A Thermodynamic and Quantum Chemical Study of the Conversion of Chorismate to (Pyruvate + 4-Hydroxybenzoate)

Published

October 22, 1998

Author(s)

Yadu D. Tewari, J Chen, Marcia J. Holden, K. N. Houk, Robert N. Goldberg

Abstract

A thermodynamic investigation of the conversion of chorismate^2-(aq) to {pyruvate^-(aq) + 4-hydroxybenzoate^-(aq)} has been performed by using microcalorimetry and high-performance liquid chromatography. The study used a genetically engineered sample of chorismate lyase that was prepared with the Escherichia. coli ubiC gene. The calorimetric measurements led to a standard molar enthalpy change {Δ}_rH _m = -(144 7) kJ mol^-1 for this reaction at the temperature T = 298.15 K and ionic strength I_m = 0. An estimated value of the standard molar entropy change {Δ}}_rS _m = 222 J K^-1 mol^-1 for the above reaction was used together with the experimental value of {Δ}_rH}^_m^o to obtain a standard molar Gibbs free energy change {Δ}^rG_m^o {approximately equal to} -210 kJ mol^-1 and an equilibrium constant K {approximately equal to} 10³⁷ for the conversion of chorismate^2-(aq) to {pyruvate^-(aq) + 4-hydroxybenzoate^-(aq)} at T = 298.15 K and I^m = 0. Quantum mechanics (Gaussian 94 with a B3LYP functional and a 6-31G* basis set) was used to calculate values of absolute energies for the neutral and ionic species pertinent to this reaction both in the gas phase and in aqueous solution. The structures of pyruvic acid and 4-hydroxybenzoic acid and their monoanions were also obtained along with values of thermodynamic reaction quantities. The effects of water solvation and solvent polarization were accounted for by using both a polarizable continuum model (PCM) and a self-consistent isodensity polarizable continuum model (SCI-PCM). The calculated value of {Δ}_rH_m^o for the conversion of chorismate^2-(aq) to {pyruvate^-(aq) + 4-hydroxybenzoate^-(aq)} at T = 298.l5 K was -154 kJ mol^-1 with the PCM model and -178 kJ mol^-1 with the SCI-PCM model. The relatively large error in the SCI-PCM calculation may arise from the ill-defined cavity size which is derived from the solute charge distribution isosurface. However, the PCM model, which employs a parameterized cavity radius, yields a result that can be considered to be in agreement with experiment.

Citation

Journal of Physical Chemistry B

Volume

102

Issue

No. 43

Pub Type

Journals

Keywords

4-hydroxybenzoic acid, chemical thermodynamics, chorismic acid, enthalpy, equilibrium, pyruvic acid, quantum chemistry

Citation

Tewari, Y. , Chen, J. , Holden, M. , Houk, K. and Goldberg, R. (1998), A Thermodynamic and Quantum Chemical Study of the Conversion of Chorismate to (Pyruvate + 4-Hydroxybenzoate), Journal of Physical Chemistry B (Accessed September 20, 2024)