STUDIES OF CONFORMATION AND INTERACTION IN DINUCLEOSIDE MONO- AND DIPHOSPHATES BY PROTON MAGNETIC RESONANCE

Proton magnetic resonance data (100 Mc) on 15 nucleosides and nucleotides and on 25 dinucleoside mono- and diphosphates (23 (3′-5′)-ribosyl dimers, TpT, and (2′-5′)-ApC) are reported. The data consist of the chemical shifts, the peak assignments, the line widths, and the coupling constants of all the base protons and the H-1′ protons, observed at two temperatures, 28-30 and 60°, and at varying concentrations in D2O. These data were analyzed on the basis of two basic guide lines established in studies on the monomers, i.e., the shielding effect of the ring current on the neighboring bases and the specific deshielding effect of the 5′-phosphate on the H-8 proton of purine nucleotides and the H-6 proton of the pyrimidine nucleotides. From these studies, a general conformational model for all the dimers is constructed. In this model the nucleosidyl units all have the anti conformation with respect to the sugar-base torsion angle, and the turn of the (3′-5′) screw axis of the stack is right handed. The general features of this model derived mainly from the data from the ribosyl dimers are similar to those of the single strand in the DNA helix. Within the temperature range of 30-60°, no major change in the ribose conformation or the sugar-base torsion angle of the dimer can be detected. The data suggest that the main effect of temperature elevation on the conformation of the dimer probably comes from the rotation of the phosphorus-oxygen bond (-P-O-) in the ester linkage. © 1969, American Chemical Society. All rights reserved.