The binding stoichiometry of a host-guest complex can be effectively controlled by the redox chemistry of the guest: a 1:1 inclusion complex of methylviologen dication (MV2+) in cucurbit[8]uril (CB[8]) converts completely and reversibly to a 2:1 inclusion complex of cation radical (MV+.) in CB[8] upon the reduction of the guest.

In 1958 he joined the faculty of The University of Texas at Austin, where he currently holds the Norman Hackerman Regents Chair in Chemistry. Guy Denuault received his DUT from The University of Reims, his MST from the University of Bordeaux, and his Ph.D. from the University of Southampton. His research has focused on the use of ultramicroelectrodes. Chongmok Lee received his B.S. from Seoul National Univeristy in 1981 and his M.S. from Korea Advanced Institute of Science and Technology In 1983. His doctoral research has focused on the use of SECM and ellipsometry In electroanalytical chemistry. Daniel Mandler received his B.Sc. in 1983 and his Ph.D. In 1988 from the Hebrew University of Jerusalem. His doctoral research was in the area of artificial models for photosynthesis. David 0. Wipf received his B.S. from the University of South Dakota in 1984. He received his Ph.D. In 1989 from Indiana University, where he worked on developing high-speed cyclic voltammetry at ultramlcroelectrodes. Guy Denuault, Daniel Mandler, and David 0. Wipf are postdoctoral fellows, and Chongmok Lee Is a doctoral candidate, currently working with Professor Bard at The University of Texas.

Picking up the thread: A large, reversible change in size as well as shape is observed in a [2]pseudorotaxane‐based molecular machine composed of cucurbit[8]uril (CB[8]; bead) and a hexamethylene‐bridged bisviologen (thread, see schematic representation) on application of external stimuli. The key feature of the machinelike behavior is the reversible formation of a molecular loop by intramolecular pairing of the terminal viologen radical cation units inside CB[8] upon electrochemical or photochemical reduction.

Salen-type ligands comprised of ethylenediamine or 1,2-cyclohexenediamine, along with an salicylaldehyde bearing a methyl substituent on its 3-position and a -[CR(CH(2)CH(2)CH(2)N(+)Bu(3))(2)] (R = H or Me) on its 5-position, unexpectedly afford cobalt(III) complexes with uncoordinated imines. In these complexes, two salen-phenoxys and two 2,4-dinitrophenolates (DNPs), which counter the quaternary ammonium cations, coordinate persistently with cobalt, while two other DNPs are fluxional between a coordinated and an uncoordinated state in THF at room temperature. The complexes of this binding mode show excellent activities in carbon dioxide/propylene oxide copolymerization (TOF, 8300-13,000 h(-1)) but with some fluctuation in induction times (1-10 h), depending on how dry the system is. The induction time is shortened (<1.0 h) and activity is increased approximately 1.5 times upon the replacement of the two fluxional DNPs with 2,4-dinitrophenol-2,4-dinitrophenolate homoconjugation ([DNP...H...DNP](-)). Imposing steric congestion either by replacing the methyl substituent on the salicylaldehyde with tert-butyl or by employing H(2)NCMe(2)CMe(2)NH(2) instead of ethylenediamine or 1,2-cyclohexenediamine results in conventional imine-coordinating complexes, which show lower activities than uncoordinated imine complexes.

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