Simultaneous diffusion and chemical activation control of the kinetics of the binding of carbon monoxide to ferroprotoporphyrin IX in glycerol–water mixtures of high viscosity

Abstract

The kinetics of the reaction of ferroprotoporphyrin IX with CO have been studied in mixed glycerol–water solvents of high viscosity in order that the simultaneous influence of chemical activation and diffusion control of the reaction might be observed. Analyses of curved Arrhenius plots indicated that in the low temperature high viscosity limits the reaction is largely diffusion controlled. The deviation of the second order diffusion rate constants, from that predicted by simple theory for reaction between uniformly reactive spheres of equal radii, is a factor of 0.3 to 0.9, depending upon the solvent composition. A couple of other models for diffusion controlled reaction, ascribing these deviations to changes of steric requirements, were also examined.