Surface activities of barbital, phenobarbital, and pentobarbital and their interaction energies with phospholipid monolayers.

The adsorption free energies of barbital, phenobarbital, and pentobarbital at the air-water interface were estimated from plots of the surface pressure (pi less than or equal to 5 dynes/cm) against the bulk concentration. Their energies of interaction with dipalmitoylphosphatidylethanolamine and dipalmitoyllecithin monolayers spread at the air-water interface were estimated from the surface pressure increase with increasing concentrations of the subphase-injected barbituric acid derivatives. Adsorption free energies and interaction energies were barbital less than phenobarbital less than pentobarbital, which correlate with their nerve blocking concentration.