Tuning Nanostructure Dimensions with Supramolecular Twisting

Abstract

Peptide amphiphiles are molecules containing a peptide segment covalently bonded to a hydrophobic tail and are known to self-assemble in water into supramolecular nanostructures with shape diversity ranging from spheres to cylinders, twisted ribbons, belts, and tubes. Understanding the self-assembly mechanisms to control dimensions and shapes of the nanostructures remains a grand challenge. We report here on a systematic study of peptide amphiphiles containing valine-glutamic acid dimeric repeats known to promote self-assembly into belt-like flat assemblies. We find that lateral growth of the assemblies can be controlled in the range of 100 nm down to 10 nm as the number of dimeric repeats is increased from two to six. Using circular dichroism, the degree of β-sheet twisting within the supramolecular assemblies was found to be directly proportional to the number of dimeric repeats in the PA molecule. Interestingly, as twisting increased a threshold is reached where cylinders rather than flat assemblies become the dominant morphology. We also show that in the belt regime, the width of the nanostructures can be decreased by raising the pH to increase charge density and therefore electrostatic repulsion among glutamic acid residues. The control of size and shape of these nanostructures should affect their functions in biological signaling and drug delivery.

Supramolecular Chirality in Self-Assembled Systems

“…77,78 In the systematic study of peptide amphiphiles containing valine−glutamic acid dimers, Stupp et al found that the dimeric repeat unit promoted self-assembly into belt-like flat assemblies. 79 The lateral growth of these assemblies can be controlled in the range from 100 nm to as little as 10 nm as the number of dimeric repeat units increased from two to six. With the growth of the peptide sequence, these flat β-sheet assemblies appeared to twist ( Figure 9).…”

The Powerful Functions of Peptide-Based Bioactive Matrices for Regenerative Medicine

“…19 Scaffold design pertaining to control over biological signal presentation, 62 nanostructure 44 and mechanical properties 51 have also been shown to influence neuronal adhesion, differentiation, neurite growth and directional guidance in a culture environment. 29,55 For example, a PA nanofiber scaffold presenting the laminin-derived epitope IKVAV was shown to selectively induce the differentiation of the neural stem cells into neurons (Fig.…”

Self-assembly of biomolecular soft matter

“…3). 80 Circular dichroism and cryo-TEM studies show that increasing the number of dimeric repeats increases β-sheet twisting and that the resultant twisting of nanobelts limits lateral growth. Cylinders become the dominant morphology over flat nanobelts above a threshold number of dimeric repeats.…”

“…As the number of dimeric repeats is increased from two to six, ribbon twisting increases and lateral width of the assemblies is reduced from 100 nm down to 10 nm. Adapted with permission from reference 80. Copyright 2013 American Chemical Society.…”