The properties of aqueous multilamellar dispersions of [2H31]16:0-alpha 18:3 PC (1-[2H31]palmitoyl-2-cis,cis,cis-octa-9,12,15- trienoylphosphatidylcholine) and of [2H31]16:0-gamma 18:3 PC (1-[2H31]palmitoyl-2-cis,cis,cis-octa-6,9,12-trienoylphosphatid ylcholine) were compared by broadline 2H NMR spectroscopy. These isomeric phospholipids differ only in the location of the unsaturations in the sn-2 chain. The alpha 18:3 chain has double bonds at delta 9, 12, and 15 positions whereas in the gamma 18:3 chain they are at positions delta 6, 9, and 12. Moment analysis of spectra recorded as a function of temperature reveals dramatically distinct phase behavior for the two isomers. The gel to liquid crystalline transition for [2H31]16:0-alpha 18:3 PC membranes exhibits broad hysteresis which is characterized by a mid point temperature of -9 degrees C and -20 degrees C on heating and cooling, respectively. In contrast, the phase transition of [2H31]16:0-gamma 18:3 PC membranes does not exhibit hysteresis and occurs over a lower temperature range centred on -27 degrees C. Appreciably different molecular ordering also exists within the membranes in the liquid crystalline state. Average order parameters SCD are smaller in [2H31] 16:0-alpha 18:3 PC than in [2H31]16:0-gamma 18:3 PC by 10% at the same temperature and by 20% at equal reduced temperature. Smoothed order parameter profiles generated from depaked spectra clarify the nature of the difference.(ABSTRACT TRUNCATED AT 250 WORDS)

443With the quantities of material available at the time has been able to characterize the isotope as decaying of these experiments, attempts to isolate the Tl 209 with a 2.2-min. half-life by emission of a 1.8-Mev betaactivity were unsuccessful. Since then one of us 30 particle. Gamma-rays if present constitute a maximum 30 French Hagemann, Phys. Rev. 79, 534 (1950).of one percent of the Geiger activity.By use of a CD 4 -filled high pressure cloud chamber, the angular distribution of recoils from 12-to 13-Mev neutrons has been studied. The angular range 0° to 140° in the center-of-mass system was covered by these measurements. The distribution indicates a rather large asymmetry in the forward and backward directions with a minimum at about 60° in the center-of-mass system. The existence of a D(w, 2n)p reaction was evident by the presence of tracks between 60° and 90° in the laboratory system which were too long to be accounted for by either deuteron or proton elastic recoils. * This report is part of a thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the University of Illinois, 1950. A preliminary report of these data was given in Phys. Rev. 77, 748 (1950).t Assisted by a joint program of the ONR and the AEC.

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Microparticles with radii greater than 2 mu m have been observed in a high-voltage vacuum accelerator tube. The charge acquired by most of the particles is similar to the contact charging of a conducting sphere on a plane.