Electrochemical evidence for catalytic water oxidation mediated by a high-valent cobalt complex

The pH-dependent electrochemical behavior for a Co(II) complex, [Co(Py5)(OH(2))](ClO(4))(2) (1; Py5 = 2,6-(bis(bis-2-pyridyl)methoxymethane)pyridine), indicates consecutive (proton-coupled) oxidation steps furnish a Co(IV) species that catalyzes the oxidation of water in basic media.     

Electrochemical hydrogen evolution over MoO3 nanowires produced by microwave-assisted hydrothermal reaction

Molybdenum trioxide (MoO₃) nanowire with unprecedentedly high aspect ratios (>200) and good crystallinity was prepared via decomposition of (NH₄)₆Mo₇O₂₄·4H₂O under a microwave-assisted hydrothermal (MH) process. The nanowire was orthorhombic MoO₃ with 50 nm in diameter and 10–12 μm in length. The conventional hydrothermal (CH) reaction required higher temperature and longer reaction times to produce one-dimensional MoO₃, yet its quality was lower. In the electrochemical hydrogen evolution reaction in a H₂SO₄ solution, MoO₃ nanowire from MH process showed much higher electrocatalytic activity than MoO₃ prepared from CH method and commercial bulk MoO₃ particles. The facile vectorial electron transport along the nanowire axis was considered to be responsible for the excellent electrocatalytic activity of the MH–MoO₃ nanowire.     

ESR evidence for main-chain scission produced by mechanical fracture of polymers at low temperature

ESR spectra have been observed from several polymers (polyethylene, polypropylene, polymethylmethacrylate, polytetrafluoroethylene, and polybutadiene) which were mechanically fractured in vacuum at 77°K. The spectra permit identification of the free radicals produced in chain scission. It has been demonstrated for the polymers of the type such as polypropylene and poly(methyl methacrylate), that the mechanical fracture produces two different scission radicals in pairs, namely, The results indicate convincingly that microscopic scission of polymer chains is caused by macroscopic destruction of polymeric material. The critical molecular size for mechanical rupture of polyethylene chains was experimentally determined to be a degree of polymerization between 70 and 100. This size agrees fairly well with the value predicted from a theoretical model.     

Electrochemical study of Cu2O/CuO composite coating produced by annealing and electrochemical methods

The electrochemical behavior of a copper oxide electrode produced by annealing and electrochemical methods was studied in an acetonitrile solvent by means of the cyclic voltammetry method. The presence of different peaks of oxidation and reduction produced by repeating the potential scans, numerous variations in the current, and shifts of peak potentials in consecutive cycles have been justified. Voltammograms proved that various oxidation species can be produced in solid-deposited forms of Cu₂O_s and CuO_s and dissolved forms of Cu(II)_sol and Cu(I)_sol ions. The experimental results indicated that higher amounts of Cu₂O_s than CuO_s can be produced in the process of copper electrode annealing. Also, the nature of copper species is responsible for different peak currents in the cyclic voltammograms, characterized by UV–Vis and XRD spectrometric methods.

     

Electrochemical properties of LiMn2O4 films produced by combustion reaction

Lithium manganese oxide powders were prepared via combustion reaction. Structural characterization of the powder using X-ray diffraction and scanning electron microscopy confirmed the formation of a LiMn₂O₄ nanosized powder. LiMn₂O₄ films were prepared by spin coating using 80 wt% of oxide, 15 wt% of polyaniline (PAni) as an electronic conductor and 5 wt% of polyvinylidene (PVDF) as a binder in N.N.-dimethyl acetamide. A Coulombic efficiency of 96% confirmed the electrochemical stability of the composite. The variation in impedance as a function of the lithium intercalation/deintercalation process reflected the interaction between the oxide and/or polyaniline particles at a high frequency range, and a diffusion tendency was observed at medium and low frequency ranges. The capacity values of the composite electrodes relative to the LiMn₂O₄ mass were 178.6/177.5 and 145/140 mAh g⁻¹ for the first and 25th charge/discharge cycles, respectively.     

Electrochemical synthesis of ferrate in presence of ultrasound using boron doped diamond anodes

The use of an ultrasound processor is proposed to enhance the efficiency of the electrosynthesis of ferrates with boron-doped diamond anodes. The chemical dissolution of the iron powder used as raw material, due to the extreme pH on the nearness of the anode surface, improves the results significantly. The application of ultrasound during electrolyses, besides having a positive effect on the dissolution of the raw material, also favors the mass transport of iron species to the electrode surface, and thus its used enhances the efficiency of the process. The hydroxyl ion concentration and the current density also have a clear influence on the results: high current density favors iron dissolution and hydroxyl radical generation, whereas high hydroxyl ions concentration contributes to the stability of produced ferrate.     

Electrochemical nanostructuring of fullerene films--spectroscopic evidence for C60 polymer formation and hydrogenation

Electrochemical reduction of ordered C60 fullerene films in aqueous solution was studied by AFM, FTIR and Raman spectroscopy, mass spectrometry and elastic recoil detection analysis. During the irreversible reduction process the film morphology changed from a heteroepitaxial (111) surface to a nanostructured array with clusters of 20 to 50 nm lateral size on average. On the molecular level the initial C60 underwent electrochemical reactions to form C60 polymers and hydrogenated C60. Chemical follow-up reactions of electrochemically formed C60- with water are responsible for the different reduction behaviour of C60 films in aqueous solution compared to C60 reduction in organic solvents and to C60 doping with alkali metals. Based on the spectroscopic analysis a reaction scheme accounting for the chemical processes at the C60 / aqueous electrolyte interface is presented.     

Electrochemical evidence of catalysis of oxygen reduction at the polarized liquid–liquid interface by tetraphenylporphyrin monoacid and diacid

Cyclic voltammetry is used to study the role of 5,10,15,20-tetraphenyl-21H,23H-porphine (H₂TPP) in the reduction of molecular oxygen by decamethylferrocene (DMFc) at the polarized water|1,2-dichloroethane (DCE) interface. It is shown that this rather slow reaction proceeds remarkably faster in the presence of tetraphenylporphyrin monoacid (H₃TPP⁺) and diacid (H₄TPP²⁺), which are formed in DCE by the successive transfer of two protons from the acidified aqueous phase. A mechanism is proposed, which includes the formation of adduct between H₃TPP⁺ or H₄TPP²⁺ and O₂ that is followed by electron transfer from DMFc to the adduct leading to the observed production of DMFc⁺ and to the regeneration of H₂TPP or H₃TPP⁺, respectively.     

Electrochemical Probing of Polymethylalumoxane by Pyridine

The dependence of the electrical conductivity of the polymethylalumoxane—pyridine system on the component ratio was studied. The structure and energy effects of the formation of complexes (including charged ones), which arise in interactions between pyridine, reactive fragments of polymethylalumoxane, and the natural concomitants of the latter (the most probable impurities that remain after the synthesis), namely, trimethylaluminum, H₂O, and “simple” alumoxane, [Me₂Al(μ-OAlMe₂)]₂, were calculated by the DFT method. It was found that, in the presence of traces of oxygen-containing donors (alumoxane and/or H₂O), the concentration of ions in solution increased by many orders of magnitude and attained the value observed experimentally. The interaction of pyridine with polymethylalumoxane fragments caused the almost complete replacement of trimethylaluminum, which formed >Al*(Me)(μ-Me)₂AlMe₂ bridges with three-coordinate Al atoms in polymethylalumoxane (Al*), by pyridine. It was shown that an analysis of the dependence of the conductivity of polymethylalumoxane solutions containing “free” trimethylaluminum on the content of pyridine added allowed the concentrations of trimethylaluminum, both free and bound with polymethylalumoxane, to be determined.     

乳液引发的电化学振荡

丹尼尔电池;可逆;蓄电池;乳液引发的电化学振荡     

Apoptosis Evaluation by Electrochemical Techniques

Apoptosis has close relevance to pathology, pharmacology, and toxicology. Accurate and convenient detection of apoptosis would be beneficial for biological study, clinical diagnosis, and drug development. Based on distinct features of apoptotic cells, a diversity of analytical techniques have been exploited for sensitive analysis of apoptosis, such as surface plasmon resonance, electrochemical methods, flow cytometry, and some imaging assays. Among them, the features of simplicity, easy operation, low cost, and high sensitivity make electrochemical techniques powerful tools to investigate electron‐transfer processes of in vitro biological systems. In this contribution, a general overview of current knowledge on various technical approaches for apoptosis evaluation is provided. Furthermore, recently developed electrochemical biosensors for detecting apoptotic cells and their advantages over traditional methods are summarized. One of the main considerations focuses on designing the recognition elements based on various biochemical events during apoptosis.     

Role of type II thioesterases: evidence for removal of short acyl chains produced by aberrant decarboxylation of chain extender units

BACKGROUND: Modular polyketide synthases (PKSs) function as molecular assembly lines in which polyketide chains are assembled by successive addition of chain extension units. At the end of the assembly line, there is usually a covalently linked type I thioesterase domain (TE I), which is responsible for release of the completed acyl chain from its covalent link to the synthase. Additionally, some PKS clusters contain a second thioesterase gene (TE II) for which there is no established role. Disruption of the TE II genes from several PKS clusters has shown that the TE II plays an important role in maintaining normal levels of antibiotic production. It has been suggested that the TE II fulfils this role by removing aberrant intermediates that might otherwise block the PKS complex. RESULS: We show that recombinant tylosin TE II behaves in vitro as a TE towards a variety of N-acetylcysteamine and p-nitrophenyl esters. The trends of hydrolytic activity determined by the kinetic parameter k(cat)/K(M) for the analogues tested indicates that simple fatty acyl chains are effective substrates. Analogues that modelled aberrant forms of putative tylosin biosynthetic intermediates were hydrolysed at low rates. CONCLUSIONS: The behaviour of tylosin TE II in vitro is consistent with its proposed role as an editing enzyme. Aberrant decarboxylation of a malonate-derived moiety attached to an acyl carrier protein (ACP) domain may generate an acetate, propionate or butyrate residue on the ACP thiol. Our results suggest that removal of such groups is a significant role of TE II.     

Electrochemical behavior of nickeladithiolene S,S'-dialkyl adducts: evidence for the formation of a metalladithiolene radical by electrochemical redox reactions

The electrochemical behavior of nickeladithiolene S,S'-dialkyl adducts (alkyl = benzyl, methyl, tert-butyl) was investigated by using cyclic voltammetry (CV), visible, near-IR, and ESR spectroscopies and bulk electrolyses. The redox potentials of the S,S'-dialkyl adducts were influenced by the electron-donating effect of the functional group on the sulfur atoms. The nickeladithiolene S,S'-dibenzyl adduct [Ni[S(SCH(2)Ph)C(2)Ph(2)](2)] (2) eliminated one benzyl radical by one-electron reduction, and then the monobenzyl adduct anion [Ni(S(2)C(2)Ph(2))[S(2)(CH(2)Ph)C(2)Ph(2)]](-) (3(-)) was formed. Anion 3(-) was also formed by the reaction of nickeladithiolene dianion [Ni(S(2)C(2)Ph(2))(2)](2)(-) (1(2-)) with 1 equiv of benzyl cation. When anion 3(-) was oxidized, the long-lived nickeladithiolene radical [Ni(S(2)C(2)Ph(2))[S(2)(CH(2)Ph)C(2)Ph(2)]] (3) was formed. The visible, near-IR, and ESR spectra of radical 3 could be measured and assigned. When radical 3 was further oxidized, the oxidant 3(+) eliminated one benzyl cation, and then free nickeladithiolene (1) was generated.     

应用超声波电化学法同时测定Pb、Cu

研究了超声波对Pb(Ⅱ）、Cu（Ⅱ）同时电分析化学测定条件的影响，并对其作用机理进行了初探。利用超声波的空化作用加快了质量传递，提高了电极活性，在电极表面即产生机械效应又产生热效应，从而提高了Pb、Cu同时电化学测定的灵敏度。     

Recent Advances in Real-Time Analysis of Electrochemical Reactions by Electrochemical Mass Spectrometry†

Electrochemical mass spectrometry (EC-MS) is a powerful tool to capture and analyze the intermediates and products during electrochemical reactions. This hyphenated technique combines electrochemistry with mass spectrometry using specific apparatuses, which helps researchers study mechanisms of redox reactions by in situ detecting chemical composition changes. Recently, various EC-MS methods have been applied in a series of electrochemical reactions to reveal the mechanisms, mainly in the areas of electrochemical sensors, organic electrochemistry, and electrocatalysis. In this review, we intend to summarize the recent advances in real-time analysis of different types of electrochemical reactions by EC-MS and offer an outlook on the perspectives in these areas.      

Two photoionization thresholds of N3 produced by ClN3 photodissociation at 248 nm: further evidence for cyclic N3

We present results of near-threshold photoionization of N3 photofragments produced by laser photodissociation of ClN3 at 248 nm. The time of flight of recoiling N3 is used to resolve two photochemical channels producing N3, which exhibit different translational energy release. The two forms of N3 resolved in this way exhibit different photoionization thresholds, consistent with their assignment to linear (X 2pi(g)) and cyclic N3. This result agrees with the existing theoretical calculations of excited and ionic states of N3 and strengthens previous experimental results which suggested that the ClN3 photolysis produces a cyclic form of N3.     

电化学还原合成1,5-二氨基萘

研究了以1,5-二硝基萘为原料电化学还原合成1,5-二氨基萘的反应. 室温下, 运用循环伏安法研究了1,5-二硝基萘的循环伏安行为, 1,5-二硝基萘的还原是一受扩散控制的不可逆反应; 循环伏安图上两个连续的还原峰对应于两个硝基的还原; 求出了反应的传递系数α₁在0.275～0.335之间, α₂在0.360～0.437之间. 探讨了电解电位(E)、底物浓度(c₁)、电解电量(Q)、硫酸浓度(c₂)以及溶剂(DMF)与水的体积比(Y)对产物产率的影响, 在最优条件下1,5-二氨基萘的产率最高可达77%.     

电化学法制备硅纳米线

Silicon nanowires were synthesized from nanometer silicon dioxide powder under potentiostatic electrolysis at -1.20 V (vs Pt reference) for 4 h in molten CaCl₂ at 900 ℃. The morphology, structure and chemical composition of the samples prepared by electroreduction method were characterized by field-emission scanning electron microscopy(FE-SEM), High-resolution transmission electron microscopy(HRTEM) coupled with electron energy dispersive spectroscopy(EDS), laser Raman and X-ray diffraction(XRD). The results revealed that silicon nanowires were crystalline with a diamond cubic structure, the diameter was distributed from 50 nm to 80 nm and the length was generally several micrometers. The formed nanowires basically consisted of silicon monocrystalline and amorphous oxide sheath.