On the affinity of cytosine towards electrophiles

Abstract

Ab initio SCF computations on the intrinsic preferences of the H+, CH3+ and C2H5+ cations towards the two principal sites of protonation or alkylation on cytosine, N3 or O2, show that this preference undergoes a continuous modification with the increase in size and complexity of the cation. N3 is the preferred site of fixation of H+, O2 the preferred site of C2H5+, while CH3+ has no marked preference. The exchange repulsion term of the binding energy appears responsible for the preference of C2H5+ for O2.