th  - 1987 - 51st ENC Conference

WF14
THE USE OF MULTIPLE ECHO ACQUISITION AND STIMULATED ECHO5
TO DETECT SLOW MOTIONS
S. D. Kennedy, S. Ganapathy, S. Swanson, R. 8. Bryant
Department of Biophysics
University of Rochester Medical Center
Rochester, New York 14642
The use of Fourier transformed echo trains was described by
Zilm at the ENC last year. The advantages for a number of
studies include increases in signal to noise, clear
demonstration of heterogeneous broadening, transverse
relaxation time measurements rapidly, as well as sensitivity
to motions of the spins various types. We have demonstrated
that the method provides a very efficient monitor of ms
motions in polymers. The techniques are equally well suited
to the study of chemical exchange in the solid or spin
exchanges caused by relaxation. In the basic spin echo train
e~:periment, the time scale limitation i~ imposed by the
effective transverse relaxation times in the system~ which
may vary considerably from sample to sample, but are
typically in the tens of ms range.
The basic e~periment may be e~:tended in time by using a
stimulated echo. The spins are phase encoded during the
period ÷ollowing the 90 degree pulse or magnetization cycle
by Hartmann-Hahn contact for example, then stored along z for
a variable time during which motion or a magnetic or chemical
exchange event may change the Larmor frequency. The read-out
is accomplished with a third 90 degree pulse and the
formation of a stimulated echo. This experiment extends the
time scale of the motion observation to the carbon T, rather
than the T2. We have applied this technique in a series of
polymers to detect slow motions. In molecules containing
nitrogen such as peptides~ the "4N may complicate
interpretation of the data in terms of motions alone. The
e~:periment, when combined with other rela~:ation time
measurements and MASS~ provides an easy method for measuring
the "4N T~, a parameter of interest in its own right. We
report results on a series of amino acids and peptides that
demonstrates the method and indicates the importance of
nitrogen relaxation times in dynamical intrepretations.