In contrast to the inactive sulfone-containing BU 10, BU 11 with triflate groups was found to be a highly active anionophore (orange curve in Figure ). This result is quite surprising given the only subtle differences between these two compounds. The lipophilicity of BUs 10 and 11 is predicted to be the same by TorchLite (Table ), while the chloride binding strength of 11 is around one order of magnitude lower than that of 10. However, as observed for BUs 1-2 and 6-8, such minor variations in binding strength of these very strongly binding macrocycles should not affect the transport capability of the BUs. The oxygen atom positioned between the triflyl group and the benzene ring in BU 11 affects the orientation of the triflyl group towards the benzene ring in comparison to 10. This variation could potentially influence the accessibility of the oxygen atoms in the triflyl group to form hydrogen bonds. A comparison of BU 11 with most active compounds 1, 2, and 5 at a 10-fold lower concentration confirmed that 11 was almost as active as 1 (Figure , Table ). In contrast, BU 12, the non-fluorinated analogue of BU 11, did not exhibit any transport activity. Based on chloride binding strength and predicted lipophilicities of these two compounds, it is possible that the lipophilicity of BU 12 and/or the Ka of 12 for Cl -are too low to be an effective anionophore.