Novel strategies for sensitivity enhancement in heteronuclear multi-dimensional NMR experiments employing pulsed field gradients

Novel strategies for sensitivity enhancement in heteronuclear multidimensional spectra are introduced and evaluated theoretically and experimentally. It is shown that in 3D sequences employing several Coherence Order Selective Coherence Transfer (COS-CT) steps, enhancement factors of up to 2 can be achieved. This sensitivity enhancement is compatible with the use of heteronuclear gradient echoes, yielding spectra with excellent water suppression. HNCO and HCCH-TOCSY pulse sequences are proposed and experimentally tested. These experiments employ recently developed coherence order selective pulse sequence elements, e.g., COS-INEPT and planar TOCSY for antiphase to in-phase transfers 2F^-S₂↔S^- or in-phaseaCOS-CT for in-phase transfer F^-↔S^-, and the well-known isotropic TOCSY mixing sequences for homo- and heteronuclear in-phase transfer.