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.