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 InS spin system employing heteronu clear gradient echos are introduced and evaluated in theory and experi ment, It is shown that the heteronuclear isotropic mixing Hamiltonian H-iso = (2 pi J/3)(FzSz + FxSx + FySy) or successive bilinear rotation s along the x, y, and z axes achieve ICOS-CT, In the absence of homonu clear S couplings, the heteronuclear isotropic mixing performs best wi th respect to sensitivity for all multiplicities, In the presence of h omonuclear S couplings, however, two pulse sequences based on successi ve bilinear rotations, yxz-ICOS-CT and xyz-ICOS-CT, represent the opti mum, These sequences were tested experimentally on a C-13-labeled prot ein and an unlabeled peptide, The performance of the two sequences is comparable, with a slight advantage for the yxz-ICOS-CT sequence. (C) 1995 Academic Press, Inc.