FORMATION OF H-addition radicals in adenine derivatives: part II

The formation of H-addition radicals in monocrystals of adenosine, adenosine-HCl, adenine-HCl-1/2H2O, and adenine-2 HCl by X-irradiation has been st-died by using electron spin resonance spectroscopy at 9.5 GHz and at 35 GHz. In all crystals, both H-addition radicals at position C2 and at position C8 were observed. The coupling constants of these two H-addition radicals are different and depend strongly on the protonation state of the adenine base. INDO calculations reproduce well the observed trends of the coupling constants. It is shown that the C2-addition radical is transformed into the C8-addition radical by heat and vice versa the C8-addition into the C2-addition by light of lambda greater than 360 nm.