No abstract

It is well known that NaCl salt crystals can easily dissolve in dilute aqueous solutions at room temperature. Herein, we reported the first computational evidence of a novel salt nucleation behavior at room temperature, i.e., the spontaneous formation of two-dimensional (2D) alkali chloride crystalline/non-crystalline nanostructures in dilute aqueous solution under nanoscale confinement. Microsecond-scale classical molecular dynamics (MD) simulations showed that NaCl or LiCl, initially fully dissolved in confined water, can spontaneously nucleate into 2D monolayer nanostructures with either ordered or disordered morphologies. Notably, the NaCl nanostructures exhibited a 2D crystalline square-unit pattern, whereas the LiCl nanostructures adopted non-crystalline 2D hexagonal ring and/or zigzag chain patterns. These structural patterns appeared to be quite generic, regardless of the water and ion models used in the MD simulations. The generic patterns formed by 2D monolayer NaCl and LiCl nanostructures were also confirmed by ab initio MD simulations. The formation of 2D salt structures in dilute aqueous solution at room temperature is counterintuitive. Free energy calculations indicated that the unexpected spontaneous salt nucleation behavior can be attributed to the nanoscale confinement and strongly compressed hydration shells of ions.

No abstract

The self-assembly of 3,10-dibromo-perylo­[1,12-b,c,d]­thiophene on Ag(111) leads to three types of ordered porous networks: honeycomb PN1, Kagome PN2, and hybrid PN3. Detailed experimental and theoretical analyses confirm the thermal stability order of the three constructed porous networks. High-resolution scanning tunneling microscopy images indicate the importance of two σ-hole interactions of Br···S and Br···Br in steering two-dimensional molecular assembly on metal surfaces.

The adsorption and assembly of individual and submonolayered TiOPc on Ag(111), Cu(111), and Au(111) have been investigated by scanning tunneling microscopy (STM) and spectroscopy. High resolution STM imaging as well as dI/dV and I−z measurements reveal that TiOPc adsorbed on Ag(111) adopts either O-up or O-down configuration. An intermolecular dipole−dipole interaction leads to the fact that neighboring TiOPc molecules in alternating O-up and O-down configurations form a highly ordered checkerboard assembly structure on Ag(111). However, no large size TiOPc assemblies are observed on Cu(111) and Au(111) due to low surface mobility and diffusivity caused by strong TiOPc−Cu(111) interaction and the templating effect by the reconstructed herringbone structure of Au(111), respectively. Instead, molecular dimers on both Au(111) and Cu(111) as well as molecular aggregates on Au(111) are routinely observed in experiments, indicating that the intermolecular dipole−dipole attraction and weak hydrogen bonding coplay an important role in steering the adsorption and assembly of the TiOPc molecules on the coinage metal surfaces.

Renewable power-derived green hydrogen distributed via natural gas networks is considered one of the viable routes to drive the decarbonization of transportation and distributed power generation, while a trace amount of sulfur impurities is one of the key factors that affect the durability and life cycle expense of proton-exchange membrane fuel cells (PEMFCs) for end users. Herein, we explore the underlying effect of sulfur resistance for Ptbased hydrogen oxidation reaction (HOR) electrocatalysts devoted to high-performance and durable PEMFCs. Two typical electrocatalysts, Pt/C with pure Pt nanoparticles (NPs) and PtCo/C with Pt 3 Co-alloy-core-Pt-skin NPs, were investigated to demonstrate the structure−property relation for Pt-based electrocatalysts. It was revealed that the PtCo/C demonstrated alleviated sulfur poisoning with the adsorption rate constant reduced by 21.7% compared with Pt/C, and the desorption of the adsorbed sulfur was also more favorable with Pt−S bond decomposition temperature lowered by approximately 25 °C. Characterization indicated that sulfur was predominantly adsorbed in the edge mode for PtCo/C, but in a comparable edge and bridge mode for Pt/C, which caused the strengthened Pt−S binding by the chelation effect for Pt/C. The lowered d-band center of surface Pt for PtCo/C, tuned by electron transfer from Co to Pt and Pt lattice strain, was also found responsible for the weakened Pt−S interaction. The recovery test based on electro-oxidation suggested that PtCo/C also outperformed Pt/C with faster and more thorough release of HOR active sites. The SO 42− species derived from electro-oxidation of S 2− was more apt to adsorb on Pt/C than PtCo/C because of its stronger affinity to SO 4 2− caused by the higher d-band center of Pt. Therefore, it is clarified that adequate modification of the Pt d-band center, for example, negatively tuned for the state-of-the-art Pt/C, is crucial to improve the sulfur resistance and recovery capability for Pt-based electrocatalysts while reserving comparable HOR activity. In particular, the investigated PtCo/C electrocatalyst is a better choice over Pt/C for more durable PEMFC anodes.

No abstract

Amyloid-β (Aβ), the major component of neuritic plaques in Alzheimer’s disease (AD), is derived from sequential proteolytic cleavage of amyloid protein precursor (APP) by secretases. In this study, we found that cystatin C (CysC), a natural cysteine protease inhibitor, is able to reduce Aβ40 secretion in human brain microvascular endothelial cells (HBMEC). The CysC-induced Aβ40 reduction was caused by degradation of β-secretase BACE1 through the ubiquitin/proteasome pathway. In contrast, we found that CysC promoted secretion of soluble APPα indicating the activated non-amyloidogenic processing of APP in HBMEC. Further results revealed that α-secretase ADAM10, which was transcriptionally upregulated in response to CysC, was required for the CysC-induced sAPPα secretion. Knockdown of SIRT1 abolished CysC-triggered ADAM10 upregulation and sAPPα production. Taken together, our results demonstrated that exogenously applied CysC can direct amyloidogenic APP processing to non-amyloidgenic pathway in brain endothelial cells, mediated by proteasomal degradation of BACE1 and SIRT1-mediated ADAM10 upregulation. Our study unveils previously unrecognized protective role of CysC in APP processing.