2002), static light scattering (Chen and Szostak, 2004) and merocyanine-540 PD0332991 clinical trial assays (Dixit and Mackay 1983). As an alternative, we used conductimetric titration (Briz and Velásquez 2002) to determine the CVC of fatty acid vesicles. When the conductance of a micellar solution of a fatty acid is measured as fatty acid concentration increases, all of the fatty acid anions and counterions are available to carry ionic current. However, when the concentration of fatty acid exceeds the CVC, half of the fatty acid anions and counterions become unavailable because they are incorporated in the inner leaflet of the vesicle bilayer membranes. When concentration is plotted against conductivity the slope decreases above the CVC, and

the intersect of the two linear fits gives the value of CVC (Williams et al. 1955). The CVC was determined by conductimetric titration. The sample temperature was kept at 25.0 ± 0.1 °C with a thermal circulating water bath. An analogue electrical conductivity meter and an electrode with cell constant of 0.55 cm−1 were used to measure LY2109761 chemical structure electrical conductivity. The cell constant was determined by calibration

with KCl samples of known concentration. Titration was performed by successive dilution of the sample with 10 mM Tris buffer (pH 7.4), lowering the decanoic acid concentration of the sample 3 mM at a time. Solutions were allowed to equilibrate a few minutes after dilution until a stable conductivity measurement was obtained. CVC values were calculated using the Williams method. The linear fits of data points at high concentration (above CVC) and low concentration (below CVC) had an R2 > 0.99. The permeability

of the mixed membranes to small solutes was studied using a turbidity assay (Monnard and Deamer 2003; Cohen and Bangham 1972). When solutes are added to vesicles in solution, osmotic pressure causes the vesicles to shrink, resulting in increased light scattering (measured as absorbance). If the membranes Forskolin purchase are permeable, solute molecules diffuse through the membrane and the vesicles swell, lowering the absorbance. The initial rate at which absorbance decreases is a measure of the relative selleck chemicals permeability of the membrane to that solute (Apel et al. 2002). Permeability measurements were performed according to Apel et al. (2002). An aliquot of each vesicle preparation (0.9 ml) was added to a 1 ml quartz cuvette. Absorbance was measured at 600 nm with a VarianCary50 UV/Vis Spectrophotometer. After 20 s, 100 μl solute was added and mixed thoroughly for a final 0.1 M solute concentration. Measurements were performed every 10 s, and data points were fitted to exponential decay using Origin Pro 8.0. The initial rate of permeation in Abs/s was determined by extrapolating to zero (point of solute injection) and calculating the first derivative. Fitting the curve to an exponential decay function provided a mean lifetime used to calculate permeability coefficients.