The dependence of 31P NMR shielding of phosphate group on its structural flexibility; towards accurate structural interpretation of 31P NMR shift in nucleic acids

Abstract

Theoretical calculations can nowadays assist in structural interpretations of NMR spectra. This applies particularly for the δ(31P) NMR shifts of phosphate group in nucleic acids where the shift magnitudes typically range only 2-4 ppm.

The DFT calculations including effect of molecular dynamic were used for interpretation of δ(31P) in two chemically similar molecules with different flexibility of phosphate (Fig. 1). Accurate and computationally affordable method for calculation of δ(31P) is presented.

The δ(31P) calculated employing explicit MD snapshot geometries was compared with δ(31P) calculated as adiabatically averaged δ(31P)-surface with MD-distribution of related geometric coordinates (Table 2). The later approach is computationally less demanding and the benchmark calculations for highly flexible diethyl phosphate (DEP) and locked cyclic phosphate (cDEP) illustrated that the method should be applicable for theoretical modelling of δ(31P) NMR spectra of DNA oligonucleotides that is currently ongoing.