Visualization and quantitation of electronic communication pathways in a series of redox-active pillar[6]arene-based macrocycles.

While oxidized pillar[5]arenes with 1-5 benzoquinone units are known, very few examples of oxidized pillar[6]arenes have been reported. We describe here the synthesis, characterization and electrochemical behavior of a series of macrocyclic hosts prepared by the stepwise oxidation of 1,4-diethoxypillar[6]arene, resulting in high-yield and high-purity isolation of two constitutional isomers for each macrocycle, in which two, three or four 1,4-diethoxybenzene units are replaced by benzoquinone residues. A careful structural comparison with their counterparts in the pillar[5]arene framework indicates that the geometries of the macrocycles are better described as non-Euclidean hyperbolic hexagons and elliptic pentagons, respectively.

Self-Assembly of Partially Oxidized Pillar[5]arene into Fibrous Structures.

Partial oxidation of the pillar[5]arene macrocycle with Fe(III) leads to the isolation of a fibrous purple solid with high porosity. Experimental and computational data indicate that the solid material is primarily composed of macrocycles in which two of the hydroquinone units have been oxidized to benzoquinone units. Self-assembly takes place through the formation of multiple quinhydrone charge-transfer complexes between hydroquinone and benzoquinone units on adjacent macrocycles, providing a rare example of self-assembly based on a pentagonal molecular symmetry.

Synthesis and Binding Properties of Monohydroxycucurbit[7]uril: A Key Derivative for the Functionalization of Cucurbituril Hosts.

We present a simple, direct method to prepare monohydroxylated cucurbit[7]uril (CB7-OH) through the direct oxidation of its precursor host, cucurbit[7]uril (CB7). Although the conversion takes place in low yield (14%), the isolation of CB7-OH from the reaction mixture is straightforward, and the unreacted CB7 can be easily recovered. ITC measurements with several selected guests confirmed that CB7-OH binds all of them in aqueous solution with similar, albeit slightly lower, binding affinities than those observed with the unmodified CB7 host.

Through-Space Communication Effects on the Electrochemical Reduction of Partially Oxidized Pillar[5]arenes Containing Variable Numbers of Quinone Units.

The electrochemical reduction of five partially oxidized pillar[5]arenes containing variable numbers (1-5) of quinone units was investigated in acetonitrile and dichloromethane solutions. The cathodic voltammetric behavior of all the macrocyclic compounds containing two or more quinone units indicates the existence of detectable levels of electronic communication between them. We have also investigated these compounds and their reduced forms using DFT computations.

Binding Interactions between a Ferrocenylguanidinium Guest and Cucurbit[n]uril Hosts.

The binding interactions between a novel ferrocenylguanidinium derivative (FcG) and the macrocyclic hosts cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) were investigated in aqueous solution. H NMR spectroscopic experiments indicated that both hosts form stable 1:1 inclusion complexes with FcG, in which the ferrocenyl group is engulfed by the host cavity. The stoichiometry of the CB7·FcG complex was also confirmed by electrospray mass spectrometric (ESI MS) experiments.

Zeolite encapsulated Ni(II)-Schiff-base complex: a novel size-selective electro-catalyst for the determination of the purity of stevioside.

Ship-in-a-bottle complex of nickel(II) containing the ligand N,N'-bis(2,4-dihydroxyacetophenone)-2,2-dimethylpropandiimine (H2{salnptn(4-OH)2}) has been synthesized in zeolite Y. The characteristics of the encapsulated complex are identified by the methods of EDX, SEM, XRD, FT-IR and cyclic voltammetry. A catalytic effect in the electrochemical oxidation of glucose, fructose and sucrose, and a blocking effect in stevioside oxidation are demonstrated on the Ni(II){salnptn(4-OH)2}-Y/CPE.