Self-assembled supramolecular structures of peptide derivatives often reflect a kinetically trapped state rather than the thermodynamically most favoured structure, which presents a challenge when trying to elucidate the molecular design rules for these systems. In this article we use thermodynamically controlled self-assembly, driven by enzymatic condensation of amino acid derivatives, to elucidate chemical composition/nanostructure relationships for four closely related Fmoc-dipeptide-methyl esters which form hydrogels; SF, SL, TF and TL. We demonstrate that each of the four systems self-assemble to form extended arrays of beta-sheets which interlock via pi-stacking of Fmoc-moieties, yet with subtle differences in molecular organisation as supported by rheology, fluorescence emission spectroscopy, infrared spectroscopy, X-ray diffraction analysis and molecular mechanics minimisation
A novel class of supramolecular hydrogels derived from amino sugars is reported, where the selfassembly of aromatic carbohydrate amphiphiles is driven by CH-p interactions, rather than p-p stacking and H-bonding associated with gelators based on aromatic peptide amphiphiles. Spectroscopic data is provided as evidence for this mode of self-assembly and in silico studies revealed that a combination of CH-p and T-stacking of the fluorenyl groups contribute to the formation of the aggregated structures.
Discovery of new catalysts for demanding aqueous reactions is challenging. Here, we describe methodology for selection of catalytic phages by taking advantage of localized assembly of the product of the catalytic reaction that is screened for. A phage display library covering 10(9) unique dodecapeptide sequences is incubated with nonassembling precursors. Phages which are able to catalyze formation of the self-assembling reaction product (via amide condensation) acquire an aggregate of reaction product, enabling separation by centrifugation. The thus selected phages can be amplified by infection of Escherichia coli. These phages are shown to catalyze amide condensation and hydrolysis. Kinetic analysis shows a minor role for substrate binding. The approach enables discovery and mass-production of biocatalytic phages.
The study of enzymatically triggered self-assembly of aromatic peptide amphiphiles has become increasingly popular in recent years and has lead to a variety of nanoscale architectures. As hydrophobic interactions have been recognised as a major driving force in their self-assembly, typically, the peptide components are found to be hydrophobic in nature, containing aromatic or aliphatic amino acid residues. In this article, we use subtilisin triggered self-assembly of four closely related Fmoc-dipeptide amphiphiles with terminal hydrophilic amino acid residues, YT, YS, YN and YQ, in order to introduce a new functionality to the self-assembled systems, and determine the influence of each amino acid side chain. We use microscopy techniques, rheology, fluorescence, FTIR and CD to demonstrate differences in molecular assembly, mechanical properties and nanoscale architecture as a direct result of the subtle molecular variance of each system. We demonstrate that the amino acid side chain in position two directly affects the molecular packing abilities in the supramolecular structure, with YT, YS and YN forming nanoscale fibres with mechanical properties being linked to the functionality of the amino acid side chain, and YQ forming spherical structures due to steric effects associated with the glutamine side chain prohibiting the adoption of the typical pi-beta assembly
A hydrogel-based sensor for screening protease specificity has been developed that combines the versatility of solid-phase synthesis (SPS) with the simplicity of liquid crystal display (LCD) technology.
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