Experimental systems diffusion with first-order reaction

Reaction (l) accounts for 0 release from the oxygen evolving system (OES), assuming a first order reaction with a time constant of 1 ms, or 10 ms. Reaction (2) was assumed to be diffusion-limited, taking a distance of 0.5 pm between the OES and the oxidase. A first order reaction with a time constant of 2 ms was taken for (3). This treatment is obviously a crude approximation, for a number of reasons such as the assumption of a fixed OES-oxidase distance, of a purely diffusion-limited reaction (2), the disregard for other redox centers (CuA and CuB) and further transfer steps (second reduction of a3, turnover of Cyt c, etc..). Nevertheless, this model accounts qualitatively for several features of the experimental data, such as the absence of a detectable lag in the oxidation, or the presence of such a lag for Cyt c. 

Substrate limitations have been documented and quantitatively described ( U, 2, 17 ). Dooley et al. (11) present an excellent description of modeling a reaction in macroreticular resin under conditions where diffusion coefficients are not constant. Their study was complicated by the fact that not all the intrinsic variables could be measured independently several intrinsic parameters were found by fitting the substrate transport with reaction model to the experimental data. Roucls and Ekerdt (16) studied olefin hydrogenation in a gel-form resin. They were able to measure the intrinsic kinetic parameters and the diffusion coefficient independently and demonstrate that the substrate transport with reaction model presented earlier is applicable to polymer-immobilized catalysts. Finally, Marconi and Ford (17) employed the same formalism discussed here to an immobilized phase transfer catalyst. The reaction was first-order and their study presents a very readable application of the principles as well as presents techniques for interpreting substrate limitations in trlphase systems. 

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