Constructing the phase diagram of water and n-octyl-β-D-thioglucoside by fluorescence spectroscopy

CHED 970

Kristen N. Chellis, Kristen_Chellis@hmc.edu, Kerry K. Karukstis, kerry_karukstis@hmc.edu, and Gerald R. Van Hecke. Department of Chemistry, Harvey Mudd College, 301 Platt Blvd, Claremont, CA 91711
Alkylglucosides are amphiphilic molecules that for specific compositions form liquid crystal phases in mixtures with water. They are green surfactants, and the phases they form have applications in drug delivery and cosmetics. To fully utilize these molecules, it is important to determine the temperatures and compositions at which these phases occur. Previous published phase diagrams of the n-octyl-β-D-thioglucoside and water system were incomplete, as they did not include two-phase regions. Fluorescence spectroscopy with a prodan probe was used to determine the phase diagram of this system. When excited with 340 nm light, the prodan in each phase emits different wavelengths between 350 and 650 nm, characteristic of the phase and the polarity of the probe microenvironment. Through analysis of the fluorescence spectrum of a sample the phases present can be determined. This method has been successfully used in previous studies to determine the aqueous phase diagrams of n-octyl-β-D-glucoside and n-nonyl-β-D-glucoside.