Dynamic behavior of the imino protons of the gamma OR3 17mer in H2O solution studied by high-resolution NMR

The imino proton resonances of gamma OR3 17mer in water were observed at 500 MHz with the time-shared Redfield pulse train. All of the 17 imino proton resonances could be assigned specifically to individual base pairs by utilizing the trace of NOE connectivities between the imino and adenine C2H protons and between imino protons themselves. AT1 and 17 showed abnormally high chemical shifts in comparison with the other AT pairs. On raising the temperature, broadening of the signal occurred in a sequential manner from the terminals except for AT10 and AT11, which were broadened at a lower temperature than GC12. The relaxation rates of the imino protons were measured by the inversion recovery method. The rates at higher temperatures represent the exchange rates of the imino protons. From the temperature dependences, activation energies of about 15 kcal/mol for the AT imino protons and 23-26 kcal/mol for the GC imino protons were obtained.