title: Long-wavelength chloride-sensitive fluorescent indicators.
abstract: The goal of this study was to develop long-wavelength fluorescent Cl indicators that have improved optical properties over quinolinium compounds. A series of quaternized tricyclic heterocycles was screened. We found that N,N-dimethyl-9,9-bisacridinium (lucigenin) had very high halide sensitivity with Stern-Volmer constants for collisional quenching of 390 M-1 (Cl), 585 M-1 (Br), 750 M-1 (I), and 590 M-1 (SCN), much higher than those for the reference compound 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ) (118 M-1 (Cl)); lucigenin fluorescence was insensitive to phosphate, sulfate, and nitrate. Lucigenin fluorescence at 505 nm was excited with molar absorbances of 34,000 M-1 cm-1 (368 nm) and 7500 M-1 cm-1 (455 nm). To examine structure-activity relationships, five 9-substituted N-methylacridinium compounds were synthesized (9-amino, 9-carboxaldehyde, 9-carboxamide, 9-N,N-dimethylcarboxamide, and 9-methylcarboxylate), of which N-methylacridinium-9-carboxamide (MACA) had the best optical properties. MACA had excitation and emission maxima at 424 and 500 nm, and Stern-Volmer constants of 225 M-1 (Cl), 480 M-1 (Br), 550 M-1 (I), and 480 M-1 (SCN). The quantum yields of lucigenin and MACA were 0.6-0.7. The acridinium compounds are useful as Cl indicators in liposomes and membrane vesicles, but are not stable in cell cytoplasm.
authors.affiliation: Department of Medicine, University of California, San Francisco 94143.
authors.forename: J
authors.initials: J
authors.lastname: Biwersi
authors.forename: B
authors.initials: B
authors.lastname: Tulk
authors.forename: A S
authors.initials: AS
authors.lastname: Verkman
mesh_terms: D016475:3T3 Cells; D000166:Acridines; D000818:Animals; D002712:Chlorides; D005456:Fluorescent Dyes; D007202:Indicators and Reagents; D051379:Mice; D013050:Spectrometry, Fluorescence / Q000379:methods*; D013053:Spectrophotometry / Q000379:methods; D013329:Structure-Activity Relationship
chemical_list: D000166:Acridines; D002712:Chlorides; D005456:Fluorescent Dyes; D007202:Indicators and Reagents; C033472:10,10'-dimethyl-9,9'-biacridinium