th  - 1987 - 51st ENC Conference

MK23
MATER SUPPRESSION TECHNIQUES FOR THE GENERATION OF PURE PHASE
TWO-DIMENSIONALNMR SPECTRA
Vladlmlr Sklenar* and Ad Bax*
Laboratory of Chemical Physics, Natlonal Institute of Diabetes
Digestive and Kidney Diseases, National Institutes of Health
Bethesda,MD.20892
A number of different approaches has been proposed for suppression of
the intense H20 resonance in 2D NMR spectra of biological compounds. Most
commonly one employs presaturatlon of the H~O resonance using a low power
irradiation prior to the observation pulse. The main disadvantage of this
method is that resonances of exchangeable protons may also be saturated.
Selective excitation using pulse sequences which have a null at the water
resonance avoids this problem. A large variety of different excitation
schemes has been designed in recent years. However, all but the slmplest
90x-T-90_x sequence yield spectra that require a large linear phase
correction. The baseline roll that result from such a phase correction can
lead to intense artifacts in phase sensitive 2D NMR spectra.
A new approach is described for water suppression in one- and
two-dlmensional NMRwhlch generates pure absorptive spectra that are free
of baseline dlstorslons. This method involves the use of a 90x-~-90_x
hard pulse as a read pulse followed by a 90~-k~-90.~ refocusing pulse
which is phase cycled for obtaining the highest possible water
suppression. Incorporation into several of the most popular 2D NHR
experiments (NOESY, HOHAHA, ROESY, HMQC and COSY) is discussed in detail.
Examples of this approach for selective water suppression are demonstrated
by recording the 2D spectra of the decapeptide LH-RH and the Dickerson
dodecamer in 90% H20.