Structure and reactions of the peroxy radicals of glycine and alanine in peptides: an ab initio study (original) (raw)

Journal of Physical Organic Chemistry, 2004

Abstract

ABSTRACT Ab initio calculations at the B3LYP/6-31G(d) and CBS-RAD level were carried out to investigate the reaction of αC-centered peroxy radicals of neutral, non-zwitterionic glycine and alanine (AH), and as residues in model peptides, N-formylglycinamide and N-formylalaninamide (PH). Bond dissociation enthalpies (BDEs) were calculated for the αC—O (D), O—O (DOO) and O—H (DOH) bonds of glycine and alanine peroxy radicals (AOO, POO) and hydroperoxides (AOOH, POOH). The predicted BDEs at 298 K, in kJ mol−1 are AOO(Gly), D = 70; AOO(Ala), D = 69; POO(Gly), D = 89; POO(Ala), D = 86; AOOH(Gly), D = 237, DOO = 203, DOH = 371; AOOH(Ala), D = 234, DOO = 195, DOH = 368; POOH(Gly), D = 266, DOO = 207, DOH = 380; POOH(Ala), D = 264, DOO = 208, DOH=383. Values of BDE of the peptides in β-sheet peptide conformations were also estimated by constraining the Ramachandran dihedral angles, Φ and Ψ to, values of −150° and +150°: (S)-POO(Gly), D = 99; (R)-POO(Gly), D = 78; (S)-POO(Ala), D = 88; (R)-POO(Ala), D = 83; (S)-POOH(Gly), D = 258, DOO = 195, DOH = 362; (R)-POOH(Gly), D = 278, DOO = 217, DOH = 404; (S)- POOH(Ala), D = 240, DOO = 192, DOH = 355; (R)-POOH(Ala), D = 270, DOO = 204, DOH = 390. The reactions of αC-peroxy radicals, POO, and αC-alkoxy radicals, PO, were studied in detail. Copyright © 2004 John Wiley & Sons, Ltd.

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