Propolis is a resin gathered by honey bees from trees and shrubs but it used in the beehive as building material or as an antibiotic paste. The aim of this study was to determine the content of flavonoids and phenols, as well as the antioxidant capacity of propolis from various regions of Guanajuato, Mexico. The content of flavonoids and phenols was determined by the aluminum nitrate method and the Folin-Ciocalteu method. The antioxidant capacity was determined using the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH•) method and the ferric reduction of Fe3+ to Fe2+ (FRAP•) assay. The flavonoid content varied from 13 to 379 mg of quercetin equivalents (QE) per g of propolis and the phenolic content ranged from 68 to 500 mg of caffeic acid equivalents (CAE) per g of propolis. The trolox equivalent antioxidant capacity (TEAC) per g of propolis varied from 39.8 to 54.4 for the DPPH• method and from 50 to 2000 for the FRAP• assay. Propolis rich in flavonoids and phenols possesses a low antioxidant capacity. The results show that propolis from different areas of Guanajuato are rich in flavonoids and phenolics compounds while their antioxidant capacity is variable.
Currently, catalysts with oxidative activity are required to create valuable chemical, agrochemical, and pharmaceutical products. The catechol oxidase activity is a model reaction that can reveal new oxidative catalysts. The use of complexes as catalysts using iron (III) and structurally simple ligands such as pyrazine (pz), quinoxaline (qx), and phenazine (fz) has not been fully explored. To characterize the composition of the solution and identify the abundant species which were used to catalyze the catechol oxidation, the distribution diagrams of these species were obtained by an equilibrium study using a modified Job method in the HypSpec software. This allows to obtain also the UV-vis spectra calculated and the formation constants for the mononuclear and binuclear complexes with Fe3+ including: [Fe(pz)]3+, [Fe2(pz)]6+, [Fe(qx)]3+, [Fe2(qx)]6+, [Fe(fz)]3+, and [Fe2(fz)]6+. The formation constants obtained were log β110 = 3.2 ± 0.1, log β210 = 6.9 ± 0.1, log β110 = 4.4 ± 0.1, log β210 = 8.3 ± 0.1, log β110 = 6.4 ± 0.2, and log β210 = 9.9 ± 0.2, respectively. The determination of the catechol oxidase activity for these complexes did not follow a traditional Michaelis–Menten behavior.
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