Mathematics – Logic
Scientific paper
Jun 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008oleb...38..195w&link_type=abstract
Origins of Life and Evolution of Biospheres, Volume 38, Issue 3, pp.195-209
Mathematics
Logic
Dft, Marcus Theory, Heterogeneous Redox, Nitrogen Reduction, Ammonia, Prebiotic Chemistry, Nitrogenase, Iron, Goethite
Scientific paper
Nitrogen reduction by ferrous iron has been suggested as an important mechanism in the formation of ammonia on pre-biotic Earth. This paper examines the effects of adsorption of ferrous iron onto a goethite (α-FeOOH) substrate on the thermodynamic driving force and rate of a ferrous iron-mediated reduction of N2 as compared with the homogeneous aqueous reaction. Utilizing density functional theory and Marcus Theory of proton coupled electron transfer reactions, the following two reactions were studied: {text{Fe}}^{2 + } _{left( {{text{aq}}} right)} + {text{N}}_{2left( {{text{aq}}} right)} + {text{H}}_2 {text{O}}_{left( {{text{aq}}} right)} to {text{N}}_2 {text{H}}^ bullet + {text{FeOH}}^{2 + } _{left( {{text{aq}}} right)} and equiv {text{Fe}}^{2 + } _{left( {{text{ads}}} right)} + {text{N}}_{2left( {{text{aq}}} right)} + 2{text{H}}_2 {text{O}}_{left( {{text{aq}}} right)} to {text{N}}_2 {text{H}}^ bullet + α - {text{FeOOH}}_{left( {text{s}} right)} + 2{text{H}}^ + _{left( {{text{aq}}} right)} Although the rates of both reactions were calculated to be approximately zero at 298 K, the model results suggest that adsorption alters the thermodynamic driving force for the reaction but has no other effect on the direct electron transfer kinetics. Given that simply altering the thermodynamic driving force will not reduce dinitrogen, we can make mechanistic connections between possible prebiotic pathways and biological N2 reduction. The key to reduction in both cases is N2 adsorption to multiple transition metal centers with competitive H2 production.
Kubicki James D.
Schoonen Martin A. A.
Wander Matthew C. F.
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