th  - 1988 - 51st ENC Conference

158 I SOME TRICKS OF THE TRADE FOR BETTER 2D NMR SPECTRA
( ou comment monter une mayonnaise ~ la main . . )
Dominique MARION *+ and Ad BAX
Lab. of Chemical Physics N.I.D.D.K.
BETHESDA MD 20892 U.S.A.
N.I.H.
The information content of most 2D NMR experiments, in the context of
conformational analysis, is presently underestimated, since several expe-
rimental imperfections still prevent one from interpreting the more subtle
pieces of information actually present in the spectrum. In any 2D map re-
corded in the phase sensitive mode, improper phase correction as well as
baseline rolls are major concerns for correct quantification of the spec-
tral parameters. On the basis of the pulse phases and durations and delays,
the necessary phase corrections can be computed ab initio, avoiding the
waste of time caused by trial-and-error iterative correction. By a proper
setting of the experiment, the phase correction can even be minimized
before acquisition. Similarly, the apparently irreproducible baseline dis-
tortions, which originate in part from an incorrect quantification of the
first data polnt(s), can be rationalized and thus minimized. These features
will be illustrated on the conformational study of maEainin (I), a 23-re-
sidue antimlcrobial peptide from the frog skin.
(I) D. Marion, M. Zasloff and A. Bax (1988) FEBS Lett 227:21
(+) on leave from the Centre de Biophysique Mol~culaire Orldans France
159 I
DEVELOPMENT OF FLUORINATED, NMR ACTIVE SPIN TRAPS FOR
STUDIES OF FREE RADICAL CHEMISTRY: Barry S. Selinsky , Louis A. Levy,
Ann G. Motten, and Robert E. London, National Institute of
Environmental Health Sciences, Research Triangle Park, NC 27709.
The use of spin traps, nitrone or nitroso compounds which react
with free radicals leading to the production of thermodynamically
stable spin adducts, has greatly enhanced the detection of reactive
radicals by electron spin resonance. Five fluorinated analogs of the
spin trap phenyl-tert-butyl nitrone (PBN) have been synthesized and
evaluated for use as NMR active traps. The introduction of the
fluorine substituent allows selective observation of chemical re-
actions involving the spin traps. Althoug~_the paramagnetic adducts
themselves are not directly observable by ~F NMR as a consequence of
extensive broadening, the reduced forms (hydroxyl amines) can be
readily observed. The series of 2-F, 4-F, 2,6-F 2-CF_, and 4-CF 3
substituted PBN analogs have been synthesized. The'relative trapping
efficiencies of the synthesized spin traps were tested by reaction
with known concentrations of phenyl radical generated from phenyl-azo-
triphenylmethane in benzene. In addition, the trapping efficiencies
of 2,6-F 2 PBN and 2-CF~ PBN relative to unsubstituted PBN could be
compared due to significant differences in ESR proton hyperfine
coupling constants of their phenyl adducts. The fluorinated spin
traps synthesized here could potentially be useful in in vivo studies
of biological free radicals, where reduction of nitroxides makes ESR
analysis difficult.
IZ8