IMPROVED HMQC-TYPE AND HSQC-TYPE 1D SPECTRA USING PULSED-FIELD GRADIENTS

A family of 1D methods are described using a combination of HSQC-type (or HMQC-type) heteronuclear preparation blocks with homonuclear trans fer schemes, such as COSY, n-step RELAY, TOCSY, ROESY, and NOESY, in o rder to reveal direct or long-range heteronuclear connectivities, as w ell as relayed (scalar or dipolar) interproton connectivities. Two ess ential features of this approach are: (i) selective carbon excitation simultaneous with a proton spin-lock period, to avoid dephasing during the selective carbon pulse length; and (ii) coherence selection by pu lsed field gradients of the desired coherences, to improve time perfor mance and get cleaner spectra devoid of artifacts usually produced by imperfect subtraction when using phase-cycling methods. The resulting high-quality 1D spectra allow the easy extraction of accurate values f or the relevant homo- and heteronuclear coupling constants. This appro ach is particularly useful when strongly overlapped proton systems pre vent the application of conventional 1D experiments based on proton-se lective excitation, Results are presented for sucrose. (C) 1995 Academ ic Press, Inc.