Simon B. Hall

Electrochemical oxidation of hydrogen peroxide at platinum electrodes. Part 1. An adsorption-controlled mechanism

The electrochemical oxidation of H2O2 at a platinum rotating disk electrode was studied at pH 7.26 for the [H2O2] range 0–80 mM and for rotation rates 630–10,000 r.p.m. A mechanism is proposed to account for the steady-state current response as a function of both rotation rate and [H2O2]. The mechanism incorporates reversible binding of hydrogen peroxide to electrochemically generated Pt(II) surface sites with inhibiting competitive adsorption of dioxygen at these sites. A further inhibiting side reaction is also identified involving protonation of the surface adsorbed H2O2 complex.

Electrochemical oxidation of hydrogen peroxide at platinum electrodes. Part II: effect of potential

The electrochemical oxidation of H2O2 at a platinum rotating disc electrode was studied in 0.1 M phosphate buffer at pH 7.26 for the [H2O2] range 0–40 mM, rotation rates 630–10000 rpm and anodic potential +264 to +712 mV vs. Ag/AgCl using staircase potentiometry over the temperature range 5–35°C. The results were interpreted in terms of a surface binding site model involving two modes of product inhibition. Potential- and temperature-invariant values of the constants for H2O2, H+ and O2 binding were determined and the rate constants for reduction and the re-oxidation of the binding site as a function of potential and temperature were evaluated together with the activation energy for the reduction of the binding site.

Electrochemical oxidation of hydrogen peroxide at platinum electrodes. Part V: inhibition by chloride

The electrochemical oxidation of H2O2 at platinum rotating disc electrodes and microelectrodes was studied in the presence of chloride in the range 0‐120 mM at pH 7.3. Oxidation was inhibited by chloride with greater inhibition at higher electrode rotation rates. The mode of inhibition was deduced to be non-competitive with the chloride interacting with precursor binding sites at the electrode surface, since increased [H2O2] did not decrease the degree of inhibition. The rotation rate dependence indicates that it is likely a soluble platinum complex involving chloride forms to remove binding sites from the electrode surface.

Electrochemical oxidation of hydrogen peroxide at platinum electrodes. Part IV: phosphate buffer dependence

Abstract The electrochemical oxidation of H 2 O 2 at platinum rotating disc electrodes and microelectrodes was studied as a function of phosphate buffer concentration in the range 0–100 mM and pH from pH 4 to pH 10. The results were interpreted in terms of development of a surface binding site for H 2 O 2 from a precursor site through interaction with H 2 PO 4 − from the electrolyte. In the absence of phosphate an alternative binding site mechanism was evident. The precursor site was shown to be inhibited by protons at low pH producing an inactive site.

A reassessment of the applicability of the DLVO theory as an explanation for the Schulze-Hardy rule for colloid aggregation

Abstract Shortcomings in the application of the DLVO theory in explaining the observations of the Schulze-Hardy rule occur because of inappropriate simplifications. Previous authors (14, 15) have commented that an approximation valid for high surface potentials is difficult to reconcile with the aggregation of low potential particles. In addition to this, we suggest that a further simplification, assuming only weak electrostatic interaction between particles, is also inappropriate in explaining the Schulze-Hardy rule. We derive a new expression that determines the critical ionic strength for the coagulation of low potential colloids in terms of the interfacial charge density. The new equation is more general than previous expressions since the ionic strength may be used to describe nonideal unsymmetrical electrolytes, and the charge density is a more fundamental parameter than surface potential. The concept of restabilization in coalescing emulsions is described and discussed in terms of the new expression for critical aggregation ionic strength.

Safer total parenteral nutrition based on speciation analysis.

Publisher Summary This chapter describes each of the fundamental components of Total parenteral nutrition (TPN) fluids––namely, water, nitrogen and energy sources, minerals, vitamins, and administered drugs. The equations governing the physical chemistry are indicated and overlapping interactions are suggested. TPN is a means of providing all the nutritional requirements of seriously ill patients using carbohydrates, fats, nitrogen (as amino acids), electrolytes, trace elements, and vitamins so that a positive nutritional status is achieved. TPN may also be used to denote ‘total parenteral nutrition’ as in TPN fluid. The clinical uses of TPN are ahead of the scientific theories, but by a concentrated attack upon quantifying the speciation present in TPN fluids and plasma-TPN mixtures, it is possible to narrow this gap and to enhance safety considerations. The basic concept is that computer simulation of the speciation can be more thorough and give a more complete appraisal of species present in solution than is possible by solely experimental measurements of just one or two of the concentrations of the species more accessible to modern instrumentation. The simulation approach is to combine total concentrations of metals, amino acids, and ligands for a particular fluid with the appropriate formation constants and solubility products.

Glassy Carbon Based Sensors

Sensing moiteies may be covalently attached to glassy carbon by reduction of functionalised diazonium salts [1,2]. The attachment of glucose oxidase with a cinnamic acid linker provides an example of simple tethering using this technique. An electrode formed in this way exhibits little susceptibility to interference from ascorbic acid and 4-acetamidophenol. A pH-reponsive (56.18 mV decade -1 ) glassy carbon electrode is formed by grafting quinone groups to the electrode with stilbene linkers.

A stochastic computer simulation of emulsion coalescence

Abstract As simple expressions cannot completely describe the phenomena of emulsion coalescence, a recursive stochastic model was developed. The model, embodied in a computer program, considers interactions between randomly selected pairs of particles from an emulsion particle size distribution; in the absence of a calculated energy barrier coalescence is predicted and a new particle is formed. The simulations produce volume histograms which confirm the restabilization phenomena introduced in a previous paper (S. B. Hall, J. R. Duffield, and D. R. Williams, J. Colloid Interface Sci. 143 , 1991), namely, that coalescence need not result in the complete separation of an emulsion into two distinct phases since particles formed by coalescence are inherently more stable than the precursor particles. The critical aggregation ionic strength derived in that paper describes only the transition point between stability and instability; only the stochastic approach determines the extent of coalescence beyond this point. The potential of this approach is illustrated with the simulation coalescence of an intravenous fat emulsion.

Vibrational Spectra and Calculations on Substituted Terthiophenes

Conjugated polymers based on β-substituted terthiophenes are a very interesting class of materials with applications in solar cells and in electroluminescent screen technologies. In order to better understand the properties of these systems we have studied the terthiophenes using ub initio calculations. These calculations reveal a good correspondence with predicted and experimental electronic and vibrational spectral data. Analysis of the normal modes suggests localized terthiophene, phenyl and ethene modes are present.

The Supramolecular Assembly of Porphyrin Arrays

The self-assembly of porphyrin arrays containing three, seven or eleven porphyrins results from the interaction of the bis-pyridyl porphyrin 1 with the zinc porphyrins 2, 3, or 4, respectively.