HR: 0800h
AN: B41A-0036    [Abstracts]
TI: Controls on Fe Isotope Fractionation During Organic Complexation: the Importance of Covalent Bonding
AU: * Domagal-Goldman, S D
EM: sgoldman@geosc.psu.edu
AF: The Pennsylvania State University Department of Geosciences, 411 Deike Building, University Park, PA 16803, United States
AU: Kubicki, J D
EM: kubicki@geosc.psu.edu
AF: The Pennsylvania State University Department of Geosciences, 411 Deike Building, University Park, PA 16803, United States
AB: Fe isotopes have been proposed as a tracer of changes to the redox state of the oceans (Rouxel et al., 2005), and for use as a biosignature (e.g., Johnson et al., 1999). Previous modeling work supports this, as they suggest redox fractionations are likely the main control over Fe isotopes.Fe isotopes have been proposed as a tracer of changes to the redox state of the oceans (Rouxel et al., 2005), and for use as a biosignature (e.g., Beard et al., 1999). Previous modeling work (Domagal-Goldman and Kubicki, submitted) that predicts greater equilibrium fractionations for redox reactions than for complexation reactions supports the former application. In this study, we try to ascertain the first-principles chemical drivers of fractionation of Fe isotopes. We do this by using Natural Bond Order (NBO) analyses and isotope fractionation predictions of Fe bound to various organic ligands at different Fe oxidation states and Fe:ligand ratios.NBO analysis re-assigns electrons in molecular orbitals to bond orbitals within a complex; this allows for the examination of the presence and strength of covalent bonding in a complex. By comparing the presence and strength of covalent Fe-O bonds in the studied complexes to other predicted variables such as bond lengths and predicted fractionation factors, we can assess the importance of these bonds to Fe isotope fractionation in nature. Byexamining the effect controlled variables such as Fe oxidation state and the number of Fe-ligand bonds have on the formation of covalent bonds, we will begin to understand what controls bonding for these types of complexes. Ultimately, this work is geared towards driving future research questions related to the isotopicfractionations of Fe and other transition metals.
DE: 0406 Astrobiology and extraterrestrial materials
DE: 0409 Bioavailability: chemical speciation and complexation
DE: 0424 Biosignatures and proxies
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 4870 Stable isotopes (0454, 1041)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting