Thermodynamics versus Kinetics Dichotomy in the Linear Self-Assembly of Mixed Nanoblocks.

We report classical and replica exchange molecular dynamics simulations that establish the mechanisms underpinning the growth kinetics of a binary mix of nanorings that form striped nanotubes via self-assembly. A step-growth coalescence model captures the growth process of the nanotubes, which suggests that high aspect ratio nanostructures can grow by obeying the universal laws of self-similar coarsening, contrary to systems that grow through nucleation and elongation. Notably, striped patterns do not depend on specific growth mechanisms, but are governed by tempering conditions that control the likelihood of depropagation and fragmentation.

Persistence length and stochastic fragmentation of supramolecular nanotubes under mechanical force.

Cyclic peptide nanotubes (CPNs) exhibit impressive structural, mechanical and chemical properties in resemblance to beta-sheet proteins found in silks and amyloids, and show potential as supramolecular nanotubes that can be utilized to generate novel nanocomposites and nanoporous thin films. Quantifying the persistence length and thermomechanical fragmentation of CPNs is of great importance for establishing a theoretical basis of how to generate rectilinear nanostructures with controlled aspect ratio and rigidity. However, factors governing the elasticity and dynamical breaking of these supramolecular nanostructures remain to be fully understood. Here we present a statistical analysis of the Young's modulus and persistence length of CPNs using fully-atomistic molecular dynamic simulations in explicit solvent. We show that the measured properties exhibit a dependence on the magnitude of the shear force applied, and extrapolation to the quasi-static deformation case yields 0.46 µm for the persistence length and 7.8 GPa for the Young's modulus, in agreement with our experimental observations from TEM images. We establish a theoretical model for the spatial and temporal distribution of stochastic fracture, which we use to explain the simulation-based observations of spontaneous fragmentation under an applied shear force. Our methodology, blending theory, simulation and experiments provide a framework that can be utilized to investigate the mechanical behavior of self-assembling protein materials, paving the way for their design towards biological and industrial applications.