Passive lipid membrane diffusion of test compounds was determined using Merck Millipore MultiScreen Filter Plates (0.45 μm pore diameter, hydrophobic PVDF). The filter inserts were coated with 1% L-α-phosphatidylcholine (Fluka Analytical) in n-dodecan. The test compounds were then added to the donor compartment at a final concentration of 500 µM in a phosphate buffer pH 7.4 containing 5% DMSO with a total volume of 150 µL. The acceptor compartment was filled with 300 µL PBS containing 5% DMSO. Additionally, three equilibrium samples were prepared by directly adding the donor solution to the acceptor compartment for the calculation of log Pe values. The filter plates were incubated for 18 h before the test compound concentrations in the acceptor compartments and in the equilibrium samples were determined by UV absorbance at 285 nm (6 and 53), 245 nm (57), 250 nm (55), 260 nm (indomethacin), 280 nm (58), 290 nm (propranolol), and 310 nm (36) with external calibration in a 96 well quartz plate on a SpectraMax M2e microplate reader (Molecular Devices, LLC, San Jose, CA, USA). logPe values were calculated according to the formula published by Sugano et al .