Furan–thiophene copolymers: Electrosynthesis and electrochemical behavior

The electrochemical copolymerization of furan and thiophene was performed at a constant electrode potential in a binary solvent system consisting of boron trifluoride/ethyl ether and an additional amount of ethyl ether (molar ratio = 1 : 2). The obtained homopolymers and copolymers were characterized with cyclic voltammetry and infrared spectroscopy. The influence of the applied electropolymerization potential and the monomer feed ratio of furan and thiophene on the copolymers was investigated. The furan–thiophene copolymers showed good stability of the redox activity in an acetonitrile‐based electrolyte solution. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Bifunctional electrodes for an integrated water-electrolysis and hydrogen-oxygen fuel cell with a solid polymer electrolyte

An alternative concept of an integrated water electrolysis/hydrogen-hydrogen fuel cell using metal electrocatalysts and a solid polymer electrolyte is described. Instead of operating both electrodes as hydrogen and oxygen electrodes respectively the electrodes are used as oxidation and reduction electrodes in both modes of operation. A more suitable selection of electrocatalysts and an improved cell design are possible; both can increase the efficiency of the cell considerably. New results on the electrocatalytic activity of various noble-metal containing catalysts with respect to both oxygen evolution and hydrogen oxidation in a proton exchange membrane-cell at 80°C are reported. Kinetic data derived from Tafel plots of the oxygen evolution polarization curves agree closely with those of experiments with aqueous sulphuric acid electrodes. This agreement allows the determination of kinetic parameters for electrocatalysts difficult to prepare in solid smooth electrodes but easy to be made into porous deposits. Polarization curves of the hydrogen oxidation reaction clearly indicate a relative activity rating of the studied catalysts. In cycling tests the lifetime stability of the new bifunctional oxidation electrode was determined. Polarization data obtained under these conditions agree with those obtained in earlier experiments where electrodes were exposed to only one type of oxidation reaction. During a test of 10 cycles (30 min of electrolyser and 30 min of fuel cell mode each) no changes in the electrode potential were observed. With the conventional cell design employing a hydrogen and an oxygen electrode both catalyzed with platinum and a current density of 100 mA cm^–2 a storage efficiency of 50% was calculated; with the alternative concept of oxidation and reduction electrodes and selected oxidation catalysts this was improved to 57%. With further improvements these efficiencies seem possible even at current densities of 500 mA cm^–2.     

Reprint of “Suppressing propylene carbonate decomposition by coating graphite electrode foil with silver”

A method has been developed to suppress the decomposition of propylene carbonate (PC) by coating graphite electrode foil with a layer of silver. Results from electrochemical impedance measurements show that the Ag-coated graphite electrode presents lower charge transfer resistance and faster diffusion of lithium ions in comparison with the virginal one. Cyclic voltammograms and discharge-charge measurements suggest that the decomposition of propylene carbonate and co-intercalation of solvated lithium ions are prevented, and lithium ions can reversibly intercalate into and deintercalate from the Ag-coated graphite electrode. These results indicate that Ag-coating is a good way to improve the electrochemical performance of graphitic carbon in PC-based electrolyte solutions.     

Electrochemical and DFT-studies of substituted thiophenes

UV-vis absorption spectra and cyclic voltammograms of a selection of substituted thiophenes and their oligomers carrying trifluoracetyl acetone functional groups have been obtained. A comparison with calculated values of HOMO-LUMO energies (the former corresponding to the ionization potentials E_i) shows strong correlations between calculated and experimentally obtained data; they are in close agreement with estimates in terms of electron-donating and -withdrawing effects from an empirical point of view.     

Copolymers—A refined way to tailor intrinsically conducting polymers

An overview is given on electrochemically prepared intrinsically conducting copolymers, their preparation, their properties, potential applications and significant differences from the respective homopolymers. Particular attention is paid to verification of the formation of true copolymers and their characteristic features in comparison to mixtures of homopolymers.     

Preparation of aqueous polyaniline dispersions by micellar‐aided polymerization

Polyaniline (PAn) dispersed in water was prepared with sodium dodecylsulfonate (SDS) as a surfactant with varying concentrations of aniline and HCl and molar ratios of SDS/aniline. The PAn dispersion was homogeneous and stable, and its pH value could be adjusted. The conductivity of PAn powder, precipitated from this dispersion, was as high as 20 S/cm. The transmission electron microscopy morphology of PAn assembled in the dispersion was particle‐like, fiber‐like, or coil‐like, depending on the initial concentration of SDS and aniline. The polymerization of aniline was accelerated by SDS, which was confirmed by open‐circuit potential measurement during the polymerization process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1550–1555, 2003     

Novel BQCA- and TBPB-Derived M1 Receptor Hybrid Ligands: Orthosteric Carbachol Differentially Regulates Partial Agonism

Recently, investigations of the complex mechanisms of allostery have led to a deeper understanding of G protein-coupled receptor (GPCR) activation and signaling processes. In this context, muscarinic acetylcholine receptors (mAChRs) are highly relevant due to their exemplary role in the study of allosteric modulation. In this work, we compare and discuss two sets of putatively dualsteric ligands, which were designed to connect carbachol to different types of allosteric ligands. We chose derivatives of TBPB [1-(1′-(2-tolyl)-1,4′-bipiperidin-4-yl)-1H-benzo[d]imidazol-2(3H)-one] as M₁-selective putative bitopic ligands, and derivatives of benzyl quinolone carboxylic acid (BQCA) as an M₁ positive allosteric modulator, varying the distance between the allosteric and orthosteric building blocks. Luciferase protein complementation assays demonstrated that linker length must be carefully chosen to yield either agonist or antagonist behavior. These findings may help to design biased signaling and/or different extents of efficacy.     

In situ characterization of N-methylpyrrole and (N-methylpyrrole-cyclodextrin) polymers on gold electrodes in aqueous and nonaqueous solution

Electrosynthesized polymers of N-methylpyrrole (NMPy) and N-methylpyrrole-2,6-dimethyl-β-cyclodextrin NMPy-β-DMCD were characterized with cyclic voltammetry and in situ conductivity measurements in aqueous and nonaqueous solutions. In situ UV–vis-spectra of PNMPy and poly(NMPy-β-DMCD) films show differences both in band absorbances and in energies of polaronic transitions. For the electrosynthesis of poly(NMPy-β-DMCD), a (1:1) (mole–mole) NMPy-β-DMCD supramolecular cyclodextrin complex of N-methylpyrrole was used as starting material, which was previously characterized with proton NMR spectroscopy. The PNMPy and poly(NMPy-β-DMCD) films were prepared from 0.05 M NMPy and 0.05 M NMPy-β-DMCD complex, respectively, in 0.1 M LiClO₄ aqueous solution and 0.1 M LiClO₄ nonaqueous solution (acetonitrile) by electropolymerization. A slight positive shift of the oxidation peak and further differences are observed for poly(NMPy-β-DMCD) electrosynthesized in comparison with PNMPy prepared in both aqueous and nonaqueous solutions. Different CVs and ΔE_p of films were observed at various scan rates. In situ conductivity values of PNMPy and poly(NMPy-β-DMCD) films prepared in nonaqueous solution (acetonitrile) show higher values than with films prepared in aqueous solutions.