Molecular Mechanics Force Field Fitting In Theoretical Investigations On The Catalytic Mechanisms Of Chalcone Synthase

Chalcone synthase exists widely in multiple plants, and it promotes many other enzymes'formation, so the study of its catalytic mechanism has been a hot issue in the theoretical chemistry. The catalysis is associated with its chalcone molecule, and the parametrization is provided for subsequent molecular dynamics simulation.The work employs Gaussian03 and CHARMM27 programs for optimizing chalcone molecule and model F, it contains geometry, atomic charge, bond, angle, and dihedral angle. Stretching frequency and its potential surface were analyzed for the interaction between model F and water. The thesis covers the following parts:First, the model F is identified through deconstructing chalcone into fragments, then the geometry is calculated at MP2/6-31G(d) level. Atomic charge is adjusted to reproduce minimum interaction energies. It shows that the interaction energy of O2 with water is larger than the other interaction energies, and the interaction energy of H6 is minimum. Because of the steric hindrance, the interaction distance of H6 is shorter than H7, the distance between O2 and water is the shortest.Second, the frequency of model F and the equilibrium bond lengths and angles are optimized, the bonds and angles are in good agreement with QM data. During optimizing of force constants, there are two scissoring of bonds are close to QM frequencies. Studying torsion of chalcone molecule from 0? to 360? stepped by 15?, the torsion of double bond is corresponded to potential surface 1, and the other is corresponded to surface 2. Optimized dihedral angles finds that the carbonyl carbon with alkene carbon mainly affects surface 2, whereas other dihedrals affects on surface 1, and surface 2 also fits QM data well. However, surface 1 has the similar trends with its QM. The optimization shows atomic charge has great influence on the interaction with water, the bond and angle parameters produce effect on vibrational frequency, and dihedral angle plays a key role in potential energy surfaces.Last, the parameters of chalcone is created, charge adjusting is on the basis of integral charge is zero, adjusting dihedral angle reveals that two torsions of bond affects potential energy, one bond is the carbonyl carbon connected with phenol, and the alternative is an alkene carbon connected with phenol. Other 12 groups of dihedral angle also have been discussed which fits the QM data well.