MOLECULAR-DYNAMICS SIMULATION STUDY OF POLY(GAMMA-BENZYL L-GLUTAMATE) IN DIMETHYLFORMAMIDE

We report on atomistic molecular dynamics simulations of poly(gamma-benzyl L-glutamate) (PBLG) in dimethylformamide (DMF), where the focus is on the structure and dynamics of the backbone-side chain-solvent interface as well as on the elastic properties of the isolated PBLG molecule. The characterization of the complex backbone-side chain-solvent interface in terms of molecular and atomic radial density and order parameter profiles together with azimuthal pair correlation functions reveals a pronounced solvation shell structure; The range of the induced solvent structure correlates well with the 30-Angstrom effective diameter obtained from light scattering experiments, indicating the importance of including the solvation zone in the molecular excluded volume. We also simulate the isolated PBLG molecule under axial tension and compression and discuss the effect of the solvent on the stability of the helical structure of the backbone. Finally, we calculate the persistence length using a simple extrapolation scheme to construct high molecular weight fragments of the helical backbone based on the simulation trajectory. Our value of 1000 +/- 50 Angstrom is well within the range of experimental persistence lengths reported for this system.