Investigation of a catalyst ink dispersion using both ultra-small-angle X-ray scattering and cryogenic TEM

The dispersion of Nafion ionomer particles and Pt/C catalyst aggregates in liquid media was studied using both ultra-small-angle X-ray scattering (USAXS) and cryogenic TEM. A systematic approach was taken to study first the dispersion of each component (i.e., ionomer particles and Pt/C aggregates), then the combination of the components, and last the catalyst ink. Multiple-level curve fitting was used to extract the particle size, size distribution, and geometry of the Pt/C aggregates and the Nafion particles in liquid media from the scattering data. The results suggest that the particle size, size distribution, and geometry are not uniform throughout the systems but rather vary significantly. It was found that the interaction of each component (i.e., the Nafion ionomer particles and the Pt/C aggregates) occurs in the dispersion. Cryogenic TEM was used to observe the size and geometry of the particles in liquid directly and to validate the scattering results. The TEM results showed excellent agreement.     

Two New 3D Lanthanide Coordination Polymers with Benzenesulfonic and Adipic Acids: Synthesis,Structure and Luminescent Properties

Two new lanthanide complexes [Sm₂(ad)_2.5(BSA)(H₂O)₂]_n ( 1 ) and [Nd₂(ad)_2.5(BSA)(H₂O)₂]_n ( 2 ) (H₂ad = adipic acid, HBSA = benzenesulfonic acid) were synthesized hydrothermally from the reaction of the lanthanide ions (Ln³⁺) with flexible aliphatic dicarboxylate and the rigid benzene sulfonic acid and characterized by elemental analysis, IR spectroscopy, and single‐crystal X‐ray diffraction. They crystallize monoclinic in space group P2₁/ c. Structural analyses revealed that the two complexes have intricate 3D net structures constructed by the bridging adipic ligand and benzenesulfonic acid. The thermogravimetric analysis of 1 and 2 , as well as photoluminescent properties of 1 are discussed in detail.     

Structure-function analysis of an enzymatic prenyl transfer reaction identifies a reaction chamber with modifiable specificity

Fungal indole prenyltransferases participate in a multitude of biosynthetic pathways. Their ability to prenylate diverse substrates has attracted interest for potential use in chemoenzymatic synthesis. The fungal indole prenyltransferase FtmPT1 catalyzes the prenylation of brevianamide F in the biosynthesis of fumitremorgin-type alkaloids, which show diverse pharmacological activities and are promising candidates for the development of antitumor agents. Here, we report crystal structures of unliganded Aspergillus fumigatus FtmPT1 as well as of a ternary complex of FtmPT1 bound to brevianamide F and an analogue of its isoprenoid substrate dimethylallyl diphosphate. FtmPT1 assumes a rare α/β-barrel fold, consisting of 10 circularly arranged β-strands surrounded by α-helices. Catalysis is performed in a hydrophobic reaction chamber at the center of the barrel. In combination with mutagenesis experiments, our analysis of the liganded and unliganded structures provides insight into the mechanism of catalysis and the determinants of regiospecificity. Sequence conservation of key features indicates that all fungal indole prenyltransferases possess similar active site architectures. However, while the dimethylallyl diphosphate binding site is strictly conserved in these enzymes, subtle changes in the reaction chamber likely allow for the accommodation of diverse aromatic substrates for prenylation. In support of this concept, we were able to redirect the regioselectivity of FtmPT1 by a single mutation of glycine 115 to threonine. This finding provides support for a potential use of fungal indole prenyltransferases as modifiable bioreactors that can be engineered to catalyze highly specific prenyl transfer reactions.     

Furostanol Glycosides from leaves of the Chinese plant <Emphasis Type="Italic">Tribulus terrestris</Emphasis>

The structures of five furostanol glycosides (1–5), of which the 26-O-β-D-glucopyranosyl-(25S),5α-furost20(22)-en-12-one-2α,3β,26-triol-3-O-β-D-glucopyranosyl-(1→4)-β-D-galactopyranoside (1) was new, from the leaves of Tribulus terrestris L. were established using chemical and NMR spectroscopic methods.     

Experimental Study of Capacitive RF <Emphasis Type="Italic">c</Emphasis>-C<Subscript>4</Subscript>F<Subscript>8</Subscript> Discharge with Synchrotron Vacuum Ultraviolet Photoionization Mass Spectrometry

Capacitive radio frequency (RF) discharge of c-C₄F₈ (octafluorocyclobutane) has been studied with synchrotron vacuum ultraviolet (SVUV) photoionization mass spectrometry (PIMS) at 4 Torr and 33.33 kHz. Various free radicals and reactive intermediates have been identified through measurement of photoionization mass spectra and photoionization efficiency (PIE) spectra. CF₂=CF₂ is main product in the plasma, indicating that the dissociation of c-C₄F₈ into CF₂=CF₂ is one of prominent reactions in the present experimental conditions. The observation of large species including C₅F₈, C₅F₁₀ and C₆F₁₀ is presented in our work. Besides, the dependences of the signals of neutral species in the discharge of c-C₄F₈ on RF power are presented in this paper.     

Real-time monitoring of induced adaptation of redox active Escherichia coli biofilm by EQCM-controlled extracellular redox environment

In this paper we report the anaerobic Escherichia coli biofilm formation on solid substrate under redox-controlled extracellular environment by an electrochemical quartz crystal microbalance (EQCM) method. Both biomass and electrochemical activity were monitored in situ. Larger biomass was yielded under redox-controlled condition comparing with natural biofilm growth, which was also confirmed by optical observation. Surface-colonizing cells responded more sensitively to their redox environment than planktonic cells. Cyclic voltammogram (CV) obtained during the time course of biofilm development indicates the emergence of redox active phenotype under redox-controlled condition but not in natural condition. Our results suggest an effective means to control biofilm development with desired metabolic adaptation and also to in situ monitor the biomass yield and the emergent catalytic property simultaneously.     

Thermal properties and liquid crystallinity of side-chain azobenzene copolymer containing pendant polyhedral oligomeric silsequioxanes

Vinylated polyhedral oligomeric silsesquioxane (POSS-M) was prepared by the reaction of POSS containing amine groups with acrylic acid. Azobenzene liquid crystalline copolymer (LCP-POSS) was then synthesized with 6.0 mol% POSS-M and 94.0 mol% acrylate monomer containing azobenzene liquid crystalline moiety (Azo-M) by free-radical copolymerization. Homopolymer of Azo-M (LCP) was also synthesized under the same conditions. Their thermal properties and liquid crystallinity were characterized by Thermal gravimetric analysis (TG), differential scanning calorimetry (DSC), Wide-angle X-ray diffraction experiments (XRD) and polarized optical micrographs (POM). The results showed that LCP-POSS has higher thermal stability and glass transition temperature than pure LCP due to the incorporation of the rigid cage-like POSS. Especially, LCP-POSS exhibits enantiotropic smectic and nematic liquid crystalline behaviors, its smectic-nematic transition temperature (T _SN) and nematic-isotropic transition temperature (T _NI) are higher than those of pure LCP, which may promote and extend its applications on stimuli-responsive materials and devices.     

Pressure‐Induced Structural Transition in WO3 Nanowires

Raman spectroscopic analysis is performed on WO₃ nanowires at room temperature at pressures from ambient conditions to 45 GPa. Linear dependence of the first‐order Raman signal on various high‐pressure (HP) sections is observed. Upon increasing the applied pressure, the WO₃ nanowires undergo four phase transitions at pressures around 1.7, 4.6, 21.5, and 26.2 GPa, which are all less than that reported for bulk WO₃. When the pressure is up to 42.5 GPa, a new high‐pressure phase (HP5) appears. This phase has never been reported and is not reversible while unloading the pressure.