th  - 1988 - 51st ENC Conference

[
~ THE SOURCE OF AN ARTIFACT IN THE IH - IH DECOUPLED
$6 I HETERONUCLEAR CHEMICAL SHIFT CORRELATION EXPERIMENT
Alex D • Bain* , Donald W. Hughes, Dept. of Chemistry, McMaster University,
Hamilton, Ontario, Canada LBS 4MI; and Howard N. Hunter, National
Research Council of Canada, Biotechnology Research Institute, Montreal,
Quebec, Canada H4P 2R2.
When the IH - IH decoupled variation of the heteronuclear
two-dimensional chemical shift correlation experiment (shown below) is
applied to methylene groups with inequivalent protons, a strong artifact
may show up at the average chemical shift of the two protons. The
artifact does not appear to be a strong coupling effect, since it appears
in methylene groups with large proton chemical shift differences•
However, it behaves apparently erratically with respect to the shift
difference. Simulations with the SIMPLTN program indicated a strong
dependence on the delay D2 in the sequence, and this led to a full
explanation. The mechanism for this artifact is presented, along with
experimental confirmation.
90 90 180 90
,H ~-] t,/2 ~ t,/2
I 3 C
180
V-
90
io2
90
F7
: ACQUIRE
57 I STRUCTURAL STUDIES OF LIPIDS IN FIELD ORDERED MODEL
MEMBRANES: Preetha Ram*, Maureen P. O'Brien* and J. H.
Prestegard, Department of Chemistry, Yale Un.iversity, New Haven,
CT 06511
. . . . . . . . . . . °
Oriented, as opposed to randomly dispersed samples of
biological membranes . o~ model membranes offer unusual
opportunities for structural characteriztion. Quadrupole
splittings in deuterium NMR spectra can, for example, be resolved
in multiply labelled compounds and interpreted in terms of
preferred orientation relative to membrane surfaces. In the past
most methods for obtaining oriented samples have relied on
mechanical orientation. More recently magnetic field ordered
systems have been developed. We compare data on two types of
magnetic field ordered micelles: potassium laurate and bile
salt/dimyristoylphosphatidylcholine with phospholipid bilayers
mechanically oriented on glass plates. The physical
characteristics of these systems are investigated using
quadrupole splittings from deuterium NMR and Carbon-13
dipolar couplings obtained from Magic Angle Spinning experiments.
Methods are presented for obtaining structural data on
conformational aspects of specifically labelled lipids and lipid
like molecules such as phosphatidylcholine, myristic acid and a
galactose terminal lipid. Resulting quadrupole coupling data are
merged with molecular energetics information derived from a
molecular mechanics program to determine probable geometry at the
bilayer interface.
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