Photocleavage of plasmid DNA by dibenzothiophene S-oxide under anaerobic conditions

Abstract

The ability of dibenzothiophene S-oxide (1) to photochemically induce strand breaks in plasmid DNA was studied under anaerobic conditions. DNA cleavage is monitored by the conversion of closed circular pUC19 DNA (form I) to the nicked (form II) and linear forms (form III) using densitometer digital imaging of ethidium stained gels. In buffered aqueous–acetonitrile (9:1) solutions the single-strand cleavage is efficient and does not require an alkaline reaction workup. Photodeoxygenation of 1 in buffered aqueous–acetonitrile (9{:}1) solutions containing benzene led to the production of phenol. The effect of solvent deuteration does not support the involvement of 1O2 from a sulfoxide dimerization reaction nor a sensitized photooxygenation reaction. The results are interpreted in terms of a sulfoxide photodeoxygenation via oxygen atoms [O(3P)] where oxidation of DNA can lead to single-strand breaks. Since the reaction of O(3P) atoms with water itself is endoergic, we propose that hydroxyl radicals do not intervene in the DNA cleaving reaction.