| Abstract: |
Microcalorimetry and high-performance liquid chromatography (HPLC) have been used to conduct a thermodynamic investigation of the reaction: {methyl ferulate(aq) + H2O(l) = methanol(aq) + ferulic acid(aq), as catlyzed by feruloyl esterase. Values of the apparent equilibrium constant K = 29.6 0.7 (temperature T = 298.15 K, citrate buffer at pH = 4.98, ionic strength I = 0.39 mol∙kg-1) and of the calorimetrically determined enthalpy of reaction ΔrH(cal) = (4.0 0.9) kJ∙mol 1 (T = 298.15 K and citrate buffer at pH = 4.81, I = 0.36 mol∙kg-1) were measured. A chemical equilibrium model, together with pKs and standard enthalpies of reaction ΔrH for the H+(aq) binding reactions of the reactants and products, was then used to calculate the values K = (1.89 0.06)∙10-4, rH = (7.3 1.7) kJ∙mol-1, ΔrG = (21.25 0.07) kJ∙mol-1, and ΔrS = (46.8 5.7) J∙K 1∙mol-1 for the chemical reference reaction {methyl ferulate(aq) + H2O(l) = methanol(aq) + ferulic acid-(aq) + H+(aq)}. These values of K and ΔrH are similar in magnitude to the corresponding values reported for the reaction {propyl gallate(aq) + H2O(l) = 3,4,5-trihydroxybenzoic acid-(aq) + 1 propanol(aq) + H+(aq)}. The results obtained in this study can be used in a chemical equilibrium model to calculate how K and other standard transformed properties such as the standard transformed enthalpy ΔrH, standard transformed Gibbs energy rG, and the change in binding of H+(aq), rN(H+), vary with the independent variables T, pH, and I. |
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