Theoretical evaluation of new nucleic acid bases. Ab initio study on tautomerism of 2,6-diaminopyrimidine (κ-base)

Abstract

Six tautomers of 2,6-diaminopyrimidine have been studied using the ab initio method. All are minima at the HF/3-21G level. The influence of the basis set and electron correlation contributions on the relative energies of the tautomers have been examined. The diamino tautomer 1 is the global minimum. Its energy difference at the MP2/6-31G**//HF/3-21G+ZPE approximation with the two closely lying on the potential energy surface amino-imino and diimino tautomers 2 and 3, amounts to 75 kJ mol −1. The calculated room temperature equilibrium constant for the 1–2 transition of 10 −13 makes κ a proper candidate for the base with reduced probability of spontaneous mutations.