We study the solvent effects on the temperature dependence of primary (1°) kinetic isotope effects (KIEs) for H-transfer reactions in solution in an attempt to understand the KIE observations in wild-type versus mutated enzymes. A hypothesis following the contemporary vibrationally assisted activated H-tunnelling model is that a greater temperature dependence of 1° KIEs, with a larger isotopic activation energy difference ΔEa (= EaD - EaH), should be observed in H/D-transfer reaction systems that have a loosely associated tunnelling ready state (TRS). The latter TRS requires more energy to sample the shorter donor-acceptor distances (DADs) for H-tunnelling to occur. Hydride transfer reactions from several dihydropyridines to various hydride acceptors, in acetonitrile versus a more polar protic water-alcohol mixture solvent, were studied to investigate this hypothesis. It is expected that the latter mixed solvent will solvate and thus stabilize the TRS well but meanwhile the solvation would pull the reaction centers away from each other loosening the TRS. The solvent effects on ΔEa’s will be discussed to provide insight into the hypothesis.

Solvent effects on the temperature dependence of the primary kinetic isotope effects for hydride transfer reactions in solution

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.