Synthesis, Characterization, and Anion Recognition of Novel Bis-macrocyclic Diamide Compounds

A series of new bis-macrocyclic diamide compounds were synthesized in good yields (۸۵% for the oxythiobis intermediate and ۴۵% for the final cyclized product) and structurally confirmed through FT-IR, ¹H/¹³C NMR, ۲D NMR (COSY, HSQC), HRMS, and CHN analyses. Motivated by the existing gap in developing macrocyclic diamide receptors with both strong and selective anion affinity in competitive polar media, this work was guided by the hypothesis that linking two diamide macrocyclic units would enhance cooperative hydrogen bonding and improve anion recognition. The bis-macrocyclic framework exhibited significantly enhanced anion-binding ability, as demonstrated by ¹H NMR titration studies. Compound ۵ showed strong and selective binding toward fluoride ions, accompanied by notable downfield shifts of the amide NH protons (Δδ = +۰.۳۷ ppm). UV–Vis measurements also revealed a measurable red shift from ۲۷۸ to ۲۸۴ nm upon fluoride addition, supporting complex formation through hydrogen bonding. The association constants followed the order F⁻ (Ka = ۱.۲ × ۱۰³ M⁻¹) > H₂PO₄⁻ (۶.۸ × ۱۰² M⁻¹) > HSO₄⁻ (۴.۲ × ۱۰² M⁻¹) > Cl⁻ (۲.۸ × ۱۰² M⁻¹) > Br⁻ (۱.۱ × ۱۰² M⁻¹). The strong preference for fluoride confirms that recognition is dominated by cooperative hydrogen bonding rather than deprotonation. Overall, compound ۵ demonstrates promising performance as an efficient and selective anion receptor, particularly for fluoride sensing applications.

Keywords:

bis-macrocyclic diamide , host-guest interaction , anion recognition , selective binding , supramolecular chemistry , NMR titration