Selective fluorescence quenching of biologically important acidic and non-acidic indoles by trivalent lanthanide ions and analysis of mixtures by a fluorimetric quenching method

Abstract

The effects of several lanthanide(II)(Ln 3+)ions(Dy 3+,Er 3+,Eu 3+,Nd 3+,Yb 3+) on the room-temperature fluorescence spectra of 2-indolecarboxylic acid, 5-indolecarboxylic acid, 5-methoxy-2-indolecarboxylic acid and 3-indoleacetic acid were investigated. It was found that the fluorescence quenching by Ln 3+ ions is much more efficient for the acidic compounds than for non-acidic indoles. Stern-Volmer relationships were obtained for most acidic indoles in the Ln 3+ concentration range 10 −7–10 −4 M, with quenching constants ranging between 3 × 10 3 and 4.6 × 10 5 l mol −1. A fluorimetric quenching method was developed for the quantitative analysis of binary mixtures of acidic and non-acidic indoles.