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

• Published in: Biochimica et biophysica acta 2011-07, Vol.1808 (7), p.1806-1810
• Main Authors: Potekhin, Sergey A., Senin, Alexander A., Abdurakhmanov, Nickolay N., Khusainova, Railya S.
• Format: Article
• Language: English
• Subjects: Belayer membrane; Calorimetry - methods; Diacylphosphatidylcholine; Gels; High pressure; Isobaric expansibility; Isothermal compressibility; Phase transition; Phosphatidylcholines - chemistry; Temperature; Thermodynamics; Volume and enthalpy increment
• ISSN: 0005-2736; 0006-3002; 1879-2642
• DOI: 10.1016/j.bbamem.2011.02.020

The bilayer phase transitions from the ripple gel phase (P′β) to the liquid-crystal phase (Lα) 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. Based on the results obtained it has been concluded that the ratio γ of volume to enthalpy increments upon transitions in 1,2-diacylphosphatidylcholines is not dependent on the acyl chain length. When pressure grows, this ratio decreases drastically remaining identical for all lipids studied. Besides it has been demonstrated that increments of coefficients of thermal expansibility and isothermal compressibility are also rigidly bound to each other. Semi-empirical equations permitting to estimate volume parameters of the gel-to-liquid transition for 1,2-diacylphosphatidylcholines are given. The reasons for invariance of γ are discussed. ► Pressure shifts of the transition temperature according to the classical relation. ► We studied effect of pressure on 6 phospholipids with different acyl chain lengths. ► The ratio of volume-to-enthalpy increments is the same for all lipids. ► Increments of expansibility and compressibility are also rigidly bound to each other.