INTRA-MOLECULAR WATER BRIDGE BETWEEN THE 2'-OH AND PHOSPHATE GROUPS OF RNA - CYCLIC NUCLEOTIDES AS A MODEL SYSTEM

The investigation of the ’H NMR spectra of cNMPs in aqueous and mixed solvents shows that the 2’-OH proton is protected from exchange with bulk water. In the presence of low salt, 0.05 M, the free energy of stabilization of the 2’-0H is about 1.5 kcal and the activation energy for exchange is about 7 kcal. The protection of the 2’-OH proton against exchange cannot be attributed to an intermolecular association. The ’H NMR results are consistent with there being an intramolecular water bridge between the 2’-OH and the phosphate group. A similar water bridge has been proposed for RNA to explain the ’H NMR results obtained for a variety of RNA samples. The energies determined for the cNMP intramolecular water bridge can be cautiously extended to RNA. © 1979, American Chemical Society. All rights reserved.