Selective Encapsulation of Chloride Ions within Novel Cage Host Complexes in the Presence of Equimolar Amounts of Chloride and Bromide Ions

Abstract

Four macrotricyclic cage hosts which feature four positive binding sites oriented toward the center of the intramolecular cavity are presented as promising candidates for anion receptors and they have been expected to play a important role in the selective encapsulation of the halide ion Cl- or Br . The complementarity between a macrotricyclic quaternary ammonium ion and Cl- was achieved by fine-tuning of the four ammonium nitrogen atoms and the endocyclic methylene groups. The cage hosts [R4N4(C5H10)4(C6H12)2]4+ (abbreviated as [556]) showed perfect encapsulation of all chloride ions in acetonitrile at 0 < r= ([Cl-]o/[[556]]o) < or = 1 within the sensitivity of the 1H NMR spectra in combination with a rather slow chemical exchange of the Cl- ion in an encapsulation/decapsulation equilibrium with [556]. Further, the selective encapsulation of all the chloride ions into [556] cage occurs unambiguously at r = 1 in the presence of equimolar amounts of Br-. The structural complementarity of the newly designed [556] host prevails over the Hofmeister-series restraints determined by differences in Gibbs free energy of halide anion solvation.

Macrotricyclic quaternary tetraammonium receptors: Halide anion recognition and interfacial activity at an aqueous interface. A molecular dynamics investigation

“…These investigations extent our work on ions and complexes at LLIs 18–21. Interestingly, it was reported that L 4+ derivatives with R = CH 2 ϕ form two‐dimensional assemblies at the interface between the NaCl(001) surface and water where they complex chloride anions 10. This suggests that the host can approach sufficiently close to the water surface to interact with the salt, i.e., that the hosts are “attracted by the interface,” unlike small hydrophilic ions which are “repelled” by the water surface 22.…”

“…Two modifications of the complex were performed, to reduce its hydrophilicity and to test the resulting interfacial behavior. First, the four exo NMe groups were replaced by NCH 2 ϕ groups ( B system), as in the compounds studied experimentally 9, 10. After 1 ns of dynamics, this CH 2 ϕ– L 4+ analog was also on the average at the surface of water, but closer to the interface (at 1.3 ± 1.2 Å), oscillating between the water side and the chloroform side (Fig.…”

“…In aqueous solution, the largest cage (six C 8 chains and four N + CH 3 corners) displays a selectivity order Cl − < Br − < I − , while with a smaller cage (six C 6 chains), the order is Cl − < I − < Br − 8. In this article, we focus on a smaller analog with three C 5 and three C 6 chains, recently developed by Ichikawa et al9, 10 Due to the different lengths of ethylene bridges, three isomeric forms can be considered, as shown schematically in Figure 1. Two of them, noted L 4+ and L , are of C 3v ‐type symmetry.…”

Selective Host–Guest Binding of Anions without Auxiliary Hydrogen Bonds: Entropy as an Aid to Design

“…A promising candidate to meet these criteria is the quaternized adamanzane derivative 3 (Scheme 1), which builds upon a variety of congeners [11][12][13][14] of proven utility in anion complexation. [15][16][17][18][19] Common to all members in this family is the mechanism of anion encapsulation, which rests on the strong Coulombic force resulting from the overlay of four positive charges.…”

Selektive Wirt‐Gast‐Bindung von Anionen ohne Hilfe von Wasserstoffbrücken: die Entropie als Designwerkzeug

“…Ein Wirt, der diese Kriterien potentiell erfüllen kçnnte, ist das quaternäre Adamanzan 3 (Schema 1), für das mehrere Analoga [11][12][13][14] eine respektable Bindungsstärke für Anionen vorweisen kçnnen. [15][16][17][18][19] Allen Mitgliedern dieser Familie ist ein Einschlussprozess als Bindungsmodus gemeinsam, der auf der starken Coulomb-Anziehung durch Überlagerung von vier positiven Ladungen gründet.…”