Effect of pressure on dimyristoylphosphatidylcholine headgroup dynamics

Abstract

${}^{2}\mathrm{H}$ NMR has been used to examine the effect of applied hydrostatic pressure on the dynamics of headgroup-deuterated dimyristoylphosphatidylcholine $(\mathrm{D}\mathrm{M}\mathrm{P}\mathrm{C}\ensuremath{-}{d}_{4})$. Quadrupole splittings, spin-lattice relaxation time ${(T}_{1})$, and quadrupole echo decay times ${(T}_{2}^{\mathrm{qe}})$ have been measured at 65 \ifmmode^\circ\else\textdegree\fi{}C for a series of pressures up to 2 kbar and for a series of temperatures at ambient pressure and at 1.5 kbar. Quadrupole Carr-Purcell-Meiboom-Gill (q-CPMG) decays have been studied under similar conditions. Within the liquid crystalline phase, application of hydrostatic pressure is observed to alter quadrupole splittings of the $\ensuremath{\alpha}$ and $\ensuremath{\beta}$ choline deuterons in a way that is consistent with a tilt of the headgroup away from the bilayer surface. Pressure also increases ${T}_{2}^{\mathrm{qe}}$ in the liquid crystalline phase. q-CPMG decays in the liquid crystalline phase are consistent with a distribution of slow motions in the bilayer. The application of pressure appears to extend the range of this distribution to longer correlation times. In the gel phase, the spin-lattice relaxation and quadrupole echo decay rate are both found to be less sensitive to the application of pressure.