Temperature dependence of the phosphorus-31 chemical shifts of nucleic acids. A probe of phosphate ester torsional conformations

Abstract

The temperature dependence of the 31P chemical shifts of the ribodinucleoside monophosphates, ApA, GpC, CpC, UpU and ApU, of the deoxyribonucleic acids, d-ApT, TpT, d-ApA and d-pApT, and of the homopolyribonucleic acids poly(G), poly(U), poly(C) and poly(A) provides information on the helix-coil transition in nucleic acids. The base stacked, helical structure with a gauche, gauche phosphate ester torsional conformation is 0.2-0.6 ppm upfield from the random coil conformation. The 31P chemical shifts of dimethyl and diethyl phosphate do not change significantly with temperature. These results support an earlier hypothesis that 31P shifts are sensitive probes of torsional conformations with phosphate esters in gauche,gauche conformations having 31P shifts upfield from non-gauche conformations.