PROBE OF CADMIUM(II) BINDING ON SOIL FULVIC-ACID INVESTIGATED BY CD-113 NMR-SPECTROSCOPY

Binding of cadmium(II) on soil fulvic acid (FA) was investigated over a range of fulvate-to-cadmium concentration ratios (8-59 equiv.mol(-1) ) using Cd-113 NMR spectroscopy. The Cd-113 chemical shift of cadmium bound on fulvate was observed in a more downfield region (delta-20.4 t o -15.6) than that bound on synthetic polymers, poly(acrylic acid) (PA A:delta-36.6 to -38.2), poly(methacrylic acid) (PMAA:delta-34.0 to -25 .4), and poly(vinyl benzoic acid) (PVBA:delta-34.7 to -31.2). The calc ulated values of individual chemical shifts for the species CdL(+) and CdL(2) (L:carboxylate) formed in Cd(II)-carboxylate systems (e.g., ac etate, benzoate) are delta-22 to -24 and delta-39 to -40, respectively . The relative downfield shift of cadmium(II)-fulvate suggests that fu nctional groups (e.g., hydroxyl and neutral N donor) other than carbox ylates may be involved in cadmium coordination. The chemical shifts of cadmium complexes of hydroxycarboxylates (e.g., glycolate) or carboxy lates containing neutral N donor (e.g., picolinate) were generally obs erved in more downfield regions than their carboxylate counterparts.