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Research Abstracts Online
January 2008 - March 2009

University of Minnesota Twin Cities
Institute of Technology
Department of Civil Engineering

PI: William A. Arnold, Associate Fellow

Nitrogen Kinetic Isotope Effects in Environmentally Relevant Transformations

Isotopic enrichment of a substrate occurs during the reaction of organic pollutants if the rate-limiting step involves bond cleavage. Recent work has used this enrichment to verify that transformation of organic pollutants is occurring (rather than dilution, which does not result in degradation or enrichment) in the field. If the kinetic isotope effects responsible for the isotopic fractionation of different possible processes are known, it should be possible to determine not only if degradation is occurring, but also the specific process responsible (hydrolysis, reduction, biodegradation). Collaborators at the Swiss Federal Institute of Technology have measured the nitrogen kinetic isotope effects associated with the reduction of nitrobenzenes. In order to obtain independent information on the effects of ring substituents on the extent and variability of nitrogen kinetic isotope effects, this researcher has calculated the kinetic isotope effects using density functional theory of two different steps in the reaction sequence. Energies of the parent molecule and the appropriate transition state(s) are determined using the Gaussian 03 electronic structure program suite. By changing the isotope of nitrogen present in the molecule, the expected difference in rate constant can be determined from the change in energy.