SPREADING OF DIPALMITOYL PHOSPHATIDYLCHOLINE ON THE SURFACE OF SODIUM DEOXYCHOLATE AQUEOUS-SOLUTION

The surface pressure vs. molecular surface area relations for dipalmitoyl phosphatidylcholine (DPPC) insoluble monolayer and sodium deoxycholate (SDC) adsorbed monolayer, L and D1, respectively, were obtained from the analyses of surface tensions measured by the Wilhelmy glass plate. The values of pi prime with various surface amounts of DPPC and bulk concentrations of SDC were analyzed using a dual surface-region model. The model enabled the estimation of pi prime . For better fitting, modified relations were constructed in place of D1. The exponential decrease of pi (t) was also observed on the SDC adsorbed monolayer which was rapidly compressed by a moving barrier. The pi (t) relaxation rate constants of the SDC monolayers which were compressed by DPPC spreading and the moving barrier agreed with each other, suggesting a desorption of SDC from the surface.