Computational investigation of thermochemical properties of non-natural C-nucloebases: Different hydrogen-bonding preferences for non-natural Watson-Crick base pairs

摘要

In the present density functional theory study, we have compared intrinsic properties of non-natural nucleobases (acA, acG, acC, and acT nucleobases) such as proton affinities, gas phase acidities, tautomerization, and hydrogen-bonding properties with those in normal Watson-Crick nucleobases (A, G, C, T nucleobases). The hydrogen-bonding interactions in non-natural and Watson-Crick base pairs were studied at B3LYP/6-311++G (d,p) level regarding their geometries, energies, and topological features of the electron density. The quantum theory of atoms-in-molecule (QTAIM) and natural bond orbital (NBO) analyses were employed to elucidate the interaction characteristics in base pairs. The electron density ρ(r) as well as its Laplacian {2} $ ρ(r) at the hydrogen bond critical point predicted by QTAIM is strongly correlated with hydrogen bond structural parameter and the second-order perturbation energies in NBO scheme. Our results show that most of hydrogen bonds in normal Watson-Crick and non-natural base pairs must be considered as electrostatic interactions. Results of calculations revealed that energetic values of hydrogen bonds in T-A base pair are more than those in ac T-ac A base pair, while values of hydrogen bonds in C-G base pair and ac C-ac G base pair are almost the same. These results confirmed stability order of stabilization energies of these base pairs.