th  - 1988 - 51st ENC Conference

AN NMR STUDY OF MISCIBLE BLENDS
IN CONCENTRATED SOLUTION
ii I *a b
olly W. Crowther ,Israel Cabasso ,and George C. Levy Department
of Chemistry, Syracuse University, Syracuse, New York, 13210
acurrent Address- New Methods Research, Inc., 719 E. Genesee Street
b Syracuse, New York, 13210
Department of Chemistry, State University of New York-ESF
Syracuse, New York, 13210
High-resolution proton spectra of the miscible polymer blend
polystyrene/poly(vinyl methyl ether) (PS/PVME) in concentrated
solution have been used to examine intermolecular interactions. The
spectral resolution achieved in solution allows the polymer components
and the chemically different types of protons within each component to
be well resolved. A one-dimensional cross-relaxation experiment shows
that the polymers are intimately mixed in toluene solution but not in
chloroform. The concentration threshold for observable magnetization
exchange between the polymer pair (in toluene) lies between 30 and 40
wt% total polymer, of which 50 wt% is polystyrene. The chemical shift
difference between the methine and methoxy resonances of PVME is found
to vary with the mole ratio of PVME to the total aromatic
functionality, from either PS or toluene. Linewidth vs. temperature
measurements seem to indicate hindrance of motion for the blend in
toluene at elevated temperatures, as the gross phase separation is
approached, that is not observed for the pure homopolymer. A
two-dimensional exchange experiment was performed at a series of
mixing times to measure the intra- and intermolecular spin-diffusion
rates. Specific intermolecular rates could not be differentiated in
the presence of the very fast intramolecular distribution of the
_magnetization via_spin diffusion.
[
~
POTENCY OF FLUORINATED ETHER ANESTHETICS CORRELATES WITH SPIN-SPIN
RELAXATION TIME IN BRAIN:
12 J D. Andre' d'Avfgnon 1. Joanna C. Haycock 2 and Alex S. Evers 2"
Departments of Chemistry I and Anesthesiology 2, Washington University, St. Louis, MO
631301 and 631102 .
19F NMR signals arising from fluorinated anesthetics can readily be observed in
brain tissue excised from anesthetized rats. When brain is suspended in D20-saline
two anesthetic environments as characterized by different spin-spin (Tp) relaxation
times can be observed I. The major anesthetic compartment (bound anesthetic) is highly
immobilized (T 2 < 5 msec) while the minor component is believed in exchange with the
aqueous phase (T 2 > 9 msec). The following observations are made:
* T 2 times of the bound component for a variety of anesthetic ethers in brain correlate
well with anesthetic potency as measured by ED50. Respective T2/EDso values
are: Methoxyflurane, T 2 = 0.62 msec, ED50 = 0.0046 arm; isoflurane, T2-& 2.39,
ED.^ = 0 016 arm; Enflurane, To = 2.90msec, ED.^ = 0.022 arm; fluroxene, T 2 = 4.30
~U " ~ ~U
ED50 = 0.035 arm.
* Hexafluorethane, a non-anesthetic, shows a far greater T 2 time (18 msec) in brain
than the anesthetics studied. Hexafluorethane partitions well into perinephric
*
adipose tissue and poorly into brain, suggesting low affinity for a binding site
in brain.
Anesthetics incorporated in adipose tissue show much longer T2's than in brain
(200 - 400 msec) while hexafluorethane is 230 msec.
Our conclusions from this work are:
* The correlation of anesthetic potency with spin-spin relaxation time suggests
anesthetics with highest binding affinity (greatest immobilization) are the most
potent anesthetics.
* Brain tissue contains b~nding sites for anesthetics which provide a markedly dif-
ferent motional environment than sites found in adipose tissue.
References: 1A~S. Evers et al. Nature 328, 157 (1987).
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