HYDROGEN-BONDING AND STACKING OF DNA BASES - A REVIEW OF QUANTUM-CHEMICAL AB-INITIO STUDIES

Ab initio quantum-chemical calculations with inclusion of electron cor relation made since 1994 (such reliable calculations were not feasible before) significantly modified our view on interactions of nucleic ac id bases. These calculations allowed to perform the first reliable com parison of the strength of stacked and hydrogen bonded pairs of nuclei c acid bases, and to characterize the nature of the base-base interact ions. Although hydrogen-bonded complexes of nucleobases are primarily stabilized by the electrostatic interaction, the dispersion attraction is also important. The stacked pairs are stabilized by dispersion att raction, however, the mutual orientation of stacked bases is determine d rather by the electrostatic energy. Some popular theories of stackin g were ruled out: The theory based on attractive interactions of polar exocyclic groups of bases with delocalized electrons of the aromatic rings (Bugg er at, Biopolymers 10, 175 (1971).), and the Pi-Pi interac tions model (C.A. Hunter, J. Mol. Biol. 230, 1025 (1993)). The calcula tions demonstrated that amino groups of nucleobases are very flexible and intrinsically nonplanar, allowing hydrogen-bond-like interactions which are oriented out of the plane of the nucleobase. Many H-bonded D NA base pairs are intrinsically nonplanar. Higher-level ab initio calc ulations provide a unique set of reliable and consistent data for para metrization and verification of empirical potentials. In this article, we present a short survey of the recent calculations, and discuss the ir significance and limitations. This summary is written for readers w hich are not experts in computational quantum chemistry.