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Carbon, Hydrogen, and Nitrogen Isotope Fractionation Associated with Oxidative Transformation of Substituted Aromatic N-Alkyl Amines

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Skarpeli-Liati Marita, Pati Sarah G., Bolotin Jakov, Eustis Soren N., Hofstetter Thomas B.,
Project Using nitrogen isotope fractionation to assess redox reactions of organic contaminants
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Original article (peer-reviewed)

Journal Environmental Science & Technology
Volume (Issue) 46(13)
Page(s) 7179 - 7198
Title of proceedings Environmental Science & Technology
DOI 10.1021/es300819v

Abstract

We investigated the mechanisms and isotope effects associated with the N-dealkylation and N-atom oxidation of substituted N-methyl- and N,N-dimethylanilines to identify isotope fractionation trends for the assessment of oxidations of aromatic N-alkyl moieties by compound-specific isotope analysis (CSIA). In laboratory batch model systems, we determined the C, H, and N isotope enrichment factors for the oxidation by MnO2 and horseradish peroxidase (HRP), derived apparent 13C-, 2H-, and 15N-kinetic isotope effects (AKIEs), and characterized reaction products. The N-atom oxidation pathway leading to radical coupling products typically exhibited inverse 15N-AKIEs (up to 0.991) and only minor 13C- and 2H-AKIEs. Oxidative N-dealkylation, in contrast, was subject to large normal 13C- and 2H-AKIEs (up to 1.019 and 3.1, respectively) and small 15N-AKIEs. Subtle changes of the compound’s electronic properties due to different types of aromatic and/or N-alkyl substituents resulted in changes of reaction mechanisms, rate-limiting step(s), and thus isotope fractionation trends. The complex sequence of electron and proton transfers during the oxidative transformation of substituted aromatic N-alkyl amines suggests highly compound- and mechanism-dependent isotope effects precluding extrapolations to other organic micropollutants reacting along the same degradation pathways.
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