title: Formation of stable radicals in catechin/nitrous acid systems: participation of dinitrosocatechin.
abstract: Catechins are transformed into dinitrosocatechins (diNOcats) and then oxidized to the quinones by salivary nitrite under conditions simulating the stomach. This manuscript deals with formation of stable radicals in the NO group of diNOcat during nitrite-induced oxidation of (+)-catechin and diNOcat at pH 2. We postulated two mechanisms for the stable radical formation; one is nitrous acid-induced oxidation of diNOcat in the A-ring, and the other intermolecular charge transfer from the A-ring of diNOcat and/or diNOcat quinone to the quinone moiety of the B-ring of diNOcat quinone. In addition, an unstable phenoxyl radical, which might be transformed into quinone, was also produced, accompanying the formation of the stable radical on the NO group. Taking the above results into account, we mainly focus on the adverse effects of the radicals and quinone, which may be produced from (+)-catechin in the stomach under the conditions of high salivary nitrite concentrations.
authors.affiliation: Institute for Multidisciplinary Research, University of Belgrade, Kneza Viseslava 1, Belgrade 11000, Serbia.
authors.forename: Filis
authors.initials: F
authors.lastname: Morina
authors.affiliation: Department of Bioscience, Kyushu Dental University, Kitakyushu 803-8580, Japan. Electronic address: takahama@toua-u.ac.jp.
authors.forename: Umeo
authors.initials: U
authors.lastname: Takahama
authors.affiliation: Faculty of Physical Chemistry, University of Belgrade, Studentski trg 12-16, 11000 Belgrade, Serbia.
authors.forename: Miloš
authors.initials: M
authors.lastname: Mojović
authors.affiliation: Faculty of Physical Chemistry, University of Belgrade, Studentski trg 12-16, 11000 Belgrade, Serbia.
authors.forename: Ana
authors.initials: A
authors.lastname: Popović-Bijelić
authors.affiliation: Institute for Multidisciplinary Research, University of Belgrade, Kneza Viseslava 1, Belgrade 11000, Serbia.
authors.forename: Sonja
authors.initials: S
authors.lastname: Veljović-Jovanović
mesh_terms: D002392:Catechin / Q000737:chemistry*; D005609:Free Radicals; D005753:Gastric Mucosa / Q000378:metabolism*; D009608:Nitrous Acid / Q000737:chemistry*; D010084:Oxidation-Reduction
chemical_list: D005609:Free Radicals; D002392:Catechin; D009608:Nitrous Acid
keywords: (+)-Catechin; (+)-Catechin (PubChem CID: 9064); (−)-Epicatechin (PubChem CID: 72276); 6,8-Dinitrosocatechin; Ascorbic acid (PubChem CID: 54670067); Charge transfer complex; Nitrous acid; Nitroxyl radical; Stomach; Thiocyanic acid (PubChem CID: 781)