the bioavailability, toxicity and speciation of copper. Organic ligands were also reported to be responsible for other trace metal speciation (e.g., Hg) in freshwater (Mantoura et al., 1978), and play 334 F. Wu et al. et al., 1996; Tanoue, 1996, 1998;Donat et al., 1997). 3DEEM and UV-VIS spectroscopy have been demonstrated to be useful methods for characterizing DOM in natural waters (Coble et al., 1990;Mopper and Schultz, 1993;Coble, 1996;Smith and Kramer, 1999;Del Castillo et al., 1999). Absorbing and fluorescing complexes such as humic substances and proteins were expected to be good candidates for organic li...

Complexation between Hg(II) and dissolved organic matter in stream waters: an application of fluorescence spectroscopy

“…Fluorescence intensity of DOM is either enhanced or decreased when it is bound to metals; this is dependent on metal speciation, binding sites or ligands of fluorophores and several other factors, e.g. pH, ionic strength, anions and cations (Ryan and Weber 1982;Cabaniss 1992;Esteves da Silva et al 1998;Lu and Jaffe 2001;Wu et al 2001;Wu and Tanoue 2001a, b).…”

“…In many cases, DOM complexation controls the speciation, toxicity, bioavailability and ultimate fate of the metals (Bidoglio and Stumm 1994). Molecular fluorescence spectroscopy, particularly three-dimensional excitation emission matrix (3DEEM) fluorescence spectroscopy, has been used often to investigate the complexation between DOM and metals, such as copper and aluminum, due to its simplicity and sensitivity (Ryan and Weber 1982;Smith and Kramer 1999;Wu et al 2001;Wu and Tanoue 2001a, b). Fluorescence intensity of DOM is either enhanced or decreased when it is bound to metals; this is dependent on metal speciation, binding sites or ligands of fluorophores and several other factors, e.g.…”

Root exudates from sunflower (Helianthus annuusL.) show a strong adsorption ability toward Cd(II)

“…In this study it was utilized for quantitating the functional groups involved in the binding of Cd(II) with root exudates. The fluorescence excitation emission matrix (EEM) spectrometry is a simple and sensitive modern technique that has been widely used to provide quantitative information on the interaction between fluorescent organic matter and metal ions (Wu et al 2001;Yamashita & Tanoue 2003;Jaffe´et al 2004;Zhang et al 2010). Since proteins are key components of root exudates with fluorescent properties, in the present study, the fluorescent components as protein in root exudates and their interaction with Cd were investigated by EEM fluorescence spectroscopy.…”

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