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Penning, H. ; Cramer, C.J. ; Elsner, M.

Rate-dependent carbon and nitrogen kinetic Isotope fractionation in hydrolysis of isoproturon.

Environ. Sci. Technol. 42, 7764-7771 (2008)
DOI
Open Access Green as soon as Postprint is submitted to ZB.
Stable isotope fractionation permits quantifying contaminant degradation in the field when the transformation reaction is associated with a consistent isotope enrichment factor ?. When interpreted in conjunction with dual isotope plots, isotope fractionation is also particularly useful for elucidating reaction mechanisms. To assess the consistency of ? and dual isotope slopes in a two-step reaction, we investigated the abiotic hydrolysis of the herbicide isoproturon (3-(4-isopropylphenyl)-1,1-dimethylurea) using a fragmentation method that allows measuring isotope ratios in different parts of the molecule. Carbon and nitrogen position-specific isotope fractionation, as well as slopes in dual isotope plots, varied linearly with rate constants kobs depending on the presence of buffers that mediate the initial zwitterion formation. The correlation can be explained by two consecutive reaction steps (zwitterion formation followed by dimethylamine elimination) each of which has a different kinetic isotope effect and may be rate-limiting. Intrinsic isotope effects for both steps, extracted from our kinetic data using a novel theoretical treatment, agree well with values computed from density functional calculations. Our study therefore demonstrates that more variable isotope fractionation may be observed in simple chemical reactions than commonly thought, but that consistent ? or dual isotope slopes may nonetheless be encountered in certain molecular fragments.
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Publication type Article: Journal article
Document type Scientific Article
ISSN (print) / ISBN 0013-936X
e-ISSN 1520-5851
Journal Environmental Science & Technology
Quellenangaben Volume: 42, Issue: 21, Pages: 7764-7771 Article Number: , Supplement: ,
Publisher American Chemical Society (ACS)
Publishing Place Washington, DC
Reviewing status Peer reviewed
Institute(s) Institute of Groundwater Ecology (IGOE)