A THEORETICAL-ANALYSIS OF DIFFUSION-CONTROLLED REACTIONS IN FROZEN-SOLUTIONS

The effects of temperature and sucrose concentration on the rate of a diffusion-controlled reaction in a frozen sucrose solution are predicted using classical theory. Two reaction regimes are identified. In the temperature range 0 degrees C to -16.5 degrees C, the effect of freeze-concentration on reactant. concentration dominates, particularly at low sucrose contents, and reaction rate enhancement is predicted. At lower temperatures, in the range -1.6.5 degrees C to -40 degrees C, the retardation of the reactant diffusivity dominates, and reaction rate is predicted to be progressively reduced as the glass transition is approached. The limitations of the use of the Stokes-Einstein relation in the classical theory are discussed, and independent measurements of diffusivity are recommended to test the theory for molecular reactants.