Kinetic studies of the oxidation of quercetin, rutin and taxifolin in the basic medium by (ethylenediaminetetraacetato) cobalt(III) complex

Kinetics of Flavonoid Degradation and Controlled Release from Functionalized Magnetic Nanoparticles

Flavonoids are naturally occurring antioxidants that have been shown to protect cell membranes from oxidative stress and have a potential use in photodynamic cancer treatment. However, they degrade at physiological pH values, which is often neglected in drug release studies. Kinetic study of flavonoid oxidation can help to understand the mechanism of degradation and to correctly analyze flavonoid release data. Additionally, the incorporation of flavonoids into magnetic nanocarriers can be utilized to mitigate degradation and overcome their low solubility, while the release can be controlled using magnetic fields (MFs). An approach that combines alternating least squares (ALS) and multilinear regression to consider flavonoid autoxidation in release studies is presented. This approach can be used in general cases to account for the degradation of unstable drugs released from nanoparticles. The oxidation of quercetin, myricetin (MCE), and myricitrin (MCI) was studied in PBS buffer (pH = 7.4) using UV-vis spectrophotometry. ALS was used to determine the kinetic profiles and characteristic spectra, which were used to analyze UV-vis data of release from functionalized magnetic nanoparticles (MNPs). MNPs were selected for their unique magnetic properties, which can be exploited for both targeted drug delivery and control over the drug release. MNPs were prepared and characterized by X-ray diffraction, infrared spectroscopy, scanning electron microscopy, superconducting quantum interference device magnetometer, and electrophoretic mobility measurements. Autoxidation of all three flavonoids follows a two-step first-order kinetic model. MCE showed the fastest degradation, while the oxidation of MCI was the slowest. The flavonoids were successfully loaded into the prepared MNPs, and the drug release was described by the first-order and Korsmeyer-Peppas models. External MFs were utilized to control the release mechanism and the cumulative mass of the flavonoids released.

Unraveling the Antioxidant Activity of 2R,3R-dihydroquercetin

It has been reported that in an oxidative environment, the flavonoid 2R,3R-dihydroquercetin (2R,3R-DHQ) oxidizes into a product that rearranges to form quercetin. As quercetin is a very potent antioxidant, much better than 2R,3R-DHQ, this would be an intriguing form of targeting the antioxidant quercetin. The aim of the present study is to further elaborate on this targeting. We can confirm the previous observation that 2R,3R-DHQ is oxidized by horseradish peroxidase (HRP), with H2O2 as the oxidant. However, HPLC analysis revealed that no quercetin was formed, but instead an unstable oxidation product. The inclusion of glutathione (GSH) during the oxidation process resulted in the formation of a 2R,3R-DHQ-GSH adduct, as was identified using HPLC with IT-TOF/MS detection. GSH adducts appeared on the B-ring of the 2R,3R-DHQ quinone, indicating that during oxidation, the B-ring is oxidized from a catechol to form a quinone group. Ascorbate could reduce the quinone back to 2R,3R-DHQ. No 2S,3R-DHQ was detected after the reduction by ascorbate, indicating that a possible epimerization of 2R,3R-DHQ quinone to 2S,3R-DHQ quinone does not occur. The fact that no epimerization of the oxidized product of 2R,3R-DHQ is observed, and that GSH adducts the oxidized product of 2R,3R-DHQ on the B-ring, led us to conclude that the redox-modulating activity of 2R,3R-DHQ quinone resides in its B-ring. This could be confirmed by chemical calculation. Apparently, the administration of 2R,3R-DHQ in an oxidative environment does not result in 'biotargeting' quercetin.

Copper-Guanosine Nanorods (Cu-Guo NRs) as a Laccase Mimicking Nanozyme for Colorimetric Detection of Rutin

Inspired by laccase activity, herein, Cu-guanosine nanorods (Cu-Guo NRs) have been synthesized for the first time through a simple procedure. The activity of the Cu-Guo NR as the laccase mimicking nanozyme has been examined in the colorimetric sensing of rutin (Rtn) by a novel and simple spectrophotometric method. The distinct changes in the absorbance signal intensity of Rtn and a distinguished red shift under the optimum condition based on pH and ionic strength values confirmed the formation of the oxidized form of Rtn (o-quinone) via laccase-like nanozyme activity of Cu-Guo NRs. A vivid and concentration-dependent color variation from green to dark yellow led to the visual detection of Rtn in a broad concentration range from 770 nM to 54.46 µM with a limit of detection (LOD) of 114 nM. The proposed methodology was successfully applied for the fast tracing of Rtn in the presence of certain common interfering species and various complex samples such as propolis dry extract, human biofluids, and dietary supplement tablets, with satisfactory precision. The sensitivity and selectivity of the developed sensor, which are bonuses in addition to rapid, on-site, cost-effective, and naked-eye determination of Rtn, hold great promise to provide technical support for routine analysis in the real world.

ESI-TOF MS analysis and DNA cleavage activity of rutin–metal complexes in aqueous extracts of medicinal plants

Rutin, a flavonoid commonly present in natural plants, can form multiple complexes at different rutin : metal ratios with various trace metal elements during the water decoction process, and these complexes exhibit novel activities.

Spectrophotometric and quantum-chemical study of acid-base and complexing properties of (±)-taxifolin in aqueous solution

This study reports the acid-base properties of taxifolin (Tf) in HCl media and aqueous complexation with Ni(II). The equilibrium processes was investigated using a spectrophotometric technique and

The Influence of Mg(II) and Ca(II) Ions on Rutin Autoxidation in Weakly Alkaline Aqueous Solutions

Rutin (quercetin-3-O-rutinoside) is one of the most abundant bioflavonoids with various biological and pharmacological activities. Considering the ubiquitous presence of Mg(II) and Ca(II) ions in biological systems we decided to investigate their influence on the autoxidation of rutin in weakly alkaline aqueous solutions. Changes in UV-Vis spectra recorded during the rutin autoxidation in aqueous solution at pH 8.4 revealed that this process was very slow in the absence of metal ions. The presence of Mg(II) and, especially Ca(II) ion, increased the transformation rate of rutin. UV-Vis spectra recorded after prolonged autoxidation indicated the formation of humic acidlike products in the presence of Mg(II) and Ca(II) ions. Four new compounds formed during the initial stage of rutin autoxidation in the presence of Mg(II) and Ca(II) ions were detected by HPLCDAD. Based on the analysis of their DAD UV-Vis spectra and comparison of their retention times with the retention time value for rutin, we concluded that the initial rutin transformation products were formed by the water addition on double bond in ring C and hydroxylation of ring B. A very small decrease of the initial rutin concentration (4%) was observed by HPLC-DAD in the absence of metal ions for the period of 90 minutes. However, rutin concentration decrease was much larger in the presence of Mg(II) and Ca(II) ions (14% and 24%, respectively). The more pronounced effect of Ca(II) ion on the rutin autoxidation may be explained by the stronger binding of Mg(II) ion to rutin and thus greater stabilizing effect on reaction intermediates caused by its higher ionic potential (charge/ionic radius ratio) in comparison to Ca(II) ion. The results of this study may contribute to the better understanding of interactions of Mg(II) and Ca(II) ions with natural phenolic antioxidants which are important for their various biological activities.

A common fungal associate of the spruce bark beetle metabolizes the stilbene defenses of Norway spruce

Norway spruce (Picea abies) forests suffer periodic fatal attacks by the bark beetle Ips typographus and its fungal associate, Ceratocystis polonica. Norway spruce protects itself against fungal and bark beetle invasion by the production of terpenoid resins, but it is unclear whether resins or other defenses are effective against the fungus. We investigated stilbenes, a group of phenolic compounds found in Norway spruce bark with a diaryl-ethene skeleton with known antifungal properties. During C. polonica infection, stilbene biosynthesis was up-regulated, as evidenced by elevated transcript levels of stilbene synthase genes. However, stilbene concentrations actually declined during infection, and this was due to fungal metabolism. C. polonica converted stilbenes to ring-opened, deglycosylated, and dimeric products. Chromatographic separation of C. polonica protein extracts confirmed that these metabolites arose from specific fungal enzyme activities. Comparison of C. polonica strains showed that rapid conversion of host phenolics is associated with higher virulence. C. polonica is so well adapted to its host's chemical defenses that it is even able to use host phenolic compounds as its sole carbon source.

Spectrophotometric studies of the reaction of quercetin with peroxynitrite at different pH

Peroxynitrite (ONOOH/ONOO-) which is formed in vivo under oxidative stress is a strong oxidizing and nitrating agent. It has been reported that several flavonoids, including quercetin, inhibit the peroxynitrite-induced oxidation and/or nitration of several molecules tested; however, the mechanism of their protective action against peroxynitrite is not univocally resolved. The kinetics of the reaction of quercetin with peroxynitrite was studied by stopped-flow as well as by conventional spectrophotometry under acidic, neutral and alkaline pH. The obtained results show that the protective mechanism of quercetin against peroxynitrite toxicity cannot be explained by direct scavenging of peroxynitrite. We propose that quercetin acts via scavenging intermediate radical products of peroxynitrite decomposition (it is an excellent scavenger of ·NO2) and/or via reduction of target radicals formed in the reaction with peroxynitrite.