Dehydration of Organic Solvents by Evaporation through Membranes Based on Polyelectrolytic Complexes

Evaporation of binary aqueous-organic mixtures through composite membranes with coatings based on polyelectrolytic complexes including different combinations of polyelectrolytic polycations and polyanions was studied. The possibility of efficient dehydration of organic solvents by their pervaporation was demonstrated.     

Derivatives of the closo-dodecaborate anion and their application in medicine

The paper presents a comparative analysis of the possibilities and characteristic features of the application of various polyhedral boron compounds, viz., the closo-decaborate anion [B₁₀H₁₀]^2–, the closo-dodecaborate anion [B₁₂H₁₂]^2–, the carba-closo-dodecaborate anion [CB₁₁H₁₂]^–, carboranes C₂B₁₀H₁₂, and the bis(dicarbollide) complexes [M(C₂B₉H₁₁)₂]^– (M = Fe, Co, or Ni), in boron neutron capture therapy (BNCT) for cancer. The requirements on compounds used in BNCT are formulated and the advantages of the application of the closo-dodecaborate anion are considered. The data on the synthesis of various derivatives of the closo-dodecaborate anion, which either already found use in BNCT or are most promising in this field, are summarized. The possibilities of the application of agents derived from the closo-dodecaborate anion in medical diagnostics are discussed.     

Synthesis of new macrocyclic aminomethylphosphines based on 4,4"-diaminodiphenylmethane and its derivatives

The reaction of bis(hydroxymethyl)phenylphosphine with 4,4"-diaminodiphenylmethane in DMF afforded 1,1",5,5"-bis[methylenedi(p-phenylene)]di(3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane) (1) whose structure was established by X-ray diffraction analysis. Sulfurization and oxidation of macrocyclic tetraphosphine 1 gave rise to products 2 and 3, respectively, compound 3 being obtained as a stable hexahydrate. The reaction of bis(hydroxymethyl)phenylphosphine with bis(4-N-methylaminophenyl)methane in DMF followed by sulfurization yielded monocyclic bis{methylenedi[p-phenylene(N-methyl)aminomethyl]}di(P-phenyl)phosphine sulfide (4).     

Analysis of Bulk and Powdered Samples Using a LAMAS-10M Laser Ionization Time-of-Flight Mass Spectrometer

The problem of the modernization of a LAMAS-10M laser desorption/ionization time-of-flight mass spectrometer was considered, and the methodological fundamentals of the quantitative analysis of bulk and powdered samples by laser desorption/ionization time-of-flight mass spectrometry were discussed. Basic modifications of certain spectrometer units were described, and the reproducibility and accuracy that can be attained using these modifications were estimated. The possibility of the quantitative analysis of bulk samples was demonstrated. These studies were performed using bulk and powdered standard reference materials. In determining precious metals in geological samples, the detection limit for powdered samples was (20–50) × 10^–9. The relative standard deviation for the repeatability of the results (RSD) of the bronze standard reference sample bronza 663 was in the limits RSD = 0.06–0.4% for the major component and 0.5–4.5% for the elements present in percent concentrations. It was shown that the majority of analytes can be determined at a semiquantitative level without using standard reference materials. The key problems of laser desorption/ionization time-of-flight mass spectrometry were considered and methods were proposed to solve these problems. Ways to further improvement of the characteristics of the mass spectrometer were demonstrated.     

Physical and chemical properties of silicon carbonitride nanocrystalline films

Nanocrystalline transparent films SiC_xN_y were obtained by plasma-enhanced chemical deposition within the temperature range 473–1173 K from low pressure gas phase from a mixture of hexamethyldisilazane vapor, ammonia, and helium. Physical chemical properties of the films obtained were studied by IR and Raman spectroscopy, ellipsometry, X-ray photoelectron spectroscopy, scanning electron microscopy, high resolution transmission electron spectroscopy and synchrotron radiation powder diffaction. Voltage-capacity and voltage-current measurements were also made. The dependence of chemical and phase composition of the films on deposition conditions was determined, and the formation of approximately 2 nm sized spherical nanocrystals within the films was established. The nanocrystals are formed by a phase similar to usual α-Si₃N₄, with silicon atoms partially substituted by carbon ones.     

Ligand-protein docking using a quantum stochastic tunneling optimization method

A novel hybrid optimization method called quantum stochastic tunneling has been recently introduced. Here, we report its implementation within a new docking program called EasyDock and a validation with the CCDC/Astex data set of ligand-protein complexes using the PLP score to represent the ligand-protein potential energy surface and ScreenScore to score the ligand-protein binding energies. When taking the top energy-ranked ligand binding mode pose, we were able to predict the correct crystallographic ligand binding mode in up to 75% of the cases. By using this novel optimization method run times for typical docking simulations are significantly shortened.     

Interlaboratory comparisons between results from testing metallurgical products for precious metal content

Problems verifying the accuracy of analyses of non-standardized materials for precious metal (PM) content have arisen at the Norilsky Nickel plant, which is a major producer of nickel, copper, and PMs in Russia. Because of the unavailability of certified reference samples for direct accuracy verification, a program of interlaboratory comparisons (ILC) was developed. This program was based on testing three semi-products of the PM production process for PM content. On program completion, a total of 826 results in 98 runs had been obtained. For each run, the calculated mean value of PM concentration was taken to be the reference value. The results obtained by Norilsky Nickel were in agreement with the reference values within the standard deviations calculated for the values. The quality of results yielded with the ILC program, as assessed via the Z-criterion, is regarded as satisfactory.Presented at the Second International Conference on Metrology – Trends and Applications in Calibration and Testing Laboratories, November 4–6, 2003, Eilat, Israel.     

Adsorptive passivation of iron by organic acid anions

Studies on the iron passivation by organic acid anions in aqueous solutions are briefly reviewed. It is shown that the passivation can be caused only by their adsorption, retarding both the iron dissolution and the formation of oxide films. Earlier, it had been believed that oxide films play a dominant role in the iron passivation in neutral solutions. The recent viewpoint is that such nonoxide iron passivation can occur in solutions of salts of not only aromatic amino acids (sodium phenylantranilate and its substitutes), but other carboxylic acids as well. An important role of chemisorption and hydrophobic properties of anions for the formation of adsorption passive films is emphasized. New possibilities for inhibitor protection of iron against corrosion, which is based on adsorptive passivation, are pointed out.Translated from Elektrokhimiya, Vol. 40, No. 12, 2004, pp. 1503–1507.Original Russian Text Copyright © 2004 by Kuznetsov.     

Size and persistence length of molecular bottle-brushes by Monte Carlo simulations

Single-chain simulations of densely branched comb polymers, or "molecular bottle-brushes" with side-chains attached to every (or every second) backbone monomer, were carried out by off-lattice Monte Carlo technique. A coarse-grained model, described by hard spheres connected by harmonic springs, was employed. Backbone lengths of up to 100 units were considered, and compared with the corresponding linear chains. The backbone molecular size was investigated as a function of its length at fixed arm size, and as a function of the arm size at fixed backbone length. The apparent swelling exponents obtained by a power-law fit were found to be larger than those for the corresponding linear polymers, indicative of stiffening of the comb backbone. The probability distribution function for the backbone end-to-end distance was also investigated for different backbone lengths and arm sizes. Analysis of this function yielded the critical exponents, which revealed an increase in the swelling exponent consistent with values found from the molecular size. The apparent persistence length of the backbone was also determined, and was found to increase with increasing branching density. Finally, the static structure factors of the whole bottle-brushes and of their backbones are discussed, which provides another consistent estimate of the swelling exponents.     

Synthesis and Photophysical Properties of Alkoxysilyl Derivatives of Dibenzoylmethanatoboron Difluoride

Alkoxysilyl derivatives of dibenzoylmethanatoboron difluoride (DBMBF₂) are synthesized by the hydrosilylation reaction of the corresponding O‐allyl derivatives of DBMBF₂ with triethoxysilane. The photophysical properties of the synthesized O‐allyl and alkoxysilyl derivatives are investigated. It is found that the absorption and fluorescence spectra of the DBMBF₂ derivatives essentially depend on the position of the O‐allyl or O‐propyl alkoxysilyl substituent. The highest fluorescence quantum yield is obtained for the para‐position, whereas the substitution at the meta‐position gives the largest bathochromic shift in the fluorescence spectrum. Density functional theory calculations of the structures and time‐dependent density functional theory calculations of the gas‐phase excitation and emission energies of alkoxysilyl derivatives are performed at the PBE0/SVP level of theory. Some spectral features of para‐, ortho‐, and meta‐substituted derivatives can be adequately explained by the overlapping of two absorption bands.