The Studies of 31P NMR of Nucleic Acids and Nucleic Acid Complexes*
With the advent of high resolution nuclear magnetic resonance (NMR) spectrometers, investigation of phosphorus nuclei of nucleic acids by 31P NMR spectroscopy has become feasible and popular. While the intensive activity in 31P NMR research can well testify to the usefulness and significance of this method, the major difficulty in 31P NMR research on nucleic acids is that the unambiguous assignment of each 31P resonance to an individual phosphorus nucleus in the oligonucleotide is often unattainable. A nonlinear chemical shift vs. temperature profile was observed for two pentanucleotides, d-CTTGG and d-CCAAT. In the concentration dependent studies, when the oligomer was diluted 10 to 20-fold, such a nonlinear property vanished and the chemical shift vs. temperature curves become nearly a straight line again. Gorenstein and co-workers 15-18 have proposed that phosphate ester 31P chemical shifts are primarily determined by the ester torsional conformation, which are directly related to phosphate-oxygen bond angles.