Products of Thymine Oxygenation by a Non-heme Oxygenation Model, Fe<sup>II</sup>(MeCN)<sub>6</sub><sup>2+</sup>&ndash;Ac<sub>2</sub>O&ndash;H<sub>2</sub>O<sub>2</sub>, and the Transition State Model between Oxoiron and Thymine
Oxidative thymine damage was investigated using a new non-heme oxygenation model, Fe(MeCN)62+–H2O2–Ac2O, based on high-spin Fe(MeCN)62+ in a non-aqueous solution, Ac2O–MeCN. Thymine and 1,3-dimethylthymine oxidized by the system gave the corresponding trans-thymine glycol derivatives in good yield. Thymineglycol is equivalent to an oxidative product as a measure of oxidative DNA damage in living cells. It is suggested that the activation of Fe(MeCN)62+–H2O2–Ac2O in Ac2O–MeCN forms the oxoiron O=FeIV(AcO)(MeCN)4+ as an active species via a hetelolytic two-electron mechanism, not a Haber–Weiss–Fenton-type reaction with a one-electron process by treatment with a radical scavenger. In addition, we also demonstrated the transition state (TS) for the interaction between thymine and O=FeIV(AcO)(MeCN)4+ in the triplet spin (spin multiplicity; M=3). This model of oxidative thymine damage may provide new insight into the oxidative mechanism of thymine glycol production in non-aqueous reactions of thymine.
Photosensitization of DNA bases by 4(5)-nitroimidazole: a steady state and flash photolysis study
作者:Maitrayee Basu Roy、Parikshit C. Mandal、Samita Basu、Sudhindra N. Bhattacharyya
DOI:10.1039/ft9959101191
日期:——
UV photolysis and laser flash photolysis of 4(5)-nitroimidazole in the presence of thymine and/or uracil generates the respective glycols under conditions where the bases do not absorb any light. The reaction is mediated through the triplet state of 4(5)-nitroimidazole which generates a highly oxidizing N-centred radical. The radical has an absorption maximum at ca. 350 nm and reacts efficiently with the DNA bases resulting in the formation of glycols. The rate constant of reaction of the radical with the DNA bases and nucleosides is of the order of ca. 108 dm3 mol–1 s–1, the rate being slower with the nucleosides than with the free bases.
Effect of Fe(III) Ions on the γ-Radiolysis of Thymine
作者:S. N. Bhattacharyya、P. C. Mandal、S. Chakrabarti
DOI:10.1246/bcsj.63.3001
日期:1990.10
Aqueous solutions of thymine (T) in the presence of Fe(III) were irradiated under deaerated conditions at pH ≈2. The products of radiolysis were separated by two dimensional thin-layer chromatography. In the absence of any metal ion, the G(-T) is 2.6 but when Fe(III) is present during radiolysis, the G(-T) increases significantly and reaches a limiting value of 3.2. The yields of the hydroxylated products