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Amyloid-β (Aβ) peptides exhibit many distinct structural morphology at the early aggregate stage, some of which are biological relevant to the pathogenesis of Alzheimer’s disease (AD). Atomic-resolution structures of the early Aβ aggregates and their conformational changes in amyloid aggregation remain elusive. Here, we perform all-atom molecular modeling and dynamics simulations to obtain two stable triangular-like Aβ structures with the lowest packing energy, one corresponding to the Tycko’s model (Paravastu, A.; Leapman, R.; Yau, W.; Tycko, R.Proc. Nat. Acad. Soc. U.S.A.2008, 105, 18349−18354) (referred to C-WT model) and the other corresponding to computational model (N-WT model). Both models have the same 3-fold symmetry but distinct β-sheet organizations in which three Aβ hexamers pack together via either C-terminal β-strand residues or N-terminal β-strand residues forming distinct hydrophobic cross section. Structural and energetic comparisons of two 3-fold Aβ oligomers, coupled with structural changes upon the mutations occurring at the interacting interfaces, reveal that although hydrophobic interactions are still dominant forces, electrostatic interactions are more favorable in the N-WT model due to the formation of more and stable intersheet salt bridges, while solvation energy is more favorable in the C-WT model due to more exposed hydrophilic residues to solvent. Both models display many common features similar to other amyloid oligomers and therefore are likely to be biologically relevant. [ABSTRACT FROM AUTHOR]

Granules polymers electrostatic behavior in a fluidized bed can be complicated by the differences in catalyst residue and surface properties among them. Electrically charged particles cling together in large aggregates and adhere to the wall of the apparatus. Polymer particles with the same chemical composition but different sizes would have their own special contributions to the generation of static charges. It is improtant to understand polymer particles role on electrostatic charge generation and dissipation. Experiments are carried out in a gas−solid fluidized bed with nitrogen as the fluidization gas to determine the relationship between the electrostatic charge level and the size of the polyethylene granule. By measuring the electrostatic potentials at different bed axial heights, it is found that the electric field inside the bed is significantly influenced by the size, weight fractions, and catalyst residue of added granular polyethylene. Consequently, an impact factor of granules (Fb) is proposed to study the influence of particle size and the weight percent of the residual catalyst to the electrostatic potentials. And it is found that the greater the degree of fineness of the granules, the more percentage of the residual catalyst in the particles, which results in the stronger affect on the electrostatic behavior in the fluidized bed. [ABSTRACT FROM AUTHOR]