Effects of gaseous anaesthetics and inert gases on the phase transition in smectic mesophases of dipalmitoyl phosphatidylcholine.

The phase transition in smectic mesophase of dipalmitoyl phosphatidyl-choline was studied under high pressures of helium (340 atm), nitrogen (340 atm), nitrous oxide (43 atm), cyclopropane (4.4 atm) and n-propane (8.2 atm), using a turbidimetric technique. Helium and nitrogen increased the transition temperature by 0.021 and 0.006 degree C/atm, respectively, compared with 0.024 degrees C/atm for hydrostatic pressure. Nitrous oxide reduced the transition by 0.58 degree C/atm. The hydrocarbon gases spread the transition width and lowered the transition temperature with increasing effect at higher doses. Comparisons with other membrane probes are made and the concentration of gases in the bilayer which lower the transition temperature by 1 degree C are estimated, in mol%: He, 10.2; N2, 13.2: N2O, 9.04; n-C3H8, 6.3 and cyclopropane, 12.8.