A GFP-chromophore-based C3V-symmetric tripodal receptor with selective recognition of Hg(ii), Fe(iii) and Cr(iii)†
A novel green-fluorescent-protein-chromophore-based tripodal receptor 1 is synthesized. Its single crystal X-ray diffraction structure looks like a straight, long tube with one end closed. The diameter of the inner cavity of the tripodal receptor 1 is 2.7 Å and its outer cavity is a little larger with the diameter of 3.5 Å. The three GFP chromophores in 1 are packed like a propeller quite well and tightly through van der Waals forces. The tripodal receptor 1 selectively captures Hg2+, Fe3+ and Cr3+ in its inner cavity through four binding sites (one tertiary amine and three amide groups) to form a 1 : 1 complex with the binding constant K of 2.6 × 104, 1.4 × 105 and 4.3 × 104, respectively. The fluorescence of the tripodal receptor 1 is quenched by Hg2+, Fe3+ or Cr3+ through a heavy-atom or a paramagnetic quenching mechanism, and they are static quenching mechanisms. Hence, the tripodal receptor 1 can be a turn-off sensor for Hg2+, Fe3+ or Cr3+.