Determination of internuclear distances by suppressing spin diffusion in rotating-frame Overhauser measurements

In off-resonance rotating-frame Overhauser spectroscopy (OFF-ROESY), spin-diffusion effects can be suppressed in selected spectral regions by doubly-selective inversion of the magnetization in the middle of the cross-relaxation interval. The resulting quenching of undesirable indirect external trouble in off-resonance rotating-frame Overhauser effect spectroscopy (QUIET-OFF-ROESY) expt. yields direct information about cross-relaxation rates between selected pairs of spins, as if the two-spin subsystems were isolated from their surroundings. When the cross-relaxation rates of a macromol. are obsd. under spin-locked conditions with an effective field tilted by an angle 35.3 Deg < q < 90 Deg with respect to the z-axis of the rotating frame, the intensity of cross-peaks may be increased if contributions due to spin diffusion are suppressed. Applications to a desoxyribonucleic acid dodecamer demonstrate that the precision of the detn. of internuclear distances can be significantly improved if spin diffusion is quenched. [on SciFinder (R)]