Solid-state optical properties of self-assembling amyloid-like peptides with different charged states at the terminal ends

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.

Non-Aromatic Fluorescence in Biological Matter: The Exception or the Rule?

“…However, very recent experiments by Accardo et. al on amyloid fibrils revealed a similar fluorescence intensity for protonated or zwitterionic ends, challenging some of these interpretations …”

“…al on amyloid fibrils revealed a similar fluorescence intensity for protonated or zwitterionic ends, challenging some of these interpretations. 42 Grisanti et al have recently provided an alternative molecular interpretation of the near-UV−vis non-aromatic emission energies. When molecular geometries of amides in amyloid proteins deviate from planarity, the amides CO and CN bonds elongate (Figure 3), and the ground state is slightly destabilized while the nπ* excited states are considerably stabilized (>1.0 eV).…”

Differently N‐Capped Analogues of Fmoc‐FF

“…Using the high electric fields associated with the electrospinning methodology, Boc‐FF, dissolved in DCM or ethanol, was incorporated in three different polymers, specifically poly(L‐lactic acid) (PLLA, MW=225 KDa), polymethylmethacrylate (PMMA, MW=120 KDa) and poly‐3‐caprolactone (PCL, MW=80 KDa). As other phenylalanine containing peptides, [19] all the electrospunned systems showed an intense blue emission, ascribable to radiative decay of excitons. In addition, due to the high number of analogues containing aromatic groups, this group was further subclassed considering the number of aromatic rings composing the end‐capping moiety and the eventual presence of heteroatoms like nitrogen or oxygen into the structure.…”

A Comprehensive Analysis of the Intrinsic Visible Fluorescence Emitted by Peptide/Protein Amyloid-like Assemblies

“…They also suggested that proton delocalization between the charged ends of the chains could play a significant role. This suggestion, however, was not corroborated by a systematic analysis of the fluorescence emission of hexa-phenylalanine variants endowed with different charged states, which all presented similar spectroscopic properties [85]. More recently, it has been proposed that the deplanarization of the amide groups makes possible the excitation in the near-UV.…”