H-BONDING IN DNA BASE PAIRS

Pavel Hobza

J. Heyrovsky Institute of Physical Chemistry Academy of Scinces of the Czech Republic, 182 23 Prague 8, Czech Republic

Structure, energetics, harmonic vibratrional frequencies and thermodynamical characteristics of more than 40 H-bonded nucleic acid base pairs were studied using nonempirical ab initio method covering important part of correlation energy. Applicability of lower-level theoretical approaches (semiempirical methods of quantum chemistry and empirical potentials) was studied. Validity of harmonic approximation was investigated in the case of adenine...thymine Watson-Crick base pair. Formation of C=O...H-N and N-H...N H-bonds in the base pairs is accompanied by significant elongation of X-H bond length and red shift of the respective X-H stretching frequency. These evidences were not found in the case of C-H...X contacts, and different mechanism of stabilization of these contacts was suggested.