Host-guest complexes of crown ethers with HN-proton-donor molecules

Crown ethers were reacted with HN-proton-donor molecules to obtain crystalline molecular host-guest complexes. It was found that complexes with crown ethers of different structure are formed, depending on the linear dimensions and mode of steric shielding of active centers of the proton-donor molecules.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 12, 2004, pp. 2030–2033.Original Russian Text Copyright © 2004 by Wang, Ganin.This revised version was published online in April 2005 with a corrected cover date.     

Molecular Beam Mass Spectrometry System for Characterization of Thermal Plasma Chemical Vapor Deposition

A molecular beam mass spectrometry system for in situ measurement of the concentration of gas phase species including radicals impinging on a substrate during thermal plasma chemical vapor deposition (TPCVD) has been designed and constructed. Dynamically controlled substrate temperature was achieved using a variable thermal contact resistance method via a backside flow of an argon/helium mixture. A high quality molecular beam with beamtobackground signal greater than 20 was obtained under film growth conditions by sampling through a small nozzle (75 m) in the center of the substrate. Mass discrimination effects were accounted for in order to quantify the species measurements. We demonstrate that this system has a minimum detection limit of under 100 ppb. Quantitative measurements of hydrocarbon species (H, H₂, C, CH₃, CH₄, C₂H₂, C₂H₄) using Ar/H₂/CH₄ mixtures and silicon species (Si, SiH, SiH₂, SiCl, SiCl₂, Cl, HCl) using Ar/H₂/SiCl₄ mixtures were obtained under thermal plasma chemical vapor deposition conditions.     

Polystyrene/thermoplastic starch blends with different plasticizers

Conventional plastics has a large impact in increasing the environment’s pollution. That’s why the interest has turned towards novel partially and completely biodegradable polymers. In this work, blends of polystyrene and thermoplastic starch with glycerol and Buriti (Mauritia flexuosa L.) oil as plasticizers were prepared. Samples were analyzed using TG/DTG and DSC techniques. The TG results indicated that the blends with Buriti oil are thermally more stable than those with glycerol. The DSC analysis that Buriti oil provides a higher degree of plasticization of PS, compared to the blends plasticized using glycerol under the studied conditions.     

Synthesis and structural characterization of a fully conjugated macrocyclic tetraaza(14)-membered Schiff base and its bivalent metal complexes

A novel 14-membered macrocyclic Schiff base derived from 3-cinnamalideneacetoacetanilide and o-phenylenediamine acts as a tetradentate and strongly conjugated ligand to form a cationic solid complex with CuCl₂/NiCl₂/CoCl₂/ZnCl₂. The ligand and the complexes were characterized by the usual spectral and analytical techniques. The main i.r. band of the macrocyclic Schiff base was compared to that of its metal complexes. The C=N bands are shifted to the lower wave number. The cyclic voltammogram of the copper complex shows that the macrocyclic ligand is able to stabilize the copper(III) oxidation state. The e.s.r. spectra of the copper complex in DMSO solution at room temperature and liquid N₂ temperature were recorded and their salient features thoroughly discussed. The antimicrobial screening tests were also recorded and gave good results in the presence of metal ions in the ligand system.     

On the mechanism of electroluminescence emission by porous silicon layers

The analytical treatment of a model considering the electrooxidation of p-porous silicon layers under galvanostatic conditions is able to give account of experimental facts such as the shape and location of the electroluminescence peak as well as of the spectral shift of the electroluminescence peak produced by oxidation. The proposed model considers electroluminescence to be the result of electron injection into the conduction band by an adsorbed intermediate produced by electrooxidation of the surface coverage with hydrogen or siloxene of the silicon nanocrystallites. The access of holes to the surface is made possible by low accumulation layer conditions and is the rate determining step in the electroluminescence mechanism. In this way it is possible to give a satisfactory explanation to the shift towards the blue experimented by the electroluminiscence emission maximum as a consequence of electrooxidation.     

Poly[3-(3,4-dihydroxyphenyl)glyceric acid] from Stems of <Emphasis Type="Italic">Symphytum asperum</Emphasis> and <Emphasis Type="Italic">S. caucasicum</Emphasis>

Two high-molecular-weight (>1000 kDa) water-soluble preparations were isolated from stems of Symphytum asperum and S. caucasicum. Their basic component was established as poly[hydroxy-1-carboxy-2-(3,4-dihydroxyphenyl)ethylene], analogous to that of high-molecular-weight (>1000 kDa) preparations from roots of these same plants, using IR and NMR spectral data. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 303–305, July–August, 2005. An erratum to this article is available at .     

Reaction of sulphoximides with diazomalonate in the presence of Cu-salt : A new synthesis and stereochemistry of optically active oxosulphonium ylides

Sulphoximides (Ia–Ie) were found to react with dimethyl diazomalonate (DDM) in the presence of a catalytic amount of Cu-salts affording the corresponding oxosulphonium ylides in moderate yields. The reaction did not proceed at all under irradiation of UV light. (?)-Methylphenyloxosulphonium bis(methoxycarbonyl)-methylide ((?)-IIb) was obtained from (+)-(S)-methylphenylsulphoximide ((+)-(S)-Ib) together with (?)-(S)-methyl phenyl sulphoxide ((?)-(S)-IIIb) by this reaction. Hydrolysis of (?)-IIb gave (+)-methylphenyloxosulphonium methoxycarbonylmethylide ((+)-IIf) which was converted to (?)-(S)-IIIb upon treatment with dibenzoylethylene. Stereochemical cycle starting from (+)-(S)-Ib to (?)-(S)-IIIb was established and the absolute configurations of both ylides, (?)-IIb and (+)-IIf were assigned as (R)-configuration. The stereochemical courses, namely from (+)-(S)-Ib or (?)-(S)-IIIb to (?)-(R)-IIb or (+)-(R)-IIf to (?)-(S)-IIIb were determined as retention processes. The optical purities of the oxosulphonium ylides obtained from both reactions, (+)-(S)-Ib→(?)-(R)-IIb and (?)-(S)-IIIb→(?)-(R)-IIb, were almost equal. These results indicate that the mechanism of the reaction of sulphoximides with carbenes (or carbenoids) involves the initial formation of the sulphoxides which react subsequently with carbenes to afford the final products.     

An overview of laboratory performance studies conducted by the IAEA for marine pollution studies of metals and organic contaminants

Aspects of the International Atomic Energy Agency (IAEA) Analytical Quality Control Services (AQCS) for marine environmental studies are discussed, focusing on recent laboratory performance studies (LPS) and the production of reference materials for trace metals and organic compounds in various marine matrices. The IAEA has organized seventeen global interlaboratory studies for a range of organic contaminants. Of note has been the inclusion of numerous polychlorinated biphenyl congeners (PCBs) and some sterols of anthropogenic origin. Concurrently, there have been eleven worldwide intercomparison exercises for trace metals in the marine environment, most of which included methylmercury. Although such interlaboratory studies can help improve performance in individual laboratories and regional laboratory networks, the results reveal that problems remain in the determination of some metals and many organic contaminants.     

CuSO<Subscript>4</Subscript> as a Mild,Green, and Efficient Catalyst for the One-pot Conversion of <Emphasis Type="Italic">THP</Emphasis> Ethers to Acetates

Summary. An efficient direct conversion of THP ethers into the corresponding acetates was achieved with acetic anhydride in the presence of CuSO₄ · 5H₂O as an available and green catalyst in high yields.