see designations in Table 2

theory in vacuum #

Conversion Δ∆GTS,

The time necessary to reach 99.9% of the equilibrium concentration of mutagenic tautomer in the system (τ99.9%) for these barriers falls within the range 3.8410-8 ÷ 2.1310-4 s, which is by orders smaller, except Cyt, than the time of an elementary act of one base pair replication (*ca.* 4·10-4 s). The barriers for the reverse reactions lead to a half-lifetime of about 10-9 s, and tunneling effects will further facilitate the reverse process. So, complexes "mutagenic tautomer-water" produced in the DPT process represent unstable intermediates, which quickly converted back into the complexes "canonical tautomer-water" in the time scale of the nucleotide-water interaction. However, if the dissociation of the water from the tautomerized complex occurs, the mutagenic tautomer would be a long-lived species, as the barrier for the reverse conversion to canonical tautomer is more than *ca.* 27 kcal/mol (see Table 2). It should be noted that electronic energy of the dissociation of the Ade\*·H2O and Thy\*·H2O complexes (Table 5) are lower than the corresponding reverse barriers. So, it can mean that these complexes more probably decay to the mutagenic tautomers and water molecule. To the contrary, in the case of Gua and Cyt – the Gua\*·H2O and Cyt\*·H2O transition to the complexes involving canonical tautomers will be more probable than the decay of the tautomerized complexes. Following the electronic energies of the interaction between bases and molecules of water, we could conclude that transition to the complexes containing mutagenic tautomers of Ade and Thy isn't preferential as they have larger electronic energies of the interaction that complicates their dissociation into mutagenic tautomers (Table 5). Interaction energy of the DNA bases with water is less than the energy of interaction with the complementary bases. So, the nucleotide bases competing with water for binding will displace water to the periphery of the interaction interface.

