Spatially resolved electrochemiluminescence on an array of electrode tips.

An array of electrode tips with 6-microm center-to-center spacing, fabricated through chemical etching of an optical fiber bundle, and coated with gold, was used for initiating electrochemiluminescence (ECL) in an aqueous solution of Ru(bpy)3(2+) and tri-n-propylamine (TPrA). ECL generated at the tips of the electrodes in the array was detected with a CCD camera and exhibited both high sensitivity and high resolution. In the case in which the ECL signal could not be distinguished from the background, ECL signals could be obtained by pulsing the array and summing multiple CCD images. The behavior of this array was compared to a second array that consisted of individual electrodes insulated with an electrophoretic paint.

Mapping concentration profiles within the diffusion layer of an electrode: application to redox catalysis.

Catalytic reductions of some aromatic halides were performed at a millimetric electrode with several redox mediators. The resulting concentration profiles were monitored amperometrically by placing an ultramicroelectrode inside the diffusion layer produced at the former electrode. The features of redox catalysis and the subsequent structuring of the diffusion layer were investigated experimentally under steady-state conditions imposed by the spontaneous convection of the solution. The concentration profiles established from the probe measurements were in agreement with our theoretical predictions, based on fast kinetics of redox catalysis. Under these conditions, very similar to preparative electrosynthesis, the diffusion layer separates into two domains where pure diffusion takes place and the concentration profiles therein are mainly linear. We demonstrate that the limit between these two zones does not depend on kinetics, but is rather fixed by the product of the ratio of the bulk concentrations of each species and the ratio of their diffusion coefficients.

Micrometrically controlled surface modification of Teflon by redox catalysis: electrochemical coupling between Teflon and a gold band ultramicroelectrode

Carbon-fluorine bonds of Teflon (polytetrafluoroethylene, PTFE) can be reduced electrochemically with the purpose of modifying its adhesive and wetting surface properties by micrometrically controlled surface carbonization of the material. This can be performed adequately by redox catalysis provided that the redox mediator couple has a sufficiently negative reduction potential. The process is investigated kinetically with benzonitrile as the mediator and a gold-band ultramicroelectrode mounted adjacent to a PTFE block, though separated from it by an insulating micrometric mylar gap. For moderate fluxes of reduced mediator, the whole device behaves as a generator-collector double-band assembly with a constant current amplification factor. This is maintained over long periods of time, during which the carbonized PTFE zones extends over distances that are much wider than the slowly expanding cylindrical diffusion layer generated at the gold-microband electrode. This establishes that the overall redox catalysis proceeds through electronic conduction in the n-doped carbonized material. Thus, carbonization progresses at the external edge of the freshly carbonized surface in a diffusion-like fashion (dependence on the square root of time), while the redox-mediator oxidized form is regenerated at the carbonized PTFE edge facing to the gold ultramicroelectrode, so that the overall rate of carbonization is controlled by solution diffusion only. For larger fluxes of mediator, the heterogeneous rate of reduction and doping of PTFE becomes limiting, and the situation is more complex. A conceptually simple model is developed which predicts and explains all the main dynamic features of the system under these circumstances and allows the determination of the heterogeneous rate constant of carbon-fluorine bonds at the interface between the carbonized zone and the fresh PTFE. This model can be further refined to account for the effect of ohmic drop inside the carbonized zone on the heterogeneous reduction rate constants and henceforth gives an extremely satisfactory quantitative agreement with the experimental data.

Neuromuscular and lethal effects of phospholipase A from Vipera ammodytes venom.

Four homogeneous proteins having phospholipase A activity were separated and studied for their i.v. lethal effects in mice and nerve-muscle activity in the guinea pig diaphragm preparation. Fraction "j" had an LD50 of 0.30 mg/kg, with 3.6 microgram/ml of bath solution causing a decrease in the indirectly-elicited nerve-muscle contractions to 20% of control, without significantly changing the directly-elicited muscle contractions. Fraction "k2" had an LD50 of 0.021 mg/kg and caused a similar nerve or nerve-muscle block at 5 micrograms/ml of bath solution, without altering the directly-elicited contractions. Fraction "k1" had an LD50 of 0.58 mg/kg and produced less distinct but dose-related changes in the nerve or in nerve-muscle transmission, as well as weakening directly-elicited muscle contractions to within 60% of control. Fraction "I" had an LD50 of 3.6 mg/kg but high doses of the fraction were required to produce changes in diaphragm contractility. High doses (60 and 195 micrograms/ml) produced marked effects on both the directly- and indirectly-elicited contractions, suggesting that this fraction affects the muscle directly.

Extracorporeal hyposensitization.

Sensitized guinea pigs were reinjected with autologous cells of the buffy coat or T-cell enriched populations of lymphocytes following incubation with sensitizing antigen. The incubated cells of the buffy coat appeared to give the animal protection from severe signs and lesser manifestations of anaphylaxis.