Title

Redox-switched and lipophilic ligands: From enhanced cation binding and transport to molecular assemblies

Date of Award

1991

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Chemistry

First Committee Member

Luis Echegoyen, Committee Chair

Abstract

Chapter 1. Unusual cyclic voltammograms were observed for anthraquinones substituted with morpholino groups in the presence of Na$\sp+$. A 2:1 (ligand:cation) complex model was proposed to account for the CV and ESR results obtained with the syn-morpholino ligand.A series of crown ethers containing the anthraquinone group were also studied using electrochemistry. The results have demonstrated the effects of ion-pairing interactions and structure of the ligand on the complexation properties of the reduced ligands.A novel, redox-active cryptand containing an anthraquinone group has been studied by cyclic voltammetric and ESR techniques in the presence and absence of Li$\sp+$, Na$\sp+$, and K$\sp+$. An unexpected 1:2 (L$\sp-\cdot$:2Li$\sp+$) symmetric complex was detected by cyclic voltammetry, ESR spectroscopy and alkali metal NMR (both $\sp{23}$Na and $\sp{7}$Li).Chapter 2. Redox-switchable anthraquinone-substituted crown ethers and podands may be reduced by treatment with NaBH$\sb4$ to afford high-binding, water-stable, anion derivatives. These macrocycles transport Na$\sp+$ through a solid-supported, ortho-nitrophenyl octyl ether membrane with rates that depend on the charge state of the ligand. These rates also depend on whether there is reduction at the source phase and oxidation at the receiving phase.Chapter 3. Novel bolaamphiphiles consisting of polymethylene chains attached to 15-crown-5 or 18-crown-6 as head groups were studied. The work reported here constitutes the first example of vesicle formation from nonionic bolaamphiphiles containing crown ethers as head groups and lipophilic chains with less than 12 methylenes. Crown ether-derived bolaamphiphiles that have lipophilic chains longer than 12 methylene groups form micelles in water. Alkali metal chlorides have little effect on the cloud points for the bolaamphiphiles whose head groups are 15-crown-5's. On the other hand, for bolaamphiphiles bearing the 18-crown-6 moiety, the cloud points increased remarkably in the presence of KCl.Chapter 4. The first example of vesicle formation from hydrophobic and steroidal ferrocene derivatives are presented. Among these redox-active amphiphiles, only those having low melting points are able to form vesicles in the neutral state. Upon oxidation of the ferrocene, all the compounds aggregated in aqueous solution. These vesicles, formed from the oxidized amphiphilic ferrocene, can be de-aggregated by electrochemically or chemically reducing the ferricinium head groups to the neutral state. This is the first example of vesicle formation using reversibly controlled redox-switched amphiphiles.

Keywords

Chemistry, Physical

Link to Full Text

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