Modeling the interactions between polyoxometalates and their environment

Abstract

To develop a force field suitable both for polyoxometalates (POMs) and organic cations, the Merck molecular force field 94x (MMFF94x) has been selected to describe the counterions used in POMs synthesis and has been combined with our force field optimized for type-II POMs with electrostatic and Van der Waals interactions included in the potential. Nontransferability of force fields is well-known and, to overcome this limitation, a charge-scaling factor (SF) has been introduced and optimized to tune the POMs force field parameters and adapt them to MMFF94x. The mixed MMFF94x/POMFF-II force field has been optimized and tested on different clusters based on hepta-molybdate. To validate our mixed force field comparison of the results obtained after molecular mechanics (MM), geometry optimizations with density-functional (DFT) calculations have been performed on the smallest system of interest. This has enabled a study of the accuracy of different functionals, especially on the description of hydrogen bonding, to be made. Results are promising in terms of structural accuracy. MM geometry optimization can be used on small POM clusters, competing reasonably well with DFT. When quantum approaches increase considerably the computational cost because of the size of the system studied, MM can be used, with the small reservation that even if the charge SF introduced improves the performance of the force field, further optimizations of the nonbonded term and the model used for the atomic charges may be necessary in further studies.

Optimization of a molecular mechanics force field for type‐II polyoxometalates focussing on electrostatic interactions: A case study

“…Its first validation was made on type-I polyanions. 16 Optimized force fields obtained for polytungstate and polymolybdate clusters were able to generate the structure of type-I POMs in a good agreement with structures optimized using DFT. The results obtained proved that the potential was well modeled and the parametrization adapted to the compounds.…”

“…16 Our GA routines, developed with the Scientific Vector Language package provided in MOE, were tested and validated for type-I POMs giving results in a good agreement with DFT-optimized structures.…”

“…Concretely, a high penalty value is added to the fitness function to enable an elimination of the chromosomes that lead to inconsistent parameters or a divergence of the MM optimization and, therefore, to keep the best candidates at each GA cycle. The same termination criteria as the one used for type-I POMs is available, 16 to speed up the algorithm convergence and to avoid the optimization getting trapped in a local minimum.…”

“…6− were selected as molecules of reference, and all the force field optimizations were performed on these two polyanions, leading to individual optimized force fields. Contrary to type-I POMs, 16 no structural database was used for the force field optimizations. Thus, for each type of atoms introduced in our parametrization, we have considered its partial atomic charge as calculated on the isolated molecule.…”

From Receptors to Ligands: Fragment-assisted Drug Design for GPCRs Applied to the Discovery of H3 and H4 Receptor Antagonists

“…Sidechain data is assembled from an extensive rotamer library generated by systematic clustering of high-resolution PDB data. After all of the backbone segment and sidechain conformations were chosen, the model was minimized using the MMFF94x force-field [71].…”