Acetalation studies-III: synthesis of 1,2:3,4:5,6-tri-O-isopropylidene-galactitol

Treatment of galactitol uith 2,2-dimethoxypropane in dimethylsulphoxide unexpeatedly yields the title triketal, containing a cis-dioxolane ring; the structure of the product has been confirmed by spectral measurements.     

Light-emitting properties of amorphous Si:C:O:H layers fabricated by oxidation of carbon-rich a-Si:C:H films

Amorphous hydrogenated carbon-rich silicon–carbon alloy film (a-Si_0.3C_0.7:H) was deposited by reactive dc-magnetron sputtering of silicon target in argon–methane gas mixture. As-deposited film exhibits white photoluminescence at room temperature. After the deposition the samples were thermally annealed in dry Ar, wet Ar, or dry O₂ flow at 450 °C for 30 minutes that resulted in the enhancement of the photoluminescence intensity by a factor of about 5, 8 and 12 respectively. Spectral distribution of light emission was almost unchanged at the annealing in dry and wet argon while the oxidation in pure oxygen resulted in strong enhancement of a “blue” shoulder in the spectrum. EPR measurements at room temperature showed the decrease of spin concentration after thermal treatment in dry and wet argon and no EPR signal was detected after annealing in oxygen. FTIR and XPS measurements evidenced the formation of a-Si:O:C:H composite material after dry oxidation. Based on the measurements of photoluminescence in the temperature range 7–300 K it is suggested that light-emitting efficiency of a-Si_0.3C_0.7:H is determined by migration of the photo-excited carriers to non-radiative recombination centers. The physical mechanisms that can be involved in the strong enhancement of visible photoluminescence in Si:C:O:H layers are discussed.     

Yb:Er:Tm:LiTaO3的上转换发白光性能研究

980 nm脉冲激光激发下,首次通过高温固相法制备Yb(10%):Er(1%):Tm(1%):LiTaO3(摩尔分数)多晶粉并实现室温上转换白光.X射线粉末衍射测试结果表明,Yb:Er:Tm:LiTaO3中的掺杂离子并没有改变晶格结构,以取代的方式存在于钽酸锂晶格中.结合功率曲线测试结果和上转换机制研究发现,产生上转换蓝光的Tm3+离子1G4态的布居主要来自双光子同时吸收过程.而单光子上转换输出的红光,则由Tm3+和Er3+离子之间的交叉弛豫过程产生,即3F2/3(Tm3+)+4I15/2(Er3+)→3H6(Tm3+)+4I9/2(Er3+).上转换绿光来源于Yb/Er离子对的二次能量传递.     

Holographic Storage Properties of In：Fe：Mn：LiNbO3 Crystals

In:Fe:Mn:LiNbO3(LN) crystals were grown in air atmosphere by Czochralski method with different concentration of In (0,1,2,3 mol%) in the melts,while the contents of Fe2O3 and MnO were 0.1 and 0.5 mol%,respectively. The location of doping ions was analyzed by Ultraviolet-visible absorption spectra and differential thermal analysis. The diffraction efficiency (η),writing time (τw) and erasure time (τe) of the crystals were measured by two-beam coupling experiment. The dynamic range and photorefractive sensitivity have also been calculated. The results showed that with the increase of In ions in the melt,the absorption edge of In:Fe:Mn:LN crystal shifts to the violet firstly and then makes the Einstein shift,the Curie temperature of crystal increases firstly and then decreases,the storage ratio speeds up,diffraction efficiency decreases,and dynamic range and photorefractive sensitivity increase. The mechanism of holographic storage properties of In:Fe: Mn:LN crystal with different doping concentration of In3+ was investigated,suggesting the In: Fe:Mn:LN crystals are excellent holographic storage materiel with better synthetical properties than Fe:Mn:LN crystals.     

The structure of a trimolecular liquid: tert-butyl alcohol:cyclohexene:water

The structure of the trimolecular liquid mixture of 2:6:1 cyclohexene, tert-butyl alcohol, and water has been investigated using hydrogen/deuterium substitution neutron scattering techniques, and a three-dimensional structural model refined to be consistent with the experimental data has been built using the technique of Empirical Potential Structure Refinement. The model shows a well-mixed solution of the three molecular components where the competing interactions between the nonpolar cyclohexene and polar water molecules are balanced in the solution leading to largely pure-alcohol-like interactions between the tert-butyl alcohol molecules. Cyclohexene molecules favor direct solvation by alcohol methyl groups while water molecules are accommodated, dispersed throughout the solution, via hydrogen bonding interactions with the alcohol molecule hydroxyl groups. Rare occurrences of direct cyclohexene-water interactions are of the classic hydrophobic hydration type and no evidence is found for microscopic heterogeneity in the trimolecular mixture in contrast to the general findings for binary alcohol-water solutions.     

High-temperature behaviour of lithium borates:: Part I: Characterization and thermal stability

Nine compounds, namely Li₃BO₃, -Li₄B₂O₅, β-Li₄B₂O₅, Li₆B₄O₉, -LiBO₂, Li₂B₄O₇, Li₃B₇O₁₂, LiB₃O₅ and Li₂B₈O₁₃ in the Li₂O–B₂O₃ system have been synthesized and characterized. The unit-cell parameters, density and solubility in water at room temperature of all the compounds are reported. The densities of the compounds were found to be in the 1.90–2.50 g cm⁻³ range, while their solubility in water at room temperature was in the 0.91–8.64×10⁻² g cm⁻³ range. Determination of the thermal stability of the compounds by quenching and differential thermal analysis (DTA) showed that only -LiBO₂ and Li₂B₄O₇ retained their original symmetry up to their congruent melting at 1121 and 1188 K, respectively, in air.     

Architecture of a validated microRNA::target interaction

MicroRNAs are small approximately 22 nucleotide regulators of numerous biological processes and bind target gene messenger RNAs to control gene expression. The C. elegans microRNA let-7 and its target lin-41 were the first microRNA::target interaction to be validated in vivo. let-7 molecules form imperfect duplexes with two required let-7 complementary sites in the lin-41 3' UTR. Here, we show that base pairing at both the 5' and 3' ends of the let-7 binding site, as well as the presence of unpaired RNA residues in the predicted duplexes, are required for lin-41 downregulation. In this study, our model for microRNA::target interactions also demonstrates that the context of a microRNA binding can be critical for function, revealing an unforeseen complexity in microRNA::target interactions.     

Propellanes-XXVIII : Electrophilic reactions of propellanes: epoxidation of olefinic propellanes

Epoxidation of 12 - oxa[4.4.3]propella - 3,8 - diene and 12 - oxa[4.4.3]propell - 3 - ene is less selective than that of 11,13 - dioxo - 12 - methyl - 12 - aza[4.4.3]propella - 3,8 - diene and 11,13 - dioxo - 12 - methyl - 12 - aza[4.4.3]propell - 3 - ene. In the latter two substrates attack syn-to the imide ring is greater than that anti- to it.     

Regioselective stannylation : Acylation of carbohydrates: coordination control

An efficient method for the regioselective enhancement of the nucleophilicity of polyhydroxy compounds has been developed. Partial stannylation of carbohydrate with (Bu₃Su)₂O and subsequent electrophilic attack with benzoyl chloride gave rise to regioselectively benzoylated product.     

Recycling of Polyolefins: Part 2: Blends of Several Polymers

Abstract

The aim of the present paper is to study the feasibility of recycling polyolefins with some additives, such as copolymers in order to improve the mechanical properties and increase the useful life of the blends. From analysis of the results of blends of polypropylene(PP) with POD(Blend of recycled Polyolefins), it can be concluded that it is possible to recycle POD up to 20%, the addition of a copolymer to the 12% composition improving the interfacial adhesion. In the case of low density polyethylene(LDPE) mixtures with POD, the optimum improvement in properties is obtained with approximately 10% of POD. The addition of copolymers did not yield any improvement in the properties.     

Encapsulation of norharmane in cyclodextrin: formation of 1:1 and 1:2 inclusion complexes

Steady state absorption and fluorometric techniques have been used to investigate the photophysics of norharmane (NHM), a bioactive fluorophore, in aqueous as well as aqueous cyclodextrin (CD) environments. The absorption and steady state fluorescence spectral studies reveal the formation of two types of inclusion complexes between the fluorophore and beta-cyclodextrin (beta-CD) depending on the relative population of the two. The stoichiometries and association constants of these complexes have been determined monitoring the fluorescence data. alpha-and gamma-cyclodextrin (alpha-CD, gamma-CD) do not have appreciable effect on the spectral pattern of the fluorophore. The differential fluorimetric behavior of NHM in different CD environments has been rationalized from the variation of the relative dimensions of the probe and the CD cavities.     

The mass spectrum of 1:12, 2:3, 4:5, 6:7, 8:9, 10:11-hexabenzocoronene

The mass-spectra of 1:12, 2:3, 4:5, 6:7, 8:9, 10:11-hexabenzocoronene and the isomer 1:2, 3:4, 5:6, 7:8, 9:10, 11:12-hexabenzocoronene have been examined. The former is typically that of an aromatic conjugated hydrocarbon and is sparse, the latter is more intense. It is conjectured that the former may be found in interstellar space.     

Chiral Polythiophenes: Part I: Syntheses of Monomeric Precursors

The purpose of this mini-review is to comprehensively present the synthetic approaches used for the preparation of non-racemic mono- and multi-substituted thiophenes, which, in turn, can be applied as precursors for the synthesis of chiral polythiophenes isolated as a single chemical entity or having supramolecular thin-layer architectures.     

Determination of phosphorus:glycerol:acyl ratios in phospholipids

Phospholipids (1–5 mg) are mixed with methyl heptadecanoate as an internal standard. One part of the sample is reduced with Vitride in tetrahydrofuran in a sealed tube at 50 2C for 1 hr. The reaction products are acetylated in the same tube by treatment with acetic acid-acetic anhydride at 140 °C. After 1 hr total O-acyl and after 16 additional hours glycerol are determined as the fully acetylated compounds by gas-liquid chromatography.Another part of the sample is subjected to acidic hydrolysis and total O-acyl and N-acyl groups are determined by GLC as fatty-acid methyl esters. The aqueous phase is heated to 100 °C with 6 N HCl for 72 hr and phosphorus is measured colorimetrically.