Modeling sequence-specific polymers using anisotropic coarse-grained sites allows quantitative comparison with experiment

TL;DR

This paper introduces a novel anisotropic coarse-grained modeling approach for sequence-specific polymers, accurately reproducing experimental scattering data and enabling multiscale simulations of complex assembly processes.

Contribution

A new minimalistic coarse-grained model with orientational degrees of freedom that accurately captures polymer behavior across multiple scales and interfaces.

Findings

Successfully reproduces experimental X-ray scattering spectra.

Accurately models bilayer nanosheet assembly pathways.

Lays groundwork for multiscale simulations of sequence-specific polymers.

Abstract

Certain sequences of peptoid polymers (synthetic analogs of peptides) assemble into bilayer nanosheets via a nonequilibrium assembly pathway of adsorption, compression, and collapse at an air-water interface. As with other large-scale dynamic processes in biology and materials science, understanding the details of this supramolecular assembly process requires a modeling approach that captures behavior on a wide range of length and time scales, from those on which individual sidechains fluctuate to those on which assemblies of polymers evolve. Here we demonstrate that a new coarse-grained modeling approach is accurate and computationally efficient enough to do so. Our approach uses only a minimal number of coarse-grained sites, but retains independently fluctuating orientational degrees of freedom for each site. These orientational degrees of freedom allow us to accurately parameterize both bonded and nonbonded interactions, and to generate all-atom configurations with sufficient accuracy to perform atomic scattering calculations and to interface with all-atom simulations. We have used this approach to reproduce all available experimental X-ray scattering spectra (for stacked nanosheets, and for peptoids adsorbed at air-water interfaces and in solution), in order to resolve the microscopic, real-space structures responsible for these Fourier-space features. By interfacing with all-atom simulations, we have also laid the foundations for future multiscale simulations of sequence-specific polymers that communicate in both directions across scales.