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) experiment 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 macromolecule are observed under spin-locked conditions with an effective field tilted by an angle 35.3° < 6 < 90° with respect to thez-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 determination of internuclear distances can be significantly improved if spin diffusion is quenched.