title: Semiquinone anion radicals from addition of amino acids, peptides, and proteins to quinones derived from oxidation of catechols and catecholamines. An ESR spin stabilization study.
abstract: Either chemical or enzymatic oxidation of catechols or catecholamines in the presence of nucleophiles (amino acids, peptides, and proteins) leads to the production of ring-substituted o-semiquinones which have been detected by ESR spin stabilization techniques. In many cases, radicals have been completely characterized and structures assigned. Chemical considerations point to a mechanism involving addition of nucleophile to o-quinone, followed by oxidation of product to o-semiquinone. These results confirm that addition occurs in oxidizing polyhydroxy aromatic systems, probably via o-quinone, in a reaction considered to account for much of the toxicity found for catechols and catecholamines.
mesh_terms: D000596:Amino Acids; D016227:Benzoquinones; D002395:Catecholamines; D002396:Catechols; D055598:Chemical Phenomena; D002621:Chemistry; D003545:Cysteine; D004578:Electron Spin Resonance Spectroscopy; D008715:Methionine; D010084:Oxidation-Reduction; D010455:Peptides; D011506:Proteins; D011809:Quinones; D014867:Water
chemical_list: D000596:Amino Acids; D016227:Benzoquinones; D002395:Catecholamines; D002396:Catechols; D010455:Peptides; D011506:Proteins; D011809:Quinones; D014867:Water; C025232:semiquinone radicals; D008715:Methionine; D003545:Cysteine