Synthetic Receptors with Micromolar Affinity for Chloride in Water

A water-soluble coordination cage was obtained by reaction of Pd(NO3)2 with a 1,3-di(pyridin-3-yl)benzene ligand featuring short PEG chain. The cavity the metal-organic contains one nitrate anion, which is readily replaced chloride. apparent association constant for chloride binding in buffered aqueous solution Ka=1.8(±0.1)×105 M−1. This value significantly higher than what has been reported other macrocyclic receptors. heavier halides Br− and I− compete or self-assembly, but receptor displays very good selectivity over common anions such as phosphate, acetate, carbonate, sulfate. further increase affinity factor 3 achieved using fluorinated dipyridyl ligand.