Kinetics and Mechanism of Iron-Ligand Exchange Reactions in the Presence of Surfactants and/or Crown Ethers

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The principal goal in this project is to elucidate the mechanism in microbes whereby iron is released from its extremely stable carrier at the appropriate time and location. Model experiments which use micelles designed to probe possible effects of the aqueous/cell interface on the labilization of iron from siderophores and other polydentate chelators will be performed. The influence of the aqueous/micelle interface on the kinetics of iron/ligand exchange between, for example, the hydrophilic siderophore ferrioxamine B and a micelle bound hydrophobic chelator, benzohydroxamic acid, will be tested. Phenanthroline will also be incorporated into the micelle in some experiments, as preliminary data show that phenanthroline accelerates iron/ligand exchange into the micellar pseudo-phase via a redox mechanism. Supramolecular assemblies in aqueous solution will be investigated in order to evaluate second coordination shell effects on iron(III)-ligand dissociation kinetics. Hydrophobic crown ethers may permit these supra- molecular assemblies to form on micelle "surfaces". These assemblies may be used as models for cell surface receptor complexes. The kinetics of ligand exchange within these supra- molecular assemblies (e.g., ferrioxamine B-crown ether- surfactant) and the influence that ternary complex formation has on these kinetics will be measured. %%% In this project in the Inorganic, Bioinorganic, and Organo- metallic Program of the Chemistry Division, Dr. Alvin L. Crumbliss of Duke University will model the way in which iron is released in microbes at the appropriate time and location. Bacteria contain molecules which bind and transport iron so efficiently that some are used as drugs in chelation therapy. The results of these bioinorganic experiments will enhance our understanding of microbial iron transport mechanisms and mechanisms related to metal extraction processes.