ASSIGNMENTS OF NONEXCHANGEABLE PROTON RESONANCES AND THE SOLUTION STRUCTURES OF D-TGGGT

In this paper, we report the studies of the solution structures of synthetic pentadcoxyribonucleotide d-TGGGT(NH4+ salt) using 2D-NMR. The 1H-NMR experiments with different temperatures and concentrations reveal an equilibrium between single strand and aggregation. In the experimental condition(22-degrees-C, 13mmol/L), the cross peaks in the COSY spectrum are mainly from single strand, and the spin systems of sugar resonances of this component can be assigned. In contrast, the cross peaks in the NOESY spectrum mainly come from aggregation and the sequential assignments of bases, sugar 1', 2' and 2'' protons can be carried out. From NOE connectivities, it is obvious that the aggregation adopts a right-handed helix conformation. It is suggested that the aggregation in our experiment corresponds to the tetramolecular complex.