Thermodynamic Properties of Weak Acids Involved in Enzyme-Catalyzed Reactions

Measurements of apparent equilibrium constants and transformed enthalpies of enzyme-catalyzed reactions are making it possible to obtain Δ_fG° and Δ_fH° of species of biochemical reactants in dilute aqueous solution that could never have been determined classically. This article is concerned with the pKs that determine the pH dependencies of the standard transformed thermodynamic properties of biochemical reactants. The database BasicBiochemData3 makes it possible to calculate 82 pKs of 60 reactants as functions of ionic strength at 298.15 K. Standard enthalpies of formation of all the species are known for 27 of these reactants, and so their pKs can be calculated as functions of temperature and ionic strength. This article also presents calculations of Δ_rG°, Δ_rH°, and Δ_rS° at 298.15 K and three ionic strengths for the 42 pKs of these 27 reactants.