Silver Ion Complexation by a Calix[4]arene bis(Crown Ether): Ambivalence Towards Ether and Polyhapto Coordinations

Resorcinarene bis-thiacrowns: prospective host molecules for silver encapsulation

Mixed-donor atom tetramethoxy resorcinarene bis-thiacrown hosts, in which the crown unit contains both hard oxygen and soft sulfur donor atoms, were synthesized for soft metal cation binding. The binding properties were investigated both in solution and in the solid state by NMR spectroscopy and X-ray crystallography. It was found that the resorcinarene bis-thiacrowns were able to complex silver cations with remarkable affinity forming readily 1:2 host-guest complexes in solution. The solid state structures also revealed that the bis-thiacrowns form silver complexes in an unanticipated endo- and exo-cavity fashion within the same host molecule. Both the solution and solid state studies indicated the sulfur atoms to be the major contributing donor atoms in forming the binding interactions with silver cations.

Resorcinarene bis-crown silver complexes and their application as antibacterial Langmuir-Blodgett films

Silver complexes of a cation binding supramolecular host, resorcinarene bis-crown (CNBC5) with propyl, nonyl, decyl and undecyl alkyl chains were investigated by NMR titration, picrate extraction and single crystal X-ray diffraction. Binding studies showed that both 1 : 1 and 1 : 2 (host-Ag(+)) complexes are present in solution with only a slight effect of the lower rim alkyl chain length on the binding constants (log K 4.0-4.2 for 1 : 2 complexes). Solid state complexes of the resorcinarene bis-crowns bearing either C(3) or C(11) chains were obtained. Single crystal X-ray analyses showed that both derivatives bind silver ions by metal-arene and Ag···O coordination from the crown ether bridges and from the solvent, and pack in layered or bilayered fashion. Furthermore, the amphiphilic nature of C11BC5 was demonstrated using the Langmuir balance technique. Langmuir-Blodgett films of the amphiphilic C11BC5-Ag complex were transferred onto a substrate and shown to possess antibacterial activity against E. coli.

Synthesis of Oligophenylene-Substituted Calix[4]crown-4s and Their Silver(I) Ion-Induced Nanocones Formation

A novel series of oligophenylene OPP(n)-substituted calix[4]crown-4s bearing up to three phenylene units, 1a-d, has been efficiently synthesized by means of either microwave-assisted or silver(I) ion-assisted Pd-catalyzed Suzuki cross-coupling of tetraiodocalix[4]crown-4 and the corresponding oligophenylboronic acids. Complexation of OPP(n)-substituted calix[4]crown-4s with silver (I) ion was substantiated by 1H NMR spectroscopic and high-resolution ESI- or MALDI-TOF- MS studies. The weak binding affinities of OPP(n)-substituted calix[4]crown-4s for silver (I) ion, which were estimated from 1H NMR titrations with binding association in the range of 30-90 M(-1), allows reversible disassembling in the presence of KI at ambient temperature. Remarkably, the single-crystal X-ray structures of OPP(n)-calix[4]crown-4.Ag+ complexes indicate the atypical silver (I) ion-crown ether binding mode resulting in the formation of rigid nanocones with volume created up to approximately 1500 A(3). Our results suggested that despite the weak binding affinity of crown ether ligands for silver (I) ion, this weak interaction is still be useful as a tool to construct supramolecular architectures.

Two structural types of 1,3-alternate tetrapropoxycalix[4]arene derivatives in the solid state

The solid state structures of seven tetrapropoxycalix[4]arene derivatives immobilised in a 1,3-alternate conformation were determined using single-crystal X-ray crystallography. The cavity shapes of investigated derivatives (upper rim unsubstituted, distally di-substituted and tetra-substituted) and the nature of intermolecular interactions in molecular packing were compared. The results indicate that there are only two structural types adopted by basic tetrapropoxycalix[4]arene derivatives in the 1,3-alternate conformation.

Systematic structural coordination chemistry of p-tert-butyltetrathiacalix[4]arene: 1. Group 1 elements and congeners

Determinations of the crystal structures of complexes of the alkali metal ions with, in the case of Li, the dianion and, in the cases Na-Cs, the monoanion of p-tert-butyltetrathiacalix[4]arene have shown that both the sulfur atoms which form part of the macrocyclic ring, as well as the pendent phenolic/phenoxide oxygen donor atoms, are involved in coordination to these metals. Although the Li and Na complex structures are similar to those of the corresponding complexes of p-tert-butylcalix[4]arene, there is no similarity in the structures of the Cs complexes, with the present structure showing no evidence of polyhapto Cs(+)-pi interactions. Instead, the complex crystallizes as a ligand-bridged (S-, O-donor) aggregate of three Cs ions, solvent molecules, and four calixarenes, somewhat like the Rb complex, though here four Rb ions are present, and higher in aggregation than the K+ complex, where two K+ ions are sandwiched between two calixarene moieties. The triethylammonium complex of the thiacalixarene monoanion, though formally analogous in that it involves a monocation, has a simpler structure than any of the alkali metal derivatives, based formally on proton coordination (H-bonding). However, interestingly, it can be isolated in both solvated (dmf, dmso) and unsolvated forms, as indeed can the "free", p-tert-butyltetrathiacalix[4]arene ligand itself.