Abstract
Nature designs chemotactic supramolecular structures that can selectively bind specific groups present on surfaces, autonomously scan them moving along density gradients, and react once a critical concentration is encountered. Since such properties are key in many biological functions, these also offer inspirations for designing artificial systems capable of similar bioinspired autonomous behaviors. One approach is to use soft molecular units that self-assemble in an aqueous solution generating nanoparticles (NPs) that display specific chemical groups on their surface, enabling multivalent interactions with complementarily functionalized surfaces. However, a first challenge is to explore the behavior of these assemblies at sufficiently high-resolution to gain insights on the molecular factors controlling their behaviors. Here, by coupling coarse-grained molecular models and advanced simulation approaches, we show that it is possible to study the (autonomous or driven) motion of self-assembled NPs on a receptor-grafted surface at submolecular resolution. As an example, we focus on self-assembled NPs composed of facially amphiphilic oligomers. We observe how tuning the multivalent interactions between the NP and the surface allows to control of the NP binding, its diffusion along chemical surface gradients, and ultimately, the NP reactivity at determined surface group densities. In silico experiments provide physical–chemical insights on key molecular features in the self-assembling units which determine the dynamic behavior and fate of the NPs on the surface: from adhesion, to diffusion, and disassembly. This offers a privileged point of view into the chemotactic properties of supramolecular assemblies, improving our knowledge on how to design new types of materials with bioinspired autonomous behaviors.
Highlights
Nature designs chemotactic supramolecular structures that can selectively bind specific groups present on surfaces, autonomously scan them moving along density gradients, and react once a critical concentration is encountered
All-atom molecular dynamics (AA-MD) simulations of protein-responsive assemblies allowed a comparison of the self-assembly stability of NPs composed of soft amphiphilic oligomers bearing biotin ligands with specific and nonspecific interactions with complementary extravidin
The contacts between the oppositely charged groups of the NP and of the surface reach a maximum of ∼132 in the case of surface density ρ4 and trivalent NP oligomers, where complete NP disassembly can be observed during the CG-MD simulation (Figure 3d: bottom-right snapshot). While these results indicate that the strength of the NP-surface binding can be in general strengthened or weakened by playing either with the NP multivalent charges or with the surface distribution of receptor groups, unbiased CG-MD simulations were found ineffective to study the dynamic behavior of the NPs after surface binding
Summary
Nature designs chemotactic supramolecular structures that can selectively bind specific groups present on surfaces, autonomously scan them moving along density gradients, and react once a critical concentration is encountered. It has been shown that ∼5 Å resolution CG models, coupled to advanced molecular simulations and analysis, allow the acquisition of precious links between the structure of monomers and the structure, dynamics, and dynamic properties of the supramolecular assemblies that these generate.[13,30,31] In silico simulations provided a privileged point of view into the response of supramolecular polymeric materials to different biorelevant stimuli, such as, for example, changes in temperature, salts, solvents, light, etc.[13,32] All-atom molecular dynamics (AA-MD) simulations of protein-responsive assemblies allowed a comparison of the self-assembly stability of NPs composed of soft amphiphilic oligomers bearing biotin ligands (monomer−monomer interactions) with specific and nonspecific interactions with complementary extravidin It was demonstrated how specific binding events with the complementary protein was capable of destabilizing the assembled NPs.[13] it is worth noting that fascinating bioinspired properties such as chemotaxis have an intrinsically dynamic character. This encourages the study of the dynamic behavior of chemotactic assemblies at high (submolecular) resolution, in search of molecularly relevant information on how to control them
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