Biopolymers and cell. 1997; 13 (3): 185 - 190

To Ihe question of laulomerism of nucleic acid bases

A. I. Boldeskul, L. F. Sukhodub

The taulotnerism of nucleic acids bases was investigated by semi-empirical method MNDO/H with optimization of all structural parameters. Utilization of MNDO method in similar investigations is fully justified, since the obtained calculated data are in good agreement with the experimental ones. Besides «classical» keto-amine tautomcric forms of the bases, there is the possibility of realization of isolated and paired liquid enole or imine forms in gaseous phase. Enole tautomer of guanine, for example, appeared 7.2 kcal/mol more preferable that keto-amine form, and O(4) enole tautomer of thy mine is 0.6 kcal/mol more preferable than dike-toform. The conclusion was drawn on the bases of proton-acceptor ability of nitrous bases that for the molecules of nitrous bases there is t/ie preference of thermodynamic control over the protonation of nucteophilic centres represented by O(2) cytozine, O(4) thymine, N(l), N(3) adenine and N(7) guanine