Thiacalix[4]arene derivatives bearing imidazole units: a ditopic hard/soft receptor for Na+ and K+/Ag+ with an allosteric effect and a reusable extractant for dichromate anions

Two novel receptors 5,11,17,23-tetra-tert-butyl-25,27-bis[(ethoxycarbonyl)methoxy]-26,28-bis-[1-methyl-(imidazole)meth-oxy]-2,8,14,20-tetra-thiacalix[4]arene (L1) and 5,11,17,23-tetra-tert-butyl-25,27-bis-[(benzyl)methoxy]-26,28-bis-[1-methyl-(imidazole)-methoxy]-2,8,14,20-tetrathiacalix[4]arene (L2) possessing imidazole moieties based on thiacalix[4]arene in the 1,3-alternate conformation have been synthesized and characterized. The crystal structures of L1 and L2 have been determined. The binding behaviour towards Li+, Na+, K+ and Ag+ ions has been examined by 1H NMR titration experiments in (CDCl3/CD3CN; 10:1, v/v) solution. The exclusive formation of mononuclear complexes of L1 with metal cations is of particular interest revealing a negative allosteric effect in the thiacalix[4]arene family. Liquid-liquid extraction experiments indicate that synthesized L2 can be utilized as an efficient reusable extractant for dichromate anion by controlling the pH of the aqueous solution

A hexahomotrioxacalix[3]arene-based ditopic receptor for alkylammonium ions controlled by Ag⁺Ions

© 2018 by the authors. A receptor cone-1 based on a hexahomotrioxacalix[3]arene bearing three pyridyl groups was successfully synthesized, which has a C 3 -symmetric conformation and is capable of binding alkylammonium and metal ions simultaneously in a cooperative fashion. It can bind alkylammonium ions through the π-cavity formed by three aryl rings. This behaviour is consistent with the cone-in/cone-out conformational rearrangement needed to reorganize the cavity for endo-complexation. As a C 3 -symmetrical pyridyl-substituted calixarene, receptor cone-1 can also bind an Ag + ion, and the nitrogen atoms are turned towards the inside of the cavity and interact with Ag + . After complexation of tris(2-pyridylamide) derivative receptor cone-1 with Ag + , the original C 3 -symmetry was retained and higher complexation selectivity for n-BuNH 3 + versus t-BuNH 3 + was observed. Thus, it is believed that this receptor will have a role to play in the sensing, detection, and recognition of Ag + and n-BuNH 3 + ions

Allosteric binding properties of a 1,3-alternate thiacalix[4]arene-based receptor having phenylthiourea and 2-pyridylmethyl moieties on opposite faces

The synthesis of three new heteroditopic receptors (5a–c) which are based on thiacalix[4]arenes in the 1,3-alternate conformation are reported herein. These new receptors each have two thiourea moieties linking phenyl groups two of which are substituted with electron-withdrawing groups at their para-positions, and at the opposite side of the thiacalix[4]arene cavity, with two 2-pyridylmethyl groups. One example (5a) was also characterized by X-ray crystallography. A limited 1H-NMR and Uv-vis anion complexation study was conducted. DFT computational determinations indicated that 5c which has the strong electron–withdrawing NO2 groups had the most effective recognition ability towards the selected anions. The binding of Ag + at the 2-pyridyl moieties and the binding of the anions at the two thiourea NH groups of the p-substituted phenylthioureido moieties, respectively, was also investigated. The appearance of a positive allosteric effect with receptor 5b was also found using 1H-NMR titration experiments.</div