Hollow Spheres of Iron Carbide Nanoparticles Encased in Graphitic Layers as Oxygen Reduction Catalysts

Nonprecious metal catalysts for the oxygen reduction reaction are the ultimate materials and the foremost subject for low‐temperature fuel cells. A novel type of catalysts prepared by high‐pressure pyrolysis is reported. The catalyst is featured by hollow spherical morphologies consisting of uniform iron carbide (Fe₃C) nanoparticles encased by graphitic layers, with little surface nitrogen or metallic functionalities. In acidic media the outer graphitic layers stabilize the carbide nanoparticles without depriving them of their catalytic activity towards the oxygen reduction reaction (ORR). As a result the catalyst is highly active and stable in both acid and alkaline electrolytes. The synthetic approach, the carbide‐based catalyst, the structure of the catalysts, and the proposed mechanism open new avenues for the development of ORR catalysts.     

The rheological properties of hydrogenated castor oil crystals

The present study focuses on the rheological performance of a surfactant-rich aqueous suspension containing hydrogenated castor oil (HCO) crystals. HCO can be typically crystallized in five distinct shapes: spherically shaped, irregularly shaped, star-shaped (also called rosettes), short needles, and thick or thin fibers. The effect of the differences in shape on the rheological performance is studied, and the rheological properties are compared to the behavior of other triacylglycerol’s (TAG) suspensions. A suspension of TAG crystals usually behaves as a colloidal gel wherein a colloidal gel is defined as a network of flocs, with each floc being an aggregate of smaller subunits. All of these surfactant-rich aqueous suspensions of HCO crystals behaved according to a colloidal gel in the transient regime, independent of the studied crystal shapes, except the long thin fibers at a concentration above 0.1 wt% HCO transitioning from a heterogeneous fractal rod network to a homogeneous rod network, shifting from a colloidal gel to a glass.     

Covalent Adaptable Networks with Tunable Exchange Rates Based on Reversible Thiol–yne Cross‐Linking

The design of covalent adaptable networks (CANs) relies on the ability to trigger the rearrangement of bonds within a polymer network. Simple activated alkynes are now used as versatile reversible cross‐linkers for thiols. The click‐like thiol–yne cross‐linking reaction readily enables network synthesis from polythiols through a double Michael addition with a reversible and tunable second addition step. The resulting thioacetal cross‐linking moieties are robust but dynamic linkages. A series of different activated alkynes have been synthesized and systematically probed for their ability to produce dynamic thioacetal linkages, both in kinetic studies of small molecule models, as well as in stress relaxation and creep measurements on thiol–yne‐based CANs. The results are further rationalized by DFT calculations, showing that the bond exchange rates can be significantly influenced by the choice of the activated alkyne cross‐linker.     

Preparation of Functionalized Aryl,Heteroaryl, and Benzylic Potassium Organometallics Using Potassium Diisopropylamide in Continuous Flow

We report the preparation of lithium‐salt‐free KDA (potassium diisopropylamide; 0.6 m in hexane) complexed with TMEDA (N,N,N′,N′‐tetramethylethylenediamine) and its use for the flow‐metalation of (hetero)arenes between ?78 °C and 25 °C with reaction times between 0.2 s and 24 s and a combined flow rate of 10 mL min^?1 using a commercial flow setup. The resulting potassium organometallics react instantaneously with various electrophiles, such as ketones, aldehydes, alkyl and allylic halides, disulfides, Weinreb amides, and Me₃SiCl, affording functionalized (hetero)arenes in high yields. This flow procedure is successfully extended to the lateral metalation of methyl‐substituted arenes and heteroaromatics, resulting in the formation of various benzylic potassium organometallics. A metalation scale‐up was possible without further optimization.     

Formation and Structure of Fluorescent Silver Nanoclusters at Interfacial Binding Sites Facilitating Oligomerization of DNA Hairpins

Fluorescent, DNA‐stabilized silver nanoclusters (DNA‐AgNCs) are applied in a range of applications within nanoscience and nanotechnology. However, their diverse optical properties, mechanism of formation, and aspects of their composition remain unexplored, making the rational design of nanocluster probes challenging. Herein, a synthetic procedure is described for obtaining a high yield of emissive DNA‐AgNCs with a C‐loop hairpin DNA sequence, with subsequent purification by size‐exclusion chromatography (SEC). Through a combination of optical spectroscopy, gel electrophoresis, inductively coupled plasma mass spectrometry (ICP‐MS), and small‐angle X‐ray scattering (SAXS) in conjunction with the systematic study of various DNA sequences, the low‐resolution structure and mechanism of the formation of AgNCs were investigated. Data indicate that fluorescent DNA‐AgNCs self‐assemble by a head‐to‐head binding of two DNA hairpins, bridged by a silver nanocluster, resulting in the modelling of a dimeric structure harboring an Ag₁₂ cluster.     

Integration of a membrane-based desalting step in a microfabricated disposable polymer injector for mass spectrometric protein analysis

A simple desalting procedure for the coupling of a polymer microchip injector to mass spectrometry is proposed. The overall process is based on the adsorption of proteins on a poly(vinylidene difluoride) (PVDF) membrane, which are then directly eluted in the spraying solution. This microchip-based approach has been successfully applied to small drugs, peptides and proteins originally diluted in phosphate-buffered saline (PBS). Moreover, when eluting the retained proteins in small volumes, a preconcentration is obtained. The combination of single-use, mass-produceable, low-sample-consumption, easy-to-automate, miniaturized polymer injectors with easy-to-handle solution-exchange membranes makes this system particularly amenable to screening applications.     

A pyrrolo-tetrathiafulvalene cage: synthesis and X-ray crystal structure

[reaction: see text] A novel type of tetrathiafulvalene-cage 4 containing three monopyrrolo-tetrathiafulvalene units has been prepared employing a general and efficient synthetic approach. X-ray crystal structure analysis revealed that the cage is able to accommodate solvent molecules within a cavity in the solid state.     

Changes in orcine muscle water characteristics during growth--an in vitro low-field NMR relaxation study

This study investigates the effects of developmental stage and muscle type on the mobility and distribution of water within skeletal muscles, using low-field (1)H-NMR transverse relaxation measurements in vitro on four different porcine muscles (M. longissimus dorsi, M. semitendinosus, M. biceps femoris, M. vastus intermedius) from a total of 48 pigs slaughtered at various weight classes between 25 kg and 150 kg. Principal component analysis (PCA) revealed effects of both slaughter weight and muscle type on the transverse relaxation decay. Independent of developmental stage and muscle type, distributed exponential analysis of the NMR T(2) relaxation data imparted the existence of three distinct water populations, T(2b), T(21), and T(22), with relaxation times of approximately 1-10, 45-120, and 200-500 ms, respectively. The most profound change during muscle growth was a shift toward faster relaxation in the intermediate time constant, T(21). It decreased by approx. 24% in all four muscle types during the period from 25 to 150 kg live weight. Determination of dry matter, fat, and protein content in the muscles showed that the changes in relaxation time of the intermediate time constant, T(21), during growth should be ascribed mainly to a change in protein content, as the protein content explained 77% of the variation in the T(21) time constant. Partial least squares (PLS) regression revealed validated correlations in the region of 0.58 to 0.77 between NMR transverse relaxation data and muscle development for all the four muscle types, which indicates that NMR relaxation measurements may be used in the prediction of muscle developmental stage.