th  - 1988 - 51st ENC Conference

146 I SO~ APPLICATIONS OF THE ~TR EXPERI~IENT: Dallas L. Rabenstein,
Uei Guo and Erin Smith, Department of Chemistry, University of
California, Riverside, California, 92521.
In the WATR (w_ater ~ttenuation by T__ 2 r_elaxation) experiment, the
water resonance is eliminated by selectively decreasing the spin-spin
relaxation time of the water protons by chemical exchange and then
measuring the spectrum by the Carr-Purcell-Meiboom-Gill (CPMG) pulse
sequence.l, 2 With this method, the water resonance can be selectively
eliminated and resonances at the chemical shift of the water resonance
can be observed. In this poster, we describe several applications of
the WATR method, including measurement of IH-NMR spectra of peptides in
99% H20/1% D20 , observation of resonances for protons bonded to
natural-abundance15N in peptide bonds, and measurement of IH-NMR
spectra for aqueous samples, including biological fluids. Resonances
for protons on the a-carbons of peptides are normally obscurred by the
water resonance, however they are readily observed by the WATR method
and can provide useful information in studies of the chemistry of peptides,
as will be illustrated by results from studies of the
thiol/disulfide chemistry of peptides.
I D.L. Rabenstein, S. Fan and T.T. Nakashima
541 (1985).
J. Magn. Reson., 64,
2 D.L. Rabenstein and S. Fan, Anal. Chem. 58, 3178 (1986).
147
-- I THERMALLY INDUCED VOLUtlE CI~NGES IN A BLOCK COPOL~IER: Franco Cau*
Serge Lacelle, D~partement de chimie, Universit6 de Sherbrooke, Sherbrooke, Quebec
CANADA JIK 2R1
Recently some temperature induced molar volume changes have been reported for
solutions of block copolymers of propylene oxide (P) and ethylene oxide (E) with
structures of the type (E) _ (D) - E (i). We have studied the expansibility of a
m n o
- P - with IH T I and lineshape as a function of the
polymer solution of El00 44 El00
temperature and concentration. The resonances of the E and "D monomers are well
resolved thereby permitting to monitor the microscopic environments in the different
blocks of the Dolymer. Our findings include I) the volume changes can be associated
with the P block, 2) determinatio~3of the overlap threshold concentration, 3) the
radius of Ryration scales with N ~ , where N is the degree of polymerization. These
results will be discussed in the light of various scalinE behavior (2).
i. R.K. ~Jilliams, H.A. Simard, C. Jolicoeur, J. Phys. Chem. 89, 179, (1985).
2. P.C. de Gennes, Scalin~ Concepts in Polymer Physics, Cornell U. Press 1979.