Vacuum Ultraviolet Photolysis of Polyethylene,Polypropylene, and Polystyrene

Using infrared reflection absorption spectroscopy (IRRAS), quartz crystal microbalance (QMB) measurements, and X-ray photoelectron spectroscopy (XPS) in combination with chemical derivatization techniques the VUV photolysis of polyethylene (PE), polypropylene (PP), and polystyrene (PS) was investigated. A mass balance obtained from the quantification of the data was used to suggest reaction path ways. Although PE and PP behave similar, the mass loss is about 8 times higher in the case of PP. These differences originate from the higher disproportionation to recombination ratio for the branched polymer. Both polymers form double bonds and at extended treatment times they tend to crosslink. PS is rather stable due to the possibility of the energy dissipation by fluorescence.     

Effect of hydrocolloids on starch thermal transitions,as measured by DSC

Differential scanning calorimetry (DSC) was used to analyze the influence of different hydrocolloids (xanthan, guar, and locust bean gums, carboxymethylcellulose and sodium alginate) on the gelatinization of corn starch in systems with starch concentration ranging between 0.1 and 0.7 g starch/g mixture. The reduction of available water produced a shift in gelatinization temperature, especially of the conclusion temperature. The effect was more marked for ionic hydrocolloids. The influence of hydrocolloids on glass transition temperature (T _g) of gelatinized starch suspensions and on the glass transition temperature of the maximally freeze-concentrated solute/unfrozen water matrix (T _g) was also studied.T _g onset values ranged between –4.5 and –5.5C for corn starch pastes with and without hydrocolloids. Those hydrocolloids that increased the viscosity of the unfrozen matrix inhibited additional ice formation during thawing (devitrification).Starch concentration and final heating temperature were found to be relevant factors affecting the kinetics of amylopectin retrogradation during frozen storage at –4C. Xanthan gum failed to prevent amylopectin retrogradation; this observation could be attributed to the fact that gums act outside the starch granule, while amylopectin retrogradation takes place within the granule.     

On the surface modification of microchannels for microcapillary electrophoresis chips

This paper presents systematic investigation of the microchannel surface properties in microCE chips. Three popular materials for microCE chips, polydimethylsiloxane (PDMS), quartz, and glass, are used. The zeta potentials of these microchannels are calculated by measuring the EOF velocity to evaluate the surface properties after surface modification. The hydrophobic PDMS is usually plasma-treated for microCE applications. In this study, a new method using a high-throughput atmospheric plasma generator is adopted to treat the PDMS surface under atmospheric conditions. In this approach, the cost and time for surface treatment can be significantly reduced compared with the conventional vacuum plasma generator method. Experimental results indicate that new functional groups could be formed on the PDMS surface after treatment, resulting in a change in the surface property. The time-dependent surface property of the plasma-treated PDMS is then measured in terms of the zeta potential. Results show that the surface property will reach a stable condition after 1 h of plasma treatment. For glass CE chips, two new methods for changing the microchannel surface properties are developed. Instead of using complicated and time-consuming chemical silanization procedures for CE channel surface modification, two simple and reliable methods utilizing organic-based spin-on-glass and water-soluble acrylic resin are reported. The proposed method provides a fast batch process for controlling the surface properties of glass-based CE channels. The proposed methods are evaluated using PhiX-174 DNA maker separation. The experimental data show that the surface property is modified and separation efficiency greatly improved. In addition, the long-term stability of both coatings is verified in this study. The methods proposed in this study show potential as an excellent solution for glass-based microCE chip surface modification.     

Spider Silk-Improved Quartz-Enhanced Conductance Spectroscopy for Medical Mask Humidity Sensing

Spider silk is one of the hottest biomaterials researched currently, due to its excellent mechanical properties. This work reports a novel humidity sensing platform based on a spider silk-modified quartz tuning fork (SSM-QTF). Since spider silk is a kind of natural moisture-sensitive material, it does not demand additional sensitization. Quartz-enhanced conductance spectroscopy (QECS) was combined with the SSM-QTF to access humidity sensing sensitively. The results indicate that the resonance frequency of the SSM-QTF decreased monotonously with the ambient humidity. The detection sensitivity of the proposed SSM-QTF sensor was 12.7 ppm at 1 min. The SSM-QTF sensor showed good linearity of ~0.99. Using this sensor, we successfully measured the humidity of disposable medical masks for different periods of wearing time. The results showed that even a 20 min wearing time can lead to a >70% humidity in the mask enclosed space. It is suggested that a disposable medical mask should be changed <2 h.     

Peptidyl-Resin Substrates as a Tool in the Analysis of Caspase Activity

Caspases, proteolytic enzymes belonging to the group of cysteine proteases, play a crucial role in apoptosis. Understanding their activity and substrate specificity is extremely important. Fluorescence-based approaches, including fluorogenic substrates, are generally used to confirm cleavage preferences. Here we present a new method of substrate specificity and activity analysis based on the application of fix-charge tagged peptides located on the resin. The proteolysis of peptide bond on the resin, occurring even with low efficiency, results in the formation of N-terminal fragments of model peptide containing ionization enhancers in the form of quaternary ammonium groups, allowing for ultrasensitive and reliable analysis by LC-MS/MS. The possibility of application of the proposed solution was tested through the analysis of substrate specificity and activity of caspase 3 or 7. The obtained results confirm the known substrate specificity of executioner caspases. Our solution also allowed us to observe that caspases can hydrolyze peptides shorter than those presented to date in the scientific literature.     

Steroidal Antimetabolites Protect Mice against Trypanosoma brucei

Trypanosoma brucei, the causative agent for human African trypanosomiasis, is an emerging ergosterol-dependent parasite that produces chokepoint enzymes, sterol methyltransferases (SMT), not synthesized in their animal hosts that can regulate cell viability. Here, we report the lethal effects of two recently described natural product antimetabolites that disrupt Acanthamoeba sterol methylation and growth, cholesta-5,7,22,24-tetraenol (CHT) and ergosta-5,7,22,24(28)-tetraenol (ERGT) that can equally target T. brucei. We found that CHT/ERGT inhibited cell growth in vitro, yielding EC₅₀ values in the low nanomolar range with washout experiments showing cidal activity against the bloodstream form, consistent with their predicted mode of suicide inhibition on SMT activity and ergosterol production. Antimetabolite treatment generated altered T. brucei cell morphology and death rapidly within hours. Notably, in vivo ERGT/CHT protected mice infected with T. brucei, doubling their survival time following daily treatment for 8–10 days at 50 mg/kg or 100 mg/kg. The current study demonstrates a new class of lead antibiotics, in the form of common fungal sterols, for antitrypanosomal drug development.     

纳米氧化镱对熔融石英析晶动力学机制的影响

本文研究引入纳米氧化镱对熔融石英析晶机制及动力学过程的影响.通过X射线衍射仪(XRD)测试结果分析了纳米氧化镱的引入对熔融石英陶瓷析晶率的影响,采用动力学方法分析了纳米氧化镱的引入对熔融石英陶瓷析晶机制的影响,同时探讨了其等温析晶动力学过程.研究表明,熔融石英陶瓷的晶粒向二维兼有一维及三维的方式生长,引入纳米氧化镱的熔...     

6H-SiC衬底片的表面处理

相比于蓝宝石,6H-SiC是制作GaN高功率器件更有前途的衬底.本文研究了表面处理如研磨、化学机械抛光对6H-SiC衬底表面特性的影响.用显微镜、原子力显微镜、拉曼光谱、卢瑟福背散射谱表征了衬底表面.结果表明经过两步化学机械抛光后提高了表面质量.经第二步化学机械抛光后的衬底具有优异的表面形貌、高透射率和极小的损伤层,其表面粗糙度RMS是0.12nm.在该衬底上用MOCVD方法长出了高质量的GaN外延膜.     

Intensification of Double Kinetic Resolution of Chiral Amines and Alcohols via Chemoselective Formation of a Carbonate–Enzyme Intermediate

Chiral amines and alcohols are synthons of numerous pharmaceutically-relevant compounds. The previously developed enzymatic kinetic resolution approaches utilize a chiral racemic molecule and achiral acyl donor (or acyl acceptor). Thus, only one enantiodivergent step of the catalytic cycle is engaged, which does not fully exploit the enzyme’s abilities. The first carbonate-mediated example of simultaneous double chemoselective kinetic resolution of chiral amines and alcohols is described. Herein, we established a biocatalytic approach towards four optically-pure compounds (>99% ee, Enantioselectivity: E > 200) via double enzymatic kinetic resolution, engaging chiral organic carbonates as acyl donors. High enantioselectivity was ensured by extraordinary chemoselectivity in lipase-catalyzed formation of unsymmetrical organic carbonates and engaged in a process applicable for the synthesis of enantiopure organic precursors of valuable compounds. This study focused not only on preparative synthesis, but additionally the catalytic mechanism was discussed and the clear impact of this rarely observed carbonate-derived acyl enzyme was shown. The presented protocol is characterized by atom efficiency, acyl donor sustainability, easy acyl group removal, mild reaction conditions, and biocatalyst recyclability, which significantly decreases the cost of the reported process.     

Spin-correlation function of the fully frustrated Ising model and ± J Ising spin glass on the square lattice

In this work we study the correlation function of the ground state of two-dimensional fully frustrated Ising model as well as spin glass. The Pfaffian method is used to calculate free energy and entropy as well as correlation function. We estimate the exponent of spin correlation function for fully frustrated model and spin glass. In this paper an overview of the latest results on the spin correlation function is presented.