The precipitation products (rain, snow and so on) of atmospheric water vapour are widely prevalent, and yet the map of its initial stage at a surface is still unclear. Here we investigate the condensation of water vapour occurring in both the hydrophobic-hydrophilic interface (graphene/mica) and the hydrophilic-hydrophilic interface (MoS 2 /mica) by in situ thermally controlled atomic force microscopy. By monitoring the dynamic dewetting/rewetting transitions process, the ice-like water adlayers, at the hydrophobic-hydrophilic interface and not at the hydrophilic-hydrophilic interface, stacked on top of each other up to three ice-I h layers (each of height 3.7 ± 0.2 Å), and the transition from layers to droplets was directly visualized experimentally. Compared with molecular dynamics simulation, the Stranski-Krastanov growth model is better suited to describe the whole water condensation process at the hydrophobic-hydrophilic interface. The initial stage of the hydrometeor is rationalized, which potentially can be utilized for understanding the boundary condition for water transport and the aqueous interfacial chemistry.
The differentiation of protein properties and biological functions arises from the variation in the primary and secondary structure. Specifically, in abnormal assemblies of protein, such as amyloid peptide, the secondary structure is closely correlated with the stable ensemble and the cytotoxicity. In this work, the early Aβ33‐42 aggregates forming the molecular monolayer at hydrophobic interface are investigated. The molecular monolayer of amyloid peptide Aβ33‐42 consisting of novel parallel β‐strand‐like structure is further revealed by means of a quantitative nanomechanical spectroscopy technique with force controlled in pico‐Newton range, combining with molecular dynamic simulation. The identified parallel β‐strand‐like structure of molecular monolayer is distinct from the antiparallel β‐strand structure of Aβ33‐42 amyloid fibril. This finding enriches the molecular structures of amyloid peptide aggregation, which could be closely related to the pathogenesis of amyloid disease.
The 3D structures
of biomolecules determine their biological function.
Established methods in biomolecule structure determination typically
require purification, crystallization, or modification of target molecules,
which limits their applications for analyzing trace amounts of biomolecules
in complex matrices. Here, we developed instruments and methods of
mobility capillary electrophoresis (MCE) and its coupling with MS
for the 3D structural analysis of biomolecules in the liquid phase.
Biomolecules in complex matrices could be separated by MCE and sequentially
detected by MS. The effective radius and the aspect ratio of each
separated biomolecule were simultaneously determined through the separation
by MCE, which were then used as restraints in determining biomolecule
conformations through modeling. Feasibility of this method was verified
by analyzing a mixture of somatostatin and bradykinin, two peptides
with known liquid-phase structures. Proteins could also be structurally
analyzed using this method, which was demonstrated for lysozyme. The
combination of MCE and MS for complex sample analysis was also demonstrated.
MCE and MCE–MS would allow us to analyze trace amounts of biomolecules
in complex matrices, which has the potential to be an alternative
and powerful biomolecule structure analysis technique.
Nanoscale Fe 3 O 4 epitaxial thin film has been synthesized on MgO/GaAs(100) spintronic heterostructure, and studied with X-ray magnetic circular dichroism (XMCD). We have observed a total magnetic moment (m l+s ) of (3.32±0.1)µ B /f.u., retaining 83% of the bulk value. Unquenched orbital moment (m l ) of (0.47µ B ±0.05)µ B /f.u. has been confirmed by carefully applying the sum rule. The results offer direct experimental evidence of the bulk-like total magnetic moment and a large orbital moment in the nanoscale fully epitaxial Fe 3 O 4 /MgO/GaAs(100) heterostructure, which is significant for spintronics applications. Liu et al.
CITATION:
Water vapor condensation
on the solid surface is ubiquitous in
nature and has considerable importance in industrial applications.
In this work, molecular dynamics simulation is used to investigate
the kinetic process of water condensation on the mica surface as well
as the properties of adsorbed water. The water molecules tend to spread
on the mica surface and develop a water film comprised of two distinct
adlayers. The growth of the first water adlayer is inhomogeneous due
to the discrepancy of adsorption tendency to different surface sites.
Interestingly, the second water adlayer begins to emerge far before
the surface sites of mica are completely occupied. Our observations
resemble the condensation process described by the Stranski–Krastanov
growth model. These findings exhibit the dependence of water condensation
on the surface properties.
Peptide assembly plays a seminal role in the fabrication of structural and functional architectures in cells. Characteristically, peptide assemblies are often dominated by β-sheet structures, wherein component molecules are connected by backbone hydrogen bonds in a parallel or an antiparallel fashion. While β-rich peptide scaffolds are implicated in an array of neurodegenerative diseases, the mechanisms by which toxic peptides assemble and mediate neuropathic effects are still poorly understood. In this work, we employ molecular dynamics simulations to study the adsorption and assembly of the fragment Aβ33-42 (taken from the Aβ-42 peptide widely associated with Alzheimer's disease) on a graphene surface. We observe that such Aβ33-42 fragments, which are largely hydrophobic in character, readily adsorb onto the graphitic surface and coalesce into a well-structured, β-strand-like assembly. Strikingly, the structure of such complex is quite unique: hydrophobic side-chains extend over the graphene surface and interact with adjacent peptides, yielding a well-defined mosaic of hydrophobic interaction patches. This ordered structure is markedly depleted of backbone hydrogen bonds. Hence, our simulation results reveal a distinct type of β-strand assembly, maintained by hydrophobic side-chain interactions. Our finding suggests the backbone hydrogen bond is no longer crucial to the peptide assembly. Further studies concerning whether such β-strand assembly can be realized in other peptide systems and in biologically-relevant contexts are certainly warranted.
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