compound with a potassium ion or a hydronium ion respectively which have much greater solubility than the uncomplexed neutral molecule. CB[10] is large enough to hold other molecular hosts such as a calixarene molecule. With a calixarene guest different chemical conformations (cone, 1,2-alternate, 1,3-alternate) are in rapid equilibrium. Allosteric control is provided when an adamantane molecule forces a cone conformation with a calixarene - adamantane inclusion complex within a CB[10] molecule. Rotaxane macrocycles Given their high affinities to form inclusion complexes cucurbiturils have been employed as the macrocycles component of a rotaxane. After formation of the supramolecular assembly or threaded complex with a guest molecule such as hexamethylene diamine the two ends of the guest can be reacted with bulky groups that will then act as a stoppers preventing the two separate molecules from dissociating. In another rotaxane system with a CB[7] wheel, the axle is a 4,4'-bipyridinium or viologen subunit with two carboxylic acid terminated aliphatic N-substituents at both ends. In water at concentration higher than 0.5 mM complexation is quantitative without need of stoppers. At pH = 2 the carboxylic end-groups are protonated and the wheel shuttles back and forth between them as evidenced by the presence of just two aromatic viologen protons in the proton NMR spectrum. At pH = 9 the wheel is locked around the viologen center. More recently, rotaxane with a CB[8] wheel was synthesized. This rotaxane can bind neutral guest molecules. Drug delivery vehicles Cucurbituril's host–guest properties have been explored for drug delivery vehicles. The potential of this application has been explored with cucurbit[7]uril that forms an inclusion compound with the important cancer fighting drug oxaliplatin. CB[7] was employed despite the fact that it is more difficult to isolate since it has much greater solubility in water and its larger cavity size can accommodate the drug molecule. The resulting complex was found to have increased stability and greater selectivity that may lead to fewer side effects. Supramolecular catalysts Cucurbiturils have also been explored as supramolecular catalysts. Larger cucurbiturils, such as cucurbit[8]uril can bind multiple guest molecules. CB[8] forms a complex 2:1 (guest:host) with (E)-diaminostilbene dihydrochloride which is accommodated by CB[8]'s larger internal diameter of 8.8 angstrom and height 9.1 angstrom. The close proximity and optimal orientation of the guest molecules within the cavity enhances the rate of the photochemical cyclization to give cyclobutane dimer with a 19:1 stereoselectivity for the syn configuration when