Calculation of Standard Formation Properties of Species from Standard Transformed Formation Properties of Reactants in Biochemical Reactions at Specified pH

Up until now, standard transformed formation properties of biochemical reactants at a specified pH have largely been calculated from Δ f G ° and Δ f H ° values of the species that make them up. The equations for doing this have been derived by using a Legendre transform to define a transformed Gibbs energy G ‘ that provides the criterion for equilibrium and spontaneous change at specified temperature T, pressure P, and pH. In the future, the Δ f G ° and Δ f H ° values of organic species in aqueous solutions will increasingly be calculated from the standard transformed properties Δ f G ‘° and Δ f H ‘° obtained from the apparent equilibrium constants of biochemical reactions and their temperature coefficients or apparent heats of reaction measured at a specified pH. It is therefore important to consider the inverse Legendre tranform that defines the Gibbs energy G in terms of the transformed Gibbs energy G ‘ and the equations for calculating the Δ f G ° and Δ f H ° values of species from thermodynamic measurements at specified T, P, and pH. The use of these equations is illustrated.