Water vapor adsorption and capillary reactions of silicates

States of disperse silicate systems classified according to their fundamental morphological types were represented by a ternary diagram. Water vapor equilibria of various silicate samples were investigated by energy levels, by equivalent pore number of potential bands determined from adsorption potential curves. The silicate adsorbents were characterized by adsorption energy, equipotential surface area and specific capillary. Electrical properties of adsorbents depending on their water contents were examined. Changes of adsorption properties of mechanical, thermal and by ion exchange treated silicates were observed. Electrical properties of adsorbents depending on their humidity were examined. Capillary reactions were observed causing irreversible adsorption-desorption cycles.     

Polymer microcapsules with "foamed" membranes

This article describes the preparation of capsules displaying craters at their surfaces and independent holes inside their membranes. These poly(methylmethacrylate) capsules of 20 to 200 microm diameter are prepared by a solvent evaporation process and typically contain a dispersant, polyvinyl alcohol, and an excipient, namely, a fatty acid triglyceride (miglyol 812). Spectroscopic methods showed that, depending on the miglyol content, the craters at the surface exhibited sizes of about 1 to 2 microm, whereas the core structure of the membrane changed significantly, typically from "soft-part-of-bread" up to "foamed"-like aspects. Among several spectroscopy techniques, confocal fluorescence microscopy confirmed that the capsules retained the miglyol in their core and not in the craters or holes, even after centrifugation and handling. This technique also showed that holes in the membrane are filled with water. A possible analysis of the "foaming" phenomenon based on the surface tensions of different oils, as well as their optimal hydrophile-lipophile balance (HLBO), is added to generalize the concept.     

Trends in liquid-phase microextraction, and its application to environmental and biological samples

Liquid phase microextraction (LPME) is a popular technique for sample pretreatment before the trace determination of target compounds from complex matrices, examples being pesticides in environmental and food samples, or drug residuals in biological samples such as blood or urine. LPME is simple, affordable, easy to operate, and highly sensitive. It is a miniaturized implementation of conventional liquid-liquid extraction in which only a few microliters of solvents are used instead of several hundreds of milliliters. This review focuses on newly developed LPME-based techniques, their application to environmental and biological samples, on their limitations, and on future applications.

Annelation of the 1,2,4-triazole ring on the basis of α-hydrazino-substituted heterocycles and their hydrazones (review)

The literature data on methods for the synthesis of annelated 1,2,4-triazole systems on the basis of -hydrazino-substituted heterocycles and their hydrazones are correlated, and their chemical properties and biological activity are examined briefly.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1587–1613, December, 1993.     

Separation of conformational isomers in the 5,10-secocardenolide series. I.

A rare case of separable conformational isomers in the 5,10-diketo-5,10-secocardenolide series has been found. Thus, the periodate oxidation of 10-hydroxy-19-norperiplogenin has given 3,14-dihydroxy-5,10-diketocard-19-nor-5,10-seco-20(22)-enolides which in fact consist of a mixture of conformers formed as the result of the inversion of the AB ring. A method for separating the four conformers, their properties, their IR, mass, and PMR spectra, the kinetics of their acetylation reactions, and their heats of transformation are described. Conformational structures as the most probable are put forward on the basis of the experimental results obtained.All-Union Scientific-Research Institute of Drug Chemistry and Technology, Khar'kov. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 76–80, January–February, 1985.     

大学化学多维度教学模式探索

Aiming at the dilemma of the traditional university chemistry teaching mode, this paper explores the multi-dimensional teaching mode from the perspective of "student-centered" and "process management". The teaching mode focuses on the four dimensions of "acceptance, application and expansion" of knowledge and "improvement" of ability. It introduces eight teaching sections, including classroom teaching, classroom practice, classroom question and answer, tutoring and answering after class, homework, classroom speech, course essay and extracurricular practice. This teaching mode has achieved initial results and provided an opportunity for students to expand their knowledge and enhance their ability.     

Capillary GC and GC-MS of porphyrins and metalloporphyrins

Summary Despite their inherent low volatility, a wide range of alkyl porphyrins and their various metallo-derivatives have been successfully analysed by gas chromatography on wall coated open tubular (WCOT) capillary columns. As a result of their superior peak shape (comparable ton-alkanes of similar retention times) and relatively low Kovat's retention indices (3300–3900), the bis(trialkylsiloxy)Si(IV) derivatives offer the greatest potential for the GC analysis of geological mixtures of alkyl porphyrins. Similar derivatives of porphyrins of biomedical importance, possessing polar side chains, are also amenable to GC and GC-MS analysis.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Intramolecular interactions in vinyloxyquinolines

The UV spectra of 2-, 3-, 4-, 6-, and 8-vinyloxyquinolines were obtained, and their structures were subjected to quantum-chemical calculation within the Pariser-Parr-Pople (PPP) -electron approximation in order to ascertain the effect of the vinyloxy group on the nature of their electron transitions and on their electronic structures. A linear relationship between the difference in the charges on the carbon atoms of the vinyl group and its integral intensity in the IR spectra was established. As a result it was concluded that there is an analogy between the orienting effect of the suhstituents in benzenes and the interaction of the vinyloxy group with the nitrogen atom in vinyloxyquinolines. The polarity of the vinyl group in vinyloxyquinoline hydrochlorides was estimated on the basis of the established dependence.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1662–1665, December, 1977.     

Statistical evaluation of single nano-object fluorescence.

Single nano-objects display strong fluctuations of their fluorescence signals. These random and irreproducible variations must be subject to statistical analysis to provide microscopic information. We review the main evaluation methods used so far by experimentalists in the field of single-molecule spectroscopy: time traces, correlation functions, distributions of "on" and "off" times, higher-order correlations. We compare their advantages and weaknesses from a theoretical point of view, illustrating our main conclusions with simple numerical simulations. We then review experiments on different types of single nano-objects, the phenomena which are observed and the statistical analyses applied to them.     

Expanding dialogues: from natural autoinducers to non-natural analogues that modulate quorum sensing in Gram-negative bacteria

Bacteria are capable of "communicating" their local population densities via a process termed quorum sensing (QS). Gram-negative bacteria use N-acylated l-homoserine lactones (AHLs), in conjunction with their cognate LuxR-type receptors, as their primary signalling circuit for QS. In this critical review, we examine AHL signalling in Gram-negative bacteria with a primary focus on the design of non-natural AHLs, their structure-activity relationships, and their application in chemical biological approaches to study QS (72 references).     

Molecular docking studies of coumarin hybrids as potential acetylcholinesterase,butyrylcholinesterase, monoamine oxidase A/B and β-amyloid inhibitors for Alzheimer’s disease

Coumarins are the phytochemicals, which belong to the family of benzopyrone, that display interesting pharmacological properties. Several natural, synthetic and semisynthetic coumarin derivatives have been discovered in decades for their applicability as lead structures as drugs. Coumarin based conjugates have been described as potential AChE, BuChE, MAO and β-amyloid inhibitors. Therefore, the objective of this review is to focus on the construction of these pharmacologically important coumarin analogues with anti-Alzheimer’s activities, highlight their docking studies and structure–activity relationships based on their substitution pattern with respect to the selected positions on the chromen ring by emphasising on the research reports conducted in between year 1968 to 2017.

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High performance liquid chromatographic separations of gas oil samples and their hydrotreated products using commercial normal phases

Three commercially available high performance liquid chromatography columns are used in normal phase or quasi-normal phase mode for the separation of gas oil samples. The columns are tested with 20 analytical standards to determine their suitability for separations of petroleum samples and their ability to separate the nitrogen group-types (pyrrole and pyridine) found in petroleum. The columns studied are polymeric hypercrosslinked polystyrene (HGN), a biphenyl phase, and a Chromegabond "DNAP" column from ES Industries. The HGN column separates gas oils based on both ring structure and heteroatom, while the biphenyl phase has low retention of most compounds studied in quasi-normal phase mode. The "DNAP" column is selective for nitrogen-containing compounds, separating them from PAHs as well as oxygen and sulphur compounds. Retention data of standards on all three columns is shown, along with chromatograms of gas oil samples on the HGN and "DNAP" columns.     

Microestimation of explosives present in different compositions

Summary High explosives having the sameR _f values on a thin-layer chromatogram and difficult to separate are readily resolved as their coloured -complexes with aromatic amines. After liberation from their complexes on the plate, up to 1.5 g of the explosives can be conveniently estimated at their characteristic absorption maxima.

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Zusammenfassung Hochexplosive Substanzen mit gleichenR _f -Werten auf Dünnschichtchromatogrammen, die sich schlecht trennen lassen, werden als gefärbte -Komplexe mit aromatischen Aminen gut voneinander getrennt. Nach Freisetzung aus den Komplexen auf der Platte können bis zu 1,5 g der Explosivstoffe bei ihrem charakteristischen Absorptionsmaximum auf übliche Weise bestimmt werden.

     

基于现代信息技术的结构化学一维势箱理论和HMO法“翻转课堂”教学设计

In the article, we presented an instructional design of "Particle in One-Dimensional Box Theory" and "HMO Theory" application based on flipped classroom teaching. The students are instructed to use both "Particle in One-Dimensional Box Theory" and "HMO Theory" to solve the electronic structure of olefins and enhance their understanding of quantum mechanics theory via comparison of "Particle in One-Dimensional Box Theory" and "HMO Theory".     

Contexts and Limits of Lavoisier's Analytical Plant Chemistry: Plant Materials and their Classification

Abstract

This paper concerns eighteenth- and early nineteenth-century chemists' ontologies of materials, along with their modes of classification. The focus is on plant substances, their place in the "chemical revolution" in the last third of the eighteenth century, and the ways in which chemists individuated, identified, and ordered plant substances in the five decades before and after that event. The main goal of the paper is to describe the problems that the "new chemists" confronted in their attempts to assimilate plant materials into their analytical taxonomic programme. Historical analysis shows that there were both external and internal obstacles to that assimilation, and these can be illuminated by studying the programme's broader historical context.     

Structure and infrared spectra of some phenothiazine series derivatives

Infrared spectra of phenothiazine, isomeric benzo- and dibenzophenothiazines, and their S-oxides and -dioxides are investigated in the N-H and S O valence bond vibration regions. On the basis of the results obtained, a hypothesis is advanced regarding intermolecular hydrogen bonding with the compounds studied, and views are put forward regarding the effect of structural factors on their formation.     

Stabilization and growth of non-native nanocrystals at low and atmospheric pressures

The stabilization and growth of nanocrystals in "non-native" structures is explored via density functional calculations. Non-native and "native" bulk structures differ in their discrete translational symmetry. Computations suggest that the lower surface energy of the non-native structures always facilitates their stabilization in the early stages of crystal growth. In the compound semiconductors considered here, the transition pathways between non-native and native structures involve planar or near-planar depolarized layers and the growth conditions have significant effects on the stabilization and growth of non-native structures. The findings of this study help in identifying heuristics for the synthesis of non-native nanocrystals.     

Probing intrazeolite space

Molecular sieves are inorganic framework structures generally composed of crystalline aluminosilicate tetrahedra which are arranged to form channels of 2–10 Å, diameters and cages with dimensions from 6–15 Å. Absorption of probe molecules of varying geometries and sizes is used to characterize the framework dimensions and topography in concert with X-ray diffraction identification of the specific structure. From unit cell dimensions and assumptions about the size of the framework forming species, a pore volume can be calculated. The volumes of the absorbed probe molecules, using their liquid densities, are then compared to the calculated pore volume. The constraint on the packing of the absorbed molecules is quantified by comparing their packing density to their density in the liquid state. Further, the packing of different probe molecules into the same pore volume is compared via a ratio technique called the packing ratio. The effect of the lattice geometry and framework dimensions on the packing ratios is to provide a set of characteristic values for a given molecular sieve. The packing ratios for zeolites rho and ZSM-5 are presented as expectation values for other scientists to use as bases of comparison.     

Phase-transfer catalysis in reactions of electrophilic aromatic substitution

Electrophilic substitution in aromatic compounds under conditions of phase-transfer catalysis is considered. Catalysts of phase transfer of electrophilic reagents are used; their efficiency and the mechanism of their action in organic solvent-water systems are discussed.This review is based on materials of the report delivered at the Conference Phase-Transfer Catalysis. New Ideas and Methods (March 1994).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1895–1900, October, 1995.