Quantum-chemical investigation of nitrosonium complexes of complementary pair 1-methylcytosine-9-methylguanine

By the method RI-MP2/L1 nitrosonium complexes were explored of 1-methylcytosine and 9-methylguanine, structural analogs of nucleotide bases cytosine and guanine, as well as of their complementary pair. The addition of a nitrosonium cation to the molecules of these compounds and to their pair leads to the formation of various types of nitrosonium complexes (1 eta-3 eta). n-Complexes with the coordination of NO+ cation to nitrogen and oxygen atoms are commonly more feasible in energy as compared with pi-complexes. The complex with cation NO+ coordinated at the oxygen atom of the carbonyl group and N-7 atom of the guanine fragment of the pair corresponds to the global minimum on the potential energy surface. The energy gain at the interaction of nitrosonium complexes of 1-methylcytosine and 9-methylguanine with 9-methylguanine and 1-methylcytosine respectively is usually larger than at the formation of a neutral pair 1-methylcytosine-9-methylguanine.