The influenza A virus infects target cells through multivalent interactions of its major spike proteins, hemagglutinin (HA) and neuraminidase (NA), with the cellular receptor sialic acid (SA). HA is ...known to mediate the attachment of the virion to the cell, whereas NA enables the release of newly formed virions by cleaving SA from the cell. Because both proteins target the same receptor but have antagonistic functions, virus infection depends on a properly tuned balance of the kinetics of HA and NA activities for viral entry to and release from the host cell. Here, dynamic single-molecule force spectroscopy, based on scanning force microscopy, was employed to determine these bond-specific kinetics, characterized by the off rate koff, rupture length xβ and on rate kon, as well as the related free-energy barrier ΔG and the dissociation constant KD. Measurements were conducted using surface-immobilized HA and NA of the influenza A virus strain A/California/04/2009 and a novel, to our knowledge, synthetic SA-displaying receptor for functionalization of the force probe. Single-molecule force spectroscopy at force loading rates between 100 and 50,000 pN/s revealed most probable rupture forces of the protein-SA bond in the range of 10–100 pN. Using an extension of the widely applied Bell-Evans formalism by Friddle, De Yoreo, and co-workers, it is shown that HA features a smaller xβ, a larger koff and a smaller ΔG than NA. Measurements of the binding probability at increasing contact time between the scanning force microscopy force probe and the surface allow an estimation of KD, which is found to be three times as large for HA than for NA. This suggests a stronger interaction for NA-SA than for HA-SA. The biological implications in regard to virus binding to the host cell and the release of new virions from the host cell are discussed.
Understanding and controlling charge transfer through molecular nanostructures at interfaces is of paramount importance, particularly for electronic devices but also for contact electrification or in ...bioelectronics. We investigate the influence of intercalation and exchange of molecularly thin layers of small molecules (water, ethanol, 2-propanol, and acetone) on charge transfer at the well-defined interface between an insulator (muscovite mica) and a conductor (graphene). Raman spectroscopy is used to probe the charge carriers in graphene. While a molecular layer of water blocks charge transfer between mica and graphene, a layer of the organic molecules allows for it. The exchange of molecular water layers with ethanol layers switches the charge transfer very efficiently from off to on and back. We propose a charge transfer model between occupied mica trap states and electronic states of graphene, offset by the electrostatic potentials produced by the molecular dipole layers, as supported by molecular dynamics simulations. Our work demonstrates how intercalation of molecules of volatile liquids can reversibly affect charge transfer at interfaces. This implies its strong impact on the function of hybrid inorganic–organic electronic devices in different ambients and potential applications, including sensors and actuators.
The matrix protein M1 plays a pivotal role in the budding of influenza virus from the plasma membrane (PM) of infected cells. This protein interacts with viral genetic material and envelope proteins ...while binding to the inner leaflet of the PM. Its oligomerization is therefore closely connected to the assembly of viral components and the formation of new virions. Of interest, the molecular details of M1 interaction with lipids and other viral proteins are far from being understood, and it remains to be determined whether the multimerization of M1 is affected by its binding to the PM and interaction with its components. To clarify the connection between M1 oligomerization and binding to lipid membranes, we applied a combination of several quantitative microscopy approaches. First, we used number and brightness (N&B) microscopy to characterize protein multimerization upon interaction with the PM of living cells. Second, we used controlled biophysical models of the PM (i.e., supported bilayers) to delve into the details of M1-lipid and M1-M1 interactions by employing a combination of raster image correlation spectroscopy (RICS), fluorescence correlation spectroscopy (FCS), and atomic force microscopy (AFM). Our results show that M1 oligomer formation is strongly enhanced by membrane binding and does not necessarily require the presence of other viral proteins. Furthermore, we propose a specific model to explain M1 binding to the lipid bilayer and the formation of multimers.
Rapid Aging of Bilayer Graphene Oxide Lin, Hu; Iakunkov, Artem; Severin, Nikolai ...
Journal of physical chemistry. C,
12/2022, Volume:
126, Issue:
48
Journal Article
Peer reviewed
Open access
Atomic force microscopy (AFM) imaging was used to study swelling of individual bilayer graphene oxide (GO) flakes in water and ethanol vapors. We found that within 5 days after sample deposition the ...swelling of bilayered Hummers GO (HGO) in ethanol vapors disappears nearly completely, whereas the swelling in water remains not affected. Swelling can therefore be used as a sensitive indicator of rapid aging of bilayered HGO, which occurs both in air and under inert gas. The surprising ability of 5-days-aged bilayered HGO to swell in water but not in ethanol fits to the effects observed in μm-thick GO membranes after several years of aging. Remarkably, bilayered Brodie GO (BGO) maintains swelling in ethanol after storing it under the same conditions as HGO. Moreover, we demonstrate that AFM can be used to detect hole defects in individual GO sheets. The BGO bilayer swelling in ethanol vapors starts either on the flake edges or in very few points, forming ∼2 Å height fronts, which propagate slowly within interlayer spaces in all directions. The increase of the average distance between HGO sheets occurs simultaneously all over the flake, demonstrating a high abundance of hole defects. Our results imply that the permeation path length in HGO membranes must be significantly shorter compared to BGO, which is important to take into account in the modeling of membrane permeation.
Self-assembled quasi one-dimensional nanostructures of pi-conjugated molecules may find a use in devices owing to their intriguing optoelectronic properties, which include sharp exciton transitions, ...strong circular dichroism, high exciton mobilities and photoconductivity. However, many applications require immobilization of these nanostructures on a solid substrate, which is a challenge to achieve without destroying their delicate supramolecular structure. Here, we use a drop-flow technique to immobilize double-walled tubular J-aggregates of amphiphilic cyanine dyes without affecting their morphological or optical properties. High-resolution images of the topography and exciton fluorescence of individual J-aggregates are obtained simultaneously with polarization-resolved near-field scanning optical microscopy. These images show remarkably uniform supramolecular structure, both along individual nanotubes and between nanotubes in an ensemble, demonstrating their potential for light harvesting and energy transport.
Efficient inhibition of cell–pathogen interaction to prevent subsequent infection is an urgent but yet unsolved problem. In this study, the synthesis and functionalization of novel multivalent 2D ...carbon nanosystems as well as their antiviral efficacy in vitro are shown. For this reason, a new multivalent 2D flexible carbon architecture is developed in this study, functionalized with sulfated dendritic polyglycerol, to enable virus interaction. A simple “graft from” approach enhances the solubility of thermally reduced graphene oxide and provides a suitable 2D surface for multivalent ligand presentation. Polysulfation is used to mimic the heparan sulfate‐containing surface of cells and to compete with this natural binding site of viruses. In correlation with the degree of sulfation and the grafted polymer density, the interaction efficiency of these systems can be varied. In here, orthopoxvirus strains are used as model viruses as they use heparan sulfate for cell entry as other viruses, e.g., herpes simplex virus, dengue virus, or cytomegalovirus. The characterization results of the newly designed graphene derivatives demonstrate excellent binding as well as efficient inhibition of orthopoxvirus infection. Overall, these new multivalent 2D polymer nanosystems are promising candidates to develop potent inhibitors for viruses, which possess a heparan sulfate‐dependent cell entry mechanism.
Efficient inhibition of orthopoxvirus infection by newly designed multivalent 2D nanosystems functionalized with dendritic polyglycerol polymers in a simple “graft from” approach is described in this study. A tunable polysulfation is used to enable virus interaction, which correlates with the degree of sulfation and the grafted polymer density. In conclusion, the innovative 2D architectures have the potential to develop new virus inhibitors.
Resonant coupling between distinct excitons in organic supramolecular assemblies and inorganic semiconductors is supposed to offer an approach to optoelectronic devices. Here, we report on colloidal ...nanohybrids consisting of self-assembled tubular J-aggregates decorated with semiconductor quantum dots (QDs) via electrostatic self-assembly. The role of QDs in the energy transfer process can be switched from a donor to an acceptor by tuning its size and thereby the excitonic transition energy while keeping the chemistry unaltered. QDs are located within a close distance (<4 nm) to the J-aggregate surface, without harming the tubular structures and optical properties of J-aggregates. The close proximity of J-aggregates and QDs allows the strong excitation energy transfer coupling, which is around 92% in the case of energy transfer from the QD donor to the J-aggregate acceptor and approximately 20% in the reverse case. This system provides a model of an organic–inorganic light-harvesting complex using methods of self-assembly in aqueous solution, and it highlights a route toward hierarchical synthesis of structurally well-defined supramolecular objects with advanced functionality.
Ultrathin gallium oxide layers with a thickness of 2.8 ± 0.2 nm were transferred from the surface of liquid gallium onto solid substrates, including conjugated polymer poly(3-hexylthiophene) (P3HT). ...The gallium oxide exhibits high mechanical stability, withstanding normal pressures of up to 1 GPa in contact mode scanning force microscopy imaging. Moreover, it lowers the rate of photodegradation of P3HT by 4 orders of magnitude, as compared to uncovered P3HT. This allows us to estimate the upper limits for oxygen and water vapor transmission rates of 0.08 cm3 m–2 day–1 and 0.06 mg m–2 day–1, respectively. Hence, similar to other highly functional coatings such as graphene, ultrathin gallium oxide layers can be regarded as promising candidates for protective layers in flexible organic (opto-)electronics and photovoltaics because they offer permeation barrier functionalities in conjunction with high optical transparency.
Single strands of azobenzene main chain polymers exhibiting alkyl side chains can be largely and reversibly contracted and extended with light. We show that upon self-assembly in a thin layered film ...they act as “molecular zippers” that can be opened and closed with UV- and blue light, respectively. Simultaneously in situ recorded time-resolved X-ray diffraction and optical spectroscopy measurements, together with scanning force microscopy show that upon the light-induced E → Z isomerization of the main chain azobenzenes the layered film morphology remains, while the initially highly ordered alkyl side chains become disordered. Already the E → Z isomerization of about 20% of all azobenzene chromophores triggers a complete disorder of the alkyl chains. The kinetics of this partial amorphization of the film is about 18 times slower than the ensemble kinetics of the initial azobenzene photoisomerization. This is the first demonstration of a rigid main chain polymer film with reversibly photoswitchable side chain crystallinity.
Triangles and zigzags: Large triangle‐shaped C3‐symmetrical polycyclic aromatic hydrocarbons with multiple zigzag peripheries were synthesized. The molecules display mesophase stability over a wide ...temperature range as a result of helical packing. Moreover, a 2D honeycomb pattern was observed for one of the larger structures (see picture).
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