Ni olivine: thermal behavior of liebenbergite

The synthetic samples of nickel olivine were measured in the temperature range 100–630 K by the X-ray powder diffraction method. Temperature dependencies of molar volumes and coefficients of bulk thermal expansion of liebenbergite were determined. Interpolation and extrapolation of the experimental data were performed by the procedure based on the Debye–Mie–Gruneisen theory of solid body in the range from 50 to 2000 K, and the Gruneisen coefficient and Debye temperature were calculated. Heat capacity and its behavior in accordance with temperature were evaluated.

     

Thin-Layer Chromatography of Metal Cations Modified with Amines and Surfactants and the Sorption-Catalytic Detection of Cobalt(II) and Copper(II)

JPC – Journal of Planar Chromatography – Modern TLC - The thin-layer chromatography (TLC) procedures of metal cations, modified with amines and cationic surfactant micelles, followed by...     

Laser ablation of paper: Raman identification of products

Old paper samples are bleached using pulsed laser radiation with a wavelength of 532 nm. The ablation products of five paper samples that differ by composition and production dates are studied using Raman microspectroscopy. Cellulose, protein, calcite, titanium dioxide (anatase, rutile, and brookite), quartz, lazurite, bonattite, and dolomite are identified as ablation products.     

Determination of montelukast sodium by capillary electrophoresis

This work verifies the potential of CE in the analysis of significant impurities of montelukast sodium - an active ingredient for the treatment of bronchial asthma. Using 20 mM borate buffer pH 9.2 with 10 mM SDS and 10 mM (2-hydroxypropyl)-gamma-CD (2HP-gamma-CD) it was possible to separate montelukast and several impurities, including its cis-isomer, after exposure to light and oxygen. The obtained method surpasses a chromatographic method for montelukast sodium in terms of time of analysis (9 min of CE analysis vs. 35 min HPLC) and efficiency (CE offered over 900 000 theoretical plates for montelukast). Good repeatability of the method was supported by the low % RSD for the migration time of montelukast (0.53%). For the first time, the capillary electrophoretic method was employed for temporal study of the degradation of montelukast. The results showed that degradation of montelukast and the formation of the cis-isomer mainly occurred during the first 2 days of exposure, and occurred to a higher degree when there was no contact with the air (oxygen) in the exposed sample.     

Self-sorting dimerization of tetraurea calix[4]arenes

Calix[4]arenes substituted by four urea functions are self-complementary molecules that spontaneously combine in apolar solvents in the presence of an ammonium salt to form dimeric capsules held together by a belt of hydrogen bonds. In the presence of tetraethylammonium salts, the Et4N+ cation is included as a guest. The sorting between dimeric capsules formed in a mixture of calix[4]arenes directly depends on the steric crowding of the substituents grafted on the urea groups whether aromatic derivatives or aliphatic chains linking urea functions in mono-, di-, or tetraloop structures. Simple rules allow one to anticipate which capsules will be exclusively formed when calix[4]arenes are mixed in different proportions. The stabilization of the dimeric structures by hydrogen bonds is thwarted by the overlaps of aliphatic loops and/or by bulky groups that cannot pass through these loops. Despite the structural similarity of the calixarenes, the exclusive formation of dimers of well-defined compositions and clear titration breaks are observed by electrospray mass spectrometry. This technique yields reliable information on stoichiometries and composition despite measurements in the gas phase rather than in solution and it does not suffer from excessive peak overlaps in contrast with NMR.     

Reasons for the exclusive formation of heterodimeric capsules between tetra-tolyl and tetra-tosylurea calix[4]arenes

The selective heterodimerization of tetra-tolyl () and tetra-tosylurea () calixarenes, serendipitously found by Rebek et al. (R. K. Castellano, B. H. Kim and J. Rebek, Jr., J. Am. Chem. Soc., 1997, 119, 12671-12672), has been used for the construction of highly sophisticated macrocycles and well-defined supramolecular assemblies. Regrettably, hitherto, neither the exact structure of these heterodimers nor the reason for their exclusive formation is known. We present molecular dynamics simulations using the AMBER force field in explicit chloroform solvent for the two homodimers, the heterodimer and the two uncomplexed tetra-urea calixarenes. The rigid rotation about the C-S-N-C bond of the tosylurea group has been calculated for a model compound (N-mesylformamide) at the RHF/6-31G* level of theory. The calculations suggest that the heterodimer . is energetically favored over the homodimers by a sterically relaxed conformation of the tosylurea hemisphere in ., by a moderate degree of reorganization of the hemispheres from the uncomplexed to the complexed state and by favorable interactions between the hemispheres. The tosylurea S=O groups are involved in the hydrogen bonding system which results in different sizes of the three capsules in increasing order . < . < .. To prove the computational predictions, 1H NMR experiments have been carried out with solvents/guests differing in shape and size. The largest capsule . prefers the larger guests toluene and p-xylene while the latter is not encapsulated in the smallest capsule ..     

A Simple Method of Synthesis of 3-Carboxy-2,2,5,5-Tetraethylpyrrolidine-1-oxyl and Preparation of Reduction-Resistant Spin Labels and Probes of Pyrrolidine Series

Stable free radicals are widely used as molecular probes and labels in various biophysical and biomedical research applications of magnetic resonance spectroscopy and imaging. Among these radicals, sterically shielded nitroxides of pyrrolidine series demonstrate the highest stability in biological systems. Here, we suggest new convenient procedure for preparation of 3-carboxy-2,2,5,5-tetraethylpyrrolidine-1-oxyl, a reduction-resistant analog of widely used carboxy-Proxyl, from cheap commercially available reagents with the yield exceeding the most optimistic literature data. Several new spin labels and probes of 2,2,5,5-tetraethylpyrrolidine-1-oxyl series were prepared and reduction of these radicals in ascorbate solutions, mice blood and tissue homogenates was studied.     

High-temperature fluorescence of low- and high concentration aqueous ATP solution

Abstract

The results of an experimental study of luminescence of an aqueous solution of adenosine triphosphate (ATP) at room temperature are presented. High-temperature fluorescence of low- and high-concentrated solution was experimentally detected and analyzed. The shape of the fluorescence spectrum, the excited state lifetime and the temperature behavior of the emission intensity indicate the formation in the high-concentrated solution of rather stable dimer-like complexes, which can form excimer states.     

A Self‐Sorting Scheme Based on Tetra‐Urea Calix[4]arenes

Size and shape do matter : When dimerized in nonpolar solvents, an equimolar mixture of eleven tetra‐urea calix[4]arenes with different wide‐rim substituents self‐sorts into only six out of 35 different homo‐ and heterodimers (see picture). Since the calixarene scaffold and the four urea units are the same in all cases, the self‐sorting process is driven only by the cooperative action of steric requirements and stoichiometry.

     

Microphase separation in multiblock copolymer melts: Nonconventional morphologies and two-length-scale switching

The phase behavior of AfmN(BN2AN2)B(1-fmN) multiblock copolymer melts is studied within the weak segregation theory. The interplay between ordering on different length scales is shown to cause dramatic changes both in the ordered phase symmetry and periodicity upon small variation of the architectural parameters of the macromolecules. Phase diagrams are presented in the (f,chiN) plane (chi is the Flory-Huggins parameter) for various values of the architecture parameters n and m. Near the critical surface, i.e., for (f-0.5)2<1, such nonconventional cubic phases as the face-centered cubic (FCC), simple cubic (SC), (double) gyroid, and the so-called BCC(2) (single gyroid) are found to be stable. The lamellar morphology is shown to be replaced by BCC2, FCC, or SC (depending on the structural parameters) as the most stable low-temperature phase.