酸性溶液中钯催化醇电化学氧化的研究

应用电化学循环伏安法(CV)和现场红外光谱(FTIR),研究了酸性溶液中钯催化甲醇、乙二醇电氧化的过程.结果表明:在酸性和中性介质中,甲醇和乙二醇在多晶Pd电极上氧化须在1.5V以上才能发生.随着溶液pH值的降低,过电位减小且峰电流密度上升.溶液的pH值以及电极表面形成的吸附含氧物种对Pd电催化氧化醇有显著的影响.现场红外光谱电化学测试显示,在高电位和强酸性介质中,乙二醇在Pd电极上的氧化产物主要是CO2和少量的乙二酸.在酸性和中性介质中,无论在低电位或高电位,甲醇和乙二醇在Pd上氧化的主要产物是CO2,没有发现CO的存在,说明该氧化过程CO2是经过非毒化的路径产生的.     

乙醇在钯电极上的电氧化机理

利用循环伏安与现场傅里叶变换红外(FTIR)光谱对乙醇在Pd电极上的电氧化机理进行了研究. 循环伏安测量表明, 乙醇在Pd上氧化的性能受pH值与乙醇浓度的影响. 当溶液pH>11.0时, Pd对乙醇才具有催化性能, 而且乙醇在Pd上氧化的性能随着pH值和乙醇浓度的增加而提高. 现场红外光谱电化学测量结果证明, 乙醇在不同pH 溶液中的氧化反应机理和产物不同. 当溶液pH>13.0 时, 产物只有乙酸盐, 说明乙醇仅发生部分氧化, 乙醇中的C—C键没有断裂. 当溶液pH≤13.0时, 尽管乙醇在Pd电极上的氧化活性受到抑制, 却发生完全氧化而产生二氧化碳, 说明乙醇的C—C键在低碱环境中容易断裂, 最后乙醇被完全氧化. 实验中没有检测到CO, 表明该反应途径是一个非毒化过程.     

Electrochemical behavior of natural and biosynthetic polynucleotides at the pyrolytic graphite electrode A new probe for studies of polynucleotide structure and reactions

The electrochemical oxidation of natural and biosynthetic polynucleotides at a pyrolytic graphite electrode (PGE) has been studied under differential pulse voltammetric conditions. Denatured DNA, ribosomal and transfer RNA give two voltammetric peaks. The first (more negative peak, peak G) corresponds to electrochemical oxidation of guanine residues where-as the second, more positive peak (peak A) corresponds to electrochemical oxidation of adenine residues. Native DNA gives rise only to a small peak A, peak G being totally absent. Denatured DNA and its voltammetric oxidation product are both strongly adsorbed at the PGE. Differential pulse voltammetric oxidation of natural and biosynthetic polynucleotides may provide a valuable technique for probing A-T and G-C regions during structural and conformational changes of these molecules and for following their interactions with other solution species.     

Electrochemical oxidation of underivatized-nucleic acids at highly boron-doped diamond electrodes

Boron-doped diamond (BDD) electrodes have been examined for the electrochemical oxidation of underivatized-nucleic acids in terms of single stranded and double stranded DNA. Cyclic voltammetry and square wave voltammetry have been used to study the oxidation reactions and to detect DNA without derivatization or hydrolysis steps. At the diamond electrode, at least two well-defined voltammetric peaks were observed for both single stranded and double stranded DNA. Diamond electrode is the first material to show a well-defined voltammetric peaks for adenine group oxidation directly in the helix structure of nucleic acid due to its wide potential window. For single stranded DNA, a third peak, related to the pyrimidine group oxidation was also observed. As-deposited diamond film with predominantly hydrogen-terminated surface exhibited superior performance over oxygen-terminated diamond in terms of sensitivity. However, by optimizing the ionic strength, sensitivity of O-terminated films could be improved. Linear calibration results have shown linearity of current with concentration in the range 0.1-8 microg mL(-1) for both guanine and adenine residues at as-deposited BDD. Detection limits (S/N = 3) of 3.7 and 10 ng mL(-1) for adenine and guanine residue in single stranded DNA, respectively, and 5.2 and 10 ng mL(-1) for adenine and guanine residue in double stranded DNA, respectively, were observed. This work shows the promising use of diamond as an electrochemical detector for direct detection of nucleic acids. The results also show the possibility of using the oxidation peak current of adenine group that is more sensitive for the direct detection of nucleicacids.     

Electrochemical measurement of phenothiazine-interacted DNA

The amount of DNA was measured by using thioridazine, which would be attached to the DNA, as an electrochemical indicator. An indicator (thioridazine) solution, a test solution (DNA solution), and a poly-l-lysine solution were successively placed on a glassy carbon electrode, and the electrode was allowed to dry; DNA was immobilized on an electrode surface by the electrostatic binding between DNA and poly-l-lysine. The electrode was immersed into a buffer solution for 15 min, and then differential pulse voltammetry (DPV) was carried out: the oxidation current peak of thioridazine was observed, and its magnitude depended on the amount of DNA in the solution which was used for preparing the electrode. It could be estimated between 0.2 microg DNA (corresponds to 630 pmol nucleotides) to 20 microg DNA (63 nmol nucleotides) from the oxidation peak current of DPV.     

聚合物电解质(PEG/LiClO4)中L-抗坏血酸氧化的现场显微红外光谱电化学研究

L-抗坏血酸(H2A)由于在生物介质氧化还原过程中的重要作用,其分子及其衍生物已有广泛研究[1～5].聚合物电解质由于能溶解电活性物质和具有离子导电性而成为一种新的溶剂,可用于研究一些物质的电化学行为[6].H2A在聚合物电解质中的电化学及光谱电化学行为还未见报道.     

In situ electrochemical evaluation of anticancer drug temozolomide and its metabolites–DNA interaction

Temozolomide (TMZ) is an antineoplastic alkylating agent with activity against serious and aggressive types of brain tumours. It has been postulated that TMZ exerts its antitumor activity via its spontaneous degradation at physiological pH. The in vitro evaluation of the interaction of TMZ and its final metabolites, 5-aminoimidazole-4-carboxamide (AIC) and methyldiazonium ion, with double-stranded DNA (dsDNA) was studied using differential pulse voltammetry at a glassy carbon electrode. The DNA damage was electrochemically detected following the changes in the oxidation peaks of guanosine and adenosine residues. The results obtained revealed the decrease of the dsDNA oxidation peaks with incubation time, showing that TMZ and AIC/methyldiazonium ion interact with dsDNA causing its condensation. Furthermore, the experiments of the in situ TMZ and AIC/methyldiazonium ion–dsDNA interaction using the multilayer dsDNA-electrochemical biosensor confirmed the condensation of dsDNA caused by these species and showed evidence for a specific interaction between the guanosine residues and TMZ metabolites, since free guanine oxidation peak was detected. The oxidative damage caused to DNA bases by TMZ metabolites was also detected electrochemically by monitoring the appearance of the 8-oxoguanine/2,8-dyhydroxyadenine oxidation peaks. Nondenaturing agarose gel electrophoresis of AIC/methyldiazonium ion–dsDNA samples confirmed the occurrence of dsDNA condensation and oxidative damage observed in the electrochemical results. The importance of the dsDNA-electrochemical biosensor in the in situ evaluation of TMZ–dsDNA interactions is clearly demonstrated.     

Anticancer Drug Modified GCFE,for the Study of Its In‐Vivo Interaction Mechanism

An anticancer drug (Adriamycin) modified Glassy Carbon Fiber Electrode (GCFE) has been prepared to study its interaction with ds‐DNA. The redox reaction of Adriamycin molecules at the chemically modified GCFE helps in understanding the in‐vivo mechanism of action of this anti cancer drug. The modified electrode has been fabricated by the adsorption of Adriamycin on GCFE surface. The results of Differential Pulse Voltammetric (DPV) analysis in acetate buffer of pH 4.5 ± 0.1, showed that the interaction between DNA guanine and adenine bases and electrode surface, is easily detected. A suitable mechanism for the oxidation and reduction of Adriamycin in‐situ intercalated in ds‐DNA immobilized on to the GCFE surface has been explained. The drug‐DNA complex formation at GCFE surface has also been studied. The prepared modified electrode is of utmost relevance because the mechanism of interaction of DNA‐Adriamycin at charged interfaces is parallel to the in‐vivo DNA‐Adriamycin complex reaction, where the nucleic acid is in close contact with charged phospholipid membranes and proteins. The interaction studies of Adriamycin at modified GCFE using DPV method help in understanding the DNA‐Adriamycin reaction mechanism.     

Polystyrene sulphonate wrapped multiwalled carbon nanotubes modified graphite electrode for simultaneous determination of ascorbic acid, dopamine and uric acid

Graphite electrode is modified by casting multi-walled carbon nanotubes (MWCNTs) wrapped with polystyrene sulphonate (PSS) onto the surface of the bare graphite electrode. The modified electrode was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The behavior of the modified electrode towards the oxidation of ascorbic acid (AA), dopamine (DA) and uric acid (UA) has been determined by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry (CA). The modified electrode showed better electrocatalytic activity towards AA, DA and UA compared to bare graphite electrode. The electrochemical oxidation signals of AA, DA and UA are well separated into three distinct peaks with peak potential difference of 222, 128 and 350 mV between AA-DA, DA-UA and AA-UA respectively in CV studies and corresponding peak potential separation in DPV are 228, 120 and 348 mV. This modified electrode was successfully used for simultaneous determination of AA, DA and UA in ternary mixture.     

459—The effect of netropsin on the electrochemical oxidation of DNA at a graphite electrode

The interaction of netropsin with calf thymus, Bacillus cereus and Micrococcus luteus DNAs and with the RNA of phage f2 was studied by means of differential pulse voltammetry at a paraffin-wax-impregnated spectroscopic graphite electrode. It was found that the oxidation voltammetric peaks of double-helical calf thymus and Bacillus cereus DNAs were lowered when netropsin was added to the DNA solution. The peak corresponding to electro-oxidation of adenine residues was lowered more than that corresponding to electro-oxidation of guanine residues. Under the same experimental conditions the oxidation peaks of double-helical Micrococcus luteus DNA, double-helical RNA and thermally denatured samples of all DNAs used were almost uninfluenced by the addition of netropsin. The results observed were explained by (i) decreased flexibility of the segments to which netropsin was bound, and (ii) the specific binding of netropsin to the segments of double-helical DNA rich in adenine thymine pairs.     

Rapid and Selective Determination of Vanillin in the Presence of Caffeine,its Electrochemical Behavior on an Au Electrode Electropolymerized with 3‐Amino‐1,2,4‐triazole‐5‐thiol

Electrochemical oxidation of vanillin (VAN) in the presence of caffeine (CAF) was studied on a gold (Au) electrode modified with 3‐amino‐1,2,4‐triazole‐5‐thiol (ATT) film by using differential pulse voltammetry (DPV) and cyclic voltammetry (CV) method. The formation of the ATT film on the Au electrode surface was characterized by the CV, fourier transform infrared spectroscopy (FTIR) and impedance spectroscopy (EIS) methods. A single irreversible oxidation peak of the VAN was obtained by using the CV method. The determination of VAN in the presence of CAF was carried out at pH 4 in Britton Robinson buffer (BR) by the DPV method. Under the optimal conditions, the oxidation peak current was proportional to the concentration of VAN in the range of 1.1 μM to 76.4 μM in the presence of CAF with the correlation coefficient of 0.997 and the detection limit of 0.19 μM (S/N=3). The selective determination of VAN in a commercial coffee sample was carried out with satisfactory results on the ATT‐Au modified electrode.     

芦丁在铂纳米/碳纳米管修饰电极上电化学行为研究

通过电沉积的方式在多壁碳纳米管(MWCNTs)修饰玻碳电极表面上沉积铂(pt)纳米粒子,并运用循环伏安法(CV)、示差脉冲伏安法(DPV)探讨了芦丁在铂纳米/碳纳米管/玻碳电极上的电化学行为.实验结果表明,芦丁在该修饰电极上呈现一对良好氧化还原峰,其氧化峰电流与浓度在3.2×10(-8)～1.2×10(-5)mol/L...     

Functionalized-graphene modified graphite electrode for the selective determination of dopamine in presence of uric acid and ascorbic acid

Graphene is chemically synthesized by solvothermal reduction of colloidal dispersions of graphite oxide. Graphite electrode is modified with functionalized-graphene for electrochemical applications. Electrochemical characterization of functionalized-graphene modified graphite electrode (FGGE) is carried out by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The behavior of FGGE towards ascorbic acid (AA), dopamine (DA) and uric acid (UA) has been investigated by CV, differential pulse voltammetry (DPV) and chronoamperommetry (CA). The FGGE showed excellent catalytic activity towards electrochemical oxidation of AA, DA and UA compared to that of the bare graphite electrode. The electrochemical oxidation signals of AA, DA and UA are well separated into three distinct peaks with peak potential separation of 193mv, 172mv and 264mV between AA-DA, DA-UA and AA-UA respectively in CV studies and the corresponding peak potential separations in DPV mode are 204mv, 141mv and 345mv. The FGGE is successfully used for the simultaneous detection of AA, DA and UA in their ternary mixture and DA in serum and pharmaceutical samples. The excellent electrocatalytic behavior of FGGE may lead to new applications in electrochemical analysis.     

肉桂酸修饰电极同时测定多巴胺和抗坏血酸的研究

用电化学聚合方法制备肉桂酸(CA)修饰的玻碳电极(PCA/GC),研究多巴胺(DA)和抗坏血酸(AA)在修饰电极上的电化学行为.结果表明,在DA和AA共存体系中,DA、AA在PCA/GC电极上氧化峰电流增大且氧化峰电位相差200 mV,据此可同时检测DA和AA.在pH 7.0磷酸盐缓冲液中,DA和AA的氧化峰电流与其浓...     

Differential Pulse Voltammetric Determination and Application of Square‐Wave Voltammetry of yRNA on a CPB‐Cellulose Modified Electrode

Electrochemical behavior of remarkably low levels of Ribonucleic acid yeast (yRNA) is studied through differential pulse voltammetry (DPV), and kinetic parameters of the electrochemical reaction have also been calculated through square‐wave voltammetry (SWV), based on immobilization of yRNA on the surface of a CPB‐cellulose modified electrode. YRNA/ CPB‐cellulose/ITO conductive glass electrode is demonstrated by Infrared reflect (IR) and electrochemical impedance spectroscopy (EIS). The oxidation peak potential of yRNA shifts negatively with increasing pH. The peak currents decrease gradually in successive scans and no corresponding reduction peaks occur, indicating that oxidation process of yRNA is completely irreversible. Variables influencing DPV response of yRNA, such as pH, pulse amplitude and electrolyte concentration, are explored and optimized. Peak currents are proportional to the concentration of yRNA in the range of 0.1 μg mL^?1–1.0 μg mL^?1, and the linear regression coefficient equals 0.9923. The detection limit for yRNA is 1.0×10^?10 g mL^?1. Interferences of L ‐cysteine, L ‐alanine, Hemoglobin, Uridine 5′‐monophosphate, Guanosine 5′‐monophosphate, Adenosine 5′‐triphosphate and some metal ions (Co³⁺, Cr³⁺, Ni²⁺, Hg²⁺, Zn²⁺, etc) are negligible. The methods adopted here are more sensitive and selective than currently applied techniques and overcome the drawback of absorption spectroscopy arising from a strong interference due to other UV‐absorbing substances.     

Docosyltrimethylammonium chloride modified glassy carbon electrode for simultaneous determination of dopamine and ascorbic acid

A glassy carbon electrode (GCE) modified with docosyltrimethylammonium chloride (DCTMACl) is used for simultaneous determination of dopamine (DA) and ascorbic acid (AA) using differential pulse voltammetry (DPV) technique in 0.10 mol·L^?1 phosphate buffer solution of pH 5.0. The cationic surfactant DCTMACl modified film has a positive charge. DA exists as the positively charged species, whereas AA is the negatively charged one in the solution. Thus, at DCTMACl film-modified GCE, the oxidation peak potential of AA shifts toward less negative potential and the peak current of AA increases a little, while the oxidation peak potential of DA shifts toward more positive potential and peak current decreases greatly in comparison with that on bare electrode. The two anodic peaks are separated around 200 mV. Under optimal conditions, the catalytic peak currents obtained from DPV increase linearly with concentrations of DA and AA in the ranges of 1.0?×?10^?5 to 1.0?×?10^?3?mol·L^?1. This electrode has good reproducibility, high stability in its voltammetric response, and low detection limit (micromolar) for both AA and DA. The modified electrode has been applied to the determination of DA and AA in injection.     

Sensitive detection of cyclophosphamide using DNA-modified carbon paste, pencil graphite and hanging mercury drop electrodes

The interaction of cyclophosphamide (CP) with calf thymus double-stranded DNA (dsDNA) and thermally denatured single-stranded DNA (ssDNA) immobilized at the carbon paste (CPE) and pencil graphite electrodes (PGE), was studied electrochemically based on oxidation signals of guanine and adenine using differential pulse voltammetry (DPV).As a result of the interaction of CP with DNA, the voltammetric signals of guanine and adenine increased in the case of dsDNA while a slight increase was observed in ssDNA. The effect of experimental parameters such as the interaction time between CP and DNA forms and the concentration of CP, were studied using DPV with CPE and PGE. Additionally, reproducibility and detection limits were determined using both electrodes. A comparison of the analytical performance between CPE and PGE was done. Our results showed that these two different DNA biosensors could be used for the sensitive, rapid and cost effective detection of CP itself as well as of CP-DNA interaction.Furthermore, the interaction of CP with dsDNA and ssDNA was studied in solution and at the electrode surface by means of alternating current voltammetry (ACV) in 0.3 M NaCl and 50 mM sodium phosphate buffer (pH 8.5) supporting electrolyte, using a hanging mercury drop electrode (HMDE) as working electrode.The conclusions of this study were mainly based on tensammetric peaks I (at −1.183 V) and II (−1.419 V) of DNA. This study involved the interaction of CP with surface-confined and solution phase DNA where experimental parameters, such as the concentration of CP and the interaction time, were studied. By increasing the concentration of CP, an increase of peak II was observed in both ds and ssDNA, while an increase of peak I was observed only in the case of dsDNA. An overall conclusion of the study using HMDE was that the interaction of CP with surface-confined DNA significantly differed from that with solution phase DNA. The increase of peaks I and II was lower in the case of interaction of CP with surface-confined DNA, probably due to steric positioning of DNA at the electrode surface.     

现场压电红外反射光谱电化学研究邻联甲苯胺的电化学行为

利用现场压电红外发射光谱电化学技术研究邻联甲苯胺(OTD)在金电极上的电化学行为.压电电化学结果表明:电位范围对OTD氧化的影响很大.当电位扫至0.6 V时,氧化过程中中间体的生成和溶解的同时,部分未溶中间体在电极表面沉积.当电位大于0.65 V时,还有OTD的电化学氧化聚合.压电红外反射光谱电化学结果表明中间体是OTD第一氧化产物之间相互作用形成的.进一步考察了肝素大阴离子对OTD的氧化的影响.     

RNA Modified Electrodes for Simultaneous Determination of Dopamine and Uric Acid in the Presence of High Amounts of Ascorbic Acid

A promising electrochemical biosensor was fabricated by electrochemical grafting of ribonucleic acid (RNA) at 1.8 V (vs. SCE) on glassy carbon electrode (GCE) (denoted as RNA/GCE), for simultaneous detection of dopamine (DA) and uric acid (UA) with coexistence of excess amount of ascorbic acid (AA). The electrode was characterized by X‐ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. The RNA modified layer on GCE exhibited superior catalytic ability and anionic exclusive ability in comparison with the DNA modified electrode. Three separated anodic DPV peaks were obtained at 0.312, 0.168 and ?0.016 V for UA, DA and AA, respectively, at the RNA/GCE in pH 7.0 PBS. In the presence of 2.0 mM AA, a linear range of 0.37 to 36 μM with a detection limit of 0.2 μM for DA, and in the range of 0.74 to 73 μM with a detection limit of 0.36 μM for UA were obtained. The co‐existence of 5000 fold AA did not interfere with the detection of DA or UA. The modified electrode shows excellent selectivity, good sensitivity and good stability.     

Selective Voltammetric Detection of Uric Acid in the Presence of Ascorbic Acid at Well‐Aligned Carbon Nanotube Electrode

The voltammetric behaviors of uric acid (UA) and L ‐ascorbic acid (L ‐AA) were studied at well‐aligned carbon nanotube electrode. Compared to glassy carbon, carbon nanotube electrode catalyzes oxidation of UA and L ‐AA, reducing the overpotentials by about 0.028 V and 0.416 V, respectively. Based on its differential catalytic function toward the oxidation of UA and L ‐AA, the carbon nanotube electrode resolved the overlapping voltammetric response of UA and L ‐AA into two well‐defined voltammetric peaks in applying both cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which can be used for a selective determination of UA in the presence of L ‐AA. The peak current obtained from DPV was linearly dependent on the UA concentration in the range of 0.2 μM to 80 μM with a correlation coefficient of 0.997. The detection limit (3δ) for UA was found to be 0.1 μM. Finally, the carbon nanotube electrode was successfully demonstrated as a electrochemical sensor to the determination of UA in human urine samples by simple dilution without further pretreatment.