Biomedical subjects

J F Rusling

Publications and source records attributed to J F Rusling.

15 recordsLinked to original sources

PubMed1994

Films formed by oxidation of ferrocene at platinum electrodes.

Oxidation of ferrocene in acetonitrile resulted in films on Pt electrodes under voltammetric conditions. Films were more readily formed with tetrabutylammonium tetrafluoroborate as the electrolyte than with perchlorate salts. No films were detected when ferrocene was oxidized in aqueous 0.05 M cetyltrimethylammonium bromide (CTAB). Analysis of the films by FT-IR and Auger spectroscopy confirmed iron-containing oxidation products on Pt, presumably from chemical reactions of ferricinium ions. Oxidation of 50-100 mM ferrocene in acetonitrile on Pt yielded insoluble precipitates. Analyses by MS, FT-IR, and UV-visible (water extract), suggested a mixture of oligomeric material and a small fraction of ferricinium ions. Film formation had much less influence on voltammograms on 12.5-micron-radius Pt microdisks than on 0.5-mm-radius Pt. This is consistent with the smaller sensitivity of microelectrodes to chemical reactions following charge transfer. The smaller apparent heterogeneous rate constants (k zero') found for ferrocene on macroelectrodes than on microelectrodes could possibly be influenced by film formation on larger Pt electrodes. Correlations between macro- and microelectrode kinetic data suggest that macroelectrode k zero' values may be valid in a relative sense when ohmic drop is negligible. Bias in k zero's on conventional-sized electrodes should be small in solutions giving minimal film formation, such as micellar CTAB.

Electrochemistry↗

PubMed1992

Stable films of cationic surfactants and phthalocyaninetetrasulfonate catalysts.

Films made from cationic surfactants and well-retained redox catalysts were investigated. Full loading of metal phthalocyaninetetrasulfonates (MPcTS4-) into water-insoluble dialkyldimethylammonium surfactants by ion exchange from aqueous solutions yielded coatings on electrodes that retain these catalyst ions for 1-2 weeks in electrolyte solutions. In contrast, partly loaded films lost most MPcTS4- ions in a few hours. All films showed gel-to-liquid crystal phase transitions at temperatures characteristic of surfactant bilayers. Cross-sectional views by SEM showed layers of 0.1-0.2 micron, as well as some disordered regions. Each larger layer is probably made up of stacks of many molecular bilayers. Retention of MPcTS4- ions seems related to their dimerization. Dimers of MPcTS4- associated with ammonium head groups may crosslink adjacent surfactant bilayers. The MPcTS4- ions that enhance stability in these films are also good redox catalysts.

Calorimetry↗

PubMed1991

Surfactant-intercalated clay films for electrochemical catalysis. Reduction of trichloroacetic acid.

Composite films made from insoluble dialkyldimethylammonium surfactants and clay colloids were evaluated for electrochemical catalysis. When cast on pyrolytic graphite (PG) electrodes from chloroform, the films act as charge-transfer barriers toward multivalent electroactive ions in solution. They take up ions with hydrophobic ligands, e.g. tris-(2,2'-bipyridyl)cobalt(II). To make catalytic electrodes, water-insoluble cobalt and iron phthalocyanines (CoPc and FePc) were dissolved in surfactant-clay dispersions in chloroform and cast on PG. Films containing CoPc were 35-fold more active than FePc films for catalytic reduction of trichloroacetic acid. CoPc films decreased overpotential for reduction of trichloroacetic acid by about 0.5 V compared to 0.05 V for FePc. These MPc films gave stable catalytic currents for at least 10 days. Catalytic current vs temperature plots for reduction of trichloroacetic acid showed linear branches with intersection points close to reported gel-to-liquid crystal-phase transition temperatures. Charge transport was faster in the liquid crystal than the gel phase of the films. Observation of phase transitions suggests a multibilayer structure.

Aluminum Silicates↗

PubMed1990

Bicontinuous microemulsions as media for electrochemical studies.

Biocontinuous microemulsions of didodecyldimethylammonium bromide (DDAB)/dodecane/water were explored as media for voltammetric reductions and oxidations of ruthenium(III) hexaammine, ferrocyanide, ferrocene, cob(II)alamin, and several polycyclic aromatic hydrocarbons (PAHs). These clear microemulsions are conductive and are believed to contain a dynamic extended network of interconnected water tubules. Agreement of simulated and experimental voltammetric data shows that electrochemical theory for homogeneous media is followed to a good approximation in DDAB microemulsions. Diffusion of electroactive solutes did not reflect the high bulk viscosities of the microemulsions. Non-polar molecules and ions diffuse as if they were in neat oil or aqueous media, respectively, and voltammograms with good signal to noise ratio are obtained. Reductions of PAHs in the microemulsions occurred by an ECE-type pathway, with nearly reversible one-electron reductions achieved at high scan rates.

Electrochemistry↗

PubMed1990

Simulation of two-electron homogeneous electrocatalysis for steady-state voltammetry at hemispherical microelectrodes.

Expanded space grid digital simulation of second-order, two-electron homogeneous electrocatalysis was extended to slow scan voltammetry at hemispherical microelectrodes. Predictions of the simulations are examined for reversible and quasireversible heterogeneous charge transfer of catalyst for a range of homogeneous catalytic rate constants (k1) and electrode radii. Working curves of catalytic efficiency vs long k1 were generated assuming reacting species with equal diffusion coefficients. As electrode radii in the less than 10-microns range decrease, progressively larger homogeneous catalytic rates are needed to yield analytically significant amplification of limiting currents. Simulations using hemispherical radii of (2/pi)rd can be used to predict catalytic efficiencies for microdisk electrodes with radii rd. Simulated working curves were used to estimate a log k1 of 3.88 +/- 0.55 (M-1 s-1) for electron transfer from the anion radical of 9,10-diphenylanthracene to 4,4'-dibromobiphenyl from steady-state catalytic efficiencies obtained at carbon microdisk electrodes. This value was in good agreement with 3.90 +/- 0.16 M-1 s-1 found previously by cyclic voltammetry.

Catalysis↗

PubMed1988