期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 133, 期 41, 页码 16553-16559出版社
AMER CHEMICAL SOC
DOI: 10.1021/ja205962b
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资金
- Australian Research Council (ARC)
- National Computing Infrastructure (NCI) National Facility and Intersect Australia Ltd
Quantum chemistry computations have been used to investigate hydrogen-atom abstraction by chlorine atom from protonated and N-acetylated amino acids. The results are consistent with the decreased reactivity at the backbone alpha-carbon and adjacent side-chain positions that is observed experimentally. The individual effects of NH3+, COOH, and NHAc substituents have been examined and reveal important insights. The NH3+ group in isolation is found to be deactivating at the alpha-position, while the acetamido group is activating. For the COOH group, polar effects lead to a contrathermodynamic deactivation of the thermodynamically most favorable alpha-abstraction. In the N-acetylamino acid, the alpha-position is deactivated by the combined inductive effect of the substituents and the presence of an early transition structure, again overriding the greater thermodynamic stability of the alpha-centered radical product. Deactivation of the alpha-, beta-, and gamma-positions results in a peculiar stability for amino acids and peptides and their derivatives with respect to radical degradation.
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