SIGNIFICANT STRUCTURAL DEFORMATION OF NUCLEIC-ACID BASES IN STACKED BASE-PAIRS - AN AB-INITIO STUDY BEYOND HARTREE-FOCK

Stacked structures of the uracil, thiouracil and cytosine dimers, aden ine-uracil and uracil-cytosine pairs were investigated by gradient opt imization at the ab initio second-order Moller-Plesset correlated leve l. The aromatic rings of bases and exocyclic groups were significantly distorted from planarity upon complexation. Nevertheless, the stabili zation energies were similar to those obtained previously with rigid m onomers, because the non-negligible improvement in intermolecular stab ilization energy is compensated for by the deformation energies of the bases. The largest distortions were found for uracil. Deformation of uracil rings leads to the formation of intermolecular H-bonds and impr oves the stabilization energy. (C) 1998 Elsevier Science B.V. All righ ts reserved.