HETERONUCLEAR CROSS POLARIZATION IN LIQUID-STATE NUCLEAR-MAGNETIC-RESONANCE MISMATCH COMPENSATION AND RELAXATION BEHAVIOR

Nuclear spin dynamics in liquid-state heteronuclear cross-polarization experiments were explored by experiments on di-N-14-labeled histidine in DMSO-d6. Compensation for Hartmann-Hahn mismatch was achieved by simultaneously shifting the phases of both spin-locking fields by pi at intervals short compared to the spin-spin coupling. With rf compensation, slightly more N-15 polarization was achieved than with the conventional selective INEPT scheme. This was attributed to relaxation by slowly fluctuating random fields associated with proton exchange. Theory for the rf mismatch compensation and relaxation behavior of the Hartmann-Hahn method is presented for the case of a heteronuclear 2-spin system.