Some aspects of quality assessment of the k0-based method of NAA

Neutron activation analysis is one of the analytical techniques often used for certification of reference materials. The k₀-based method of instrumental neutron activation analysis can also be applied in intercomparison runs in the certification process and therefore it is desirable to know its accuracy in advance. Possible systematic errors related to the application of nuclear data at given neutron flux rate parameters, that can affect the uncertainties of the results obtained by this specific method, are elucidated and error propagation factors calculated for a typical irradiation position in the TRIGA Mark II reactor of the Jozef Stefan Institute. It was found that these uncertainties are at the level of 1–2% on the average.     

Hexagonal high pressure phase of copper(I)tetraiodomercurate (Cu2HgI4)

Summary Using a high pressure X-ray camera Cu₂HgI₄ was subjected at room temperature to pressures up to about 8 GPa. A hexagonal high pressure phase (a=8.28 (2) Å,c=3.40 (0) Å, space group P lm,Z=1) could be detected. This phase shows a reversible transformation with pressure hysteresis. The transition occurs at 7 GPa when the pressure is increased but at 6 GPa when the pressure is decreased.

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Hexagonale Hochdruckphase von Kupfer(I)tetraiodomercurat (Cu₂HgI₄)

Zusammenfassung Cu₂HgI₄ wurde in einer Hochdruckkamera bei Raumtemperatur mit einem Druck bis zu 8 GPa belastet. Dabei bildete sich eine hexagonale Hochdruckmodifikation (a=8.28 (2) Å,c=3.40 (0) Å, Raumgruppe P lm,Z=1). Für diese Phase wurde eine reversible Umwandlung mit Druckhysterese festgestellt. Mit steigendem Druck findet die Umwandlung bei 7 GPa mit sinkendem Druck jedoch bei 6 GPa statt.

     

Clathrate formation in binary aqueous systems with CH2Cl2, CHCl3 and CCl4 at high pressures

P,T,X phase diagrams of the CH₂Cl₂-H₂O, the CHCl₃-H₂O and the CCl₄-H₂) systems have been studied by DTA in the pressure range 10^–3 to 5.0 kbar. Under pressure the cubic structure II (CS-II) hydrates forming in all the systems are replaced by hydrates with the composition M·7.3 H₂O whose stoichiometry and positive dT/dP values of melting lead us to believe that they are CS-I hydrates.In the CH₂Cl₂ and CHCl₃ systems the nonvariant point coordinates of the hydrate transformationQ ₂ ^h (l₁h17h7l₂, where l₁ and l₂ are liquid phases abundant in water and hydrate former, respectively, h₁₇ and h₇ are hydrates with hydrate numbers 17 and 7, respectively) areP = 0.6 kbar, T = –1.5°C andP =2.65 kbar,T = –10.5°C, respectively. In the CCl₄ system the 4-phaseQ ₃ ^h point (l₁h₁₇h₇s, where s is crystalline CCl₄) has coordinatesP = 0.75 kbar and T = 0.4°C.The main obstacle of the present study, the very slow achievement of equilibrium, has been eliminated by adding small amounts (0.25% by mass) of surfactants followed by ultrasonic mixing. We have shown that this accelerates the achievement of equilibrium without changing its position.     

Catalytic Enantioselective Reduction of Prochiral Ketones with Chiral Ferrocenyl Amino Alcohols

The asymmetric reduction of prochiral ketones was catalyzed by a class of recoverable and highly stable chiral ferrocenyl amino alcohols derived from natural amino acids to yield optically active secondary alcohols in high chemical yields and moderate to good enantiomeric excesses.     

三氮宾分子的磁性设计

采用量子化学ＧＡＵＳＳＩＡＮ９４ａｂｉｎｉｔｉｏＵＨＦ方法和ＳＴＯ－３Ｇ基组设计一系列三氮宾分子，讨论分子的几何结构和取代基对其磁性的影响，计算结果表明，这些分子都具有铁磁性并有高自旋基态，有效交换积分值随代基的变化而变化，其中一种具有较代的总能量和高的有效交换积分值的分子，可期望被合成。     

Polymeric pH indicators immobilized PVA membranes for optical sensors of high basicity based on a kinetic process

Two kinds of polymeric pH indicators PPF (phenolphthalein-formaldehyde product) and CPF (o-cresolphthalein-formaldehyde product) immobilized cross-linked poly(vinyl alcohol) membranes (PPF-PVA and CPF-PVA) for optical intermittent determination of high basicity ([OH⁻] = 1-8 M) based on a kinetic process were developed. In our previous work, we had demonstrated that PPF-PVA and CPF-PVA could perform the determination of high pH values from pH 10.0 to 14.0. Here the discoloring kinetic behaviors of PPF-PVA and CPF-PVA were compared with those of free phenolphthalein, o-cresolphthalein and thymolphthalein. Experimental results and theoretical analysis indicated that the response behaviors of the optodes’ membranes in concentrated NaOH solutions were diffusion-independent and still complied with the pseudo-first-order kinetics. In addition, two data analysis methods for determination were presented. One was directly based on the reduced absorbance; the other was based on the discoloring kinetic constant. It was found that the latter could perform a rapid (60 s) and reliable (relative standard deviation: 2.6%) determination for high basicity. These kinds of optodes can be used repeatedly when they are immersed in low-pH solutions to regain the protonated form after each determination.     

Achieving high yield of Ti3C2Tx MXene few-layer flakes with enhanced pseudocapacior performance by decreasing precursor size

Ti₃C₂T_x, a most studied member of MXene family, shows promise as a candidate electrode for pseudocapacitor due to its electronic conductivity and hydrophilic surface. However, the unsatisfactory yield of Ti₃C₂T_x few-layer flakes significantly restricted it in real applications. Here, we proposed a simple solution to boost the yield of Ti₃C₂T_x few-layer flakes by decreasing precursor size. When using the small 500 mesh Ti₃AlC₂ powders as raw material, high yield of 65% was successfully achieved. Moreover, the as-received small flakes also exhibit an enhanced pseudocapacior performance owing to their excellent electrical conductivity, expanded interlayer space and more O content on the surface. This work not only sheds light on the cost effective mass production of Ti₃C₂T_x few-layer flakes, but also provides an efficient solution for the design of MXene electrodes with high pseudocapacior performance.     

Improving (Q)SAR predictions by examining bias in the selection of compounds for experimental testing

ABSTRACT

Existing data on structures and biological activities are limited and distributed unevenly across distinct molecular targets and chemical compounds. The question arises if these data represent an unbiased sample of the general population of chemical-biological interactions. To answer this question, we analyzed ChEMBL data for 87,583 molecules tested against 919 protein targets using supervised and unsupervised approaches. Hierarchical clustering of the Murcko frameworks generated using Chemistry Development Toolkit showed that the available data form a big diffuse cloud without apparent structure. In contrast hereto, PASS-based classifiers allowed prediction whether the compound had been tested against the particular molecular target, despite whether it was active or not. Thus, one may conclude that the selection of chemical compounds for testing against specific targets is biased, probably due to the influence of prior knowledge. We assessed the possibility to improve (Q)SAR predictions using this fact: PASS prediction of the interaction with the particular target for compounds predicted as tested against the target has significantly higher accuracy than for those predicted as untested (average ROC AUC are about 0.87 and 0.75, respectively). Thus, considering the existing bias in the data of the training set may increase the performance of virtual screening.     

Comparison by capillary SFC and SFC-MS of soxhlet and supercritical fluid extraction of hamster feces

Components of hamster feces ranging from low molecular weight fatty acids through the expected range of triglycerides have been eluted in a single SFC run with simultaneous pressure and temperature programming. Temperature programming from 140°C to 240°C was required to provide optimum conditions for separation of the fatty acids and to move the elution region of the sterol esters away from that of the triglycerides. Data from chemical ionization and electron impact mass spectrometry of compounds separated by SFC were used to confirm identities suggested by retention measurements and to provide tentative identities of unknown compounds. SFC with flame ionization detection was used to compare Soxhlet extraction, off-line supercritical fluid extraction (SFE), and on-line SFE of the feces. Although samples obtained by Soxhlet extraction and SFE produced very similar chromatograms, SFE required far less time and consumed much smaller quantities of organic solvent.     

Adsorption of large macromolecules on fine colloidal particles

A simple model of adsorption of large macromolecules on ultra-fine colloidal particles is presented. The basic assumption of the model is that the number of particles attached to a single molecule is a random quantity. Both the reversible and irreversible polymerparticle binding is considered. Also, effects of the non-ideal mixing of polymer solution with suspension and of the polymer/particle size ratio on the shape of the adsorption isotherm are examined. The predictions of the model are confronted with experimental results of the study on the adsorption of very high molecular weight polyacrylamide on fine AgI colloidal particles.