Fluorescence Decay of Tryptophan Conformers in Aqueous Solution

Abstract

The fluorescence decay parameters of aqueous solutions of tryptophan and several tryptophan and indole derivatives are reported. The fluorescence decays of tryptophan, tryptophan ethyl ester, and 5-methyl- and 6-methyltryptophan are all described by double exponential kinetics. The relative proportions of the two components vary with emission wavelength. The fluoresence of all other derivatives obeys single exponential decay kinetics. In the case of tryptophan the two components, t1 = 3.1 ns and t2 = 0.51 ns, had fluorescence maxima at 350 and 335 nm, respectively. The origin of this behavior is discussed in terms of several models but is most consistent with the assignment of the emission to different rotamers or conformers of the alanyl side chain of tryptophan. © 1980, American Chemical Society. All rights reserved.