Complexation of Zn²⁺ by the Fluorophore 2-((E)-2-Phenyl)ethenyl-8-(N-4-methylbenzenesulfonyl)aminoquinol-6-yloxyacetic Acid: A Preparative, Potentiometric, UV-visible, and Fluorescence Study

Abstract

The preparation of the Zn²⁺ specific fluorophore 2-((E)-2-phenyl)ethenyl-8-(N-4-methylbenzene-sulfonyl)aminoquinol-6-yloxyacetic acid, H₂3, is described. The protonated form, H33+, is characterized by pKₐ values of 2.71 ± 0.03, 4.92 ± 0.03, and 10.46 ± 0.03 in 25% (v/v) aqueous ethanol 0.10 mol L⁻¹ in NaClO₄ at 298.2 K determined by potentiometric titration. At pH 6.6, but otherwise under the same conditions, the dianion, 3²⁻, forms the fluorescent complexes [Zn(3)] and [Zn(3)₂]²⁻, characterized by log(K1/L mol⁻¹) = 10.5 ± 0.20 and log(K₂/L mol⁻¹) = 11.1 ± 0.1, respectively, as determined by fluorimetry. These data are compared with analogous data for the structurally similar and widely used fluorophore 2-methyl-8-p-toluenesulfonamido-6-quinolyloxyacetic acid (Zinquin A).