The adsorption of quinizarin on boron-doped diamond

The voltammetric response of the quinone species 'quinizarin' (QZ) and its electrocatalytic reduction of oxygen are studied at a boron doped diamond electrode (BDD). It is demonstrated that, contrary to the widespread belief that adsorption of organic molecules on BDD is minimal, not only does QZ readily adsorb to the electrodes surface but this adsorption is also influenced at low surface coverages by the pre-exposure of the electrode to organic solvents. Furthermore, the nature of this adsorbed QZ species is investigated and a potential dependent phase transition is observed. This is to the authors knowledge the first system to exhibit a phase transition of an adsorbed species on a boron doped diamond surface. At low scan rates the system is found to oscillate; these oscillations are ascribed to the presence of a 'negative differential resistance'.     

Electrochemical determination of glutathione: a review

The physiological importance of glutathione and glutathione disulfide is evident from their implications in an array of medical conditions including diabetes, Parkinson's disease and cancer. As such the need for simple, rapid and cheap assays to aid clinical diagnostics and treatment is clear. These requirements are, in principle at least, ideally suited to electrochemical detection. Accordingly a large array of voltammetric methods ultimately aimed at making cheap and most likely disposable electrodes have been reported. This critical review analyses the context in which physiological glutathione measurement can be undertaken electrochemically and compares it to current assay approaches, while also covering the current literature for glutathione disulfide detection. The various characteristics and limitations of the methodologies are compared and contrasted, with the analytical parameters (matrix, pH, limit of detection, etc.) tabulated to aid comparison.     

Formic acid electro-synthesis from carbon dioxide in a room temperature ionic liquid

The novel synthesis of formic acid has been achieved in a room temperature ionic liquid via the reaction of electro-activated carbon dioxide and protons on pre-anodised platinum. Only mild reaction conditions of room temperature and 1 atm CO(2) were used. This work highlights the effect of pre-anodisation on Pt surfaces.     

The optical activity of carvone: a theoretical and experimental investigation

The optical rotatory dispersion (ORD) and circular dichroism of the conformationally flexible carvone molecule has been investigated in 17 solvents and compared with results from calculations for the "free" (gas phase) molecule. The G3 method was used to determine the relative energies of the six conformers. The optical rotation of (R)-(-)-carvone at 589 nm was calculated using coupled cluster and density functional methods, including temperature-dependent vibrational corrections. Vibrational corrections are significant and are primarily associated with normal modes involving the stereogenic carbon atom and the carbonyl group, whose n → π? excitation plays a significant role in the chiroptical response of carvone. Without the inclusion of vibrational corrections the optical rotation calculated with CCSD and DFT has the opposite sign of experimental data. Calculations of optical rotation performed in solution using the polarizable continuum model were also opposite in sign when compared to that of the experiment.     

Ammonium-directed olefinic epoxidation: kinetic and mechanistic insights

The ammonium-directed olefinic epoxidations of a range of differentially N-substituted cyclic allylic and homoallylic amines (derived from cyclopentene, cyclohexene, and cycloheptene) have been investigated, and the reaction kinetics have been analyzed. The results of these studies suggest that both the ring size and the identity of the substituents on nitrogen are important in determining both the overall rate and the stereochemical outcome of the epoxidation reaction. In general, secondary amines or tertiary amines with nonsterically demanding substituents on nitrogen are superior to tertiary amines with sterically demanding substituents on nitrogen in their ability to promote the oxidation reaction. Furthermore, in all cases examined, the ability of the (in situ formed) ammonium substituent to direct the stereochemical course of the epoxidation reaction is either comparable or superior to that of the analogous hydroxyl substituent. Much slower rates of ring-opening of the intermediate epoxides are observed in cyclopentene-derived and cycloheptene-derived allylic amines as compared with their cyclohexene-derived allylic and homoallylic amine counterparts, allowing for isolation of these intermediates in both of the former cases.     

Mass transport at electrodes of arbitrary geometry. Reversible charge transfer reactions in square wave voltammetry

The basis for mass transport of the electroactive species in different diffusion fields is examined, pointing out important insights in relation to the value of the surface concentrations for the case of fast electrode processes. Moreover, a general analytical solution for the transient current is given for several geometries, when an arbitrary sequence of potentials pulses is applied to macroelectrodes (planar), spheres, cylinders, discs and bands. The results are particularized for Square Wave Voltammetry. Explicit solutions for the net current and the forward and backward components are given. The effects of frequency, pulse amplitude and electrode size or shape on the peak current are studied. Moreover, the conditions for the attainment of the steady state response are analyzed in the different geometries as well as the characteristics of this response.     

In Situ Formation of a Uniform Distribution of Silver Nanoparticles in PVDF: Kinetics of Formation and Resulting Properties

Hybrid organic/silver nanoparticle thermoplastic films have been prepared using a single step process where the silver nanoparticles were formed during a cure cycle applied to the film. Figure 1 is a TEM demonstrating the ability of our technique to produce silver nanoparticles in the semi-crystalline polymer Poly(vinylidene fluoride) (PVDF). The current laboratory focus is on characterizing kinetics and particularly the diameter growth and inter-particle distance as a function of time and temperature using the techniques of small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). Using the Beaucage model, the SAXS data demonstrates that the particle size reaches equilibrium after approximately 70 minutes of curing at 240 °C. This result is also observed in the XRD results where the half width of the diffraction peaks becomes smaller quickly during the initial hour. In a parallel experiment using DSC, the exothermic heat flow increases rapidly during the first hour but does not reach completion until almost 150 minutes.     

Microwave activation of electrochemical processes: enhanced PbO2 electrodeposition, stripping and electrocatalysis

Microwave activation of electrochemical processes has recently been introduced as a new technique for the enhancement and control of processes at electrode|solution (electrolyte) interfaces. This methodology is extended to processes at glassy carbon and boron-doped diamond electrodes. Deposition of both Pb metal and PbO₂ from an aqueous solution of Pb²⁺ (0.1 M HNO₃) are affected by microwave radiation. The formation of PbO₂ on anodically pre-treated boron-doped diamond is demonstrated to change from kinetically sluggish and poorly defined at room temperature to nearly diffusion controlled and well defined in the presence of microwave activation. Calibration of the temperature at the electrode|solution (electrolyte) interface with the Fe^3+/2+ (0.1 M HNO₃) redox system allows the experimentally observed effects to be identified as predominantly thermal in nature and therefore consistent with a localized heating effect at the electrode|solution interface. The microwave-activated deposition of PbO₂ on boron-doped diamond remains facile in the presence of excess oxidizable organic compounds such as ethylene glycol. An increase of the current for the electrocatalytic oxidation of ethylene glycol at PbO₂/boron-doped diamond electrodes in the presence of microwave radiation is observed. Preliminary results suggest that the electrodissolution of solid microparticles of PbO₂ abrasively attached to the surface of a glassy carbon electrode is also enhanced in the presence of microwave radiation. Electronic Publication