Spectrophotometric Studies of the Interaction of Noble Metals with Quercetin and Quercetin-5′-Sulfonic Acid

Abstract

Results of some studies on the interaction of noble metals with quercetin (Q) and quercetin-5′-sulfonic acid (QSA), the compounds of flavonoid group, are presented. The reactions of chloride complexes of the metals: RuOHCl₅^2–, PdCl₄^2–, OsCl₆^2–, PtCl₆^2– and AuCl₄^– with both reagents were examined. The redox reactions of ruthenium and gold with Q and QSA have been identified. The reaction of the metals with both reagents results in the formation of the oxidized form of Q that exhibits maximum absorbance at 291 nm. Ruthenium and gold react with the examined reagents under similar conditions: 0.04 M HCl and 1 × 10^–4 M Q (or QSA). The CH₃OH + H₂O (1:1) (Q) and pure aqueous (QSA) media can be used. The reaction of gold with Q is slow at room temperature. It can be accelerated by heating the solution being examined. The reaction proceeds significantly faster when the water-soluble sulfonic derivative of quercetin, quercetin-5′-sulfonic acid, is used as a reagent. The new species formed can make the basis of spectrophotometric methods for the determination of ruthenium and gold. The molar absorptivities at 291 nm are equal to 5.0 × 10³ and 2.2 × 10⁴ L mol^–1 cm^–1 for Ru and Au, respectively, independently of the reagent used. Some methods for the determination of the content of gold (0.04%) in a cosmetic cream were developed.