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Fe3O4 Nanoparticles Grown on Cellulose/GO Hydrogels as Advanced Catalytic Materials for the Heterogeneous Fenton-like Reaction
Cellulose/graphene oxide (GO)/iron oxide (Fe3O4) composites were prepared by coprecipitating iron salts onto cellulose/GO hydrogels in a basic solution. X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared, and X-ray diffraction characterization showed that Fe3O4 was successfully coated on GO sheets and cellulose. Cellulose/GO/Fe3O4 composites showed excellent catalytic activity by maintaining almost 98% of the removal of acid orange 7 (AO7) and showed stability over 20 consecutive cycles. This performance is attributable to the synergistic effect of Fe3O4 and GO during the heterogeneous Fenton-like reaction. Especially, the cellulose/GO/Fe3O4 composites preserve their activity by keeping the ratio of Fe3+/Fe2+ at 2 even after 20 catalysis cycles, which is supported by XPS analysis.
Magnetic superexchange interactions: Trinuclear bis(oxamidato) versus bis(oxamato) type complexes
The diethyl ester of o-phenylenebis(oxamic acid) (opbaH2Et2) was treated with an excess of RNH2 in MeOH to cause the exclusive formation of the respective o-phenylenebis(N(R)-oxamides) (opboH4R2, R = Me 1, Et 2, nPr 3) in good yields. Treatment of 1–3 with half an equivalent of [Cu2(AcO)4(H2O)2] or one equivalent of [Ni(AcO)2(H2O)4] followed by the addition of four equivalents of [nBu4N]OH resulted in the formation of mononuclear bis(oxamidato) type complexes [nBu4N]2[M(opboR2)] (M = Ni, R = Me 4, Et 5, nPr 6; M = Cu, R = Me 7, Et 8, nPr 9). By addition of two equivalents of [Cu(pmdta)(NO3)2] to MeCN solutions of 7–9, novel trinuclear complexes [Cu3(opboR2)(L)2](NO3)2 (L = pmdta, R = Me 10, Et 11, nPr 12) could be obtained. Compounds 4–12 have been characterized by elemental analysis and NMR/IR spectroscopy. Furthermore, the solid state structures of 4–10 and 12 have been determined by single-crystal X-ray diffraction studies. By controlled cocrystallization, diamagnetically diluted 8 and 9 (1%) in the host lattice of 5 and 6 (99%) (8@5 and 9@6), respectively, in the form of single crystals have been made available, allowing single crystal ESR studies to extract all components of the g-factor and the tensors of onsite CuA and transferred NA hyperfine (HF) interaction. From these studies, the spin density distribution of the [Cu(opboEt2)]2− and [Cu(opbonPr2)]2− complex fragments of 8 and 9, respectively, could be determined. Additionally, as a single crystal ENDOR measurement of 8@5 revealed the individual HF tensors of the N donor atoms to be unequal, individual estimates of the spin densities on each N donor atom were made. The magnetic properties of 10–12 were studied by susceptibility measurements versus temperature to give J values varying from −96 cm−1 (10) over −104 cm−1 (11) to −132 cm−1 (12). These three trinuclear CuII-containing bis(oxamidato) type complexes exhibit J values which are comparable to and slightly larger in magnitude than those of related bis(oxamato) type complexes. In a summarizing discussion involving experimentally obtained ESR results (spin density distribution) of 8 and 9, the geometries of the terminal [Cu(pmdta)]2+ fragments of 12 determined by crystallographic studies, together with accompanying quantum chemical calculations, an approach is derived to explain these phenomena and to conclude if the spin density distribution of mononuclear bis(oxamato)/bis(oxamidato) type complexes could be a measure of the J couplings of corresponding trinuclear complexes.
Quantification of silver nanoparticle uptake and distribution within individual human macrophages by FIB/SEM slice and view
Background: Quantification of nanoparticle (NP) uptake in cells or tissues is very important for safety assessment. Often, electron microscopy based approaches are used for this purpose, which allow imaging at very high resolution. However, precise quantification of NP numbers in cells and tissues remains challenging. The aim of this study was to present a novel approach, that combines precise quantification of NPs in individual cells together with high resolution imaging of their intracellular distribution based on focused ion beam/ scanning electron microscopy (FIB/SEM) slice and view approaches. Results: We quantified cellular uptake of 75 nm diameter citrate stabilized silver NPs (Ag 75 Cit) into an individual human macrophage derived from monocytic THP-1 cells using a FIB/SEM slice and view approach. Cells were treated with 10 μg/ml for 24 h. We investigated a single cell and found in total 3138 ± 722 silver NPs inside this cell. Most of the silver NPs were located in large agglomerates, only a few were found in clusters of fewer than five NPs. Furthermore, we cross-checked our results by using inductively coupled plasma mass spectrometry and could confirm the FIB/SEM results. Conclusions: Our approach based on FIB/SEM slice and view is currently the only one that allows the quantification of the absolute dose of silver NPs in individual cells and at the same time to assess their intracellular distribution at high resolution. We therefore propose to use FIB/SEM slice and view to systematically analyse the cellular uptake of various NPs as a function of size, concentration and incubation time.
ROMP-Derived cyclooctene-based monolithic polymeric materials reinforced with inorganic nanoparticles for applications in tissue engineering
Porous monolithic inorganic/polymeric hybrid materials have been prepared via ring-opening metathesis copolymerization starting from a highly polar monomer, i.e., ciw-5-cyclooctene-trans-1,2-diol and a 7-oxanorborn-2-ene-derived cross-linker in the presence of porogenic solvents and two types of inorganic nanoparticles (i.e., CaCO3 and calcium hydroxyapatite, respectively) using the third-generation Grubbs initiator RuCl2(Py) 2(IMesH2)(CHPh). The physico-chemical properties of the monolithic materials, such as pore size distribution and microhardness were studied with regard to the nanoparticle type and content. Moreover, the reinforced monoliths were tested for the possible use as scaffold materials in tissue engineering, by carrying out cell cultivation experiments with human adipose tissue-derived stromal cells. © 2010 Weichelt et al; licensee Beilstein-Institut.
Degradation Behavior of Silk Nanoparticles - Enzyme Responsiveness
Silk nanoparticles are viewed as promising vectors for intracellular drug delivery as they can be taken up into cells by endocytosis and trafficked to lysosomes, where lysosomal enzymes and the low pH trigger payload release. However, the subsequent degradation of the silk nanoparticles themselves still requires study. Here, we report the responsiveness of native and PEGylated silk nanoparticles to degradation following exposure to proteolytic enzymes (protease XIV and α-chymotrypsin) and papain, a cysteine protease. Both native and PEGylated silk nanoparticles showed similar degradation behavior over a 20 day exposure period (degradation rate: protease XIV > papain ≫ α-chymotrypsin). Within 1 day, the silk nanoparticles were rapidly degraded by protease XIV, resulting in a ∼50% mass loss, an increase in particle size, and a reduction in the amorphous content of the silk secondary structure. By contrast, 10 days of papain treatment was necessary to observe any significant change in nanoparticle properties, and α-chymotrypsin treatment had no effect on silk nanoparticle characteristics over the 20-day study period. Silk nanoparticles were also exposed ex vivo to mammalian lysosomal enzyme preparations to mimic the complex lysosomal microenvironment. Preliminary results indicated a 45% reduction in the silk nanoparticle size over a 5-day exposure. Overall, the results demonstrate that silk nanoparticles undergo enzymatic degradation, but the extent and kinetics are enzyme-specific.
Cobalt-based nanoparticles prepared from MOF-carbon templates as efficient hydrogenation catalysts
The development of efficient and selective nanostructured catalysts for industrially relevant hydrogenation reactions continues to be an actual goal of chemical research. In particular, the hydrogenation of nitriles and nitroarenes is of importance for the production of primary amines, which constitute essential feedstocks and key intermediates for advanced chemicals, life science molecules and materials. Herein, we report the preparation of graphene shell encapsulated Co3O4- and Co-nanoparticles supported on carbon by the template synthesis of cobalt-terephthalic acid MOF on carbon and subsequent pyrolysis. The resulting nanoparticles create stable and reusable catalysts for selective hydrogenation of functionalized and structurally diverse aromatic, heterocyclic and aliphatic nitriles, and as well as nitro compounds to primary amines (>65 examples). The synthetic and practical utility of this novel non-noble metal-based hydrogenation protocol is demonstrated by upscaling several reactions to multigram-scale and recycling of the catalyst.
Time-resolved study of site-specific corrosion in a single crystalline silver nanoparticle
We followed over 24 h a corrosion process in monocrystalline triangular-shaped nanoparticles at a single-particle level by atomic force microscopy and optical spectroscopy techniques under ambient laboratory conditions. The triangular-shaped form of the particles was selected, because the crystallographic orientation of the particles is well defined upon their deposition on a substrate. We observed that the particles already start to alter within this time frame. Surprisingly, the corrosion starts predominantly from the tips of the particles and it creates within few hours large protrusions, which strongly suppress the plasmon character of the particles. These observations support the crystallographic model of these particles consisting of a high-defect hexagonal closed packed layer, and they could help material scientists to design more stable silver nanoparticles. Moreover, this described technique can be used to reveal kinetics of the corrosion in the nanoscale of other materials.
Improving the zT value of thermoelectrics by nanostructuring: Tuning the nanoparticle morphology of Sb2Te3 by using ionic liquids
A systematic study on the microwave-assisted thermolysis of the single source precursor (Et2Sb)2Te (1) in different asymmetric 1-alkyl-3-methylimidazolium- and symmetric 1,3-dialkylimidazolium-based ionic liquids (ILs) reveals the distinctive role of both the anion and the cation in tuning the morphology and microstructure of the resulting Sb2Te3 nanoparticles as evidenced by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS). A comparison of the electrical and thermal conductivities as well as the Seebeck coefficient of the Sb2Te3 nanoparticles obtained from different ILs reveals the strong influence of the specific IL, from which C4mimI was identified as the best solvent, on the thermoelectric properties of as-prepared nanosized Sb2Te3. This work provides design guidelines for ILs, which allow the synthesis of nanostructured thermoelectrics with improved performances.
An efficient two-polymer binder for high-performance silicon nanoparticle-based lithium-ion batteries: A systematic case study with commercial polyacrylic acid and polyvinyl butyral polymers
Silicon is one of the most promising anode materials for high energy density lithium ion batteries (LIBs) due to its high theoretical capacity and natural abundance. Unfortunately, significant challenges arise due to the large volume change of silicon upon lithiation/delithiation which inhibit its broad commercialization. An advanced binder can, in principle, reversibly buffer the volume change, and maintain strong adhesion toward various components as well as the current collector. In this work, we present the first report on the applicability of polyvinyl butyral (PVB) polymer as a binder component for silicon nanoparticles-based LIBs. Characteristic binder properties of commercial PVB and polyacrylic acid (PAA) polymers are compared. The work focuses on polymer mixtures of PVB polymers with PAA, for an improved binder composition which incorporates their individual advantages. Different ratios of polymers are systematically studied to understand the effect of particular polymer chains, functional groups and mass fractions, on the electrochemical performance. We demonstrate a high-performance polymer mixture which exhibits good binder-particle interaction and strong adhesion to Cu-foil. PAA/PVB-based electrode with a Si loading of ∼1 mg/cm2 tested between 0.01 and 1.2 V vs. Li/Li+ demonstrate specific capacities as high as 2170 mAh/g after the first hundred cycles. © The Author(s) 2019.
Novel monomers in radical ring-opening polymerisation for biodegradable and pH responsive nanoparticles
Responsive and biodegradable nanoparticles are essential for functional drug delivery systems. We herein report the first pH sensitive polyester from radical ring-opening polymerisation of novel amine-bearing cyclic ketene acetals (CKAs). The CKAs were synthesised via an intermediate carbonate and the resulting polyesters showed a pKa around pH 6. Together with an initial application in biodegradable nanoparticles, they open the pathway for a new generation of functional polyesters.