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Method for Determination of Association and Dissociation Rate Constants of Reversible Bimolecular Reactions by Isothermal Titration Calorimeters
journal contribution
posted on 2007-04-01, 00:00 authored by Tsuyoshi Egawa, Antonio Tsuneshige, Makoto Suematsu, Takashi YonetaniThe rate law equation for reversible bimolecular reactions,
which are describable by association and dissociation rate
constants (k1 and k-1), is not solvable to a plain formula
under stoichiometric reaction conditions. Therefore, it is
a general technique to observe such reactions under
pseudo first-order conditions, which make the reactions
a single-exponential process, and enable us to determine
k1 and k-1 without any complicated iterative computations
needed to analyze the same reactions under stoichiometric reaction conditions. However, the accelerated reaction
rates under pseudo first-order conditions are not always
favorable to the physicochemical tools employing a slow
or medium response time, such as thermal analysis
instruments. In this study, we have developed a simple
non-iterative analytical method to determine k1 and k-1
of reversible bimolecular reactions under stoichiometric
conditions on the basis of experimental data of isothermal
titration calorimetry (ITC), which is generally used to
determine thermodynamic parameters rather than kinetic
constants. Our method is principally based on the general
principle of chemical bindings caused along with the
titration processes, that is, the chemical relaxation kinetics, which had been hitherto considered in the analysis
on the ITC data.