19159-06-9

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• 117-39-5 quercetol 

Relevant academic research and scientific papers

Qualitative observation of chemical change rate for quercetin in basic medium characterized by time resolved UV-vis spectroscopy

Time resolved spectroscopy was applied to a real time investigation of chemical reaction of quercetin (5.0 × 10- 5 mol L- 1) with various concentrations of sodium hydroxide (from 5.0 × 10- 3 to 1.0 mol L- 1). Th

Flavonol-serum albumin complexation. Two-electron oxidation of flavonols and their complexes with serum albumin

Quercetin (3,3′,4′,5,7-pentahydroxyflavone) and quercetin derivatives (3-methylquercetin, isoquercitrin, rutin) are strong polyphenolic antioxidants abundant in plants and in the human diet. Recent investigations have shown that significant concentrations of albumin-bound quercetin conjugates are present in the plasma of humans fed a quercetin-rich diet. In this work, binding of quercetin and quercetin glycosides to bovine serum albumin (BSA) is quantitatively investigated by fluorescence spectroscopy. The strong fluorescence enhancement of quercetin upon binding points to the fact that a significant fraction of quercetin adopts a pyrylium-like structure in the complex. On the other hand, the observation of a very efficient quenching of tryptophan fluorescence by quercetin is consistent with a binding occurring in the IIA domain. Flavonoid-derived quinones may be formed upon quenching of reactive oxygen species by flavonoids (antioxidant activity). In this work, the quinones are conveniently formed upon periodate oxidation of the selected flavonoids in methanol and in aqueous buffers with and without BSA. A kinetic investigation by UV-visible spectroscopy shows that albumin-bound flavonoids are oxidized as quickly as free flavonoids. Interestingly, the quercetin quinone, which is merely detectable in the absence of BSA because of fast solvent addition, is efficiently stabilized in the complex by charge transfer interactions (pH 9). No evidence for quercetin-BSA conjugates could be found, thus showing that water addition (and subsequent degradation) remains the sole significant pathway of quinone transformation in the complex.

Sr-Doped NiO3 nanorods synthesized by a simple sonochemical method as excellent materials for voltammetric determination of quercetin

The simple and novel surfactant-free synthesis of flower-like strontium-doped nickel oxide nanorods (SNO NRs) via a simple sonochemical co-precipitation method was used for electrochemical sensing of quercetin (QCT). The structure and morphology of the as

Photo-oxidation of some flavonoids with photochemically generated t-BuO? radicals in a t-BuOH water system using a kinetic approach

As a dietary component, flavonoids are thought to have a variety of pharmacological and health-promoting properties in both in vivo and in vitro systems. This variety is attributed to their high antioxidant capacity, which in turn is associated with their free radical scavenging properties. In order to understand the mechanism of t-BuO? radical scavenging properties of some flavonoids, viz, quercetin (QU), apigenin (AP), daidzein (DA), genistein (GE), myricetin (MY), and kaempferol (KA), a kinetic study of photo-oxidation of these flavonoids with photochemically generated t-BuO? radicals in a t-BuOH water (2:1 v/v) system was carried out. The oxidation of flavonoids by t-BuO? radicals was performed spectrophotometrically by measuring the absorbance of quercetin (375 nm), apigenin (340 nm), daidzein (250 nm), genistein (263 nm), myricetin (255 nm), and kaempferol (375 nm) at their respective λmax. The initial rates of oxidation of flavonoids increased with [flavonoid], [t-BuOOH], and light intensity. The quantum yields (φ) were considered from the initial rate of oxidation of flavonoids by t-BuO? radicals and measured light intensity at 254 nm. The order on [flavonoid] and [t-BuOOH] was found to be fractional, whereas the order on light intensity was found to be one. The products of the oxidation of flavonoids by t-BuO? radicals were identified using LC–MS and FTIR analysis.

Reactions of flavonoids with o-quinones interfere with the spectrophotometric assay of tyrosinase activity

Flavonoids are important food components with antioxidant properties and many of them have been described as tyrosinase inhibitors. Oxidation of quercetin, kaempferol, morin, catechin, and naringenin by mushroom tyrosinase and their influence on the oxidation of l-dopa and l-tyrosine was studied. Reaction rates measured spectrophotometrically and by oxygen consumption differed substantially. All tested flavonoids reacted with 4-tert-butyl-o-benzoquinone and/or 4-methyl-o-benzoquinone, although at different rates. These reactions generated products whose UV-vis spectra either overlapped or did not overlap with the spectrum of dopachrome. They therefore strongly influence the kinetic analysis performed by measuring the absorbance at 475 nm during oxidation of l-dopa or l-tyrosine generating false inhibition or activation effects. This method is therefore inappropriate for monitoring the activity of this enzyme in the presence of flavonoids and other compounds possessing strong nucleophilic or reducing groups.

Method for preparing o-benzoquinone derivative based on quercetin structure

The invention discloses a method for preparing an o-benzoquinone derivative based on a quercetin structure, and belongs to the field of organic synthesis. The method comprises the following steps: by taking quercetin as a raw material, ethanol as a reacti

Hydroethidine as a probe for measuring superoxide formation rates during air oxidation of myricetin and quercetin

In the presence of the flavonols myricetin and quercetin, oxidation of hydroethidine (HE) by superoxide yielded ethidium (E+) instead of 2-hydroxyethidium (2-OH-E+). As a known pro-oxidant, myricetin alone was also found to be able to catalyze air oxidation of HE yielding exclusively E+. The reaction is inhibited by added superoxide dismutase, suggesting that superoxide is involved in the rate limiting step of the oxidation.

Study of the reaction products of flavonols with 2,2-diphenyl-1- picrylhydrazyl using liquid chromatography coupled with negative electrospray ionization tandem spectrometry

The products obtained after the reaction between flavonols and the stable free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH⊕) in both methanol and acetonitrile were characterized using liquid chromatography coupled with negative electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) and NMR spectroscopy. The flavonols studied were quercetin, kaempferol and myricetin. In methanol, two reaction products of oxidized quercetin were identified using LC/ESI-MS/MS and NMR. Quercetin was oxidized through a transfer of two H-atoms to DPPH⊕ and subsequently incorporated either two CH3OH molecules or one CH3OH- and one H2O molecule giving the products 2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxy-2,3-dimethoxy-2,3- dihydrochromen-4-one and 2-(3,4-dihydroxyphenyl)-3,3,5,7-tetrahydroxy-2-methoxy- 2,3-dihydrochromen-4-one, respectively. LC/ESI-MS/MS analysis revealed that in methanol, kaempferol and myricetin also gave rise to methoxylated oxidation products similar to that identified for quercetin. Kaempferol, in addition, also exhibited products where a kaempferol radical, obtained by a transfer of one H-atom to DPPH⊕, reacted with CH3OH through the addition of CH3O⊕, yielding two isomeric products. When the reaction took place in acetonitrile, LC/ESI-MS/MS analysis showed that both quercetin and myricetin formed stable isomeric quinone products obtained by a transfer of two H-atoms to DPPH⊕. In contrast, kaempferol formed two isomeric products where a kaempferol radical reacted with H2O through the addition of OH⊕, i.e. similar to the reaction of kaempferol radicals with CH 3OH. Copyright

Kinetic Study of Flavonoid Reactions with Stable Radicals

The antiradical activities of some flavonols (kaempferol, quercetin, robinetin, quercetagetin, and myricetin), flavones (apigenin, baicalein, and luteolin), flavanones (naringenin and dihydroquercetin), and flavanols [(+)-catechin and (-)-epicatechin] wer

One-electron oxidation of quercetin and quercetin derivatives in protic and non protic media

Quercetin (3,3′,4′,5,7-pentahydroxyflavone) and quercetin derivatives (3-methylquercetin, rutin) are strong flavonoid antioxidants abundant in plants and in human diet. Their oxidation by DPPH, CAN or dioxygen (autoxidation) is studied in protic and non protic solvents. From kinetic investigations by UV-visible spectroscopy, oxidation rate constants are estimated. Fast disproportionation of flavonoid radicals is shown to give quinones which can be identified by their adducts with methanol (quercetin quinone) or sodium benzenesulfinate (rutin quinone). In strongly alkaline non aqueous conditions, the quercetin quinone can also be evidenced by strong charge transfer absorption bands in the range 700-800 nm. The consequences of these observations for the antioxidant properties of quercetin and quercetin derivatives are discussed.