Electron Transfer Behavior through Densely Packed Self‐Assembled Monolayers of a Novel Heteroaromatic Thiol Derivative onto the Gold Surface

This article is describing the electrical characteristics of the self‐assembled monolayers (SAMs) formed during spontaneous chemical adsorption of a recently synthesized heteroaromatic thiol 2‐(2‐mercaptophenylnitrilomethylidyne)‐phenol ( L ). Some surfactants were used to regulate the electron transfer through the resulting SAMs, as investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results revealed that the surface structure is approximately complete and fractional coverage is very close to unity. The use of surfactants clearly improved the electron transfer properties. Furthermore, complementary experiments were carried out to investigate the electron transfer from modified surface to cytochrome C (cyt‐C), as a biological iron containing protein, which exists in living cells with important life roles. It was found that cyt‐C is able to interact with the modified surface so that it can be used as a scaffold to study the electrochemical characteristics of sensitive biological compounds like proteins. The voltammetric behavior of the redox protein on the resulting SAMs was found to be highly reproducible, emphasizing the fact that the protein denaturation is greatly suppressed.     

Flavin Derivatives with Tailored Redox Properties: Synthesis,Characterization, and Electrochemical Behavior

This study establishes structure–property relationships for four synthetic flavin molecules as bioinspired redox mediators in electro‐ and photocatalysis applications. The studied flavin compounds were disubstituted with polar substituents at the N1 and N3 positions (alloxazine) or at the N3 and N10 positions (isoalloxazines). The electrochemical behavior of one such synthetic flavin analogue was examined in detail in aqueous solutions of varying pH in the range from 1 to 10. Cyclic voltammetry, used in conjunction with hydrodynamic (rotating disk electrode) voltammetry, showed quasi‐reversible behavior consistent with freely diffusing molecules and an overall global 2e^?, 2H⁺ proton‐coupled electron transfer scheme. UV/Vis spectroelectrochemical data was also employed to study the pH‐dependent electrochemical behavior of this derivative. Substituent effects on the redox behavior were compared and contrasted for all the four compounds, and visualized within a scatter plot framework to afford comparison with prior knowledge on mostly natural flavins in aqueous media. Finally, a preliminary assessment of one of the synthetic flavins was performed of its electrocatalytic activity toward dioxygen reduction as a prelude to further (quantitative) studies of both freely diffusing and tethered molecules on various electrode surfaces.     

Study of the Electrochemical Behavior of Biodiesel Microemulsion

Microemulsions have become a widely employed technique for the control of biodiesel quality but are still poorly understood as regard to their electrochemical behavior. In this work, we report the fundamental importance associated with the knowledge of electrochemical behavior of microemulsions composed of water in the presence of a supporting electrolyte, soybean biodiesel and propan‐1‐ol as consolute, along with the ferrocyanide–ferricyanide redox system applied as probe. The voltammetric results showed that for different compositions of microemulsions, variation in peak currents and change in system reversibility as well as in the electron transfer process were clearly noted. Furthermore, through the study of the diffusion coefficient, three different types of microemulsions including Oil/Water, Bicontinuous, and Water/Oil were successfully identified. Electrochemical impedance spectroscopy studies were also carried out aiming at obtaining more information regarding the electrode/solution interface. All the studies performed demonstrated that different types of microemulsions were formed upon exerting a direct influence on the electrochemical behavior of the redox probe. These results, in essence, point to the possibility of choosing a more suitable and advantageous microemulsion type for the development of an analytical method, as in the case, for example, of the microemulsions ME‐2 and ME‐3 which presented high voltammetric response in redox probe oxidation.     

Photoinduced Electron Transfer of Porphyrin Isomers: Impact of Molecular Structures on Electron‐Transfer Dynamics

Porphyrins have been investigated for a long time in various fields of chemistry owing to their excellent redox and optical properties. Structural isomers of porphyrins have been synthesized, namely, porphycene, hemiporphycene, and corrphycene. Although the number of studies on these structural isomers is limited, they exhibit interesting properties suitable for various applications such as photovoltaic devices, photocatalysts, and photodynamic therapy. In the present review, we summarized their photoinduced electron‐transfer processes, which are key steps of various photofunctions. Their electrochemical and photophysical properties are summarized as basic properties for the electron transfer. Furthermore, differences among these isomers in the electron‐transfer processes are clarified, and its origin has been discussed on the basis of their molecular structures.     

Electrochemical methods in understanding the redox processes of drugs and biomolecules and their sensing

Progression of the biochemical information of drugs and its interaction with biological substances require efficient methodologies suitable for generating information without incurring any significant damage to the analytes. Electrochemical methods provide useful information and compatible to the biological environments, without any significant alterations in the analyte, the methods are capable in onsite applications. Present review discusses about the application of the electrochemical techniques in evaluating the mechanism of interaction of drugs with the biomaterials like proteins, lipids, and DNA. The redox process leads to the determination of the drugs and biomolecules through the development of modified electrodes. The modified ultra-microelectrodes (UMEs) or nano electrodes are useful in sensing at the extracellular level of single cells. The electrochemical collision using UMEs provides information about the single molecular level. Present article discusses a brief review of some of the drug and biomolecule interactions using macro and also UMEs.     

Influence of redox molecules on the electronic conductance of single-walled carbon nanotube field-effect transistors: application to chemical and biological sensing

In an effort to develop sensitive nanoscale devices for chemical and biological sensing, we have examined, using liquid gating, the conductance of semiconducting single-walled carbon nanotube-based field-effect transistors (SWCNT-FETs) in the presence of redox mediators. As examples, redox couples K3Fe(CN)6/K4Fe(CN)6 and K2IrCl6/K3IrCl6 are shown to modulate the SWCNT-FET conductance in part through their influence via the electrolyte gate on the electrostatic potential of the solution, as described by Larrimore et al. (Nano Lett. 2006, 6, 3129-1333) and in part through electron transfer between the redox mediators and the nanotubes. In the latter case, the rate of electron transfer is determined by the difference in chemical potential between the redox mediator and the SWCNTs and by the concentrations of the oxidized and reduced forms of the redox couple. Furthermore, these devices can detect the activity of redox enzymes through their sensitivity to the change in oxidation state of the enzyme substrate. An example is given for the blue copper oxidase, Trametes versicolor laccase, in which the rate of change of the SWCNT device conductance is linearly proportional to the rate of oxidation of the substrate 10-(2-hydroxyethyl)phenoxazine, varied over 2 orders of magnitude by the laccase concentration in the picomolar range. The behavior described in this work provides a highly sensitive means with which to do chemical and biological sensing using SWCNTs that is different from the amperometric, capacitive, and field-effect type sensing methods previously described in the literature for this material.     

Electrochemical Impedance Analysis of Thermogalvanic Cells

Thermogalvanic cells(also known as thermo-electrochemical cells) that convert waste heat energy to electricity are a new type of energy conversion device. However, the electron transfer kinetics and mass transfer of redox couples have not been thoroughly studied. Here, the ion reaction and charge transport in thermogalvanic cells are investigated by electrochemical impedance analysis. We first propose the detailed impedance model followed experimental verification on three types of electrode materials. Parameters including kinetic rate constants and ion diffusion coefficients for the electrodes are obtained by fitting the impedance data. Our study shows explicitly that impedance analysis can provide useful information on selecting suitable electrode materials for thermogalvanic cells.     

New perspectives in hydrogenase direct electrochemistry

Electrochemical studies of hydrogenases, the biological catalysts of H₂ oxidation and production, have proven wrong the old saying that enzymes do not easily transfer electrons to electrodes in the absence of mediators. Many distinct hydrogenases have actually been directly connected to electrodes or particles, for studying their catalytic mechanism or for designing solar-fuels catalysts. In this review, we list the electrodes that have proved successful for direct electron transfer to hydrogenases, and we discuss recent results which illustrate new directions in this research field: the study of the biosynthesis of FeFe hydrogenase, the electrochemical characterization of non-standard NiFe or FeFe hydrogenases, the general discussion of what makes a catalyst better in one particular direction of the reaction, and the elucidation of the molecular mechanisms of hydrogenase catalysis by combining electrochemistry and theoretical chemistry, spectroscopy or photochemistry. The electrochemical methods described herein will probably prove useful for studying or using other redox enzymes.     

1,10-Phenanthroline-5,6-dione and 9,10-phenanthrenequinone as redox mediators for amperometric glucose biosensors

In this study, two ortho-quinoidal compounds, 1,10-phenanthroline-5,6-dione (PD) and 9,10-phenanthrenequinone (PQ), were examined as electron transfer mediators suitable for amperometric glucose biosensors. The dependences of the electrochemical responses of PD- and PQ-based amperometric glucose biosensors on varied concentrations of glucose were investigated under aerobic and anaerobic conditions. The PD-modified graphite rod (GR) electrode revealed a current response seven times higher than that of the PQ-modified GR electrode. The reactivity indices of ortho-quinoidals assessed by means of B3LYP functional method applying 6-311G(D) basis set showed that the electron-accepting potency for PD was markedly higher as compared with that of PQ. Compared to PQ, considerably higher reactivity of PD has been defined in the reactions with NADP⁺-ferredoxin reductase (FNR, EC 1.18.1.2) as a model single-electron transfer FAD-dependent enzyme, which provided an additional evidence for PD as a more efficient mediator compared to PQ. This study illustrates that PD can be applied as a redox mediator for glucose oxidase and it could be more suitable for a reagent-less biosensor design than PQ.     

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.     

Electrochemistry of redox-active self-assembled monolayers

Redox-active self-assembled monolayers (SAMs) provide an excellent platform for investigating electron transfer kinetics. Using a well-defined bridge, a redox center can be positioned at a fixed distance from the electrode and electron transfer kinetics probed using a variety of electrochemical techniques. Cyclic voltammetry, AC voltammetry, electrochemical impedance spectroscopy, and chronoamperometry are most commonly used to determine the rate of electron transfer of redox-activated SAMs. A variety of redox species have been attached to SAMs, and include transition metal complexes (e.g., ferrocene, ruthenium pentaammine, osmium bisbipyridine, metal clusters) and organic molecules (e.g., galvinol, C₆₀). SAMs offer an ideal environment to study the outer-sphere interactions of redox species. The composition and integrity of the monolayer and the electrode material influence the electron transfer kinetics and can be investigated using electrochemical methods. Theoretical models have been developed for investigating SAM structure. This review discusses methods and monolayer compositions for electrochemical measurements of redox-active SAMs.     

Electrochemical Catalysis of the Reduction of 1,1,2-Trifluorotrichloroethane (Freon 113) by Outer-Sphere Electron Transfer Mediators

Cyclic voltammetry and preparative electrolysis in DMF were used to study the electrochemical catalytic reduction of 1,1,2-trifluorotrichloroethane with aromatic electron transfer mediators (p-dicyanobenzene, p-diacetylbenzene, fluoranthen, perylene, and (E)-azobenzene), leading to trichloroethylene in high yield. The results of a kinetic study of these systems indicate that the efficiency of other mediators of this class may be estimated relative to their redox properties. In comparison with direct electrochemical reduction of Freon 113, the use of aromatic electron transfer agents significantly raises the efficiency of Freon conversion and permits us to perform the reaction at less negative potentials.     

Electrochemical reversibility of vinylferrocene monolayers covalently attached on H-terminated p-Si(100)

A reversible electrochemical behavior is demonstrated on a specially prepared redox-functionalized H-Si(100) surface, obtained via an extra-mild grafting procedure from vinylferrocene. The results of a detailed XPS and electrochemical characterization of the resulting hybrid are reported and discussed to propose it as a reference system for high-quality electroactive monolayers on Si. The investigated ferrocene derivative bears a functional group suitable for a mild route to covalent anchoring on Si, which is based on a photoinduced reaction with visible light under an inert atmosphere. Electrochemical reversibility is shown by sharp symmetric voltammograms on freshly prepared p-Si electrodes. Anodic oxide growth is responsible for the progressive degradation of the electrochemical response. Still, fast electron transfer to the surface redox species is maintained during several thousands cycles.     

质子惰性介质中硝基苯在铂微盘电极上的电化学行为

采用循环伏安法, 以铂微盘电极为工作电极, 铂片为辅助电极, 饱和甘汞电极为参比电极, 研究了硝基苯在含有四丁基高氯酸铵(TBAP)电解质的N,N-二甲基甲酰胺(DMF)有机溶液中的电化学行为, 并探讨了扫描速度和底物浓度等因素对硝基苯电化学特性的影响. 结果表明,该反应属扩散控制的准可逆反应.     

Electron transfer kinetics on composite diamond (sp3)–graphite (sp2) electrodes

The concept of non-diamond sp² impurity states as charge transfer mediators on boron-doped diamond (BDD) surface was suggested as an explanation for the electrochemical behavior of synthetic diamond based electrodes. In order to verify this concept, graphite particles (sp²) were deposited on diamond electrodes (sp³) by mechanical abrasion. The behavior of the so prepared diamond–graphite composite electrodes were compared with those of as-grown (BDD_ag) and those after mild anodic polarization (BDD_mild).Outer-sphere electron transfer processes such as ferri/ferrocyanide (Fe(CN)₆III/II) and inner-sphere charge transfer reactions such as 1,4-benzoquinone/hydroquinone (Q/H₂Q) were chosen in order to investigate the electrochemical properties of these composite electrodes. Both redox systems became more reversible as the graphite (sp²) loading increased. A strong analogy existed between as-grown diamond electrodes and diamond–graphite composite electrodes.Finally a model is proposed which describes the BDD electrode surface as a diamond matrix in which non-diamond (sp²) impurity states are dispersed. These non-diamond sp² states on BDD surface acts as charge mediators for both inner-sphere and outer-sphere reactions.     

1,4-二氧六环介质中辣根过氧化物酶电极的性能研究

用交联法制备辣根过氧化物酶(HRP)电极, 在1,4-二氧六环介质中研究其电化学行为。实验表明, 固定化的HRP在有机相中仍保持活性并可与电极进行直接电子传递, 因而能在没有其它电子传递体存在的条件下催化H~2O~2的电化学还原反应。当亚铁氰化物与酶共修饰至电极上之后, 它起着电子传递体的作用, 使HRP电极的性能大为改善。根据不同条件下得到的动力学参数, 讨论了影响酶电极性能的因素。     

有序中孔炭/四氧化三铁复合材料的制备及其用于血红蛋白的电化学研究

采用微湿含浸法制备了有序中孔炭/四氧化三铁磁性材料.采用透射电镜和X射线衍射对复合材料进行了表征.将血红蛋白(Hb)固定于材料表面,对其直接电化学行为进行了研究,结果表明Hb在该材料内仍保持了其生物活性,在pH=7.0的PBS缓冲液中,血红蛋白表现出一对峰形良好的准可逆氧化还原峰,为Hb的Fe(Ⅲ)/Fe(Ⅱ)电对的特征峰,求出式电位E0’为-0.306 V,电子转移数为n=1.226,电荷传递系数为α=0.51,表观异相电子转移速率常数为KS=0.0144s-1.在3.00×10-6到1.50×10-4mol/L浓度范围内,血红蛋白的浓度与其响应电流呈良好的线性关系,线性相关系数为R=0.9924,最低检测限为0.270×10-6mol/L.     

Electron transfer and interfacial behavior of redox proteins

This paper reviews the recent progress in the electron transfer and interfacial behavior of redox proteins. Significant achievements in the relevant fields are summarized including the direct electron transfer between proteins and electrodes, the thermodynamic and kinetic properties, catalytic activities and activity regulation of the redox proteins. It has been demonstrated that the electrochemical technique is an effective tool for protein studies, especially for probing into the electron transfer and int...     

Review: electrochemical studies on some metal complexes having anti-cancer activities

Cancer is a leading cause of death worldwide. Since the discovery of cisplatin, a platinum-based anti-cancer metallodrug, research on metal-based compounds and complexes as potential anti-cancer agents has gained importance in modern medical and chemical sciences. Electrochemical techniques provide useful complements to other analytical methods of analysis such as UV–vis and fluorescence spectroscopy. Since the redox active metal complexes are not amenable to spectroscopic techniques either due to weak absorption bands or overlap of electronic transitions with those of DNA, they can potentially be studied via electrochemical techniques. Due to the resemblance between the electrochemical and biological redox reactions, the application of electrochemical measurements of metal-based anti-cancer drugs is a highly sensitive method. Cyclic voltammetry is a versatile technique to investigate redox activities during drug–DNA interactions. Variations in peak potentials and peak currents of a cyclic voltammogram during a redox reaction resulting from intercalation or electrostatic interactions can be used to determine equilibrium constants (K) and the number of base pair sites. This review is focused on some electrochemical studies of potential metal-based anti-cancer drug candidate?DNA interactions and the correlation between binding studies and anti-cancer activities.