巧制无水硫酸铜

在中学化学实验中,通常用无水硫酸铜来检验少量水的存在,然而,无水硫酸铜的吸湿性很强,需要时现制现用.制取无水硫酸铜时,通常将硫酸铜晶体放在蒸发皿中用小火慢慢加热并用玻璃棒不停搅拌,往往由于加热时温度稍高便有少量硫酸铜分解,使得一部分变黑,而且易结块,操作比较麻烦,而笔者为了克服以上缺点,不需加热便能巧妙制得无水硫酸铜,不但操作简单,而且实验效果明显.     

用无水硫酸铜检验普通酒精里的水的实验结果

用白色无水硫酸铜来检验普通酒精里所含的水,这是中学化学沿用了几十年的传统方法。“关于乙醇中含水检验的商榷”的短文,断然否定了这一传统方法的可靠性和正确性,而代之以用无水氯化钴来检验普通酒精里的水。笔者在重新进行多次实验之后认为,该文的论据不足。在8支干燥试管中分别注入5ml不同的酒精,再分别加入不同量(估计量)的无水硫酸铜粉末,实验结果见下表。     

也谈乙醇中含水的检验

“化学教育”1989年第3期,“关于乙醇中含水检验的商榷”一文(以下简称黎文),认为普通乙醇(95％)中含水量不能用无水硫酸铜来检验,即使含水量接近50％都不能使无水硫酸铜变蓝,并从实验和理论上加以解释。我们认为,上述观点无论从理论解释还是实验结论来说,都缺乏根据,即使在含水量低于普通乙醇(如98％乙醇)的情况下,也是可以用无水硫酸铜检出水的。首先,我们认为,黎文中所述的实验是不准确的。我们按所述的实验方法,反复多次验证所得结果与黎文结果相反。     

1,3,4,6-四-O-苄基-β-D-氨基葡萄糖盐酸盐的合成方法改进

以D-氨基葡萄糖盐酸盐为原料,制得D-氨基葡萄糖希夫碱(1);在无水DMF溶液中,1与苄溴反应得1,3,4,6-四-O-苄基-β-D-氨基葡萄糖希夫碱(2);2经酸解,甲醇/水重结晶合成了高纯度的1,3,4,6-四-O-苄基-β-D-氨基葡萄糖盐酸盐,其结构经1H NMR和IR确证。     

中学化学实验的成功经验

介绍中学化学实验的成功经验,其中包括铁钉与硫酸铜溶液反应,明矾和绿矾净水实验,重金属盐使蛋白质变性实验,溴乙烷与氢氧化钠反应产物的检验,蛋白质与硝酸的反应,水的硬度,铜与硝酸银溶液反应等.     

镁与硫酸铜溶液反应产物的研究

通过实验探究了镁与硫酸铜溶液反应的产物。研究结果表明,镁与硫酸铜溶液的反应是并不单一的复杂反应,反应生成的棕褐色不溶物不只是单质铜,还含有氧化亚铜,生成的蓝绿色沉淀是碱式硫酸铜。     

高活性烷烃异构化催化剂：二氧化硅为载体的三氯化铝-硫酸铜

三氯化铝是常用的烷烃异构化催化剂之一,但需要有少量的水存在,如果用无水三氯化铝,需要较高的反应温度.Ono等用等克分子的无水三氯化铝和无水硫酸铜的混合物作为催化剂,可以使正戊烷在较低的温度(28℃)下进行异构化反应,3小时后总转化率为21％,选择性为92％.但这种催化剂对于正己烷的异构化反应,活性很低,总转化率只有1％.何纪纲等制备了聚氯乙烯—三氯化铝·硫酸铜催化剂,证明它在15℃下能够催化正己烷的异构化反应,总转化率为25％,但选择性只有58％.     

关于使用无水硫酸铜检验乙醇中水分的再商榷

2007年第5期《化学教育》上刊登了田宗学老师撰写的论文《一个不可靠的结论》。在此文中,田宗学老师从实验观察和理论分析2个方面得出结论:只有当乙醇中含水量超过一定的比例(体积大于1∶1)时,无水硫酸铜才开始变蓝。所以,用无水硫酸铜检验乙醇中是否含水的结论并不可靠,更是一     

用~(119)Sn、~(121)Sb及~(13)C NMR研究无水SnCl_4、SbCl_5与Lewis碱的相互作用

无水SnCl_4及SbCl_5是典型的Lewis酸,是有机反应中常用的催化剂。它们的溶剂化热效应早已受到人们的关注,然而用NMR方法来研究它们的溶剂化作用至今未见报道。本工作用~(119)Sn、~(121)Sb及(13)C NMR考察了典型Lewis酸无水SnCl_4、SnCl_5与二十几种Lewis碱的相互作用,直接证实了Lewis酸碱反应为电子的授受过程。     

不能用无水硫酸铜来检验酒精里的水吗

用白色无水硫酸铜来检验普通酒精里所含的水,这是中学化学沿用了上百年的传统方法.《化学教育》1989年3期第45页,一篇《关于乙醇中含水检验的商榷》的短文,曾质疑过这一传统方法的可靠性和正确性:     

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     

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.     

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.     

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.     

Substitution of 2-phosphaindolizines by bromine and by chlorophosphines

Bromine does not add to phosphorus in a 2-phosphaindolizine 1 but substitutes its 1-position. The 1-bromo derivatives 2 are best prepared with Br₂/NEt₃ or N-bromosuccinimide. Their hydrolysis is remarkable; it involves a debromination of C-1, an oxidation of P and a selective opening of the P/C-3 bond. PCl₃ also causes a substitution of the 1-position. The resulting 1-dichlorophosphino derivatives 5 easily undergo a substituent exchange at the exocyclic phosphorus. More 1-phosphino derivatives are formed in the reaction of 1 with phenyl and diazaphospholyl dichlorophosphine.     

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.