DETERMINATION OF ANTIOXIDANT PROPERTIES OF SUBSTANCES USING REDUCTION OF IRON (III) COMPLEX WITH 2,2′-DIPYRIDINE

It has been shown that to obtain reliable results when determining antioxidant properties using the iron-reducing technique in samples for measuring optical density, it is necessary to create a ratio of the molar concentrations of iron (III) ions to the concentration of dipyridine in a molar ratio of about 1: 6.4. This is due to the low rate of ligand exchange for intraorbital low-spin octahedic complexes with configurations (t2g)5 and (t2g)6, for the initial iron (III) complex and the final reduction product, since product of reduction coordinats three dipyridine molecules instead of one or two in the case of the original complex. It has been experimentally established that the transfer of this ligand from the initial particle to the reduction product ([Fe(dipy)3]2+) occurs slowly. A simple calibration of the oxidant-antioxidant system in this case allows one to recalculate the antioxidant property by the number of moles of electrons lost by one mole of antioxidant. This in turn allows us to estimate the depth of transformation - the number of successive oxidation stages, i.e. antioxidant capacity of the original antioxidant. An analysis of the antioxidant capacity of some substances taken to express antioxidant properties as reference substances was performed. It has been established that one mole of ascorbic acid in this version of determining antioxidant properties quickly loses two moles of electrons, and the reaction practically ends. Caffeic acid also loses two electrons but much more slowly, and the process continues through the second stage. In this case, para-coumaric acid oxidizes extremely slowly compared to caffeic acid. The addition of the ortho position from the hydroxyl group of coumaric acid the methoxy group accelerates oxidation, and the addition of two methoxy groups at both ortho positions results in oxidation activity even greater than that of caffeic acid. In this case, ferulic, caffeic and sinapic acids can be used as substances to compare the antioxidant properties of slowly oxidizing (after an initial rapid period) mixture of substances in real extracts. When using caffeic acid as a comparison sample when determining the antioxidant properties of coffee (drink), obtained results are only slightly dependent on the exposure time of the reaction mixtures, even with constantly changing optical density. For citation: Blinova I.P., Nuzhnykh T.E., Deineka V.I., Denyeka L.A., Anh Van Nguyen Determination of antioxidant properties of substances using reduction of iron (III) complex with 2,2′-dipyridine. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2025. V. 68. N 6. P. 6-14. DOI: 10.6060/ivkkt.20256806.7182.