Aqueous N-methylacetamide: New analytic potentials and a molecular dynamics study

- A semiempirical intermolecular potential for N-methylacetamide-water system is proposed.
- H-bond interactions modeling is correct and reliable.
- The model potential is validated and portable to larger biomolecule simulations.

Recently formulated intermolecular potentials for the N-methylacetamide-water system have been used to model the hydrogen-bond like interactions in classical molecular dynamics (MD) simulations of aqueous solutions of N-methylacetamide (NMA). The MD calculations have been performed covering a wide concentration range at a temperature of 308K, in order to validate the model potential through the reproduction of structural and dynamical properties of liquid NMA. The analytic intermolecular potential energy surface (PES), obtained by decomposing the involved molecules into a number of interacting centers, is represented as sum of van der Waals and electrostatic pair interaction terms. The van der Waals terms contain parameters directly connected to physical observables, such as atomic and bond polarizabilities, and can be easily optimized in order to embody more collective contributions such as hydrogen bonding like interactions. The parametrization is flexible enough to correctly match the electrostatic contributions, reproducing the results on N-methylacetamide solutions, as available from previous studies based on dynamics simulations and ab initio calculations. The use of the PES, combined with classical trajectories, provides a computationally effective alternative to ab initio MD simulations, widely used to simulate similar systems. Moreover, the characterization of the interacting centers is portable to different molecular environments, so that the PES can be extended for perspective applications to larger molecular systems and biomolecules.