Biopolymers and Cell. 2011; 27(3): 221-230
INTRAMOLECULAR TAUTOMERIZATION AND THE CONFORMATIONAL VARIABILITY OF SOME CLASSICAL MUTAGENS – CYTOSINE DERIVATIVES: QUANTUM CHEMICAL STUDY
O. O. Brovarets’1, 2, D. M. Hovorun1, 2
1Institute of Molecular Biology and Genetics, NAS of Ukraine
150, Akademika Zabolotnogo Str., Kyiv, Ukraine, 03680
2Institute of High Technologies, Taras Shevchenko National University of Kyiv
2, korp.5, Pr. Akademika Hlushkova, Kyiv, Ukraine, 03127
Aim. To determine the lifetime of the mutagenic cytosine derivatives through the investigation of the physicochemical mechanisms of their intramolecular proton transfer. Methods. Non-empirical quantum chemistry, the analysis of the electron density by means of Bader’s atoms in molecules (AIM) theory and physicochemical kinetics were used. Results. It is shown that the modification of all investigated compounds, except DCyt, prevents their pairing in both mutagenic and canonical tautomeric forms with a base which is an interacting partner. This effect can inhibit their mutagenic potential. It is also established that Watson-Crick tautomeric hypothesis can be formally expanded for the investigated molecules so far as a lifetime of the mutagenic tautomers much more exceeds characteristic time for the incorporation of one nucleotides pair by DNA biosynthesis machinery. It seems that just within the frame of this hypothesis it will be possible to give an adequate explanation of the mechanisms of mutagenic action of N4-aminocytosine, N4-methoxycytosine, N4-hydroxycytosine and N4dehydrocytosine, which have much more energy advantageous imino form in comparison with amino form. Conclusions. For the first time the comprehensive conformational analysis of a number of classical mutagens, namely cytosine derivatives, has been performed using the methods of non-empirical quantum chemistry at the MP2/6-311++G (2df,pd)//B3LYP/6-311++G(d,p) level of theory.
Keywords: point mutations of DNA, derivatives of cytosine, intramolecular tautomerization, Gibbs energy of activation, structural non-rigidity, analysis of the electron density topology.