Interaction of DPPC monolayers with soluble surfactants: electrostatic effects of membrane perturbants.

We studied the effects of four soluble surfactants on DPPC monolayers to elucidate the action of these membrane perturbants. The presence of nonionic N-9 and amphoteric C31G strongly affected the pure DPPC isotherm, while anionic SDS and cationic DTAB had little effect. The impact of surfactant on DPPC domain shape in the liquid condensed-liquid expanded coexistence region showed the opposite result. Neutral surfactants had minimal effect on the shape of DPPC domains; charged surfactants, on the other hand, induced a new shape transition at high surface pressures previously unreported for DPPC domains. All of these results are discussed with particular attention given to electrostatic effects at the interface.