Title

Lariat ethers: From electrochemically enhanced cation transport to supramolecular assemblies

Date of Award

1990

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Chemistry

First Committee Member

George W. Gokel, Committee Chair

Abstract

Chapter 1. Anthraquinone undergoes one- and two-electron reduction to form either radical anions or dianions. When a crown-ether type macrocycle or a polyethyleneoxy side chain is attached, the reduced aromatic and the oxygen donor groups cooperate to bind the cation. Binding of Li$\sp+$ or Na$\sp+$ is greater when anthraquinone is reduced because there is a coulombic interaction between it and the cation. This property has been used to enhance cation transport. Thus, a new method involving electrochemical control of cation transport through a CH$\sb2$Cl$\sb2$ bulk-liquid membrane has been developed. The procedure involves reduction of the anthraquinone substituted ligands near the aqueous donor interphase to enhance cation uptake. Oxidation near the aqueous receiving interphase enhances cation release. Increases in overall transport rates as high as 5-fold have been observed.Chapter 2. Studies on the aggregation properties of cholesteryl-substituted crown ethers and a cryptand surfactant have been carried out in aqueous media in the presence and absence of several alkali and alkaline earth metal ions. The nature of the aggregates formed depends on the size of the head group, the cation present, and the structure of the lipid tail. Two monoaza-15-crown-5 steriodal derivatives aggregate in water to form the first examples of niosomes based on amphiphiles having an uncomplexed crown ether residue as the head group. Formation of micelles is observed for an 18-crown-6 analog of the latter. The membranes formed from these steroidal derivatives are so rigid that ESR spectra of nitroxide radical probes imbeded in the membranes are almost identical to spectra observed for frozen systems. The cryptand surfactant forms micelles in the presence and absence of all cations studied. Studies on its thermodynamics of micellization indicate that the micellization process is entropy driven. The differences observed with the two different cations studied are, however, of enthalpic origin.

Keywords

Chemistry, Physical

Link to Full Text

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