T-x-y diagram of the Ni-Bi-Se system

Some polythermal sections of the Ni-Bi-Se system have been investigated by DTA, X-ray powder diffraction, microstructural analysis, and microhardness measurements. The liquidus surface has been constructed for this system. The compounds NiBi₂Se₄ and Ni₃Bi₂Se₂ are formed by dystectic reactions and melt at 1088 and 980 K, respectively. The regions of primary and joint phase crystallization have been determined. A commutation of Bi₂Se₃-based thermoelements with a metal nickel bus-bar has been proposed.     

Synthesis, characterization, and electrochemical and electrochromic properties of sandwich dilutetium tetraphthalocyanine

A new sandwich-tpype dilutetium tetraphthalocyanine 4 has been synthesized by the reaction of dimeric lutetium(III) phthalocyanine 3 with two equiv. of dilithium octakishexylthiophthalocyanine in amyl alcohol. Compound 3 was prepared from 4',5',4",5"-tetraiminoisoindoline(1,4,7,10-tetrathia-12-crown-4) 1, 4,5-bis(hexylthio)-1,2-diiminoisoindoline and lutetium acetate in amyl alcohol. Compounds 3 and 4 were characterized by elemental analysis, UV/visible, IR, (1)H NMR and ESR spectroscopy. The electrochemical and electrochromic properties of 3 and 4 have been examined by cyclic voltammetry. Both 3 and 4 displayed well-defined electrochromic behavior.     

Determination of heavy metal concentrations in plants exposed to different degrees of pollution using ICP-AES

Plant samples (Plantago lanceolata - narrow leaf plantain and Cichorium endiviae - endive) were collected in the surroundings of heavy metal emission sources and in other less contaminated areas. After digestion in a closed microwave system using HNO(3), the concentrations of Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, and Zn were determined using ICP-AES. Detection limits for all the elements of interest are given. Differences in heavy metal uptake rate between both plant species were observed. The uptake is more intensive for endive than for narrow leaf plantain. High concentrations of some heavy metals were determined in the unwashed plant samples as a result of exposure to aerosols. Tukey's statistical test was used to confirm the discrepancy of Cr concentration in plant samples from various areas. Washing the leaves with water was found to remove a large amount of water-soluble aerosols.     

Insight into the extractability of metals from soils using an implementation of the linear adsorption isotherm model

This paper deals with an often overlooked artifact in sequential and single extraction of metals from soils, viz. the volume to mass (V/m) ratio as a potential source for inadequate extraction yields. We offer a theoretical framework to get a grip on this intricate parameter and came up with a model based on a linear adsorption isotherm to derive the correct maximal metal extractability for a certain extractant. We verified the model experimentally using 0.1 mol l⁻¹ nitric acid for extraction of seven metals (Cr, Co, Cu, Cd, Pb, Ni and Zn) from an urban soil sample, and concluded that commonly used V/m ratios in the range of 10-40 ml g⁻¹ may give as much as 50% too low extraction yields. Thus, a strong caveat is in place as to be very critical what V/m ratios to use and preferably apply the model derived to obtain the correct maximal extractability using a variable V/m ratio method.     

Reaktionen cyclischer Oxalylverbindungen, 34. Mitt.: Synthese von Dibenzoylacet-N-carboxyalkylamiden und semiempirische Rechnungen zur Keto-Enol Tautomerie

Summary 4-Benzoyl-5-phenylfuran-2,3-dione (1) and the urethanes2 combine under loss of carbon monoxide yielding the open chain dibenzoylacetic acid derivatives3 and4. 3a, b only can be cyclized to the oxazinone5. The keto-enole tautomerism3 4 is further investigated with aid of semiempirical quantum chemical calculations, based upon the molecular geometry of3a, deduced from an X-ray study.

Frau Univ. Prof. Dr. Helga Wittmann mit den besten Wünschen zum 70. Geburtstag gewidmet.     

Processes associated with ionic current rectification at a 2D-titanate nanosheet deposit on a microhole poly(ethylene terephthalate) substrate

Films of titanate nanosheets (approx. 1.8-nm layer thickness and 200-nm size) having a lamellar structure can form electrolyte-filled semi-permeable channels containing tetrabutylammonium cations. By evaporation of a colloidal solution, persistent deposits are readily formed with approx. 10-μm thickness on a 6-μm-thick poly(ethylene-terephthalate) (PET) substrate with a 20-μm diameter microhole. When immersed in aqueous solution, the titanate nanosheets exhibit a p.z.c. of − 37 mV, consistent with the formation of a cation conducting (semi-permeable) deposit. With a sufficiently low ionic strength in the aqueous electrolyte, ionic current rectification is observed (cationic diode behaviour). Currents can be dissected into (i) electrolyte cation transport, (ii) electrolyte anion transport and (iii) water heterolysis causing additional proton transport. For all types of electrolyte cations, a water heterolysis mechanism is observed. For Ca²⁺ and Mg²⁺ions, water heterolysis causes ion current blocking, presumably due to localised hydroxide-induced precipitation processes. Aqueous NBu₄⁺ is shown to ‘invert’ the diode effect (from cationic to anionic diode). Potential for applications in desalination and/or ion sensing are discussed.

     

Enantioselective Sulfoxidation Catalyzed by a Bisguanidinium Diphosphatobisperoxotungstate Ion Pair

The first enantioselective tungstate‐catalyzed oxidation reaction is presented. High enantioselectivities were achieved for a variety of drug‐like phenyl and heterocyclic sulfides under mild conditions with H₂O₂, a cheap and environmentally friendly oxidant. Synthetic utility was demonstrated through the preparation of (S)‐Lansoprazole, a commercial proton‐pump inhibitor. The active ion‐pair catalyst was identified to be bisguanidinium diphosphatobisperoxotungstate using Raman spectroscopy and computational studies.     

Centerband-Only Detection of Exchange NMR with Natural-Abundance Correction Reveals an Expanded Unit Cell in Phenylalanine Crystals

The NMR pulse sequence CODEX (centerband-only detection of exchange) is a widely used method to report on the number of magnetically inequivalent spins that exchange magnetization via spin diffusion. For crystals, this rules out certain symmetries, and the rate of equilibration is sensitive to distances. Here we show that for ¹³C CODEX, consideration of natural abundance spins is necessary for crystals of high complexity, demonstrated here with the amino acid phenylalanine. The NMR data rule out the C₂ space group that was originally reported for phenylalanine, and are only consistent with a larger unit cell containing eight magnetically inequivalent molecules. Such an expanded cell was recently described based on single crystal data. The large unit cell dictates the use of long spin diffusion times of more than 200 seconds, in order to equilibrate over the entire unit cell volume of 1622 ų.     

Efficient eco-friendly syntheses of dithiocarbazates and thiosemicarbazones

ABSTRACT

Eight Schiff bases have been synthesized by conventional and three different eco-friendly methods, whereby two aromatic carbonyl compounds viz. 2-thiophenecarboxaldehyde and salicylaldehyde were reacted with S-methyl, S-benzyl, and S-n-octyl-dithiocarbazates and thiosemicarbazide. In order to evaluate the efficiency of the synthesis methods, the time to complete the reaction and the yield of the Schiff base synthezised by eco-friendly methods, such as solvent-free grinding, water as a solvent, and lemon juice as catalyst, were compared with those synthesized by the conventional method. The chemical structures of all the synthesized Schiff bases, where two of them are novel and reported for the first time, were fully characterized by a variety of physico-chemical, analytical, and spectroscopic techniques. The molecular and crystal structures of the Schiff bases especially those having 2-thiophene moiety were further elucidated by single crystal X-ray diffraction analyzes.