Interaction of indole and tryptophan derivatives with sodium dodecyl sulfate micelles measured with ultraviolet absorption and fluorescence quenching.

The distribution of indole and tryptophan derivatives between sodium dodecyl sulfate (SDS) micellar and aqueous phases was analyzed using conventional methods of ultraviolet (UV) absorption spectroscopy and measurement of fluorescence quenching by succinimide. On the assumption of a simple pseudo-phase equilibrium between both phases the distribution coefficient was easily obtained by the measurement of the ratio Rpv of the absorbance intensity in the peak to that in the valley of the UV spectra or the fluorescence quenching constant Ksv. The possibilities and limitations of utilizing the ratio of the collisional quenching constant estimating from the Ksv value in the micellar phase to that in the aqueous phase for a measure of polarity of the microenvironment around the tryptophan derivatives in the SDS micelle is discussed in comparison with the Rpv values for the UV spectra. The indole ring in the derivatives in the SDS micelle is localized near or on the micelle-water interface with its imino group directed toward the aqueous phase. Thus it can serve as a feasible model for interpreting the distribution coefficients and Rpv values obtained for the various indole and tryptophan derivatives.