Molecular self-assembly of peptides into ordered nanotubes is highly important for various technological applications. Very short peptide building blocks, as short as dipeptides, can form assemblies with unique mechanical, optical, piezoelectric, and semiconductive properties. Yet, the control over nanotube length in solution has remained challenging, due to the inherent sequential self-assembly mechanism. Here, in line with polymer chemistry paradigms, we applied a supramolecular polymer coassembly methodology to modulate peptide nanotube elongation. Utilizing this approach, we achieved a narrow, controllable nanotube length distribution by adjusting the molecular ratio of the diphenylalanine assembly unit and its end-capped analogue. Kinetic analysis suggested a slower coassembly organization process as compared to the self-assembly dynamics of each of the building blocks separately. This is consistent with a hierarchal arrangement of the peptide moieties within the coassemblies. Mass spectrometry analysis demonstrated the bimolecular composition of the coassembled nanostructures. Moreover, the peptide nanotubes' length distribution, as determined by electron microscopy, was shown to fit a fragmentation kinetics model. Our results reveal a simple and efficient mechanism for the control of nanotube sizes through the coassembly of peptide entities at various ratios, allowing for the desired end-product formation. This dynamic size control offers tools for molecular engineering at the nanoscale exploiting the advantages of molecular coassembly.
Supramolecular materials are widely studied and used for a variety of applications; in most applications, these materials are in contact with surfaces of other materials. Whilst much focus has been placed on elucidating factors that affect supramolecular material properties, the influence of the material surface on gel formation is poorly characterised. Here, we demonstrate that surface properties directly affect the fibre architecture and mechanical properties of self-assembled cytidine based gel films.
The filamentous peptide-based nanowires
produced by some dissimilatory
metal-reducing bacteria, such as Geobacter sulfurreducens, display excellent natural conductivity. Their mechanism of conduction
is assumed to be a combination of delocalized electrons through closely
aligned aromatic amino acids and hopping/charge transfer. The proteins
that form these microbial nanowires are structured from a coiled-coil,
for which the design rules have been reported in the literature. Furthermore,
at least one biomimetic system using related synthetic peptides has
shown that the incorporation of aromatic residues can be used to enhance
conductivity of peptide fibers. Herein, the de novo design of peptide
sequences is used to enhance the conductivity of peptide gels, as
inspired by microbial nanowires. A critical factor hampering investigations
in both microbiology and materials development is inconsistent reporting
of biomaterial conductivity measurements, with consistent methodologies
needed for such investigations. We have reported a method herein to
analyze non-Ohmic behavior using existing parameters, which is a statistically
insightful approach for detecting small changes in biologically based
samples. Aromatic residues were found to contribute to peptide gel
conductivity, with the importance of the peptide confirmation and
fibril assembly demonstrated both experimentally and computationally.
This is a small step (in combination with parallel research under
way by other researchers) toward developing effective peptide-based
conducting nanowires, opening the door to the use of electronics in
water and physiological environments for bioelectronic and bioenergy
applications.
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