[Nuclear magnetic resonance study of C--H...O type hydrogen bonds in analogs of nucleic acid base]

Concentration and temperature dependence of nuclear magnetic resonance spectra of 1,3-dimethyluracil (m2 1,3Ura) in organic solvents has been investigated. The results indicate m2 1,3Ura dimer formation via C(6)--H...O hydrogen bond. In addition to that the formation of C--H...O H-bonds between solvent molecules and m2 1,3Ura take place. delta H of C---H...O H-bond formation between chloroform and m2 1,3Ura dimers have the value of about -2.5 and -2.0 kcal/mol, respectively. Interaction energy calculations by atom-atom potential functions for different types of m2 1,3Ura dimers are in good agreement with experimental data. The possible role of C--H...O H-bonds in intermolecular interactions and biological functions of nucleic acids are discussed.