Novel 1,8-disulfonamidocarbazole-isophthalamide hybrid macrocycle 1 and its thioamide analogue 2 containing ortho-substituted benzyl spacers are reported, together with their anion recognition properties as determined by 1H NMR and UV-vis titration studies conducted in a dimethyl sulfoxide solution and X-ray crystallographic analyses. Notable differences in their anion affinity and selectivity were observed for these two macrocyclic receptors. In particular, thioamide-bearing macrocycle 2 demonstrated nearly 20- and 30-fold improvement in its affinities for PhCOO- and H2PO4-, respectively, as compared to those of amide-containing macrocycle 1. In contrast, the conversion of amides into thioamides within the discussed macrocycles proved to be exceptionally unfavorable for AcO- binding, as supported by a reduction in affinity by a factor of at least 27. Moreover, the 1:1 binding complexes formed by macrocycle 1 with Cl- and macrocycle 2 with AcO- in the solid state were unambiguously confirmed via single-crystal X-ray diffraction analysis. These findings provide deeper insight into the contrasting anion recognition behaviors of thioamide-based anion receptors versus their amide counterparts.
Li et al. (Fri,) studied this question.