Abstract

Laser excitation of DNA in aqueous solution leads to biphotonic formation of base radical cations and solvated electrons in addition to monophotonic products. The chemical pathways from the radical cations to strand breakage for several polynucleotides and single-stranded DNA are reviewed. An important feature of the mechanism is that the base radical cations are converted into neutral radicals prior to H abstraction from the sugar at pH 7. The neutral base radicals lead to single-strand break formation with the same yield as that obtained from the radical generated from the bases by reaction with OH. From this it can be inferred that, as far as ionisation by high energy irradiation is concerned, similar radicals are produced in DNA by direct ionisation as by reaction with OH radicals.

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