Andrew M. Waller

Simultaneous alternating current impedance/electron spin resonance study of electrochemical doping in polypyrrole

The electrochemical doping of polypyrrole has been studied using simultaneous a.c. impedance and in-situ electrochemical e.s.r. measurements. A quantitative estimate of the polypyrrole conductivity as a function of doping level has been obtained and the corresponding change in the polaron concentration measured by in-situ electrochemical e.s.r. It was found that at low doping levels there was a good correlation between these two properties. It is suggested that the polaron may be responsible for the conduction process under such conditions. At higher doping levels conduction would appear to involve the bipolaron.

Hydrotalcite-derived mixed oxides containing copper: catalysts for the removal of nitric oxide

Hydrotalcite structures containing copper, magnesium and aluminium in the metal hydroxide layers have been investigated for their potential as precursors to the formation of catalysts for the decomposition and reduction of nitrogen oxides. These CuIIMgIIAlIII hydrotalcites are catalytically active towards both the decomposition of nitric oxide and its reduction in the presence of an appropriate coreductant, such as propane. The copper centred active species, identified using EXAFS spectroscopy and combined EXAFS/XRD under operating conditions, have been found to be CuI for the decomposition and Cu0 for the reduction.

The oxidation potential of 1,4-diaminobenzene: Calculation versus experiment

Abstract The oxidation potential of 1,4-diaminobenzene has been calculated theoretically using a combination of ab-initio calculations and molecular dynamics simulations. An experimental determination of the same quantity is presented. Data obtained from cyclic voltammetric experiments, at a platinum electrode, were consistent with an EC electrode reaction mechanism. Cyclic voltammograms recorded at high voltage scan rates ( v ⪢ 500 mV s −1 ), such that the following homogeneous kinetics were outrun, indicated the oxidation to be quasi-reversible and this enabled the standard oxidation potential to be estimated. Comparison of the theoretical and experimental values for the oxidation potential showed agreement to within 25 mV. The level of agreement between theory and experiment was considered to be highly satisfactory.

An improved cell for in-situ electrochemical ESR

Abstract An improved cell for simultaneous electrochemical ESR based on a coaxial cylindrical cavity is described and shown to have high sensitivity whilst behaving as a satisfactory hydrodynamic electrode as evidenced by Tafel analysis, by Levich analysis and comparison with theory for the dependence of the ESR signal on electrode currents and electrolyte flow rate.

Electron paramagnetic resonance spectroscopy of electrodeposited species from solutions of 1,1′-bis-(p-cyanophenyl)-4,4′-bipyridilium (cyanophenyl paraquat, CPQ)

EPR spectra of electro-reduced CPQ (cyanophenyl paraquat, 1,1-bis-(p-cyanophenyl)-4,4′-bipyridilium) in radical cation form have been studied in propylene carbonate solution and as solid deposited with various anions from aqueous solution. In either milieu, no hyperfine coupling is seen, and with sulphate the low intensities indicate some dimerisation. Further (solid-state) reduction to CPQ° produced diamagnetic product (contrast solution-phase comproportionation with CPQ2+) except in the presence of aqueous ferrocyanide, where not only comproportionation but also de-dimerisation are to be inferred.

A general computational method for mass-transport problems involving wall-jet electrodes and its application to simple electron-transfer, ECE and DISP1 reactions

A computational procedure based on the Backwards Implicit Method is shown to be a powerful and general method of solving problems of mass transport to a wall-jet electrode. Conventional numerical methods based on a Cartesian grid are unsatisfactory because the electrode is very non-uniformly accessible. An expanding grid which increases in size in proportion to the diffusion layer thickness across the electrode surface, is shown to be effective in computing the limiting current-flow rate behaviour of (a) a simple electron-transfer reaction, (b) ECE, and (c) DISP1 processes.

Photoelectrochemical electron spin resonance. Part 2.—The reduction of crystal violet in acetonitrile

The reduction of the dye crystal violet in acetonitrile solution at platinum electrodes has been investigated using in situ electrochemical e.s.r. and a channel electrode flow cell. In the dark, in the rigorous absence of oxygen, a one-electron reversible reduction takes place, producing the stable crystal violet radical, the e.s.r. spectrum of which was recorded. The behaviour in the presence of oxygen is also discussed. On irradiation with light of wavelength ca. 400 nm the radical is thought to undergo a chemical reaction with the solvent, and the electrode reduction process has the characteristics of an EC mechanism. The nature of this reaction is deduced from the e.s.r. signal strength/current/electrolyte flow rate data together with pure electrochemical measurements, and kinetic parameters are reported.

Molecular Radiotherapy Using Cleavable Radioimmunoconjugates That Target EGFR and γH2AX

Many anticancer therapies, including ionizing radiation (IR), cause cytotoxicity through generation of DNA double-strand breaks (DSB). Delivery of therapeutic radionuclides to DNA DSB sites can amplify this DNA damage, for additional therapeutic gain. Herein, we report on two radiopharmaceuticals, radiolabeled with the Auger electron emitter 111In, with dual specificity for both the intranuclear, DNA damage repair signaling protein γH2AX and the EGF receptor (EGFR). The EGFR ligand EGF was conjugated to a fluorophore- or 111In-labeled anti-γH2AX antibody, linked via a nuclear localization sequence (NLS) to ensure nuclear translocation. EGF conjugation was achieved either through a noncleavable PEG linker (PEO6) or a cleavable disulfide bond. Both conjugates selectively bound EGFR on fixed cells and γH2AX in cell extracts. Both compounds enter EGFR-expressing cells in an EGF/EGFR-dependent manner. However, only the cleavable compound was seen to associate with γH2AX foci in the nuclei of irradiated cells. Intracellular retention of the cleavable compound was prolonged in γH2AX-expressing cells. Clonogenic survival was significantly reduced when cells were exposed to IR (to induce γH2AX) plus 111In-labeled cleavable compound compared to either alone and compared to nonspecific controls. In vivo, uptake of 111In-labeled cleavable compound in MDA-MB-468 xenografts in athymic mice was 2.57 ± 0.47 percent injected dose/g (%ID/g) but increased significantly to 6.30 ± 1.47%ID/g in xenografts where γH2AX was induced by IR (P < 0.01). This uptake was dependent on EGF/EGFR and anti-γH2AX/γH2AX interactions. We conclude that tumor-specific delivery of radiolabeled antibodies directed against intranuclear epitopes is possible using cleavable antibody–peptide conjugates. Mol Cancer Ther; 12(11); 2472–82. ©2013 AACR.

An alternating current impedance study of polypyrrole/poly(vinyl chloride) composites

A.c. impedance studies of poly(vinyl chloride)–polypyrrole composites deposited on platinum electrodes and in contact with an acetonitrile solution containing 0.1 mol dm–3 tetrabutylammonium tetrafluoroborate (as supporting electrolyte) are described. Data are presented for the frequency range 0.1 Hz–65 kHz, and in this way the conductivity of the composite is found. The latter is related to the potential applied via the platinum electrode to the composite, and to the amount of polypyrrole incorporated within the composite. In-situ electrochemical e.s.r. measurements on the composite are also described, and these, together with the a.c. data, indicate the electrical properties and behaviour of the composite material to be similar to polypyrrole itself.

Chapter 7 In-Situ Electrochemical ESR

Publisher Summary This chapter discusses In-Situ Electrochemical electron spin resonance spectroscopy (ESR). The existence of radicals as intermediates in a great variety of electrode reactions is well established. Such paramagnetic species may be detected and identified using ESR and so for nearly thirty years electrochemists have used ESR as a method for the investigation of those complex electrode reactions that proceed via radical intermediates. ESR spectra are characterized by three parameters, the g factor, the hyperfine coupling, and the line width. It is these parameters that allow identification of the nature and environment of radicals. The spin-orbit coupling is dependent upon the orientation of the radical within the applied field, making g anisotropic, and thus the position of the observed ESR spectrum is dependent upon the orientation of the radical. Fortunately, for radicals in solution, such as those observed commonly in electrochemical ESR, there is rapid tumbling of the radicals and, effectively, an average g factor is observed.