In this work,we developed the CHARMM all-atom force field parameters for the nonstandard biological residue chalcone,followed by the standard protocol for the CHARMM27 force field development.Target data were generated via ab initio calculations at the MP2/6-31G* and HF/6-31G* levels.The reference data included interaction energies between water and the model compound F(a fragment of chalcone).Bond,angle,and torsion parameters were derived from the ab initio calculations and renormalized to maintain compatibility with the existing CHARMM27 parameters of standard residues.The optimized CHARMM parameters perform well in reproducing the target data.We expect that the extension of the CHARMM27 force field parameters for chalcone will facilitate the molecular simulation studies of the reaction mechanism of intramolecular cyclization of chalcone catalyzed by chalcone isomerase.
