83-30-7Relevant articles and documents
Catalytic evaluation of biocompatible chitosan-stabilized gold nanoparticles on oxidation of morin
Bulut, Onur,Yilmaz, M. Deniz
, (2021)
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.
Synthesis of narrowly dispersed silver and gold nanoparticles and their catalytic evaluation for morin oxidation
Ilunga, Ali K.,Meijboom, Reinout
, p. 17 - 29 (2016)
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.
Effect of alkali and alkaline earth metal dopants on catalytic activity of mesoporous cobalt oxide evaluated using a model reaction
Bingwa, Ndzondelelo,Bewana, Semakaleng,Ndolomingo, Matumuene Joe,Mawila, Naphtaly,Mogudi, Batsile,Ncube, Phendukani,Carleschi, Emanuela,Doyle, Bryan P.,Haumann, Marco,Meijboom, Reinout
, p. 189 - 195 (2018)
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).
Bleach catalysis in aqueous medium by iron(III)-isoindoline complexes and hydrogen peroxide
Kaizer, József,Keszei, Soma,Lakk-Bogáth, Dóra,Meena, Bashdar I.
, p. 351 - 360 (2021/11/09)
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.
Exploring the oxidation and iron binding profile of a cyclodextrin encapsulated quercetin complex unveiled a controlled complex dissociation through a chemical stimulus
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.
, p. 1913 - 1924 (2018/07/03)
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.
On the difference in decomposition of taxifolin and luteolin vs. fisetin and quercetin in aqueous media
Sokolová, Romana,Rame?ová, ?árka,Kocábová, Jana,Kolivo?ka, Viliam,Degano, Ilaria,Pitzalis, Emanuela
, p. 1375 - 1383 (2016/08/12)
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.]
Modification of quercetin with l-cysteine by horseradish peroxidase
Savic, Sasa,Keckes, Silvio,Petronijevic, Zivomir
, p. 226 - 235 (2016/12/16)
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]–).
Nitroxygenation of quercetin by HNO
Han, Xiaozhen,Kumar, Murugaeson R.,Farmer, Patrick J.
, p. 399 - 402 (2016/01/12)
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.
On the thermal degradation of anthocyanidins: Cyanidin
Cabrita, Luis,Petrov, Vesselin,Pina, Fernando
, p. 18939 - 18944 (2014/05/20)
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.
Regioselective ortho-carboxylation of phenols catalyzed by benzoic acid decarboxylases: A biocatalytic equivalent to the Kolbe-Schmitt reaction
Wuensch, Christiane,Gross, Johannes,Steinkellner, Georg,Lyskowski, Andrzej,Gruber, Karl,Glueck, Silvia M.,Faber, Kurt
, p. 9673 - 9679 (2014/03/21)
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.
