No abstract

Membrane proteins govern many important functions in cells via dynamic oligomerization into active complexes. However, analytical methods to study their distribution and functional state in relation to the cellular structure are currently limited. Here, we introduce a technique for studying single-membrane proteins within their native context of the intact plasma membrane. SKBR3 breast cancer cells were grown on silicon microchips with thin silicon nitride windows. The cells were fixed, and the epidermal growth factor receptor ErbB2 was specifically labeled with quantum dot (QD) nanoparticles. For correlative fluorescence- and liquid-phase electron microscopy, we enclosed the liquid samples by chemical vapor deposited (CVD) graphene films. Depending on the local cell thickness, QD labels were imaged with a spatial resolution of 2 nm at a low electron dose. The distribution and stoichiometric assembly of ErbB2 receptors were determined at several different cellular locations, including tunneling nanotubes, where we found higher levels of homodimerization at the connecting sites. This experimental approach is applicable to a wide range of cell lines and membrane proteins and particularly suitable for studies involving both inter- and intracellular heterogeneity in protein distribution and expression.

Palladium nanoparticles (NPs) of different mean particle size have been synthesized in the host structure of the porous coordination polymer (or metal-organic framework: MOF) MIL-101. The metal-organic chemical vapor deposition method was used to load MIL-101 with the Pd precursor complex [(η(5)-C(5)H(5))Pd(η(3)-C(3)H(5))]. Loadings higher than 50 wt.% could be accomplished. Reduction of the Pd precursor complex with H(2) gave rise to Pd NPs inside the MIL-101 (Pd@MIL-101). The reduction conditions, especially the temperature, allows us to make size-conform (size of the Pd NPs correlates with the size of the cavities of the host structure of MIL-101) and undersized Pd NPs. The Pd@MIL-101 samples were characterized by X-ray diffraction, IR spectroscopy, Brauner-Emmett-Teller (BET) analysis, elemental analysis, and transmission electron microscopy (TEM). Catalytic studies, hydrogenation of ketones, were performed with selected Pd@MIL-101 catalysts. Activity, selectivity, and recyclability of the catalyst family are discussed.

The fabrication of supported catalysts consisting of colloidal iron oxide nanocrystals with tunable size, geometry, and loading—homogeneously dispersed on carbon nanotube (CNT) supports—is described herein. The catalyst synthesis is performed in a two‐step approach. First, colloidal iron and iron oxide nanocrystals with a narrow size distribution are produced. Second, the nanocrystals are attached to CNT grains serving as support structure. Important features, like iron loading and nanocrystal density on the CNT support, are controlled by changing the nanocrystal concentration and ligand concentration, respectively. The Fischer–Tropsch performance reveals these new materials to be active, selective toward lower olefins (60% C of hydrocarbons produced in the absence of promoters), and remarkably stable against particle growth.

It was studied how the chemistry of gold nanoparticles in water is influenced by solution parameters such as the pH or the NaCl concentration under electron beam irradiation. We found that depending on these parameters the gold nanoparticles either dissolved, merged or remained unchanged.

SiC materials with tailored porosity and integrated Ni NPs (Ni@SiC) were synthesized via microphase separation of polycarbosilane-block-polyethylene followed by its pyrolysis. Changing the length of organic block allowed the synthesis of micro, meso and hierarchical Ni@SiC materials which were characterized by PXRD, TEM, TGA, and nitrogen physisorption. Selective hydrogenolysis of aryl ethers mimicking the most abundant linkages of lignin was achieved in water avoiding the possible hydrogenation of aromatic rings.The sustainable production of fine chemicals and fuels from renewable resources is a burgeoning and challenging research area.[1] Lignocellulose biomass (cellulose, hemi-cellulose and lignin) is a key resource whose availability is plentiful and its utilisation will allay the fears regarding competition with food supplies. [1, 2] Although cellulose can be depolymerised in many ways, [3] selective cleavage of aryl ether (C Ar ÀO) and especially diaryl ether substructures of lignin is challenging.[4] Lignin constitutes 15-30 % of woody biomass [5] with an energy content of up to 40 % of this biomass [6] and its selective depolymerisation (through hydrogenolysis) is crucial for the generation of fuel and chemicals from renewable resources. Selective cleavage of the C Ar ÀO bond of lignin model compounds in organic solvents has been reported by the use of molecular catalysts (V, [7] Ru [8] and Ni [9] complexes) and heterogeneous catalysts (Ni [10] and Zn/Pd [11] ). The molecular catalysts offer better chemoselectivity in the selective cleavage of C Ar ÀO bonds and are operative under mild conditions (80-135 8C). Unfortunately, they are mostly sensitive to high concentrations of water, the removal of which from the crude biomass is challenging and uneconomical. Heterogeneous catalysts, on the other hand, are not very selective and require higher reaction temperatures or hydrogen pressures, leading to the reduction of arenes and subsequent hydrogen loss. The Lercher group has reported some elegant work on the use of heterogeneous catalysts for the cleavage of ethers in water. [12][13][14] The substantial reduction of arenes was also observed. Reports on the reusability of the hitherto applied catalysts are rare. Thus, there is a need for reusable catalysts offering hydrothermal stability for the selective cleavage of C Ar ÀO bonds.In the past few years, others and ourselves have developed late transition metal-containing polymer-derived SiCN materials (M@SiCN) as robust heterogeneous catalysts.[15] The Wiesner group fabricated Pt@SiCN materials which, despite the structural control over multiple length scales, showed a rather low surface area.[16] By the controlled pyrolysis of Ni modified polysilazane, we managed to get microporous high surface area materials. They were found to be selective and active catalysts for the semi-hydrogenation of acetylenes.[17] Unfortunately, the SiÀN bonds of the materials pyrolysed at 600 8C were under harsh conditions. SiC materials do not contain such bonds and ...

Robust microporous nanocomposites (specific surface area ≈ 400 m 2 /g) containing nickel nanoparticles have been synthesized and characterized by thermogravimetric analysis (TGA), differential thermal analysis (DTA), Fourier transform infrared (FT-IR) spectroscopy, nitrogen physisorption, powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and 13 C and 29 Si solid-state nuclear magnetic resonance (NMR) spectroscopy. The commercially available polysilazane (HTT-1800) is chemically modified using an N-ligand-stabilized nickel complex that catalyzes the crosslinking of the polymer via hydrosilylation at room temperature. Upon pyrolysis at 600°C under an inert atmosphere, nickel nanoparticles and micropores are generated in a concerted process. The specific surface area, pore volume, and size of the nickel particles can be tuned. The materials show excellent shape retention upon pyrolysis providing the possibility to fabricate monoliths. The composites are stable in the presence of moisture and are both thermally and solvothermally robust, as indicated by the nitrogen adsorption, FT-IR, and TGA measurements. Continuous-flow, hyperpolarized 129 Xe NMR methods were used in tandem to evaluate the effects of the nickel content and annealing time on the pore structure of the microporous nanocomposite. The adsorption enthalpy is rather independent of nickel particle inclusion. The interior adsorption sites are lined with methyl groups and the nickel particles seem to be located near the external surface of the composites and within the internal voids. The nickel nanoparticles were used to catalyze selective hydrogenation reactions indicating applications of the nanocomposites as catalyst itself or as catalyst support.

Liquid-phase transmission electron microscopy (TEM) is used for in-situ imaging of nanoscale processes taking place in liquid, such as the evolution of nanoparticles during synthesis or structural changes of nanomaterials in liquid environment. Here, it is shown that the focused electron beam of scanning TEM (STEM) brings about the dissolution of silica nanoparticles in water by a gradual reduction of their sizes, and that silica redeposites at the sides of the nanoparticles in the scanning direction of the electron beam, such that elongated nanoparticles are formed. Nanoparticles with an elongation in a different direction are obtained simply by changing the scan direction. Material is expelled from the center of the nanoparticles at higher electron dose, leading to the formation of doughnut-shaped objects. Nanoparticles assembled in an aggregate gradually fuse, and the electron beam exposed section of the aggregate reduces in size and is elongated. Under TEM conditions with a stationary electron beam, the nanoparticles dissolve but do not elongate. The observed phenomena are important to consider when conducting liquid-phase STEM experiments on silica-based materials and may find future application for controlled anisotropic manipulation of the size and the shape of nanoparticles in liquid.