GEOC 79 |
| A. L. Crumbliss and S. Dhungana. Chemistry Department, Duke University, Box 90346, Durham, NC 27708-0346 |
| We will present an environmental iron scheme consisting of inter-related controls, whereby the first coordination shell of iron modulates iron's redox potential (E1/2) and the oxidation state of iron controls the chemistry of the first coordination sphere, and therefore the immediate chemical environment of the iron. Siderophores (microbially generated iron-specific chelating agents) may be viewed as iron redox mediators. Siderophore chelation of environmental iron in a reduced oxidation state results in facile air oxidation of iron due to the negative E1/2 values observed for Fe-siderophore complexes. This solubilizes the iron and locks it into a specific coordination environment, thereby preventing hydrolysis and precipitation. The Fe(III)=> Fe(II) electron transfer process may be viewed as a switch which controls the thermodynamic stability and kinetic lability of the first coordination shell. In siderophore-iron(III) complexes reduction to iron(II) decreases thermodynamic stability, increases the rate of ligand exchange, and increases the facility of donor atom protonation, and thus facilitates a rapid turnover of the first coordination shell. We will present results for iron-siderophore pH and oxidation state dependent speciation studies that are relevant to environmental and microbial iron mobility and transport. |
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Microbially Mediated Manganese and Iron Oxidation in the Biosphere
1:30 PM-5:05 PM, Tuesday, March 30, 2004 Marriott -- Marquis NE, Oral
Division of Geochemistry |