Stephanie Mabry - High-pressure proton NMR study of lateral self-diffusion of phosphatidylcholines in sonicated unilamellar vesicles Phys. Lipids, 1995, 78, 103-117

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  B.-S. Lee, S. A. Mabry, A. Jonas, and J. Jonas, Chem. Phys.   Lipids, 1995, 78, 103-117


  Effects of pressure on the lateral diffusion of phospholipid   molecules in sonicated pure 1,2-dipalmitoylphosphatidylcholine   (DPPC) and 1-palmitoyl-2-oleoylphosphatidylcholine (POPC)   vesicles (15 wt%) in D2O were examined using the high-pressure   proton NMR rotating frame spin-lattice relaxation time (T1rho)   method. Proton T1rho were measured at pressures from 1 bar to   5000 bar and at temperatures of 50 degrees C to 70 degrees C for   DPPC and 5 degrees C to 35 degrees C for POPC. The T(-1)1rho   values were plotted as a function of the square root of the   spin-locking field angular frequency (omega1(1/2) and the lateral   diffusion coefficient (D) calculated from the slope. Pressure   effects on lateral diffusion were observed in the   liquid-crystalline (LC) phase. The lateral diffusion coefficient   exhibited sharp decreases in response to the various   pressure-induced phase transitions encountered. However, pressure   had little, if any, effect on lateral diffusion in the   pressure-induced gel I (GI) phase and pressure-induced   interdigitated gel (Gi) phase. The activation volumes for   diffusion were calculated from the slopes from plots of In D   versus pressure for both DPPC (37 ml/mol at 50 degrees C, 34   ml/mol at 60 degrees C and 25 ml/mol at 70 degrees C) and POPC   (16 ml/mol at 5 degrees C, 9 ml/mol at 20 degrees C and 6 ml/mol   at 35 degrees C) sonicated vesicles in the LC phase. The   activation energy for diffusion (Ea) was calculated using the   slopes from plots of In D versus the inverse of the temperature   (1/T) for both DPPC and POPC in the LC phase (3.5 kcal/mol and   3.9 kcal/mol, respectively) and for both DPPC and POPC in the GI   phase (6.0 kcal/mol and 4.4 kcal/mol, respectively). From the   lateral diffusion coefficient and line width data   pressure-temperature phase diagrams for sonicated pure DPPC and   POPC vesicles were constructed. The values of the temperature to   pressure equivalence of DPPC (dTm/dP) were estimated to be 22.1   degrees C/kbar for the LC to GI phase transition and 28.6 degrees   C/kbar for the GI to Gi phase transition. The value of the   temperature to pressure equivalence of POPC for the LC to GI   phase transition was estimated to be 19.0 degrees C/kbar.

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