Yamada Hisatsugu, Tanabe Kazuhito, Ito Takeo, Nishimoto Sei-ichi
Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Kyoto 615-8510, Japan.
Nucleic Acids Symp Ser (Oxf). 2008(52):447-8. doi: 10.1093/nass/nrn227.
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.
