SCRF study of the conformational equilibrium of chorismate in water

The conformational equilibrium between the diequatorial and diaxial forms of chorismate molecule in water has been studied with a self-consistent reaction field (SCRF) model. Conformational energies in the gas phase have been calculated at the MP2/6-31 + G*//HF/6-31G* level, and solvation energies have been obtained with PCM/6-31G* and PCM/6-31 + G* calculations. The cavity definition of the united atom model for Hartree–Fock (UAHF) was used in the polarizable continuum model (PCM) calculations. The conformational energy surface as a function of the two main degrees of freedom of the principal side-chain has been constructed for the chorismate molecule in the gas phase and in water solution. These surfaces allow a more exhaustive search for conformational minima and the calculation of the entropic contribution to the conformational equilibrium. Five diaxial minima, three of them not described before, two diequatorial minima and a planar ring minimum have been detected. One of the new diaxial minima is essential to correctly reproduce the experimental diaxial–diequatorial proportions in water.