Theoretical study on the alkylation and protonation of the nucleic acid bases

Protonation and alkylation by H+, CH3+ and C2H5+ of nucleic acid bases (cytosine, thymine, uracil, adenine and guanine) have been studied. Different theoretical approaches, namely semi-empirical MINDO/3 and ab initio calculations, have been compared, together with experimental values. The necessity of supermolecular approach to the study of alkylation is indicated. It is also shown that changes of size of attacking agents cause considerable changes in the order of affinities of the target sites and consequences in the mutagenic and carcinogenic processes can be expected.