Analysis and improvement of rate constant determination of reactions involving charged reactants.
Kinetics of tris(2,2'-bipyridine)ruthenium(ii), Ru(bpy)(3)(2+), luminescence quenching by copper(ii) (in the form of chloride, nitrate, sulfate and perchlorate salt) was studied using pulse laser photolysis technique. The pseudo-first order rate constant versus quencher concentration plots obtained were found to be nonlinear, bending upward. The ionic strength effect contribution was evaluated by applying the Debye-Hückel extended law and was found to be as important as other effects such as cation-counter anion complex and ion-pairing complex formation which were all found to be dependent on the counter anion. It is shown that the slope of the tangent line to the pseudo-first order curve at zero quencher concentration is equal to the quenching rate constants at zero ionic strength. Also, this value corresponds to quenching solely by Cu(2+) and is free from contributions from other species that are present at higher concentrations. This method produced a value, (1.6 +/- 0.2) x 10(7) M(-1) s(-1), (lower than previously published ones) which is in agreement with the quenching rate constant measurement analysis presented. Comparison between Stern-Volmer plots obtained using steady-state fluorimetry data and laser photolysis data showed that in 50 mM CuCl(2) and CuSO(4) aqueous solutions about 5% of Ru(bpy)(3)(2+) is in the form of ion-pairing complexes. Our method was also applied to quenching by another divalent cation, methyl viologen, where it was found that charge transfer complexation effect contribution was about 50% of that of ionic strength effect, while ion-pairing complexation was not significant in the concentration range used. The quenching rate constant at zero ionic strength was found to be (2.3 +/- 0.2) x 10(8) M(-1) s(-1). The method proposed is also applicable to pulse radiolysis and stopped flow measurements.
Salt effects on nearly diffusion controlled electron-transfer reactions: bimolecular rate constants and cage escape yields in oxidative quenching of tris(2,2'-bipyridine)ruthenium(II)
The rate constants for the quenching of excited Ru(bpy)/sub 3//sup 2 +/ by methylviologen (MV/sup 2 +/) and Ru(NH/sub 3/)/sub 5/py/sup 3 +/ have been studied in aqueous solution as a function of the concentration (0.01-1 M) and type (NaCl, NaClO/sub 4/, CaCl/sub 2/) of added electrolyte. With MV/sup 2 +/ as quencher, the yield of products escaping cage recombination and the rate constant of their back electron transfer reaction have also been studied as a function of the concentration of added NaCl. The results have been compared with prediction based on expressions available in the literature for the ionic strength dependence of diffusional parameters k/sub d/ and k/sub -d/. With uni-univalent electrolytes, the Debye and Eigen equations appear to be adequate for the calculation of k/sub d/ and k/sub -d/, respectively, provided that the appropriate numerical integration over the interreactant distance is performed. Approximations leading to more tractable expressions (such as, e.g., those leading to a Broensted-Bjerrum ionic strength dependence of k/sub d/) give rise to serious disagreement with experiments. Specific counterion effects (ClO/sub 4//sup -/ faster than Cl/sup -/) are observed that can be best interpreted in terms of changes in the rate of the unimolecular electron-transfer stepmore » within an encounter complex including the counterion. Also, counterion concentration rather than ionic strength better represents (Olson-Simonson effect) the salt effects obtained with the CaCl/sub 2/ electrolyte.« less
The development of a liquid antihistaminic preparation with sustained release properties.
The relative capacity of several cation exchange resins to adsorb methapyrilene has been determined by an in vitro method. It was demonstrated that methapyrilene adsorbed on sulfonic acid cation exchange resin possessed pharmacological activity approximating that of a solution of methapyrilene hydrochloride as measured by the protection against histamine-induced asthma in the intact guinea pig. It is suggested that the use of ion exchange resins as carriers of drugs in liquid dosage forms may be useful in sustained release preparations.