Watson-Crick Base Pairing between Guanosine and Cytidine Studied by 13C Nuclear Magnetic Resonance Spectroscopy

Article abstract of DOI:10.1021/ja00408a006

Watson-Crick base pairing in dimethyl sulfoxide/methanol (2/1 v/v) between the nucleosides guanosine and cytidine has been studied by carbon -13 nuclear magnetic resonance (13C NMR) spectroscopy at 67.89 MHz.The equilibrium constant for the base pairing complex has been obtained at two different temperatures by a nonlinear least-squares analysis of the experimental shift data for the base carbons, and the enthalpy of interaction has been found to be ca. -3.8 kcal/mol.The analysis furthermore indicates that while base pairing and changes in the syn/anti conformation ratio are independent processes in the case of guanosine, a change from syn to anti conformation occurs simultaneously with the base pairing in the case of cytidine, in agreement with the Watson-Crick base pairing model.As inferred from the results base pairing alters the polarizabilities of the nucleosides.