Mechanisms of Iron-Ligand Exchange Reactions and the Influence of Ionophore Hosts in the Second-Sphere

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Alvin L. Crumbliss of Duke University is supported by the Inorganic, Bioinorganic, and Organometallic Chemistry Program for research on mechanisms of ligand-metal exchange reactions-- with emphasis on second sphere-influences. He is PI of NSF grant 9709105 ($345K for 36 months) in this same area, and earlier grants extending to 1976. Aims of the present grant include elucidation of: kinetics and mechanisms of dissociation of Fe(III) from chelate complexes, aspects of host-guest chemistry in the second sphere, Fe(III-II) redox potentials of complexes and second-sphere aggregates, and second-sphere effects on mobility of Fe(III) in various environments.Metal ions are centrally involved in important changes that figure in all areas of science, including geology, biology, medicine and ecology. Ferric iron -- Fe(III) -- is one of the most common, versatile, and important metal ions. Since it tends to be rather sluggish in regard to replacing atoms in its near neighborhood ("first coordination sphere") there are many advantages in selecting that ion for detailed study. Results of this group and others have shown that atoms beyond the first coordination sphere ("second coordination sphere") influence, modulate, and control what goes on near the metal ion, and thereby have dramatic effect on the overall chemistry that can be observed in macroscopic systems (geology, biology, ecology). This program is making good progress in unrraveling the subtle factors that govern this important class of chemistry.