th  - 1987 - 51st ENC Conference

MK37
IMPROVEMENT OF INVERSE CORRELATION EXPERIMENTS BY SHAPED PULSES
W. Bermel* a), C. Griesinger* b) , S. Steuernagel c),
K. Wagner c), H. Kessler c).
a) Bruker Analytische Messtechnik GmbH, Silberstreifen,
D-7512 Rheinstetten 4, West Germany
b) Laboratorium fur physikalische Chemie, ETH-Zentrum,
CH-8Og2 ZUrich, Switzerland
c) Institut fur organische Chemie, J. W. Goethe Universit~t,
Niederurseler Hang, D-6000 Frankfurt/M, West Germany
Correlation experiments via heteronuclear long range couplings provide
useful information for the assignment of resonances and about connec-
tivities of substructures in oligopeptides and other classes of organic
and bioorganic compounds.
The corresponding inverse experiment, which has a better signal to noise
ratio than conventional techniques, has been introduced recently 1). For
the application to peptides mainly the carbonyl carbons which cover a
small range of chemical shifts in F 1 are of interest, whereas the whole
proton spectrum is required in F 2.
The selection of a small frequency window in the F 1 dimension is there-
fore a prerequisite to obtain sufficient digitization with a reasonable
amount of tl-values. This can be done with semiselective pulses. We used
Gaussian shaped pulses for this kind of semiselective 2D experiments.
The reduction of the F 1 frequency range of more than 10 kHz to a few
hundred Hz results in a considerable resolution gain. The sensitivity is
also improved due to good digitization.
Modifications of the basic sequence will be discussed, which allow to
adjust the experiment to one's needs: either to obtain a maximum number
of correlation peaks or to derive qualitative information about the size
of heteronuclear coupling constants.
1) L. MUller, J. Am. Chem. Soc 101, 4481 (1979);
A. Bax, R. H. Griffey and B. L. Hawkins, J. Magn. Reson. 55,
301 (1983)