Controlling Exchange Pathways in Dynamic Supramolecular Polymers by Controlling Defects.

Anna L De Marco,Davide Bochicchio,Giovanni M Pavan,Giovanni Doni,Andrea Gardin

doi:10.1021/acsnano.1c01398

Abstract

Supramolecular fibers composed of monomers that self-assemble directionally via noncovalent interactions are ubiquitous in nature, and of great interest in chemistry. In these structures, the constitutive monomers continuously exchange in-and-out the assembly according to a well-defined supramolecular equilibrium. However, unraveling the exchange pathways and their molecular determinants constitutes a nontrivial challenge. Here, we combine coarse-grained modeling, enhanced sampling, and machine learning to investigate the key factors controlling the monomer exchange pathways in synthetic supramolecular polymers having an intrinsic dynamic behavior. We demonstrate how the competition of directional vs. nondirectional interactions between the monomers controls the creation/annihilation of defects in the supramolecular polymers, from where monomers exchange proceeds. This competition determines the exchange pathway, dictating whether a fiber statistically swaps monomers from the tips or from all along its length. Finally, thanks to their generality, our models allow the investigation of molecular approaches to control the exchange pathways in these dynamic assemblies.

Highlights

Supramolecular fibers, composed of fundamental building blocks that self-assemble directionally (1D) via noncovalent interactions, are ubiquitous in nature and play fundamental roles in living systems.[1,2] Notable examples are cellular microtubules (MTs), dynamic assemblies composed of protein units whose dynamic polymerization and depolymerization are key for regulating the mechanical properties, motion, and differentiation of cells.[3,4] The constitutive tubulin units bind to one end of the tubular assembly and detach from the other end, which makes MTs existing as dynamic entities, continuously growing on one side and shortening on the other
When considering a straight and ordered stack of monomers, we can assume that monomer exchange in these fibers may occur at the fiber tip or at any point of the entire fiber, but only after the creation of a defect
We used the coordination of each monomer core with the other cores in the system to distinguish between fiber tips, perfectly stacked bulk monomers, and monomers in solution

Summary

Introduction

Supramolecular fibers, composed of fundamental building blocks that self-assemble directionally (1D) via noncovalent interactions, are ubiquitous in nature and play fundamental roles in living systems.[1,2] Notable examples are cellular microtubules (MTs), dynamic assemblies composed of protein (tubulin) units whose dynamic polymerization and depolymerization are key for regulating the mechanical properties, motion, and differentiation of cells.[3,4] The constitutive tubulin units bind to one end of the tubular assembly and detach from the other end, which makes MTs existing as dynamic entities, continuously growing on one side and shortening on the other. Learning how to customize the monomer structure in order to control the exchange pathways in the assembly would be appealing This would enable the rational design of supramolecular polymers that exchange monomers from the tips rather from their side surface (or vice versa), controlling their polymerization/ depolymerization processes and the adaptivity of the assembly. This would allow one to design supramolecular entities that communicate with the external environment

Methods

Results

Conclusion