th  - 1987 - 51st ENC Conference

MKI5
NA-23 NMR-INVISIBILITY IN LIVING SYSTEMS:
2D MULTIPLE QUANTUM NMR AND NUTATION DIMENSION EFFECTS
S
William D. Rooney , Thomas M. Barbara and
Charles S. Springer, Jr.
Department of Chemistry, State University of New York,
Stony Brook, New York 11794-3400
The Na + ion is ubiquitous in nature in both extent and
amount. Its major, stable, isotope, 23Na (I00%), is magnetic
and gives a strong NMR signal. However, It is well-known
that, for living systems, a portion of this signal is not
observed when high resolution acquisition conditions are
employed. There is general agreement that this is due to the
effects of microscopic electric field gradients on this
quadrupolar (I = 3/2) nucleus. There are two mechanistic
extremes: a homogeneous interaction in which fluctuations of
these gradients average the frequencies of the satellite
transitions (~i/2 to ~3/2) to the same value but drastically
shorten their T2 relaxation times, and an inhomogeneous
interaction in which these frequencies are widely dispersed
because of variations in the orientation of these gradients
in the magnetic field. We have undertaken to discriminate
these extremes with two kinds of multiple pulse 2D NMR
experiments. In one, the projection of the 2D spectrum onto
the v, axis displays the forbidden double quantum NMR
spectrum. In the other, the projection onto the wl
axis displays the effective nutatlon (Rabi) frequency of the
central transition (I/2 to -I/2). We have prepared mode]
systems, mostly consisting of long chain alkyl sulfate
esters, which exhibit each of the four possible types of
23Na NMR spectrum: oriented (lyotropic) liquid
crystalline (same as single crystalline), unoriented liquid
crystalline ("powder pattern"), homogeneously relaxed, and
extreme-narrowed. The second and third represent the two
mechanistic extremes for NMR-invisibility possible in nature.
Our two kinds of 2D NMR experiments easily discriminate the
second and third spectral types in the ~2 dimension.
Both experiments share the property of taking advantage of
the strong, sharp, central transition. In recent studies, we
have conducted these experiments on living systems.
Supported in part from NIH GM 32125 and NSF PCM 84-08339.