th  - 1988 - 51st ENC Conference

70 I 2H NMR STUDIES OF MOTIONS IN SOLID D2S AND D2Se:
M.J. Collins, C.I. Ratcliffe,* and J.A. Ripmeester, Chemistry Division,
Research Council of Canada, Ottawa, Ontario, Canada KIA OR9
National
There have been a number of tH and 2H NMR studies of motions in the three solid phases
of H2S. There are, however, a number of ambiguities concerning these results, and the
also yield little insight into the nature of the motion in phase II. The current work
mainly concerns 2H powder lineshapes of D2S as a function of temperature. New work on
phase II of D2Se is also included, since the behaviour appears similar to that of D2S
phase II. In phase III of D2S close to the phase transition the lineshapes indicate
the onset of a motion which is best explained as 180" flips, though other alternatives
suggested by earlier IH T I_ results will be discussed. To be compatible with
dielectric results this motion must be about the dipole axis of the molecule. Phase I
of D 25 and D2Se proved to be much more interesting. The narrowed lineshapes indicate
an axially symmetric motion in the fast motion limit, over the whole temperature range
of phase II, but the averaged quadrupole coupling constant decreases substantially as
the temperature increases. This suggests a fast motion for which angular parameters
are varying as a function of T. Although a unique motion cannot be assigned possible
models will be presented.
71 ] STUDIES OF FLAVODOXIN BY HOMONUCLEAR AND
HETERONUCLEAR 2D NMR TECHNIQUES. V. Thanabal* & Gerhard Wagner,
Biophysics Research Division, Institute of Science and Technology, University
of Michigan, Ann Arbor, MI 48109
Most studies of protein conformations by NMR have concentrated so far on molecules of
molecular masses below 10 kDalton. We have approached assignments of flavodoxin from
Megasphaera elsdenii which has a molecular weight of 15 kDahon (137 residues). Although the
classical 2D NMR pulse sequences (COSY, NOESY, RELAY) yielded satisfactory spectra we
have heavily used TOCSY (HOHAHA) spectra and heteronuclear techniques for characterization of
the amino acid spin systems. Compared to COSY and RELAY experiments these techniques suffer
much less from cancellation of antiphase cross peaks due to a large linewidth. TOCSY spectra
were recorded with an MLEV17 spin lock as described by Bax and Davis. Experiments with
different mixing times were used to obtain a complete set of connectivities. Heteronuclear 1H-13C
COSY experiments were recorded either with a heteronuclear multiple quantum evolution period or
with a double DEPT editing sequence to separate CH, CH2 and CH3 carbons. The purpose of the
heteronuclear experiments was mainly to elucidate the spin systems of the coupled protons. First
sequential assignments obtained with these techniques will be presented.
A.Bax and D.G.Davis J. Magn. Reson. 65, 355-360 (1985).
134