[3+2] Annulation of 2-substituted 3-nitro-2H-chromenes with mercaptoacetaldehyde: stereoselective synthesis of tetrahydro-4H-thieno[3,2-c]chromen-3-ols

Chemistry of Heterocyclic Compounds - A diastereoselective method was developed for the synthesis of 4-trifluoromethyl- and 4-phenyl-substituted...     

Mono- and Mixed Metal Complexes of Eu3+, Gd3+, and Tb3+ with a Diketone,Bearing Pyrazole Moiety and CHF2-Group: Structure,Color Tuning,and Kinetics of Energy Transfer between Lanthanide Ions

Three novel lanthanide complexes with the ligand 4,4-difluoro-1-(1,5-dimethyl-1H-pyrazol-4-yl)butane-1,3-dione (HL), namely [LnL₃(H₂O)₂], Ln = Eu, Gd and Tb, were synthesized, and, according to single-crystal X-ray diffraction, are isostructural. The photoluminescent properties of these compounds, as well as of three series of mixed metal complexes [Eu_xTb_1-xL₃(H₂O)₂] (Eu_xTb_1-xL₃), [EuxGd_1-xL₃(H₂O)₂] (Eu_xGd_1-xL₃), and [Gd_xTb_1-xL₃(H₂O)₂] (Gd_xTb_1-xL₃), were studied. The Eu_xTb_1-xL₃ complexes exhibit the simultaneous emission of both Eu³⁺ and Tb³⁺ ions, and the luminescence color rapidly changes from green to red upon introducing even a small fraction of Eu³⁺. A detailed analysis of the luminescence decay made it possible to determine the observed radiative lifetimes of Tb³⁺ and Eu³⁺ and estimate the rate of excitation energy transfer between these ions. For this task, a simple approximation function was proposed. The values of the energy transfer rates determined independently from the luminescence decays of terbium(III) and europium(III) ions show a good correlation.     

Peculiarities of pπ?pπ conjugation in aminosubstituted phosphaalkenes

Effets of p_π p_π conjugation in phosphaalkenes have been considered by taking into account the results of X-ray structural studies and ab initio quantum-chemical calculations. The structural consequences of the conjugation depend to a certain extent on the character of the substituent and the place of its attachment to the double PC bond. Depending on the location of the substituent, bond polarization may strengthen or weaken (compensate for) the conjugation effects. A high contribution of the s-character of the lone electron pair of the P atom is an essential feature of the electron structure of a phosphaalkene.     

Design of materials for solid oxide fuel cells,permselective membranes,and catalysts for biofuel transformation into syngas and hydrogen based on fundamental studies of their real structure,transport properties,and surface reactivity

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Effects of the photocathode non-uniformity on radon measurements by plastic scintillation spectrometry

Journal of Radioanalytical and Nuclear Chemistry - This work shows a study of the effect of the non-uniformity of photocathode response on the energy resolution of plastic scintillators optimized...     

Controlled crystallization of CaCO(3) on hyperbranched polyglycerol adsorbed to self-assembled monolayers

The formation of biominerals by living organisms is governed by the cooperation of soluble and insoluble macromolecules with peculiar interfacial properties. To date, most of the studies on mineralization processes involve model systems that only account for the existence of one organic matrix and thus disregard the interaction between the soluble and insoluble organic components that is crucial for a better understanding of the processes taking place at the inorganic-organic interface. We have set up a model system composed of a matrix surface, namely, a self-assembled monolayer (SAM), and a soluble component, hyperbranched polyglycerol. The model mineral calcium carbonate displays diverse polymorphism. It could be demonstrated that the phase selection of calcium carbonate is controlled by the cooperative interaction of the SAM and hyperbranched polyglycerol of different molecular weights (M(n) = 500-6000 g/mol) adsorbed to the SAM. Our studies showed that hyperbranched polyglycerol is adsorbed to polar as well as to nonpolar SAMs. This effect can be related to its highly flexible structure and its amphiphilic character. The adsorption of hyperbranched polyglycerol to the SAMs with different surface polarities resulted in the formation of aragonite for alkyl-terminated SAMs and no phase selection for carboxylate-terminated SAMs.     

Copper-polymer nanocomposite: An efficient catalyst for green Huisgen click synthesis

A new method for Huisgen [3+2] cycloaddition synthesis of 1,4- and 1,4,5-substituted-1H-1,2,3-triazoles was reported. The reaction was catalyzed by the product of thermolysis of copper (II) poly-5-vinyltetrazolate. Heterogeneous catalyst includes copper nanoparticles which supported on polymeric matrix. It presents recovered and recycled catalyst and the catalyzed reaction proceeds in aerobic conditions at room temperature in aqueous media.     

Synthesis and Characterization of Oxazaborinin Phosphonate for Blue OLED Emitter Applications

A blue-light emitting material based on a boron complex containing heteroaromatic phosphonate ligand is synthesized and characterized. The Phospho-Fries rearrangement is used in the synthesis route of the ligand as a convenient method of introducing phosphonate groups into phenols. Structural, thermal and photophysical properties of the resulting oxazaborinin phosphonate compound have been characterized. DFT geometry optimizations were studied as well as the spatial position and symmetry of the HOMO and LUMO. Good thermal stability up to 250 °C enables vacuum deposition methods next to solution processing. Combining the work function with the optical band gap from UV-Vis measurements shows that band alignment is possible with standard contact materials. Photoluminescence reveals an emission peak at 428 nm, which is suitable for a blue light-emitter.     

An Overview on the Dehydrogenation of Alkylbenzenes with Carbon Dioxide over Supported Vanadium–Antimony Oxide Catalysts

Utilization of carbon dioxide as a soft oxidant for the catalytic dehydrogenation of ethylbenzene (CO₂-EBDH) has been recently attempted to explore a new technology for producing styrene selectively. This article summarizes the results of our recent attempts to develop effective catalyst systems for the CO₂-EBDH on the basis of alumina-supported vanadium oxide catalysts. Its initial activity and on-stream stability were essentially improved by the introduction of antimony oxide as a promoter into the alumina-supported catalyst. Insertion of zirconium oxide into alumina support substantially increased the catalytic activity. Modification of alumina with magnesium oxide yielded an increase of catalyst stability of alumina-supported V–Sb oxide due to the coking suppression. Carbon dioxide has been confirmed to play a beneficial role of selective oxidant in improving the catalytic performance through the oxidative pathway, avoiding excessive reduction and maintaining desirable oxidation state of vanadium ion (V⁵⁺). The positive effect of carbon dioxide in dehydrogenation reactions of several alkylbenzenes such as 4-diethylbenzene, 4-ethyltoluene, and iso- and n-propylbenzenes was also observed. Along with the easier redox cycle between fully oxidized and partially reduced vanadium species, the optimal surface acidity of the catalyst is also responsible for achieving high activity and catalyst stability. It is highlighted that supra-equilibrium EBDH conversions were obtained over alumina-supported V–Sb oxide catalyst in CO₂-EBDH as compared with those in steam-EBDH in the absence of carbon dioxide.     

Air-oxidized products of multi-component reactions between 3-amino-1,2,4-triazole, aromatic aldehydes and isonitriles

The Groebke-type multi-component reaction (MCR) between 3-amino-1,2,4-triazole, aromatic aldehydes and isonitriles has been studied from the viewpoint of convenient generation of combinatorial arrays of imidazo[1,2-b][1,2,4]triazoles. However, it was established that the desired heterocyclic structures can be produced in moderate to good yields in an oxidized form, when benzylic isonitriles are used. Oxidation occurred at the benzylic position to produce N-alkylidene-4H-imidazo[1,2-b][1,2,4]triazol-6-amines that proved to be unusually stable towards acid hydrolysis and reduction. The presence of an easily oxidized benzylic position in the target structures is thought to be the prerequisite for successful Groebke-type MCR of 3-amino-1,2,4-triazole.