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STRAND BREAKAGE IN POLY(C), POLY(A), SINGLE‐AND DOUBLE‐STRANDED DNA INDUCED BY NANOSECOND LASER EXCITATION AT 193 nm *
Author(s) -
Görner Helmut,
Wala Malgorzata,
SchulteFrohlinde Dietrich
Publication year - 1992
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.1751-1097.1992.tb04225.x
Subject(s) - chemistry , polynucleotide , radical , dna , excitation , electron , aqueous solution , laser , nanosecond , quantum yield , analytical chemistry (journal) , ionization , nucleic acid , photochemistry , fluorescence , physics , organic chemistry , ion , optics , biochemistry , quantum mechanics
— Single‐ and double‐stranded calf thymus DNA and two polynucleotides (0.4 m M ) were studied in aqueous solution at pH ≅ 7 using pulsed, 20 ns laser excitation at 193 nm. Monophotonic ionization of the nucleic acids is suggested from the linear dependences of the concentration of ejected electrons and the number of single‐ and double‐strand breaks (ssb, dsb, respectively) on laser intensity ( I L ) in the range (0.2–3) × 10 6 W cm ‐2 . The quantum yields of formation of hydrated electrons (φ e ‐) and ssb and dsb (φ SSb and φ dsb ) are therefore independent of I L . In contrast, under 248 nm excitation these quantum yields increase linearly with I L under otherwise comparable conditions. Nevertheless, several effects and mechanistic implications are analogous using Λ exc = 193 and 248 nm. For polycytidylic acid, poly(C), in Ar‐saturated solution for example, the efficiency of ssb per radical cation (η RC =φ ssb /φ e ‐) is similar to the efficiency of ssb per OH radical (η OH ). For polyadenylic acid, poly(A), and single‐ and double‐stranded DNA η RC (Λ exc = 193 nm) is significantly smaller than η OH . The ratio φ ssb (N 2 O)/φ ssb (Ar) is =2 for poly(C), =4 for poly(A) and =10 for DNA; the conversion of hydrated electrons into OH radicals in N 2 O‐saturated solution and smaller η RC than η OH values in the case of DNA account for these results. For double‐stranded DNA φ dsb does not depend on I L but increases linearly with the dose, indicating an accumulative effect of two ssb to generate one dsb. The critical distance for this event is 60–85 phosphoric acid diester bonds.