To further investigate the relationship between the selectivity of BU 1 to different anions and the selectivities of the transport processes, we investigated Br -/NO3 -, I -/NO3 -, Br -/HCO3 -and I -/HCO3 - antiport by 1, using the lucigenin and SPBA assays. Additionally, Cl -, NO3 -, and SO4 2-uniport activities by 1 were measured using the HPTS assay. Other previously investigated transport processes by BU 1 were Cl -/AcO -and Cl -/SO4 2-antiport and the transport of F -. All these transport processes by BU 1 are summarised in Table . [a] Lucigenin or SPBA assays; [Eu.L 1 ] + assay; HPTS assay; this work.