The preparation of the OPH systems, which are WT OPH complexed to paraoxon and the five different mutants of OPH complexed each to paraoxon was done as described in the previous section: using AMBER ff14SB for the receptors and GAFF force fields for the substrate. Using YANK, each receptor was complexed with paraoxon and the respective receptor-substrate complex was solvated with OBC2-GBSA model. For the solvent phase, the files of the solvated paraoxon were generated through YANK. We ran 30 ns/lambda value for each of the described complexes.