Structural changes during the overoxidation of electro-chemically deposited poly(3,4-ethylenedioxythiophene) films

Electrochemical, mechanical and morphological properties of thin poly(3,4-ethyl-enedioxy-thiophene) (PEDOT) films deposited on gold were investigated in aqueous sulfuric acid and sodium sulphate solutions. At sufficiently positive electrode potentials overoxidation of the polymer took place and resulted in morphological changes and structure evolution. These effects were monitored by electrochemical impedance spec-troscopy (EIS), scanning electron microscopy (SEM) and X-ray diffraction. Significant changes in the film stress caused by overoxidation were detected by using the electro-chemical bending beam method. Results of the EIS measurements proved that the charge transfer process at the metal/film interface is more hindered in case of the degraded film. According to SEM images the overoxidation/degradation of PEDOT films can result in random-like but quite well-ordered arrays of islands and trench-like structures. The diffraction peaks of PEDOT became sharper and more intensive during the subsequent oxidation cycles indicating an increase in the degree of crystallinity of the polymer

Apparatus and methods for using a rotating ring–disk electrode with potentiodynamic control of both working electrodes = Aufbau und Anwendungen einer rotierenden Ringscheibenelektrode mit potentiodynamischer Kontrolle beider Arbeitselektroden

Abstract When studying electrochemical processes, one of the most widely used methods of determining the reaction pathway is an electrochemical assay of products using a rotating ring–disk electrode (RRDE). An RRDE tip consists of two electron conducting parts: a centrally located disk and a ring around it. When brought into contact with an electrolyte solution, the disk and the ring both form electrodes, the potentials of which can be independently controlled by a bi-potentiostat. When the tip is rotated, reactants from the solution arrive at the disk where they undergo an electrode reaction (oxidation or reduction) at a given rate, depending on the rotation speed. The formed products leave the disk surface and due to forced convection make their way towards the ring electrode where they can undergo another electrode reaction and can thus be detected. Normally, one applies potentiostatic control to at least one of the electrodes when carrying out an RRDE experiment; albeit the simultaneous potentiodynamic perturbation of the electrodes offers an increased applicability range. This paper presents the construction of a measuring system capable for the “bi-potentiodynamic” perturbation of two working electrodes, and demonstrates the use of such methods in case of a few chosen example systems.</jats:p

Characterization of the Capacitance of a Rotating Ring–Disk Electrode

The use of rotating ring–disk electrodes as generator-collector systems has so far been limited to the detection of Faradaic currents at the ring. As opposed to other generator-collector configurations, non-Faradaic detection has not yet been carried out with rotating ring–disk electrodes. In this study, a.c. perturbation based detection for measurement of the ring impedance is introduced. By using a conducting polymer-modified disk electrode in combination with a bare gold ring as a model, it is shown that the measured ring capacitance correlates with the polarization of the polymer film, most probably due to counter-ion exchange. A method of calculating the ring capacitance based on a small-signal sinusoid perturbation is described and the most important instrumental limitations are identified

Where do ferrate ions form? A dual dynamic voltammetry study

One of the most effective methods to produce ferrate ions (FeO42–) is electrochemical synthesis. During the transpassive anodic dissolution of iron, the formation of ferrate ions and the evolution of oxygen occur simultaneously, and only the sum of the currents generated by the two processes can be observed in the voltammetric curves. Products of the above process have been investigated in 45 % (m/m) aqueous NaOH solutions by using the dual dynamic voltammetry (DDV)&rotating ring-disk electrode (RRDE) method (i.e., applying dynamic potential programs to the disk and the ring electrodes of the RRDE disk electrode and the RRDE ring electrode simultaneously) combined with spectrophotometric measurements. Fe disk/Pt ring and Pt disk/Pt ring RRDE tips were used in the voltammetric experiments. The electrode potential regions where ferrate ions and oxygen are forming could effectively be identified. The results imply that, under the applied experimental conditions, the oxygen evolved at the disk cannot be reduced at the ring. This can be explained by the fact that elemental oxygen practically does not dissolve in concentrated aqueous sodium hydroxide solutions due to the “salting-out effect”. By using the dual voltammetric method, it was also possible to determine the optimal potential range for the electrochemical production of ferrate ions in terms of charging efficiency. The latter quantity has an important impact on the economics of practical applications. The approach proposed in this study proved to be very promising for the simultaneous detection of different dissolution products

Synthesis and SAR Analysis of Novel 4-Hydroxytamoxifen Analogues Based on Their Cytotoxic Activity and Electron-Donor Character

Utilizing McMurry reactions of 4,4&prime;-dihydroxybenzophenone with appropriate carbonyl compounds, a series of 4-Hydroxytamoxifen analogues were synthesized. Their cytotoxic activity was evaluated in vitro on four human malignant cell lines (MCF-7, MDA-MB 231, A2058, HT-29). It was found that some of these novel Tamoxifen analogues show marked cytotoxicity in a dose-dependent manner. The relative ROS-generating capability of the synthetized analogues was evaluated by cyclic voltammetry (CV) and DFT modeling studies. The results of cell-viability assays, CV measurements and DFT calculations suggest that the cytotoxicity of the majority of the novel compounds is mainly elicited by their interactions with cellular targets including estrogen receptors rather than triggered by redox processes. However, three novel compounds could be involved in ROS-production and subsequent formation of quinone-methide preventing proliferation and disrupting the redox balance of the treated cells. Among the cell lines studied, HT-29 proved to be the most susceptible to the treatment with compounds having ROS-generating potency