The total π-electron energy as a problem of moments: application of the Backus–Gilbert method

The total π-electron energy problem can be formulated as a classical problem of moments. This observation allows us to apply general methodologies developed in the field of moment’s theory to solve the total π-electron energy problem. In the present article, we apply the Backus–Gilbert method to obtain analytical expressions for the total π-electron energy in terms of its spectral moments.AMS subject classification: 30E05, 05C50, 92E10, 78M05     

Chemical Industry,the Environment,and Russian Provincial Society: The Case of the Kokshan Chemical Works (1850–1925)

This article explores interactions between the chemical industry, the environment, and Russian provincial society in the late nineteenth and early twentieth centuries, using the example of the Kokshan chemical works, in the Elabuga District, Viatka Province, Russian Empire (today Mendeleevsk District, Republic of Tatarstan, Russian Federation). The plant’s location facilitated its rapid development due to a number of factors, including a cheap labour force, the availability of raw materials, and the absence of local competition. However, the factory’s development came in conjunction with the deterioration of the environment and subsequent health problems for employees and the surrounding population. Conflicts connected with the Kokshan works illustrate differences between this case and similar examples in Russia and Europe. In Viatka Province, the local community remained mostly silent regarding these issues, and made no demands for improving sanitary control and working conditions or reducing pollution; rather, it was distant activists who personally suffered no harm who intervened in the interest of social justice. The history of the company reflects the contrast between the transfer of European technological innovations to Russia and laborious efforts to increase national wealth on the one hand, and the exploitation of the environment and endangerment of workers’ health on the other.     

Chemical Reactions and Kinetics of the Carbon Monoxide Coupling in the Presence of Hydrogen

The chemical reactions and kinetics of the catalytic coupling reaction of carbon monoxide to diethyl oxalate were studied in the presence of hydrogen over a supported palladium catalyst in the gaseous phase at the typical coupling reaction conditions. The experiments were performed in a continuous flow fixed-bed reactor. The results indicated that hydrogen only reacts with ethyl nitrite to form ethanol, and kinetic studies revealed that the rate-determining step is the surface reaction of adsorbed hydrogen and the ethoxy radical (EtO-). A kinetic model is proposed and a comparison of the observed and calculated conversions showed that the rate expressions are of rather high confidence.     

Unprecedented polymer-supported π-acid: Synthesis and its application as a promoter to the monothioacetalization of acetals

A novel polymer was synthesized by copolymerization of styrene monomer bearing dicyanoketene acetal functionality and ethylene glycol dimethacrylate, and used successfully as a recyclable π-acid catalyst in monothioacetalization of aromatic, aliphatic, acyclic, and cyclic acetals with thiophenol and phenylthiotrimethylsilane.     

Chemical and Transport Properties of Carbon–Oxygen–Hydrogen Plasmas in Isochoric Conditions

The composition and transport properties of CO₂, CO, CH₄, CO + Ar (50 vol%), CO + Fe (50 vol%) have been calculated at constant volume assuming local thermodynamic equilibrium (LTE). Except at low temperature (T < 3000 K), when the formation of condensed species or more complex molecules can occur, pressure increases with temperature at constant volume. For example, for 1 mol of CH₄ starting at 0.1 MPa and 298 K the pressure can reach 40 MPa at 20,000 K. The consequence is a shift to higher temperatures of dissociation and ionization. The electrical conductivity σ_e at constant volume increases drastically relative to that obtained at 0.1 MPa over 15,000 K, in spite of the decrease of the electron density n_e This is due to the increase in the neutral species density. n_i, with a much lower electron-neutral species collision cross section σ_ei (σ_e is inversely proportional to n_i,σ_ei). The viscosity always exhibits a maximum when the ionization degree increases over 1–30%, but this maximum is shifted to higher temperatures and its peak value is higher. The thermal conductivity peaks due to dissociation and ionization are shifted to higher temperatures and their values are reduced compared to those obtained at constant pressure.     

Selectivity Control of the Ligand Exchange at Carbon in α-Metallated Ylides as a Route to Ketenyl Anions**

α-Metallated ylides have recently been reported to undergo phosphine by CO exchange at the ylidic carbon atom to form isolable ketenyl anions. Systematic studies on the tosyl-substituted yldiides, R₃P=C(M)Ts (M=Li, Na, K), now reveal that carbonylation may lead to a competing metal salt (MTs) elimination. This side-reaction can be controlled by the choice of phosphine, metal cation, solvent and co-ligands, thus enabling the selective isolation of the ketenyl anion [Ts−CCO]M ( 2-M ). Complexation of 2-Na by crown ether or cryptand allowed structure elucidation of the first free ketenyl anion [Ts−CCO]⁻, which showed an almost linear Ts−C−C linkage indicative for a pronounced ynolate character. However, DFT studies support a high charge at the ketenyl carbon atom, which is reflected in the selective carbon-centered reactivity. Overall, the present study provides important information on the selectivity control of ketenyl anion formation which will be crucial for future applications.     

What's in an Atom? A Comparison of Carbon and Silicon-Centred Amidinium⋅⋅⋅Carboxylate Frameworks**

Despite their apparent similarity, framework materials based on tetraphenylmethane and tetraphenylsilane building blocks often have quite different structures and topologies. Herein, we describe a new silicon tetraamidinium compound and use it to prepare crystalline hydrogen bonded frameworks with carboxylate anions in water. The silicon-containing frameworks are compared with those prepared from the analogous carbon tetraamidinium: when biphenyldicarboxylate or tetrakis(4-carboxyphenyl)methane anions were used similar channel-containing networks are observed for both the silicon and carbon tetraamidinium. When terephthalate or bicarbonate anions were used, different products form. Insights into possible reasons for the different products are provided by a survey of the Cambridge Structural Database and quantum chemical calculations, both of which indicate that, contrary to expectations, tetraphenylsilane derivatives have less geometrical flexibility than tetraphenylmethane derivatives, that is, they are less able to distort away from ideal tetrahedral bond angles.     

Chemical reactivity of the imidazole: a semblance of pyridine and pyrrole?

It has been suggested that pyridine and pyrrole could be patterns for imidazole reactivity studies due to the amine (-NH-) and aza (-N═) nitrogen atoms. The analyses of the local and global electronic indexes prove and quantify that imidazole has an intermediate analogy between pyrrole and pyridine.     

Comparison of fluorescence and QCM technologies: Example of explosives detection with a π-conjugated thin film

A π-conjugated compound was synthesized as a sensitive material for explosives detection. The detection of vapors of 2,4-dinitrotoluene was demonstrated with quartz crystal microbalance (QCM) and fluorescence transduction methods. The fluorescence intensity monitoring shows a higher sensitivity and selectivity than the monitoring of the QCM frequency. Both methods appear to be synergic when used simultaneously as the sensor helps to discriminate interferent vapors from nitroaromatics.     

Comparison of LC–UV, LC–ELSD and LC–MS Methods for the Determination of Sesquiterpenoids in Various Species of Artemisia

Simple and specific analytical methods for the quantitative determination of sesquiterpenoids from various species of Artemisia plant samples were developed. By LC–UV, LC–ELSD, the separation was achieved by reversed-phase chromatography on a C18 column with water and acetonitrile both containing 0.025% trifluoroacetic acid as the mobile phase. In the LC–MS system, trifluoroacetic acid was replaced by 0.1% formic acid. The wavelength used for quantification of sesquiterpenoids with a diode array detector was 205 nm. The limits of detection by LC–MS was found to be 5, 10, 25, 50, 50 ng mL^?1. The limits of detection by LC–UV and LC–ELSD were found to be 5.0, 3.0, 100, 100, 7.5 μg mL^?1, by LC–UV and 50, 25, 30, 100 and 75 μg mL^?1 by LC–ELSD. LC–mass spectrometry coupled with electrospray ionization (ESI) interface is described for the identification and quantification of sesquiterpenoids in various plant samples. This method involved the use of the [M + H]⁺ ions of sesquiterpenoids in the positive ion mode with extractive ion monitoring.     

A Comparison of Three Methods of Extraction for the Determination of Polyphenols and Organic Acids in Tobacco by UPLC–MS–MS

Matrix solid phase dispersion (MSPD), ultrasonic extraction followed by a solid phase extraction (USE–SPE) and reflux extraction (REFLUX) were studied for the analysis of polyphenols and organic acids in tobacco. The analysis was by ultra-high performance liquid chromatography tandem mass spectrometry (UPLC–MS–MS). The multi-mode support sorbent Zirconia/AA12S50 in MSPD is more suitable for the extraction of tobacco polyphenols than conventional silica or C18 silica. Although the matrix effect of USE–SPE is slightly stronger than MSPD and REFLUX for most target compounds, it gave higher extraction capacity, recoveries and sensitivity.     

1, 1‐Dianthrimide as a Reagent for the Spectrophotometric Determination of Boron

Abstract

The optimum conditions for the formation of the blue 1:1 complex by the reaction of 1, 1‐dianthrimide and boric acid in 95% by weight sulfuric acid have been determined. The effect of certain diverse ions are reported. The procedure is applicable to the determination of 1 to 10 μ of boron.     

Insights into the Role of Glucose and Glycerol as a Mixed Carbon Source in the Improvement of ε-Poly-l-Lysine Productivity

Using glucose–glycerol mixed carbon source has proved to be an effective strategy for ε-poly-l-lysine (ε-PL) production with rapid cell growth and much higher ε-PL productivity. In this study, we attempt to focus on key enzymes and intracellular energy cofactors to reveal the underlying mechanisms involved in such significant improvements. The activities of key enzymes involved in the pentose phosphate pathway, TCA cycle, anaplerotic pathway and the aspartate family amino acid biosynthesis pathway as well as ε-PL synthetase showed overall enhancement with the mixed carbon source, especially in the late stages of fermentation, compared with those in either glucose or glycerol single carbon sources. Moreover, the intracellular cofactors in terms of NADH and ATP kept higher formation and consumption rates in the mixed carbon source, respectively, throughout batch fermentation. As a result, Streptomyces sp. M-Z18 could be accelerated in cell growth and precursor l-lysine biosynthesis in the mixed carbon source, thus finally shortening fermentation time and enhancing ε-PL productivity. Understanding this process will provide information for the rational regulation of the metabolism network of the quantative production of ε-PL by metabolic engineering.     

Defect-Free Synthesis of a Fully π-Conjugated Helical Ladder Polymer and Resolution into a Pair of Enantiomeric Helical Ladders**

Fully π-conjugated ladder polymers with a spiral geometry represent a new class of helical polymers with great potential for organic nanodevices, but there is no precedent for an optically active helical ladder polymer totally composed of achiral units. We now report the defect-free synthesis and resolution of a fully π-conjugated helical ladder polymer with a rigid helical cavity, which has been achieved by quantitative and chemoselective acid-promoted alkyne benzannulations of a rationally designed, random-coil achiral polymer followed by chromatographic enantioseparation. Because of a sufficiently high helix-inversion barrier, the isolated excess one-handed helical ladder polymer with a degree of polymerization of more than 15 showed a strong circular dichroism with a dissymmetry factor of up to 1.7×10⁻² and is thermally stable, maintaining its optical activity in solution even at 100 °C, as well-supported by molecular dynamics simulation.     

C–O,C–S,C–N,and C–C Bond Formation at the Periphery of the Macrocycle during Chemical Modification of Phytochlorins: Key Methods and Synthetic Applications

Russian Journal of General Chemistry - The main methods of C-O, C-S, C-N, and C-C bond formation at the periphery of the macocrocycle during chemical modification of phytochlorins in the synthesis...     

Rhamnogalacturonan II: Chemical Synthesis of a Substructure Including α-2,3-Linked Kdo**

The synthesis of a fully deprotected Kdo-containing rhamnogalacturonan II pentasaccharide is described. The strategy relies on the preparation of a suitably protected homogalacturonan tetrasaccharide backbone, through a post-glycosylation oxidation approach, and its stereoselective glycosylation with a Kdo fluoride donor.     

Aqueous Solutions of Colloidal Ruthenium: the Radiation–Chemical Preparation and Optical Absorption

The radiation-chemical reduction of Ru(III) is studied in aqueous RuCl₃ solutions containing isopropyl alcohol. In the presence of sodium polyacrylate, the stable sols of metal are formed with spherical particles 4–8 nm in diameter. The optical spectrum of nanoparticles is characterized by an increasing absorption in the UV spectral region with no maximum (₂₀₀ = 7.2 × 1030 l mol^–1 cm^–1). The colloids of ruthenium in an aqueous solution are stable in the open air.