Electrochemical Behavior and Determination of L‐Tyrosine at Single‐walled Carbon Nanotubes Modified Glassy Carbon Electrode

Based on single‐walled carbon nanotubes (SWCNTs) modified glassy carbon electrode (GCE/SWCNTs), a novel method was presented for the determination of L ‐tyrosine. The GCE/SWCNTs exhibited remarkable catalytic and enhanced effects on the oxidation of L ‐tyrosine. In 0.10 mol/L citric acid‐sodium citrate buffer solution, the oxidation potential of L ‐tyrosine shifted negatively from +1.23 V at bare GCE to +0.76 V at GCE/SWCNTs. Under the optimized experimental conditions, the linear range of the modified electrode to the concentration of L ‐tyrosine was 5.0×10^?6–2.0×10^?5 mol/L (R₁=0.9952) and 2.7×10^?5–2.6×10^?4 mol/L (R₂=0.9998) with a detection limit of 9.3×10^?8 mol/L. The kinetic parameters such as α (charge transfer coefficient) and D (diffusion coefficient) were evaluated to be 0.66, 9.82×10^?5 cm² s^?1, respectively. And the electrochemical mechanism of L ‐tyrosine was also discussed.     

氢气在单壁碳纳米管束的吸附的密度泛函研究

作者利用密度泛函理论（DFT）计算了氢气在单壁碳纳米管束（SWNTs)中管内 和管间的吸附。考察了温度,孔径以及压力对吸附的分子数密度,重量百分比,单 位体积储存能力以及超额吸附量的影响。DFT计算发现,较大的孔径有利于氢气在 SWNTs中的吸附且氢气在管隙中的吸附不可忽略。计算表明在77 K和6 MPa时,氢气 在2.719 mm的SWNTs的总的吸附的重量百分比分别可达到13.2 wt%,这约是美国能 源部（DOE）目标值的两倍,而单位体积储存能力在DOE目标值附近,而在300 K和 6 MPa时,氢气在2.719 nm的SWNTs的总的吸附的重量百分比仅为1.5 wt%。通过实 验结果与计算结果的比较表明,密度泛函理论的计算结果支持SWNTs有较高的吸附 储氢能力的实验结论。     

Electrochemical DNA Sensing at Single‐walled Carbon Nanotubes Chemically Assembled on Gold Surfaces

An electrochemical DNA sensor was constructed using single‐walled carbon nanotubes (SWNTs) attached to a self‐assembled monolayer of 11‐amino‐1‐undecanethiol on a gold surface. The voltammetric peak of methylene blue (MB), which interacts with the DNA guanine bases specifically, was used to follow the DNA hybridization process. After DNA hybridization with its complementary DNA strand, the MB electrochemical signal response decreased and the change in MB signal response was used as the basis for the electrochemical sensing of DNA hybridization. The as described DNA sensor demonstrated to have good stability, selectivity, a linear response over the DNA concentration range from 100 to 1,000 nM and a limit of detection of 7.24 nM.     

聚碳酸酯修饰多壁碳纳米管的制备和表征

为了制备聚合物/碳纳米管复合物,采用聚碳酸酯修饰了多壁碳纳米管。选择聚碳酸环氧丙烷己内酯,聚碳酸亚丁酯己内酯和聚碳酸亚丙酯马来酸酐酯三种聚碳酸酯修饰多壁碳纳米管,仅仅碳酸环氧丙烷己内酯修饰的碳纳米管复合物可分离得到可溶解性产物。分别采用红外光谱、扫描电镜和透射电镜表征了碳纳米管的表面修饰基团及形貌。热重分析表明,可溶解聚碳酸环氧丙烷己内酯修饰多壁碳纳米管相对接枝了较多的聚合物,因此促进了碳纳米管的溶解性,可能是因为聚碳酸环氧丙烷己内酯具有较多的端羟基提高了修饰接枝效果。可溶解聚碳酸环氧丙烷己内酯修饰多壁碳纳米管接枝了生物活性的部分,并具有一定溶解性,在药物载体领域将具有潜在用途。     

微波辅助有机过氧化物功能化修饰单壁碳纳米管

本文报道了微波辅助下,利用过氧化月桂酰分解得到的十一烷基,化学功能化修饰单壁碳纳米管。这种快速、高效的方法将反应时间缩短至10分钟,并得到了比传统回流方法具有更高接枝率的产物。利用傅立叶变换红外光谱(FT-IR),热失重分析(TGA),拉曼光谱,探究了不同的反应时间和微波功率对单壁碳纳米管的接枝率的影响。结果表明：过长的反应时间会导致部分的去功能化的发生,而过高的微波功率(大于900瓦),则会将单壁碳纳米管上起初键连上的十一烷基剥落下来。分散性照片和高分辨率透射电子显微镜(HRTEM)照片显示出,功能化后的单壁碳纳米管与原始的碳管相比,在有机溶剂中的分散性有了明显的提高。     

Electrocatalytic Oxidation of Diethylaminoethanethiol and Hydrazine at Single‐walled Carbon Nanotubes Modified with Prussian Blue Nanoparticles

In this work, edged plane pyrolytic graphite electrode EPPGE was modified with functionalised single‐walled carbon nanotubes and Prussian blue nanoparticles (PB). The modified electrode was characterised by techniques such as TEM, FTIR, XPS, EDX and cyclic voltammetry. The EPPGE‐SWCNT‐PB platform exhibited enhanced electron transport and catalytic efficiency towards the oxidation of Diethylaminoethanethiol (DEAET) and hydrazine compared with the other electrodes studied. The EPPGE‐SWCNT‐PB showed good electrochemical stability in the analytical solution, showing limit of detection in the micromolar range and catalytic rate constant of 3.71×10⁶ and 7.56×10⁶ cm³ mol^?1 s^?1 for DEAET and hydrazine respectively. The adsorption properties of these analytes that impact on their detection at the SWCNT‐PB film modified electrode were evaluated and discussed.     

NH3在硼纳米管表面吸附的密度泛函理论研究

利用密度泛函理论研究了NH₃在完整和含有缺陷的硼纳米管上的吸附行为以及相关电子性质. 计算结果表明, 对于α硼纳米管, 在不同的直径和手性条件下, NH₃均倾向于吸附在配位数为6的顶位上. 电子结构计算结果表明, NH₃能够吸附在纳米管表面主要是由于N和B原子产生了较强的相互作用. 表明硼纳米管是一种潜在的NH₃气气敏材料.     

Single‐Walled Carbon Nanotubes on Tungsten Wires: A New Class of Microelectrochemical Sensors

This paper reports the fabrication and the outstanding performance characteristics of novel microelectrodes consisting of tungsten (W) wires coated with homogeneous layers of single‐walled C nanotubes (SWNT). A series of studies using cyclic voltammetry indicate that the SWNT‐modified W electrodes possess interesting electrochemical features. In fact, they are able to catalyse electron transfer reactions involving a series of inorganic and biological molecules. These electrodes are characterized by a fast electron transfer, a wide working potential window, and a low background current. Moreover they demonstrate excellent reproducibility, good stability in various chemical media, and very high sensitivity towards a series of inorganic and organic compounds. The SWNT modified microelectrodes have been tested for the capacity to electrochemically detect ferrocene monocarboxylic acid and potassium hexacyanoferrate as well of a series of interesting biological molecules which include catechol, caffeic acid, DOPAC, ascorbic acid, L ‐tyrosine, acetaminophen, guanine, uric acid, and the neurotransmitters dopamine, epinephrine, and serotonin (5‐HT) hydrochloride. The advantages of the SWNT‐modified W electrodes are illustrated by comparing their analytical performance with that of conventional electrodes.     

A New Amperometric Hydrazine Sensor Based on Prussian Blue/Single‐walled Carbon Nanotube Nanocomposites

A slow reaction process has been successfully used to synthesize Prussian blue/single‐walled carbon nanotubes (PB/SWNTs) nanocomposites. Electrochemical and surface characterization by cyclic voltammetry (CV), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV‐vis absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy and X‐ray diffraction (XRD) confirmed the presence of PB nanocrystallites on SWNTs. PB/SWNTs modified glassy carbon electrode (GCE) exhibits efficient electron transfer ability and high electrochemical response towards hydrazine. The fabricated hydrazine sensor showed a wide linear range of 2.0×10^?6–6.0×10^?3 M with a response time less than 4 s and a detection limit of 0.5 μM. PB/SWNTs modified electrochemical sensors are promising candidates for cost‐effective in the hydrazine assays.     

Interaction of Mitomycin C with DNA Immobilized onto Single‐walled Carbon Nanotube/Polymer Modified Pencil Graphite Electrode

The electrochemical investigation of the interaction between the anticancer drug mitomycin C (MC) and DNA was described using a single‐walled carbon nanotube (SWCNT)/poly(vinylferrocenium) (PVF⁺) modified pencil graphite electrode (PGE). The electrochemical oxidation signals of guanine were monitored before and after the interaction between MC and DNA by using differential pulse voltammetry. The effects of DNA and MC concentration and MC interaction time were examined based on the electrode response. Cyclic voltammetry and electrochemical impedance spectroscopy were used for the characterization of SWCNT/PVF⁺ modified and PVF⁺ modified PGEs. The detection limit corresponded to 625 ng/mL for MC using calf thymus double‐stranded DNA immobilized SWCNT/PVF⁺ modified PGE.     

Electrooxidation of Chlorophenols Catalyzed by Nickel Octadecylphthalocyanine Adsorbed on Single‐Walled Carbon Nanotubes

We described the synthesis of nickel octadecylphthalocyanine (NiPc(C₁₀H₂₁)₈), followed by its adsorption on single‐walled carbon nanotubes (SWCNT) to form SWCNT‐NiPc(C₁₀H₂₁)₈ conjugates. SWCNT‐NiPc(C₁₀H₂₁)₈ was used to modify a glassy carbon electrode (GCE) and for the electrooxidation of 4‐chlorophenol and 2,4‐dichlorophenol. The SWCNT and NiPc(C₁₀H₂₁)₈ have a synergistic effect on each other in terms of improving electrocatalysis for the detection of chlorophenols. The stability of the electrode improved in the presence of NiPc(C₁₀H₂₁)₈ or NiPc compared to the bare GCE. The presence of SWCNT improves the electrocatalytic behaviour of NiPc(C₁₀H₂₁)₈ but not of unsubstituted NiPc. All modified electrodes showed improved stability towards the detection of 2,4‐dichlorophenol. The best stability for 4‐CP detection was observed in the presence of SWCNT for NiPc(C₁₀H₂₁)₈.     

Voltammetric Determination of L‐Dopa on Poly(3,4‐ethylenedioxythiophene)‐Single‐Walled Carbon Nanotube Composite Modified Microelectrodes

In the present communication, it is shown that platinum microelectrodes electrochemically coated with a composite of poly(3,4‐)ethylenedioxythiophene and single‐walled carbon nanotubes (PEDOT/SWNT) enable determinations of 3,4‐dihydroxy‐L ‐phenylalaines (L ‐dopa) in neutral phosphate buffer solutions containing an excess of ascorbic acid. The interpenetrated networked nanostructure of the composite was characterized by scanning electron microscope (SEM) and Raman spectroscopy. It is shown that the presence of the composite gives rise to an increase in the electroactive area of an order of magnitude in compared to the area for the bare microelectrodes. The composite film‐coated microelectrode, which yielded reversible cyclic voltammograms for the ferro/ferricyanide redox couple for scan rates between 0.01 and 0.10 V s^?1, also gave rise to two well‐resolved oxidation peaks for L ‐dopa and ascorbic acid (AA). The latter effect, which was not seen in the absence of the composite, enabled differential pulse voltammetric determinations of L ‐dopa in the concentration range between 0.1 to 20 μM with a detection limit of 100 nM.     

椅型碳纳米管吸附氢原子电子结构的密度泛函研究

采用密度泛函方法对氢原子在(5,5)椅型碳纳米管上的吸附进行了研究, 分别考察了氢原子覆盖度为5%和10%时的构型和吸附能. 研究结果表明, H原子吸附在管外壁要比管内壁能量上更为有利, 同时第二个H原子倾向于吸附在前一个H原子的吸附位置邻近的碳原子上. 由能带计算结果得知, 吸附一个H原子时, 椅型碳纳米管将由导体转变为半导体; 当第二个H原子处在偶数位时, 纳米管仍保持较好的导电性能, 而吸附在奇数位时将使管的传输能力减弱. 本文进一步通过分析纳米管(共轭体系的分布情况对管传输性质的变化进行解释.     

Electrocatalysis of 2‐Diethylaminoethanethiol at Nickel Nanoparticle‐Electrodecorated Single‐Walled Carbon Nanotube Platform: An Adsorption‐Controlled Electrode Process

Electrocatalytic behavior of diethylaminoethanethiol (DEAET) at nickel nanoparticle‐electrodecorated single‐walled carbon nanotube (SWCNT‐Ni) platform is presented. We demonstrate that the electrocatalytic response is governed by adsorption‐controlled kinetics and that adsorptive stripping voltammetry (AdsSV) represents a viable analytical voltammetry for the sensitive detection of this hydrolysis product of a V‐type nerve agent.     

The Heterogeneity of Multiwalled and Single‐Walled Carbon Nanotubes: Iron Oxide Impurities Can Catalyze the Electrochemical Oxidation of Glucose

It is well established that the heterogeneity of carbon nanotubes must be determined before the origin of the electrochemical performance can be attributed. Recently it has been diligently reported that for the case of multiwalled carbon nanotube modified electrodes, copper oxide impurities are responsible for the electrochemical activity facilitating a nonenzymatic sensing strategy towards glucose. We have explored both commercially available multiwalled and single‐walled carbon nanotubes for the sensing of glucose and find that iron oxide impurities remaining from the fabrication process are the electroactive sites facilitating the nonenzymatic detection of glucose. Given that the multiwalled carbon nanotubes in this work are purchased from the same leading supplier as that used recently, discrepancies in the fabrication process exist which clearly has implications in the commercialization of electrochemical sensors based on multiwalled carbon nanotubes.     

Direct Electrochemistry of Hemoglobin on Single‐Walled Carbon Nanotubes Modified Carbon Ionic Liquid Electrode and Its Electrocatalysis

In this article we report on the fabrication of a carbon ionic liquid electrode (CILE) by using a room temperature ionic liquid of 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIMPF₆) as binder. It was further modified by single‐walled carbon nanotubes (SWCNTs) to get a SWCNTs modified CILE denoted as SWCNTs/CILE. The redox protein of hemoglobin (Hb) was further immobilized on the surface of SWCNTs/CILE with the help of Nafion film. UV‐vis and FT‐IR spectra indicated that the immobilized Hb retained its native conformation in the composite film. The direct electrochemistry of Hb on the SWCNTs/CILE was carefully studied in pH 7.0 phosphate buffer solution (PBS). Cyclic voltammetric results indicated that a pair of well‐defined and quasireversible voltammetric peaks of Hb heme Fe(III)/Fe(II) was obtained with the formal potential (E°') at ?0.306 V (vs. SCE). The electrochemical parameters such as the electron transfer coefficient (α), the electron transfer number (n) and the apparent heterogeneous electron transfer rate constant (k_s) were calculated as 0.34, 0.989 and 0.538 s^?1, respectively. The fabricated Hb modified electrode showed good electrocatalytic ability to the reduction of trichloroacetic acid (TCA) in the concentration range from 20.0 to 150.0 mmol/L with the detection limit of 10.0 mmol/L (3σ).     

Single‐Walled Carbon Nanotubes Modified Gold Electrodes as an Impedimetric DNA Sensor

A gold surface modified with a self‐assembled monolayer of 11‐amino‐1‐undecanethiol (AUT) was used for the covalent immobilization of oxidized single‐walled carbon nanotubes (SWNTs). The as‐described SWNTs‐modified substrate was subsequently used to attach single‐stranded deoxyribonucleic acid (ssDNA) used as a substrate for DNA hybridization. Electrochemical impedance spectroscopy measurements were performed to follow the DNA hybridization process by using the redox couple [Fe(CN)₆]^3−/4− as a marker ion. Specifically, changes in charge transfer resistance obtained from the Nyquist plots were used as the sensing parameter of DNA hybridization. The substrate sensitivity towards changes in target DNA concentration, its selectivity toward different DNA sequences and its reusability are successfully demonstrated in this report.     

DFT Studies of Ag‐Loading Intrinsic and Functionalized Single‐Walled Carbon Nanotubes

The first principles study was performed on the stability of Ag adsorbed on the internal walls of single‐walled carbon nanotube (SWCNT) and loaded on acid modified SWCNT. The calculation results show that Ag can be adsorbed stably on the internal walls of SWCNT. With the increase of SWCNT diameter, the adsorption energy increases in a certain range. Ag can also be loaded on the modified SWCNT surface in the form of COOAg and OAg groups, and COOAg group is more stable than OAg group. For either the adsorption on the inner SWCNT or the load on the modified SWCNT surface, only a small proportion of the Ag ions can be stably bonded to the walls of SWCNT.     

Palladium‐Catalyzed Desymmetrization of Silacyclobutanes with Alkynes to Silicon‐Stereogenic Silanes: A Density Functional Theory Study

The palladium‐catalyzed desymmetrization of silacyclobutanes using electron‐deficient alkynes proceeds with high enantioselectivity in the presence of a chiral P ligand; this provides a facile approach for the synthesis of novel silicon‐stereogenic silanes. In this work, we used hybrid density functional theory (DFT) to elucidate the mechanism of the palladium‐catalyzed desymmetrization of silacyclobutanes with dimethyl acetylenedicarboxylate. Full catalytic cycle including two different initiation modes that were proposed to be a possible initial step to the formation of the 1‐pallada‐2‐silacyclopentane/alkyne intermediate—the oxidative addition of the palladium complex to the silacyclobutane Si?C bond (cycle MA) or coordination of the Pd⁰ complex with the alkyne C≡C bond (cycle MB)—have been studied. It was found that the ring‐expansion reaction began with cycle MB is energetically more favorable. The formation of a seven‐membered metallocyclic Pd^II intermediate was found to be the rate‐determining step, whereas the enantioselectivity‐determining step, oxidative addition of silacyclobutane to the three‐membered metallocyclic Pd^II intermediate, was found to be quite sensitive to the steric repulsion between the chiral ligand and silacyclobutane.