银电极在Na2SO4溶液中氧化还原过程的原位拉曼光谱研究

采用原位拉曼光谱结合循环伏安法研究银电极在０．１ｍｏｌ／Ｌ的Ｎａ２ＳＯ４溶液中不同电位下的氧化还原过程，在电位扫描过程中，实时记录的拉曼光谱表明，电极表面在０．２Ｖ开始生成吸附原子氧物种，当电位正于０．４Ｖ，部分吸附的原子氧扩散进入电极的亚表面区，而另一些则通过强的化学吸附与银表面成键；同时部分银氧化为＋１价，各谱带的产生和消失与氧化还原电流峰有很好的对应关系，表明电化学原位拉曼光谱能在分子水平上     

银表面罗丹明6G的电化学表面增强拉曼光谱研究

罗丹明6G（Rhodamine 6G,R6G）是单分子表面增强拉曼光谱（SM-SERS）研究中最常用的探针分子之一,对R6G分子在表面吸附行为的研究有助于了解R6G分子和表面的相互作用. 本文应用电化学和电化学表面增强拉曼光谱技术,研究不同电位下R6G的银电极表面的吸附行为. 结果表明,随着电位负移罗丹明6G在银表面上从垂直吸附转为倾斜吸附,该变化和碱性条件下吸附于金纳米粒子上R6G的吸附构象一致. 这说明,在部分单分子实验中所发现的R6G反常光谱其来源是单个R6G分子在表面吸附取向变化. 本研究对后续详细分析SM-SERS研究中单分子SERS谱峰变化的机制有一定的参考价值.     

苯乙炔吸附在金电极上的现场表面增强拉曼光谱研究

采用电化学现场表面增强拉曼光谱研究了苯乙炔在金电极上的吸附行为及表面反应过程. 负电位下拉曼光谱的变化表明, 苯乙炔分子的炔端碳与金属电极成键, 分子垂直吸附于金电极表面. 在所研究的负电位区间内, 分子在电极表面的吸附取向并未随电位发生改变. 电化学现场光谱研究表明, 苯乙炔分子随电位负移, 碳碳叁键被加氢还原. 通过对比苯乙烯的现场表面增强拉曼光谱发现, 在－0.6 V至－1.2 V的电位区间内, 苯乙炔经过中间步骤生成苯乙烯, 最终被完全加氢为苯乙烷.     

寡聚脱氧核苷酸吸附状态随电位的变化

利用原位电化学及表面增强拉曼散射（SERS）光谱方法对寡聚脱氧核苷酸（26-mers ODN和13-mers ODN）在银电极表面上的吸附状态进行了研究. 实验表明, 单链寡聚脱氧核苷酸在银电极上有很好的SERS光谱,单链寡聚脱氧核苷酸在银表面上主要以碱基腺嘌呤（A）为吸附点,吸附状态随电位变化而变化, 链长较短的寡聚脱氧核苷酸在银电极表面的吸附态对电位变化较敏感.     

银电极表面异亮氨酸单分子膜结构和表面性质的表面增强拉曼光谱研究

利用表面增强拉曼光谱(SERS)技术研究了在粗糙化银电极表面吸附的异亮氨酸自组装单层膜结构及其表面性质随溶液酸碱性和电极电位改变的特征.研究结果表明溶液pH值的变化并没有显著改变异亮氨酸分子在银电极表面以去质子化羧基吸附为主的特征.借助于高氯酸根离子这一SERS光谱探针,对异亮氨酸单分子膜的表面酸碱性质进行了表征和分析.而就电位改变对该单分子膜结构的影响而言,在所研究的电位范围内,单分子膜中的异亮氨酸分子是通过去质子化羧基与氨基两个位点而吸附的,且吸附作用随电位负移而呈现有规律的变化.     

增感染料1556、798吸附在银电极上的表面增强拉曼光谱

本文利用表面增强拉曼光谱研究了增感染料1556、798在银电极上的吸附,通过比较染料的固体拉曼光谱和染料的表面增强光谱,我们发现两种染料在银电极表面的吸附行为不完全相同,吸附时染料分子的平面基本上与电极表面相垂直。     

Au@SiO2膜/Ti电极吸附吡啶的表面增强拉曼光谱研究

基于壳层隔绝纳米粒子增强拉曼光谱技术,合成了Au@SiO₂纳米粒子,并对其进行了相关表征. 结果表明,包裹的二氧化硅层连续、致密,Au@SiO₂膜/Ti电极上可获得金属钛电极上吸附吡啶分子的高质量表面增强拉曼光谱（SERS）信号. 通过Pt、Ni电极的测试,证实该信号源于吸附在基底表面的吡啶分子. 此外,Au@SiO₂膜/Ti电极上吸附吡啶分子的现场SERS光谱研究表明,在-0.1 V ~ -0.6 V电位区间,吡啶分子平躺吸附,从-0.6 V起吸附的吡啶分子由平躺逐转变为垂直,而当电位为-1.2 V时,电极表面析氢,吡啶脱附.     

银电极上4-氨基安替比林原位表面增强拉曼光谱电化学

在银电极表面4-氨基安替比林(4-AAP)分子自组装,形成单分子膜层.应用表面增强拉曼散射(SERS)光谱原位考察不同电位下4-AAP在电极表面的吸附机理及其组装液pH值对组装分子与银作用方式的影响.依据密度泛函数(DFT)理论预测4-AAP分子振动模式及其SERS光谱归属.结果表明:在开路电位下,组装层中的4-AAP分子以N15和O3为位点,由苯环倾斜和比林环垂直的方式吸附在银表面;但随着外加电位负移,4-AAP分子的苯环趋于垂直吸附而比林环则逐渐以平行方式靠近银表面.在-0.8V电位下,4-AAP分子从银表面脱附.酸性溶液中组装,形成的4-AAP膜层以N15和O3为位点吸附于银表面,比林环倾斜而苯环直立;碱性条件下,分子的吸附位点不变,比林环呈平行取向,而苯环倾斜于银表面.     

铂电极上自组装铁原卟啉单分子层的表面增强振动光谱初探(英文)

应用现场表面增强拉曼光谱和衰减全反射表面增强红外光谱初步研究了0.1mol·L-1HClO4溶液中Pt电极表面铁原卟啉(FePP)自组装单层的电化学和结构特性.以514nm波长为激发线,得到了增强因子约为40的粗糙Pt电极上FePP在不同电位下的表面增强拉曼光谱.分析0.5～-0.3V(SCE)区间内谱峰变化,得到近似的吸附等温式,由此可估算出Fe3+/Fe2+的式量电位大约为-0.2V.原位表面增强红外光谱的测试结果表明,FePP分子主要以斜立方式吸附在Pt膜电极表面,其中一个环外羧酸根与电极表面相接触,而另一羧酸基团以氢键与相邻的FePP分子相连.这样的吸附结构在-0.1～0.9V(SCE)的电位区间内并没有显著的变化.     

表面增强拉曼光谱研究稳定剂TAI在银上的吸附

用表面增强拉曼光谱的方法研究 4-羟基--甲基-1,3,3a,7-四氮茚(TAI)在金属银上的吸附.实验表明TAI分子是通过分子上的N原子以化学吸附的方式吸附在银电极上.电极处理的氧化-还原循环次数并不影响振动频率,但在一定范围内对表面增强拉曼光谱的吸收强度有明显影响.     

Adsorption of adenine derivatives on a gold electrode studied by specular reflectivity measurement

The adsorption of adenine, deoxyadenosine, deoxyadenosine-5′-monophosphate,-diphosphate and-triphosphate on a gold electrode has been studied by specular reflectivity measurement in 0.1 M NaClO₄ solution. In the presence of these compounds, a marked decrease in reflectivity was found on reflectivity-potential curves in the potential region more positive than ?0.8 V vs. Ag/AgCl, the decrease being ascribed to the adsorption of them. The magnitude of change in reflectivity was dependent on both the concentration and the electrode potential. The reflectivity change observed in the negative potential region was analyzed quantitatively according to the procedure previously described. The results were elucidated on the basis of the same isotherm as used by Green and Dahms in their adsorption study of aromatic hydrocarbons, and the number of solvent molecules being replaced through the adsorption of one organic molecule and the free energy change of adsorption were obtained. The former is suggestive of a flat orientation of the adsorbed molecule in contact with its adenine moiety on the electrode surface. It is also suggested from the latter that the presence of phosphate groups leads to a decrease in ΔG_ad⁰ resulting from their hydrophilic properties and a repulsive interaction between these groups and the negative charges on the surface.     

Interactive adsorption behavior of NAD+ at a gold electrode surface

The adsorption of an oxidized form of nicotinamide adenine dinucleotide, NAD+, on a polycrystalline gold electrode surface and the subsequent surface conformation of the molecule were investigated over a wide temperature and potential range, using electrochemical differential capacitance and PM-IRRAS techniques. The adsorption process was described by the Langmuir adsorption isotherm. The corresponding thermodynamic parameters were determined: the Gibbs energy, enthalpy, and entropy of adsorption. The large negative Gibbs energy of adsorption (-43 +/- 4 kJ mol-1 and -39 +/- 2 kJ mol-1 on a positively and negatively charged surface, respectively) confirms that the NAD+ adsorption process is highly spontaneous, while the large entropy gain (285 J K-1 mol-1 and 127 J K-1 mol-1 on a positively and negatively charged surface, respectively) was found to represent the adsorption driving force. It was demonstrated that the energetics of the adsorption process is surface-charge controlled, while its kinetics is both mass-transport and surface-charge controlled. A surface-charge dependent conformation model for the adsorbed NAD+ molecule is proposed. These findings suggest that the origin of the NAD+ reduction overpotential is related to the surface conformation of the adsorbed NAD+ molecule, rather than to the electrode Fermi level position.     

Electrocatalytic oxidation of reduced nicotinamide adenine dinucleotide (NADH) at thick-film gold electrodes

Cyclic voltammetric and electrochemical impedance spectroscopic investigations of screen-printed, thick-film gold electrodes reveal significant differences when compared with conventional polished gold disk electrodes of comparable size. The rough and porous structure of the thick-film electrode surface leads to an actual electrode area which is increased six-fold compared to polished disk electrodes. Due to the catalytic properties of these surface structures it is possible to perform the electrochemical oxidation of reduced nicotinamide adenine dinucleotide (NADH) at relatively low overpotentials, i.e. +0.145 V vs. SCE. By operating electrodes at this potential, electrode fouling processes and interference from electroactive species, e.g. acetaminophen, are minimized. An amperometric glucose sensor based on polymer matrix-entrapped glucose dehydrogenase with a working potential of +0.145 V vs. SCE was successfully incorporated into a flow injection analysis (FIA) system.     

Effect of organic vapors and potential-dependent Raman scattering of 2,6-dimethylphenylisocyanide on platinum nanoaggregates

The surface-enhanced Raman scattering characteristics of 2,6-dimethylphenylisocyanide (2,6-DMPI) on Pt nanoaggregates, in ambient and electrochemical environments and in the presence of organic vapors, were examined and compared with those on Au nanoaggregates. Due to the exclusive adsorption via the isocyanide group, the NC stretching band was very susceptible to the measurement conditions although the ring associated bands showed negligible peak shifts. In ambient conditions, the peak shift of the NC stretching vibration on Pt (29 cm(-1)) was one half of that on Au (61 cm(-1)), suggesting that the electron donation capability of the isocyanide group to Au was greater than that to Pt. In the electrochemical environment, the NC stretching peak varied linearly with slopes of ～42 and ～36 cm(-1) V(-1) on Pt and Au, respectively. On the other hand, the NC stretching bands of 2,6-DMPI on Pt red-shifted by as much as 15 and 41 cm(-1), in the presence of acetone and ammonia, respectively, corresponding to the lowering of the surface potential of Pt nanoaggregates from +0.2 to -0.2 and -0.8 V, respectively. On Au nanoaggregates, however, acetone appeared to increase the surface potential of Au from +0.2 to +0.3 V, although ammonia decreased the surface potential from +0.2 to -0.4 V. Acetone must then act as an electron donor when interacting with Pt while it serves as an electron acceptor when interacting with Au, in agreement with an ab initio quantum mechanical calculation.     

Adsorption behavior of dinucleotides on bare and ru-modified glassy carbon electrode surfaces

The interactive behavior of flavin adenine dinucleotide (FAD) with a bare glassy carbon electrode (GCE) and a Ru-modified GCE was investigated. The reduction of FAD at a GCE/ruthenium-modified GCE surface is a quasi-reversible, surface-controlled process, and our data implied that the attachment of FAD onto the surface is caused by nonspecific adsorption instead of covalent linkage, in which the adenine ring of FAD adopts a flat orientation on the GCE surface in neutral and dilute solutions in order to maximize the pi-pi stacking with the carbon surface and reorients to a perpendicular orientation as the surface gets more crowded. FAD desorption during the exchange with nicotinamide adenine dinucleotide (NAD+) is one order of magnitude slower than desorption in the absence of NAD+, which indicates a strong interaction between FAD and NAD+. General knowledge of the interactive behavior of NAD+ on a FAD-adsorbed GCE provides useful information for the design of a modified electrode surface for the generation of NADH from NAD+.     

Surface enhanced raman study of benzidine on a silver electrode: an interpretation for different adsorption configurations at various applied voltages

The surface enhanced Raman spectra of benzidine in a silver sol and on a silver electrode at different applied voltages are reported. These spectra are compared with those in the crystalline form and in dimethyl sulfoxide (DMSO) solution, with group theoretical analysis. It is interpreted that in the silver sol and on the silver electrode with voltages larger than −0.2 V (with respect to the standard calomel electrode) the benzidine molecule is adsorbed perpendicularly with one of its two amino groups attached on the silver surface. When the applied voltage on the silver surface is less than −0.4 V both of its amino groups are adsorbed on the silver surface with the flat configuration. The adsorption mechanism for these two configurations is also proposed in the report.     

血红蛋白在裸银电极上的直接电化学及其分析应用

报道了血红蛋白(Hb)在裸银电极上的电化学氧化还原行为。在+0.4～-0.2V(vs.SCE)电位范围内于pH=4.5的0.1mol/LNaAc-HAc底液中,血红蛋白产生一对灵敏的氧化还原峰。峰电位之差△E为0.25V(扫描速度20mV/s).动力学研究表明:电极反应的电子转移数n为0.94,表现电子传递速率常数Ks为0.032.连续电位扫描30min,峰电流变化分别为0.2μA(还原峰)和0.15μA(氧化峰).两峰与血红蛋白浓度在2×10^-7～2×10^-6mol/L和2×10^-6～1.5×10^-5mol/L范围内均呈良好线性关系,已应用于血红蛋白的分析测定。     

An investigation of the surface enhanced Raman scattering (SERS) from a new substrate of silver-modified silver electrode by magnetron sputtering

'Pure' silver nanoparticles on silver electrode were prepared by magnetron sputtering. The silver-modified silver electrode has good stability and the silver nanoparticles on silver electrode have homogeneous size distribution. Compared with the silver colloid modified silver electrode, there were no any extraneous component ions on the electrode, for the modified silver nanoparticles are prepared by magnetron sputtering. Synchronously, we obtained much higher quality SERS spectra of adenine molecules on the silver electrode modified by magnetron sputtering (SEMMS), and the study of the adsorption behavior of adenine on the silver-modified silver electrode by surface enhanced Raman scattering (SERS) indicated that the silver-modified silver electrode was highly efficient substrates for SERS investigation. From the rich information on the SEMMS obtained from high-quality potential-dependent SERS, we may deduce the adsorption behavior of adenine and the probable SERS mechanism in the process. The probable reasons are given.     

Kinetic approach for the purification of nucleotides with magnetic separation

The isolation of β‐nicotinamide adenine dinucleotide is of great importance since it is widely used in different scientific and technologic fields such as biofuel cells, sensor technology, and hydrogen production. In order to isolate β‐nicotinamide adenine dinucleotide, first 3‐aminophenyboronic acid functionalized magnetic nanoparticles were prepared to serve as a magnetic solid support and subsequently they were used for reversible adsorption/desorption of β‐nicotinamide adenine dinucleotide in a batch fashion. The loading capacity of the 3‐aminophenyboronic acid functionalized nanoparticles for β‐nicotinamide adenine dinucleotide adsorption was 13.0 μmol/g. Adsorption kinetic and isotherm studies showed that the adsorption process followed a pseudo‐second‐order kinetic model and the experimental data can be represented using Langmuir isotherm model. The 3‐aminophenyboronic acid functionalized magnetic nanoparticles were proposed as an alternative support for the β‐nicotinamide adenine dinucleotide purification. The results elucidated the significance of magnetic separation as a fast, relatively simple, and low‐cost technique. Furthermore, the magnetic supports can be reused at least five times for purification processes.     

Surface-enhanced Raman scattering at the silver electrode/ionic liquid (BMIPF6) interface

This is the first report of in situ SER spectra of chemical species adsorbed on a Ag/room temperature ionic liquid (RTIL) interface. We have investigated the dependence of the SERS intensity of the RTIL derived from 1-n-butyl-3-methylimidazolium hexafluorophosfate (BMIPF6) adsorbed on a silver electrode. It has been shown that the BMI+ adsorbs on the silver electrode for potentials more negative than -0.4 V vs a Pt quasireference electrode (PQRE). In the -0.4 to -1.0 V potential range the SER spectra are similar to the Raman spectrum of the RTIL BMIPF6. At potentials more negative than -1.0 V some imidazolium ring vibrational modes and N-CH3 vibrations are enhanced, suggesting that the imidazolium ring is parallel to the surface and for potentials <-2.8 V the BMI+ is reduced to the BMI carbene. The potential dependence of the SERS intensities of Py adsorbed on a silver electrode in BMIPF6 has also been investigated. The results have shown that at potentials less negative than -0.8 V (vs PQRE) Py adsorbs at an end-on configuration forming an Ag-N bond. In the -0.9 to -1.4 V potential range Py molecules lie flat on the electrode surface and at potentials <-1.4 V Py is replaced by the BMI+. The electrochemical and SERS results have shown that Py has the effect of changing the oxidation of silver in that medium as well as the reduction of BMI+ to the BMI carbene. In the presence of Py the BMI+ reduction is observed at potentials near -2.4 V. The Ag electrode has presented SERS activity from 0.0 to -3.0 V.