Effect of Temperature on Standard Transformed Gibbs Energies of Formation of Reactants at Specified pH and Ionic Strength and Apparent Equilibrium Constants of Biochemical Reactions

Abstract

When standard Gibbs energies of formation and standard enthalpies of formation are known for the species of a biochemical reactant at 298.15 K, it is possible to calculate the standard transformed Gibbs energy of formation and standard transformed enthalpy of formation of the reactant at any desired pH and low ionic strengths at 298.15 K. This article is concerned with the estimation of standard transformed Gibbs energies of formation of reactants, standard transformed Gibbs energies of reaction, and apparent equilibrium constants K‘ of biochemical reactions at specified pH and ionic strength in the temperature range 283.15−313.15 K on the basis of the assumption that the standard enthalpies of formation of the species are independent of temperature in this range. The standard transformed Gibbs energies of formation and standard transformed enthalpies of formation are given for 14 reactants as a function of pH and ionic strength at temperatures of 283.15, 298.15, and 313.15 K, and standard transformed Gibbs energies of reaction, standard transformed enthalpies of reaction, and apparent equilibrium constants are given for six biochemical reactions over this temperature range at pH 6, 7, and 8. When the limiting Debye−Hückel slope for the contribution of ionic strength to the transformed Gibbs energy of a species is expressed by a quadratic in temperature, it is possible to estimate the standard transformed properties of reactants and reactions at any temperature in the range 273.15−313.15 K, provided the standard enthalpies of formation of the species involved are known.