Title

Electrochemical and spectroscopic properties of viologen-based catenanes, rotaxanes and cyclophanes

Date of Award

1993

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Chemistry

First Committee Member

Angel E. Kaifer, Committee Chair

Abstract

Part I. Selected physical characteristics of a series of bis-viologen complexes were evaluated with cyclic voltammetry and ESR spectroscopy. The series contained opened, cyclophane, rotaxane and catenane bis-viologen complexes. Well behaved electrochemistry was routinely observed. Cyclization increased the reduction potential of the bis-viologen backbone by lowering intramolecular repulsion effects. Incorporation of electron donating groups between the viologen moieties act to lessen these repulsions. Additionally, the electron donating groups create unique intramolecular energy environments. These environments create $\Delta$G$\sb{\rm reduction}$ differences that are observed in the voltammograms as variances in the E$\sb{1\over 2}$ of the viologen subunits. In the (2) catenanes, two resolved waves are observed for the monoelectronically reduced (yet structurally identical) viologen moieties. In each reduced complex, an intramolecular electron transfer process is evident between the viologen subunits. The frequency of this process is dependent on the degree of charge transfer stabilization present between the donating groups and the accepting viologens. An increasing charge transfer interaction produces a potential energy difference between the electroactive subunits that reduces the frequency of the intramolecular electron transfer process.Part II. The complexation of bis-viologen cyclophane (9) and the aromatic amino acids tyrosine, tryptophan and phenylalanine was studied by UV/Visible spectroscopy and $\sp1$H-NMR. A binding constants of 572 M$\sp{-1}$ was observed for tyrosine, 1036 M$\sp{-1}$ for tryptophan and 41 M$\sp{-1}$ for phenylalanine in a neutral pH aqueous medium. $\sp1$H-NMR spectroscopy indicated that the aromatic portions of the substrates were included within the center of the cyclophane and were stabilized by charge transfer interactions. The resonances corresponding to the phenylene ring protons were observed to be significantly broadened and shifted upfield, whereas the nonaromatic protons were essentially unperturbed.Appendix. The ability of ferrocenyl- (2.2) -cryptand to complex alkali, alkaline-earth and transition metals was evaluated by CV. The complex is observed to exhibit redox switchable properties with the generation of a new redox wave. Simulation of the electrochemical data allows for the determination of the efficiency of binding in both redox states. A strong switching ability is observed with most cations including silver. The electrochemical data support the results of additional characterization techniques that detail this unique complexation process.

Keywords

Chemistry, Analytical; Chemistry, Biochemistry; Chemistry, Physical

Link to Full Text

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