title: pH effect on the one-electron photooxidation of 5-methylcytosine with naphthoquinone sensitizer.
abstract: The pH effect on the one-electron photooxidation of 5-methyl-2'-deoxycytidine (d(m)C) by sensitization with 1,4-naphthoquinone (NQ) was investigated. Upon photoirradiation of d(m)C in the presence of NQ under slightly acidic conditions such as pH 5.0, 5-formyl-2'- deoxycytidine (d(f)C) was formed efficiently, whereas similar NQ-photosensitized oxidation of d(m)C proceeded to lesser extent under neutral or basic conditions. Under slightly acidic conditions, dmC radical cation favors to undergo irreversible deprotonation at the C(5)-methyl group to form a methyl-centered radical, leading to a higher yield of the alkali-labile oxidation products including d(f)C. In contrast, the d(m)C radical cation competitively undergoes deprotonation at the exocyclic N(4)-amino group under neutral or basic conditions, resulting in a decreased yield of NQ-photosensitized oxidation products.
authors.affiliation: Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Kyoto 615-8510, Japan. hisatsugu@t03.mbox.media.kyoto-u.ac.jp
authors.forename: Hisatsugu
authors.initials: H
authors.lastname: Yamada
authors.forename: Kazuhito
authors.initials: K
authors.lastname: Tanabe
authors.forename: Takeo
authors.initials: T
authors.lastname: Ito
authors.forename: Sei-ichi
authors.initials: S
authors.lastname: Nishimoto
mesh_terms: D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000528:radiation effects; D004583:Electrons; D006863:Hydrogen-Ion Concentration; D009285:Naphthoquinones / Q000737:chemistry*; D010084:Oxidation-Reduction; D017319:Photosensitizing Agents / Q000737:chemistry*
chemical_list: D009285:Naphthoquinones; D017319:Photosensitizing Agents; D003841:Deoxycytidine; C016569:5-methyldeoxycytidine; C035342:1,4-naphthoquinone