Can Hydridic-to-Protonic Hydrogen Bonds Catalyze Hydride Transfers in Biological Systems?
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- 作者：Simona Marincean ; James E. Jackson
- 刊名：Journal of Physical Chemistry A
- 出版年：2010
- 出版时间：December 30, 2010
- 年：2010
- 卷：114
- 期：51
- 页码：13376-13380
- 全文大小：187K
- 年卷期：v.114,no.51(December 30, 2010)
- ISSN：1520-5215
文摘
Catalysis of hydride transfer by hydridic-to-protonic hydrogen (HHH) bonding in α-hydroxy carbonyl isomerization reactions was examined computationally in the lithium salts of 7-substituted endo-3-hydroxybicyclo[2.2.1]hept-5-en-2-ones. The barrier for intramolecular hydride transfer in the parent system was calculated to be 17.2 kcal/mol. Traditional proton donors, such as OH and NH3+, stabilized the metal cation-bridged transition state by 1.4 and 3.3 kcal/mol, respectively. Moreover, among the conformers of the OH systems, the one in which the proton donor is able to interact with the migrating hydride (Hm) has an activation barrier lower by 1.3 and 1.7 kcal/mol than the other possible OH conformers. By contrast, the presence of an electronegative group such as F, which disfavors the migration electronically by opposing development of hydridic charge, destabilizes the hydride migration by 1.5 kcal/mol relative to the epimeric exo system. In both ground and transition states the Hm···H distance decreased with increasing acidity of the proton donor, reaching a minimum of 1.58 Å at the transition state for NH3+. Both Mulliken and NPA charges show enhancement of negative character of the migrating hydride in the cases in which HHH bonding is possible.