Kinetics and mechanisms of monolayer interactions V: surface activities of alkylamides, alkylmonocarboxylic acids, and alkylketones and their interaction energies with phospholipid monolayers.

The adsorption free energies of the C1-C6 alkylamides, C3-C8 alkylketones, and C1-C10 alkylmonocarboxylic acids at the air-water interface, estimated from plots of the surface pressure (less than or equal to 5 dynes/cm) versus the bulk concentration, were linear functions of the total surface area per molecule (square angstroms per molecule), with a slope 46% higher for the alkylamides and 25% lower for the alkylketones than that for the monocarboxylic acids. The interaction energies of alkylamides with dipalmitoyl lecithin and dipalmitoyl phosphatidylethanolamine spread at the air-water interface, estimated from the surface pressure increase with increasing concentrations of the injected C1-C5 compounds, were linear functions of the total surface area per molecule. The diffusion free energies, delta Gdif, of the alkylamides within a phospholipid bilayer, predicted from the permeability equation and their interaction energies with dipalmitoyl lecithin monolayers by assuming the additivity of their free energies of adsorption and dehydration at the solution-bilayer interface, agreed with the literature data.