On thermodynamic and kinetic equivalence of chemical systems

Abstract

A composite reaction is represented by a number of elementary reactions describing its mechanisms. By a linear transformation, the chemical flow and flux can be changed and one might obtain a new mechanism. The present report works out the selection rule to be imposed on the transformation matrix if the two mechanisms are thermodynamically and/or, kinetically indistinguishable (or equivalent). The net free energy change, entropy production, Onsager symmetry, and the detailed balance condition are considered to be the invariants of the transformation for thermodynamic equivalence. The selection rule has to be slightly modified for cyclic reactions. Two cyclic reactions with equivalent mechanisms are also worked out. It is proposed that for biochemical systems predominated by cyclic reactions, the selection rule is more permissive, and occurrence of multiple mechanisms has a higher probability, resulting in an enhancement of the fidelity of the net reaction in the presence of random environmental ‘error variables’.