Ligand exchange is essential to dynamic metal ion speciation of in environmental systems. It has been noted that metal biouptake rates increase in the presence of “spectator” low molecular weight organic acids (LMWOAs) despite their participation in only a small fraction of total metal ion species at equilibrium. To study possible abiotic mechanisms, we examined the kinetics of disjunctive ligand exchange of nickel between aminocarboxylate multidentate ligands, nitrilotriacate (NTA) and <i>trans</i>-1,2-cyclohexylenedinitrilotetraacetate (CDTA), in the presence of structurally-related LMWOAs and under varied reaction conditions. We observe that LMWOAs catalyze disjunctive ligand exchange rates as a function of Lewis base identity and chelate ring size. We propose a reaction mechanism for catalysis and describe a kinetic model to predict disjunctive ligand exchange rates in the presence of LMWOAs. This work is part of our effort to develop structure-reactivity relationships for multidentate ligand exchange reactions that inform predictive metal ion speciation in dynamic environmental systems.

Effect of low molecular weight organic acids on the kinetics of disjunctive ligand exchange: Lewis base identity and chelate ring size

2019 Spring National Meeting

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