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A7Li and 133Cs NMR relaxation study of macroscopically oriented hydrated Li- and Cs-DNA fibers at three different magnetic fields is presented. Two-dimensional quadrupolarecho and spin-echo techniques were used to determine the homogeneous linewidths free from the broadening due to magnetic field inhomogeneity and to a small distribution of the orientation of DNA helix axes. The relaxation rates obtained show the presence of quadrupolar, dipolar, and paramagnetic relaxation processes in Li-DNA. The separation of these relaxation contributions was made by studying H2O/ D2O exchanged samples and (for Li-DNA) 6Li relaxation. For Cs-DNA, the dipolar and paramagnetic contributions are negligible, but relaxation caused by site-exchange modulation of the Cs chemical shift can be observed. The observed relaxation behavior of the two ions is interpreted in terms of two molecular motions on different time scales.

Quadrupolar ion NMR splittings and self-diffusion of {sup 7}Li{sup +} (I = 3/2) ions have been studied in macroscopically oriented Li-(B)DNA fibers. The {sup 7}Li splittings were measured with a double quantum filter pulse sequence, followed by subsequent fitting of the out-of-phase doublet spectrum. Lithium(I) self-diffusion was measured with the pulsed field gradient NMR spin-echo method. Diffusion was found to be restricted in both the parallel and perpendicular direction with respect to the fiber axis.

The nuclear spin relaxation in isotropic spin systems with I = 3 2 , I = 5 2 , and I = 7 2 in the nonextreme narrowing regime is analyzed. The effect of the higher rank multipoles (rank ⩾3) of the spin density operator on a 180°-τi-Θ pulse experiment is twofold. The recorded NMR lineshape is τ1 and φ dependent. The multiexponentiality of the spin-lattice relaxation may be exaggerated by recording the amplitudes of the Lorentzian-like signals, instead of the full integrated signal. The influence of the detection pulse angle φ is discussed and we suggest that by choosing the detection angle φ = 63° the effects of the higher multipoles may be diminished.

133Cs NMR spectra of macroscopically oriented CsDNA are reported. The quadrupolar splitting measured as a function of the orientation of the sample in the magnetic field is in agreement with the predictions for an uniaxial system. The order-selective multiple-quantum NMR spectra for the I = 7 2 133 Cs nucleus are also reported.