The sensitivity of the anion transport by BUs to the cholesterol content in the membrane appears to be associated with the presence of hydrogen bond accepting groups on the BU substituents. For instance, BUs 5 and 11 are highly active in the LUVs made of pure POPC, but complete inactive in the presence of cholesterol. Similarly, moderately active BU 9 lost its activity in the presence of cholesterol. BU 8, on the other hand, was not impacted despite containing an oxygen atom in the substituent. Potential reasons could be the steric hindrance by the -CF3 group or a decrease in the electron density on the oxygen atom, both of which would reduce the hydrogen bond accepting ability of the oxygen. We hypothesise that the -OH group of the cholesterol might interact with these hydrogen bond acceptors in BUs 5, 9, and 11, as visualised schematically in Figure . BUs 2-4 and 6 exhibited a slight decrease in their transport activities in LUVs composed of POPC/cholesterol, as is commonly observed for anionophores. As the BU anionophores are relatively large molecules, a tighter packing of the lipids with cholesterol can slow down the diffusion of the BUs through the membrane.