Mutual diffusion in binary mixtures of ionic liquids and molecular liquids by dynamic light scattering (DLS)

The present study shows that dynamic light scattering (DLS) is capable of measuring mutual diffusion coefficients for binary mixtures of ionic liquids (ILs) with different molecular liquids over the complete composition range. Evidence is given that the light scattering signals are related to true molecular binary diffusion. The method stands out due to its ability to work non-invasively in macroscopic thermodynamic equilibrium with reasonable accuracy and within convenient measurement periods. Compared with other techniques, mixtures with distinctly higher viscosities can be probed. For exemplary binary mixtures of 1-ethyl-3-methylimidazolium ethylsulfate ([EMIM][EtSO(4)]) with acetone, acetonitrile, dichloromethane, ethanol, or water as well as of 1-ethyl-3-methylimidazolium methanesulfonate ([EMIM][MeSO(3)]) with acetone, water, or methanol, mutual diffusivity data were measured over a wide range of composition at a temperature of 293.15 K. In general, the mutual diffusivity increases with increasing mole fraction of the molecular liquid and similarities to aqueous solutions of classical inorganic salts can be found. The characteristic behavior of the mutual diffusion coefficients is influenced by the nature of the chosen molecular liquid. For IL water mixtures, low light scattering intensities were observed despite the large refractive index difference of the pure components. The reason for this behavior may be the existence of water clusters in the mixtures. Additional measurements for IL acetone mixtures at temperatures ranging from 278.15 K to 323.15 K showed that the temperature dependence of the mutual diffusivity can be represented by Arrhenius functions and is increasing for decreasing mole fractions of acetone.     

Facile synthesis of Ag@Pd satellites-Fe3O4 core nanocomposites as efficient and reusable hydrogenation catalysts

Well-dispersed Ag@Pd supported on magnetite nanoparticles have been obtained through a simple colloidal impregnation method. The as-synthesised nanocomposite exhibits greatly enhanced catalytic reactivity and reusability towards 4-nitrophenol hydrogenation.     

Synthesis,characterization, and antibacterial activities of copper(I) bromide complexes of thioureas: X-ray structure of [Cu(Metu)<Subscript>4</Subscript>]Br

Copper(I) complexes of thioureas having the general formulae [CuL_nBr] and [CuL_n]Br [where, n = 1 − 4 and L = thiourea (Tu), N-methylthiourea (Metu), N-ethylthiourea (Ettu), N,N^′-dipropylthiourea (Dprtu), N,N^′-dibutylthiourea (Dbtu) or N,N^′-diphenylthiourea (Dphtu)] were prepared and characterized by elemental analysis, IR, and NMR (¹H and ¹³C) spectroscopy. The crystal structure of one of them, [Cu(Metu)₄]Br (1), was determined by X-ray crystallography. The X-ray structure of 1 describes a tetrahedral geometry around copper(I) with all Metu ligands binding through sulfur atoms. An upfield shift in the ¹³C NMR and downfield shift in the ¹H NMR spectra are consistent with the thione coordination to copper(I). Antimicrobial activities of the complexes were evaluated by the minimum inhibitory concentration method. The results showed that only [Cu(Ettu)₃Br] was effective in inhibiting the growth of all the tested organisms (gram-positive, gram-negative bacteria, and Candida sp.), while the other complexes were not effective against all the organisms.     

Effort on calibration of infrared spark ablation of copper with synthetic copper standards

Two types of copper samples, compact certified copper reference materials and calibration samples prepared from liquid doped, pressed copper powders, were studied in terms of accuracy of obtained calibration functions originating from infrared spark ablation. Additionally, corresponding particle size distributions of the aerosols from infrared spark ablation were recorded. It is shown that the differences in quantification results, originating from the two sets of calibration functions, could not mainly be ascribed to different particle size distributions of the two copper sample types. Possible other causes, as different ablation rates, parts of melting and differences of the chemical constitutions of the two sample types were explored.     

A robust zirconium N-heterocyclic carbene complex for the living and highly stereoselective ring-opening polymerization of rac-lactide

A readily accessible and robust Zr-NHC complex was found to polymerize rac-lactide in a highly controlled, living and stereoselective manner to afford heterotactic PLA.     

New chiral discotics with helical organization of the mesophase—liquid crystalline derivatives of dibenzotetraaza[14]annulene

Two optically pure derivatives of dibenzotetraaza[14]annulene, bearing four (S)- or (R)- 3,7-dimethyloctoxy peripheral chiral tails, respectively, and two hydroxybenzoyl meso substituents were synthesized using a convergent multi-step route. The structure of the products was determined by ¹H and ¹³C NMR spectroscopy, ESI-MS, and elemental analysis. The mesomorphic behavior of the two chiral compounds, deciphered by differential scanning calorimetry (DSC), small-angle X-ray diffractometry (SA-XRD), and polarizing optical microscopy (POM) investigations, revealed the induction of two lamello-columnar phases, i.e., columnar stacks confined in smectic layers, whose columns may be arranged either according to the pg rectangular planar symmetry (for the low-temperature phase) or without registry between vicinal layers (for the high-temperature mesophase). Evidence of a helical organization of the molecules in the mesophases was obtained using a combination of electronic circular dichroism (ECD) and SA-XRD results, Molecular Dynamics simulations and quantum-chemical calculations.     

Der Wittelsbacher und der Hope‐Diamant

Diamonds are formed from carbon at high pressures and high temperatures in the inner part of the earth. Doping with very small amounts of boron leads to diamonds with blue colour. Two of the most famous historical blue diamonds, the Wittelsbach and Hope Diamond, were found in the Indian Kollur mine. The latter was brought to Europe by the French gem merchant Tavernier. Today it is displayed in the Smithsonian Institute. The Wittelsbach Diamond was for a long time in the possession of the House Wittelsbach until it was secretly sold in Antwerp in 1951. In 2008, it was purchased by auction by the jeweller Graff who recut the gem. In 2011, it was sold to an unknown buyer. As the Wittelsbach and the Hope diamond share origin and colour, it was assumed for a long time that both are pieces from a larger crystal. By optical investigation it was now shown that they have indeed some similar optical properties, but differ strikingly in other ones. Hence, they cannot originate from the same crystal.     

1,2‐Bis(trifluoromethyl)ethene‐1,2‐dicarbonitrile: (2+2) Cycloadditions with Vinyl Ethers

The title compound (short version: BTE) occurs in (E)‐ and (Z)‐isomers (both with b.p. of ca. 100°) which equilibrate with nucleophilic catalysts. Both undergo (2+2) cycloadditions with methyl vinyl ether at 25°. Three stereogenic centers in the cyclobutanes led to four rac‐diastereoisomers, which were obtained in pure and crystalline state. The structures were elucidated by ¹⁹F‐NMR spectroscopy and confirmed by two X‐ray analyses. The cycloadditions were not stereospecific: e.g., (E)‐BTE furnished 73% trans‐adducts (with respect to the CF₃ groups) and 27% cis‐adducts. The loss of stereochemical integrity occurs in the intermediate gauche‐zwitterions which can cyclize or rotate, but not dissociate. Under extreme conditions (2M LiClO₄ in Et₂O, 70°, 3 months), the thermodynamic equilibrium of the four cyclobutanes was achieved. Considerations of Coulombic attraction and conformational strain in the zwitterionic intermediates allow us to rationalize the observed proportions of diastereoisomeric cyclobutanes. Ethyl vinyl ether and butyl vinyl ether furnished cyclobutanes in similar diastereoisomer ratios.     

A microscopic model of annealed vacancies in long-period structures

The axial next-nearest-neighbour Ising (ANNNI) model is a spin model which locks into an infinite number of modulated phases as a function of the interaction parameters and the temperature. In this paper we discuss the effect of allowing this system to contain annealed vacancies. We find that a small concentration of vacancies does not qualitatively affect the structure of the phase diagram and that the vacancies form defect-density waves which mirror the periodicity of the underlying modulated structure.     

The level of cross-linking and the structure of anisotropic magnetorheological elastomers

The influence of the concentration of the magnetic powder on the level of cross-linking of magnetorheological elastomers (MREs) has been studied. Afterwards the structural characterisation of manufactured MREs has been performed by using non-destructive method, specifically the computed tomography. The correlation between internal structures of MREs and the developing of its cross-linking level during the curing was found. It was shown that changes in the concentration of the powder significantly affect morphologies of the sample.