- Catalytic evaluation of biocompatible chitosan-stabilized gold nanoparticles on oxidation of morin
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Herein, we present a study on the catalytic evaluation of biocompatible chitosan-stabilized gold nanoparticles (CH-AuNPs) on the oxidation of morin as a model reaction. Biocompatible CH-AuNPs have been characterized through several analytical methods such as TEM, UV–vis, DLS and zeta potential analyses. CH-AuNPs have a small size (10 ± 0.4 nm) with a narrow size distribution and high positive surface charge (+40.1 mV). CH-AuNPs has been demonstrated to be highly active nanocatalysts for the oxidation of morin with the assistance of H2O2 as an oxidant compared with control experiments. The oxidation reaction follows a pseudo-first-order reaction. The kinetic studies show that apparent rate constant (kapp) is positively correlated with the concentrations of CH-AuNPs and H2O2, while it is negatively correlated with morin concentration. Furthermore, the reusability tests have been performed and the results demonstrate the long-term stability and reusability of CH-AuNPs without any loss of catalytic activity. Cytotoxicity studies exhibit that CH-AuNPs have low toxicity and they are biocompatible with HeLa and MCF-7 cells.
- Bulut, Onur,Yilmaz, M. Deniz
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- Synthesis of narrowly dispersed silver and gold nanoparticles and their catalytic evaluation for morin oxidation
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We present a study on the synthesis of narrowly dispersed silver and gold nanoparticles using generation five amino-terminated poly(amidoamine) dendrimers as a template. UV-vis spectrophotometry was performed to monitor the synthesis process and to characterize the metal nanoparticles. Infrared (IR) spectroscopy, and transmission electron microscopy (TEM) were also used to characterize the metal nanoparticles. A catalytic oxidation of morin (quercetin) in the presence of hydrogen peroxide was performed as a model reaction to evaluate the metal nanoparticle activities. Ultra high performance liquid chromatography analysis was performed to identify the reaction products. The kinetic data obtained were modeled to the Langmuir-Hinshelwood equation. The encapsulated silver and gold nanoparticles show high activity which confirm the passive interaction with the dendrimer.
- Ilunga, Ali K.,Meijboom, Reinout
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- Effect of alkali and alkaline earth metal dopants on catalytic activity of mesoporous cobalt oxide evaluated using a model reaction
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Herein we report the synthesis of mesoporous cobalt oxides in pure (Co3O4) and alkali and alkaline earth metal doped form (Li-, Ca-, Cs-, and Na-, K-, and Mg/Co3O4) via the inverse micelle method. The as-prepared materials were characterized by powder X-ray diffraction (pXRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), nitrogen sorption (BET), hydrogen-temperature-programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). Characterization results suggested that the as-synthesized materials are of amorphous and mesoporous nature. Their catalytic activity was investigated using a model reaction, namely the liquid-phase morin oxidation. Results revealed pure cobalt oxide to be the better catalyst compared to its doped counterparts. The stability of Li/Co3O4 material was investigated exemplarily by recycling and reusing the catalysts for as many as four catalytic cycles. Conversion of morin was complete in all runs and no significant metal leaching could be detected by the use of inductively coupled plasma mass spectrometry (ICP-MS).
- Bingwa, Ndzondelelo,Bewana, Semakaleng,Ndolomingo, Matumuene Joe,Mawila, Naphtaly,Mogudi, Batsile,Ncube, Phendukani,Carleschi, Emanuela,Doyle, Bryan P.,Haumann, Marco,Meijboom, Reinout
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- Bleach catalysis in aqueous medium by iron(III)-isoindoline complexes and hydrogen peroxide
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Hydrogen peroxide and peroxymonocarbonate anion-based bleach reactions are important for many applications such as paper bleach, waste water treatment and laundry. Nonheme iron(III) complexes, [FeIII(L1?4)Cl2] with the 1,3-bis(20-Ar-imino)isoindolines ligands (HLn, n =1–4, Ar = pyridyl, thiazolyl, benzimidazolyl and N-methylbenzimidazolyl, respectively) have been shown to catalyze the oxidative degradation of morin as a soluble model of a bleachable stain by H2O2 in buffered aqueous solution. In these experiments the bleaching activity of the catalysts was significantly influenced by the Lewis acidity and redox properties of the metal centers, and showed a linear correlation with the FeIII/FeII redox potentials (in the range of 197–415 mV) controlled by the modification of the electron donor properties of the ligand introducing various aryl groups on the bis-iminoisoindoline moiety. A similar trend but with low yields was observed for the disproportionation of H2O2 (catalase-like reaction) which is a major side reaction of catalytic bleach with transition metal complexes. The effect of bicarbonate ions might be explained by the reduction of Fe(III) ions and/or the formation of peroxymonocarbonate monoanion, which is a much stronger oxidant and could increase the formation of the catalytically active high-valent oxoiron species.
- Kaizer, József,Keszei, Soma,Lakk-Bogáth, Dóra,Meena, Bashdar I.
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p. 351 - 360
(2021/11/09)
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- Exploring the oxidation and iron binding profile of a cyclodextrin encapsulated quercetin complex unveiled a controlled complex dissociation through a chemical stimulus
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Background: Flavonoids possess a rich polypharmacological profile and their biological role is linked to their oxidation state protecting DNA from oxidative stress damage. However, their bioavailability is hampered due to their poor aqueous solubility. This can be surpassed through encapsulation to supramolecular carriers as cyclodextrin (CD). A quercetin- 2HP-β-CD complex has been formerly reported by us. However, once the flavonoid is in its 2HP-β-CD encapsulated state its oxidation potential, its decomplexation mechanism, its potential to protect DNA damage from oxidative stress remained elusive. To unveil this, an array of biophysical techniques was used. Methods: The quercetin-2HP-β-CD complex was evaluated through solubility and dissolution experiments, electrochemical and spectroelectrochemical studies (Cyclic Voltammetry), UV–Vis spectroscopy, HPLC-ESI-MS/MS and HPLC-DAD, fluorescence spectroscopy, NMR Spectroscopy, theoretical calculations (density functional theory (DFT)) and biological evaluation of the protection offered against H2O2-induced DNA damage. Results: Encapsulation of quercetin inside the supramolecule's cavity enhanced its solubility and retained its oxidation profile. Although the protective ability of the quercetin-2HP-β-CD complex against H2O2 was diminished, iron serves as a chemical stimulus to dissociate the complex and release quercetin. Conclusions: We found that in a quercetin-2HP-β-CD inclusion complex quercetin retains its oxidation profile similarly to its native state, while iron can operate as a chemical stimulus to release quercetin from its host cavity. General significance: The oxidation profile of a natural product once it is encapsulated in a supramolecular carrier was unveiled as also it was discovered that decomplexation can be triggered by a chemical stimilus.
- Diamantis, Dimitrios A.,Ramesova, Sarka,Chatzigiannis, Christos M.,Degano, Ilaria,Gerogianni, Paraskevi S.,Karadima, Konstantina E.,Perikleous, Sonia,Rekkas, Dimitrios,Gerothanassis, Ioannis P.,Galaris, Dimitrios,Mavromoustakos, Thomas,Valsami, Georgia,Sokolova, Romana,Tzakos, Andreas G.
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p. 1913 - 1924
(2018/07/03)
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- Nitroxygenation of quercetin by HNO
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The flavonol quercetin undergoes both enzymatic and non-enzymatic reactions with nitroxyl (HNO/NO-), similar to analogous reactions with dioxygen, but in which N is regioselectively found in the ring-cleaved product. Here we report on kinetic and thermodynamic analysis of the non-enzymatic nitroxygenation reaction in water, which is orders of magnitude faster than the comparable dioxygenation. The second order rate constants were determined from variable temperature reactions, which allowed determination of the reaction activation enthalpy (ΔH≠ = 9.4 kcal/mol), entropy (ΔS≠ = -8.3 cal/mol K), and free energy (ΔG≠ = 11.8 kcal/mol). The determined standard state energy (ΔGo) and activation free energy, as well as the low entropic energy of reaction, are consistent with a proposed single electron transfer (SET) rate determining step.
- Han, Xiaozhen,Kumar, Murugaeson R.,Farmer, Patrick J.
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p. 399 - 402
(2016/01/12)
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- Modification of quercetin with l-cysteine by horseradish peroxidase
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Horseradish peroxidase is a well-known member of the peroxidase family that catalyzes oxidation of flavonoids and phenolic substrates to free phenoxyl or semiquinone radicals. Aim of this study was to investigate in vitro oxidation of quercetin by horseradish peroxidase in the presence of l-cysteine as nucleophilic agent, and its influence on previously formed semiquinone- and quinone-type metabolites. The obtained results showed that in the reaction without l-cysteine several products were present, such as quercetin quinone methide, phloroglucinol carboxylic acid, protocatechuic acid, as well as quercetin heterodimer and derivates of quercetin heterodimer. On the other hand, in the presence of l-cysteine only three products were obtained, quercetin quinone methide and two new isomeric mono-cysteine derivatives of quercetin with mass exp. m/z 420.04 ± 0.1 [quercetin + cysteine–H]– (theor. m/z 420.0389 [quercetin + cysteine–H]–).
- Savic, Sasa,Keckes, Silvio,Petronijevic, Zivomir
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p. 226 - 235
(2016/12/16)
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- On the difference in decomposition of taxifolin and luteolin vs. fisetin and quercetin in aqueous media
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Abstract: The decomposition of flavonols quercetin and fisetin, flavone luteolin and flavanone taxifolin was studied in slightly alkaline solution under ambient conditions. The study was based on spectrophotometry and high-pressure liquid chromatography. Products formed by atmospheric oxygen oxidation and hydrolysis were identified by HPLC–DAD and HPLC–ESI-MS/MS. Only small differences in the chemical structure of flavonoids resulted in extremely variable oxidation pathways and products. Oxidation of flavonols led to the formation of both a benzofuranone derivative and several open structures. On the contrary, the benzofuranone derivative was not found as a product of taxifolin and luteolin oxidative decomposition. These compounds were oxidized to their hydroxylated derivatives and typical open structures. Quercetin was not identified as a possible oxidation product of taxifolin. Graphical Abstract: [Figure not available: see fulltext.]
- Sokolová, Romana,Rame?ová, ?árka,Kocábová, Jana,Kolivo?ka, Viliam,Degano, Ilaria,Pitzalis, Emanuela
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p. 1375 - 1383
(2016/08/12)
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- Regioselective ortho-carboxylation of phenols catalyzed by benzoic acid decarboxylases: A biocatalytic equivalent to the Kolbe-Schmitt reaction
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The enzyme catalyzed carboxylation of electron-rich phenol derivatives employing recombinant benzoic acid decarboxylases at the expense of bicarbonate as CO2 source is reported. In contrast to the classic Kolbe-Schmitt reaction, the biocatalytic equivalent proceeded in a highly regioselective fashion exclusively at the ortho-position of the phenolic directing group in up to 80% conversion. Several enzymes were identified, which displayed a remarkably broad substrate scope encompassing alkyl, alkoxy, halo and amino- functionalities. Based on the crystal structure and molecular docking simulations, a mechanistic proposal for 2,6-dihydroxybenzoic acid decarboxylase is presented.
- Wuensch, Christiane,Gross, Johannes,Steinkellner, Georg,Lyskowski, Andrzej,Gruber, Karl,Glueck, Silvia M.,Faber, Kurt
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p. 9673 - 9679
(2014/03/21)
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- On the thermal degradation of anthocyanidins: Cyanidin
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Cyanidin was studied by direct pH jumps (from equilibrated solutions at very low pH values to higher pH values) and reverse pH jumps (from equilibrated or not equilibrated solutions at higher pH values to very low ones). The kinetic steps of the direct and reverse pH jumps were followed by stopped flow, absorption spectroscopy and HPLC, at different timescales. The pH dependent rate constant of the slower kinetic process to reach the equilibrium follows a bell shaped curve as described for many synthetic flavylium compounds. Unlike anthocyanins, it was proved that there is no pH dependent reversibility in the system, since the chalcone suffers an irreversible degradation process. The mathematical expression to describe the bell shaped behaviour was deduced. These results contribute to explain why in plants glycosylation is crucial for the stabilization of the anthocyanins.
- Cabrita, Luis,Petrov, Vesselin,Pina, Fernando
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p. 18939 - 18944
(2014/05/20)
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- Oxidation of aromatic aldehydes with potassium bromate-bromide reagent and an acidic catalyst
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We report herein an easy oxidation procedure for converting aromatic aldehydes to aromatic carboxylic acids by use of a combination of commercially and readily available potassium bromate with potassium bromide in the presence of hydrochloric acid catalyst.
- Sharma,Robert, Alice R.
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p. 3251 - 3254
(2013/09/23)
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- The influence of the host-guest interaction on the oxidation of natural flavonoid dyes
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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.
- Ramesova, Sarka,Sokolova, Romana,Degano, Ilaria,Hromadova, Magdalena,Gal, Miroslav,Kolivoska, Viliam,Colombini, Maria Perla
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experimental part
p. 1651 - 1667
(2012/05/19)
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- PROCESS FOR STRAIGHTENING KERATIN FIBRES WITH A HEATING MEANS AND DENATURING AGENTS
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The invention relates to a process for straightening keratin fibres, comprising: (i) a step in which a straightening composition containing at least two denaturing agents is applied to the keratin fibres, (ii) a step in which the temperature of the keratin fibres is raised, using a heating means, to a temperature of between 110 and 250° C.
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- Spectral alteration and degradation of cyanidin-3-glucoside exposed to pulsed electric field
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Anthocyanins are polyphenol antioxidants that have been shown to prevent many chronic diseases. The compounds are not stable, so they tend to be decolorized or degraded during processing and storage. In this study, the spectral characteristics alteration and degradation products of cyanidin-3glucoside (Cyd-3-glc) exposed to pulsed electric field (PEF) were investigated, and the reaction kinetics was discussed. The intensity of the UV-vis spectra decreased noticeably upon PEF treatment without modification of the spectral pattern. Protocatechuic acid and 2,4,6-trihydroxybenzoic acid were identified as degradation products of both PEF and thermally treated Cyd-3-glc, but cyanidin present in thermally treated Cyd-3-glc was absent in PEF-treated Cyd-3-glc, indicating that the first step of Cyd-3-glc degradation induced by PEF was not the hydrolysis of glycosidic bonds, which was different from that of thermal degradation. With increased electric field intensity or treatment time, the degradation of Cyd-3-glc and the formation of protocatechuic acid were enhanced; their kinetics (except 7 kV/cm for protocatechuic acid formation) were well fitted to a first-order reaction. Meanwhile, a good correlation was present between Cyd-3-glc degradation and protocatechuic acid formation. 2010 American Chemical Society.
- Zhang, Yan,Sun, Jianxia,Hu, Xiaosong,Liao, Xiaojun
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experimental part
p. 3524 - 3531
(2011/07/07)
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- Reactivity pattern of in situ generated tetraethylammoniun superoxide with some flavonoids
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A number of flavonoids have been allowed to react under the mild reaction conditions of tetraethylammonium superoxide in dry dimethylformamide at room temperature. As an outcome, 3-hydroxyflavones 1a-c undergo oxidative ring cleavage to afford 2-benzoyloxyphenylglyoxylic acids 2a-c, whereas the substrates 1d-f result in the formation of acids 2d-f alongwith 3d-f.
- Singh, Krishna Nand,Kumar, Rajesh
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p. 1554 - 1557
(2008/09/19)
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- Identification of the products of oxidation of quercetin by air oxygen at ambient temperature
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Oxidation of quercetin by air oxygen takes place in water and aqueous ethanol solutions under mild conditions, namely in moderately-basic media (pH ~ 8-10) at ambient temperature and in the absence of any radical initiators, without enzymatic catalysis or irradiation of the reaction media by light. The principal reaction products are typical of other oxidative degradation processes of quercetin, namely 3,4-dihydroxy-benzoic (protocatechuic) and 2,4,6-trihydroxybenzoic (phloroglucinic) acids, as well as the decarboxylation product of the latter - 1,3,5-trihydroxybenzene (phloroglucinol). In accordance with the literature data, this process involves the cleavage of the γ-pyrone fragment (ring C) of the quercetin molecule by oxygen, with primary formation of 4,6-dihydroxy-2-(3,4-dihydroxybenzoyloxy)benzoic acid (depside). However under such mild conditions the accepted mechanism of this reaction (oxidative decarbonylation with formation of carbon monoxide, CO) should be reconsidered as preferably an oxidative decarboxylation with formation of carbon dioxide, CO2. Direct head-space analysis of the gaseous components formed during quercetin oxidation in aqueous solution at ambient temperature indicates that the ratio of carbon dioxide/carbon monoxide in the gas phase after acidification of the reaction media is ca. 96:4 %. Oxidation under these mild conditions is typical for other flavonols having OH groups at C3 (e.g., kaempferol), but it is completely suppressed if this hydroxyl group is substituted by a glycoside fragment (as in rutin), or a methyl substituent. An alternative oxidation mechanism involving the direct cleavage of the C2-C3 bond in the diketo-tautomer of quercetin is proposed.
- Zenkevich, Igor G.,Eshchenko, Anna Yu.,Makarova, Svetlana V.,Vitenberg, Alexander G.,Dobryakov, Yuri G.,Utsal, Viktor A.
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p. 654 - 672
(2008/02/01)
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- Synergistic compositions for the selective control of tumor tissue
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According to the invention, compositions are made available which have a strong cytotoxic effect which is largely selective on tumor tissue. The invention is based on the fact that certain benzoic acid derivatives have a strong synergistic effect as a mixture and destroy cancer cells selectively in a pH range of 7 or below, such as from 6.5 to 7.
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- Synergistically acting compositions for selectively combating tumor tissue
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According to the invention, compositions are made available which have a strong cytotoxic effect which is largely selective on tumor tissue. The invention is based on the fact that certain benzoic acid derivatives have a strong synergistic effect as a mixture and destroy cancer cells selectively in a pH range of 7 or below, such as from 6.5 to 7.
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- Flavonol-serum albumin complexation. Two-electron oxidation of flavonols and their complexes with serum albumin
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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.
- Dangles, Olivier,Dufour, Claire,Bret, Stephan
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p. 737 - 744
(2007/10/03)
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