Ab initio calculations of intramolecular parameters for a class of arylamide polymers.

Using DFT methods, we have determined intramolecular parameters for an important class of arylamide polymers displaying antimicrobial and anticoagulant inhibitory properties. A strong link has been established between these functions and the conformation that the polymers adopt in solution and at lipid bilayer interfaces. Thus, it is imperative for molecular dynamics simulations designed to probe the conformational behavior of these systems to accurately describe the torsional degrees of freedom. Standard force fields were shown to be deficient in this respect. Therefore, we have computed the relevant torsional energy profiles using a series of constrained geometry optimizations. We have also determined electrostatic parameters using our results in combination with standard RESP charge optimization. Force constants for bond and angle potentials were calculated by iteratively matching quantum and classical normal modes via a Monte Carlo scheme. The resulting new set of parameters accurately described the conformation and dynamical behavior of the arylamide polymers.