Trifluoromethanesulfonic acid mediated Friedel-Crafts reaction of (E)-3-aryl-2-(diethoxyphosphoryl)acrylic acids with electron-rich hydroxyarenes. A convenient approach to α-methylene-δ-valerolactones

The synthesis of trans-3-diethoxyphosphoryl-4-aryl-3,4-dihydrocoumarins from electron-rich hydroxyarenes and (E)-3-aryl-2-(diethoxyphosphoryl)acrylic acids has been achieved by using CF₃SO₃H as a catalyst. The products could be easily transformed to the corresponding α-methylene-δ-valerolactones by means of the Horner-Wadsworth-Emmons reaction.     

Structure and magnetic properties of the orthorhombic n=2 Ruddlesden-Popper phases Sr3Co2O5+δ (δ=0.91, 0.64 and 0.38)

The reduced Ruddlesden-Popper phases, Sr₃Co₂O_5+δ with δ=0.91, 0.64 and 0.38, have been prepared in a nitrogen atmosphere. The crystal structures were determined by powder neutron diffraction. Oxygen vacancies are found both in O(3) and O(4) sites but the majority are along one crystallographic axis in the CoO₂ plane, inducing an orthorhombic distortion of the normally tetragonal n=2 Ruddelsden-Popper structure. Superstructures due to oxygen ordering are observed by electron microscopy. The magnetic measurements reveal complex behavior with some ferromagnetic interactions present for Sr₃Co₂O_5.91 and Sr₃Co₂O_5.64.     

Phase stability of La1−xCaxCrO3−δ in oxidizing atmosphere

The chemical stability of perovskite-type La_1−xCa_xCrO_3−δ (x=0.1, 0.2, 0.3) in high oxygen partial pressure, P_O2, was investigated with three methods: thermogravimetry, XRD analysis, and thermodynamic calculation. The second phase, CaCrO₄ was observed by XRD analysis on the powder equilibrated in high P_O2. Thermogravimetry under fixed temperatures sensitively detected the segregation of the second phase in the form of oxygen incorporation, because oxidation of chromium ion accompanies the segregation. The second phase tended to appear in high P_O2 and at low temperature. The single-phase regions of La_1−xCa_xCrO_3−δ obtained from the two experimental methods well agreed with each other. The results of thermodynamic calculation on the assumption of ideality of the solid solution also agreed with the experimental results. These results suggested the sufficient chemical stability of La_1−xCa_xCrO_3−δ in high P_O2 concerning the application to an interconnector of high-temperature solid oxide fuel cells; for example, La_0.7Ca_0.3CrO_3−δ is stable at 1273 K in air.     

New Δ-tocotrienol derivatives from Colombian propolis

Abstract

Two new δ-tocotrienol derivatives with oxidized terminal chain: 5,6-dioxo-garcinoic acid (trans-13′-carboxy-5,6-dioxo-δ-tocotrienol) (2) and 5-hydroxy-8b-oxo garcinoic acid (trans-13′-carboxy-5-hydroxy-8b-oxo-δ-tocotrienol) (3), together with one known derivative garcinoic acid (trans-13′-carboxy-δ-tocotrienol) (1) were isolated from a Colombian propolis. Garcinoic acid was found as a propolis constituent for the first time. The isolated compounds and crude ethanolic extract demonstrated high antimicrobial activity against Staphylococcus aureus and Candida albicans (MICs range: 10–39?μg/ml) as well as promising antioxidant potential in DPPH assay. Compound 3 displayed highest radical scavenging activity, even higher than that of dl-α-tocopherol, used as a positive control.     

High resolution and in situ neutron powder diffraction study of the crystal structure and the stability of Ba4CaCu3O8+δ

The crystal structure and stability of Ba₄CaCu₃O_8+δ have been investigated by neutron powder diffraction, differential thermal analysis and thermogravimetry. It is found that the phase is not stable below 1065 K in p(O₂)=1 bar and decomposes according to the eutectoid reaction Ba₄CaCu₃O_8+δ+x O₂⇒Ba₂CuO_3.4+CaO+2BaCuO₂. However, the equilibrium with the outer gas is not reached for sintered ceramics so that Ba₄CaCu₃O_8+δ can be obtained in a metastable state after normal cooling conditions. In this case, the crystal structure is cubic (Im-3m, , δ=0.68, Z=2, R_wp=2.5%, R_Bragg=5.4%) as reported in the literature. In reduced oxygen partial pressure (p(O₂)<10⁻⁶ bar), Ba₄CaCu₃O_8+δ is stable down to room temperature and has a tetragonal structure with a significant lower oxygen content (P4/mmm, , , δ=-0.81, Z=2, R_wp=2.8%, R_Bragg=5.1%). The difference between the two crystal structures is discussed in terms of oxygen content, copper formal valence and cation coordination. The influence of the oxygen pressure on the stability of Ba₄CaCu₃O_8+δ is also discussed.     

Synthesis and dark toxicity of 5-(4-carboxyphenyl)-10,15,20-tris(phenyl)-porphyrinato chlorido gallium(III) when conjugated to δ-aminolevulinic acid

5-(4-Carboxyphenyl)-10,15,20-tris(phenyl)-porphyrinato chlorido gallium(III) (2) was synthesized and then linked to ethyl ester δ-aminolevulinic acid to form 3. There was no shift in Soret band following conjugation. The fluorescence and singlet oxygen generating behavior of the porphyrins were also investigated. The highest singlet oxygen quantum yield (Φ_Δ) obtained was that of 3. Complexes 2 and 3 as well as metal free 5-(4-carboxyphenyl)-10,15,20-tris(phenyl)-porphyrinato showed no dark toxicity on MCF-7 breast cancer cells.     

低温熔盐法制备球状多孔 La1-xSrxMn0.8Fe0.2O3（0≤x≤0.6）及其催化 CO氧化性能

汽车尾气中 CO, HC, NOx,硫化物及其颗粒粉尘严重危害人们身体健康和大气环境,是大气环境的主要污染源之一.目前,尾气净化是其减排的最主要方式.汽车尾气催化剂的发展经历了几代的研究,一直以来广泛采用 Pt, Pd和 Rh等贵金属,但因其资源匮乏,价格昂贵,容易被 S和 P中毒,因此人们逐渐将目光投向非贵金属催化剂的研发.钙钛矿复合氧化物因具有独特的物理化学性质以及灵活的“化学剪裁”特性而在材料研究等领域颇受青睐,有望成为贵金属催化剂的替代品.一般而言,催化剂的比表面积越大,表面活性位点越多,其催化活性越高,且会明显降低起燃温度.目前,一些制备工艺,如水热法、共沉淀法、微乳液法和硬模板法,虽可在一定程度上提高催化剂的比表面积,但却存在费时、耗能及制备工艺复杂等缺点.因此,如何简单有效地制备出大比表面积的钙钛矿型催化剂依然是一个难题.本文以合成的分级多孔δ-MnO2微球为模板,采用熔盐法制备出球状多孔 La1-xSrxMn0.8Fe0.2O3(0≤x≤0.6)钙钛矿氧化物,研究了球状多孔钙钛矿氧化物的形成过程和合适的制备温度,以及 B位 Fe3+掺杂量为20%时 A位 Sr2+掺杂量对钙钛矿催化剂结构和催化活性的影响.采用 X射线粉末衍射、扫描电子显微镜、透射电子显微镜、N2吸附-脱附、傅里叶红外光谱(FT-IR)和 X射线能谱(XPS)等方法对催化剂进行了表征.在固定床石英管反应器上评价了催化剂催化 CO氧化活性及稳定性,采用气相色谱联接氢火焰离子化检测器检测了产物和反应物的组成.结果表明,以分级多孔δ-MnO2微球为模板,采用熔盐法在450oC反应4 h制备出的球状多孔 La1-xSrxMn0.8Fe0.2O3(0≤x≤0.6)钙钛矿氧化物具有良好的结晶性、较大的比表面积(55.73 m2/g)和孔体积(0.37 cm3/g).其球状多孔结构的形成可分为两个阶段：原位形成钙钛矿相和纳片表面析出钙钛矿晶粒及钙钛矿晶粒的再生长.另外, FT-IR光谱表明, Fe3+和 Sr2+成功进入 A, B位.同时, CO转化曲线表明, B位 Fe3+的掺杂量为20%时, A位 Sr2+的掺杂量高于30%时可以明显改善催化剂催化 CO氧化活性： La1-xSrxMn0.8Fe0.2O3(0≤x≤0.3)的T50和T90分别在180和198oC左右;而 La0.55Sr0.45Mn0.8Fe0.2O3和 La0.4Sr0.6Mn0.8Fe0.2O3的T50均低于125oC; La0.55Sr0.45Mn0.8Fe0.2O3的T90为181oC,而 La0.4Sr0.6Mn0.8Fe0.2O3却仍低于125oC. XPS结果则证明,较高的催化活性得益于 La0.4Sr0.6Mn0.8Fe0.2O3表面存在较多的 Mn4+、氧空位及吸附氧.最后, La0.55Sr0.45Mn0.8Fe0.2O3和 La0.4Sr0.6Mn0.8Fe0.2O3的稳定性测试结果表明,采用熔盐法以δ-MnO2为模板在450oC焙烧4 h制备的多孔球状钙钛矿具有较好的催化稳定性.虽然催化剂制备工艺简单,周期短,但比表面积最大只有55.73 m2/g,为硬模板法的1/2,因此提高比表面积将是今后研究的方向.     

Systematic investigation on new SrCo1−yNbyO3−δ ceramic membranes with high oxygen semi-permeability

SrCo_1−yNb_yO_3−δ (y = 0.025–0.4) were synthesized for oxygen separation application. The crystal structure, phase stability, oxygen nonstoichiometry, electrical conductivity, and oxygen permeability of the oxides were systematically investigated. Cubic perovskite, with enhanced phase stability at higher Nb concentration, was obtained at y = 0.025–0.2. However, the further increase in niobium concentration led to the formation of impurity phase. The niobium doping concentration also had a significant effect on electrical conductivity and oxygen permeability of the membranes. SrCo_0.9Nb_0.1O_3−δ exhibited the highest electrical conductivity and oxygen permeability among the others. It reached a permeation flux of ∼2.80 × 10⁻⁶ mol cm⁻² s⁻¹ at 900 °C for a 1.0-mm membrane under an air/helium oxygen gradient. The further investigation demonstrated the oxygen permeation process was mainly rate-limited by the oxygen bulk diffusion process.     

Synthesis and characterization of the K2NiF4 phases La1+xSr1−xCo0.5Fe0.5O4−δ (x=0, 0.2)

The K₂NiF₄ phases LaSrCo_0.5Fe_0.5O₄ and La_1.2Sr_0.8Co_0.5Fe_0.5O₄, and their reduced forms LaSrCo_0.5Fe_0.5O_3.75 and La_1.2Sr_0.8Co_0.5Fe_0.5O_3.85, have been successfully prepared by solid-state reactions, followed by reduction in 10% H₂/N₂ in order to produce oxygen-deficient materials. All materials crystallize in a tetragonal K₂NiF₄ structure (space group I4/mmm) with Co and Fe randomly distributed over the B-sites of the structure. Mössbauer spectra have confirmed the trivalent state of Fe in these materials. In the reduced materials, oxide ion vacancies are confined to the equatorial planes of the K₂NiF₄ structure and the Co is present almost entirely as Co²⁺ ions; low-temperature neutron powder diffraction data reveal that these reduced phases are antiferromagnetically ordered with a tetragonal noncollinear arrangement of the moments. The Co³⁺ ions, present in stoichiometric LaSrCo_0.5Fe_0.5O₄ and La_1.2Sr_0.8Co_0.5Fe_0.5O₄, inhibit magnetic order and are assumed to be in the low-spin state.