A unifying focus of my research is the study of classes of amphiphilic molecules that have the ability to self-assemble into complex three-dimensional structures using transient intermolecular forces when placed in water and other solvents. My undergraduates and I have pioneered the practice of examining the complete emission spectrum of an extrinsic fluorescent probe to reveal heterogeneity in the probe distribution and thereby efficiently characterize the diverse microregions of amphiphilic aggregates. The basis for this approach is the fact that an overall fluorescence spectrum is the sum of the emission spectra of a fluorophore in its multiple environments within a given system. We use the fluorophore prodan (6-propionyl-2-(dimethylamino)-naphthalene) which has the potential to distribute throughout the diverse microregions of self-assembled aggregates as a consequence of its solubility in a variety of media. Furthermore, unlike many fluorophores, prodan exhibits an extreme sensitivity of its maximum emission wavelength to its environment. We have used prodan to characterize a wide variety of surfactant aggregates including aqueous micelles with cationic, anionic, zwitterionic, and nonionic headgroups; reverse micelles of varying water pool size; unilamellar vesicles of varying dimension; liquid crystalline mesophases of amphiphilic alkyl glucosides; supramolecular assemblies of polymeric dendrimers and surfactants; and aggregates of chromonic dyes.<br/><br/>We have also used this spectroscopic approach to construct thermodynamically correct binary surfactant-water phase diagrams representing phase behavior as a function of surfactant concentration and temperature. In a study of aqueous mixtures of n-octyl-β-D-glucoside, we highlighted several significant advantages of this method including the use of a single technique to demarcate distinct single-phase and multi-phase regions of a binary system in a rapid and streamlined fashion. This presentation will feature some of the key findings of my undergraduate research students throughout my career.

Fluorescence delineation of self-assembled aggregates of amphiphilic surfactants and chromonic dyes

ACS Spring Meeting 2021

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