Amyloid-β peptide (Aβ) aggregates are known to be correlated with pathological neurodegenerative diseases. The fibril formation process of such peptides in solution is influenced by several factors, such as the ionic strength of the buffer, concentration, pH, and presence of other molecules, just to mention a few. In this paper, we report a detailed analysis of in vitro Aβ42 fibril formation in the presence of cortisol at different relative concentrations. The thioflavin T fluorescence assay allowed us to monitor the fibril formation kinetics, while a morphological characterization of the aggregates was obtained by atomic force microscopy. Moreover, infrared absorption spectroscopy was exploited to investigate the secondary structure changes along the fibril formation path. Molecular dynamics calculations allowed us to understand the intermolecular interactions with cortisol. The combined results demonstrated the influence of cortisol on the fibril formation process: indeed, at cortisol-Aβ42 concentration ratio (ρ) close to 0.1 a faster organization of Aβ42 fragments into fibrils is promoted, while for ρ = 1 the formation of fibrils is completely inhibited.

The demand for next-generation multifunctional nanovectors, combining therapeutic effects with specific cellular targeting, has significantly grown during the last few years, pursuing less invasive therapy strategies. Polyphenol-conjugated silver nanoparticles (AgNPs) appear as potential multifunctional nanovectors, integrating the biorecognition capability and the antioxidant power of polyphenols, the antimicrobial activity of silver, and the drug delivery capability of NPs. We present a spectroscopic and microscopic investigation on polyphenol-synthesized AgNPs, selecting caffeic acid (CA) and catechol (CT) as model polyphenols and using them as reducing agents for the AgNP green synthesis, both in the presence and in the absence of a capping agent. We exploit the plasmonic properties of AgNPs to collect Surface-Enhanced Raman Scattering (SERS) spectra from the nanosized region next to the Ag surface and to characterize the molecular environment in the proximity of the NP, assessing the orientation and tunable deprotonation level of CA, depending on the synthesis conditions. Our results suggest that the SERS investigation of such nanovectors can provide crucial information for their perspective biomedical application.

Intrinsically disordered proteins (IDPs) often associate into biomolecular condensates. While micron‐sized condensates are observed above a well‐defined saturation concentration, the formation of nanoscale clusters also occurs at subsaturated concentrations. The diversity and physical nature of such nanoscale clusters remain underexplored with respect to the well‐established condensate state. Here we show that the Parkinson's disease‐associated protein α‐synuclein forms highly monodisperse assemblies at low ionic strength, distinct from the larger polydisperse assemblies previously observed at higher ionic strengths. Using a range of biophysical methods, we identify monodisperse clusters of α‐synuclein composed of ∼20 molecules that maintain their size over a broad concentration range. These clusters are stable over time and do not progress to amyloid fibril formation. Their response to mutational perturbations and chemical destabilization, as well as their thermal cycling support a micelle‐like assembly. Increasing ionic strength shifts the system toward the formation of larger, polydisperse nanoclusters and condensates that promote amyloid fibril formation. Our results reveal a hitherto uncharacterized assembly state of α‐synuclein and highlight the complexity of nanoscale assembly processes by IDPs.