Phase Diagram of the Ethylene Glycol–Dimethylsulfoxide System

The phase diagram of ethylene glycol (EG)–dimethylsulfoxide (DMSO) system is studied in the temperature range of +25 to ?140°C via differential scanning calorimetry. It is established that the EG–DMSO system is characterized by strong overcooling of the liquid phase, a glass transition at ?125°C, and the formation of a compound with the composition of DMSO · 2EG. This composition has a melting temperature of ?60°C, which is close to those of neighboring eutectics (?75 and ?70°C). A drop in the baseline was observed in the temperature range of 8 to ?5°C at DMSO concentrations of 5–50 mol %, indicating the existence of a phase separation area in the investigated system. The obtained data is compared to the literature data on the H₂O–DMSO phase diagram.     

Buffers for the Physiological pH Range: Studies of 4-(N-Morpholino)butanesulfonic Acid (MOBS) from 5 to 55 °C

In this study, we report the pH values of two buffer solutions without chloride ion and eight buffer solutions with NaCl with an ionic strength I=0.16 mol?kg^?1. Electromotive force (emf) techniques have been used to get the cell potentials at 12 temperatures from 5 to 55?°C, including 37?°C. An extended form of the Bates-Guggenheim convention is used in the entire ionic strength range, 0.04 to 0.16?mol?kg^?1. The residual liquid junction potentials (??E _j ) of the buffer solutions of MOBS have been estimated from previous measurements with a flowing junction cell. These values of ??E _j have been used for correction in order to ascertain the operational pH values of four buffer solutions of MOBS at 25 and 37?°C. These solutions are recommended as pH standards for physiological application in the pH range 7.4 to 7.7.     

A calorimetric setup for measuring heat effects of processes in solutions

A calorimetric setup was developed to determine the heat effects of chemical processes in solutions with a sensitivity of ～10^?5 K and an accuracy of temperature control in the thermostat of better than ±0.001 K. The performance of the calorimeter was tested by measuring the heat effects of solution of 1-propanol (m = 0.02–0.08 mol/kg), potassium chloride (m = 0.01–0.73 mol/kg), and L-phenylalanine (m = 0.0008–0.03 mol/kg) in water at 25°C.     

Dependence of the properties of Ce-Zr-Y-La-M-O systems on synthetic conditions and on the nature of the transition metal M (Mn,Fe, Co)

The effects of synthetic conditions, component ratios, and the nature of the transition metal on the physicochemical and catalytic properties of Ce-Zr-Y-La-M-O (M = Mn, Fe, Co) systems are studied. The Ce-Zr-Y-La-M-O samples precipitated at ～23°C and calcined at 600°C are single-phase and are solid solutions with a fluorite structure, which persists upon calcination at 1150°C. The Ce-Zr-Y-La-Fe(Co)-O samples precipitated at 70°C and calcined at 1150°C consist of two solid solutions, one cubic, and the other tetragonal. The specific surface area (S _sp) of the samples precipitated at ～23°C and calcined at 600°C increases in the order Ce-Zr-Y-La-O < Ce-Zr-Y-La-Mn-O < Ce-Zr-Y-La-Co-O ≈ Ce-Zr-Y-La-Fe-O. The specific surface area of the samples precipitated at 70°C is independent of M and is ～110 m²/g. Calcination at 1150°C reduces S _sp approximately by two orders of magnitude. The TPR of the unpromoted systems in H₂ proceeds in two steps at 600–650 and 750–840°C. The introduction of M decreases the reduction temperatures and gives rise to a lower temperature peak between 150 and 300°C. The most effective promoter is cobalt. The fluorite-type catalysts containing no noble metal are active in NO reduction (X _NO ≈ 100%) at T _react = 400–450°C. The cobalt-containing catalysts are the most active in the oxidation of CO (X _max = 28%) and hydrocarbons (X _max = 4.3%).     

Apparent molal volumes and heat capacities of some alkali halides and tetraalkylammonium bromides in aqueoustert-butanol solutions

The densities and volumetric specific heats of hydrochloric acid, alkali chlorides and bromides, and tetraalkylammonium bromides were measured in 0 to 40% by weighttert-butanol (t-BuOH) in water with a flow densimeter and a flow microcalorimeter. The effect of salt concentration was investigated in the case of NaCl. The apparent molal volumes and heat capacities and the derived transfer functions of the electrolytes from water tot-BuOH-water mixtures can be interpreted through solute-solute pair and triplet interactions by analogy with the transfer functions oft-BuOH from water to electrolyte solutions, with the salting-in and salting-out effects, and with the influence of electrolytes on the thermodynamics of micellization. At lowt-BuOH concentrations, the transfer functions seem to be reflecting primarily electrolyte-nonelectrolyte pair interactions. At intermediatet-BuOH concentration, wheret-BuOH associates, the hydrophobic bonding is enhanced by hydrophilic ions through a salting-out effect on monomers and by hydrophobic salts through triplet interaction (mixed association complexes). The Me ₄ NBr and Et ₄ NBr are intermediate electrolytes which do not have much effect on thet-BuOH hydrophobic bonding. At hight-BuOH concentrations the transfer functions tend to the values they would have in puret-BuOH.     

Kinetics and Mechanism of Monomolecular Heterolysis of Commercial Organohalogen Compounds: XLI. Solvent Effect on the Rate of 3-Methyl-3-chloro-1-butene Solvolysis. Correlation Analysis of Solvation Effects and Role of Solvent Nucleophilicity

The kinetics of 3-methyl-3-chloro-1-butene solvolysis at 25°C in MeOH, EtOH, BuOH, i-BuOH, PentOH, 2-PrOH, 2-BuOH, HexOH, OctOH, t-BuOH, t-PentOH, cyclohexanol, and allyl alcohol was studied by the verdazyl method; v = k[C₅H₉Cl], SN1 + E1 mechanism. The reaction rate shows a satisfactory correlation with the parameter of the solvent ionizing power E _T and is independent of the solvent nucleophilicity.     

Free-radical polymerization of guanidine acrylate and methacrylate and the conformational behavior of growing chains in aqueous solutions

Monomer salts based on acrylic acids and guanidine—guanidine acrylate and methacrylate—have been synthesized, and the kinetic features of their free-radical polymerization in aqueous solutions have been studied. When polymerization is carried out in organic solvents (methanol, ethanol, or dioxane), the system is heterogeneous over the entire range of monomer concentrations. In aqueous solutions, the reaction systems are homogeneous only at small initial monomer concentrations (less than 1.30 and 0.40 mol/l for guanidine acrylate and methacrylate, respectively; the ammonium persulfate concentration is 5 × 10^?3 mol/l; pH ～ 6.5; 60°C). At higher concentrations, microheterogeneity appears from small conversions (～1%). This phenomenon is associated with the coiling of growing polymer chains owing to associative interactions between guanidine groups occurring in the monomer solution and carboxyl groups of (meth)acrylate polymer units. In aqueous solutions over the entire range of monomer concentrations (0.2–2.5 mol/l), the kinetic orders are the same as in the case of corresponding acrylic acids. The effects of composition of reaction solutions on changes in the initial rate of polymerization and the conformational behavior of the systems under study have been ascertained.     

Thermodynamics of the In|In+3 Electrode in HCl + InCl3 Solutions

Electromotive force measurements have been made using the cell $$\mbox{In(s)}|\mbox{HCl }(m_{\mathrm{A}}),\mbox{InCl}_{3}(m_{\mathrm{B}}),\mbox{H}_{2}\mbox{O}|\mbox{AgCl, Ag}$$ in the ionic strength range of I=0.05, 0.1, 0.25, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 mol?kg^?1 at 25?°C. The value of E ^o, the standard potential of the In/In³⁺ electrode, has been determined at 25?°C. Our value of E ^o (?0.3371 V) at 25?°C obtained from our measurements is in good agreement with ?0.336 (Hakomori, J. Am. Chem. Soc. 52: 2372–2376, 1930) and ?0.3382 V (Covington et al., J. Chem. Soc. 4394–4401, 1963). The activity coefficients of InCl₃ as well as Harned interaction coefficients have been determined at 25?°C for each of the experimental ionic strengths at ionic strength fractions of 0.1, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and 0.9 of HCl. Harned’s rule for the salt is obeyed at I=0.05,0.1 and 0.25 mol?kg^?1 but the quadratic terms are needed for higher ionic strengths. These data, together with others for the activity coefficient of HCl in the same solutions, have been treated by the ion-interaction (Pitzer, Activity Coefficients in Electrolyte Solutions, CRC Press, 1991) equations in a previous publication.     

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.     

T-x diagram and transport properties of the GeSe-GeI2 solid electrolyte

The T-x diagram for the GeSe-GeI₂ system was plotted based on DTA, XRD, and conductivity data. The diagram features a simple eutectic and a limited region of solid solutions with prevalent GeSe content. It was established that, in the region of solid solutions, the properties of the GeSe-GeI₂ solid electrolyte are substantially dependent on the concentration of the GeI₂ dopant. The highest conductivity (10^?3?10^?4 S/cm at 150°C), lowest activation energy of electric conduction (0.3–0.4 eV), and lowest electronic (hole) transport numbers (10^?5?10^?7 at 150°C) at high ionic (～1.0) and cationic (0.9–1.0) transport numbers were observed at a GeI₂ concentration of 3–6 mol %. In the two-phase region, the transport properties (conductivity and activation energy of conduction) only slightly depend on the dopant concentration.     

Die Konzentration an freiem molekularem Jod in wäßrigen PVP-jodhaltigen Systemen und ihre Änderung mit der Temperatur

The concentration of free iodine and its variation in the temperature range 10–40°C has been determined by the potentiometric method in nine commercial PVP-iodine products as well as in pure aqueous solutions (1, 5 and 10%) of PVP-iodine of the type 17/12 and 90/04. In addition, aqueous solutions of PVP-iodine 30/06 of the same concentrations have been measured in the temperatur range 0–70°C. The commercial products showed a remarkably great spread in the concentration of free iodine (0.2–10 ppm at 25°C), which may be attributed to the different compositions, especially the ratio of total iodine to iodide as well as the kind and quantity of organic-pharmaceutical constituents. All tested PVP-iodine systems showed a significant—and unexpectedly similar—change of the concentration of free iodine by the temperature. The results concerning its relative alteration fit to an exponential function of the form $$\Delta \% [I_2 ]_{\Delta t} = 100[10^{(0.23 \pm 0.0026)\Delta t} 1]$$ which is valid from 10 to 40°C. Following this equation [I₂] increases about 5.4 resp. 100% if the temperature raises about 1.0 resp. 13.1°C. This increase of [I₂] must be considered in the application of PVP-iodine preparations as disinfectants or antiseptics at living tissues. Because of their higher temperature (c. 30–36°C) the applicated PVP-iodine preparations exhibit a significant higher [I₂] than at room temperature (Δt=10–16°C: Δ% [I₂]=70–130%). Therefore also a significant higher degerming efficiency can be expected compared toin vitro experiments, which are conducted in general at room temperature.     

Buffer Standards for the Physiological pH of the Zwitterionic Compound, HEPPSO from 5 to 55 °C

The values of the thermodynamic second dissociation constant, pK ₂, and related thermodynamic quantities of N-(2-hydroxyethyl)piperazine-N′-2-hydroxypropanesulfonic acid (HEPPSO) have already been reported from 5 to 55?°C, including 37?°C, by the emf method. This paper reports the results for the pH of one chloride-free buffer solution containing the composition: (a) HEPPSO (0.08 mol?kg^?1)+NaHEPPSO (0.04 mol?kg^?1). The remaining seventeen buffer solutions contain a saline medium of ionic strength I=0.16 mol?kg^?1, matching closely that of physiological fluids. Conventional pH values, denoted as pa _H, for all eighteen buffer solutions from 5 to 55?°C have been calculated. The operational pH values, designated as pH, with residual liquid-junction corrections for five buffer solutions, one without NaCl, and four with buffer solutions in saline media of I=0.16 mol?kg^?1 are recommended as pH standards in the range of physiological application. These are based on the NBS/NIST standard scale for pH measurements.     

Effects of pressure on the behavior of (hydroxypropyl)cellulose in aqueous solution

The effects of pressure and temperature on the phase behavior of aqueous solutions of (hydroxypropyl)cellulose (HPC) were in¶vestigated at low and high concentrations. In dilute solutions, the transition temperature (T _t) as measured by apparent light scattering increased with an increase in pressure at lower pressures, but decreased with increasing pressure above 100?MPa. At lower temperatures, the transition pressure (P _t) increased slightly with increasing temperature, but decreased with at temperatures above 10–15?°C. Both T _t and P _t showed a moderate polymer-concentration dependence and they also showed strong concentration dependence on salt; T _t and P _t decreased with increasing concentrations of KCl and K₂SO₄, whereas the addition of KI or KSCN increased T _t and P _t. The apparent absorbance of concentrated solutions (62.5%) of HPC, in a cholesteric (chiral nematic) mesophase, was also measured. The spectrum shifted to a longer wavelength under high pressure. These results could be explained by assuming that the helicoidal pitch was increased under elevated pressure, probably due to a decrease in the angle between the two semiflexible and twisted HPC molecules in adjacent planes under high pressure.     

Effect of autoclaving on zinc oxide in the presence of sulphate ions

The effect of autoclaving a zinc oxide preparation containing SO^2?₄ under 5 and 10 atmospheres is studied by combining X-ray diffraction, differential thermal analysis, thermogravimetry and IR spectroscopy. Textural measurements are also carried out on the parent samples and those produced in the temperature range 200–1000°C.A new phase of a basic carbonates?ulphate, including ammonia in its coordination shell, is observed in the original preparation and having its d distances at 11.060, 8.954 and 2.714 Å. This is transformed to another phase at ～180°C which is also the main phase characterizing the autoclaved samples, and belongs to a basic zinc oxide—sulphate possessing d distances at 7.055, 2.468 and 2.805 Å. Autoclaving the oxide preparation under 10 atm gives hexagonal zinc oxide of high purity and crystallinity at 1000°C. An empirical formula is given for the oxide preparation which describes the different decomposition stages observed. At ～390°C, a reversible reduction process comprising oxygen evolution is observed.Autoclaving increases the area of the parent oxide and at temperatures below 600°C is a function of the structural changes. The autoclaving pressure is insignificant ?600°C.Pore structure analysis showed all the samples to be predominantly mesoporous, coexisting with some micropores except that autoclaved under 5 atm and heated at 250°C which is predominantly microporous. Autoclaving under 5 atm causes narrowing of the pores for products below 600°C. Autoclaving has little effect on the average pore radius ?600°C.Evaluation of the average pore radius from the constructed t-curves for parallel-plate pore idealization is discussed.     

PMR studies on the structures of water-ethyl alcohol mixtures

The PMR signals of each individual proton species present in water-ethanol mixtures were analyzed throughout the entire range of composition. Chemical shifts and line shapes were studied as a function of ethanol mole fraction (f), temperature, and working frequency, from ?50 to +80°C, at 60, 100 and 220 MHz.The experimental results are discussed in terms of possible mechanisms of molecular aggregation in the various regions of ethanol concentration. There is evidence that addition of small quantities of ethanol to water promotes H-bonding association among water molecules (at t = 20°C, f ? 0.08). At intermediate ethanol concentrations (at t = 20°C, 0.25 ? f ? 0.75), the linear dependence of f exhibited the chemical shift of the water signal evidences that the water structures are progressively disrupted by increasing alcohol concentration. At the higher ethanol concentration (at 20°C, f ? 0.8) the substantial independence of both ethanol and water O$\text{H}$ chemical shifts from the concentration suggests that water molecules either coordinate or/and are incorporated into the linear aggregates peculiar to pure ethanol.The width of the f range in which the hydroxyl signals coalesce is progressively reduced with decreasing temperature.We qualitatively tested the applicability of an adiabatic two-site exchange model to the hydroxyl protons of these mixtures. This model is correctly applicable to solutions at both extremes of the concentration range, but it cannot describe the linewidth behaviour of the mixtures at intermediate concentrations.     

Effect of two Macrocyclic Aminals on the Temperature of Maximum Density of Water

Densities of several aqueous solutions of two macrocyclic aminals, 1,3,5,7-tetraazatricyclo[3.3.1.1(3,7)]decane (HMT) and 1,3,6,8-tetraazatricyclo[4.4.1.1(3,8)]dodecane (TATD) at concentrations from 0.001 up to 0.2?mol?kg^?1 (molal) between 2.0 and 5.0?°C every 0.5?°C, were obtained using a magnetic float densimeter designed, constructed and calibrated according to the available literature. The effect of the two solutes on the temperature of the maximum density of the water ?? was established. The dependence of density with molality is linear in the entire range of concentration, at all temperatures, and the dependence of ???? with composition, for both aqueous systems, does not follow the Despretz law. Based on the variation of ???? with composition, the solutes are classified as liquid water structure breakers; the effect of TATD on the solvent is greater. The results are discussed in terms of solute?Csolvent and solute?Csolute interactions.     

Temperature responsive carbon nanotubes/poly(N-isopropylacrylamide)-modified electrodes for electrochemical selective determination of dopamine, uric acid, and ascorbic acid

Poly(N-isopropylacrylamide)(PNIPAAm) with a lower critical solution temperature of about 32?°C was used as matrix to prepare temperature responsive carbon nanotubes (CNT) and functionalized CNT (fCNT) composites to modify glassy carbon electrode (GCE) as working electrode for electrochemical selective detection of dopamine, uric acid, and ascorbic acid. The GCE modification temperature (25 and 37?°C, denoted as 25f and 37f), working temperature (25 and 37?°C, denoted as 25aq and 37aq), and the type of CNT (CNT and fCNT) were found to significantly affect the electrocatalytic activity of the composites toward redox reactions of Fe(CN) ₆ ^3?/4? as a probe and the selective detection ability for the three analytes. The fCNT/PNIPAAm composite with the 25f–37aq temperature combination exhibited strong electrocatalytic activity and highly selective detection ability for the three analytes. In contrast, the same composite with the other three combinations (25f–25aq, 37f–25aq, and 37f–37aq) and the CNT/PNIPAAm composite with all four combinations exhibited insignificant electrocatalytic activity and no selective detection ability.     

Kinetic studies of colloidal crystallization of thermo-sensitive gel spheres of poly(N-isopropylacrylamide)

Crystal growth rate coefficients, k of the colloidal crystallization of thermo-sensitive gel spheres of poly(N-isopropylacrylamide) were measured from the time-resolved reflection spectroscopy mainly by the inverted mixing method in the deionized state. Crystallization of colloidal silica spheres were also measured for comparison. The k values of gel and silica systems increased sharply as the sphere concentration and suspension temperature increased. The k values of gel system were insensitive to the degree of cross-linking in the range from 10 to 2?mol% of cross-linker against amount of the monomer in mole and decreased sharply when the degree of cross-linking decreased further to 0.5?%. The k values increased as gel size increased. The k values of gel systems at 20?°C were small and observed only at the very high sphere concentration in volume fraction, whereas those at 45?°C were high but smaller than those of silica systems. Induction time (t _i) after which crystallization starts, increased as the degree of cross-linking increased and/or the gel size decreased at any temperatures, when comparison was made at the same gel concentration. The t _i values at 45?°C were high and decreased sharply with increasing sphere concentration, whereas those at 20?°C were high only at the very high sphere concentrations. Significant difference in the k and t _i values between the soft gels and hard silica spheres was clarified. These kinetic results support that the electrical double layers play an important role for the gel crystallization in addition to the excluded volume of gel spheres. It is deduced further that the electrical double layers of the gel system form from the vague interfaces (between soft gel and water phases) compared with those of typical colloidal hard sphere system.     

Solvent influence on complex formation between Cd<Superscript>2+</Superscript> and 2-hydroxy-1,4-naphthoquinone in binary mixed nonaqueous solvents at 15–45°C

The complexation reaction of Cd²⁺ cation with 2-hydroxy-1,4-naphthoquinone (HNQ) was studied in acetonitrile (AN), 2-PrOH, ethyl acetate (EtOAc), EtOH, dimethylformamide (DMF) and in binary solutions AN–2-PrOH, AN–DMF, AN–EtOH, and AN–EtOAc using conductometric method at 15–45°C. The conductance data show that the stoichiometry of the Cd²⁺ complex with HNQ in all solvent systems is 1 : 1. In the pure solvents the stability of the complex changes in the order AN > 2-PrOH > EtOH > DMF. The stability of the complex at 25°C in the studied mixtures changes in the following order : AN?EtOAc > AN?2-PrOH > AN?EtOH > AN?DMF. These orders are affected by the nature and composition of the solvent systems and by the temperature. From the temperature dependence data, the thermodynamic functions values (ΔH° and ΔS°) for the complex formation were calculated.     

Sorption and addition of bromine from aqueous solutions on cis-1,4-polyisoprene

The sorption of bromine from bromine water on cis-1,4-polyisoprene film and the initial stages of bromination are studied at concentrations of 0.002–0.1 mol/l and temperatures of 15–35°C. The diffusion coefficient of bromine into natural rubber (NR) is 1.3–2.0 × 10^?6 cm²/sec for the total sorption and 5–13 × 10^?7 cm²/sec for the irreversible sorption. The partition coefficient of bromine between water and rubber increased from 17.3 at 15°C to 37.1 l/kg at 35°C. The chemical potential, enthalpy and change in entropy of partition are, at 25°C, respectively: ?1.9 kcal/mol, 6.6 kcal/mol and 28.4 cal/mol. K. The irreversible sorption is due to a charge-transfer complex between bromine molecules and double bonds of the rubber. The complex is the first stage of the addition reaction, which becomes noticeable at concentrations above 0.012 mol/l. With increasing bromine concentration the concentration of the complex decreases and the added bromine increases. The charge transfer complex appears to change the conformation of the cis-NR chains so that the bromine addition occurs in the trans-conformation, as shown by FT–IR spectra. The bromination is accompanied by a marked crystallization effect as illustrated by thermal analysis and WAXS measurements.