Geometries and properties of guanine–BH 3 complex: an investigation with density functional theory (DFT) method

Abstract

Geometries and binding energies are predicted at B3LYP/6-311+G* level for the guanine–BH 3 systems and seven conformers with no imaginary frequencies have been obtained. Single energy calculations using much larger basis sets (6-311+G(2df,p)) and the analyses for the combining interaction between BH 3 and guanine with the theory of atom-in-molecules (AIM) have been performed. The results indicate that four conformers (a)–(d), in which the pyridine-type nitrogen atoms or carbonyl oxygen or nitrogen of amino group offers their lone pair electron to the empty p orbital of born atom, are the stable ones with the stabilization energies of 29.55, 26.10, 21.76 and 18.39 kcal/mol (with BSSE correction), respectively, while the remaining conformers in which the pyrrole-type nitrogen atom or carbon atom offers π electron to the empty p orbital of born atom are fairly unstable. Four of the seven conformers, (a), (c), (d) and (f), exist dihydrogen bonds between guanine and BH 3 fragments and conformer (a), in which pyridine-type nitrogen interacted with boron and two dihydrogen bonds were formed in it according to the analysis from AIM, is the most stable one.