Abstract
The self-assembling of small peptides not only leads to the formation of intriguing nanoarchitectures, but also generates materials with unexpected functional properties. Oligopeptides can form amyloid-like cross-β assemblies that are able to emit intrinsic photoluminescence (PL), over the whole near-UV/visible range, whose origin is still largely debated. As proton transfer between the peptide chain termini within the assembly is one of the invoked interpretations of this phenomenon, we here evaluated the solid state PL properties of a series of self-assembled hexaphenylalanine peptides characterized by a different terminal charge state. Overall, our data indicate that the charge state of these peptides has a marginal role in the PL emission as all systems exhibit very similar multicolour PL associated with a violation of the Kasha’s rule. On the other hand, charged/uncharged ends occasionally produce differences in the quantum yields. The generality of these observations has been proven by extending these analyses to the Aβ16–21 peptide. Collectively, the present findings provide useful information for deciphering the code that links the spectroscopic properties of these assemblies to their structural/electronic features.
Highlights
The self-assembling of small peptides leads to the formation of intriguing nanoarchitectures, and generates materials with unexpected functional properties
In 2016, Pinotsi et al reported an interesting study in which PL emission from amyloid-like fibrils was correlated to the proton transfer between the C- and the N- termini of two adjacent strands in the β-sheet s tructure[23,24]
Prior to PL characterization, we evaluated the morphology of the peptide nanostructures at both the concentrations by Scanning Electron Microscopy (SEM)
Summary
The self-assembling of small peptides leads to the formation of intriguing nanoarchitectures, and generates materials with unexpected functional properties. Peptide-based nanostructures are progressively gaining research interest as they represent innovative tools in different fields including biomedicine and biotechnology[1,2,3,4,5,6] Depending on their primary sequence, peptides are able to self-assemble into a variety of supramolecular structures characterized by different architectures. Despite an alternative explanation, involving the deformation of the peptide bond planarity in the assembly, has been successively reported[27], the contribution of the proton transfer in the origin of the PL properties has not been further highlighted from the experimental point of view[27] In this framework, we have recently undertaken extensive structural and spectroscopic investigations on analogous amyloidogenic systems constituted by selfassembled phenylalanine-based homopeptides, in form of hexa-Phe (F6). The generality of the findings obtained for the F6 peptides are proven by studying the completely charged and uncharged variants of the Aβ16–21 peptide ( H+-Aβ16–21-O− and Ac-Aβ16–21-Am), which self-assemble in amyloid-like structures analogously to F6 variants
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