Supramolecular Ladders from Dimerlc Cucurbit[6]uril

摘要

The cucurbit[n]uril (CB[n]; n = 5, 6, 7, 8, 10) family of molecular containers have become the object of intense focus in the field of supramolecular chemistry over the past decade. This surge in interest is due to the ability of CB[n] compounds to bind to suitable cationic guests with both high affinity (K_a up to 10~(15)m~(-1)) and high selectivity in water and the stimuli responsiveness (e.g. pH, chemical, photochemical, electrochemical) of the corresponding CB[n]·guest complexes. The remarkable recognition properties of CB[n]·guest complexes have been used as the basis for numerous applications of CB[n] compounds including chemical-sensing ensembles, membrane-protein fishing, drug solubilization and delivery, and supramolecular catalysis. Of highest utility for the construction of functional CB[n] derived systems is the ability of CB to form CB·guest2 ternary complexes—generally with heteropairs of electron-deficient and electron-rich aromatic guests—which has been exploited by the Kim, Urbach, Scherman, and Brunsveld research groups to construct molecular machines, sensing systems, promotors of protein dimerization, and complex macromo-lecular and nanoparticle architectures. Over the years, our research group has investigated the related ability of CB and bis-ns-CB to form ternary complexes that perform biomimetic functions (e.g. homotropic allostery, metallopor-phyrin sensing) or form supramolecular polymers. Recently, we and others have developed routes to prepare monofunctionalized derivatives of CB and CB. We envisioned that it would be possible to adapt this chemistry toward the construction of CB[n] dimers containing two covalently connected, fully formed CB[n] groups. Because each CB[n] cavity of such CB[n] dimers would separately retain the ability to bind to a wide array of guests with high affinity and selectivity, we surmised that dimeric CB[n] would extend the range of appropriate (hetero) guest pairs and thereby complement the use of CB in biomolecular derivatization and dimerization events, the formation of supramolecular polymers, and the assembly of nanoscale systems. Herein, we demonstrate the synthesis of dimeric CB compounds 1 and 2 and the ability of 1 to form supramolecular ladders when combined with oligomeric viologen-containing guests.