THEORY FOR THE EQUATION OF STATE OF PHOSPHOLIPID MONOLAYERS

We present a simple theory for the interactions among the phospholipids in bilayers and monolayers over a wide range of surface densities, temperatures, and chain lengths. This work draws from three recent efforts: (1) lattice-based interphase theory which explicitly treats the chain conformations in three-dimensional interfacial phases of short-chain molecules, (2) a recent 'equation of state' treatment of van der Waals interactions which predicts volume changes, enthalpies, and temperatures of melting of the 'rotator' phases of n-alkanes, and (3) detailed study of the extensive measurements of Mingins et al. of pressure-area isotherms of phosphatidylcholines at the heptane/water interface which we have used to assess empirical characteristics of the head group interactions and of the 'solid state'.