Noncovalent interactions of azo dyes with anionic surfactant micelles

CHED 1012

Jonathan P. Litz,, Matthew Garber, and Kerry K. Karukstis, Department of Chemistry, Harvey Mudd College, 301 Platt Blvd, Claremont, CA 91711
In aqueous solution, surfactants molecules form ordered supramolecular structures with definitive hydrophobic and hydrophilic regions. We have probed the non-covalent interactions of dodecyltrimethylammonium bromide (DTAB) micelles with a wide variety of anionic azo dyes through the use of UV-vis spectrophotometry. The rich variation in UV/visible absorption properties of these azo dyes supports their use as sensitive probes of the nanostructures of surfactant aggregates. The effects of deprotonation and solvent polarity on the azo dye UV-vis spectra were determined and compared with the spectral changes resulting from dye-micelle interactions. Dyes with a hydrophobic dialkyl amine substituent were discovered to penetrate into the non-polar micellar core. Dyes with a hydroxyl group ortho to the azo functionality were found to experience a shift in equilibrium from the azo form to the hydrazone form in order to minimize repulsive interactions of hydrophobic substituents with the aqueous environment of the micellar surface.