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High Activity (high + activity)
Kinds of High Activity Selected AbstractsTellurium-Based Polymeric Surfactants as a Novel Seleno-Enzyme Model with High ActivityMACROMOLECULAR RAPID COMMUNICATIONS, Issue 24 2006Xin Huang Abstract Summary: A tellurium-based polymeric sufactant as a seleno-enzyme model has been constructed by employing 11-acryloyloxyundecyltriethylammonium bromide (AUTEAB, 4) and a tellurium-containing compound (1). It demonstrates strong substrate binding ability for thiols and high glutathione peroxidase (GPx) activity about 6 orders of magnitude more efficient than the well-known GPx mimic PhSeSePh in an ArSH assay system. More importantly, a series of tellurium-based polymeric micelle catalysts with the catalytic tellurium center located at various positions in the micelle have been constructed, and the dramatic difference in activity indicates that the exact match of the catalytic center and binding site plays a key role in enzyme catalytic efficiency. Schematic representation of the proposed mode of the telluro-micelle catalysts. [source] Electrostatic Self-Assembly of a Pt-around-Au Nanocomposite with High Activity towards Formic Acid Oxidation,ANGEWANDTE CHEMIE, Issue 12 2010Sheng Zhang Gegensätze ziehen sich an: ,Pt-auf-Au"-Nanokomposite entstehen durch elektrostatische Selbstorganisation (siehe Bild; PDDA=Poly(diallyldimethylammoniumchlorid)) und sind in der Oxidation von Ameisensäure viel aktiver als reine Pt-Katalysatoren. Ein möglicher Grund hierfür ist der effiziente HCOO-Übertritt vom Au- auf die umgebenden Pt-Nanopartikel, wo HCOO zu CO2 weiteroxidiert wird. [source] Rhodium,Tris(3,5-bis(trifluoromethyl)phenyl)phosphine Catalyzed Hydroformylation of Dienes to Dialdehydes in Supercritical Carbon Dioxide with High Activity.CHEMINFORM, Issue 19 2004Shin-ichiro Fujita Abstract For Abstract see ChemInform Abstract in Full Text. [source] High Activity of Pt/AlPO4 Catalyst for Selective Catalytic Reduction of Nitrogen Monoxide by Propene in Excess Oxygen.CHEMINFORM, Issue 47 2003Ryuta Fujii Abstract For Abstract see ChemInform Abstract in Full Text. [source] Insecticide resistance spectra and resistance mechanisms in populations of Japanese encephalitis vector mosquitoes, Culex tritaeniorhynchus and Cx. gelidus, in Sri LankaMEDICAL AND VETERINARY ENTOMOLOGY, Issue 4 2000S. H. P. P. Karunaratne Summary Culex tritaeniorhynchus Giles and Cx. gelidus Theobald (Diptera: Culicidae), both vectors of Japanese encephalitis, were collected in 1984 and 1998 from two disease endemic localities in Sri Lanka: Anaradhapura and Kandy. Using wild-caught adult mosquitoes from light traps, log dosage-probit mortality curves for insecticide bioassays were obtained for three insecticides: malathion (organophosphate), propoxur (carbamate) and permethrin (pyrethroid). LD50 values showed that, in 1998, Cx. tritaeniorhynchus was ,100-fold more resistant to malathion and 10-fold more resistant to propoxur than was Cx. gelidus. This difference was attributed to Cx. tritaeniorhynchus breeding mostly in irrigated rice paddy fields, where it would have been exposed to pesticide selection pressure, whereas Cx. gelidus breeds in other types of aquatic habitats less prone to pesticide applications. Resistance in Cx. tritaeniorhynchus increased between 1984 and 1998, whereas Cx. gelidus remained predominantly susceptible. Propoxur inhibition of acetylcholinesterase (AChE) activity (the target site of organophosphates and carbamates) indicated that in 1998, frequencies of insensitive AChE-based resistance were 9% in Cx. gelidus and 2,23% in Cx. tritaeniorhynchus, whereas in 1984 this resistance mechanism was detected only in 2% of the latter species from Anaradhapura. The AChE inhibition coefficient (ki) with propoxur was 1.86 ± 0.24 × 105 m,1 min,1 for Cx. tritaeniorhynchus from Anaradhapura in 1998. Both species were tested for activity levels of detoxifying glutathione S-trans- ferases (GSTs) and malathion-specific as well as general carboxylesterases. High activities of GSTs and carboxylesterases were detected in Cx. tritaeniorhynchus but not Cx. gelidus. Malathion-specific carboxylesterase was absent from both species. Native polyacrylamide gel electrophoresis resolved two elevated general carboxylesterases, CtrEst,1 and CtrEst,1, from Cx. tritaeniorhynchus and none from Cx. gelidus. CtrEst,1 was the most intensely staining band. Gel inhibition experiments showed that both elevated esterases were inhibited by organophosphates and carbamates but not by pyrethroids. The major elevated esterase CtrEst,1 was partially purified (15-fold) by sequential Q-Sepharose and phenyl Sepharose column chromatography. The bimolecular rate constant (ka) and the deacylation rate constant (k3) for the malaoxon/ enzyme interaction were 9.9 ± 1.1 × 103 m,1 min,1 and 3.5 ± 0.05 × 10,4m,1 min,1, respectively, demonstrating that the role of this enzyme in organophosphorus insecticide resistance is sequestration. [source] Human brain aminopeptidase A: biochemical properties and distribution in brain nucleiJOURNAL OF NEUROCHEMISTRY, Issue 1 2008Nadia De Mota Abstract Aminopeptidase A (APA) generated brain angiotensin III, one of the main effector peptides of the brain renin angiotensin system, exerting a tonic stimulatory effect on the control of blood pressure in hypertensive rats. The distribution of APA in human brain has not been yet studied. We first biochemically characterized human brain APA (apparent molecular mass of 165 and 130 kDa) and we showed that the human enzyme exhibited similar enzymatic characteristics to recombinant mouse APA. Both enzymes had similar sensitivity to Ca2+. Kinetic studies showed that the Km (190 ,mol/L) of the human enzyme for the synthetic substrate- l -glutamyl-,-naphthylamide was close from that of the mouse enzyme (256 ,mol/L). Moreover, various classes of inhibitors including the specific and selective APA inhibitor, (S)-3-amino-4-mercapto-butyl sulfonic acid, had similar inhibitory potencies toward both enzymes. Using (S)-3-amino-4-mercapto-butyl sulfonic acid, we then specifically measured the activity of APA in 40 microdissected areas of the adult human brain. Significant heterogeneity was found in the activity of APA in the various analyzed regions. The highest activity was measured in the choroids plexus and the pineal gland. High activity was also detected in the dorsomedial medulla oblongata, in the septum, the prefrontal cortex, the olfactory bulb, the nucleus accumbens, and the hypothalamus, especially in the paraventricular and supraoptic nuclei. Immunostaining of human brain sections at the level of the medulla oblongata strengthened these data, showing for the first time a high density of immunoreactive neuronal cell bodies and fibers in the motor hypoglossal nucleus, the dorsal motor nucleus of the vagus, the nucleus of the solitary tract, the Roller nucleus, the ambiguus nucleus, the inferior olivary complex, and in the external cuneate nucleus. APA immunoreactivity was also visualized in vessels and capillaries in the dorsal motor nucleus of the vagus and the inferior olivary complex. The presence of APA in several human brain nuclei sensitive to angiotensins and involved in blood pressure regulation suggests that APA in humans is an integral component of the brain renin angiotensin system and strengthens the idea that APA inhibitors could be clinically tested as an additional therapy for the treatment of certain forms of hypertension. [source] Ultrastructure of the vegetative gametophytic cells of Porphyra leucosticta (Rhodophyta) grown in red, blue and green lightPHYCOLOGICAL RESEARCH, Issue 4 2002Ioannes Tsekos SUMMARY The ultrastructure of the vegetative gametophytic cells of Porphyra leucosticta Thuret grown in red, blue and green light was studied both in ultrathin sections and in replicas of rapidly frozen cells. High activity of dictyosornes and mucilage sacs results in a dramatic decrease of the protoplasmic area and in thicker cell walls in red light in comparison with blue light and the control. There are numerous well-formed phycobili-somes in blue light, whereas not well-formed ones are present in red and especially in green light. There are also many phycobilisomes in the intrapyrenoidal thylakoids in blue light, fewer in green light, but they are absent in red light and in the control. It seems that in red and especially in green light, the phycobilisomes have fewer rods than in blue light. In green light, chloroplasts bear numerous genophores in contrast to blue and red light. The spacings of neighboring parallel thylakoids are as follows: control 64.3 nm, blue light 90.6 nm, red light 41.3 nm, green light 43.7 nm. Due to the relatively small spacing of the neighboring parallel thylakoids in red (41.3 nm) and in green light (43.7 nm) and of the given height of phycobilisomes (35 nm), the alternate phycobilisomes attached to neighboring lamellae are forced to interdigitate. The density of phycobilisomes per square micrometer of thylakoid surface dramatically increases in blue light (800 ,m,2) in relation to red (250 ,m,2) and green light (180 ,m,2). The protoplasmic fracture face of the thylakoids reveals numerous, tightly packed, but randomly distributed particles. The particle size distribution is uniform in the two types of fracture faces, with an average diameter of about 11.5 nm. In blue light, both the phycobilisomes and exoplasmic face particles are organized into rows with a spacing of 60,70 nm. The results (changes: in the protoplasmic area; in the spacing of the thylakoids; in phycobilisome arrangement; in structure, shape and size of phycobilisomes; and in the accumulation of plastoglobuli), have shown that the monochromatic light (blue, red and green) brings about marked changes in the package effect and consequently in the efficiency of light absorption. In addition, the blue light contributes to the intense production of chlorophyll a, phycoerythrin, phycocyanin and soluble proteins, while intense production of polysaccharidic material is attributed to red light. [source] Changes in estrogenic and androgenic activities at different stages of treatment in wastewater treatment worksENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 2002Lucy A. Kirk Abstract Estrogenic and androgenic activities of wastewater were determined during treatment in five wastewater treatment works (WWTWs) in the Untied Kingdom. With one exception, both estrogenic and androgenic activities decreased markedly as wastewater progressed through the plants; removal rates were generally 70% or higher, sometimes reaching 100%. Most of the reduction in activity occurred during secondary (biological) treatment. In both influents and effluents, estrogenic and androgenic activities were appreciably lower in samples collected in August, when the amount of rain had been substantial, compared with samples collected in April and May. Most final effluents contained very low (or nondetectable) estrogenic activity (undetectable to 13 ng/L of estradiol equivalents) and androgenic activity (undetectable to 143 ng/L of dihydrotestosterone [DHT] equivalents), although one (from a WWTW that had only primary treatment) contained relatively high activities (40 ng/L of estradiol equivalents; 4,033 ng/L of DHT equivalents). The type of treatment available at the various WWTWs also affected the activity of the final effluent. The biological significance of these results will depend upon which chemicals contribute to the estrogenic and androgenic activities, because of widely different potencies of different estrogenic chemicals, and on the degree of dilution of the effluents in their receiving waters. [source] Norbornene Bidentate Ligands: Coordination Chemistry and Enantioselective Catalytic ApplicationsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2010Fernando Fernández Abstract N - and P-donor derivatives have been prepared by functionalization of a readily available norbornene precursor. Palladium catalytic systems containing these new ligands were applied in allylic substitution, and yielded high activities and excellent enantioselectivities for the allylic alkylation and amination reactions (ee up to 97,%). A full coordination analysis of the catalytic precursors including modelling studies was also carried out. [source] Nickel Complexes and Cobalt Coordination Polymers with Organochalcogen (S, Se) Ligands Bearing an N -Methylimidazole Moiety: Syntheses, Structures, and Properties,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 26 2008Wei-Guo Jia Abstract The organochalcogen ligands (S, Se) derived from 3-methylimidazole-2-thione/selone groups mbit (2a), mbis (2b), ebit (2c), and ebis (2d) [mbit = 1,1,-methylenebis(1,3-dihydro-3-methyl-2H -imidazole-2-thione), mbis = 1,1,-methylenebis(1,3-dihydro-3-methyl-2H -imidazole-2-selone), ebit = 1,1,-(1,2-ethanediyl)bis(1,3-dihydro-3-methyl-1H -imidazole-2-thione), ebis = 1,1,-(1,2-ethanediyl)bis(1,3-dihydro-3-methyl-1H -imidazole-2-selone)] were synthesized and characterized. Mononuclear NiII complexes NiBr2mbit (3a), NiBr2mbis (3b), NiBr2ebit (3c), and NiBr2ebis (3d) were obtained by the reactions of Ni(PPh3)2Br2 with 2a, 2b, 2c, and 2d, respectively. However, when the corresponding ligands 2a, 2b, 2c, and 2d were treated with CoCl2 in thf solution CoII 1D coordination polymers (CoCl2mbit)n (4a), (CoCl2mbis)n (4b), (CoCl2ebit)n (4c), and (CoCl2ebis)n (4d) were obtained. All compounds were fully characterized by IR spectroscopy and elemental analysis. The crystal structures of 2c, 3a, 3b, 3c, 4a, 4b, and 4c were determined by X-ray crystallography. The local geometry around the nickel atom in complexes 3a,c was distorted tetrahedron with coordinated S(Se) and two Br atoms, and the organochalcogen ligands form an eight- or a nine-membered ring with the nickel atom included. The cobalt atom coordination polymers 4a and 4b coexist as left-handed and right-handed helical chains, but 4c formed a zigzag chain with a CH3CN solvent molecule taken up in the channel structure. After activation with methylaluminoxane (MAO), the nickel complexes exhibited high activities for addition polymerization of norbornene (1.42,×,108 g,PNBmol,1,Nih,1 for 3a). The effects of the Al/Ni ratio, reaction temperature, and reaction time to norbornene polymerization were also investigated.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] One-Pot Synthesis of Catalytically Stable and Active Nanoreactors: Encapsulation of Size-Controlled Nanoparticles within a Hierarchically Macroporous Core@Ordered Mesoporous Shell SystemADVANCED MATERIALS, Issue 13 2009Xiao-Yu Yang Size-controlled, catalytically active nanoparticles are successfully encapsulated in a one-pot synthesis to form novel hierarchical macroporous core@mesoporous shell structures, where macroporous cores are connected by uniform and ordered mesoporous channels. Most importantly, the encapsulated nanoparticles can be used as "nanoreactors", with high activities and excellent long-term recycling stability. [source] Alternating Copolymerization of Cyclohexene Oxide and CO2 Catalyzed by Zinc Complexes with New 3-Amino-2-cyanoimidoacrylate LigandsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2005Mario Kröger Abstract New 3-amino-2-cyanoimidoacrylate ligands with varying steric demands have been synthesized. Zinc acetate complexes of these ligands catalyze the copolymerisation of CO2 and cyclohexene oxide, showing high activities (TOF up to over 200,h,1). [source] Modular Furanoside Diphosphite Ligands for Pd-Catalyzed Asymmetric Allylic Substitution Reactions: Scope and LimitationsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2005Montserrat Diéguez Abstract We have synthesized a library of furanoside diphosphite ligands for the Pd-catalyzed allylic substitution reactions of acyclic and cyclic allylic esters. The library has been designed to rapidly screen the ligands to uncover their important structural features and to determine the scope of diphosphite ligands in these catalytic reactions. After the systematic variation of the sugar backbone, the substituent at C-5 and the phosphite moieties, the diphosphite ligand 4c was found to be optimal in the Pd-catalyzed asymmetric allylic substitution of hindered (S1) and unhindered (S2,S5) substrates, yielding high activities [TOFs up to >3000,mol×(mol×h),1] and enantioselectivities (ees up to 99%). In addition, the screening of the library enabled us to find other suitable ligands for hindered disubstituted linear substrate S1 (ligands 1b,d, g and 4b, d, g) and for unhindered cyclic substrates S3,S5 (ligands 6c and 7c). [source] Exopolysaccharide (EPS) biosynthesis by Lactobacillus sakei 0,1: production kinetics, enzyme activities and EPS yieldsJOURNAL OF APPLIED MICROBIOLOGY, Issue 3 2001B. Degeest Aims:,To determine optimal exopolysaccharide (EPS) production conditions of the mesophilic lactic acid bacterium strain Lactobacillus sakei 0,1 and to detect possible links between EPS yields and the activity of relevant enzymes. Methods and Results:,Fermentation experiments at different temperatures using either glucose or lactose were carried out. EPS production took place during the exponential growth phase. Low temperatures, applying glucose as carbohydrate source, resulted in the best bacterial growth, the highest amounts of EPS and the highest specific EPS production. Activities of 10 important enzymes involved in the EPS biosynthesis and the energy formation of Lact. sakei 0,1 were measured. The obtained results revealed that there is a clear link for some enzymes with EPS biosynthesis. It was also demonstrated clearly that the presence of rhamnose in the EPS building blocks is due to high activities of the enzymes involved in the rhamnose synthetic branch. Conclusions:,EPS production in Lact. sakei 0,1 is growth-associated and displays primary metabolite kinetics. Glucose as carbohydrate source and low temperatures enhance the EPS production. The enzymes involved in the biosynthesis of the activated sugar nucleotides play a major role in determining the monomeric composition of the synthesized EPS. Significance and Impact of the Study:,The proposed results contribute to a better understanding of the physiological factors influencing EPS production and the key enzymes involved in EPS biosynthesis by Lact. sakei. [source] OPTIMIZATION OF PERMEABILIZATION PROCESS FOR LACTOSE HYDROLYSIS IN WHEY USING RESPONSE SURFACE METHODOLOGYJOURNAL OF FOOD PROCESS ENGINEERING, Issue 3 2009GURPREET KAUR ABSTRACT To overcome the permeability barrier and prepare whole cell biocatalysts with high activities, permeabilization of Kluyveromyces marxianus var. lactis NCIM 3566 in relation to, -galactosidase activity was optimized using cetyltrimethylammonium bromide (CTAB) as permeabilizing agent. Permeabilized whole cells can be advantageous over pure enzyme preparations in terms of cost-effectiveness and increased stability maintained by the intracellular environment. Response surface methodology (RSM) was applied to optimize concentration of CTAB, temperature and the treatment time for maximum permeabilization of yeast cells. The optimum operating conditions for permeabilization process to achieve maximum enzyme activity obtained by RSM were 0.06% (w/v) CTAB concentration, 28C temperature and process duration of 14 min. At these conditions of process variables, the maximum value of enzyme activity was found to be 1,334 IU/g. The permeabilized yeast cells were highly effective and resulted in 90.5% lactose hydrolysis in whey. PRACTICAL APPLICATION , -Galactosidase is one of the most promising enzymes, which has several applications in the food, fermentation and dairy industry. However, the industrial applications of , -galactosidase have been hampered by the costs involved in downstream processing. The present investigation was focused on developing the low-cost technology for lactose hydrolysis based on permeabilization process. Disposal of lactose in whey and whey permeates is one of the most significant problems with regard to economics and environmental impact faced by the dairy industries. Keeping this in view, lactose hydrolysis in whey has been successfully performed using permeabilized Kluyveromyces marxianus cells. Hydrolysis of lactose using , -galactosidase converts whey into a potentially very useful food ingredient, which has immense applications in food industries. Its use has increased significantly in recent years, mainly in the dairy products and in digestive preparations. Lactose hydrolysis causes several potential changes in the manufacture and marketing of dairy products, including increased solubility, sweetness and broader fermentation possibilities. [source] TMAOase Activity of European Hake (Merluccius merluccius) Organs: Influence of Biological Condition and SeasonJOURNAL OF FOOD SCIENCE, Issue 9 2002M. Rey-Mansilla ABSTRACT: Trimethylamine N-oxide demethylase (TMAOase) activity of several internal organs of hake were studied for 2 consecutive y. The correlation between enzymatic activity and season of year, sex, weight, and length were analyzed. While kidney and spleen showed the highest activities, liver, heart, bile, and gall bladder activities were much lower, and in some cases they were below the detection limit. A correlation between TMAOase activity of kidney and season was found. During winter and spring (February to May), the months matching the spawning peak, high activities were detected, while in summer months the activity level was lower. TMAOase activity in the rest of the organs did not seem to have a seasonal influence. Keywords: TMAOase, season, biological condition, hake, soluble protein [source] Endopeptidase Isoenzyme Characteristics in Cucumis sativus Leaves During Dark-induced SenescenceJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 4 2007Peng Zhang Abstract The changes and characteristics of endopeptidase (EP) isoenzymes in cucumber (Cucumis sativus L.) leaves during dark-induced senescence were investigated by activity staining after gradient-polyacrylamide gel electrophoresis (G-PAGE) containing co-polymerized gelatin as substrate. The results showed that both the chlorophyll and the protein contents of leaves were decreased, and the protein degradation was correlated with the increase of proteolytic activity during the course of leaf senescence. Meanwhile, nine cucumber endopeptidases isoenzymes (CEP) with 140, 120, 106, 94, 76, 55, 46, 39 and 35 kDa molecular weights were detected. Four of these, CEP2, 3, 4 and CEP9 appeared all the time, but the changes of the activity were different during incubation. Another four CEPs (CEP5, 6, 7 and CEP8) whose activities increased with dark-induced time were only detected in senescent leaves. Furthermore, the biochemical properties of these nine CEP were also characterized. All the CEPs had high activities from 35 °C to 45 °C, and the optimum temperature was found to be 40 °C. However, the activities of CEPs were not detected below 25 °C or over 60 °C. The activity bands appeared at a wide range of pH from 5.0 to 9.0, but the optimum pH was found at 7.0. No CEPs were detected at pH 4 or pH 10. By inhibition analysis we concluded that CEP2, 3, 4 and CEP9 were serine endopeptidases and CEP6 was a kind of cysteine protease. It is suggested that serine endopeptidases might play a major role in cucumber leaf senescence, and for the first time, six senescence-related endopeptidases (CEP1, 5, 6, 7, 8 and 9) were found in cucumber leaves. [source] Thermally latent synthesis of networked polymers from multifunctional hemiacetal ester and diepoxide catalyzed by Schiff-base-zinc chloride complexJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2008Hiroyuki Komatsu Abstract Thermally latent reaction of a copolymer (P1) bearing hemiacetal ester and n -butyl methacrylate moieties and glycidyl phenyl ether (2) was catalyzed by bis(p -methoxybenzylidene)-1,2-diiminoethane/zinc chloride complex (ZnCl2/3) at 30,150 °C for 6 h. No reaction of P1 and 2 took place below 70 °C, and it smoothly proceeded above 120 °C. The latencies and activities mean that ZnCl2/3 meets both the high latencies at ambient conditions and the high activities at desired temperatures. Thermal crosslinking reaction employing multifunctional derivatives was carried out using ZnCl2/3 at 140 °C for 6 h to afford a networked polymer in high yields. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3682,3689, 2008 [source] Micron-granula polyolefin with self-immobilized nickel and iron diimine catalysts bearing one or two allyl groupsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2004Guoxin Jin Abstract Self-immobilized nickel and iron diimine catalysts bearing one or two allyl groups of [ArNC]2(C10H6)NiBr2 [Ar = 4-allyl-2,6-(i -Pr)2C6H2] (1), [ArNC(Me)][Ar,N C(Me)]C5H3NFeCl2 [Ar = Ar, = 4-allyl-2,6-(i -Pr)2C6H3, Ar = 2,6-(i -Pr)2C6H3, and Ar, = 4-allyl-2,6-(i -Pr)2C6H3] were synthesized and characterized. All three catalysts were investigated for olefin polymerization. As a result, these catalysts not only showed high activities as the catalyst free from the allyl group, such as [ArNC]2C10H6NiBr2 (Ar = 2,6-(i-Pr)2C6H2)], but also greatly improved the morphology of polymer particles to afford micron-granula polyolefin. The self-immobilization of catalysts, the formation mechanism of microspherical polymer, and the influence on the size of the particles are discussed. The molecular structure of self-immobilized nickel catalyst 1 was also characterized by crystallographic analysis. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1018,1024, 2004 [source] Syndiospecific polymerization of styrene with BzCpTiCl3 and methylaluminoxane as cocatalystsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2001Constantin Schwecke Abstract Benzyl cyclopentadienyl titanium trichloride (BzCpTiCl3) was synthesized from benzyl bromide, cyclopentadienyl lithium, and titanium tetrachloride and used in combination with methylaluminoxane (MAO) for the syndiospecific polymerization of styrene. Kinetic measurements of the polymerization were carried out at different temperatures. The polymerization with BzCpTiCl3/MAO differs from the polymerization with cyclopentadienyl titanium trichloride in its behavior toward the Al/Ti ratio. In addition, high activities are observed at high Al/Ti ratios. By analyzing the polymerization runs and the physical properties of the polymers with differential scanning calorimetry, 13C NMR spectroscopy, wide-angle X-ray scattering measurements, and gel permeation chromatography, we found that the phenyl ring coordinates to the titanium atom during polymerization. Other known substitutions of the cyclopentadienyl ring (V. Scholz, Dissertation, University of Hamburg, 1998) in principle influence the polymerization activity. The physical properties of the polymers produced by the catalysts already known are nearly identical. BzCpTiCl3 is the first catalyst that leads to polystyrene obviously different from the polystyrene produced by other highly active catalysts. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2805,2812, 2001 [source] Syndiospecific polymerization of styrene catalyzed by CpTiCl2(OR) complexesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2001Haiyan Ma Abstract Five new CpTiCl2(OR) alkoxyl-substituted half-sandwich complexes, where R was methoxyethyl (1), methoxypropyl (2), methoxyisopropyl (3), o -methoxyphenyl (4), or tetrahydrofurfuryl (5), were synthesized, characterized, and tested as catalyst precursors for the syndiospecific polymerization of styrene. These precursors were more active than (,5 -cyclopentadienyl)trichlorotitanium (CpTiCl3). The different structures of the alkoxyl ligands affected the activity slightly. When the polymerization was carried out in bulk, all the complexes (1,5) exhibited high activities, even at the low molar ratio of Al/Ti = 300. The syndiotactic polystyrene (s-PS) percentage of the polymer produced by alkoxyl-substituted complexes was much higher than that of CpTiCl3. The really active center might be described as [CpTiMe]+ · [MAOX], · nMAO (where MAO is methylaluminoxane). The normal active species [CpTiMe]+ made up the core and the anion mass [MAOX], · nMAO surrounded the core and constituted the outer shell circumstance. They activated the syndiospecific polymerization of styrene as a whole. For a high concentration of MAO, the function of the alkoxyl group was weak because of the limited proportion in the outer shell. For a low concentration of MAO, the proportion of alkoxyl ligands in the outer shell increased greatly, and their influence also became significant, as reflected in a higher s-PS percentage of the obtained polymer. The existence of the additional oxygen atom in the alkoxyl ligand stabilized the active species more effectively; this was reflected in the higher temperature of the maximum activities. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1817,1824, 2001 [source] Effects of Transition-Metal Substitution on the Catalytic Properties of Barium HexaaluminogallateJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2002Toshiaki Yamaguchi The effects of the substitution of transition-metal ions and/or reductant gases on the catalytic properties of barium hexaaluminogallate were investigated. Transition-metal-substituted hexaaluminogallates (BaM(Al,Ga)11O19, M = transition metal, Al/Ga = 9/3) were synthesized from aqueous metal nitrates and ammonium carbonate by the coprecipitation followed by crystallization at 1100°C. The direct NOx reduction was observed over BaM(Al,Ga)11O19 to be around 10%. The NOx removal activity of BaM(Al,Ga)11O19 powders was improved by addition of C3H6 as a reductant gas. Co-, Ni- and Cu-substituted BaM(Al,Ga)11O19 catalysts exhibited about 40% NOx reduction with C3H6 in excess oxygen at a high space velocity of 10 000 h,1. The NOx reduction on Mn- and Fe-substituted BaM(Al,Ga)11O19 catalysts was less than 10% even in the presence of C3H6. The temperature of the effective NOx reduction on BaM(Al,Ga)11O19 catalysts could be adjusted from 350° to 500°C by the selection of the transition-metal substitution in the catalysts. The catalysts hold high activities for NOx reduction even at 500°C in water vapor produced in the combustion system of reductant gases. [source] Effect of culturing processes and copper addition on laccase production by the white-rot fungus Fomes fomentarius MUCL 35117LETTERS IN APPLIED MICROBIOLOGY, Issue 1 2009M. Neifar Abstract Aim:, To produce high laccase activities from the white-rot fungus Fomes fomentarius. Methods and Results:, Different culturing methods, viz, cell immobilization on stainless steel sponges and plastic material and solid-state fermentation (SSF) using wheat bran as substrate were used for laccase production by the white-rot fungus F. fomentarius. The SSF study expresses the highest laccase activities, nearly to 6400 U l,1 after 13 days of laboratory flasks cultivation. When the wheat bran medium was supplemented with 2 mmol l,1 copper sulfate, laccase activity increased by threefold in comparison to control cultures, reaching 27 864 U l,1. With the medium thus optimized, further experiments were performed in a 3 l fixed-bed bioreactor (working volume 1·5 l) leading to a laccase activity of about 6230 U l,1 on day 13. Conclusions:, The results obtained clearly showed the superiority of wheat bran for laccase production over stainless steel sponges and plastic material. Supplementing the wheat bran solid medium with 2 mmol l,1 copper sulfate allowed obtaining high activities at flask scale. The system was scaled to fixed-bed laboratory reactor. Significance and Impact of the Study:, The high enzyme production along with the low-cost of the substrate, showed the suitability of the system F. fomentarius, SSF for industrial purposes. [source] Comparison of leaf structure and photosynthetic characteristics of C3 and C4Alloteropsis semialata subspeciesPLANT CELL & ENVIRONMENT, Issue 2 2006O. UENO ABSTRACT Alloteropsis semialata (R. Br.) Hitchcock includes both C3 and C4 subspecies: the C3 subspecies eckloniana and the C4 subspecies semialata. We examined the leaf structural and photosynthetic characteristics of these plants. A. semialata ssp. semialata showed high activities of photosynthetic enzymes involved in phosphoenolpyruvate carboxykinase-type C4 photosynthesis and an anomalous Kranz anatomy. Phosphoenolpyruvate carboxylase; pyruvate, Pi dikinase and glycine decarboxylase (GDC) were compartmentalized between the mesophyll (M) and inner bundle sheath cells, whereas ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) occurred in both cells. A. semialata ssp. eckloniana also showed an anomalous non-Kranz anatomy, in which the mestome sheath cells included abundant chloroplasts and mitochondria. Rubisco and GDC accumulated densely in the M and mestome sheath cells, whereas the levels of C4 enzymes were low. The activity levels of photorespiratory enzymes in both subspecies were intermediate between those in typical C3 and C4 plants. The values of CO2 compensation points in A. semialata ssp. semialata were within the C4 range, whereas those in A. semialata ssp. eckloniana were somewhat lower than the C3 range. These data suggest that the plants are C3 -like and C4 -like but not typical C3 and C4, and when integrated with previous findings, point to important variability in the expression of C4 physiology in this species complex. A. semialata is therefore an intriguing grass species with which to study the evolutionary linkage between C3 and C4 plants. [source] Tobacco Mg protoporphyrin IX methyltransferase is involved in inverse activation of Mg porphyrin and protoheme synthesisTHE PLANT JOURNAL, Issue 2 2005Ali E. Alawady Summary Protoporphyrin, a metabolic intermediate of tetrapyrrole biosynthesis, is metabolized by Mg chelatase and ferrochelatase and is directed into the Mg-branch for chlorophyll synthesis and in the Fe-branch for protoheme synthesis respectively. Regulation of the enzyme activities at the beginning of this branchpoint ensures accurate partition of protoporphyrin, but is still not entirely understood. Transgenic tobacco plants were generated that express antisense or sense RNA for inhibited and excessive expression of Mg protoporphyrin methyltransferase (MgPMT) respectively. This enzyme accepts Mg protoporphyrin from Mg chelatase and catalyses the transfer of a methyl group to the carboxyl group of the C13-propionate side chain. Low MgPMT activity is correlated with reduced Mg chelatase activity and a low synthesis rate of 5-aminolevulinate, but with enhanced ferrochelatase activity. In contrast, high MgPMT activity leads to inverse activity profiles: high activities of Mg chelatase and for 5-aminolevulinate synthesis, but reduced activity of ferrochelatase, indicating a direct influence of MgPMT in combination with Mg chelatase on the metabolic flux of ALA and the distribution of protoporphyrin into the branched pathway. The modified enzyme activities in tetrapyrrole biosynthesis in the transgenic plants can be explained with changes of certain corresponding mRNA contents: increased 5-aminolevulinate synthesis and Mg chelatase activity correlate with enhanced transcript levels of the HemA, Gsa, and CHLH gene encoding glutamyl-tRNA reductase, glutamate-1-semialdehyde aminotransferase and a Mg chelatase subunit respectively. It is proposed that reduced and increased MgPMT activity in chloroplasts is communicated to the cytoplasm for modulating transcriptional activities of regulatory enzymes of the pathway. [source] The bridged cyclopentadienyl indenyl (fluorenyl) zirconocene complexes for polyethylene macromonomersAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 10 2010Wenzhong Huang Abstract The synthesis of long-chain branched polyethylene includes the generation of vinyl-terminated polyethylene macromonomers and the copolymerization of these macromonomers with ethylene. Four new bridged cyclopentadienyl indenyl (fluorenyl) zirconocene complexes 1a,b, 2a,b were prepared and showed high activities for ethylene homopolymerization upon the activation of methylaluminoxane. The steric bulk of bridged substituent has a profound effect on the catalytic activity as well as on the molecular weight of resulting polyethylene. Complex 1b showed the highest activity of up to 5.32 × 106 g PE/(mol Zr h) for ethylene homopolymerization at 70 °C, which was higher than that of Cp2ZrCl2. The polyethylenes produced with complexes 1a,d/MAO are mostly vinyl-terminated, possess low molecular weight and fit as macromonomers. The (p -MePh)2C-bridged cyclopentadienyl indenyl zirconocene complex 1a could produce polyethylene macromonomer with selectivity for the vinyl-terminal as high as 94.9%. Copyright © 2010 John Wiley & Sons, Ltd. [source] Heck reaction catalyzed by a recyclable palladium supported on shell powderAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 9 2010Yong-Miao Shen Abstract A novel palladium catalyst supported on shell powder has been prepared, and its application to the Heck reaction of aryl iodides with olefins has been reported. The results showed that the novel catalyst had extremely high activities for the reactions with the average yield over 90%. Also, this catalyst showed excellent stability in Heck reactions, being reused three times. The catalyst was characterized by X-ray powder diffraction and field-emission scanned electron microscopy images, and the energy dispersive X-ray analyzer. Copyright © 2010 John Wiley & Sons, Ltd. [source] Design, synthesis, characterization and antibacterial properties of copper(II) complexes with chromone-derived compoundsAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 1 2010Zahid H. Chohan Abstract A new series of six chromone-derived compounds and their Cu(II) complexes was synthesized and characterized by their physical, spectral and analytical data The elemental analysis data of the complexes agree well with the proposed composition of the compounds, which were found to be dimeric in nature with two hydrazine molecules bridging the two copper atoms through coordination. The ligands and their Cu(II) complexes were screened for their in-vitro antibacterial activity against four Gram-negative (Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi, Shigella flexneri) and two Gram-positive (Bacillus subtilis, Staphylococcus aureus) bacterial strains by the agar-well diffusion method. The ligands were found to exhibit either no or low to moderate activities against one or more of the bacterial species, whereas all the metal complexes exhibited moderate to high activities against different bacterial species. The ligands which were inactive before complexation turned active and less active ones became more active upon coordination with copper ions. Overall, the complexes 7,12 showed comparatively much higher activities than the ligands. Copyright © 2009 John Wiley & Sons, Ltd. [source] Metabolic systems maintain stable non-equilibrium via thermodynamic bufferingBIOESSAYS, Issue 10 2009Abir U. Igamberdiev Abstract Here, we analyze how the set of nucleotides in the cell is equilibrated and how this generates simple rules that help the cell to organize itself via maintenance of a stable non-equilibrium state. A major mechanism operating to achieve this state is thermodynamic buffering via high activities of equilibrating enzymes such as adenylate kinase. Under stable non-equilibrium, the ratios of free and Mg-bound adenylates, Mg2+ and membrane potentials are interdependent and can be computed. The adenylate status is balanced with the levels of reduced and oxidized pyridine nucleotides through regulated uncoupling of the pyridine nucleotide pool from ATP production in mitochondria, and through oxidation of substrates non-coupled to NAD+ reduction in peroxisomes. The set of adenylates and pyridine nucleotides constitutes a generalized cell energy status and determines rates of major metabolic fluxes. As the result, fluxes of energy and information become organized spatially and temporally, providing conditions for self-maintenance of metabolism. [source] Metal Triflates as Highly Stable and Active Catalysts for the "Immortal" Ring-Opening Polymerization of Trimethylene CarbonateCHEMCATCHEM, Issue 3 2010Marion Helou Abstract The controlled "immortal" ring-opening polymerization of trimethylene carbonate (TMC) using a two-component catalyst system based on a metal Lewis acid, such as a metal triflate M(OTf)n(M=Ca, Sc, Zn, Al, Bi; OTf=CF3SO3,) or the metallic salt Fe(acac)3, (acac=acetylacetonate) and an alcohol (ROH) as co-initiator and chain-transfer agent, is carried out in bulk at 110,150,°C. As a result of the water-tolerance of these systems, experimental operating conditions do not require any special care. The approach, valorized both with various ROH transfer agents and with either purified or unpurified monomer sources, is highly versatile. Functional telechelic polycarbonates HPTMCOR, devoid of decarboxylation sequences, are obtained [PTMC=poly(trimethylene carbonate)]. The molar mass of the PTMCs can be readily predicted by a simple model, taking into account the [TMC]0/[ROH]0 ratio and the amount of transferring impurities present in the raw/unpurified reagents. Such simple, air- and moisture-robust catalytic systems, which display quite high activities (TOF up to 28,200,h,1) and productivities (TON up to 45,000) are thus extremely valuable, especially industrially. The performances of these systems are described in comparison to the previously established valuable inorganic and organometallic catalytic systems, namely metal amido complexes ([M{N(SiMe3)2}3]) and [(BDI)Zn{N(SiMe3)2}] (BDI=,-diiminate ligand) derivatives. [source] | ||||||||||||||||||||||||||||||||||||||||