Novel tocopherol compounds I. Bromination of α-tocopherol — reaction mechanism and synthetic applications

Rosenau, Thomas; Habicher, Wolf D.

doi:10.1016/0040-4020(95)00421-4

Cited by 51 publications

(44 citation statements)

References 18 publications

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“…11 Despite this, the electrochemical behavior of quercetin has been almost always studied in organic solvents due to constrains imposed by its solubility characteristics. Evidently, the stability of intermediate species originated by oxidation reactions is substantially different depending on the surroundings (organic or aqueous media), 12 offering a very rich chemistry as consequence. In this framework, the knowledge of its electrochemical behavior in biological-like conditions is relevant to get insight into the quercetin action as antioxidant.…”

Section: Introductionmentioning

confidence: 99%

Electrochemical oxidation of quercetin in hydro-alcoholic solution

Timbola¹,

Souza²,

Giacomelli³

et al. 2006

J. Braz. Chem. Soc.

135

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O comportamento eletroquímico da quercetina em meio hidro-alcoólico foi estudado na faixa de pH 2,2-9,2 aplicando-se as técnicas voltametria cíclica, eletrólise com potencial controlado e espectroscopia UV-Vis. Voltamogramas cíclicos para a quercetina mostraram três picos de oxidação e um pico de redução dependente das condições experimentais. Um processo de oxidação envolvendo dois prótons e dois elétrons no primeiro pico conduziu à formação da orto-quinona correspondente, a qual é uma espécie eletroquimicamente ativa e instável, como evidenciado pela dependência do perfil dos voltamogramas cíclicos com a velocidade de variação de potencial, em concordância com um mecanismo do tipo eletroquímico-químico (EC). Eletrólises com potencial controlado geraram três produtos caracterizados por espectroscopia UV-Vis. Um esquema reacional envolvendo as etapas eletroquímica e química foi proposto para a eletro-oxidação da quercetina em solução hidro-alcoólica, com base em dados obtidos da literatura e em evidências experimentais.The electrochemistry of quercetin hydro-alcoholic solutions of pH 2.2 to 9.2 was studied by cyclic voltammetry, controlled-potential electrolysis and UV-Vis spectroscopy. Cyclic voltammograms for quercetin showed three oxidation peaks and one reduction peak depending on the experimental conditions. The two-electron two-proton oxidation process at the first peak led to the formation of the corresponding ortho-quinone, which is an electrochemically active and unstable species, as evidenced by the dependence of the cyclic voltammogram profile on the applied scan rate, in agreement with the EC mechanism. Controlled-potential electrolysis yielded three products as characterized by UV-Vis spectroscopy. A reaction scheme comprising electrochemical and chemical steps was proposed for the electro-oxidation of the quercetin in hydro-alcoholic solutions on basis of experimental evidences obtained in this work and elsewhere.

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Section: Introductionmentioning

confidence: 99%

Electrochemical oxidation of quercetin in hydro-alcoholic solution

Timbola¹,

Souza²,

Giacomelli³

et al. 2006

J. Braz. Chem. Soc.

135

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“…[3][4][5][6][7][8][9][10][11] In this work, we have indeed observed a number of novel characteristics for the electrochemistry vitamin E in hydro-alcoholic solutions. It is clear in Figure 2 that water deeply influences the voltammetric profile of vitamin E through a drastic increase in the peak V current intensity, also producing two novel oxidation peaks (II and III) in the positive scan in homogeneous solutions.…”

Section: Discussionmentioning

confidence: 71%

“…It is well-known that the chemical stability of vitamin E related species is substantially different depending on the surroundings (for instance, the solvent) 4 resulting in a very rich chemistry as consequence. [3][4][5][6][7][8][9][10][11] In this work, we have indeed observed a number of novel characteristics for the electrochemistry vitamin E in hydro-alcoholic solutions.…”

Section: Discussionmentioning

confidence: 99%

“…In the case of B, only a small drop of a brown oil could be isolated, being not possible to properly handle with for further studies. 4 The numbering of carbon atoms is shown in Figure 1. Figure 2 shows a typical cyclic voltammogram at a glassy carbon working electrode in pH 7.4 hydro-alcoholic 1:1 (v/v) solution containing 1.0 mmol L -1 vitamin E for a scan rate (v) of 100 mV s -1 .…”

Section: Column Chromatography and Characteristics Of The Productsmentioning

confidence: 99%

“…The stability of intermediate species originated by oxidation reactions is substantially different depending on the surroundings, 4 offering a very rich chemistry as consequence. [3][4][5][6][7][8][9][10][11] In this way, the knowledge of its electrochemical behavior in more biological-like conditions is relevant to get insight into vitamin E action as antioxidant. The proton concentration influence on the antioxidant activity, 12,13 for example, is an important subject that is not satisfactorily approached in electrochemical measurements in organic media.…”

Section: Introductionmentioning

confidence: 99%

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Electrochemistry of vitamin E hydro-alcoholic solutions

Giacomelli¹,

Giacomelli²,

Alves³

et al. 2004

J. Braz. Chem. Soc.

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O comportamento eletroquímico da vitamina E em meio hidro-alcoólico foi estudado na faixa de pH 3,1-12,1 aplicando-se as técnicas voltametria cíclica, eletrólise com potencial controlado e espectroscopias UV-Vis, IR e 13 C RMN. Observou-se que a presença de água tem conseqüências importantes na estabilidade química das espécies geradas eletroquimicamente. Em meio hidro-alcoólico e sobre eletrodos de carbono vítreo, a vitamina E apresenta três picos de oxidação, enquanto que apenas um pico é observado em outros solventes. Embora a reação eletroquímica no primeiro pico seja a mesma na presença e na ausência de água, a qual compreende a transferência de dois elétrons em uma etapa, duas reações eletroquímicas e três químicas subseqüentes ao primeiro pico foram pela primeira vez estabelecidas com base em evidências eletroquímicas em meio hidro-alcoólico. Estes resultados são considerados muito importantes levando-se em consideração o papel mediador na transferência de elétrons entre a fase aquosa e lipídica que a vitamina E exerce no organismo.The electrochemistry of vitamin E hydro-alcoholic solutions of pH 3.1 to 12.1 was studied by cyclic voltammetry, controlled potential electrolysis, thin layer chromatography and UV-Vis, IR and 13 C NMR spectroscopy. The presence of water was found to have important implications on the chemical stability of electrogenerated species. Vitamin E exhibits three oxidation peaks in hydroalcoholic solutions at glassy carbon electrodes in contrast to just a single peak in other solvents. Although the electrochemical reaction at the first peak was found to be the same in presence and in absence of water, which is a one-step two-electron transfer process, two heterogeneous electrochemical reactions and three homogeneous chemical reactions following this peak were established based on electrochemical evidences for the first time in alcohol aqueous conditions. This insight is considered to be very important provided the mediator character of vitamin E in the electron transfer between aqueous and lipid phase in the organism.

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The “Tocopherol−Acetaminophen Reaction” − A New [1,4]-Rearrangement Discovered in Vitamin E Chemistry

Rosenau¹,

Kosma²

2001

Eur. J. Org. Chem.

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Novel tocopherol compounds I. Bromination of α-tocopherol — reaction mechanism and synthetic applications

Cited by 51 publications

References 18 publications

Electrochemical oxidation of quercetin in hydro-alcoholic solution

Electrochemical oxidation of quercetin in hydro-alcoholic solution

Electrochemistry of vitamin E hydro-alcoholic solutions

The “Tocopherol−Acetaminophen Reaction” − A New [1,4]-Rearrangement Discovered in Vitamin E Chemistry

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