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

In off-resonance rotating-frame Overhauser spectroscopy (OFF-ROESY), spin-d iffusion effects can be suppressed in selected spectral regions by doubly-s elective inversion of the magnetization in the middle of the cross-relaxati on interval, The resulting "quenching of undesirable indirect external trou ble in off-resonance rotating-frame Overhauser effect spectroscopy" (QUIET- OFF-ROESY) experiment yields direct information about cross-relaxation rate s between selected pairs of spins, as if the two-spin subsystems were isola ted from their surroundings. When the cross-relaxation rates of a macromole cule are observed under spin-locked conditions with an effective field tilt ed by an angle 35.3 degrees < theta < 90 degrees with respect to the z-axis of the rotating Frame, the intensity of cross-peaks may be increased if co ntributions due to spin diffusion are suppressed. Applications to a desoxyr ibonucleic acid dodecamer demonstrate that the precision of the determinati on of internuclear distances can be significantly improved if spin diffusio n is quenched.