The pH Changes at the Electrode Surface Caused the New Voltammetric Waves in PCET Reactions

Wang, Jianguo; Wang, Haiying; Guo, Shujie; Jia, Xiang Feng; Zhong, Yan; Han, Yongqin; Lin, Mi; Wang, Shuang; Zhao, Fangmin; Fu, Jiabao; Zhao, Jian

doi:10.1149/2.0181409jes

Cited by 25 publications

(47 citation statements)

References 38 publications

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“…The complex between phosphate and QH 2 could not be detected as the spectrum of QH 2 is independent of phosphate. Therefore, we attribute wave 1 to the drastic decrease in pH at the electrode surface instead of new species . HPO 4 2− is the proton acceptor in phosphate buffer solution.…”

Section: Resultsmentioning

confidence: 92%

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The Adequate Amount of Acid‐Base Buffer for Electrochemical Investigation of Proton‐Coupled Electron Transfer Reactions

Zhang

Liu

et al. 2018

ChemistrySelect

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The effective pH occurs near the electrode surface in dilute solutions as protons are released or absorbed during proton‐coupled electron transfer (PCET) reactions. We utilize cyclic voltammetry to study the electrochemical behavior of hydroquinone, p‐benzoquinone, ascorbic acid, and dopamine in phosphate buffer. The effective pH causes peak potential changes and new peak formation. However, the electrochemical behavior of hydroquinone is independent of the buffer when the HPO42−(proton acceptor) concentration is 4.05–6 times greater than that of hydroquinone. Similar results are obtained for quinone in phosphate buffer solution. Dopamine undergoes cyclization during electrochemical oxidation, which also releases protons. Therefore, a high amount of buffer is required. Moreover, the amount of acid‐base buffer strongly affects the electrochemical behaviors of quinone and hydroquinone in acetonitrile. Our results provide a fundamental guide for determining the adequate amount of buffer for the electrochemical investigation of PCET reactions.

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Section: Resultsmentioning

confidence: 92%

“…We observed that three Q peaks occur in dilute phosphate or phosphite solution (pH=3.35). We concluded that the new waves are generated by acute pH changes near the electrode surface . Therefore, the addition of buffer is necessary for electrochemical research on PCET reactions.…”

Section: Introductionmentioning

confidence: 95%

The Adequate Amount of Acid‐Base Buffer for Electrochemical Investigation of Proton‐Coupled Electron Transfer Reactions

Zhang

Liu

et al. 2018

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“…According Figure , the reduction of ferric EDDHA involves the protonation of the phenolic groups, which however is a fast reaction within the time scale of the CV experiments performed . As a result, the solution pH in the diffusion layer of the electrode increases during the cathodic scan of a CV experiment …”

Section: Resultsmentioning

confidence: 99%

Electrochemistry of Iron(II/III)‐N,N'‐ethylene‐bis‐(o‐hydroxyphenylglycine) Complexes in Aqueous Solution Indicates Potential for Use in Redox Flow Batteries

Schröder

Obendorf

Bechtold³

2019

ChemElectroChem

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The iron complexes of the two diastereomers of N,N′‐ethylene‐bis‐(o‐hydroxyphenylglycine) (EDDHA), racemic (R,R−S,S) and meso (R,S−S,R) were isolated from commercial Fe‐EDDHA fertilizer. Cyclic voltammetry in aqueous solution in the pH range between 4.0 and 11.5 indicated reversible behaviour at both mercury and glassy carbon electrodes and quasi reversible characteristics at a copper electrode. An E1/2 value of −642 mV (racemic diastereomer) and −615 mV (meso form) vs. Ag/AgCl 1 M NaCl reference electrode was observed at pH 9. In unbuffered solutions the complex of the racemic diastereomer shows almost pH independent redox behaviour over the whole pH range studied. The iron complex of the meso isomer hydrolyses at pH values above 9. Diffusion coefficients of the complex species were determined from the voltammograms for the meso isomer and the racemic form with 5.4 10−6 cm2 s−1 and 5.8 10−6 cm2 s−1 respectively. Bulk electrolysis experiments at pH 9 demonstrated the chemical stability of both the FeII‐ and the FeIII‐form of the complex with racemic EDDHA. Good cycling stability and current efficiency were obtained in subsequent charge/discharge experiments using a carbon felt electrode. The redox properties and the stability of FeII/III‐EDDHA complexes make them interesting candidates for future use as negative redox electrolytes in redox flow batteries (RFB).

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“…4 are attributed to the sharp pH change at the electrode surface. 33,34 Thus, the buffer capacity will affect the cyclization reaction of catecholamines.…”

Section: H758mentioning

confidence: 99%

“…We have investigated the electrochemical behavior of hydroquinone and p-benzoquinone in the dilute buffer solution. 34 We revealed that the sharp pH change at the electrode surface caused the new voltammetric waves in proton-coupled electron transfer (PCET) reactions. According to our previous study, the pH at the electrode surface regulates the electrochemical behavior of the PCET reactions, not the pH of the bulk solution.…”

Section: H758mentioning

confidence: 99%

Effect of Buffer Capacity and Ascorbic Acid on the Cyclization Reaction of Electrochemically Oxidized Dopamine, Levodopa, and Adrenaline on the Glassy Carbon Electrode

Zhu

Liu

et al. 2016

J. Electrochem. Soc.

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The intramolecular cyclization step of oxidized catecholamines is crucial for neuromelanin (NM) and polydopamine (PDA). The product of the cyclization reaction of catecholamines has electrochemical activity, and its anodic and cathodic peaks occur at a more negative position than that of catecholamines. Moreover, in low pH, the amine group is protonated to a considerable extent; thus, the cyclization reaction is precluded. Our cyclic voltammetric results show that, in dilute buffer solution, the buffer concentration promotes the extent of the cyclization reaction of dopamine (DA), levodopa (L-D), and adrenaline (AD). A buffer component accepts the protons released by oxidized catecholamines, which suppresses the pH decrease near the electrode surface and protonation of amine group. Ascorbic acid (AA) more significantly inhibits the cyclization reaction of oxidized DA than those of L-D and AD. AA reduces catecholamine-quinone, and the cyclization rate constant of oxidized DA is smaller than those of L-D and AD. Consequently, buffer capacity and AA can be used to regulate the synthesis of NM and PDA.Parkinson's disease (PD), one of the most common neurological disorders in the elderly, is characterized by a progressive and massive loss of midbrain dopaminergic neurons. 1 Neuromelanin (NM) is found in deep brain regions, specifically in loci that degenerate in PD patients. 2 To date, the formation, structure, and biological significance of NM are not clearly defined. 3 However, evidence from several studies strongly indicates that the main component of the nigral pigment is formed through the oxidative copolymerization of dopamine (DA). [4][5][6][7] In recent years, the study on polydopamine (PDA) has been an important topic in the biology and chemistry fields. Stepien et al. 8 showed that DA-melanin can suppress the yield of hydroxyl radicals generated via Fenton reaction; however, after saturation with ferric ions, it promotes the formation of hydroxyl radicals via redox activation of the ions. Wang et al. 9 fabricated a novel core-shell structure based on upconversion fluorescent nanoparticles and developed DAmelanin for the evaluation of the antioxidant capacity of biological fluids. Klosterman et al. 10 analyzed the influence of surface composition on the growth of DA-melanin films formed through the polymerization of 5,6-dihydroxyindole and 5,6-dihydroxyindole-2-carboxylic acid precursor solution in vitro. Wu et al. 11 developed a method of DA-melanin nanofilms for biomimetic structural coloration.The mechanism of DA in eumelanin-type polymer was fully investigated in vitro, 12-16 and the reaction pathway is shown in Scheme 1. DA can be easily oxidized in an aqueous solution through a two-electron and two-proton process transforming into quinone (1a→2a); 17 dopamine-quinone (DAQ) undergoes a cyclization reaction to form leucoaminochrome (LAC) (2a→4a); and LAC reacts immediately with DAQ to form aminochrome (AC) and DA (4a + 2a→5a + 1a). 16,18 AC has a short lifespan and ultimately reacts to form NM, a polyme...

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The pH Changes at the Electrode Surface Caused the New Voltammetric Waves in PCET Reactions

Cited by 25 publications

References 38 publications

The Adequate Amount of Acid‐Base Buffer for Electrochemical Investigation of Proton‐Coupled Electron Transfer Reactions

The Adequate Amount of Acid‐Base Buffer for Electrochemical Investigation of Proton‐Coupled Electron Transfer Reactions

Electrochemistry of Iron(II/III)‐N,N'‐ethylene‐bis‐(o‐hydroxyphenylglycine) Complexes in Aqueous Solution Indicates Potential for Use in Redox Flow Batteries

Effect of Buffer Capacity and Ascorbic Acid on the Cyclization Reaction of Electrochemically Oxidized Dopamine, Levodopa, and Adrenaline on the Glassy Carbon Electrode

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