STRAND BREAKAGE IN POLY(C), POLY(A), SINGLE‐AND DOUBLE‐STRANDED DNA INDUCED BY NANOSECOND LASER EXCITATION AT 193 nm*

Publisher Website
Google Scholar
Abstract
Abstract—Single‐ and double‐stranded calf thymus DNA and two polynucleotides (0.4 mM) 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 (IL) in the range (0.2–3) × 106W cm‐2. The quantum yields of formation of hydrated electrons (φe‐) and ssb and dsb (φSSband φdsb) are therefore independent ofIL. In contrast, under 248 nm excitation these quantum yields increase linearly withILunder otherwise comparable conditions. Nevertheless, several effects and mechanistic implications are analogous using Λexc= 193 and 248 nm. For polycytidylic acid, poly(C), in Ar‐saturated solution for example, the efficiency of ssb per radical cation (ηRC=φssb/φe‐) is similar to the efficiency of ssb per OH radical (ηOH). For polyadenylic acid, poly(A), and single‐ and double‐stranded DNA ηRC(Λexc= 193 nm) is significantly smaller than ηOH. The ratio φssb(N2O)/φssb(Ar) is =2 for poly(C), =4 for poly(A) and =10 for DNA; the conversion of hydrated electrons into OH radicals in N2O‐saturated solution and smaller ηRCthan ηOHvalues in the case of DNA account for these results. For double‐stranded DNA φdsbdoes not depend onILbut 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.

This publication has 61 references indexed in Scilit: