137717-05-6Relevant articles and documents
Solid complexes of iron(II) and iron(III) with rutin
Nowak, Dorota,Kuzniar, Anna,Kopacz, Maria
, p. 323 - 330 (2010)
Solid complex compounds of Fe(II) and Fe(III) ions with rutin were obtained. On the basis of the elementary analysis and thermogravimetric investigation, the following composition of the compounds was determined: (1) FeOH(C27H29Osub
Study of the reaction products of flavonols with 2,2-diphenyl-1- picrylhydrazyl using liquid chromatography coupled with negative electrospray ionization tandem spectrometry
Hvattum, Erlend,Stenstroom, Yngve,Ekeberg, Dag
, p. 1570 - 1581 (2004)
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
Quenching of triplet-excited flavins by flavonoids. Structural assessment of antioxidative activity
Huvaere, Kevin,Olsen, Karsten,Skibsted, Leif H.
experimental part, p. 7283 - 7293 (2010/01/16)
(Figure Presented) The mechanism of flavin-mediated photooxidation of flavonoids was investigated for aqueous solutions. Interaction of triplet-excited flavin mononucleotide with phenols, as determined by laser flash photolysis, occurred at nearly diffusion-controlled rates (k～1.6x10 9 Lmol-1 s-1 for phenol at pH 7, 293 K), but protection of the phenolic function by methylation inhibited reaction. Still, electron transfer was proposed as the dominating mechanism due to the lack of primary kinetic hydrogen/ deuterium isotope effect and the low activation enthalpy (-1) for photooxidation. Activation entropy worked compensating in a series of phenolic derivatives, supporting a common oxidation mechanism. Anortho-hydroxymethoxy pattern was equally reactive (k～2.3x109Lmol-1 s-1 for guaiacol at pH 7) as compounds with ortho-dihydroxy substitution (k～2.4x109 L mol-1 s-1 for catechol at pH 7), which are generally referred to as good antioxidants. This refutes the common belief that stabilization of incipient phenoxyl radicals through intramolecular hydrogen bonding is the driving force behind the reducing activity of catechol-like compounds. Instead, such bonding improves ionization characteristics of the substrates, hence the differences in reactivity with (photo)oxidation of isolated phenols. Despite the similar reactivity, radicals from ortho-dihydroxy compounds are detected in high steady-state concentrations by electron paramagnetic resonance (EPR) spectroscopy, while those resulting from oxidation of ortho-hydroxymethoxy (or isolated phenolic) patterns were too reactive to be observed. The ability to deprotonate and form the corresponding radical anions at neutral pH was proposed as the decisive factor for stabilization and, consequently, for antioxidative action. Thus, substituting other ionizable functions for the ortho- or para-hydroxyl in phenolic compounds resulted in stable radical anion formation, as demonstrated for para-hydroxybenzoic acid, in contrast to its methyl ester. 2009 American Chemical Society.
