Molecular dynamics simulation of Na+-DMP− and Na+-MP2− ion pair in aqueous solution

Molecular dynamics simulations with an umbrella potential function in solution were carried out to obtain the potential of mean force for sodium-dimethyl phosphate (Na + -DMP − ) and sodium-methyl phosphate (Na + -MP 2− ). The Na + -DMP − showed two minima in pmf profile, a less stable minimum of ca. 3.5 A and a more stable minimum of ca. 5.0 A, resulting in direct and indirect contact between two ions. On the other hand, the Na + -MP 2− showed one prominent minimum in pmf profile, at approximately ca. 4.5 A. Water molecules around Na + -DMP − better formed a hydrogen-bonded network than around Na + -MP 2− , showing a stronger interaction between water and the Na + -MP 2− .