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UV‐INDUCED FREE RADICALS IN ORIENTED DNA †
Author(s) -
Gräslund A.,
Ehrenberg A.,
Rupprecht A.,
Ström G.
Publication year - 1979
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1979.tb07045.x
Subject(s) - radical , electron paramagnetic resonance , chemistry , photochemistry , thymine , irradiation , guanine , dna , nuclear magnetic resonance , organic chemistry , physics , nucleotide , biochemistry , nuclear physics , gene
— Samples of oriented DNA containing 30% water were UV‐irradiated at 77 K and investigated by electron paramagnetic resonance (EPR). The EPR spectra recorded in directions parallel and perpendicular to the DNA fibre direction showed that at low UV doses the induced free radicals are very similar to those induced by γ‐irradiation at the same temperature. The γ‐induced free radicals have previously been analysed and found to consist mainly of anionic free radicals on thymine and cationic free radicals on guanine. At higher UV doses or by suitable annealing of the samples given a low UV dose, significant amounts of hydrogen‐addition radicals on thymine were observed. The quantum yield of free radical formation for irradiation at 300nm ± 10nm was estimated to 10 ‐ ‐ 4 . We also made a quantitative determination of the UV‐induced free radicals inside an optically effective volume of the sample. The following free radical induction frequencies at 77 K were estimated: γ‐rays: 2 × 10 ‐ ‐ 12 free radicals per rad per dalton and UV (300nm): 6 × 10 ‐ ‐ 12 free radicals per J/m 2 per dalton.