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

Abstract

It was established conformational transformations of the G·C nucleobase pairs, occurring via the mutual rotation of the G and C bases around the intermolecular H-bonds.

Novel mechanisms of the transformations of the G·C base pairs in Watson-Crick and Hoogsteen configurations via the mutual rotations of the bases and proton transfer: A quantum-chemical investigation

“…Equilibrium geometries of the investigated G•C base pairs and transition states (TSs) of their mutual conformational or tautomeric transformations, as well as their harmonic vibrational frequencies have been calculated, using Gaussian'09 program package [32] at the B3LYP/6-311++G(d,p) level of theory [33][34][35][36][37], which approved itself successfully for the calculations of the similar systems and processes and shown acceptable level of accuracy and adequacy of the obtained results [37,38]. A scaling factor that is equal to 0.9668 has been applied in the present work for the correction of the harmonic frequencies for all complexes [30,31,39].…”

“…3. G•C(WC)↔G•C* ↑ (w)/G*•C ↓ (w)/G•C* ↓ (w)/G*•C ↑ (w) [28] and G*•C*(rWC)↔G•C* O2 (rWC)↔G•C* (rw WC )↔G*•C(rw WC )/G* N2 •C(rWC)/G*t N2 •C(rWC)/ G* N2 •C*(rw WC )↔G*•C* O2 (rw WC ), G* t •C* (H)↔G* N7 •C(H)↔G* t •C* O2 (w H )↔G* N7 •C*(w H )/ G* t •C(w H )↔G* t N7 •C*(w H ), G* t •C* (rH)↔G* t N7 •C(rH)/G* t •C* O2 (rw H )↔G* t N7 •C*(rw H )/ G* t •C*(rw H )↔G* N7 •C*(rw H )[29,30] mechanisms , occurring through the intermolecular proton transfer and relative shifting of the bases, which nally lead to the novel biologically important G•C nucleobase pairs in Watson-Crick, Hoogsteen and wobble con gurations, that conformationally interconvert through the mutual rotations of the bases around the intermolecular H-bonds[31].As a result of these comprehensive investigations, it was revealed various novel conformers of the G•C base pair by the participation of the rare tautomers. However, reaction pathways, interconnecting them, have not been widely presented so far.Inthis work we aimed to established conformationally-tautomeric pathways of the interconversion of the different unusual G•C base pairs.…”