Cyclic Voltammetric Studies of Ferrocene in Nonaqueous Solvents in the Temperature Range from 248.15 to 298.15 K

In the present work the oxidation of ferrocene, Fe(C₅H₅)₂, to the ferrocenium cation, Fe(C₂H₅)₂ ⁺, was examined in the solvents acetonitrile (ACN), acetone (ACE), N-methylformamide (NMF), N,N-dimethylformamide (DMF), N,N-dimethylacetanide (DMA), 3-pentanone (PEN), dimethyl sulfoxide (DMSO) and dichloromethane (DCM) over the temperature range from 248.15 to 298.15 K using the technique of cyclic voltammetry. The anodic (E _pa) and the cathodic (E _pc) peak potentials, as well as the corresponding anodic (i _pa) and cathodic (i _pc) peak currents, were obtained at different scan rates (0.02, 0.05, 0.08 and 0.10 V ·s^–1). The half-wave potentials (E _1/2) of the Fe(C₂H₅)₂ ⁺/Fe(C₅H₅)₂ couple in the investigated solvent media have been evaluated. The diffusion coefficients (D) have been calculated using the Randles-Sevcik equation. The effects of changing the scan rate, the temperature and properties of the solvent medium such as viscosity and donor number on the electrochemical behavior of ferrocene have been examined.     

普鲁士蓝膜修饰电极循环伏安行为的研究

本文研究普鲁士蓝(PB)膜修饰电极的循环伏安行为,结果表明,膜中电活性中心间的相互作用导致PB膜电极的伏安行为偏离理想表面波.用有限扩散边界模型解释了高电位扫速下膜电极的伏安行为.在含钾离子的电解质溶液中测得PB膜中电荷传输扩散系数为10~(-9)～10~(-11)cm~2/s.     

An Extended Method for the Practical Evaluation of the Standard Rate Constant from Cyclic Voltammetric Data

The Nicholson's treatment for the evaluation of the heterogeneous standard rate constant k⁰ of electron transfer from cyclic voltammetric (CV) data is combined with the Klingler and Kochi method suitable to totally irreversible systems in order to use very large ΔE_p x n values, where n is the number of electrons involved in a simple electron‐transfer process O+n e^??R. An empirical relationship between the dimensionless parameter Ψ=k⁰ [πDnvF/(RT)]^?1/2 and ΔE_p x n which practically replaces the Nicholson's working curve up to about 200 mV is reported.     

循环伏安法研究天青A与dsDNA的相互作用

用循环伏安法研究了染料天青A(AA)与鲱鱼精DNA(dsDNA)在0.20 mol/L pH4.5的HAc-NaAc缓冲溶液中的相互作用。AA在玻碳电极上分别于-0.134 V和-0.082 V(vs.SCE)有一个还原峰和相应的氧化峰。加入dsDNA后,AA的还原峰和氧化峰电流均明显减小,但电子转移系数和电极反应标准速率常数基本不变。AA与dsDNA相互作用生成了一种非电活性的超分子复合物。求得AA与dsDNA复合物的结合比为n(AA)∶n(DNA)=3∶1,结合常数β=2.51×1015。紫外-可见吸收光谱法结果与循环伏安法结果一致。     

Cyclic Voltammetry and Structural Studies of Nitric Oxide Monolayers Adsorbed on Pt(111)

The structural analysis of the adsorption of NO monolayers on Pt(111) from solution has been explored by cyclic voltammetry (CV) and X‐ray photoelectron spectroscopy (XPS) techniques. The monolayers were formed from acid solutions saturated with NO gas as well and from nitrite solutions in sulfuric acid. Results by both techniques indicate a maximum coverage of 0.2 monolayers as well as the presence of NO molecularly adsorbed on the surface with different orientations. The voltammetric oxidation of NO gives rise to two peaks separated in the voltammogram by 50 mV. This value is in agreement with the theoretical value of 9 kJ corresponding to the difference between different adsorption sites. A mechanism for the surface mediated oxidation process from adsorbed NO to NO₂ under potential control is proposed.     

Comparison Between a Charge Transfer Process and an Electrocatalytic Process in Cyclic Voltammetry and Cyclic Voltcoulommetry. Application to the Oxidation of Ferrocyanide at a Ferrocene‐Monolayer Modified Gold Electrode

Ferrocyanide oxidation catalyzed by a ferrocene‐alkylthiolate monolayer at gold electrodes has been investigated by using cyclic voltammetry (CV) and cyclic voltcoulommetry (CVC). The voltammetric current‐potential curves obtained present a stationary sigmoidal feature which points out to a very high rate constant for the chemical step, whereas the charge‐potential curves do not reach an stationary behavior in any case. Simple expressions are presented for the characterization of the CV and CVC curves under Nernstian conditions for the charge transfer step. From these expressions, a value for the chemical rate constant 2.5×10⁴ M^?1 s^?1 has been easily obtained from an anodic plateau of the CV curves or from the linear anodic region of the CVC curves.     

Carbon‐Supported Pt Particles as a Catalyst for Electrooxidation of Methanol and Cyclic Voltammetry Studies Under Acidic Conditions

Electrooxidation of methanol on glassy carbon (GC) electrode modified by optimum carbon supported Pt electrocatalyst (Pt‐C/GC) in acid media is investigated. The catalyst is prepared by ultrasonicating Pt/C powders in aqueous media. The activity of prepared Pt‐C/GC electrode is studied in potential range of 0–1000 mV (versus SCE) by cyclic voltammetry. The results showed that the Pt/C dispersed layer at the surface of glassy carbon electrode, behaves as an electrocatalyst for the oxidation of methanol in acid medium by optimum loading of Pt (0.2 mg cm^?2). The electrochemical properties of prepared electrode are studied under various conditions. However the effect of various parameters in the catalytic enhancement of Pt/C, such as platinum loading, sulfuric acid concentration, different scan rates, different final potentials, and medium temperature are considered and examined.     

Cyclic and linear amidine catalysts for the efficient synthesis of cyclic trithiocarbonates from carbon disulfide and episulfides under mild conditions

Cyclic and linear amidines effectively catalyzed the reaction of carbon disulfide and episulfides under mild conditions, such as ordinary pressure and ambient temperature, to give the corresponding cyclic trithiocarbonates in high yields.     

Cyclic voltammetric studies of heat treated and oxidized carbon fibres in organic and aqueous solutions

Summary Cyclic voltammetry was used to compare the electrochemical behaviour ofPAN-based carbon fibre electrodes in aqueous (differentpH), acetonitrile and methanol solutions. The sets of fibres used were produced at three temperatures and were oxidized with conc. HNO₃ or left nonmodified. The electrode reaction meachanisms probably occurring on the carbon fibre surfaces were analyzed.

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Untersuchung thermisch behandelter und oxydierter Kohlefasern mittels zyklischer Voltammetrie in organische und wässrigen Lösungen

Zusammenfassung Es wurde das elektrochemische Verhalten von Kohlefaserelektroden in wassrigen (verschiedenerpH-werl), acetonitrilischen und methanolischen Lösungen verglichen. Die Kohlefasern aufPAN(Polyacrylnitril)-Basis, die sich voneinander in der Temperatur der termischen Behandlung unterscheiden und nicht oder mit konzentrierter Salpetersäure oxidiert wurden, wurden mittels zyklischer Voltammetrie untersucht. Der wahrscheinliche Verlauf der Elektrodeprozesse auf den Kohlefasernoberflächen wurde analysiert.

     

Tribological Studies on Two Novel Borate Esters with Nitrogen-Containing Heterocyclic and Alkanolamide as Multifunctional Additives in Rapeseed Oil

Borate esters have good load carrying capacity and lubricating properties. However, borate esters are susceptible to hydrolyzation, which limits their applications. To improve the hydrolysis resistance of borate esters, nitrogen-containing heterocyclic and alkanolamide were introduced into their structures. Two novel multifunctional borate esters were synthesized, and their tribological properties were evaluated in rapeseed oil. The two novel borate esters showed superior tribological properties, as well as excellent anti-rust, anti-corrosion, and anti-oxidant properties. During friction, the mixed film containing B₂O₃ and nitrogen-containing organic compounds were formed, iron oxide generated on the worn surface, which were important to anti-wear.     

Cyclic Voltammetric Study of the Oxidation of Catechols in the Presence of Cyanide Ion

Electrochemical oxidation of catechols has been studied in the presence of cyanide ion as nucleophile in aqueous solution, by means of cyclic voltammetry and controlled‐potential coulometry. The results indicate that the participation of catechols in the Michael reaction with cyanide ion to form the corresponding o‐dihydroxybenzonitrile. Based on an EC mechanism, the homogeneous rate constants were estimated by comparing the experimental cyclic voltammetric responses with the digital simulated results.     

吖啶酮类衍生物的光电性质研究

测定了8个吖啶酮类衍生物的紫外吸收光谱、荧光光谱和荧光量子产率,以研究它们的结构与光学性质之间的关系,用循环伏安法测出它们各自的电子势．发现吖啶酮类衍生物都具有较高的电子亲和势,表现出比常用的电子传输材料2-(4-联苯基)-5-(叔丁苯基1—1,3,4-二唑(PBD)更容易被还原的优良电化学性能。     

稀土离子对DNA作用的循环伏安法和光谱法研究

运用循环伏安法，紫外光谱和拉曼光谱等方法研究了Ｅｕ＾３＋，Ｃｅ＾３＋，Ｅｒ＾３＋，Ｓｍ＾３＋，Ｔｂ＾３＋，Ｌａ＾３＋，Ｎｄ＾３＋等稀土金属离子与ＤＮＡ（小牛胸腺）的相互作用，Ｃｅ＾３＋与ＤＮＡ作用后，Ｃｅ＾３＋的ＣＶ曲线的峰电流密度明显降低，且氧化峰降低的程度大于还原峰，Ｃｅ＾３＋的差示ＵＶ曲线呈减色效应，且在２７２ｎｍ处出现新峰，ＤＮＡ的差示ＵＶ曲线呈增色效应；ＤＮＡ的拉曼谱线中８１４ｃｍ＾－１     

Synthesis,Characterization and Theoretical Study of the Chemical Reactivity of New Cyclic Sulfamides Linked to Tetrathiafulvalene

Abstract

The synthesis of the title compounds has been carried out by condensation via a Wittig-type reaction of a pyridinium hexafluorophosphate with a phosphonate ester to give the desired (4-nitrophenyl)tetrathiafulvalene the nitro group of which was reduced to an amino group. Reaction of the amine with chlorosulfonyl isocyanate and subsequently with tert-butyl alcohol gave the corresponding open-chain sulfamide. Cyclization under basic conditions and de-protection led to 2-[4-(4′,5′-dipropyltetrathiafulvalen-4-yl)]phenyl-1,2,6-thiadiazinane 1,1-dioxide. Finally, N-alkylated and N-acylated cyclic sulfamides linked to tetrathiafulvalene were obtained. Their electron donor ability was measured by cyclic voltammetry. A detailed DFT study based on B3LYP/6–31G (d,p) of electronic properties is also presented. The calculated molecular electrostatic potential shows that, the negative charge covers the nitro and sulfamide function, while positive charge is located at the hydrogen atoms of the amine and sulfamide rings. The calculated HOMO and LUMO energy reveals that charge transfer occurs within the molecule. The chemical reactivity parameters reveal that tetrathiafulvalene 1 is highly reactive, which facilitates the desired formation of the cyclic sulfamide. The first hyperpolarizability β_tot shows that compounds 1 and 5 are good candidates as a NLO material.     

Use of Retention Data as the First Step in the Identification of Cyclic Organic Peroxides in Temperature-Programmed Gas Chromatography

Temperature-programmed retention indices for eleven cyclic organic peroxides were determined by gas chromatography on slightly polar 5% biphenyl 95% dimethylpolysiloxane columns (DB-5 and Rtx-5MS) at three heating rates (5, 10, and 20° min⁻¹) from 60 to 300°C, using different chromatographs. Cyclic organic diperoxides and triperoxides had nearly constant retention indices when different heating rates and a short isothermal hold time (5 min) before the programmed increase in temperature were used. The usefulness of temperature-programmed retention indices was shown by using the data to predict the retention times and structures of unknown diperoxides or triperoxides derived from ketones. This is the first step in the identification of unknown cyclic organic peroxides, a process would otherwise require the availability of reference compounds. Revised: 7 and 17 November 2005     

Cyclic voltammograms of iron and C-steels in oxalic acid solutions and investigation of the effect of phenyl phthalimide as corrosion inhibitors

Summary The electrochemical behaviour of Fe and C-steel samples in oxalic acid solutions was studied by the use of cyclic voltammetry. Two peaks were observed; the first one was the anodic peak and the second one an unexpected reductive dissolution peak which could be observed in the cathodic branch of cyclic voltammograms of all electrodes studied. The carbon content was found to increase the active dissolution of steels and to decrease their tendency towards passivation. The inhibitive efficiency of phenyl phthalimide derivatives on the active dissolution of Fe and steel samples in 0.1M oxalic acid were investigated.

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Cyclische Voltammogramme von Eisen und C-Stählen in Oxalsäurelösungen und der Einfluß von Phenylphthalimiden als Korrosionsinhibitoren

Zusammenfassung Das elektrochemische Verhalten von Eisen und C-Stählen in Oxalsäurelösungen wurde mit Hilfe cyclischer Voltammetrie studiert. Dabei treten zwei Signale auf: das anodische Signal sowie ein unerwartetes reduktives Lösungssignal. Letzteres wurde im kathodischen Zweig der cyclischen Voltammogramme aller untersuchten Elektroden gefunden. Der Kohlenstoffgehalt erhöht die aktive Auflösung von Stählen und erniedrigt ihre Tendenz zur Passivierung. Die Inhibitionseffizienz von Phenylphthalimiden für die aktive Auflösung von Eisen und Stahlproben in 0.1M Oxalsäure wurde untersucht.

     

Comparative Studies of the Redox Behaviour and the Antioxidative Activity of Arylnaphthoquinones

Summary.  Comparative studies of redox behaviour and antioxidative activity (AOA) were carried out with two series of arylnaphthoquinone derivatives. For the electrochemical investigations, a voltammetric procedure combined with a glassy carbon electrode was applied. The AOA was examined using the photo-chemiluminometric method with the Photochem^? measuring device according to Popov et al. and the chemical procedure with the radical quencher DPPH (diphenylpicrylhydrazyl). Both the redox potential and the antioxidative activity of the investigated compounds are influenced by their substituents. Compounds with the OH-group at position 3 are easiest to oxidize (E _p = 0.18 V; pH 7.4). The lag phases (AOA) of these compounds are five to ten times greater than those of the strong antioxidants ascorbic acid and Trolox^?. As suggested for other natural compounds, we also found a good correlation between the oxidation potential and the AOA. Therefore, it seems that a good antioxidative activity requires a low redox potential. Corresponding authors. E-mail: wurglics@pharmchem.uni-frankfurt.de Received March 1, 2002; accepted March 28, 2002     

3,6-二氧杂-1,8-辛二硫醇-汞(Ⅱ)配合物修饰碳糊电极的制备及循环伏安行为研究

利用3，6-二氧杂-1，8-辛二硫醇（H2L）和HgCl2反应，得到组成为Hg3L2Cl2的配合物。制备了Hg3L2Cl2修饰的碳糊电极，研究了在1mol／L KCl水溶液中的循环伏安行为。研究结果表明在1mol／L KCl介质中，在0．3～-0．8V（vs．SCE）范围内出现Hg3L2Cl2的还原和L^2-在汞膜表面的吸附，在一0．30—0．30V范围内出现汞膜的氧化还原反应。     

DNA与维生素B2相互作用的电化学研究

研究了维生素 B2 与 DNA在 p H4.5 6条件下相互作用的电化学行为。DNA的存在能导致维生素 B2 氧化还原峰电流降低 ,峰电位基本不变。通过测定 DNA引入前后的一些电化学参数 ,推测维生素 B2 与 DNA在该条件下结合生成了一种非电活性的超分子化合物。针对该类型体系 ,推导出一系列方程求得该超分子化合物的组成为 1∶ 1 ,结合常数β =6.0 2× 1 0