Title

Analysis of the Reactivities of Protein C-H Bonds to H Atom Abstraction by OH Radical

Document Type

Article

Journal/Book Title

J. Am. Chem. Soc.

Publication Date

1-1-2010

Volume

132

First Page

16450

Last Page

16459

DOI

10.1021/ja105204v.

Abstract

Ab initio and density functional theory calculations are used to monitor the process wherein a OH· radical is allowed to approach the various CH groups of a Leu dipeptide, with its CH(2)CH(CH(3))(2) side chain. After forming an encounter complex, the OH· abstracts the pertinent H atom, and the resulting HOH is then dissociated from the complex. The energy barriers for H· abstraction from the β, γ, and δ CH groups are all less than 8 kcal/mol, but a significantly higher barrier is computed for the C(α)H removal. This higher barrier is the result of the strong H-bonds formed in the encounter complex between the OH· and the NH and C═O groups of the peptide units that surround the C(α) atom. This low-energy complex represents a kinetic trap which raises the energy needed to surmount the ensuing H· transfer barrier.

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