QUANTUM-CHEMICAL ANALYSIS OF GEOMETRIC AND ENERGETIC CHARACTERISTICS OF HETERO ASSOCIATES m9Ade·m1Ura IN MAIN TAUTOMERIC FORM

Abstract

For the first time, on the quantum-mechanical level of theory MP2/6-311++G(2df,pd)//B3LYP/6-311++G(d,p), a full set of hydrogen (H)-bonded hetero associates m⁹Ade·m¹Ura in the main tautomeric forms consisting of 18 different structures was obtained. Their structural and energetical parameters were characterized and basic physical and chemi­cal characteristics of intermolecular H-bonds that stabilize the investigated complexes were described. It was shown that global minimum of Gibbs free energy corresponds to Hoogsteen pair, after it with a small margin follow Watson–Crick pair, inverse Hoogsteen pair and inverse Watson–Crick pair. It was found that in stabilization of identified hetero associates four types of H-bonds – NH...O, NH...N, CH...O and CH...N are involved. In this case non-canonical CH...O and CH...N bonds show a linear dependence of energy on electron density in the corresponding critical point. Obtained data may be useful for experimental interpretation of the features of non-canonical base pairs association by common methods of spectroscopy, including NMR and vibrational spectroscopy. They are also important for understanding the problem of mutational variability that is caused by formation of non-complementary pairs of nucleotide bases whose role is not clear yet.