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.     

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.     

Pseudo-potentiostatic electrolysis by potential buffering induced by the oxygen evolution reaction

A new approach is proposed in order to perform electrochemical oxidation of organics by working under galvanostatic conditions with the potential ‘buffered’ by the competing side reaction of oxygen evolution (OER). According to this process the working potential is fixed by the nature of electrode material and is buffered during organics oxidation by the side reaction of OER. This principle has been used for the selective oxidation of some model organic compounds on Ti/IrO₂ anode.     

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.     

Production of Enzymes by Plant Cells Immobilized by Sol-Gel Silica

Ajuga reptans cells are cultivated and used for production of invertase. These plant cells are immobilized by a sol-gel SiO₂ membrane, which is built up directly on the cell surface by exposure to a gaseous flow of silicon alcoxide precursors. The immobilization modifies the metabolic activity of cells, resulting in a 40-fold increase in invertase production with respect of free cells. Results concerning total release of proteins, cell growth and produced invertase activity are discussed, considering the absence of breeding, induced by SiO₂ immobilization, the prominent factor promoting the observed exceptional increase in invertase productivity.     

Determination of furosemide in urine by HPLC with preconcentration by micellar-extraction

The micellar extraction of furosemide by the nonionic surfactant (NS) Triton X-100 at the cloud point was studied; it was performed in a conventional heating mode and upon induction with phenol. It was shown that the quantitative recovery of the preparation was attained using hydrophobic micellar phases of NS modified with phenol. A procedure was developed for determining furosemide in urine by reversed-phase HPLC with preconcentration by micellar extraction in the presence of phenol. The preconcentration ratio was 80 and the detection limit for furosemide, 3 mg/L. The procedure was used to analyze urine samples by the standard addition method.     

Pretreatment of softwood by acid-catalyzed steam explosion followed by alkali extraction

A process for converting lignocellulosic biomass to ethanol hydrolyzes the hemicellulosic fraction to soluble sugars (i.e., pretreatment), followed by acid- or enzyme-catalyzed hydrolysis of the cellulosic fraction. Enzymatic hydrolysis may be improved by using an alkali to extract a fraction of the lignin from the pretreated material. The removal of the lignin may increase the accessibility of the cellulose to enzymatic attack, and thus improve overall economics of the process, if the alkali-treated material can still be effectively converted to ethanol. Pretreated Douglas fir produced by a sulfuric-acid-catalyzed steam explosion was treated with NaOH, NH₄OH, and lime to extract some of the lignin. The treated material, along with an untreated control sample, was tested by an enzymatic-digestion procedure, and converted to ethanol by simultaneous saccharification and fermentation using a glucose-fermenting yeast. NaOH was most effective at removing lignin (removed 29%), followed by NH4OH and lime. However, the susceptibility of the treated material to enzymatic digestion was lower than the control and decreased with increasing lignin removal. Ethanol production was similar for the control and NaOH-treated material, and lower for NH₄OH- and lime-treated material.     

双子季铵盐稳定的纳米钯催化Suzuki反应的研究

双子座季铵盐能够稳定现场产生的纳米钯粒子,该纳米钯粒子能有效地催化一系列芳基硼酸和芳基卤代烃发生Suzuki偶联反应.双子座季铵盐稳定的纳米钯粒子能够在空气中稳定存在,透射电镜(TEM)分析纳米钯粒子呈圆球形,粒径分布在5～25 nm.该方法具有反应条件温和、反应时间短、后处理简单方便等优点.     

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.     

Immobilization of a recombinant cutinase by entrapment and by covalent binding

Fusarium solani pisi recombinant cutinase, immobilized by entrapment in calcium alginate and by covalent binding on porous silica, was used to catalyze the hydrolysis of tricaprylin. The influence of relevant parameters on the catalytic activity such as pH, temperature, and the substrate concentration were studied. Cutinase immobilized by entrapment presented a Michaelis-Menten kinetics for tricaprylin concentrations up to 200 mM. At higher concentrations of substrate, inhibition was observed. For covalent binding immobilization, diffusional limitations were observed at low substrate concentrations and substrate inhibition occurred for concentrations higher than 150 mM. The stability of immobilized cutinase was also evaluated. The enzyme immobilized by entrapment showed a high stability, in contrast to the immobilization on porous silica.     

Preconcentration of phenols by adsorption on organo-clay followed by capillary electrophoretic determination

The organo-clay adsorbent used was prepared by modification of montmorillonite from Kur?unlu, Turkey with the cationic surfactant cetyltrimethlyammonium bromide. The modification process involves replacing the inorganic exchange cations of the clay by organic cations containing long chain alkyl groups. The retention of phenolic compounds from aqueous solution on the organo-clay was studied. The analytes are quantitatively retained on the proposed adsorbent at pH 7 and recovered by elution with ethanol. The determination of phenols was performed by capillary electrophoresis.     

The periodic table: revelation by quest rather than by revolution

The concept of major scientific advances occurring as a short-term ‘revolutionary’ change in thinking interspersed by long periods of so-called ‘normal’ science seems to be losing ground to more ecological models, which are more inimical of the twists and turns of life. From this idea it is a short step to charting science’s progress against stages used in fictional storytelling, which after all is life-based. This paper explores the development of the periodic table in terms of the achievement of a fictional ‘quest’, and finds the stages of such a story are well represented. While Mendeleev or perhaps Meyer might be considered by some to be the hero of the quest, its first stage—the call—is represented by the Karlsruhe conference in 1860, with an international cast of ‘companions’ and ‘helpers’ who contributed to the Table’s early development. The ‘journey’ may have been frustrated by lack of appropriate data and understanding of concepts, but the ‘arrival’ phase is clearly marked by the award of the Davy medal jointly to Mendeleev and Meyer in 1882, Throughout these stages there are lesser, although still significant contributions made by “little people” of science to the overall progress of the Table. The end of the journey is not the end of the quest: the discovery of new elements—“new ordeals”—and their incorporation into an increasing range of types and styles of periodic table, which—akin to the “life-renewing goal” of the fictional quest—continue.     

紫外光引发Pickering乳液聚合制备中空复合微球的研究

用光引发剂2-羟基-4-(2-羟乙氧基)-2-甲基苯丙酮(IHT-PI 659)对纳米SiO₂表面进行接枝使之兼具两亲性及光引发特性|以该功能性纳米SiO₂为稳定剂构筑O/W(水包油)型Pickering乳液|用紫外光引发处于内油相的甲基丙烯酸甲酯单体聚合, 制备出具有中空结构的SiO₂/PMMA复合微球, 采用傅里叶变换红外光谱(FTIR)、热失重分析仪(TGA)、透射电镜(TEM)及扫描电子显微镜(SEM)对复合微球进行了表征, 并提出了紫外光引发Pickering乳液聚合制备中空复合微球的机理.     

Protein modification by arginylation

The modification of protein by arginine catalyzed by arginyltransferases (ATE1) described by the Kashina group in this issue shows that arginylation of protein occurs widely in biology and is being recognized as a key regulatory reaction such as phosphorylation of proteins (Wang et?al., 2011).     

Preconcentration of phenols by adsorption on organo-clay followed by capillary electrophoretic determination

The organo-clay adsorbent used was prepared by modification of montmorillonite from Kurşunlu, Turkey with the cationic surfactant cetyltrimethlyammonium bromide. The modification process involves replacing the inorganic exchange cations of the clay by organic cations containing long chain alkyl groups. The retention of phenolic compounds from aqueous solution on the organo-clay was studied. The analytes are quantitatively retained on the proposed adsorbent at pH 7 and recovered by elution with ethanol. The determination of phenols was performed by capillary electrophoresis. Received: 28 July 1997 / Revised: 15 December 1997 / Accepted: 8 January 1998     

A straightforward synthesis of conhydrine by hetero Diels-Alder strategy mediated by microwaves

Synthesis of optically active conhydrines has been achieved by hetero Diels-Alder cycloaddition assisted by microwaves.     

Ring opening of aziridines by aromatic thiols followed by amino-substitution

Ring opening of 2-aziridinecarboxylic acid methyl ester by a number of aromatic thiols under solvent-free and non-catalytic conditions resulted in bis-arylsulfanyl propanoic acid esters.     

TiCl4处理分子筛催化氧化苯乙烯

通过气相ＴｉＣｌ４对多种分子筛进行处理，用Ｈ２Ｏ２对苯乙烯的氧化反应作探针反应，考察了所得分子筛的催化活性，发现用ＺＳＭ－５制备的催化剂的催化性能最好，得到苯乙烯的转化率可达～１２％生成苯乙醛和环氧苯乙烷的选择性可达～５５．９％，并用ＩＲ对用于ＴｉＣｌ４处理过的ＺＳＭ－５进行了表征，证实了钛原子进入ＺＳＭ－５沸石骨架，生成了钛硅分子筛。     

Olefin epoxidation followed by epoxide transformation into 1,2-dibromoalkane by a peroxonickel-dibromomolybdenum bimetallic-system

The interaction of bis(t-butylisocyano)peroxonickel(II) and bis(triphenylphosphine oxide)dibromodioxomolybdenum(VI) in the presence of cyclohexene yields 1,2-dibromocyclohexane as the main product. This result is explained by the prior epoxidation of cyclohexene, followed by its conversion into the 1,2-dibromoalkane.The epoxidation step implies peroxidation of the dioxomolybdenum by the peroxonickel species. It is shown that this occurs by a dioxygen-ligand transfer accompanied by the back transfer of two bromine atom and two triphenylphosphine oxide molecules.     

Inactivation of Vaccinia Virus by Natural Sunlight and by Artificial UVB Radiation

This study determined the sensitivity of vaccinia virus, an orthopox virus commonly used as a surrogate for variola virus (etiological agent of smallpox), exposed to UVB radiation emitted by a solar simulator, or to direct natural sunlight. The data obtained indicate that: (1) the virucidal effect of natural sunlight can be mimicked adequately by an artificial light source with similar spectral characteristics in the UVB, (2) viral sensitivity to UVB or to solar radiation can be correlated with experimental data previously obtained with UVC, (3) the correlation factor between virus inactivation by solar radiation (measured at 300 ± 5 nm) and by UVC (254 nm) is between 33 and 60, and (4) the sensitivity of viruses either dry on glass surfaces or in liquid suspension is similar when in the presence of similar amounts of cellular debris and growth media. The findings reported in this study should assist in estimating the threat posed by the persistence of virus during epidemics or after an accidental or intentional release.