High Pressure Nmr PDF Download

The effects of pressure, up to 5 kbar, on phospholipid vesicles were measured using high pressure NMR techniques. Specifically, two sets of experiments were performed. First, sonicated vesicles of 1-palmitoyl-2-oleyl-3-sn-phosphatidyl-choline at 28$spcirc$C were studied using two-dimensional phase sensitive NOESY as an indicator of cross-relaxation in the bilayer. Results indicated a dramatic buildup of cross-peak intensity with pressure. A qualitative explanation of the results, using a well-known model of cross-relaxation in the lipid bilayer, was that high pressure causes an increase in the order parameter throughout the acyl chains, directly increasing the measured cross-relaxation rate and steady-state value of the NOE. The second set of experiments were done on multilamellar vesicles of tail-perdeuterated dipalmitoyl phosphatidylcholine, using high pressure deuterium MMR as a probe of the order in this system as pressure was varied at several different temperatures. Measurements were taken both in the liquid-crystalline and gel states of pure lipid bilayers. Effects and reversal of action of the local anesthetic tetracaine were studied. The results showed that the order parameters of all segments of the chain were increased with pressure. The addition of tetracaine disordered the chain, and this effect was shown to be reversed by pressure by both changes in lineshape and the measured order parameters. The application of pressure in the gel state had the same effect as lowering the temperature, in that the gel state lineshape slowly changed from a motionally averaged to a rigid lattice type spectrum as pressure was increased. At very high pressures, even the methyl portion of the spectrum indicated no motion on the MMR timescale. A phase which corresponded to an interdigitated gel was observed, and a general phase diagram constructed.