Characterization and Stability of the Antimony-Quercetin Complex

Quercetin is a flavonoid known for its therapeutic properties and for formingcomplexes. Although the antimony-quercetin (SbQ) complex has been produced before, noprevious exploration of its characteristics has been published in literature. Thus, this study aimedto characterize this complex, assess its stability and investigate its complexation site through itsantibacterial activity. The SbQ complex was synthetized using Sb(III) potassium tartrate trihydrate andquercetin anhydrous (1:1) (v/v) as a solution and dried using three rotaevaporation,lyophilization and spray drying. The material, in solution, was analyzed by UV-vis andfluorimetry; and, in the powder, by X-ray diffraction (XRD), both scanning electronic andfluorescence microscopy and infrared spectroscopy (FT-IR). Antimicrobial activity was evaluatedvia broth microdilution. UV-vis exhibited a shoulder peak at 291 nm indicating metal chelation at C-ring ofquercetin and confirmed 1:1 stoichiometry. Spectrofluorimetry showed an increase of intensitywith the complex formation with an emission band (525 nm). After drying, XRD and SEMindicated loss of crystallinity and a difference in shape and size of the complex compared to itsprecursors. FT-IR suggested by a shift of frequency of the carbonyl group (1661 cm-1) that thequercetin bond to antimony by the C-3, followed by positions C-5 and C-4 carbonyl, which hasbeen confirmed by MIC through the structure-activity relationship of the antibacterial activityof quercetin. These results provided a characterization of SbQ complex with the confirmation ofits binding site, working as a guide for future studies involving this complex.