Resumen

MADARIAGA, SANDRA T; CONTRERAS, J.GUILLERMO  y  SEGUEL, C.GLORIA. INTERACTION ENERGIES IN NON WATSON-CRICK PAIRS: AN AB INITIO STUDY OF G·U AND U·U PAIRS. J. Chil. Chem. Soc. [online]. 2005, vol.50, n.1, pp. 435-438. ISSN 0717-9707.  doi: 10.4067/S0717-97072005000100013.

Ab initio calculations at the MP2/6-31G^** level have been carried out on the non-Watson-Crick nucleic acids pairs G·U and U·U to obtain the interaction energies and to see whether the derived values are comparable or not with the canonical G-C, A-T and A-U pairs. Optimized geometries of the pairs show that the structural parameters of the isolated bases differ very little on pairing. The guanine -NH₂ group does not participate in the hydrogen bonding formation and possesses a pyramidal structure; its intrinsic nonplanarity plays an important role in the out-of-plane intermolecular interactions. Thus, the G·U pair projects three hydrogen bonding acceptor sites, namely, N7(G), O6(G) and O4(U) to the RNA major groove. The interaction energy (DH^o_int) calculated for the G·U pair (-13.6 kcal/mol) is comparable to that determined for A-T (-13.0 kcal/mol), but considerable smaller than the experimental value reported for G-C (-21.0 kcal/mol). The U·U pair follows the trend that pairing between pyrimidines bases should have lower interacting energies than purine-pyrimidine pairs

Palabras clave : Ab initio; interaction energies; G·U; ·U pairs.