Tritopic Bis-Urea Receptors for Anion and Ion-Pair Recognition

Mutual synergistic regulation of chloride anion and cesium cation binding using a new designed macrocyclic multi-functional sites receptor: A case of DFT computational prediction

The mutual synergistic regulation of the multi-functional sites on a single receptor molecule for ion-binding/recognition is vital for the new receptor design and needs to be well explored from experiment and theory. In this work, a new macrocyclic ion receptor (BEBUR) with three functional zones, including two ether holes and one biurea groups, is designed expecting to mutually enhance the ion-binding performance. The binding behaviors of BEBUR mainly for Cl- and Cs+ are deeply investigated by using density functional theoretical calculations. It is found that Cl-/Cs+ binding can be mutually enhanced and synergistically regulated via corresponding conformational changes of the receptor, well reflecting an electrical complementary matching and mutual reinforcement effect. Moreover, solvent effect calculations indicate that BEBUR may be an excellent candidate structure for Cl--binding with the enhancement of counter ion (Cs+) in water and toluene. In addition, visualization of intermolecular noncovalent interaction is used for analysis on the nature of the binding interactions between receptor and ions.

Synergistic regulation of chloride anion recognition using a triple-functional sites receptor with two different cationic effectors

The synergistic regulation of the multi-functional sites on one receptor molecule with different cationic effectors for anion recognition is scarce to be well understood from the experiment and theory. In this work, a new anion receptor with three functional zones including ether hole, biurea and double bipyridine groups (EUPR) is designed expecting to enhance the chloride anion recognition together with a rational synthesis path being proposed based on four simple and mature organic reaction steps. The conformational structures of the designed receptor EUPR and the binding behaviors for three kinds of ions (Cl-, Na+, and Ag+) are deeply investigated by using density functional theoretical calculations. It is found that Cl- binding via the hydrogen bond interaction can be significantly enhanced and synergistically regulated by the two kinds of cations and the corresponding conformational changes of receptor EUPR. Especially, the conformational pre-organization of receptor caused by the encapsulation of sodium ion into ether hole is benefit to the binding for Cl- in both thermodynamics and kinetics. Na+ binding, in turn, can ever be enhanced by chloride anion, whereas it seems that Ag+ binding cannot always be enhanced by chloride anion, reflecting an electrical complementary matching and mutual enhancement effect for different counter ions. Moreover, solvent effect calculations indicate that EUPR may be an ideal candidate structure for Cl- recognition by strategy of counter ion enhancement in water. Additionally, a visual study of intermolecular noncovalent interaction (NCI) and molecular electrostatic potential (ESP) are used for the analysis on the nature of interactions between receptor and bound ions.

Remote control of anion binding by CH-based receptors

We show that the substitution of tetra(benzimidazole)resorcin[4]arenes with electron withdrawing groups on the upper rim enhances anion binding at the opposite edge by more than three orders of magnitude. Moreover, selective anion binding at either the OH/NH or CH binding sites is demonstrated.

Highly soluble bisurea derivatives for anion recognition

Highly soluble bisurea derivatives having 1,2-phenoxyethane (receptors 2) and 1,2-ethoxyethane (3) moieties as spacer groups were designed and prepared based on previously reported receptors with the 2,2'-binaphthyl group as a spacer (1). The receptors can be prepared in fewer steps from commercially available starting materials. The solubilities and anion recognition abilities were evaluated by UV-vis and NMR spectral methods. Receptors 2 and 3 bearing a flexible linker showed good solubilities in common organic solvents such as CHCl₃, MeCN, 2-butanone, toluene, and THF. Although the anion recognition abilities of receptors 2 and 3 were lower than those of receptors 1, the greatly improved solubilities of receptors 2 and 3 allow the association of anions under more concentrated conditions for the solubilisation of salts such as lithium chloride in organic solvents.