Molecular masses and chromophoric properties of dissolved /organic ligands for copper II in oceanic water

.The distribution of molecular masses of organic ligands for copper II in oceanic water was investigated. The bulk .dissolved organic matter DOM was fractionated by ultrafiltration and organic ligands were extracted from the resultant .fractions by using immobilized metal ion affinity chromatography IMAC. Contributions of total organic ligands were 2.0–4.4 % of the bulk DOM in surface waters, as determined by the UV absorbance. In the distribution of molecular masses . .of organic ligands, relative contribution of the fraction with low molecular masses-1000 Da was dominant 49–62 %, while 26–33 % of the total organic ligands was in the 1000–10,000 Da fraction, leaving 10–19 % in the)10,000 Da fraction. The distribution of molecular masses of organic ligands shifted to higher molecular masses, as compared with that of the bulk DOM. The fluorescence intensities of organic ligands were shown to be associated with carboxyl contents, based on peak excitationremission wavelengths and the pH-dependence of fluorescence. Two ligand classes with different X.conditional stability constants log K f7 and 9 were determined from fluorescence quenching of ligand fractions duringCuL .copper II titration. Organic ligands in low molecular mass fractions were relatively weak and strong ligands occurred in higher molecular mass fractions. It is suggested that the weaker ligand sites would consist of two or more carboxyl groups X. X.log K s4, whereas carboxyl groups log K s2, which are protonated at lower pH, and primary amine mayHL H L2 .additionally contribute to the formation of more stable copper II complexes of the stronger ligand. q 1998 Elsevier Science B.V. All rights reserved