Spatially Designed Supramolecular Anion Receptors Based on Pillar[5]arene Scaffolds: Synthesis and Halide Anion Binding Properties

Abstract

Urea-functionalized anion receptors based on brominated functionalized pillar[5]arenes were prepared. The binding affinity toward halide anions was investigated and probed using 1H NMR titration and isothermal titration calorimetry (ITC). The complexation behavior was affected by the structure of the receptor and the nature of the anionic guest. The synthesized receptors are highly selective toward fluoride resulting in the formation of a 1:2 host-to-guest complex. The anion receptor based on the 1,3-alternate pillar[5]arene regioisomer shows the highest affinity toward fluorine anions. No significant interactions were observed with larger bromine anions. The formation of a self-assembled supramolecular polymer driven by hydrogen bonds in solution was demonstrated by diffusion-ordered spectroscopy (DOSY), ITC, and dynamic light scattering (DLS) measurements. From ITC dilution experiments, we found that the supramolecular polymer self-assembly at higher concentrations is a spontaneous process as indicated by the positive value of Gibbs free energy (ΔG = 12.04 kJ mol–1).

Crystal structure and supramolecular features of a bis-urea-functionalized pillar[5]arene

“…As a result, the number and relative position of the N-H groups with respect to the pillararene macrocycle is very crucial in such molecular receptors. Recently, we have reported the synthesis of ureafunctionalized anionic receptors based on di-and tetra-functionalized pillar [5]arenes (Vinodh et al, 2023). The influence of the receptor structure on the selectivity and binding ability toward different halides was investigated by 1 H NMR titrations, diffusion-order spectroscopy (DOSY) and isothermal titration calorimetry (ITC) experiments.…”

“…Other structurally related pillararene crystals reported include an A1/A2-bis-imidazolium-functionalized pillar[5]arene (QONPEQ; Gao et al, 2014), an A1/A2-bis-N-(9-anthrylmethy)triazole-functionalized pillar[5]arene (QACFEI; Bi et al, 2016) and an A1/A2-bis-2-azidoethoxy-functionalized pillar[5]arene (KEWLIL; Vinodh et al, 2023). Crystal structures of isomeric A1/A2, B1/B2-tetrakis-2-azidoethoxy-functionalized pillar [5]arene and A1/A2, C1/C2-tetrakis-2azidoethoxy functionalized pillar [5]arene have also been reported (KEWLEH and KEWLOR; Vinodh et al, 2023). Crystal structures of per-functionalized pillararenes in which…”

“…The synthesis and characterization of DUP have been described earlier (Al-Azemi et al, 2019;Vinodh et al, 2023). The first step is the synthesis of A1/A2-dibromoethoxy-pillar-[5]arene by the co-condensation method.…”

1-[1,4-Bis(but-3-en-1-yloxy)]-2,3,4,5-(1,4-dimethoxy)pillar[5]arene–1,4-dibromobutane 1:1 inclusion complex

“…Pillar [n]arenes are characterized by guest encapsulation and molecular recognition properties, which are due to their pillar-shaped structures, nano-sized cavities and availability of multiple rim sites for substitutions, and which makes them useful functional materials for several applications in materials chemistry, nanotechnology and biomimmetic systems (Ogoshi et al, 2016;Li et al, 2020). Appropriate derivatization of pillararene macrocycles can be achieved by selective functionalization of pillararene rims (Zhang et al, 2021;Al-Azemi & Vinodh, 2022;Vinodh et al, 2023). Selective derivatization of pillarene rims enables self-assembly of these macromolecules to form supramolecular polymers or make them capable of interacting with flexible binding sites, for example proteins (Liu et al, 2023).…”