ESR study of the generation and decay of peroxy radicals in mechanically destructed polyamide 6

Polyamide 6 has been mechanically destructed in vacuo. At -70°, the ESR spectrum corresponds to the sum of the component spectra of three radicals NH?HCH₂, ·CH₂NHCO, and ·CH₂CONH. After introducing air into the ampoule, the spectrum changes even at -70°; the changes have been studied up to 0°. The spectrum of the peroxy radical ROO· (with line width 1.57 mT, g₁ = 2.0089 and g_| = 2.0301) predominates.     

Molecular complex formation between l-phenylalanine and 18-crown-6 in H2O–DMSO solvents studied by titration calorimetry at T = 298.15 K

The standard thermodynamic parameters (Δ_r G°, Δ_r H°, TΔ_r S°) of the reaction of molecular complex formation between 18-crown-6 ether (18C6) and l-phenylalanine (Phe), [Phe18C6], have been obtained from calorimetric titration experiments carried out by means of the microcalorimetric system TAM III (TA Instruments, USA) at T = 298.15 K in water–dimethylsulfoxide (H₂O–DMSO) solvents. Results show that the increase of the DMSO concentration in the mixed solvents brings about an increase of the [Phe18C6] complex stability and of the exothermicity of the reaction of complex formation.     

The solvation of L-serine in mixtures of water with some aprotic solvents at 298.15 K

The integral enthalpies of solution Δ_sol H ^m of L-serine in mixtures of water with acetonitrile, 1,4-dioxane, dimethylsulfoxide (DMSO), and acetone were measured by solution calorimetry at organic component concentrations up to 0.31 mole fractions. The standard enthalpies of solution (Δ_sol H°), transfer (Δ_tr H°), and solvation (Δ_solv H°) of L-serine from water into mixed solvents were calculated. The dependences of Δ_sol H°, Δ_solv H°, and Δ_tr H° on the composition of aqueous-organic solvents contained extrema. The calculated enthalpy coefficients of pair interactions of the amino acid with cosolvent molecules were positive and increased in the series acetonitrile, 1,4-dioxane, DMSO, acetone. The results obtained were interpreted from the point of view of various types of interactions in solutions and the influence of the nature of organic solvents on the thermochemical characteristics of solutions.     

Electrochemical kinetics of gold electrodes in SCN−/dimethylsulfoxide solutions

The electrochemical behaviour of the Au/SCN^? (DMSO) interface is studied at 25°C≤T≤65°C, by means of the triangular potential sweep technique and the RDE. Within a relatively limited potential range the main electrode process is:3 SCN^?=(SCN)₃^?+2e The kinetics of this reaction involves a mixed control. At higher potentials the electrodissolution of the base metal takes place. Side reactions occurring there make the overall process rather complex. The electrochemical behaviours of the Au/SCN^? (DMSO) and Au/SCN^? (ACN) are compared.     

Elucidating Interactions between DMSO and Chelate‐Based Ionic Liquids

The C?D bond stretching vibrations of deuterated dimethyl sulfoxide ([D₆]DMSO) and the C₂?H bond stretching vibrations of 1,1,1,5,5,5‐hexafluoropentane‐2,4‐dione (hfac) ligand in anion are chosen as probes to elucidate the solvent–solute interaction between chelate‐based ionic liquids (ILs) and DMSO by vibrational spectroscopic studies. The indirect effect from the interaction of the adjacent S=O functional group of DMSO with the cation [C₁₀mim]⁺ and anion [Mn(hfac)₃]^? of the ILs leads to the blue‐shift of the C?D stretching vibrations of DMSO. The C₂?H bond stretching vibrations in hfac ligand is closely related to the ionic hydrogen bond strength between the cation and anion of chelate‐based ILs. EPR studies reveal that the crystal field of the central metal is kept when the chelate‐based ILs are in different microstructure environment in the solution.     

Thermomechanical investigation of a thick film of aniline-formaldehyde copolymer and poly(methyl methacrylate)

A thick film of aniline-formaldehyde copolymer and PMMA is synthesized via dispersion of aniline-formaldehyde copolymer powder as filler particles in PMMA with two different concentrations. Variation of the complex elastic modulus and mechanical loss factor (tanδ) with temperature is studied. It is observed that the complex elastic modulus decreases with temperature owing to thermal expansion of films. On the other hand, tanδ increases up to a characteristic temperature beyond which it shows a decreasing trend toward melting. Transition temperature T _g of sample S₁ (pure PMMA) is found to be 80°C. In sample S₂ (1 wt % aniline formaldehyde copolymer), the peak of tanδ at a lower temperature (66°C) corresponds to glass transition temperature T _g of the PMMA matrix, while the peak of tanδ at a higher temperature (107.8°C) corresponds to T _g of a polymer chain restricted by filler particles of aniline-formaldehyde copolymer. A further increase (10 wt % aniline-formaldehyde copolymer) in the concentration of filler particles of aniline-formaldehyde copolymer results in a more compact structure and a shift of T _g to a higher temperature, 122.2°C. This shift in the glass transition temperature of thick films of aniline-formaldehyde copolymer and PMMA is dependent upon the concentration of filler particles in the sample.     

Temperaturabhängige Phasenumwandlungen natriumreicher Amalgame

Temperature Dependent Phase Transitions of Sodium-rich Amalgams Starting from thermoanalytical measurements the temperature dependent phase transitions of the microcrystalline, sodium rich amalgams Na 8 Hg₃ (? Na_2.67Hg) and Na₃Hg are investigated using a fast, position sensitive X-Ray detector in combination with a modified counter Guinier system. Near the melting point (64°C) Na₈Hg₃ shows two phase transitions. At 54°C α-Na 8 Hg₃ forms a slightly distorted monoclinic defect variant of the cubic Li₃Bi-structure (β-Na₈Hg₃). At 62°C this modification transforms into the corresponding undistorted cubic phase (γ-Na 8 Hg₃). The increase of symmetry results mainly from the fact, that small deviations of the mercury atoms from the positions of an ideal close packing vanish due to strong thermal vibrations. The “literature-melting point” of Na₃Hg (33°C) corresponds to a phase transition from α-Na₃Hg (hexagonal, modified Na₃As type) into β-Na₃Hg (monoclinic distorted Li₃Bi type, corresponding to β-Na 8 Hg₃). The actual melting point of Na₃Hg is 59°C.     

Effect of solvation on the thermodynamics of the formation of molecular complexes of 18-crown-6 ether with glycine in water-dimethylsulfoxide solutions

Complexation of the 18-crown-6 ether (18C6) with glycine (Gly) in mixed H₂O-DMSO solvents with the composition of 0.1, 0.2, and 0.25 mole fraction of DMSO (T = 298.15 K) was studied calorimetrically. Thermodynamic characteristics of the reaction of the formation of the molecular Gly18C6 complex (Δ_r G°, Δ_r H°, TΔ_r S°) were calculated from the calorimetric data. It was established that the change in the stability of the Gly18C6 complex is mainly determined by the predominance of the enthalpy component of the Gibbs energy over the entropy component. It was shown during the analysis of the enthalpy contributions of the reagents to the enthalpy of the reaction of the formation of Gly18C6 that the change in the enthalpy of the reaction upon a change the solvent composition was due to changes in the solvation state of 18C6.     

An independent investigation of the crystal structure of 1,8-dinitronaphthalene (orthorhombic form) at 22 and 97°C

The crystal and molecular structure of the orthorhombic form of 1,8-dinitronaphthalene, C₁₀H₆N₂O₄, has been reinvestigated at 22°C and examined at 97°C using single-crystal diffractometer data in order to throw some light on the structural aspects of the polymorphism of the title compound. The space group of the crystal is P2₁2₁2₁ with a = 11.375 (1), b = 14.974 (5), c = 5.388 (1) Å at 22°C and a = 11.475 (1), b = 15.002 (1), c = 5.425 (6) Å at 97°C. Z = 4 at both temperatures. The data, collected with CuK_α radiation, were refined by full-matrix least squares to R = 0.049 for 1087 reflexions (22°C) and R = 0.061 for 1078 reflexions (97°C). The structure was found to be in agreement with that determined by Z. A. Akopian, A. I. Kitaigorodskii, T. J. Struchkov (Zh. Strukt. Khim.6, 729 (1965)). Changes occurring on heating to a temperature of 97°C, which is close to the transition temperature (of c → pc type) 100–105°C, suggest that the possible mechanism of the phase transition is that of the displacive transformation of secondary coordination. Anistotropic temperature factors of the majority of atoms increased by ca. 50% with no particular direction of atom vibrations being distinguished.     

Effet sterique sur les vitesses de transfert protonique: cyclohexanols substitues dans le dimethylsulfoxyde

Steric effects on proton transfer from, and to, hydroxylic oxygen have been studied in a series of seventeen α-methyl and a-benzyl cyclohexanols in anhydrous DMSO, under both acid and base catalysed conditions, using dynamic MNR techniques. The protonation rate constants (k₁ ? 10⁶ M^-1 s^-1 at 25°C) obey a Taft-Ingold relationship, containing only a steric contribution E_s = E_s^OH + E_s^α, where: E_s^OH = 0 or 0.15 for an axial or equatorial hydroxyl respectively and E_s^α = ?0.070 (or ?0.115) for substituting an α-hydrogen by a methyl (or benzyl) group. An equatorial hydroxylic function is therefore 40% more reactive than its axial homologue. These kinetic data are fairly consistent with structural information resulting from IR spectroscopy (v_co and v_OH vibrations) and from NMR (hydroxylic chemical shifts and coupling constants).     

The polarized absorption spectrum of 5-methyl indole in polyethylene and polyvinylalcohol films

The stretched film technique has been used to resolve the two overlapping ¹L_a and ¹L_b transitions of indole. 5-Methyl indole was studied as a model compound in two polymer matrices, polyethylene (PE) and polyvinylalcohol (PVA). The directions of the transition moments with respect to the long molecular axis are found to be in PE − 10° and +22° for ¹L_a and ¹L_b, respectively. These angles are found to be −25° and +29° in PVA. ¹L_a has two prominent vibrations in PE at 2040 and 2895 cm⁻¹ from the origin. ¹L_b has four prominent vibrations in PE at 761, 1308, 1937 and 3196 cm⁻¹ from the origin. In PVA, ¹L_a has two prominent vibrations at 2149 and 2874 cm⁻¹ from the origin and ¹L_b has four prominent vibrations at 1049, 1352, 2229 and 3196 cm⁻¹ from the origin.     

The Properties of Solutions of Isoniazid in Water and Dimethylsulfoxide

The density, viscosity and conductivity of binary mixtures of the front line antitubercular drug isoniazid (INH), in aqueous solution and dimethylsulfoxide (DMSO) solution, were determined at various temperatures (25, 37 and 55?°C) up to 0.3 mol?L^?1 of INH. The apparent molar volumes were calculated from the density data. In the INH + water system the apparent molar volume of INH changed smoothly, whereas in the INH + DMSO system it passes through a maximum. Also, both systems showed pronounced maxima in their viscosity and conductivity isotherms. In addition, UV?CVis, FT-IR and ¹H NMR spectroscopy were performed on the solutions. On the basis of this data, the predominant molecular interactions occurring between INH and water and between INH and DMSO were found to be hydrogen bonds. Furthermore, the susceptibility profile of DMSO, INH and its combination was studied against M. tuberculosis H₃₇Rv and the minimum inhibitory concentration (MIC) determined. The results suggest a synergistic effect of INH at sub-MIC concentrations and DMSO.     

Low temperature relaxation in polypyromellitimide

The effect of heat treatment at temperatures above 300°C on the low temperature relaxation of poly(4,4′-oxydiphenylenepyromellitimide) (Kapton H-film) was studied by wide-line nuclear magnetic resonance (NMR), mechanical, and dielectric measurements. In the NMR line spectrum of the as-received film, a narrow component above ?60°C and a broad component which begins to narrow at about ?100°C were observed. It is proposed that the narrow component is associated with absorbed water, because it disappeared in the heat-treated film at 300°C in N₂. On the other hand, the behavior of the broad component was not influenced by heating to 300°C in N₂. Mechanical and dielectric loss peaks were observed at ?75°C (11 Hz) and ?65°C (1 kHz), respectively, in the as-received film. These loss peaks did not change in intensity with heating to 300°C in N₂. It is proposed that the mechanical and dielectric loss peaks corresponding to the narrowing of the NMR broad component are associated with the local-mode motion of the diphenylether portion of the polypyromellitimide chain. It was found that crosslinks are formed by heating to 374°C in air through coupling of the diphenylether portions of the molecular chains. With the formation of crosslinks the dielectric loss peak shifted toward higher temperature and the intensity decreased through restriction of the local-mode motion of the diphenylether portion of the molecular chain.     

Ionization enthalpy of benzoic acid in water—dimethylsulfoxide mixtures

The ionization enthalpy of benzoic acid has been measured calorimetrically at 25°C in H₂ODMSO mixtures ranging from pure water to a maximum DMSO molar ratio X_DMSO = 0.80. With the increase of DMSO content, the ionization becomes more and more endothermic, and for X_DMSO = 0.8 the ionization enthalpy is about 6 kcal mol^?1 higher than in water. By also measuring the solution enthalpy of crystalline benzoic acid in the mixtures, it has been shown that the solvation of the undissociated molecule is the main cause for the increase of the dissociation enthalpy. A comparison has been made between the relative enthalpies of benzoic and hydroxide ions in H₂ODMSO mixtures.     

Synthesis and structure of platinum complexes [Ph4P]+[PtCl3(DMSO)]− and [Ph4P]+[PtCl5(DMSO)]−

The reaction of tetraphenylphosphonium chloride with an equimolar amount of potassium tetrachloroplatinate or hexachloroplatinic acid in dimethyl sulfoxide gave the complexes [Ph₄P]⁺[PtCl₃(DMSO)]^? (I) and [Ph₄P]⁺[PtCl₅(DMSO)]^? (II), respectively. The phosphorus atoms in the cations have tetrahedral environment, the CPC angles and P-C distances 105.63(13)°–112.13(14)°, 1.795(3)–1.797(3) Å I) and 105.7(3)°–112.9(3)°, 1.783(7)–1.791(6) Å II). The platinum coordination polyhedra in the anions [PtCl₃(DMSO)]^? and [PtCl₅(DMSO)]^? are distorted square (Pt-S, 2.1937(8); Pt-Cl, 2.2894(10)–2.3024(10) Å; trans-angles: SPtCl, 177.38(4)°; ClPtCl, 175.40(4)°) and octahedron (Pt-S 2.291(2) Å; Pt-Cl, 2.312(2)–2.334(2) Å, trans-angles: SPtCl, 178.28(9)°; ClPtCl, 178.80(9)° and 178.88(8)°).     

Bromo dimethyl sulfoxide osmium(II) complexes. Molecular structure of cis,fac-[OsBr2(dmso-S)3(dmso-O)]

Bromo dimethyl sulfoxide osmium(II) complexes were synthesized: trans-[OsBr₂(dmso-S)₄] (1) was obtained by the reaction of K₂[OsBr₆] with DMSO in the presence of SnBr₂ at 100°C and cis,fac-[OsBr₂(dmso-S)₃(dmso-O)] (2) was prepared by thermal isomerization of 1 in a DMSO solution at 150°C. The coordination mode of DMSO molecules was determined by IR and ¹H and ¹³C NMR spectroscopy. X-ray diffraction analysis showed that compound 2 crystallizes in the monoclinic system, space group P2₁/n; a = 8.4711(5) Å, b = 27.7876(15) Å, c = 8.5569(5) Å, β = 115.7110(10)°; Z = 4. The coordination polyhedron of osmium is a distorted octahedron; the osmium environment is formed by two cis-arranged bromine atoms and three fac-S-coordinated and one O-coordinated DMSO molecules. The interconversion of complexes in solutions was studied by UV/Vis and ¹H and ¹³C NMR spectroscopy. In chloroform and DMSO, complex 2 isomerizes to cis-[OsBr₂(dmso-S)₄] and (in the light) to 1. The complexes trans-[OsX₂(dmso-d₆)₄], where X = Cl, Br, were isolated from DMSO-d ₆ and characterized by the IR spectra.     

Thermal,structural, and impedance analysis of nanocrystalline magnesium chromite spinel synthesized via hydrothermal process

Nanocrystalline magnesium chromite spinel was synthesized through hydrothermal reaction of metal nitrate solutions in stoichiometric amount at different pH, temperature and time intervals. The synthesized products were characterized for crystallinity, phase identification, and surface morphology by X-ray diffraction (XRD) and scanning electron microscope (SEM). XRD patterns showed that as-synthesized product remained amorphous up to 250 °C. However, well-crystallized magnesium chromite spinel structure is formed after calcination at 850 °C. Rietveld refinement study confirms the formation of single-phase cubic structure MgCr₂O₄ with lattice parameter a = 8.3347 Å, and Fd3m space group. The as-processed MgCr₂O₄ products showed extensive XRD line broadening, and the mean crystallite size of such crystals was found to be mainly in size range of 85–124 nm. Surface SEM images of calcined specimens revealed that the matrix is uniform, and no separation of secondary phase was detected. Thermal stability was examined by thermogravimetry (TG), differential thermal analysis (DTA), and differential scanning calorimetry. TG/DTA reveals that MgCr₂O₄ is thermally stable above 700 °C. Fourier transform infrared (FTIR) spectra studies shows two strong bands, one around 600 cm^?1 which is attributed to the intrinsic vibrations of tetrahedral and other at 400 cm^?1 is due to octahedral one. FTIR confirms the formation of metal oxides. The bandgap energy was estimated by absorption spectroscopy in ultraviolet–visible range and was found to be 0.693 eV for MgCr₂O₄ specimen sintered at 1,000 °C. Isothermal shrinkage characteristic and coefficient of thermal expansion were determined by dilatometry. The powder specimens showed excellent densification at 1,250 °C temperature and uniformly fine grain sintered ceramics (>90 % relative density) with submicron grain size (2–5 μm) were obtained after sintering at 1,000–1,250 °C. Impedance studies were carried out at room temperature and equivalent circuit model (R ₁ Q ₁) (R ₂ Q ₂) (R ₃ Q ₃) is used to explain different relaxation processes. We report largest impedance values i.e., 6.74 × 10⁸ Ω, reduced dielectric constant (≈1.0), and low tangent loss (0.8) for MgCr₂O₄ sintered at 1,250 °C.     

The molecular structure and conformation of acetamides in the vapour phase: Part III. Thioacetamide (ethanethioamide)

Thioacetamide has been studied by electron diffraction in the gas phase, utilizing a new nozzle construction and using a broad electron beam. The molecule has C_s symmetry, and one C-H bond eclipses the CS bond. The most important structural parameters are: r_g(C-N) = 135.6(3) pm, r_g(C—C) = 151.2(4) pm, r_g(CS) = 164.7(3) pm,∠_αCCS = 122.9(3)° and ∠_αCCN = 114.8(4)°. Parenthesized values are one standard deviation where correlation among data and uncertainty in the electron wavelength have been included. The methyl barrier, V₃, is found from the electron diffraction data to be 4.56 kJ mol^?1. This corresponds to a torsional frequency of 131 cm^?1.     

Raman and Infrared Spectra for All-trans-astaxanthin in Dimethyl Sulfoxide Solvent

The Raman and infrared spectra of all-trans-astaxanthin (AXT) in dimethyl sulfoxide (DMSO) solvent were investigated experimentally and theoretically. Density functional cal-culations of the Raman spectra predict the splitting of the υ₁ band into υ_1-1 and υ_1-2 compo-nents. The absence of splitting in Raman experimental spectra is ascribed to the competition between the two symmetric C=C stretching vibrations of the backbone chain. The υ₁ band is very sensitive to the excitation wavelength: resonance excitation stimulates the higher-frequency υ_1-2 mode, and off-resonance excitation corresponds to the lower-frequency υ_1-1 mode. Analyses of the intramolecular hydrogen bonding between C=O and O-H in the AXT/DMSO system reveal that the C4=O1...H1-O3 and C4'=O2...H2-O4 bonds are strengthened and weakened, respectively, in the electronically excited state compared with those in the ground state. This result reveals significant variations of the AXT molecular structure in different electronic states.     

Molecular structure of carbonyl fluoride as studied by gas electron diffraction and microwave data

The molecular structure of carbonyl fluoride has been determined by electron diffraction. The results have been used in conjunction with the rotational constants reported by Carpenter in a combined structure analysis. The values so obtained are r_z (C=O) = 1.1717 ± 0.0013 Å, r_z (C-F) = 1.3157 ± 0.0005 Å, and ∠_zF-C-F = 107.71 ± 0.08°. These agree with the corresponding parameters estimated by Carpenter from the rotational constants alone. The effective constants, α₃, representing the cubic anharmonicity of bond stretching vibrations have been estimated.