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Unexpected A·T(WC)↔A·T(rWC)/A·T(rH) and A·T(H)↔A·T(rH)/A·T(rWC) conformational transitions between the classical A·T DNA base pairs: A QM/QTAIM comprehensive study

2018; Wiley; Volume: 118; Issue: 18 Linguagem: Inglês

10.1002/qua.25692

1097-461X

Ol’ha O. Brovarets’, Kostiantyn S. Tsiupa, Dmytro М. Hovorun,

Metal complexes synthesis and properties

Abstract In this study, using QM/QTAIM calculations in the continuum with ε = 1 under normal conditions, we have revealed for the first time the nondissociative A·T(WC)↔A·T(rWC)/A·T(rH) and A·T(H)↔A·T(rH)/A·T(rWC) conformational transitions. It was established that they proceed via the essentially nonplanar transition states (С 1 symmetry) through the intermediates, which are wobbled conformers (С 1 symmetry) theoretically predicted in our previous work (Brovarets’ et al., Frontiers in Chemistry , 2018, 6:8, 10.3389/fchem.2018.00008) of the classical А·Т DNA base pairs—Watson–Crick А·Т(WC), reverse Watson–Crick А·Т(rWC), Hoogsteen А·Т(Н) and reverse Hoogsteen А·Т(rН). At this, the A·T(H)↔A·T(rWC) and A·T(WC)↔A·T(rH) conformational transformations are controlled by the transition states (TSs) stabilized by the participation of the intermolecular (T)N3H···N6(A) H‐bond (∼3.70 kcal·mol −1 ) between the imino group N3H of T and pyramidilized amino group N6H 2 of A. Gibbs free energies of activation for these processes consist 12.22 and 11.11 kcal·mol −1 , accordingly, under normal conditions. TSs, which control the A·T(WC)↔A·T(rWC) and A·T(H)↔A·T(rH) conformational transitions are stabilized by the participation of the intermolecular (T)N3H···N6(A) H‐bond (5.82 kcal·mol −1 ) and bifurcating intermolecular (T)N3H···N6(A) (5.00) and (T)N3H···N7(A) (0.61 kcal·mol −1 ) H‐bonds, accordingly. Notably, in these two TSs amino group N6H 2 of A is significantly pyramidilized; Gibbs free energies of activation for these reactions are 19.07 and 19.71 kcal·mol −1 , accordingly.