Small-angle X-ray scattering study of the influence of solvent replacement (from H<Subscript>2</Subscript>O to D<Subscript>2</Subscript>O) on the initial crystallization stage of tetragonal lysozyme

The composition of lysozyme solutions in D₂O under conditions favorable for the formation of tetragonal crystals has been investigated at different protein concentrations by small-angle X-ray scattering using the synchrotron radiation. In addition to lysozyme monomers, dimeric and octameric species are found in the crystallization solutions; the octamer content increases with an increase in the protein concentration. A comparison of the data with those obtained under similar conditions but with H₂O used as a solvent has shown that the replacement of light water with heavy one leads to increase of octamer volume fraction in solution.     

Thermochemical transformations of polycarbosilane precursors into a ceramic matrix

The possibility of preparing polymeric ceramic-forming precursors from polycarbosilane and oligosilazane was examined. Oligosilazane as a component of polycarbosilane formulations acts as a curing agent, ensuring curing at 150–300°C in the absence of oxygen and modifier. Pyrolysis of the cross-linked copolymer in argon yields an inorganic matrix whose yield is 1.3 times higher than that of pyrolyzates of the starting components. The major phase of the ceramic products obtained, according to the results of X-ray diffraction and chemical analyses, is X-ray amorphous silicon carbide. The ceramic obtained is highly resistant to thermal oxidation (up to 1400°C). The composition of the ceramic and the heat resistance and service characteristics of ceramic-matrix composite materials prepared on its basis using the “polymer technology” can be controlled by varying the ratio of the initial oligomers.     

An investigation of the effect of Rolivsan on the process of synthesis of ceramic matrix from polycarbosilane precursor

Effect of Rolivsan MV-1 on the process of curing and pyrolysis of polycarbosilane PCS-M in argon and on the properties of the ceramic matrix being formed. Use of Rolivsan in polycarbosilane formulations provides effective curing of the latter to give network block-copolymers. Pyrolysis of the resulting precursors in the atmosphere of argon yields ceramic matrices, with the yield of these being 1.3–1.4 times that of the pyrolyzate of the starting components. A study of the elemental and phase composition demonstrated that the matrices belong to the class of amorphous ceramics of nonstoichiometric composition, which contain microcrystalline silicon carbide SiC. The ceramic obtained has a high thermo-oxidative stability (up to 1400°C) and changing the relative amounts of the starting oligomers enables a purposeful variation of its composition, temperature stability, and service characteristics of ceramic-matrix composite materials obtained on its basis by the “polymer technology.”     

Structural and electrochemical properties of spray deposited molybdenum trioxide (α-MoO3) thin films

Journal of Solid State Electrochemistry - Nanostructured molybdenum trioxide (α-MoO3) thin films were deposited to investigate effect of substrate temperature on microstructural,...     

Oxidation stability of various Ti-alloys

Since titanium metal first became a commercial reality in 1950, corrosion resistance has been an important consideration in its selection as an engineering structural material. Titanium has gained acceptance in many media where its corrosion resistance and engineering properties have provided the corrosion and design engineer with a reliable and economic material. Titanium, like any other metal, is subject to corrosion in environments of air, oxygen, moisture, and so on. In this work, high-temperature stability of Ti and various Ti-alloys (by ASTM standard) was investigated. The best results showed that for Ti-Gr.5 alloy, the oxidation at 800 °C was 3.39% and at 900 °C 8.35%. For the comparison, commercial pure Ti-alloys Ti-Gr.2 and Ti-Gr.37 containing Al were used, whereas the oxidation resistance was much worse.     

Flow Injection/Sequential Injection Chromatography: A Review of Recent Developments in Low Pressure with High Performance Chemical Separation

This review focuses on the developments of the various parts of instrumentation and the operation of low to medium pressure flow injection and sequential injection chromatography (FIC and SIC) systems. The report and discussion include solution delivery system, separation column, flow cell and detector, mobile phase management, and online sample pretreatment. Applications of FIC and SIC and their differences as compared to HPLC are also presented.     

One-pot synthesis of 1-substituted-5-alkylselanyl-1H-tetrazoles from isoselenocyanates: unexpected formation of N-alkyl-N-arylcyanamides and (Z)-Se-alkyl-N-cyano-N,N′-diarylisoselenoureas

1-Substituted-5-alkylsulfanyl-1H-tetrazoles are well known class of organic substances with various applications in medicinal chemistry or photographic industry. Their selenium analogues, 1-substituted-5-alkylselanyl-1H-tetrazoles are, however, much less explored because of the lack of suitable methods for their preparation. In this work we investigated the synthesis of 1-alkyl/aryl-5-alkylselanyl-1H-tetrazoles from synthetically available alkyl/arylisoselenocyanates. One-pot reactions of arylisoselenocyanates with sodium azide and alkylating agent led to the target 5-alkylselanyl-1-aryl-1H-tetrazoles but also to interesting side products, namely N-alkyl-N-arylcyanamides and (Z)-Se-alkyl-N-cyano-N,N′-diarylisoselenoureas. Nevertheless, when alkylisoselenocyanates were utilized as the substrates, the reactions led exclusively to the formation of 1-alkyl-5-alkylselanyl-1H-tetrazoles in good yields. This simple one-pot procedure brings new possibilities for the preparation of variously substituted selenium compounds. It also opens the way to further investigations of selenium isosteres of the widely utilized 5-thiotetrazole moiety in biomedical applications.     

Novel ferroelectric liquid crystals based on fused thieno[3,2‐b]furan and thieno[3,2‐b]thiophene cores

Several series of new benzofused thieno[3,2‐b]furan‐ and thieno[3,2‐b]thiophene‐based derivatives have been synthesized and their mesomorphic properties investigated. All the studied compounds exhibit a SmC* phase with very wide temperature interval. Additionally, some types of the compounds show the cholesteric, SmA or blue phase. In the ferroelectric SmC* phase we evaluated physical properties of relevance for possible applications.     

Study of the retention behavior of small polar molecules on different types of stationary phases used in hydrophilic interaction liquid chromatography

The retention behavior of a large group of analytes (35) with varied properties (pK_a and logP) was studied on eight hydrophilic interaction LC columns with different surfaces, stationary phase chemistries, and types of particles. The acetonitrile content (5–95%), buffer concentration (0.5–200 mM), and pH of the mobile phase (3.8 and 6.8) were evaluated for their effects on the retention behavior. The type of stationary phase had a significant impact on the selectivity and retention time of the tested analytes. Completely different selectivity was observed on the aminopropyl stationary phase. In this study, the influence of the buffer concentration was similar for all tested columns, except for the aminopropyl stationary phase. Increasing the buffer concentration led to decreased retention times for the basic compounds and increased retention times for the acidic compounds, while the inverse behavior was observed on the aminopropyl stationary phase. The selectivity of the individual stationary phases was evaluated at pH 3.8 and 6.8. Much lower selectivity differences between the stationary phases were observed at pH 6.8 than pH 3.8. Bare silica stationary phases were used in the comparison of the particles (fused‐core and fully porous particles of 3 and 1.7 μm) and the columns provided by different manufacturers.