Thermodynamics of the Conversion of Chorismate to Prephenate: Experimental Results and Theoretical Predictions

Abstract

A thermodynamic investigation of the Claisen rearrangement of chorismate2-(aq) to prephenate2-(aq) has been performed using microcalorimetry and high-performance liquid chromatography. The study used a well-characterized monofunctional chorismate mutase from Bacillus subtilis that was devoid of prephenate dehydrogenase and prephenate dehydratase activities. The calorimetric measurements led to a standard molar enthalpy change = −(55.4 ± 2.3) kJ mol-1 at 298.15 K for this reaction. An estimated value of the standard molar entropy change = 3 J K-1 mol-1 for the above reaction was used together with the experimental value of to obtain a standard molar Gibbs free energy change ≈ −56 kJ mol-1 and an equilibrium constant K ≈ 7 × 109 for the conversion of chorismate2-(aq) to prephenate2-(aq) at 298.15 K. Thus, for all practical purposes, this reaction can be considered to be “irreversible”. Quantum mechanics (Gaussian 94 with a B3LYP functional and a 6-31G* basis set) was used to calculate values of absolute and...