Inclusion of Electrochemically Active Guests by Novel Oxacalixarene Hosts

We demonstrate for the first time the utility of oxacalixarenes as hosts and investigate the forces that influence the thermodynamics of binding

Voltammetric Characterization of Redox-Inactive Guest Binding to Ln III [15-Metallacrown-5] Hosts Based on Competition with a Redox Probe

A novel competitive binding assay was implemented to monitor the binding of a redox inactive substrate to a redox inactive metallacrown host based on its competition with ferrocene carboxylate (FcC − ) using cyclic voltammetry (CV). First, the binding of FcC − to Ln III [15-MC Cu II ,N,L-pheHA -5] (LnMC) hosts was characterized by cyclic voltammetry. It was shown that the voltammetric half wave potentials, E 1/2 , shifted to more positive potentials upon the addition of LnMC. The explicit dependence of E 1/2 with the concentration of LnMC was used to determine the association constants for the complex. The FcC − binding strength decreased with larger central lanthanide metals in the LnMC hosts, and substantially weaker binding was observed with La III . X-ray crystallography revealed that the hydrophobic host cavity incompletely encapsulated FcC − when the guest was bound to the nine-coordinate La III , suggesting the LnMC’s ligand side chains play a substantial role in guest recognition. With knowledge of the MC-FcC − solution thermodynamics, the binding affinity of a redox inactive guest was then assessed. Addition of sodium benzoate to a LnMC and FcC − mixture resulted in E 1/2 shifting back to the value observed for FcC − in the absence of LnMC. The association constants between benzoate and LnMC’s were calculated via the competitive binding approach. Comparison with literature values suggests this novel assay is a viable method for determining association constants for host–guest systems that exhibit the proper electrochemical behavior. Notably, this CV competitive binding approach does not require the preparation of a modified electrode or a tethered guest, and thus can be generalized to a number of host–guest systems.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77442/1/chem_200903015_sm_miscellaneous_information.pd

Dendritic and metallic nanoassemblies

This dissertation investigates the synthesis and electrochemical properties of dendrimers and their supramolecular interactions with different host molecules. Additionally, the author describes the self-assembly of metallic nanostructures by wire-like bis-ruthenium metallaynes. These studies were carried out by a wide range of techniques including, cyclic voltammetry, NMR spectroscopy, mass spectroscopy, UV-vis spectroscopy and TEM.Chapter one is a brief introduction into the science of dendrimers and describes the evolution of these molecules from mere intellectual curiosities to their present emerging applications which take advantage of their unique properties. The potential of dendrimers is limitless and this field is still relatively young.Chapter two describes the synthesis and electrochemical characterization of dendrimers which have electroactive cores and their supramolecular interaction with the host molecule CB7. The electroactive core served as a probe for the dendritic microenvironment and gave information about the conformational changes of these dendrimers. Additionally, the electroactive moiety on these molecules also served as a probe to investigate the host binding properties of the CB7 molecule and reveals the importance of electrostatic forces in the modes of binding of CB7.Chapter three describes the interaction of electroactive hydrophobic dendrimers with a resorcinarene host molecule. This interaction was found to increase with dendrimer generation and this binding was aided by the polyvalence of dendrimers and cooperativity of multiple non-covalent interactions including hydrogen bonding and cation-pi interactions.Chapter four describes the use of wire-like ruthenium complexes as tethers for self-assembly of metallic nanostructures. The transition metal backbone was previously shown to aid electronic communication between the ends of conjugated systems. This work demonstrates that wiring of components can be achieved by self-assembly

Electrochemically Switchable Cucurbit[7]uril-Based Pseudorotaxanes

The binding location of cucurbit[7]uril can be controlled via redox conversions in these novel, structurally simple pseudorotaxanes

New Dendrimers Containing a Single Cobaltocenium Unit Covalently Attached to the Apical Position of Newkome Dendrons: Electrochemistry and Guest Binding Interactions with Cucurbit[7]uril

Two new dendrimer series were prepared and characterized. These dendrimers contain a single bis(cyclopentadienyl)cobalt(III) (cobaltocenium, Cob+) unit covalently attached to the apical (focal) position of Newkome-type dendrons, ranging in size from first to third generation. The dendrimers in the first series (1ECob + − 3ECob +) are hydrophobic and have 3, 9, and 27 tert-butyl esters on their peripheries, whereas the dendrimers in the second series (1Cob + − 3Cob +) are hydrophilic with 3, 9, and 27 carboxylic acid groups on their surfaces, respectively. In voltammetric experiments, all dendrimers showed the expected one-electron reversible reduction of the cobaltocenium center, and the heterogeneous rate of electron transfer decreased with generation in both dendrimer series. The host−guest binding interactions between water-soluble dendrimers 1Cob + − 3Cob + and the cucurbit[7]uril (CB7) host were investigated using 1H NMR spectroscopy, MALDI-TOF mass spectrometry, and electrochemical techniques. The association equilibrium constants (K) for all dendrimer guests were significantly lower than that measured for the inclusion complex between underivatized Cob + and CB7 (K = 5.7 × 109 M-1). Nonetheless, among the three dendrimers surveyed, the second-generation dendrimer, 2Cob +, afforded optimum stabilization for the CB7 inclusion complex

Binding interactions between the host cucurbit[7]uril and dendrimer guests containing a single ferrocenyl residue

The stability of the inclusion complexes formed between the host cucurbit[7]uril and dendrimers containing a single ferrocene residue is strongly affected by the solution pH and the growth of the dendrimer, reaching its highest values on the second and third generation dendrimers, whereas no complex is formed with the first generation compound

Electrochemically Switchable Cucurbit[7]uril-Based Pseudorotaxanes

The binding location of cucurbit[7]uril can be controlled via redox conversions in these novel, structurally simple pseudorotaxanes

New Dendrimers Containing a Single Cobaltocenium Unit Covalently Attached to the Apical Position of Newkome Dendrons: Electrochemistry and Guest Binding Interactions with Cucurbit[7]uril^†

Two new dendrimer series were prepared and characterized. These dendrimers contain a single bis(cyclopentadienyl)cobalt(III) (cobaltocenium, Cob+) unit covalently attached to the apical (focal) position of Newkome-type dendrons, ranging in size from first to third generation. The dendrimers in the first series (1ECob+−3ECob+) are hydrophobic and have 3, 9, and 27 tert-butyl esters on their peripheries, whereas the dendrimers in the second series (1Cob+−3Cob+) are hydrophilic with 3, 9, and 27 carboxylic acid groups on their surfaces, respectively. In voltammetric experiments, all dendrimers showed the expected one-electron reversible reduction of the cobaltocenium center, and the heterogeneous rate of electron transfer decreased with generation in both dendrimer series. The host−guest binding interactions between water-soluble dendrimers 1Cob+−3Cob+ and the cucurbit[7]uril (CB7) host were investigated using 1H NMR spectroscopy, MALDI-TOF mass spectrometry, and electrochemical techniques. The association equilibrium constants (K) for all dendrimer guests were significantly lower than that measured for the inclusion complex between underivatized Cob+ and CB7 (K = 5.7 × 109 M-1). Nonetheless, among the three dendrimers surveyed, the second-generation dendrimer, 2Cob+, afforded optimum stabilization for the CB7 inclusion complex

Cucurbit[8]uril‐Mediated Redox‐Controlled Self‐Assembly of Viologen‐Containing Dendrimers

The dimerization of dendrimers that contain a single 4,4′‐bipyridinium (viologen) unit, upon one‐electron reduction, is strongly enhanced by the presence of the host cucurbit[8]uril. This behavior is attributed to the formation of a stable inclusion complex between the host and two π‐stacked viologen radical‐cation guests—the one‐electron‐reduced form of viologen (see scheme)

Proton and Electron Transfer Control of the Position of Cucurbit[n]uril Wheels in Pseudorotaxanes

This paper presents an overview of recent work on the binding interactions between a series of 4,4'‐bipyridinium (viologen) derivatives and the hosts cucurbit[6]uril (CB6) and cucurbit[7]uril (CB7), which give rise to stable ‘wheel‐on‐an‐axle' inclusion complexes (pseudorotaxanes) in aqueous solution. The carboxylic acid termini on the pseudorotaxane axle can be used as handles to control—via proton transfer reactions—the relative position of the CB wheel along the axle. We also report on a different type of pseudorotaxane in which the reversible oxidation of the axle's ferrocenyl end groups leads to controlled displacement of the CB7 wheel. Known binding properties of the cucurbit[n]uril hosts are utilized in the design and preparation of new, water‐soluble “wheel‐on‐an‐axle” inclusion complexes (pseudorotaxanes), in which the average location of the wheel or its sliding motion can be controlled via proton‐ or electron‐transfer reactions (see figure) with suitable functional groups inserted on the axle component