Effect of penetration enhancers on the dynamic behavior of phosphatidylcholine headgroups in liposomes

The results of a time-domain dielectric spectroscopy (TDDS) study of the ef fect of two skin penetration modulators on phosphatidylcholine (PC) bilayer vesicles are presented. The complex dielectric permittivity spectra of PC vesicle suspensions were described as the sum of two processes: thr: interf acial polarization of the bilayer and the reorientation of the zwitterionic PC headgroups in a plane approximately tangential to the bilayer surface. The influence of two additives (Azone and Transcutol) on the structure and dynamic behavior of PC headgroups of the bilayer vesicles was analyzed in, terms of the interconnection of the dielectric spectra Cole-Davidson parame ter, beta, and the correlation factor, g, of the dielectric relaxation Kirk wood cell model. Analytically, these parameters are connected in the propos ed model via the spatial distribution of headgroup dipole nonhomogeneities. In terms of the physical modulation of the polar surface phase, it appears that these additives can behave either as enhancers or as retarders. Their activity in this respect depends on the concentration of additive and temp erature.