Pressure-area isotherms of DPPC/CL containing differing levels of (A) (18:2)4CL, (B) (14:0)4CL, (C) (18:1)4CL, and (D) (22:6)4CL. Isotherms were acquired at 23 °C using a 10 mM sodium phosphate buffer (pH 7.4). Isotherms were used for calculating excess area/molecule, elasticity modulus, and Gibbs free energy of mixing. Data are average ± S.E.M. from 3 independent experiments.