Analysis of the reactivities of protein C-H bonds to H atom abstraction by OH radical.
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.
Department of Chemistry & Biochemistry, Utah State University, Logan, Utah 84322, United States. steve.scheiner@usu.edu
Steve
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Tapas
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D004151:Dipeptides / Q000737:chemistry*; D006860:Hydrogen Bonding; D017665:Hydroxyl Radical / Q000737:chemistry*; D007930:Leucine / Q000737:chemistry*; D008958:Models, Molecular; D011789:Quantum Theory
D004151:Dipeptides; D017665:Hydroxyl Radical; D007930:Leucine