CHEMICAL-ANALYTICAL PROPERTIES OF A FLUORESCENT PROBE BASED ON ALUMINIUM(III) COMPLEX WITH 4ꞌ-CARBOXYMETHOXYFLAVONOL
DOI: https://doi.org/10.17721/1728-2209.2025.1(60).8
Keywords:
3-hydroxyflavone, complex formation, fluorimetry, anions determination, ESIPT, keto-enol tautomerismAbstract
Background. Fluorescence spectroscopy is a highly sensitive analytical method that is successfully used in biochemical and medical research, for environmental objects analysis, in the pharmaceutical and food industries. For the determination of substances without their own fluorescence, various fluorescent probes sensitive to metal cations, inorganic and organic ions, and biomacromolecules have been proposed. 3-Hydroxyflavones and their transition metal complexes are actively used for creating new fluorescent probes. The effective use of such complexes in analysis requires a comprehensive study of their chemical and analytical properties, clarification of the complex formation mechanism, and the influence of metal ions on phenomena inherent in 3-hydroxyflavones, such as intramolecular charge and proton transfer. This work presents the results of a study of the optimal conditions for the formation of a Al(III) with 2-[4-(3-hydroxy-4-oxo-4H-chromen-2-yl)phenoxy]acetic acid (F4O) complex, its stoichiometric composition, stability, fluorescent properties, and the possibility of its use as an optical probe for anion detection.
Methods. The spectral characteristics of F4O in different solvents, its protolytic properties, the features of its complex formation with Al(III) ions, and the possibility of using the complex for the fluorescent determination of citrate anions were investigated using spectrofluorimetric and spectrophotometric methods. The pH values of the solutions were measured by the potentiometric method using a combined glass electrode.
Results. The interaction between Al(III) and F4O is accompanied by a significant increase in fluorescence intensity. In aqueous solutions, the optimal pH value for the formation of the F4O-Al complex is in the range of 5.15–5.20. In these conditions, in the solution, a complex with the simplest stoichiometry and medium stability forms. The conditional stability constant of the complex, determined by the Benesi-Hildebrand method, is 6,44⋅104 L/mol. In the presence of citrate anions, the luminescence intensity of the complex decreases. The corresponding fluorescence quenching curve is linearized in the coordinates of the modified Stern-Volmer equation. The quenching constant is 4,88∙106 L/mol.
Conclusions. The optimal conditions for the formation and the main chemical-analytical characteristics of the Al(III) complex with F4O were investigated. Using citrate anions as an example, it was shown that the F4O-Al complex can be promising as an "On-Off" fluorescent probe for the determination of anions in aqueous solutions. The quenching of luminescence in the presence of citrate is probably due to the destruction of the Al(III) complex with 4'-carboxymethoxyflavonol as a result of the anion binding to the metal.
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