Influence of the Micellar Electric Field on Electron-Transfer Processes (II): A Study of the Ru(NH3)5pz2+ + Co(C2O4)33- Reaction in SDS Micellar Solution Containing NaCl
Abstract:Micellar effects on the oxidation reaction of [Ru(NH3)5pz]2+ with [Co(C2O4)3]3- in the presence of different
NaCl concentrations were studied. Experimental results are discussed by using an approach based on the
transition-state theory. It is shown that this approach used here is better than others based on the
pseudophase model, which can also be used, because the former is able to give a clear meaning to the
parameters of the model. Changes in the observed reactivity are explained by a change in the degree o… Show more
“…After this minimum, k obs increases as the CTACl concentration does. This variation of k obs is qualitatively similar to that observed for this reaction in the presence of micelles of SDS (see ref ). 2 Plot of k obs (s -1 ) of the process [Ru(NH 3 ) 5 pz] 2+ + [Co(C 2 O 4 ) 3 ] 3- versus CTACl concentration.…”
Section: Discussionsupporting
confidence: 88%
“…It should be mentioned that the reaction studied here has been previously studied in micellar solutions of sodium dodecyl sulfate (SDS) . The results obtained in this work will also be considered here for comparative purposes.…”
The kinetics of the electron-transfer reaction between pentaaminepyrazine ruthenium(II), [Ru(NH3)5-pz] 2+ , and trisoxalatecobaltate(III), [Co(C2O4)3] 3-, was studied in sodium bis(2-ethylhexyl)sulfosuccinateoil-water microemulsions and in micellar solutions of hexadecyltrimethylammonium chloride. 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. In this way, two different equations result for this model in the two reaction media studied. The influence of the surface potential on the parameters (equilibrium and rate constants) of the model is shown.
“…After this minimum, k obs increases as the CTACl concentration does. This variation of k obs is qualitatively similar to that observed for this reaction in the presence of micelles of SDS (see ref ). 2 Plot of k obs (s -1 ) of the process [Ru(NH 3 ) 5 pz] 2+ + [Co(C 2 O 4 ) 3 ] 3- versus CTACl concentration.…”
Section: Discussionsupporting
confidence: 88%
“…It should be mentioned that the reaction studied here has been previously studied in micellar solutions of sodium dodecyl sulfate (SDS) . The results obtained in this work will also be considered here for comparative purposes.…”
The kinetics of the electron-transfer reaction between pentaaminepyrazine ruthenium(II), [Ru(NH3)5-pz] 2+ , and trisoxalatecobaltate(III), [Co(C2O4)3] 3-, was studied in sodium bis(2-ethylhexyl)sulfosuccinateoil-water microemulsions and in micellar solutions of hexadecyltrimethylammonium chloride. 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. In this way, two different equations result for this model in the two reaction media studied. The influence of the surface potential on the parameters (equilibrium and rate constants) of the model is shown.
“…Of course, these are only estimated values because they depend on the location of the species which binds to the receptor, that is, on the α value. In any case, the values obtained assuming α = 1 are of the same order as those obtained previously by us in DNA and other charged receptors using other methods. , …”
The process *Ru(bpy)(3)(2+) + S(2)O(8)(2-) in two different reaction media, the SB4.5G dendrimer and DNA solutions, was studied. In both media, the receptors have anionic characteristics. This fact will produce a binding of the ruthenium complex to the two receptors by attractive electrostatic interactions. On the contrary, the peroxodisulfate ions will be preferentially located in the aqueous solution due to electrostatic repulsions with the receptors. Despite the similarities of the receptors, some differences are observed in these two reaction media. These differences arise from the fact that the binding of the *Ru(bpy)(3)(2+) complex to DNA shows a negative cooperativity, whereas the binding to the dendrimer is noncooperative in character. The anticooperative character of the binding that happens in DNA solutions becomes noncooperative when an electrolyte, NaNO(3), is added to the medium. This is related to a condensation of the salt's counterions on the surface of the DNA which produces a decrease of the equilibrium constant corresponding to the binding of the complex to the receptor. Therefore, it is shown that the ionic strength of the reaction medium exerts a great influence on the cooperative nature of the ligand/receptor binding. This also explains the different behavior observed in DNA and dendrimer solutions.
“…According to the CMC model, the dependence of k obs as a function of bile salt concentrations (see Fig. ) can be written as where T is equal to the total [bile salt] minus the CMC, k aq and k m are the rate constants in the aqueous (at the CMC) and in the micellar pseudophases, respectively, and K M is the binding equilibrium constant of the [Ru(NH 3 ) 5 pz] 2+ molecules to bile anion micelles. Application of Eq.…”
Section: Resultsmentioning
confidence: 99%
“…The main conclusion was that the binding of ruthenium species to NaC aggregates can suitably be described by using a kinetic stepwise self‐association model. In addition, the comparison of the kinetic results for NaC aggregates and sodium dodecyl sulfate (SDS) micelles indicated that the aggregation feature of cholate ions did not lead to the formation of the Stern layer , which is a characteristic of the micellar alkyl systems.…”
The electron transfer reaction between [Ru(NH3)5pz]2+ and [Co(C2O4)3]3− was studied in the presence of monomers and aggregates of bile salts (sodium deoxycholate, sodium taurodeoxycholate, and sodium glycocholate) at 298.2 ± 0.1 K. The results show a decreasing rate constant with the successive addition of bile salts. To rationalize the trends of the reaction rate on the [bile salts], two models were used. One of them takes into account the aggregation feature by considering a stepwise self‐association between monomers, whereas the other assumes the formation of a critical micellar concentration. Binding constants between [Ru(NH3)5pz]2+ species and deoxycholate or taurodeoxycholate aggregates were higher than that for glycocholate aggregates. These results are consistent with the way in which the monomers are added to form the bile anion aggregates.
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