Structure and redox properties of one-electron oxidized radicals from adenine and derivatives

The reaction of sulphate radical anion (SO(4•-)) with adenine and its derivatives results in the formation of a neutral radical at pH 7, whose spin distribution and hence the oxidizing properties are strongly dependent on the position and nature of the substituents. This reaction proceeds by one electron transfer, followed by rapid deprotonation of the incipient radical cation, the sequence of these reactions being equivalent to hydrogen abstraction. In adenine radical cation, deprotonation was found to occur either from N(6)-H or N(9)-H, leading to the formation of a strong and a less oxidizing radical, respectively. Among adenine derivatives, adenosine was shown to give rise to the most oxidizing neutral radical, whilst the least oxidizing radical was formed from N(6),N(6)-dimethyladenine.