that the transport of anions is faster than the transport of Stopped flow measurements to determine the permeability of cations. The effect was assumed to be due to the alignment vesicles are presented. The kinetics of the reaction between of the permanent dipoles of the phospholipid headgroups at FeSCN 2/ and F 0 ions is used to monitor the permeability of vesi-the interface. The positive poles of these phospholipid dicles. Samples with vesicles that have been equilibrated with the poles are oriented toward the hydrocarbon interior of the iron complex are mixed with F 0 solutions. The reaction is followed membranes which makes the permeation more difficult for by UV/VIS absorption. The influence of temperature and surfaccations than for anions.
tant concentration on the membrane permeability of large unila-
A method for the measurement of the water (D 2 O/H 2 O) mellar phospholipid vesicles was studied. A dramatic increase of the permeability of the LUVs is observed when 30 to 40 mol% of permeation across vesicular lipid bilayers was presented by the surfactant OP-10 (main component of Triton X-100) is added Engelbert and Lawaczeck (2). This method was based on to the lipid. It is assumed that the increased permeability is due the change of the light scattering intensity by the solvent to the stabilization of transient defects in the bilayers of the vesicles isotope effect, a consequence of the different indices of reas shown previously by other groups. Furthermore, a strong bindfraction of D 2 O and H 2 O. The stopped-flow technique was ing of the iron (III) thiocyanate complex to the phospholipid is used to determine the exchange rates and permeability coefobserved by UV/VIS spectroscopy and z-potential measurements. ficients. Furthermore, the influence of the transition of the Additional experiments with vesicles from a fluorocarbon surfacmembrane from the crystalline to the liquid-crystalline state tant show a much higher permeability than the phospholipid syson the permeation has been described.
tem. Models for the diffusion of either the iron (III) complex or
The diffusion of H / /OH 0 across phospholipid vesicle memthe fluoride ions through the vesicles bilayer are discussed for LUV as well as for vesicles from a fluorocarbon surfactant. The results branes was investigated by several groups (3,4). The net H / / indicate that the rate-determining step is the diffusion of the iron OH 0 permeability coefficient was found to be about 10 04 cm/ complex through the membrane.