Internal motions in deoxyribonucleic acid II.

We have measured the 1H, 31P, and 13C NMR parameters of monodisperse deoxyribonucleic acid (DMA) fragments 260 and 140 base pairs long as a function of temperature and solvent viscosity. On the basis of these measurements, we calculate that within a rodlike DNA helix, the base planes, the deoxyribose sugar, and the sugar-phosphate backbone all experience large fast internal motions. The best fit of the data to a two-state model for internal motion specifies for the internal motions the following amplitudes A and correlation times tau: for the base planes, A = +/-20 degrees and tau = 1 X 10(-9) s; for position 2' of the deoxyribose sugar, A = +/-20 to +/-33 degrees and tau = 1 X 10(-9) s; for the P-H vectors of the sugar-phosphate backbone, A = +/-27 degrees and tau = 2.2 X 10(-9) s.