Voltammetric,UV–Vis Spectrometric and Fluorescence Study of the Interaction of Ractopamine and DNA with the Aid of Multivariate Curve Resolution‐Alternating Least Squares

Interaction of a steroid drug, Ractopamine (RAC), and DNA was investigated by electroanalysis‐differential pulse and cyclic voltammetry (DPV and CV), and UV‐vis and fluorescence spectroscopy. DPV showed that RAC intercalated with DNA, and CV indicated that the reaction mechanism of RAC and dsDNA involved irreversible oxidation with the loss of two H⁺ and a transfer of two electrons. Reaction binding parameters were obtained. Pure spectra of RAC, DNA and the RAC‐DNA complex, and their concentrations were extracted by multivariate curve resolution‐alternating least squares method (MCR‐ALS). Concentration profiles indicated quantitatively the course of the reaction.     

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.     

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.     

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.     

Catechin mediated green synthesis of Au nanoparticles: Experimental and theoretical approaches to the determination HOMO-LUMO energy gap and reactivity indexes for the (+)-epicatechin (2S, 3S)

This work suggests a green method for synthesizing Au nanoparticles (AuNPs) using the aqueous extract of Salix aegyptiaca extract. The mechanism of green synthesized AuNPs was examined by molecular electrostatic potential (MEP) calculations. AuNPs were characterized with different techniques such as Ultraviolet–visible spectroscopy (UV–vis), Fourier-transform infrared spectroscopy (FT-IR) spectroscopy, X-ray diffraction (XRD), and Transmission electron microscopy (TEM). Electrochemical investigation of modified glassy carbon electrode using AuNPs (AuNPs/GCE) shows that the electronic transmission rate between the modified electrode and [Fe (CN)₆]^3?/4? increased. Process of oxidation, energy gap, and chemical reactivity indexes of the (+)-epicatechin (2S,3S) were investigated using electrochemical techniques (cyclic voltammetry (CV) and differential pulse voltammetry (DPV) as well as UV–Visible spectroscopy and compared with quantum mechanical calculations. DPV and CV were used to obtain HOMO energies of the (+)-epicatechin (2S,3S), an optical energy gap was obtained from the UV–Vis spectroscopy. Frontier molecular orbitals analysis (FMO) and reactivity indexes such as chemical hardness (?), electrophilicity (?), electronic chemical potential (μ), electron acceptor power (?⁺), electron donor power (?^?) were determined with functional theory (DFT) calculations. In summary, the HOMO energy obtained from the experimental analyses (E_HOMO (from DPV) = -5.24 eV, and E_HOMO (from CV) = -5.28 eV) has a relative agreement with the HOMO energy calculated by B3LYP/6–31 g (d, p) including the solvent effect (water) (E_HOMO (from B3LYP) = -5.75 eV). Also, UV–Vis spectroscopy gives the bandgap energy equal to 4.31 eV, while the 4.13 eV is calculated by TD-DFT-b3lyp/6–31 + g(d).     

Some Properties of Sodium Dodecyl Sulfate Functionalized Multiwalled Carbon Nanotubes Electrode and Its Application on Detection of Dopamine in the Presence of Ascorbic Acid

A sodium dodecyl sulfate (SDS) functionalized multiwalled carbon nanotubes (MWNTs) electrode (SDS/MWNTs) was successfully constructed in this study. The electrochemical property of the SDS/MWNTs electrode has been characterized by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Nyquist plots suggest that the immersion time of SDS affects the resistances of the MWNTs electrodes. The thickness of adsorbed SDS on MWNTs surface is estimated to be 1.23 nm, which is close to the value of SDS monolayer. CV results demonstrate a 5‐fold enhanced response for dopamine (DA) at the SDS/MWNTs electrode compared to the bare MWNTs one. DPV results illustrate that DA can be selectively determined in the presence of high concentration ascorbic acid (AA) with a linear range from 20 μM to 0.20 mM and a sensitivity of 0.024 μA μM^?1 at the SDS/MWNTs electrode.     

OH functionalized Multi-Walled Carbon Nanotube modified electrode as electrochemical sensor for the detection of Aceclofenac

ABSTRACT

The rapid electrochemical determination of Aceclofenac (ACF) has been employed by cyclic voltammetry (CV), differential pulse voltammetry (DPV) using developed OH-functionalised multiwalled carbon nanotube carbon paste electrode (OH-MWCNT/CPE). Modified electrode was characterised by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX), X-ray diffraction spectroscopy (XRD), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The ACF exhibits two oxidation peaks at +0.4 V, +0.66 V and one reduction peak at +0.3 V. The active surface area of the bare carbon paste electrode (BCPE) and modified electrode have been characterised by using K₃[Fe(CN)₆] solution containing 0.1 M KCl. In DPV mode, variation of ACF gave the limit of detection (LOD = 3s/m) 0.246 μM over the concentration range 1.0 to 190.0 μM (R² = 0.9994). The developed electrode has good stability, reproducibility and could be successfully validated for the detection of ACF in pharmaceutical samples and biological fluids.     

Covalent modification of glassy carbon electrodes with beta-alanine for voltammetric separation of dopamine and ascorbic acid.

beta-Alanine was covalently grafted on a glassy carbon electrode (GCE) by amine cation radical formation in the electrooxidation process of the amino-containing compound. X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV) proved the immobilization of beta-alanine monolayer on GCE. The electrode shows strong electrocatalytic functions to dopamine (DA) and ascorbic acid (AA), reducing the overpotentials by 0.20 V and 0.23 V, respectively. Due to its different catalytic effects toward DA and AA, the modified electrode resolved the overlapping voltammetric responses of DA and AA into two well-defined voltammetric peaks by CV or differential pulse voltammetry (DPV), which can be used for the simultaneous determination of these species in a mixture. The catalytic peak current obtained from DPV was linearly related to DA and AA concentrations in the ranges of 4.0 x 10(-6)-5.0 x 10(-4) mol/L and 2.0 x 10(-5)-6.0 x 10(-3) mol/L with correlation coefficients of 0.997 and 0.995, respectively. The detection limits (3 sigma) for DA and AA were 2.4 x 10(-6) mol/L and 1.2 x 10(-5) mol/L, respectively. The electrode shows good sensitivity, selectivity and stability, and has been applied to the determination of DA and AA simultaneously in samples with satisfactory results.     

Electrodeposition of Silver Amalgam on Thin Gold Film Electrodes for Voltammetric Detection of 4‐Nitrophenol and DNA Labeled with Osmium Tetroxide‐Bipyridine Complex

Alternative electrode materials suitable to prepare novel working electrode applicable in detecting biopolymers such as nucleic acids, proteins or glycoproteins, represent a significant contribution to bio‐electroanalysis. Herein, electrodes made of vapor‐deposited thin gold films (vAuE) were used as an alternative substrate for the electrodeposition of silver amalgam particles (AgAPs), next to indium tin oxide and pyrolytic graphite, which are already used. The conditions and parameters of double pulse chronoamperometry were optimized for the most‐sensitive voltammetric detection of 4‐nitrophenol (4‐NP). The resulting electrodes were characterized by scanning electron microscope with energy dispersive X‐ray spectroscopy. While 4‐NP could not be detected by bare nonactivated vAuEs at all, their electrochemical activation offered a limit of detection (LoD) of 25 and 5 μmol.l^?1 by means of CV and DPV, respectively. AgAP electrodeposited on vAuE, offered 2.5‐times lower LoDs 10 μmol.l^?1 by CV and comparable LoD 5 μmol.l^?1 by DPV. Advantageously, AgAPs could be repeatedly deposited on and anodically dissolved from the vAuE with a relative standard deviation 13 % of the ten‐times repeated DPV signal of 4‐NP (100 μmol.l^?1). In comparison to vAuE, the vAuE‐AgAP offered about 400 mV broader potential window, which allowed detection of single strand DNA fragment labeled by osmium tetroxide?bipyridine complex down to 2 ng.μl^?1 by means of DPV.     

碳纳米管修饰电极同时测定邻苯二酚和对苯二酚

用十二烷基磺酸钠(SDS)分散碳纳米管(CNTs),通过层层组装(LBL)聚二甲基二烯丙基氯化铵(PDDA)和CNTs构筑PDDA/CNTs多层膜电极.利用紫外-可见光谱法对PDDA/CNTs多层膜的组装过程进行监测,用循环伏安法(CV)和差分脉冲伏安法(DPV)研究了邻苯二酚和对苯二酚同时存在时PDDA/CNTs多层膜电极上的电化学行为.结果表明,碳纳米管修饰电极对邻苯二酚和对苯二酚有较好的电催化活性和电分离作用,邻苯二酚和对苯二酚无需经过分离即可同时被检出.在修饰电极上的线性范围如下:邻苯二酚为2.0×10-6~1.4×10-4mol/L,线性相关系数R=0.9991;对苯二酚为2.0×10-6~1.4×10-4mol/L,线性相关系数R=0.9987.     

钴(Ⅱ)取代铜锌超氧化物岐化酶金属重组衍生物的电化学和光谱电化学研究

80年代Hill等［"在蛋白质的电化学研究中加人氧化还原促进剂以提高电极反应速率．但最近的研究表明,电极材料的选择、蛋白质的纯度和溶液的离子强度等都影响反应速率和吸附行为［'．我们曾选用悬汞电极在不加促进剂的情况下研究铜锌超氧化物歧化酶Cu。Zn。SOD的电化学性质,并获得较好的结果［'j．本文研究了钻（I）取代铜锌超氧化物歧化酶CO。CO。SOD的氧化还原行为,首先用热解石墨电极对CO。CO。SOD进行循环伏安研究,获得了电极反应为扩散控制的可逆的电化学过程;然后用光谱电化学技术进行论证,由2种方法得到了在CO。CO。…     

Electrochemical behaviour of carbon paste electrodes enriched with tin oxide nanoparticles using voltammetry and electrochemical impedance spectroscopy

The effect of the SnO(2) nanoparticles (SNPs) on the behaviour of voltammetric carbon paste electrodes were studied for possible use of this material in biosensor development. The electrochemical behaviour of SNP modified carbon paste electrodes (CPE) was first investigated by using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) techniques. The performance of the SNP modified electrodes were compared to those of unmodified ones and the parameters affecting the response of the modified electrode were optimized. The SNP modified electrodes were then tested for the electrochemical sensing of DNA purine base adenine to explore their further development in biosensor applications.     

硫酸特布他林在聚铬黑T修饰电极上的电化学行为及其测定

采用电化学聚合法制备了聚铬黑T膜修饰电极,应用扫描电镜、交流阻抗法和循环伏安法对修饰电极进行表征,以循环伏安法研究硫酸特布他林在修饰电极上的电化学行为,并以差示脉冲伏安法对其含量进行测定.该方法对硫酸特布他林有明显的电催化作用,在pH 7.0磷酸盐缓冲液中,氧化峰电流与硫酸特布他林浓度在1.2x10^-7~2.0x10^-6mol•L^-1范围内呈良好的线性关系,检测限为1.5x10^-8 mol•L^-1,回收率在97.9%～104.6%之间,RSD在2.8 % (C=8x10^-7mol•L^-1,n=11).该方法简便灵敏,结果准确可靠,方法重复性好,可用于硫酸特布他林及其片剂的质量控制.     

以聚硫堇为电化学探针的非标记型核酸适配体传感器

采用电聚合法制备了聚硫堇氧化还原电化学探针, 以金纳米粒子为固定核酸适配体的载体构建了非标记型核酸适配体传感器. 用电化学阻抗谱对传感器的组装过程进行了监测, 用循环伏安法和差分脉冲伏安法考察了传感器的电化学行为. 结果表明, 该传感器对凝血酶的检测在1.0 pg/mL～500 ng/mL范围内呈良好的线性关系, 相关系数为0.998, 检出限为0.38 pg/mL. 该传感器制备简单、 灵敏度高且抗干扰能力强.     

Characterization of the bis-silylated endofullerene Sc3N@C80

The photochemical reaction of Sc(3)N@C(80) with 1,1,2,2-tetramesityl-1,2-disilirane affords the adduct as a bis-silylated product. The adduct was characterized by NMR spectroscopy and single-crystal X-ray structure analysis. The dynamic behavior of the disilirane moiety and the encapsulated Sc(3)N cluster were also investigated. The unique redox property of the adduct is reported by means of CV and DPV. Experimental results were confirmed by density functional calculations.     

Electrocatalytic Activation of Silver Nanowires‐modified Pt Electrode by Cyclic Voltammetry in Comparison with Differential Pulse Voltammetry in Halide Determination

Cyclic voltammetric (CV) and differential pulse voltammetric (DPV) measurements were carried out to assess the changes in electrode reactivity in halide determination with a silver nanowire‐modified platinum electrode. With DPV, successive voltammograms of the halide solution revealed progressive deterioration of the oxidation currents corresponding to Br^? and Cl^?, while those of I^? increased largely. Comparatively, CV is stable and effective to remove precipitates due to the reduction process, in which, the concentrated effect alleviated and the amount of AgI decreased. CV was consequently suggested to be favorable for halide determination, while playing a role in electrocatalytic activation of the electrode.     

Electrochemical Behavior of Uric Acid and Epinephrine at a Meso-2,3-Dimercaptosuccinic Acid Self-Assembled Gold Electrode

A self-assembled electrode with a meso-2,3-dimercaptosuccinic acid (DMSA) monolayer has been characterized by electrochemical quartz crystal microbalance and complex impedance analysis, surface enhanced Raman spectroscopy and cyclic voltammetry. The self-assembled electrode was used for the simultaneous electrochemical detection of epinephrine (EP) and uric acid (UA) in phosphate buffer of pH 7.7. The simultaneous oxidation of EP and UA was performed by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), and the signals for each method were well separated with a potential difference of over 330 mV and without interference by each other. The detection limit of EP is 5.4 × 10⁻⁸ mol L⁻¹ by CV and 5.3 × 10⁻⁸ mol L⁻¹ by DPV and that of UA is 8.4 × 10⁻⁸ mol L⁻¹ by CV and 4.2 × 10⁻⁸ mol L⁻¹ by DPV. The DMSA self-assembled electrode can be applied to the simultaneous determination of EP and UA.     

Photo-labeling of C60 with 3-trifluoromethyl-3-phenyldiazirine

The photochemical reaction of C₆₀ with 3-trifluoromethyl-3-phenyldiazirine affords a photo-labeled C₆₀ derivative. The derivative was characterized by mass, UV-vis absorption, NMR spectroscopy, and X-ray crystallographic analysis. The redox potentials of this derivative were also investigated by means of CV and DPV. This photo-labeling method to the fullerene surface is expected to be effective for constructing various kinds of bio-functionalized fullerenes.     

Synthesis of donor-acceptor chromophores by the [2 + 2] cycloaddition of arylethynyl-2H-cyclohepta[b]furan-2-ones with 7,7,8,8-tetracyanoquinodimethane

Arylethynyl-2H-cyclohepta[b]furan-2-ones reacted with 7,7,8,8-tetracyanoquinodimethane (TCNQ) in a formal [2 + 2] cycloaddition reaction, followed by ring opening of the initially formed cyclobutene derivatives, to afford the corresponding dicyanoquinodimethane (DCNQ) chromophores in excellent yields. The intramolecular charge-transfer (ICT) interactions between the 2H-cyclohepta[b]furan-2-one ring and DCNQ acceptor moiety were investigated by UV/Vis spectroscopy and theoretical calculations. The redox behavior of the novel DCNQ derivatives was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which revealed their multistep electrochemical reduction properties depended on the number of DCNQ units in the molecule. Moreover, a significant color change was observed by visible spectroscopy under electrochemical reduction conditions.     

Uracil Grafted Carbon Electrode:Electrocatalytic Behavior of Tryptophan,Tyrosine, Catecholamine and Related Compounds

基于尿嘧啶作为一种碱基,具备一定的分子识别能力,制备了一种新颖的尿嘧啶共价修饰电极,用X射线光电子能谱和电化学方法进行了表征,并研究了酪氨酸、色氨酸、儿茶酚胺（如多巴胺,肾上腺素,去甲肾上腺素）及相关的化合物尿酸、抗坏血酸在该电极上的电化学行为,获得相应的氧化电位、电流灵敏度、线性范围和检测限等信息。其中,色氨酸检测线性范围：1.8 - 120 mM,检测限（s/n=3）：0.8 mM;酪氨酸检测线性范围：1.8 - 89mM,检测限（s/n=3）：0.8 mM。实验表明,尿嘧啶修饰电极能催化氧化上述电活性物质,但催化能力不同,据此,我们讨论了尿嘧啶与上述物质的相互作用,详细探讨了催化机理,扩展了对基于分子识别的传感器的研究。