Electrochemical behavior and antioxidant and prooxidant activity of natural phenolics

We have investigated the electrochemical oxidation of a number natural phenolics (salicylic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, protocatechuic acid, o-coumaric acid, m-coumaric acid, p-coumaric acid, caffeic acid, quercetin and rutin) using cyclic voltammetry. The antioxidant properties of these compounds were also studied. A structural analysis of the tested phenolics suggests that multiple OH substitution and conjugation are important determinants of the free radical scavenging activity and electrochemical behavior. Compounds with low oxidation potentials (Epa lower than 0.45) showed antioxidant activity, whereas compounds with high Epa values (>0.45) act as prooxidants.     

Electrochemical Study of Phenolic Compounds as Enhancers in Laccase‐Catalyzed Oxidative Reactions

Sixteen phenolic compounds, twelve of which derived from lignin, were evaluated as potential mediators for laccase‐assisted bleaching of pulp. The electrochemical behavior of these phenols, alone and in the presence of the lignin model compound veratryl alcohol, was studied by means of cyclic voltammetry. All phenolic compounds showed catalytic effect on the veratryl alcohol electrochemical oxidation. However, they could not be considered as mediators, since their oxidation products are not stable and regeneration of their reduced forms was not observed. The redox potentials of the phenolic compounds seem to have a negligible effect on their catalytic efficiency, supporting a H‐abstraction oxidation mechanism. This mechanism was also confirmed by electrochemical studies of 2,4,6‐trimethylphenol in acetonitrile and in the presence of benzyl alcohols.     

有机溶剂中联苯和联三苯的电化学氧化聚合

应用电化学石英晶体微天平和反射光谱电化学方法研究了 0 .10molL 1四氟硼酸化四丁铵 二氯甲烷溶液中联苯和联三苯在铂电极上的氧化聚合 .结果表明 ,联苯和联三苯经氧化后在溶液中偶合成聚合物 ,生成的聚合物沉积在铂电极表面 .聚合反应是通过单体氧化后生成的自由基离子偶合进行的 .聚合物的生成量与单体氧化生成的自由基离子的量有关 .由于联三苯的氧化电位低于联苯 ,因此在相同的实验条件下前者在铂电极上的聚合沉积速度较快 .聚合过程的吸收光谱红移说明随着电解的进行 ,氧化的联苯和联三苯的自由基离子聚合成长链的聚合物     

Dodecyl gallate as a pro-ecological antioxidant for food packing materials

Electrochemical oxidation of dodecyl gallate (lauryl gallate), the main monomer flavanol found in green tea, was investigated on platinum electrodes using cyclic voltammetry (CV) and differential pulse (DPV) methods. The rate constant, electron transfer coefficient and diffusion coefficients were determined for dodecyl gallate electrochemical oxidation. The oxidation mechanism proceeds in sequential steps related to the hydroxyl groups in the aromatic ring of dodecyl gallate. The confirmed antioxidant activity of lauryl gallate justified its use in polymers, for instance, in an environment-friendly stabiliser aimed at improving the resistance to aging of elastomeric materials. Based on energy change during deformation, cross-linking density and oxygen induction time in the TG method, we confirmed the high antioxidant activity of lauryl gallate in polymers. Moreover, the research on biodegradation confirmed the environmentally friendly interest of the antioxidant by the fact that it increases the susceptibility of the elastomeric materials to disintegration by mildew mushrooms.     

Effect of 3‐O‐Galloyl Substitution on the Electrochemical Oxidation of Quercetin and Silybin Galloyl Esters at Glassy Carbon Electrode

The galloyl substitution effect on the antioxidant potential of quercetin‐3‐O‐gallate (QG) and silybin‐3‐O‐gallate (SBG), and the oxidation of QG and SBG were studied by cyclic, differential and square‐wave voltammetry using a glassy carbon electrode, and compared with their structural components, quercetin (Q), silybin (SB), gallic acid and gallic acid methyl ester. Their multi‐step pH‐dependent anodic behaviour, first oxidation followed by oxidation of the hydroxyl groups at ring A, is similar to Q and SB. The galloyl substitution significantly improved the antioxidant potential of SB compared to Q, and brought useful knowledge about the antioxidant activity of Q and SB monogalloyl esters.     

磁场对微乳液法合成聚苯胺结构及其电化学行为的影响

在不同磁场强度下,采用微乳液聚合法合成导电聚苯胺(PANI),以碳纸负载PANI为工作电极,通过循环伏安测试方法,探讨了磁场、氧化剂浓度和聚合时间对微乳液聚合法合成PANI电化学性能的影响;并通过X射线衍射(XRD)、四探针电导率测试和傅立叶红外光谱(FTIR)对产物结构和性能的表征分析,印证了循环伏安分析结果的可靠性.实验结果表明,与无磁条件下制备的PANI相比,磁场条件下制备的PANI具有较高的导电性和规整度;FTIR谱图分析表明,由于磁场的取向作用使分子间相互作用力降低,分子链离域程度增大,使磁场条件下合成PANI的主要特征峰有向低频方向移动的趋势,但分子的基本结构单元没有发生变化.研究结果显示,利用负载PANI的碳纸为工作电极,能够对微乳液法合成PANI的电化学行为进行有效的实时表征.     

A New Kinetic‐Mechanistic Approach to Elucidate Formaldehyde Electrooxidation on Copper Electrode

Electrocatalytic oxidation of formaldehyde was investigated on copper electrode in alkaline solution. The process of oxidation involved and its kinetics were established by using cyclic voltammetry, chronoamperometry as well as steady state polarization measurements. In cyclic voltammetry (CV) studies, in the presence of formaldehyde the peak current increase of the oxidation of Cu(III) is followed by a decrease in the corresponding cathodic current. A new mechanism based on the electrochemical generation of Cu(III) active sites and their subsequent consumption by the formaldehyde in question was also investigated.     

槲皮素在氧化锆修饰玻碳电极上的伏安行为及检测

制备了氧化锆修饰的玻碳电极,采用示差脉冲伏安法和循环伏安法探究了槲皮素在该电极上的电化学行为。结果表明,制备的修饰电极在pH=7.00的磷酸盐缓冲溶液（PBS）中对槲皮素的氧化还原具有明显的电催化作用。采用槲皮素的氧化峰电流作为分析信号。在浓度为2.5×10-8~5×10-5 mol/L的范围内,氧化峰电流和浓度成良好的线性关系,线性方程为ip（μA）=0.0825c-9.861 84,检出限为5.35×10-9 mol/L。     

A new electrocatalytic mechanism for the oxidation of phenols at platinum electrodes

Electrochemical oxidation of phenolic compounds generally produces unstable phenoxy radicals that readily polymerize to passivate the surface of solid electrodes. In this study, the electrocatalytic oxidation of phenol in the presence and absence of methanol was investigated by cyclic voltammetry on a platinum electrode. The cyclic voltammogram of phenol in a mixture of phosphate buffer/methanol solution showed well-defined peaks at ∼600 mV vs. Ag/AgCl reference electrode, which surprising, gradually increased with repetitive scanning, stabilizing after 50 cycles. This unexpected behavior is in contrast to previous studies involving phenolic compounds, which always show a decrease in intensity during continuous potential scanning. Scanning electrochemical spectroscopy (SEM) was further used to investigate the changes in the surface morphology of the Pt electrode after electrodeposition. A new electrocatalytic mechanism for phenol oxidation on the surface of a Pt electrode is suggested in the presence of methanol. The proposed mechanism is based on the formation of a film of Pt oxide/hydroxides onto which the phenol and the products of its electrochemical oxidation are further deposited. The mechanism was also studied using more complex phenolic compounds including resveratrol, quercetin and bisphenol A. The results emphasized the effect of aryl substituents on the electrochemistry of this particular class of compounds.     

Electrochemical Oxidation of Quercetin

The mechanism of electrochemical oxidation of quercetin on a glassy carbon electrode has been studied using cyclic, differential pulse and square‐wave voltammetry at different pH. It proceeds in a cascade mechanism, related with the two catechol hydroxyl groups and the other three hydroxyl groups which all present electroactivity, and the oxidation is pH dependent. Quercetin also adsorbs strongly on the electrode surface; and the final oxidation product is not electroactive and blocks the electrode surface. The oxidation of the catechol 3′,4′‐dihydroxyl electron‐donating groups, occurs first, at very low positive potentials, and is a two electron two proton reversible reaction. The hydroxyl group oxidized next was shown to undergo an irreversible oxidation reaction, and this hydroxyl group can form a intermolecular hydrogen bond with the neighboring oxygen. The other two hydroxyl groups also have an electron donating effect and their oxidation is reversible.     

圆盘状a-Co(OH)2的控制合成及其电化学性能

采用AAO模板及后处理方法合成了圆盘状a-Co(OH)2并研究了其电化学电容性能.在该合成方法中,先采用阳极氧化铝模板结合交流电沉积的方法获得钴纳米线,而后将其在碱液中通过溶解氧氧化生成终端产物.用红外光谱(FT-IR),X射线衍射(XRD)和场发射扫描电子显微镜(FE-SEM)表征了产物的结构和形貌;用循环伏安、恒电流充放电测试方法对其电化学性能进行了测试.此外,对圆盘状Co(OH)2的形成机理进行了初步探讨.结果表明,用此方法合成的Co(OH)2具有圆盘状形貌,属a相态,且表现出较好的电容特性.     

Kinetic Study of the Electro-Catalytic Oxidation of Hydrazine on Cobalt Hydroxide Modified Glassy Carbon Electrode

Electrocatalytic oxidation of hydrazine was investigated on a cobalt hydroxide modified glassy carbon (CHM-GC) electrode in alkaline solution. The process of oxidation involved and its kinetics were established by using cyclic voltammetry, chronoamperometry techniques as well as steady state polarization measurements. In cyclic voltammetry (CV) studies, in the presence of hydrazine the peak current increase of the oxidation of cobalt hydroxide is followed by a decrease in the corresponding cathodic current. This indicates that hydrazine is oxidized on the redox mediator that is immobilized on the electrode surface via an electrocatalytic mechanism. A mechanism based on the electrochemical generation of Co(IV) active sites and their subsequent consumption by the hydrazine in question was also investigated.     

Electrochemical antioxidant detection technique based on guanine-bonded graphene and magnetic nanoparticles composite materials

An antioxidant (AO) amperometric technique based on guanine attached to graphene and Fe(3)O(4) nanoparticles (NPs) magnetic materials was developed. Guanine molecules acted as an antioxidant competitor were bonded with graphene nanosheets, onto which magnetic Fe(3)O(4) NPs were attached and the as-prepared magnetic composite can be attracted to the electrode surface by an external magnetic field. When applied with negative potentials, the dissolved oxygen was reduced to H(2)O(2) at the electrode surface, and then reacted with the EDTA-Fe(ii) complex via a Fenton-like reaction to produce OH radicals. After oxidation damage by OH radicals, the electrochemical oxidation of guanine gave a decreased current. In the presence of AOs, the reactive oxygen species (ROS, e.g. OH radicals and H(2)O(2)) were scavenged by AOs and fewer guanine probe molecules were oxidized, thus inducing a higher electrochemical oxidation current of guanine. So AOs competed with the guanine probe molecules toward oxidation by ROS. The current signals of the guanine probe molecules were proportional to the concentrations of AOs. A kinetic model was proposed to quantify the ROS scavenging capacities of the AOs. Using guanine as an oxidizable probe and OH radicals and H(2)O(2) as endogenous ROS, this kind of AO detection technique mimicks the antioxidant protection mechanism by small AO molecules in the human body.     

一硝基四苯基卟啉及其Cu(Ⅱ)、Zn(Ⅱ)配合物的电化学和光谱电化学

以卟啉环为配体的金属卟啉配合物具有特殊的光、电、磁及生物功能．在卟啉骨架的吡咯环上引入拉电子基团如ＣＮ或Ｂｒ等,能改变卟啉的氧化还原电位;当有ＰｈＩＯ、Ｈ２Ｏ２、ＮａＯＣｌ、ＲＣＯ３Ｈ等氧化剂存在时,这类卟啉衍生物可作为有机环氧化的催化剂．因此对环取...     

Morphology and performance of CoOOH films synthesized via electrochemical oxidation: substrate effects

In the present work, CoOOH films are synthesized from the electrochemical oxidation of α-Co(OH)₂ as precursor. The substrate influences on the material electrochemical properties are studied. The samples are structural and morphologically characterized using techniques of X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy techniques are used for the electrochemical characterization. The films deposited on steel substrate grew in the vertical hexagonal platelet form. Meanwhile, films on Ti plate presented morphology in agglomerated sphere form. After electrochemical oxidation, the film initial morphology is maintained. The films deposited on steel plate have a structure which favors charge storage showing a high specific capacity value (110.92 mA h g^?1) and cyclic stability of 92% after 1000 cycles. Finally, the relaxation time constant value calculated was 5.6 s. This fact is making this material as a possible good candidate for application as electrode material or additive for other materials, in energy storage devices.     

焦粉活性炭/Al-Ni(OH)2复合电极材料的制备及其超级容器性能

以焦粉为原料,用HNO3预处理除灰,采用KOH浸渍-煅烧活化法制备焦粉活性炭(CPAC),通过场发射扫描电子显微镜、X射线衍射等表征其形貌,采用BET测试其比表面积、孔结构及孔径分布。初步考察了活化温度、活化时间等对焦粉活性炭电极材料电化学性能的影响。采用共沉淀法制备CPAC/Al-Ni(OH)2复合电极材料,通过恒电流充放电测试及循环伏安测试表征CPAC/Al-Ni(OH)2复合电极材料的电化学性能。结果表明,当活化温度为800℃、活化时间为3 h制得的焦粉活性炭电极材料的电化学性能最佳,比电容达到211 F/g。CPAC-800℃-3 h/Al-Ni(OH)2复合电极材料随Al掺杂量的增大呈现先增大后减小的趋势。在固定Al质量掺杂量为4%,炭镍质量比为1∶1时所得复合材料的比电容量最大:1173.6 F/g。恒电流充放电及循环伏安测试表明Al掺杂量为4%、炭镍比为1∶1的复合材料具有较好的电化学性能。     

Selective Determination of Quercetin Using Carbon Nanotube‐Modified Electrodes

Electrochemical detection of quercetin has been carried out on glassy carbon electrodes modified with carbon nanotubes and Nafion (GC/Nafion‐CNT). GC/Nafion‐CNT electrodes did not show passivation effect that occurs on the unmodified electrodes and displayed better stability and reproducibility. Quercetin oxidation was most favorable in acidic conditions and current gradually decreased as the solution pH increased. No oxidation was observed when two ? OH groups in a catechol moiety were fully deprotonated. These electrodes enabled selective determination of quercetin in the presence of interfering species such as ascorbic acid, uric acid, glucose, and catechol in large excess. Quantification of quercetin in a yellow onion has been made and favorably compared with reported values. Good selectivity and high sensitivity obtained by Osteryoung sSquare‐wave voltammetry can open new possibilities of direct quercetin determination in vegetables with a minimal sample treatment.     

Electrochemistry and electrocatalytic activity of catechin film on a glassy carbon electrode toward the oxidation of hydrazine

A very stable electroactive film of catechin was electrochemically deposited on the surface of activated glassy carbon electrode. The electrochemical behavior of catechin modified glassy carbon electrode (CMGCE) was extensively studied using cyclic voltammetry. The properties of the electrodeposited films, during preparation under different conditions, and the stability of the deposited film were examined. The charge transfer coefficient (α) and charge transfer rate constant (k _s) for catechin deposited film were calculated. It was found that the modified electrode exhibited excellent electrocatalytic activity toward hydrazine oxidation and it also showed a very large decrease in the overpotential for the oxidation of hydrazine. The CMGCE was employed to study electrocatalytic oxidation of hydrazine using cyclic voltammetry, rotating disk voltammetry, chronoamperometry, amperometry and square-wave voltammetry as diagnostic techniques. The catalytic rate constant of the modified electrode for the oxidation of hydrazine was determined by cyclic voltammetry, chronoamperometry and rotating disk voltammetry and was found to be around 10⁻³ cm s⁻¹ . In the used different voltammetric methods, the plot of the electrocatalytic current versus hydrazine concentration is constituted of two linear segments with different ranges of hydrazine concentration. Furthermore, amperometry in stirred solution exhibits a detection limit of 0.165 μM and the precision of 4.7% for replicate measurements of 40.0 μM solution of hydrazine.     

The enhanced electronic communication in ferrocenemethanol molecular cluster based on intermolecular hydrogen-bonding

The electronic communication has been enhanced by regulating the intermolecular hydrogen-bonding in ferrocenemethanol molecular clusters. This enhanced electronic communication facilitates the electron transfer of ferrocenemethanol and increases the standard rate constant of the electron transfer process.     

Investigations on the kinetics of electron transfer reactions in magnetic fields

There is a controversial debate if a magnetic field can influence the rate of electron transfer (ET) reactions. In this paper, we report kinetic measurements of the ET rate constants for the redox couples [IrCl6]2-/[IrCl6]3-, [Fe(CN)6]3-/[Fe(CN)6]4-, and [Fe(H2O)6]3+/[Fe(H2O)6]2+ in magnetic fields up to 1 T. To reduce effects arising from magnetically induced mass transport (magnetohydrodynamic effect), disk microelectrodes with a diameter of 50 microm were used in potentiodynamic (cyclic and linear sweep voltammetry) and in electrochemical impedance spectroscopy experiments. None of the investigated redox couples showed a magnetic field effect on the ET rate constant.