Biomedical subjects

W Ronald Fawcett

Publications and source records attributed to W Ronald Fawcett.

9 recordsLinked to original sources

PubMed2006

New developments in the theory of the diffuse double layer.

The role of ion size effects in determining diffuse layer properties is considered. Monte Carlo data relevant to this question are reviewed. Then the integral equation approach to the problem is considered with an emphasis on attempts to derive an analytical equation for the potential drop across the diffuse layer. An empirical model for ion size effects is described that allows one to estimate not only the diffuse layer potential drop but also the diffuse layer capacity, the ionic surface excesses, and the potential distribution in the diffuse layer. It is demonstrated that the resulting model can easily be applied by experimentalists to the analysis of experimental data for double layer phenomena in electrochemistry and colloid science.

Journal Article↗

PubMed2006

Medium effects for very fast electron transfer reactions at electrodes: the [Ru(NH3)6]3+/2+ system in water.

The reduction kinetics of [Ru(NH(3))(6)](3+) was studied at Au(111) and Au(100) single-crystal ultramicroelectrodes in dilute perchloric acid electrolytes. Both heterogeneous rate constants and experimental transfer coefficients varied with the crystallographic orientation of the gold surface. The value of the heterogeneous rate constant at Au(111) was significantly larger than that at Au(100). The experimental transfer coefficients also increased but in the opposite order. Standard rate constants at both electrodes increased with an increase in electrolyte concentration. Using double-layer data obtained in 0.01 M HClO(4), it is shown that the true transfer coefficient for this reaction is 0.5 within experimental error. The effective charge on the reactant which has a nominal charge of +3 is close to +1. The latter result reflects the distribution of charge within the polyatomic reactant.

Journal Article↗

PubMed2006

High-performance liquid chromatography-ultraviolet-visible spectroscopy-electrospray ionization mass spectrometry method for acrylic and polyester forensic fiber dye analysis.

A critical point of comparison between a fiber collected from a crime scene and a fiber from a known source is the color. Fiber dye analysis using thin-layer chromatography or ultraviolet (UV)-visible (Vis) microspectrophotometry provides useful, although limited, data for comparison. High-performance liquid chromatography-electrospray ionization mass spectrometry (LC/MS) overcomes these limitations by integrating chromatography, ultraviolet-visible spectroscopy, and mass spectrometry into a single instrument. In order to evaluate the applicability of the LC/MS to forensic fiber dye analysis, a multi-stage chromatographic method using acidified water and acidified acetonitrile was developed that separated and identified a mixture of 15 basic and 13 disperse dye standards. The LC/MS also detected and analyzed dyes extracted from individual 0.5 cm acrylic and polyester fibers, demonstrating its applicability to this type of analysis. With regard to the analysis of disperse dyes in polyester fibers, the replacement of pyridine with acetonitrile in the extraction system allowed direct injection of the extracts into the LC/MS. The advantage of the LC/MS over other instrumental methods of textile dye analysis is demonstrated by the analysis and differentiation of three black acrylic fibers: two fibers had similar UV-Vis spectra but were differentiated with chromatography and two had similar UV-Vis spectra and chromatograms but were differentiated using the mass spectrometer.

Journal Article↗

PubMed2005

Infrared (attenuated total reflection) study of propylene carbonate solutions containing lithium and sodium perchlorate.

Attenuated total reflection infrared spectroscopy was used to examine the concentration dependent solvation of LiClO4 and NaClO4 electrolytes in propylene carbonate (PC). Factor analysis and curve fitting techniques were performed on the measured spectra and the results compared with ab initio computations to provide evidence for ion-solvent solution geometries. Factor analysis of the measured data allowed the identification of the spectrum of ion-associated PC that is uniquely different from the self-associated PC spectrum. The results indicate Li+ and ClO4- ions are contact ion-paired even at relatively low electrolyte concentrations whereas Na+ and ClO4- ions are not, up to approximately 2 mol dm-3.

Cations↗

PubMed2005

Application of the hypernetted chain approximation to the electrical double layer for 2:1 and 1:2 electrolytes.

The equations needed to estimate the potential drop across the diffuse layer according to the hypernetted chain approximation (HNCA) are derived in this paper for 2:1 and 1:2 electrolytes at the restricted primitive level. It is shown that HNCA results can be expressed in the same format as the corresponding Gouy-Chapman equations with inclusion of two modifying functions. One function depends on the fraction of the solution volume occupied by the ions, and the other depends on the reciprocal thickness of the ionic atmosphere surrounding each ion. In addition, an expression for the potential profile in the diffuse layer for 2:1 and 1:2 electrolyte solutions is derived according to Gouy-Chapman theory. The modifying functions in the HNCA are then estimated using the Henderson-Blum approach for solutions containing ions with diameters of 300 and 400 pm for concentrations in the range from 0.1 to 2 M. It is shown that the Henderson-Blum approach is inadequate for systems with multivalent ions except for charge densities very close to the point of zero charge.

Journal Article↗

PubMed2005

Role of charge distribution in the reactant and product in double layer effects: construction of corrected Tafel plots.

The effect of charge distribution within Cr(III) and Eu(III) aquacomplexes on the kinetics of simple electron-transfer reactions at electrodes is considered. The construction of corrected Tafel plots using noninteger effective charges for the reactant and product estimated on the basis of quantum-chemical data was shown to be more reasonable than the traditional approach in which integer charges are assumed. The potential distribution near the electrode has been estimated both by the Gouy-Chapman model and from Monte Carlo simulations for 1-1 supporting electrolytes. Kinetic parameters obtained using the two approaches are compared.

Journal Article↗

PubMed2005

Assessment of ion size effects in the diffuse double layer with use of an integral equation approach.

An analytical expression is developed for the potential drop across the diffuse layer phi(d) in terms of a cubic polynomial in the corresponding estimate in the Gouy-Chapman approximation, phi(d)(GC). The coefficients of this polynomial are defined in terms of the MSA volume fraction eta and the reciprocal distance parameter Gamma. The resulting expression is shown to describe the Monte Carlo estimates of phi(d) obtained in a primitive level simulation of diffuse layer properties.

Journal Article↗

PubMed2004

Use of ac admittance voltammetry to study very fast electron-transfer reactions. The [Ru(NH3)6]3+/2+ system in water.

The kinetics of electroreduction of Ru(NH3)6(3+) has been studied at a polycrystalline gold electrode using high-frequency ac admittance voltammetry. It is shown that precise kinetic data may be obtained for a very fast electron-transfer reaction using this technique. The kinetic data show a small double layer effect when the concentration of HClO4 used as background electrolyte is varied. This is discussed in terms of the point of zero charge, which is very close to the standard potential for the studied reaction.

Conductometry↗

PubMed2003

Fabrication and AFM investigation of the temperature-dependent surface morphology of Au (100) single crystal ultramicroelectrodes.

A previously reported method for preparation of gold (111) single-crystal utramicroelectrodes (scumes) has been used to fabricate gold (100) scumes with effective diameters from 20 to 50 microm. Cyclic voltammograms for these ultramicroelectrodes obtained in perchloric acid show similar features to gold (100) single-crystal electrodes of more conventional sizes, but with differences that are a result of different surface preparation methods used before the measurement. The gold crystals used to prepare Au (100) scumes were grown at room temperature so that the cyclic voltammetric characteristics reflect the unique properties of a room temperature-ordered surface. The AFM images of the (100) facets of these crystals are also presented. The effects of annealing Au (100) at 800 degrees C for a short time were studied both electrochemically and using AFM and are discussed with respect to the data obtained for crystals grown at room temperature.

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