Autocatalytic redox process

During electroless plating, metal is deposited onto the desired surface from solution through an autocatalytic redox process [36]. Specifically, a reductant in the... 

Electroless deposition takes place by an autocatalytic redox process, in which the cation of the metal to be deposited is reduced by a soluble reductant at the surface... 

Substitution and oxidation can often both be involved in reactions of tris(diimine)-iron(II) complexes with oxidizing agents. Thus, for example, reaction with hydrogen peroxide involves rate-determining dissociation as the first step. Similarly, initial dissociation seems to be the first step in the predominant pathway for superoxide oxidation of the [Fe(phen)3] cation. Dissociation may also be involved in reactions of diimine-iron(II) complexes with nitrous acid. Here and elsewhere it is recognized that these complexes react with nitric acid—in the initial stages aquation may be the only important path, but autocatalytic redox processes usually become dominant before aquation is complete, especially for the more easily oxidizable ligands and complexes. ... 

Zhabrova etal. [151] identified the reactions of nickel, cobalt and copper oxalates ( , = 150, 159 and 129 kJ mol respectively) as redox processes in which there is an autocatalytic effect by product metal on the electron transfer step. The decomposition rate was determined by the area of the reactant and results were fitted by the Prout-Tompkins equation. In contrast, the reactions of magnesium, manganese and iron oxalates (f, = 200,167 and 184 kJ mol ) are not autocatalytic and the area... 

Platinum group metal phthalocyanine monomers adsorbed on GCE auto-catalyze the oxidation of cysteine depending on the nature of axial ligands. Table 7.2. When DMSO or cyanide were employed as axial ligands, autocatalytic behavior was observed. Figure 7.2. These complexes also catalyzed the oxidation of methionine, hydroxylamin, and hydrazine. Ring based redox processes were implicated in the catalytic process shown by the following mechanism (Equations (7.8H7.10)) ... 

Actually, the kinetics study of the redox potential of transient clusters (Section 20.3.2) has shown that beyond the critical nuclearity, they receive electrons without delay from an electron donor already present. The critical nuclearity depends on the donor potential and then the autocatalytic growth does not stop until the metal ions or the electron donor are not exhausted (Fig. 8c). An extreme case of the size development occurs, despite the presence of the polymer, when the nucleation induced by radiolytic reduction is followed by a chemical reduction. The donor D does not create new nuclei but allows the supercritical clusters to develop. This process may be used to select the cluster final size by the choice of the radiolytic/chemical reduction ratio. But it also occurs spontaneously any time when even a mild reducing agent is present during the radiolytic synthesis. The specificity of this method is to combine the ion reduction successively ... 

The redox salt which decomposes at 100°C, evolving nitrogen and oxygen [1] is overall an oxidant but has been used as a reducant in actinide processing [2]. Even in the absence of actinides dilute solutions for this may concentrate by evaporation of watrer until there is an autocatalytic runaway. A widely publicised explosion from this cause (there have been others) generated official reports [6]. Stability studies... 

Cluster properties, mostly those that control electron transfer processes such as the redox potential in solution, are markedly dependent on their nuclearity. Therefore, clusters of the same metal may behave as electron donor or as electron acceptor, depending on their size. Pulse radiolysis associated with time-resolved optical absorption spectroscopy is used to generate isolated metal atoms and to observe transitorily the subsequent clusters of progressive nuclearity yielded by coalescence. Applied to silver clusters, the kinetic study of the competition of coalescence with reactions in the presence of added reactants of variable redox potential allows us to describe the autocatalytic processes of growth or corrosion of the clusters by electron transfer. The results provide the size dependence of the redox potential of some metal clusters. The influence of the environment (surfactant, ligand, or support) and the role of electron relay of metal clusters in electron transfer catalysis are discussed. 

Rate constants of the process and the nuclearity-redox potential correlation will be compared with corresponding data obtained in another environment, particularly when a surfactant or an associated ligand is present. The complete analysis of the autocatalytic transfer mechanism will also be compared with the photographic process of electron transfer from hydroquinone developer to clusters supported on silver bromide. 

The redox potentials of short-lived silver clusters have been determined through kinetics methods using reference systems. Depending on their nuclearity, the clusters change behavior from electron donor to electron acceptor, the threshold being controlled by the reference system potential. Bielectronic systems are often used as electron donors in chemistry. When the process is controlled by critical conditions as for clusters, the successive steps of monoelectronic transfer (and not the overall potential), of which only one determines the threshold of autocatalytical electron transfer (or of development) must be separately considered. The present results provide the nuclearity dependence of the silver cluster redox potential in solution close to the transition between the mesoscopic phase and the bulk metal-like phase. A comparison with other literature data allows emphasis on the influence of strong interaction of the environment (surfactant, ligand, or support) on the cluster redox potential and kinetics. Rela-... 

The growth of the polymer film can be followed by cyclic voltammetry since the current peaks related to the polymer redox transformations increase as more and more polymer is deposited. The increase of the surface mass can be detected by using an -> electrochemical quartz microbalance. Such an example is shown in the Figure. In this experiment the positive potential limit of cycling was gradually decreased in order to avoid overoxidation of the polyaniline (PANl) formed. It does not affect the rate of polymerization, i.e., the film growth, since the electrooxidation of aniline is an autocatalytic process. 

Presumably, this very substantial difference reflects the greater contribution of an autocatalytic component of the reaction. This could arise fi-om the fact that superoxide reacts effectively with DTT as shown in Eqn. 6 (Scheme 3) and that the one-electron oxidized product (comparable to the ascorbate radical formed in Scheme 2) produced in this way can, in turn, react with MGd (eqn. S Scheme 3). Apart from illustrating the effectiveness of SOD in inhibiting free radical processes, these findings lead us to suggest that SOD might serve to attenuate the oxidative stress caused by MGd redox cycling in cells. 

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