Kannath S, Adamczyk P, Ferro-Costas D, Fernández-Ramos A, Major DT, Dybala-Defratyka A. Role of Microsolvation and Quantum Effects in the Accurate Prediction of Kinetic Isotope Effects: The Case of Hydrogen Atom Abstraction in Ethanol by Atomic Hydrogen in Aqueous Solution.
J Chem Theory Comput 2020;
16:847-859. [PMID:
31904954 PMCID:
PMC7588029 DOI:
10.1021/acs.jctc.9b00774]
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Abstract
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Hydrogen abstraction from ethanol
by atomic hydrogen in aqueous
solution is studied using two theoretical approaches: the multipath
variational transition state theory (MP-VTST) and a path-integral
formalism in combination with free-energy perturbation and umbrella
sampling (PI-FEP/UM). The performance of the models is compared to
experimental values of H kinetic isotope effects (KIE). Solvation
models used in this study ranged from purely implicit, via mixed–microsolvation
treated quantum mechanically via the density functional theory (DFT)
to fully explicit representation of the solvent, which was incorporated
using a combined quantum mechanical-molecular mechanical (QM/MM) potential.
The effects of the transition state conformation and the position
of microsolvating water molecules interacting with the solute on the
KIE are discussed. The KIEs are in good agreement with experiment
when MP-VTST is used together with a model that includes microsolvation
of the polar part of ethanol by five or six water molecules, emphasizing
the importance of explicit solvation in KIE calculations. Both, MP-VTST
and PI-FEP/UM enable detailed characterization of nuclear quantum
effects accompanying the hydrogen atom transfer reaction in aqueous
solution.
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