ESTIMATION OF THE HYDROPHOBICITY IN MICROENVIRONMENTS BY PYRENE FLUORESCENCE MEASUREMENTS - N-BETA-OCTYLGLUCOSIDE MICELLES

A simple and reliable method was developed for estimating the hydropho bicity of microenvironments, such as the internal region of aqueous de tergent micelles, using a fluorescence probe, pyrene. The partition co efficient of pyrene between hydrophobic environments and water was use d as a measure of the hydrophobicity. To validate our method, the part itioning of pyrene between organic solvents of various dielectric cons tants (n-hexane, 1-octanol, 1-propanol, ethanol, and methanol) and wat er was measured. This calibration set was then used to estimate the hy drophobicity of the internal region of n-beta-octylglucoside micelles. Combining the spectral changes of pyrene as a function of the n-beta- octylglucoside concentration with a theoretical model of the micelliza tion process, the partitioning of pyrene between the internal region o f the micelles and the surrounding water was calculated. The partition coefficient of pyrene was calculated to be about 1.5 x 10(4) based on an assumed aggregation number of 90 for the aqueous n-beta-octylgluco side micelles. Our results demonstrate that the interior of the micell e becomes very hydrophobic once the structure forms.