Ultraviolet Difference Spectral Studies in the γ-radiolysis of DNA and Model Compounds. II. Oxygen and Temperature Dependence in Adenine Radiation Chemistry

Abstract

Ultraviolet difference spectra between gamma-irradiated and unirradiated aqueous solutions of oxygenated adenine reveal spectral maxima at 224, 286 and 360 nm, and suggest the existence of multiple radiation products. The presence of long-wavelength absorbing products implies the extension of the conjugation of the adenine ring. The product absorbing at 360 nm appears only in the presence of oxygen, with its yield dependent on both oxygen concentration and temperature. The absorbance peak at 360 nm in the UV difference spectra appears to demonstrate simple first-order decay kinetics, with a half-life of 50 min at 3 degrees C. At temperatures below 23 degrees C relative yields of the radiation products are approximately constant, suggesting a common mechanism. Higher temperatures apparently induce a mechanistic alteration. Since the temperature during and subsequent to irradiation, as well as the oxygen concentration of the solution, affects the absolute yields and distribution of the radiation products, great care must be exercised in controlling these variables.