Thermotropic liquid crystalline properties of semiperfluoroalkyloxyphenyl and perfluoroalkylphenyl β-D-glucopyranosides

The synthesis of two series of semiperfluoroalkyloxyphenyl and perfluoroalkylphenyl β-D-glucopyranosides is described. Their mesomorphic properties are studied by DSC, polarized optical microscopy and X-ray diffraction. All mesophases are identified as smectic A with a bimolecular in-layer arrangement.     

Fluorescence and photochemical properties of crystalline boron difluorides β-diketonato

The fluorescence and photochemical properties of crystalline β-diketonatoboron difluorides (DBD) RCOCHCOR¹BF₂ were studied. These compounds are characterized by relatively high photochemical stability. The introduction of electron-donating groups into the aromatic α-substituent of the chelate ring increases and the introduction of electron-withdrawing groups decreases the fluorescence intensity of DBD. Anisoylbenzoylmethanotoboron difluoride was found to exhibit the highest fluorescence intensity. The substituents were shown to influence the relative arrangement of singlet and triplet ηπ^* and ππ^* levels and luminescence properties of compounds. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1030–1033, June, 2000.     

α-MnO2 nanotubes: high surface area and enhanced lithium battery properties

A simple one-step route for preparing α-MnO(2) nanotubes is reported. The α-MnO(2) nanotubes exhibit a high surface area of 226 m(2) g(-1) and reversible capacity of 512 mA h g(-1) at a high current density of 800 mA g(-1) after 300 cycles, as well as cycling stability when measured as an anode in lithium batteries.     

Liquid Co–Sn alloys at high temperatures: structure and physical properties

The Co–Sn system is an important subsystem for Sn-based anode materials of lithium-ion batteries. Experimental results on the physical–chemical properties of this system in the liquid state, however, are rather sparse. In this work, the atomic structure and structure-sensitive thermophysical properties (viscosity, electrical resistivity, and thermoelectric power) of liquid Co–Sn alloys were investigated in a wide temperature range with special attention to the melting-solidification region. The obtained experimental results were combined with differential thermal analysis (DTA) data in order to verify the liquidus curve in the Sn-rich part of the Co–Sn phase diagram.     

New β-carotene-xylan complexes: preparation and characterization

Cellulose - The study aimed to propose a new system based on xylan for β-carotene delivery into aqueous environments. The xylan fraction of low molecular weight of...     

Efficient and high yield one-pot synthesis of cyclometalated platinum(II) β-diketonates at ambient temperature

Cyclometalated Pt(II) β-diketonates are widely used as efficient luminescent materials but are typically prepared at high temperatures in low yields using excess reagents. A one-pot synthesis of these complexes is described employing stoichiometric reagents and short reaction times at ambient temperature, giving yields of up to 94%. The method is applicable to a broad range of substrates including N^C, P^C, and C^C chelate Pt(II) complexes and different β-diketonate ligands.     

Pressure-induced structure and properties of crystalline β-FOX-7 by LDA and GGA calculations

The structural, electronic, and absorption properties of crystalline β-FOX-7 were studied by density functional theory–generalized gradient approximation (GGA) and local density approximation (LDA) calculations. The results indicate that there are irregular changes occurred at 9, 17, 32, and 37 GPa for the GGA results and at 2, 7, 22, and 32 GPa for the LDA ones, in agreement with previous reports that the LDA generally underestimated, while the GGA overestimated the structure and properties of the crystals. The compression ratios of the lattice constants suggest that the structure of β-FOX-7 is much stiffer in a- and c-directions than in b-direction. The total decrease ratio of C–NO₂ band lengths is larger than that of other bond lengths, indicating that the C–NO₂ bond cleavage may trigger the initiation decomposition of β-FOX-7. An analysis of density of states suggests that the interactions between electrons are strengthened under the influence of pressure. The absorption spectra indicate that the bands in the fundamental absorption region have relatively high optical activity at high pressure.     

A new class of protein mimics: preparation and electrophoretic properties of polycationic β-alanine-based dendrimers

The synthesis and characterization of a series of polyammonium β-alanine containing dendrimers 4-6 were reported. Such polycationic species were shown to exhibit electrophoretic behavior similar to that of protein molecules such as lysozyme and aprotinin in acidic polyacrylamide gel electrophoresis. It was also found that their electromobility was directly related to their molecular size, and hence such biomimetic dendrimers are potential molecular weight markers for protein analysis.     

Thermoluminescence properties of natural zoisite mineral under γ-irradiations and high temperature annealing

Natural silicate mineral of zoisite, Ca(2)Al(3)(SiO(4))(Si(2)O(7))O(OH), has been investigated concerning γ-radiation, UV-radiation and high temperature annealing effects on thermoluminescence (TL). X-ray diffraction (XRD) measurement confirmed zoisite structure and X-ray fluorescence (XRF) analysis revealed besides Si, Al and Ca that are the main crystal components, other oxides of Fe, Mg, Cr, Na, K, Sr, Ti, Ba and Mn which are present in more than 0.05 wt%. The TL glow curve of natural sample contains (130-150), (340-370) and (435-475)°C peaks. Their shapes indicated a possibility that they are result of composition of two or more peaks strongly superposed, a fact confirmed by deconvolution method. Once pre-annealed at 600°C for 1h, the shape of the glow curves change and the zoisite acquires high sensitivity. Several peaks between 100 and 400°C appear superposed, and the high temperature peak around 435°C cannot be seen. The ultraviolet radiation, on the other hand, produces one TL peak around 130°C and the second one around 200°C and no more.     

Invited review “sol-gel” preparation of high temperature superconducting oxides

This review article focuses on the sol-gel preparation of high temperature superconducting oxides wherein different classes of gel technologies were utilized. These involve: 1) the sol-gel route based upon hydrolysis-condensation of metal-alkoxides, 2) the gelation route based upon concentration of aqueous solutions involving metal-chelates, often called as chelate gel or amorphous chelate route, and 3) the organic polymeric gel route. This paper reviews the current status of these sol-gel processes, and illustrates the underlying chemistry involved in each sol-gel technology. It is demonstrated that the chemical homogeneity of the gel is often disturbed by the differences in the chemistries of the cations. Prior to gelation the starting precursor solution containing various forms of metal-complexes must be chemically modified to overcome this problem. Illustration of a variety of strategies for success in obtaining a homogeneous multicomponent gel with no precipitation is focal point of this review article.strictly speaking, sol-gel must include processing, in which a sol (often defined as a suspension of small but discrete particles remaining dispersed in a liquid phase) undergoes a transition to a gel characterized by an infinite three-dimensional network structure spreading uniformly throughout the liquid medium. Thus a gel has to be distinguished either from a viscous liquid of one continuous phase or from a gelatinous precipitate in which a liquid phase is not involved in the solid network. It is generally accepted that a true gel can be prepared in two major chemical ways: (1) a molecular route based upon hydrolysis and polycondensation of metal alkoxides (alkoxide gels) and (2) a network formation route based upon destabilization of dispersed colloidal particles in a liquid medium (particulate gels). According to the rigorous definition of gel, some solution processes, started from metal-organics (other than metal alkoxide), would not be classified into a true sol-gel process. In this paper, however, the term sol-gel is broadly used to describe the preparation of inorganic materials by a variety of solution routes. A chemical process which can produce a solid matter or a highly viscous liquid matter with no precipitation is treated as the so-called sol-gel process, even when it is likely that the system contains no infinite rigid network.     

Multiple-step preparation and physicochemical characterization of crystalline α-germanium hydrogenphosphate

The reaction between germanium oxide and phosphoric acid has previously been described and led to impure germanium hydrogenphosphate samples with low crystallinity. A new multiple-step route involving the same reaction under refluxing and soft hydrothermal conditions is described for the preparation of pure and crystalline α-GeP. The physicochemical characterization of the samples allows accompaniment of the reaction evolution as well as determining short- and long-range structural organization. The phase purity of the α-GeP sample was confirmed by applying Rietveld's profile analysis, which also determined the cell parameters of its crystals.     

The preparation and fluorescence properties of europium nanoparticles

A new structured metallic nanomaterial of europium nanoparticle was prepared using tannic acid as the reductive agent,and nanoeuropium protein conjugates were synthesized by the method of lipoic acid modification on the surface of nanoparticle,which opens a new field of application of lanthanides in nanotechniques.Their properties were also characterized by UV-vis absorption spectroscopy,transmission electron microscopy (TEM),and fluorescence spectroscopy.The europium nanoparticle and its protein conjugates solution were stable and water-soluble.The fluorescence intensity of the composite europium nanoparticles was significantly increased in the presence of trace protein,and was linear proportional to the concentration of proteins under optimum conditions.According to this,a fluorimetric method for the determination of protein was developed in this paper.     

Organocatalytic preparation of simple β-hydroxy and β-amino esters: low catalyst loadings and gram-scale synthesis

A combined amino- and N-heterocyclic carbene (NHC)-catalyzed one-pot reaction sequence for the synthesis of simple enantioenriched β-hydroxy and β-amino esters using commercially available catalysts at low catalyst loadings has been developed. The desired products were obtained in high yield and excellent enantiopurity. The generation of quaternary stereocenters and application in gram-scale synthesis were also realized, with no requirements of inert or anhydrous reaction conditions, thus making this transformation a highly practical protocol.     

Peculiarities of phosphorescence of complexes between aromatic molecules and β-cyclodextrin at room temperature

Luminescence of complexes between -cyclodextrin and phenanthrene, fluorene, or naphthalene-d₈ in aqueous solutions was studied at room temperature. It is found that the addition of acetone, in the absence of heavy atoms, results in the phosphorescence of these complexes at 293 K due to triplet-triplet energy transfer. The conclusion is drawn that a heavy atom is necessary for population of a triplet level, because the intersystem crossing of an aromatic molecule in the cyclodextrin cavity is suppressed due to restriction of vibration-relaxation interactions with a medium. The phosphorescence multiply increases when lightscattering polycomplexes between an aromatic molecule and cyclodextrin in the presence of a heavy atom and a sensitizer are formed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1966–1969, October, 1995.The work was financially supported by the Russian Foundation for Basic Research (Project No. 94-03-O9961).     

Palladium-catalyzed dehydrogenative β'-functionalization of β-keto esters with indoles at room temperature

The dehydrogenative β'-functionalization of α-substituted β-keto esters with indoles proceeds with high regioselectivities (C3-selective for the indole partner and β'-selective for the β-keto ester) and good yields under mild palladium catalysis at room temperature with a variety of oxidants. Two possible mechanisms involving either late or early involvement of indole are presented.     

Non-symmetrical discotic liquid crystalline dimers: molecular design,synthesis and mesomorphic properties‡

The synthesis and mesomorphic properties of novel non-symmetrical discotic dimers have been investigated. Dimers have been prepared by the combination of electron-deficient (n-type) anthraquinone and electron-rich (p-type) triphenylene discotic monomers. The mesophases have been characterised using polarising optical microscopy, differential scanning calorimetry and X-ray diffraction. Most of the dimers have been shown to exhibit a rectangular columnar mesophase and one has a nematic columnar mesophase also. Charge transfer behaviour has been studied by UV–Vis spectroscopy.     

Synthesis of faceted β-SnWO4 microcrystals with enhanced visible-light photocatalytic properties

Highly crystalline β-SnWO(4) truncated rhombic dodecahedrons with sharp edges and smooth faces are prepared via a wet-chemical route. The compound exhibits a much higher photocatalytic activity than spherical β-SnWO(4) nanoparticles or conventionally prepared bulk β-SnWO(4) as well as faceted microcrystals of m-BiVO(4) and Ag(3)PO(4).     

Diastereo- and enantioselective preparation of β-alkylhomoallylic alcohols : Synthesis of serricornin and corynomycolic acid

A new and efficient method for the preparation of four possible stereoisomers of β-alkylhomoallylic alcohols 1 has been developed which is based on the diastereoselective addition of nucleophiles to optically active α-alkyl-β-trimethylsilyl-β,γ-unsaturated carbonyl compounds. The utility of this reaction is demonstrated by the synthesis of naturally occurring serricornin and corynomycolic acid.     

Cationic β-diketonato molybdenum nitrosyl complexes: redox and structural properties

Summary -Diketones react with [Mo(NO){HB(dmpz)₃}I₂] [HB (dmpz)₃ = tris (3,5-dimethylpyrazolyl)borate] giving the cationic complexes [Mo(NO) {HB(dmpz)₃}{OC(R)CRC-(R)O}]⁺ (R = R = Me, R = H, Me or n-Bu; R = R = Ph, R = H; R = Me, R = n-Bu, R = H), isolated as triiodide salts. Electrochemical studies show that these complexes exhibit three electrode processes: two associated with oxidation of I _inf3 ^sup– and one with reduction of the metal-containing cation. Reduction of the cation where R = R = R = Me with cobaltocene afforded the neutral paramagnetic [Mo(NO) {HB(dmpz)₃} {OC(Me)CMeC(Me)O}], which was characterized by i.r. and e.p.r. spectroscopy. In contrast, 3-chloropentane-2, 4-dione reacts efficiently with [Mo(NO){HB(dmpz)₃}I₂] giving the known chloro-analogue, [Mo(NO)-{HB(dmpz)₃}Cl₂], and no -diketonate complex was detected. The X-ray crystal structure determination of [Mo(NO){HB(dmpz)₃} {OC(Me)CMeC(Me)O}]I₃ confirms that the cation is six-coordinate and shows that the 559-01 (diketonate) bonds are slightly longer than in comparable compounds, implying that the -diketonate ligand is not such a strong -donor as alkoxide groups.