Two carbazole disulfonamide-diamide macrocycles with semi-flexible meta -xylyl linkages for anion recognition

Two novel carbazole disulfonamide-diamide macrocycles 1 and 2 with semi-flexible meta -xylyl linkages were designed, synthesized, and assessed for their anion binding properties, via 1 H NMR and UV-vis titration studies. The single-crystal X-ray diffraction analysis indicated that all five of the NH groups in macrocycle 1 pointed into its inner cavity, with a favorable geometrical conformation for the complexation of anionic guests. The 1 H NMR titration results demonstrated that both macrocycles bound strongly and selectively to fluoride ions in DMSO-d 6 solution with the affinities in the order of magnitude of 10 3 M −1 through the formation of 1 : 1 complexes, which was higher than other ten anions tested (including its competitors acetate and dihydrogen phosphate ions). The binding affinities of the two macrocycles were found to follow the order F − ≫ AcO − > PhCOO − > H 2 PO 4 − > Cl − > NO 2 − /N 3 − /Br − /HSO 4 − /NO 3 − /ClO 4 − (no measurable binding), which was not in accordance with the basicity order of these anions. In particular, macrocycle 1 containing the pyridine-2,6-diamide moiety displayed a preference for F − over AcO − and H 2 PO 4 − (having the selectivity factors of 30 and 182, respectively), which was improved by nearly 3-fold after comparison with those for macrocycle 2 bearing the isophthalamide moiety.