th  - 1987 - 51st ENC Conference

Tuesday - AM
INDIRECT DETECTION OF lSN and 13C:
INSTRUMENTAL CONSIDERATIONS AND BIOCHEMICAL APPLICATIONS.
David Cowburn
The Rockefeller University,
New York, New York, 10021
Biochemical applications of NMR are usually limited by sensitivity of detection, and selectivity
and resolution of signals from individual groups. Indirect detection, via protons, of hetronuclei like ~SN,
t3C, and 113Cd permit gains of sensitivity of the order of the ratios ~'n/)'x to more than the power of 2,
and selectivity and resolution are increased by the usual advantages of two-dimensional NMR methods.
For natural abundence samples, these experiments are especially demanding of instrumental precision
and stability. Methods for evaluating and improving probe, radiofreqency, and numerical processing
performance will be described. The various pulse sequences for indirect detection differ in their
sensitivity to instrumental factors, and choice of sequence should be tailored to application.
These methods have, however, some apparent disadvantages. Relatively long evolution and
preparation times may permit excessive transverse relaxation, limiting f~ resolution. For natural
abundence studies for lSN and ~3C, there is an apparent disadvantage compared to direct detection
methods with proton decoupling. In indirect detection experiments, the abundent protons' homonuclear
couplings are superimposed on the spectra, while in more conventional direct detection, the signals are
decoupled from protons, and show only low intensity homonuclear satellites. These and other apparent
disadvantages can be alleviated in part by use of Linear Predictive Singular Value Decomposition
0__,PSVD) analysis, and recombination of filtered roots(I).
Supported by grants from NSF, and NIH.
1. Schussheim, A. E., Cowbum, D. 1987 J. Magn. Res., in press.