Catalytic Properties (catalytic + property)

Distribution by Scientific Domains
Distribution within Chemistry


Selected Abstracts


Synthesis, Crystal Structure, and Catalytic Properties of Novel Dioxidomolybdenum(VI) Complexes with Tridentate Schiff Base Ligands in the Biomimetic and Highly Selective Oxygenation of Alkenes and Sulfides

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2010
Abdolreza Rezaeifard
Abstract Four novel dioxidomolybdenum(VI) complexes [MoO2(Lx)(CH3OH)] have been synthesized, using 2[(E)-(2-hydroxy-2-phenylethylimino)methyl]phenol derivatives as tridentate ONO donor Schiff base ligands (H2Lx) and MoO2(acac)2. A monoclinic space group was determined by X-ray crystallography from single-crystal data of a sample of these new complexes. The epoxidation of alkenes by using tert -butyl hydroperoxide and oxidation of sulfides to sulfoxides by urea hydrogen peroxide were efficiently enhanced with excellent selectivity under the catalytic influence these new MoVI complexes. The high efficiency and relative stability of the catalysts have been observed by turnover numbers and UV/Vis investigations. The electron-poor and bulky ligands promoted the effectiveness of the catalysts. [source]


Controllable Synthesis of Shuttle-Shaped Ceria and Its Catalytic Properties for CO Oxidation

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 26 2009
Chunwen Sun
Abstract Shuttle-shaped ceria was obtained in a high yield via a surfactant octadecylamine and urea assisted solvothermal process. The crystalline structure and morphology were characterized with powder X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM). Preliminary catalytic measurement shows that the shuttle-shaped CeO2 exhibits an enhanced activity for CO oxidation, which may be attributed to its higher porosity and more oxygen vacancies.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]


An Atropo-Stereogenic Diphosphane Ligand with a Proximal Cationic Charge: Specific Catalytic Properties of a Palladium Complex Thereof

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2008
Nathalie Debono
Abstract A class of cationic diphosphane ligands combining phosphane and amidiniophosphane moieties is illustrated on the N -methyl,N -naphthylbenzimidazolium framework. The palladium(II) complex thereof is described and compared to the corresponding complex of the analogous neutral diphosphane. Contrary to first-level expectations, the N2C,P and N2CP,Pd bonds in the cationic diphosphane complex are not longer than those occurring in its neutral counterpart. In the cationic ligand, the proximal positive charge is indeed conjugated to one phosphanyl group, and the coordination scheme is tentatively interpreted by resonance of the phosphane,metal dative bond (+N2C,P:,[Pd]) with a carbene,phosphenium dative bond (N2C:,[+P:,Pd]). Despite this peculiar structural feature, the electronic , donation (vs. , acceptation) towards the palladium centre remains lowered in the cationic ligand. This specific property can be a priori valuable in a catalytic process where oxidative addition is not the limiting step. It is indeed shown that although the neutral complex is more active in Suzuki coupling reactions, the cationic complex is more active in Sonogashira-type coupling reactions involving predissociated halide substrates, namely an acyl chloride. These likely atropo-chiral ligands deserve to be resolved for application in asymmetric catalysis.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]


In Situ Synthesis, Characterization of SiPMo-X, and Different Catalytic Properties of SiPMo-X and SiPW-X

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2006
Chunfeng Shi
Abstract SBA-15 frameworks with encapsulated Keggin type heteropolyacids (HPAs) were synthesized in situ under strongly acidic conditions (pH,<,0). During the hydrolysis of tetraethyl orthosilicate (TEOS), a P- and a Mo source were added into the initial sol,gel system to form Keggin type HPAs. The texture of the final products was studied by the N2 adsorption,desorption isotherms and transmission electron microscopy (TEM), and their structure was systematically characterized by X-ray diffraction (XRD), UV/Vis diffuse reflectance- (DRS), infrared- (IR), and 31P magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. Characterization results suggest that the samples show very ordered hexagonal mesostructure, and the HPAs that are incorporated into the framework of meso-silica are insoluble during catalysis. Results of catalytic tests indicate that the materials demonstrated catalytic activity comparable with or even surpassing those of the bulk HPAs in catalytic tests implementing chemical reactions of bulky molecules (1,3,5-triisopropylbenzene cracking, esterification of benzoic acid with tert -butyl alcohol, and 2,3,6-trimethylphenol hydroxylation with H2O2). Additionally, some other properties, such as easy separation and stability when recycled, ensure their potential applications in the chemical industries. Here, we report not only the in situ synthesis and characterization of SiPMo-X, but also the difference in the catalytic properties of SiPMo-X and SiPW-X. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]


Organic Ligands Made Porous: Magnetic and Catalytic Properties of Transition Metals Coordinated to the Surfaces of Mesoporous Organosilica

ADVANCED FUNCTIONAL MATERIALS, Issue 7 2010
Andreas Kuschel
Abstract Inorganic solids with porosity on the mesoscale possess a high internal surface area and a well-accessible pore system. Therefore, it is a relevant task to equip the surfaces of such materials with a maximum density of various organic functional groups. Among these functions it is the capability of coordinating to metal species as a ligand that is of extraordinary importance in many areas, for example, in catalysis. This paper describes how prominent ligands containing donor functions such as carboxylic, thio, chelating, or amine groups can be obtained in the form of nanoporous organosilica materials. The coordination of metal centers such as CoII, MnII, VIV, or PtIV is studied in detail. The magnetic properties of the corresponding materials and some applications in catalysis are reported. A quantitative determination of the surface density of donor atoms by distance measurements using EPR spectroscopy is shown. [source]


The Nanocrystalline Nickel with Catalytic Properties on Methanol Oxidation in Alkaline Medium

FUEL CELLS, Issue 5 2009
R. M. A. Tehrani
Abstract The hexagonal closed packed (hcp) nanocrystalline nickel (Ni), with an average diameter of 9.7,±,2.27,nm was deposited uniformly on composite graphite (CG) by the rapid scanning (6,500,mVs,1) voltammetry technique. The hcp-nano Ni-modified CG electrode was investigated for the catalytic oxidation of methanol in alkaline medium through the formation of NiOOH. A high anodic current was obtained at peak potential of +570,mV vs Ag/AgCl. Both the scan rate and the methanol concentration affected the oxidation of methanol. The results showed that catalytic activity had increased with decrease in Ni particle diameter. It was also shown that the hcp-nano Ni/CG modified electrode was the most efficient catalyst in the oxidation of methanol. [source]


Immobilisation of the BINAP Ligand on Dendrimers and Hyperbranched Polymers: Dependence of the Catalytic Properties on the Linker Unit

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2009
Jutta
Abstract A series of immobilised Carbo-BINAP ligands has been synthesised using poly(propylene imine) (PPI) dendrimers as soluble supports. They contain up to 64 BINAP ligands at their periphery without an additional linking unit. Despite the high steric requirements of the ligand, all dendrimers could be completely functionalised, resulting in the immobilised systems in good yields. Furthermore, the immobilisation strategy that worked out for the fixation of AMINAP ligands with additional linking units as well as of Carbo-BINAP ligands without additional linking units on dendrimers has thus been extended to less regularly hyperbranched poly(ethylene imines) (PEI) as soluble supports. In that way it has been possible to attach on average 9, 26, and 138 Glutaroyl-AMINAP or Carbo-BINAP ligands to PEIs of different molecular weights. The catalytic properties of these systems in the copper-catalysed hydrosilylation of acetophenone were investigated. The dendritic PPI-bound Carbo-BINAP ligands displayed a strong dependence of enantioselectivity and activity on the generation of the dendrimer. For the Carbo-BINAP and Glutaroyl-AMINAP ligands immobilised on the hyperbranched polymers, however, activities and enantioselectivities comparable to those of the mononuclear catalysts were found. The macromolecular, immobilised BINAP ligands could be recycled several times without any observable loss of activity or enantioselectivity. [source]


Preparation, Characterization and Catalytic Properties of Polyaniline-Supported Metal Complexes

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 12-13 2006
Boyapati
Abstract Polyaniline-supported Sc, In, Pd, Os and Re catalysts were prepared by using a simple protocol and the thus prepared catalysts were well characterized using FTIR, XPS, UV-Vis/DRS, TGA-DTA. All the catalysts were successfully employed in a wide range of organic transformations such as cyanation and allylation of carbonyl compound, Suzuki coupling of aryl halides and boronic acids, and, most importantly, in asymmetric dihydroxylation of olefins to afford optically active vicinal diols. All the catalysts were separated from the reaction mixture by simple filtration and reused with consistent activity for five cycles without noticeable leaching of metal from the support. [source]


Effects of Transition-Metal Substitution on the Catalytic Properties of Barium Hexaaluminogallate

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2002
Toshiaki 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]


A Universal Approach to the Synthesis of Noble Metal Nanodendrites and Their Catalytic Properties,

ANGEWANDTE CHEMIE, Issue 29 2010
Ashok Mohanty Dr.
Blumen-Katalysatoren: Die pH-abhängige Selbstorganisation in Gegenwart des Tensids Natrium- N -(4- n -dodecyloxybenzoyl)- L -isoleucinat ist bei dem vorgestellten allgemeinen Ansatz zur Synthese von Au-, Pt- und Pd-Nanoblumen in hoher Ausbeute entscheidend. Die Pt- und Pd-Nanoblumen katalysieren Suzuki-Miyaura-Reaktionen und Heck-Kupplungen besser als ihre kugelförmigen Analoga. [source]


Synthetic Tuning of the Catalytic Properties of Au-Fe3O4 Nanoparticles,

ANGEWANDTE CHEMIE, Issue 7 2010
Youngmin Lee
Hantelförmige Au-Fe3O4 -Nanopartikel und ihre separaten Gegenstücke, Au und Fe3O4, wurden hinsichtlich ihrer Effizienz bei der H2O2 -Reduktion verglichen. Die höhere Aktivität der Au-Fe3O4 -Nanopartikel wird auf die Polarisation von Fe3O4 durch Au zurückgeführt. Die Aktivität lässt sich außerdem noch über die Nanopartikelgröße einstellen. [source]


Adsorption and Catalytic Properties of the Inner Nanospace of a Gigantic Ring-Shaped Polyoxometalate Cluster,

ANGEWANDTE CHEMIE, Issue 46 2009
Shin-ichiro Noro Dr.
Funktionelle Innenräume: Riesige ringförmige {Mo154}-Polyoxometallat-Clusteranionen werden durch Zusatz von Dimethyldioctadecylammonium(DODA)-Kationen stabilisiert. Die Cluster können in ihrem nanoskaligen Innenraum Gase und Dämpfe adsorbieren, und sie wirken außerdem als wasserunempfindliche feste Säurekatalysatoren (siehe Schema). [source]


ChemInform Abstract: New Catalytic Properties of Iron Complexes: Dehydration of Amides to Nitriles.

CHEMINFORM, Issue 51 2009
Shaolin Zhou
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]


Catalytic Properties of Nanostructured Pt and Ru Metal Clusters over Alumina Promoted by CeO2.

CHEMINFORM, Issue 28 2007
K. Dossumov
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]


Preparation, Characterization and Catalytic Properties of Polyaniline-Supported Metal Complexes.

CHEMINFORM, Issue 47 2006
Boyapati M. Choudary
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]


Preparation and Catalytic Properties of Nanosized Gold Catalysts

CHEMINFORM, Issue 26 2006
Yu-Wen Chen
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]


ChemInform Abstract: Preparation and Catalytic Properties of Immobilized Chiral Dirhodium(II) Carboxamidates.

CHEMINFORM, Issue 34 2002
Michael P. Doyle
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]


Controlled Synthesis of Water-Dispersible Faceted Crystalline Copper Nanoparticles and Their Catalytic Properties

CHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2010
Dr. Yanfei Wang
Abstract We report a solution-phase synthetic route to copper nanoparticles with controllable size and shape. The synthesis of the nanoparticles is achieved by the reduction of copper(II) salt in aqueous solution with hydrazine under air atmosphere in the presence of poly(acrylic acid) (PAA) as capping agent. The results suggest that the pH plays a key role for the formation of pure copper nanoparticles, whereas the concentration of PAA is important for controlling the size and geometric shape of the nanoparticles. The average size of the copper nanoparticles can be varied from 30 to 80,nm, depending on the concentration of PAA. With a moderate amount of PAA, faceted crystalline copper nanoparticles are obtained. The as-synthesized copper nanoparticles appear red in color and are stable for weeks, as confirmed by UV/Vis and X-ray photoemission (XPS) spectroscopy. The faceted crystalline copper nanoparticles serve as an effective catalyst for N-arylation of heterocycles, such as the CN coupling reaction between p -nitrobenzyl chloride and morpholine producing 4-(4-nitrophenyl)morpholine in an excellent yield under mild reaction conditions. Furthermore, the nanoparticles are proven to be versatile as they also effectively catalyze the three-component, one-pot Mannich reaction between p -substituted benzaldehyde, aniline, and acetophenone affording a 100,% conversion of the limiting reactant (aniline). [source]


Synthesis of an Enzyme-like Imprinted Polymer with the Substrate as the Template, and Its Catalytic Properties under Aqueous Conditions

CHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2004
Zhiyong Cheng Dr.
Abstract Transition state analogues (TSAs) have long been regarded as ideal templates for the preparation of catalytically active synthetic imprinted polymers. In the current work, however, a new type of molecularly imprinted polymer (MIP) was synthesized with the substrate (homovanillic acid, HVA) as the template and hemin introduced as the catalytic center, with the use of plural functional monomers to prepare the active sites. The MIP successfully mimicked natural peroxidase, suggesting that it may not be imperative to employ a TSA as the template when preparing enzyme-like imprinted polymers and that the imprinted polymer matrix provided an advantageous microenvironment around the catalytic center (hemin), essentially similar to that supplied by apo-proteins in natural enzymes. Significantly, by taking advantage of the special structure of hemin and multiple-site interactions provided by several functional monomers, the intrinsic difficulties for MIPs in recognizing template molecules in polar solutions were overcome. The newly developed polymer showed considerable recognizing ability toward HVA, catalytic activity, substrate specificity and also stability, which are the merits lacked by the natural peroxidase. Meanwhile, the ease of recovery and reuse the MIP implies the potential for industrial application. [source]


Catalytic Properties of Nanoscale Iron-Doped Zirconia Solid-Solution Aerogels,

CHEMPHYSCHEM, Issue 7 2008
Lifang Chen
Abstract Nanoscale iron-doped zirconia solid-solution aerogels are prepared via a simple ethanol thermal route using zirconyl nitrate and iron nitrate as starting materials, followed by a supercritical fluid drying process. Structural characteristics are investigated by means of powder X-ray diffraction (XRD), thermal analyses (TG/DTA), N2 adsorption measurements and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results show that the resulting iron-doped solid solutions are metastable tetragonal zirconia which exhibit excellent dispersibility and high solubility of iron oxide. Further, when the Fe:(Fe+Zr) ratio x is lower than 0.10, all of the Fe3+ ions can be incorporated into ZrO2 by substituting Zr4+ to form Zr1,xFexOy solid solutions. Moreover, for the first time, an additional hydroxyl group band that is not present in pure ZrO2 is observed by DRIFTS for the Zr(Fe)O2 solid solution. This is direct evidence of Fe3+ ions incorporated into ZrO2. These Zr1,xFexOy solid solutions are excellent catalysts for the solvent-free aerobic oxidation of n -hexadecane using air as the oxidant under ambient conditions. The Zr0.8Fe0.2Oy solid-solution catalyst demonstrates the best catalytic properties, with the conversion of n -hexadecane reaching 36.2,% with 48,% selectivity for ketones and 24,% selectivity for alcohols and it can be recycled five times without significant loss of activity. [source]


Formation of Cross-Linked Chloroperoxidase Aggregates in the Pores of Mesocellular Foams: Characterization by SANS and Catalytic Properties

CHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 2 2009
Dirk Jung
Abstract No escape: The formation of cross-linked chloroperoxidase aggregates (CPO-CLEAs) in the pores of mesocellular foam materials results in active biocatalysts that are more resistant to leaching than the conventional catalyst prepared by physisorption of chloroperoxidase. Small-angle neutron scattering (SANS) experiments clearly confirm that the CPO-CLEAs are located in the pores of the mesocellular foams. [source]


Structure and reactivity of Trypanosoma brucei pteridine reductase: inhibition by the archetypal antifolate methotrexate

MOLECULAR MICROBIOLOGY, Issue 6 2006
Alice Dawson
Summary The protozoan Trypanosoma brucei has a functional pteridine reductase (TbPTR1), an NADPH-dependent short-chain reductase that participates in the salvage of pterins, which are essential for parasite growth. PTR1 displays broad-spectrum activity with pterins and folates, provides a metabolic bypass for inhibition of the trypanosomatid dihydrofolate reductase and therefore compromises the use of antifolates for treatment of trypanosomiasis. Catalytic properties of recombinant TbPTR1 and inhibition by the archetypal antifolate methotrexate have been characterized and the crystal structure of the ternary complex with cofactor NADP+ and the inhibitor determined at 2.2 Å resolution. This enzyme shares 50% amino acid sequence identity with Leishmania major PTR1 (LmPTR1) and comparisons show that the architecture of the cofactor binding site, and the catalytic centre are highly conserved, as are most interactions with the inhibitor. However, specific amino acid differences, in particular the placement of Trp221 at the side of the active site, and adjustment of the ,6-,6 loop and ,6 helix at one side of the substrate-binding cleft significantly reduce the size of the substrate binding site of TbPTR1 and alter the chemical properties compared with LmPTR1. A reactive Cys168, within the active site cleft, in conjunction with the C-terminus carboxyl group and His267 of a partner subunit forms a triad similar to the catalytic component of cysteine proteases. TbPTR1 therefore offers novel structural features to exploit in the search for inhibitors of therapeutic value against African trypanosomiasis. [source]


Pyridine Carboxylate Complexes of MoII as Active Catalysts in Homogeneous and Heterogeneous Polymerization

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2007
Maria Vasconcellos-Dias
Abstract New lamellar materials intercalated with molybdenum(II) complexes with potential catalytic properties were prepared by a stepwise procedure. The lamellar material was first calcined at 823 K for four hours to eliminate all the carbonate ions; the layered structure was reconstructed after treatment with a solution of either pycH (pyridine-2-carboxylic acid) or pydcH2 (pyridine-2,6-dicarboxylic acid) in a KOH solution of dmf at 343 K. Impregnation with a solution of the organometallic precursor [Mo(CO)3I2(NCCH3)2] led to substitution of the nitrile groups by two pyridine ligands. All the materials were characterized by powder X-ray diffraction, FTIR, and 13C CP MAS and 27Al MAS solid-state NMR spectroscopy. Similar MoII complexes were also prepared by using pycH or pydcH2 and characterized by elemental analysis as well as FTIR and 1H and 13C solution NMR spectroscopy. These new materials and the complexes of pyc or pydc ligands containing 4.54 wt.-% and 6.33 wt.-% of Mo respectively, catalyze the ring-opening-metathesis polymerization of norbornene and the polymerization of styrene at 333 K, their performance increasing upon the addition of methylalumoxane (MAO) as cocatalyst.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]


In Situ Synthesis, Characterization of SiPMo-X, and Different Catalytic Properties of SiPMo-X and SiPW-X

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2006
Chunfeng Shi
Abstract SBA-15 frameworks with encapsulated Keggin type heteropolyacids (HPAs) were synthesized in situ under strongly acidic conditions (pH,<,0). During the hydrolysis of tetraethyl orthosilicate (TEOS), a P- and a Mo source were added into the initial sol,gel system to form Keggin type HPAs. The texture of the final products was studied by the N2 adsorption,desorption isotherms and transmission electron microscopy (TEM), and their structure was systematically characterized by X-ray diffraction (XRD), UV/Vis diffuse reflectance- (DRS), infrared- (IR), and 31P magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. Characterization results suggest that the samples show very ordered hexagonal mesostructure, and the HPAs that are incorporated into the framework of meso-silica are insoluble during catalysis. Results of catalytic tests indicate that the materials demonstrated catalytic activity comparable with or even surpassing those of the bulk HPAs in catalytic tests implementing chemical reactions of bulky molecules (1,3,5-triisopropylbenzene cracking, esterification of benzoic acid with tert -butyl alcohol, and 2,3,6-trimethylphenol hydroxylation with H2O2). Additionally, some other properties, such as easy separation and stability when recycled, ensure their potential applications in the chemical industries. Here, we report not only the in situ synthesis and characterization of SiPMo-X, but also the difference in the catalytic properties of SiPMo-X and SiPW-X. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]


Supported Chiral Monodentate Ligands in Rhodium-Catalysed Asymmetric Hydrogenation and Palladium-Catalysed Asymmetric Allylic Alkylation

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 33 2009
Bert H. G. Swennenhuis
Abstract A family of monodentate polystyrene-supported phosphites, phosphoramidites and phosphanes has been prepared and evaluated as ligands in rhodium-catalysed asymmetric hydrogenation and palladium-catalysed asymmetric allylic alkylation. The supported ligands yielded active and enantioselective catalysts, which in selected cases match the performance of the nonsupported counterparts. As expected, the performance of the supported ligands in the rhodium-catalysed hydrogenation depends on the nature of the ligand, the type of polymeric support, as well as on the substrate. Additionally, the supported ligands have been applied in the monodentate ligand combination approach, by combining them with nonsupported monodentate ligands. The partially supported heteroligand combinations possess different catalytic properties than the related nonsupported combinations. The heteroligand species, however, are not formed selectively, and nonsupported homoleptic complexes also contribute to the overall activity. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]


Effects of Extended Aryl-Substituted Bisoxazoline Ligands in Asymmetric Synthesis , Efficient Synthesis and Application of 4,4,-Bis(1-Naphthyl)-, 4,4,-Bis(2-Naphthyl)- and 4,4,-Bis(9-Anthryl)-2,2,-isopropylidenebis(1,3-oxazolines)

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 23 2005
Hester L. van Lingen
Abstract The steric influence of extended aryl substituents on 2,2,-bis(1,3-oxazoline) ligands was investigated in a series of asymmetric catalytic reactions such as Mukaiyama aldol and Michael reactions, hetero-Diels,Alder processes, and allylic alkylation reactions. 4,4,-(2-Naphthyl)- and 4,4,-(9-anthryl)-substituted isopropylidene-bridged 2,2,-bis(1,3-oxazolines) were synthesized and their enantioselective and catalytic properties in combination with different metals evaluated. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]


Mutagenic probes of the role of Ser209 on the cavity shaping loop of human monoamine oxidase A

FEBS JOURNAL, Issue 16 2009
Jin Wang
The available literature implicating human monoamine oxidase A (MAO A) in apoptotic processes reports levels of MAO A protein that do not correlate with activity, suggesting that unknown mechanisms may be involved in the regulation of catalytic function. Bioinformatic analysis suggests Ser209 as a possible phosphorylation site that may be relevant to catalytic function because it is adjacent to a six-residue loop termed the ,cavity shaping loop' from structural data. To probe the functional role of this site, MAO A Ser209Ala and Ser209Glu mutants were created and investigated. In its membrane-bound form, the MAO A Ser209Glu phosphorylation mimic exhibits catalytic and inhibitor binding properties similar to those of wild-type MAO A. Solubilization in detergent solution and purification of the Ser209Glu mutant results in considerable decreases in these functional parameters. By contrast, the MAO A Ser209Ala mutant exhibits similar catalytic properties to those of wild-type enzyme when purified. Compared to purified wild-type and Ser209Ala MAO A proteins, the Ser209Glu MAO A mutant shows significant differences in covalent flavin fluorescence yield, CD spectra and thermal stability. These structural differences in the purified MAO A Ser209Glu mutant are not exhibited in quantitative structure,activity relationship patterns using a series of para -substituted benzylamine analogs similar to the wild-type enzyme. These data suggest that Ser209 in MAO A does not appear to be the putative phosphorylation site for regulation of MAO A activity and demonstrate that the membrane environment plays a significant role in stabilizing the structure of MAO A and its mutant forms. [source]


Improving thermostability and catalytic activity of pyranose 2-oxidase from Trametes multicolor by rational and semi-rational design

FEBS JOURNAL, Issue 3 2009
Oliver Spadiut
The fungal homotetrameric flavoprotein pyranose 2-oxidase (P2Ox; EC 1.1.3.10) catalyses the oxidation of various sugars at position C2, while, concomitantly, electrons are transferred to oxygen as well as to alternative electron acceptors (e.g. oxidized ferrocenes). These properties make P2Ox an interesting enzyme for various biotechnological applications. Random mutagenesis has previously been used to identify variant E542K, which shows increased thermostability. In the present study, we selected position Leu537 for saturation mutagenesis, and identified variants L537G and L537W, which are characterized by a higher stability and improved catalytic properties. We report detailed studies on both thermodynamic and kinetic stability, as well as the kinetic properties of the mutational variants E542K, E542R, L537G and L537W, and the respective double mutants (L537G/E542K, L537G/E542R, L537W/E542K and L537W/E542R). The selected substitutions at positions Leu537 and Glu542 increase the melting temperature by approximately 10 and 14 °C, respectively, relative to the wild-type enzyme. Although both wild-type and single mutants showed first-order inactivation kinetics, thermal unfolding and inactivation was more complex for the double mutants, showing two distinct phases, as revealed by microcalorimetry and CD spectroscopy. Structural information on the variants does not provide a definitive answer with respect to the stabilizing effects or the alteration of the unfolding process. Distinct differences, however, are observed for the P2Ox Leu537 variants at the interfaces between the subunits, which results in tighter association. [source]


Roles of adenine anchoring and ion pairing at the coenzyme B12 -binding site in diol dehydratase catalysis

FEBS JOURNAL, Issue 24 2008
Ken-ichi Ogura
The X-ray structure of the diol dehydratase,adeninylpentylcobalamin complex revealed that the adenine moiety of adenosylcobalamin is anchored in the adenine-binding pocket of the enzyme by hydrogen bonding of N3 with the side chain OH group of Ser,224, and of 6-NH2, N1 and N7 with main chain amide groups of other residues. A salt bridge is formed between the ,-NH2 group of Lys,135 and the phosphate group of cobalamin. To assess the importance of adenine anchoring and ion pairing, Ser,224 and Lys,135 mutants of diol dehydratase were prepared, and their catalytic properties investigated. The S,224A, S,224N and K,135E mutants were 19,2% as active as the wild-type enzyme, whereas the K,135A, K,135Q and K,135R mutants retained 58,76% of the wild-type activity. The presence of a positive charge at the ,135 residue increased the affinity for cobalamins but was not essential for catalysis, and the introduction of a negative charge there prevented the enzyme,cobalamin interaction. The S,224A and S,224N mutants showed a kcat/kinact value that was less than 2% that of the wild-type, whereas for Lys,135 mutants this value was in the range 25,75%, except for the K,135E mutant (7%). Unlike the wild-type holoenzyme, the S,224N and S,224A holoenzymes showed very low susceptibility to oxygen in the absence of substrate. These findings suggest that Ser,224 is important for cobalt,carbon bond activation and for preventing the enzyme from being inactivated. Upon inactivation of the S,224A holoenzyme during catalysis, cob(II)alamin accumulated, and a trace of doublet signal due to an organic radical disappeared in EPR. 5,-Deoxyadenosine was formed from the adenosyl group, and the apoenzyme itself was not damaged. This inactivation was thus considered to be a mechanism-based one. [source]


Multifunctional Au-Coated TiO2 Nanotube Arrays as Recyclable SERS Substrates for Multifold Organic Pollutants Detection

ADVANCED FUNCTIONAL MATERIALS, Issue 17 2010
Xuanhua Li
Abstract A multifunctional Au-coated TiO2 nanotube array is made via synthesis of a TiO2 nanotube array through a ZnO template, followed by deposition of Au particles onto the TiO2 surface using photocatalytic deposition and a hydrothermal method, respectively. Such arrays exhibit superior detection sensitivity with high reproducibility and stability. In addition, due to possessing stable catalytic properties, the arrays can clean themselves by photocatalytic degradation of target molecules adsorbed to the substrate under irradiation with UV light into inorganic small molecules using surface-enhanced Raman spectroscopy (SERS) detection, so that recycling can be achieved. Finally, by detection of Rhodamine 6G (R6G) dye, herbicide 4-chlorophenol (4-CP), persistent organic pollutant (POP) dichlorophenoxyacetic acid (2,4-D), and organophosphate pesticide methyl-parathion (MP), the unique recyclable properties indicate a new route in eliminating the single-use problem of traditional SERS substrates and show promising applications for detecting other organic pollutants. [source]