The kinetics of the electron-transfer reaction between pentaamminepyridine ruthenium (II) perchlorate, [Ru(NH3)5py](ClO4)2, and sodium peroxodisulfate, Na2S2O8, was studied in DNA and SDS micellar solutions. The results can be interpreted by taking as a starting point the pseudophase model. However, the model must be modified according to the characteristics of the reaction media. Thus, the binding of the substrate (the ruthenium complex) to DNA is anticooperative in character, in such a way that the binding constant increases as the [DNA]/[Ru(NH3)5py] 2+ ratio increases. On the other hand, the binding of the ruthenium complex to SDS micelles decreases as the [SDS]/[Ru(NH3)5py] 2+ ratio increases as a consequence of the changes of the surface potential of the micelles.
A study of the metal-to-metal charge-transfer transition within the binuclear complex pentaammineruthenium(III)(µ-cyano)pentacyanoiron(II), (NH3)5Ru III -NC-Fe II (CN)5 -, was carried out in salt solutions, water-cosolvent mixtures, and micellar solutions containing sodium dodecyl sulfate and hexadecyltrimethylammonium chloride (CTACl). Using these data, as well as the reaction free energies (obtained from electrochemical measurements), the rate constants, ket, for the forward and reverse electron-transfer processes have been estimated and compared with data for this and related electron-transfer processes existing in the literature for electrolyte and water-cosolvent solutions. The approximations involved in the method of estimating electron-transfer rate constants are discussed. In the case of micellar solutions, the reorganization energies and driving forces were obtained. The results in these microheterogeneous systems are interpreted taking into account the long-range (Colulombic) interactions between the mixed valence complex and the micellar electric field, along with the short-range electric field derived effects, the latter coming through the dielectric saturation phenomenom produced by the micellar electric field on the solvent surrounding the binuclear complex, when it is near the micellar (CTACl) surface.
A T-jump study of the 3,5-dinitrohydroxybenzoic acid (DNSA)/ammonia system has been undertaken, as a
function of the nature and concentration of the added salt. Rate constants for the different possible proton-transfer reactions have been obtained from the experimental relaxation curves. The mechanism has been
analyzed with the aid of a theoretical model based on Marcus- like free energy surfaces for each elementary
step. Despite possible uncertainties in the estimations and approximations used, two conclusions seem to be
well founded: first, the stepwise character of the proton-transfer reactions involving DNSA, and second, the
possible change in the mechanism connected with the change in the final proton acceptor in the deprotonation
of DNSA. This result, not previously assessed in the literature, is relevant for analyzing the salt effects, as
is discussed in this work, and also for the hypothetical application of such a system in a molecular protonic
device, an area of current research interest. Finally, the use of the well-known plot of log(k) versus ΔpK
a for
analyzing the negative or positive salt effects on the proton-transfer reactions is suggested.
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