Through the careful manipulation of non-covalent supramolecular chemical interactions, it is envisioned that work can be performed by transferring energy through molecular assemblies.  Molecular machines, such as shuttles, can involve the use of host-guest chemistry that reacts to stimuli such as light, pH level, electric potential, and temperature.  The study herein highlights the reasons that the application of cucurbit[n]uril should be in the forefront of this emerging field.  Cucurbit[n]uril (CB[n]) is a particularly unique macrocycle consisting of electron dense amide groups that create a negative electrostatic potential around two open portals.  Due to this feature, cucurbit[n]uril can bind cationic, electrostatically positive, and hydrophobic molecules, leading to very high binding constant to a wide variety of guests.  CB[7] binds particularly well with ammonium and viologen species, whose size, shape, and electronic properties are ideally suited for the cavity.  Viologens themselves are of particular interest to the construction of molecular machines due to their unique binding and redox properties.  For example, a one-electron reduction of the viologen guest results in a two-fold decrease of the binding constant with CB[7].This type of switching could easily be envisioned to be useful in the construction of a molecular shuttle, but redox applications of this molecule have had limited success due to the tendency of viologen to undergo diligamerization, a problem that would potentially be solved with CB[7].  In this work, the modes of binding and the equilibrium binding constants have been determined by 1H NMR for six new viologen and dipyridinium host-guest complexes with CB[7], which could lead to the strategic incorporation of these molecules into molecular machines and devices.  Not only has previously held knowledge about the interactions of this macrocycle been confirmed, but the results herein have increased the sphere of knowledge and may also guide future studies in this promising field.

Investigation of host-guest complexes of cucurbit[7]uril with a series of new viologens and pyridinium compounds toward the construction of molecular shuttles

247th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.