电化学活化玻碳电极上葡萄糖氧化酶的吸附与直接电化学

利用循环伏安法和SNIFTIRS法研究了葡萄糖氧化酶(GOD)在经电化学活化的玻碳(GC)电极上的吸附与直接电化学行为。GC电极经活化后对GOD的吸附大为增强。吸附速度与吸附量同GC电极活化时高电位氧化时间、GOD浓度、溶液pH值及通氮搅拌有关。SNIFTIRS实验表明,GOD可能主要吸附于活化新生石墨结构晶棱或晶面上。表面微晶石墨结构可能为吸附GOD同GC电报的直接电子传递场所。     

镍铁异常共沉积研究

本文应用环盘电极并根据环电极上Fe~(2+)离子氧化的极限电量及盘电板上Fe~(2+)离子阴极还原对上述环电极过程的屏蔽效应分别建立两种分解Ni-Fe共沉积极化曲线的方法。应用上述方法研究Hg, Ni, Fe和Ni-Fe等电极上Ni和Fe共沉积的动力学规律。结果表明, Ni~(2+)和Fe~(2+)同时在Hg上电沉积遵循它们单独电沉积的动力学规律, 而在Fe电极上Ni~(2+)电沉积被活化, 在Ni电极上Fe~(2+)电沉积却被阻化。此外, 还讨论Ni-Fe异常共沉积的机理。     

氯丙嗪在离子液体BMIMPF6修饰玻碳电极上的伏安行为

对氯丙嗪(CPZ)在离子液体BMIMPF6修饰玻碳电极(BMIMPF6/GC)上的伏安行为进行了研究.发现CPZ在该修饰电极上于065V左右产生氧化还原峰,峰的可逆性比玻碳电极(GC)有较大改进,其电极过程为吸附控制.在0050 mol/L磷酸缓冲溶液(pH 4)中,CPZ在BMIMPF6/GC上的氧化峰的峰电流约为GC上的2倍.在优化实验条件的基础上,采用微分脉冲伏安法对不同浓度CPZ溶液进行了测定.结果表明,CPZ在BMIMPF6/GC上的氧化峰电流与浓度在56×10-9～30 ×10-5mol/L范围内有线性关系.将此方法用于尿样的测定,其加入回收率为97％左右.用3种电极测定了CPZ的表观扩散系数,其大小为D(BMIMPF6/GC)＞DOMIMBF6/GC)＞D(GC),这与电极表面积变化及膜内扩散有一定关系.     

YCl_3—NaCl·KCl熔体中Y~(3+)在钼和镍电极上的电极过程

用循环伏安法和计时电位法研究了YCl_3-KCl·NaCl熔体中Y~(3+)在钼和镍电极上的电极过程。Y~(3+)的还原是分步反应过程:Y~3+c=Y~(2+),Y~(2+)+2c=Y。Y~(3+)在镍电极上还原后能与镍形成合金,对不同条件下形成的合金组成进行了X射线分析。     

碳纳米管促进氧化还原蛋白质和酶的直接电子转移

将血红蛋白(Hb)、辣根过氧化物酶(HRP)和葡萄糖氧化酶(GOx)分别固定在经碳纳米管修饰的玻碳电极(CNT/GC)上,制成Hb CNT/GC、HRP CNT/GC和GOx CNT/GC电极.Hb、HRP和GOx在CNT/GC电极表面均能发生有效和稳定的直接电子转移反应,其相应的循环伏安曲线均显示出一对几近对称的氧化还原峰;在60mV/s下,其式量电位E0'分别为-0.343V、-0.319V和-0.456V(vs.SCE,pH6.9),且不随扫速而变;以上三者在CNT/GC电极表面直接电子转移的表观速率常数ks依次为1.25±0.25、2.07±0.56和1.74±0.42s-1;根据式量电位E0'随缓冲溶液pH值的变化关系,确知在CNT/GC电极上,Hb或HRP发生的直接电化学遵从(1e+1H+)电极过程机理,而GOx发生的直接电化学反应则遵从(2e+2H+)机理.此外,固定在CNT/GC电极表面的Hb、HRP和GOx也同时表现出对各自底物的生物电催化活性.由本文制备的碳纳米管修饰电极及其固定生物蛋白质(酶)的方法具有简单、易于操作等优点,并可用于对其它生物氧化还原蛋白质和酶的直接电子转移测试.     

离子液体修饰电极上氧氟沙星的电化学行为及测定

制备了1-丁基-3-甲基咪唑六氟磷酸盐(BM IMPF6)室温离子液体修饰电极,用循环伏安法研究氧氟沙星在该修饰电极上的电化学行为,结果表明该电极过程受吸附控制。计算了电极过程的部分动力学参数:转移电子数n=2,电极有效面积A=0.0502 cm2。用方波溶出伏安法优化了测定参数,测定了浓度与峰电流ipa的线性关系,发现ipa与氧氟沙星浓度在5.0×10-7～6.0×10-5mol/L范围内呈线性关系,检出限为2.8×10-7mol/L,样品回收率为93.2%～108.2%,可直接用于实际样品中氧氟沙星含量的测定。     

肌酐-铜(Ⅱ)体系的电化学氧化及分析应用

肌酐能够和Cu~(2+)生成络合物,该络合物可以吸附于玻碳电极表面,在pH3.50的NH_4Cl-HCl底液中,吸附于电极表面的肌酐-Cu~(2+)络合物在较负的电位下还原为肌酐-Cu~+,当电极向正向扫描时,产生一个灵敏的表面催化波,其峰电流和肌酐的浓度在1.0×10~(-5)～1.0×10~(-8)mol/L范围内有良好的线性关系,其检出限为1.0×10~(-9)mol/L(富集5min).研究了肌酐-Cu~(2+)络合物在玻碳电极上的氧化还原机理,选择了测定肌酐的最佳实验条件,建立了测定肌酐的新的灵敏的方法.     

改性钠基蒙脱土修饰电极上百草枯的电化学行为及测定

制备了十六烷基三甲基溴化铵(CTAB)改性钠基蒙脱土修饰电极,用循环伏安法研究了百草枯在该修饰电极上的电化学行为,结果表明该电极过程受扩散控制。计算了电极过程的部分动力学参数：电极的电活化面积Aeff=2.108mm2,扩散系数D=5.73×10-4cm2/s。用方波溶出伏安法优化了测定参数,测定了浓度与峰电流ipa1的线性关系,发现ipa1与百草枯浓度在9.660×10-7~3.865×10-4 mol/L范围内呈线性关系,检测限为3.297×10–7 mol/L,用该方法测定了实际水样中百草枯的含量,增敏回收率为：94.55%~108.25%。     

Pt/巯基乙酸/玻碳电极的表面形貌与电催化性能

以巯基乙酸为偶联层在玻碳(GC)电极上组装 Pt纳米颗粒, 得到Pt /巯基乙酸/GC电极, 利用扫描电镜(SEM)和循环伏安法(CV)研究了不同条件下复合电极的表面形貌和电化学性能. 研究结果表明, 巯基乙酸在GC电极表面具有特性吸附, 形成了具有一定致密性的吸附层. 在0.5 mol/L H2SO4+1.0 mol/L CH3OH溶液中, 组装19 h的复合电极对甲醇氧化表现出较好的电催化性能.     

十二烷基磺酸钠增强的吡啶鎓对芘的荧光猝灭

水溶液中三种吡啶鎓盐(吡啶盐酸盐,HP~+;N-苄基吡啶,BP~+;苄基紫精,BV~(2+))对芘的荧光猝灭因十二烷基磺酸钠(SLS)的引入而增强,且猝灭常数对SLS浓度的敏感性BV~(2+)>BP~+>HP~+,电导实验表明体系中无簇集体形成。认为SLS与吡啶鎓的静电作用及表面活性剂分子中烷基链的绕曲是导致猝灭增强的原因。     

烷基链长对紫精分子在Cu(100)电极表面吸附结构的影响

用循环伏安法(CV)和原位扫描隧道显微镜(STM)研究了烷基取代的紫精分子在Cu(100)电极上的氧化还原行为及其吸附结构对电极电势的依赖性. 对乙基紫精(DHV)和庚基紫精(DEV)在含有KCl电解质溶液中进行循环伏安曲线的测定, 两者呈现出不同的氧化还原行为. 从STM所得图像观察, 二价庚基紫精在Cl-c(2×2)-Cu(100)电极上呈现出二维有序的点阵组装结构,而二价乙基紫精却未出现任何的吸附结构. 降低电极电势至单电子转移反应发生时, 形成的自由基庚基紫精在电极表面呈现出稳定的条带状组装结构, 而自由基乙基紫精出现的条带组装结构比较密集且不能稳定存在. 继续降低电极电势, 庚基紫精的吸附结构会随之出现明显的变化,而乙基紫精不会有吸附结构改变的响应.     

聚邻苯二胺/镍氢氧化物修饰电极的研究

采用循环伏安法(CV)在聚邻苯二胺修饰玻碳电极表面络合Ni2+,然后将其置于NaOH溶液中CV扫描成功制备了镍氢氧化物/聚邻苯二胺/玻碳修饰电极(Ni(OH)2/PoPD/GC).通过CV探讨了聚合和负载机理,电化学交流阻抗谱(EIS)表征了电极修饰过程中界面阻抗变化,扫描电镜表征了PoPD膜负载Ni(OH)2后的形态...     

Motion of redox molecules in solution monitored by the highly-sensitive EQCM technique

The behavior of redox molecules in solution that was not detected by electrochemical techniques was measured by a highly-sensitive electrochemical quartz crystal microbalance (EQCM) technique that has been improved in this study to obtain a high sensitivity of EQCM measurement in solution. The improved EQCM technique allowed to monitor the motion of a redox molecule, that is an access of the molecule to an electrode surface and repulsion from the surface during redox. An EQCM technique currently in use has measured adsorption of redox molecules on an electrode surface or polymerization on the surface caused by a chemical reaction following redox, which exhibits an enough large mass change response to detect with an EQCM measurement. However, access and repulsion of redox molecule, which is a slight motion of the molecule near on electrode surface, has not been detected and investigated by an EQCM technique, because the mass change response seems to be very small. In this study, the redox behavior of methyl viologen on a bare gold surface, pyridinethiol surface and methylpyridinethiol surface was investigated. Although the three electrodes give the same cyclic voltammogram of methyl viologen, the three are different in QCM response recorded at the same time as the voltammetry. Access/repulsion of methyl viologen within an electrical double layer was monitored by the highly-sensitive EQCM technique.     

碳纳米管的快速功能化及电催化

将耐尔兰(Nile Blue, NB)分子修饰到碳纳米管(CNT)表面形成NB-CNT纳米复合体, 谱学结果表明, NB不仅能快速、高效地修饰到CNT表面, 而且还能有效地改善CNT在水溶液中的分散性能. 将NB-CNT修饰到玻碳(GC)电极表面制备了NB-CNT/GC电极, 循环伏安结果显示, 其伏安曲线上不仅表现出一对良好的、几乎对称的NB单体的氧化还原峰, 式量电位E⁰'几乎不随扫速而变化[其平均值为(－0.422±0.002) V (vs. SCE, 0.1 mol/L PBS, pH 7.0)]; 而且还显示出NB聚合体分子的氧化还原峰, E⁰'为－0.191 V (100 mV/s时). 进一步的实验结果表明, NB和CNT对NADH(即还原型β-烟酰胺腺嘌呤二核苷酸, 又称还原型辅酶I)的电化学氧化具有协同催化作用, 能使其氧化过电位降低多于560 mV; NB-CNT/GC电极还能较好地响应脱氢酶催化底物氧化过程中体系内NADH浓度的变化. 本文对碳纳米管功能化方法具有简单快速、电极制作容易以及催化效率高等优点, NB-CNT/GC电极有望在制作脱氢酶传感器方面得到应用.     

Minor groove binding of a novel tetracationic diviologen

Novel tetracationic diviologen compounds of the general formula CH3(CH2)nV2+(CH2)6V2+(CH2)nCH3 (where V2+ = 4,4'-bipyridinium and n = 5 or 11) were investigated as electrochemical reporters of DNA duplex formation. These compounds bind to both single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) when the DNA is either present in solution or immobilized at electrode surfaces. Binding to thiolated ssDNA and dsDNA immobilized at Au electrodes was characterized using the electrochemical response for the reduction of the V2+ state to the V+ (viologen radical cation) state. An analysis of the charge for this reduction provided isotherms and binding constants for binding of these diviologens to both forms of immobilized DNA. Saturation of the binding is achieved at solution concentrations near 20 microM. For both the n = 5 and 11 diviologens, binding to ssDNA is driven by electrostatic charge neutralization. For the n = 11 case, the binding is cooperative. In the presence of dsDNA, the n = 11 diviologen exhibits a unique reduction potential for the V2+/+ redox couple that is shifted approximately 100 mV negative of that in the presence of ssDNA. This new electrochemical signature is attributed to the reduction of viologen groups bound in the minor groove of the DNA duplex. For dsDNA in solution, an increase in the thermal denaturation temperature (Tm) from 60 to 66 degrees C as a function of the n = 11 diviologen concentration confirmed its interaction with the duplex. Circular dichroism (CD) spectroscopy also was used to investigate the binding of both the V2+ and V+ redox states of the n = 11 diviologen to dsDNA in solution. For the V+ state, a CD signal was observed that is consistent with the presence of face-to-face pi dimers of the viologen groups. This unambiguously demonstrates the binding of this redox state of the diviologen in the dsDNA minor groove and the formation of such dimers in the minor groove.     

Motion of redox molecules in solution monitored by the highly-sensitive EQCM technique

The behavior of redox molecules in solution that was not detected by electrochemical techniques was measured by a highly-sensitive electrochemical quartz crystal microbalance (EQCM) technique that has been improved in this study to obtain a high sensitivity of EQCM measurement in solution. The improved EQCM technique allowed to monitor the motion of a redox molecule, that is an access of the molecule to an electrode surface and repulsion from the surface during redox. An EQCM technique currently in use has measured adsorption of redox molecules on an electrode surface or polymerization on the surface caused by a chemical reaction following redox, which exhibits an enough large mass change response to detect with an EQCM measurement. However, access and repulsion of redox molecule, which is a slight motion of the molecule near on electrode surface, has not been detected and investigated by an EQCM technique, because the mass change response seems to be very small. In this study, the redox behavior of methyl viologen on a bare gold surface, pyridinethiol surface and methylpyridinethiol surface was investigated. Although the three electrodes give the same cyclic voltammogram of methyl viologen, the three are different in QCM response recorded at the same time as the voltammetry. Access/repulsion of methyl viologen within an electrical double layer was monitored by the highly-sensitive EQCM technique.     

Electrocatalytic Activities of 1,2-Naphthoquinone Modified Carbon Nanotube to the Electrochemical Oxidation of β-Nicotinamide Adenine Dinucleotide

The carbon nanotube (CNT) was functionalized with the electroactive species of 1,2-naphthoquinone (Nq) by a method of adsorption to form Nq-CNT nanocomposite. The Nq-CNT was characterized by spectroscopic techniques, for example UV-Vis, FTIR, SEM, etc., and the results showed that Nq can rapidly and effectively be adsorbed on the surface of CNT with high stability. Moreover, it was shown that the dispersion ability of CNT in aqueous solution had a significant improvement after CNT functionalized with Nq. The Nq-CNT/GC electrode was fabricated by modifying Nq-CNT nanocomposite on the GC electrode surface and its electrochemical properties were investigated by voltammetry, which indicated that CNT could improve the electrochemical behavior of Nq and greatly enhance its redox peak currents. The Nq-CNT/GC electrode exhibited a pair of well-defined and nearly symmetrical redox peaks with the formal potential of –87.3 ± 4.5 mV (vs. SCE, 0.1 M PBS, pH 7.0), which was almost independent on the scan rates. The experimental results also demonstrated that Nq and CNT could synergistically catalyze the electrochemical oxidation of NADH, and Nq-CNT exhibited a high performance with lowering the overpotential by more than 510 mV. The presented method had some advantages, such as rapid and facile CNT functionalization, easy electrode fabrication, and high electrocatalytic activity, etc.     

Electroless Deposition of Thionin onto Glassy Carbon Electrode Modified with Single Wall and Multiwall Carbon Nanotubes: Improvement of the Electrochemical Reversibility and Stability

A simple procedure was developed to prepare a glassy carbon electrode modified with carbon nanotubes (CNTs) and thionin. Abrasive immobilization of CNTs on a GC electrode was achieved by gently rubbing the electrode surface on a filter paper supporting carbon nanotubes, then immersing the GC/CNTs‐modified electrode into a thionin solution (electroless deposition) for a short period of time (5–50 s for MWCNTs and 5–120 s for SWCNTs ). Cyclic voltammograms of the resulting modified electrode show stable and a well defined redox couple with surface confined characteristic at wide pH range 2–12. The electrochemical reversibility and stability of modified electrode prepared with incorporation of thionin into CNTs film was compared with usual methods for attachment of thionin to electrode surfaces such as electropolymerization and adsorption on the surface of preanodized electrodes. The formal potential of redox couple (E°′) shifts linearly toward the negative direction with increasing solution pH. The surface coverage of thionin immobilized on CNTs glassy carbon electrode was approximately 1.95×10^?10 mol cm^?2 and 3.2×10^?10 mol cm^?2 for MWCNTs and SWCNTs, respectively. The transfer coefficient (α) was calculated to be 0.3 and 0.35 and heterogeneous electron transfer rate constants (K_s) were 65 s^?1 and 55 s^?1 for MWCNTs/thionin and SWCNTs/thionin‐modified GC electrodes, respectively. The results clearly show a great facilitation of the electron transfer between thionin and CNTs adsorbed on the electrode surface. Excellent electrochemical reversibility of redox couple, high stability, technically simple and possibility of preparation at short period of time are of great advantages of this procedure for modification of electrodes.     

Amperometric detection of pyridine nucleotides via immobilized viologen-accepting pyridine nucleotide oxidoreductase or immobilized diaphorase

The immobilization and electrical connection of a viologen-accepting pyridine nucleotide oxidoreductase (VAPOR) on an electrode surface by coadsorption with an amphiphilic pyrrole viologen and electropolymerization of this pyrrole monomer are described. The immobilized VAPOR catalyzes the reduction of NAD(P)(+) to NAD(P)H by the viologen redox couple (V(2+2+)). The sensitivity of this biosensor is 1.4 and 2.5 mA M(-1) cm(-2) for NAD(+) and NADP(+) respectively. The immobilization of diaphorase within a laponite gel adsorbed on an electrode surface is described. The incorporation and electropolymerization of Methylene Blue in the biolayer allows an electron transfer communication between diaphorase molecules and the electrode surface. The diaphorase electrode thus obtained responds to NADH at 0 V. The sensitivity and detection limit of this biosensor are 11.2 mA M(-1) cm(-2) and 1 muM respectively.     

Encapsulation of ferrocene and peripheral electrostatic attachment of viologens to dimeric molecular capsules formed by an octaacid, deep-cavity cavitand

In aqueous media the deep-cavity cavitand octaacid 1 forms stable dimeric molecular capsules 1(2), which are stabilized by hydrophobic effects. In this work we investigate the binding interactions in aqueous solution between these capsules and the redox active guests, ferrocene (Fc) and three 4,4'-bipyridinium (viologen) dications: methyl viologen (MV(2+)), ethyl viologen (EV(2+)), and butyl viologen (BV(2+)). Using NMR spectroscopic and electrochemical techniques we clearly show that the hydrophobic Fc guest is encapsulated inside 1(2). An interesting effect of this encapsulation is that the reversible voltammetric response of Fc is completely eliminated when it resides inside the 1(2) capsular assembly, a finding that is attributed to very slow electrochemical kinetics for the oxidation of Fc@1(2). Diffusion coefficient measurements (PGSE NMR spectroscopy) reveal that all three viologen guests are strongly bound to the dimeric capsules. However, the (1)H NMR spectroscopic data are not consistent with encapsulation and the measured diffusion coefficients indicate that two viologen guests can strongly associate with a single dimeric capsule. Furthermore, the (V(2+))(2)*1(2) complex is capable of encapsulating ferrocene, clearly suggesting that the viologen guests are bound externally, via coulombic interactions, to the anionic polar ends of the capsule. The electrochemical kinetic rate constants for the reduction of the viologen residue in the V(2+)*1(2) complexes were measured and found to be substantially lower than those for the free viologen guests.