Correlating the 31P NMR chemical shielding tensor and the 2J(P,C) spin-spin coupling constants with torsion angles ζ and α in the backbone of nucleic acids.

Determination of nucleic acid (NA) structure with NMR spectroscopy is limited by the lack of restraints on conformation of NA phosphate. In this work, the 31P chemical shielding tensor, the ΓP,C5′H5′1 and ΓP,C5′H5′2 cross-correlated relaxation rates, and the 2JP,C3′, 2JP,C5′, and 3JP,C4′ coupling constants were calculated in dependence on NA backbone torsion angles ζ and α. While the orientation of the 31P chemical shielding tensor was almost independent of the NA phosphate conformation, the principal tensor components varied by up to ∼40 ppm. This variation and the dependence of the phosphate geometry on torsion angles ζ and α had only a minor influence on the calculated ΓP,C5′H5′1 and ΓP,C5′H5′2 cross-correlated relaxation rates, and therefore, the so-called rigid tensor approximation was here validated. For the first time, the 2JP,C spin–spin coupling constants were correlated with the conformation of NA phosphate. Although each of the two J-couplings was significantly modulated by both torsions ζ and ...