Oxygen uptake in the radiolysis of aqueous solutions of nucleic acids and their constituents.

Abstract

The 60Co-gamma-irradiation of organic compounds in oxygenated aqueous solution leads to consumption of oxygen. G (O2 uptake) have been measured for 27 compounds in N2O/O2 (4:1)- saturated solutions using an oxygen sensitive electrode. G (O2 uptake) (in brackets, measured at 20 degrees C and a dose rate of 0.4 Gy s-1) for isopropanol (3.0), sodium formate (3.0), D-glucose (3.2), 2-deoxy-D-ribose (3.0), t-butanol (4.2) and diethyl ether (4.5) were found to be in agreement with th expectation based on product yields and/or known mechanisms. High O2 uptake was observed with polyethyleneoxide (10.2), which increases with decreasing dose rate and/or increasing temperature (G(O2 uptake) = 40 at 0.04 Gy s-1 and 50 degrees C). These results are explained by assuming a chain reaction. The nucleotides 5'-thymidylic acid (4.4), 5'-deoxy-cytidylic acid (4.8), 5'-deoxyadenylic acid (1.9) and 5'-deoxyguanylic acid (1.6) show that the pyrimidine derivatives consume considerably more oxygen than the purine derivatives. Analogous results are obtained with the nucleobases and nucleosides. The pyrimidine-purine difference is even more pronounced in the corresponding polymer, poly U (21) and poly A (3.5). The large value of poly U shows that a significant contribution of a chain reaction is present. G(O2 uptake) for DNA are dose-rate, temperature and concentration-dependent. The O2 uptake for single-stranded DNA (6.8) and double-stranded DNA (4.6) is higher than for an equivalent mixture of nucleotides (3.2). These results indicate that in DNA also a short chain reaction takes place.