QUANTUM-CHEMICAL INVESTIGATION OF TAUTOMERIZATION WAYS
OF WATSON-CRICK DNA BASE PAIR GUANINE?CYTOSINE
Institute of Molecular Biology and Genetics, National Academy of Sciences of Ukraine, Kyiv;
Institute of High Technologies of Taras Shevchenko Kyiv National University, Ukraine;
A novel physico-chemical mechanism of the Watson-Crick DNA base pair Gua·Cyt tautomerization Gua·Cyt*?Gua·Cyt?Gua*·Cyt (mutagenic tautomers of bases are marked by asterisks) have been revealed and realized in a pathway of single proton transfer through two mutual isoenergetic transition states with Gibbs free energy of activation 30.4 and 30.6 kcal/mol and they are ion pairs stabilized by three (N2H…N3, N1H…N4– and O6+H…N4–) and five (N2H…O2, N1H…O2, N1H…N3, O6+H…N4– and O6+H…N4–) H-bonds accordingly. Stable base pairs Gua·Cyt* and Gua*·Cyt which dissociate comparably easy into monomers have acceptable relative Gibbs energies – 12.9 and 14.3 kcal/mol – for the explanation of the nature of the spontaneous transitions of DNA replication. Results are obtained at the MP2/6-311++G(2df,pd)//B3LYP/6-311++G(d,p) level of theory in vacuum approach.
Key words: spontaneous point mutations of DNA replication, transitions, mutagenic tautomers of DNA bases, mispairs, transition state, intermolecular hydrogen bonds, analysis of the electron density topology, DFT.
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