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Publication Date

2009-05-18

Availability

UM campus only

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Chemistry (Arts and Sciences)

Date of Defense

2009-04-14

First Committee Member

Angel E. Kaifer - Committee Chair

Second Committee Member

Francisco Raymo - Committee Member

Third Committee Member

Vadyanathan Ramamurthy - Committee Member

Fourth Committee Member

Milagros Delgado - Outside Committee Member

Abstract

This dissertation describes the effective encapsulation of redox active compounds inside deep-cavity cavitands: Gibb's octaacid40 and Rebek's 41 tetracarboxylate cavitand. Gibb's octaacid is a water-soluble, deep-cavity cavitand that forms well-characterized dimeric molecular capsules around hydrophobic guests. Both 1H NMR spectroscopic and voltammetric experiments clearly reveal that ferrocene plays the role of hydrophobic guest effectively. Ferrocene derivatives (ferrocenylmethyltrimethylammonium (FcNMe3+), ferrocenemethanol (FcOH), and ferrocene carboxylic acid (FcCOOH)) were also found to form inclusion complexes with octaacid cavitand however, in this case 1:1 (host to guest) ratio complexes are formed. This is in strong contrast with the dimeric capsule formed around ferrocene. Under the surveyed experimental conditions encapsulated ferrocene is electrochemically silent. We have also found that the negative charges around this dimeric molecular capsule play a very important role. For instance, hydrophobic cations, such as viologens,60 bind to the outer surface of the capsule. This opened a possibility of mediated electron transfer reactions between molecules bound inside the octaacid capsule and tightly attached to its outer surface in purely synthetic system. The cationic ferrocene derivative, ferrocenylmethyltrimethylammonium (FcNMe3+), was used as a mediator since its electrochemical potential range makes it suitable as a mediator molecule. In fact, our data clearly support that FcNMe3+ mediates electron transfer between encapsulated ferrocene and the electrode surface. Ferrocene, its derivatives (FcNMe3+ and FcOH), and cobaltocenium (Cob+) also form 1:1 inclusion complexes with Rebek's tetracarboxylate cavitand, which surprisingly are all voltammetrically silent. The formation of these inclusion complexes seems to be driven by hydrophobic interactions between the host and the guest. The lack of voltammetric response observed in this work is a very intriguing finding.

Keywords

Molecular Capsules; Supramolecular Chemistry; Viologen; Electron Transfer; Electrochemistry; Ferrocene

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