New Paper: One-Electron Potentials for Contaminant Reduction Reactions

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This chapter describes methods for calculating one-electron reduction potentials for dechlorination and nitro reduction using ab initio quantum chemistry methods. New results are presented for both types reduction reactions, and they are compared to results reported previously using both experimental and theoretical methods. A meta-analysis of the existing data is presented, which show areas of good agreement and areas were better methods are still needed.

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Bylaska, E. J., A. J. Salter-Blanc, and P. G. Tratnyek. 2011. One-electron reduction potentials from chemical structure theory calculations. In: P. G. Tratnyek, T. J. Grundl , and S. B. Haderlein (ed.), Aquatic Redox Chemistry. ACS Symposium Series, American Chemical Society, Washington, DC, Vol. 1071, Ch. 3, pp 37-64.

Many redox reactions of importance in aquatic chemistry involve elementary steps that occur by single-electron transfer (SET). This step is often the first and rate limiting step in redox reactions of environmental contaminants, so there has been a great deal of interest in the corresponding one-electron reduction potentials (E 1). Although E 1 can be obtained by experimental methods, calculation from first-principles chemical structure theory is becoming an increasingly attractive alternative. Sufficient data are now available to perform a critical assessment of these methods?and their results?for two types of contaminant degradation reactions: dehalogenation of chlorinated aliphatic compounds (CACs) and reduction of nitro aromatic compounds (NACs). Early datasets containing E 1?s for dehalogenation of CACs by dissociative SET contained a variety of errors and inconsistencies, but the preferred datasets show good agreement between values calculated from thermodynamic data and quantum mechanical models. All of the datasets with E 1?s for reduction of NACs by SET are relatively new, were calculated with similar methods, and yet yield a variety of systematic differences. Further analysis of these differences is likely to yield computational methods for E 1?s of NAC nitro reduction that are similar in reliability to those for CAC dechlorination. However, comparison of the E 1 data compiled here with those calculated with a more universal predictive model (like SPARC) highlight a number of challenges with implementation of models for predicting properties over a wide range of chemical structures.

DOI: http://dx.doi.org/10.1021/bk-2011-1071.ch003