A Self‐Assembled Cage Binding Iodide Anions over Other Halide Ions in Water

Abstract

A triangular‐prism shaped cage was self‐assembled by the formation of a dynamic covalent bond, namely a hydrazone, in acidic aqueous solution. The hexacationic host bears a number of relatively acidic protons pointing inside the cage cavity, which is able to accommodate an iodide anion selectively in water over other halide anions such as F−, Cl−, and Br−, which are more hydrated. As a comparison, a macrocycle analogue bearing fewer positive charges and fewer hydrogen bond donors shows no anion binding ability. As inferred from the single‐crystal structure and theoretical calculations, the ability of the cage to selectively recognize iodide anions results from the combination of electrostatic forces, C−H⋅⋅⋅I− hydrogen bonds, and the hydrophobic effect.

Enhanced molecular binding affinity toward aromatic dications by anthracene-derived crown ethers in water

“…It is interesting to note that the positive charge center of the nitrogen atom on pyridinium is very far away from the negative charge center of the sulfonate group on 1 , and the N–S distances are 5.64, 5.80, 6.81, and 7.11 Å, respectively, which is farther than our previously reported tetrasulfonated crown ethers. 4 This means that electrostatic interaction might have less influence on the binding of G3 ⊂ 1 as compared to other effects like π-stacking interaction. This result should be attributed to the fact that anthracene is a large π-group which can form strong π-stacking interaction with π-electron-deficient G3 and this effect is very strong in an aqueous environment.…”

“…Progress in the field of supramolecular chemistry has been driven by the need for rationally designed synthetic receptors for applications in self-assembly processes, 1 molecular machines, 2 and functional materials, 3 especially in aqueous environments. 4 In this context, a variety of macrocyclic receptors, including crown ethers, 5 cyclodextrins, 6 calixarenes, 7 and cucurbiturils, 8 have drawn considerable attention in recent decades owing to their strong binding affinities toward a wide range of molecules and organic cations. Moreover, considering water is a unique, ubiquitous solvent in many chemical and biological processes, water-soluble macrocyclic receptors are of particular interest and are widely used as molecular sensors, 9 amphiphilic assemblies, 10 and hydrogels.…”

Amidoboronates: bringing together the synthesis of BN-heterocyclesviaa reductive coupling and dynamic covalent chemistry

“…Dynamic covalent chemistry 15–19 is a diverse research field encompassing a variety of reversible covalent bonds from CN 22,24–28 to B–O 19,22,32–34 bonds. The combination of several dynamic covalent bonds offers the potential for addressing the different functional groups orthogonally, thus increasing the complexity of the system.…”

“…Dynamic covalent chemistry combines the strength of covalent bonds with the reversibility of bond formation, enabling for example the self-assembly of supramolecular architectures from mechanically interlocked molecules to cages from smaller building blocks under thermodynamic control. [15][16][17][18][19] While the dynamic covalent chemistry of a variety of bonds including S-S, 16,[20][21][22] CvC, 23,24 CvN, 22,[24][25][26][27][28] C-O, 17,29 Si-O 30,31 and B-O 19,22,[32][33][34] bonds has been established, the discovery of new types of dynamic covalent bonds, e.g. based on B-N bonds, could open up new avenues for applications.…”

Large anion binding in water

“…1–4 In contrast, the binding of large anions such as I − , SCN − , ClO 4 − , and PF 6 − , which have a lower charge density and are weakly hydrated, has received comparably less attention, among others, due to the fact that they play, with the notable exception of I − , less critical natural roles. 5–9 On the other hand, the diametrically opposed effects that the two groups of anions can exert on biological systems have been recognized since long by the Hofmeister series, which conventionally classifies the character of ions as being salting-out (kosmotropic) or salting-in (chaotropic) in nature. 10 Recently, the supramolecular chemistry of long-known synthetic cluster anions of the borate- 11,12 and polyoxometalate-type 13 has moved into the focus, driven by the observation that their affinity with hydrophobic binding sites does exceed, 14 against expectation, those of hydrophobic guest molecules.…”