Local structure of ionic liquid–monohydric alcohol solutions

The method of molecular dynamics is used to investigate the effect of monohydric alcohols on the formation of the local structure of ionic liquids based on the dimethylimidazolium cation at T = 400 K. The intermolecular interaction energies are analyzed to find that the increase in the length of the alkyl chain in the alcohol molecule reduces the influence of the solute molecule on the formation of the local structure of the dmim⁺/Cl^––solute molecule systems. An analysis of the radial distribution function shows that the change in the structure and physical characteristics of the solute molecule does not affect the interaction between the hydroxyl group proton of the alcohol molecule and the ionic liquid anions, whose interactions form the hydrogen bond H^alcohol…Cl^– with a length of 2.3 Å.     

Luminescent-probe study of the structure of alcohol — Water solutions

Journal of Structural Chemistry -     

Micellisation thermodynamics of sodium lauroylsarcosinate in water–alcohol binary mixtures

Aggregation of sodium lauroylsarcosinate (SLS) in aqueous solutions of methanol, ethanol, propanol and ethylene glycol at 288–313 K has been determined from conductivity measurement in the range 0–20% v/v of additives. The precise values of the critical micelle concentration (CMC) and the degree of counter-ion dissociation of micelles were obtained at each temperature by fitting the specific conductivity-surfactant concentration curve to the integrated form of the Boltzmann-sigmoid equation. The CMC was found to increase with increase in additive concentrations in the case of methanol and ethylene glycol, while it decreases with increase in ethanol and propanol concentration. The equilibrium model of micelle formation was applied to obtain the thermodynamic parameters of micellisation. The Gibbs free energies were observed to vary only slightly with temperature and additive concentrations. Enthalpy–entropy compensation was observed for all the systems with a constant compensation temperature of ≈300 K and negative compensation enthalpy.     

Iron speciation in human cancer cells by K-edge total reflection X-ray fluorescence–X-ray absorption near edge structure analysis

X-ray absorption near edge structure (XANES) analysis in combination with synchrotron radiation induced total reflection X-ray fluorescence (SR-TXRF) acquisition was used to determine the oxidation state of Fe in human cancer cells and simultaneously their elemental composition by applying a simple sample preparation procedure consisting of pipetting the cell suspension onto the quartz reflectors.XANES spectra of several inorganic and organic iron compounds were recorded and compared to that of different cell lines. The XANES spectra of cells, independently from the phase of cell growth and cell type were very similar to that of ferritin, the main Fe store within the cell. The spectra obtained after CoCl₂ or NiCl₂ treatment, which could mimic a hypoxic state of cells, did not differ noticeably from that of the ferritin standard. After 5-fluorouracil administration, which could also induce an oxidative-stress in cells, the absorption edge position was shifted toward higher energies representing a higher oxidation state of Fe. Intense treatment with antimycin A, which inhibits electron transfer in the respiratory chain, resulted in minor changes in the spectrum, resembling rather the N-donor Fe-α,α′-dipyridyl complex at the oxidation energy of Fe(III), than ferritin. The incorporation of Co and Ni in the cells was followed by SR-TXRF measurements.     

Half or full core hole in density functional theory X-ray absorption spectrum calculations of water?

We analyze the performance of two different core-hole potentials in the theoretical modeling of XAS of ice, liquid and gas phase water; the use of a full core-hole (FCH) in the calculations, as suggested by Hetenyi et al. [B. Hetenyi, F. De Angelis, P. Giamozzi and R. Car, J. Chem. Phys., 2004, 120(18), 8632], gives poor agreement with experiment in terms of intensity distribution as well as transition energies, while the half core hole (HCH) potential, in the case of water, provides a better compromise between initial and final state effects, leading to good agreement with the experimental data.     

The shear hysteresis in lamellar structure of surfactant–water binary system

We study the shear effect on the lamellar structure of surfactants in water using dissipative particle dynamics simulations. Starting from a lamellar structure without shear flow, we increase the shear rate and then decrease it stepwisely. A weak shear changes the lamellar plane to be parallel to the shear direction though the lamellar normal has no specific direction on the plane normal to the shear direction. By increasing the shear rate, the lamellar normal eventually flips to the vorticity direction regardless of the initial configuration. Lamellar normal would stay along the vorticity direction on decreasing the shear rate. The hysteresis is also found in shear-stress. By varying the shear rate, the time needed to reach the final unique state is significantly shortened compared with that observed with a constant shear rate. We find a correlation between the excess shear-stress and the tilt angle of surfactant in lamellar.     

Thermodynamic characteristics of acid–base equilibria of glycyl-glycyl-glycine in water–ethanol solutions at 298 K

The enthalpies of the acid dissociation of glycyl-glycyl-glycine zwitterions and triglycinium ions are determined calorimetrically in water–ethanol solvents containing 0.0, 0.10, 0.30, and 0.50 molar fractions of ethanol at ionic strengths of 0.1 (maintained by sodium perchlorate) and Т = 298.15 K. It is found that increasing the ethanol content in the solvent enhances the endothermic effect of triglycinium ion dissociation and reduces the endothermic effect of glycyl-glycyl-glycine dissociation. The results are discussed in terms of the solvation thermodynamics.     

Rational synthesis and X-ray structural study of manganese–pyridine–alcohol derivatives

Systematic syntheses of manganese derivatives with 2-pyridineethanol, 2-pyridinemethanol and 2,6-pyridinedimethanol as chelating ligands have been undertaken to produce [trans-Mn(C₅H₄N-2-CH₂CH₂OH)₂Cl₂] (1), [cis-Mn₂(μ-Cl)₂(Cl)₂(C₅H₄N-2-CH₂CH₂OH)₂(OH₂)₂] (2), [cis-Mn₂(μ-Cl)₂(C₅H₄N-2-CH₂OH)₄]Cl₂ (3) and [MnCl{η₃-C₅H₃N-2,6-(CH₂OH)₂}{η₂-(C₅H₃N-2,6-(CH₂OH)₂)}]Cl (4). The complexes were characterized by single-crystal X-ray diffraction. The oxidation state of the manganese ions in these complexes is 2+. Magnetic data are measured down to 2?K; in dimer complexes (2 and 3) a significant antiferromagnetic interaction is observed between two manganese ions.     

Laser Raman spectroscopic study of water in gelatin–surfactant solutions and gels

A Raman spectroscopic study was carried out on water in gelatin at 4% w/v in gel (25 °C) and sol (40–60 °C) states at various concentrations (0.5, 1, 5, 10 and 15 mM) of anionic surfactant, sodium dodecyl sulfate (SDS). The in-phase collective stretching mode vibration of hydrogen-bonded -OH oscillators, centered around 3250 cm⁻¹ in a tetrahedral network of water molecules, was observed to be significantly affected by temperature and the presence of SDS. According to our observation this may be due to the thinning of the hydration water around the gelatin molecules due to strong thermal agitation. The peak center of the collective bands of water decreased linearly with SDS concentration in the gel state which implied that with the increase in concentration of SDS, the -OH oscillators gradually lost their attachment to gelatin chains and were replaced by SDS molecules. Ultimately this resulted in a thinning of the hydration layer around the gelatin and the oscillation frequency of -OH oscillators moved towards 3250 cm⁻¹ at 1 mM SDS concentration resulting in increased coupling of -OH oscillators to form the tetrahedral network at the critical micelle concentration (cmc) of SDS. The variation in the peak amplitudes and the systematic reversal of their trend about the cmc axis was surprising. At 40 °C the amplitude of the peak at 3250 cm⁻¹ increased drastically due to a possible coil expansion by about 7–8% which accommodated more interstitial water into the pseudonetwork leading to an increase in the number of nearest neighbors and for about 6% increase in the C value. However, at the cmc the peak amplitude was observed to be independent of temperature. Continuous shifting of the peak center and full width at half-maxima towards lower values was observed with increasing SDS concentrations in the gel state. Received: 28 September 1998 Accepted in revised form: 8 March 1999     

Small-angle X-ray scattering of the gadolinium triacetate–undecane–water system

By small-angle X-ray scattering a gadolinium triacetate–undecane–water system is studied at hydrotrope concentrations of 0.05-0.5 М on the line of saturation with undecane at 298 K. In the ternary system mixed hydrotrope/undecane lamellar micelles form with lateral dimensions of hydrophilic and hydrophobic plates of 0.4 nm. It is shown that the Gibbs energy of the hydrophobic interaction and the micelle shape are determined by a joint (cooperative) effect of the hydrotrope and hydrocarbon on water.     

Correlation and prediction of salt effects on vapor–liquid equilibrium in alcohol–water–salt systems

A modification of the solvation model of Ohe is proposed for the calculation of vapor–liquid equilibria (VLE) in alcohol–water–salt systems. The modified method employs the Bromley equation to calculate the activity of water in salt solutions, and a one-parameter empirical expression to calculate the activity of the alcohol. The single parameter is obtained by fitting ternary alcohol–water–salt data. The method is simple to use and does not require data on the vapor-pressures of alcohol–salt mixtures that are seldom available in the literature. Experimental data for 17 salts in 36 alcohol–water–salt systems, covering a temperature range from 298 to 375 K, and salt concentrations up to about 8 m, were correlated using the new approach. In all, 69 data sets and 1045 data points were correlated satisfactorily. The method was also used to predict VLE in four ternary alcohol–alcohol–salt systems and one quaternary alcohol–alcohol–water–salt system with satisfactory results.     

Characterization of TcCl4 and β-TcCl3 by X-ray absorption fine structure spectroscopy

Technetium tetrachloride and β-TcCl₃, synthesized from the reaction of Tc metal and Cl_2(g) in sealed tubes, were characterized by X-ray absorption fine structure spectroscopy. Extended X-ray absorption fine structure (EXAFS) spectroscopy measurements are in good agreement with the X-ray diffraction structures of the two compounds. For TcCl₄, the absorbing Tc atom is surrounded by Cl atoms at 2.34(2) Å and Tc atoms at 3.66(4) Å. For β-TcCl₃, the absorbing Tc atom is surrounded by Cl atoms at 2.40(2) Å and Tc atoms at 2.81(3), 3.66(4) and 5.71(6) Å. EXAFS spectroscopy indicates that the TcCl₄ and β-TcCl₃ samples obtained by sealed tube reactions are single phase. The X-ray absorption near edge structure spectra of TcCl₄ and β-TcCl₃ were recorded; the positions of the Tc K-edges of β-TcCl₃ (21,050.5 eV) and TcCl₄ (21,053.0 eV) are compared to the ones measured for α-TcCl₃ (21,051.0 eV) and TcCl₂ (21,048.8 eV). A correlation between the positions of the Tc K-edges and the oxidation state of the Tc atom in technetium binary chlorides was determined.     

Dopant position of Co atom in Zn1−xCoxO nanoparticles studied by extended X-ray absorption fine structure

Zn_1?xCo_xO nanoparticles were prepared by sol–gel method. The microstructure and dopant position were studied by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and extended X-ray absorption fine structure (EXAFS). The XRD patterns did not show any signal of impurity in the Zn_1?xCo_xO nanoparticles with Co concentration from x = 0.01 to 0.08. Neither did the HRTEM image for the highest concentration sample with x = 0.08. The nanoparticles have also been investigated by the EXAFS measurements at Co k-edge. The radical distribution functions, the fitting result of bond length and coordination numbers, indicated there was an impurity in the highest Co concentration sample with x = 0.08. Although most of the Co atoms were substituted for Zn sites in ZnO with x = 0.08, a few of Co atoms formed a microstructure similar to Co₃O₄, which was not found in the XRD and HRTEM. The room temperature ferromagnetic behaviour was found for x = 0.01 sample by superconducting quantum interference device .     

Iron analysis in atmospheric water samples by atomic absorption spectroscopy (AAS) in water–methanol

To distinguish between Fe(II) and Fe(III) species in atmospheric water samples, we have adapted an analytical procedure based on the formation of a specific complex between Fe(II) and ferrozine (FZ) on a chromatographic column. After elution of Fe(III), the Fe(II) complex is recovered with water–methanol (4:1). The possibility of trace iron measurements in this complex medium by graphite-furnace atomic-absorption spectrometry has been investigated. A simplex optimization routine was required to complete the development of the analytical method.     

Premicellar aggregation in water–salt solutions of sodium alkyl sulfonates and dodecyl sulfate

The features of premicellar aggregation in aqueous solutions of sodium n-octyl, n-nonyl, and n-decyl sulfonate, as well as sodium n-dodecyl sulfate, at a constant ionic strength maintained by adding NaCl are studied by potentiometry using modified ion-selective electrodes reversible with respect to the ions of these surfactants. For the studied surfactants, the critical micelle concentrations are refined, the compositions of the products of premicellar aggregation are determined, and the stability constants of aggregates are evaluated.