­­Molecular dynamics simulations of the self-assembly of polypeptoid nanocrystals

The formation of nanosheets, nanofibrils and nanotubes have been reported for amphiphilic diblock copolypeptoids. To tune the morphology through chemical variations, it is important to know the atomic details of the self-assembly. This work utilizes molecular dynamic simulations to study the morphologies of the solvated poly(N-decylglycine)-b-poly(N-2-(2-(2-methoxyethoxy)ethoxy)ethylglycine) [Ndc-Nte] in aqueous solutions. Computational models were established based on previously developed force fields and measured cryoTEM images. Ndc blocks were preassembled into nanocrystals, while Nte blocks were left to extend into the solvent. We explored different thicknesses of nanocrystals to determine thermodynamic origins for preferential nanofiber formation vs. extended nanosheets. To explain the origins of these thermodynamic differences, we explored factors which are seen to control nanoscale morphology in experiment, but which are not evident in imaging due to inherent disorder: (1) functionalization of the N-terminus; (2) the morphology of the disordered Nte blocks; and (3) the presence and possible aggregation of urea molecules at the nanocrystal/solvent interface.