title: Kinetic radical-scavenging activity of platonin, a cyanine photosensitizing dye.
abstract: Platonin is known to possess antioxidant activity. However, the kinetics of the radical-scavenging activities of this compound remain unknown. The aim of this study was to investigate the radical-scavenging activities of platonin by the induction period method in the polymerization of methyl methacrylate (MMA), initiated by thermal decomposition of 2,2'-azobis (isobutyronitrile) (AIBN) (a carbon-centered radical, R*), and benzoyl peroxide (BPO) (an oxygen-centered radical, PhCOO*), under nearly anaerobic conditions. The number of moles of R* or PhCOO* radicals trapped by platonin calculated with respect to 1 mole of inhibitor moiety unit (stoichiometric factor, n) was determined, and this showed that the n of fully oxidized platonin was 4. The inhibition rate constant (k(inh)) of platonin showed a wide range of 0.8 x 10(3) M(-1)s(-1) to 1.6 x 10(4) M(-1)s(-1). To clarify the interaction between platonin and thiols, 2-mercapto-1-methylimidazole (MMI) was used as a representative thiol, because glutathiones were unsuitable due to their limited solubility in MMA. MMI in the presence of platonin showed neither catalytic activities nor synergistic activities. Platonin possesses radical-scavenging activities and acts as an antioxidant. On the basis of our experimental results, the radical-scavenging mechanism is discussed.
authors.affiliation: Division of Chemistry, Department of Oral Biology and Tissue Engineering, Meikai University School of Dentistry, Sakado, Saitama 350-0283, Japan. mariko@dent.meikai.ac.jp
authors.forename: Mariko
authors.initials: M
authors.lastname: Ishihara
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Kadoma
authors.forename: Seiichiro
authors.initials: S
authors.lastname: Fujisawa
mesh_terms: D001585:Benzoyl Peroxide / Q000737:chemistry; D002152:Calorimetry, Differential Scanning; D016166:Free Radical Scavengers / Q000737:chemistry*; D007093:Imidazoles / Q000737:chemistry; D007700:Kinetics; D020366:Methylmethacrylate / Q000737:chemistry; D015394:Molecular Structure; D009570:Nitriles / Q000737:chemistry; D011108:Polymers / Q000138:chemical synthesis; D013844:Thiazoles / Q000737:chemistry*
chemical_list: C107674:2-mercapto-1-methylimidazole; D016166:Free Radical Scavengers; D007093:Imidazoles; D009570:Nitriles; D011108:Polymers; D013844:Thiazoles; C032149:platonin; D020366:Methylmethacrylate; C004526:azobis(isobutyronitrile); D001585:Benzoyl Peroxide