Phase diagram of a tetrapropylammonium bromide-water system according to DTA data

The phase diagram of a tetrapropylammonium bromide-water binary system is studied by means of differential thermal analysis. Three tetrapropylammonium bromide hydrates are identified that include one stable compound of 1: 4 composition (bromide: water; mp, ?32.6°C) and two metastable hydrates of 1: 6 (mp, ?70.4°C) and 1: 24 compositions (mp, ?57.0°C).     

Porous structure of rigid and swelling adsorbents according to pulsed NMR data on the mobility of adsorbed water and benzene molecules

Potentialities of pulsed NMR technique to estimate parameters of the porous structure of microporous adsorbents according to the data on nuclear magnetic relaxation and self-diffusion of adsorbed molecules are analyzed. Main attention was focused on the adsorbed systems studied by the adsorption and NMR techniques. Measurements of nuclear magnetic relaxation of adsorbed molecules make it possible to analyze the porous structure at the scale of pore sizes; data on self-diffusion, at the scale of different-porosity zones. Specific features of the translational mobility of water and benzene molecules with different mechanisms of adsorption in active carbons having relatively rigid structure and polymer adsorbents capable of swelling are discussed. In general, data obtained by the NMR technique agree with and supplement the results of adsorption measurements.     

Self-diffusion in the isotropic and mesomorphic states of the lanthanide-containing system based on nonionic surfactant according to the NMR data

Molecular self-organization in a system based on lanthanum nitrate and the nonionogenic surfactant, viz., decaethylene glycol monododecyl ether, was studied in an aqueous solution and in the liquid-crystalline state. Molecular motion and phase transitions in the system were characterized by the high-resolution pulsed gradient spin-echo ¹H NMR method. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 488–494, March, 2008.     

Structures of silver nitrate complexes with quinolines according to NMR data

Silver(I) nitrate complexes [AgNO₃(L)₂], where L is quinoline or 2-, 4-, and 8-methylquinoline, are synthesized and studied by the multinuclear NMR (¹H, ¹³C, ¹⁵N) method in acetonitrile. The influence of steric and electronic factors of the organic ligand on the NMR spectral parameters is revealed. The fast chemical exchange of the free and coordinated ligands is observed at room temperature. The ¹⁵N NMR spectra are most informative. The formation of a complex with 8-methylquinoline is impeded because of steric hindrances.     

Features of rubber swelling in transformer oil,according to NMR data

NMR spectroscopy, NMR relaxation, and NMR with a pulsed magnetic field gradient methods are used to study the swelling of the elastomers based on ethylene-propylene rubber, butadiene-nitrile rubber, and fluororubber SKF-26 in transformer oil. Components corresponding to the fractions of oil and polymer network are identified. It is shown that the affinity of the polymers toward transformer oil displays an increase in the orderly sequence of ethylene-propylene rubber, fluororubber, and butadiene-nitrile rubber; the stability of the polymers towards carbon tetrachloride falls in the same sequence. Based on an analysis of the spin–spin relaxation time depending on the degree of swelling, it is found that fluororubber elastomers are characterized by the formation of a polymer network that prevents further sorption, In contrast, elastomer based on ethylene-propylene rubber gives no indication of the formation of a rigid polymer network.     

Energy characteristics of adsorbed water in active carbons according to the NMR relaxation data

Nuclear magnetic relaxation measurements were used to determine activation energy E _act of the motion of water molecules adsorbed in active carbons. The E _act value was found to depend on the filling of active carbon pores due to changes in the state of water molecules under adsorption. It was established that the E _act = f(p/p _s) plots, where p/p _s is the relative pressure of water vapor observed for microporous active carbons (FAS-1, 2, N-15, SKT-6A), are similar in form to the corresponding plots of changes in water adsorption heats. In particular, we concluded that the plateau in the E _act = f(p/p _s) dependences, as in the case of adsorption heats, reflects the volumetric filling of active carbon micropores with water. We show that a linear function describes the increase in E _act values for water upon the complete filling of micropores with an increase in the volume of adsorbed water clusters per one primary adsorption center (W ₀/a _m ). We establish that, for water in the FAS-3 sample, the deviation of E _act values from this linear function was due to the contribution from the vapor phase in the mesopores (x ₀ = 0.7−1.2 nm) that make up a considerable part of the active carbon’s porous system.     

Relative stability of 1-substituted perfluoromethallyl cations according to19F NMR data

Conclusions The relative stability of perfluoromethallyl cations substituted at the 1 position decreases, depending on the substituent, in the following series: OMe > I > Br > Cl > F.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1054–1057, May, 1986.The authors wish to express their gratitude to Yu. V. Zeifman and S. A. Postovoi for providing the samples of 1-bromo- and 1-iodoperfluoroisobutylenes.     

Molecular structure of a water-polyethylene glycol-KOH system, according to densitometry and viscometry data

The dynamic viscosity and density of a water-polyethylene glycol-KOH system are measured at temperatures of 293.15 to 323.15 K in concentrations ranging from 0.00001 and 0.001 (mole fractions). The activation parameters of viscous flow (ΔG _η ^≠ , ΔH _η ^≠ , and ΔS _η ^≠ ), structural temperature (T ₀), the partial molar volume of polyethylene glycol (PEG) in solution $\left( {\tilde V} \right)$ , intrinsic viscosity([η]), and the Huggins constant (K _H), are calculated. It is found that PEG has a structuring effect on water in water-PEG and water-PEG-KOH systems, with the PEG structuring effect in the latter being somewhat attenuated by the destructuring influence of KOH.     

Construction of a wheat-flour state diagram

We use pressure-variable differential scanning calorimetry to detect and characterize thermally induced transitions (glass, melting, gelatinization) in pre- and post-extruded wheat flour. The resulting data allow us to construct a two-dimensional state diagram which maps the physical states that pre- and post-extruded wheat flour can assume, at constant pressure, as a function of moisture content, temperature, and the specific mechanical energy, SME, generated in the extruder. We describe how this state diagram can be used to map the path of extrusion processing, to assess the impact of extrusion conditions, and, ultimately, to design formulations and processing conditions that result in desired end-product attributes. For the extrudates, we find that the extent of processing-induced fragmentation, as monitored by reductions in the extrudate glass transition temperature,T _g, increases with the SME generated in the extruder. We demonstrate that a wheat-flour state diagram, which includes the glass curve of the wheat-flour extrudates produced at various SME values, allows one to predict and control the impact of processing conditions on extrudate properties.     

Solid state NMR of a molecular self-assembly: multinuclear approach to the cyanuric acid-melamine system

[see structure]. Trinuclear MAS NMR, involving naturally abundant (13C, 15N) and easily deuterated (2H) nuclei, is shown to offer newer opportunities to study molecular self-assembly in noncrystalline supramolecular systems.     

The temperature dependence of the solubility of oxygen in sea water according to the pulsed NMR data

The temperature dependences of the solubility of oxygen in distilled and sea water were obtained over the temperature range 0–90°C on the basis of proton spin—lattice relaxation measurements in degassed and not degassed samples. The temperature dependence of O₂ solubility is approximated by the sum of exponential functions according to not only relaxation measurement results but also literature data. The temperature dependence of the solubility of O₂ in distilled water can be written as the sum of two exponential functions with the predominance of the first component over the low-temperature interval. The best approximation for sea water has the form of the sum of three exponential functions, the relative contributions of the second and third components being approximately equal. The conclusion was drawn from the temperature dependences obtained that the main mechanism of the solution of oxygen in water was the filling of ice-like formation voids.     

The solubility of oxygen in sea water and solutions of electrolytes according to the pulse proton NMR data

The possibility of determining the content of dissolved oxygen (O₂) in distilled water, sea water, and aqueous solutions of electrolytes with errors of ～2% without preliminary instrument calibration was demonstrated. The reasons for different relaxation efficiency coefficients reported by various authors were analyzed. The results of the determination of the content of O₂ from the rate of spin-lattice relaxation in sea water and separate solutions of sea water components at 25°C depending on water salinity (S) up to 180‰ inclusive are presented. Noticeable changes in the steepness of the dependence of the content of O₂ on S at 80–90‰ were observed; these changes were related to the attainment of the boundaries of the complete solvation of the main sea water ions. The main reasons for the discrepancies between the oxygen salting out coefficients K _S found by various authors were explained, and the interrelation between the solubility of O₂ and ion hydration characteristics was revealed. The O₂ salting out constants for sea water and solutions of slats contained in sea water obtained from relaxation measurement data are given. The filling of “ice-like formation” voids was shown to be the main mechanism of the solution of O₂ in water and aqueous solutions of electrolytes.     

Methanol and acetonitrile associates in aqueous and chloroform solutions according to 1H NMR spectroscopic data

Association of methanol and acetonitrile in a nonpolar (CDCl₃) and polar (H₂O and D₂O) solvents was studied by ¹H NMR spectroscopy and quantum chemistry. The results were compared with the data obtained by decomposition of the spectral curves in the range 800–1100 nm by the independent component analysis (ICA) technique. The content of homoassociates consisting of four and two or three molecules in the case of methanol and acetonitrile, respectively, gradually increased with the amount of the organic solvent in solution. The aqueous solutions under study consisted of few associates of compositions 1: 1, 1: 2, and 1: 4.5 for acetonitrile and 1: 1 and 1: 3 for methanol (water: organic solvent). The quantum-chemical calculation of the NMR spectra of the particles existing in solution confirmed our conclusions about the structure of the solutions.     

Structure of vinyl ethers of a number of azoles according to1H and13C NMR data and quantum-chemical calculations

NMR¹H and¹³C spectra have been used to establish the conformational states of a number of azole vinyl ethers and to study the nature of the conjugation of the unshared pair of electrons of the oxygen atom with the azole and vinyl moieties. The H¹ NMR spectra of the vinyl ethers of indazole, 4,5-diphenylimidazole, benzimidazole, and 1,2,4-triazole revealed anomalous downfield shifts of the signal of the proton of the vinyl group, which are attributed to specific interactions, resembling weak hydrogen bonds, between these hydrogen atoms and the pyridine nitrogen. This conclusion agrees with the results of quantum-chemical calculations for the vinyl ether of indazole.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1031–1036, May, 1990.