Novel Pulse Sequences with Sensitivity Enhancement for In-phase Coherence Transfer Employing Pulsed Field Gradients

Novel pulse sequences for in-phase coherence order selective coherence transfer (ICOS-CT) S^- → F^- in an I_nS spin system employing heteronuclear gradient echos are introduced and evaluated in theory and experiment, It is shown that the heteronuclear isotropic mixing Hamiltonian H^iso = (2πJ/3)(F_zS_z + F_xS_x + F_yS_y) or successive bilinear rotations along the x, y, and z axes achieve ICOS-CT, In the absence of homonuclear S couplings, the heteronuclear isotropic mixing performs best with respect to sensitivity for all multiplicities, In the presence of homonuclear S couplings, however, two pulse sequences based on successive bilinear rotations, yxz-ICOS-CT and xyz-ICOS-CT, represent the optimum, These sequences were tested experimentally on a ¹³C-labeled protein and an unlabeled peptide, The performance of the two sequences is comparable, with a slight advantage for the yxz-ICOS-CT sequence.