Electronic structural studies of pyrrolidinium-based ionic liquids for electrochemical application

Electrochemical stability and noncovalent interactions escorting the cyclic ammonium-based ionic liquids composed of N-alkyl-substituted N-methyl pyrrolidinium (P_yr1R) (R = methyl, ethyl, propyl, butyl, pentyl, hexyl) cations and four anions hexafluorophosphate (PF₆), tetrafluoroborate (BF₄), bis(trifluoromethylsulfonyl-imide (TFSI), and trifluoromethane sulfonate (TFO) have been analyzed using the density functional theory. Electronic structures, electrochemical window, frontier orbital energy difference (HOMO-LUMO gap), binding energies, vibrational spectra of these ion pairs were characterized. It has been established that ion pair formation is largely reigned by C H⋯F interactions between anionic fluorine for BF₄⁻ and PF₆⁻ anions and C H⋯O interactions between anionic oxygen for TFSI and TFO anions and pyrrolidinic proton, methyl, or alkyl group protons of the cations. The effect of alkyl chain length and pairing anions of the alkyl substituted N-methyl pyrrolidinium-based ionic liquids on the electrochemical window was investigated. The results revealed that the HOMO energy of pairing anions is the key factor to decide the electrochemical window. Further quantification of noncovalent interactions in terms of electrostatic and hydrogen bonding interactions has been brought out employing a novel method with the aid of Mulliken and Merz-Singh-Kollman charges, prevailed in pyrrolidinium-based ionic liquids.     

Pyrrole derivatives for electrochemical coating of metallic medical devices

Electropolymerization of medical devices such as cardiovascular stents may posses advantages including a simple and reproducible process with the ability to control the thickness, adherence, and composition of the coating by the duration and intensity of the applied current, the monomer composition and concentration, the solvent, and the reaction conditions. The properties of the polymer can also be controlled by copolymerization of different monomers, grafting substituents to a functionalized polymer, and by entrapping biomolecules. This article describes the synthesis of a range of pyrrole‐based monomers and their electrocoating onto stainless steel surfaces. N‐substituted pyrrole monomers with C1–C18 alkyl chains and poly (ethylene glycol) chains were synthesized in good yields and purity. Electropolymerization of these monomers provided uniform coatings with different hydrophobicities. Studies now focus on the incorporation of drugs in the coated device for release from the surface. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1658–1667, 2004     

Basic investigations on zeolite application for electrochemical analysis

Basic investigations on the electrochemical behavior of alumosilicate zeolites were conduced in gas atmosphere and aqueous solution using impedance spectroscopy under in situ conditions where "zeolitically" bound water molecules are present in the channel and cage system. Natural stilbite (STI) and heulandite (HEU), zeolites of structure types with the same 4 - 4 = 1 building units, were used for these investigations. At a given temperature, well defined water partial pressures were applied in the gas atmosphere (in situ conditions) and the effect of polar organic molecules on conductivity was investigated. Furthermore, the effect of complete water saturation of the channel system on the Arrhenius type activation energy of conductivity was investigated in aqueous solution in comparison. The ion-exchange behavior of zeolite materials could be monitored under these conditions. These results show that, dependent on the different parameters affecting the zeolite conductivity behavior, they are applicable in the field of electrochemical analysis if these basic results on single crystals are transferable to polycrystalline materials.     

Modular solid-state unit for electrochemical studies

A relatively inexpensive unit based upon solid-state operational amplifiers is described; its modular design makes it an extremely versatile instrument for many electrochemical techniques, e.g., normal direct current polarography and linear sweep voltammetry, cyclic voltammetry, alternating current polarography, and coulometry and electrolysis at controlled electrode potential. It can be readily adapted to many other functions.     

十五种氯灭酸金属盐的研究

氯灭酸[N-(间氯苯基)-邻氨基苯甲酸]是我国首先合成并筛选出来的解热消炎镇痛药,临床效果较好,但有不少副作用.近年来的无机药物研究表明,金属配合物与人体的关系十分密切.我们曾制出十六种氯灭酸的稀土盐,其毒性比相应的氯化物小.其他金属的氯灭酸盐尚未见报道.本文在水中以氯灭酸钠(以NaA表示)与Mg(Ⅱ),Ca(Ⅱ),Sr(Ⅱ),Ba(Ⅱ),In(Ⅱ),Tl(I),Mn(Ⅱ),Fe(Ⅲ),Co(Ⅱ),Ni(Ⅱ),Cu(Ⅱ),Zn(Ⅱ),Ag(Ⅰ),Cd(Ⅱ),Pb(Ⅱ)等金属离子制备出十五种氯灭酸金属盐,测定了它们的化学组成,UV,IR,摩尔电导率及热谱,其结果汇总于表1及表2.     

Kinetics and electrochemical studies on superoxide

Rate constants for the reaction of superoxide O^- ₂ with various substrates were obtained through stationary electrode polarography theory and technique. In solvent acetonitrile, the substrate and the rate constants of the reaction O^- ₂ + AH^{- k2}Product, are, AH = isopropanol (k₂ < 0.01 M^-1 s^-1); ethanol (k₂ = 1.42 × 10² M^-1 s^-1); methanol (k₂ = 1.1 × 10⁷ M^-1 s^-1), H₂O (k₂ = 1.0 × 10⁵ M^-1 s^-1). In MeCN, O^-2 was found to be rather unreactive towards glucose and acetone but it reacts with fructose and sucrose catalytically. However, in DMF2, O^- ₂reacts with glucose and fructose with k2 order of 105 M-1 s-1. The mechanism of the reaction of O^- ₂ with the substrates (AH) is proposed as O^- ₃ + AH k₂O, AH^k2 _k-1 k [O₂H + AH]^-, _k-2O₂H + A^- with k₁ = 10⁹ M^-1 s^-1 and k^-1 = 10⁸ -10⁹ s^-1. With these values of k_-1 and k₁, k k₂(obs). The reversible E_1/2 for O₂ + e O^- ₂ in various solvents: MeCN, acetone, isopropanol, methanol, H₂O were obtained either directly from the reversible voltammogram or from experimental voltammograms and the rate constants obtained (as above) using stationary electrode polargraphy theory; E_1/2 being -0.82 (MeCN),-0.85 (acetone),-0.72 (isopropanol);-0.66 (MeOH),-0.56 (H2O) vs SCE.     

A general-purpose minicomputer system for electrochemical studies

A software system (SYS) is described for a 16-bit minicomputer interfaced to a potentiostat and electrochemical cells, as well as various display and signal devices. The software controls the functions common to all electrochemical experiments, such as applying cell voltage, timing, sampling signals, displaying these on graphic devices, and smoothing data; it also loads specific user programs into core, for experiments requiring these functions. In this way, a new experiment can quickly be programmed and running; the software also contains some debugging aids. While the system described is specific to the minicomputer used, its general structure should be capable of implementation on any mini- or micro-computer.     

Zn nanosheets:An earth-abundant metallic catalyst for efficient electrochemical ammonia synthesis

Ammonia(NH₃),a critical raw material for various industrial chemicals,is also recognized as a clean and efficient energy carrier for the future energy economy[1].However,the industrial-scale production of NH₃ strongly relies on the Haber-Bosch process,which involves massive fuel consumption and enormous greenhouse gas emissions[2].Therefore,there is an urgent need to develop sustainable and energy-saving alternative routes for artificial NH3 production.     

An original electrochemical method for assembling multilayers of terpyridine-based metallic complexes on a gold surface

A new method based on the electrochemical oxidation of thiols was used to easily generate multilayer assemblies of coordination complexes on a gold surface. For this purpose, two complexes bearing two anchoring groups for surface attachment have been prepared: [Ru(tpySH)(2)](2+) (1) and [Fe(tpySH)(2)](2+) (2) (tpySH = 4'-(2-(p-phenoxy)ethanethiol)-2,2':6',2″-terpyridine). Cyclic voltammetry of 1 in CH(3)CN exhibits two successive oxidation processes. The first is irreversible and attributed to the oxidation of the thiol substituents, whereas the second is reversible and corresponds to the 1 e(-) metal-centered oxidation. In the case of 2 both processes are superimposed. Monolayers of 1 or 2 have been formed on gold electrodes by spontaneous adsorption from micromolar solutions of the complexes in CH(3)CN. SAMs (self-assembled monolayers) exhibit redox behavior similar to the complexes in solution. The high surface coverage value obtained (Γ = 6 × 10(-10) and 4 × 10(-10) mol cm(-2) for 1 and 2, respectively) is consistent with a vertical orientation for the complexes; thus, one thiol is bound to the gold electrode, with the second unreacted thiol moiety exposed to the outer surface. Successive cyclic voltammetry induced a layer-by-layer nanostructural growth at the surface of the SAMs, and this is presumably due to the electrochemical formation of disulfide bonds, where the thiol moieties play a double role of both an anchoring group and an electroactive coupling agent. The conditions of the deposition are studied in detail. Modified electrodes containing both 1 and 2 alternatively can be easily prepared following this new approach. The film proved to be stable, displaying a similar current/voltage response for more than 10 repeating cycles in oxidation up to 0.97 V vs Ag/AgNO(3) (10(-2) M).     

System for electrochemical studies with a four-electrode potentiostat

A four-electrode potentiostat and a system for electrochemical studies are described. The system is suitale for studies of an interface separating immiscible elecrolyte solutions by voltammetric, chronoamperometric and polarographric methods. The described systems are based on integrated operational amplifiers.     

Synthesis,characterizations, and electrochemical studies of ZnO/reduced graphene oxide nanohybrids for supercapacitor application

Herein the present article reports the fabrication of ZnO/reduced graphene oxide (ZnG) nanohybrid following a reduction-based process using a non-hazardous material, i.e., ascorbic acid. The morphology, structure, and bonding in the nanohybrid were analyzed using different techniques. Atomic force microscopy and scanning electron microscopy images show spherical particles of ZnO distributed over reduced graphene oxide (rGO). The X-ray diffraction analysis gives calculated values of crystallite size for ZnO as 15.62 nm. The successful incorporation of ZnO nanoparticles into rGO was confirmed using energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analyses. The electrochemical studies were performed using an electrolyte (0.5 M H₂SO₄). The calculated value of specific capacitance for the nanohybrid was 345 Fg^-1, which was found to be almost double as compared to that of rGO, which is having a value of only 190.5 Fg^-1 at the same scan rate. The nanohybrid also showed excellent capacitance retention after 1,000 cycles.     

Complex rate constant for an electrochemical system involving an adsorbed intermediate

Two different methods of obtaining the impedance of a system involving an electrochemical reaction with an adsorbed intermediate are compared. The earlier method combines in parallel an impedance derived separately for the overall reaction with that for the rest of the system. It is appropriate for a fully supported electrolyte system but seems much less applicable to the unsupported situation. In contrast, the method derived and discussed herein involves complex reaction rate constants which may be directly incorporated in expressions for the total system impedance. This method may, therefore, be applied to either supported or unsupported situations. Several specific cases of the general complex rate constant results are discussed, particularly, various frequency dependencies possible. The overall small-signal impedance may be inductive in some parts of the frequency range and the low frequency limiting differential resistance negative, zero, or positive under various conditions.     

基于多肽的电化学传感器在蛋白质检测中应用的研究进展

生物体内的细胞通常会分泌各种各样的蛋白质,这些蛋白质在生物体中发挥着重要作用,尤其是可被用于诊断各种疾病的发生和发展。多肽具有良好选择性、空间适应能力和识别灵活的特点,可与不同类型的蛋白分子形成非共价键,用于蛋白质的生物检测。将多肽与电化学生物传感器结合用于蛋白质的广谱检测具有良好的发展前景。本文介绍了多肽修饰的电化学传感器在不同蛋白质检测方面的研究进展,分析了待测蛋白质的不同对多肽修饰的电化学传感器分类的影响及其优缺点,提出了基于多肽的电化学传感器在不同蛋白质检测中存在的问题,并展望了其未来发展。     

High-yield bamboo-shaped carbon nanotubes from cresol for electrochemical application

High-yield bamboo-shaped carbon nanotubes (BCNTs) have been produced by using cresol as the precursor, for the first time and there are almost no straight CNTs or amorphous carbon found in the product: the role of cresol in promoting the growth of BCNTs is discussed; improved cycle stability and electric conductivity of the BCNTs as an anode additive in a lithium ion battery are achieved.     

Nanoporous Ge coated by Au nanoparticles for electrochemical application

We present an innovative device based on a nanoporous Ge electrode decorated by gold nanoparticles (AuNPs). A study aimed at obtaining the best AuNP deposition conditions, which allow the decoration of Ge walls with AuNPs, avoiding particles aggregation is reported.The performance of the electrode has been evaluated by the electrocatalytic reduction of iodoethane in acetonitrile solution, a model reaction in organic electrocatalysis.     

Carbon nanomaterials and metallic nanoparticles-incorporated electrochemical sensors for small metabolites: Detection methodologies and applications

Detection of small metabolite biomarkers at different concentrations could be powerfully used for disease diagnosis and progression. To enhance detection capabilities, nanomaterials possessing excellent optical and electrochemical properties have been integrated into a wide range of sensing or detection platforms. This review will highlight recent developments in creating electrochemical sensors alongside biosensors using carbon nanomaterials and metallic nanoparticles that target small metabolites. Moreover, electrochemical sensors having different detection strategies toward metabolites (such as amino acids, amino acid–derived neurotransmitters, vitamins, adenosine triphosphate, and purine derivatives) will be discussed. Finally, certain challenging issues and future aspects of nanomaterials-integrated electrochemical sensors for small metabolites will be discussed.     

An improved solution-tight electrode holder for variable temperature electrochemical studies

With the help of oscillopolarographic methods, the formation of additional adsorption-desorption peaks or incisions in the curves i=f(E) and dE/dt=f(E) was observed for saturated solutions of higher fatty acids in 1 M H₂SO₄. In virtue of the analysis of the first and second polarization cycle, it was found, that, a previous electrode polarization to the adsorption potentials was necessary, if the additional peaks were to be formed. A supposition was made, that the additional peaks originate in the desorption and adsorption of the dimerized molecules of the acids.     

Novel intense metallic monolith for automotive applications: Experimental versus numerical studies

Three-dimensional numerical analysis for simultaneously developing fluid flow and heat transfer through triangular and sinusoidal channels is simulated in this paper. ANSYS FLUENT 12 was used for simulations. Numerical results were compared with experimental ones for the same channels dimensions. The research was conducted to verify that very short metallic monoliths could be applied to engine pre-turbo catalytic converters. It was shown that short monoliths have high potential to reduce HC/CO emissions due to higher temperatures and flow velocities in front of the turbocharger, resulting in increased heat and mass transfer and reaction kinetics accompanied with reduced flow resistance.     

Rapid-scan time-resolved FT-IR spectroelectrochemistry studies on the electrochemical redox process

The electron transfer to or from molecules containing multiple redox centers has been extensively investigated. Rapid scan time-resolved FT-IR-RAS spectroelectrochemistry was used to investigate the electron-transfer mechanism in this report. The electron transfer of two typical compounds, 1,4-benzoquinone and 1,4-bis(2-ferrocenylvinyl)benzene, was examined with this method. Although the two compounds show two-electron transfer in the redox process, 1,4-benzoquinone exhibits two single electron waves while 1,4-bis(2-ferrocenylvinyl)benzene exhibits a single wave in cyclic voltammetric experiments. The IR absorption of the intermediate, BQ*- and p-(Fc-CH=CH)+2-benzene, at 1506 and 1589 cm(-1), respectively, appeared and disappeared on the experimental time scale in the oxidation and reduction process was observed. In the oxidation process of the p-(Fc-CH=CH)2-benzene molecule, one Fc was oxidated to Fc+ first and the electron-withdrawing ability of Fc+ was stronger than that of Fc, which resulted in the D-pi-A structure and the band at 1589 cm(-1) becoming visible. Then as the oxidation continues, the other Fc was oxidated to Fc+ too, which resulted in the reforming of the symmetry of the benzene ring A-pi-A, so the band at 1589 cm(-1) disappeared. Similar phenomenon can be elucidated in the reduction process but the configuration type changed from A-pi-A to D-pi-A and finally to D-pi-D. Hence, not only 1,4-benzoquinone but also 1,4-bis(2-ferrocenylvinyl)benzene show two consecutive one-electron processes. In addition, it is observed that the existing time of the electrochemical reaction intermediate (BQ*- and p-(Fc-CH=CH)+2-benzene) is prolonged at low temperatures due to slow reaction kinetics.