Thermodynamic invariants of gel to the liquid-crystal 1,2-diacylphosphatidylcholines transition.

The bilayer phase transitions from the ripple gel phase (P'(β)) to the liquid-crystal phase (L(α)) of a series of 1,2-diacylphosphatidylcholines containing a linear saturated acyl chain (C=14-19) have been studied by high-pressure scanning microcalorimetry. It has been shown that at ambient pressure, the transition temperature increases non-linearly depending on the acyl chain length. Pressure stabilizes the gel phase of lipids in a similar way; the pressure derivatives of the logarithm transition temperature as function of pressure are identical for all lipids.