COMPUTER-SIMULATION OF DAMPED OSCILLATIONS DURING PEROXIDASE-CATALYZED OXIDATION OF INDOLE-3-ACETIC-ACID

Oscillation patterns in horseradish peroxidase (HRP)-catalyzed oxidati on of indole-3-acetic acid (IAA) at neutral pH were studied using comp uter simulation. Under certain conditions, such as the presence of a r eaction promoter and continuous intake of oxygen from the gaseous phas e, the simulated system exhibits damped oscillations of the concentrat ions of oxygen in the aqueous phase, [O-2](aq), and of all the reactio n intermediates. The critical concentration of oxygen in aqueous phase , [O-2](cr)(aq), was used to describe the nature of the oscillations. The critical concentration is the concentration at which the system ab ruptly changes its properties. If [O-2](aq) is higher than [O-2](cr)(a q) then the reaction develops as an avalanche, otherwise, the reaction stops. The nature of oscillations is accounted for by the interaction of two processes: the consumption/accumulation of oxygen and the accu mulation/consumption of reaction intermediates. Oscillations are alway s damped. Neither HRP or umbelliferone (Umb) deactivation nor IAA cons umption can account for the damping. The nature of the damping is dete rmined by the termination reactions of free radical intermediates and ROOH. The three major parameters of oscillations: period of oscillatio ns, initial amplitude of oscillations and the rate of damping were stu died as functions of: (i) oxygen concentration in the gaseous phase, ( ii) initial oxygen concentration in aqueous phase, (iii) the concentra tion of IAA and (iv) the initial concentration of HRP. (C) 1998 Publis hed by Elsevier Science B.V. All rights reserved.