Novel mechanisms of the conformational transformations of the biologically important G·C nucleobase pairs in Watson-Crick, Hoogsteen and wobble configurations the mutual rotations of the bases around the intermolecular H-bonds: a QM/QTAIM study.

At the MP2/6-311++G(2df,pd)//B3LYP/6-311++G(d,p) level of quantum-mechanical theory, we provide for the first time a comprehensive investigation of the physico-chemical mechanisms of the 55 conformational transformations of the biologically-important G·C nucleobase pairs - Watson-Crick (WC), reverse Watson-Crick (rWC), Hoogsteen (H), reverse Hoogsteen (rH), wobble (w) and reverse wobble (rw) base pairs by the participation of the G and C bases in the canonical and rare tautomeric forms ("r" - means reverse configuration of the base pair). It was established that all these G·C nucleobase pairs can conformationally transform into each other without the changing of the tautomeric status of the G and C bases. These transitions occur through significantly non-planar transition states the mutual rotation of the G and C bases relative to each other within the G·C nucleobase pair around the upper, middle or lower intermolecular H-bonds: WC ↔ rWC, WC ↔ rw, rWC ↔ WC, rWC ↔ w, w ↔ rw, H ↔ rH, H ↔ rw, rH ↔ H, rH ↔ w, w ↔ rw.

Atomistic mechanisms of the tautomerization of the G·C base pairs through the proton transfer: quantum-chemical survey.

This study is devoted to the investigation of the G·C*(WC)↔G*·C*(WC), G·C*(WC)↔G*·C*(WC) and G*·C*(WC)↔G*·C(w) tautomerization reactions occurring through the proton transfer, obtained at the MP2/6-311++G(2df,pd)//B3LYP/6-311++G(d,p) level of theory in gas phase under normal conditions ('WC' means base pair in Watson-Crick configuration, T=298.15 K). These reactions lead to the formation of the G*·C*(WC), G*·C*(WC) and G*·C(w) base pairs by the participation of the G* base with NH group.

A Quantum-Mechanical Looking Behind the Scene of the Classic G·C Nucleobase Pairs Tautomerization.

For the first time, at the MP2/6-311++G(2df,pd)//B3LYP/6-311++G(d,p) level of theory, a comprehensive quantum-mechanical investigation of the physico-chemical mechanism of the tautomeric wobblization of the four biologically-important G·C nucleobase pairs by the participation of the monomers in rare, in particular mutagenic, tautomeric forms (marked with an asterisk) was provided. These novel tautomeric transformations (wobblization or shifting of the bases within the pair) are intrinsically inherent properties of the G·C nucleobase pairs. In this study, we have obtained intriguing results, lying far beyond the existing representations.