th  - 1988 - 51st ENC Conference

86 THE USE OF J-SPECTRUM TYPE PULSE SEQUENCES
IN COUPLED RELAXATION STUDIES
Liu Fang*, Charles L. Mayne, David M. Grant
Department Of Chemistry, University of Utah, Salt Lake City, Utah 84112
The accuracy with which one can determine spectral densities in a coupled spin relaxation experiment is
strongly dependent on the nature of the non-equilibrium states from which the spin system is allowed to relax.
Pulse sequences similar to those used to obtain 2D J-spectra have been used to prepare initial non-equilibrium
states of an AX2 spin system. Figure 1 shows partially relaxed 13C spectra from such a preparation. The sample
studied was 1-decanol-l-13C. Table I compares the values of the relaxation parameters (spectral densities) and
marginal standard deviations obtained from a dataset including the J-spectral preparation to those obtained from a
dataset including only the preparations previously reported. Inclusion of data obtained using the new preparation
significantly reduces the marginal standard deviations of several of the spectral densities and reduces correlations
among the spectral densities. Thus, a significant improvement in the structural and dynamical parameters extracted
from the spectral densities is achieved.
V ----V---'
Figure 1
Table I: Spectral Densities for 1-Decanol-1-13C in Diglyme at 0 C.
Spectral
Density
JAX
JXX
JXAX
JAXX
JA
Jx
i)o(
Without J-Spectral
Preparation
0.09751 (0.00093)
0.06625 (0.0068)
0.00606 (0.0027)
0.05794 (0.0013)
0.0 (locked)
0.05553 (0.0074)
0.065 (0.0323)
With J-Spectral
Preparation
0.09645 (0.00076)
0.06219 (0.0033)
0.00399 (0.0025)
0.05635 (0.00091)
0.0 (locked)
0.06456 (0.0038)
0.033 (0.0047)
87 12D CHEMICAL SHIFT ANISOTROPY CORRELATION SPECTROSCOPY. A NEW
SAMPLE POSITIORING MECHANISM WHICH SIMPLIFIES MEASUREMENT OF CHEMICAL SHIFT
ANISOTROPIES IN COMPLEX SINGLE CRYSTALS. Mark H. Sherwood*, D.W. Alderman, &
D.M. Grant, Dept. of Chemistry, University of Utah, Salt Lake City, UT 84112
2D chemical shift anisotropy (CSA) correlation spectroscopy permits the
measurement of CSA tensors in complex single crystals with far more peaks than
have been tractable with 1D techniques (1). Such measurements open the
possibility of using CSA tensors as structural and conformational probes in
large molecules. The basis of the technique is to obtain 2D spectra in which
the peaks are located by the chemical shift at two different single crystal
orientations. The spectra are obtained by moving the crystal between the two
orientations during the mixing time of a chemical exchange 2D pulse sequence.
It will be shown how the complete CSA tensors for all the nuclei in a
complex single crystal can be determined by measuring peak frequencies at only
six well chosen orientations of the crystal and correlating these measurements
with the 2D technique. The special geometry of a mechanism to accomplish the
necessary orientation and reorientation will be explained and the device itself
installed in a 200 MHz probe exhibited. In order to measure all the tensors in
a single crystal the sample need be mounted only once in the mechanism and six
2D spectra obtained.
Six 2D spectra which determine the carbon-13 CSA tensors in a single
crystal of sucrose will be shown. Sucrose has 12 carbons per molecule and two
molecules per unit cell so that 24 peaks are observed.
The possibilities of the technique for measurement of tensors in
much more complicated molecules will be discussed.
(1) C.M. Carter, D.W. Alderman, and D.M. Grant, J. Magn. Reson.
6_55, 183 (1985) and 73, 114 (1987).
142