On the stability of the bioactive flavonoids quercetin and luteolin under oxygen-free conditions

Ramešová, Šárka; Sokolová, Romana; Degano, Ilaria; Bulíčková, Jana; Žabka, Ján; Gál, Miroslav

doi:10.1007/s00216-011-5504-3

Cited by 95 publications

(60 citation statements)

References 37 publications

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“…Quercetin has two different pharmacophores: the catechol group in ring B and the three hydroxyl groups in rings A and C, of which the catechol moiety is the most reactive one where deprotonation occurs easily [51,52]. The pK a values of quercetin are 5.87 and 8.48 [16,53]. The pK a values for the phenolic-OH group in phenol, p-coumaric acid, ferulic acid and thymol are 10, 9.5, 9.4, and 10.6, respectively [51,53,54].…”

Section: Resultsmentioning

confidence: 99%

“…As far as phenols are concerned they are in the undissociated form at low pH, i.e., pH < pK a , but they are in the form of phenolate ions at high pH, i.e., pH > pK a . Further in more acidic condition, the reducing capacity of the phenols may be suppressed due to protonation, whereas in more basic condition, the reducing capacity of the phenols enhances due to the formation of phenolate ions [16,17]. When the phenols are in the undissociated form, the formation of phenoxyl radical involves the removal of hydrogen atom.…”

Section: Introductionmentioning

confidence: 99%

“…The mechanism of oxidation of polyphenols and their stability in solution depend on pH [16,17]. The oxidation potential decreases with an increase in the number of phenolic -OH groups [18].…”

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confidence: 99%

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Photoluminescence electron transfer quenching of ruthenium(II)-polypyridyl complexes with biologically important phenolate ions in aqueous acetonitrile solution

Daniel¹,

George²

2014

J IRAN CHEM SOC

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involve the oxidation of phenols. Phenoxyl-type radicals are involved in biological redox processes and in the biosynthesis of natural products. The conversion of phenol to phenoxyl radical is of interest to chemists because of its involvement in important biological and industrial processes and in the degradation of chemical waste [8][9][10][11]. The one electron oxidation of phenolate to the resulting phenoxyl radical is a key step in the oxidation of phenols. The generation of phenoxyl radical involves either H-atom or electron abstraction from phenol and phenolate ion, respectively. The study of the kinetic and thermodynamic aspects of electron transfer (ET) to generate phenoxyl radicals bearing bulky groups in the ortho-and para-positions may help to understand the different biological roles of phenols [12][13][14][15].The oxidation potential of a polyphenol provides an estimate of the energy required to donate an electron; the lower the oxidation potential, lesser the energy required to donate an electron, hence it undergoes oxidation easily. The mechanism of oxidation of polyphenols and their stability in solution depend on pH [16,17]. The oxidation potential decreases with an increase in the number of phenolic -OH groups [18].Ruthenium polypyridyl complexes, such as [Ru(bpy) 3 ] 2+ (bpy = 2,2′-bipyridine), are among the most investigated in fields that include solar energy conversion [19,20], artificial photosynthesis [21], optical sensing [22,23], and luminescent probes for characterizing microheterogeneous environments, owing to their favorable photophysical properties, excited state reactivity, and chemical stability [24,25]. The excited state properties like emission lifetime, quantum yield, wavelength of emission maximum and redox potential of [Ru(bpy) 3 ] 2+ are largely affected by the introduction of electron-donating and electron-withdrawing groups in the 4,4′-position of 2,2′-bipyridine [26]. AbstractThe photoinduced electron transfer reactions of three Ru(II) complexes with phenolate ions of polyphenols (gallic acid, quercetin, p-coumaric acid, and ferulic acid) and thymol have been measured in 50 % aqueous acetonitrile at pH 11 and the observed quenching constant (k q ) values are sensitive to the nature of the ligand and the structure of the phenolate ion. The change of k q values with ΔG 0 is in accordance with the Marcus semiclassical theory of electron transfer. The static as well as dynamic nature of quenching is confirmed from the ground-state absorption studies. The reductive quenching of the Ru(II) complexes by the phenolate ions has been confirmed from the transient absorption spectra. The formation of phenoxyl radical as a transient is confirmed by its characteristic absorption at 400 nm.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Photoluminescence electron transfer quenching of ruthenium(II)-polypyridyl complexes with biologically important phenolate ions in aqueous acetonitrile solution

Daniel¹,

George²

2014

J IRAN CHEM SOC

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“…It has been demonstrated that the presence of atmospheric oxygen causes photodegradation in many flavonoids, decreasing their biological properties, including their luminescence/fluorescence [70][71][72]. In this regard, some authors have claimed that the dye performance can be affected when is attached to the surface of carriers, e.g., it causes spectral shifts of both absorption and emission, it affects photo stability, and it alters the fluorescence lifetime [73][74][75][76].…”

Section: Photoluminescence Of Epef Compounds and Nps-aptes-epefmentioning

confidence: 99%

Synthesis and functionalization of silica-based nanoparticles with fluorescent biocompounds extracted from Eysenhardtia polystachya for biological applications

Ferreira

Hernández-Martínez

Pool

et al. 2015

Materials Science and Engineering: C

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“…There are many studies dealing with estimation of dissociation constant in the literature. The controversy reported on the acid-base properties of both flavonoids was explained by strong influence of the oxygen on the stability of their dissociation forms in our recent paper 7,8 . We reported values of dissociation constant pK 1 = 5.87 ± 0.14 and pK 2 = 8.48 ± 0.09 of quercetin and pK 1 = 5.99 ± 0.32 and pK 2 = 8.40 ± 0.42 of luteolin, which were found under strict anaerobic conditions.…”

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confidence: 92%

The influence of the host–guest interaction on the oxidation of natural flavonoid dyes

Ramešová

Sokolová

Degano

et al. 2011

Collect. Czech. Chem. Commun.

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Šárka RAMEŠOVÁ a1 , Romana SOKOLOVÁ a2, *, Ilaria DEGANO b1 , Magdaléna HROMADOVÁ a3 , Miroslav GÁL a4 , Viliam KOLIVOŠKA a5 and a special issue of CCCC devoted to "distinguished followers of the J. Heyrovský School of Polarography". This work is dedicated to Dr. L. Pospíšil on the occasion of his 70th birthday.The influence of the molecular cavity protection on degradation processes of bioorganic compounds quercetin and luteolin used as the original dyes in old tapestries was studied. The degradation processes were studied by electrochemical methods in aqueous media. The products of the exhaustive electrolysis were separated and identified by GC-MS analysis. Cyclic voltammetry characteristics indicate that the inclusion complex is formed. The inclusion affects the redox potentials of both oxidation waves related to the different dissociation forms of the flavonoid molecule. It was shown that decomposition products formed by the oxidation of quercetin are stabilized in the cavity of β-cyclodextrin, including the main oxidation product 2(3′,4′-dihydroxybenzoyl)-2,4,6-trihydroxybenzofuran-3(2H)-one. The formation of the 1:1 inclusion complex of luteolin with β-cyclodextrin is supported by the enhancement of fluorescence intensity. In the case of quercetin, a decrease of fluorescence intensity occurs when 1:1 inclusion complex with β-cyclodextrin is formed.

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On the stability of the bioactive flavonoids quercetin and luteolin under oxygen-free conditions

Cited by 95 publications

References 37 publications

Photoluminescence electron transfer quenching of ruthenium(II)-polypyridyl complexes with biologically important phenolate ions in aqueous acetonitrile solution

Photoluminescence electron transfer quenching of ruthenium(II)-polypyridyl complexes with biologically important phenolate ions in aqueous acetonitrile solution

Synthesis and functionalization of silica-based nanoparticles with fluorescent biocompounds extracted from Eysenhardtia polystachya for biological applications

The influence of the host–guest interaction on the oxidation of natural flavonoid dyes

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