Geometries and properties of guanine-BH3 complex:: an investigation with density functional theory (DFT) method

Geometries and binding energies are predicted at B3LYP/6-311 + G* level for the guanine-BH3 systems and seven conformers with no imaginary frequencies have been obtained. Single energy calculations using much larger basis sets (6-311 + G(2dfp)) and the analyses for the combining interaction between BH3 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 pi 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 BH3 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. (C) 2004 Elsevier B.V. All rights reserved.