Application of pressure perturbation calorimetry to the aqueous system of phospholipid vesicle dispersion

Abstract

Pressure perturbation calorimetry (PPC) is a relatively new technique which provides the thermal expansion coefficient α₂ of a solute. We give a detailed description on the theoretical background of this technique for a binary solution and a theoretical explanation for the method to estimate the volume change Δ v _{app, 2} with a phase transition. In this theory, a reversible isothermal pressure change is assumed, although an irreversible pressure change is applied in the PPC experiment. In order to verify the effect of this inconsistency, we carried out the PPC measurements for the dimyristoylphosphatidylcholine bilayer membrane. The Δ v _{app, 2} value with the gel-to-liquid-crystalline transition was estimated at 18.3 ml mol⁻¹, which is in agreement with the literature values obtained by other techniques. This indicates that the irreversibility has virtually no effect on the Δ v _{app, 2} value and also supports the validity of the method for estimating the Δ v _{app, 2} value that we adopted.

Keywords:

• pressure perturbation calorimetry
• volume change
• apparent molar volume
• bilayer phase transition
• dimyristoylphosphatidylcholine