Genetically Programmed Regioselective Immobilization of Enzymes in Biosilica Microparticles

Diatoms are single‐celled microalgae that produce a large variety of hierarchically porous, silica‐based microparticles as cell wall material. The presence of genetically encoded silica nanopatterns endows the biosilica with favorable properties for a wide range of applications including catalysis, chemical sensing, photonics, and drug delivery. Enhancing the performance of diatom biosilica requires i) a better understanding of the structure–property relationship in this material, and ii) methods that enable the manipulation of the biosilica structure and properties in a targeted manner. Here, genetic engineering of the diatom Thalassiosira pseudonana is employed to immobilize enzymes (glucose oxidase and horseradish peroxidase) into structurally distinct regions of the biosilica, which are termed valves and girdle bands. Remarkably, glucose oxidase in girdle bands exhibits >3‐fold higher catalytic activities compared to its location in valves. It is demonstrated through enzyme accessibility studies, protein engineering, and genetic engineering of biosilica morphology that the divergent enzyme activities are caused by the differences in the inherent silica nanopatterns of valves and girdle bands. This work highlights the importance of silica nanoscale architecture for the activity of immobilized enzymes and provides unprecedented tools for the biotechnological production of silica microparticles with tailored catalytic activities and anisotropic functionalities.     

GSM协议分析仪CRTU-G

罗德与施瓦茨(Rohde & Schwarz)公司的通用协议测试仪CRTU-G基于可升级的射频单元,可以不断更新以符合将来的标准,能仿真GSM基站,并且可以用用户定义的任何信令模式对移动电话进行测试.此外,CRTU-G也实现了GSM基站的参考功能.CRTU-G用于开发移动系统及其相应的芯片组,并支持协议栈的软件开发,向更高的协议层提供规范接口.CRTU-G还用于测试移动系统是否符合GSM认证论坛(GCF)规范.     

Polylactide‐block‐Polypeptide‐block‐Polylactide Copolymer Nanoparticles with Tunable Cleavage and Controlled Drug Release

A versatile nanoparticle system is presented in which drug release is triggered by enzymatic polymer cleavage, resulting in a physicochemical change of the carrier. The polylactide‐block‐peptide‐block‐polylactide triblock copolymer is generated by initiation of the ring‐opening polymerization of L‐lactide with a complex bifunctional peptide having an enzymatic recognition and cleavage site (Pro‐Leu‐Gly‐Leu‐Ala‐Gly). This triblock copolymer is specifically bisected by matrix metalloproteinase‐2 (MMP‐2), an enzyme overexpressed in tumor tissues. Triblock copolymer nanoparticles formed by nonaqueous emulsion polymerization are readily transferred into aqueous media without aggregation, even in the presence of blood serum. Cleavage of the triblock copolymer leads to a significant decrease of the glass transition temperature (T_g) from 39 °C to 31 °C, likely mediating cargo release under physiological conditions. Selective drug targeting is demonstrated by hampered mitosis and increased cell death resulting from drug release via MMP‐2 specific cleavage of triblock copolymer carrier. On the contrary, nanocarriers having a scrambled (non‐recognizable) peptide sequence do not cause enhanced cytotoxicity, demonstrating the enzyme‐specific cleavage and subsequent drug release. The unique physicochemical properties, cleavage‐dependent cargo release, and tunability of carrier bioactivity by simple peptide exchange highlight the potential of this polymer‐nanoparticle concept as platform for custom‐designed carrier systems.     

CVD-based tungsten carbide schottky contacts to 6H-SiC for very high-temperature operation

In this study, tungsten carbide, with its hardness, chemical inertness, thermal stability and low resistivity (25 μΩ cm)¹ is shown as a reliable contact material to n- and p-type 6H-SiC for very high temperature applications. WC films with thicknesses of 100–150 nm were deposited by chemical vapor deposition (CVD) from a WF₆/C₃H₈/H₂ mixture at 1173 K. A method to pattern CVD-tungsten carbide is suggested. TEM analysis of as deposited samples displayed a clear and unreacted interface. The electrical investigations of the p-type 6H-SiC Schottky contacts revealed a high rectification ratio and a low reverse current density (6.1 × 10⁻⁵ A cm⁻², −10 V) up to 773 K. On n-type, a low barrier (Φ_Bn=0.79 eV) at room temperature was observed. The low Φ_Bn value suggests WC to be promising as an ohmic contact material on highly doped n-type epi-layers. We will show a temperature dependence for the barrier height of tungsten carbide contacts that can be related to the simultaneous change in the energy bandgap, which should be considered when designing SiC devices intended for high temperature operation.     

Sulfur in wheat gluten: In situ analysis by X-ray absorption near edge structure (XANES) spectroscopy

The sulfur containing gluten proteins largely determine the baking quality of wheat. In order to probe the speciation of sulfur, gluten proteins [gliadin, high molecular weight (HMW) and low molecular weight (LMW) subunits of glutenin], stored glutenin subunits as well as flour were investigated in situ by S K-edge X-ray near edge absorption structure (XANES) spectroscopy. The spectra confirmed the existence of disulfide bonds in oxidised (oxygen stream) glutenin subunits, supporting their significance for the formation of gluten networks. Additionally, glutenin subunits, which were stored under ambient air and temperature conditions, predominantly contained sulfur of higher oxidation states (sulfoxide, sulfonic acid). The disulfide state and also sulfoxide and sulfonic acid states were detected after reoxidation of glutenin subunits with potassium bromate.     

What’s the middle ground? Institutionalized vs. emerging water-related stakeholder engagement processes

Abstract

In this day and age, it is widely argued that stakeholder engagement in water-related decision-making processes yields many benefits, including legitimacy, acceptance and trust. Key legal frameworks, such as the European Water Framework Directive and the Aarhus Convention, have spurred the emergence of formal forms of stakeholder engagement. On the other hand, many engagement processes are spontaneous and self-organized. This article investigates the strategies used in formal (government-led) and informal (bottom-up) engagement processes in search of a middle ground. To this end, case studies in the Netherlands, the United States, Uganda and Ethiopia are analyzed using the OECD’s stakeholder engagement checklist. We conclude with reflection on the ways forward to make formal and informal stakeholder engagement complementary.     

GC–MS analysis of oxysterols and their formation in cultivated liver cells (HepG2)

Oxysterols play a key role in many (patho)physiological processes and they are potential biomarkers for oxidative stress in several diseases. Here we developed a rapid gas chromatographic-mass spectrometry-based method for the separation and quantification of 11 biologically relevant oxysterols bearing hydroxy, epoxy, and dihydroxy groups. Efficient chromatographic separation (resolution ≥ 1.9) was achieved using a medium polarity 35%-diphenyl/65%-dimethyl polysiloxane stationary phase material (30 m × 0.25 mm inner diameter and 0.25 μm film thickness). Based on thorough analysis of the fragmentation during electron ionization we developed a strategy to deduce structural information of the oxysterols. Optimized sample preparation includes (i) extraction with a mixture of n-hexane/iso-propanol, (ii) removal of cholesterol by solid phase extraction with unmodified silica, and (iii) trimethylsilylation. The method was successfully applied on the analysis of brain samples, showing consistent results with previous studies and a good intra- and interday precision of ≤20%. Finally, we used the method for the investigation of oxysterol formation during oxidative stress in HepG2 cells. Incubation with tert-butyl hydroperoxide led to a massive increase in free radical formed oxysterols (7-keto-chol > 7β-OH-chol >> 7α-OH-chol), while 24 h incubation with the glutathione peroxidase 4 inhibitor RSL3 showed no increase in oxidative stress based on the oxysterol pattern. Overall, the new method described here enables the robust analysis of a biologically meaningful pattern of oxysterols with high sensitivity and precision allowing us to gain new insights in the biological formation and role of oxysterols.