Variable Scan Rate Cyclic Voltammetry and Theoretical Studies on Tocopherol (Vitamin E) Model Compounds

Yao, Wei; Peng, Hong Mei; Webster, Richard D.; Gill, Peter M. W.

doi:10.1021/jp710995n

Cited by 24 publications

(54 citation statements)

References 60 publications

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“…[8,20,35–48] The generic electrochemical mechanism for α‐TOH (which also applies to the β‐, γ‐ and δ‐tocopherols) in the organic solvents CH 3 CN or CH 2 Cl 2 is given in Scheme . [35–48] The exact reaction pathway varies depending on whether the oxidation is carried out in the presence or absence of organic‐soluble acids and bases. The phytyl chain does not affect the electrochemical properties; therefore, identical voltammetric behavior is obtained when the phytyl chain is replaced with a methyl group in a model compound.…”

Section: Discussionmentioning

confidence: 99%

“…The deprotonation rate constant was obtained by digital simulation of variable scan rate CV data in CH 3 CN and was estimated to be 3(±2) × 10 4 s −1 . [45,48] Because the oxidation potential of α‐TO· (that was obtained by digital simulation of CV data and estimated to be +0.1 (±0.1) V vs. Fc/Fc + )[45,48] is less than that of α‐TOH, α‐TO· is immediately further oxidized at the electrode surface to form the diamagnetic cation, α‐TO + . Overall, the oxidation mechanism can be considered to occur via an ECE mechanism (where E represents an electron transfer and C represents a chemical step).…”

Section: Discussionmentioning

confidence: 99%

“…[35,36,39] However, another possibility exists where the second electron‐transfer step occurs by a homogeneous disproportionation mechanism which would also produce α‐TO + ( Scheme ). [45,48,49] Irrespective of the exact pathway, the oxidation in CH 3 CN or CH 2 Cl 2 is completely chemically reversible on the fast CV (milliseconds) and electrolysis (hours) timescales so that applying a reducing potential allows the starting material to be regenerated quantitatively. [39,40]…”

Section: Discussionmentioning

confidence: 99%

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Voltammetry of the liposoluble vitamins (A, D, E and K) in organic solvents

Webster

2011

The Chemical Record

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A review summarizing the voltammetric literature of the liposoluble vitamins A, D, E and K in organic solvents containing supporting electrolyte is presented. Electrochemical studies that were performed by attaching the vitamins to electrode surfaces and performing voltammetric scans in aqueous solutions are also summarized. Vitamins A (retinol and retinal) and D (cholecaliferol and ergocalciferol) undergo chemically irreversible voltammetric oxidation processes in organic solvents to form complicated or unknown compounds that cannot be electrochemically converted back to the starting materials. In contrast to vitamins A and D, vitamins E and K undergo chemically reversible electron-transfer processes that are often coupled to proton-transfer reactions. Vitamin E (a phenol) is voltammetrically oxidized in aprotic organic solvents in a -2e(-)/-H(+) process to form a diamagnetic cation, which is unusually long-lived compared to the analogous cations produced during the oxidation of other phenols. In an aqueous environment, vitamin E is electrochemically oxidized to the hydroquinone in a chemically irreversible -2e(-) process. In low moisture content aprotic solvents, vitamin K (a quinone) is reduced in two one-electron chemically reversible steps to form first a radical anion (semiquinone, at E(1)) and then at more negative potentials a dianion is formed (at E(2)). The dianion is especially prone to strong hydrogen-bonding interactions with trace water present in the organic solvents, resulting in a shift in the formal reduction potential of E(2) to more positive potentials as more water is added to the solvent.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Voltammetry of the liposoluble vitamins (A, D, E and K) in organic solvents

Webster

2011

The Chemical Record

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“…Hydrophobic dl--tocopherol is one of the reducing reagents [9], which is known as vitamin E. In our previous report, aqueous AuCl 4 -was directly reduced by dl--tocopherol at the dodecane/water interface and gold particles were formed at the interface [10]. The gold particles were, however, aggregated at the interface over time and finally chains of gold particles were formed at the interface.…”

Section: Introductionmentioning

confidence: 99%

<i>In Situ</i> Microscope Measurements of the Formation of Nanometer-Sized Gold Particles at the Dodecane/Water Interface through the Direct Reduction of Aqueous Tetrachloroaurate(III) by Hydrophobic <i>dl</i>-α-Tocopherol in the Presence of 1,10-Phenanthroline

Tsukahara

Kobayashi

Fujiwara

2014

SERDJ

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The contact of a dodecane solution of hydrophobic dl--tocopherol with an aqueous solution of tetrachloroaurate(III) resulted in the direct reduction of tetrachloroaurate(III) and the formation of gold particles at the dodecane/water interface. Without other additives, the gold particles were unfavorably aggregated with each other and chains of gold particles were formed. In the present study, a chemical preventing the aggregation was sought. Fourteen types of chemicals were individually added to the two-phase system, and then the size, shape, and movements of the gold particles formed at the dodecane/water interface were observed through an optical microscope using bright-field illumination, using dark-field illumination, or with scattered laser light under total internal reflection conditions. Of the 14 chemicals, 1,10-phenanthroline (phen) effectively prevented the aggregation of gold particles at the interface. The gold particles formed in the presence of phen under the optimized conditions were recovered on a coverslip, and their size and shape were recorded using an atomic force microscope. Almost all of the recovered gold particles were not higher than 50 nm and this meant that nanometer-sized gold particles were formed.

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“…The fully methylated derivative produces stable phenoxonium cations upon oxidation in acetonitrile. Compounds with less methyl substitution are more reactive following oxidation and form additional oxidation products (hemiketals and p-quinones) [22].…”

Section: Introductionmentioning

confidence: 99%

MWNT-modified electrodes for voltammetric determination of lipophilic vitamins

Ziyatdinova

Morozov

Budnikov

2011

J Solid State Electrochem

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Multi-walled carbon nanotube modified graphite electrodes (MWNT-GEs) have been created for the voltammetric determination of α-tocopherol and retinol. The electrode surface was characterized by atomic force microscopy. The MWNT-GEs presented structured surfaces and a significant (26-fold) increase in roughness over unmodified graphite electrodes (8.2 vs. 0.32 nm for MWNT-GEs and GEs, respectively). Their surfaces consisted of aggregates with a highly regular "thorn-like" structure. α-Tocopherol and retinol were oxidized on the bare GEs and the MWNT-GEs in 0.1 M HClO 4 in acetonitrile. Decreases in the overpotential of 0.2 and 0.04 V for α-tocopherol and retinol, respectively, and increased oxidation currents were observed on the MWNT-GEs in comparison with the unmodified electrodes. The calibration graphs were linear in the range 0.065-2.00 mM for α-tocopherol and 0.05-1.50 mM for retinol. The detection limits were found to be 0.05 and 0.04 mM for α-tocopherol and retinol, respectively. The developed electrodes were applied to determine α-tocopherol and retinol in pharmaceuticals. The results obtained agreed well with coulometric titration data.

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Variable Scan Rate Cyclic Voltammetry and Theoretical Studies on Tocopherol (Vitamin E) Model Compounds

Cited by 24 publications

References 60 publications

Voltammetry of the liposoluble vitamins (A, D, E and K) in organic solvents

Voltammetry of the liposoluble vitamins (A, D, E and K) in organic solvents

<i>In Situ</i> Microscope Measurements of the Formation of Nanometer-Sized Gold Particles at the Dodecane/Water Interface through the Direct Reduction of Aqueous Tetrachloroaurate(III) by Hydrophobic <i>dl</i>-α-Tocopherol in the Presence of 1,10-Phenanthroline

MWNT-modified electrodes for voltammetric determination of lipophilic vitamins

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