Cyclic cohomology and algebra extensions

We construct a spectral sequence to study cyclic cohomology for an extension A = R/I of algebras. When R is a free algebra we describe the cyclic cohomology of A in terms of traces defined on R or powers of I. Explicit cyclic cocycles representing the cyclic cohomology class belonging to the trace are constructed as analogues of Chern character and Chern-Simons forms.Dedicated to Alexander Grothendieck     

Synthesis and electrochemistry of Group 6 tetracarbonyl (N,N′-bis(ferrocenylmethylene)ethylenediamine)metal(0) complexes

Thermal substitution reaction of Cr(CO)₄(η^2:2-1,5-cyclooctadiene), Mo(CO)₄(η^2:2-norbornadiene), and W(CO)₅(η²-bis(trimethylsilyl)ethyne) with N,N′-bis(ferrocenylmethylene)ethylenediamine (bfeda) yields M(CO)₄(bfeda) complexes which could be isolated from the reaction solution and characterized by elemental analysis, MS, IR, and NMR spectroscopy. In the case of tungsten, W(CO)₅(bfeda) is formed as intermediate and then undergoes the ring closure reaction yielding the ultimate product W(CO)₄(bfeda). The electrochemical behavior of the M(CO)₄(bfeda) complexes was studied by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in dichloromethane with tetrabutylammonium tetrafluoroborate as electrolyte. Constant potential electrolysis of the complexes was performed successively at their peak potentials at 0 °C in their CH₂Cl₂ solution and the electrolysis was followed by in situ recording the electronic absorption spectra in every 5 mC. In the electrolysis of Cr(CO)₄(bfeda), the central Cr(0) is oxidized first and electrolysis continues with oxidations of two ferrocenyl groups until the end of totally three moles of electron passage per mole of complex. In the electrolysis of Mo(CO)₄(bfeda) and W(CO)₄(bfeda) the first oxidation occurs on the central atom forming a short-lived species which undergoes an intramolecular one-electron transfer and is reduced back to M(0) while one of the ferrocene units is oxidized to the ferrocenium cation at the same time. This indicates that the electron is transferred from iron to the central metal atom.     

Voltammetric determination of hafnium with calconcarboxylic acid

The interaction of Hf(IV) with calconcarboxylic acid (1-(2-hydroxy-4-sulfo-1-naphtylazo)-3-naphtolic acid) was investigated by cyclic voltammetry varying various factors (pH, ionic strength, contents of ethanol and scan rate). Optimal conditions of Hf(IV) determination in the presence of calconcarboxylic acid were found: acetic buffer solution pH 2.6, scan rate 0.5 Vs⁻¹. The detection limit of Hf(IV) concentration was 2.46 × 10⁻⁷ mol L⁻¹. The influence of foreign ions on the Hf(IV) determination was studied. It was established that some metals like cadmium, nickel, zinc, copper and titanium could be determined with Hf(IV) simultaneously. The method of voltammetric determination of hafnium was tested on model solutions and used in the determination of Hf(IV) in terbium-base alloy.     

The Synthesis of Unusual Organic Molecules Using Cyclic Peroxides. New synthetic methods (3)

The photodecarboxylation of malonyl peroxides into α-lactones^[1] and the thermal conversion of the 1,4-endo-peroxide 4,5-epoxy-3,6-epidioxy-1-cyclohexene into the novel benzene trioxide^[2] are two recent examples of the potential of cyclic peroxides in the synthesis of unusual organic molecules. The former transformation entails a fragmentation, the latter a rearrangement process. Most reported examples fall into one of these two gross reaction types. Of the numerous examples that have been reported in the literature during the last two decades, only those shall be focused on that lead to unusual compounds or constitute efficient syntheses of known compounds, in order to stress the convenience of cyclic peroxides in the synthesis of organic compounds.     

Studies of the electrochemical behavior of epinephrine at a homocysteine self-assembled electrode

The self-assembled electrode with the homocysteine monolayer (Hcy/Au) has been characterized by infrared spectroscopy and ac impedance spectroscopy in electrolyte. The Hcy/Au electrode is demonstrated to promote the electrochemical response of epinephrine (E) by cyclic voltammetry. A pair of well-defined redox waves was obtained and the calculated standard rate constant (k_s) is 2.1×10⁻² cm s⁻¹ at the self-assembled electrode. The reduction peak of E can be used to determine the concentration of E in presence of ascorbic acid (AA) owing to the Hcy/Au also promoting the electrochemical oxidation of AA.     

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.

     

Fabrication and electrochemistry study of multi-thiol coronary molecule monolayers

Single-component monolayer of novel multi-thiol coronary molecule and two-component mixed monolayer composed of coronary molecule and n-alkanethiol on gold substrates are described. The assembly of monolayers is characterized by ellipsometry, infrared spectroscopy and X-ray photoelectron spectroscope. The electrochemical properties of the single- and two-component monolayers are evaluated by cyclic voltammetry and electrochemical impedance spectroscopy experiments. Coronary molecule with multi-thiol groups has the ability to form stable monolayer via the interaction of mercapto groups and Au surface. Electrochemical impedance measurements indicate that 89.9% of the gold surface is blocked by the coronary molecule, which is attributed to the special spatial structure of the coronary molecule. The uncovered site on gold surface in coronary molecule monolayer could be occupied by the second suitable molecule. The mixed monolayer prepared by stepwise assembly of coronary molecule and n-alkanethiol has complete compact packing and few defects.     

Synthesis of glycoluril catalyzed by potassium hydroxide under ultrasound irradiation

Synthesis of the glycolurils catalyzed by potassium hydroxide was carried out in 17–75% yield at 40 °C in EtOH under ultrasound irradiation. Compared to the method using stirring, the main advantage of the present procedure is milder conditions and shorter reaction time.     

Ultrasonically assisted synthesis of barium stannate incorporated graphitic carbon nitride nanocomposite and its analytical performance in electrochemical sensing of 4-nitrophenol

We describe the ultrasonic assisted preparation of barium stannate-graphitic carbon nitride nanocomposite (BSO-gCN) by a simple method and its application in electrochemical detection of 4-nitrophenol via electro-oxidation. A bath type ultrasonic cleaner with ultrasonic power and ultrasonic frequency of 100 W and 50 Hz, respectively, was used for the synthesis of BSO-gCN nanocomposite material. The prepared BSO-gCN nanocomposite was characterized by employing several spectroscopic and microscopic techniques such as X-ray diffraction, X-ray photoelectron spectroscopy, fourier transform infra-red, field emission scanning electron microscopy, and high resolution transmission electron microscopy, to unravel the structural and electronic features of the prepared nanocomposite. The BSO-gCN was drop-casted on a pre-treated glassy carbon electrode (GCE), and their sensor electrode was utilized for electrochemical sensing of 4-nitrophenol (4-NP). The BSO-gCN modified GCE exhibited better electrochemical sensing behavior than the bare GCE and other investigated electrodes. The electroanalytical parameters such as charge transfer coefficient (α = 0.5), the rate constant for electron transfer (k_s = 1.16 s⁻¹) and number of electron transferred were calculated. Linear sweep voltammetry (LSV) exhibited increase in peak current linearly with 4-NP concentration in the range between 1.6 and 50 μM. The lowest detection limit (LoD) was calculated to be 1 μM and sensitivity of 0.81 μA μM⁻¹ cm⁻²_. A 100-fold excess of various ions, such as Ca²⁺, Na⁺, K⁺, Cl⁻, I⁻, CO₃²⁻, NO₃, NH₄⁺ and SO₄²⁻ did not able to interfere with the determination of 4-NP and high sensitivity for detecting 4-NP in real samples was achieved. This newly developed BSO-gCN could be a potential candidate for electrochemical sensor applications.     

Quantitative nanoscopic impedance measurements on silver-ion conducting glasses using atomic force microscopy combined with impedance spectroscopy

Nanoscopic impedance measurements were carried out on silver ion conducting glasses by coupling an impedance spectrometer with an atomic force microscope. When ac voltages were applied to a conducting AFM tip being in contact with the glass surface, silver nanoparticles were formed during the cathodic half cycle, which were not completely reoxidized in the anodic half cycle. We describe two protocols allowing for a controlled particle growth. The electrochemical oxidation/reduction processes led to low tip/sample interfacial impedances, and the formed silver particles acted as nanoelectrodes sensing the spreading resistance of the glass below the particles. We made a quantitative check of the spreading resistance formula under the assumption that spreading of the electric field is governed by the lateral diameter of the particles and found good agreement between the mean value of the local conductivities obtained at different tip positions and the macroscopic conductivity.