title: Kinetics of the interaction of sulfate and hydrogen phosphate radicals with small peptides of glycine, alanine, tyrosine and tryptophan.
abstract: The kinetics and mechanism of the oxidation of Glycine (Gly), Alanine (Ala), Tyrosine (Tyr), Tryptophan (Trp) and some di-(Gly-Gly, Ala-Ala, Gly-Ala, Gly-Trp, Trp-Gly, Gly-Tyr, Tyr-Gly), tri-(Gly-Gly-Gly, Ala-Gly-Gly) and tetrapeptides (Gly-Gly-Gly-Gly) mediated by sulfate (SO(4) (-)) and hydrogen phosphate (HPO(4) (-)) radicals was studied, employing the flash-photolysis technique. The substrates were found to react with sulfate radicals (SO(4) (-), produced by photolysis of the S(2)O(8)(2-)) faster than with hydrogen phosphate radicals (HPO(4) (-), generated by photolysis of P(2)O(8)(4-) at pH = 7.1). The reactions of the zwitterions of the aliphatic amino acids and peptides with SO(4) (-) radicals take place by electron transfer from the carboxylate moiety to the inorganic radical, whereas those of the HPO(4) (-) proceed by H-abstraction from the alpha carbon atom. The phenoxyl radical of Tyr-Gly and Gly-Tyr are formed as intermediate species of the oxidation of these peptides by the inorganic radicals. The radical cations of Gly-Trp and Trp-Gly (at pH = 4.2) and their corresponding deprotonated forms (at pH = 7) were detected as intermediates species of the oxidation of these peptides with SO(4) (-) and HPO(4) (-). Reaction mechanisms which account for the observed intermediates are proposed.
authors.affiliation: Instituto de Investigaciones Físicoquímicas Teóricas y Aplicadas (INIFTA) Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Argentina.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Bosio
authors.forename: Susana
authors.initials: S
authors.lastname: Criado
authors.forename: Walter
authors.initials: W
authors.lastname: Massad
authors.forename: Felipe J
authors.initials: FJ
authors.lastname: Rodríguez Nieto
authors.forename: Mónica C
authors.initials: MC
authors.lastname: Gonzalez
authors.forename: Norman A
authors.initials: NA
authors.lastname: García
authors.forename: Daniel O
authors.initials: DO
authors.lastname: Mártire
mesh_terms: D000409:Alanine / Q000737:chemistry*; D005998:Glycine / Q000737:chemistry*; D007700:Kinetics; D010455:Peptides / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry*; D010777:Photochemistry; D013431:Sulfates / Q000737:chemistry*; D014364:Tryptophan / Q000737:chemistry*; D014443:Tyrosine / Q000737:chemistry*
chemical_list: D010455:Peptides; D010710:Phosphates; D013431:Sulfates; D014443:Tyrosine; D014364:Tryptophan; D000409:Alanine; D005998:Glycine