The cucurbit[7]uril (CB7) host forms rotaxane-type complexes with dumbbell-shaped, cationic guests bis(3,5-dimethoxybenzyl)-4,4'-bipyridinium (1(2+)) and bis(3,5-diethoxybenzyl)-4,4'-bipyridinium (2(2+)). The kinetics of complex formation is slower with the latter guest because of its bulkier end groups. Rotaxane formation was found to be thermodynamically more favorable and kinetically faster in D2O than in DMSO-d6 solution, which highlights the importance of hydrophobic interactions in the assembly of cucurbituril complexes.

The cathodic voltammetric behavior of pillar[5]quinone was investigated in dichloromethane solution. Our data show that the symmetry of the macrocycle has a pronounced effect on the electron uptake sequence. The uptake of the first five electrons follows a 2-1-2 pattern, and only a total of eight electrons could be injected into the macrocycle under our experimental conditions.

The cathodic voltammetric behavior of N,N'-dimethyl-4,4'-bipyridinium (methylviologen, MV(2+)), N,N'-dipropyl-4,4'-bipyridinium (propylviologen, PV(2+)), N,N'-dibutyl-4,4'-bipyridinium (butylviologen, BV(2+)), and N-heptyl-N'-ethyl-4,4'-bipyridinium (heptyl-ethylviologen, HEV(2+)) was investigated in aqueous solution containing variable concentrations of sodium cholate. In general, the presence of cholate was found to solubilize the more hydrophobic forms of the viologen probes. Among the three accessible viologen oxidation states (V(2+), V(+•), and V), the intermediate cation radical (V(+•)) was preferentially stabilized by the cholate aggregates regardless of the nature of the N-alkyl substituents. This stabilization leads to anodic shifts in the first half-wave potential (V(2+)/V(+•)) and cathodic shifts in the second half-wave potential (V(+•)/V) for viologen reduction. Both potential shifts were considerably more pronounced as the hydrophobic character of the viologen probe increased. The presence of the cucurbit[7]uril host in the solution leads to the formation of very stable inclusion complexes with the viologen probes, which tend to eliminate or substantially decrease the interactions between the viologens and the cholate micellar aggregates.

Polyamines have been used as active materials to capture carbon dioxide gas based on its well-known reaction with amines to form carbamates. This work investigates the reactions between three amino-terminated poly(amidoamine) (PAMAM) dendrimers (G1, G3 and G5) and CO2(g) in aqueous (D2O) and methanolic (CD3OD) solutions. The reactions were monitored using 1H NMR spectroscopy, and yielded dendrimers with a combination of terminal carbamate and terminal ammonium groups. In aqueous media the reaction was complicated by the generation of soluble carbonate and bicarbonate ions. The reaction was cleaner in CD3OD, where the larger G5 dendrimer solution formed a gel upon exposure to CO2(g). All reactions were reversible, and the trapped CO2 could be released by treatment with N2(g) and mild heating. These results highlight the importance of the polyamine dendrimer size in terms of driving changes to the solution’s physical properties (viscosity, gel formation) generated by exposure to CO2(g).