Freund reaction mechanisms

The mechanism of Freund reaction is more likely as same as the Wurtz reaction, a free-radical mechanism. In the presence of iodide ions, the pathways might be a combination of substitution (SnI or Sn2) with a free-radical mechanism. ... 

Most experimental reports on the dependence of the rate of reaction on the concentration of nanoparticles in solution provide similar conclusions. The earliest study on this dependence sums up these conclusions and was conducted by Freund and Spiro [19] using colloidal gold solutions to catalyze the reduction of ferricyanide by thiosulfate. As the concentration of nanoparticles increases, there is a linear increase in the reaction rate, which is expected whether the catalytic mechanism is heterogeneous or homogeneous. They reported that the strength of this dependence on concentration was dependent on the size of the gold nanoparticles. While it was postulated that the catalysis occurred on the surface of the particle, these results do not prove that the catalysis is heterogeneous, but only that the catalyst concentration increases as the particle concentration is increased. 

Elucidation of the mechanism of the catalytic process is a relatively complicated task because of the variety of factors influencing the catalytic reaction. For instance, preconcentration of redox species in the porous films can result in an apparent surface excess, similar to adsorption. Here, semi-integral analysis of voltammetric curves can aid in separating diffusional and surface-confined components (Freund and Brajter-Toth, 1992). 

Apart from the acute anti-inflammatory activity described in the preceding section, taraxasterol acetate was also tested for chronic activity in the model of Freund s adjuvant-induced rat arthritis. When 80 mg/kg of this compound were administered i.p., a 57% decrease with respect to the control value for the injected limb was observed at 18 h. After 21 days, the secondary reaction, which is measured on the non-injected limb, was reduced by 78%. Given the fact that in this condition the injected limb suffered a comparable reduction of 67%, it seems that taraxasterol acetate did not act by modifying immune mechanisms [64]. Duwiejua et al. [66] also reported appreciable anti-arthritic activity for glutin-3-one 44% and 74% reductions in the ipsilateral and contralateral paw swelling, respectively, after 10 days. 

Chance (1943) and Theorell Chance (1951) observed the formation and decomposition of complexes of enzymes with substrates and products by following changes in light absorption. In these pioneering studies the theories and techniques of pre-steady-state kinetics were only applied to reactions in which the complexes had distinct absorption spectra. It became apparent that transients of a much wider range of enzyme reactions could be studied when the initial rate of product formation is analysed (Gut-freund, 1955). Observations with a time resolution of milliseconds showed that there are often three distinct phases in product formation. These are determined in turn by the rate of formation of the enzyme-substrate complex, the enzyme-product complex and of free product. Of course, as we shall see, the most fruitful investigations into enzyme mechanisms resulted when it was possible to combine the observation of transients of product formation with those of spectral changes of complexes. 

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