Adsorption rates of phospholipid vesicles to the air/water interface at temperatures near the gel to liquid crystalline phase transition

Abstract

The adsorption rate of phospholipid vesicles has been determined as a function of temperature about the gel to liquid crystalline phase transition. An 8.4:1 molar ratio of dipalmitoylphosphatidylcholine:1-palmitoyl-2-oleoyl-phosphatidylglycerol was used to prepare a unimodal dispersion of large vesicles (mean diameter = 220 nm). Through thermal analysis, this phospholipid mixture was found to undergo the gel to liquid crystalline phase transition at 39.8°C. While the mixture was stirred vesicles were injected into the bulk phase, and the resulting change in the surface pressure was determined as a function of time. At temperatures below the onset of the phase transition, a very slow and an apparently linear change in surface pressure was observed. At the phase transition and above, the change in surface pressure with time was more rapid and could be described by a monoexponential function. The fitted adsorption rate constants increased dramatically at the phase transition and then further increased at temperatures above the phase transition. Although these results reinforce the supposition that rapid adsorption occurs with lipids in the liquid crystalline state, there is no indication that enhanced fluctuations associated with the phase transition influence the adsorption rate.