Activation of Hydrogen Peroxide by Ionic Liquids: Mechanistic Studies and Application in the Epoxidation of Olefins

Imidazolium‐based ionic liquids that contain perrhenate anions are very efficient reaction media for the epoxidation of olefins with H₂O₂ as an oxidant, thus affording cyclooctene in almost quantitative yields. The mechanism of this reaction does not follow the usual pathway through peroxo complexes, as is the case with long‐known molecular transition‐metal catalysts. By using in situ Raman, FTIR, and NMR spectroscopy and DFT calculations, we have shown that the formation of hydrogen bonds between the oxidant and perrhenate activates the oxidant, thereby leading to the transfer of an oxygen atom onto the olefin demonstrating the special features of an ionic liquid as a reaction environment. The influence of the imidazolium cation and the oxidant (aqueous H₂O₂, urea hydrogen peroxide, and tert‐butyl hydrogen peroxide) on the efficiency of the epoxidation of cis‐cyclooctene were examined. Other olefinic substrates were also used in this study and they exhibited good yields of the corresponding epoxides. This report shows the potential of using simple complexes or salts for the activation of hydrogen peroxide, owing to the interactions between the solvent medium and the active complex.     

Polymer‐Coated PtCo Nanoparticles Deposited on Diblock Copolymer Templates: Chemical Selectivity versus Topographical Effects

Metal–polymer hybrid films are prepared by deposition of polymer‐coated PtCo nanoparticles onto block copolymer templates. For templating, a thin film of the lamella‐forming diblock copolymer poly(styrene‐b‐methyl methacrylate) P(S‐b‐MMA) is chemically etched and a topographical surface relief with 3 nm height difference is created. Two types of polymer‐grafted PtCo nanoparticles are compared to explore the impact of chemical selectivity versus the topographical effect of the nanotemplate. A preferable wetting of the polystyrene (PS) domains with poly(styrenesulfonate) (PSS)‐coated PtCo nanoparticles (instead of residing in the space between the domains) is observed. Our investigation reveals that the interaction between PSS‐coated nanoparticles and PS domains dominates over the topographical effects of the polymer surface. In contrast, a non‐selective deposition of poly(N‐vinyl‐2‐pyrrolidone) (PVP)‐coated PtCo nanoparticles and the formation of large metal‐particle aggregates on the film is observed.     

Mode conversion and round-trip gain of ultrasonic flux in n-GaAs

Round-trip acoustoelectric gain has been observed in n-GaAs filaments oriented along the [110] axis. The special conditions required for this effect are obtained through partial conversion upon reflection of active transverse to non-active longitudinal waves. Experiments in which the relative contributions of the two reflected modes to round-trip gain is varied are described.     

Lipase-catalyzed solvent-free transesterification of wood sterols

Eighteen commercial lipase preparations, either immobilized or crude enzyme powders, were screened for the transesterification of wood sterols. The reactions were carried out in a solvent-free system, at the optimum temperature of the enzyme preparations as reported by the manufacturer and at the pressure of 2 mbar, with 5 or 10% in weight of the enzyme relative to the wood sterol content of the reacting mixture. Methyl esters of sunflower fatty acids were used as transesterifying agent. Of all the enzymes assayed, only Lipase TL from Pseudomonas stutzeri PL-836 (Meito Sangyo) exhibited any significant transesterifying capacity, 85 and 95% of conversion after 2 and 8 h of reaction, respectively, when 10% in weight of enzyme was used.     

Polymorphic forms of bisoprolol fumarate

Bisoprolol fumarate is a beta blocker-type drug substance which has been well known for several decades. However, no relevant data can be found in the literature about its crystal polymorphism. The purpose of this paper was to present two anhydrous forms (Form I and Form II) and a hydrate of bisoprolol fumarate substance. Crystalline forms were studied by various solid-state analytical methods: Fourier transform infrared (FT-IR) spectroscopy, X-ray powder diffraction (XRPD), dynamic vapor sorption (DVS) and thermoanalytical methods (thermogravimetry and differential scanning calorimetry). Thermodynamic stability and solubility of the presented polymorphs were also investigated. Both FT-IR and XRPD methods were found to be suitable for the characterization of the different crystal structures. Thermoanalytical measurements showed that (1) Form I and Form II own clearly different melting points and (2) both Form II and hydrate forms can transform into Form I at higher temperature values. Results of the DVS measurements prove that both Form I and Form II became metastable under extremely humid conditions (>?80% RH) and converted into the hydrate. Thermodynamic stability studies showed that Form I and Form II polymorphs are in enantiotropic relationship with an enantiotropic point at about 40–45 °C. Solubility studies indicated that all of the prepared forms are highly soluble, and no difference was found between them. Considering the recommendations of the corresponding International Conference of Harmonization guideline, it can be stated that no specification is required for crystal polymorphism in case of this substance.

     

Adsorption of the first row of transition metals on the perfect and defective MgO(1 0 0) surface

We present DFT calculations for adsorption of the first row of transition metal atoms on a MgO(1 0 0) surface and on a surface exhibiting defects. Some atoms exhibit a high adsorption energy on the defect (e.g. Co, Ni and Cu), but others (Ca, Sc) rather adsorb on a clean surface and another set is indifferent to the presence of defect. The adsorption becomes energetically unfavorable when the σ anti-bonding orbitals become populated; this is worse on a defective surface than on a terrace. The π back-donation to the surface contributes to favor the adsorption on the center.     

Mixed metal hydroxycarboxylic acid complexes. Spectrophotometric study of complexes of U(VI) with In(III), Cu(II), Zn(II) and Cd(II)

The formation of mixed metal complexes between uranium (VI), as the central metal ion, and aluminium (III), indium (III), copper (II), zinc (II) and cadmium (II), as the additional metal ions, with a hydroxycarboxylic acid chosen between citric, tartaric or malic, has been studied using spectrophotometric methods.The effect of pH has been examined, and the results show that at pH=4 stable complexes are formed for most of the systems. At this pH the method of mole ratio and Job's method of continuous variations, were employed to determine the stoichiometry of the mixed metal complexes. Al(III), In(III) and Cu(II) showed a high tendency to form mixed metal complexes with U(VI), while the formation of complexes is uncertain for Cd(II) and Zn(II). The ratio of the ligand to the total metal ion has been found to be 21 and metal:metal ratios of 11 and 12 have been observed.Represents part of the Ph.D. thesis submitted by Emanuel Manzurola to Ben Gurion University of the Negev.     

First-row transition metal atoms adsorption on rutile TiO2(110) surface

We performed periodic DFT calculations for adsorption of metal atoms on a perfect rutile TiO₂(110) surface (at low coverage, ???=?1/3) to investigate the interaction of an individual metal atom with TiO₂ and to compare it with a study previously done on MgO(100). We considered partial period of Mendeleev??s table from K to Zn. The overall evolution of the adsorption energies shows two maxima as for MgO(100). Two main differences, however, exist: the adsorption energy is much stronger and the first maximum is enhanced relative to the second one. This is attributed to the reducibility of the surface titanium cation. When the adsorbed metal is electropositive, it is oxidized under adsorption transferring electrons to titanium cations. We present the effect of introducing a Hubbard term to the gradient-corrected approximation band-structure Hamiltonian (GGA?+?U). The introduction of a reasonable Hubbard correction preserves the trends and allows localizing the electron of the reduction on Ti atoms in the near surface region. Finally, our results conclude that for heavier M atoms of the period, insertion is energetically favored relative to adsorption.     

Kationische oberfl?chenaktive Substanzen in organischen L?sungsmitteln. II. Viskosit?t und Leitf?higkeit von Trilaurylammoniumsalzen in Kohlenstofftetrachlorid und Benzol

Ohne Zusammenfassung     

Prediction of solid solution formation in a family of diastereomeric salts. A molecular modeling study

The possibility of solid solution behavior of diastereomeric salts, containing multiple resolving agents of the same family (Dutch Resolution), is predicted by molecular modeling. Super-cells containing different ratios of resolving agents in the diastereomeric salt are constructed and optimized, and their lattice energy is computed. The energy difference between these "simulated solid solutions" and the native structures is related in an understandable fashion to the probability of solid solution formation. This procedure is applied to a family of diastereomeric salts of ephedrine and cyclic phosphoric acids, for which the ternary diagrams have been determined experimentally at 25 degrees C in ethanol. Good agreement between experimental and computational results indicates that this relatively simple and fast method could predict the stable character of solid solution behavior in binary systems.