首页 | 本学科首页   官方微博 | 高级检索  
   检索      


An Integrated Experimental and Computational Approach for Characterizing the Kinetics and Mechanism of Triadimefon Racemization
Authors:Qianyi Cheng  Quincy Teng  Satori A Marchitti  Caleb M Dillingham  John F Kenneke
Institution:1. Student Services Authority Contractor, National Exposure Research Laboratory, U.S. Environmental Protection Agency, Athens, Georgia, USA;2. National Exposure Research Laboratory, U.S. Environmental Protection Agency, Athens, Georgia, USA;3. ORISE Fellow, National Exposure Research Laboratory, U.S. Environmental Protection Agency, Athens, Georgia, USA
Abstract:Enantiomers of chiral molecules commonly exhibit differing pharmacokinetics and toxicities, which can introduce significant uncertainty when evaluating biological and environmental fates and potential risks to humans and the environment. However, racemization (the irreversible transformation of one enantiomer into the racemic mixture) and enantiomerization (the reversible conversion of one enantiomer into the other) are poorly understood. To better understand these processes, we investigated the chiral fungicide, triadimefon, which undergoes racemization in soils, water, and organic solvents. Nuclear magnetic resonance (NMR) and gas chromatography / mass spectrometry (GC/MS) techniques were used to measure the rates of enantiomerization and racemization, deuterium isotope effects, and activation energies for triadimefon in H2O and D2O. From these results we were able to determine that: 1) the alpha‐carbonyl carbon of triadimefon is the reaction site; 2) cleavage of the C‐H (C‐D) bond is the rate‐determining step; 3) the reaction is base‐catalyzed; and 4) the reaction likely involves a symmetrical intermediate. The B3LYP/6–311 + G** level of theory was used to compute optimized geometries, harmonic vibrational frequencies, nature population analysis, and intrinsic reaction coordinates for triadimefon in water and three racemization pathways were hypothesized. This work provides an initial step in developing predictive, structure‐based models that are needed to identify compounds of concern that may undergo racemization. Chirality 28:633–641, 2016. © 2016 Wiley Periodicals, Inc.
Keywords:chirality  conazoles  enantiomerization  environmental chemicals  pesticides  risk assessment  stereochemistry
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号