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The electrochemical study of the degradation of the natural dyes from historical objects
Ramešová, Šárka ; Schwarzová, Karolina (advisor) ; Navrátil, Tomáš (referee)
The oxidation of quercetin (3,3',4',5,7-pentahydroxyflavone) and luteolin (3',4',5,7-tetrahydroxyflavone) has been studied. These intensively coloured polyphenolic compounds belong to a large group of naturally occuring flavonoid compounds. They were used with advantage as colourants in old tapestries. The study concerns the analysis of degradation processes of the original dyes. Degradation products formed during the ageing process can be used as fingerprints for the determination of the original colours. The degradation processes of flavonoid compounds were studied by electrochemical methods, absorption spectrometry and separation methods in aqueous media. The oxidation mechanism involves electron transfer coupled with chemical reaction and is influenced by the acidobasic properties of quercetin. The dissociation constants pK1 and pK2 of quercetin and pK1 and pK2 of luteolin were determined by combining of independent methods: acid-base titration and UV-Vis spectroscopy. The stability of both compounds significantly depends on the presence of the oxygen. The distribution of the oxidation products of quercetin in aqueous media within the exposure to oxygen was monitored by LC-MS/MS and LC- DAD analysis.
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Electrochemical oxidation mechanism of flavonoid compounds
Ramešová, Šárka
M.Sc. Šárka Ramešová Title: Electrochemical oxidation mechanism of flavonoid compounds Supervisor: M.Sc. Romana Sokolová, Dr. Study programme: Chemistry Subprogramme: Physical Chemistry SUMMARY The oxidation of rhamnazin (3,5-dihydroxy-2-(4-hydroxy-3-methoxyphenyl)-7- methoxychromen-4-one), fisetin (2-(3,4-dihydroxyfenyl)-3,7-dihydroxychromen-4-one) and rhamnetin (2-(3,4-dihydroxyfenyl)-3,5-dihydroxy-7-methoxychromen-4-one) has been studied. These intensively coloured flavonoid compounds belong to group of natural occuring compounds. Rhamnazin, fisetin and rhamnetin are important bioactive compounds with antioxidative, anti-carcinogenic, antiviral, anti-allergic and anti-inflammatory properties. Flavonoids have been studied using electrochemical methods and UV/Vis spectroscopy in aqueous, buffered or unbuffered solution. This thesis is focused on the determination of oxidation mechanism of the flavonol structure. The oxidation mechanism involves electron transfer coupled with chemical reaction. Stability of these compounds significantly depends on the presence of the oxygen. The distribution of oxidation products of these compounds was monitored by HPLC-MS/MS and HPLC-DAD. Powered by TCPDF (www.tcpdf.org)
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Differences in Oxidation Mechanism of Selected Bioflavonoids, UV-Vis and IR Spectroelectrochemical Study
Sokolová, Romana ; Fiedler, Jan ; Ramešová, Šárka ; Kocábová, Jana ; Degano, I. ; Quinto, A. ; Křen, Vladimír
The oxidation of selected bioflavonoids (quercetin, rhamnazin, fisetin, rhamnetin, taxifolin, luteolin, silybin and 2,3-dehydrosilybin) was studied by electrochemical and spectroscopic methods. The oxidation mechanism and formation of oxidation products depends on the chemical structure. Only small differences in the chemical structure of compounds with flavone, flavanone and flavonol motif result in extremely variable oxidation pathways and products. Products of oxidation and further decomposition were determined by HPLC-ESIMS/MS and HPLC-DAD.
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Electrochemical oxidation mechanism of flavonoid compounds
Ramešová, Šárka
M.Sc. Šárka Ramešová Title: Electrochemical oxidation mechanism of flavonoid compounds Supervisor: M.Sc. Romana Sokolová, Dr. Study programme: Chemistry Subprogramme: Physical Chemistry SUMMARY The oxidation of rhamnazin (3,5-dihydroxy-2-(4-hydroxy-3-methoxyphenyl)-7- methoxychromen-4-one), fisetin (2-(3,4-dihydroxyfenyl)-3,7-dihydroxychromen-4-one) and rhamnetin (2-(3,4-dihydroxyfenyl)-3,5-dihydroxy-7-methoxychromen-4-one) has been studied. These intensively coloured flavonoid compounds belong to group of natural occuring compounds. Rhamnazin, fisetin and rhamnetin are important bioactive compounds with antioxidative, anti-carcinogenic, antiviral, anti-allergic and anti-inflammatory properties. Flavonoids have been studied using electrochemical methods and UV/Vis spectroscopy in aqueous, buffered or unbuffered solution. This thesis is focused on the determination of oxidation mechanism of the flavonol structure. The oxidation mechanism involves electron transfer coupled with chemical reaction. Stability of these compounds significantly depends on the presence of the oxygen. The distribution of oxidation products of these compounds was monitored by HPLC-MS/MS and HPLC-DAD. Powered by TCPDF (www.tcpdf.org)
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The electrochemical study of the degradation of the natural dyes from historical objects
Ramešová, Šárka ; Schwarzová, Karolina (advisor) ; Navrátil, Tomáš (referee)
The oxidation of quercetin (3,3',4',5,7-pentahydroxyflavone) and luteolin (3',4',5,7-tetrahydroxyflavone) has been studied. These intensively coloured polyphenolic compounds belong to a large group of naturally occuring flavonoid compounds. They were used with advantage as colourants in old tapestries. The study concerns the analysis of degradation processes of the original dyes. Degradation products formed during the ageing process can be used as fingerprints for the determination of the original colours. The degradation processes of flavonoid compounds were studied by electrochemical methods, absorption spectrometry and separation methods in aqueous media. The oxidation mechanism involves electron transfer coupled with chemical reaction and is influenced by the acidobasic properties of quercetin. The dissociation constants pK1 and pK2 of quercetin and pK1 and pK2 of luteolin were determined by combining of independent methods: acid-base titration and UV-Vis spectroscopy. The stability of both compounds significantly depends on the presence of the oxygen. The distribution of the oxidation products of quercetin in aqueous media within the exposure to oxygen was monitored by LC-MS/MS and LC- DAD analysis.
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Oxidation Mechanism of Rhamnetin, a Bioflavonoid Compound
Ramešová, Šárka ; Sokolová, Romana ; Degano, I.
The natural flavonoid rhamnetin (2-(3,4-dihydroxyfenyl)-3,5-dihydroxy-7-methoxychromen-4-one) is important bioactive compound. Rhamnetin was studied in aqueous solution by electrochemical methods. The oxidation mechanism proceeds in sequential steps, which correspond to the hydroxyl oxidation of groups in the three aromatic rings. The study is based on in situ spectroelectrochemistry and identification of products by HPLC-DAD and HPLC–ESI MS/MS.
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Reduction and Oxidation of Hydroxyquinolines in Acetonitrile and Dimethylsulfoxide
Sokolová, Romana ; Ramešová, Šárka ; Fiedler, Jan ; Kolivoška, Viliam ; Degano, I. ; Gál, M. ; Szala, M. ; Nycz, J. E.
This study is focused on investigation of oxidation and reduction pathways of selected hydroxyquinoline compounds in nonaqueous solutions. The experimentally obtained reduction potentials are reported to well correlate with calculated values of LUMO energies as well as the obtained oxidation potentials are in a good agreement with theoretical HOMO energies. The cyclic voltammetry, in situ UV/Vis spectroelectrochemistry and in situ IR spectroelectrochemistry confirmed that the oxidation mechanism is complicated. Oxidation unexpectedly proceeds together with protonation of the starting compound. This behaviour was found for all studied compounds, hydroxyquinoline carboxylic acids and also for compounds, where a methyl group is present instead of carboxylic group.
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