Transition metal ions are of great significance in biological processes, with a presence in approximately one third of known human proteins. Computational modeling of transition metal ions, however, has remained limited. Using molecular dynamics simulations, very large chemical systems can be studied due to the use of a 'force field' which simplifies atomic interactions to an easily calculable form. Unfortunately, 'traditional' force fields used in molecular dynamics fail to accurately portray the properties of transition metal ions. By modifying the 12-6 Lennard-Jones potential to include an r-4 term, the Lennard-Jones type 12-6-4 potential has shown to be a successful replacement for the 12-6 potential, with an accurate portrayal of important properties of solvated transition metal ions (hydration free energies, coordination number, ion-oxygen distance). We have built on the foundation of the 12-6-4 potential by applying it in the field of small molecule coordination chemistry. The 12-6-4 potential is parameterized for accurate binding energies in the reaction of ethylenediamine with various divalent transition metal ions. In comparing these results with the similar reaction of the same metal ions with methylamine ligands, we demonstrate that the 12-6-4 model naturally reproduces the chelate effect. Therefore, continued use of the 12-6-4 potential is proposed for the use in modeling coordination chemistry reactions.
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