仿生膜的电化学研究

仿生膜电化学是一门新兴的、也是当前很活跃的电化学和电分析化学的前沿领域。本文简要评述了生物膜领域的发展过程及研究现状，介绍了关于生物膜的一些基本性质和理论。概要总结了作为生物膜的研究模型一仿生膜在各个领域的研究情况及现状，展望了仿生膜在诸多领域应用的前景。采用电化学方法对支撑双层磷脂膜（s一BLM）和液／液界面等不同的模拟生物膜体系进行了研究，并结合AFM、XPS以及IR等谱学手段对蛋白质、核酸与生物膜之间的相互作用进行了初步探讨。主要结果如下：1．我们在玻碳电极表面成功地制备了嵌有DNA支撑双层磷脂膜，并用循环伏安法和阻抗谱图法证明了所形成的磷脂膜是双层。用循环伏安法、傅立叶红外和原子力显微镜表征了膜内DNA.此功能化膜表现出离子通道的行为，对其机理加以探讨，并且离子通道的形成通过电化学阻抗谱图证明。通道在激发物存在时形成打开，通道电流随激发物的增加而增强；反之，则通道关闭。此过程可反复多次。这种DNA修饰的电极可制成电化学传感器，利用离子通道原理，应用在基因检测和研究DNA与其它分子的反应等方面。2．我们提出了一种在云母上成膜的全新方法一直接将DMPC磷脂膜制备在新解理的云母片上。通过AFM和XP S证明了DMPC磷脂在云母上直接形成双层膜。用AFM观察了膜的形成与时间的关系，在成膜过程中，随着在KCI溶液中的浸泡时间的增长，逐渐由多层膜变成双层膜，整个成膜过程需20分钟，最后形成双层膜。探讨了成膜机理。此种成膜方法快速、简便、易行，且在空气中非常稳定。此种成膜方法为深入研究膜提供必要的前提和机会、为进一步研究生物材料提供了基础，有助于结构生物学的研究。 3．谷胺酸是基本的神经递质。用聚谷胺酸嵌入双层磷脂膜作为钙离子的接受器。研究了固定有功能基团的S一BLM的离子通道行为，探讨了离子通道形成的机理。在钙离子存在的情况下，离子通道打开，反之则离子通道处于关闭状态。此过程可反复多次。对钙离子的伏安响应快速，离子通道电流仅与钙离子的浓度有关，而与加入钙离子时间无关。 4．在玻碳电极表面上制备了由玻碳支持的磷脂膜，借助电化学阻抗分析技术，我们证明了在玻碳电极表面上的磷脂膜为双层磷脂膜。研究了六氟磷酸根阴离子(PF6-)与双层磷脂膜的相互作用及玻碳电极上的s一BLM的离子通道行为，s一BLM显示了较为敏感的通透性的变化，所产生的通道电流大小不仅与通道激发物浓度有关，而且也与时间有关。离子通道行为可用于测定PF6一。 5．我们用简单的方法制备了水一琼脂微电极，并且用此电极研究了简单离子和推动离子的转移过程。简单离子和推动离子在水一琼脂／1，2_二氯乙烷界面的转移过程的特点与其在水／1，2一二氯乙烷界面的转移过程的特点相似。进一步证明了，硅烷化对琼脂一水微电极几乎没有影响，此类琼脂一水微电极和固体微电极有着相似的特性，并且可作sECM的探头。6．用循环伏安法研究新型载体一端烯基液晶冠醚推动钠离子的转移，并且表明钠离子的转移是由扩散控制。探讨了影响钠离子转移的因素，诸如：端烯基液晶冠醚和钠离子浓度等。求算出端烯基液晶冠醚在1，2一二氯乙烷中的扩散系数是（2.61±0.12) * 10~(-6)CM~2s~(-1)，端烯基液晶冠醚和7.用循环伏安法对简单离子一四乙基钱阳离子（TEA~+）转移进行了研究。结果表明：TEA~+随微玻管内径减小（小于3μm），电流逐渐呈现拟稳态。随TEA~+浓度减小，i_p值也减小。峰电流与扫描速度的平方根成正比，并且符合Randles-Sevcik关系。同时讨论了微液／液界面TEA~+体系简单离子的转移机理。

液/液界面上电子转移反应的研究

应用扫描电化学显微镜研究电荷在液／液界面上的转移过程是目前电化学和电分析化学领域的研究热点之一。本文简要地回顾了液／液界面电分析化学研究的发展历程，介绍了液／液界面电分析化学的基本理论。围绕着扫描电化学显微镜和微电极技术，分别研究了极化和非极化液／液界面上的电子转移反应。主要结果如下：1．通过选择合适的共同离子控制界面电位差，应用扫描电化学显微镜(SECM )和微电极技术研究离子诱导的反向电子转移反应。这一研究对于生命科学及模拟生物模的研究具有重要意义。2.应用扫描电化学显微镜研究了类冰相／有机相界面上的电子转移反应。构筑了可用于作为SECM研究基底的微观上平整和稳定的1,2一二氯乙烷(DCE)／冰界面，研究了温度对异相电子转移速率的影响。这一研究对于扩展液／液界面电分析化学的研究，以及有机相的选择范围具有重要意义；对于研究界面结构问题有一定的应用前景。3.将含有氧化还原电对的水溶液滴支持在铂电极上，然后将该电极插入到有机溶液中，与参比电极和对电极构成常规佩狗三电极系统。利用扫描电化学显微镜研究了水相与有机相之间界面上佩狗电子转移反应。以铁氰化钾／亚铁氰化钾为电对研究了亚铁氰化钾与二茂铁阳离子之间的电子转移反应以及铁氰化钾与TCNQ阴离子自由基之间的电子转移反应。结果表明这一方法实现了独立控制极化界面和SECM数据收集的目的，可以研究的可控电位范围较使用共同离子控制界面电位方法大大增宽，在国际上首次成功地将扫描电化学显微镜与极化的液／液界面研究结合起来。4.应用扫描电化学显微镜对4一氨基苯甲酸修饰的玻碳电极进行了电化学表征，研究了酸度对电极表面修饰的4一氨基苯甲酸解离形态的影响，及不同的荷电中介体在此修饰电极表面的电化学行为。通过分析pH值与电子转移速率常数的关系，得到了电极表面修饰的4一氨基苯甲酸的表面pKa.

Directing single-walled carbon nanotubes to self-assemble at water/oil interfaces and facilitate electron transfer

Both the behavior and the general key factors for assembling flexible SWNT films at the water/oil interface were investigated; the electron transfer, one of the most fundamental chemical processes, at the SWNT-sandwiched water/oil interface was also firstly illustrated using scanning electrochemical microscopy.

Investigation of facilitated ion-transfer reactions at high driving force by scanning electrochemical Microscopy

The kinetics of facilitated ion-transfer (FIT) reactions at high driving force across the water/1,2-dichloroethane (W/DCE) interface is investigated by scanning electrochemical microscopy (SECM). The transfers of lithium and sodium ions facilitated by dibenzo-18-crown-6 (DB18C6) across the polarized W/DCE interface are chosen as model systems because they have the largest potential range that can be controlled externally. By selecting the appropriate ratios of the reactant concentrations (Kr c(M)+/c(DB18C6)) and using nanopipets as the SECM tips, we obtained a series of rate constants (k(f)) at various driving forces (Delta(O)(W) phi(ML+)(0') - Es, Delta(O)(W) phi(ML+)(0') is the formal potential of facilitated ion transfer and Es is the potential applied externally at the substrate interface) based on a three-electrode system. The FIT rate constants k(f) are found to be dependent upon the driving force. When the driving force is low, the dependence of 1n k(f) on the driving force is linear with a transfer coefficient of about 0.3. It follows the classical Butler-Volmer theory and then reaches a maximum before it decreases again when we further increase the driving forces. This indicates that there exists an inverted region, and these behaviors have been explained by Marcus theory.

Effects of solution viscosity on heterogeneous electron transfer across a liquid/liquid interface

Scanning electrochemical microscopy (SECM) is employed to investigate the effect of solution viscosity on the rate constants of electron transfer (ET) reaction between potassium ferricyanide in water and 7,7,8,8-tetracyanoquinodimethane (TCNQ) in 1,2-dichloroethane. Either tetrabutylammonium (TBA(+)) or ClO4- is chosen as the common ion in both phases to control the interfacial potential drop. The rate constant of heterogeneous ET reaction between TCNQ and ferrocyanide produced in-situ, k(12), is evaluated by SECM and is inversely proportional to the viscosity of the aqueous solution and directly proportional to the diffusion coefficient of K4Fe(CN)(6) in water when the concentration of TCNQ in the DCE phase is in excess. The k(12) dependence on viscosity is explained in terms of the longitudinal relaxation time of the solution. The rate constant of the heterogeneous ET reaction between TCNQ and ferricyanide, k(21), is also obtained by SECM and these results cannot be explained by the same manner.

Study of electron-transfer reactions across an externally polarized water/1,2-dichloroethane interface by scanning electrochemical microscopy

A novel method to study electron-transfer (ET) reactions between ferrocene in 1,2-dichloroethane (DCE) and a redox couple of K3Fe(CN)(6) and K4Fe(CN)(6) in water using scanning electrochemical microscopy (SECM) with a three-electrode setup is reported. In this work, a water droplet that adheres to the Surface of a platinum disk electrode is immersed in a DCE solution. The aqueous redox couple serves both as a reference electrode on the platinum disk and as an electron donor/acceptor at the polarized liquid/liquid inter-face. With the present experimental approach, the liquid/liquid interface can be polarized externally, while the electron-transfer reactions between the two phases can be monitored independently by SECM. The apparent heterogeneous rate constants for the ET reactions were obtained by fitting the experimental approach curves to the theoretical values. These rate constants obey the Butler-Volmer theory i.e., them, are found to be potential dependent.

Study of electron transfer across the liquid/ice-like matrix interface by scanning electrochemical microscopy

In this work, we report the findings of a study on scanning electrochemical microscopy (SECM) to investigate the interfacial electron-transfer (ET) reaction between the 7,7,8,8-tetracyanoquinodimethane radical anion (TCNQ(.-)) in 1,2-dichloroethane and ferricyanide in an ice-like matrix (a mixture of insulting ice and conductive liquid) under low temperatures. Experimental results indicate that the formed liquid/ice-like matrix interface is superficially similar in electrochemical characteristics to a liquid/liquid interface at temperatures above -20 degreesC. Furthermore, imaging data show that the surface of the ice-like matrix is microscopically flat and physically stable and can be applied as either a conductive or an insulting substrate for SECM studies. Perchlorate ion was selected as the common ion in both phases, the concentrations of which controlled the interfacial potential difference. The effect of perchlorate concentration in the DCE phase on interfacial reactions has been studied in detail. The apparent heterogeneous rate constants for TCNQ(.-) oxidation by Fe(CN)(6)(3-) in another phase under different temperatures have been calculated by a best-fit analysis, where the experimental approach curves are compared with the theoretically derived relationships. Reaction rate data obey Butler-Volmer formulation before and after the freezing point, which is similar to most other known cases of ET reactions at liquid/liquid interfaces. However, there is a sharp change observed for heterogeneous rate constants around the freezing point of the aqueous phase, which reflects the phase transition. At temperatures below -20 degreesC, surface-confined voltammograms for the reduction of ferricyanide were obtained, and the ice-like matrix became an insulating one, which indicates that the aqueous phase is really a frozen phase.

应用扫描电化学显微镜研究冰/1,2-二氯乙烷界面上电子转移反应

分别以亚铁氰化钾和现场所产生的二茂铁阳离子(Fc+)作为冰相和有机相的电活性物质,应用扫描电化学显微镜(SECM)和微电极技术研究了在低温条件下冰/1,2-二氯乙烷界面上的电子转移反应.选择合适的共同离子四丁基铵阳离子(TBA+)来控制界面电位,利用SECM得到的正、负反馈信息,研究了不同温度下界面电位差驱动的液/液界面上的电子转移反应,并通过拟合实验和理论数据得到了此异相界面电子反应速率常数等.实验结果验证了此反应动力学常数是由界面电位差所决定的.在相变的温度时,电子转移反应速率常数有一个大的改变,实验结果反映了相变的过程.

Fabrication of nanometer-sized electrodes and tips for scanning electrochemical microscopy

A novel method for fabrication of nanometer-sized electrodes and tips suitable for scanning electrochemical microscopy (SECM) is reported. A fine etched Pt wire is coated with polyimide, which was produced by polymerization on the Pt surface initiated by heat. This method can prepare electrodes with effective radii varying from a few to hundreds of nanometers. Scanning electron microscopy, cyclic voltammetry, and SECM were used to characterize these electrodes. Well-defined steady-state voltammograms could be obtained in aqueous or in 1,2-dichloroethane solutions. Ibis method produced the nanoelectrodes with exposed Pit on the apex, and they can also be employed as the nanotips for SECM investigations. Different sizes of Pt nanotips made by this method were employed to evaluate the kinetics of the redox reaction of Ru(NH3)6(3+) on the surface of a large Pt electrode by SECM, and the standard rate constant kappa (o) of this system was calculated from the best fit of the SECM approach curve. This result is similar to the values obtained by analysis of the obtained voltammetric data.

Investigation of the model compounds at 4-aminobenzoic acid modified glassy carbon electrode by scanning electrochemical microscopy

In this paper, we studied the reactions of both potassium ferricyanide and hexaammineruthenium(III) chloride at a 4-aminobenzoic acid (4-ABA) modified glassy carbon electrode (GCE) by scanning electrochemical microscopy (SECM) in different pH solutions. The surface of the modified electrode has carboxyl groups, the dissociation of which are strongly dependent upon the solution pH values. The rate constant kb of the oxidation of ferrocyanide on the modified electrode can be obtained by fitting the experimental tip current-distance (I-T-d) curves with the theoretical values. The surface pK(a) of the 4-ABA modified GCE was estimated from the plot of standard rate constant k(o) versus the solution pH and is equal to 3.2, which is in good agreement with the reported result. The SECM approach curves for Ru(NH3)(6)(3+) both on the bare and the modified electrodes show similar diffusion control processes. These results can be explained by the electrostatic interactions between the modified electrode surface and the model compounds with different charges. (C) 2001 Elsevier Science BN. All rights reserved.

Scanning electrochemical microscopy study of electron transfer across the water/1,2-dichloroethane interface induced by common ions

In this work, we report the reverse electron transfer reaction between TCNQ in 1, 2-dichloroethane (DCE) and ferrocyanide in water. This process is a thermodynamic unfavorable reaction and the reverse electron transfer reaction can only be obtained by scanning electrochemical microscopy(SECM) in the presence of suitable potential-determining ions, which govern the interfacial potential difference. In our case, the potential determining ions are tetrabutylammonium ion(TBA(+)) and tetraphenylarsonium ion (TPAs+). The effects of the concentrations of TBA(+) and TPAs+ in two phases and other parameters have been studied in detail. The apparent heterogeneous rate constants(k(i)) were obtained under different values of K-p(K-p=c(i)(w)/c(i)(o)) for both cases by fitting the SECM approach curves with theoretical ones and the results showed that they were controlled by the interfacial potential differences. The relationship between apparent heterogeneous rate constants and the interfacial potential differences obeys Butler-Volmer theory.