Bent-core 6-thioxoverdazyl: a comparison of mesogenic properties with the 6-oxo analogue

Two bent-core verdazyl radicals, 2[16] and 3[16], containing 6-thioxo and 6-oxo groups, respectively, were prepared and their physical properties were compared. Analysis of binary mixtures with bent-core mesogen 1[12] gave virtual N-I ([T_NI]) and N-I_re ([T_NIre]) transition temperatures. Results indicate that the thioxo derivative 2[16] has greater stabilising effect on the nematic phase than the 6-oxo analogue 3[16], presumably due to the higher dipole moment of the core (1.90 D vrs 0.83 D) despite the less favourable conformational properties.     

Equation of state of initially liquid carbon monoxide and nitrogen mixture

The modified liquid perturbation variational theory and the improved vdW-1f model were applied to calculating the equation of the state of liquid CO-N₂ mixture with the ratio of 1:1, 4:1 and 1:4, respectively, in the shock pressure range of 9–49 GPa. It was shown that the calculated result for CO-N₂ mixture with the ratio of 1:1 is well consistent with the earlier experimental data. The thermodynamics equilibrium, chemical equilibrium and phase equilibrium were all considered in detail. It was found that Hugoniot of liquid CO-N₂ mixture is moderately softened in the pressure range of 20–30 GPa and 30–49 GPa for different initial proportions, and that the Hugoniot is more softened in the latter pressure range, which means that the structural phase transition occurs near 20 GPa and 30 GPa. Since the shock productions may absorb a plenty of systematic energy, the shock temperature and pressure decline compared with the case of no chemical reaction. Pressures and temperatures increase gradually with the increase in the mole fraction of nitrogen composition. The results for the 1:1 CO-N₂ mixture lie in the middle of two others. Therefore, it was shown that the modified Lorentz-Berthelor rule used in the scheme is effective to study shock-compression properties of liquid CO-N₂ mixture under high temperatures and high pressures. Supported by the National Natural Science Foundation of China (Grant No. 10576020)     

Particular solutions of the linearized Boltzmann equation for a binary mixture of rigid spheres

Particular solutions that correspond to inhomogeneous driving terms in the linearized Boltzmann equation for the case of a binary mixture of rigid spheres are reported. For flow problems (in a plane channel) driven by pressure, temperature, and density gradients, inhomogeneous terms appear in the Boltzmann equation, and it is for these inhomogeneous terms that the particular solutions are developed. The required solutions for temperature and density driven problems are expressed in terms of previously reported generalized (vector-valued) Chapman–Enskog functions. However, for the pressure-driven problem (Poiseuille flow) the required particular solution is expressed in terms of two generalized Burnett functions defined by linear integral equations in which the driving terms are given in terms of the Chapman–Enskog functions. To complete this work, expansions in terms of Hermite cubic splines and a collocation scheme are used to establish numerical solutions for the generalized (vector-valued) Burnett functions.     

The influence of pressure on the electrical conductivity of molten zinc chloride and its Mixtures with potassium chloride

Abstract

The electrical conductivities of molten ZnCl₂ and its mixtures with KCl were measured as functions of pressure, temperature, and composition. The measuremkents were performed in an internally heated pressure vessel in which the melts were contained in open quartz glass cells. The addition of KCl to molten ZnCl₂ causes a large increase of the conductivity at all pressures and temperatures. With increasing pressure the conductivity increases in pure molten ZnCl₂ and in mixtures rich in ZnCl₂ and decreases in mixtures with more than 30 mol% of KCl.     

Selection of aptamers by systematic evolution of ligands by exponential enrichment: addressing the polymerase chain reaction issue

Aptamers are DNA oligonucleotides capable of binding different classes of targets with high affinity and selectivity. They are particularly attractive as affinity probes in multiplexed quantitative analysis of proteins. Aptamers are typically selected from large libraries of random DNA sequences in a general approach termed systematic evolution of ligands by exponential enrichment (SELEX). SELEX involves repetitive rounds of two processes: (i) partitioning of aptamers from non-aptamers by an affinity method and (ii) amplification of aptamers by the polymerase chain reaction (PCR). New partitioning methods, which are characterized by exceptionally high efficiency of partitioning, have been recently introduced. For the overall SELEX procedure to be efficient, the high efficiency of new partitioning methods has to be matched by high efficiency of PCR. Here we present the first detailed study of PCR amplification of random DNA libraries used in aptamer selection. With capillary electrophoresis as an analytical tool, we found fundamental differences between PCR amplification of homogeneous DNA templates and that of large libraries of random DNA sequences. Product formation for a homogeneous DNA template proceeds until primers are exhausted. For a random DNA library as a template, product accumulation stops when PCR primers are still in excess of the products. The products then rapidly convert to by-products and virtually disappear after only 5 additional cycles of PCR. The yield of the products decreases with the increasing length of DNA molecules in the library. We also proved that the initial number of DNA molecules in PCR mixture has no effect on the by-products formation. While the increase of the Taq DNA polymerase concentration in PCR mixture selectively increases the yield of PCR products. Our findings suggest that standard procedures of PCR amplification of homogeneous DNA samples cannot be transferred to PCR amplification of random DNA libraries: to ensure efficient SELEX, PCR has to be optimized for the amplification of random DNA libraries.     

Titrimetric determination of silicon dissolved in concentrated HF-HNO3-etching solutions

The wet chemical etching of silicon by concentrated HF-HNO₃ mixtures in solar and semiconductor wafer fabrication requires the strict control of the etching conditions. Surface morphology and etch rates are mainly affected by the amount of dissolved silicon, that is continuously enriched in the etching solution with each etching run. A fast and robust method for the titrimetric determination of the total dissolved silicon content out of the concentrated etching solution is presented. This method is based on the difference between the two equivalence points of the total amount of acid and the hydrolysis of the hexafluorosilicic anion. This approach allows a silicon determination directly from the etching process in spite of the presence of dissolved nitric oxides in the etching solution. The influences of different acid mixing ratios and of the etching solution density depending on the silicon content is considered and discussed in detail.     

A novel spectrophotometric method for the simultaneous kinetic analysis of ternary mixtures by mean centering of ratio kinetic profiles

In this paper, a novel and very simple method was developed for the simultaneous spectrophotometric determination of ternary mixtures, without prior separation steps. The method is based on the mean centering of ratio kinetic profiles. The mathematical explanation of the procedure is illustrated. In order to investigate the applicability of the proposed method, it was applied to the simultaneous spectrophotometric determination of hydrazine, phenylhydrazine and acetylhydrazine based on their condensation reactions with p-(dimethylamino)benzaldehyde (DAB) and p-nitrobenzaldehyde (NB) in micellar sodium dodecyl sulfate (SDS) media as a typical ternary mixture. The analytical characteristics of the method such as accuracy, precision, relative standard deviation (R.S.D.) and relative standard error (R.S.E.) were calculated.     

High-temperature liquid chromatography. Part II: Determination of the viscosities of binary solvent mixtures—Implications for liquid chromatographic separations

This paper is the second in a series of consecutive publications, explaining the concept of high temperature liquid chromatography under various important aspects. The second publication deals with the determination of the viscosity of binary solvent mixtures used in reversed phase liquid chromatography in a temperature range between 25 and 250 °C. In literature, only limited data of the temperature dependent viscosities of liquid solvents or binary solvent mixtures can be found. Therefore, the viscosities of the pure solvents as well as the binary mixtures had to be determined experimentally up to 250 °C. The viscosity data were used to estimate the pressure drop in a capillary connecting a high-temperature HPLC system with a mass spectrometer. The solvent perturbation could be avoided by adjusting the diameter of the transfer capillary to the viscosity and vapour pressure of the mobile phase. The viscosity data were also used to show that a significant gain in analysis speed is theoretically feasible. This factor clearly depends on the nature of the solvent system, because for mixtures with a large viscosity maximum at ambient temperature, this effect is most pronounced.