镁铁和镁铁铝催化剂氢还原过程的研究

以水滑石为前体 ,制备了镁铁和镁铁铝复合氧化物催化剂 ,运用原位穆斯堡尔谱研究了催化剂在H2 气氛中的还原行为。结果表明 :由于Mg、Al的加入和固溶体的形成 ,相对地稳定了FeO物相 ,阻碍了H2 对铁离子的还原 ,使得Fe2 进一步还原为金属Fe0 的能力减弱 ;在还原过程中催化剂首先生成含Fe2 的固溶体FeO MgO或FeO MgO Al2O3,然后再完全还原成金属Fe0。     

镁与消化系统疾病

镁是人体必需的元素，具有重要的生理功能。本文简要介绍了镁的生理作用和在消化系统的应用及发展。     

原子吸收光谱法测定动物性食品中铜锌铁钙镁

铜、锌、铁、钙、镁都是人体必不可缺的矿物质和微量元素 ,它们对造血、细胞生长、酶活性的激发 ,RNA、DNA和蛋白质的合成 ,维持核酸结构的稳定 ,抑制神经兴奋以及正常的生长发育等起着极其重要的作用[1] 。膳食是人体补充这些物质的最主要的途径 ,而动物性食品对人类的膳食平衡起着极其重要的作用 ,某些矿物质及微量元素的不足或过多均会影响到食品的营养价值。因此 ,动物性食品中矿物质与微量元素的测定 ,无论是从营养学还是卫生学的角度而言 ,都显得极度重要和必不可少。本法采用原子吸收光谱法连续测定动物食品中微量元素和矿物质铜…     

铁酸镁在2，3，6－三甲基苯酚羟基化反应中的催化性能

 采用共沉淀法与柠檬酸法合成了铁酸镁，并用X射线衍射和红外光谱等对不同样品进行了表征．以三甲基苯酚为原料，以铁酸镁为催化剂，以双氧水为氧化剂，实现了一步羟化为三甲基对苯二酚（维生素E重要中间体）的目的．详细考察了催化剂、温度、溶剂和双氧水等因素对该反应体系的影响．结果表明，铁酸镁对该反应体系具有很好的催化效果，较常用的羟化催化剂TS－1分子筛等的催化性能好得多．该过程可以进一步研究发展成为一个环境友好催化过程．     

原子吸收光谱法测定氮化硅陶瓷材料中微量钙镁铁

氮化硅(Si_3N_4)陶瓷材料中微量钙,镁和铁的测定,目前大都采用化学分析法。这种方法操作繁琐,实验条件苛刻,所需分析试剂种类多,分析时间长,难以满足科研和生产的要求。本文采用空气-乙炔火焰原子吸收光谱法测定,较好地解决了Si_3N_4中钙、镁和铁的测定。方法具有简便、快速、准确等优点。拟定的方法用于样品分析,结果令人满意。一、主要试剂、仪器及测定条件钙和镁标准溶液:分别称取高纯氧化钙0.1400g和高纯氧化镁0.1658g,用盐酸(1+1)溶解煮沸,冷却后移入100L容量瓶中,水定容,配成1mg/mL标准溶液,用     

乙二胺四乙酸滴定法测定钙镁保健食品中钙、镁的含量

<正>钙和镁是人体必需元素。钙对人机体十分重要,除密切关乎骨骼健康外,还参与神经、肌肉活动及激素分泌、血液凝固等[1],每日保证摄入一定量的钙可预防骨质疏松症[2];镁参与人体内数百种酶的新陈代谢[3],与人体健康密切相关[4]。因地域及饮食差异,不同人之间的钙、镁日摄入量不尽相同。为保证每日摄入量满足人体所需[5],服用钙镁保健食品成为大多数人的选择之一,其中以钙镁片居多。钙镁片的主要成分为碳酸钙和碳酸镁,     

镁——人体能量代谢中重要的辅助因子

人体中镁的含量虽然不高,但它是维持人体正常生理功能的重要因素。本文仅从人体分解和利用ATP、分解仿物和分解体内物质以获得能量的过程,阐明镁是人体能量代谢中的重要辅助因子。     

铁与人体健康

铁是人体必需的营养元素,在人体内承担着重要的生理功能。本文探讨了人体对铁的吸收利用及其影响因素,人体铁的来源和供给机理,以及铁在人体内的运输和贮存形式。     

镁的正常代谢及其调节

镁是一种人体必需微量元素，对人体健康有重要意义。镁的代谢受肾脏、消化道及内分泌多种因素调节，其调节机制尚未完全清楚。     

稀土在球铁和蠕铁中的作用

通过对稀土在球铁和蠕铁中作用的研究得出稀土蠕化能力比镁强,蠕化剂应以稀土为主同时含少量镁,镁的球化能力比稀土强,球化剂应以镁为主同时含少量稀土的结论。“球铁中含适量稀土可降低球化所需的残余镁量,使石墨球数增加,白口倾向和壁厚敏感性减小,同时能减少氧化夹渣和消除干扰元素的影响。     

Regioselectivity of olefin oxidation by iodosobenzene catalyzed by metalloporphyrins : control by the catalyst

The regioselectivity of the oxidation of three monosubstituted olefins, 6-phenoxyhex-1-ene, hex-1-ene and styrene, by iodosobenzene in the presence of various Fe-, Mn- or Cr-tetraaryl-porphyrins, was studied. It was found that, besides epoxides, known products from such systems, allylic alcohols and aldehydes were formed, the latter not being derived from the corresponding epoxides. The relative importance of these reactions greatly depends upon both the metal and porphyrin constituents of the catalyst. More particularly, the competition between epoxidation and allylic hydroxylation can be efficiently controlled by non-bonded interactions between the olefin and porphyrin substituents. No hydroxylation of the aromatic rings and no oxidative dealkylation of the ether function was detected.     

Enantiomer separation by CEC——Enantiomer separation by packed-capillary electrochromatography

Three chiral compounds were successfully separated in a short time with two enantiomer separation models on packed-capillary electrochromatography (CEC). (i) 75 μm I.D. capillaries were packed with 5 μm β-cyclodextrin (β-CD) chiral stationary phase (CSP). Effects of voltage, pH and concentration of organic modifier on electroosmotic flow (EOF) and chiral separations were investigated systematically. Enantiomers of a neutral compound (benzoin) and a neutral drug (mephenytoin) were separated within a short time with high efficiency. Efficiency of 32 000 theoretical plates per meter and resolution (R_s) of 1.42 were achieved for enantiomers of benzoin using a βCD packed column with 6.2 cm packed length. Efficiency of 45 000 theoretical plates per meter and R_s of 3.40 were obtained for enantiomers of mephenytoin. Especially, the enantiomer separation of mephenytion was performed in just 3.4 min with R_s of 2.60. (ⅱ) 75 μm I.D. capillary was packed with octadecylsilica particles (ODS). Chiral separat     

Multitargeting by curcumin as revealed by molecular interaction studies

Curcumin (diferuloylmethane), the active ingredient in turmeric (Curcuma longa), is a highly pleiotropic molecule with anti-inflammatory, anti-oxidant, chemopreventive, chemosensitization, and radiosensitization activities. The pleiotropic activities attributed to curcumin come from its complex molecular structure and chemistry, as well as its ability to influence multiple signaling molecules. Curcumin has been shown to bind by multiple forces directly to numerous signaling molecules, such as inflammatory molecules, cell survival proteins, protein kinases, protein reductases, histone acetyltransferase, histone deacetylase, glyoxalase I, xanthine oxidase, proteasome, HIV1 integrase, HIV1 protease, sarco (endo) plasmic reticulum Ca(2+) ATPase, DNA methyltransferases 1, FtsZ protofilaments, carrier proteins, and metal ions. Curcumin can also bind directly to DNA and RNA. Owing to its β-diketone moiety, curcumin undergoes keto-enol tautomerism that has been reported as a favorable state for direct binding. The functional groups on curcumin found suitable for interaction with other macromolecules include the α, β-unsaturated β-diketone moiety, carbonyl and enolic groups of the β-diketone moiety, methoxy and phenolic hydroxyl groups, and the phenyl rings. Various biophysical tools have been used to monitor direct interaction of curcumin with other proteins, including absorption, fluorescence, Fourier transform infrared (FTIR) and circular dichroism (CD) spectroscopy, surface plasmon resonance, competitive ligand binding, Forster type fluorescence resonance energy transfer (FRET), radiolabeling, site-directed mutagenesis, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), immunoprecipitation, phage display biopanning, electron microscopy, 1-anilino-8-naphthalene-sulfonate (ANS) displacement, and co-localization. Molecular docking, the most commonly employed computational tool for calculating binding affinities and predicting binding sites, has also been used to further characterize curcumin's binding sites. Furthermore, the ability of curcumin to bind directly to carrier proteins improves its solubility and bioavailability. In this review, we focus on how curcumin directly targets signaling molecules, as well as the different forces that bind the curcumin-protein complex and how this interaction affects the biological properties of proteins. We will also discuss various analogues of curcumin designed to bind selective targets with increased affinity.     

Antibiotic recognition by binuclear metallo-beta-lactamases revealed by X-ray crystallography

Metallo-beta-lactamases are zinc-dependent enzymes responsible for resistance to beta-lactam antibiotics in a variety of host bacteria, usually Gram-negative species that act as opportunist pathogens. They hydrolyze all classes of beta-lactam antibiotics, including carbapenems, and escape the action of available beta-lactamase inhibitors. Efforts to develop effective inhibitors have been hampered by the lack of structural information regarding how these enzymes recognize and turn over beta-lactam substrates. We report here the crystal structure of the Stenotrophomonas maltophilia L1 enzyme in complex with the hydrolysis product of the 7alpha-methoxyoxacephem, moxalactam. The on-enzyme complex is a 3'-exo-methylene species generated by elimination of the 1-methyltetrazolyl-5-thiolate anion from the 3'-methyl group. Moxalactam binding to L1 involves direct interaction of the two active site zinc ions with the beta-lactam amide and C4 carboxylate, groups that are common to all beta-lactam substrates. The 7beta-[(4-hydroxyphenyl)malonyl]-amino substituent makes limited hydrophobic and hydrogen bonding contacts with the active site groove. The mode of binding provides strong evidence that a water molecule situated between the two metal ions is the most likely nucleophile in the hydrolytic reaction. These data suggest a reaction mechanism for metallo-beta-lactamases in which both metal ions contribute to catalysis by activating the bridging water/hydroxide nucleophile, polarizing the substrate amide bond for attack and stabilizing anionic nitrogen intermediates. The structure illustrates how a binuclear zinc site confers upon metallo-beta-lactamases the ability both to recognize and efficiently hydrolyze a wide variety of beta-lactam substrates.     

Membrane solubilization by detergent: resistance conferred by thickness

The commonly held model for membrane dissolution by detergents/surfactants requires lipid transport from the inner to the outer bilayer leaflet ('flip-flop'). Although applicable to many systems, it fails in cases where cross-bilayer transport of membrane components is suppressed. In this paper we investigate the mechanism for surfactant-induced solubilization of polymeric bilayers. To that end, we examine the dissolution of a series of increasingly thick, polymer-based vesicles (polymersomes) by a nonionic surfactant, Triton X-100, using dynamic light scattering. We find that increasing the bilayer thickness imparts better resistance to dissolution, so that the concentration required for solubilization, after a fixed amount of time, increases nearly linearly with membrane thickness. Combining our experimental data with a theoretical model, we show that the dominant mechanism for the surfactant-induced dissolution of polymeric vesicles, where polymer flip-flop across the membrane is suppressed, is the surfactant transport through the bilayer. This mechanism is different both qualitatively and quantitatively from the mechanisms by which surfactants dissolve pure lipid vesicles.     

DNA damage by sulfite autoxidation catalyzed by cobalt complexes

DNA damage was investigated in the presence of sulfite, dissolved oxygen and cobalt(II) complexes with glycylglycylhistidine, glycylhistidyllysine, glycylglycyltyrosylarginine and tetraglycine. These studies indicated that only Co(II) complexed with glycylglycylhistidine (GGH) induced DNA strand breaks at low sulfite concentrations (1-80 microM) via strong oxidants formed in the reaction. In the presence of the other complexes, some damage occurred only in the presence of high sulfite concentrations (0.1-2.0 mM) after incubation for 4 h. In the presence of GGH, Co(II) and dissolved O2, DNA damage must involve a reactive high-valent cobalt complex. The damaging effect was increased by adding S(IV), due to the oxysulfur radicals formed as intermediates in S(IV) autoxidation catalyzed by the complex. SO3 -, HO and H radicals were detected by EPR-spin trapping experiments with DMPO (5,5-dimethyl-1-pyrroline N-oxide). The results indicate that Co(II) binds O2 in the presence of GGH, and leads to the formation of a DMPO-HO adduct without first forming free superoxide or hydroxyl radical, supporting the participation of a reactive high-valent cobalt complex.