The influence of ultrasonic irradiation on the electrochemiluminescence evolved from the electrochemical oxidation reaction of tris(2,2′-bipyridyl)ruthenium(II) chloride [Ru(bpy) 3 Cl 2 ] or tris(1,10-phenanthroline)ruthenium (II)chloride [Ru(phen) 3 Cl 2 ] in aqueous oxalate has been examined. Under the conditions described here, insonation resulted in an increase in the luminescence yield of over 100%, in a highly reproducible manner. These effects were found to result from ultrasonic irradiation and can be understood with reference to the changes in mass transport of reactants through the bulk solution and modification of the electrode Nernst diffusion layer that have been observed by other workers. A relationship between the light intensity and the square of the cell current was observed under various ultrasound powers, and it was found that this is consistent with the kinetic scheme proposed by Bard et al. for the electrooxidation reaction under silent conditions. This indicates that the reaction mechanism under insonation is consistent with that proposed for the silent reaction. The electrochemiluminescence spectrum under insonation was measured with greater precision than previously and was shown to be identical to that under silent conditions. Luminescence quenching by oxygen, problematic in earlier reports, was measured under insonation and also with greater precision than previously in the silent system. The Stern-Volmer relationship was obeyed under both sets of conditions, and oxygen quenching phenomena appear to be unaffected by insonation of the system.

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The Modified Simplex Method (MSM) coupled with contour diagrams is used to determine the rate constants of a kinetic scheme involving three sequential second order processes.Reaction between glutathione and the dithiocarbamate fungicide tetramethylthiuram disulfide produces the oxidized form of glutathione which is then reduced in the presence of NADPH. The concentration of the reducing agent is monitored as a function of time. In the absence of simplifying assumption a closed form solution of the rate equations does not exist. Computed curves of NADPH concentration versus time were generated using the software SIMULCIN.The rate constant values are optimized by the MSM procedure to obtain the best agreement between calculated and experimental data. The significance, validity limits of the estimated rate constants and the relevance of these in vitro data to previous in vivo studies are discussed.

Laboratoire de Chimie Organique Physique -C.P. 160/08, Universite Libre de Bruxelles -50, av. F.D. Roosevelt, 1050 Bruxelles (Belgium) Dedicated to Professor Jacqiies Nasielski (ULB) oti the occasiori of his retiretiterit ABSTRACTThe luminescence spectra of tris(pheny1pyridine)iridium embedded in Arnberlite (polystyrene adsorbent) have been measured under various 0dN2 mixtures (total pressure = 1 atm). It is shown that the Stern-Volmer plots are downward curved and that the curvature can be explained either by a two-site model or by a negative deviation from Henry's law. A curve fitting procedure cannot distinguish between the two models.Using a frequency modulated blue LED and a fiber optic set-up, 0 2 partial pressure of 0.4 mbar could be detected. Oxygen can be determined at 200 mbar with a f 1.5% accuracy.