金与银电极表面甘氨酸分子吸附作用的SERS光谱研究

本文利用表面增强拉曼光谱(SERS)技术研究了甘氨酸在金与银基底表面的吸附作用特征。研究表明甘氨酸分子以COO-的不对称形式吸附于金电极表面,且NH2也是其可能的吸附位点;而在银电极表面,则主要是通过COO-的对称形式而吸附。在此基础上,进一步研究了电极电位与溶液酸碱性对吸附于粗糙化银电极表面甘氨酸分子吸附作用的影响。研究结果表明,甘氨酸分子中去质子化羧基的吸附作用受电位影响较小,而电位对-NH3+吸附作用的影响程度较大。另一方面,溶液pH值对银电极表面的甘氨酸分子吸附行为的影响也较为显著。随着溶液酸性减小羧基倾向于相对于电极表面平行吸附。这是由于随着溶液碱性增大氨基质子化程度的减小,有利于氨基在银电极表面吸附。这将改变分子的吸附构型使其更接近于电极表面。这些变化主要出现在pH值大于10的条件下。     

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.     

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.     

咪唑对锌缓蚀机理的表面增强拉曼光谱研究

利用电化学现场表面增强拉曼光谱技术(SERS)研究了咪唑在锌表面的成膜和缓蚀行为, 讨论了电位和pH值对咪唑分子和金属表面作用的影响. 锌电极上的表面拉曼光谱研究结果表明, 中性溶液中咪唑对锌的缓蚀作用明显, 它通过氮端垂直吸附在锌表面, 从而阻止锌的腐蚀, 其吸附取向不随电位的变化而改变; 在碱性溶液中咪唑和锌的作用较弱, 而且电位变化可以使其吸附取向发生改变, 在较正电位下咪唑以氮端垂直吸附, 在较负电位下以咪唑环倾斜吸附.     

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.     

对巯基苯甲酸的表面增强拉曼光谱

应用表面增强拉曼光谱研究了吸附于粗糙银电极表面的对巯基苯甲酸。对巯基苯甲酸以去质子的形式通过巯基端进行吸附,表面Ag-S键的形成及羧基的结构改变直接影响苯环的电子结构。羧基的振动谱峰均对其质子化较为敏感,其峰强度随pH值的变化表明吸附态对巯基苯甲酸的pKa约为5．9。铜离子可与吸附对巯基苯甲酸形成表面络合物,配位反应与羧基的质子化反应密切相关。     

基于活性金电极上硫代水杨酸自组装单分子层的电化学表面增强拉曼光谱

采用原位电化学表面增强拉曼光谱(EC-SERS)研究了硫代水杨酸(TSA)吸附在活性Au电极表面的自组装单分子层(SAMs).TSA在活性Au表面的化学吸附及不同酸碱度下的TSA浸饰单层膜的SERS光谱,表明随pH值的增加,峰强呈现2个不同的下降阶段.通过EC-SERS考察不同电富集时间和电位的影响,显示在酸性介质和0.7 V及70 s富集时间下,可以获得最大EC-SERS信号,并随着电位负移,信号逐渐减弱,直至基本消失,表明TSA分子在Au表面排布状态会随外加条件的改变而发生变化.通过计算TSA在不同pH值下的分布分数以及探针分子在不同电位下的增强因子(EF),结合SERS和EC-SERS的变化走势对比,得出TSA在活性Au表面自组装形成单分子层/膜的机理,指出由于TSA不同的电化学吸附取向,以及高负电位下的还原/脱附作用,使得Au表面拉曼活性降低,造成EF显著减小,不可逆地失去了SERS的活性.     

电极表面Ag(δ+)-NH_3络合物的表面增强拉曼散射效应

本文采用氧化还原循环处理电极首次得到Ag/0.1mol L~(-1)NH_3+0.1mol L~(-1)NH_4Cl体系中吸附在银电极上氨分子的表面增强拉曼散射(SERS)效应。按氨分子在电极表面上的吸附量为每平方厘米8×10~(15)计算,增加因子为1.2×10~5.谱峰强度及位置随电极电位改变。吸附氨分子的SERS谱与Ag(NH_3)_2~+的正常拉曼光谱类似。本文结果表明电极表面上存在Ag(δ+)络合物,它可能是SERS效应的活性中心,用这个概念可较好地解释本文实验结果。通过谱图分析给出了Ag(δ+)表面络合物的可能结构模式。     

金纳米粒子组装体系中偶联单分子层膜结构的SERS光谱表征与分析

通过分子自组装方法制备4,4′-二硫联吡啶(PySSPy)单分子膜修饰的金电极. 利用所形成的对巯基吡啶自组装单分子膜(SAMs)作为偶联层进行金纳米粒子有序膜的组装. 对该纳米粒子组装体系进行Raman光谱测定, 得到了具有良好信噪比的对巯基吡啶单分子膜的表面增强拉曼散射(SERS)光谱. 在此基础上, 进一步采用电化学现场SERS光谱技术研究了该纳米粒子组装体系的SERS光谱随电位变化的规律. 在该体系稳定的电位范围内表征对巯基吡啶单分子膜的特征谱峰1011与1093 cm^-1、1575与1610 cm^-1以及1206与1215 cm^-1这三对谱峰其强度随着所施加电位的改变呈现出明显的规律性. 分析表明, 偶联单分子层中吡啶环芳香性随着所施加电位的改变而有规律地变化是SERS光谱特征改变的内在原因.     

电位扫描过程中NAD+在银电极上的原位表面增强拉曼光谱

利用共焦激光拉曼系统，原位测定了电位扫描过程中NAD^ 分子在银电极上的表面增强拉曼光谱的变化.通过分析0.4→-0.2→-0.4V电位区间的拉曼光谱的变化，推断由于NAD^ 分子中存在着具有空间旋转自由度的磷酸二酯键，分子中腺嘌呤和烟酰胺两结构单元在银电极上的吸附构型都随电位变化而发生改变.     

Adsorption of enantiomeric and racemic cysteine on a silver electrode--SERS sensitivity to chirality of adsorbed molecules

The adsorption of both (L- and D-) enantiomeric forms of cysteine on the silver electrode surface was studied by surface-enhanced Raman scattering spectroscopy (SERS) as a function of electrode potential and pH value of the solution. It was demonstrated that at potentials more positive than -0.7 V (for pH 3) or -0.8 V (for pH 2 or lower), in acidic environment L-cysteine molecules are adsorbed mainly as P(H) (gauche) conformer, in zwitterionic form with the COO- groups close to the surface. At more negative potentials, NH3+ groups deprotonate at the surface with simultaneous weakening of the interaction of the carboxylic groups with the surface. Spectroscopic evidence for at least partial protonation of the COO- groups at strongly acidic solutions was given by observing the C=O stretching band at frequency lowered by about 30 cm(-1) in comparison with that observed for crystalline cysteine hydrochloride. It points to the considerable enhancement of the strength of hydrogen bonds and may be ascribed to the formation of cyclic L-cysteine dimers at the electrode surface. In neutral and alkaline solutions, adsorbed L-cysteine molecules have deprotonated amino groups at wide potential range. Similar spectroelectrochemical experiments were performed for D-cysteine and for a racemic mixture of D,L-cysteine. As expected, results for D-cysteine were similar to those for L-cysteine. However, for racemic mixture at acidic pH, the spectral effects corresponding to potential-induced transition from adsorbed zwitterions to neutral molecule were considerably smaller. This effect was discussed in terms of stereoselective dimerization of cysteine molecule at the electrode surface.     

Orientation of 6-mercaptopurine SAMs at the silver electrode as studied by Raman mapping and in situ SERS

Self-assembled monolayers (SAMs) of 6-mercaptopurine (6MP) on a silver electrode in acid and alkaline media were investigated by a combination protocol of the SERS technique with Raman mapping, and it was found that the adsorption mode of 6MP SAMs changed with the pH value of the environment. Quantum calculations for the vibrational mode were performed by the BLYP/6-31G method. 6MP was adsorbed on the silver electrode with a tilted orientation via S, N1, and N7 atoms in acid medium, while the SAMs adopted head-on adsorption modes with the S atom and the N1 atom anchoring the silver surface in alkaline medium. However, 6MP SAMs turned to the same upright orientation on the electrode through the S and N7 atoms when either acid or basic solution was removed. Stability of 6MP SAMs was observed by in situ SERS spectroelectrochemical measurements. The results reveal that the desorption potentials of 6MP SAMs formed under acid and alkaline conditions from the Ag electrode were at ca. -1.3 V and -1.6 V vs SCE, respectively.     

乙腈溶液中银电极的表面增强拉曼光谱研究

利用共焦显微拉曼系统研究了非水体系0.1mol·L^-1LiClO4/CH3CN溶液中,乙腈分子在粗糙银和金电极表面的吸附和解离行为。结果表明非水体系中乙腈可在银、金表面发生还原反应,产物CN^-离子与电极表面作用形成的表面配合物可以较宽的电位区间吸附于电极表面。溶液中的微量水、激光照射以及电极电位均对该反应有较大的影响。通过拉曼谱图的比较,得出乙腈分子解离出的CN^-在金电极表面比在银电极表面有更强的吸附作用。     

时间分辨表面增强拉曼光谱(TRSERS)研究硫脲衍生物与ClO4^-的共吸附行为

运用时间分辨表面增强拉曼光谱(TRSERS)结合电位双阶跃的方法, 研究了硫脲衍生物甲基硫脲(MTU)和烯丙基硫脲(ATU)在银电极表面与ClO4^-离子的共吸附行为, SERS强度-时间曲线表明它们各自相应的SERS谱峰强度随电位阶跃的响应速率不同, 离电极表面较近的基团的特征谱峰强度的响应速率较快; MTU以S端且垂直吸附在电极表面,ATU也以S端和表面发生化学吸附, 但整个分子斜躺吸附在电极表面上。     

电化学方法获得具有表面增强拉曼活性镍电极的研究

利用纯电化学手段获得了具有较强表面增强拉曼活性的镍电极, 改进了原有的镍电极表面预处理方法. 结果表明, 在0.5 mol/L的NaClO4溶液中, 结合电化学阶跃技术和循环伏安技术, 可以得到合适的粗糙镍电极; 同时, 还得到了探针分子吡啶在该粗糙镍电极表面随电极电位变化的表面增强拉曼光谱(SERS), 此时谱峰强度获得了极大的增强; 还研究了粗糙镍电极的扫描电子显微镜(SEM)图像, 并估算出其SERS增强因子约为104, 此结果比以前的镍电极表面粗糙方法所能达到的增强因子高一个数量级.     

Voltammetric and surface-enhanced resonance Raman spectroscopic characterization of cytochrome C adsorbed on a 4-mercaptopyridine monolayer on silver electrodes

To combine voltammetric techniques with surface-enhanced resonance Raman scattering (SERRS), cytochrome c (cyt c) was immobilized on a roughened silver electrode chemically modified with a self-assembled monolayer (SAM) of 4-mercaptopyridine (PySH). All measurements were performed on the same electrode in a homemade spectroelectrochemical cell suitable for such applications. Cyt c on a PySH-SAM shows a quasi-reversible, monoelectronic, adsorption-controlled CV response with a formal reduction potential of -0.061 V (vs SCE), which is comparable to the values found for native cyt c adsorbed on different SAMs. SERRS spectra proved that cyt c adsorbed on a PySH monolayer is present in the native conformer (the B1 state). Voltammetric and SERRS experiments at high ionic strength revealed that the interaction between the SAM and the protein is electrostatic in nature. In conclusion, PySH was found to be suitable for adsorption of cyt c at SERRS-active silver surfaces. In comparison with other SAMs, PySH requires less time (10 min vs 12-18 h) to form a long-time durable and reproducible coating on the roughened electrode surface.     

Surface-enhanced Raman scattering study of riboflavin on borohydride-reduced silver colloids: Dependence of concentration, halide anions and pH values

The influences of concentration, halide anions and pH on the surface-enhanced Raman scattering (SERS) of riboflavin adsorbed on borohydride-reduced silver colloids were studied. The optimum concentration for the SERS of riboflavin is 10(-6)mol/L while the SERS enhancement varies for different modes. The addition of 0.2mol/L halide (NaCl, NaBr, and NaI) aqueous solutions, leads to a general decrease of the SERS intensity and a change of spectral profile of riboflavin excited at 514.5nm. Riboflavin interacts with the silver surface possibly through the CO and N-H modes of the uracil ring. The SERS spectra of riboflavin were recorded in the 3.4-11.6 pH range. By analyzing several SERS marker bands, the protonated, deprotonated or the coexistence of both molecular species adsorbed on the colloidal silver particles was proved.     

Surface-enhanced Raman scattering studies on the adsorption of p-nitrobenzoic acid at Au electrode under different potential with ultraviolet excitation

The potential-dependent surface-enhanced Raman spectrum of adsorbed p-nitrobenzoic acid (PNBA) on the roughened Au electrode has been obtained by using ultraviolet (UV) excitation at 325 nm. The surface-enhanced Raman spectra of PNBA intensely changed when the voltage was in the rang of negative value, and the electrode potential at which the resonance (potential of maximum intensity) occurs varied when the vibrational mode changes, indicating that the PNBA molecules were chemisorbed on the roughened Au surface. The charge transfer (CT) mechanism could probably explain the experiment results in the present work.