The influence of water content on the 23Na and 31P NMR spectral parameters in solid Na-DNA

23Na and 31P MAS NMR spectra and spin-lattice relaxation times in a solid sample of Na-DNA were measured under very carefully controlled conditions of relative ambient humidity. The observed substantial changes of the NMR parameters are related to the water-induced transitions between the different molecular configurations of DNA, with the transition between A- and B-DNA occurring in the 30-60% range of relative humidity. Our work demonstrates that the previously measured NMR parameters are in error because the relative humidity of the system had not been controlled, rendering the results irreproducible.