Fig 1.
Surface pressure versus area per molecule for an ideal gas model.
Experimental (black line) and calculated (red line) π/A per lipid curves for DPPC considering the lipid monolayer as an ideal gas dispersed on an (inert) water surface, according to equation at 25°C (a) and 45°C (b) Experimental data of area per lipid were taken from bibliography and surface pressure calculated by means of the ideal gas equation.
Fig 2.
Surface pressure versus area per molecule for monolayer considered as van der Waals bidimensional gas.
Same data of experimental curves as in Fig 1 (black line) are compared with a calculated π/A per lipid curves for DPPC considering the lipid monolayer as a van der Waals gas dispersed on an (inert) water surface at 25°C(a) and 45°C(b). The procedure was similar to that described in Fig 1.
Fig 3.
Schematic representation of lipid interphase showing lipids and its hydration shells.
Fig 4.
Schematic representation of the compression of a lipid monolayer by a mobile barrier on the surface of a water solution.
Horizontal violet arrow represents the surface pressure that produces area changes by the compression. Vertical red arrow represents the water outflux from the interphase upon compession. The increase in surface concentration of lipids at the surface of the left-hand compartment consequently decreases the chemical potential of water. Vertical violet arrow corresponds to the water influx to the interphase due to the difference in the chemical potential of water between bulk and the interphase. Horizontal red arrow is the expansion (area increase) produced by the water influx. If expansion is produced mechanically the area increased induces the water influx.
Fig 5.
Surface pressures versus area per molecule for the TPI model at 45°C.
Experimental (Black line) and calculated lipid curves for DPPC above the critical point according to Eq (21) at 45°C for a set of parameters corresponding to membranes.
Fig 6.
Surface pressures versus area per molecule fitted according to the TPI model at different region of the isotherm.
Experimental curve as in Fig 1 (black line) were compared with calculated surface pressure vs area / molecule curves of DPPC considering the lipid monolayer as an open system according Eq (21) at 25°C. Green curve: region corresponding to the liquid expanded state. Red curve: region corresponding to the region of coexistence of liquid expanded and liquid condensed states. Blue curve: region corresponding to liquid condensed phase below the collapse. The parameters for the fitting in each region are summarized in Table 1.
Table 1.
Fitting parameters of π/A curves of Fig 5 for different regions of monolayer compression.
Fig 7.
Errors at T = 45°C for ideal gas, van der Waals and TIP model.
a) Error, E b) Eint, integral error normalized. In both cases, TIP model has the smallest error.
Table 2.
Calculated coefficients for the diffusion of water in lipids (DwL) and the diffusion of lipid (with its hydration shell) in water (DLw) in the different regions of the surface pressure / are per lipid isotherm.