We performed density functional theory (DFT) based calculations to investigate the effects of O-vacancies on the adsorption of O 2 on anatase TiO 2 (001). Our calculation results show that we can promote O 2 adsorption on an initially inert stoichiometric TiO 2 (001) by introducing O-vacancy. The resulting excess electrons from the introduction of the O-vacancy redistribute around the neighboring Ti ions. An incoming O 2 can then adsorb at the O-vacancy site, either in the superoxide state (O − 2) or the peroxide state (O 2− 2). In the O − 2 state, the O-O bond is oriented parallel to the surface, along [010]. In the O 2− 2 state, the O-O bond is oriented perpendicular to the surface, along [001]. Healing of the surface occurs when one of the O atoms of the perpendicularly adsorbed O 2 fills the vacant site and the other atom diffuses, recovering the stoichiometric surface.

Alzheimer's disease is presumed to be caused by the formation of intracellular plaques of amyloid β (Aβ) peptides inside neurons. The most abundant Aβ forms are Aβ40 and Aβ42 comprising, respectively, 40 and 42 residues. Recent experiments showed that the triple Gly33Val-Val36Pro-Gly38Val (VPV) mutation causes Aβ42 to become "super-Aβ42" with elevated aggregation rates and toxicity. Upon VPV mutation, oligomerization pathways of Aβ40 become similar to those of the Aβ42 wild type. It was hypothesized that the super behavior of Aβ42 occurs due to an enhanced content of the β-turn and β-hairpin, centered at residues 36-37, and the similarity in oligomerization pathways of Aβ40-VPV and Aβ42-WT comes from the increased β-turn population. As this is based on simulation of the truncated fragments, this hypothesis may not be valid for the full-length case, motivating us to perform all-atom molecular dynamics simulations for full-length Aβ sequences. We showed that the results obtained for truncated peptides fall short in explaining the similarity of self-assembly pathways of Aβ40-VPV and Aβ42-WT. Instead, we propose that the similarity is due to not only increased β-turn population but also due to the elevated β-structure of the entire sequence. Similar to VPV, the Gly33Val-Val36Asn-Gly38Leu mutation enhances the β-structure and the C-terminal β-turn making the behavior of Aβ40 similar to that of Aβ42-WT.

No abstract