Penetration of Langmuir monolayers by soluble amphiphilic molecules

A theoretical model is developed which describes the penetration of amphiph iles (surfactants, polymers, proteins) dissolved in an aqueous substrate in to a Langmuir monolayer. Penetrated monolayers capable of 2D aggregation ar e treated theoretically within the framework of the generalized Volmer equa tion of state and the quasichemical model of the aggregational equilibrium. The equations of state are derived far mixed monolayers, just as the solub le amphiphile adsorption isotherm equations by the simultaneous solution of the corresponding equation of state and Pethica's equation. The theoretica l model is used for the description of equilibrium protein penetration into Langmuir phospholipid monolayers where after the main phase transition poi nt condensed phase structures are formed by 2D aggregation. In this case th e general thermodynamic approach has to be extended to consider the existen ce of free charges and multiple states of the adsorbed protein molecules. T he protein isotherm equation derived accounts for the 2D aggregation of the lipid. The experimental data for the lysozyme pentration into DPPC monlaye rs agree satisfactorily with the theoretical calculations. It is theoretica lly predicted that if the bulk concentration of lysozyme exceeds a certain limit; 2D aggregation of DPPC is induced.