Dissertation Abstract

Spectroscopic Probing of Aot Reverse Micelles via Selected Aromatic Nitrogen Heterocycles (Fluorescence, Thiabendazole, Absorption, Microenvironment, Benzimidazole)

The absorption and fluorescence spectra of certain pyridine, quinoline, and benzimidazole derivatives undergo large wavelength, intensity, and configurational changes when subjected to pH, polarity, and viscosity alterations. Incorporation of these into AOT (sodium di-2-ethylhexylsulfosuccinate) reverse micelles, aggregated in cyclohexane solvent, allows investigation of the micelle-solute partition equilibria and discernment of the nature of the solubilization sites for included aromatic nitrogen heterocycle probes.

Certain benzimidazole derivatives, particularly 5-aminothiabendazole and 5-aminobenzimidazole, are shown to be noteworthy probes for the AOT system. From their absorption and fluorescence spectra, strong evidence is given for multiple sites of solubilization. At low R, where R = H2O / AOT = 0.1, the spectra reveal that the lone pair electrons of the amino moieties of some of these probe molecules are bound by the interactive water of hydration in the aqueous interior of the AOT micelles. Concomitantly, a quantity of the probe reflects a polar, nonaqueous environment spectroscopically, and these molecules probably reside in a different locale. Water content studies, where R was varied, show decreased bonding with the primary water, immersion of the probe into an aqueous environment, and an increase in excited state protonation of the pyridinic nitrogens of these micelle incorporated molecules as R is enlarged.

A size effect, such that larger molecules reflect a less polar environment and are prevented sterically from having access to the water at the core, is evidenced from the fluorescence studies performed on the series. Surfactant concentration studies, from which distribution ratios for the aminopyridines were estimated and the order of solubilization of the benzimidazole series was derived, imply that the solute-micelle interaction is similar to a microscopic phase separation, but modified due to the presence of the monomer-bulk solvent interface and multiple solubilization sites. A change in the diameter of the water core as surfactant concentration is varied is inferred from data utilizing the polarity, viscosity and pH sensitive fluorescence of 5-hydroxythiabendazole. (Abstract shortened with permission of author.)

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