MODELS OF METAL-BINDING STRUCTURES IN FULVIC-ACID FROM THE SUWANNEE-RIVER, GEORGIA

Fulvic acid, isolated from the Suwannee River, Georgia, was assessed f or its ability to bind Ca2+, Cd2+, Cu2+, Ni2+, and Zn2+ ions at pH 6 b efore and after extensive fractionation that was designed to reveal th e nature of metal binding functional groups; The binding constant for Ca2+ ion had the greatest increase of all the ions in a metal binding fraction that was selected for intensive characterization for the purp ose of building quantitative average model structures. The ''metal bin ding'' fraction was characterized by quantitative C-13 NMR, H-1 NMR, a nd FT-IR spectrometry and elemental, titrimetric, and molecular weight determinations. The characterization data revealed that carboxyl grou ps were clustered in short-chain aliphatic dibasic acid structures. Th e Ca2+ binding data suggested that ether-substituted oxysuccinic acid structures are good models for the metal binding sites at pH 6. Struct ural models were derived based upon oxidation and photolytic rearrange ments of cutin, lignin, and tannin precursors. These structural models rich in substituted dibasic acid structures revealed polydentate bind ing sites with the potential for both inner-sphere and outer-sphere ty pe binding. The majority of the fulvic acid molecule was involved with metal binding rather than a small substructural unit.