The T,x,p‐phase diagram of binary phospholipid mixtures

Abstract

High pressure differential thermal analysis (MA) has been applied to the study of the temperature-composition-pressure phase diagram of the binary saturated phospholipid mixtures dimyristoyl/palmitoyl phosphatidylcholine (DMPC/DPPC) and dimyristoyl/stearoyl phosphatidylcholine (DMPCIDPPC) in excess water. A temperature range from 10 to 100°C and a pressure range from ambient up to 1500 bar has been covered. The experimentally obtained phase equilibria of these binary systems are compared with thermodynamic calculations for ideal and non-ideal mixing behaviour, and with recent results from Monte Carlo computer simulation studies, which not only permit determination of the phase diagram but also reveal a pictorial view of the local structure of the mixtures in the different parts of the phase diagrams.

Pressure effects on the structure of lyotropic lipid mesophases and model biomembrane systems

“…18 at 1 bar a slope of À3.3 AE 0.1 is obtained which yields a surfacefractal dimension of D s 2.7 AE 0.1. With increasing pressure, the gel-fluid coexistence region of a DMPC/DSPC mixture is shifted toward higher temperatures (Landwehr, Winter, 1994b). A shift of about 22 C/kbar is observed, similar to the slope of the gel-fluid transition line of the pure components (Fig.…”

Enthalpy and Volume Changes in Lipid Membranes. I. The Proportionality of Heat and Volume Changes in the Lipid Melting Transition and Its Implication for the Elastic Constants

“…The pressure dependence of the melting transition has been investigated before by various authors. 12,13,16,[18][19][20][21]36,37 It has been shown that the shift of the lipid melting transition is linear with the applied hydrostatic pressure in a pressure range up to at least 2 kbar. However, these authors were mainly interested in the shift of the transition point.…”

Effect of pressure on membranes

“…depending on their molecular structure, hydration level, pH, ionic strength, temperature and pressure. 14,15,[20][21][22][23][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] The basic structural element of biological membranes consists of a lamellar phospholipid bilayer matrix (Fig. 2a).…”

“…In addition to these thermotropic phase transitions, a variety of pressure-induced phase transformations have been observed. [26][27][28][30][31][32][33] Because the average end-to-end distance of disordered hydrocarbon chains in the L a -phase is smaller than that of ordered (all-trans) chains, the bilayer becomes thinner during melting at the P b 0 /L a -transition, even though the partial lipid volume increases. This is demonstrated in Fig.…”

“…[26][27][28] Assuming the validity of the Clapeyron relation describing first-order phase transitions for this quasi-one-component lipid system, dT m /dp ¼ T m DV m (T m , p)/ DH m (T m , p), the positive slope can be explained by an endothermic enthalpy change, DH m , and a partial molar volume increase, DV m , for the gel-to-fluid transition, which have indeed been determined in direct thermodynamic measurements. 32,33,37 The transition enthalpy at atmospheric pressure is about 36 kJ/mol, for DPPC at ambient pressure and decreases slightly with pressure (dDH m /dp) ¼ À3.4 kJ mol À1 kbar À1 ). 39 As dDH m /dp ¼ ÀT m (dDV m /dT) p + DC p,m (dT m /dp), the drop of enthalpy change with pressure evidences a significant difference in the coefficients of thermal expansion of the two phases.…”