Use of a water flip-back pulse in the homonuclear NOESY experiment.
A simple modification to the WATERGATE water suppression scheme [Piotto, M., Saudek, V. and Sklenář, V. (1992) J. Biomol. NMR, 2, 661-665] is proposed. Radiation damping is used as an active element during the mixing time of a NOESY experiment, in order to obtain a reproducable state of the water magnetization at the end of the mixing time. Through the use of a water flip-back pulse and a gradient-tailored excitation scheme, we obtain both an excellent water suppression and a water magnetization close to equilibrium at the beginning of the acquisition time. We show experimentally that this modification results in a 20% gain in intensity for all signals when using a relaxation delay of 1.5 s, and also that avoiding a semisaturated state for the water magnetization allows the amide protons as well as other proton resonances to relax to equilibrium with their proper relaxation time.
CNRS URA 1309, Institut Pasteur de Lille, F-59000, Lille, France.
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Lippens
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Dhalluin
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Wieruszeski