The effect of micelles on the steady-state and time-resolved fluorescence of indole, 1-methylindole, and 3-methylindole in aqueous media

3-Methylindole (skatole) is a component of animal waste and is, consequently, a primary component in odor problems arising in livestock management, notably swine production, The ability to probe and to exploit the interactions of 3-methylindole with micelles has important implications for monitoring and controlling odor problems. The effect of a surfactant (Brij-35) on the fluorescence properties of indole, 1-methylindole, and 3-methylindole in aqueous solutions is reported. Steady-state fluorescence spectra reveal a blue shift in the emission as the surfactant concentration is increased, while the absorption spectra are practically unaffected, Time-resolved fluorescence measurements reveal shorter average lifetimes for 3-methylindole (3-MI) as the Brij-35 concentration is increased, The fluorescence decay of 3-MI in water is described well by a single exponential, whereas, at the highest Brij-35 concentration, a triple exponential is necessary to describe the fluorescence decay. The contributions of each component in the fluorescence decay are used to determine the extent of 3-MI partitioning into the micelle phase, It is found that 93% of the 3-MI molecules partition into the micelle at the highest Brij-35 concentration used, The equilibrium constant for the association between the micelles and the 3-MI molecules is determined to be 2.6 x 10(4) M-1. In addition, the reduction of 3-MI in the vapor phase by addition of a dry surfactant, lecithin, is also demonstrated.