Short-time isoprene polymerization under the action of a titanium–magnesium catalyst

The short-time polymerization of isoprene under the action of a TiCl₄/MgCl2?i-Bu₃Al heterogeneous catalyst has been investigated. Pulse mixing of the catalyst and monomer in a cylindrical tubular reactor with a certain length followed by ethanol injection has made it possible to carry out polymerization for 0.1?0.7 s. In the first 0.3 s, when there is a considerable rise in the activity of the catalyst, living polymerization of isoprene takes place. In this period, polyisoprene has up to 95% trans-1,4 units. Extending the polymerization time to 0.7 s diminishes the average molar mass of polyisoprene, broadens its molar mass distribution, and decreases the concentration of trans-1,4 units to 83%. The data of this study have been analyzed on the basis of the kinetic continuity of the polymer chain initiation and growth.     

Structure of a Na<Superscript>+</Superscript> cation hydration shell on heating in a planar nanopore

Resistance to heating above the boiling point of water of the molecular structure of a single-charged sodium cation hydration shell growing under the conditions of a model planar nanopore with a width of 5 Å is studied by computer simulation. Monte Carlo calculations of spatial correlation functions are performed in a detailed model with regard to many-body interactions between the ion and water molecules. The system demonstrates an increased resistance to thermal fluctuations along the pore plane and a decreased one in the transverse direction. The heating is accompanied by an enhanced coating effect of molecules around the ion and a diminished effect of extruding the ion out of its own hydration shell. The orientational molecular order due to strong spatial anisotropy inside the nanopore is much more stable than the hydrogen bonds between the molecules.     

Molecular kinetic aspects of vaporization of volatile coordination compounds with organic ligands

We present results of the experimental study and numerical simulation of radiation-convective heat and mass transfer during the sublimation of spherical particles of metal β-diketonates in a high-temperature inert gas flow (argon or helium). The sublimation process is visualized, and experimental data on the temperature variation dynamics and particle size are obtained. It is shown that at stable transfer of the compound from the particle surface the sublimation proceeds with the formation of large pores in its structure. The effect of inert gas properties on the kinetics of the vaporization process of precursor particles with various initial diameters is analyzed in the temperature range from 200 °C to 330 °C. Due to a higher thermal conductivity and heat capacity of helium as compared with argon, the choice of helium as carrier gas causes an increase in the sublimation intensity.     

Manifestation of the <Emphasis Type="Italic">gauche</Emphasis> effect in conformers of benzenesulfonic acid hydrazide

Conformational properties of a benzenesulfonic acid hydrazide molecule and its para-nitro and para-methyl derivatives, which have found wide application as porofors and biologically active compounds, are studied. It is found that the benzenesulfonic acid hydrazide molecule has six conformers with relative energies of 0//0 kcal/mol, 0.34//0.98 kcal/mol, 2.51//2.25 kcal/mol, 2.54//2.56 kcal/mol, 2.90//3.28 kcal/mol, 6.64//6.43 kcal/mol (MP2//DFT(B3LYP) with the cc-pVTZ basis set), each conformer has enantiomer. The conformers differ from each other in the relative orientation of the fragments of the–SO2NHNH2 group, the energies of the frontier orbitals, the direction and value of the dipole moments. It is shown that the introduction of a nitro or methyl group into the para-position practically does not affect the conformational properties of the sulfonyl hydrazide group. Change in the structure of benzenesulfonic acid hydrazide during the crystal–gas transition is considered and it is revealed that in the crystal the conformation similar in structure to one of the high-energy conformers of the free molecule is stabilized. The NBO analysis of the electron density distribution is performed and it is shown that the occurrence of the gauche effect in all conformers of the molecules under study can be interpreted by the manifestation of the total action of strong anomeric effects between the lone pairs of nitrogen atoms and antibonding orbitals of S=O, N–H, C–S, and N–S bonds.     

The use of 2D diffractometry data for oriented samples in the choice of a unit cell

An approach for the substantiated choice of the indexing procedure of a diffraction pattern is described. The technique is based on a combined use of powder X-ray diffraction data in Bragg–Brentano schemes and 2D GIXD of mainly oriented polycrystalline samples.     

X-ray photoelectron and X-ray emission study of the electronic structure of hexanuclear Mn(II,III) pivalate complexes

The electronic structure of hexanuclear Mn(II,III) pivalate complexes with tetrahydrofuran and isonicotinamide are studied by X-ray photoelectron spectroscopy and X-ray emission spectroscopy. It is shown that when isonicotinamide substitutes for tetrahydrofuran the spin state of manganese ions is retained; the electron density increases on the manganese and oxygen atoms of the [Mn₆(O)₂Piv₁₀] core.     

Properties of methylammonium lead iodide perovskite single crystals

The technique for growing CH₃NH₃PbI₃ single crystals from saturated solutions in concentrated hydroiodic acid is improved by introducing a reducing agent (hypophosphorous acid). The structure of perovskite is confirmed by single crystal XRD. By energy dispersive spectroscopy and X-ray photoelectron spectroscopy it is established that the stoichiometry of the grown crystals corresponds to the CH₃NH₃PbI₃ compound. Changes in the photoluminescence intensity during in-air measurements show that the crystals synthesized using the reducing agent are more stable in the external environment with laser exposure than without it.     

Anti-inflammatory chromone alkaloids and glycoside from Dysoxylum binectariferum

Herein we report isolation of a new chromone alkaloid chrotacumine K (12) from fruits and a chromone glycoside schumaniofioside A (13) from leaves of Dysoxylum binectariferum Hook f. Schumaniofioside A is reported for the first time from Meliaceae family. Other known alkaloids isolated include rohitukine (1) and chrotacumine E (6). The structure of new alkaloid 12 was elucidated on the basis of extensive 1D and 2D NMR analysis, synthesis and chemical hydrolysis. Chemically, chrotacumine K (12) is a 3′-O-acetyl rohitukine which on chemical or enzymatic hydrolysis produces rohitukine. The new alkaloid 12 is also present in seeds and stem-barks of this plant. The glycoside schumaniofioside A (13) is present only in leaves, and in abundance (～1% w/w of dried leaves). The isolated compounds and extracts were evaluated for in vitro effect on the proinflammatory cytokines (TNF-α and IL-6) in human monocytic THP-1 cells. The alkaloid 12 displayed potent inhibition (57%) of TNF-α at 0.3 µM, and was non-toxic to THP-1 cells up to 40 µM, indicating its excellent therapeutic window. Furthermore, a nitrobenzoyl ester analog 15e showed better inhibition of IL-6 than parent natural product chrotacumine K.     

Instrumental neutron activation analysis (INAA) of Nok sculptures in I. P. Stanback Museum

Biochar prepared from Triticum aestivum straw (SB) was used to investigate the sorption separation of Cd²⁺ and Co²⁺ ions in single and binary systems. The maximum adsorption capacity of SB was higher for Cd²⁺ ions and the process was strongly pH dependent. Adsorption data in the binary system Cd²⁺–Co²⁺ were well described by the extended Langmuir model and the values of affinity parameter b indicate a higher affinity of SB to Cd²⁺ in comparison with Co²⁺ ions. The mechanisms for the removal of Cd and Co by biochar were evidenced by the different instrumental analyses as well as by chemical speciation modeling. Elemental mapping of SB revealed spatial distributions of cobalt and cadmium on biochar surfaces. The role of functional groups in metal sorption was confirmed by FTIR. Results demonstrate that SB is a promising heavy metal-immobilizing agent for contaminated soils or water.     

Arbitrage without borrowing or short selling?

We show that a trader, who starts with no initial wealth and is not allowed to borrow money or short sell assets, is theoretically able to attain positive wealth by continuous trading, provided that she has perfect foresight of future asset prices, given by a continuous semimartingale. Such an arbitrage strategy can be constructed as a process of finite variation that satisfies a seemingly innocuous self-financing condition, formulated using a pathwise Riemann–Stieltjes integral. Our result exemplifies the potential intricacies of formulating economically meaningful self-financing conditions in continuous time, when one leaves the conventional arbitrage-free framework.