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Fluoride nanoparticles (NPs) are materials utilized in the biomedical field for applications including imaging of the brain. Their interactions with biological systems and molecules are being investigated, but the mechanism underlying these interactions remains unclear. We focused on possible changes in the secondary structure and aggregation state of proteins on the surface of NPs and investigated the principle underlying the changes using the amyloid β peptide (Aβ 16–20 ) based on infrared spectrometry. CeF 3 NPs (diameter 80 nm) were synthesized via thermal decomposition. Infrared spectrometry showed that the presence of CeF 3 NPs promotes the formation of the β-sheet structure of Aβ 16–20 . This phenomenon was attributed to the hydrophobic interaction between NPs and Aβ peptides in aqueous environments, which causes the Aβ peptides to approach each other on the NP surface and form ordered hydrogen bonds. Because of the coexisting salts on the secondary structure and assembly of Aβ peptides, the formation of the β-sheet structure of Aβ peptides on the NP surface was suppressed in the presence of NH 4 + and NO 3 – ions, suggesting the possibility that Aβ peptides were adsorbed and bound to the NP surface. The formation of the β-sheet structure of Aβ peptides was promoted in the presence of NH 4 + , whereas it was suppressed in the presence of NO 3 – because of the electrostatic interaction between the lysine residue of the Aβ peptide and the ions. Our findings will contribute to comparative studies on the effect of different NPs with different physicochemical properties on the molecular state of proteins.

One of the environmental health and safety concerns is the toxicological impact of ultrafine particles (UFPs) and secondary inorganic ions on human health, particularly on the development of neurodegenerative diseases. According to recent research studies, UFPs can be absorbed to human blood and have a toxicological effect on human organs. Due to their small particle size, UFPs can translocate to the human brain and contribute to the progression of neurodegenerative diseases. In this work, a molecular dynamics study was performed to investigate the impact of carbon-based UFP, mimicked by fullerene C 60 molecule, on the aggregation of amyloid β (Aβ) peptides, which is related to the progression of Alzheimer's disease. Moreover, the synergistic effect of the UFP and environmental pollutants was analyzed at various concentrations of the ions found in the environmental realm. In particular, the effect of C 60 on the aggregation kinetics of eight Aβ 16−21 peptides, the segment of Aβ peptide, was studied in the presence of NH 4 NO 3 by varying the salt concentrations from 50 to 150 mM. Overall, the results showed the formation of large amounts of β-sheets in the systems with a slow initial rate of the aggregation of Aβ 16−21 peptide octamer. In the absence of the UFP, the slowest initial rate of the aggregation of Aβ 16−21 peptide octamer was observed at 50 mM salt concentration, while, in the presence of C 60 , the slowest aggregation kinetics of Aβ 16−21 peptides was observed at 150 mM salt concentration. Moreover, in general, the presence of carbon-based UFP reduced the interpeptide interactions and decreased the initial rate of the aggregation of peptides due to the binding of peptides to C 60 .

Long-time exposure to ambient ultrafine particles is associated with an increased risk of neurodegenerative diseases such as Alzheimer’s disease (AD), which is triggered by the aggregation of Aβ peptide monomers into toxic oligomers. Among different ultrafine air pollutants, polycyclic aromatic hydrocarbons (PAHs) are known to have a negative neural impact; however, the impact mechanism remains obscure. We herein examined the effect of Benzo[a]Pyrene (B[a]P), one of the typical PAHs on Aβ42 oligomerization using all-atom molecular dynamics simulations. In particular, the simulations were performed using four molecules of Aβ42 in the presence of 5.00 mM, 12.5 mM, and 50.0 mM of B[a]P. The results revealed strong hydrophobic interactions between Aβ42 peptides and B[a]P, which in turn resulted in increased interpeptide electrostatic interactions. Furthermore, 5.00 mM of B[a]P accelerated the kinetics of the formation of peptide tetramer by 30%, and stabilized C-terminus in Aβ42 peptides, suggesting consequent progression of AD in the presence of 5.00 mM B[a]P. In contrast, 12.5 mM and 50.0 mM of B[a]P decreased interpeptide interactions and H-bonding due to the aggregation of numerous B[a]P clusters with the peptides, suppressing oligomerization kinetics of Aβ42 peptides by 13% and 167%, respectively. While the study elucidates the effect of small environmental hydrophobic molecules on the formation of Aβ oligomers, the impact of ambient ultrafine particles on AD in the complex composition of the environmental realm requires further systematic delving into the field.