Chloride-sensitive fluorescent indicators

Three fluorescent halide-sensitive quinolinium dyes have been produced by t he reaction of the 6-methylquinoline heterocyclic nitrogen base with methyl bromide, methyl iodide, and 3-bromo-1-propanol. The quaternary salts, unli ke the precursor molecule, are readily water soluble and the fluorescence i ntensity of these salts is reduced in the presence of aqueous chloride, bro mide, and iodide ions, allowing halide solution concentrations to be determ ined using well-known Stern-Volmer kinetics. One of the dyes, dye 1, has a chloride Stern-Volmer constant of 255 mol(-1) dm(3) which is more than twic e that of SPQ [6-methoxy-N-(3-sulfopropyl)quinolinium] used in recent physi ological measurements to measure intracellular chloride levels. The dyes ha ve been characterized using steady-state fluorescence spectroscopy and are compared to three similar dyes based on the 6-methoxyquinoline nucleus, rep orted earlier by the authors, and also to dyes reported by Krapf et al. (An al. Biochem. 169, 142-150, 1988). The interference of aqueous anions and th e potential for using these dyes in biological halide-sensing applications are discussed. (C) 2001 Academic Press.