The title reaction was studied in different reaction media: aqueous salt solutions (NaNO3) and water-cosolvent (methanol) mixtures. The observed rate constants, k(obs), show normal behavior in the solutions containing the electrolyte, that is, a negative salt effect. However, the solvent effect is abnormal, because a decrease of the rate constant is observed when the dielectric constant of the reaction medium decreases. These effects (the normal and the abnormal) can be explained using the Marcus-Hush treatment for electron transfer reactions. To apply this treatment, the true, unimolecular, electron-transfer rate constants, k(et), have been obtained from k(obs) after calculation of the rate constants corresponding to the formation of the encounter complex from the separate reactants, k(D), and the dissociation of this complex, k(-D). This calculation has been carried out using an exponential mean spherical approach (EMSA).

The title reaction was studied in different water-cosolvent (methanol) mixtures. The results have been rationalized employing the Marcus-Hush treatment. To apply this treatment, the true, unimolecular, electron-transfer rate constants (k et ) were obtained from the experimentally measured rate constants after calculation of the equilibrium constant for the processes of formation of the encounter complex. This calculation was carried out using EigenFuoss (EF) and exponential mean spherical (EMSA) approaches employing effective values of the solvent dielectric constant. These effective values were obtained from the measured association constants corresponding to other ion pairs. The results reveal that in these media there is an additional component of reorganization energy, absent in neat solvents. An explanation of the origin of this component is given. C 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 658

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We explore the possibilities of the CIELab chromaticity system parameters' evolution in order to study the interaction between four non-colored biological reactants and the red-colored, non-functionalized citrate gold nanoparticles.

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