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Sample records for acid catalytic activity

  1. Catalytic Ethanol Dehydration over Different Acid-activated Montmorillonite Clays.

    PubMed

    Krutpijit, Chadaporn; Jongsomjit, Bunjerd

    2016-01-01

    In the present study, the catalytic dehydration of ethanol to obtain ethylene over montmorillonite clays (MMT) with mineral acid activation including H2SO4 (SA-MMT), HCl (HA-MMT) and HNO3 (NA-MMT) was investigated at temperature range of 200 to 400°C. It revealed that HA-MMT exhibited the highest catalytic activity. Ethanol conversion and ethylene selectivity were found to increase with increased reaction temperature. At 400°C, the HA-MMT yielded 82% of ethanol conversion having 78% of ethylene yield. At lower temperature (i.e. 200 to 300°C), diethyl ether (DEE) was a major product. The highest activity obtained from HA-MMT can be attributed to an increase of weak acid sites and acid density by the activation of MMT with HCl. It can be also proven by various characterization techniques that in most case, the main structure of MMT did not alter by acid activation (excepted for NA-MMT). Upon the stability test for 72 h during the reaction, the MMT and HA-MMT showed only slight deactivation due to carbon deposition. Hence, the acid activation of MMT by HCl is promising to enhance the catalytic dehydration of ethanol. PMID:27041515

  2. Pillared clays and pillared acid-activated clays: A comparative study of physical, acidic, and catalytic properties

    SciTech Connect

    Mokaya, R.; Jones, W.

    1995-04-15

    The preparation, characterisation, and catalytic properties of alumina-pillared materials derived from an acid-treated host clay matrix is described. Various levels of acid treatment are studied in order to ascertain the level of acid treatment which yields pillared materials with the most suitable physicochemical properties and thermal stability. The pillared acid-activated clays prepared possess basal spacing (19.3 {angstrom} after thermal treatment at 500{degrees}C) and surface areas (315-374 m{sup 2}/g) comparable to conventional pillared clays but significantly higher pore volume (0.33-0.48 cm{sup 3}/g), average pore diameter and surface acidity. The improvement in acidity is mainly of the Broensted acid type. As a result of improved acidity, the pillared acid-activated clays are better catalysts compared to conventional pillared clays and they exhibit activity indicative of the presence of strong Broensted acid sites in the temperature range 250-400{degrees}C. 36 refs., 5 figs., 6 tabs.

  3. Stable and catalytically active iron porphyrin-based porous organic polymer: Activity as both a redox and Lewis acid catalyst

    PubMed Central

    Oveisi, Ali R.; Zhang, Kainan; Khorramabadi-zad, Ahmad; Farha, Omar K.; Hupp, Joseph T.

    2015-01-01

    A new porphyrin-based porous organic polymer (POP) with BET surface area ranging from 780 to 880 m2/g was synthesized in free-base form via the reaction of meso-tetrakis(pentafluorophenyl) porphyrin and a rigid trigonal building block, hexahydroxytriphenylene. The material was then metallated with Fe(III) imparting activity for Lewis acid catalysis (regioselective methanolysis ring-opening of styrene oxide), oxidative cyclization catalysis (conversion of bis(2-hydroxy-1-naphthyl)methanes to the corresponding spirodienone), and a tandem catalytic processes: an in situ oxidation-cyclic aminal formation-oxidation sequence, which selectively converts benzyl alcohol to 2-phenyl-quinazolin-4(3H)-one. Notably, the catalyst is readily recoverable and reusable, with little loss in catalytic activity. PMID:26177563

  4. Preparation and Acid Catalytic Activity of TiO2 Grafted Silica MCM-41 with Sulfate Treatment

    NASA Astrophysics Data System (ADS)

    Guo, Dai-shi; Ma, Zi-feng; Yin, Chun-sheng; Jiang, Qi-zhong

    2008-02-01

    TiO2 grafted silica MCM-41 catalyst with and without sulfate treatment were prepared. The structural and acid properties of these materials were investigated by XRD, N2 adsorption-desorption, element analysis, thermal analysis, Raman and FTIR measurements. Their acid-catalytic activities were evaluated using the cyclization reaction of pseudoionone. It was found that the obtained materials possess well-ordered mesostructure, and the grafted TiO2 components were in highly dispersed amorphous form. T/MCM41 without sulfation contained only Lewis acid sites, while Brønsted and Lewis acidities were remarkably improved for the sulfated materials ST/MCM41 and d-ST/MCM41. T/MCM-41 was not active for the cyclization reaction of pseudoionone, but ST/MCM-41 and d-ST/MCM-41 possessed favorable catalytic activities. The catalytic performance of ST/MCM-41 was comparable with that of the commercial solid acid catalyst of Amberlyst-15, and better than that of d-ST/MCM-41, although the latter underwent a second TiO2 grafting process and accordingly had higher Ti and S content. The specific surface structure of Si-O-Ti-O-S=O in ST/MCM-41 and the bilateral induction effect of Si and S=O on Si-O-Ti bonds were speculated to account for its higher acid catalytic activity.

  5. Catalytic activity of the two-component flavin-dependent monooxygenase from Pseudomonas aeruginosa toward cinnamic acid derivatives.

    PubMed

    Furuya, Toshiki; Kino, Kuniki

    2014-02-01

    4-Hydroxyphenylacetate 3-hydroxylases (HPAHs) of the two-component flavin-dependent monooxygenase family are attractive enzymes that possess the catalytic potential to synthesize valuable ortho-diphenol compounds from simple monophenol compounds. In this study, we investigated the catalytic activity of HPAH from Pseudomonas aeruginosa strain PAO1 toward cinnamic acid derivatives. We prepared Escherichia coli cells expressing the hpaB gene encoding the monooxygenase component and the hpaC gene encoding the oxidoreductase component. E. coli cells expressing HpaBC exhibited no or very low oxidation activity toward cinnamic acid, o-coumaric acid, and m-coumaric acid, whereas they rapidly oxidized p-coumaric acid to caffeic acid. Interestingly, after p-coumaric acid was almost completely consumed, the resulting caffeic acid was further oxidized to 3,4,5-trihydroxycinnamic acid. In addition, HpaBC exhibited oxidation activity toward 3-(4-hydroxyphenyl)propanoic acid, ferulic acid, and coniferaldehyde to produce the corresponding ortho-diphenols. We also investigated a flask-scale production of caffeic acid from p-coumaric acid as the model reaction for HpaBC-catalyzed syntheses of hydroxycinnamic acids. Since the initial concentrations of the substrate p-coumaric acid higher than 40 mM markedly inhibited its HpaBC-catalyzed oxidation, the reaction was carried out by repeatedly adding 20 mM of this substrate to the reaction mixture. Furthermore, by using the HpaBC whole-cell catalyst in the presence of glycerol, our experimental setup achieved the high-yield production of caffeic acid, i.e., 56.6 mM (10.2 g/L) within 24 h. These catalytic activities of HpaBC will provide an easy and environment-friendly synthetic approach to hydroxycinnamic acids.

  6. Building, characterising and catalytic activity testing of Co-C-protected amino acid complexes covalently grafted onto chloropropylated silica gel

    NASA Astrophysics Data System (ADS)

    Varga, G.; Timár, Z.; Csendes, Z.; Bajnóczi, É. G.; Carlson, S.; Canton, S. E.; Bagi, L.; Sipos, P.; Pálinkó, I.

    2015-06-01

    Co-C-protected amino acid (C-protected L-histidine, L-tyrosine, L-cysteine and L-cystine) complexes were covalently grafted onto chloropropylated silica gel, and the materials thus obtained were structurally characterised by mid/far IR and X-ray absorption spectroscopies. The superoxide dismutase-like activities of the substances were determined via the Beauchamp-Fridovich test reaction. It was found that covalent grafting and the preparation of the anchored complexes were successful in most cases. The coordinating groups varied upon changing the conditions of the syntheses. All materials displayed catalytic activity, although catalytic activities differed widely.

  7. Mesoporous Silica Supported Pd-MnOx Catalysts with Excellent Catalytic Activity in Room-Temperature Formic Acid Decomposition

    NASA Astrophysics Data System (ADS)

    Jin, Min-Ho; Oh, Duckkyu; Park, Ju-Hyoung; Lee, Chun-Boo; Lee, Sung-Wook; Park, Jong-Soo; Lee, Kwan-Young; Lee, Dong-Wook

    2016-09-01

    For the application of formic acid as a liquid organic hydrogen carrier, development of efficient catalysts for dehydrogenation of formic acid is a challenging topic, and most studies have so far focused on the composition of metals and supports, the size effect of metal nanoparticles, and surface chemistry of supports. Another influential factor is highly desired to overcome the current limitation of heterogeneous catalysis for formic acid decomposition. Here, we first investigated the effect of support pore structure on formic acid decomposition performance at room temperature by using mesoporous silica materials with different pore structures such as KIE-6, MCM-41, and SBA-15, and achieved the excellent catalytic activity (TOF: 593 h‑1) by only controlling the pore structure of mesoporous silica supports. In addition, we demonstrated that 3D interconnected pore structure of mesoporous silica supports is more favorable to the mass transfer than 2D cylindrical mesopore structure, and the better mass transfer provides higher catalytic activity in formic acid decomposition. If the pore morphology of catalytic supports such as 3D wormhole or 2D cylinder is identical, large pore size combined with high pore volume is a crucial factor to achieve high catalytic performance.

  8. Mesoporous Silica Supported Pd-MnOx Catalysts with Excellent Catalytic Activity in Room-Temperature Formic Acid Decomposition

    PubMed Central

    Jin, Min-Ho; Oh, Duckkyu; Park, Ju-Hyoung; Lee, Chun-Boo; Lee, Sung-Wook; Park, Jong-Soo; Lee, Kwan-Young; Lee, Dong-Wook

    2016-01-01

    For the application of formic acid as a liquid organic hydrogen carrier, development of efficient catalysts for dehydrogenation of formic acid is a challenging topic, and most studies have so far focused on the composition of metals and supports, the size effect of metal nanoparticles, and surface chemistry of supports. Another influential factor is highly desired to overcome the current limitation of heterogeneous catalysis for formic acid decomposition. Here, we first investigated the effect of support pore structure on formic acid decomposition performance at room temperature by using mesoporous silica materials with different pore structures such as KIE-6, MCM-41, and SBA-15, and achieved the excellent catalytic activity (TOF: 593 h−1) by only controlling the pore structure of mesoporous silica supports. In addition, we demonstrated that 3D interconnected pore structure of mesoporous silica supports is more favorable to the mass transfer than 2D cylindrical mesopore structure, and the better mass transfer provides higher catalytic activity in formic acid decomposition. If the pore morphology of catalytic supports such as 3D wormhole or 2D cylinder is identical, large pore size combined with high pore volume is a crucial factor to achieve high catalytic performance. PMID:27666280

  9. One-step and rapid synthesis of porous Pd nanoparticles with superior catalytic activity toward ethanol/formic acid electrooxidation

    NASA Astrophysics Data System (ADS)

    Hong, Wei; Fang, Youxing; Wang, Jin; Wang, Erkang

    2014-02-01

    Porous Pd nanoparticles are successfully prepared by a rapid, one-step, and efficient route with high yield in aqueous solution. The developed method is very simple, just by mixing sodium tetrachloropalladate, polyvinylpyrrolidone and hydroquinone and heated at 70 °C for 15 min. The structure and composition are analyzed by transmission electron microscope, selected-area electron diffraction, inductively coupled plasma optical emission spectrometer, X-ray diffraction, energy dispersive X-ray spectrum and X-ray photoelectron spectroscopy. Electrochemical catalytic measurement results prove that the as synthesized porous Pd nanoparticles exhibit superior catalytic activity towards ethanol and formic acid electrooxidation.

  10. Efficient Catalytic Ozonation over Reduced Graphene Oxide for p-Hydroxylbenzoic Acid (PHBA) Destruction: Active Site and Mechanism.

    PubMed

    Wang, Yuxian; Xie, Yongbing; Sun, Hongqi; Xiao, Jiadong; Cao, Hongbin; Wang, Shaobin

    2016-04-20

    Nanocarbons have been demonstrated as promising environmentally benign catalysts for advanced oxidation processes (AOPs) upgrading metal-based materials. In this study, reduced graphene oxide (rGO) with a low level of structural defects was synthesized via a scalable method for catalytic ozonation of p-hydroxylbenzoic acid (PHBA). Metal-free rGO materials were found to exhibit a superior activity in activating ozone for catalytic oxidation of organic phenolics. The electron-rich carbonyl groups were identified as the active sites for the catalytic reaction. Electron spin resonance (ESR) and radical competition tests revealed that superoxide radical ((•)O2(-)) and singlet oxygen ((1)O2) were the reactive oxygen species (ROS) for PHBA degradation. The intermediates and the degradation pathways were illustrated from mass spectroscopy. It was interesting to observe that addition of NaCl could enhance both ozonation and catalytic ozonation efficiencies and make ·O2(-) as the dominant ROS. Stability of the catalysts was also evaluated by the successive tests. Loss of specific surface area and changes in the surface chemistry were suggested to be responsible for catalyst deactivation. PMID:27007603

  11. Mutational analysis of amino acid residues involved in catalytic activity of a family 18 chitinase from tulip bulbs.

    PubMed

    Suzukawa, Keisuke; Yamagami, Takeshi; Ohnuma, Takayuki; Hirakawa, Hideki; Kuhara, Satoru; Aso, Yoichi; Ishiguro, Masatsune

    2003-02-01

    We expressed chitinase-1 (TBC-1) from tulip bulbs (Tulipa bakeri) in E. coli cells and used site-directed mutagenesis to identify amino acid residues essential for catalytic activity. Mutations at Glu-125 and Trp-251 completely abolished enzyme activity, and activity decreased with mutations at Asp-123 and Trp-172 when glycolchitin was the substrate. Activity changed with the mutations of Trp-251 to one of several amino acids with side-chains of little hydrophobicity, suggesting that hydrophobic interaction of Trp-251 is important for the activity. Molecular dynamics (MD) simulation analysis with hevamine as the model compound showed that the distance between Asp-123 and Glu-125 was extended by mutation of Trp-251. Kinetic studies of Trp-251-mutated chitinases confirmed these various phenomena. The results suggested that Glu-125 and Trp-251 are essential for enzyme activity and that Trp-251 had a direct role in ligand binding.

  12. Increased Biomass Yield of Lactococcus lactis by Reduced Overconsumption of Amino Acids and Increased Catalytic Activities of Enzymes

    PubMed Central

    Adamberg, Kaarel; Seiman, Andrus; Vilu, Raivo

    2012-01-01

    Steady state cultivation and multidimensional data analysis (metabolic fluxes, absolute proteome, and transcriptome) are used to identify parameters that control the increase in biomass yield of Lactococcus lactis from 0.10 to 0.12 C-mol C-mol−1 with an increase in specific growth rate by 5 times from 0.1 to 0.5 h−1. Reorganization of amino acid consumption was expressed by the inactivation of the arginine deiminase pathway at a specific growth rate of 0.35 h−1 followed by reduced over-consumption of pyruvate directed amino acids (asparagine, serine, threonine, alanine and cysteine) until almost all consumed amino acids were used only for protein synthesis at maximal specific growth rate. This balanced growth was characterized by a high glycolytic flux carrying up to 87% of the carbon flow and only amino acids that relate to nucleotide synthesis (glutamine, serine and asparagine) were consumed in higher amounts than required for cellular protein synthesis. Changes in the proteome were minor (mainly increase in the translation apparatus). Instead, the apparent catalytic activities of enzymes and ribosomes increased by 3.5 times (0.1 vs 0.5 h−1). The apparent catalytic activities of glycolytic enzymes and ribosomal proteins were seen to follow this regulation pattern while those of enzymes involved in nucleotide metabolism increased more than the specific growth rate (over 5.5 times). Nucleotide synthesis formed the most abundant biomonomer synthetic pathway in the cells with an expenditure of 6% from the total ATP required for biosynthesis. Due to the increase in apparent catalytic activity, ribosome translation was more efficient at higher growth rates as evidenced by a decrease of protein to mRNA ratios. All these effects resulted in a 30% decrease of calculated ATP spilling (0.1 vs 0.5 h−1). Our results show that bioprocesses can be made more efficient (using a balanced metabolism) by varying the growth conditions. PMID:23133574

  13. Understanding the enhanced catalytic activity of Cu1@Pd3(111) in formic acid dissociation, a theoretical perspective

    NASA Astrophysics Data System (ADS)

    He, Feng; Li, Kai; Xie, Guangyou; Wang, Ying; Jiao, Menggai; Tang, Hao; Wu, Zhijian

    2016-06-01

    The bimetallic Cu1@Pd3(111) catalyst has been synthesized recently and exhibits better catalytic activity and durability compared with pure Pd(111) as anode catalyst in direct formic acid fuel cells (DFAFCs). In this work, we studied the reaction mechanism of formic acid dissociation on both Pd(111) and Cu1@Pd3(111) by using the density functional method. Our calculations showed that the surface adsorption of the poisoning species CO on Cu1@Pd3(111) is weakened mainly by the strain effect rather than the Cusbnd Pd ligand effect. The Cu1@Pd3(111) can effectively promote the catalytic activity for formic acid dissociation by decreasing the barrier of CO2 formation from the preferential trans-COOH intermediate and increasing the barrier of CO formation from the reduction of CO2. We found that the H atom accumulation, electron accumulation and low electrode potential could accelerate the catalyst deactivation due to the contamination of the poisoning species CO. Furthermore, under low anode potential, the Cu1@Pd3(111) has better durability than pure Pd(111), which can be attributed to the unfavorable CO formation and the favorable CO desorption.

  14. Catalytic Decarboxylation of Fatty Acids to Aviation Fuels over Nickel Supported on Activated Carbon

    PubMed Central

    Wu, Jianghua; Shi, Juanjuan; Fu, Jie; Leidl, Jamie A.; Hou, Zhaoyin; Lu, Xiuyang

    2016-01-01

    Decarboxylation of fatty acids over non-noble metal catalysts without added hydrogen was studied. Ni/C catalysts were prepared and exhibited excellent activity and maintenance for decarboxylation. Thereafter, the effects of nickel loading, catalyst loading, temperature, and carbon number on the decarboxylation of fatty acids were investigated. The results indicate that the products of cracking increased with high nickel loading or catalyst loading. Temperature significantly impacted the conversion of stearic acid but did not influence the selectivity. The fatty acids with large carbon numbers tend to be cracked in this reaction system. Stearic acid can be completely converted at 370 °C for 5 h, and the selectivity to heptadecane was around 80%. PMID:27292280

  15. Catalytic Decarboxylation of Fatty Acids to Aviation Fuels over Nickel Supported on Activated Carbon

    NASA Astrophysics Data System (ADS)

    Wu, Jianghua; Shi, Juanjuan; Fu, Jie; Leidl, Jamie A.; Hou, Zhaoyin; Lu, Xiuyang

    2016-06-01

    Decarboxylation of fatty acids over non-noble metal catalysts without added hydrogen was studied. Ni/C catalysts were prepared and exhibited excellent activity and maintenance for decarboxylation. Thereafter, the effects of nickel loading, catalyst loading, temperature, and carbon number on the decarboxylation of fatty acids were investigated. The results indicate that the products of cracking increased with high nickel loading or catalyst loading. Temperature significantly impacted the conversion of stearic acid but did not influence the selectivity. The fatty acids with large carbon numbers tend to be cracked in this reaction system. Stearic acid can be completely converted at 370 °C for 5 h, and the selectivity to heptadecane was around 80%.

  16. Catalytic Decarboxylation of Fatty Acids to Aviation Fuels over Nickel Supported on Activated Carbon.

    PubMed

    Wu, Jianghua; Shi, Juanjuan; Fu, Jie; Leidl, Jamie A; Hou, Zhaoyin; Lu, Xiuyang

    2016-01-01

    Decarboxylation of fatty acids over non-noble metal catalysts without added hydrogen was studied. Ni/C catalysts were prepared and exhibited excellent activity and maintenance for decarboxylation. Thereafter, the effects of nickel loading, catalyst loading, temperature, and carbon number on the decarboxylation of fatty acids were investigated. The results indicate that the products of cracking increased with high nickel loading or catalyst loading. Temperature significantly impacted the conversion of stearic acid but did not influence the selectivity. The fatty acids with large carbon numbers tend to be cracked in this reaction system. Stearic acid can be completely converted at 370 °C for 5 h, and the selectivity to heptadecane was around 80%. PMID:27292280

  17. Synthesis, characterization and catalytic activity of acid-base bifunctional materials through protection of amino groups

    SciTech Connect

    Shao, Yanqiu; Liu, Heng; Yu, Xiaofang; Guan, Jingqi; Kan, Qiubin

    2012-03-15

    Graphical abstract: Acid-base bifunctional mesoporous material SO{sub 3}H-SBA-15-NH{sub 2} was successfully synthesized under low acidic medium through protection of amino groups. Highlights: Black-Right-Pointing-Pointer The acid-base bifunctional material SO{sub 3}H-SBA-15-NH{sub 2} was successfully synthesized through protection of amino groups. Black-Right-Pointing-Pointer The obtained bifunctional material was tested for aldol condensation. Black-Right-Pointing-Pointer The SO{sub 3}H-SBA-15-NH{sub 2} catalyst containing amine and sulfonic acid groups exhibited excellent acid-basic properties. -- Abstract: Acid-base bifunctional mesoporous material SO{sub 3}H-SBA-15-NH{sub 2} was successfully synthesized under low acidic medium through protection of amino groups. X-ray diffraction (XRD), N{sub 2} adsorption-desorption, transmission electron micrographs (TEM), back titration, {sup 13}C magic-angle spinning (MAS) NMR and {sup 29}Si magic-angle spinning (MAS) NMR were employed to characterize the synthesized materials. The obtained bifunctional material was tested for aldol condensation reaction between acetone and 4-nitrobenzaldehyde. Compared with monofunctional catalysts of SO{sub 3}H-SBA-15 and SBA-15-NH{sub 2}, the bifunctional sample of SO{sub 3}H-SBA-15-NH{sub 2} containing amine and sulfonic acid groups exhibited excellent acid-basic properties, which make it possess high activity for the aldol condensation.

  18. Immobilized Cu (II)—Amino Acid Complexes as Prospective Highly Efficient Catalytic Materials: Synthesis, Structural Characterization and Catalytic Activities

    NASA Astrophysics Data System (ADS)

    Pálinkó, István; Ordasi, Adrien; Kiss, János T.; Labádi, Imre

    2008-11-01

    In this work the covalent anchoring of N-or C-protected Cu(II)—L-tyrosine complexes onto a swellable resin or surface-modified silica gel is described. Experimental conditions (solvents, the availability of ligands) of the synthesis were varied; the structures (by IR spectroscopy) and the superoxide dismutase activities of the anchored complexes were studied.

  19. A Ta/W mixed addenda heteropolyacid with excellent acid catalytic activity and proton-conducting property

    NASA Astrophysics Data System (ADS)

    Li, Shujun; Peng, Qingpo; Chen, Xuenian; Wang, Ruoya; Zhai, Jianxin; Hu, Weihua; Ma, Fengji; Zhang, Jie; Liu, Shuxia

    2016-11-01

    A new HPAs H20[P8W60Ta12(H2O)4(OH)8O236]·125H2O (H-1) which comprises a Ta/W mixed addenda heteropolyanion, 20 protons, and 125 crystalline water molecules has been prepared through ion-exchange method. The structure and properties of H-1 have been explored in detail. AC impedance measurements indicate that H-1 is a good solid state proton conducting material at room temperature with a conductivity value of 7.2×10-3 S cm-1 (25 °C, 30% RH). Cyclic voltammograms of H-1 indicate the electrocatalytic activity towards the reduction of nitrite. Hammett acidity constant H0 of H-1 in CH3CN is -2.91, which is the strongest among the present known HPAs. Relatively, H-1 exhibits excellent catalytic activities toward acetal reaction.

  20. Solubilizing properties of new surface-active agents, products of catalytic oxyethylation of cholic acid.

    PubMed

    Kołodziejczyk, Michał Krzysztof; Nachajski, Michal Jakub; Lukosek, Marek; Zgoda, Marian Mikołaj

    2013-01-01

    Solubilizing properties of aqueous solutions of a series of surface-active agents, products of oxyethylation of cholic acid, were examined in the present study. The content of oxyethylated segments determined by means of the 1H NMR method enabled the verification of the molecular mass of surfactants along with the calculation of the structural hydrophilic-lipophilic balance (HLB), the solubility parameter delta1/2, and the required solubility level of balance HLB(R). Viscosimetric measurements enabled the calculation of the limiting viscosity number, the content-average molecular mass, the effective volume, the hydrodynamic radius of the surfactant micelle and their equilibrium adducts with rutin, diclofenac and loratadine (BCS Class II and III). By means of the spectrophotometric method (UV) the amount of the solubilized diclofenac, loratadine and rutin (rutoside) was determined in the equilibrium system (saturated solution) in the environment of aqueous solutions of cholic acid derivatives of n(TE) = 20-70. The obtained results serve as a basis for determining the solubilization mechanism of lipophilic therapeutic products and indirectly for estimating the influence of the above process on pharmaceutical as well as biological availability of a micellar adduct from model drug forms (Lindbladt lithogenolitic index).

  1. EPR characterization of the catalytic activity of clays for PCE removal by gamma-radiation induced by acid and thermal treatments.

    PubMed

    Chung, Hung-Ho; Choi, Sang-Won; Ok, Yong-Sik; Jung, Jinho

    2004-12-01

    Clays from tidal flat sediments showed efficient catalytic activity in the decomposition of PCE by gamma-radiation. The highest PCE removal of 98.6% was obtained with clays heated to 700 degrees C after acid treatment. The improved catalytic activity was identified by electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra of clays were significantly changed by the acid and thermal treatments. The intensity of a narrow signal at g=2 (signal III) was decreased with increasing thermal treatment temperature and this increased the PCE removal efficiency. The acid treatment completely removed a broad signal at g=2 (signal II), decreased the intensity of signal III, and improved the gamma-radiation treatment of PCE.

  2. Structure and catalytic activities of ferrous centers confined on the interface between carbon nanotubes and humic acid

    NASA Astrophysics Data System (ADS)

    Wang, Bing; Zhou, Xiaoyan; Wang, Dongqi; Yin, Jun-Jie; Chen, Hanqing; Gao, Xingfa; Zhang, Jing; Ibrahim, Kurash; Chai, Zhifang; Feng, Weiyue; Zhao, Yuliang

    2015-01-01

    Preparation of heterogeneous catalysts with active ferrous centers is of great significance for industrial and environmental catalytic processes. Nanostructured carbon materials (NCM), which possess free-flowing π electrons, can coordinate with transition metals, provide a confinement environment for catalysis, and act as potential supports or ligands to construct analogous complexes. However, designing such catalysts using NCM is still seldom studied to date. Herein, we synthesized a sandwich structured ternary complex via the coordination of Fe-loaded humic acid (HA) with C&z.dbd;C bonds in the aromatic rings of carbon nanotubes (CNTs), in which the O/N-Fe-C interface configuration provides the confinement environment for the ferrous sites. The experimental and theoretical results revealed octahedrally/tetrahedrally coordinated geometry at Fe centers, and the strong hybridization between CNT C π* and Fe 3d orbitals induces discretization of the atomic charges on aromatic rings of CNTs, which facilitates O2 adsorption and electron transfer from carbon to O2, which enhances O2 activation. The O2 activation by the novel HA/Fe-CNT complex can be applied in the oxidative degradation of phenol red (PR) and bisphenol A (BPA) in aqueous media.Preparation of heterogeneous catalysts with active ferrous centers is of great significance for industrial and environmental catalytic processes. Nanostructured carbon materials (NCM), which possess free-flowing π electrons, can coordinate with transition metals, provide a confinement environment for catalysis, and act as potential supports or ligands to construct analogous complexes. However, designing such catalysts using NCM is still seldom studied to date. Herein, we synthesized a sandwich structured ternary complex via the coordination of Fe-loaded humic acid (HA) with C&z.dbd;C bonds in the aromatic rings of carbon nanotubes (CNTs), in which the O/N-Fe-C interface configuration provides the confinement environment for the

  3. Lewis base activation of Lewis acids: catalytic, enantioselective vinylogous aldol addition reactions.

    PubMed

    Denmark, Scott E; Heemstra, John R

    2007-07-20

    The generality of Lewis base catalyzed, Lewis acid mediated, enantioselective vinylogous aldol addition reactions has been investigated. The combination of silicon tetrachloride and chiral phosphoramides is a competent catalyst for highly selective additions of a variety of alpha,beta-unsaturated ketone-, 1,3-diketone-, and alpha,beta-unsaturated amide-derived dienolates to aldehydes. These reactions provided high levels of gamma-site selectivity for a variety of substitution patterns on the dienyl unit. Both ketone- and morpholine amide-derived dienol ethers afforded high enantio- and diastereoselectivity in the addition to conjugated aldehydes. Although alpha,beta-unsaturated ketone-derived dienolate did not react with aliphatic aldehydes, alpha,beta-unsaturated amide-derived dienolates underwent addition at reasonable rates affording high yields of vinylogous aldol product. The enantioselectivities achieved with the morpholine derived-dienolate in the addition to aliphatic aldehydes was the highest afforded to date with the silicon tetrachloride-chiral phosphoramide system. Furthermore, the ability to cleanly convert the morpholine amide to a methyl ketone was demonstrated.

  4. Enhancement of the catalytic activity of ferulic acid decarboxylase from Enterobacter sp. Px6-4 through random and site-directed mutagenesis.

    PubMed

    Lee, Hyunji; Park, Jiyoung; Jung, Chaewon; Han, Dongfei; Seo, Jiyoung; Ahn, Joong-Hoon; Chong, Youhoon; Hur, Hor-Gil

    2015-11-01

    The enzyme ferulic acid decarboxylase (FADase) from Enterobacter sp. Px6-4 catalyzes the decarboxylation reaction of lignin monomers and phenolic compounds such as p-coumaric acid, caffeic acid, and ferulic acid into their corresponding 4-vinyl derivatives, that is, 4-vinylphenol, 4-vinylcatechol, and 4-vinylguaiacol, respectively. Among various ferulic acid decarboxylase enzymes, we chose the FADase from Enterobacter sp. Px6-4, whose crystal structure is known, and produced mutants to enhance its catalytic activity by random and site-directed mutagenesis. After three rounds of sequential mutations, FADase(F95L/D112N/V151I) showed approximately 34-fold higher catalytic activity than wild-type for the production of 4-vinylguaiacol from ferulic acid. Docking analyses suggested that the increased activity of FADase(F95L/D112N/V151I) could be due to formation of compact active site compared with that of the wild-type FADase. Considering the amount of phenolic compounds such as lignin monomers in the biomass components, successfully bioengineered FADase(F95L/D112N/V151I) from Enterobacter sp. Px6-4 could provide an ecofriendly biocatalytic tool for producing diverse styrene derivatives from biomass.

  5. Enhancement of the catalytic activity of ferulic acid decarboxylase from Enterobacter sp. Px6-4 through random and site-directed mutagenesis.

    PubMed

    Lee, Hyunji; Park, Jiyoung; Jung, Chaewon; Han, Dongfei; Seo, Jiyoung; Ahn, Joong-Hoon; Chong, Youhoon; Hur, Hor-Gil

    2015-11-01

    The enzyme ferulic acid decarboxylase (FADase) from Enterobacter sp. Px6-4 catalyzes the decarboxylation reaction of lignin monomers and phenolic compounds such as p-coumaric acid, caffeic acid, and ferulic acid into their corresponding 4-vinyl derivatives, that is, 4-vinylphenol, 4-vinylcatechol, and 4-vinylguaiacol, respectively. Among various ferulic acid decarboxylase enzymes, we chose the FADase from Enterobacter sp. Px6-4, whose crystal structure is known, and produced mutants to enhance its catalytic activity by random and site-directed mutagenesis. After three rounds of sequential mutations, FADase(F95L/D112N/V151I) showed approximately 34-fold higher catalytic activity than wild-type for the production of 4-vinylguaiacol from ferulic acid. Docking analyses suggested that the increased activity of FADase(F95L/D112N/V151I) could be due to formation of compact active site compared with that of the wild-type FADase. Considering the amount of phenolic compounds such as lignin monomers in the biomass components, successfully bioengineered FADase(F95L/D112N/V151I) from Enterobacter sp. Px6-4 could provide an ecofriendly biocatalytic tool for producing diverse styrene derivatives from biomass. PMID:26059194

  6. Lewis base activation of Lewis acids: catalytic, enantioselective addition of glycolate-derived silyl ketene acetals to aldehydes.

    PubMed

    Denmark, Scott E; Chung, Won-Jin

    2008-06-20

    A catalytic system involving silicon tetrachloride and a chiral, Lewis basic bisphosphoramide catalyst is effective for the addition of glycolate-derived silyl ketene acetals to aldehydes. It was found that the sense of diastereoselectivity could be modulated by changing the size of the substituents on the silyl ketene acetals. In general, the trimethylsilyl ketene acetals derived from methyl glycolates with a large protecting group on the alpha-oxygen provide enantiomerically enriched alpha,beta-dihydroxy esters with high syn-diastereoselectivity, whereas the tert-butyldimethylsilyl ketene acetals derived from bulky esters of alpha-methoxyacetic acid provide enantiomerically enriched alpha,beta-dihydroxy esters with high anti-diastereoselecitvity.

  7. MCM-41 supported 12-tungstophosphoric acid mesoporous materials: Preparation, characterization, and catalytic activities for benzaldehyde oxidation with H2O2

    NASA Astrophysics Data System (ADS)

    Chen, Ya; Zhang, Xiao-Li; Chen, Xi; Dong, Bei-Bei; Zheng, Xiu-Cheng

    2013-10-01

    Mesoporous molecular sieves MCM-41 and bulk 12-tungstophosphoric acid (HPW) were synthesized and employed to prepare 5-45 wt.% HPW/MCM-41 mesoporous materials. Characterization results suggested the good dispersion of HPW within MCM-41 when the loading of HPW was less than 35 wt.% and HPW/MCM-41 retained the typical mesopore structure of the supports. The results of the catalytic oxidation of benzaldehyde to benzoic acid with 30% H2O2, in the absence of any organic solvent and co-catalysts, indicated that HPW/MCM-41 was an efficient catalyst and 30 wt.% HPW/MCM-41 sample exhibited the highest catalytic activity among these materials.

  8. Ionizable Side Chains at Catalytic Active Sites of Enzymes

    PubMed Central

    Jimenez-Morales, David; Liang, Jie

    2012-01-01

    Catalytic active sites of enzymes of known structure can be well defined by a modern program of computational geometry. The CASTp program was used to define and measure the volume of the catalytic active sites of 573 enzymes in the Catalytic Site Atlas database. The active sites are identified as catalytic because the amino acids they contain are known to participate in the chemical reaction catalyzed by the enzyme. Acid and base side chains are reliable markers of catalytic active sites. The catalytic active sites have 4 acid and 5 base side chains, in an average volume of 1072 Å3. The number density of acid side chains is 8.3 M (in chemical units); the number density of basic side chains is 10.6 M. The catalytic active site of these enzymes is an unusual electrostatic and steric environment in which side chains and reactants are crowded together in a mixture more like an ionic liquid than an ideal infinitely dilute solution. The electrostatics and crowding of reactants and side chains seems likely to be important for catalytic function. In three types of analogous ion channels, simulation of crowded charges accounts for the main properties of selectivity measured in a wide range of solutions and concentrations. It seems wise to use mathematics designed to study interacting complex fluids when making models of the catalytic active sites of enzymes. PMID:22484856

  9. Catalytic upgrading of butyric acid towards fine chemicals and biofuels

    PubMed Central

    Sjöblom, Magnus; Matsakas, Leonidas; Christakopoulos, Paul; Rova, Ulrika

    2016-01-01

    Fermentation-based production of butyric acid is robust and efficient. Modern catalytic technologies make it possible to convert butyric acid to important fine chemicals and biofuels. Here, current chemocatalytic and biocatalytic conversion methods are reviewed with a focus on upgrading butyric acid to 1-butanol or butyl-butyrate. Supported Ruthenium- and Platinum-based catalyst and lipase exhibit important activities which can pave the way for more sustainable process concepts for the production of green fuels and chemicals. PMID:26994015

  10. Carboxylic acid-grafted mesoporous material and its high catalytic activity in one-pot three-component coupling reaction

    NASA Astrophysics Data System (ADS)

    Gomes, Ruth; Dutta, Saikat; Bhaumik, Asim

    2014-11-01

    A new carboxylic acid functionalized mesoporous organic polymer has been synthesized via in situ radical polymerization of divinylbenzene and acrylic acid using a mesoporous silica as a seed during the polymerization process under solvothermal conditions. The mesoporous material MPDVAA-1 has been thoroughly characterized employing powder XRD, solid state 13C cross polarization magic angle spinning-nuclear magnetic resonance, FT-IR spectroscopy, N2 sorption, HR-TEM, and NH3 temperature programmed desorption-thermal conductivity detector (TPD-TCD) analysis to understand its porosity, chemical environment, bonding, and surface properties. The mesoporous polymer was used as a catalyst for a three comp onent Biginelli condensation between various aldehydes, β-keto esters, and urea/thioureas to give 3,4-dihydropyrimidine-2(1H)-ones. The reactions were carried out under conventional heating as well as solvent-free microwave irradiation of solid components, and in both the cases, the mesoporous polymer MPDVAA-1 proved to be a powerful, robust, and reusable catalyst with high catalytic efficiency.

  11. Carboxylic acid-grafted mesoporous material and its high catalytic activity in one-pot three-component coupling reaction

    SciTech Connect

    Gomes, Ruth; Bhaumik, Asim; Dutta, Saikat

    2014-11-01

    A new carboxylic acid functionalized mesoporous organic polymer has been synthesized via in situ radical polymerization of divinylbenzene and acrylic acid using a mesoporous silica as a seed during the polymerization process under solvothermal conditions. The mesoporous material MPDVAA-1 has been thoroughly characterized employing powder XRD, solid state {sup 13}C cross polarization magic angle spinning-nuclear magnetic resonance, FT-IR spectroscopy, N{sub 2} sorption, HR-TEM, and NH{sub 3} temperature programmed desorption-thermal conductivity detector (TPD-TCD) analysis to understand its porosity, chemical environment, bonding, and surface properties. The mesoporous polymer was used as a catalyst for a three comp onent Biginelli condensation between various aldehydes, β-keto esters, and urea/thioureas to give 3,4-dihydropyrimidine-2(1H)-ones. The reactions were carried out under conventional heating as well as solvent-free microwave irradiation of solid components, and in both the cases, the mesoporous polymer MPDVAA-1 proved to be a powerful, robust, and reusable catalyst with high catalytic efficiency.

  12. Investigation of catalytic activity towards oxygen reduction reaction of Pt dispersed on boron doped graphene in acid medium.

    PubMed

    Pullamsetty, Ashok; Sundara, Ramaprabhu

    2016-10-01

    Boron doped graphene was prepared by a facile method and platinum (Pt) decoration over boron doped graphene was done in various chemical reduction methods such as sodium borohydride (NaBH4), polyol and modified polyol. X-ray diffraction analysis indicates that the synthesized catalyst particles are present in a nanocrystalline structure and transmission and scanning electron microscopy were employed to investigate the morphology and particle distribution. The electrochemical properties were investigated with the help of the rotating disk electrode (RDE) technique and cyclic voltammetry. The results show that the oxygen reduction reaction (ORR) takes place by a four-electron process. The kinetics of the ORR was evaluated using K-L and Tafel plots. The electrocatalyst obtained in modified polyol reduction method has shown the better catalytic activity compared to other two electrocatalysts. PMID:27393888

  13. CuFe2O4/activated carbon composite: a novel magnetic adsorbent for the removal of acid orange II and catalytic regeneration.

    PubMed

    Zhang, Gaosheng; Qu, Jiuhui; Liu, Huijuan; Cooper, Adrienne T; Wu, Rongcheng

    2007-06-01

    CuFe2O4/activated carbon magnetic adsorbents, which combined the adsorption features of activated carbon with the magnetic and the excellent catalytic properties of powdered CuFe2O4, were developed using a simple chemical coprecipitation procedure. The prepared magnetic composites can be used to adsorb acid orange II (AO7) in water and subsequently, easily be separated from the medium by a magnetic technique. CuFe2O4/activated carbon magnetic adsorbents with mass ratio of 1:1, 1:1.5 and 1:2 were prepared. Magnetization measurements, BET surface area measurements, powder XRD and SEM were used to characterize the prepared adsorbents. The results indicate that the magnetic phase present is spinel copper ferrite and the presence of CuFe2O4 did not significantly affect the surface area and pore structure of the activated carbon. The adsorption kinetics and adsorption isotherm of acid orange II (AO7) onto the composites at pH 5.2 also showed that the presence of CuFe2O4 did not affect the adsorption capacity of the activated carbon. The thermal decomposition of AO7 adsorbed on the activated carbon and the composite was investigated by in situ FTIR, respectively. The results suggest that the composite has much higher catalytic activity than that of activated carbon, attributed to the presence of CuFe2O4. The variation of the adsorption capacity of the composites after several adsorption-regeneration cycles has also been studied.

  14. Increased Crystalline Cellulose Activity via Combinations of Amino Acid Changes in the Family 9 Catalytic Domain and Family 3c Cellulose Binding Module of Thermobifida fusca Cel9A ▿

    PubMed Central

    Li, Yongchao; Irwin, Diana C.; Wilson, David B.

    2010-01-01

    Amino acid modifications of the Thermobifida fusca Cel9A-68 catalytic domain or carbohydrate binding module 3c (CBM3c) were combined to create enzymes with changed amino acids in both domains. Bacterial crystalline cellulose (BC) and swollen cellulose (SWC) assays of the expressed and purified enzymes showed that three combinations resulted in 150% and 200% increased activity, respectively, and also increased synergistic activity with other cellulases. Several other combinations resulted in drastically lowered activity, giving insight into the need for a balance between the binding in the catalytic cleft on either side of the cleavage site, as well as coordination between binding affinity for the catalytic domain and CBM3c. The same combinations of amino acid variants in the whole enzyme, Cel9A-90, did not increase BC or SWC activity but did have higher filter paper (FP) activity at 12% digestion. PMID:20173060

  15. The acidic domain of the endothelial membrane protein GPIHBP1 stabilizes lipoprotein lipase activity by preventing unfolding of its catalytic domain

    PubMed Central

    Mysling, Simon; Kristensen, Kristian Kølby; Larsson, Mikael; Beigneux, Anne P; Gårdsvoll, Henrik; Fong, Loren G; Bensadouen, André; Jørgensen, Thomas JD; Young, Stephen G; Ploug, Michael

    2016-01-01

    GPIHBP1 is a glycolipid-anchored membrane protein of capillary endothelial cells that binds lipoprotein lipase (LPL) within the interstitial space and shuttles it to the capillary lumen. The LPL•GPIHBP1 complex is responsible for margination of triglyceride-rich lipoproteins along capillaries and their lipolytic processing. The current work conceptualizes a model for the GPIHBP1•LPL interaction based on biophysical measurements with hydrogen-deuterium exchange/mass spectrometry, surface plasmon resonance, and zero-length cross-linking. According to this model, GPIHBP1 comprises two functionally distinct domains: (1) an intrinsically disordered acidic N-terminal domain; and (2) a folded C-terminal domain that tethers GPIHBP1 to the cell membrane by glycosylphosphatidylinositol. We demonstrate that these domains serve different roles in regulating the kinetics of LPL binding. Importantly, the acidic domain stabilizes LPL catalytic activity by mitigating the global unfolding of LPL's catalytic domain. This study provides a conceptual framework for understanding intravascular lipolysis and GPIHBP1 and LPL mutations causing familial chylomicronemia. DOI: http://dx.doi.org/10.7554/eLife.12095.001 PMID:26725083

  16. The acidic domain of the endothelial membrane protein GPIHBP1 stabilizes lipoprotein lipase activity by preventing unfolding of its catalytic domain.

    PubMed

    Mysling, Simon; Kristensen, Kristian Kølby; Larsson, Mikael; Beigneux, Anne P; Gårdsvoll, Henrik; Fong, Loren G; Bensadouen, André; Jørgensen, Thomas Jd; Young, Stephen G; Ploug, Michael

    2016-01-01

    GPIHBP1 is a glycolipid-anchored membrane protein of capillary endothelial cells that binds lipoprotein lipase (LPL) within the interstitial space and shuttles it to the capillary lumen. The LPL•GPIHBP1 complex is responsible for margination of triglyceride-rich lipoproteins along capillaries and their lipolytic processing. The current work conceptualizes a model for the GPIHBP1•LPL interaction based on biophysical measurements with hydrogen-deuterium exchange/mass spectrometry, surface plasmon resonance, and zero-length cross-linking. According to this model, GPIHBP1 comprises two functionally distinct domains: (1) an intrinsically disordered acidic N-terminal domain; and (2) a folded C-terminal domain that tethers GPIHBP1 to the cell membrane by glycosylphosphatidylinositol. We demonstrate that these domains serve different roles in regulating the kinetics of LPL binding. Importantly, the acidic domain stabilizes LPL catalytic activity by mitigating the global unfolding of LPL's catalytic domain. This study provides a conceptual framework for understanding intravascular lipolysis and GPIHBP1 and LPL mutations causing familial chylomicronemia. PMID:26725083

  17. The acidic domain of the endothelial membrane protein GPIHBP1 stabilizes lipoprotein lipase activity by preventing unfolding of its catalytic domain.

    PubMed

    Mysling, Simon; Kristensen, Kristian Kølby; Larsson, Mikael; Beigneux, Anne P; Gårdsvoll, Henrik; Fong, Loren G; Bensadouen, André; Jørgensen, Thomas Jd; Young, Stephen G; Ploug, Michael

    2016-01-03

    GPIHBP1 is a glycolipid-anchored membrane protein of capillary endothelial cells that binds lipoprotein lipase (LPL) within the interstitial space and shuttles it to the capillary lumen. The LPL•GPIHBP1 complex is responsible for margination of triglyceride-rich lipoproteins along capillaries and their lipolytic processing. The current work conceptualizes a model for the GPIHBP1•LPL interaction based on biophysical measurements with hydrogen-deuterium exchange/mass spectrometry, surface plasmon resonance, and zero-length cross-linking. According to this model, GPIHBP1 comprises two functionally distinct domains: (1) an intrinsically disordered acidic N-terminal domain; and (2) a folded C-terminal domain that tethers GPIHBP1 to the cell membrane by glycosylphosphatidylinositol. We demonstrate that these domains serve different roles in regulating the kinetics of LPL binding. Importantly, the acidic domain stabilizes LPL catalytic activity by mitigating the global unfolding of LPL's catalytic domain. This study provides a conceptual framework for understanding intravascular lipolysis and GPIHBP1 and LPL mutations causing familial chylomicronemia.

  18. Improvement of catalytic activity of lipase in the presence of calix[4]arene valeric acid or hydrazine derivative.

    PubMed

    Akoz, Enise; Sayin, Serkan; Kaplan, Selcuk; Yilmaz, Mustafa

    2015-03-01

    Sol-gel encapsulation is a simple but powerful method to enhance the enantioselectivity of lipase-catalyzed transformations in an isooctane/aqueous buffer solution. Candida rugosa lipase was encapsulated according to a sol-gel procedure in the presence and absence of calix[4]arene hydrazine or carboxylic acid derivatives with Fe3O4 magnetic nanoparticles as an additive. The activity of the encapsulated lipases was evaluated for the enantioselective hydrolysis of racemic Naproxen methyl ester and the hydrolysis of p-Nitrophenylpalmitate. The results indicate that the encapsulated lipase without calix[4]arene derivative has lower conversion and enantioselectivity compared to the encapsulated lipase with calix[4]arene derivative. It was found that the calix[4]arene hydrazine and carboxylic acid-based encapsulated lipases have excellent activity and enantioselectivity (E >300) compared to encapsulated lipase without the calix[4]arene derivatives.

  19. Characterization of a catalytically efficient acidic RNA-cleaving deoxyribozyme.

    PubMed

    Kandadai, Srinivas A; Li, Yingfu

    2005-01-01

    We previously demonstrated--through the isolation of RNA-cleaving deoxyribozymes by in vitro selection that are catalytically active in highly acidic solutions--that DNA, despite its chemical simplicity, could perform catalysis under challenging chemical conditions [Liu,Z., Mei,S.H., Brennan,J.D. and Li,Y. (2003) J. Am. Chem. Soc. 125, 7539-7545]. One remarkable DNA molecule therefrom is pH4DZ1, a self-cleaving deoxyribozyme that exhibits a k(obs) of approximately 1 min(-1) at pH 3.8. In this study, we carried out a series of experiments to examine the sequence and catalytic properties of this acidic deoxyribozyme. Extensive nucleotide truncation experiments indicated that pH4DZ1 was a considerably large deoxyribozyme, requiring approximately 80 out of the original 123 nt for the optimal catalytic activity. A reselection experiment identified ten absolutely conserved nucleotides that are distributed in three catalytically crucial sequence elements. In addition, a trans deoxyribozyme was successfully designed. Comparison of the observed rate constant of pH4DZ1 with experimentally determined rate constant for the uncatalyzed reaction revealed that pH4DZ1 achieved a rate enhancement of approximately 10(6)-fold. This study provides valuable information about this low-pH-functional deoxyribozyme and paves way for further structural and mechanistic characterization of this unique catalytic DNA. PMID:16391005

  20. Catalytic Activities Of [GADV]-Peptides

    NASA Astrophysics Data System (ADS)

    Oba, Takae; Fukushima, Jun; Maruyama, Masako; Iwamoto, Ryoko; Ikehara, Kenji

    2005-10-01

    We have previously postulated a novel hypothesis for the origin of life, assuming that life on the earth originated from “[GADV]-protein world”, not from the “RNA world” (see Ikehara's review, 2002). The [GADV]-protein world is constituted from peptides and proteins with random sequences of four amino acids (glycine [G], alanine [A], aspartic acid [D] and valine [V]), which accumulated by pseudo-replication of the [GADV]-proteins. To obtain evidence for the hypothesis, we produced [GADV]-peptides by repeated heat-drying of the amino acids for 30 cycles ([GADV]-P30) and examined whether the peptides have some catalytic activities or not. From the results, it was found that the [GADV]-P30 can hydrolyze several kinds of chemical bonds in molecules, such as umbelliferyl-β-D-galactoside, glycine-p-nitroanilide and bovine serum albumin. This suggests that [GADV]-P30 could play an important role in the accumulation of [GADV]-proteins through pseudo-replication, leading to the emergence of life. We further show that [GADV]-octapaptides with random sequences, but containing no cyclic compounds as diketepiperazines, have catalytic activity, hydrolyzing peptide bonds in a natural protein, bovine serum albumin. The catalytic activity of the octapeptides was much higher than the [GADV]-P30 produced through repeated heat-drying treatments. These results also support the [GADV]-protein-world hypothesis of the origin of life (see Ikehara's review, 2002). Possible steps for the emergence of life on the primitive earth are presented.

  1. Monolayer structures of niobic acids supported on SiO[sub 2] and their catalytic activities for esterification of acetic acid with ethanol

    SciTech Connect

    Shirai, Masayuki; Asakura, Kiyotaka; Iwasawa, Yasuhiro )

    1991-11-28

    New submonolayer niobic acid catalysts were prepared by the reaction of Nb(OC[sub 2]H[sub 5])[sub 5] with surface OH groups of SiO[sub 2], followed by H[sub 2]O treatment. The surface structures were characterized by means of EXAFS, XRD, XRF, and FT-IR. The niobic acids on SiO[sub 2] up to 8.0 wt % Nb loadings were found to grow in a monolayer mode. These catalysts showed activities 20 times as large as that of a niobic acid bulk catalyst for the esterification of acetic acid with ethanol. The activity was referred to Lewis acid sites in the monolayer structure, which was stable even after evacuation at high temperatures such as 873 K.

  2. Template-free synthesis of a porous organic-inorganic hybrid tin(IV) phosphonate and its high catalytic activity for esterification of free fatty acids.

    PubMed

    Dutta, Arghya; Patra, Astam K; Uyama, Hiroshi; Bhaumik, Asim

    2013-10-23

    Here we have synthesized an organic-inorganic hybrid mesoporous tin phosphonate monolith (MLSnP-1) with crystalline pore walls by a template-free sol-gel route. N2 sorption analysis shows Brunauer-Emmett-Teller (BET) surface area of 347 m2 g(-1). Wide-angle powder X-ray diffraction (PXRD) pattern shows few broad diffraction peaks indicating crystalline pore wall of the material. High-resolution transmission electron microscopic (HR TEM) image further reveals the crystal fringes on the pore wall. Framework bonding and local environment around phosphorus and carbon were examined by Fourier transform infrared (FT IR) spectroscopy and solid-state MAS NMR spectroscopy. The material exhibits remarkable catalytic activity for esterification of long chain fatty acids under mild reaction conditions at room temperature.

  3. Computational Introduction of Catalytic Activity into Proteins.

    PubMed

    Bertolani, Steve J; Carlin, Dylan Alexander; Siegel, Justin B

    2016-01-01

    Recently, there have been several successful cases of introducing catalytic activity into proteins. One method that has been used successfully to achieve this is the theozyme placement and enzyme design algorithms implemented in Rosetta Molecular Modeling Suite. Here, we illustrate how to use this software to recapitulate the placement of catalytic residues and ligand into a protein using a theozyme, protein scaffold, and catalytic constraints as input. PMID:27094294

  4. Catalytic activities of zeolite compounds for decomposing aqueous ozone.

    PubMed

    Kusuda, Ai; Kitayama, Mikito; Ohta, Yoshio

    2013-12-01

    The advanced oxidation process (AOP), chemical oxidation using aqueous ozone in the presence of appropriate catalysts to generate highly reactive oxygen species, offers an attractive option for removing poorly biodegradable pollutants. Using the commercial zeolite powders with various Si/Al ratios and crystal structures, their catalytic activities for decomposing aqueous ozone were evaluated by continuously flowing ozone to water containing the zeolite powders. The hydrophilic zeolites (low Si/Al ratio) with alkali cations in the crystal structures were found to possess high catalytic activity for decomposing aqueous ozone. The hydrophobic zeolite compounds (high Si/Al ratio) were found to absorb ozone very well, but to have no catalytic activity for decomposing aqueous ozone. Their catalytic activities were also evaluated by using the fixed bed column method. When alkali cations were removed by acid rinsing or substituted by alkali-earth cations, the catalytic activities was significantly deteriorated. These results suggest that the metal cations on the crystal surface of the hydrophilic zeolite would play a key role for catalytic activity for decomposing aqueous ozone.

  5. Catalytic activities of zeolite compounds for decomposing aqueous ozone.

    PubMed

    Kusuda, Ai; Kitayama, Mikito; Ohta, Yoshio

    2013-12-01

    The advanced oxidation process (AOP), chemical oxidation using aqueous ozone in the presence of appropriate catalysts to generate highly reactive oxygen species, offers an attractive option for removing poorly biodegradable pollutants. Using the commercial zeolite powders with various Si/Al ratios and crystal structures, their catalytic activities for decomposing aqueous ozone were evaluated by continuously flowing ozone to water containing the zeolite powders. The hydrophilic zeolites (low Si/Al ratio) with alkali cations in the crystal structures were found to possess high catalytic activity for decomposing aqueous ozone. The hydrophobic zeolite compounds (high Si/Al ratio) were found to absorb ozone very well, but to have no catalytic activity for decomposing aqueous ozone. Their catalytic activities were also evaluated by using the fixed bed column method. When alkali cations were removed by acid rinsing or substituted by alkali-earth cations, the catalytic activities was significantly deteriorated. These results suggest that the metal cations on the crystal surface of the hydrophilic zeolite would play a key role for catalytic activity for decomposing aqueous ozone. PMID:25078817

  6. Formation and catalytic activity of high molecular weight soluble polymers produced by heating amino acids in a modified sea medium

    NASA Astrophysics Data System (ADS)

    Okihana, Hiroyuki

    1982-06-01

    Eighteen protein amino acids with milk casein composition were heated in a modified sea medium. Marigranules were formed in the precipitates and soluble polymers were formed in the supernatant. Time course of the reaction (ultraviolet spectra, the concentration of metal ions, and the concentration of amino acids in the supernatant) were measured. The time course of the formation of the soluble polymers was also studied by Bio-Gel P-2 column. High molecular weight soluble polymers (HMWSP) were separated from low molecular weight ones by dialysis. It was shown that these polymers catalyzed the dehydrogenation of NADH. These polymers also catalyzed the coupled reaction between dehydrogenation of NADH and reduction of resazurin. This coupled reaction was accelerated by the light.

  7. Reducing-Agent-Free Instant Synthesis of Carbon-Supported Pd Catalysts in a Green Leidenfrost Droplet Reactor and Catalytic Activity in Formic Acid Dehydrogenation

    NASA Astrophysics Data System (ADS)

    Lee, Dong-Wook; Jin, Min-Ho; Lee, Young-Joo; Park, Ju-Hyoung; Lee, Chun-Boo; Park, Jong-Soo

    2016-05-01

    The development of green synthesis methods for supported noble metal catalysts remains important challenges to improve their sustainability. Here we first synthesized carbon-supported Pd catalysts in a green Leidenfrost droplet reactor without reducing agents, high-temperature calcination and reduction procedures. When the aqueous solution containing Pd nitrate precursor, carbon support, and water is dripped on a hot plate, vapor layer is formed between a solution droplet and hot surface, which allow the solution droplet to be levitated on the hot surface (Leidenfrost phenomena). Subsequently, Pd nanoparticles can be prepared without reducing agents in a weakly basic droplet reactor created by the Leidenfrost phenomena, and then the as-prepared Pd nanoparticles are loaded on carbon supports during boiling down the droplet on hot surface. Compared to conventional incipient wetness and chemical synthetic methods, the Leidenfrost droplet reactor does not need energy-consuming, time-consuming, and environmentally unfriendly procedures, which leads to much shorter synthesis time, lower carbon dioxide emission, and more ecofriendly process in comparison with conventional synthesis methods. Moreover, the catalysts synthesized in the Leidenfrost droplet reactor provided much better catalytic activity for room-temperature formic acid decomposition than those prepared by the incipient wetness method.

  8. Reducing-Agent-Free Instant Synthesis of Carbon-Supported Pd Catalysts in a Green Leidenfrost Droplet Reactor and Catalytic Activity in Formic Acid Dehydrogenation.

    PubMed

    Lee, Dong-Wook; Jin, Min-Ho; Lee, Young-Joo; Park, Ju-Hyoung; Lee, Chun-Boo; Park, Jong-Soo

    2016-05-20

    The development of green synthesis methods for supported noble metal catalysts remains important challenges to improve their sustainability. Here we first synthesized carbon-supported Pd catalysts in a green Leidenfrost droplet reactor without reducing agents, high-temperature calcination and reduction procedures. When the aqueous solution containing Pd nitrate precursor, carbon support, and water is dripped on a hot plate, vapor layer is formed between a solution droplet and hot surface, which allow the solution droplet to be levitated on the hot surface (Leidenfrost phenomena). Subsequently, Pd nanoparticles can be prepared without reducing agents in a weakly basic droplet reactor created by the Leidenfrost phenomena, and then the as-prepared Pd nanoparticles are loaded on carbon supports during boiling down the droplet on hot surface. Compared to conventional incipient wetness and chemical synthetic methods, the Leidenfrost droplet reactor does not need energy-consuming, time-consuming, and environmentally unfriendly procedures, which leads to much shorter synthesis time, lower carbon dioxide emission, and more ecofriendly process in comparison with conventional synthesis methods. Moreover, the catalysts synthesized in the Leidenfrost droplet reactor provided much better catalytic activity for room-temperature formic acid decomposition than those prepared by the incipient wetness method.

  9. Reducing-Agent-Free Instant Synthesis of Carbon-Supported Pd Catalysts in a Green Leidenfrost Droplet Reactor and Catalytic Activity in Formic Acid Dehydrogenation

    PubMed Central

    Lee, Dong-Wook; Jin, Min-Ho; Lee, Young-Joo; Park, Ju-Hyoung; Lee, Chun-Boo; Park, Jong-Soo

    2016-01-01

    The development of green synthesis methods for supported noble metal catalysts remains important challenges to improve their sustainability. Here we first synthesized carbon-supported Pd catalysts in a green Leidenfrost droplet reactor without reducing agents, high-temperature calcination and reduction procedures. When the aqueous solution containing Pd nitrate precursor, carbon support, and water is dripped on a hot plate, vapor layer is formed between a solution droplet and hot surface, which allow the solution droplet to be levitated on the hot surface (Leidenfrost phenomena). Subsequently, Pd nanoparticles can be prepared without reducing agents in a weakly basic droplet reactor created by the Leidenfrost phenomena, and then the as-prepared Pd nanoparticles are loaded on carbon supports during boiling down the droplet on hot surface. Compared to conventional incipient wetness and chemical synthetic methods, the Leidenfrost droplet reactor does not need energy-consuming, time-consuming, and environmentally unfriendly procedures, which leads to much shorter synthesis time, lower carbon dioxide emission, and more ecofriendly process in comparison with conventional synthesis methods. Moreover, the catalysts synthesized in the Leidenfrost droplet reactor provided much better catalytic activity for room-temperature formic acid decomposition than those prepared by the incipient wetness method. PMID:27198855

  10. Reducing-Agent-Free Instant Synthesis of Carbon-Supported Pd Catalysts in a Green Leidenfrost Droplet Reactor and Catalytic Activity in Formic Acid Dehydrogenation.

    PubMed

    Lee, Dong-Wook; Jin, Min-Ho; Lee, Young-Joo; Park, Ju-Hyoung; Lee, Chun-Boo; Park, Jong-Soo

    2016-01-01

    The development of green synthesis methods for supported noble metal catalysts remains important challenges to improve their sustainability. Here we first synthesized carbon-supported Pd catalysts in a green Leidenfrost droplet reactor without reducing agents, high-temperature calcination and reduction procedures. When the aqueous solution containing Pd nitrate precursor, carbon support, and water is dripped on a hot plate, vapor layer is formed between a solution droplet and hot surface, which allow the solution droplet to be levitated on the hot surface (Leidenfrost phenomena). Subsequently, Pd nanoparticles can be prepared without reducing agents in a weakly basic droplet reactor created by the Leidenfrost phenomena, and then the as-prepared Pd nanoparticles are loaded on carbon supports during boiling down the droplet on hot surface. Compared to conventional incipient wetness and chemical synthetic methods, the Leidenfrost droplet reactor does not need energy-consuming, time-consuming, and environmentally unfriendly procedures, which leads to much shorter synthesis time, lower carbon dioxide emission, and more ecofriendly process in comparison with conventional synthesis methods. Moreover, the catalysts synthesized in the Leidenfrost droplet reactor provided much better catalytic activity for room-temperature formic acid decomposition than those prepared by the incipient wetness method. PMID:27198855

  11. Catalytic activity of acid and base with different concentration on sol-gel kinetics of silica by ultrasonic method.

    PubMed

    Das, R K; Das, M

    2015-09-01

    The effects of both acid (acetic acid) and base (ammonia) catalysts in varying on the sol-gel synthesis of SiO2 nanoparticles using tetra ethyl ortho silicate (TEOS) as a precursor was determined by ultrasonic method. The ultrasonic velocity was received by pulsar receiver. The ultrasonic velocity in the sol and the parameter ΔT (time difference between the original pulse and first back wall echo of the sol) was varied with time of gelation. The graphs of ln[ln1/ΔT] vs ln(t), indicate two region - nonlinear region and a linear region. The time corresponds to the point at which the non-linear region change to linear region is considered as gel time for the respective solutions. Gelation time is found to be dependent on the concentration and types of catalyst and is found from the graphs based on Avrami equation. The rate of condensation is found to be faster for base catalyst. The gelation process was also characterized by viscosity measurement. Normal sol-gel process was also carried out along with the ultrasonic one to compare the effectiveness of ultrasonic. The silica gel was calcined and the powdered sample was characterized with scanning electron microscopy, energy dispersive spectra, X-ray diffractogram, and FTIR spectroscopy.

  12. Catalytic activity of acid and base with different concentration on sol-gel kinetics of silica by ultrasonic method.

    PubMed

    Das, R K; Das, M

    2015-09-01

    The effects of both acid (acetic acid) and base (ammonia) catalysts in varying on the sol-gel synthesis of SiO2 nanoparticles using tetra ethyl ortho silicate (TEOS) as a precursor was determined by ultrasonic method. The ultrasonic velocity was received by pulsar receiver. The ultrasonic velocity in the sol and the parameter ΔT (time difference between the original pulse and first back wall echo of the sol) was varied with time of gelation. The graphs of ln[ln1/ΔT] vs ln(t), indicate two region - nonlinear region and a linear region. The time corresponds to the point at which the non-linear region change to linear region is considered as gel time for the respective solutions. Gelation time is found to be dependent on the concentration and types of catalyst and is found from the graphs based on Avrami equation. The rate of condensation is found to be faster for base catalyst. The gelation process was also characterized by viscosity measurement. Normal sol-gel process was also carried out along with the ultrasonic one to compare the effectiveness of ultrasonic. The silica gel was calcined and the powdered sample was characterized with scanning electron microscopy, energy dispersive spectra, X-ray diffractogram, and FTIR spectroscopy. PMID:25600993

  13. Assembly of acid and sintering resistant honeycomb washcoat and catalytically active phase using sols of silica, zirconia, and platinum

    SciTech Connect

    Felthouse, T.R. |; Berkel, D.A.; Jost, S.R.

    1995-12-01

    Development of high performance honeycomb catalysts containing platinum active phase for gas phase air oxidation of sulfur dioxide is described. Stepwise assembly of these washcoated honeycombs consists of: (1) selection of honeycomb composition (mullite substrate) and cell density based on pressure drop requirements; (2) identification of washcoat slurry composition (silica-precursor sol, silica powder, and surfactants if needed); (3) processing of the washcoat-substrate by dip coating, drying, and calcining; (4) loading of the platinum active phase through a facilitated adsorption technique followed by drying and activation steps; and (5) reactor loading and evaluation. Details of these steps will be presented that include thermal and chemical stability tests. Characterization by transmission electron microscopy of the final Pt/(ZrO{sub 2}-SiO{sub 2}) composite attached to the mullite substrate will be reported.

  14. Catalytic hydroxylation of benzoic acid by hydrogen peroxide

    SciTech Connect

    Pulippurasseril, C.R.; Filippova, T.Yu.; Dedov, A.G.

    1992-12-31

    An effective catalytic system based on Fe(III) and surfactants is proposed for the hydroxylation of benozic acid by hydrogen peroxide in an aqueous medium at a temperature of 30-80{degrees}C. 8 refs., 1 tab.

  15. Characteristics of post-impregnated SBA-15 with 12- Tungstophosphoric acid and its correlation with catalytic activity in selective esterification of glycerol to monolaurate

    NASA Astrophysics Data System (ADS)

    Hoo, P. Y.; Abdullah, A. Z.

    2016-06-01

    Selective esterification of glycerol and lauric acid to monolaurin was conducted using 12-tungstophosphoric acid (HPW) incorporated SBA-15 as catalyst. They were synthesized with HPW loadings of 10-40 wt. % via post impregnation and characterized in terms of surficial and structural characteristic, acidity and morphology. Relatively high lauric acid conversion (up to 95%) and monolaurin yield (53%) were observed while the activity was successfully correlated to the material behaviours, i.e. highly acidic active acid sites within highly uniformed mesopores. The effects of different reaction parameters including reactant ratio (1:1-5:1), catalyst loading (1-5 wt. %) and length of fatty acid were also elucidated. Reduced fatty acid conversion was observed when longer fatty acids were used, thus further strengthen the idea of size selectivity effect provided by the synthesized catalysts.

  16. Treatment of activated carbon to enhance catalytic activity for reduction of nitric oxide with ammonia

    SciTech Connect

    Ku, B.J.; Rhee, H.K. . Dept. of Chemical Engineering); Lee, J.K.; Park, D. )

    1994-11-01

    Catalytic activity of activated carbon treated with various techniques was examined in a fixed bed reactor for the reduction of nitric oxide with ammonia at 150 C. Activated carbon derived from coconut shell impregnated with an aqueous solution of ammonium sulfate, further treated with sulfuric acid, dried at 120 C, and then heated in an inert gas stream at 400 C, showed the highest catalytic activity within the range of experimental conditions. The enhancement of catalytic activity of modified activated carbon could be attributed to the increase in the amount of oxygen function groups which increased the adsorption site for ammonia. Catalytic activity of activated carbons depended on the surface area and the oxygen content as well.

  17. [Preparation of Cu/ZrO2/S2O8(2-)/gamma-Al2O3 solid acid catalyst and its catalytic activity to selective reduction of NO].

    PubMed

    Guo, Xi-kun; Wang, Xiao-ming

    2008-06-01

    Cu/ZrO2/S2O8(2-)/gamma-Al2O3 solid acid catalyst was prepared by loading of (NH4)2S2O8, ZrOCl2, and Cu(NO3)2 onto gamma-Al2O3 step by step, which was obtained from calcining of pseudoboehmite. The catalytic property of Cu/ZrO2/S2O8(2-)/gamma-Al2O3 on the selective reduction of NO by C3H6 in excess oxygen was investigated. The relationship between the structure and the catalytic property of Cu/ZrO2/S2O8(2-)/gamma-Al2O3 catalyst was also explored by means of SEM, XRD, Py-IR and TPR. The experimental results of catalytic activity of the title catalyst indicated that the maximum conversion rate of NO could reach 82.9% in the absence of water and was up to 80.2% even in the presence of 10% water vapor. The results of the structural characterization toward the catalyst showed that S2O8(2-) and ZrO2 could restrain the sinteration of gamma-Al2O3 particles and the formation of CuAl2O4 spinelle, and also facilitate the formation of new acidic sites (Brönsted acid) and the enhance of the acidity on the surface of the catalyst. In addition, ZrO2 could increase the reducibility of Cu on the catalyst. Consequently, the catalytic activity and hydrothermal stability of the catalyst were improved effectively.

  18. Clay Minerals as Solid Acids and Their Catalytic Properties.

    ERIC Educational Resources Information Center

    Helsen, J.

    1982-01-01

    Discusses catalytic properties of clays, attributed to acidity of the clay surface. The formation of carbonium ions on montmorillonite is used as a demonstration of the presence of surface acidity, the enhanced dissociation of water molecules when polarized by cations, and the way the surface can interact with organic substances. (Author/JN)

  19. Catalytically active nanomaterials: a promising candidate for artificial enzymes.

    PubMed

    Lin, Youhui; Ren, Jinsong; Qu, Xiaogang

    2014-04-15

    cancer cells, nucleic acids, proteins, metal ions, and other small molecules. In addition, we also introduce three exciting advances in the use of efficient modulators on artificial enzyme systems to improve the catalytic performance of existing nanozymes. For example, we report that graphene oxide could serve as a modulator to greatly improve the catalytic activity of lysozyme-stabilized gold nanoclusters at neutral pH, which will have great potential for applications in biological systems. We show that, through the incorporation of modulator into artificial enzymes, we can offer a facile but highly effective way to improve their overall catalytic performance or realize the catalytic reactions that were not possible in the past. We expect that nanozymes with unique properties and functions will attract increasing research interest and lead to new opportunities in various fields of research.

  20. Preparation, characterization and catalytic properties of MCM-48 supported tungstophosphoric acid mesoporous materials for green synthesis of benzoic acid

    SciTech Connect

    Wu, Hai-Yan; Zhang, Xiao-Li; Chen, Xi; Chen, Ya; Zheng, Xiu-Cheng

    2014-03-15

    MCM-48 and tungstophosphoric acid (HPW) were prepared and applied for the synthesis of HPW/MCM-48 mesoporous materials. The characterization results showed that HPW/MCM-48 obtained retained the typical mesopore structure of MCM-48, and the textural parameters decreased with the increase loading of HPW. The catalytic oxidation results of benzyl alcohol and benzaldehyde with 30% H{sub 2}O{sub 2} indicated that HPW/MCM-48 was an efficient catalyst for the green synthesis of benzoic acid. Furthermore, 35 wt% HPW/MCM-48 sample showed the highest activity under the reaction conditions. Highlights: • 5–45 wt% HPW/MCM-48 mesoporous catalysts were prepared and characterized. • Their catalytic activities for the green synthesis of benzoic acid were investigated. • HPW/MCM-48 was approved to be an efficient catalyst. • 5 wt% HPW/MCM-48 exhibited the highest catalytic activity.

  1. GABA production by glutamic acid decarboxylase is regulated by a dynamic catalytic loop.

    PubMed

    Fenalti, Gustavo; Law, Ruby H P; Buckle, Ashley M; Langendorf, Christopher; Tuck, Kellie; Rosado, Carlos J; Faux, Noel G; Mahmood, Khalid; Hampe, Christiane S; Banga, J Paul; Wilce, Matthew; Schmidberger, Jason; Rossjohn, Jamie; El-Kabbani, Ossama; Pike, Robert N; Smith, A Ian; Mackay, Ian R; Rowley, Merrill J; Whisstock, James C

    2007-04-01

    Gamma-aminobutyric acid (GABA) is synthesized by two isoforms of the pyridoxal 5'-phosphate-dependent enzyme glutamic acid decarboxylase (GAD65 and GAD67). GAD67 is constitutively active and is responsible for basal GABA production. In contrast, GAD65, an autoantigen in type I diabetes, is transiently activated in response to the demand for extra GABA in neurotransmission, and cycles between an active holo form and an inactive apo form. We have determined the crystal structures of N-terminal truncations of both GAD isoforms. The structure of GAD67 shows a tethered loop covering the active site, providing a catalytic environment that sustains GABA production. In contrast, the same catalytic loop is inherently mobile in GAD65. Kinetic studies suggest that mobility in the catalytic loop promotes a side reaction that results in cofactor release and GAD65 autoinactivation. These data reveal the molecular basis for regulation of GABA homeostasis.

  2. Structural insights into the recovery of aldolase activity in N-acetylneuraminic acid lyase by replacement of the catalytically active lysine with γ-thialysine by using a chemical mutagenesis strategy.

    PubMed

    Timms, Nicole; Windle, Claire L; Polyakova, Anna; Ault, James R; Trinh, Chi H; Pearson, Arwen R; Nelson, Adam; Berry, Alan

    2013-03-01

    Chemical modification has been used to introduce the unnatural amino acid γ-thialysine in place of the catalytically important Lys165 in the enzyme N-acetylneuraminic acid lyase (NAL). The Staphylococcus aureus nanA gene, encoding NAL, was cloned and expressed in E. coli. The protein, purified in high yield, has all the properties expected of a class I NAL. The S. aureus NAL which contains no natural cysteine residues was subjected to site-directed mutagenesis to introduce a cysteine in place of Lys165 in the enzyme active site. Subsequently chemical mutagenesis completely converted the cysteine into γ-thialysine through dehydroalanine (Dha) as demonstrated by ESI-MS. Initial kinetic characterisation showed that the protein containing γ-thialysine regained 17 % of the wild-type activity. To understand the reason for this lower activity, we solved X-ray crystal structures of the wild-type S. aureus NAL, both in the absence of, and in complex with, pyruvate. We also report the structures of the K165C variant, and the K165-γ-thialysine enzyme in the presence, or absence, of pyruvate. These structures reveal that γ-thialysine in NAL is an excellent structural mimic of lysine. Measurement of the pH-activity profile of the thialysine modified enzyme revealed that its pH optimum is shifted from 7.4 to 6.8. At its optimum pH, the thialysine-containing enzyme showed almost 30 % of the activity of the wild-type enzyme at its pH optimum. The lowered activity and altered pH profile of the unnatural amino acid-containing enzyme can be rationalised by imbalances of the ionisation states of residues within the active site when the pK(a) of the residue at position 165 is perturbed by replacement with γ-thialysine. The results reveal the utility of chemical mutagenesis for the modification of enzyme active sites and the exquisite sensitivity of catalysis to the local structural and electrostatic environment in NAL.

  3. Catalytic conversion of lactic acid and its derivatives

    SciTech Connect

    Kokitkar, P.B.; Langford, R.; Miller, D.J.; Jackson, J.E.

    1993-12-31

    The catalytic upgrading of lactic acid and methyl lactate is being investigated. With the commercialization of inexpensive starch fermentation technologies, US production of lactic acid is undergoing a surge. Dropping cost and increased availability offer a major opportunity to develop lactic acid as a renewable feedstock for chemicals production. IT can be catalytically converted into several important chemical intermediates currently derived from petroleum including acrylic acid, propanoic acid, and 2,3-pentanedione. The process can expand the potential of biomass as a substitute feedstock for petroleum and can benefit both the US chemical process industry and US agriculture via increased production of high-value, non-food products from crops and crop byproducts. Reaction studies of lactic acid and its ester are conducted in fixed bed reactors at 250-380{degrees}C and 0.1-0.5 MPa (1-5 atm) using salt catalysts on low surface area supports. Highest selectivities achieved are 42% to acrylic acid and 55% to 2,3-pentanedione from lactic acid over NaNO{sub 3} catalyst on low surface area silica support. High surface area (microporous) or highly acidic supports promote fragmentation to acetaldehyde and thus reduce yields of desirable products. The support acidity gives rice to lactic acid from neat methyl lactate feed but the lactic acid yield goes down after the nitrate salt is impregnated on the support. Both lactic acid and methyl lactate form 2,3-pentanedione. Methyl lactate reactions are more complex since it forms all the products obtained from lactic acid as well as many corresponding esters of the acids obtained from lactic acid (mainly methyl acrylate, methyl propionate, methyl acetate). At high temperatures, methyl acetate and acetic acid yields become significant from methyl lactate whereas lactic acid gives significant amount of acetol at high temperatures.

  4. The first catalytic asymmetric thioacetalization by chiral phosphoric acid catalysis.

    PubMed

    Yu, Jin-Sheng; Wu, Wen-Biao; Zhou, Feng

    2016-02-21

    We report here the first catalytic asymmetric thioacetalization of salicylaldehyde and dithiol. Chiral phosphoric acid STRIP C5 is identified as a powerful catalyst for this reaction to afford various chiral dithioacetals in high to excellent yields and enantioselectivities under mild conditions. PMID:26810819

  5. Catalytic C-H bond activation at nanoscale Lewis acidic aluminium fluorides: H/D exchange reactions at aromatic and aliphatic hydrocarbons.

    PubMed

    Prechtl, Martin H G; Teltewskoi, Michael; Dimitrov, Anton; Kemnitz, Erhard; Braun, Thomas

    2011-12-16

    Nanoscopic amorphous Lewis acidic aluminium fluorides, such as aluminium chlorofluoride (ACF) and high-surface aluminium fluoride (HS-AlF(3)), are capable of activating C-H bonds of aliphatic hydrocarbons. H/D exchange reactions are catalysed under mild conditions (40 °C).

  6. Kinetics of the catalytic esterification of diglycerin with capric acid

    SciTech Connect

    Trufanova, T.N.; Nechesnyuk, G.P.; Bumina, N.A.; Kruchinin, V.A.; Slapygina, O.L.

    1988-06-10

    The object of this investigation was a further study of the rate of esterification of polyglycerins with fatty acids in the presence of acids, organometallic compounds, and metal salts. The catalytic effects of the following substances were studied (in wt. % of the reaction mixture): potassium, magnesium, copper, and zinc sulfates (analytical grade) first dried by calcination, 1%; pure grade tetrabutoxytitanate, 0.5-1%; and pure grade p-toluenesulfonic acid, recrystallized from concentrated hydrochloric acid, 1.0-3%. Samples taken after measured time intervals were analyzed by titration with an alcoholic solution of potassium hydroxide. The investigation was carried out in the kinetic regime.

  7. Catalytic cyclometallation in steroid chemistry III: Synthesis of steroidal derivatives of 5Z,9Z-dienoic acid and investigation of its human topoisomerase I inhibitory activity.

    PubMed

    D'yakonov, Vladimir A; Dzhemileva, Lilya U; Tuktarova, Regina A; Makarov, Aleksey A; Islamov, Ilgiz I; Mulyukova, Alfiya R; Dzhemilev, Usein M

    2015-10-01

    Two approaches to stereoselective synthesis of steroid 5Z,9Z-dienoic acids were developed, the first one being based on the cross-cyclomagnesiation of 2-(hepta-5,6-dien-1-yloxy)tetrahydro-2H-pyran and 1,2-diene cholesterol derivatives on treatment with EtMgBr catalyzed by Cp2TiCl2, while the other involving the synthesis of esters of hydroxy steroids with (5Z,9Z)-tetradeca-5,9-dienedioic acid, prepared in two steps using homo-cyclomagnesiation of 2-(hepta-5,6-dien-1-yloxy)tetrahydro-2H-pyran as the key step. High inhibitory activity of the synthesized acids against human topoisomerase I (hTop1) was found.

  8. Using Catalytic Atom Maps to Predict the Catalytic Functions Present in Enzyme Active Sites

    PubMed Central

    Nosrati, Geoffrey R.; Houk, K. N.

    2012-01-01

    Catalytic Atom Maps (CAMs) are minimal models of enzyme active sites. The structures in the Protein Data Bank (PDB) were examined to determine if proteins with CAM-like geometries in their active sites all share the same catalytic function. We combined the CAM-based search protocol with a filter based on the weighted contact number (WCN) of the catalytic residues, a measure of the “crowdedness” of the microenvironment around a protein residue. Using this technique, a CAM based on the Ser-His-Asp catalytic triad of trypsin was able to correctly identify catalytic triads in other enzymes within 0.5 Å RMSD of the Catalytic Atom Map with 96% accuracy. A CAM based on the Cys-Arg-(Asp/Glu) active site residues from the tyrosine phosphatase active site achieved 89% accuracy in identifying this type of catalytic functionality. Both of these Catalytic Atom Maps were able to identify active sites across different fold types. Finally, the PDB was searched to locate proteins with catalytic functionality similar to that present in the active site of orotidine 5′-monophosphate decarboxylase (ODCase), whose mechanism is not known with certainty. A CAM, based on the conserved Lys-Asp-Lys-Asp tetrad in the ODCase active site, was used to search the PDB for enzymes with similar active sites. The ODCase active site has a geometry similar to that of Schiff base-forming Class I aldolases, with lowest aldolase RMSD to the ODCase CAM at 0.48 Å. The similarity between this CAM and the aldolase active site suggests that ODCase has the correct catalytic functionality present in its active site for the generation of a nucleophilic lysine. PMID:22909276

  9. Tuning the Catalytic Activity of Subcellular Nanoreactors.

    PubMed

    Jakobson, Christopher M; Chen, Yiqun; Slininger, Marilyn F; Valdivia, Elias; Kim, Edward Y; Tullman-Ercek, Danielle

    2016-07-31

    Bacterial microcompartments are naturally occurring subcellular organelles of bacteria and serve as a promising scaffold for the organization of heterologous biosynthetic pathways. A critical element in the design of custom biosynthetic organelles is quantitative control over the loading of heterologous enzymes to the interior of the organelles. We demonstrate that the loading of heterologous proteins to the 1,2-propanediol utilization microcompartment of Salmonella enterica can be controlled using two strategies: by modulating the transcriptional activation of the microcompartment container and by coordinating the expression of the microcompartment container and the heterologous cargo. These strategies allow general control over the loading of heterologous proteins localized by two different N-terminal targeting peptides and represent an important step toward tuning the catalytic activity of bacterial microcompartments for increased biosynthetic productivity.

  10. Fluorogenic, catalytic, photochemical reaction for amplified detection of nucleic acids.

    PubMed

    Dutta, Subrata; Fülöp, Annabelle; Mokhir, Andriy

    2013-09-18

    Photochemical, nucleic acid-induced reactions, which are controlled by nontoxic red light, are well-suited for detection of nucleic acids in live cells, since they do not require any additives and can be spatially and temporally regulated. We have recently described the first reaction of this type, in which a phenylselenyl derivative of thymidine (5'-PhSeT-ODNa) is cleaved in the presence of singlet oxygen (Fülöp, A., Peng, X., Greenberg, M. M., Mokhir, A. (2010) A nucleic acid directed, red light-induced chemical reaction. Chem. Commun. 46, 5659-5661). The latter reagent is produced upon exposure of a photosensitizer 3'-PS-ODNb (PS = Indium(III)-pyropheophorbide-a-chloride: InPPa) to >630 nm light. In 2012 we reported on a fluorogenic version of this reaction (Dutta, S., Flottmann, B., Heilemann, M., Mokhir, A. (2012) Hybridization and reaction-based, fluorogenic nucleic acid probes. Chem. Commun. 47, 9664-9666), which is potentially applicable for the detection of nucleic acids in cells. Unfortunately, its yield does not exceed 25% and no catalytic turnover could be observed in the presence of substrate excess. This problem occurs due to the efficient, competing oxidation of the substrate containing an electron rich carbon-carbon double bonds (SCH═CHS) in the presence of singlet oxygen with formation of a noncleavable product (SCH═CHSO). Herein we describe a related, but substantially improved photochemical, catalytic transformation of a fluorogenic, organic substrate, which consists of 9,10-dialkoxyanthracene linked to fluorescein, with formation of a bright fluorescent dye. In highly dilute solution this reaction occurs only in the presence of a nucleic acid template. We developed three types of such a reaction and demonstrated that they are high yielding and generate over 7.7 catalytic turnovers, are sensitive to single mismatches in nucleic acid targets, and can be applied for determination of both the amount of nucleic acids and potentially their

  11. Catalytic production of conjugated fatty acids and oils.

    PubMed

    Philippaerts, An; Goossens, Steven; Jacobs, Pierre A; Sels, Bert F

    2011-06-20

    The reactive double bonds in conjugated vegetable oils are of high interest in industry. Traditionally, conjugated vegetable oils are added to paints, varnishes, and inks to improve their drying properties, while recently there is an increased interest in their use in the production of bioplastics. Besides the industrial applications, also food manufactures are interested in conjugated vegetable oils due to their various positive health effects. While the isomer type is less important for their industrial purposes, the beneficial health effects are mainly associated with the c9,t11, t10,c12 and t9,t11 CLA isomers. The production of CLA-enriched oils as additives in functional foods thus requires a high CLA isomer selectivity. Currently, CLAs are produced by conjugation of oils high in linoleic acid, for example soybean and safflower oil, using homogeneous bases. Although high CLA productivities and very high isomer selectivities are obtained, this process faces many ecological drawbacks. Moreover, CLA-enriched oils can not be produced directly with the homogeneous bases. Literature reports describe many catalytic processes to conjugate linoleic acid, linoleic acid methyl ester, and vegetable oils rich in linoleic acid: biocatalysts, for example enzymes and cells; metal catalysts, for example homogeneous metal complexes and heterogeneous catalysts; and photocatalysts. This Review discusses state-of-the-art catalytic processes in comparison with some new catalytic production routes. For each category of catalytic process, the CLA productivities and the CLA isomer selectivity are compared. Heterogeneous catalysis seems the most attractive approach for CLA production due to its easy recovery process, provided that the competing hydrogenation reaction is limited and the CLA production rate competes with the current homogeneous base catalysis. The most important criteria to obtain high CLA productivity and isomer selectivity are (1) absence of a hydrogen donor, (2

  12. Catalytic production of conjugated fatty acids and oils.

    PubMed

    Philippaerts, An; Goossens, Steven; Jacobs, Pierre A; Sels, Bert F

    2011-06-20

    The reactive double bonds in conjugated vegetable oils are of high interest in industry. Traditionally, conjugated vegetable oils are added to paints, varnishes, and inks to improve their drying properties, while recently there is an increased interest in their use in the production of bioplastics. Besides the industrial applications, also food manufactures are interested in conjugated vegetable oils due to their various positive health effects. While the isomer type is less important for their industrial purposes, the beneficial health effects are mainly associated with the c9,t11, t10,c12 and t9,t11 CLA isomers. The production of CLA-enriched oils as additives in functional foods thus requires a high CLA isomer selectivity. Currently, CLAs are produced by conjugation of oils high in linoleic acid, for example soybean and safflower oil, using homogeneous bases. Although high CLA productivities and very high isomer selectivities are obtained, this process faces many ecological drawbacks. Moreover, CLA-enriched oils can not be produced directly with the homogeneous bases. Literature reports describe many catalytic processes to conjugate linoleic acid, linoleic acid methyl ester, and vegetable oils rich in linoleic acid: biocatalysts, for example enzymes and cells; metal catalysts, for example homogeneous metal complexes and heterogeneous catalysts; and photocatalysts. This Review discusses state-of-the-art catalytic processes in comparison with some new catalytic production routes. For each category of catalytic process, the CLA productivities and the CLA isomer selectivity are compared. Heterogeneous catalysis seems the most attractive approach for CLA production due to its easy recovery process, provided that the competing hydrogenation reaction is limited and the CLA production rate competes with the current homogeneous base catalysis. The most important criteria to obtain high CLA productivity and isomer selectivity are (1) absence of a hydrogen donor, (2

  13. Dual catalytic activity of hydroxycinnamoyl-coenzyme A quinate transferase from tomato allows it to moonlight in the synthesis of both mono- and dicaffeoylquinic acids.

    PubMed

    Moglia, Andrea; Lanteri, Sergio; Comino, Cinzia; Hill, Lionel; Knevitt, Daniel; Cagliero, Cecilia; Rubiolo, Patrizia; Bornemann, Stephen; Martin, Cathie

    2014-12-01

    Tomato (Solanum lycopersicum), like other Solanaceous species, accumulates high levels of antioxidant caffeoylquinic acids, which are strong bioactive molecules and protect plants against biotic and abiotic stresses. Among these compounds, the monocaffeoylquinic acids (e.g. chlorogenic acid [CGA]) and the dicaffeoylquinic acids (diCQAs) have been found to possess marked antioxidative properties. Thus, they are of therapeutic interest both as phytonutrients in foods and as pharmaceuticals. Strategies to increase diCQA content in plants have been hampered by the modest understanding of their biosynthesis and whether the same pathway exists in different plant species. Incubation of CGA with crude extracts of tomato fruits led to the formation of two new products, which were identified by liquid chromatography-mass spectrometry as diCQAs. This chlorogenate:chlorogenate transferase activity was partially purified from ripe fruit. The final protein fraction resulted in 388-fold enrichment of activity and was subjected to trypsin digestion and mass spectrometric sequencing: a hydroxycinnamoyl-Coenzyme A:quinate hydroxycinnamoyl transferase (HQT) was selected as a candidate protein. Assay of recombinant HQT protein expressed in Escherichia coli confirmed its ability to synthesize diCQAs in vitro. This second activity (chlorogenate:chlorogenate transferase) of HQT had a low pH optimum and a high Km for its substrate, CGA. High concentrations of CGA and relatively low pH occur in the vacuoles of plant cells. Transient assays demonstrated that tomato HQT localizes to the vacuole as well as to the cytoplasm of plant cells, supporting the idea that in this species, the enzyme catalyzes different reactions in two subcellular compartments.

  14. Catalytic Activity of a Binary Informational Macromolecule

    NASA Technical Reports Server (NTRS)

    Reader, John S.; Joyce, Gerald F.

    2003-01-01

    RNA molecules are thought to have played a prominent role in the early history of life on Earth based on their ability both to encode genetic information and to exhibit catalytic function. The modern genetic alphabet relies on two sets of complementary base pairs to store genetic information. However, due to the chemical instability of cytosine, which readily deaminates to uracil, a primitive genetic system composed of the bases A, U, G and C may have been difficult to establish. It has been suggested that the first genetic material instead contained only a single base-pairing unie'. Here we show that binary informational macromolecules, containing only two different nucleotide subunits, can act as catalysts. In vitro evolution was used to obtain ligase ribozymes composed of only 2,6-diaminopurine and uracil nucleotides, which catalyze the template-directed joining of two RNA molecules, one bearing a 5'-triphosphate and the other a 3'-hydroxyl. The active conformation of the fastest isolated ribozyme had a catalytic rate that was about 36,000-fold faster than the uncatalyzed rate of reaction. This ribozyme is specific for the formation of biologically relevant 3',5'-phosphodiester linkages.

  15. Uniquely localized intra-molecular amino acid concentrations at the glycolytic enzyme catalytic/active centers of Archaea, Bacteria and Eukaryota are associated with their proposed temporal appearances on earth.

    PubMed

    Pollack, J Dennis; Gerard, David; Pearl, Dennis K

    2013-04-01

    The distributions of amino acids at most-conserved sites nearest catalytic/active centers (C/AC) in 4,645 sequences of ten enzymes of the glycolytic Embden-Meyerhof-Parnas pathway in Archaea, Bacteria and Eukaryota are similar to the proposed temporal order of their appearance on Earth. Glycine, isoleucine, leucine, valine, glutamic acid and possibly lysine often described as prebiotic, i.e., existing or occurring before the emergence of life, were localized in positional and conservational defined aggregations in all enzymes of all Domains. The distributions of all 20 biologic amino acids in most-conserved sites nearest their C/ACs were quite different either from distributions in sites less-conserved and further from their C/ACs or from all amino acids regardless of their position or conservation. The major concentrations of glycine, e.g., perhaps the earliest prebiotic amino acid, occupies ≈ 16 % of all the most-conserved sites within a volume of ≈ 7-8 Å radius from their C/ACs and decreases linearly towards the molecule's peripheries. Spatially localized major concentrations of isoleucine, leucine and valine are in the mid-conserved and mid-distant sites from their C/ACs in protein interiors. Lysine and glutamic acid comprise ≈ 25-30 % of all amino acids within an irregular volume bounded by ≈ 24-28 Å radii from their C/ACs at the most-distant least-conserved sites. The unreported characteristics of these amino acids: their spatially and conservationally identified concentrations in Archaea, Bacteria and Eukaryota, suggest some common structural organization of glycolytic enzymes that may be relevant to their evolution and that of other proteins. We discuss our data in relation to enzyme evolution, their reported prebiotic putative temporal appearances on Earth, abundances, biological "cost", neighbor-sequence preferences or "ordering" and some thermodynamic parameters.

  16. Uniquely Localized Intra-Molecular Amino Acid Concentrations at the Glycolytic Enzyme Catalytic/Active Centers of Archaea, Bacteria and Eukaryota are Associated with Their Proposed Temporal Appearances on Earth

    NASA Astrophysics Data System (ADS)

    Pollack, J. Dennis; Gerard, David; Pearl, Dennis K.

    2013-04-01

    The distributions of amino acids at most-conserved sites nearest catalytic/active centers (C/AC) in 4,645 sequences of ten enzymes of the glycolytic Embden-Meyerhof-Parnas pathway in Archaea, Bacteria and Eukaryota are similar to the proposed temporal order of their appearance on Earth. Glycine, isoleucine, leucine, valine, glutamic acid and possibly lysine often described as prebiotic, i.e., existing or occurring before the emergence of life, were localized in positional and conservational defined aggregations in all enzymes of all Domains. The distributions of all 20 biologic amino acids in most-conserved sites nearest their C/ACs were quite different either from distributions in sites less-conserved and further from their C/ACs or from all amino acids regardless of their position or conservation. The major concentrations of glycine, e.g., perhaps the earliest prebiotic amino acid, occupies ≈16 % of all the most-conserved sites within a volume of ≈7-8 Å radius from their C/ACs and decreases linearly towards the molecule's peripheries. Spatially localized major concentrations of isoleucine, leucine and valine are in the mid-conserved and mid-distant sites from their C/ACs in protein interiors. Lysine and glutamic acid comprise ≈25-30 % of all amino acids within an irregular volume bounded by ≈24-28 Å radii from their C/ACs at the most-distant least-conserved sites. The unreported characteristics of these amino acids: their spatially and conservationally identified concentrations in Archaea, Bacteria and Eukaryota, suggest some common structural organization of glycolytic enzymes that may be relevant to their evolution and that of other proteins. We discuss our data in relation to enzyme evolution, their reported prebiotic putative temporal appearances on Earth, abundances, biological "cost", neighbor-sequence preferences or "ordering" and some thermodynamic parameters.

  17. Probing the Lewis acidity and catalytic activity of the metal-organic framework [Cu3(btc)2] (BTC=benzene-1,3,5-tricarboxylate).

    PubMed

    Alaerts, Luc; Séguin, Etienne; Poelman, Hilde; Thibault-Starzyk, Frédéric; Jacobs, Pierre A; De Vos, Dirk E

    2006-09-25

    An optimized procedure was designed for the preparation of the microporous metal-organic framework (MOF) [Cu3(btc)2] (BTC=benzene-1,3,5-tricarboxylate). The crystalline material was characterized by X-ray diffraction, optical microscopy, SEM, X-ray photoelectron spectroscopy, N2 sorption, thermogravimetry, and IR spectroscopy of adsorbed CO. CO adsorbs on a small number of Cu2O impurities, and particularly on the free CuII coordination sites in the framework. [Cu3(btc)2] is a highly selective Lewis acid catalyst for the isomerization of terpene derivatives, such as the rearrangement of alpha-pinene oxide to campholenic aldehyde and the cyclization of citronellal to isopulegol. By using the ethylene ketal of 2-bromopropiophenone as a test substrate, it was demonstrated that the active sites in [Cu3(btc)2] are hard Lewis acids. Catalyst stability, re-usability, and heterogeneity are critically assessed. PMID:16881030

  18. [Reductive dechlorination of trichloroacetic acid by bioelectrochemically catalytic method].

    PubMed

    Li, Yu-Ping; Cao, Hong-Bin; Zhang, Yi

    2005-07-01

    Direct electrochemical behaviors of hemoglobin (Hb) immobilized on carbon nanotube (CNT) modified carbon paste electrode with adsorption were investigated. Cyclic voltammetry of Hb-CNT-modified electrode showed a pair of well-defined and nearly reversible peaks for HbhemeFe(III) /Fe(II) redox couple in pH = 7 PBS buffers. The electrocatalytic behaviors of Hb-CNT-modified electrode for the reductive dechlorination of trichloroacetic acid (TCA) were studied by cyclic voltammmetry and fixed-potential electrolysis technique, and the reductive mechanism of TCA was discussed by analysis of reduction products. The results showed that Hb-CNT-modified electrode possessed good electro-catalytic activity for reduction of TCA and the dechlorination of TCA was stepwise, following the pathway of trichloroacetic--> dichloroacetic--> monochloroacetic--> acetic. The dechlorination of TCA in waster water was investigated using a two-compartment flow reactor with working electrode compartment packed with Hb-CNT-modified graphite electrode. The conversion of TCA was 40.13% with electrolysis for 180 min at - 0.60V (vs. SCE).

  19. Catalytic esterification of methacrylic acid with methyl alcohol

    SciTech Connect

    Lunin, A.F.; Zheleznaya, L.L.; Karakhanov, R.A.; Meshcheryakov, S.V.; Magadov, R.S.; Mkrtychan, V.R.; Fomin, V.A.

    1987-08-10

    The authors contend that virtually all methods for the production of methacrylic acid esters suffer from the drawbacks of low conversion, dependence on costly catalysts, low feed rates, and the need to use inhibitors in the process. To eliminate these drawbacks, they propose and test a new catalyst, sulfopolyphenyl ketone, which contains an extensive conjugated bond system together with ionic hydroxide groups. The catalytic esterification rate and yield is given for this catalyst and chromatography is performed for the resulting esters.

  20. Catalytical Conversion of Carbohydrates into Lactic Acid via Hydrothermal Reaction

    NASA Astrophysics Data System (ADS)

    Wei, Zhen; Jin, Fangming; Zhang, Guangyi; Zhang, Shiping; Yao, Guodong

    2010-11-01

    This paper focuses on catalytical conversion of carbohydrates into lactic acid, under the hydrothermal conditions, which may have a promising future for its high speediness and effectiveness. The catalysis of ZnO was investigated to improve the lactic acid yields. The results showed that the lactic acid yields increased immensely by the addition of ZnO. The effects of the reaction time and the addition amount of ZnO on the conversion of carbohydrates to lactic acid were studied. The highest lactic acid yields reached up to 28% starting from glucose after the reaction time of 60 s under the conditions of 0.2 mmol ZnO, 300° C, the filling rate of 35%, and over 30% starting from fructose at the same temperature and filling rate when the reaction time of 40 s and 2.0 mmol ZnO were employed. The collaborative effects of ZnO and NaOH used as the catalysts together at the same time were also studied. Furthermore, the catalytic mechanism of ZnO in the hydrothermal conversion of carbohydrates into lactic acid was discussed.

  1. Concentration of Specific Amino Acids at the Catalytic/Active Centers of Highly-Conserved ``Housekeeping'' Enzymes of Central Metabolism in Archaea, Bacteria and Eukaryota: Is There a Widely Conserved Chemical Signal of Prebiotic Assembly?

    NASA Astrophysics Data System (ADS)

    Pollack, J. Dennis; Pan, Xueliang; Pearl, Dennis K.

    2010-06-01

    In alignments of 1969 protein sequences the amino acid glycine and others were found concentrated at most-conserved sites within ˜15 Å of catalytic/active centers (C/AC) of highly conserved kinases, dehydrogenases or lyases of Archaea, Bacteria and Eukaryota. Lysine and glutamic acid were concentrated at least-conserved sites furthest from their C/ACs. Logistic-regression analyses corroborated the “movement” of glycine towards and lysine away from their C/ACs: the odds of a glycine occupying a site were decreased by 19%, while the odds for a lysine were increased by 53%, for every 10 Å moving away from the C/AC. Average conservation of MSA consensus sites was highest surrounding the C/AC and directly decreased in transition toward model’s peripheries. Findings held with statistical confidence using sequences restricted to individual Domains or enzyme classes or to both. Our data describe variability in the rate of mutation and likelihoods for phylogenetic trees based on protein sequence data and endorse the extension of substitution models by incorporating data on conservation and distance to C/ACs rather than only using cumulative levels. The data support the view that in the most-conserved environment immediately surrounding the C/AC of taxonomically distant and highly conserved essential enzymes of central metabolism there are amino acids whose identity and degree of occupancy is similar to a proposed amino acid set and frequency associated with prebiotic evolution.

  2. Concentration of specific amino acids at the catalytic/active centers of highly-conserved "housekeeping" enzymes of central metabolism in archaea, bacteria and Eukaryota: is there a widely conserved chemical signal of prebiotic assembly?

    PubMed

    Pollack, J Dennis; Pan, Xueliang; Pearl, Dennis K

    2010-06-01

    In alignments of 1969 protein sequences the amino acid glycine and others were found concentrated at most-conserved sites within approximately 15 A of catalytic/active centers (C/AC) of highly conserved kinases, dehydrogenases or lyases of Archaea, Bacteria and Eukaryota. Lysine and glutamic acid were concentrated at least-conserved sites furthest from their C/ACs. Logistic-regression analyses corroborated the "movement" of glycine towards and lysine away from their C/ACs: the odds of a glycine occupying a site were decreased by 19%, while the odds for a lysine were increased by 53%, for every 10 A moving away from the C/AC. Average conservation of MSA consensus sites was highest surrounding the C/AC and directly decreased in transition toward model's peripheries. Findings held with statistical confidence using sequences restricted to individual Domains or enzyme classes or to both. Our data describe variability in the rate of mutation and likelihoods for phylogenetic trees based on protein sequence data and endorse the extension of substitution models by incorporating data on conservation and distance to C/ACs rather than only using cumulative levels. The data support the view that in the most-conserved environment immediately surrounding the C/AC of taxonomically distant and highly conserved essential enzymes of central metabolism there are amino acids whose identity and degree of occupancy is similar to a proposed amino acid set and frequency associated with prebiotic evolution.

  3. MOF-Derived Tungstated Zirconia as Strong Solid Acids toward High Catalytic Performance for Acetalization.

    PubMed

    Wang, Peng; Feng, Jian; Zhao, Yupei; Wang, Shaobin; Liu, Jian

    2016-09-14

    A strong solid acid, tungstated zirconia (WZ), has been prepared first using tungstate immobilized UiO-66 as precursors through a "double-solvent" impregnation method under mild calcination temperature. With moderate W contents, the as-synthesized WZ catalysts possess a high density of acid sites, and the proper heat treatment also has facilely led to a bunch of oligomeric tungsten clusters on stabilized tetragonal ZrO2. The resultant solid acids show an improved catalytic performance toward the benzaldehyde's acetalization in comparison with traditional zirconium hydroxide-prepared WZ. Notably, due to large surface area and additionally introduced strong acid sites, the MOF-derived WZ catalysts afforded conversion up to 86.0%. The facile method endows the WZ catalysts with superior catalytic activities and excellent recyclability, thus opening a new avenue for preparation of metal oxide-based solid superacids and superbases. PMID:27557351

  4. Using catalytic atom maps to predict the catalytic functions present in enzyme active sites.

    PubMed

    Nosrati, Geoffrey R; Houk, K N

    2012-09-18

    Catalytic atom maps (CAMs) are minimal models of enzyme active sites. The structures in the Protein Data Bank (PDB) were examined to determine if proteins with CAM-like geometries in their active sites all share the same catalytic function. We combined the CAM-based search protocol with a filter based on the weighted contact number (WCN) of the catalytic residues, a measure of the "crowdedness" of the microenvironment around a protein residue. Using this technique, a CAM based on the Ser-His-Asp catalytic triad of trypsin was able to correctly identify catalytic triads in other enzymes within 0.5 Å rmsd of the CAM with 96% accuracy. A CAM based on the Cys-Arg-(Asp/Glu) active site residues from the tyrosine phosphatase active site achieved 89% accuracy in identifying this type of catalytic functionality. Both of these CAMs were able to identify active sites across different fold types. Finally, the PDB was searched to locate proteins with catalytic functionality similar to that present in the active site of orotidine 5'-monophosphate decarboxylase (ODCase), whose mechanism is not known with certainty. A CAM, based on the conserved Lys-Asp-Lys-Asp tetrad in the ODCase active site, was used to search the PDB for enzymes with similar active sites. The ODCase active site has a geometry similar to that of Schiff base-forming Class I aldolases, with lowest aldolase rmsd to the ODCase CAM at 0.48 Å. The similarity between this CAM and the aldolase active site suggests that ODCase has the correct catalytic functionality present in its active site for the generation of a nucleophilic lysine. PMID:22909276

  5. A series of hybrid P450 BM3 enzymes with different catalytic activity in the light-initiated hydroxylation of lauric acid

    PubMed Central

    Tran, Ngoc-Han; Huynh, Ngoc; Chavez, Garrett; Nguyen, Angelina; Dwaraknath, Sudharsan; Nguyen, Thien-Anh; Nguyen, Maxine; Cheruzel, Lionel

    2012-01-01

    We have developed a series of hybrid P450 BM3 enzymes to perform the light-activated hydroxylation of lauric acid. These enzymes contain a Ru(II)-diimine photosensitizer covalently attached to single cysteine residues of mutant P450 BM3 heme domains. The library of hybrid enzymes includes four non-native single cysteine mutants (K97C, Q397C, Q109C and L407C). In addition, mutations around the heme active site, F87A and I401P, were inserted in the Q397C mutant. Two heteroleptic Ru(II) complexes, Ru(bpy)2phenA (1) and Ru(phen)2phenA (2) (bpy=bipyridine, phen=1,10-phenanthroline, and phenA=5-acetamido-1,10-phenanthroline), are used as photosensitizers. Upon visible light irradiation, the hybrid enzymes display various total turnover numbers in the hydroxylation of lauric acid, up to 140 for the L407C-1 mutant, a 16-fold increase compared to the F87A/Q397C-1 mutant. CO binding studies confirm the ability of the photogenerated Ru(I) compound to reduce the fraction of ferric high spin species present in the mutants upon substrate binding. PMID:22922311

  6. Liquid-Phase Catalytic Transfer Hydrogenation of Furfural over Homogeneous Lewis Acid-Ru/C Catalysts.

    PubMed

    Panagiotopoulou, Paraskevi; Martin, Nickolas; Vlachos, Dionisios G

    2015-06-22

    The catalytic performance of homogeneous Lewis acid catalysts and their interaction with Ru/C catalyst are studied in the catalytic transfer hydrogenation of furfural by using 2-propanol as a solvent and hydrogen donor. We find that Lewis acid catalysts hydrogenate the furfural to furfuryl alcohol, which is then etherified with 2-propanol. The catalytic activity is correlated with an empirical scale of Lewis acid strength and exhibits a volcano behavior. Lanthanides are the most active, with DyCl3 giving complete furfural conversion and a 97 % yield of furfuryl alcohol at 180 °C after 3 h. The combination of Lewis acid and Ru/C catalysts results in synergy for the stronger Lewis acid catalysts, with a significant increase in the furfural conversion and methyl furan yield. Optimum results are obtained by using Ru/C combined with VCl3 , AlCl3 , SnCl4 , YbCl3 , and RuCl3 . Our results indicate that the combination of Lewis acid/metal catalysts is a general strategy for performing tandem reactions in the upgrade of furans.

  7. Interface dynamics explain assembly dependency of influenza neuraminidase catalytic activity

    PubMed Central

    von Grafenstein, Susanne; Wallnoefer, Hannes G.; Kirchmair, Johannes; Fuchs, Julian E.; Huber, Roland G.; Schmidtke, Michaela; Sauerbrei, Andreas; Rollinger, Judith M.; Liedl, Klaus R.

    2015-01-01

    Influenza virus neuraminidase (iNA) is a homotetrameric surface protein of the influenza virus and an established target for antiviral drugs. In contrast to neuraminidases (NAs) of other biological systems (non-iNAs), enzymatic activity of iNA is only observed in a quaternary assembly and iNA needs the tetramerization to mediate enzymatic activity. Obviously, differences on a molecular level between iNA and non-iNAs are responsible for this intriguing observation. Comparison between protein structures and multiple sequence alignment allow the identification of differences in amino acid composition in crucial regions of the enzyme, such as next to the conserved D151 and the 150-loop. These differences in amino acid sequence and protein tetramerization are likely to alter the dynamics of the system. Therefore, we performed molecular dynamics simulations to investigate differences in the molecular flexibility of monomers, dimers, and tetramers of iNAs of subtype N1 (avian 2004, pandemic 1918 and pandemic 2009 iNA) and as comparison the non-iNA monomer from Clostridium perfringens. We show that conformational transitions of iNA are crucially influenced by its assembly state. The protein–protein interface induces a complex hydrogen-bonding network between the 110-helix and the 150-loop, which consequently stabilizes the structural arrangement of the binding site. Therefore, we claim that these altered dynamics are responsible for the dependence of iNA’s catalytic activity on the tetrameric assembly. Only the tetramerization-induced balance between stabilization and altered local flexibility in the binding site provides the appropriate arrangement of key residues for iNA’s catalytic activity. PMID:24279589

  8. Nonenzymatic catalytic signal amplification for nucleic acid hybridization assays

    NASA Technical Reports Server (NTRS)

    Fan, Wenhong (Inventor); Cassell, Alan M. (Inventor); Han, Jie (Inventor)

    2006-01-01

    Devices, methods, and kits for amplifying the signal from hybridization reactions between nucleic acid probes and their cognate targets are presented. The devices provide partially-duplexed, immobilized probe complexes, spatially separate from and separately addressable from immobilized docking strands. Cognate target acts catalytically to transfer probe from the site of probe complex immobilization to the site of immobilized docking strand, generating a detectable signal. The methods and kits of the present invention may be used to identify the presence of cognate target in a fluid sample.

  9. Occurrence of acid rain in Baton Rouge, Louisiana, Summer 1981. The role of the catalytic converter

    SciTech Connect

    Robinson, J.W.; Ghane, H.

    1982-01-01

    Between June and October 1981, acid rain falling in Baton Rouge, LA was studied. The acidity of the rain ranged for pH 3.9 to pH 5.8. Preliminary data showed that rain associated with thermal cumulo nimbus tended to be more acidic, but rain associated with active cold fronts were less acid. This may relate to dispersion and dilution of the acid aerosols by the cold front. It is proposed that exhaust from automobiles fitted with catalytic converters is a substantial contributor to the acid rain problem, and that their net value to the abatement of pollution must be questioned, particularly in regions of the country where smog is not a problem. (JMT)

  10. Synthesis and catalytic activity of polysaccharide templated nanocrystalline sulfated zirconia

    NASA Astrophysics Data System (ADS)

    Sherly, K. B.; Rakesh, K.

    2014-01-01

    Nanoscaled materials are of great interest due to their unique enhanced optical, electrical and magnetic properties. Sulfate-promoted zirconia has been shown to exhibit super acidic behavior and high activity for acid catalyzed reactions. Nanocrystalline zirconia was prepared in the presence of polysaccharide template by interaction between ZrOCl2ṡ8H2O and chitosan template. The interaction was carried out in aqueous phase, followed by the removal of templates by calcination at optimum temperature and sulfation. The structural and textural features were characterized by powder XRD, TG, SEM and TEM. XRD patterns showed the peaks of the diffractogram were in agreement with the theoretical data of zirconia with the catalytically active tetragonal phase and average crystalline size of the particles was found to be 9 nm, which was confirmed by TEM. TPD using ammonia as probe, FTIR and BET surface area analysis were used for analyzing surface features like acidity and porosity. The BET surface area analysis showed the sample had moderately high surface area. FTIR was used to find the type species attached to the surface of zirconia. UV-DRS found the band gap of the zirconia was found to be 2.8 eV. The benzylation of o-xylene was carried out batchwise in atmospheric pressure and 433K temperature using sulfated zirconia as catalyst.

  11. Synthesis and catalytic activity of polysaccharide templated nanocrystalline sulfated zirconia

    SciTech Connect

    Sherly, K. B.; Rakesh, K.

    2014-01-28

    Nanoscaled materials are of great interest due to their unique enhanced optical, electrical and magnetic properties. Sulfate-promoted zirconia has been shown to exhibit super acidic behavior and high activity for acid catalyzed reactions. Nanocrystalline zirconia was prepared in the presence of polysaccharide template by interaction between ZrOCl{sub 2}⋅8H{sub 2}O and chitosan template. The interaction was carried out in aqueous phase, followed by the removal of templates by calcination at optimum temperature and sulfation. The structural and textural features were characterized by powder XRD, TG, SEM and TEM. XRD patterns showed the peaks of the diffractogram were in agreement with the theoretical data of zirconia with the catalytically active tetragonal phase and average crystalline size of the particles was found to be 9 nm, which was confirmed by TEM. TPD using ammonia as probe, FTIR and BET surface area analysis were used for analyzing surface features like acidity and porosity. The BET surface area analysis showed the sample had moderately high surface area. FTIR was used to find the type species attached to the surface of zirconia. UV-DRS found the band gap of the zirconia was found to be 2.8 eV. The benzylation of o-xylene was carried out batchwise in atmospheric pressure and 433K temperature using sulfated zirconia as catalyst.

  12. Manganese salen complexes with acid-base catalytic auxiliary: functional mimetics of catalase.

    PubMed

    Noritake, Yukinobu; Umezawa, Naoki; Kato, Nobuki; Higuchi, Tsunehiko

    2013-04-01

    Antioxidant therapies have been considered for a wide variety of disorders associated with oxidative stress, and synthetic catalytic scavengers of reactive oxygen species would be clinically superior to stoichiometric ones. Among them, salen-manganese complexes (Mn(Salen)) seem promising, because they exhibit dual functions, i.e. superoxide dismutase- and catalase-mimetic activities. We have been developing enzyme-mimetic Mn(Salen) complexes bearing a functional group that enhances their catalytic activity. Here, we describe the design and synthesis of novel Mn(Salen) complexes with general acid-base catalytic functionality, inspired by the reaction mechanism of catalase. As expected, these Mn(Salen) complexes showed superior catalase-like activity and selectivity, while retaining moderate SOD-like activity. An unsubstituted pyridyl group worked well as a functionality to promote catalase-like activity. The introduced functionality did not alter the redox potential suggesting that the auxiliary-modified complex acted as an acid-base catalyst analogous to catalase. We believe that our approach provides a new design principle for sophisticated catalyst design. Further, the compounds described here appear to be good candidates for use in antioxidant therapy.

  13. Computational evaluation of factors governing catalytic 2-keto acid decarboxylation.

    PubMed

    Wu, Di; Yue, Dajun; You, Fengqi; Broadbelt, Linda J

    2014-06-01

    Recent advances in computational approaches for creating pathways for novel biochemical reactions has motivated the development of approaches for identifying enzyme-substrate pairs that are attractive candidates for effecting catalysis. We present an improved structural-based strategy to probe and study enzyme-substrate binding based on binding geometry, energy, and molecule characteristics, which allows for in silico screening of structural features that imbue higher catalytic potential with specific substrates. The strategy is demonstrated using 2-keto acid decarboxylation with various pairs of 2-keto acids and enzymes. We show that this approach fitted experimental values for a wide range of 2-keto acid decarboxylases for different 2-keto acid substrates. In addition, we show that the structure-based methods can be used to select specific enzymes that may be promising candidates to catalyze decarboxylation of certain 2-keto acids. The key features and principles of the candidate enzymes evaluated by the strategy can be used to design novel biosynthesis pathways, to guide enzymatic mutation or to guide biomimetic catalyst design.

  14. Preparation, characterization and catalytic properties of MCM-48 supported tungstophosphoric acid mesoporous materials for green synthesis of benzoic acid

    NASA Astrophysics Data System (ADS)

    Wu, Hai-Yan; Zhang, Xiao-Li; Chen, Xi; Chen, Ya; Zheng, Xiu-Cheng

    2014-03-01

    MCM-48 and tungstophosphoric acid (HPW) were prepared and applied for the synthesis of HPW/MCM-48 mesoporous materials. The characterization results showed that HPW/MCM-48 obtained retained the typical mesopore structure of MCM-48, and the textural parameters decreased with the increase loading of HPW. The catalytic oxidation results of benzyl alcohol and benzaldehyde with 30% H2O2 indicated that HPW/MCM-48 was an efficient catalyst for the green synthesis of benzoic acid. Furthermore, 35 wt% HPW/MCM-48 sample showed the highest activity under the reaction conditions.

  15. ECUT: Energy Conversion and utilization Technologies program biocatalysis research activity. Generation of chemical intermediates by catalytic oxidative decarboxylation of dilute organic acids

    NASA Technical Reports Server (NTRS)

    Distefano, S.; Gupta, A.; Ingham, J. D.

    1983-01-01

    A rhodium-based catalyst was prepared and preliminary experiments were completed where the catalyst appeared to decarboxylate dilute acids at concentrations of 1 to 10 vol%. Electron spin resonance spectroscoy was used to characterize the catalyst as a first step leading toward modeling and optimization of rhodium catalysts. Also, a hybrid chemical/biological process for the production of hydrocarbons has been assessed. These types of catalysts could greatly increase energy efficiency of this process.

  16. Correlation of zeolite ZSM-5 acid strength with catalytic activity and selectivity. Final report. [Cobalt and cobalt/thorium impregnated H-ZSM-5

    SciTech Connect

    Hayhurst, D.T.

    1984-04-01

    Isosteric heats of ammonia adsorption were determined for several cobalt and cobalt/thorium impregnated H-ZSM-5. Samples were impregnated to the 3, 6 and 9 wt % levels using an incipient wetness technique and either acetone or water for dissolving the metal nitrate salt. The metal impregnation resulted in a lowering of the maximum heat of ammonia adsorption and in a corresponding lowering of the maximum acid site strength. The ammonia adsorption capacity and adsorption heat was unaltered by a reduction of the metal-impregnated samples in hydrogen, indicating that the incipient wetness method leads to cobalt which was most likely ion-exchanged into the zeolite rather than impregnated into the sieve in a reducable form. In addition, the impregnated cobalt caused a slight steric hinderance to the diffusion of n-butane into the metal-loaded zeolite. The use of either water or acetone for dissolving the metal nitrate salt altered the acid-strength distribution. Water was found to lower the acid-site strength to a greater degree than the acetone. 11 references, 8 figures.

  17. Central-metal exchange, improved catalytic activity, photoluminescence properties of a new family of d(10) coordination polymers based on the 5,5'-(1H-2,3,5-triazole-1,4-diyl)diisophthalic acid ligand.

    PubMed

    Wang, Huarui; Huang, Chao; Han, Yanbing; Shao, Zhichao; Hou, Hongwei; Fan, Yaoting

    2016-05-01

    The rigid and planar tetracarboxylic acid 5,5'-(1H-2,3,5-triazole-1,4-diyl)diisophthalic acid (H4L), incorporating a triazole group, has been used with no or different pyridine-based linkers to construct a family of d(10) coordination polymers, namely, {[H2N(CH3)2]3[Cd3(L)2(HCOO)]}n (), {[Cd2(L)(py)6]·H2O}n (), {[H2N(CH3)2] [Cd2(L)(HCOO)(H2O)4]}n (), {[Zn(H2L)]·H2O}n (), and {[Zn(H2L)(4,4'-bipy)0.5]·C2H5OH·H2O}n () (py = pyridine, 4,4'-bipy = 4,4'-bipyridine). constructs a 3D porous network containing two kinds of channels: one is filled with coordinated HCOO(-) anions, and the other with [H2N(CH3)2](+) cations. The framework of can be described as a rare (5,6,7)-connected net with the Schläfli symbol of (4(12)·5·6(2))(4(5)·5(3)·6(2))2(4(8)·5(3)·6(8)·8(2))2. The Cd(ii) ions in are connected through the carboxylate ligands to form a 2D layer, with aperture dimensions of ∼15.1 Å × 16.2 Å. The network of features a 3D (3,4)-connected (6·8·10)2(6·8(3)·10(2)) topology. A 3D network with the (4(2)·6·8(3)) topology of possesses an open 1D channel with the free volume of 29.2%. is a 2D layer structure with the (4(2)·6(3)·8)(4(2)·6) topology. The fluorescence lifetime τ values of are on the nanosecond timescale at room temperature. In particular, central-metal exchange in leads to a series of isostructural M(ii)-Cd frameworks [M = Cu (), Co (), Ni ()] showing improved catalytic activity for the synthesis of 1,4,5,6-tetrahydropyrimidine derivatives. Based on this, a plausible mechanism for the catalytic reaction has been proposed and the reactivity-structure relationship has been further clarified. PMID:27063339

  18. Voltage-dependent motion of the catalytic region of voltage-sensing phosphatase monitored by a fluorescent amino acid

    PubMed Central

    Sakata, Souhei; Jinno, Yuka; Kawanabe, Akira; Okamura, Yasushi

    2016-01-01

    The cytoplasmic region of voltage-sensing phosphatase (VSP) derives the voltage dependence of its catalytic activity from coupling to a voltage sensor homologous to that of voltage-gated ion channels. To assess the conformational changes in the cytoplasmic region upon activation of the voltage sensor, we genetically incorporated a fluorescent unnatural amino acid, 3-(6-acetylnaphthalen-2-ylamino)-2-aminopropanoic acid (Anap), into the catalytic region of Ciona intestinalis VSP (Ci-VSP). Measurements of Anap fluorescence under voltage clamp in Xenopus oocytes revealed that the catalytic region assumes distinct conformations dependent on the degree of voltage-sensor activation. FRET analysis showed that the catalytic region remains situated beneath the plasma membrane, irrespective of the voltage level. Moreover, Anap fluorescence from a membrane-facing loop in the C2 domain showed a pattern reflecting substrate turnover. These results indicate that the voltage sensor regulates Ci-VSP catalytic activity by causing conformational changes in the entire catalytic region, without changing their distance from the plasma membrane. PMID:27330112

  19. [Surface-active agents from the group of polyoxyethylated glycerol esters of fatty acids. Part II. Chromatographic analysis and basic viscosity parameters as a estimate criterion of efficiency of catalytic oxyethylation of Lard's fractions (Adeps suillus FP VII)].

    PubMed

    Piotrowska, Jowita Barbara; Nachajski, Michał Jakub; Lukosek, Marek; Kosno, Jacek; Zgoda, Marian Mikołaj

    2011-01-01

    The catalytic oxyethylation products of Lard's fractions and Tweens--as a reference products, were analised by chromatographic analysis HPLC and GPC. The above part was determination average molecular weights dispersion (Mw I Mn) and the content of polyethylene glycols (PEG), which are obtained during catalytic oxyethylation, and determination iodine value of the product (L(J2)). Viscosity measurements were carried out by Ubelohde method and enabled determination of basic viscosity and hydrodynamic parameters. The obtained results indicate that, comparing reference products--polysorbates, Tweens, products of triglycerides oxyethylation contain significantly less, in some cases very small amount of polyethylene glycols (PEG), and also maintained a high amount of unsaturated fatty acids (oleic acid), which is proven by the iodine value. Numerical value n(s) /H2O/ confirms important disparity of micells palisad structure, which are created based on oxyethylated triglycerides nTE = 40. That indicates significant solubilization possibilities of their aqueous solutions Cexp < or = Cmc.

  20. Mechanism for enhanced degradation of clofibric acid in aqueous by catalytic ozonation over MnOx/SBA-15.

    PubMed

    Sun, Qiangqiang; Wang, Yu; Li, Laisheng; Bing, Jishuai; Wang, Yingxin; Yan, Huihua

    2015-04-01

    Comparative experiments were conducted to investigate the catalytic ability of MnO(x)/SBA-15 for the ozonation of clofibric acid (CA) and its reaction mechanism. Compared with ozonation alone, the degradation of CA was barely enhanced, while the removal of TOC was significantly improved by catalytic ozonation (O3/MnO(x)/SBA-15). Adsorption of CA and its intermediates by MnO(x)/SBA-15 was proved unimportant in O3/MnO(x)/SBA-15 due to the insignificant adsorption of CA and little TOC variation after ceasing ozone in stopped-flow experiment. The more remarkably inhibition effect of sodium bisulfite (NaHSO3) on the removal of TOC in catalytic ozonation than in ozonation alone elucidated that MnO(x)/SBA-15 facilitated the generation of hydroxyl radicals (OH), which was further verified by electron spin-resonance spectroscopy (ESR). Highly dispersed MnO(x) on SBA-15 were believed to be the main active component in MnO(x)/SBA-15. Some intermediates were indentified and different degradation routes of CA were proposed in both ozonation alone and catalytic ozonation. The amounts of small molecular carboxylic acids (i.e., formic acid (FA), acetic acid (AA) and oxalic acid (OA)) generated in catalytic ozonation were lower than in ozonation alone, resulting from the generation of more OH.

  1. Scaleable catalytic asymmetric Strecker syntheses of unnatural α-amino acids

    PubMed Central

    Zuend, Stephan J.; Coughlin, Matthew P.; Lalonde, Mathieu P.; Jacobsen, Eric N.

    2009-01-01

    α-Amino acids are essential building blocks for protein synthesis, and are also widely useful as components of medicinally active molecules and chiral catalysts.1,2,3,4,5 Efficient chemo-enzymatic methods for the synthesis of enantioenriched α-amino acids have been devised, but the scope of these methods for the synthesis of unnatural amino acids is limited.6,7 Alkene hydrogenation is broadly useful for enantioselective catalytic synthesis of many classes of amino acids,8,9 but this approach is not applicable to the synthesis of α-amino acids bearing aryl or quaternary alkyl α-substituents. The Strecker synthesis—the reaction of an imine or imine equivalent with hydrogen cyanide, followed by nitrile hydrolysis—is an especially versatile chemical method for the synthesis of racemic α-amino acids (Fig. 1).10,11 Asymmetric Strecker syntheses using stoichiometric chiral reagents have been applied successfully on gram-to-multi-kilogram scales to the preparation of enantiomerically enriched α-amino acids.12,13,14 In principle, Strecker syntheses employing sub-stoichiometric quantities of a chiral reagent provide a practical alternative to these approaches, but the reported catalytic asymmetric methods have seen only limited use on preparative scales (e.g., > 1 gram).15,16 The limited use of existing catalytic methodologies may be ascribed to several important practical drawbacks, including the relatively complex and precious nature of the catalysts, and the requisite use of hazardous cyanide sources. Herein we report a new catalytic asymmetric method for the syntheses of highly enantiomerically enriched non-proteinogenic amino acids using a simple chiral amido-thiourea catalyst to control the key hydrocyanation step. Because this catalyst is robust and lacks sensitive functional groups, it is compatible with safely handled aqueous cyanide salts, and is thus adaptable to large-scale synthesis. This new methodology can be applied to the efficient syntheses of

  2. Catalytic activity of bovine seminal ribonuclease is essential for its immunosuppressive and other biological activities.

    PubMed Central

    Kim, J S; Soucek, J; Matousek, J; Raines, R T

    1995-01-01

    Bovine seminal ribonuclease (BS-RNase) is a homologue of RNase A with special biological properties, including potent immunosuppressive activity. A mutant BS-RNase was created in which His-119, the active-site residue that acts as a general acid during catalysis, was changed to an aspartic acid. H119D BS-RNase formed a dimer with quaternary structure similar to that of the wild-type enzyme but with values of kcat. and kcat./Km for the cleavage of UpA [uridylyl(3'-->5')adenosine] that were 4 x 10(3)-fold lower. The mutant protein also demonstrated dramatically decreased immunosuppressive, anti-tumour, aspermatogenic, and embryotoxic activities. The catalytic activity of BS-RNase is therefore necessary for its special biological properties. PMID:7772040

  3. Heparin enhances the catalytic activity of des-ETW-thrombin.

    PubMed

    Goodwin, C A; Deadman, J J; Le Bonniec, B F; Elgendy, S; Kakkar, V V; Scully, M F

    1996-04-01

    The thrombin mutant, des-ETW-thrombin, lacking Glu(146), Thr(147), and Trp(148) within a unique insertion loop located at the extreme end of the primary specificity pocket, has been shown previously to exhibit reduced catalytic activity with respect to macromolecular and synthetic thrombin substrates and reduced or enhanced susceptibility to inhibition. Investigation of the hydrolysis of peptidyl p-nitroanilide substrates by des-ETW-thrombin showed increased activity in the presence of heparin and other sulphated glycosaminoglycans. No effect was observed upon the activity of wild-type thrombin. Heparin was found to decrease the K(m) for cleavage of four thrombin-specific substrates by des-ETW-thrombin by 3-4-fold. Similarly, pentosan polysulphate (PPS) decreased the K(m) with these substrates by 8-10-fold. Heparin also increased the rate of inhibition of des-ETW-thrombin by antithrombin III and D-phenylalanyl-prolyl-arginylchloromethane (PPACK). The inhibition of des-ETW-thrombin by a number of thrombin-specific peptide boronic acids also showed significant reduction in the final K(i) in the presence of heparin, due to reduction in the off-rate. A peptide analogue of a sequence of hirudin which binds thrombin tightly to exosite I (fibrinogen recognition site) potentiated the activity of des-ETW-thrombin against peptide p-nitroanilide substrates in a manner similar to heparin. The K(i) for the inhibition of des-ETW-thrombin by p-aminobenzamidine was decreased by these ligands from 9.7 mM to 7.5 mM, 5.1 mM, and 2.5 mM in the presence of heparin, hirudin peptide and PPS respectively, suggesting the increased catalytic activity is due to enhanced access to the primary specificity pocket. The positive influence of these ligands on des-ETW-thrombin was reversed in the presence of ATP or ADP; the latter has previously been shown to inhibit thrombin activity by blocking initial interaction with fibrinogen at exosite 1. Because the effect of heparin and PPS is similar to

  4. Catalytic Growth of Macroscopic Carbon Nanofibers Bodies with Activated Carbon

    SciTech Connect

    Abdullah, N.; Muhammad, I. S.; Hamid, S. B. Abd.; Rinaldi, A.; Su, D. S.; Schlogl, R.

    2009-06-01

    Carbon-carbon composite of activated carbon and carbon nanofibers have been synthesized by growing Carbon nanofiber (CNF) on Palm shell-based Activated carbon (AC) with Ni catalyst. The composites are in an agglomerated shape due to the entanglement of the defective CNF between the AC particles forming a macroscopic body. The macroscopic size will allow the composite to be used as a stabile catalyst support and liquid adsorbent. The preparation of CNT/AC nanocarbon was initiated by pre-treating the activated carbon with nitric acid, followed by impregnation of 1 wt% loading of nickel (II) nitrate solutions in acetone. The catalyst precursor was calcined and reduced at 300 deg. C for an hour in each step. The catalytic growth of nanocarbon in C{sub 2}H{sub 4}/H{sub 2} was carried out at temperature of 550 deg. C for 2 hrs with different rotating angle in the fluidization system. SEM and N{sub 2} isotherms show the level of agglomeration which is a function of growth density and fluidization of the system. The effect of fluidization by rotating the reactor during growth with different speed give a significant impact on the agglomeration of the final CNF/AC composite and thus the amount of CNFs produced. The macrostructure body produced in this work of CNF/AC composite will have advantages in the adsorbent and catalyst support application, due to the mechanical and chemical properties of the material.

  5. Activation of carboxylic acids in asymmetric organocatalysis.

    PubMed

    Monaco, Mattia Riccardo; Poladura, Belén; Diaz de Los Bernardos, Miriam; Leutzsch, Markus; Goddard, Richard; List, Benjamin

    2014-07-01

    Organocatalysis, catalysis using small organic molecules, has recently evolved into a general approach for asymmetric synthesis, complementing both metal catalysis and biocatalysis. Its success relies to a large extent upon the introduction of novel and generic activation modes. Remarkably though, while carboxylic acids have been used as catalyst directing groups in supramolecular transition-metal catalysis, a general and well-defined activation mode for this useful and abundant substance class is still lacking. Herein we propose the heterodimeric association of carboxylic acids with chiral phosphoric acid catalysts as a new activation principle for organocatalysis. This self-assembly increases both the acidity of the phosphoric acid catalyst and the reactivity of the carboxylic acid. To illustrate this principle, we apply our concept in a general and highly enantioselective catalytic aziridine-opening reaction with carboxylic acids as nucleophiles.

  6. Mammalian Dopa decarboxylase: structure, catalytic activity and inhibition.

    PubMed

    Bertoldi, Mariarita

    2014-03-15

    Mammalian Dopa decarboxylase catalyzes the conversion of L-Dopa and L-5-hydroxytryptophan to dopamine and serotonin, respectively. Both of them are biologically active neurotransmitters whose levels should be finely tuned. In fact, an altered concentration of dopamine is the cause of neurodegenerative diseases, such as Parkinson's disease. The chemistry of the enzyme is based on the features of its coenzyme pyridoxal 5'-phosphate (PLP). The cofactor is highly reactive and able to perform multiple reactions, besides decarboxylation, such as oxidative deamination, half-transamination and Pictet-Spengler cyclization. The structure resolution shows that the enzyme has a dimeric arrangement and provides a molecular basis to identify the residues involved in each catalytic activity. This information has been combined with kinetic studies under steady-state and pre-steady-state conditions as a function of pH to shed light on residues important for catalysis. A great effort in DDC research is devoted to design efficient and specific inhibitors in addition to those already used in therapy that are not highly specific and are responsible for the side effects exerted by clinical approach to either Parkinson's disease or aromatic amino acid decarboxylase deficiency. PMID:24407024

  7. Dinuclear complexes of copper and zinc with m-xylene/cyclohexane-linked bis-aspartic acids: synthesis, characterization, dioxygen activation, and catalytic oxidation of nitrobenzene in pure aqueous solution.

    PubMed

    Zhu, Shourong; Qiu, Zhixiang; Ni, Tianjun; Zhao, Xiujuan; Yan, Shikai; Xing, Feifei; Zhao, Yongmei; Bai, Yueling; Li, Mingxing

    2013-08-14

    Two new m-xylene/cyclohexane-linked bis-aspartic acid ligands, L(b) and L(c), were synthesized via Michael addition in basic aqueous solution. Their structures were characterized by elemental analysis, NMR and MS spectrometry. Both ligands react with Cu(II) and Zn(II) to form dinuclear complexes, with M2L(OH)(-) the major species in neutral/weak basic aqueous solution. To quantify the relative interaction strength between a Lewis acid and base, a new parameter σ = log K/14 was proposed which compares the stability constant with the binding constant between H(+) and OH(-). The dinuclear copper complexes (L(b)-2Cu and L(c)-2Cu) react with H2O2 in aqueous solution. The reaction in 0.020 M phosphate buffer at pH 7.5 is first-order for [L(c)-2Cu], but second-order for [L(b)-2Cu]. The oxidation products are oxygenated and/or dehydrogenated species. Radical trapping tests indicate that both complexes slightly scavenge the OH˙ radical, but generate the H˙ radical. L(c)-2Cu generates the H˙ radical much more effectively than that of L(b)-2Cu when reacted with H2O2. Both complexes are excellent catalysts for the oxidation of nitrobenzene in the presence of H2O2 in weakly basic aqueous solution. The oxidation follows the rate-law v = k[complex][nitrobenzene][H2O2]. The k values in pH 8.0 phosphate buffer at 25 °C are 211.2 ± 0.3 and 607.9 ± 1.7 mol(-2) L(2) s(-1) for L(b)-2Cu and L(c)-2Cu, respectively. The Arrhenius activation energies are 69.4 ± 2.2 and 70.0 ± 4.3 kJ mol(-1) for L(b)-2Cu and L(c)-2Cu, respectively, while the Arrhenius pre-exponential factors are 2.62 × 10(14) and 1.06 × 10(15), respectively. The larger pre-exponential factor makes L(c)-2Cu more catalytically active than L(b)-2Cu. These complexes are some of the most effective oxidation catalysts known for the oxidation of nitrobenzene.

  8. Thermal and sonochemical synthesis of porous (Ce,Zr)O2 mixed oxides from metal β-diketonate precursors and their catalytic activity in wet air oxidation process of formic acid.

    PubMed

    Cau, Camille; Guari, Yannick; Chave, Tony; Larionova, Joulia; Nikitenko, Sergey I

    2014-07-01

    Porous (Ce0.5Zr0.5)O2 solid solutions were prepared by thermolysis (T=285 °C) or sonolysis (20 kHz, I=32 W cm(-2), Pac=0.46 W mL(-1), T=200 °C) of Ce(III) and Zr(IV) acetylacetonates in oleylamine or hexadecylamine under argon followed by heat treatment of the precipitates obtained in air at 450 °C. Transmission Electron Microscopy images of the samples show nanoparticles of ca. 4-6 nm for the two synthetic approaches. The powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray and μ-Raman spectroscopy of solids obtained after heat treatment indicate the formation of (Ce0.5Zr0.5)O2 solid solutions with a metastable tetragonal crystal structure for the two synthetic routes. The specific surface area of the samples varies between 78 and 149 m(2) g(-1) depending on synthesis conditions. The use of Barrett-Joyner-Halenda and t-plot methods reveal the formation of mixed oxides with a hybrid morphology that combines mesoporosity and microporosity regardless of the method of preparation. Platinum nanoparticles were deposited on the surface of the mixed oxides by sonochemical reduction of Pt(IV). It was found that the materials prepared by sonochemistry exhibit better resistance to dissolution during the deposition process of platinum. X-ray photoelectron spectroscopy analysis shows the presence of Pt(0) and Pt(II) on the surface of mixed oxides. Porous (Ce0.5Zr0.5)O2 mixed oxides loaded with 1.5%wt. platinum exhibit high activity in catalytic wet air oxidation of formic acid at 40 °C.

  9. Catalytic wet air oxidation of carboxylic acids on TiO{sub 2}-supported ruthenium catalysts

    SciTech Connect

    Beziat, J.C.; Besson, M.; Gallezot, P.; Durecu, S.

    1999-02-15

    The total oxidation of aqueous solutions of carboxylic acids by air was studied in a slurry reactor over the temperature range 180--100 C and oxygen partial pressure of 0.3--1.8 MPa in the presence of a 2.8%Ru/TiO{sub 2} catalyst. The influence of various parameters is presented: the catalytic wet air oxidation of succinic acid is 0 order with respect to succinic acid; the order with respect to oxygen pressure is 0.4, and the activation energy is ca. 125 kJ/mol. It was found that acetic acid, which is one of the intermediates, and CO{sub 2} have no retarding effect on the total organic carbon abatement rate of succinic acid. Substitution of one hydrogen atom of the methyl group in acetic acid by Cl, OH, or NH{sub 2} gives an increase of the oxidation rate. However, it was proposed that the low activity of acetic acid oxidation is due not only to the difficulty to oxidize the methyl group, but also to the low adsorption coefficient of acetic acid on ruthenium surface. Inorganic salts, such as sodium chloride, only slightly decrease the oxidation rate of acetic acid. The absence of metal ions (Ru, Ti) in the effluents after reaction and the absence of particle sintering indicate also a high stability of the catalyst under the conditions employed. The catalyst can be recycled without loss of activity after the second run. The activity becomes stable after the attainment of a steady-state coverage of the Ru particles by oxygen. The study of the effect of reduction-oxidation treatments of the catalyst showed that the activity depends on the oxidation state of the surface.

  10. Catalytic ozonation of sulfosalicylic acid over manganese oxide supported on mesoporous ceria.

    PubMed

    Xing, Shengtao; Lu, Xiaoyang; Liu, Jia; Zhu, Lin; Ma, Zichuan; Wu, Yinsu

    2016-02-01

    Manganese oxide supported on mesoporous ceria was prepared and used as catalyst for catalytic ozonation of sulfosalicylic acid (SA). Characterization results indicated that the manganese oxide was mostly incorporated into the pores of ceria. The synthesized catalyst exhibited high activity and stability for the mineralization of SA in aqueous solution by ozone, and more than 95% of total organic carbon was removed in 30 min under various conditions. Mechanism studies indicated that SA was mainly degraded by ozone molecules, and hydroxyl radical reaction played an important role for the degradation of its ozonation products (small molecular organic acids). The manganese oxide in the pores of CeO2 improved the adsorption of small molecular organic acids and the generation of hydroxyl radicals from ozone decomposition, resulting in high TOC removal efficiency.

  11. [Catalytic ozonation of nitrobenzene in water by acidification-activated red mud].

    PubMed

    Kang, Ya-ning; Li, Hua-nan; Xu, Bing-bing; Qi, Fei; Zhao, Lun

    2013-05-01

    Red mud as one kind of aluminum industrial wastes was used as raw material for catalyst preparation. It was activated by acidification in order to enhance its catalytic activity in the system of catalytic ozonation. Furthermore, removal performance and reaction mechanism in degradation of organic pollutants were discussed. Results showed that acid modified red mud had more significant catalytic activity than the raw red mud. The removal efficiency of nitrobenzene by catalytic ozonation with acidified red mud (RM6.0) increased with the increasing ozone concentration. When the ozone concentration was increased from 0.4 mg x L(-1) to 1.7 mg x L(-1), the removal efficiency of nitrobenzene increased from 45% to 92%. There was a consistent effect of water pH on the removal efficiency and the ozone concentration variation. The variation of the removal efficiency depended on the initial water pH. This was because the concentration of OH(-) led to ozone decomposition to generate hydroxyl radicals. The higher water pH value led to the quenching of hydroxyl radicals, resulting in the reduction of catalytic activity of RM6.0. The experimental results of aqueous ozone concentration variation in the presence of RM6.0 and inhibition by hydroxyl radicals indicated that the main reaction mechanism was catalytic ozonation of NB. Firstly, aqueous ozone was absorbed onto the surface of RM6.0, and then the concentrated ozone oxidized NB in water which was with a combination of direct and indirect oxidation. In catalytic reaction, hydroxyl radicals were present, which were generated during the oxidation of NB on the surface of RM6.0.

  12. [Catalytic ozonation of nitrobenzene in water by acidification-activated red mud].

    PubMed

    Kang, Ya-ning; Li, Hua-nan; Xu, Bing-bing; Qi, Fei; Zhao, Lun

    2013-05-01

    Red mud as one kind of aluminum industrial wastes was used as raw material for catalyst preparation. It was activated by acidification in order to enhance its catalytic activity in the system of catalytic ozonation. Furthermore, removal performance and reaction mechanism in degradation of organic pollutants were discussed. Results showed that acid modified red mud had more significant catalytic activity than the raw red mud. The removal efficiency of nitrobenzene by catalytic ozonation with acidified red mud (RM6.0) increased with the increasing ozone concentration. When the ozone concentration was increased from 0.4 mg x L(-1) to 1.7 mg x L(-1), the removal efficiency of nitrobenzene increased from 45% to 92%. There was a consistent effect of water pH on the removal efficiency and the ozone concentration variation. The variation of the removal efficiency depended on the initial water pH. This was because the concentration of OH(-) led to ozone decomposition to generate hydroxyl radicals. The higher water pH value led to the quenching of hydroxyl radicals, resulting in the reduction of catalytic activity of RM6.0. The experimental results of aqueous ozone concentration variation in the presence of RM6.0 and inhibition by hydroxyl radicals indicated that the main reaction mechanism was catalytic ozonation of NB. Firstly, aqueous ozone was absorbed onto the surface of RM6.0, and then the concentrated ozone oxidized NB in water which was with a combination of direct and indirect oxidation. In catalytic reaction, hydroxyl radicals were present, which were generated during the oxidation of NB on the surface of RM6.0. PMID:23914529

  13. Catalytic residues are shared between two pseudosubunits of the dehydratase domain of the animal fatty acid synthase.

    PubMed

    Pasta, Saloni; Witkowski, Andrzej; Joshi, Anil K; Smith, Stuart

    2007-12-01

    Expression, characterization, and mutagenesis of a series of N-terminal fragments of an animal fatty acid synthase, containing the beta-ketoacyl synthase, acyl transferase, and dehydratase domains, demonstrate that the dehydratase domain consists of two pseudosubunits, derived from contiguous regions of the same polypeptide, in which a single active site is formed by the cooperation of the catalytic histidine 878 residue of the first pseudosubunit with aspartate 1032 of the second pseudosubunit. Mutagenesis and modeling studies revealed an essential role for glutamine 1036 in anchoring the position of the catalytic aspartate. These findings establish that sequence elements previously assigned to a central structural core region of the type I fatty acid synthases and some modular polyketide synthase counterparts play an essential catalytic role as part of the dehydratase domain.

  14. Degradation of paracetamol by catalytic wet air oxidation and sequential adsorption - Catalytic wet air oxidation on activated carbons.

    PubMed

    Quesada-Peñate, I; Julcour-Lebigue, C; Jáuregui-Haza, U J; Wilhelm, A M; Delmas, H

    2012-06-30

    The concern about the fate of pharmaceutical products has raised owing to the increasing contamination of rivers, lakes and groundwater. The aim of this paper is to evaluate two different processes for paracetamol removal. The catalytic wet air oxidation (CWAO) of paracetamol on activated carbon was investigated both as a water treatment technique using an autoclave reactor and as a regenerative treatment of the carbon after adsorption in a sequential fixed bed process. Three activated carbons (ACs) from different source materials were used as catalysts: two microporous basic ACs (S23 and C1) and a meso- and micro-porous acidic one (L27). During the first CWAO experiment the adsorption capacity and catalytic performance of fresh S23 and C1 were higher than those of fresh L27 despite its higher surface area. This situation changed after AC reuse, as finally L27 gave the best results after five CWAO cycles. Respirometry tests with activated sludge revealed that in the studied conditions the use of CWAO enhanced the aerobic biodegradability of the effluent. In the ADOX process L27 also showed better oxidation performances and regeneration efficiency. This different ageing was examined through AC physico-chemical properties.

  15. Hydrostatic Pressure Increases the Catalytic Activity of Amyloid Fibril Enzymes.

    PubMed

    Luong, Trung Quan; Erwin, Nelli; Neumann, Matthias; Schmidt, Andreas; Loos, Cornelia; Schmidt, Volker; Fändrich, Marcus; Winter, Roland

    2016-09-26

    We studied the combined effects of pressure (0.1-200 MPa) and temperature (22, 30, and 38 °C) on the catalytic activity of designed amyloid fibrils using a high-pressure stopped-flow system with rapid UV/Vis absorption detection. Complementary FT-IR spectroscopic data revealed a remarkably high pressure and temperature stability of the fibrillar systems. High pressure enhances the esterase activity as a consequence of a negative activation volume at all temperatures (about -14 cm(3)  mol(-1) ). The enhancement is sustained in the whole temperature range covered, which allows a further acceleration of the enzymatic activity at high temperatures (activation energy 45-60 kJ mol(-1) ). Our data reveal the great potential of using both pressure and temperature modulation to optimize the enzyme efficiency of catalytic amyloid fibrils.

  16. Hydrostatic Pressure Increases the Catalytic Activity of Amyloid Fibril Enzymes.

    PubMed

    Luong, Trung Quan; Erwin, Nelli; Neumann, Matthias; Schmidt, Andreas; Loos, Cornelia; Schmidt, Volker; Fändrich, Marcus; Winter, Roland

    2016-09-26

    We studied the combined effects of pressure (0.1-200 MPa) and temperature (22, 30, and 38 °C) on the catalytic activity of designed amyloid fibrils using a high-pressure stopped-flow system with rapid UV/Vis absorption detection. Complementary FT-IR spectroscopic data revealed a remarkably high pressure and temperature stability of the fibrillar systems. High pressure enhances the esterase activity as a consequence of a negative activation volume at all temperatures (about -14 cm(3)  mol(-1) ). The enhancement is sustained in the whole temperature range covered, which allows a further acceleration of the enzymatic activity at high temperatures (activation energy 45-60 kJ mol(-1) ). Our data reveal the great potential of using both pressure and temperature modulation to optimize the enzyme efficiency of catalytic amyloid fibrils. PMID:27573584

  17. Catalytic biofilms on structured packing for the production of glycolic acid.

    PubMed

    Li, Xuan Zhong; Hauer, Bernhard; Rosche, Bettina

    2013-02-01

    While structured packing modules are known to be efficient for surface wetting and gas-liquid exchange in abiotic surface catalysis, this model study explores structured packing as a growth surface for catalytic biofilms. Microbial biofilms have been proposed as self-immobilized and self-regenerating catalysts for the production of chemicals. A concern is that the complex and dynamic nature of biofilms may cause fluctuations in their catalytic performance over time or may affect process reproducibility. An aerated continuous trickle-bed biofilm reactor system was designed with a 3 L structured packing, liquid recycling and pH control. Pseudomonas diminuta established a biofilm on the stainless steel structured packing with a specific surface area of 500 m2 m-3 and catalyzed the oxidation of ethylene glycol to glycolic acid for over two months of continuous operation. A steady-state productivity of up to 1.6 gl-1h-1 was achieved at a dilution rate of 0.33 h-1. Process reproducibility between three independent runs was excellent, despite process interruptions and activity variations in cultures grown from biofilm effluent cells. The results demonstrate the robustness of a catalytic biofilm on structured packing, despite its dynamic nature. Implementation is recommended for whole-cell processes that require efficient gas-liquid exchange, catalyst retention for continuous operation, or improved catalyst stability. PMID:23412062

  18. Structure and catalytic properties of magnesia-supported copper salts of molybdovanadophosphoric acid.

    PubMed

    Zhou, Guangdong; Yang, Xiaomei; Liu, Jie; Zhen, Kaiji; Wang, Haishui; Cheng, Tiexin

    2006-05-25

    The structure and stability of magnesia-supported copper salts of molybdovanadophosphoric acid (Cu(2)PMo(11)VO(40)) were characterized by different techniques. The catalyst was prepared in ethanol by impregnation because this solvent does not hurt texture of the water-sensitive MgO and Cu(2)PMo(11)VO(40). The Keggin-type structure compound may be degraded partially to form oligomerized polyoxometalate when supported on MgO. However, the oligomers can rebuild as the Keggin structure again after thermal treatment in air or during the reaction. Meanwhile, the V atoms migrate out of the Keggin structure to form a lacunary structure, as observed by Fourier transform IR spectroscopy. Moreover, the presence of Cu(2+) as a countercation showed an affirmative influence on the migration of V atoms, and the active sites derived from the lacunary species generated after release of V from the Keggin anion. The electron paramagnetic resonance data imply that V(5+) autoreduces to V(4+) in the fresh catalyst, and during the catalytic reaction a large number of V(4+) ions are produced, which enhance the formation of O(2-) vacancies around the metal atoms. These oxygen vacancies may also improve the reoxidation function of the catalyst. This behavior is correlated to higher catalytic properties of this catalyst. The oxidative dehydrogenation of hexanol to hexanal was studied over this catalyst. After reaction at 553.2 K for 50 h, catalytic properties did not decrease and exhibited higher selectivity (>96.0%) toward hexanal. PMID:16706435

  19. Engineering Clostridia Neurotoxins with elevated catalytic activity.

    PubMed

    Guo, Jiubiao; Pan, Xuehua; Zhao, Yanxiang; Chen, Sheng

    2013-11-01

    BoNT/B and TeNT cleave substrate VAMP2 at the same scissile bond, yet these two toxins showed different efficiency on substrate hydrolysis and had different requirements for the recognition of P2' site of VAMP2, E(78). These differences may be due to their different composition of their substrate recognition pockets in the active site. Swapping of LC/T S1' pocket residue, L(230), with the corresponding isoleucine in LC/B increased LC/T activity by ∼25 fold, while swapping of LC/B S1' pocket residue, S(201), with the corresponding proline in LC/T increased LC/B activity by ∼10 fold. Optimization of both S1 and S1' pocket residues of LC/T, LC/T (K(168)E, L(230)I) elevated LC/T activity by more than 100-fold. The highly active LC/T derivative engineered in this study has the potential to be used as a more effective tool to study mechanisms of exocytosis in central neuron. The LC/B derivative with elevated activity has the potential to be developed into novel therapy to minimize the impact of immunoresistance during BoNT/B therapy.

  20. Aged nano-structured platinum based catalyst: effect of chemical treatment on adsorption and catalytic activity.

    PubMed

    Shim, Wang Geun; Nahm, Seung Won; Park, Hyuk Ryeol; Yun, Hyung Sun; Seo, Seong Gyu; Kim, Sang Chai

    2011-02-01

    To examine the effect of chemical treatment on the adsorption and catalytic activity of nanostructured platinum based catalyst, the aged commercial Pt/AC catalyst was pretreated with sulfuric acid (H2SO4) and a cleaning agent (Hexane). Several reliable methods such as nitrogen adsorption, X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and inductively coupled plasma (ICP) were employed to characterize the aged Pt/AC catalyst and its chemically pretreated Pt/AC catalysts. The catalytic and adsorption activities of nano-structured heterogeneous Pt/AC catalyst were investigated on the basis of toluene oxidation and adsorption isotherm data. In addition, the adsorption isotherms of toluene were used to calculate the adsorption energy distribution functions for the parent catalyst and its pre-treated nano-structured Pt/AC catalysts. It was found that sulfuric acid aqueous treatment can enhance the catalytic performance of aged Pt/AC catalyst toward catalytic oxidation of toluene. It was also shown that a comparative analysis of the energy distribution functions for nano-structured Pt/AC catalysts as well as the pore size distribution provides valuable information about their structural and energetic heterogeneity.

  1. Identifying the catalytic acid/base in GH29 α-L-fucosidase subfamilies.

    PubMed

    Shaikh, F Aidha; Lammerts van Bueren, Alicia; Davies, Gideon J; Withers, Stephen G

    2013-08-27

    While the catalytic nucleophile in the configuration-retaining α-L-fucosidases from family GH29 is fully conserved with respect to sequence, there is no fully sequence-conserved acid/base residue candidate across the family. X-ray crystallographic studies and kinetic characterizations have allowed the identification of this residue in a few cases, and a recent combination of phylogenetic tree analyses with substrate specificity data has allowed the division of GH29 enzymes into two subfamilies, A and B, allowing the probable assignment of these residues. Here, we perform detailed kinetic and mechanistic characterizations of the corresponding alanine mutants and other candidates. Through comparison of kinetic parameters obtained for the hydrolysis of fucosyl substrates with activated leaving groups by these mutants with those of the corresponding wild-type enzymes, in conjunction with the demonstration of azide rescue, we largely confirm the acid/base residue predictions for the GH29 fucosidases from the two subfamilies.

  2. Effect of catalyst preparation on catalytic activity

    SciTech Connect

    Huang, Y.J.R.

    1987-01-01

    Design parameters have been identified for Ni/Al{sub 2}O{sub 3} catalysts prepared by wet impregnation and incipient wetness from nickel nitrate solution in contact with a {gamma}-Al{sub 2}O{sub 3} support. The metal dispersion, activity for C{sub 1}, C{sub 2}, and C{sub 3} formation under synthesis conditions, and the carbon deposited during reaction have been shown to be predictable based solely on the properties of the electrolytes from which these catalysts were formed. Regardless of the method of preparation, NiAl{sub 2}O{sub 4} was found to be the only active Ni species on low weight loading Ni/Al{sub 2}O{sub 3} catalysts; both Ni and NiAl{sub 2}O{sub 4} are present on high weight loading catalysts. The high-temperature methane peak observed only from CO-TRP spectra of low weight loading catalysts is due to NiAl{sub 2}O{sub 4}; the low-temperature peak that appears as the weight loading is increased is due to Ni. Steady-state reaction kinetics for CH{sub 4} production yield activation energies which increase with increasing weight loading. The apparent activation energies for catalysts with a single methane peak in their CO-TPR spectra were found to be normally distributed. The apparent activation energies for catalysts with two methane peaks in their CO-TPR spectra were found to also be normally distributed when the method of preparation was considered in testing the statistical nature of the distribution. Titration experiments of the carbon pool subsequent to steady-state reaction of H{sub 2} and CO in conjunction with temperature-programmed surface reaction were used to asses the impact of Ni speciation on the rate-determining in step in the methanation reaction. In situ ESCA experiments and microreactor studies were used to examined the existence of metal-support interaction between dispersed Ni and the Al{sub 2}O{sub 3} carrier.

  3. Atomistic details of the Catalytic Mechanism of Fe(III)-Zn(II) Purple Acid Phosphatase.

    PubMed

    Alberto, Marta E; Marino, Tiziana; Ramos, Maria J; Russo, Nino

    2010-08-10

    In the present work, we performed a theoretical investigation of the reaction mechanism of the Fe(III)-Zn(II) purple acid phosphatase from red kidney beans (rkbPAP), using the hybrid density functional theory and employing different exchange-correlation potentials. Characterization of the transition states and intermediates involved and the potential energy profiles for the reaction in different environments (gas phase, protein environment, and water) are reported. Our results show that the Fe(III)-Zn(II)PAP catalyzes the hydrolysis of methylphosphate via direct attack by a bridging metals-coordinated hydroxide leading to the cleavage of the ester bond. From our study emerges that the rate-limiting step of the reaction is the nucleophilic attack followed by the less energetically demanding release of the leaving group. Furthermore, we provide insights into some important points of contention concerning the precatalytic complex and the substrate coordination mode into the active site prior to hydrolysis. In particular: (i) Two models of enzyme-substrate with different orientations of the substrate into the active site were tested to evaluate the possible roles played by the conserved histidine residues (His 202 and His 296); (ii) Different protonation states of the substrate were taken into account in order to reproduce different pH values and to verify its influence on the catalytic efficiency and on the substrate binding mode; (iii) The metals role in each step of the catalytic mechanism was elucidated. We were also able to ascertain that the activation of the leaving group by the protonated His 296 is decisive to reach an optimal catalytic efficiency, while the bond scission without activation requires higher energy to occur. PMID:26613496

  4. Is Dimerization Required for the Catalytic Activity of Bacterial Biotin Carboxylase?

    SciTech Connect

    Shen,Y.; Chou, C.; Chang, G.; Tong, L.

    2006-01-01

    Acetyl-coenzyme A carboxylases (ACCs) have crucial roles in fatty acid metabolism. The biotin carboxylase (BC) subunit of Escherichia coli ACC is believed to be active only as a dimer, although the crystal structure shows that the active site of each monomer is 25 Angstroms from the dimer interface. We report here biochemical, biophysical, and structural characterizations of BC carrying single-site mutations in the dimer interface. Our studies demonstrate that two of the mutants, R19E and E23R, are monomeric in solution but have only a 3-fold loss in catalytic activity. The crystal structures of the E23R and F363A mutants show that they can still form the correct dimer at high concentrations. Our data suggest that dimerization is not an absolute requirement for the catalytic activity of the E. coli BC subunit, and we propose a new model for the molecular mechanism of action for BC in multisubunit and multidomain ACCs.

  5. Identification of acid-base catalytic residues of high-Mr thioredoxin reductase from Plasmodium falciparum.

    PubMed

    McMillan, Paul J; Arscott, L David; Ballou, David P; Becker, Katja; Williams, Charles H; Müller, Sylke

    2006-11-01

    High-M(r) thioredoxin reductase from the malaria parasite Plasmodium falciparum (PfTrxR) contains three redox active centers (FAD, Cys-88/Cys-93, and Cys-535/Cys-540) that are in redox communication. The catalytic mechanism of PfTrxR, which involves dithiol-disulfide interchanges requiring acid-base catalysis, was studied by steady-state kinetics, spectral analyses of anaerobic static titrations, and rapid kinetics analysis of wild-type enzyme and variants involving the His-509-Glu-514 dyad as the presumed acid-base catalyst. The dyad is conserved in all members of the enzyme family. Substitution of His-509 with glutamine and Glu-514 with alanine led to TrxR with only 0.5 and 7% of wild type activity, respectively, thus demonstrating the crucial roles of these residues for enzymatic activity. The H509Q variant had rate constants in both the reductive and oxidative half-reactions that were dramatically less than those of wild-type enzyme, and no thiolateflavin charge-transfer complex was observed. Glu-514 was shown to be involved in dithiol-disulfide interchange between the Cys-88/Cys-93 and Cys-535/Cys-540 pairs. In addition, Glu-514 appears to greatly enhance the role of His-509 in acid-base catalysis. It can be concluded that the His-509-Glu-514 dyad, in analogy to those in related oxidoreductases, acts as the acid-base catalyst in PfTrxR.

  6. [Catalytic ozonation of oxalic acid in water with Pt/graphite catalyst].

    PubMed

    Liu, Zheng-Qian; Ma, Jun; Zhao, Lei

    2007-06-01

    Pt/graphite catalyst was prepared by incipient wetness impregnation using H2PtCl6 x 6H2O as precursor substance. The removal efficiencies of oxalic acid by Pt/graphite, graphite catalyzed ozonation and ozonation alone were compared. It was found that the removal efficiency of oxalic acid in ozonation alone, graphite and Pt/graphite catalyzed ozonation was 3.0%, 47.6% and 99.3% respectively under the present experimental conditions. Results showed that loading of Pt could significantly increase the catalytic activity of graphite. Taking oxalic acid degradation efficiency as indication, the preparation conditions of Pt/graphite were optimized. The pretreatment of graphite had no favor to improve the activity of Pt/graphite catalyst. The optimal preparation conditions of Pt/graphite catalyst are as follow: impregnant, distilled water; impregnation time, 24 h; the loading amount of Pt, 1.0%; reduction temperature, 35 degrees C. The Pt/graphite catalyst was used for five times with no significant decrease of its activity and more than 90% oxalic acid removal was obtained. PMID:17674732

  7. Phosphorylation Modulates Catalytic Activity of Mycobacterial Sirtuins

    PubMed Central

    Yadav, Ghanshyam S.; Ravala, Sandeep K.; Malhotra, Neha; Chakraborti, Pradip K.

    2016-01-01

    Sirtuins are NAD+-dependent deacetylases involved in the regulation of diverse cellular processes and are conserved throughout phylogeny. Here we report about in vitro transphosphorylation of the only NAD+-dependent deacetylase (mDAC) present in the genome of Mycobacterium tuberculosis by eukaryotic-type Ser/Thr kinases, particularly PknA. The phosphorylated mDAC displayed decreased deacetylase activity compared to its unphosphorylated counterpart. Mass-spectrometric study identified seven phosphosites in mDAC; however, mutational analysis highlighted major contribution of Thr-214 for phosphorylation of the protein. In concordance to this observation, variants of mDAC substituting Thr-214 with either Ala (phospho-ablated) or Glu (phosphomimic) exhibited significantly reduced deacetylase activity suggesting phosphorylation mediated control of enzymatic activity. To assess the role of phosphorylation towards functionality of mDAC, we opted for a sirtuin knock-out strain of Escherichia coli (Δdac), where interference of endogenous mycobacterial kinases could be excluded. The Δdac strain in nutrient deprived acetate medium exhibited compromised growth and complementation with mDAC reversed this phenotype. The phospho-ablated or phosphomimic variant, on the other hand, was unable to restore the functionality of mDAC indicating the role of phosphorylation per se in the process. We further over-expressed mDAC or mDAC-T214A as His-tagged protein in M. smegmatis, where endogenous eukaryotic-type Ser/Thr kinases are present. Anti-phosphothreonine antibody recognized both mDAC and mDAC-T214A proteins in western blotting. However, the extent of phosphorylation as adjudged by scanning the band intensity, was significantly low in the mutant protein (mDAC-T214A) compared to that of the wild-type (mDAC). Furthermore, expression of PknA in the mDAC complemented Δdac strain was able to phosphorylate M. tuberculosis sirtuin. The growth profile of this culture in acetate medium was

  8. Facile route to hierarchical silver microstructures with high catalytic activity for the reduction of p-nitrophenol

    SciTech Connect

    Gu, Sasa; Wang, Wei Tan, Fatang; Gu, Jian; Qiao, Xueliang; Chen, Jianguo

    2014-01-01

    Graphical abstract: - Highlights: • A facile route was developed to prepare hierarchical silver microstructures. • The shape and size of secondary units can be tailed by varying reaction conditions. • Hierarchical silver microstructures have excellent catalytic activity. • The morphology and crystallinity of silver particles affect the catalytic activity. - Abstract: A facile, cost-effective and environmentally friendly route was developed to synthesize hierarchical silver microstructures consisting of different shaped secondary units through reducing concentrated silver nitrate with ascorbic acid in the absence of any surfactant. The as-obtained samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The investigation on the morphology evolution revealed that the molar ratio of ascorbic acid to silver nitrate was critical to control the shape of secondary structures. The length of plate-like secondary structures which composed hierarchical silver particles could be controlled by changing the reactant concentrations, and it had a key relationship with the catalytic activity for the reduction of p-nitrophenol by NaBH{sub 4}. The catalytic activity of these surfactant-free silver microstructures was about ten times higher than that of silver nanoparticles, and even comparable to that of gold nanoplates, which indicates that the as-obtained silver microstructures are very promising candidates for the catalytic reduction of p-nitrophenol due to the simple synthesis route and high catalytic activity.

  9. SWI/SNF mutant cancers depend upon catalytic and non–catalytic activity of EZH2

    PubMed Central

    Kim, Kimberly H.; Kim, Woojin; Howard, Thomas P.; Vazquez, Francisca; Tsherniak, Aviad; Wu, Jennifer N.; Wang, Weishan; Haswell, Jeffrey R.; Walensky, Loren D.; Hahn, William C.; Orkin, Stuart H.; Roberts, Charles W. M.

    2016-01-01

    Human cancer genome sequencing has recently revealed that genes encoding subunits of SWI/SNF chromatin remodeling complexes are frequently mutated across a wide variety of cancers, and several subunits of the complex have been shown to have bona fide tumor suppressor activity1. However, whether mutations in SWI/SNF subunits result in shared dependencies is unknown. Here we show that EZH2, a catalytic subunit of the Polycomb repressive complex 2 (PRC2), is essential in all tested cancer cell lines and xenografts harboring mutations of the SWI/SNF subunits ARID1A, PBRM1, and SMARCA4, which are several of the most frequently mutated SWI/SNF subunits in human cancer but that co–occurrence of a Ras pathway mutation correlates with abrogation of this dependence. Surprisingly, we demonstrate that SWI/SNF mutant cancer cells are primarily dependent upon a non–catalytic role of EZH2 in stabilization of the PRC2 complex, and only partially dependent on EZH2 histone methyltransferase activity. These results not only reveal a shared dependency of cancers with genetic alterations in SWI/SNF subunits, but also suggest that EZH2 enzymatic inhibitors now in clinical development may not fully suppress the oncogenic activity of EZH2. PMID:26552009

  10. SWI/SNF-mutant cancers depend on catalytic and non-catalytic activity of EZH2.

    PubMed

    Kim, Kimberly H; Kim, Woojin; Howard, Thomas P; Vazquez, Francisca; Tsherniak, Aviad; Wu, Jennifer N; Wang, Weishan; Haswell, Jeffrey R; Walensky, Loren D; Hahn, William C; Orkin, Stuart H; Roberts, Charles W M

    2015-12-01

    Human cancer genome sequencing has recently revealed that genes that encode subunits of SWI/SNF chromatin remodeling complexes are frequently mutated across a wide variety of cancers, and several subunits of the complex have been shown to have bona fide tumor suppressor activity. However, whether mutations in SWI/SNF subunits result in shared dependencies is unknown. Here we show that EZH2, a catalytic subunit of the polycomb repressive complex 2 (PRC2), is essential in all tested cancer cell lines and xenografts harboring mutations of the SWI/SNF subunits ARID1A, PBRM1, and SMARCA4, which are several of the most frequently mutated SWI/SNF subunits in human cancer, but that co-occurrence of a Ras pathway mutation is correlated with abrogation of this dependence. Notably, we demonstrate that SWI/SNF-mutant cancer cells are primarily dependent on a non-catalytic role of EZH2 in the stabilization of the PRC2 complex, and that they are only partially dependent on EZH2 histone methyltransferase activity. These results not only reveal a shared dependency of cancers with genetic alterations in SWI/SNF subunits, but also suggest that EZH2 enzymatic inhibitors now in clinical development may not fully suppress the oncogenic activity of EZH2.

  11. Thrombomodulin Binding Selects the Catalytically Active Form of Thrombin.

    PubMed

    Handley, Lindsey D; Treuheit, Nicholas A; Venkatesh, Varun J; Komives, Elizabeth A

    2015-11-01

    Human α-thrombin is a serine protease with dual functions. Thrombin acts as a procoagulant, cleaving fibrinogen to make the fibrin clot, but when bound to thrombomodulin (TM), it acts as an anticoagulant, cleaving protein C. A minimal TM fragment consisting of the fourth, fifth, and most of the sixth EGF-like domain (TM456m) that has been prepared has much improved solubility, thrombin binding capacity, and anticoagulant activity versus those of previous TM456 constructs. In this work, we compare backbone amide exchange of human α-thrombin in three states: apo, D-Phe-Pro-Arg-chloromethylketone (PPACK)-bound, and TM456m-bound. Beyond causing a decreased level of amide exchange at their binding sites, TM and PPACK both cause a decreased level of amide exchange in other regions including the γ-loop and the adjacent N-terminus of the heavy chain. The decreased level of amide exchange in the N-terminus of the heavy chain is consistent with the historic model of activation of serine proteases, which involves insertion of this region into the β-barrel promoting the correct conformation of the catalytic residues. Contrary to crystal structures of thrombin, hydrogen-deuterium exchange mass spectrometry results suggest that the conformation of apo-thrombin does not yet have the N-terminus of the heavy chain properly inserted for optimal catalytic activity, and that binding of TM allosterically promotes the catalytically active conformation. PMID:26468766

  12. Catalytic activities enhanced by abundant structural defects and balanced N distribution of N-doped graphene in oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Bai, Xiaogong; Shi, Yantao; Guo, Jiahao; Gao, Liguo; Wang, Kai; Du, Yi; Ma, Tingli

    2016-02-01

    N-doped graphene (NG) is a promising candidate for oxygen reduction reaction (ORR) in the cathode of fuel cells. However, the catalytic activity of NG is lower than that of commercial Pt/C in alkaline and acidic media. In this study, NG samples were obtained using urea as N source. The structural defects and N distribution in the samples were adjusted by regulating the pyrolysis temperature. The new NG type exhibited remarkable catalytic activities for ORR in both alkaline and acidic media.

  13. How absorbed hydrogen affects the catalytic activity of transition metals.

    PubMed

    Aleksandrov, Hristiyan A; Kozlov, Sergey M; Schauermann, Swetlana; Vayssilov, Georgi N; Neyman, Konstantin M

    2014-12-01

    Heterogeneous catalysis is commonly governed by surface active sites. Yet, areas just below the surface can also influence catalytic activity, for instance, when fragmentation products of catalytic feeds penetrate into catalysts. In particular, H absorbed below the surface is required for certain hydrogenation reactions on metals. Herein, we show that a sufficient concentration of subsurface hydrogen, H(sub) , may either significantly increase or decrease the bond energy and the reactivity of the adsorbed hydrogen, H(ad) , depending on the metal. We predict a representative reaction, ethyl hydrogenation, to speed up on Pd and Pt, but to slow down on Ni and Rh in the presence of H(sub) , especially on metal nanoparticles. The identified effects of subsurface H on surface reactivity are indispensable for an atomistic understanding of hydrogenation processes on transition metals and interactions of hydrogen with metals in general.

  14. Acid-catalytic decomposition of peracetic acid in the liquid phase

    SciTech Connect

    Kharchuk, V.G.; Kolenko, I.P.; Petrov, L.A.

    1985-12-01

    This paper elucidates the kinetic relationships of peracetic acid (PAA) decomposition in the presence of mineral acids and their heterogeneous analogs, polystyrene-di-vinylbenzene cation-exchangers, differing in physicochemical and morphological parameters. It is shown that the thermal decomposition of PAA in acetic acid is an acid-catalyzed reaction. The controlling step of the reaction is protonation of the substrate with formation of an active intermediate form. Sulfonated cation-exchangers are twice as effective as sulfuric acid in this process. Polystyrene-divinylbenzene sulfonated cation-exchangers can be used with success as acid catalysts in oxidation processes involving PAA, because of their high effectiveness, stability, and availability.

  15. Study of Single Catalytic Events at Copper-in-Charcoal: Localization of Click Activity Through Subdiffraction Observation of Single Catalytic Events.

    PubMed

    Decan, Matthew R; Scaiano, Juan C

    2015-10-15

    Single molecule fluorescence microscopy reveals that copper-in-charcoal--a high performance click catalyst- has remarkably few catalytic sites, with 90% of the charcoal particles being inactive, and for the catalytic ones the active sites represent a minute fraction (∼0.003%) of the surface. The intermittent nature of the catalytic events enables subdiffraction resolution and mapping of the catalytic sites.

  16. Commercial Activated Carbon for the Catalytic Production of Hydrogen via the Sulfur-Iodine Thermochemical Water Splitting Cycle

    SciTech Connect

    Daniel M. Ginosar; Lucia M. Petkovic; Kyle C. Burch

    2011-07-01

    Eight activated carbon catalysts were examined for their catalytic activity to decompose hydroiodic acid (HI) to produce hydrogen; a key reaction in the sulfur-iodine (S-I) thermochemical water splitting cycle. Activity was examined under a temperature ramp from 473 to 773 K. No statistically significant correlation was found between catalyst sample properties and catalytic activity. Four of the eight samples were examined for one week of continuous operation at 723 K. All samples appeared to be stable over the period of examination.

  17. Conversion of Acetic Acid from the Catalytic Pyrolysis of Xylan Over CeO2.

    PubMed

    Lee, Heejin; Ko, Jeong Huy; Kwon, Woo Hyun; Park, Young-Kwon

    2016-05-01

    CeO2 was synthesized hydrothermally in supercritical water and applied to the catalytic pyrolysis of xylan. Acetic acid, which is the main component in bio-oil produced from the non-catalytic pyrolysis of xylan, deteriorates the fuel quality of the oil. Catalysis over CeO2 effectively converted the acetic acid to ketone species, such as acetone, thereby reducing the acidity of the oil considerably. The content of aromatics in bio-oil was also increased substantially by catalysis. PMID:27483777

  18. Guiding Catalytically Active Particles with Chemically Patterned Surfaces

    NASA Astrophysics Data System (ADS)

    Uspal, W. E.; Popescu, M. N.; Dietrich, S.; Tasinkevych, M.

    2016-07-01

    Catalytically active Janus particles suspended in solution create gradients in the chemical composition of the solution along their surfaces, as well as along any nearby container walls. The former leads to self-phoresis, while the latter gives rise to chemiosmosis, providing an additional contribution to self-motility. Chemiosmosis strongly depends on the molecular interactions between the diffusing chemical species and the wall. We show analytically, using an approximate "point-particle" approach, that by chemically patterning a planar substrate one can direct the motion of Janus particles: the induced chemiosmotic flows can cause particles to either "dock" at the chemical step between the two materials or follow a chemical stripe. These theoretical predictions are confirmed by full numerical calculations. Generically, docking occurs for particles which tend to move away from their catalytic caps, while stripe following occurs in the opposite case. Our analysis reveals the physical mechanisms governing this behavior.

  19. Iridium complexes containing mesoionic C donors: selective C(sp3)-H versus C(sp2)-H bond activation, reactivity towards acids and bases, and catalytic oxidation of silanes and water.

    PubMed

    Petronilho, Ana; Woods, James A; Mueller-Bunz, Helge; Bernhard, Stefan; Albrecht, Martin

    2014-11-24

    Metalation of a C2-methylated pyridylimidazolium salt with [IrCp*Cl2]2 affords either an ylidic complex, resulting from C(sp(3))-H bond activation of the C2-bound CH3 group if the metalation is performed in the presence of a base, such as AgO2 or Na2CO3, or a mesoionic complex via cyclometalation and thermally induced heterocyclic C(sp(2))-H bond activation, if the reaction is performed in the absence of a base. Similar cyclometalation and complex formation via C(sp(2))-H bond activation is observed when the heterocyclic ligand precursor consists of the analogous pyridyltriazolium salt, that is, when the metal bonding at the C2 position is blocked by a nitrogen rather than a methyl substituent. Despite the strongly mesoionic character of both the imidazolylidene and the triazolylidene, the former reacts rapidly with D(+) and undergoes isotope exchange at the heterocyclic C5 position, whereas the triazolylidene ligand is stable and only undergoes H/D exchange under basic conditions, where the imidazolylidene is essentially unreactive. The high stability of the Ir-C bond in aqueous solution over a broad pH range was exploited in catalytic water oxidation and silane oxidation. The catalytic hydrosilylation of ketones proceeds with turnover frequencies as high as 6,000 h(-1) with both the imidazolylidene and the triazolylidene system, whereas water oxidation is enhanced by the stronger donor properties of the imidazol-4-ylidene ligands and is more than three times faster than with the triazolylidene analogue. PMID:25302630

  20. Iridium complexes containing mesoionic C donors: selective C(sp3)-H versus C(sp2)-H bond activation, reactivity towards acids and bases, and catalytic oxidation of silanes and water.

    PubMed

    Petronilho, Ana; Woods, James A; Mueller-Bunz, Helge; Bernhard, Stefan; Albrecht, Martin

    2014-11-24

    Metalation of a C2-methylated pyridylimidazolium salt with [IrCp*Cl2]2 affords either an ylidic complex, resulting from C(sp(3))-H bond activation of the C2-bound CH3 group if the metalation is performed in the presence of a base, such as AgO2 or Na2CO3, or a mesoionic complex via cyclometalation and thermally induced heterocyclic C(sp(2))-H bond activation, if the reaction is performed in the absence of a base. Similar cyclometalation and complex formation via C(sp(2))-H bond activation is observed when the heterocyclic ligand precursor consists of the analogous pyridyltriazolium salt, that is, when the metal bonding at the C2 position is blocked by a nitrogen rather than a methyl substituent. Despite the strongly mesoionic character of both the imidazolylidene and the triazolylidene, the former reacts rapidly with D(+) and undergoes isotope exchange at the heterocyclic C5 position, whereas the triazolylidene ligand is stable and only undergoes H/D exchange under basic conditions, where the imidazolylidene is essentially unreactive. The high stability of the Ir-C bond in aqueous solution over a broad pH range was exploited in catalytic water oxidation and silane oxidation. The catalytic hydrosilylation of ketones proceeds with turnover frequencies as high as 6,000 h(-1) with both the imidazolylidene and the triazolylidene system, whereas water oxidation is enhanced by the stronger donor properties of the imidazol-4-ylidene ligands and is more than three times faster than with the triazolylidene analogue.

  1. Acid-base and catalytic properties of the products of oxidative thermolysis of double complex compounds

    NASA Astrophysics Data System (ADS)

    Pechenyuk, S. I.; Semushina, Yu. P.; Kuz'mich, L. F.; Ivanov, Yu. V.

    2016-01-01

    Acid-base properties of the products of thermal decomposition of [M(A)6] x; [M1(L)6] y (where M is Co, Cr, Cu, Ni; M1 is Fe, Cr, Co; A is NH3, 1/2 en, 1/2 pn, CO(NH2)2; and L is CN, 1/2C2O4) binary complexes in air and their catalytic properties in the oxidation reaction of ethanol with atmospheric oxygen are studied. It is found that these thermolysis products are mixed oxides of the central atoms of complexes characterized by pH values of the zero charge point in the region of 4-9, OH-group sorption limits from 1 × 10-4 to 4.5 × 10-4 g-eq/g, OH-group surface concentrations of 10-50 nm-2 in 0.1 M NaCl solutions, and S sp from 3 to 95 m2/g. Their catalytic activity is estimated from the apparent rate constant of the conversion of ethanol in CO2. The values of constants are (1-6.5) × 10-5 s-1, depending on the gas flow rate and the S sp value.

  2. An active immunization approach to generate protective catalytic antibodies.

    PubMed Central

    Wang, J; Han, Y; Wilkinson, M F

    2001-01-01

    We report that mice immunized with a phosphate immunogen produced polyclonal catalytic antibodies (PCAbs) that catalysed the hydrolysis of carbaryl, a widely used broad-spectrum carbamate insecticide that exerts toxic effects in animals and humans. The reaction catalysed by the PCAbs (IgGs) obeyed Michaelis-Menten kinetics in vitro with the following values at pH 8.0 and 25 degrees C: K(m) approximately 8.0 microM, k(cat)=4.8x10(-3)-5.8x10(-1), k(cat)/k(non-cat)=5.6x10(1)-6.8x10(3) (where k(non-cat) is the rate constant of the reaction in the absence of added catalyst). The PCAbs were also active in whole sera under physiological conditions in vitro. The PCAbs induced in vivo were also active in vivo, as immunization with the phosphate immunogen decreased the mouse blood concentration of carbaryl. To our knowledge, this is the first report demonstrating that active immunization generates antibodies possessing therapeutic catalytic function in vivo. We propose that active immunization schemes that induce enzymically active antibodies may provide a highly specific therapeutic approach for degrading toxic substances. PMID:11696002

  3. Catalytic dehydration of xylose to furfural: vanadyl pyrophosphate as source of active soluble species.

    PubMed

    Sádaba, Irantzu; Lima, Sérgio; Valente, Anabela A; López Granados, Manuel

    2011-12-13

    The acid-catalysed, aqueous phase dehydration of xylose (a monosaccharide obtainable from hemicelluloses, e.g., xylan) to furfural was investigated using vanadium phosphates (VPO) as catalysts: the precursors, VOPO(4)·2H(2)O, VOHPO(4)·0.5H(2)O and VO(H(2)PO(4))(2), and the materials prepared by calcination of these precursors, that is, γ-VOPO(4), (VO)(2)P(2)O(7) and VO(PO(3))(2), respectively. The VPO precursors were completely soluble in the reaction medium. In contrast, the orthorhombic vanadyl pyrophosphate (VO)(2)P(2)O(7), prepared by calcination of VOHPO(4)·0.5H(2)O at 550°C/2 h, could be recycled by simply separating the solid acid from the reaction mixture by centrifugation, and no drop in catalytic activity and furfural yields was observed in consecutive 4 h-batch runs (ca. 53% furfural yield, at 170°C). However, detailed catalytic/characterisation studies revealed that the vanadyl pyrophosphate acts as a source of active water-soluble species in this reaction. For a concentration of (VO)(2)P(2)O(7) as low as 5 mM, the catalytic reaction of xylose (ca. 0.67 M xylose in water, and toluene as solvent for the in situ extraction of furfural) gave ca. 56% furfural yield, at 170°C/6 h reaction. PMID:22055820

  4. Acidic 1,3-propanediaminetetraacetato lanthanides with luminescent and catalytic ester hydrolysis properties

    SciTech Connect

    Chen, Mao-Long; Shi, Yan-Ru; Yang, Yu-Chen; Zhou, Zhao-Hui

    2014-11-15

    In acidic solution, a serials of water-soluble coordination polymers (CPs) were isolated as zonal 1D-CPs 1,3-propanediaminetetraacetato lanthanides [Ln(1,3-H{sub 3}pdta)(H{sub 2}O){sub 5}]{sub n}·2Cl{sub n}·3nH{sub 2}O [Ln=La, 1; Ce, 2; Pr, 3; Nd, 4; Sm, 5] (1,3-H{sub 4}pdta=1,3-propanediaminetetraacetic acid, C{sub 11}H{sub 18}N{sub 2}O{sub 8}) in high yields. When 1 eq. mol potassium hydroxide was added to the solutions of 1D-CPs, respectively, two 1D-CPs [Ln(1,3-H{sub 2}pdta)(H{sub 2}O){sub 3}]{sub n}·Cl{sub n}·2nH{sub 2}O [Ln=Sm, 6; Gd, 7] were isolated at room temperature and seven 2D-CPs [Ln(1,3-H{sub 2}pdta)(H{sub 2}O){sub 2}]{sub n}·Cl{sub n}·2nH{sub 2}O [Ln=La, 8; Ce, 9; Pr, 10; Nd, 11; Sm, 12; Eu, 13; Gd, 14] were isolated at 70 °C. When the crystals of 1–4 were hydrothermally heated at 180 °C with 1–2 eq. mol potassium hydroxide, four 3D-CPs [Ln(1,3-Hpdta)]{sub n}·nH{sub 2}O [Ln=La, 15; Ce, 16; Pr, 17; Nd, 18] were obtained. The two 2D-CPs [Ln(1,3-Hpdta)(H{sub 2}O)]{sub n}·4nH{sub 2}O (Sm, 19; Eu, 20) were isolated in similar reaction conditions. With the increments of pH value in the solution and reaction temperature, the structure becomes more complicated. 1–5 are soluble in water and 1 was traced by solution {sup 13}C({sup 1}H) NMR technique, the water-soluble lanthanides 1 and 5 show catalytic activity to ester hydrolysis reaction respectively, which indicate their important roles in the hydrolytic reaction. The europium complexes 13 and 20 show visible fluorescence at an excitation of 394 nm. The structure diversity is mainly caused by the variation of coordinated ligand in different pH values and lanthanide contraction effect. Acidic conditions are favorable for the isolations of lanthanide complexes in different structures and this may helpful to separate different lanthanides. The thermal stability investigations reveal that acidic condition is favorable to obtain the oxides at a lower temperature. - Graphical abstract: A series

  5. Highly ordered three dimensional macroporous carbon spheres and their acid catalytic properties

    NASA Astrophysics Data System (ADS)

    Huang, Hui; Zhang, Jianming; Zhang, Yuxiao; Lian, Suoyuan; Liu, Yang

    2013-10-01

    Highly ordered three dimensional macroporous carbon spheres bearing sulfonic acid groups (MPCS-SO3H) were prepared by incomplete carbonization of glucose in silica crystal bead template, followed by sulfonation and removal of the template. The composition and porous structure of the obtained carbon spheres were investigated by physical adsorption of nitrogen, scanning electron microscopy, energy dispersive X-ray spectroscopy, and transmission electron microscopy techniques. While the Fourier-transform infrared spectroscopy was used to characterize the functional groups on the surface of carbon spheres. The catalytic properties of the MPCS-SO3H were evaluated by esterification of ethanol with acetic acid, indicating that MPCS-SO3H possess remarkable catalytic performance (high stability and acid catalytic ability) for the esterification.

  6. Highly Selective Synthesis of Catalytically Active Monodisperse Rhodium Nanocubes

    SciTech Connect

    Zhang, Y.; Grass, M.E.; Kuhn, J.N.; Tao, F.; Habas, S.E.; Huang, W.; Yang, P.; Somorjai, G.A.

    2009-02-21

    Synthesis of monodisperse and shape-controlled colloidal inorganic nanocrystals (NCs) is of increasing scientific interest and technological significance. Recently, shape control of Pt, Pd, Ag, Au, and Rh NCs has been obtained by tuning growth kinetics in various solution-phase approaches, including modified polyol methods, seeded growth by polyol reduction, thermolysis of organometallics, and micelle techniques. Control of reduction kinetics of the noble metal precursors and regulation of the relative growth rates of low-index planes (i.e. {l_brace}100{r_brace} and {l_brace}111{r_brace}) via selective adsorption of selected chemical species are two keys for achieving shape modification of noble metal NCs. One application for noble metal NCs of well-defined shape is in understanding how NC faceting (determines which crystallographic planes are exposed) affects catalytic performance. Rh NCs are used in many catalytic reactions, including hydrogenation, hydroformylation, hydrocarbonylation, and combustion reactions. Shape manipulation of Rh NCs may be important in understanding how faceting on the nanoscale affects catalytic properties, but such control is challenging and there are fewer reports on the shape control of Rh NCs compared to other noble metals. Xia and coworkers obtained Rh multipods exhibiting interesting surface plasmonic properties by a polyol approach. The Somorjai and Tilley groups synthesized crystalline Rh multipods, cubes, horns and cuboctahedra, via polyol seeded growth. Son and colleagues prepared catalytically active monodisperse oleylamine-capped tetrahedral Rh NCs for the hydrogenation of arenes via an organometallic route. More recently, the Somorjai group synthesized sizetunable monodisperse Rh NCs using a one-step polyol technique. In this Communication, we report the highly selective synthesis of catalytically active, monodisperse Rh nanocubes of < 10 nm by a seedless polyol method. In this approach, Br{sup -} ions from trimethyl

  7. Catalytic air oxidation of biomass-derived carbohydrates to formic acid.

    PubMed

    Li, Jiang; Ding, Dao-Jun; Deng, Li; Guo, Qing-Xiang; Fu, Yao

    2012-07-01

    An efficient catalytic system for biomass oxidation to form formic acid was developed. The conversion of glucose to formic acid can reach up to 52% yield within 3 h when catalyzed by 5 mol% of H(5)PV(2)Mo(10)O(40) at only 373 K using air as the oxidant. Furthermore, the heteropolyacid can be used as a bifunctional catalyst in the conversion of cellulose to formic acid (yield=35%) with air as the oxidant. PMID:22499553

  8. Catalytic air oxidation of biomass-derived carbohydrates to formic acid.

    PubMed

    Li, Jiang; Ding, Dao-Jun; Deng, Li; Guo, Qing-Xiang; Fu, Yao

    2012-07-01

    An efficient catalytic system for biomass oxidation to form formic acid was developed. The conversion of glucose to formic acid can reach up to 52% yield within 3 h when catalyzed by 5 mol% of H(5)PV(2)Mo(10)O(40) at only 373 K using air as the oxidant. Furthermore, the heteropolyacid can be used as a bifunctional catalyst in the conversion of cellulose to formic acid (yield=35%) with air as the oxidant.

  9. Catalytically and biologically active silver nanoparticles synthesized using essential oil

    NASA Astrophysics Data System (ADS)

    Vilas, Vidya; Philip, Daizy; Mathew, Joseph

    2014-11-01

    There are numerous reports on phytosynthesis of silver nanoparticles and various phytochemicals are involved in the reduction and stabilization. Pure explicit phytosynthetic protocol for catalytically and biologically active silver nanoparticles is of importance as it is an environmentally benign green method. This paper reports the use of essential oil of Myristica fragrans enriched in terpenes and phenyl propenes in the reduction and stabilization. FTIR spectra of the essential oil and the synthesized biogenic silver nanoparticles are in accordance with the GC-MS spectral analysis reports. Nanosilver is initially characterized by an intense SPR band around 420 nm, followed by XRD and TEM analysis revealing the formation of 12-26 nm sized, highly pure, crystalline silver nanoparticles. Excellent catalytic and bioactive potential of the silver nanoparticles is due to the surface modification. The chemocatalytic potential of nanosilver is exhibited by the rapid reduction of the organic pollutant, para nitro phenol and by the degradation of the thiazine dye, methylene blue. Significant antibacterial activity of the silver colloid against Gram positive, Staphylococcus aureus (inhibition zone - 12 mm) and Gram negative, Escherichia coli (inhibition zone - 14 mm) is demonstrated by Agar-well diffusion method. Strong antioxidant activity of the biogenic silver nanoparticles is depicted through NO scavenging, hydrogen peroxide scavenging, reducing power, DPPH and total antioxidant activity assays.

  10. Catalytically and biologically active silver nanoparticles synthesized using essential oil.

    PubMed

    Vilas, Vidya; Philip, Daizy; Mathew, Joseph

    2014-11-11

    There are numerous reports on phytosynthesis of silver nanoparticles and various phytochemicals are involved in the reduction and stabilization. Pure explicit phytosynthetic protocol for catalytically and biologically active silver nanoparticles is of importance as it is an environmentally benign green method. This paper reports the use of essential oil of Myristica fragrans enriched in terpenes and phenyl propenes in the reduction and stabilization. FTIR spectra of the essential oil and the synthesized biogenic silver nanoparticles are in accordance with the GC-MS spectral analysis reports. Nanosilver is initially characterized by an intense SPR band around 420 nm, followed by XRD and TEM analysis revealing the formation of 12-26 nm sized, highly pure, crystalline silver nanoparticles. Excellent catalytic and bioactive potential of the silver nanoparticles is due to the surface modification. The chemocatalytic potential of nanosilver is exhibited by the rapid reduction of the organic pollutant, para nitro phenol and by the degradation of the thiazine dye, methylene blue. Significant antibacterial activity of the silver colloid against Gram positive, Staphylococcus aureus (inhibition zone--12 mm) and Gram negative, Escherichia coli (inhibition zone--14 mm) is demonstrated by Agar-well diffusion method. Strong antioxidant activity of the biogenic silver nanoparticles is depicted through NO scavenging, hydrogen peroxide scavenging, reducing power, DPPH and total antioxidant activity assays. PMID:24956490

  11. [Role of antioxidants in electro catalytic activity of cytochrome P450 3A4].

    PubMed

    Shumiantseva, V V; Makhova, A A; Bulko, T V; Shikh, E V; Kukes, V G; Usanov, S A; Archakov, A I

    2014-01-01

    The electrochemical analysis of cytochrome Р450 3А4 catalytic activity has shown that vitamins C, A and Е influence on electron transfer and Fe3+/Fe2+ reduction process of cytochrome Р450 3А4. These data allow to assume possibility of cross effects and interference of vitamins-antioxidants with drugs metabolised by cytochrome Р450 3А4, at carrying out of complex therapy. This class of vitamins shows antioxidant properties that lead to increase of the cathodic current corresponding to heme reduction of this functionally significant haemoprotein. Ascorbic acid of 0.028-0.56 mM concentration stimulates cathodic peak (an electrochemical signal) of cytochrome Р450 3А4. At the presence of diclofenac (Voltaren) - a typical substrate of cytochrome Р450 3А4 - the increase growth of a catalytic current testifying to an electrocatalysis and stimulating action of ascorbic acid is observed. In the presence of vitamins A and Е also is registered dose-dependent (in a range of 10-100 M) increase in a catalytic current of cytochrome Р450 3А4: the maximum increase corresponds to 229 ± 20% for 100 M of vitamin A, and 162±10% for 100 M of vitamin E. Vitamin E in the presence of P450's inhibitor itraconazole doesn't give essential increase in a reductive current, unlike retinol (vitamin A). This effect can manifest substrate properties of tocopherol (vitamin E). The electrochemical approach for the analysis of catalytic activity of cytochrome Р450 3А4 and studies of influence of biologically active compounds on an electrocatalysis is the sensitive and effective sensor approach, allowing to use low concentration of protein on an electrode (till 10-15 mol/electrode), to carry out the analysis without participation of protein redox partners, and to reveal drug-drug or drug-vitamins interaction in pre-clinical experiments.

  12. A substrate-driven allosteric switch that enhances PDI catalytic activity

    PubMed Central

    Bekendam, Roelof H.; Bendapudi, Pavan K.; Lin, Lin; Nag, Partha P.; Pu, Jun; Kennedy, Daniel R.; Feldenzer, Alexandra; Chiu, Joyce; Cook, Kristina M.; Furie, Bruce; Huang, Mingdong; Hogg, Philip J.; Flaumenhaft, Robert

    2016-01-01

    Protein disulfide isomerase (PDI) is an oxidoreductase essential for folding proteins in the endoplasmic reticulum. The domain structure of PDI is a–b–b′–x–a′, wherein the thioredoxin-like a and a′ domains mediate disulfide bond shuffling and b and b′ domains are substrate binding. The b′ and a′ domains are connected via the x-linker, a 19-amino-acid flexible peptide. Here we identify a class of compounds, termed bepristats, that target the substrate-binding pocket of b′. Bepristats reversibly block substrate binding and inhibit platelet aggregation and thrombus formation in vivo. Ligation of the substrate-binding pocket by bepristats paradoxically enhances catalytic activity of a and a′ by displacing the x-linker, which acts as an allosteric switch to augment reductase activity in the catalytic domains. This substrate-driven allosteric switch is also activated by peptides and proteins and is present in other thiol isomerases. Our results demonstrate a mechanism whereby binding of a substrate to thiol isomerases enhances catalytic activity of remote domains. PMID:27573496

  13. Chaperones are necessary for the expression of catalytically active potato apyrases in prokaryotic cells.

    PubMed

    Porowińska, Dorota; Czarnecka, Joanna; Komoszyński, Michał

    2014-07-01

    NTPDases (nucleoside triphosphate diphosphohydrolases) (also called in plants apyrases) hydrolyze nucleoside 5'-tri- and/or diphosphate bonds producing nucleosides di or monophosphate and inorganic phosphate. For years, studies have been carried out to use both plant and animal enzymes for medicine. Therefore, there is a need to develop an efficient method for the quick production of large amounts of homogeneous proteins with high catalytic activity. Expression of proteins in prokaryotic cells is the most common way for the protein production. The aim of our study was to develop a method of expression of potato apyrase (StAPY4, 5, and 6) genes in bacterial cells under conditions that allowed the production of catalytically active form of these enzymes. Apyrase 4 and 6 were overexpressed in BL21-CodonPlus (DE3) bacteria strain but they were accumulated in inclusion bodies, regardless of the culture conditions and induction method. Co-expression of potato apyrases with molecular chaperones allowed the expression of catalytically active apyrase 5. However, its high nucleotidase activity could be toxic for bacteria and is therefore synthesized in small amounts in cells. Our studies show that each protein requires other conditions for maturation and even small differences in amino acid sequence can essentially affect protein folding regardless of presence of chaperones.

  14. Experimental study of humic acid degradation and theoretical modelling of catalytic ozonation.

    PubMed

    Turkay, Ozge; Inan, Hatice; Dimoglo, Anatoli

    2015-01-01

    The efficiency of TiO2 as a catalyst in the ozonation of humic acid (HA) was evaluated in a comprehensive manner. Ozonation, catalytic ozonation and adsorption experiments were conducted using both synthetic HA solution and natural water. HA degradation was evaluated in terms of DOC, VIS400 and UV254. It was shown that the addition of catalyst positively affects the mechanism of ozonation. An increase in HA degradation was observed for all these parameters. The impact of catalyst dose and initial pH value of HA on the efficacy of catalytic ozonation was investigated. The highest removal efficiencies were achieved with the dose of 1 g l(-1) of TiO2 (Degussa P-25) and in the acidic pH region. The catalytic ozonation process was efficient also on natural water component although not at the same level as it was on synthetic water. The adsorptive feature of P-25 was considered to have a clear evidence of the catalytic ozonation mechanism. The mechanism of catalysis on the surface of metal oxides was elucidated with the help of quantum-chemical calculations. In the framework of Density Function Theory (DFT), the O3 decomposition was calculated in the catalytic and non-catalytic processes. Donor-acceptor properties of the frontier (highest occupied and lowest unoccupied molecular orbitals, HOMO/LUMO) orbitals are discussed. Electron density distribution and reaction mechanism of superoxide particles formation, which participate in the process of HA ozonation are analyzed. PMID:25056748

  15. Insights into the different catalytic activities of Clostridium neurotoxins.

    PubMed

    Chen, Sheng; Karalewitz, Andrew P A; Barbieri, Joseph T

    2012-05-01

    The clostridial neurotoxins are among the most potent protein toxins for humans and are responsible for botulism, a flaccid paralysis elicited by the botulinum toxins (BoNT), and spastic paralysis elicited by tetanus toxin (TeNT). Seven serotypes of botulinum neurotoxins (A-G) and tetanus toxin showed different toxicities and cleave their substrates with different efficiencies. However, the molecular basis of their different catalytic activities with respect to their substrates is not clear. BoNT/B light chain (LC/B) and TeNT light chain (LC/T) cleave vesicle-associated membrane protein 2 (VAMP2) at the same scissile bond but possess different catalytic activities and substrate requirements, which make them the best candidates for studying the mechanisms of their different catalytic activities. The recognition of five major P sites of VAMP2 (P7, P6, P1, P1', and P2') and fine alignment of sites P2 and P3 and sites P2 and P4 by LC/B and LC/T, respectively, contributed to their substrate recognition and catalysis. Significantly, we found that the S1 pocket mutation LC/T(K(168)E) increased the rate of native VAMP2 cleavage so that it approached the rate of LC/B, which explains the molecular basis for the lower k(cat) that LC/T possesses for VAMP2 cleavage relative to that of LC/B. This analysis explains the molecular basis underlying the VAMP2 recognition and cleavage by LC/B and LC/T and provides insight that may extend the pharmacologic utility of these neurological reagents.

  16. Structural properties of cyanase. Denaturation, renaturation, and role of sulfhydryls and oligomeric structure in catalytic activity.

    PubMed

    Little, R M; Anderson, P M

    1987-07-25

    Cyanase is an inducible enzyme in Escherichia coli that catalyzes bicarbonate-dependent decomposition of cyanate to give ammonia and bicarbonate. The enzyme is composed of 8-10 identical subunits (Mr = 17,008). The objective of this study was to clarify some of the structural properties of cyanase for the purpose of understanding the relationship between oligomeric structure and catalytic activity. Circular dichroism studies showed that cyanase has a significant amount of alpha-helix and beta-sheet structure. The one sulfhydryl group per subunit does not react with 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) unless cyanase is denatured. Denaturation is apparently complete in 10 M urea or 6 M guanidine hydrochloride, but is significantly reduced in 10 M urea by the presence of azide (analog of cyanate) and is incomplete in 8 M urea. Denatured cyanase could be renatured and reactivated (greater than 85%) by removal of denaturants. Reactivation was greatly facilitated by the presence of certain anions, particularly bicarbonate, and by high ionic strength and protein concentration. The catalytic activity of renatured cyanase was associated only with oligomer. Cyanase that had been denatured in the presence of DTNB to give a cyanase-DTNB derivative could also be renatured at 26 degrees C to give active cyanase-DTNB oligomer. The active oligomeric form of the cyanase-DTNB derivative could be converted reversibly to inactive dimer by lowering the temperature to 4 degrees C or by reduction of the ionic strength and removal of monoanions. These results provide evidence that free sulfhydryl groups are not required for catalytic activity and that catalytic activity may be dependent upon oligomeric structure.

  17. Hollow-shelled nanoreactors endowed with high catalytic activity.

    PubMed

    Pérez-Lorenzo, Moisés; Vaz, Belén; Salgueiriño, Verónica; Correa-Duarte, Miguel A

    2013-09-01

    Hollow-shelled nanoreactors have emerged as efficient structures to maximize the potential of nanoparticles in the field of catalysis. In this Concept article, we underline the importance of both the morphology of the active nanoparticles as well as the composition and porosity of the shell for the catalytic performance of the overall nanocomposite. Different configurations are discussed, with a focus on preparative methods and applications in organic synthesis. Perspectives on future designs that may offer new opportunities to improve the selectivity of the catalyzed transformations and add additional features are also addressed, in order to illustrate the potential of these unique nanostructures.

  18. Catalytic Intramolecular Ketone Alkylation with Olefins by Dual Activation.

    PubMed

    Lim, Hee Nam; Dong, Guangbin

    2015-12-01

    Two complementary methods for catalytic intramolecular ketone alkylation reactions with unactivated olefins, resulting in Conia-ene-type reactions, are reported. The transformations are enabled by dual activation of both the ketone and the olefin and are atom-economical as stoichiometric oxidants or reductants are not required. Assisted by Kool's aniline catalyst, the reaction conditions can be both pH- and redox-neutral. A broad range of functional groups are thus tolerated. Whereas the rhodium catalysts are effective for the formation of five-membered rings, a ruthenium-based system that affords the six-membered ring products was also developed.

  19. Amino acid network for prediction of catalytic residues in enzymes: a comparison survey.

    PubMed

    Zhou, Jianhong; Yan, Wenying; Hu, Guang; Shen, Bairong

    2016-01-01

    Catalytic residues play a significant role in enzyme functions. With the recent accumulation of experimentally determined enzyme 3D structures and network theory on protein structures, the prediction of catalytic residues by amino acid network (AAN, where nodes are residues and links are residue interactions) has gained much interest. Computational methods of identifying catalytic residues are traditionally divided into two groups: sequence-based and structure-based methods. Two new structure- based methods are proposed in current advances: AAN and Elastic Network Model (ENM) of enzyme structures. By concentrating on AAN-based approach, we herein summarized network properties for predictions of catalytic residues. AAN attributes were showed responsible for performance improvement, and therefore the combination of AAN with previous sequence and structural information will be a promising direction for further improvement. Advantages and limitations of AAN-based methods, future perspectives on the application of AAN to the study of protein structure-function relationships are discussed.

  20. Lethal Factor Active-Site Mutations Affect Catalytic Activity In Vitro

    PubMed Central

    Hammond, S. E.; Hanna, P. C.

    1998-01-01

    The lethal factor (LF) protein of Bacillus anthracis lethal toxin contains the thermolysin-like active-site and zinc-binding consensus motif HEXXH (K. R. Klimpel, N. Arora, and S. H. Leppla, Mol. Microbiol. 13:1093–1100, 1994). LF is hypothesized to act as a Zn2+ metalloprotease in the cytoplasm of macrophages, but no proteolytic activities have been previously shown on any target substrate. Here, synthetic peptides are hydrolyzed by LF in vitro. Mass spectroscopy and peptide sequencing of isolated cleavage products separated by reverse-phase high-pressure liquid chromatography indicate that LF seems to prefer proline-containing substrates. Substitution mutations within the consensus active-site residues completely abolish all in vitro catalytic functions, as does addition of 1,10-phenanthroline, EDTA, and certain amino acid hydroxamates, including the novel zinc metalloprotease inhibitor ZINCOV. In contrast, the protease inhibitors bestatin and lysine CMK, previously shown to block LF activity on macrophages, did not block LF activity in vitro. These data provide the first direct evidence that LF may act as an endopeptidase. PMID:9573135

  1. Kinetics of Non-Catalytic Esterification of Free Fatty Acids Present in Jatropha Oil.

    PubMed

    Prasanna Rani, Karna Narayana; Ramana Neeharika, Tulasi Sri Venkata; Kumar, Thella Prathap; Satyavathi, Bankupalli; Sailu, Chintha

    2016-05-01

    Non-catalytic esterfication of free fatty acids (FFA) present in vegetable oils is an alternative pretreatment process for the biodiesel production. Biodiesel, consists of long-chain fatty acid methyl esters (FAME) and is obtained from renewable sources such as vegetable oils or animal fat. This study presents kinetics of thermal esterification of free fatty acids present in jatropha oil with methanol. The effect of process parameters like reaction time (1-5 h), temperature (170-190°C) and oil to methanol ratio (1:3-1:5) at constant pressure was investigated. The optimal conditions were found to be oil to methanol ratio of 1:4, 190°C, at 27.1 bar and 5 h which gave a maximum conversion of 95.1%. A second order kinetic model for both forward and backward reactions was proposed to study the reaction system. A good agreement was observed between the experimental data and the model values. The activation energy for forward reaction and the heat of reaction were found to be 36.364 Kcal/mol and 1.74 Kcal/mol respectively.

  2. Kinetics of Non-Catalytic Esterification of Free Fatty Acids Present in Jatropha Oil.

    PubMed

    Prasanna Rani, Karna Narayana; Ramana Neeharika, Tulasi Sri Venkata; Kumar, Thella Prathap; Satyavathi, Bankupalli; Sailu, Chintha

    2016-05-01

    Non-catalytic esterfication of free fatty acids (FFA) present in vegetable oils is an alternative pretreatment process for the biodiesel production. Biodiesel, consists of long-chain fatty acid methyl esters (FAME) and is obtained from renewable sources such as vegetable oils or animal fat. This study presents kinetics of thermal esterification of free fatty acids present in jatropha oil with methanol. The effect of process parameters like reaction time (1-5 h), temperature (170-190°C) and oil to methanol ratio (1:3-1:5) at constant pressure was investigated. The optimal conditions were found to be oil to methanol ratio of 1:4, 190°C, at 27.1 bar and 5 h which gave a maximum conversion of 95.1%. A second order kinetic model for both forward and backward reactions was proposed to study the reaction system. A good agreement was observed between the experimental data and the model values. The activation energy for forward reaction and the heat of reaction were found to be 36.364 Kcal/mol and 1.74 Kcal/mol respectively. PMID:27086997

  3. Ultra-high electrochemical catalytic activity of MXenes

    NASA Astrophysics Data System (ADS)

    Pan, Hui

    2016-09-01

    Cheap and abundant electrocatalysts for hydrogen evolution reactions (HER) have been widely pursued for their practical application in hydrogen-energy technologies. In this work, I present systematical study of the hydrogen evolution reactions on MXenes (Mo2X and W2X, X = C and N) based on density-functional-theory calculations. I find that their HER performances strongly depend on the composition, hydrogen adsorption configurations, and surface functionalization. I show that W2C monolayer has the best HER activity with near-zero overpotential at high hydrogen density among all of considered pure MXenes, and hydrogenation can efficiently enhance its catalytic performance in a wide range of hydrogen density further, while oxidization makes its activity reduced significantly. I further show that near-zero overpotential for HER on Mo2X monolayers can be achieved by oxygen functionalization. My calculations predict that surface treatment, such as hydrogenation and oxidization, is critical to enhance the catalytic performance of MXenes. I expect that MXenes with HER activity comparable to Pt in a wide range of hydrogen density can be realized by tuning composition and functionalizing, and promotes their applications into hydrogen-energy technologies.

  4. Ultra-high electrochemical catalytic activity of MXenes.

    PubMed

    Pan, Hui

    2016-09-08

    Cheap and abundant electrocatalysts for hydrogen evolution reactions (HER) have been widely pursued for their practical application in hydrogen-energy technologies. In this work, I present systematical study of the hydrogen evolution reactions on MXenes (Mo2X and W2X, X = C and N) based on density-functional-theory calculations. I find that their HER performances strongly depend on the composition, hydrogen adsorption configurations, and surface functionalization. I show that W2C monolayer has the best HER activity with near-zero overpotential at high hydrogen density among all of considered pure MXenes, and hydrogenation can efficiently enhance its catalytic performance in a wide range of hydrogen density further, while oxidization makes its activity reduced significantly. I further show that near-zero overpotential for HER on Mo2X monolayers can be achieved by oxygen functionalization. My calculations predict that surface treatment, such as hydrogenation and oxidization, is critical to enhance the catalytic performance of MXenes. I expect that MXenes with HER activity comparable to Pt in a wide range of hydrogen density can be realized by tuning composition and functionalizing, and promotes their applications into hydrogen-energy technologies.

  5. Ultra-high electrochemical catalytic activity of MXenes

    PubMed Central

    Pan, Hui

    2016-01-01

    Cheap and abundant electrocatalysts for hydrogen evolution reactions (HER) have been widely pursued for their practical application in hydrogen-energy technologies. In this work, I present systematical study of the hydrogen evolution reactions on MXenes (Mo2X and W2X, X = C and N) based on density-functional-theory calculations. I find that their HER performances strongly depend on the composition, hydrogen adsorption configurations, and surface functionalization. I show that W2C monolayer has the best HER activity with near-zero overpotential at high hydrogen density among all of considered pure MXenes, and hydrogenation can efficiently enhance its catalytic performance in a wide range of hydrogen density further, while oxidization makes its activity reduced significantly. I further show that near-zero overpotential for HER on Mo2X monolayers can be achieved by oxygen functionalization. My calculations predict that surface treatment, such as hydrogenation and oxidization, is critical to enhance the catalytic performance of MXenes. I expect that MXenes with HER activity comparable to Pt in a wide range of hydrogen density can be realized by tuning composition and functionalizing, and promotes their applications into hydrogen-energy technologies. PMID:27604848

  6. Ultra-high electrochemical catalytic activity of MXenes.

    PubMed

    Pan, Hui

    2016-01-01

    Cheap and abundant electrocatalysts for hydrogen evolution reactions (HER) have been widely pursued for their practical application in hydrogen-energy technologies. In this work, I present systematical study of the hydrogen evolution reactions on MXenes (Mo2X and W2X, X = C and N) based on density-functional-theory calculations. I find that their HER performances strongly depend on the composition, hydrogen adsorption configurations, and surface functionalization. I show that W2C monolayer has the best HER activity with near-zero overpotential at high hydrogen density among all of considered pure MXenes, and hydrogenation can efficiently enhance its catalytic performance in a wide range of hydrogen density further, while oxidization makes its activity reduced significantly. I further show that near-zero overpotential for HER on Mo2X monolayers can be achieved by oxygen functionalization. My calculations predict that surface treatment, such as hydrogenation and oxidization, is critical to enhance the catalytic performance of MXenes. I expect that MXenes with HER activity comparable to Pt in a wide range of hydrogen density can be realized by tuning composition and functionalizing, and promotes their applications into hydrogen-energy technologies. PMID:27604848

  7. Resonant active sites in catalytic ammonia synthesis: A structural model

    NASA Astrophysics Data System (ADS)

    Cholach, Alexander R.; Bryliakova, Anna A.; Matveev, Andrey V.; Bulgakov, Nikolai N.

    2016-03-01

    Adsorption sites Mn consisted of n adjacent atoms M, each bound to the adsorbed species, are considered within a realistic model. The sum of bonds Σ lost by atoms in a site in comparison with the bulk atoms was used for evaluation of the local surface imperfection, while the reaction enthalpy at that site was used as a measure of activity. The comparative study of Mn sites (n = 1-5) at basal planes of Pt, Rh, Ir, Fe, Re and Ru with respect to heat of N2 dissociative adsorption QN and heat of Nad + Had → NHad reaction QNH was performed using semi-empirical calculations. Linear QN(Σ) increase and QNH(Σ) decrease allowed to specify the resonant Σ for each surface in catalytic ammonia synthesis at equilibrium Nad coverage. Optimal Σ are realizable for Ru2, Re2 and Ir4 only, whereas other centers meet steric inhibition or unreal crystal structure. Relative activity of the most active sites in proportion 5.0 × 10- 5: 4.5 × 10- 3: 1: 2.5: 3.0: 1080: 2270 for a sequence of Pt4, Rh4, Fe4(fcc), Ir4, Fe2-5(bcc), Ru2, Re2, respectively, is in agreement with relevant experimental data. Similar approach can be applied to other adsorption or catalytic processes exhibiting structure sensitivity.

  8. Nickel-doped ceria nanoparticles for promoting catalytic activity of Pt/C for ethanol electrooxidation

    NASA Astrophysics Data System (ADS)

    Tan, Qiang; Du, Chunyu; Sun, Yongrong; Du, Lei; Yin, Geping; Gao, Yunzhi

    2014-10-01

    This paper reports the facile synthesis of monodispersed nickel-doped ceria nanoparticles by a thermal decomposition method, which is used to promote catalytic properties of Pt/C. The Pt/Ni-doped CeO2/C catalyst obtained exhibits remarkably high activity and stability towards the ethanol electrooxidation in acidic media. This is attributed to higher oxygen releasing capacity and stronger interaction of Ni-doped CeO2 with Pt than pure CeO2 nanoparticles that contribute positively to the removal of poisoning intermediates. We believe that the design concept and synthetic strategy of metal doped oxides used for fuel cell catalysts can be potentially extended to other catalytic fields.

  9. Origin of the catalytic activity of bovine seminal ribonuclease against double-stranded RNA

    NASA Technical Reports Server (NTRS)

    Opitz, J. G.; Ciglic, M. I.; Haugg, M.; Trautwein-Fritz, K.; Raillard, S. A.; Jermann, T. M.; Benner, S. A.

    1998-01-01

    Bovine seminal ribonuclease (RNase) binds, melts, and (in the case of RNA) catalyzes the hydrolysis of double-stranded nucleic acid 30-fold better under physiological conditions than its pancreatic homologue, the well-known RNase A. Reported here are site-directed mutagenesis experiments that identify the sequence determinants of this enhanced catalytic activity. These experiments have been guided in part by experimental reconstructions of ancestral RNases from extinct organisms that were intermediates in the evolution of the RNase superfamily. It is shown that the enhanced interactions between bovine seminal RNase and double-stranded nucleic acid do not arise from the increased number of basic residues carried by the seminal enzyme. Rather, a combination of a dimeric structure and the introduction of two glycine residues at positions 38 and 111 on the periphery of the active site confers the full catalytic activity of bovine seminal RNase against duplex RNA. A structural model is presented to explain these data, the use of evolutionary reconstructions to guide protein engineering experiments is discussed, and a new variant of RNase A, A(Q28L K31C S32C D38G E111G), which contains all of the elements identified in these experiments as being important for duplex activity, is prepared. This is the most powerful catalyst within this subfamily yet observed, some 46-fold more active against duplex RNA than RNase A.

  10. Catalytic Mesoporous Janus Nanomotors for Active Cargo Delivery

    PubMed Central

    2015-01-01

    We report on the synergy between catalytic propulsion and mesoporous silica nanoparticles (MSNPs) for the design of Janus nanomotors as active cargo delivery systems with sizes <100 nm (40, 65, and 90 nm). The Janus asymmetry of the nanomotors is given by electron beam (e-beam) deposition of a very thin platinum (2 nm) layer on MSNPs. The chemically powered Janus nanomotors present active diffusion at low H2O2 fuel concentration (i.e., <3 wt %). Their apparent diffusion coefficient is enhanced up to 100% compared to their Brownian motion. Due to their mesoporous architecture and small dimensions, they can load cargo molecules in large quantity and serve as active nanocarriers for directed cargo delivery on a chip. PMID:25844893

  11. Triggering activity of catalytic rod-like supramolecular polymers.

    PubMed

    Huerta, Elisa; van Genabeek, Bas; Lamers, Brigitte A G; Koenigs, Marcel M E; Meijer, E W; Palmans, Anja R A

    2015-02-23

    Supramolecular polymers based on benzene-1,3,5-tricarboxamides (BTAs) functionalized with an L- or D-proline moiety display high catalytic activity towards aldol reactions in water. High turnover frequencies (TOF) of up to 27×10(-4) s(-1) and excellent stereoselectivities (up to 96% de, up to 99% ee) were observed. In addition, the catalyst could be reused and remained active at catalyst loadings and substrate concentrations as low as 0.1 mol % and 50 mM, respectively. A temperature-induced conformational change in the supramolecular polymer triggers the high activity of the catalyst. The supramolecular polymer's helical sense in combination with the configuration of the proline (L- or D-) is responsible for the observed selectivity. PMID:25614098

  12. Phosphotungstic acid encapsulated in the mesocages of amine-functionalized metal-organic frameworks for catalytic oxidative desulfurization.

    PubMed

    Wang, Xu-Sheng; Huang, Yuan-Biao; Lin, Zu-Jin; Cao, Rong

    2014-08-21

    Highly dispersed Keggin-type phosphotungstic acid (H3PW12O40, PTA) encapsulated in the mesocages of amine-functionalized metal-organic frameworks MIL-101(Cr)-NH2 has been prepared by an anion-exchange method. PTA anions (PW12O40(3-)) are stabilized in the mesocages via the electrostatic interaction with amino groups of the MIL-101(Cr)-NH2. The obtained catalyst (denoted PTA@MIL-101(Cr)-NH2) exhibits high catalytic activity in the extractive and catalytic oxidative desulfurization (ECODS) system under mild conditions. Moreover, it can be easily recovered and recycled several times without leaching and loss of activity. PMID:24967570

  13. Catalytic Hydrogenation of Maleic Acid at Moderate Pressures: A Laboratory Demonstration

    ERIC Educational Resources Information Center

    Amoa, Kwesi

    2007-01-01

    Moderate-pressure catalytic hydrogenation is often overlooked as a classroom demonstration because of the awkwardness of the equipment and the time constraints required for the conversion of reactants to products. This article demonstrates the reduction of maleic acid in about 90 minutes. (Contains 1 table and 1 figure.)

  14. Synthesis and catalytic activity of heteroatom doped metal-free single-wall carbon nanohorns.

    PubMed

    Wu, Xiaohui; Cui, Longbin; Tang, Pei; Hu, Ziqi; Ma, Ding; Shi, Zujin

    2016-04-01

    Boron-, phosphorus-, nitrogen-doped and co-doped single-wall carbon nanohorns were produced using an arc-vaporization method. These as-prepared doped materials consist of uniform isolated nanohorns and exhibit greatly enhanced catalytic capabilities in the reduction reaction of nitrobenzene and a volcano-shape trend between their activities with a B dopant content is found. Moreover, the B-C3 and P-C3 species in doped nanohorns might act as the acidic and basic sites to promote this reaction. PMID:27006980

  15. Polyvinylpyrrolidone adsorption effects on the morphologies of synthesized platinum particles and its catalytic activity

    SciTech Connect

    Ooi, Mahayatun Dayana Johan; Aziz, Azlan Abdul

    2015-04-24

    Flower-like Platinum micro-structures were synthesized from different concentration of the PVP using solvothermal method. At 5.0×10{sup −3} mmol of PVP, well-defined flower-like pattern consists of triangular petals radiating from the centre were produced whereas larger flower network developed at higher PVP concentration. High degree of crystallinity was obtained upon each increment of PVP. The well defined flower like pattern synthesized using 5.0×10{sup −3} mmol PVP exhibit the highest catalytic activity and stability towards electro-oxidation of formic acid.

  16. Catalytic activity of nuclease P1: Experiment and theory

    SciTech Connect

    Miller, J.H.; Falcone, J.M.; Shibata, M.; Box, H.C.

    1994-10-01

    Nuclease P1 from Penicillium citrinum is a zinc dependent glyco-enzyme that recognizes single stranded DNA and RNA as substrates and hydrolyzes the phosphate ester bond. Nuclease Pl seems to recognize particular conformations of the phosphodiester backbone and shows significant variation in the rate of hydrolytic activity depending upon which nucleosides are coupled by the phosphodiester bond. The efficiency of nuclease Pl in hydrolyzing the phosphodiester bonds of a substrate can be altered by modifications to one of the substrate bases induced by ionizing radiation or oxidative stress. Measurements have been made of the effect of several radiation induced lesions on the catalytic rate of nuclease Pl. A model of the structure of the enzyme has been constructed in order to better understand the binding and activity of this enzyme on various ssDNA substrates.

  17. Catalytic asymmetric protonation of lithium enolates using amino acid derivatives as chiral proton sources.

    PubMed

    Mitsuhashi, Kaori; Ito, Rie; Arai, Takayoshi; Yanagisawa, Akira

    2006-04-13

    [reaction: see text] Asymmetric protonation of lithium enolates was examined using commercially available amino acid derivatives as chiral proton sources. Among the amino acid derivatives tested, Nbeta-l-aspartyl-l-phenylalanine methyl ester was found to cause significant asymmetric induction in the protonation of lithium enolates. The enantiomeric excess (up to 88% ee) of the products obtained in the presence of a catalytic amount of the chiral proton source was higher than those obtained in the stoichiometric reaction. PMID:16597150

  18. Catalytic asymmetric protonation of lithium enolates using amino acid derivatives as chiral proton sources.

    PubMed

    Mitsuhashi, Kaori; Ito, Rie; Arai, Takayoshi; Yanagisawa, Akira

    2006-04-13

    [reaction: see text] Asymmetric protonation of lithium enolates was examined using commercially available amino acid derivatives as chiral proton sources. Among the amino acid derivatives tested, Nbeta-l-aspartyl-l-phenylalanine methyl ester was found to cause significant asymmetric induction in the protonation of lithium enolates. The enantiomeric excess (up to 88% ee) of the products obtained in the presence of a catalytic amount of the chiral proton source was higher than those obtained in the stoichiometric reaction.

  19. Guiding catalytically active particles with chemically patterned surfaces

    NASA Astrophysics Data System (ADS)

    Uspal, William; Popescu, Mihail; Dietrich, Siegfried; Tasinkevych, Mykola

    Catalytically active Janus particles in solution create gradients in the chemical composition of the solution along their surfaces, as well as along any nearby container walls. The former leads to self-phoresis, while the latter gives rise to chemi-osmosis, providing an additional contribution to self-motility. Chemi-osmosis strongly depends on the molecular interactions between the diffusing chemical species and the wall. We show analytically, using an approximate ``point-particle'' approach, that by chemically patterning a planar substrate (e.g., by adsorbing two different materials) one can direct the motion of Janus particles: the induced chemi-osmotic flows can cause particles to either ``dock'' at a chemical step between the two materials, or to follow a chemical stripe. These theoretical predictions are confirmed by full numerical calculations. Generically, docking occurs for particles which tend to move away from their catalytic caps, while stripe-following occurs in the opposite case. Our analysis reveals the physical mechanisms governing this behavior.

  20. Study of Single Catalytic Events at Copper-in-Charcoal: Localization of Click Activity Through Subdiffraction Observation of Single Catalytic Events.

    PubMed

    Decan, Matthew R; Scaiano, Juan C

    2015-10-15

    Single molecule fluorescence microscopy reveals that copper-in-charcoal--a high performance click catalyst- has remarkably few catalytic sites, with 90% of the charcoal particles being inactive, and for the catalytic ones the active sites represent a minute fraction (∼0.003%) of the surface. The intermittent nature of the catalytic events enables subdiffraction resolution and mapping of the catalytic sites. PMID:26722775

  1. Dual Catalytic Activity of Hydroxycinnamoyl-Coenzyme A Quinate Transferase from Tomato Allows It to Moonlight in the Synthesis of Both Mono- and Dicaffeoylquinic Acids1[W][OPEN

    PubMed Central

    Moglia, Andrea; Lanteri, Sergio; Comino, Cinzia; Hill, Lionel; Knevitt, Daniel; Cagliero, Cecilia; Rubiolo, Patrizia; Bornemann, Stephen

    2014-01-01

    Tomato (Solanum lycopersicum), like other Solanaceous species, accumulates high levels of antioxidant caffeoylquinic acids, which are strong bioactive molecules and protect plants against biotic and abiotic stresses. Among these compounds, the monocaffeoylquinic acids (e.g. chlorogenic acid [CGA]) and the dicaffeoylquinic acids (diCQAs) have been found to possess marked antioxidative properties. Thus, they are of therapeutic interest both as phytonutrients in foods and as pharmaceuticals. Strategies to increase diCQA content in plants have been hampered by the modest understanding of their biosynthesis and whether the same pathway exists in different plant species. Incubation of CGA with crude extracts of tomato fruits led to the formation of two new products, which were identified by liquid chromatography-mass spectrometry as diCQAs. This chlorogenate:chlorogenate transferase activity was partially purified from ripe fruit. The final protein fraction resulted in 388-fold enrichment of activity and was subjected to trypsin digestion and mass spectrometric sequencing: a hydroxycinnamoyl-Coenzyme A:quinate hydroxycinnamoyl transferase (HQT) was selected as a candidate protein. Assay of recombinant HQT protein expressed in Escherichia coli confirmed its ability to synthesize diCQAs in vitro. This second activity (chlorogenate:chlorogenate transferase) of HQT had a low pH optimum and a high Km for its substrate, CGA. High concentrations of CGA and relatively low pH occur in the vacuoles of plant cells. Transient assays demonstrated that tomato HQT localizes to the vacuole as well as to the cytoplasm of plant cells, supporting the idea that in this species, the enzyme catalyzes different reactions in two subcellular compartments. PMID:25301886

  2. Experimental and Mechanistic Understanding of Aldehyde Hydrogenation Using Au25 Nanoclusters with Lewis Acids: Unique Sites for Catalytic Reactions.

    PubMed

    Li, Gao; Abroshan, Hadi; Chen, Yuxiang; Jin, Rongchao; Kim, Hyung J

    2015-11-18

    The catalytic activity of Au25(SR)18 nanoclusters (R = C2H4Ph) for the aldehyde hydrogenation reaction in the presence of a base, e.g., ammonia or pyridine, and transition-metal ions M(z+), such as Cu(+), Cu(2+), Ni(2+) and Co(2+), as a Lewis acid is studied. The addition of a Lewis acid is found to significantly promote the catalytic activity of Au25(SR)18/CeO2 in the hydrogenation of benzaldehyde and a number of its derivatives. Matrix-assisted laser desorption ionization (MALDI) and electrospray ionization (ESI) mass spectrometry in conjunction with UV-vis spectroscopy confirm the generation of new species, Au25-n(SR)18-n (n = 1-4), in the presence of a Lewis acid. The pathways for the speciation of Au24(SR)17 from its parent Au25(SR)18 nanocluster as well as its structure are investigated via the density functional theory (DFT) method. The adsorption of M(z+) onto a thiolate ligand "-SR-" of Au25(SR)18, followed by a stepwise detachment of "-SR-" and a gold atom bonded to "-SR-" (thus an "Au-SR" unit) is found to be the most likely mechanism for the Au24(SR)17 generation. This in turn exposes the Au13-core of Au24(SR)17 to reactants, providing an active site for the catalytic hydrogenation. DFT calculations indicate that M(z+) is also capable of adsorbing onto the Au13-core surface, producing a possible active metal site of a different kind to catalyze the aldehyde hydrogenation reaction. This study suggests, for the first time, that species with an open metal site like adducts [nanoparticle-M]((z-1)+) or fragments Au25-n(SR)18-n function as the catalysts rather than the intact Au25(SR)18.

  3. Antibacterial and catalytic activities of green synthesized silver nanoparticles.

    PubMed

    Bindhu, M R; Umadevi, M

    2015-01-25

    The aqueous beetroot extract was used as reducing agent for silver nanoparticles synthesis. The synthesized nanoparticles were characterized using UV-visible spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The surface plasmon resonance peak of synthesized nanoparticles was observed at 438 nm. As the concentration of beetroot extract increases, absorption spectra shows blue shift with decreasing particle size. The prepared silver nanoparticles were well dispersed, spherical in shape with the average particle size of 15 nm. The prepared silver nanoparticles are effective in inhibiting the growth of both gram positive and gram negative bacteria. The prepared silver nanoparticles reveal faster catalytic activity. This natural method for synthesis of silver nanoparticles offers a valuable contribution in the area of green synthesis and nanotechnology avoiding the presence of hazardous and toxic solvents and waste. PMID:25093965

  4. [Effect Of Polyelectrolytes on Catalytic Activity of Alcohol Dehydrogenase].

    PubMed

    Dubrovsky, A V; Musina, E V; Kim, A L; Tikhonenko, S A

    2016-01-01

    Fluorescent and optical spectroscopy were used to study the interaction of alcohol dehydrogenase (ADH) with negatively charged polystyrene sulfonate (PSS) and dextran sulfate (DS), as well as positively charged poly(diallyldimethylammonium) (PDADMA). As found, DS and PDADMA did not affect the structural and catalytic enzyme properties. In contrast, PSS slightly decreased the protein self-fluorescence over 1 h of incubation, which is associated with partial destruction of its quaternary (globular) structure. Investigation of the ADH activity with and without PSS showed its dependency on the incubation time and the PSS presence. Sodium chloride (2.0 M and 0.2 M) or ammonium sulfate (0.1 M) added to the reaction mixture did not completely protect the enzyme quaternary structure from the PSS action. However ammonium sulfate or 0.2 M sodium chloride stabilized the enzyme and partially inhibited the negative PSS effect. PMID:27266256

  5. Antibacterial and catalytic activities of green synthesized silver nanoparticles

    NASA Astrophysics Data System (ADS)

    Bindhu, M. R.; Umadevi, M.

    2015-01-01

    The aqueous beetroot extract was used as reducing agent for silver nanoparticles synthesis. The synthesized nanoparticles were characterized using UV-visible spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The surface plasmon resonance peak of synthesized nanoparticles was observed at 438 nm. As the concentration of beetroot extract increases, absorption spectra shows blue shift with decreasing particle size. The prepared silver nanoparticles were well dispersed, spherical in shape with the average particle size of 15 nm. The prepared silver nanoparticles are effective in inhibiting the growth of both gram positive and gram negative bacteria. The prepared silver nanoparticles reveal faster catalytic activity. This natural method for synthesis of silver nanoparticles offers a valuable contribution in the area of green synthesis and nanotechnology avoiding the presence of hazardous and toxic solvents and waste.

  6. Catalytically active and hierarchically porous SAPO-11 zeolite synthesized in the presence of polyhexamethylene biguanidine.

    PubMed

    Liu, Yan; Qu, Wei; Chang, Weiwei; Pan, Shuxiang; Tian, Zhijian; Meng, Xiangju; Rigutto, Marcello; van der Made, Alexander; Zhao, Lan; Zheng, Xiaoming; Xiao, Feng-Shou

    2014-03-15

    Hierarchically porous SAPO-11 zeolite (H-SAPO-11) is rationally synthesized from a starting silicoaluminophosphate gel in the presence of polyhexamethylene biguanidine as a mesoscale template. The sample is well characterized by XRD, N2 sorption, SEM, TEM, NMR, XPS, NH3-TPD, and TG techniques. The results show that the sample obtained has good crystallinity, hierarchical porosity (mesopores at ca. 10 nm and macropores at ca. 50-200 nm), high BET surface area (226 m(2)/g), large pore volume (0.25 cm(3)/g), and abundant medium and strong acidic sites (0.36 mmol/g). After loading Pt (0.5 wt.%) on H-SAPO-11 by using wet impregnation method, catalytic hydroisomerization tests of n-dodecane show that the hierarchical Pt/SAPO-11 zeolite exhibits high conversion of n-dodecane and enhanced selectivity for branched products as well as reduced selectivity for cracking products, compared with conventional Pt/SAPO-11 zeolite. This phenomenon is reasonably attributed to the presence of hierarchical porosity, which is favorable for access of reactants on catalytically active sites. The improvement in catalytic performance in long-chain paraffin hydroisomerization over Pt/SAPO-11-based catalyst is of great importance for its industrial applications in the future.

  7. Catalytic activity of silicon nanowires decorated with silver and copper nanoparticles

    NASA Astrophysics Data System (ADS)

    Amdouni, Sonia; Coffinier, Yannick; Szunerits, Sabine; Zaïbi, Mohammed Ali; Oueslati, Meherzi; Boukherroub, Rabah

    2016-01-01

    The paper reports on the elaboration of silicon nanowires decorated with silver (SiNWs-Ag NPs) or copper (SiNWs-Cu NPs) nanoparticles and the investigation of their catalytic properties for the reduction of 4-nitrophenol to 4-aminophenol. The SiNW arrays were produced through chemical etching of crystalline silicon in HF/AgNO3 aqueous solution. The metal nanoparticles were deposited on the SiNW substrates through chemical bath immersion in a metal salt/hydrofluoric acid aqueous solution. The SiNWs decorated with Ag NPs and Cu NPs were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). The catalytic activity of the SiNWs loaded with metal nanoparticles was evaluated for the reduction of 4-nitrophenol to 4-aminophenol in the presence of sodium borohydride (NaBH4). The substrates exhibited good catalytic performance toward nitrophenol with a full reduction in less than 30 s for the SiNWs-Cu NPs.

  8. Investigating the performance of CoxOy/activated carbon catalysts for ethyl acetate catalytic combustion

    NASA Astrophysics Data System (ADS)

    Xie, Hongmei; Zhao, Xiaoping; Zhou, Guilin; He, Xiaoling; Lan, Hai; Jiang, Zongxuan

    2015-01-01

    The catalytic properties of Co-supported activated carbon (AC) catalysts for ethyl acetate catalytic elimination in air were investigated. Results showed that air atmosphere promoted the generation of high-valence state cobalt oxides, and promote the production of reactive oxygen species (ROS) in the Co3O4/AC catalyst. ROS crucially functioned in improving the catalytic activity of Co3O4/AC catalysts. Therefore, CoACA catalyst prepared in air exhibited higher catalytic activity than CoACN catalyst prepared in nitrogen, and CoACA catalyst led to high ethyl acetate conversion (>93%) and stability at a low reaction temperature (210 °C).

  9. Acidic Properties and Structure-Activity Correlations of Solid Acid Catalysts Revealed by Solid-State NMR Spectroscopy.

    PubMed

    Zheng, Anmin; Li, Shenhui; Liu, Shang-Bin; Deng, Feng

    2016-04-19

    Solid acid materials with tunable structural and acidic properties are promising heterogeneous catalysts for manipulating and/or emulating the activity and selectivity of industrially important catalytic reactions. On the other hand, the performances of acid-catalyzed reactions are mostly dictated by the acidic features, namely, type (Brønsted vs Lewis acidity), amount, strength, and local environment of acid sites. The latter is relevant to their location (intra- vs extracrystalline), and possible confinement and Brønsted-Lewis acid synergy effects that may strongly affect the host-guest interactions, reaction mechanism, and shape selectivity of the catalytic system. This account aims to highlight some important applications of state-of-the-art solid-state NMR (SSNMR) techniques for exploring the structural and acidic properties of solid acid catalysts as well as their catalytic performances and relevant reaction pathway invoked. In addition, density functional theory (DFT) calculations may be exploited in conjunction with experimental SSNMR studies to verify the structure-activity correlations of the catalytic system at a microscopic scale. We describe in this Account the developments and applications of advanced ex situ and/or in situ SSNMR techniques, such as two-dimensional (2D) double-quantum magic-angle spinning (DQ MAS) homonuclear correlation spectroscopy for structural investigation of solid acids as well as study of their acidic properties. Moreover, the energies and electronic structures of the catalysts and detailed catalytic reaction processes, including the identification of reaction species, elucidation of reaction mechanism, and verification of structure-activity correlations, made available by DFT theoretical calculations were also discussed. Relevant discussions will focus primarily on results obtained from our laboratories in the past decade, including (i) quantitative and qualitative acidity characterization utilizing assorted probe molecules

  10. Structural Basis for Catalytic Activation of a Serine Recombinase

    SciTech Connect

    Keenholtz, Ross A.; Rowland, Sally-J.; Boocock, Martin R.; Stark, W. Marshall; Rice, Phoebe A.

    2014-10-02

    Sin resolvase is a site-specific serine recombinase that is normally controlled by a complex regulatory mechanism. A single mutation, Q115R, allows the enzyme to bypass the entire regulatory apparatus, such that no accessory proteins or DNA sites are required. Here, we present a 1.86 {angstrom} crystal structure of the Sin Q115R catalytic domain, in a tetrameric arrangement stabilized by an interaction between Arg115 residues on neighboring subunits. The subunits have undergone significant conformational changes from the inactive dimeric state previously reported. The structure provides a new high-resolution view of a serine recombinase active site that is apparently fully assembled, suggesting roles for the conserved active site residues. The structure also suggests how the dimer-tetramer transition is coupled to assembly of the active site. The tetramer is captured in a different rotational substate than that seen in previous hyperactive serine recombinase structures, and unbroken crossover site DNA can be readily modeled into its active sites.

  11. Development of novel catalytically active polymer-metal-nanocomposites based on activated foams and textile fibers

    NASA Astrophysics Data System (ADS)

    Domènech, Berta; Ziegler, Kharla K.; Carrillo, Fernando; Muñoz, Maria; Muraviev, Dimitri N.; Macanás, Jorge

    2013-05-01

    In this paper, we report the intermatrix synthesis of Ag nanoparticles in different polymeric matrices such as polyurethane foams and polyacrylonitrile or polyamide fibers. To apply this technique, the polymer must bear functional groups able to bind and retain the nanoparticle ion precursors while ions should diffuse through the matrix. Taking into account the nature of some of the chosen matrices, it was essential to try to activate the support material to obtain an acceptable value of ion exchange capacity. To evaluate the catalytic activity of the developed nanocomposites, a model catalytic reaction was carried out in batch experiments: the reduction of p-nitrophenol by sodium borohydride.

  12. Development of novel catalytically active polymer-metal-nanocomposites based on activated foams and textile fibers

    PubMed Central

    2013-01-01

    In this paper, we report the intermatrix synthesis of Ag nanoparticles in different polymeric matrices such as polyurethane foams and polyacrylonitrile or polyamide fibers. To apply this technique, the polymer must bear functional groups able to bind and retain the nanoparticle ion precursors while ions should diffuse through the matrix. Taking into account the nature of some of the chosen matrices, it was essential to try to activate the support material to obtain an acceptable value of ion exchange capacity. To evaluate the catalytic activity of the developed nanocomposites, a model catalytic reaction was carried out in batch experiments: the reduction of p-nitrophenol by sodium borohydride. PMID:23680063

  13. Characterization of a soluble, catalytically active form of Escherichia coli leader peptidase: requirement of detergent or phospholipid for optimal activity.

    PubMed

    Tschantz, W R; Paetzel, M; Cao, G; Suciu, D; Inouye, M; Dalbey, R E

    1995-03-28

    Leader peptidase is a novel serine protease in Escherichia coli, which functions to cleave leader sequences from exported proteins. Its catalytic domain extends into the periplasmic space and is anchored to the membrane by two transmembrane segments located at the N-terminal end of the protein. At present, there is no information on the structure of the catalytic domain. Here, we report on the properties of a soluble form of leader peptidase (delta 2-75), and we compare its properties to those of the wild-type enzyme. We find that the truncated leader peptidase has a kcat of 3.0 S-1 and a Km of 32 microM with a pro-OmpA nuclease A substrate. In contrast to the wild-type enzyme (pI of 6.8), delta 2-75 is water-soluble and has an acidic isoelectric point of 5.6. We also show with delta 2-75 that the replacement of serine 90 and lysine 145 with alanine residues results in a 500-fold reduction in activity, providing further evidence that leader peptidase employs a catalytic serine/lysine dyad. Finally, we find that the catalysis of delta 2-75 is accelerated by the presence of the detergent Triton X-100, regardless if the substrate is pro-OmpA nuclease A or a peptide substrate. Triton X-100 is required for optimal activity of delta 2-75 at a level far below the critical micelle concentration. Moreover, we find that E. coli phospholipids stimulate the activity of delta 2-75, suggesting that phospholipids may play an important physiological role in the catalytic mechanism of leader peptidase. PMID:7696258

  14. Catalytic hydrothermal pretreatment of corncob into xylose and furfural via solid acid catalyst.

    PubMed

    Li, Huiling; Deng, Aojie; Ren, Junli; Liu, Changyu; Lu, Qi; Zhong, Linjie; Peng, Feng; Sun, Runcang

    2014-04-01

    Selectively catalytic hydrothermal pretreatment of corncob into xylose and furfural has been developed in this work using solid acid catalyst (SO4(2-)/TiO2-ZrO2/La(3+)). The effects of corncob-to-water ratio, reaction temperature and residence time on the performance of catalytic hydrothermal pretreatment were investigated. Results showed that the solid residues contained mainly lignin and cellulose, which was indicative of the efficient removal of hemicelluloses from corncob by hydrothermal method. The prepared catalyst with high thermal stability and strong acid sites originated from the acid functional groups was confirmed to contribute to the hydrolysis of polysaccharides into monosaccharides followed by dehydration into furfural. Highest furfural yield (6.18 g/100g) could be obtained at 180°C for 120 min with 6.80 g/100g xylose yield when the corncob/water ratio of was 10:100. Therefore, selectively catalytic hydrothermal pretreatment of lignocellulosic biomass into important platform chemicals by solid acids is considered to be a potential treatment for biodiesel and chemical production.

  15. Catalytic asymmetric direct Mannich reaction: a powerful tool for the synthesis of alpha,beta-diamino acids.

    PubMed

    Arrayás, Ramón Gómez; Carretero, Juan C

    2009-07-01

    Optically active alpha,beta-diamino acids are very attractive targets in organic synthesis because of their wide-ranging biological significance and high versatility as synthetic building blocks. Efficient synthesis of such non-proteinogenic amino acid derivatives must face the challenge of generating two contiguous stereocenters with complete diastereo- and enantiocontrol in flexible, acyclic molecules. The catalytic asymmetric direct Mannich reaction has provided elegant and efficient solutions for the stereocontrolled assembly of both syn- and anti-alpha,beta-diamino acid derivatives, including those with a alpha-tetrasubstituted carbon stereocenter, with the aid of either organometallic or purely organic chiral catalysts (or the combination of both). This tutorial review highlights progress in this area, which has recently been boosted through two complementary strategies: the direct Mannich reaction of glycine ester Schiff bases with imines and the direct aza-Henry reaction between nitro compounds and imines. PMID:19551174

  16. Bacillus pumilus Cyanide Dihydratase Mutants with Higher Catalytic Activity

    PubMed Central

    Crum, Mary A.; Sewell, B. Trevor; Benedik, Michael J.

    2016-01-01

    Cyanide degrading nitrilases are noted for their potential to detoxify industrial wastewater contaminated with cyanide. However, such application would benefit from an improvement to characteristics such as their catalytic activity and stability. Following error-prone PCR for random mutagenesis, several cyanide dihydratase mutants from Bacillus pumilus were isolated based on improved catalysis. Four point mutations, K93R, D172N, A202T, and E327K were characterized and their effects on kinetics, thermostability and pH tolerance were studied. K93R and D172N increased the enzyme’s thermostability whereas E327K mutation had a less pronounced effect on stability. The D172N mutation also increased the affinity of the enzyme for its substrate at pH 7.7 but lowered its kcat. However, the A202T mutation, located in the dimerization or the A surface, destabilized the protein and abolished its activity. No significant effect on activity at alkaline pH was observed for any of the purified mutants. These mutations help confirm the model of CynD and are discussed in the context of the protein–protein interfaces leading to the protein quaternary structure. PMID:27570524

  17. Bacillus pumilus Cyanide Dihydratase Mutants with Higher Catalytic Activity.

    PubMed

    Crum, Mary A; Sewell, B Trevor; Benedik, Michael J

    2016-01-01

    Cyanide degrading nitrilases are noted for their potential to detoxify industrial wastewater contaminated with cyanide. However, such application would benefit from an improvement to characteristics such as their catalytic activity and stability. Following error-prone PCR for random mutagenesis, several cyanide dihydratase mutants from Bacillus pumilus were isolated based on improved catalysis. Four point mutations, K93R, D172N, A202T, and E327K were characterized and their effects on kinetics, thermostability and pH tolerance were studied. K93R and D172N increased the enzyme's thermostability whereas E327K mutation had a less pronounced effect on stability. The D172N mutation also increased the affinity of the enzyme for its substrate at pH 7.7 but lowered its k cat. However, the A202T mutation, located in the dimerization or the A surface, destabilized the protein and abolished its activity. No significant effect on activity at alkaline pH was observed for any of the purified mutants. These mutations help confirm the model of CynD and are discussed in the context of the protein-protein interfaces leading to the protein quaternary structure. PMID:27570524

  18. Nanostructured Samarium Doped Fluorapatites and Their Catalytic Activity towards Synthesis of 1,2,4-Triazoles.

    PubMed

    Gangu, Kranthi Kumar; Maddila, Suresh; Maddila, Surya Narayana; Jonnalagadda, Sreekantha B

    2016-01-01

    An investigation was conducted into the influence of the amino acids as organic modifiers in the facile synthesis of metal incorporated fluorapatites (FAp) and their properties. The nanostructured Sm doped fluorapatites (Sm-FAp) were prepared by a co-precipitation method using four different amino acids, namely glutamic acid, aspartic acid, glycine and histidine. The materials were characterized by various techniques including X-ray diffraction (XRD), Fourier transform infra-red spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), high resolution transmission electron microscopy (HR-TEM), N₂-adsorption/desorption isotherm, temperature programmed desorption (TPD) and fluorescence spectrophotometry. Under similar conditions, Sm-FAp prepared using different amino acids exhibited distinctly different morphological structures, surface area and pore properties. Their activity as catalysts was assessed and Sm-FAp/Glycine displayed excellent efficiency in the synthesis of 1,2,4-triazole catalyzing the reaction between 2-nitrobenzaldehyde and thiosemicarbazide with exceptional selectivity and 98% yield in a short time interval (10 min). The study provides an insight into the role of organic modifiers as controllers of nucleation, growth and aggregation which significantly influence the nature and activity of the catalytic sites on Sm-FAp. Sm-FAp could also have potential as photoactive material. PMID:27669208

  19. Catalytic activities of platinum nanotubes: a density functional study

    NASA Astrophysics Data System (ADS)

    Mukherjee, Prajna; Gupta, Bikash C.; Jena, Puru

    2015-10-01

    In this work we investigate the catalytic properties of platinum nanotubes using density functional theory based calculations. In particular, we study the dissociation of hydrogen and oxygen molecules as well as oxidation of CO molecules. The results indicate that platinum nanotubes have good catalytic properties and can be effectively used in converting CO molecule to CO2.

  20. Synthesis of gold nanoparticles using renewable Punica granatum juice and study of its catalytic activity

    NASA Astrophysics Data System (ADS)

    Dash, Shib Shankar; Bag, Braja Gopal

    2014-01-01

    Punica granatum juice, a delicious multivitamin drink of great medicinal significance, is rich in different types of phytochemicals, such as terpenoids, alkaloids, sterols, polyphenols, sugars, fatty acids, aromatic compounds, amino acids, tocopherols, etc. We have demonstrated the use of the juice for the synthesis of gold nanoparticles (AuNPs) at room temperature under very mild conditions. The synthesis of the AuNPs was complete in few minutes and no extra stabilizing or capping agents were necessary. The size of the nanoparticles could be controlled by varying the concentration of the fruit extract. The AuNPs were characterized by surface plasmon resonance spectroscopy, high resolution transmission electron microscopy, fourier transform infrared spectroscopy and X-ray diffraction studies. Catalytic activity of the synthesized colloidal AuNPs has also been demonstrated.

  1. [Catalytic ozonation by ceramic honeycomb for the degradation of oxalic acid in aqueous solution].

    PubMed

    Zhao, Lei; Sun, Zhi-Zhong; Ma, Jun

    2007-11-01

    Comparative experiments for the degradation of oxalic acid in aqueous solution were carried out in the three processes of ozonation alone, ceramic honeycomb-catalyzed ozonation and ceramic honeycomb adsorption. The results show that the degradation rates of oxalic acid in the ceramic honeycomb-catalyzed ozonation, ozonation alone and ceramic honeycomb adsorption systems are 37.6%, 2.2% and 0.4%, and the presence of ceramic honeycomb catalyst significantly improves the degradation rate of oxalic acid compared to the results from non-catalytic ozonation and adsorption. With the addition of tert-butanol, the degradation rates of oxalic acid in catalytic ozonation system decrease by 24.1%, 29.0% and 30.1%, respectively, at the concentration of 5, 10 and 15 mg x L(-1). This phenomenon indicates that ceramic honeycomb-catalyzed ozonation for the degradation of oxalic acid in aqueous solution follows the mechanism of *OH oxidation, namely the heterogeneous surface of catalyst enhances the initiation of *OH. The results of TOC analysis demonstrate that the process of ceramic honeycomb-catalyzed ozonation can achieve the complete mineralization level without the formation of intermediary degradation products. The experimental results suggest that the reaction temperature has positive relationship with the degradation rate of oxalic acid. The degradation rates of oxalic acid in the ceramic honeycomb-catalyzed ozonation system are 16.4%, 37.6%, 61.3% and 68.2%, at the respective reaction temperature of 10, 20, 30 and 40 degrees C.

  2. Catalytic conversion of carbohydrates to 5-hydroxymethylfurfural from the waste liquid of acid hydrolysis NCC.

    PubMed

    Sun, Yonghui; Liu, Pengtao; Liu, Zhong

    2016-05-20

    The principal goal of this work was to reuse the carbohydrates and recycle sulfuric acid in the waste liquid of acid hydrolysis nanocrystalline cellulose (NCC). Therefore, in this work, the optimizations of further hydrolysis of waste liquid of acid hydrolysis NCC and catalytic conversion of L4 to 5-hydroxymethylfurfural (5-HMF) were studied. Sulfuric acid was separated by spiral wound diffusion dialysis (SWDD). The results revealed that cellulose can be hydrolyze to glucose absolutely under the condition of temperature 35 °C, 3 h, and sulfuric acid's concentration 62 wt%. And 78.3% sulfuric acid was recovered by SWDD. The yield of 5-HMF was highest in aqueous solution under the optimal condition was as follows, temperature 160 °C, 3 h, and sulfuric acid's concentration 12 wt%. Then the effect of biphasic solvent systems catalytic conversion and inorganic salt as additives were still examined. The results showed that both of them contributed to prepare 5-HMF. The yield and selectivity of 5-HMF was up to 21.0% and 31.4%, respectively.

  3. DGKθ Catalytic Activity is Required for Efficient Recycling of Presynaptic Vesicles at Excitatory Synapses

    PubMed Central

    Goldschmidt, Hana L.; Tu-Sekine, Becky; Volk, Lenora; Anggono, Victor; Huganir, Richard L.; Raben, Daniel M.

    2015-01-01

    Summary Synaptic transmission relies on coordinated coupling of synaptic vesicle (SV) exocytosis and endocytosis. While much attention has focused on characterizing proteins involved in SV recycling, the roles of membrane lipids and their metabolism remain poorly understood. Diacylglycerol, a major signaling lipid produced at synapses during synaptic transmission, is regulated by diacylglycerol kinase (DGK). Here we report a role for DGKθ in the mammalian central nervous system in facilitating recycling of presynaptic vesicles at excitatory synapses. Using synaptophysin- and vGlut1-pHluorin optical reporters, we found that acute and chronic deletion of DGKθ attenuated the recovery of SVs following neuronal stimulation. Rescue of recycling kinetics required DGKθ kinase activity. Our data establish a role for DGK catalytic activity and its byproduct, phosphatidic acid, at the presynaptic nerve terminal in SV recycling. Together these data suggest DGKθ supports synaptic transmission during periods of elevated neuronal activity. PMID:26748701

  4. Electronic and geometric effects of phosphatriazaadamantane ligands on the catalytic activity of an [FeFe] hydrogenase inspired complex.

    PubMed

    Vannucci, Aaron K; Wang, Shihua; Nichol, Gary S; Lichtenberger, Dennis L; Evans, Dennis H; Glass, Richard S

    2010-03-28

    The [FeFe] hydrogenase enzyme active site inspired complexes [Fe(2)(mu-C(6)H(4)S(2))(CO)(5)PTA] (1PTA) and [Fe(2)(mu-C(6)H(4)S(2))(CO)(4)PTA(2)] (1PTA(2)) (PTA = 1,3,5-triaza-7-phosphaadamantane) were synthesized and characterized. The ability of 1PTA and 1PTA(2) to catalytically produce molecular hydrogen in solution from the weak acid acetic acid was examined electrochemically and compared to previous studies on the all carbonyl containing analogue [Fe(2)(mu-C(6)H(4)S(2))(CO)(6)] (1). Computational methods and cyclic voltammograms indicated that the substitution of CO ligands by PTA in 1 resulted in markedly different reduction chemistry. Both 1PTA and 1PTA(2) catalytically produce molecular hydrogen from acetic acid, however, the mechanism by which and 1PTA and 1PTA(2) catalyze hydrogen differ in the initial reductive processes. PMID:20221539

  5. Synthesis, characterization and catalytic activity of carbon-silica hybrid catalyst from rice straw

    NASA Astrophysics Data System (ADS)

    Janaun, J.; Safie, N. N.; Siambun, N. J.

    2016-07-01

    The hybrid-carbon catalyst has been studied because of its promising potential to have high porosity and surface area to be used in biodiesel production. Silica has been used as the support to produce hybrid carbon catalyst due to its mesoporous structure and high surface area properties. The chemical synthesis of silica-carbon hybrid is expensive and involves more complicated preparation steps. The presence of natural silica in rice plants especially rice husk has received much attention in research because of the potential as a source for solid acid catalyst synthesis. But study on rice straw, which is available abundantly as agricultural waste is limited. In this study, rice straw undergone pyrolysis and functionalized using fuming sulphuric acid to anchor -SO3H groups. The presence of silica and the physiochemical properties of the catalyst produced were studied before and after sulphonation. The catalytic activity of hybrid carbon silica acid catalyst, (H-CSAC) in esterification of oleic acid with methanol was also studied. The results showed the presence of silica-carbon which had amorphous structure and highly porous. The carbon surface consisted of higher silica composition, had lower S element detected as compared to the surface that had high carbon content but lower silica composition. This was likely due to the fact that Si element which was bonded to oxygen was highly stable and unlikely to break the bond and react with -SO3H ions. H-CSAC conversions were 23.04 %, 35.52 % and 34.2 7% at 333.15 K, 343.15 K and 353.15 K, respectively. From this research, rice straw can be used as carbon precursor to produce hybrid carbon-silica catalyst and has shown catalytic activity in biodiesel production. Rate equation obtained is also presented.

  6. Formic Acid Free Flowsheet Development To Eliminate Catalytic Hydrogen Generation In The Defense Waste Processing

    SciTech Connect

    Lambert, Dan P.; Stone, Michael E.; Newell, J. David; Fellinger, Terri L.; Bricker, Jonathan M.

    2012-09-14

    The Defense Waste Processing Facility (DWPF) processes legacy nuclear waste generated at the Savannah River Site (SRS) during production of plutonium and tritium demanded by the Cold War. The nuclear waste is first treated via a complex sequence of controlled chemical reactions and then vitrified into a borosilicate glass form and poured into stainless steel canisters. Converting the nuclear waste into borosilicate glass canisters is a safe, effective way to reduce the volume of the waste and stabilize the radionuclides. Testing was initiated to determine whether the elimination of formic acid from the DWPF's chemical processing flowsheet would eliminate catalytic hydrogen generation. Historically, hydrogen is generated in chemical processing of alkaline High Level Waste sludge in DWPF. In current processing, sludge is combined with nitric and formic acid to neutralize the waste, reduce mercury and manganese, destroy nitrite, and modify (thin) the slurry rheology. The noble metal catalyzed formic acid decomposition produces hydrogen and carbon dioxide. Elimination of formic acid by replacement with glycolic acid has the potential to eliminate the production of catalytic hydrogen. Flowsheet testing was performed to develop the nitric-glycolic acid flowsheet as an alternative to the nitric-formic flowsheet currently being processed at the DWPF. This new flowsheet has shown that mercury can be reduced and removed by steam stripping in DWPF with no catalytic hydrogen generation. All processing objectives were also met, including greatly reducing the Slurry Mix Evaporator (SME) product yield stress as compared to the baseline nitric/formic flowsheet. Ten DWPF tests were performed with nonradioactive simulants designed to cover a broad compositional range. No hydrogen was generated in testing without formic acid.

  7. Catalytic trifluoromethylation of aryl- and vinylboronic acids by 2-cyclopropyl-1-(trifluoromethyl)benzo[b]thiophenium triflate.

    PubMed

    Arimori, Sadayuki; Shibata, Norio

    2015-04-01

    Catalytic trifluoromethylation of aryl- and vinylboronic acids by 2-cyclopropyl-1-(trifluoromethyl)benzo[b]thiophenium triflate is described. In the presence of a catalytic amount of CuOAc and 2,4,6-collidine in ethyl acetate, the reaction proceeded in good to high yields for various substrates under mild reaction conditions at room temperature. PMID:25783441

  8. Generation of a chickenized catalytic anti-nucleic acid antibody by complementarity-determining region grafting.

    PubMed

    Roh, Jooho; Byun, Sung June; Seo, Youngsil; KIm, Minjae; Lee, Jae-Ho; Kim, Songmi; Lee, Yuno; Lee, Keun Woo; Kim, Jin-Kyoo; Kwon, Myung-Hee

    2015-02-01

    In contrast to a number of studies on the humanization of non-human antibodies, the reshaping of a non-human antibody into a chicken antibody has never been attempted. Therefore, nothing is known about the animal species-dependent compatibility of the framework regions (FRs) that sustain the appropriate conformation of the complementarity-determining regions (CDRs). In this study, we attempted the reshaping of the variable domains of the mouse catalytic anti-nucleic acid antibody 3D8 (m3D8) into the FRs of a chicken antibody (“chickenization”) by CDR grafting, which is a common method for the humanization of antibodies. CDRs of the acceptor chicken antibody that showed a high homology to the FRs of m3D8 were replaced with those of m3D8, resulting in the chickenized antibody (ck3D8). ck3D8 retained the biochemical properties (DNA binding, DNA hydrolysis, and cellular internalizing activities) and three-dimensional structure of m3D8 and showed reduced immunogenicity in chickens. Our study demonstrates that CDR grafting can be applied to the chickenization of a mouse antibody, probably due to the interspecies compatibility of the FRs.

  9. Development of nitric oxide catalytic coatings by conjugating 3,3-disulfodipropionic acid and 3,3-diselenodipropionic acid for improving hemocompatibility.

    PubMed

    Yang, Ying; Li, Yalong; Li, Xiangyang; Qi, Pengkai; Tu, Qiufen; Yang, Zhilu; Huang, Nan

    2015-01-01

    Nitric oxide (NO), discovered as an endothelium-derived relaxing factor, has been found to have multiple intracellular effects in vascular diseases including vasorelaxation regulation, endothelial regeneration, inhibition of leukocyte chemotaxis, and platelet activation. In the work described here, the authors have developed a NO-catalytic bioactive coating for improving hemocompatibility. The authors first prepared a dopamine and hexamethylendiamine (PDAM/HD) amine-rich adherent copolymer coating to introduce amine groups onto 316L stainless steel, followed by covalently conjugating 3,3-disulfodipropionic acid (S-S) and 3,3-diselenodipropionic acid (Se-Se), which mimic glutathione peroxidase-like catalytic production of NO. S-S and Se-Se were immobilized on the PDAM/HD surface via carbodiimide coupling chemistry. X-ray photoelectron spectroscopy analysis revealed clear S2p and Se3d signals, confirming the immobilization of S-S and Se-Se on the PDAM/HD surface. The NO release behavior of different samples was investigated. In detail, two species of thionitrites (RSNO), S-nitrosoglutathione (GSNO, endogenous NO donors) and S-nitrosoacetylpenicillamine (SNAP) were chosen as NO donors to investigate the NO catalytic properties of S-S and Se-Se modified PDAM/HD surfaces. Not only Se-Se@PDAM/HD but also S-S@PDAM/HD coatings showed the ability to continuously catalyze RSNO to generate NO in the presence of proper thiol reducing agent. For the Se-Se@PDAM/HD coating, the NO release amount and rate were greater than S-S@PDAM/HD in both GSNO and SNAP conditions. The results showed that organosulfide species possesses NO catalytic ability as well as organoselenium species. The authors demonstrated that both S-S@PDAM/HD and Se-Se@PDAM/HD coatings exhibited outstanding inhibition effect on platelet adhesion, aggregation and activation via the cyclic guanylate monophosphate signal pathway. Thus these results suggested that NO catalytic coatings based on organoselenium and

  10. Catalytic Fast Pyrolysis of Lignin over High-Surface-Area Mesoporous Aluminosilicates: Effect of Porosity and Acidity.

    PubMed

    Custodis, Victoria B F; Karakoulia, Stamatia A; Triantafyllidis, Kostas S; van Bokhoven, Jeroen A

    2016-05-23

    Catalytic fast pyrolysis (CFP) of lignin with amorphous mesoporous aluminosilicates catalysts yields a high fraction of aromatics and a relatively low amount of char/coke. The relationship between the acidity and porosity of Al-MCM-41, Al-SBA-15, and Al-MSU-J with product selectivity during lignin CFP is determined. The acid sites (mild Brønsted and stronger Lewis) are able to catalyze pyrolysis intermediates towards fewer oxygenated phenols and aromatic hydrocarbons. A generalized correlation of the product selectivity and yield with the aluminum content and acidity of the mesoporous aluminosilicates is hard to establish. Zeolitic strong acid sites are not required to achieve high conversion and selectivity to aromatic hydrocarbon because nanosized MCM-41 produces a high liquid yield and selectivity. The two most essential parameters are diffusion, which is influenced by pore and grain size, and the active site, which may be mildly acidic, but is dominated by Lewis acid sites. Nanosized grains and mild acidity are essential ingredients for a good lignin CFP catalyst. PMID:27079742

  11. Catalytic Fast Pyrolysis of Lignin over High-Surface-Area Mesoporous Aluminosilicates: Effect of Porosity and Acidity.

    PubMed

    Custodis, Victoria B F; Karakoulia, Stamatia A; Triantafyllidis, Kostas S; van Bokhoven, Jeroen A

    2016-05-23

    Catalytic fast pyrolysis (CFP) of lignin with amorphous mesoporous aluminosilicates catalysts yields a high fraction of aromatics and a relatively low amount of char/coke. The relationship between the acidity and porosity of Al-MCM-41, Al-SBA-15, and Al-MSU-J with product selectivity during lignin CFP is determined. The acid sites (mild Brønsted and stronger Lewis) are able to catalyze pyrolysis intermediates towards fewer oxygenated phenols and aromatic hydrocarbons. A generalized correlation of the product selectivity and yield with the aluminum content and acidity of the mesoporous aluminosilicates is hard to establish. Zeolitic strong acid sites are not required to achieve high conversion and selectivity to aromatic hydrocarbon because nanosized MCM-41 produces a high liquid yield and selectivity. The two most essential parameters are diffusion, which is influenced by pore and grain size, and the active site, which may be mildly acidic, but is dominated by Lewis acid sites. Nanosized grains and mild acidity are essential ingredients for a good lignin CFP catalyst.

  12. Synthesis, structure characterization and catalytic activity of nickel tungstate nanoparticles

    NASA Astrophysics Data System (ADS)

    Pourmortazavi, Seied Mahdi; Rahimi-Nasrabadi, Mehdi; Khalilian-Shalamzari, Morteza; Zahedi, Mir Mahdi; Hajimirsadeghi, Seiedeh Somayyeh; Omrani, Ismail

    2012-12-01

    Taguchi robust design was applied to optimize experimental parameters for controllable, simple and fast synthesis of nickel tungstate nanoparticles. NiWO4 nanoparticles were synthesized by precipitation reaction involving addition of nickel ion solution to the tungstate aqueous reagent and then formation of nickel tungstate nucleolus which are insoluble in aqueous media. Effects of various parameters such as nickel and tungstate concentrations, flow rate of reagent addition and reactor temperature on diameter of synthesized nickel tungstate nanoparticles were investigated experimentally by the aid of orthogonal array design. The results for analysis of variance (ANOVA) showed that particle size of nickel tungstate can be effectively tuned by controlling significant variables involving nickel and tungstate concentrations and flow rate; while, temperature of the reactor has a no considerable effect on the size of NiWO4 particles. The ANOVA results proposed the optimum conditions for synthesis of nickel tungstate nanoparticles via this technique. Also, under optimum condition nanoparticles of NiWO4 were prepared and their structure and chemical composition were characterized by means of EDAX, XRD, SEM, FT-IR spectroscopy, UV-vis spectroscopy, and photoluminescence. Finally, catalytic activity of the nanoparticles in a cycloaddition reaction was examined.

  13. Controlling the Growth and Catalytic Activity of Platinum Nanoparticles Using Peptide and Polymer Ligands

    NASA Astrophysics Data System (ADS)

    Forbes, Lauren Marie

    Heterogeneous catalysts have widespread industrial applications. Platinum nanomaterials in particular, due to their particularly high electrocatalytic activity and durability, are used to catalyze a wide variety of reactions, including oxygen reduction, which is frequently used as the cathode reaction in fuel cells. As platinum is a very expensive material, a high priority in fuel cell research is the exploration of less expensive, more efficient catalysts for the oxygen reduction reaction (ORR). We demonstrate here the use of phage display to identify peptides that bind to Pt (100) which were then used to synthesize platinum cubes in solution. However, while the peptides were able to control particle growth, the bio-synthesized Pt particles showed extremely poor activity when tested for ORR. This could be attributed to peptide coverage on the surface or strong interactions between particular amino acids and the metal that are detrimental for catalysis. To investigate this further, we decided to investigate the role of individual amino acids on Pt nanocrystal synthesis and catalysis. For this, we conjugated the R-groups of single amino acids to polyethylene glycol (PEG) chains. Through this work we have determined that the identity of the amino acid R-group is important in both the synthesis and the catalytic activity of the particles. For Pt nanoparticle synthesis, we found that the hydrophobicity of the functional groups affected their ability to interact well with the particles during nucleation and growth, and thus only the hydrophilic functional groups were capable of mediating the synthesis to produce well-defined faceted particles. With respect to ORR, we found distinct trends that showed that the inclusion of certain amino acids could significantly enhance catalysis---even at high polymer loadings. This work presents evidence that counters the common conception that organic capping ligands decrease catalytic activity; in fact activity may actually be

  14. Green synthesis of silver nanoparticles from Gloriosa superba L. leaf extract and their catalytic activity

    NASA Astrophysics Data System (ADS)

    Ashokkumar, S.; Ravi, S.; Velmurugan, S.

    2013-11-01

    The present work focuses the use of aqueous extract of Gloriosa superba Linn. (Glory Lily) for producing silver nanoparticles (AgNPs) from silver nitrate aqueous solution. Phytochemical analysis of the extract revealed the presence of alkaloid, amino acids, carbohydrates and proteins in the extract and they serve as effective reducing and capping agents for converting silver nitrate to silver nanoparticles. The nanoparticles were characterised by UV (Ultra violet), FT-IR (Fourier Transform Infrared), XRD (X-ray diffraction), TEM (Transmission Electron Microscope) SEM-EDX (Scanning Electron Microscopy-Energy Dispersive X-ray), and PL (Photoluminescence) studies. Moreover, the catalytic activity of synthesized AgNPs in the reduction of methylene blue was studied by UV-vis spectrophotometer. The synthesized AgNPs are observed to have a good catalytic activity on the reduction of methylene blue by G. superba extract which is confirmed by the decrease in absorbance maximum values of methylene blue with respect to time using UV-vis spectrophotometer.

  15. Active Site, Catalytic Cycle, and Iodination Reactions of Vanadium Iodoperoxidase: A Computational Study.

    PubMed

    Pacios, Luis F; Gálvez, Oscar

    2010-05-11

    A combined computational study using molecular surfaces and Poisson-Boltzmann electrostatic potentials for proteins and quantum calculations on complexes representing the vanadate cofactor throughout the catalytic cycle is employed to study the activity of vanadium iodoperoxidase (VIPO) from alga Laminaria digitata . A model structure of VIPO is compared with available crystal structures of chloroperoxidases (VClPOs) and bromoperoxidases (VBrPOs) focusing on properties of the active site that concern halogen specificity. It is found that VIPO displays distinctive features regarding electrostatic potentials at the site cavity and the local topography of the cavity entrance. Quantum calculations on cofactor stages throughout the catalytic cycle reveal that, while steps involving binding of hydrogen peroxide and halide oxidization agree with available data on VBrPO, final formation and subsequent release of hypohalous acid could follow a different pathway consisting of His476-assisted protonation of bonded hypoiodite and further displacement by a water molecule. Ab initio free energies of reaction computed to explore iodination of organic substrates predict strongly exoergonic reactions with HOI, whereas other possible iodination reagents give thermodynamically disfavored reactions.

  16. Conjugate-base-stabilized Brønsted acids: catalytic enantioselective Pictet-Spengler reactions with unmodified tryptamine.

    PubMed

    Mittal, Nisha; Sun, Diana X; Seidel, Daniel

    2014-02-01

    A conjugate-base-stabilized Brønsted acid facilitates catalytic enantioselective Pictet-Spengler reactions with unmodified tryptamine. The chiral carboxylic acid catalyst is readily assembled in just two steps and enables the formation of β-carbolines with up to 92% ee. Achiral acid additives or in situ Boc-protection facilitate catalyst turnover.

  17. A Lamellar Coordination Polymer with Remarkable Catalytic Activity.

    PubMed

    Mendes, Ricardo F; Antunes, Margarida M; Silva, Patrícia; Barbosa, Paula; Figueiredo, Filipe; Linden, Anthony; Rocha, João; Valente, Anabela A; Almeida Paz, Filipe A

    2016-09-01

    A positively charged lamellar coordination polymer based on a flexible triphosphonic acid linker is reported. [Gd(H4 nmp)(H2 O)2 ]Cl⋅2 H2 O (1) [H6 nmp=nitrilotris(methylenephosphonic acid)] was obtained by a one-pot approach by using water as a green solvent and by forcing the inclusion of additional acid sites by employing HCl in the synthesis. Compound 1 acts as a versatile heterogeneous acid catalyst with outstanding activity in organic reactions such as alcoholysis of styrene oxide, acetalization of benzaldehyde and cyclohexanaldehyde and ketalization of cyclohexanone. For all reaction systems, very high conversions were reached (92-97 %) in only 15-30 min under mild conditions (35 °C, atmospheric pressure). The coordination polymer exhibits a protonic conductivity of 1.23×10(-5)  S cm(-1) at 98 % relative humidity and 40 °C. PMID:27505712

  18. Effect of citrate on Aspergillus niger phytase adsorption and catalytic activity in soil

    NASA Astrophysics Data System (ADS)

    Mezeli, Malika; Menezes-Blackburn, Daniel; Zhang, Hao; Giles, Courtney; George, Timothy; Shand, Charlie; Lumsdon, David; Cooper, Patricia; Wendler, Renate; Brown, Lawrie; Stutter, Marc; Blackwell, Martin; Darch, Tegan; Wearing, Catherine; Haygarth, Philip

    2015-04-01

    Current developments in cropping systems that promote mobilisation of phytate in agricultural soils, by exploiting plant-root exudation of phytase and organic acids, offer potential for developments in sustainable phosphorus use. However, phytase adsorption to soil particles and phytate complexion has been shown to inhibit phytate dephosphorylation, thereby inhibiting plant P uptake, increasing the risk of this pool contributing to diffuse pollution and reducing the potential benefits of biotechnologies and management strategies aimed to utilise this abundant reserve of 'legacy' phosphorus. Citrate has been seen to increase phytase catalytic efficiency towards complexed forms of phytate, but the mechanisms by which citrate promotes phytase remains poorly understood. In this study, we evaluated phytase (from Aspergillus niger) inactivation, and change in catalytic properties upon addition to soil and the effect citrate had on adsorption of phytase and hydrolysis towards free, precipitated and adsorbed phytate. A Langmuir model was fitted to phytase adsorption isotherms showing a maximum adsorption of 0.23 nKat g-1 (19 mg protein g-1) and affinity constant of 435 nKat gˉ1 (8.5 mg protein g-1 ), demonstrating that phytase from A.niger showed a relatively low affinity for our test soil (Tayport). Phytases were partially inhibited upon adsorption and the specific activity was of 40.44 nKat mgˉ1 protein for the free enzyme and 25.35 nKat mgˉ1 protein when immobilised. The kinetics of adsorption detailed that most of the adsorption occurred within the first 20 min upon addition to soil. Citrate had no effect on the rate or total amount of phytase adsorption or loss of activity, within the studied citrate concentrations (0-4mM). Free phytases in soil solution and phytase immobilised on soil particles showed optimum activity (>80%) at pH 4.5-5.5. Immobilised phytase showed greater loss of activity at pH levels over 5.5 and lower activities at the secondary peak at pH 2

  19. Synthesis and characterization of vanadium nanoparticles on activated carbon and their catalytic activity in thiophene hydrodesulphurization

    NASA Astrophysics Data System (ADS)

    Pinto, Susana; D'Ornelas, Lindora; Betancourt, Paulino

    2008-06-01

    Vanadium nanoparticles (˜7 nm) stabilized on activated carbon were synthesized by the reduction of VCl 3·3THF with K[BEt 3H]. This material was characterized by inductive coupled plasma-atomic emission spectroscopy (ICP-AES), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) analyses. The catalytic performance of the carbon-supported vanadium was studied using thiophene hydrodesulfurization (HDS) as model reaction at 300 °C and P = 1 atm. The catalytic activity of the vanadium carbide phase on the activated carbon carrier was more significant than that of the reference catalysts, alumina supported NiMoS. The method proposed for the synthesis of such a catalyst led to an excellent performance of the HDS process.

  20. Scandium trifluoromethanesulfonate as an extremely active Lewis acid catalyst in acylation of alcohols with acid anhydrides and mixed anhydrides

    SciTech Connect

    Ishihara, K.; Kubota, M.; Kurihara, H.; Yamamoto, H.

    1996-07-12

    Scandium triflate catalyzes the acylation of alcohols with acid anhydrides or the esterification of alcohols by carboxylic acids in the presence of p-nitrobenzoic anhydrides. The catalytic activity of the scandium triflates is found to be quite high allowing the acylation of secondary and tertiary alcohols.

  1. Degradation of 4-hydroxybenzoic acid by combined ultrasound irradiation and catalytic wet peroxide oxidation.

    PubMed

    Nikolopoulos, Apostolos N; Igglessi-Markopoulou, Olga; Papayannakos, Nikolaos

    2004-05-01

    The aim of this study is to explore the potential benefits from the combined use of ultrasound irradiation and catalytic wet peroxide oxidation for the degradation of 4-hydroxybenzoic acid (4-HBA). The target compound degradation was studied under direct and indirect sonication, while silent conditions were employed as reference. The catalyst, a mixed (Al-Fe) pillared clay named FAZA, was in the form of powder and of extrudates. In the case of extrudates it was observed that ultrasound improves the catalyst performance due to reduction of diffusion resistance, thereby increasing the conversion after 4 h by 12-15 times. Increasing the initial concentration of 4-HBA was found to lead to lower conversion. The combined ultrasonic/catalytic process appears very promising for environmental applications. PMID:15081978

  2. Effects of surface activation on the structural and catalytic properties of ruthenium nanoparticles supported on mesoporous silica

    NASA Astrophysics Data System (ADS)

    Ma, Xianfeng; Lin, Rui; Beuerle, Christopher; Jackson, James E.; Obare, Sherine O.; Ofoli, Robert Y.

    2014-01-01

    Using colloid-based methods to prepare supported catalytic metallic nanoparticles (NPs) often faces the challenge of removing the stabilizer used during synthesis and activating the catalyst without modifying the particles or the support. We explored three surface activation protocols (thermal oxidation at 150 ° C, thermal reduction at 350 ° C, and argon-protected calcination at 650 ° C) to activate ruthenium NPs supported on mesoporous silica (MSU-F), and assessed their effects on the structural and catalytic properties of the catalysts, and their activity by the aqueous phase hydrogenation of pyruvic acid. The NPs were synthesized by polyol reduction using poly-N-vinyl-2-pyrrolidone (PVP) as a stabilizer, and supported on MSU-F by sonication-assisted deposition. The NPs maintained their original morphology on the support during activation. Ar-protected calcination was the most efficient of the three for completely removing PVP from particle surfaces, and provided the highest degree of particle crystallinity and a metal dispersion comparable to commercial Ru/SiO2. Its catalytic performance was significantly higher than the other two protocols, although all three thermally activated catalysts achieved higher activity than the commercial catalyst at the same Ru loading. Post-reaction analysis also showed that the supported catalyst activated at 650 ° C retained its morphology during the reaction, which is an important requirement for recyclability.

  3. Optical activity of catalytic elements of hetero-metallic nanostructures

    NASA Astrophysics Data System (ADS)

    Antosiewicz, Tomasz J.; Apell, S. Peter; Wadell, Carl; Langhammer, Christoph

    2015-05-01

    Interaction of light with metals in the form of surface plasmons is used in a wide range of applications in which the scattering decay channel is important. The absorption channel is usually thought of as unwanted and detrimental to the efficiency of the device. This is true in many applications, however, recent studies have shown that maximization of the decay channel of surface plasmons has potentially significant uses. One of these is the creation of electron-hole pairs or hot electrons which can be used for e.g. catalysis. Here, we study the optical properties of hetero-metallic nanostructures that enhance light interaction with the catalytic elements of the nanostructures. A hybridized LSPR that matches the spectral characteristic of the light source is excited. This LSPR through coupling between the plasmonic elements maximizes light absorption in the catalytic part of the nanostructure. Numerically calculated visible light absorption in the catalytic nanoparticles is enhanced 12-fold for large catalytic disks and by more 30 for small nanoparticles on the order of 5 nm. In experiments we measure a sizable increase in the absorption cross section when small palladium nanoparticles are coupled to a large silver resonator. These observations suggest that heterometallic nanostructures can enhance catalytic reaction rates.

  4. The catalytic role of aspartic acid-92 in a human dual-specific protein-tyrosine-phosphatase.

    PubMed

    Denu, J M; Zhou, G; Guo, Y; Dixon, J E

    1995-03-14

    The mechanism of catalysis for the human dual-specific (vaccinia H1-related) protein-tyrosine-phosphatase was investigated. The pH dependence of the kcat value is bell-shaped when p-nitrophenyl phosphate was employed as a model substrate. The kcat/Km pH profile rises with a slope of 2 and decreases with a slope of -1, indicating that two groups must be unprotonated and one group must be protonated for activity. An amino acid residue with an apparent pKa value of 5.5 +/- 0.2 must be unprotonated and a residue with a pKa value of 5.7 must be unprotonated for activity. The pKa value of the catalytic cysteine-124 (C124) was 5.6 +/- 0.1. The aspartic acid-92-asparagine (D92N) mutant enzyme was 100-fold less active than the native enzyme and exhibited the loss of the basic limb in the pH profiles, suggesting that in the native enzyme D92 must be protonated for activity. The D92 residue is conserved throughout the entire family of dual-specific phosphatases. Mutants glutamic acid-6-glutamine, glutamic acid-32-glutamine, aspartic acid-14-asparagine, and aspartic acid-110-asparagine had less than a 2-fold effect on the kinetic parameters when compared to native enzyme. Based upon the lack of a "burst" in rapid reaction kinetics, formation of the intermediate is rate-limiting with both native and D92N mutant enzymes. In agreement with rate-limiting formation of the intermediate, the pKa value of 5.5 for the group which must be unprotonated for activity was assigned to C124.(ABSTRACT TRUNCATED AT 250 WORDS)

  5. Single-Molecule Nanocatalysis Reveals Catalytic Activation Energy of Single Nanocatalysts.

    PubMed

    Chen, Tao; Zhang, Yuwei; Xu, Weilin

    2016-09-28

    By monitoring the temperature-dependent catalytic activity of single Au nanocatalysts for a fluorogenic reaction, we derive the activation energies via multiple methods for two sequential catalytic steps (product formation and dissociation) on single nanocatalysts. The wide distributions of activation energies across multiple individual nanocatalysts indicate a huge static heterogeneity among the individual nanocatalysts. The compensation effect and isokinetic relationship of catalytic reactions are observed at the single particle level. This study exemplifies another function of single-molecule nanocatalysis and improves our understanding of heterogeneous catalysis.

  6. Direct Catalytic Asymmetric Synthesis of β-Hydroxy Acids from Malonic Acid.

    PubMed

    Gao, Hang; Luo, Zhenli; Ge, Pingjin; He, Junqian; Zhou, Feng; Zheng, Peipei; Jiang, Jun

    2015-12-18

    A nickel(II) catalyzed asymmetric synthesis of β-hydroxy acids from malonic acid and ketones was developed, revealing for the first time the synthetic utility of malonic acid in the construction of chiral carboxyl acids; importantly, the synthetic potential of this strategy was further demonstrated by the rapid construction of cephalanthrin A, phaitanthrin B, cruciferane, and rice metabolites.

  7. Phoenix dactylifera L. leaf extract phytosynthesized gold nanoparticles; controlled synthesis and catalytic activity

    NASA Astrophysics Data System (ADS)

    Zayed, Mervat F.; Eisa, Wael H.

    2014-03-01

    A green synthesis route was reported to explore the reducing and capping potential of Phoenix dactylifera extract for the synthesis of gold nanoparticles. The processes of nucleation and growth of gold nanoparticles were followed by monitoring the absorption spectra during the reaction. The size and morphology of these nanoparticles was typically imaged using transmission electron microscopy (TEM). The particle size ranged between 32 and 45 nm and are spherical in shape. Fourier transform infrared (FTIR) analysis suggests that the synthesized gold nanoparticles might be stabilized through the interactions of hydroxyl and carbonyl groups in the carbohydrates, flavonoids, tannins and phenolic acids present in P. dactylifera. The as-synthesized Au colloids exhibited good catalytic activity for the degradation of 4-nitrophenol.

  8. DEVELOPMENT OF HIGH ACTIVITY, CATALYTIC SYSTEMS FOR NOx REDUCTION

    SciTech Connect

    Unknown

    2001-12-01

    This project was directed at an investigation of catalytic NO{sub x} reduction on carbonaceous supports at low temperatures. The experimental work was conducted primarily in a packed bed reactor/gas flow system that was constructed for this work. The analytical techniques employed were mass spectrometry, NO{sub x} chemiluminescence, and gas chromatography. The experimental plan was focused on steady-state reactivity experiments, followed by temperature programmed desorption (TPD) of surface intermediates, and also selected temperature-programmed reaction (TPR) experiments. Both uncatalyzed and catalyzed (potassium-promoted) phenolic resin char, were investigated as well as the catalytic effect of additional CO in the gas phase.

  9. High performing and stable supported nano-alloys for the catalytic hydrogenation of levulinic acid to γ-valerolactone

    NASA Astrophysics Data System (ADS)

    Luo, Wenhao; Sankar, Meenakshisundaram; Beale, Andrew M.; He, Qian; Kiely, Christopher J.; Bruijnincx, Pieter C. A.; Weckhuysen, Bert M.

    2015-03-01

    The catalytic hydrogenation of levulinic acid, a key platform molecule in many biorefinery schemes, into γ-valerolactone is considered as one of the pivotal reactions to convert lignocellulose-based biomass into renewable fuels and chemicals. Here we report on the development of highly active, selective and stable supported metal catalysts for this reaction and on the beneficial effects of metal nano-alloying. Bimetallic random alloys of gold-palladium and ruthenium-palladium supported on titanium dioxide are prepared with a modified metal impregnation method. Gold-palladium/titanium dioxide shows a marked,~27-fold increase in activity (that is, turnover frequency of 0.1 s-1) compared with its monometallic counterparts. Although ruthenium-palladium/titanium dioxide is not only exceptionally active (that is, turnover frequency of 0.6 s-1), it shows excellent, sustained selectivity to γ-valerolactone (99%). The dilution and isolation of ruthenium by palladium is thought to be responsible for this superior catalytic performance. Alloying, furthermore, greatly improves the stability of both supported nano-alloy catalysts.

  10. High performing and stable supported nano-alloys for the catalytic hydrogenation of levulinic acid to γ-valerolactone

    PubMed Central

    Luo, Wenhao; Sankar, Meenakshisundaram; Beale, Andrew M.; He, Qian; Kiely, Christopher J.; Bruijnincx, Pieter C. A.; Weckhuysen, Bert M.

    2015-01-01

    The catalytic hydrogenation of levulinic acid, a key platform molecule in many biorefinery schemes, into γ-valerolactone is considered as one of the pivotal reactions to convert lignocellulose-based biomass into renewable fuels and chemicals. Here we report on the development of highly active, selective and stable supported metal catalysts for this reaction and on the beneficial effects of metal nano-alloying. Bimetallic random alloys of gold-palladium and ruthenium-palladium supported on titanium dioxide are prepared with a modified metal impregnation method. Gold-palladium/titanium dioxide shows a marked,~27-fold increase in activity (that is, turnover frequency of 0.1 s−1) compared with its monometallic counterparts. Although ruthenium-palladium/titanium dioxide is not only exceptionally active (that is, turnover frequency of 0.6 s−1), it shows excellent, sustained selectivity to γ-valerolactone (99%). The dilution and isolation of ruthenium by palladium is thought to be responsible for this superior catalytic performance. Alloying, furthermore, greatly improves the stability of both supported nano-alloy catalysts. PMID:25779385

  11. The stability and catalytic activity of W13@Pt42 core-shell structure

    PubMed Central

    Huo, Jin-Rong; Wang, Xiao-Xu; Li, Lu; Cheng, Hai-Xia; Su, Yan-Jing; Qian, Ping

    2016-01-01

    This paper reports a study of the electronic properties, structural stability and catalytic activity of the W13@Pt42 core-shell structure using the First-principles calculations. The degree of corrosion of W13@Pt42 core-shell structure is simulated in acid solutions and through molecular absorption. The absorption energy of OH for this structure is lower than that for Pt55, which inhibits the poison effect of O containing intermediate. Furthermore we present the optimal path of oxygen reduction reaction catalyzed by W13@Pt42. Corresponding to the process of O molecular decomposition, the rate-limiting step of oxygen reduction reaction catalyzed by W13@Pt42 is 0.386 eV, which is lower than that for Pt55 of 0.5 eV. In addition by alloying with W, the core-shell structure reduces the consumption of Pt and enhances the catalytic efficiency, so W13@Pt42 has a promising perspective of industrial application. PMID:27759038

  12. Synthesis of Water Dispersible and Catalytically Active Gold-Decorated Cobalt Ferrite Nanoparticles.

    PubMed

    Silvestri, Alessandro; Mondini, Sara; Marelli, Marcello; Pifferi, Valentina; Falciola, Luigi; Ponti, Alessandro; Ferretti, Anna Maria; Polito, Laura

    2016-07-19

    Hetero-nanoparticles represent an important family of composite nanomaterials that in the past years are attracting ever-growing interest. Here, we report a new strategy for the synthesis of water dispersible cobalt ferrite nanoparticles (CoxFe3-xO4 NPs) decorated with ultrasmall (2-3 nm) gold nanoparticles (Au NPs). The synthetic procedure is based on the use of 2,3-meso-dimercaptosuccinic acid (DMSA), which plays a double role. First, it transfers cobalt ferrite NPs from the organic phase to aqueous media. Second, the DMSA reductive power promotes the in situ nucleation of gold NPs in proximity of the magnetic NP surface. Following this procedure, we achieved a water dispersible nanosystem (CoxFe3-xO4-DMSA-Au NPs) which combines the cobalt ferrite magnetic properties with the catalytic features of ultrasmall Au NPs. We showed that CoxFe3-xO4-DMSA-Au NPs act as an efficient nanocatalyst to reduce 4-nitrophenol to 4-aminophenol and that they can be magnetically recovered and recycled. It is noteworthy that such nanosystem is more catalytically active than Au NPs with equal size. Finally, a complete structural and chemical characterization of the hetero-NPs is provided.

  13. Surface engineering on CeO2 nanorods by chemical redox etching and their enhanced catalytic activity for CO oxidation

    NASA Astrophysics Data System (ADS)

    Gao, Wei; Zhang, Zhiyun; Li, Jing; Ma, Yuanyuan; Qu, Yongquan

    2015-07-01

    Controllable surface properties of nanocerias are desired for various catalytic processes. There is a lack of efficient approaches to adjust the surface properties of ceria to date. Herein, a redox chemical etching method was developed to controllably engineer the surface properties of ceria nanorods. Ascorbic acid and hydrogen peroxide were used to perform the redox chemical etching process, resulting in a rough surface and/or pores on the surface of ceria nanorods. Increasing the etching cycles induced a steady increase of the specific surface area, oxygen vacancies and surface Ce3+ fractions. As a result, the etched nanorods delivered enhanced catalytic activity for CO oxidation, compared to the non-etched ceria nanorods. Our method provides a novel and facile approach to continuously adjust the surface properties of ceria for practical applications.Controllable surface properties of nanocerias are desired for various catalytic processes. There is a lack of efficient approaches to adjust the surface properties of ceria to date. Herein, a redox chemical etching method was developed to controllably engineer the surface properties of ceria nanorods. Ascorbic acid and hydrogen peroxide were used to perform the redox chemical etching process, resulting in a rough surface and/or pores on the surface of ceria nanorods. Increasing the etching cycles induced a steady increase of the specific surface area, oxygen vacancies and surface Ce3+ fractions. As a result, the etched nanorods delivered enhanced catalytic activity for CO oxidation, compared to the non-etched ceria nanorods. Our method provides a novel and facile approach to continuously adjust the surface properties of ceria for practical applications. Electronic supplementary information (ESI) available: Diameter distributions of as-prepared and etched samples, optical images, specific catalytic data of CO oxidation and comparison of CO oxidation. See DOI: 10.1039/c5nr01846c

  14. Correction: Towards the rationalization of catalytic activity values by means of local hyper-softness on the catalytic site: a criticism about the use of net electric charges.

    PubMed

    Martínez-Araya, Jorge Ignacio; Grand, André; Glossman-Mitnik, Daniel

    2016-01-28

    Correction for 'Towards the rationalization of catalytic activity values by means of local hyper-softness on the catalytic site: a criticism about the use of net electric charges' by Jorge Ignacio Martínez-Araya et al., Phys. Chem. Chem. Phys., 2015, DOI: 10.1039/c5cp03822g.

  15. Correction: Towards the rationalization of catalytic activity values by means of local hyper-softness on the catalytic site: a criticism about the use of net electric charges.

    PubMed

    Martínez-Araya, Jorge Ignacio; Grand, André; Glossman-Mitnik, Daniel

    2016-01-28

    Correction for 'Towards the rationalization of catalytic activity values by means of local hyper-softness on the catalytic site: a criticism about the use of net electric charges' by Jorge Ignacio Martínez-Araya et al., Phys. Chem. Chem. Phys., 2015, DOI: 10.1039/c5cp03822g. PMID:26524565

  16. Cu-SSZ-39, an active and hydrothermally stable catalyst for the selective catalytic reduction of NOx.

    PubMed

    Moliner, Manuel; Franch, Cristina; Palomares, Eduardo; Grill, Marie; Corma, Avelino

    2012-08-25

    A Cu-exchanged SSZ-39 zeolite has been synthesized and tested for the selective catalytic reduction (SCR) of NOx. This material shows an excellent catalytic activity, and most importantly, an extraordinary hydrothermal stability.

  17. Physicochemical properties and catalytic activity of metal tetraphenyl porphins in the oxidation of alkylaromatic hydrocarbons

    NASA Astrophysics Data System (ADS)

    Kobotaeva, N. S.; Skorokhodova, T. S.; Kokova, D. A.

    2013-06-01

    We consider the effect of complexing metal in a tetraphenylporphin molecule on its catalytic activity in oxidizing alkylaromatic hydrocarbons by molecular oxygen. The catalytic activity of metal porphyrins (Co, Cu, Zn, Mn, and In TPP) is found to depend on their oxidation potentials and the distribution of electron density in the molecule. The electron-donating compound imidazole is shown to affect the oxidation rate.

  18. Characterization of AlFe-pillared Unye bentonite: A study of the surface acidity and catalytic property

    NASA Astrophysics Data System (ADS)

    Caglar, Bulent; Cubuk, Osman; Demir, Ersin; Coldur, Fatih; Catir, Mustafa; Topcu, Cihan; Tabak, Ahmet

    2015-06-01

    Aluminium-iron-pillared bentonite has been prepared by incorporation of the iron mixed aluminium-polyoxocation into bentonite layers and characterized by the powder X-ray diffraction, Fourier transform infrared, thermal analysis and surface area measurement techniques. The characteristic d001 basal spacing of raw bentonite increased with the pillaring process and reached to 18.05 Å. The siloxane layers of bentonite were perturbed and the positions of Si-O stretching vibrations were altered by pillaring process. However, these pillars in the interlayer gallery spacing enhanced the thermal stability of bentonite. The new micropores were formed by the pillaring process and the specific surface area of raw bentonite increased by ca. 2-fold for aluminium-iron-pillared bentonite. FTIR spectra and thermal analysis curves of pyridine adsorbed samples clearly show that the surface Lewis acidity of aluminium-iron-pillared bentonite is greater than that of raw bentonite. Raw and aluminium-iron-pillared bentonites have been utilized as solid catalysts for benzoylation of benzene with benzoyl chloride. The aluminium-iron-pillared bentonite catalyst showed promising catalytic activity whereas raw bentonite showed no catalytic activity in benzoylation of benzene with benzoyl chloride.

  19. Simultaneous realization of high catalytic activity and stability for catalytic cracking of n-heptane on highly exposed (010) crystal planes of nanosheet ZSM-5 zeolite.

    PubMed

    Xiao, Xia; Zhang, Yaoyuan; Jiang, Guiyuan; Liu, Jia; Han, Shanlei; Zhao, Zhen; Wang, Ruipu; Li, Cong; Xu, Chunming; Duan, Aijun; Wang, Yajun; Liu, Jian; Wei, Yuechang

    2016-08-01

    Nanosheet ZSM-5 zeolite with highly exposed (010) crystal planes demonstrates high reactivity and good anti-coking stability for the catalytic cracking of n-heptane, which is attributed to the synergy of high external surface area and acid sites, fully accessible channel intersection acid sites, and hierarchical porosity caused by the unique morphology.

  20. Catalytic activity for nitrate electroreduction of nano-structured polypyrrole films electrochemically synthesized onto a copper electrode

    NASA Astrophysics Data System (ADS)

    Phuong Thoa Nguyen, Thi; Thinh Nguyen, Viet; Hai Le, Viet

    2010-03-01

    Polypyrrole film was synthesized electrochemically onto a copper electrode in oxalate, oxalic acid and salicylic acid solutions. The electrochemical oxidation of pyrrole to form polypyrrole film and the electroreduction of nitrate and nitrite ions at synthesized Ppy modified copper electrodes (Ppy/Cu) in potassium chloride aqueous solutions were studied by cyclic voltammetry. Polypyrrole nano-porous film formation and the activity of the modified Ppy/Cu electrode for nitrate reduction were found to be dependent on the synthesis medium and conditions: pH; content and concentrations of the electrolytes; pyrrole concentration; electrode potential; electrolysis duration; drying time and temperature for finishing the Ppy/Cu electrode and immersion time in water for storing the Ppy/Cu electrode before use. High catalytic activity for nitrate reduction was found for composite electrodes with nano-porous structured Ppy films. The Ppy/Cu electrodes prepared in oxalate buffer and salicylic acid solutions perform more stable catalytic activity for nitrate reduction; their service life is about ten times longer than for an electrode prepared in oxalic acid solution.

  1. Copper metal-organic framework nanocrystal for plane effect nonenzymatic electro-catalytic activity of glucose

    NASA Astrophysics Data System (ADS)

    Liu, Yuanying; Zhang, Youjuan; Chen, Jing; Pang, Huan

    2014-09-01

    This work describes the first demonstration of nanocrystal plane dependent nonenzymatic electro-catalytic glucose activity of [Cu3(btc)2] nanocrystals with different shapes (nanocube, truncated cube, cuboctahedron, and octahedron). From electrochemical results, the obtained [Cu3(btc)2] nanocube modified electrode shows the best nonenzymatic electro-catalytic glucose activity. Interestingly, decreasing the {100} crystal planes from cubes to octahedra, changes the nonenzymatic electro-catalytic activity from highly sensitive to general.This work describes the first demonstration of nanocrystal plane dependent nonenzymatic electro-catalytic glucose activity of [Cu3(btc)2] nanocrystals with different shapes (nanocube, truncated cube, cuboctahedron, and octahedron). From electrochemical results, the obtained [Cu3(btc)2] nanocube modified electrode shows the best nonenzymatic electro-catalytic glucose activity. Interestingly, decreasing the {100} crystal planes from cubes to octahedra, changes the nonenzymatic electro-catalytic activity from highly sensitive to general. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr03396e

  2. pH dependent catalytic activities of platinum nanoparticles with respect to the decomposition of hydrogen peroxide and scavenging of superoxide and singlet oxygen

    NASA Astrophysics Data System (ADS)

    Liu, Yi; Wu, Haohao; Li, Meng; Yin, Jun-Jie; Nie, Zhihong

    2014-09-01

    Recently, platinum (Pt) nanoparticles (NPs) have received increasing attention in the field of catalysis and medicine due to their excellent catalytic activity. To rationally design Pt NPs for these applications, it is crucial to understand the mechanisms underlying their catalytic and biological activities. This article describes a systematic study on the Pt NP-catalyzed decomposition of hydrogen peroxide (H2O2) and scavenging of superoxide (O2&z.rad;-) and singlet oxygen (1O2) over a physiologically relevant pH range of 1.12-10.96. We demonstrated that the catalytic activities of Pt NPs can be modulated by the pH value of the environment. Our results suggest that Pt NPs possess peroxidase-like activity of decomposing H2O2 into &z.rad;OH under acidic conditions, but catalase-like activity of producing H2O and O2 under neutral and alkaline conditions. In addition, Pt NPs exhibit significant superoxide dismutase-like activity of scavenging O2&z.rad;- under neutral conditions, but not under acidic conditions. The 1O2 scavenging ability of Pt NPs increases with the increase in the pH of the environment. The study will provide useful guidance for designing Pt NPs with desired catalytic and biological properties.Recently, platinum (Pt) nanoparticles (NPs) have received increasing attention in the field of catalysis and medicine due to their excellent catalytic activity. To rationally design Pt NPs for these applications, it is crucial to understand the mechanisms underlying their catalytic and biological activities. This article describes a systematic study on the Pt NP-catalyzed decomposition of hydrogen peroxide (H2O2) and scavenging of superoxide (O2&z.rad;-) and singlet oxygen (1O2) over a physiologically relevant pH range of 1.12-10.96. We demonstrated that the catalytic activities of Pt NPs can be modulated by the pH value of the environment. Our results suggest that Pt NPs possess peroxidase-like activity of decomposing H2O2 into &z.rad;OH under acidic conditions

  3. Oxidative Dehydrogenation on Nanocarbon: Intrinsic Catalytic Activity and Structure-Function Relationships.

    PubMed

    Qi, Wei; Liu, Wei; Guo, Xiaoling; Schlögl, Robert; Su, Dangsheng

    2015-11-01

    Physical and chemical insights into the nature and quantity of the active sites and the intrinsic catalytic activity of nanocarbon materials in alkane oxidative dehydrogenation (ODH) reactions are reported using a novel in situ chemical titration process. A study on the structure-function relationship reveals that the active sites are identical both in nature and function on various nanocarbon catalysts. Additionally, the quantity of the active sites could be used as a metric to normalize the reaction rates, and thus to evaluate the intrinsic activity of nanocarbon catalysts. The morphology of the nanocarbon catalysts at the microscopic scale exhibits a minor influence on their intrinsic ODH catalytic activity. The number of active sites calculated from the titration process indicates the number of catalytic centers that are active (that is, working) under the reaction conditions. PMID:26388451

  4. Biodiesel production from algae oil high in free fatty acids by two-step catalytic conversion.

    PubMed

    Chen, Lin; Liu, Tianzhong; Zhang, Wei; Chen, Xiaolin; Wang, Junfeng

    2012-05-01

    The effect of storage temperature and time on lipid composition of Scenedesmus sp. was studied. When stored at 4°C or higher, the free fatty acid content in the wet biomass increased from a trace to 62.0% by day 4. Using two-step catalytic conversion, algae oil with a high free fatty acid content was converted to biodiesel by pre-esterification and transesterification. The conversion rate of triacylglycerols reached 100% under the methanol to oil molar ratio of 12:1 during catalysis with 2% potassium hydroxide at 65°C for 30 min. This process was scaled up to produce biodiesel from Scenedesmus sp. and Nannochloropsis sp. oil. The crude biodiesel was purified using bleaching earth. Except for moisture content, the biodiesel conformed to Chinese National Standards. PMID:22401712

  5. Enhancing the catalytic repertoire of nucleic acids: a systematic study of linker length and rigidity

    PubMed Central

    Lee, Sarah E.; Sidorov, Alexander; Gourlain, Thierry; Mignet, Nathalie; Thorpe, Simon J.; Brazier, John A.; Dickman, Mark J.; Hornby, David P.; Grasby, Jane A.; Williams, David M.

    2001-01-01

    The incorporation of potentially catalytic groups in DNA is of interest for the in vitro selection of novel deoxyribozymes. A series of 10 C5-modified analogues of 2′-deoxyuridine triphosphate have been synthesised that possess side chains of differing flexibility and bearing a primary amino or imidazole functionality. For each series of nucleotide analogues differing degrees of flexibility of the C5 side chain was achieved through the use of alkynyl, alkenyl and alkyl moieties. The imidazole function was conjugated to these C5-amino-modified nucleotides using either imidazole 4-acetic acid or imidazole 4-acrylic acid (urocanic acid). The substrate properties of the nucleotides (fully replacing dTTP) with Taq polymerase during PCR have been investigated in order to evaluate their potential applications for in vitro selection experiments. 5-(3-Aminopropynyl)dUTP and 5-(E-3-aminopropenyl)dUTP and their imidazole 4-acetic acid- and urocanic acid-modified conjugates were found to be substrates. In contrast, C5-amino-modified dUTPs with alkane or Z-alkene linkers and their corresponding conjugates were not substrates. The incorporation of these analogues during PCR has been confirmed by inhibition of restriction enzyme digestion using XbaI and by mass spectrometry of the PCR products. PMID:11266559

  6. Organic acid-catalyzed polyurethane formation via a dual-activated mechanism: unexpected preference of N-activation over O-activation of isocyanates.

    PubMed

    Sardon, Haritz; Engler, Amanda C; Chan, Julian M W; García, Jeannette M; Coady, Daniel J; Pascual, Ana; Mecerreyes, David; Jones, Gavin O; Rice, Julia E; Horn, Hans W; Hedrick, James L

    2013-10-30

    A systematic study of acid organocatalysts for the polyaddition of poly(ethylene glycol) to hexamethylene diisocyanate in solution has been performed. Among organic acids evaluated, sulfonic acids were found the most effective for urethane formations even when compared with conventional tin-based catalysts (dibutyltin dilaurate) or 1,8-diazabicyclo[5.4.0]undec-7-ene. In comparison, phosphonic and carboxylic acids showed considerably lower catalytic activities. Furthermore, sulfonic acids gave polyurethanes with higher molecular weights than was observed using traditional catalyst systems. Molecular modeling was conducted to provide mechanistic insight and supported a dual activation mechanism, whereby ternary adducts form in the presence of acid and engender both electrophilic isocyanate activation and nucleophilic alcohol activation through hydrogen bonding. Such a mechanism suggests catalytic activity is a function of not only acid strength but also inherent conjugate base electron density. PMID:24083673

  7. Thermal activation of catalytic microjets in blood samples using microfluidic chips.

    PubMed

    Soler, Lluís; Martínez-Cisneros, Cynthia; Swiersy, Anka; Sánchez, Samuel; Schmidt, Oliver G

    2013-11-21

    We demonstrate that catalytic microjet engines can out-swim high complex media composed of red blood cells and serum. Despite the challenge presented by the high viscosity of the solution at room temperature, the catalytic microjets can be activated at physiological temperature and, consequently, self-propel in diluted solutions of blood samples. We prove that these microjets self-propel in 10× diluted blood samples using microfluidic chips.

  8. Asymmetric Intramolecular Alkylation of Chiral Aromatic Imines via Catalytic C-H Bond Activation

    SciTech Connect

    Watzke, Anja; Wilson, Rebecca; O'Malley, Steven; Bergman, Robert; Ellman, Jonathan

    2007-04-16

    The asymmetric intramolecular alkylation of chiral aromatic aldimines, in which differentially substituted alkenes are tethered meta to the imine, was investigated. High enantioselectivities were obtained for imines prepared from aminoindane derivatives, which function as directing groups for the rhodium-catalyzed C-H bond activation. Initial demonstration of catalytic asymmetric intramolecular alkylation also was achieved by employing a sterically hindered achiral imine substrate and catalytic amounts of a chiral amine.

  9. Thermal activation of catalytic microjets in blood samples using microfluidic chips†

    PubMed Central

    Soler, Lluís; Martínez-Cisneros, Cynthia; Swiersy, Anka; Sánchez, Samuel; Schmidt, Oliver G.

    2014-01-01

    We demonstrate that catalytic microjet engines can out-swim high complex media composed of red blood cells and serum. Despite the challenge presented by the high viscosity of the solution at room temperature, the catalytic microjets can be activated at physiological temperature and, consequently, self-propel in diluted solutions of blood samples. We prove that these microjets self-propel in 10× diluted blood samples using microfluidic chips. PMID:24089195

  10. Surface engineering on CeO₂ nanorods by chemical redox etching and their enhanced catalytic activity for CO oxidation.

    PubMed

    Gao, Wei; Zhang, Zhiyun; Li, Jing; Ma, Yuanyuan; Qu, Yongquan

    2015-07-21

    Controllable surface properties of nanocerias are desired for various catalytic processes. There is a lack of efficient approaches to adjust the surface properties of ceria to date. Herein, a redox chemical etching method was developed to controllably engineer the surface properties of ceria nanorods. Ascorbic acid and hydrogen peroxide were used to perform the redox chemical etching process, resulting in a rough surface and/or pores on the surface of ceria nanorods. Increasing the etching cycles induced a steady increase of the specific surface area, oxygen vacancies and surface Ce(3+) fractions. As a result, the etched nanorods delivered enhanced catalytic activity for CO oxidation, compared to the non-etched ceria nanorods. Our method provides a novel and facile approach to continuously adjust the surface properties of ceria for practical applications.

  11. Substrate Orientation and Catalytic Specificity in the Action of Xanthine Oxidase: The Sequential Hydroxylation of Hypoxanthine to Uric Acid

    SciTech Connect

    Cao, Hongnan; Pauff, James M.; Hille, Russ

    2010-11-29

    Xanthine oxidase is a molybdenum-containing enzyme catalyzing the hydroxylation of a sp{sup 2}-hybridized carbon in a broad range of aromatic heterocycles and aldehydes. Crystal structures of the bovine enzyme in complex with the physiological substrate hypoxanthine at 1.8 {angstrom} resolution and the chemotherapeutic agent 6-mercaptopurine at 2.6 {angstrom} resolution have been determined, showing in each case two alternate orientations of substrate in the two active sites of the crystallographic asymmetric unit. One orientation is such that it is expected to yield hydroxylation at C-2 of substrate, yielding xanthine. The other suggests hydroxylation at C-8 to give 6,8-dihydroxypurine, a putative product not previously thought to be generated by the enzyme. Kinetic experiments demonstrate that >98% of hypoxanthine is hydroxylated at C-2 rather than C-8, indicating that the second crystallographically observed orientation is significantly less catalytically effective than the former. Theoretical calculations suggest that enzyme selectivity for the C-2 over C-8 of hypoxanthine is largely due to differences in the intrinsic reactivity of the two sites. For the orientation of hypoxanthine with C-2 proximal to the molybdenum center, the disposition of substrate in the active site is such that Arg880 and Glu802, previous shown to be catalytically important for the conversion of xanthine to uric acid, play similar roles in hydroxylation at C-2 as at C-8. Contrary to the literature, we find that 6,8-dihydroxypurine is effectively converted to uric acid by xanthine oxidase.

  12. Cold catalytic recovery of loaded activated carbon using iron oxide-based nanoparticles.

    PubMed

    Bach, Altai; Zelmanov, Grigory; Semiat, Raphael

    2008-01-01

    A novel approach for the recovery of spent activated carbon by an advanced oxidation process using iron oxide-based nanocatalysts was proposed and investigated. Model organic contaminants, such as ethylene glycol and phenol, were chosen for this study as water pollutants. It was shown that there are several advantages in using catalytic oxidation recovery of activated carbon with iron oxide-based nanocatalysts: low temperature reactivity of catalytic recovery without heating; and a relatively large number of adsorption-recovery cycles, without a reduction in the adsorptive properties of the virgin activated carbon or without a performance decrease from the first adsorption-recovery cycle of the new modified adsorptive properties of the activated carbon. The catalytic recovery takes place without ultraviolet light or any visible radiation sources. Results show a high efficiency of catalytic recovery of spent activated carbon using iron oxide-based nanocatalysts. A 97-99% efficiency of spent activated carbon catalytic regeneration was achieved under chosen conditions after 15-20 min of reaction. The process may be also considered as cold in situ recovery of active carbon.

  13. Reactivity and Catalytic Activity of Hydrogen Atom Chemisorbed Silver Clusters.

    PubMed

    Manzoor, Dar; Pal, Sourav

    2015-06-18

    Metal clusters of silver have attracted recent interest of researchers as a result of their potential in different catalytic applications and low cost. However, due to the completely filled d orbital and very high first ionization potential of the silver atom, the silver-based catalysts interact very weakly with the reacting molecules. In the current work, density functional theory calculations were carried out to investigate the effect of hydrogen atom chemisorption on the reactivity and catalytic properties of inert silver clusters. Our results affirm that the hydrogen atom chemisorption leads to enhancement in the binding energy of the adsorbed O2 molecule on the inert silver clusters. The increase in the binding energy is also characterized by the decrease in the Ag-O and increase in the O-O bond lengths in the case of the AgnH silver clusters. Pertinent to the increase in the O-O bond length, a significant red shift in the O-O stretching frequency is also noted in the case of the AgnH silver clusters. Moreover, the hydrogen atom chemisorbed silver clusters show low reaction barriers and high heat of formation of the final products for the environmentally important CO oxidation reaction as compared to the parent catalytically inactive clusters. The obtained results were compared with those of the corresponding gold and hydrogen atom chemisorbed gold clusters obtained at the same level of theory. It is expected the current computational study will provide key insights for future advances in the design of efficient nanosilver-based catalysts through the adsorption of a small atom or a ligand.

  14. Identification of Amino Acid Determinants in CYP4B1 for Optimal Catalytic Processing of 4-Ipomeanol

    PubMed Central

    Wiek, Constanze; Schmidt, Eva M; Roellecke, Katharina; Freund, Marcel; Nakano, Mariko; Kelly, Edward J; Kaisers, Wolfgang; Yarov-Yarovoy, Vladimir; Kramm, Christof M; Rettie, Allan E; Hanenberg, Helmut

    2014-01-01

    Mammalian CYP4B1 enzymes are cytochrome P450 monooxygenases that are responsible for the bioactivation of several exogenous pro-toxins including 4-ipomeanol (4-IPO). In contrast to the orthologous rabbit enzyme, we show here that native human CYP4B1 with a serine at position 427 is unable to bio-activate 4-IPO and does not cause cytotoxicity in HepG2 cells and primary human T-cells that overexpress these enzymes. We also demonstrate that a proline residue in the meander region at position 427 in human CYB4B1 and 422 in rabbit CYP4B1 is important for protein stability and rescues the 4-IPO bioactivation of the human enzyme, but is not essential for the catalytic activity of the rabbit CYP4B1 protein. Systematic substitution of native and p.S427P human CYP4B1 with peptide regions from the highly active rabbit enzyme reveals that 18 amino acids in the wild-type rabbit CYP4B1 protein are key for conferring high 4-IPO metabolizing activity. Introduction of 12 of the 18 amino acids that are also present at corresponding positions in other human CYP4 family members into the p.S427P human CYP4B1 protein results in a mutant human enzyme (P+12) that is as stable and as active as the rabbit wild-type CYP4B1 protein. These 12 mutations cluster in the predicted B–C loop through F-helix regions and reveal new amino acid regions important to P450 enzyme stability. Finally, by minimally re-engineering the human CYP4B1 enzyme for efficient activation of 4-IPO, we have developed a novel human suicide gene system that is a candidate for adoptive cellular therapies in humans. PMID:25247810

  15. Modeling of catalytically active metal complex species and intermediates in reactions of organic halides electroreduction.

    PubMed

    Lytvynenko, Anton S; Kolotilov, Sergey V; Kiskin, Mikhail A; Eremenko, Igor L; Novotortsev, Vladimir M

    2015-02-28

    The results of quantum chemical modeling of organic and metal-containing intermediates that occur in electrocatalytic dehalogenation reactions of organic chlorides are presented. Modeling of processes that take place in successive steps of the electrochemical reduction of representative C1 and C2 chlorides - CHCl3 and Freon R113 (1,1,2-trifluoro-1,2,2-trichloroethane) - was carried out by density functional theory (DFT) and second-order Møller-Plesset perturbation theory (MP2). It was found that taking solvation into account using an implicit solvent model (conductor-like screening model, COSMO) or considering explicit solvent molecules gave similar results. In addition to modeling of simple non-catalytic dehalogenation, processes with a number of complexes and their reduced forms, some of which were catalytically active, were investigated by DFT. Complexes M(L1)2 (M = Fe, Co, Ni, Cu, Zn, L1H = Schiff base from 2-pyridinecarbaldehyde and the hydrazide of 4-pyridinecarboxylic acid), Ni(L2) (H2L2 is the Schiff base from salicylaldehyde and 1,2-ethylenediamine, known as salen) and Co(L3)2Cl2, representing a fragment of a redox-active coordination polymer [Co(L3)Cl2]n (L3 is the dithioamide of 1,3-benzenedicarboxylic acid), were considered. Gradual changes in electronic structure in a series of compounds M(L1)2 were observed, and correlations between [M(L1)2](0) spin-up and spin-down LUMO energies and the relative energies of the corresponding high-spin and low-spin reduced forms, as well as the shape of the orbitals, were proposed. These results can be helpful for determination of the nature of redox-processes in similar systems by DFT. No specific covalent interactions between [M(L1)2](-) and the R113 molecule (M = Fe, Co, Ni, Zn) were found, which indicates that M(L1)2 electrocatalysts act rather like electron transfer mediators via outer-shell electron transfer. A relaxed surface scan of the adducts {M(L1)2·R113}(-) (M = Ni or Co) versus the distance between the

  16. The Influence of Elastic Strain on Catalytic Activity in the Hydrogen Evolution Reaction.

    PubMed

    Yan, Kai; Maark, Tuhina Adit; Khorshidi, Alireza; Sethuraman, Vijay A; Peterson, Andrew A; Guduru, Pradeep R

    2016-05-17

    Understanding the role of elastic strain in modifying catalytic reaction rates is crucial for catalyst design, but experimentally, this effect is often coupled with a ligand effect. To isolate the strain effect, we have investigated the influence of externally applied elastic strain on the catalytic activity of metal films in the hydrogen evolution reaction (HER). We show that elastic strain tunes the catalytic activity in a controlled and predictable way. Both theory and experiment show strain controls reactivity in a controlled manner consistent with the qualitative predictions of the HER volcano plot and the d-band theory: Ni and Pt's activities were accelerated by compression, while Cu's activity was accelerated by tension. By isolating the elastic strain effect from the ligand effect, this study provides a greater insight into the role of elastic strain in controlling electrocatalytic activity. PMID:27079940

  17. Oxygen reduction at carbon supported ruthenium-selenium catalysts: Selenium as promoter and stabilizer of catalytic activity

    NASA Astrophysics Data System (ADS)

    Schulenburg, Hendrik; Hilgendorff, Marcus; Dorbandt, Iris; Radnik, Jörg; Bogdanoff, Peter; Fiechter, Sebastian; Bron, Michael; Tributsch, Helmut

    Carbon supported ruthenium-based catalysts (Ru/C) for the oxygen reduction in acid electrolytes were investigated. A treatment of Ru/C catalysts with selenious acid had a beneficial effect on catalytic activity but no influence on intrinsic kinetic properties, like Tafel slope and hydrogen peroxide generation. Reasons for the increased activity of RuSe x/C catalysts are discussed. Potential step measurements suggest that at potentials around 0.8 V (NHE) a selenium or selenium-oxygen species protects the catalyst from formation of inactive RuO 2-films. This protective effect leads to an enhanced activity of RuSe x/C compared to Ru/C. No evidence was found for a catalytically active stoichiometric selenium compound. The active phase may be described as a ruthenium suboxide RuO x (x < 2) layer integrated in a RuSe y phase or RuSe yO v (y < 2, v < 2) layer at the particle surface.

  18. Determinants of ligand binding and catalytic activity in the myelin enzyme 2′,3′-cyclic nucleotide 3′-phosphodiesterase

    PubMed Central

    Raasakka, Arne; Myllykoski, Matti; Laulumaa, Saara; Lehtimäki, Mari; Härtlein, Michael; Moulin, Martine; Kursula, Inari; Kursula, Petri

    2015-01-01

    2′,3′-cyclic nucleotide 3′-phosphodiesterase (CNPase) is an enzyme highly abundant in the central nervous system myelin of terrestrial vertebrates. The catalytic domain of CNPase belongs to the 2H phosphoesterase superfamily and catalyzes the hydrolysis of nucleoside 2′,3′-cyclic monophosphates to nucleoside 2′-monophosphates. The detailed reaction mechanism and the essential catalytic amino acids involved have been described earlier, but the roles of many amino acids in the vicinity of the active site have remained unknown. Here, several CNPase catalytic domain mutants were studied using enzyme kinetics assays, thermal stability experiments, and X-ray crystallography. Additionally, the crystal structure of a perdeuterated CNPase catalytic domain was refined at atomic resolution to obtain a detailed view of the active site and the catalytic mechanism. The results specify determinants of ligand binding and novel essential residues required for CNPase catalysis. For example, the aromatic side chains of Phe235 and Tyr168 are crucial for substrate binding, and Arg307 may affect active site electrostatics and regulate loop dynamics. The β5-α7 loop, unique for CNPase in the 2H phosphoesterase family, appears to have various functions in the CNPase reaction mechanism, from coordinating the nucleophilic water molecule to providing a binding pocket for the product and being involved in product release. PMID:26563764

  19. A single point mutation leading to loss of catalytic activity in human thiopurine S-methyltransferase.

    PubMed Central

    Krynetski, E Y; Schuetz, J D; Galpin, A J; Pui, C H; Relling, M V; Evans, W E

    1995-01-01

    Thiopurine S-methyltransferase (TPMT; S-adenosyl-L-methionine:thiopurine S-methyltransferase, EC 2.1.1.67) activity exhibits genetic polymorphism, with approximately 0.33% of Caucasians and African-Americans inheriting TPMT deficiency as an autosomal recessive trait. To determine the molecular genetic basis for this polymorphism, we cloned the TPMT cDNA from a TPMT-deficient patient who had developed severe hematopoietic toxicity during mercaptopurine therapy. Northern blot analysis of RNA isolated from leukocytes of the deficient patient demonstrated the presence of TPMT mRNAs of comparable size to that in subjects with high TPMT activity. Sequencing of the mutant TPMT cDNA revealed a single point mutation (G238-->C), leading to an amino acid substitution at codon 80 (Ala80-->Pro). When assessed in a yeast heterologous expression system, this mutation led to a 100-fold reduction in TPMT catalytic activity relative to the wild-type cDNA, despite a comparable level of mRNA expression. A mutation-specific PCR amplification method was developed and used to detect the G238-->C mutation in genomic DNA of the propositus and her mother. This inactivating mutation in the human TPMT gene provides insights into the genetic basis for this inherited polymorphism in drug metabolism. Images Fig. 1 Fig. 2 Fig. 4 Fig. 5 PMID:7862671

  20. Synthesis, characterization and catalytic activity of ordered macroporous silicas functionalized with organosulfur groups

    SciTech Connect

    Wu Quanzhou Liao Jufang; Yin Qiang; Li Yuguang

    2008-05-06

    Hybrid three-dimensionally ordered macroporous (3DOM) SiO{sub 2}-SO{sub 3}H materials with different S/Si ratio have been prepared by colloidal crystal templating method. The process involved preparation of 3DOM SiO{sub 2}-SH materials by co-condensation of (3-mercaptopropyl)triethoxysilane and tetraethoxysilane via sol-gel transformation, and following oxidation of -SH group to -SO{sub 3}H group by H{sub 2}O{sub 2}. Materials were characterized by scanning electron microscopy (SEM), Fourier transform infra-red spectrometer (FTIR), thermogravimetric analysis (TGA), and nitrogen adsorption measurement. SEM observation shows that the macropores are highly ordered with a typical 'surface-templated' structure. The surface area of 3DOM SiO{sub 2}-SH material is 25.1 m{sup 2}/g and SiO{sub 2}-SO{sub 3}H material is 18.6 m{sup 2}/g. Catalytic activity test shows that 3DOM SiO{sub 2}-SO{sub 3}H materials possess a high activity for the esterification of acetic acid and n-butanol, and the activity is increased with the amount of sulfur in the materials. This study provided significant results for developing new application of 3DOM materials.

  1. Examination of an active-site electrostatic node in the cAMP-dependent protein kinase catalytic subunit.

    PubMed Central

    Grant, B. D.; Tsigelny, I.; Adams, J. A.; Taylor, S. S.

    1996-01-01

    The active site of the cAMP-dependent protein kinase catalytic subunit harbors a cluster of acidic residues-Asp 127, Glu 170, Glu 203, Glu 230, and Asp 241-that are not conserved throughout the protein kinase family. Based on crystal structures of the catalytic subunit, these amino acids are removed from the site of phosphoryl transfer and are implicated in substrate recognition. Glu 230, the most buried of these acidic residues, was mutated to Ala (rC[E230A]) and Gln (rC[E230Q]) and overexpressed in Escherichia coli. In contrast to the mostly insoluble and destabilized rC[E230A], rC[E230Q] is largely soluble, purifies like wild-type enzyme, and displays wild-type-like thermal stability. The mutation in rC[E230Q] causes an order of magnitude decrease in the affinity for a heptapeptide substrate, Kemptide. In addition, two independent kinetic techniques were used to dissect phosphoryl transfer and product release steps in the reaction pathway. Viscosometric and pre-steady-state quench-flow analyses revealed that the phosphoryl transfer rate constant decreases by an order of magnitude, whereas the product release rate constant remains unperturbed. Electrostatic alterations in the rC[E230Q] active site were assessed using modeling techniques that provide molecular interpretations for the substrate affinity and phosphoryl transfer rate decreases observed experimentally. These observations indicate that subsite recognition elements in the catalytic subunit make electrostatic contributions that are important not only for peptide affinity, but also for catalysis. Protein kinases may, therefore, discriminate substrates by not only binding them tightly, but also by only turning over ones that complement the electrostatic character of the active site. PMID:8819164

  2. Selective Catalytic Oxidation of Hydrogen Sulfide on Activated Carbons Impregnated with Sodium Hydroxide

    SciTech Connect

    Schwartz, Viviane; Baskova, Svetlana; Armstrong, Timothy R.

    2009-01-01

    Two activated carbons of different origin were impregnated with the solution of sodium hydroxide (NaOH) of various concentrations up to 10 wt %, and the effect of impregnation on the catalytic performance of the carbons was evaluated. The catalytic activity was analyzed in terms of the capacity of carbons for hydrogen sulfide (H2S) conversion and removal from hydrogen-rich fuel streams and the emission times of H2S and the products of its oxidation [e.g., sulfur dioxide (SO2) and carbonyl sulfide (COS)]. The results of impregnation showed a significant improvement in the catalytic activity of both carbons proportional to the amount of NaOH introduced. NaOH introduces hydroxyl groups (OH-) on the surface of the activated carbon that increase its surface reactivity and its interaction with sulfur-containing compounds.

  3. 3-Nitropropionic Acid is a Suicide Inhibitor of MitochondrialRespiration that, Upon Oxidation by Complex II, Forms a Covalent AdductWith a Catalytic Base Arginine in the Active Site of the Enzyme

    SciTech Connect

    Huang, Li-shar; Sun, Gang; Cobessi, David; Wang, Andy C.; Shen,John T.; Tung, Eric Y.; Anderson, Vernon E.; Berry, Edward A.

    2005-12-01

    We report three new structures of mitochondrial respiratory Complex II (succinate ubiquinone oxidoreductase, E.C. 1.3.5.1) at up to 2.1 {angstrom} resolution, with various inhibitors. The structures define the conformation of the bound inhibitors and suggest the residues involved in substrate binding and catalysis at the dicarboxylate site. In particular they support the role of Arg297 as a general base catalyst accepting a proton in the dehydrogenation of succinate. The dicarboxylate ligand in oxaloacetate-containing crystals appears to be the same as that reported for Shewanella flavocytochrome c treated with fumarate. The plant and fungal toxin 3-nitropropionic acid, an irreversible inactivator of succinate dehydrogenase, forms a covalent adduct with the side chain of Arg297. The modification eliminates a trypsin cleavage site in the flavoprotein, and tandem mass spectroscopic analysis of the new fragment shows the mass of Arg 297 to be increased by 83 Da and to have potential of losing 44 Da, consistent with decarboxylation, during fragmentation.

  4. Comparison of Two Preparation Methods on Catalytic Activity and Selectivity of Ru-Mo/HZSM5 for Methane Dehydroaromatization

    DOE PAGES

    Petkovic, Lucia M.; Ginosar, Daniel M.

    2014-01-01

    Catalytic performance of Mo/HZSM5 and Ru-Mo/HZSM5 catalysts prepared by vaporization-deposition of molybdenum trioxide and impregnation with ammonium heptamolybdate was analyzed in terms of catalyst activity and selectivity, nitrogen physisorption analyses, temperature-programmed oxidation of carbonaceous residues, and temperature-programmed reduction. Vaporization-deposition rendered the catalyst more selective to ethylene and coke than the catalyst prepared by impregnation. This result was assigned to lower interaction of molybdenum carbide with the zeolite acidic sites.

  5. Catalytic activation of carbohydrates as formaldehyde equivalents for Stetter reaction with enones.

    PubMed

    Zhang, Junmin; Xing, Chong; Tiwari, Bhoopendra; Chi, Yonggui Robin

    2013-06-01

    We disclose the first catalytic activation of carbohydrates as formaldehyde equivalents to generate acyl anions as one-carbon nucleophilic units for a Stetter reaction. The activation involves N-heterocyclic carbene (NHC)-catalyzed C-C bond cleavage of carbohydrates via a retro-benzoin-type process to generate the acyl anion intermediates. This Stetter reaction constitutes the first success in generating formal formaldehyde-derived acyl anions as one-carbon nucleophiles for non-self-benzoin processes. The renewable nature of carbohydrates, accessible from biomass, further highlights the practical potential of this fundamentally interesting catalytic activation.

  6. Inhibition of miR-21 in glioma cells using catalytic nucleic acids

    PubMed Central

    Belter, Agnieszka; Rolle, Katarzyna; Piwecka, Monika; Fedoruk-Wyszomirska, Agnieszka; Naskręt-Barciszewska, Mirosława Z.; Barciszewski, Jan

    2016-01-01

    Despite tremendous efforts worldwide, glioblastoma multiforme (GBM) remains a deadly disease for which no cure is available and prognosis is very bad. Recently, miR-21 has emerged as a key omnipotent player in carcinogenesis, including brain tumors. It is recognized as an indicator of glioma prognosis and a prosperous target for anti-tumor therapy. Here we show that rationally designed hammerhead ribozymes and DNAzymes can target miR-21 and/or its precursors. They decrease miR-21 level, and thus silence this oncomiR functions. We demonstrated that anti-miRNA catalytic nucleic acids show a novel terrific arsenal for specific and effective combat against diseases with elevated cellular miR-21 content, such as brain tumors. PMID:27079911

  7. Preparation of acid-base bifunctional mesoporous KIT-6 (KIT: Korea Advanced Institute of Science and Technology) and its catalytic performance in Knoevenagel reaction

    SciTech Connect

    Xu, Ling; Wang, Chunhua; Guan, Jingqi

    2014-05-01

    Acid-base bifunctional mesoporous catalysts Al-KIT-6-NH{sub 2} containing different aluminum content have been synthesized through post synthetic grafting method. The materials were characterized by X-ray diffraction (XRD), scanning electron micrographs (SEM), transmission electron micrographs (TEM), Fourier-transform infrared spectroscopy (FTIR), IR spectra of pyridine adsorption, NH{sub 3}-TPD and TG analysis. The characterization results indicated that the pore structure of KIT-6 was well kept after the addition of aluminum and grafting of aminopropyl groups. The acid amount of Al-KIT-6 increased with enhancing aluminum content. Catalytic results showed that weak acid and weak base favor the Knoevenagel reaction, while catalysts with strong acid and weak base exhibited worse catalytic behavior. - Graphical abstract: The postulated steps of mechanism for the acid-base catalyzed process are as follows: (1) the aldehyde gets activated by the surface acidic sites which allow the amine undergoes nucleophilic to attack the carbonyl carbon of benzaldehyde. (2) Water is released in the formation of imine intermediate. (3) The ethyl cyanoacetate reacts with the intermediate. (4) The benzylidene ethyl cyanoacetate is formed and the amine is regenerated. - Highlights: • KIT-6 and Al-KIT-6-NH{sub 2} with different Si/Al ratios has been successfully prepared. • 79.4% Yield was obtained over 46-Al-KIT-6-NH{sub 2} within 20 min in Knoevenagel reaction. • Low Al-content Al-KIT-6-NH{sub 2} shows better catalytic stability than high Al-content catalysts. • There is acid-base synergistic effect in Knoevenagel reaction.

  8. Effects of Particle Size on the Gas Sensitivity and Catalytic Activity of In2O3

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoshui; Gu, Ruiqin; Zhao, Jinling; Jin, Guixin; Zhao, Mengke; Xue, Yongliang

    2015-10-01

    Nanosized In2O3 powders with different particle sizes were prepared by the microemulsion synthetic method. The effects of particle size on the gas-sensing and catalytic properties of the as-prepared In2O3 were investigated. Reductions in particle size to nanometer levels improved the sensitivity and catalytic activity of In2O3 to i-C4H10 and C2H5OH. The sensitivity of nanosized In2O3 (<42 nm) sensors to i-C4H10, H2 and C2H5OH was 2-4 times higher than that of chemically precipitated In2O3 (130 nm) sensor. A nearly linear relationship was observed between the catalytic activity and specific surface area of In2O3 for the oxidation of i-C4H10 and C2H5OH at 275 °C. The relationship between gas sensitivity and catalytic activity was further discussed. The results of this work reveal that catalytic activity plays a key role in enhancing the sensitivity of gas-sensing materials.

  9. Three-phase catalytic system of H2O, ionic liquid, and VOPO4-SiO2 solid acid for conversion of fructose to 5-hydroxymethylfurfural.

    PubMed

    Tian, Chengcheng; Zhu, Xiang; Chai, Song-Hai; Wu, Zili; Binder, Andrew; Brown, Suree; Li, Lin; Luo, Huimin; Guo, Yanglong; Dai, Sheng

    2014-06-01

    Efficient transformation of biomass-derived feedstocks to chemicals and fuels remains a daunting challenge in utilizing biomass as alternatives to fossil resources. A three-phase catalytic system, consisting of an aqueous phase, a hydrophobic ionic-liquid phase, and a solid-acid catalyst phase of nanostructured vanadium phosphate and mesostructured cellular foam (VPO-MCF), is developed for efficient conversion of biomass-derived fructose to 5-hydroxymethylfurfural (HMF). HMF is a promising, versatile building block for production of value-added chemicals and transportation fuels. The essence of this three-phase system lies in enabling the isolation of the solid-acid catalyst from the aqueous phase and regulation of its local environment by using a hydrophobic ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][Tf2N]). This system significantly inhibits the side reactions of HMF with H2O and leads to 91 mol % selectivity to HMF at 89 % of fructose conversion. The unique three-phase catalytic system opens up an alternative avenue for making solid-acid catalyst systems with controlled and locally regulated microenvironment near catalytically active sites by using a hydrophobic ionic liquid. PMID:24729382

  10. Three-phase catalytic system of H2O, ionic liquid, and VOPO4-SiO2 solid acid for conversion of fructose to 5-hydroxymethylfurfural.

    PubMed

    Tian, Chengcheng; Zhu, Xiang; Chai, Song-Hai; Wu, Zili; Binder, Andrew; Brown, Suree; Li, Lin; Luo, Huimin; Guo, Yanglong; Dai, Sheng

    2014-06-01

    Efficient transformation of biomass-derived feedstocks to chemicals and fuels remains a daunting challenge in utilizing biomass as alternatives to fossil resources. A three-phase catalytic system, consisting of an aqueous phase, a hydrophobic ionic-liquid phase, and a solid-acid catalyst phase of nanostructured vanadium phosphate and mesostructured cellular foam (VPO-MCF), is developed for efficient conversion of biomass-derived fructose to 5-hydroxymethylfurfural (HMF). HMF is a promising, versatile building block for production of value-added chemicals and transportation fuels. The essence of this three-phase system lies in enabling the isolation of the solid-acid catalyst from the aqueous phase and regulation of its local environment by using a hydrophobic ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][Tf2N]). This system significantly inhibits the side reactions of HMF with H2O and leads to 91 mol % selectivity to HMF at 89 % of fructose conversion. The unique three-phase catalytic system opens up an alternative avenue for making solid-acid catalyst systems with controlled and locally regulated microenvironment near catalytically active sites by using a hydrophobic ionic liquid.

  11. Identification of olivetolic acid cyclase from Cannabis sativa reveals a unique catalytic route to plant polyketides

    PubMed Central

    Gagne, Steve J.; Stout, Jake M.; Liu, Enwu; Boubakir, Zakia; Clark, Shawn M.; Page, Jonathan E.

    2012-01-01

    Δ9-Tetrahydrocannabinol (THC) and other cannabinoids are responsible for the psychoactive and medicinal properties of Cannabis sativa L. (marijuana). The first intermediate in the cannabinoid biosynthetic pathway is proposed to be olivetolic acid (OA), an alkylresorcinolic acid that forms the polyketide nucleus of the cannabinoids. OA has been postulated to be synthesized by a type III polyketide synthase (PKS) enzyme, but so far type III PKSs from cannabis have been shown to produce catalytic byproducts instead of OA. We analyzed the transcriptome of glandular trichomes from female cannabis flowers, which are the primary site of cannabinoid biosynthesis, and searched for polyketide cyclase-like enzymes that could assist in OA cyclization. Here, we show that a type III PKS (tetraketide synthase) from cannabis trichomes requires the presence of a polyketide cyclase enzyme, olivetolic acid cyclase (OAC), which catalyzes a C2–C7 intramolecular aldol condensation with carboxylate retention to form OA. OAC is a dimeric α+β barrel (DABB) protein that is structurally similar to polyketide cyclases from Streptomyces species. OAC transcript is present at high levels in glandular trichomes, an expression profile that parallels other cannabinoid pathway enzymes. Our identification of OAC both clarifies the cannabinoid pathway and demonstrates unexpected evolutionary parallels between polyketide biosynthesis in plants and bacteria. In addition, the widespread occurrence of DABB proteins in plants suggests that polyketide cyclases may play an overlooked role in generating plant chemical diversity. PMID:22802619

  12. Identification of olivetolic acid cyclase from Cannabis sativa reveals a unique catalytic route to plant polyketides.

    PubMed

    Gagne, Steve J; Stout, Jake M; Liu, Enwu; Boubakir, Zakia; Clark, Shawn M; Page, Jonathan E

    2012-07-31

    Δ(9)-Tetrahydrocannabinol (THC) and other cannabinoids are responsible for the psychoactive and medicinal properties of Cannabis sativa L. (marijuana). The first intermediate in the cannabinoid biosynthetic pathway is proposed to be olivetolic acid (OA), an alkylresorcinolic acid that forms the polyketide nucleus of the cannabinoids. OA has been postulated to be synthesized by a type III polyketide synthase (PKS) enzyme, but so far type III PKSs from cannabis have been shown to produce catalytic byproducts instead of OA. We analyzed the transcriptome of glandular trichomes from female cannabis flowers, which are the primary site of cannabinoid biosynthesis, and searched for polyketide cyclase-like enzymes that could assist in OA cyclization. Here, we show that a type III PKS (tetraketide synthase) from cannabis trichomes requires the presence of a polyketide cyclase enzyme, olivetolic acid cyclase (OAC), which catalyzes a C2-C7 intramolecular aldol condensation with carboxylate retention to form OA. OAC is a dimeric α+β barrel (DABB) protein that is structurally similar to polyketide cyclases from Streptomyces species. OAC transcript is present at high levels in glandular trichomes, an expression profile that parallels other cannabinoid pathway enzymes. Our identification of OAC both clarifies the cannabinoid pathway and demonstrates unexpected evolutionary parallels between polyketide biosynthesis in plants and bacteria. In addition, the widespread occurrence of DABB proteins in plants suggests that polyketide cyclases may play an overlooked role in generating plant chemical diversity.

  13. Catalytic activities of Werner protein are affected by adduction with 4-hydroxy-2-nonenal

    PubMed Central

    Czerwińska, Jolanta; Poznański, Jarosław; Dębski, Janusz; Bukowy, Zuzanna; Bohr, Vilhelm A.; Tudek, Barbara; Speina, Elżbieta

    2014-01-01

    4-Hydroxy-2-nonenal (HNE) is a reactive α,β-unsaturated aldehyde generated during oxidative stress and subsequent peroxidation of polyunsaturated fatty acids. Here, Werner protein (WRN) was identified as a novel target for modification by HNE. Werner syndrome arises through mutations in the WRN gene that encodes the RecQ DNA helicase which is critical for maintaining genomic stability. This hereditary disease is associated with chromosomal instability, premature aging and cancer predisposition. WRN appears to participate in the cellular response to oxidative stress and cells devoid of WRN display elevated levels of oxidative DNA damage. We demonstrated that helicase/ATPase and exonuclease activities of HNE-modified WRN protein were inhibited both in vitro and in immunocomplexes purified from the cell extracts. Sites of HNE adduction in human WRN were identified at Lys577, Cys727, His1290, Cys1367, Lys1371 and Lys1389. We applied in silico modeling of the helicase and RQC domains of WRN protein with HNE adducted to Lys577 and Cys727 and provided a potential mechanism of the observed deregulation of the protein catalytic activities. In light of the obtained results, we postulate that HNE adduction to WRN is a post-translational modification, which may affect WRN conformational stability and function, contributing to features and diseases associated with premature senescence. PMID:25170083

  14. Copper on responsive polymer microgels: a recyclable catalyst exhibiting tunable catalytic activity.

    PubMed

    Wu, Qingshi; Cheng, Han; Chang, Aiping; Bai, Xue; Lu, Fan; Wu, Weitai

    2014-11-25

    Copper has been immobilized on a chitosan-based responsive polymer microgel by simply stirring the microgel dispersion with copper sulfate. The ensuing catalyst is highly active for a model azide-alkyne [3+2]-cycloaddition reaction, and can be recycled at least 5 times; the catalytic activity can be tuned via swelling-deswelling transitions of the polymer gels. PMID:25283806

  15. Tremendous effect of the morphology of birnessite-type manganese oxide nanostructures on catalytic activity.

    PubMed

    Hou, Jingtao; Li, Yuanzhi; Mao, Mingyang; Ren, Lu; Zhao, Xiujian

    2014-09-10

    The octahedral layered birnessite-type manganese oxide (OL-1) with the morphologies of nanoflowers, nanowires, and nanosheets were prepared and characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric/differential scanning calorimetry (TG/DSC), Brunnauer-Emmett-Teller (BET), inductively coupled plasma (ICP), and X-ray photoelectron spectroscopy (XPS). The OL-1 nanoflowers possess the highest concentration of oxygen vacancies or Mn(3+), followed by the OL-1 nanowires and nanosheets. The result of catalytic tests shows that the OL-1 nanoflowers exhibit a tremendous enhancement in the catalytic activity for benzene oxidation as compared to the OL-1 nanowires and nanosheets. Compared to the OL-1 nanosheets, the OL-1 nanoflowers demonstrate an enormous decrease (ΔT(50) = 274 °C; ΔT(90) > 248 °C) in reaction temperatures T50 and T90 (corresponding to 50 and 90% benzene conversion, respectively) for benzene oxidation. The origin of the tremendous effect of morphology on the catalytic activity for the nanostructured OL-1 catalysts is experimentally and theoretically studied via CO temperature-programmed reduction (CO-TPR) and density functional theory (DFT) calculation. The tremendous catalytic enhancement of the OL-1 nanoflowers compared to the OL-1 nanowires and nanosheets is attributed to their highest surface area as well as their highest lattice oxygen reactivity due to their higher concentration of oxygen vacancies or Mn(3+), thus tremendously improving the catalytic activity for the benzene oxidation.

  16. The importance of hinge sequence for loop function and catalytic activity in the reaction catalyzed by triosephosphate isomerase.

    PubMed

    Xiang, J; Sun, J; Sampson, N S

    2001-04-01

    We have determined the sequence requirements for the N-terminal protein hinge of the active-site lid of triosephosphate isomerase. The codons for the hinge (PVW) were replaced with a genetic library of all possible 8000 amino acid combinations. The most active of these 8000 mutants were selected using in vivo complementation of a triosephosphate isomerase-deficient strain of Escherichia coli, DF502. Approximately 0.3 % of the mutants complement DF502 with an activity that is between 10 and 70 % of wild-type activity. They all contain Pro at the first position. Furthermore, the sequences of these hinge mutants reveal that hydrophobic packing is very important for efficient formation of the enediol intermediate. However, the reduced catalytic activities observed are not due to increased rates of loop opening. To explore the relationship between the N-terminal and C-terminal hinges, three semi-active mutants from the N-terminal hinge selection experiment (PLH, PHS and PTF), and six active C-terminal hinge mutants from previous work (NSS, LWA, YSL, KTK, NPN, KVA) were combined to form 18 "double-hinge" mutants. The activities of these mutants suggest that the N-terminal and C-terminal hinge structures affect one another. It appears that specific side-chain interactions are important for forming a catalytically active enzyme, but not for preventing release of the unstable enediol intermediate from the active site of the enzyme. The independence of intermediate release on amino acid sequence is consistent with the absence of a "universal" hinge sequence in structurally related enzymes. PMID:11286559

  17. The importance of hinge sequence for loop function and catalytic activity in the reaction catalyzed by triosephosphate isomerase.

    PubMed

    Xiang, J; Sun, J; Sampson, N S

    2001-04-01

    We have determined the sequence requirements for the N-terminal protein hinge of the active-site lid of triosephosphate isomerase. The codons for the hinge (PVW) were replaced with a genetic library of all possible 8000 amino acid combinations. The most active of these 8000 mutants were selected using in vivo complementation of a triosephosphate isomerase-deficient strain of Escherichia coli, DF502. Approximately 0.3 % of the mutants complement DF502 with an activity that is between 10 and 70 % of wild-type activity. They all contain Pro at the first position. Furthermore, the sequences of these hinge mutants reveal that hydrophobic packing is very important for efficient formation of the enediol intermediate. However, the reduced catalytic activities observed are not due to increased rates of loop opening. To explore the relationship between the N-terminal and C-terminal hinges, three semi-active mutants from the N-terminal hinge selection experiment (PLH, PHS and PTF), and six active C-terminal hinge mutants from previous work (NSS, LWA, YSL, KTK, NPN, KVA) were combined to form 18 "double-hinge" mutants. The activities of these mutants suggest that the N-terminal and C-terminal hinge structures affect one another. It appears that specific side-chain interactions are important for forming a catalytically active enzyme, but not for preventing release of the unstable enediol intermediate from the active site of the enzyme. The independence of intermediate release on amino acid sequence is consistent with the absence of a "universal" hinge sequence in structurally related enzymes.

  18. Catalytic Conversion of Biomass for the Production of Hydrogen; Decomposition of Formic Acid

    NASA Astrophysics Data System (ADS)

    Azadi Manzour, Faraz

    Highly active bimetallic catalysts were synthesized and used for the decomposition of formic acid for the production of hydrogen. Ruthenium alloys were prepared and resulted in a maximum formic acid conversion of 68% (after one hour at 180 °C) and a turnover frequency of 0.7/s (at 5 wt% formic acid). The most promising catalysts were characterized by the means of X-ray diffraction and scanning electron microscopy. Kinetic studies were also carried out over these catalysts for the determination of reaction rate and turnover frequency. Promotion of Ru/C with tin, barium and cesium increased the formic acid conversion by 55%, 18% and 11% respectively.

  19. Physical and chemical activation of reduced graphene oxide for enhanced adsorption and catalytic oxidation.

    PubMed

    Liu, Shizhen; Peng, Wenchao; Sun, Hongqi; Wang, Shaobin

    2014-01-21

    Physical and chemical activation of reduced graphene oxide (RGO) using different reagents, CO2, ZnCl2 and CO2/ZnCl2, to obtain highly porous and metal-free carbonaceous materials was carried out and their adsorption and catalytic behavior were investigated. Physical activation using CO2 was proved to be much more effective than chemical ZnCl2 activation, and increased the specific surface area (SSA) of RGO from ~200 to higher than 600 m(2) g(-1). Methylene blue (MB) was then used to evaluate the adsorption and catalytic activity of the activated RGO (A-RGO) materials with peroxymonosulfate (PMS) as an oxidant. It was found that the SSA and oxygen containing groups are two important factors determining the adsorptive and catalytic performance of the A-RGO materials. RGO by physicochemical CO2/ZnCl2 activation presented the best adsorption and RGO by physical CO2 activation exhibited the highest catalytic degradation of MB.

  20. The Role of Organic Capping Layers of Platinum Nanoparticles in Catalytic Activity of CO Oxidation

    SciTech Connect

    Park, Jeong Y.; Aliaga, Cesar; Renzas, J. Russell; Lee, Hyunjoo; Somorjai, Gabor A.

    2008-12-17

    We report the catalytic activity of colloid platinum nanoparticles synthesized with different organic capping layers. On the molecular scale, the porous organic layers have open spaces that permit the reactant and product molecules to reach the metal surface. We carried out CO oxidation on several platinum nanoparticle systems capped with various organic molecules to investigate the role of the capping agent on catalytic activity. Platinum colloid nanoparticles with four types of capping layer have been used: TTAB (Tetradecyltrimethylammonium Bromide), HDA (hexadecylamine), HDT (hexadecylthiol), and PVP (poly(vinylpyrrolidone)). The reactivity of the Pt nanoparticles varied by 30%, with higher activity on TTAB coated nanoparticles and lower activity on HDT, while the activation energy remained between 27-28 kcal/mol. In separate experiments, the organic capping layers were partially removed using ultraviolet light-ozone generation techniques, which resulted in increased catalytic activity due to the removal of some of the organic layers. These results indicate that the nature of chemical bonding between organic capping layers and nanoparticle surfaces plays a role in determining the catalytic activity of platinum colloid nanoparticles for carbon monoxide oxidation.

  1. Ag–Fe2O3 nanocomposites with enhanced catalytic activity for reduction of 4-nitrophenol

    NASA Astrophysics Data System (ADS)

    Liu, Shiben; Chen, Yingjie; Dong, Lifeng

    2016-07-01

    Hybrid nanostructures can be multifunctional and even possess enhanced properties. Ag–Fe2O3 nanocomposites and Ag nanoparticles (NPs) were fabricated and applied to catalyze the reduction of 4-nitrophenol. Compared with Ag NPs, Ag–Fe2O3 nanocomposites demonstrated enhanced catalytic activities. Furthermore, due to their magnetic properties, Ag–Fe2O3 nanocomposites could be easily separated from the reaction mixture and recycled through an external magnetic field. These findings will help us design hybrid nanostructures with catalytic activity and explore other potential applications of magnetic nanocomposites.

  2. Activity and hydrothermal stability of CeO₂-ZrO₂-WO₃ for the selective catalytic reduction of NOx with NH₃.

    PubMed

    Song, Zhongxian; Ning, Ping; Zhang, Qiulin; Li, Hao; Zhang, Jinhui; Wang, Yancai; Liu, Xin; Huang, Zhenzhen

    2016-04-01

    A series of CeO2-ZrO2-WO3 (CZW) catalysts prepared by a hydrothermal synthesis method showed excellent catalytic activity for selective catalytic reduction (SCR) of NO with NH3 over a wide temperature of 150-550°C. The effect of hydrothermal treatment of CZW catalysts on SCR activity was investigated in the presence of 10% H2O. The fresh catalyst showed above 90% NOx conversion at 201-459°C, which is applicable to diesel exhaust NOx purification (200-440°C). The SCR activity results indicated that hydrothermal aging decreased the SCR activity of CZW at low temperatures (below 300°C), while the activity was notably enhanced at high temperature (above 450°C). The aged CZW catalyst (hydrothermal aging at 700°C for 8 hr) showed almost 80% NOx conversion at 229-550°C, while the V2O5-WO3/TiO2 catalyst presented above 80% NOx conversion at 308-370°C. The effect of structural changes, acidity, and redox properties of CZW on the SCR activity was investigated. The results indicated that the excellent hydrothermal stability of CZW was mainly due to the CeO2-ZrO2 solid solution, amorphous WO3 phase and optimal acidity. In addition, the formation of WO3 clusters increased in size as the hydrothermal aging temperature increased, resulting in the collapse of structure, which could further affect the acidity and redox properties.

  3. Acid Strength and Bifunctional Catalytic Behavior of Alloys Comprised of Noble Metals and Oxophilic Metal Promoters

    SciTech Connect

    Hibbitts, David D.; Tan, Qiaohua; Neurock, Matthew

    2014-06-01

    The promotion of metal catalysts with partially oxidized oxophilic MOx species, such as ReOx-promoted Rh, has been demonstrated to produce Brønsted acid sites that can promote hydrogenolysis of oxygenate intermediates such as those found in biomass-derived species. A wide variety of alloy compositions and structures are examined in this work to investigate strongly acidic promoters by using DFT-calculated deprotonation energies (DPE) as a measure of acid strength. Sites with the highest acid strength had DPE less than 1100 kJ mol-1, similar to DPE values of heteropolyacids or acid-containing zeolites, and were found on alloys composed of an oxophilic metal (such as Re or W) with a noble metal (such as Rh or Pt). NH3 adsorbs more strongly to sites with increasing acid strength and the activation barriers for acid-catalyzed ring opening of a furan ring decrease with increasing acid strength, which was also shown to be stronger for OH acid sites bound to multiple oxophilic metal atoms in a three-fold configuration rather than OH sites adsorbed in an atop configuration on one oxophilic metal, indicating that small MOx clusters may yield sites with the highest acid strength.

  4. The Impact of Enzyme Orientation and Electrode Topology on the Catalytic Activity of Adsorbed Redox Enzymes

    PubMed Central

    McMillan, Duncan G. G.; Marritt, Sophie J.; Kemp, Gemma L.; Gordon-Brown, Piers; Butt, Julea N.; Jeuken, Lars J. C.

    2014-01-01

    It is well established that the structural details of electrodes and their interaction with adsorbed enzyme influences the interfacial electron transfer rate. However, for nanostructured electrodes, it is likely that the structure also impacts on substrate flux near the adsorbed enzymes and thus catalytic activity. Furthermore, for enzymes converting macro-molecular substrates it is possible that the enzyme orientation determines the nature of interactions between the adsorbed enzyme and substrate and therefore catalytic rates. In essence the electrode may impede substrate access to the active site of the enzyme. We have tested these possibilities through studies of the catalytic performance of two enzymes adsorbed on topologically distinct electrode materials. Escherichia coli NrfA, a nitrite reductase, was adsorbed on mesoporous, nanocrystalline SnO2 electrodes. CymA from Shewanella oneidensis MR-1 reduces menaquinone-7 within 200 nm sized liposomes and this reaction was studied with the enzyme adsorbed on SAM modified ultra-flat gold electrodes. PMID:24634538

  5. The Impact of Enzyme Orientation and Electrode Topology on the Catalytic Activity of Adsorbed Redox Enzymes.

    PubMed

    McMillan, Duncan G G; Marritt, Sophie J; Kemp, Gemma L; Gordon-Brown, Piers; Butt, Julea N; Jeuken, Lars J C

    2013-11-01

    It is well established that the structural details of electrodes and their interaction with adsorbed enzyme influences the interfacial electron transfer rate. However, for nanostructured electrodes, it is likely that the structure also impacts on substrate flux near the adsorbed enzymes and thus catalytic activity. Furthermore, for enzymes converting macro-molecular substrates it is possible that the enzyme orientation determines the nature of interactions between the adsorbed enzyme and substrate and therefore catalytic rates. In essence the electrode may impede substrate access to the active site of the enzyme. We have tested these possibilities through studies of the catalytic performance of two enzymes adsorbed on topologically distinct electrode materials. Escherichia coli NrfA, a nitrite reductase, was adsorbed on mesoporous, nanocrystalline SnO2 electrodes. CymA from Shewanella oneidensis MR-1 reduces menaquinone-7 within 200 nm sized liposomes and this reaction was studied with the enzyme adsorbed on SAM modified ultra-flat gold electrodes.

  6. Catalytic Hydrotreatment of Humins in Mixtures of Formic Acid/2-Propanol with Supported Ruthenium Catalysts.

    PubMed

    Wang, Yuehu; Agarwal, Shilpa; Kloekhorst, Arjan; Heeres, Hero Jan

    2016-05-10

    The catalytic hydrotreatment of humins, which are the solid byproducts from the conversion of C6 sugars (glucose, fructose) into 5-hydroxymethylfurfural (HMF) and levulinic acid (LA), by using supported ruthenium catalysts has been investigated. Reactions were carried out in a batch setup at elevated temperatures (400 °C) by using a hydrogen donor (formic acid (FA) in isopropanol (IPA) or hydrogen gas), with humins obtained from d-glucose. Humin conversions of up to 69 % were achieved with Ru/C and FA, whereas the performance for Ru on alumina was slightly poorer (59 % humin conversion). Humin oils were characterized by using a range of analytical techniques (GC, GC-MS, GCxGC, gel permeation chromatography) and were shown to consist of monomers, mainly alkyl phenolics (>45 % based on compounds detectable by GC) and higher oligomers. A reaction network for the reaction is proposed based on structural proposals for humins and the main reaction products. PMID:26836970

  7. Catalytic deactivation of methane steam reforming catalysts. I. Activation

    SciTech Connect

    Agnelli, M.E.; Demicheli, M.C.; Ponzi, E.N.

    1987-08-01

    An alumina-supported catalyst was studied both in its original state and after activation and sintering. Chemical composition and textural properties were determined, and crystalline compounds were identified. Active-phase and support transformations occurring during activation were determined by differential thermoanalysis (DTA), temperature-programmed reduction (TPR), and X-ray diffraction. The catalyst activated by means of various procedures was characterized by measuring crystallite size.

  8. pH control of the structure, composition, and catalytic activity of sulfated zirconia

    SciTech Connect

    Ivanov, Vladimir K.; Baranchikov, Alexander Ye.; Kopitsa, Gennady P.; Lermontov, Sergey A.; Yurkova, Lyudmila L.; Gubanova, Nadezhda N.; Ivanova, Olga S.; Lermontov, Anatoly S.; Rumyantseva, Marina N.; Vasilyeva, Larisa P.; Sharp, Melissa; Pranzas, P. Klaus; Tretyakov, Yuri D.

    2013-02-15

    We report a detailed study of structural and chemical transformations of amorphous hydrous zirconia into sulfated zirconia-based superacid catalysts. Precipitation pH is shown to be the key factor governing structure, composition and properties of amorphous sulfated zirconia gels and nanocrystalline sulfated zirconia. Increase in precipitation pH leads to substantial increase of surface fractal dimension (up to {approx}2.7) of amorphous sulfated zirconia gels, and consequently to increase in specific surface area (up to {approx}80 m{sup 2}/g) and simultaneously to decrease in sulfate content and total acidity of zirconia catalysts. Complete conversion of hexene-1 over as synthesized sulfated zirconia catalysts was observed even under ambient conditions. - Graphical abstract: Surface fractal dimension of amorphous sulfated zirconia and specific surface area and catalytic activity of crystalline sulfated zirconia as a function of precipitation pH. Highlights: Black-Right-Pointing-Pointer Structural transformation of amorphous hydrous zirconia into sulfated zirconia is studied. Black-Right-Pointing-Pointer Precipitation pH controls surface fractal dimension of amorphous zirconia gels. Black-Right-Pointing-Pointer Precipitation pH is the key factor governing properties of sulfated zirconia.

  9. A Catalytic DNA Activated by a Specific Strain of Bacterial Pathogen

    PubMed Central

    Shen, Zhifa; Wu, Zaisheng; Chang, Dingran; Zhang, Wenqing; Tram, Kha; Lee, Christine; Kim, Peter; Salena, Bruno J.

    2015-01-01

    Abstract Pathogenic strains of bacteria are known to cause various infectious diseases and there is a growing demand for molecular probes that can selectively recognize them. Here we report a special DNAzyme (catalytic DNA), RFD‐CD1, that shows exquisite specificity for a pathogenic strain of Clostridium difficile (C. difficile). RFD‐CD1 was derived by an in vitro selection approach where a random‐sequence DNA library was allowed to react with an unpurified molecular mixture derived from this strain of C. difficle, coupled with a subtractive selection strategy to eliminate cross‐reactivities to unintended C. difficile strains and other bacteria species. RFD‐CD1 is activated by a truncated version of TcdC, a transcription factor, that is unique to the targeted strain of C. difficle. Our study demonstrates for the first time that in vitro selection offers an effective approach for deriving functional nucleic acid probes that are capable of achieving strain‐specific recognition of bacterial pathogens. PMID:26676768

  10. A supramolecular ruthenium macrocycle with high catalytic activity for water oxidation that mechanistically mimics photosystem II

    NASA Astrophysics Data System (ADS)

    Schulze, Marcus; Kunz, Valentin; Frischmann, Peter D.; Würthner, Frank

    2016-06-01

    Mimicking the ingenuity of nature and exploiting the billions of years over which natural selection has developed numerous effective biochemical conversions is one of the most successful strategies in a chemist's toolbox. However, an inability to replicate the elegance and efficiency of the oxygen-evolving complex of photosystem II (OEC-PSII) in its oxidation of water into O2 is a significant bottleneck in the development of a closed-loop sustainable energy cycle. Here, we present an artificial metallosupramolecular macrocycle that gathers three Ru(bda) centres (bda = 2,2‧-bipyridine-6,6‧-dicarboxylic acid) that catalyses water oxidation. The macrocyclic architecture accelerates the rate of water oxidation via a water nucleophilic attack mechanism, similar to the mechanism exhibited by OEC-PSII, and reaches remarkable catalytic turnover frequencies >100 s-1. Photo-driven water oxidation yields outstanding activity, even in the nM concentration regime, with a turnover number of >1,255 and turnover frequency of >13.1 s-1.

  11. A supramolecular ruthenium macrocycle with high catalytic activity for water oxidation that mechanistically mimics photosystem II

    NASA Astrophysics Data System (ADS)

    Schulze, Marcus; Kunz, Valentin; Frischmann, Peter D.; Würthner, Frank

    2016-06-01

    Mimicking the ingenuity of nature and exploiting the billions of years over which natural selection has developed numerous effective biochemical conversions is one of the most successful strategies in a chemist's toolbox. However, an inability to replicate the elegance and efficiency of the oxygen-evolving complex of photosystem II (OEC-PSII) in its oxidation of water into O2 is a significant bottleneck in the development of a closed-loop sustainable energy cycle. Here, we present an artificial metallosupramolecular macrocycle that gathers three Ru(bda) centres (bda = 2,2‧-bipyridine-6,6‧-dicarboxylic acid) that catalyses water oxidation. The macrocyclic architecture accelerates the rate of water oxidation via a water nucleophilic attack mechanism, similar to the mechanism exhibited by OEC-PSII, and reaches remarkable catalytic turnover frequencies >100 s–1. Photo-driven water oxidation yields outstanding activity, even in the nM concentration regime, with a turnover number of >1,255 and turnover frequency of >13.1 s–1.

  12. Size effect of silver nanoclusters on their catalytic activity for oxygen electro-reduction

    NASA Astrophysics Data System (ADS)

    Lu, Yizhong; Chen, Wei

    2012-01-01

    Two different sized silver nanoclusters are prepared by two different synthetic routs. First, a small nanocluster (NC) which is 0.7 nm in diameter was synthesized by using meso-2, 3-dimercapto-succinic acid (DMSA) as a capping ligand, and second a larger nanoparticle (NP) which is 3.3 nm in diameter was prepared by chemical reduction and coated with DMSA. The as-prepared silver nanoclusters or nanoparticles are then loaded onto a glassy carbon electrode and the size effect on their electrocatalytic activity toward oxygen reduction reaction (ORR) is investigated with electrochemical techniques in alkaline electrolyte. The cyclic voltammetric (CV) studies show that the onset potential of ORR on 0.7 nm silver nanoclusters is 150 mV more positive than that from 3.3 nm silver nanoparticles. And compared to the larger nanoparticles, five times higher current density of ORR at -0.80 V is obtained from the 0.7 nm silver nanoclusters. These CV results indicate that the smaller Ag nanoclusters exhibit higher catalytic performance for ORR. Rotating disk voltammetric studies show ORR on both DMSA monolayer-protected silver clusters is dominated first by a two-electron transfer pathway to produce H2O2 and then peroxide is reduced by 2 more electrons to produce water.

  13. Nickel-cobalt nanoparticles supported on single-walled carbon nanotubes and their catalytic hydrogenation activity.

    PubMed

    Lekgoathi, Mpho D S; Augustyn, Willem G; Heveling, Josef

    2011-08-01

    Single-walled carbon nanotubes were synthesized from graphite using the arc discharge technique. A nickel/yttrium/graphite mixture was used as the catalyst. After purification by sonication in a Triton X-100 solution, nickel-cobalt metal nanoparticles were deposited on the surface of the single-walled carbon nanotubes. The resulting material and/or the nanotubes themselves were characterized by physisorption, Raman spectroscopy, high-resolution transition electron microscopy and X-ray diffraction. Raman spectroscopy indicates that the nanotubes, prepared by the arc discharge technique, are semi-conducting with a diameter centering at 1.4 nm. The average nickel-cobalt particle size is estimated to be in the region of 8 nm. The catalytic activity of the material was examined for the hydrogenation of unsaturated fatty acid methyl esters obtained from avocado oil. The carbon nanotube supported nickel-cobalt particles effectively hydrogenate polyunsaturated methyl linoleate to monounsaturated methyl oleate. In contrast to a conventional nickel on kieselghur catalyst, further hydrogenation of methyl oleate to undesired methyl stearate was not observed. PMID:22103112

  14. A supramolecular ruthenium macrocycle with high catalytic activity for water oxidation that mechanistically mimics photosystem II.

    PubMed

    Schulze, Marcus; Kunz, Valentin; Frischmann, Peter D; Würthner, Frank

    2016-06-01

    Mimicking the ingenuity of nature and exploiting the billions of years over which natural selection has developed numerous effective biochemical conversions is one of the most successful strategies in a chemist's toolbox. However, an inability to replicate the elegance and efficiency of the oxygen-evolving complex of photosystem II (OEC-PSII) in its oxidation of water into O2 is a significant bottleneck in the development of a closed-loop sustainable energy cycle. Here, we present an artificial metallosupramolecular macrocycle that gathers three Ru(bda) centres (bda = 2,2'-bipyridine-6,6'-dicarboxylic acid) that catalyses water oxidation. The macrocyclic architecture accelerates the rate of water oxidation via a water nucleophilic attack mechanism, similar to the mechanism exhibited by OEC-PSII, and reaches remarkable catalytic turnover frequencies >100 s(-1). Photo-driven water oxidation yields outstanding activity, even in the nM concentration regime, with a turnover number of >1,255 and turnover frequency of >13.1 s(-1).

  15. Preliminary X-ray crystallographic studies of BthTX-II, a myotoxic Asp49-phospholipase A{sub 2} with low catalytic activity from Bothrops jararacussu venom

    SciTech Connect

    Corrêa, L. C.; Marchi-Salvador, D. P.; Cintra, A. C. O.; Soares, A. M.

    2006-08-01

    A myotoxic Asp49-PLA{sub 2} with low catalytic activity from B. jararacussu (BthTX-II) was crystallized in the monoclinic crystal system; a complete X-ray diffraction data set was collected and a molecular-replacement solution was obtained. The oligomeric structure of BthTX-II resembles those of the Asp49-PLA{sub 2} PrTX-III and all bothropic Lys49-PLA{sub 2}s. For the first time, a complete X-ray diffraction data set has been collected from a myotoxic Asp49-phospholipase A{sub 2} (Asp49-PLA{sub 2}) with low catalytic activity (BthTX-II from Bothrops jararacussu venom) and a molecular-replacement solution has been obtained with a dimer in the asymmetric unit. The quaternary structure of BthTX-II resembles the myotoxin Asp49-PLA{sub 2} PrTX-III (piratoxin III from B. pirajai venom) and all non-catalytic and myotoxic dimeric Lys49-PLA{sub 2}s. In contrast, the oligomeric structure of BthTX-II is different from the highly catalytic and non-myotoxic BthA-I (acidic PLA{sub 2} from B. jararacussu). Thus, comparison between these structures should add insight into the catalytic and myotoxic activities of bothropic PLA{sub 2}s.

  16. Preparation of zeolite supported TiO2, ZnO and ZrO2 and the study on their catalytic activity in NOx reduction and 1-pentanol dehydration

    NASA Astrophysics Data System (ADS)

    Fatimah, Is

    2016-03-01

    Preparation of zeolite supported TiO2, ZnO and ZrO2 and their catalytic activity was studied. Activated natural zeolite from Indonesia was utilized for the preparation and catalytic activity test on NOx reduction by NH3 and also 1-pentanol dehydration were examined. Physicochemical characterization of materials was studied by x-ray diffraction (XRD) measurement, scanning electron microscope, solid acidity determination and also gas sorption analysis. The results confirmed that the preparation gives some improvements on physicochemical characters suitable for catalysis mechanism in those reactions. Solid acidity and specific surface area contributed significantly to the activity.

  17. Novel Dextranase Catalyzing Cycloisomaltooligosaccharide Formation and Identification of Catalytic Amino Acids and Their Functions Using Chemical Rescue Approach*

    PubMed Central

    Kim, Young-Min; Kiso, Yoshiaki; Muraki, Tomoe; Kang, Min-Sun; Nakai, Hiroyuki; Saburi, Wataru; Lang, Weeranuch; Kang, Hee-Kwon; Okuyama, Masayuki; Mori, Haruhide; Suzuki, Ryuichiro; Funane, Kazumi; Suzuki, Nobuhiro; Momma, Mitsuru; Fujimoto, Zui; Oguma, Tetsuya; Kobayashi, Mikihiko; Kim, Doman; Kimura, Atsuo

    2012-01-01

    A novel endodextranase from Paenibacillus sp. (Paenibacillus sp. dextranase; PsDex) was found to mainly produce isomaltotetraose and small amounts of cycloisomaltooligosaccharides (CIs) with a degree of polymerization of 7–14 from dextran. The 1,696-amino acid sequence belonging to the glycosyl hydrolase family 66 (GH-66) has a long insertion (632 residues; Thr451–Val1082), a portion of which shares identity (35% at Ala39–Ser1304 of PsDex) with Pro32–Ala755 of CI glucanotransferase (CITase), a GH-66 enzyme that catalyzes the formation of CIs from dextran. This homologous sequence (Val837–Met932 for PsDex and Tyr404–Tyr492 for CITase), similar to carbohydrate-binding module 35, was not found in other endodextranases (Dexs) devoid of CITase activity. These results support the classification of GH-66 enzymes into three types: (i) Dex showing only dextranolytic activity, (ii) Dex catalyzing hydrolysis with low cyclization activity, and (iii) CITase showing CI-forming activity with low dextranolytic activity. The fact that a C-terminal truncated enzyme (having Ala39–Ser1304) has 50% wild-type PsDex activity indicates that the C-terminal 392 residues are not involved in hydrolysis. GH-66 enzymes possess four conserved acidic residues (Asp189, Asp340, Glu412, and Asp1254 of PsDex) of catalytic candidates. Their amide mutants decreased activity (11,500 to 140,000 times), and D1254N had 36% activity. A chemical rescue approach was applied to D189A, D340G, and E412Q using α-isomaltotetraosyl fluoride with NaN3. D340G or E412Q formed a β- or α-isomaltotetraosyl azide, respectively, strongly indicating Asp340 and Glu412 as a nucleophile and acid/base catalyst, respectively. Interestingly, D189A synthesized small sized dextran from α-isomaltotetraosyl fluoride in the presence of NaN3. PMID:22461618

  18. A novel peroxisome proliferator-activated receptor alpha/gamma agonist, BPR1H0101, inhibits topoisomerase II catalytic activity in human cancer cells.

    PubMed

    Kao, Yu-Hsun; Hsieh, Hsing-Pang; Chitlimalla, Santhosh Kumar; Pan, Wen-Yu; Kuo, Ching-Chuan; Tsai, Yuan-Chin; Lin, Wen-Hsing; Chuang, Shuang-En; Chang, Jang-Yang

    2008-02-01

    Peroxisome proliferator-activated receptor (PPAR) gamma agonists are used clinically for treating diabetes mellitus and cancer. 2-Methyl-2[(1-{3-phenyl-7-propylbenzol[d]isoxazol-6-yl}oxy)propyl]-1H-4-indolyl) oxy]propanoic acid (BPR1H0101) is a novel synthetic indole-based compound, discovered through research to identify new PPARgamma agonists, and it acts as a dual agonist for PPARgamma and PPARalpha. Isobologram analysis demonstrated that BPR1H0101 is capable of antagonistic interaction with the topoisomerase (topo) II poison, VP16. A study of its mechanism showed that BPR1H0101 could inhibit the catalytic activity of topo II in vitro, but did not produce detectable topo II-mediated DNA strand breaks in human oral cancer KB cells. Furthermore, BPR1H0101 could inhibit VP16-induced topo II-mediated DNA cleavage and ataxia-telangiectasia-mutated phosphorylation in KB cells. The results suggest that BPR1H0101 can interfere with the topo II reaction by inhibiting catalytic activity before the formation of the intermediate cleavable complex; consequently, it can impede VP16-induced topo II-mediated DNA cleavage and cell death. This is the first identified PPARalpha/gamma agonist that can serve as a topo II catalytic inhibitor, to interfere with VP16-induced cell death. The result might have relevance to the clinical use of the PPARalpha/gamma agonist in combination chemotherapy. PMID:18176111

  19. Structural and mechanistic analysis of trans-3-chloroacrylic acid dehalogenase activity

    SciTech Connect

    Pegan, Scott D.; Serrano, Hector; Whitman, Christian P.; Mesecar, Andrew D.

    2008-12-01

    The X-ray structure of a noncovalently modified trans-3-chloroacrylic acid dehalogenase with a substrate-homolog acetate bound in the active site has been determined to 1.7 Å resolution. Elucidation of catalytically important water is reported and multiple conformations of the catalytic residue αGlu52 are observed. Trans-3-chloroacrylic acid dehalogenase (CaaD) is a critical enzyme in the trans-1, 3-dichloropropene (DCP) degradation pathway in Pseudomonas pavonaceae 170. This enzyme allows bacteria to use trans-DCP, a common component in commercially produced fumigants, as a carbon source. CaaD specifically catalyzes the fourth step of the pathway by cofactor-independent dehalogenation of a vinyl carbon–halogen bond. Previous studies have reported an X-ray structure of CaaD under acidic conditions with a covalent modification of the catalytic βPro1 residue. Here, the 1.7 Å resolution X-ray structure of CaaD under neutral (pH 6.5) conditions is reported without the presence of the covalent adduct. In this new structure, a substrate-like acetate molecule is bound within the active site in a position analogous to the putative substrate-binding site. Additionally, a catalytically important water molecule was identified, consistent with previously proposed reaction schemes. Finally, flexibility of the catalytically relevant side chain αGlu52 is observed in the structure, supporting its role in the catalytic mechanism.

  20. HIGH-THROUGHPUT IDENTIFICATION OF CATALYTIC REDOX-ACTIVE CYSTEINE RESIDUES

    EPA Science Inventory

    Cysteine (Cys) residues often play critical roles in proteins; however, identification of their specific functions has been limited to case-by-case experimental approaches. We developed a procedure for high-throughput identification of catalytic redox-active Cys in proteins by se...

  1. Reversible amorphization and the catalytically active state of crystalline Co3O4 during oxygen evolution

    PubMed Central

    Bergmann, Arno; Martinez-Moreno, Elias; Teschner, Detre; Chernev, Petko; Gliech, Manuel; de Araújo, Jorge Ferreira; Reier, Tobias; Dau, Holger; Strasser, Peter

    2015-01-01

    Water splitting catalysed by earth-abundant materials is pivotal for global-scale production of non-fossil fuels, yet our understanding of the active catalyst structure and reactivity is still insufficient. Here we report on the structurally reversible evolution of crystalline Co3O4 electrocatalysts during oxygen evolution reaction identified using advanced in situ X-ray techniques. At electrode potentials facilitating oxygen evolution, a sub-nanometre shell of the Co3O4 is transformed into an X-ray amorphous CoOx(OH)y which comprises di-μ-oxo-bridged Co3+/4+ ions. Unlike irreversible amorphizations, here, the formation of the catalytically-active layer is reversed by re-crystallization upon return to non-catalytic electrode conditions. The Co3O4 material thus combines the stability advantages of a controlled, stable crystalline material with high catalytic activity, thanks to the structural flexibility of its active amorphous oxides. We propose that crystalline oxides may be tailored for generating reactive amorphous surface layers at catalytic potentials, just to return to their stable crystalline state under rest conditions. PMID:26456525

  2. Aligned carbon nanotube with electro-catalytic activity for oxygen reduction reaction

    DOEpatents

    Liu, Di-Jia; Yang, Junbing; Wang, Xiaoping

    2010-08-03

    A catalyst for an electro-chemical oxygen reduction reaction (ORR) of a bundle of longitudinally aligned carbon nanotubes having a catalytically active transition metal incorporated longitudinally in said nanotubes. A method of making an electro-chemical catalyst for an oxygen reduction reaction (ORR) having a bundle of longitudinally aligned carbon nanotubes with a catalytically active transition metal incorporated throughout the nanotubes, where a substrate is in a first reaction zone, and a combination selected from one or more of a hydrocarbon and an organometallic compound containing an catalytically active transition metal and a nitrogen containing compound and an inert gas and a reducing gas is introduced into the first reaction zone which is maintained at a first reaction temperature for a time sufficient to vaporize material therein. The vaporized material is then introduced to a second reaction zone maintained at a second reaction temperature for a time sufficient to grow longitudinally aligned carbon nanotubes over the substrate with a catalytically active transition metal incorporated throughout the nanotubes.

  3. Hollow mesoporous ceria nanoreactors with enhanced activity and stability for catalytic application.

    PubMed

    Liu, Baocang; Yu, Shengli; Wang, Qin; Hu, Wenting; Jing, Peng; Liu, Yang; Jia, Wenjing; Liu, Yongxin; Liu, Lixia; Zhang, Jun

    2013-05-01

    Novel hollow mesoporous @M/CeO(2) (M = Au, Pd, and Au-Pd) nanospheres are created. The nanospheres can be used as effective nanoreactors with superior catalytic activity and stability for reduction of 4-nitrophenol due to their hollow mesoporous structural features.

  4. A highly sensitive technique for detecting catalytically active nanoparticles against a background of general workplace aerosols

    NASA Astrophysics Data System (ADS)

    Neubauer, N.; Weis, F.; Binder, A.; Seipenbusch, M.; Kasper, G.

    2011-07-01

    A new measurement technique was studied using catalysis to specifically detect airborne nanoparticles in presence of background particles in the workplace air. Catalytically active nanoparticles produced by spark discharge were used as aerosol catalysts. According to these particles suitable catalytic test reactions were chosen and investigated by two different approaches: catalysis on airborne nanoparticles and catalysis on deposited nanoparticles. The results indicate that catalysis is applicable for the specific measurement of nanoparticles in the workplace air. Catalysis on airborne particles is suitable for the specific detection of very active nanoparticles, e.g. platinum or nickel, at high concentrations of about 107 #/cm3. The approach of catalysis on deposited particles is better suited for nanoparticle aerosols at low concentrations, for slow catalytic reactions or less active nanoparticles like iron oxide (Fe2O3). On the basis of the experimental results detection limits in the range of μg or even ng were calculated which assure the good potential of catalysis for the specific detection of nanoparticles in the workplace air based on their catalytic activity.

  5. Confined iron nanowires enhance the catalytic activity of carbon nanotubes in the aerobic oxidation of cyclohexane.

    PubMed

    Yang, Xixian; Yu, Hao; Peng, Feng; Wang, Hongjuan

    2012-07-01

    Inside job: New applications of carbon materials pave the way towards greener chemical syntheses. The encapsulation of metallic Fe within CNTs improves electron transfer between the metal and the CNTs. The resulting material offers a high catalytic activity and easy magnetic separation of catalyst in the heterogeneous selective oxidation of cyclohexane. PMID:22488987

  6. Self-propulsion and interactions of catalytic particles in a chemically active medium

    NASA Astrophysics Data System (ADS)

    Banigan, Edward J.; Marko, John F.

    2016-01-01

    Enzymatic "machines," such as catalytic rods or colloids, can self-propel and interact by generating gradients of their substrates. We theoretically investigate the behaviors of such machines in a chemically active environment where their catalytic substrates are continuously synthesized and destroyed, as occurs in living cells. We show how the kinetic properties of the medium modulate self-propulsion and pairwise interactions between machines, with the latter controlled by a tunable characteristic interaction range analogous to the Debye screening length in an electrolytic solution. Finally, we discuss the effective force arising between interacting machines and possible biological applications, such as partitioning of bacterial plasmids.

  7. Modeling the heterogeneous catalytic activity of a single nanoparticle using a first passage time distribution formalism

    NASA Astrophysics Data System (ADS)

    Das, Anusheela; Chaudhury, Srabanti

    2015-11-01

    Metal nanoparticles are heterogeneous catalysts and have a multitude of non-equivalent, catalytic sites on the nanoparticle surface. The product dissociation step in such reaction schemes can follow multiple pathways. Proposed here for the first time is a completely analytical theoretical framework, based on the first passage time distribution, that incorporates the effect of heterogeneity in nanoparticle catalysis explicitly by considering multiple, non-equivalent catalytic sites on the nanoparticle surface. Our results show that in nanoparticle catalysis, the effect of dynamic disorder is manifested even at limiting substrate concentrations in contrast to an enzyme that has only one well-defined active site.

  8. Catalytic cracking of vacuum gasoil in the presence of activating additives

    SciTech Connect

    Abdul'menov, R.G.; Serikov, P.Y.; Smidovich, E.V.; Syunyaev, Z.I.

    1985-07-01

    These authors perform catalytic cracking of vacuum gas oil in a singlepass laboratory flow unit with mechanized mixing of a bed of the microbead zeolitic catalyst KMTsR. They present data in a series of three tables and in a set of three charts. Analysis of these data leads them to conclude that the use of activating additives makes it possible to reduce the coke yield and bring coke deposition down to a preassigned level. They further conclude that their method for intensifying catalytic cracking is especially promising for heavy types of feed with high carbon residues.

  9. Activity prediction of substrates in NADH-dependent carbonyl reductase by docking requires catalytic constraints and charge parameterization of catalytic zinc environment.

    PubMed

    Dhoke, Gaurao V; Loderer, Christoph; Davari, Mehdi D; Ansorge-Schumacher, Marion; Schwaneberg, Ulrich; Bocola, Marco

    2015-11-01

    Molecular docking of substrates is more challenging compared to inhibitors as the reaction mechanism has to be considered. This becomes more pronounced for zinc-dependent enzymes since the coordination state of the catalytic zinc ion is of greater importance. In order to develop a predictive substrate docking protocol, we have performed molecular docking studies of diketone substrates using the catalytic state of carbonyl reductase 2 from Candida parapsilosis (CPCR2). Different docking protocols using two docking methods (AutoDock Vina and AutoDock4.2) with two different sets of atomic charges (AM1-BCC and HF-RESP) for catalytic zinc environment and substrates as well as two sets of vdW parameters for zinc ion were examined. We have selected the catalytic binding pose of each substrate by applying mechanism based distance criteria. To compare the performance of the docking protocols, the correlation plots for the binding energies of these catalytic poses were obtained against experimental Vmax values of the 11 diketone substrates for CPCR2. The best correlation of 0.73 was achieved with AutoDock4.2 while treating catalytic zinc ion in optimized non-bonded (NBopt) state with +1.01 charge on the zinc ion, compared to 0.36 in non-bonded (+2.00 charge on the zinc ion) state. These results indicate the importance of catalytic constraints and charge parameterization of catalytic zinc environment for the prediction of substrate activity in zinc-dependent enzymes by molecular docking. The developed predictive docking protocol described here is in principle generally applicable for the efficient in silico substrate spectra characterization of zinc-dependent ADH.

  10. Structural Basis for the Catalytic Activity of Human SER/THR Protein Phosphatase-5

    NASA Technical Reports Server (NTRS)

    Swingle, M. R.; Honkanen, R.; Ciszak, E.

    2004-01-01

    Serinekhreonine protein phosphatase-5 (PP5) affects many signaling networks that regulate cell growth. Here we report the 1.6 Angstrom resolution crystal structure of PP5 catalytic domain with metal and phosphate ions in the active site. The structure reveals a mechanism for PPS-mediated catalysis that requires the precise positioning of two metal ions within a conserved Asp(sup 271)-M(sub 1),-M(sub 2)-His(sup 427)-W(sup 2)-His(sup 304)-Asp(sup 274) catalytic motif, and provides a structural basis for the exceptional catalytic proficiency of protein phosphatases placing them among the most powerful catalysts. Resolution of the entire C-terminus revealed a novel subdomain, and the structure of PP5 should aid development of specific inhibitors.

  11. Superior Catalytic Activity of Electrochemically Reduced Graphene Oxide Supported Iron Phthalocyanines toward Oxygen Reduction Reaction.

    PubMed

    Liu, Dong; Long, Yi-Tao

    2015-11-01

    Structure and surface properties of supporting materials are of great importance for the catalytic performance of the catalysts. Herein, we prepared the iron phthalocyanine (FePc) functionalized electrochemically reduced graphene oxide (ERGO) by the electrochemical reduction of FePc/GO. The resultant FePc/ERGO exhibits higher catalytic activity toward ORR than that of FePc/graphene. More importantly, the onset potential for ORR at FePc/ERGO positively shifts by 45 mV compared with commercial Pt/C in alkaline media. Besides, FePc/ERGO displays enhanced durability and selectivity toward ORR. The superior catalytic performance of FePc/ERGO for ORR are ascribed to the self-supported structure of ERGO, uniformly morphology and size of FePc nanoparticles.

  12. Dynamic formation of single-atom catalytic active sites on ceria-supported gold nanoparticles

    PubMed Central

    Wang, Yang-Gang; Mei, Donghai; Glezakou, Vassiliki-Alexandra; Li, Jun; Rousseau, Roger

    2015-01-01

    Catalysis by gold supported on reducible oxides has been extensively studied, yet issues such as the nature of the catalytic site and the role of the reducible support remain fiercely debated topics. Here we present ab initio molecular dynamics simulations of an unprecedented dynamic single-atom catalytic mechanism for the oxidation of carbon monoxide by ceria-supported gold clusters. The reported dynamic single-atom catalytic mechanism results from the ability of the gold cation to strongly couple with the redox properties of the ceria in a synergistic manner, thereby lowering the energy of redox reactions. The gold cation can break away from the gold nanoparticle to catalyse carbon monoxide oxidation, adjacent to the metal/oxide interface and subsequently reintegrate back into the nanoparticle after the reaction is completed. Our study highlights the importance of the dynamic creation of active sites under reaction conditions and their essential role in catalysis. PMID:25735407

  13. Catalytic ozonation of 2,4-dichlorophenoxyacetic acid using alumina in the presence of a radical scavenger.

    PubMed

    Guzman-Perez, Carlos A; Soltan, Jafar; Robertson, Jared

    2012-01-01

    Using a laboratory-scale mixed reactor, the performance of alumina in degrading 2,4-Dichlorophenoxyacetic acid with ozone in the presence of tert-butyl alcohol radical scavenger was studied. The operating variables investigated were the dose of alumina catalyst and solution pH. Results showed that using ozone and alumina leads to a significant increase in 2,4-D removal in comparison to non-catalytic ozonation and adsorption processes. The observed reaction rate constants (k(obs)) for 2,4-D during ozonation were found to increase linearly with increasing catalyst dose. At pH 5, the k(obs) value increased from 19.3 to 26 M(-1) s(-1) and 67 M(-1) s(-1) when varying the alumina dose from 1 to 2 and 4 g L(-1), respectively. As pH was increased, higher reaction rates were observed for both non-catalytic ozonation and catalytic ozonation processes. Thus, at pH 3 and using a catalyst dose of 8 g L(-1), the k(obs) values for non-catalytic ozonation and catalytic ozonation processes were 3.4 and 58.9 M(-1) s(-1), respectively, whereas at pH 5 reaction rate constants of 6.5 and 128.5 M(-1) s(-1) were observed, respectively. Analysis of total organic carbon suggested that catalytic ozonation with alumina achieved a considerable level of mineralization of 2,4-D. Adsorption of 2,4-D on alumina was found to play an important role in the catalytic ozonation process.

  14. Catalytic properties of NiSO{sub 4}/ZrO{sub 2} promoted with Fe{sub 2}O{sub 3} for acid catalysis

    SciTech Connect

    Sohn, Jong Rack . E-mail: jrsohn@knu.ac.kr; Lim, Jun Seob

    2006-07-13

    A series of catalysts, NiSO{sub 4}/Fe{sub 2}O{sub 3}-ZrO{sub 2}, for acid catalysis were prepared by the impregnation method, where support, Fe{sub 2}O{sub 3}-ZrO{sub 2} was prepared by the co-precipitation method using a mixed aqueous solution of zirconium oxychloride and iron nitrate solution followed by adding an aqueous ammonia solution. No diffraction line of nickel sulfate was observed up to 20 wt.%, indicating good dispersion of nickel sulfate on the surface of Fe{sub 2}O{sub 3}-ZrO{sub 2}. The addition of nickel sulfate (or Fe{sub 2}O{sub 3}) to ZrO{sub 2} shifted the phase transition of ZrO{sub 2} from amorphous to tetragonal to higher temperature because of the interaction between nickel sulfate (or Fe{sub 2}O{sub 3}) and ZrO{sub 2}. 15-NiSO{sub 4}/Fe{sub 2}O{sub 3}-ZrO{sub 2} containing 15 wt.% NiSO{sub 4} and 5 mol% Fe{sub 2}O{sub 3}, and calcined at 700 deg. C exhibited maximum catalytic activities for both reactions, 2-propanol dehydration and cumene dealkylation. The catalytic activities for both reactions were correlated with the acidity of catalysts measured by the ammonia chemisorption method. The addition of Fe{sub 2}O{sub 3} up to 5 mol% enhanced the acidity, thermal property, and catalytic activities of NiSO{sub 4}/Fe{sub 2}O{sub 3}-ZrO{sub 2} gradually due to the interaction between Fe{sub 2}O{sub 3} and ZrO{sub 2} and consequent formation of Fe-O-Zr bond.

  15. In situ generation of o-iodoxybenzoic acid (IBX) and the catalytic use of it in oxidation reactions in the presence of Oxone as a co-oxidant.

    PubMed

    Thottumkara, Arun P; Bowsher, Michael S; Vinod, Thottumkara K

    2005-07-01

    [structure: see text] Catalytic use of o-iodoxybenzoic acid (IBX) in the presence of Oxone as a co-oxidant is demonstrated for the oxidation of primary and secondary alcohols in user- and eco-friendly solvent mixtures. Also demonstrated is the in situ (re)oxidation of 2-iodosobenzoic acid (IBA) and even commercially available 2-iodobenzoic acid (2IBAcid) by Oxone to IBX allowing one to use these less hazardous reagents, in place of potentially explosive IBX, as catalytic oxidants.

  16. mTOR Ser-2481 Autophosphorylation Monitors mTORC-specific Catalytic Activity and Clarifies Rapamycin Mechanism of Action*

    PubMed Central

    Soliman, Ghada A.; Acosta-Jaquez, Hugo A.; Dunlop, Elaine A.; Ekim, Bilgen; Maj, Nicole E.; Tee, Andrew R.; Fingar, Diane C.

    2010-01-01

    The mammalian target of rapamycin (mTOR) Ser/Thr kinase signals in at least two multiprotein complexes distinguished by their different partners and sensitivities to rapamycin. Acute rapamycin inhibits signaling by mTOR complex 1 (mTORC1) but not mTOR complex 2 (mTORC2), which both promote cell growth, proliferation, and survival. Although mTORC2 regulation remains poorly defined, diverse cellular mitogens activate mTORC1 signaling in a manner that requires sufficient levels of amino acids and cellular energy. Before the identification of distinct mTOR complexes, mTOR was reported to autophosphorylate on Ser-2481 in vivo in a rapamycin- and amino acid-insensitive manner. These results suggested that modulation of mTOR intrinsic catalytic activity does not universally underlie mTOR regulation. Here we re-examine the regulation of mTOR Ser-2481 autophosphorylation (Ser(P)-2481) in vivo by studying mTORC-specific Ser(P)-2481 in mTORC1 and mTORC2, with a primary focus on mTORC1. In contrast to previous work, we find that acute rapamycin and amino acid withdrawal markedly attenuate mTORC1-associated mTOR Ser(P)-2481 in cycling cells. Although insulin stimulates both mTORC1- and mTORC2-associated mTOR Ser(P)-2481 in a phosphatidylinositol 3-kinase-dependent manner, rapamycin acutely inhibits insulin-stimulated mTOR Ser(P)-2481 in mTORC1 but not mTORC2. By interrogating diverse mTORC1 regulatory input, we find that without exception mTORC1-activating signals promote, whereas mTORC1-inhibitory signals decrease mTORC1-associated mTOR Ser(P)-2481. These data suggest that mTORC1- and likely mTORC2-associated mTOR Ser-2481 autophosphorylation directly monitors intrinsic mTORC-specific catalytic activity and reveal that rapamycin inhibits mTORC1 signaling in vivo by reducing mTORC1 catalytic activity. PMID:20022946

  17. Efficient Diethylzinc/Gallic Acid and Diethylzinc/Gallic Acid Ester Catalytic Systems for the Ring-Opening Polymerization of rac-Lactide.

    PubMed

    Żółtowska, Karolina; Piotrowska, Urszula; Oledzka, Ewa; Sobczak, Marcin

    2015-12-08

    Polylactide (PLA) represents one of the most promising biomedical polymers due to its biodegradability, bioresorbability and good biocompatibility. This work highlights the synthesis and characterization of PLAs using novel diethylzinc/gallic acid (ZnEt₂/GAc) and diethylzinc/propyl gallate (ZnEt₂/PGAc) catalytic systems that are safe for human body. The results of the ring-opening polymerization (ROP) of rac-lactide (rac-LA) in the presence of zinc-based catalytic systems have shown that, depending on the reaction conditions, "predominantly isotactic", disyndiotactic or atactic PLA can be obtained. Therefore, the controlled and stereoselective ROP of rac-LA is discussed in detail in this paper.

  18. Conformational Stability and Catalytic Activity of PTEN Variants Linked to Cancers and Autism Spectrum Disorders

    PubMed Central

    Johnston, Sean B.; Raines, Ronald T.

    2015-01-01

    Phosphoinositides are membrane components that play critical regulatory roles in mammalian cells. The enzyme PTEN, which catalyzes the dephosphorylation of the phosphoinositide PIP3, is damaged in most sporadic tumors. Mutations in the PTEN gene have also been linked to autism spectrum disorders and other forms of delayed development. Here, human PTEN is shown to be on the cusp of unfolding under physiological conditions. Variants of human PTEN linked to somatic cancers and disorders on the autism spectrum are shown to be impaired in their conformational stability, catalytic activity, or both. Those variants linked only to autism have higher activity than those linked to cancers. PTEN-L, which is a secreted trans-active isoform, has greater conformational stability than does the wild-type enzyme. These data indicate that PTEN is a fragile enzyme cast in a crucial role in cellular metabolism, and suggest that PTEN-L is a repository for a critical catalytic activity. PMID:25647146

  19. Engineering a hyper-catalytic enzyme by photo-activated conformation modulation

    SciTech Connect

    Agarwal, Pratul K

    2012-01-01

    Enzyme engineering for improved catalysis has wide implications. We describe a novel chemical modification of Candida antarctica lipase B that allows modulation of the enzyme conformation to promote catalysis. Computational modeling was used to identify dynamical enzyme regions that impact the catalytic mechanism. Surface loop regions located distal to active site but showing dynamical coupling to the reaction were connected by a chemical bridge between Lys136 and Pro192, containing a derivative of azobenzene. The conformational modulation of the enzyme was achieved using two sources of light that alternated the azobenzene moiety in cis and trans conformations. Computational model predicted that mechanical energy from the conformational fluctuations facilitate the reaction in the active-site. The results were consistent with predictions as the activity of the engineered enzyme was found to be enhanced with photoactivation. Preliminary estimations indicate that the engineered enzyme achieved 8-52 fold better catalytic activity than the unmodulated enzyme.

  20. Enhancement of biomass conversion in catalytic fast pyrolysis by microwave-assisted formic acid pretreatment.

    PubMed

    Feng, Yu; Li, Guangyu; Li, Xiangyu; Zhu, Ning; Xiao, Bo; Li, Jian; Wang, Yujue

    2016-08-01

    This study investigated microwave-assisted formic acid (MW-FA) pretreatment as a possible way to improve aromatic production from catalytic fast pyrolysis (CFP) of lignocellulosic biomass. Results showed that short duration of MW-FA pretreatment (5-10min) could effectively disrupt the recalcitrant structure of beech wood and selectively remove its hemicellulose and lignin components. This increased the accessibility of cellulose component of biomass to subsequent thermal conversion in CFP. Consequently, the MW-FA pretreated beech wood produced 14.0-28.3% higher yields (26.4-29.8C%) for valuable aromatic products in CFP than the untreated control (23.2C%). In addition, the yields of undesired solid residue (char/coke) decreased from 33.1C% for the untreated control to 28.6-29.8C% for the MW-FA pretreated samples. These results demonstrate that MW-FA pretreatment can provide an effective way to improve the product distribution from CFP of lignocellulose. PMID:27176672

  1. Triosephosphate isomerase of Taenia solium (TTPI): phage display and antibodies as tools for finding target regions to inhibit catalytic activity.

    PubMed

    Sanabria-Ayala, Víctor; Belmont, Iaraset; Abraham, Landa

    2015-01-01

    Previous studies demonstrated that antibodies against triosephosphate isomerase of Taenia solium (TTPI) can alter its enzymatic catalysis. In the present study, we used antibodies produced against the NH2-terminal region of TTPI (1/3NH2TTPI) and the phage display technology to find target regions to inhibit TTPI activity. As a first step, we obtained polyclonal antibodies against non-conserved regions from the 1/3NH2TTPI, which had an inhibitory effect of about 74 % on catalytic activity. Afterward, they were used to screen a library of phage-displayed dodecapeptides; as a result, 41 phage mimotope clones were isolated and grouped according to their amino acid sequence, finding the consensus A1 (VPTXPI), A2 (VPTXXI), B (LTPGQ), and D (DPLPR). Antibodies against selected phage mimotope clones were obtained by rabbit's immunization; these ones clearly recognized TTPI by both Western blot and ELISA. However, only the mimotope PDTS16 (DSVTPTSVMAVA) clone, which belongs to the VPTXXI consensus, raised antibodies capable of inhibiting the TTPI catalytic activity in 45 %. Anti-PDTS16 antibodies were confronted to several synthetic peptides that encompass the 1/3NH2TTPI, and they only recognized three, which share the motif FDTLQK belonging to the helix-α1 in TTPI. This suggests that this motif is the main part of the epitope recognized by anti-PDTS16 antibodies and revealed its importance for TTPI catalysis.

  2. Gold Sulfinyl Mesoionic Carbenes: Synthesis, Structure, and Catalytic Activity.

    PubMed

    Frutos, María; Avello, Marta G; Viso, Alma; Fernández de la Pradilla, Roberto; de la Torre, María C; Sierra, Miguel A; Gornitzka, Heinz; Hemmert, Catherine

    2016-08-01

    Gold mesoionic carbenes having a chiral sulfoxide group attached to the C4 position of the five membered ring have been prepared and tested as catalysts in the cycloisomerization of enynes. These new catalysts are very efficient, with the sulfoxide moiety playing a key role in their activity and the N1-substituent in control of the regioselectivity of these processes. PMID:27403763

  3. Gold Sulfinyl Mesoionic Carbenes: Synthesis, Structure, and Catalytic Activity.

    PubMed

    Frutos, María; Avello, Marta G; Viso, Alma; Fernández de la Pradilla, Roberto; de la Torre, María C; Sierra, Miguel A; Gornitzka, Heinz; Hemmert, Catherine

    2016-08-01

    Gold mesoionic carbenes having a chiral sulfoxide group attached to the C4 position of the five membered ring have been prepared and tested as catalysts in the cycloisomerization of enynes. These new catalysts are very efficient, with the sulfoxide moiety playing a key role in their activity and the N1-substituent in control of the regioselectivity of these processes.

  4. Converting Transaldolase into Aldolase through Swapping of the Multifunctional Acid-Base Catalyst: Common and Divergent Catalytic Principles in F6P Aldolase and Transaldolase.

    PubMed

    Sautner, Viktor; Friedrich, Mascha Miriam; Lehwess-Litzmann, Anja; Tittmann, Kai

    2015-07-28

    Transaldolase (TAL) and fructose-6-phosphate aldolase (FSA) both belong to the class I aldolase family and share a high degree of structural similarity and sequence identity. The molecular basis of the different reaction specificities (transferase vs aldolase) has remained enigmatic. A notable difference between the active sites is the presence of either a TAL-specific Glu (Gln in FSA) or a FSA-specific Tyr (Phe in TAL). Both residues seem to have analoguous multifunctional catalytic roles but are positioned at different faces of the substrate locale. We have engineered a TAL double variant (Glu to Gln and Phe to Tyr) with an active site resembling that of FSA. This variant indeed exhibits aldolase activity as its main activity with a catalytic efficiency even larger than that of authentic FSA, while TAL activity is greatly impaired. Structural analysis of this variant in complex with the dihydroxyacetone Schiff base formed upon substrate cleavage identifies the introduced Tyr (genuine in FSA) to catalyze protonation of the central carbanion-enamine intermediate as a key determinant of the aldolase reaction. Our studies pinpoint that the Glu in TAL and the Tyr in FSA, although located at different positions at the active site, similarly act as bona fide acid-base catalysts in numerous catalytic steps, including substrate binding, dehydration of the carbinolamine, and substrate cleavage. We propose that the different spatial positions of the multifunctional Glu in TAL and of the corresponding multifunctional Tyr in FSA relative to the substrate locale are critically controlling reaction specificity through either unfavorable (TAL) or favorable (FSA) geometry of proton transfer onto the common carbanion-enamine intermediate. The presence of both potential acid-base residues, Glu and Tyr, in the active site of TAL has deleterious effects on substrate binding and cleavage, most likely resulting from a differently organized H-bonding network. Large-scale motions of the

  5. Catalytic activity, duplication and evolution of the CYP98 cytochrome P450 family in wheat.

    PubMed

    Morant, Marc; Schoch, Guillaume A; Ullmann, Pascaline; Ertunç, Tanya; Little, Dawn; Olsen, Carl Erik; Petersen, Maike; Negrel, Jonathan; Werck-Reichhart, Danièle

    2007-01-01

    A burst of evolutionary duplication upon land colonization seems to have led to the large superfamily of cytochromes P450 in higher plants. Within this superfamily some clans and families are heavily duplicated. Others, such as genes involved in the phenylpropanoid pathway have led to fewer duplication events. Eight coding sequences belonging to the CYP98 family reported to catalyze the 3-hydroxylation step in this pathway were isolated from Triticum aestivum (wheat) and expressed in yeast. Comparison of the catalytic properties of the recombinant enzymes with those of CYP98s from other plant taxa was coupled to phylogenetic analyses. Our results indicate that the unusually high frequency of gene duplication in the wheat CYP98 family is a direct or indirect result from ploidization. While ancient duplication led to evolution of enzymes with different substrate preferences, most of recent duplicates underwent silencing via degenerative mutations. Three of the eight tested CYP98s from wheat have phenol meta-hydroxylase activity, with p-coumaroylshikimate being the primary substrate for all of these, as it is the case for CYP98s from sweet basil and Arabidopsis thaliana. However, CYP98s from divergent taxa have acquired different additional subsidiary activities. Some of them might be significant in the metabolism of various free or conjugated phenolics in different plant species. One of the most significant is meta-hydroxylation of p-coumaroyltyramine, predominantly by the wheat enzymes, for the synthesis of suberin phenolic monomers. Homology modeling, confirmed by directed mutagenesis, provides information on the protein regions and structural features important for some observed changes in substrate selectivity. They indicate that the metabolism of quinate ester and tyramine amide of p-coumaric acid rely on the same recognition site in the protein. PMID:17160453

  6. Enhanced catalytic activity of gold nanoparticle-carbon nanotube hybrids for influenza virus detection.

    PubMed

    Ahmed, Syed Rahin; Kim, Jeonghyo; Suzuki, Tetsuro; Lee, Jaebeom; Park, Enoch Y

    2016-11-15

    Multifunctional nanohybrids have created new and valuable opportunities for a wide range of catalysis and biotechnology applications. Here, we present a relatively simple method for producing nanohybrids composed of gold nanoparticles (Au NPs) and carbon nanotubes (CNTs) that does not require an acidic pre-treatment of the CNTs. Transmission electron microscopy (TEM) images and ultraviolet-visible (UV-vis) spectra revealed that Au NPs bonded to the CNT surface. Surface-enhanced Raman scattering (SERS) revealed a stronger signal from Au-CNT nanohybrids than from pristine CNTs. The Au-CNT nanohybrids showed catalytic activity in the oxidation of 3, 3', 5, 5'-tetramethyl-benzidine (TMB) by H2O2 and developed a unique blue colour in aqueous solution. Because of the enhanced peroxidase-like activity of these Au-CNT nanohybrids, they were selected for use as part of a highly sensitive colorimetric test for influenza virus A (H3N2). In the presence of influenza A virus (H3N2) in the test system (specific antibody-conjugated Au CNT nanohybrids-TMB-H2O2), a deep blue colour developed, the optical density of which was dependent on the virus concentration (10-50,000 PFU/ml). The limit of detection of this proposed method was 3.4 PFU/ml, a limit 385 times lower than that of conventional ELISA (1312 PFU/ml). The sensitivity of this test was also 500 times greater than that of commercial immunochromatography kits. The nanohybrid preparation and colorimetric detection methods reported herein may be easily adapted to other nanohybrid structures with enzyme mimetic properties for broader applications in catalysis and nanobiotechnology. PMID:27209577

  7. Enhanced catalytic activity of gold nanoparticle-carbon nanotube hybrids for influenza virus detection.

    PubMed

    Ahmed, Syed Rahin; Kim, Jeonghyo; Suzuki, Tetsuro; Lee, Jaebeom; Park, Enoch Y

    2016-11-15

    Multifunctional nanohybrids have created new and valuable opportunities for a wide range of catalysis and biotechnology applications. Here, we present a relatively simple method for producing nanohybrids composed of gold nanoparticles (Au NPs) and carbon nanotubes (CNTs) that does not require an acidic pre-treatment of the CNTs. Transmission electron microscopy (TEM) images and ultraviolet-visible (UV-vis) spectra revealed that Au NPs bonded to the CNT surface. Surface-enhanced Raman scattering (SERS) revealed a stronger signal from Au-CNT nanohybrids than from pristine CNTs. The Au-CNT nanohybrids showed catalytic activity in the oxidation of 3, 3', 5, 5'-tetramethyl-benzidine (TMB) by H2O2 and developed a unique blue colour in aqueous solution. Because of the enhanced peroxidase-like activity of these Au-CNT nanohybrids, they were selected for use as part of a highly sensitive colorimetric test for influenza virus A (H3N2). In the presence of influenza A virus (H3N2) in the test system (specific antibody-conjugated Au CNT nanohybrids-TMB-H2O2), a deep blue colour developed, the optical density of which was dependent on the virus concentration (10-50,000 PFU/ml). The limit of detection of this proposed method was 3.4 PFU/ml, a limit 385 times lower than that of conventional ELISA (1312 PFU/ml). The sensitivity of this test was also 500 times greater than that of commercial immunochromatography kits. The nanohybrid preparation and colorimetric detection methods reported herein may be easily adapted to other nanohybrid structures with enzyme mimetic properties for broader applications in catalysis and nanobiotechnology.

  8. Development of High Activity, Coal-Derived, Promoted Catalytic Systems for NOx Reduction at Low Temperatures

    SciTech Connect

    J. M. Calo

    1998-05-01

    This project is directed at an investigation of catalytic NO{sub x} reduction mechanisms on coal-derived, activated carbon supports at low temperatures. Promoted carbon systems offer some potentially significant advantages for heterogeneous NO{sub x} reduction. These include: low cost; high activity at low temperatures, which minimizes carbon loss; oxygen resistance; and a support material which can be engineered with respect to porosity, transport and catalyst dispersion characteristics.

  9. Chelating ruthenium phenolate complexes: synthesis, general catalytic activity, and applications in olefin metathesis polymerization.

    PubMed

    Kozłowska, Anna; Dranka, Maciej; Zachara, Janusz; Pump, Eva; Slugovc, Christian; Skowerski, Krzysztof; Grela, Karol

    2014-10-20

    Cyclic Ru-phenolates were synthesized, and these compounds were used as olefin metathesis catalysts. Investigation of their catalytic activity pointed out that, after activation with chemical agents, these catalysts promote ring-closing metathesis (RCM), enyne and cross-metathesis (CM) reactions, including butenolysis, with good results. Importantly, these latent catalysts are soluble in neat dicyclopentadiene (DCPD) and show good applicability in ring-opening metathesis polymeriyation (ROMP) of this monomer. PMID:25204738

  10. Chelating ruthenium phenolate complexes: synthesis, general catalytic activity, and applications in olefin metathesis polymerization.

    PubMed

    Kozłowska, Anna; Dranka, Maciej; Zachara, Janusz; Pump, Eva; Slugovc, Christian; Skowerski, Krzysztof; Grela, Karol

    2014-10-20

    Cyclic Ru-phenolates were synthesized, and these compounds were used as olefin metathesis catalysts. Investigation of their catalytic activity pointed out that, after activation with chemical agents, these catalysts promote ring-closing metathesis (RCM), enyne and cross-metathesis (CM) reactions, including butenolysis, with good results. Importantly, these latent catalysts are soluble in neat dicyclopentadiene (DCPD) and show good applicability in ring-opening metathesis polymeriyation (ROMP) of this monomer.

  11. Probing the correlations between the defects in metal-organic frameworks and their catalytic activity by an epoxide ring-opening reaction.

    PubMed

    Liu, Yangyang; Klet, Rachel C; Hupp, Joseph T; Farha, Omar

    2016-06-14

    Seven Zr/Hf-based MOFs with different degrees of defects were obtained by modulating the synthetic conditions. The number of missing linkers in these MOFs was calculated based on potentiometric acid-base titration. The number of defects was found to correlate quantitatively with the catalytic activity of UiO-type MOFs for an acid-catalyzed epoxide ring-opening reaction. More importantly, we were able to identify a MOF with inherent defective Zr6 nodes, which showed great activity and regio-selectivity for the epoxide ring-opening reaction. PMID:27229848

  12. Spectroscopic properties and the catalytic activity of new organo-lead supramolecular coordination polymer containing quinoxaline

    NASA Astrophysics Data System (ADS)

    Etaiw, Safaa El-din H.; Abdou, Safaa N.

    2015-01-01

    The 3D-supramolecular coordination polymer (SCP) 3∞[ Cu2(CN)3(Me3Pb)(qox)], 1, as the first example of the CuCN SCP containing the (Me3Pb) fragment, was explored to investigate its catalytic and photo-catalytic activities. The structure of 1 contains two chemically identical but crystallographically different [Cu2(CN)3ṡMe3Pbṡqox]2 units with four Cu(I) sites assuming distorted TP-3 geometry. Two non-linear chains of equal abundance are formed producing corrugated parallel chains which are connected laterally by quinoxaline creating 2D-layers which are arranged parallel in an (AB⋯AB⋯AB)n fashion forming 3D-network. IR, mass, electronic absorption and fluorescence spectra are also investigated. The SCP 1 is diamagnetic and exhibits good catalytic and photo-catalytic activities for the degradation of methylene blue (MB). The reaction is first order with respect to MB dye. The irradiation of the reaction with UV-light enhanced the rate of MB mineralization. The efficiency of recycled the 1 and the mechanism of degradation of MB dye were investigated.

  13. Spectroscopic properties and the catalytic activity of new organo-lead supramolecular coordination polymer containing quinoxaline.

    PubMed

    Etaiw, Safaa El-din H; Abdou, Safaa N

    2015-01-25

    The 3D-supramolecular coordination polymer (SCP) (3)∞[ Cu2(CN)3(Me3Pb)(qox)], 1, as the first example of the CuCN SCP containing the (Me3Pb) fragment, was explored to investigate its catalytic and photo-catalytic activities. The structure of 1 contains two chemically identical but crystallographically different [Cu2(CN)3⋅Me3Pb⋅qox]2 units with four Cu(I) sites assuming distorted TP-3 geometry. Two non-linear chains of equal abundance are formed producing corrugated parallel chains which are connected laterally by quinoxaline creating 2D-layers which are arranged parallel in an (AB⋯AB⋯AB)n fashion forming 3D-network. IR, mass, electronic absorption and fluorescence spectra are also investigated. The SCP 1 is diamagnetic and exhibits good catalytic and photo-catalytic activities for the degradation of methylene blue (MB). The reaction is first order with respect to MB dye. The irradiation of the reaction with UV-light enhanced the rate of MB mineralization. The efficiency of recycled the 1 and the mechanism of degradation of MB dye were investigated.

  14. Elucidating dz2 orbital selective catalytic activity in brownmillerite Ca2Mn2O5

    NASA Astrophysics Data System (ADS)

    Lu, Yue; Lu, Feng; Yang, Zhi; Wu, Jie; Yu, Hongyun; Xie, Xinjian; Xu, Jianping; Cheng, Fangyi; Chen, Jun; Xiong, Ka; Liu, Hui; Wang, Wei-Hua; Zhao, Jianzhou; Wang, Weichao

    2016-09-01

    3d-orbital filling in transition metal oxide is crucial to govern the catalytic activity in oxygen evolution reduction, nevertheless, it is not fundamentally accessible why specific orbital occupation produces a highest catalytic performance. Here, we utilize brownmillerite Ca2Mn2O5 to clarify the orbital selective catalytic behavior due to the crystal field splitting and on-site coulomb interactions. Within density functional theory plus dynamical mean field theory, Ca2Mn2O5 shows a paramagnetic Mott insulating behavior at room temperature, consistent with optical adsorption spectra and magnetic susceptibility. As the center of the dz2 orbital locates in the lower Hubbard sub-band, the unit occupation on dz2 orbital provides a moderate bonding with external O* species to cause a high catalytic activity of Ca2Mn2O5 with a square pyramid crystal field. Such concept of unit occupation of dz2 near Fermi level could be extended to other crystal fields for future design of oxide catalysts.

  15. Spectroscopic properties and the catalytic activity of new organo-lead supramolecular coordination polymer containing quinoxaline.

    PubMed

    Etaiw, Safaa El-din H; Abdou, Safaa N

    2015-01-25

    The 3D-supramolecular coordination polymer (SCP) (3)∞[ Cu2(CN)3(Me3Pb)(qox)], 1, as the first example of the CuCN SCP containing the (Me3Pb) fragment, was explored to investigate its catalytic and photo-catalytic activities. The structure of 1 contains two chemically identical but crystallographically different [Cu2(CN)3⋅Me3Pb⋅qox]2 units with four Cu(I) sites assuming distorted TP-3 geometry. Two non-linear chains of equal abundance are formed producing corrugated parallel chains which are connected laterally by quinoxaline creating 2D-layers which are arranged parallel in an (AB⋯AB⋯AB)n fashion forming 3D-network. IR, mass, electronic absorption and fluorescence spectra are also investigated. The SCP 1 is diamagnetic and exhibits good catalytic and photo-catalytic activities for the degradation of methylene blue (MB). The reaction is first order with respect to MB dye. The irradiation of the reaction with UV-light enhanced the rate of MB mineralization. The efficiency of recycled the 1 and the mechanism of degradation of MB dye were investigated. PMID:25124847

  16. Role of hydroxyl groups on the stability and catalytic activity of Au clusters on rutile surface

    SciTech Connect

    Kent, Paul R

    2011-01-01

    Hydroxyls are present as surface terminations of transition metal oxides under ambient conditions and may modify the properties of supported catalysts. We perform first-principles density functional theory calculations to investigate the role of hydroxyls on the catalytic activity of supported gold clusters on TiO{sub 2} (rutile). We find that they have a long-range effect increasing the adhesion of gold clusters on rutile. While hydroxyls make one gold atom more electronegative, a more complex charge-transfer scenario is observed on larger clusters which are important for catalytic applications. This enhances the molecular adsorption and coadsorption energies of CO and O{sub 2}, thereby increasing the catalytic activity of gold clusters for CO oxidation, consistent with reported experiments. Hydroxyls at the interface between gold and rutile surface are most important to this process, even when not directly bound to gold. As such, accurate models of catalytic processes on gold and other catalysts should include the effect of surface hydroxyls.

  17. Three critical hydrogen bonds determine the catalytic activity of the Diels–Alderase ribozyme

    PubMed Central

    Kraut, Stefanie; Bebenroth, Dirk; Nierth, Alexander; Kobitski, Andrei Y.; Nienhaus, G. Ulrich; Jäschke, Andres

    2012-01-01

    Compared to protein enzymes, our knowledge about how RNA accelerates chemical reactions is rather limited. The crystal structures of a ribozyme that catalyzes Diels–Alder reactions suggest a rich tertiary architecture responsible for catalysis. In this study, we systematically probe the relevance of crystallographically observed ground-state interactions for catalytic function using atomic mutagenesis in combination with various analytical techniques. The largest energetic contribution apparently arises from the precise shape complementarity between transition state and catalytic pocket: A single point mutant that folds correctly into the tertiary structure but lacks one H-bond that normally stabilizes the pocket is completely inactive. In the rate-limiting chemical step, the dienophile is furthermore activated by two weak H-bonds that contribute ∼7–8 kJ/mol to transition state stabilization, as indicated by the 25-fold slower reaction rates of deletion mutants. These H-bonds are also responsible for the tight binding of the Diels–Alder product by the ribozyme that causes product inhibition. For high catalytic activity, the ribozyme requires a fine-tuned balance between rigidity and flexibility that is determined by the combined action of one inter-strand H-bond and one magnesium ion. A sharp 360° turn reminiscent of the T-loop motif observed in tRNA is found to be important for catalytic function. PMID:21976731

  18. Carbon Nanotube Materials for Substrate Enhanced Control of Catalytic Activity

    SciTech Connect

    Heben, M.; Dillon, A. C.; Engtrakul, C.; Lee, S.-H.; Kelley, R. D.; Kini, A. M.

    2007-05-01

    Carbon SWNTs are attractive materials for supporting electrocatalysts. The properties of SWNTs are highly tunable and controlled by the nanotube's circumferential periodicity and their surface chemistry. These unique characteristics suggest that architectures constructed from these types of carbon support materials would exhibit interesting and useful properties. Here, we expect that the structure of the carbon nanotube support will play a major role in stabilizing metal electrocatalysts under extreme operating conditions and suppress both catalyst and support degradation. Furthermore, the chemical modification of the carbon nanotube surfaces can be expected to alter the interface between the catalyst and support, thus, enhancing the activity and utilization of the electrocatalysts. We plan to incorporate discrete reaction sites into the carbon nanotube lattice to create intimate electrical contacts with the catalyst particles to increase the metal catalyst activity and utilization. The work involves materials synthesis, design of electrode architectures on the nanoscale, control of the electronic, ionic, and mass fluxes, and use of advanced optical spectroscopy techniques.

  19. Aspartame and aspartame derivatives effect human thrombin catalytic activity.

    PubMed

    Scheffler, Julie E; Berliner, Lawrence J

    2004-12-20

    The study of small Asp-Phe analogs was undertaken since this dipeptide sequence is critical in fibrinogen recognition and catalysis. The inhibition of clotting activity by Asp-Phe-methyl ester (aspartame), formyl-Asp-Phe-methyl ester and acetyl-Asp-Phe was biphasic in all cases, indicating the presence of at least two binding sites. The N-terminally blocked derivatives are stronger inhibitors than aspartame. In contrast, tosyl-Gly-Pro-Arg-p'-nitroanilide hydrolysis was inhibited minimally by Asp-Phe-methyl, ester [Ki(app)=98 mM]. Acetyl-Asp-Phe inhibition of thrombin amidase activity was biphasic, tenfold stronger and appeared to be strongly cooperative. These results are discussed with respect to the inhibition of alpha-thrombin by ATP.

  20. VaSP1, catalytically active serine proteinase from Vipera ammodytes ammodytes venom with unconventional active site triad.

    PubMed

    Kurtović, Tihana; Brgles, Marija; Leonardi, Adrijana; Lang Balija, Maja; Sajevic, Tamara; Križaj, Igor; Allmaier, Günter; Marchetti-Deschmann, Martina; Halassy, Beata

    2014-01-01

    VaSP1, a serine proteinase from Vipera ammodytes ammodytes venom, is a glycosylated monomer of 31.5 kDa, as determined by MALDI mass spectrometry, showing multiple isoelectric points between pH 6.5 and pH 8.5. Partial amino acid sequencing of VaSP1 by Edman degradation and MS/MS analysis identified sequences which allowed its classification among the so-called snake venom serine proteinase homologues, members of the peptidase S1 family, however being devoid of the canonical catalytic triad. Only few representatives of this group have been identified so far with just two of them characterised in detail at the protein level. Despite substitution of His57 with Arg, VaSP1 possesses proteolytic activity which can be inhibited by Pefabloc, benzamidine, Zn²⁺ ions, DTT and trypsin inhibitor II, a Kunitz/BPTI group member. It hydrolyses N(α)-benzoyl-Phe-Val-Arg-p-NA, exhibiting Michaelis-Menten behaviour with K(m) = 48.2 μM and V(m) = 0.019 nM s⁻¹. The pH for optimal activity on tested substrate is around 9.0. VaSP1 also cleaves insulin B-chain, digesting it at positions His¹⁰-Leu¹¹, Ala¹⁴-Leu¹⁵ and Tyr¹⁶-Leu¹⁷. Furthermore, the novel serine proteinase is active towards wide array of proteins involved in haemostasis where its degradation of fibrinogen, fibrin, prothrombin, factor X and plasminogen in vivo probably results in depletion of coagulation factors in blood circulation. The possibility that VaSP1 possesses anticoagulant properties has been further indicated by its ability to prolong prothrombin time and activated partial thromboplastin time.

  1. Green diesel production via catalytic hydrogenation/decarboxylation of triglycerides and fatty acids of vegetable oil and brown grease

    NASA Astrophysics Data System (ADS)

    Sari, Elvan

    than activated carbon itself for both decarboxylation of oleic acid and hydrogenation of alkenes. In an additional effort to reduce Pd amount in the catalyst, Pd2Co/C catalysts with various Pd content were prepared and the catalytic activity study showed that 0.5 wt% Pd2Co/C catalyst performs even better than a 5 wt% Pd/C catalyst. Pd and Co alloys were very well dispersed and formed fine clusters, which led to a higher active metal surface area and hence favored the decarboxylation of oleic acid. This study showed that an alloy of Pd on carbon with a significantly low Pd content is much more active and selective to diesel hydrocarbons production from an unsaturated fatty acid in super-critical water and may be regarded as a prospective feasible decarboxylation catalyst for the removal of oxygen from vegetable oil/animal fat without the need of additional hydrogen.

  2. Comparative catalytic activity of PET track-etched membranes with embedded silver and gold nanotubes

    NASA Astrophysics Data System (ADS)

    Mashentseva, Anastassiya; Borgekov, Daryn; Kislitsin, Sergey; Zdorovets, Maxim; Migunova, Anastassiya

    2015-12-01

    Irradiated by heavy ions nanoporous polyethylene terephthalate track-etched membranes (PET TeMs) after +15Kr84 ions bombardment (1.75 MeV/nucl with the ion fluency of 1 × 109 cm-2) and sequential etching was applied in this research as a template for development of composites with catalytically enriched properties. A highly ordered silver and gold nanotubes arrays were embedded in 100 nm pores of PET TeMs via electroless deposition technique at 4 °C during 1 h. All "as-prepared" composites were examined for catalytic activity using reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by sodium borohydride as a common reaction to test metallic nanostructures catalysts. The effect of temperature on the catalytic activity was investigated in range of 292-313 K and activation energy were calculated. Kapp of Ag/PET composites linearly increase with an increase of the temperature thus normal Arrhenius behavior have been seen and the activation energy was calculated to be 42.13 kJ/mol. Au/PET composites exhibit not only more powerful catalytic activity but also non-linear dependence of rate constant from temperature. Kapp increased with increasing temperature throughout the 292-308 K temperature range; the reaction had an activation energy 65.32 kJ/mol. In range 311-313 K rate constant dramatically decreased and the apparent activation energy at this temperature rang was -91.44 kJ/mol due some structural changes, i.e. agglomeration of Au nanoparticles on the surface of composite.

  3. Plant lipases: biocatalyst aqueous environment in relation to optimal catalytic activity in lipase-catalyzed synthesis reactions.

    PubMed

    Caro, Yanis; Pina, Michel; Turon, Fabrice; Guilbert, Stephane; Mougeot, Estelle; Fetsch, David V; Attwool, Philip; Graille, Jean

    2002-03-20

    Adsorption and desorption isotherms of two commercial enzyme preparations of papain and bromelain were determined with a Dynamic Vapor System. The Guggenheim-Anderson-deBoer (GAB) modeling of the obtained sorption isotherms allowed the definition of different levels of hydration of those samples. Afterward, these enzyme preparations were used as biocatalysts in water and solvent-free esterification and alcoholysis reactions. The evolution of the obtained fatty acid ester level as a function of the initial hydration level of the biocatalyst, i.e., thermodynamic water activity (a(w)) and water content, was studied. The results show an important correlation between the initial hydration level of the biocatalyst and its catalytic activity during the lipase-catalyzed synthesis reactions. Thus, the Carica papaya lipase (crude papain preparation) catalytic activity is highly dependent on the biocatalyst hydration state. The optimized synthesis reaction yield is obtained when the a(w) value of the enzyme preparation is stabilized at 0.22, which corresponds to 2% water content. This optimal level of hydration occurs on the linear part of the biocatalyst's sorption isotherm, where the water molecules can form a mono- or multiple layer with the protein network. The synthesis reaction yield decreases when the a(w) of the preparation is higher than 0.22, because the excess water molecules modify the system equilibrium leading to the reverse and competitive reaction, i.e., hydrolysis. These results show also that an optimal storage condition for the highly hydrophilic crude papain preparation is a relative humidity strictly lower than 70% to avoid an irreversible structural transition leading to a useless biocatalyst. Concerning the bromelain preparation, no effect of the hydration level on the catalytic activity during esterification reactions was observed. This biocatalyst has too weak a catalytic activity which makes it difficult to observe any differences. Furthermore, the

  4. Unprecedented Catalytic Wet Oxidation of Glucose to Succinic Acid Induced by the Addition of n-Butylamine to a Ru(III) Catalyst.

    PubMed

    Podolean, Iunia; Rizescu, Cristina; Bala, Camelia; Rotariu, Lucian; Parvulescu, Vasile I; Coman, Simona M; Garcia, Hermenegildo

    2016-09-01

    A new pathway for the catalytic wet oxidation (CWO) of glucose is described. Employing a cationic Ru@MNP catalyst, succinic acid is obtained in unprecedently high yield (87.5 %) for a >99.9 % conversion of glucose, most probably through a free radical mechanism combined with catalytic didehydroxylation of vicinal diols and hydrogenation of the resulted unsaturated intermediate. PMID:27511900

  5. Fabrication of Pt-loaded NiCo nanochains with superior catalytic dehydrogenation activity.

    PubMed

    Wen, Ming; Wu, Qingnan; Peng, Jin; Wu, Qingsheng; Wang, Chenxiang

    2014-02-15

    A new magnetic Pt-loaded NiCo nanochain, with the diameter from 80 nm to 120 nm, has been prepared through microwave-induced assembly process followed by the galvanic displacement performance. Pt nanoparticles are distributed on the surface of NiCo nanochains. The products are investigated as hydrolytic dehydrogenation catalyst for potential hydrogen energy applications. Compared with NiCo nanochains, the Pt-loaded NiCo nanochains present exceedingly high catalytic activity toward the hydrolytic dehydrogenation of ammonia borane aqueous under ambient atmosphere at room temperature, where the Ni16Co80/Pt4 nanochains exhibit high catalytic activity with a lower activation energy of 45.72 kJ mol(-1) and a superior dehydrogenation rate of 1.17 × 10(4) mL min(-1) g(-1), suggesting the potential application in hydrogen fuel and chemical industry. PMID:24370425

  6. Chemoselective Catalytic Oxidation of 1,2-Diols to α-Hydroxy Acids Controlled by TEMPO-ClO2 Charge-Transfer Complex.

    PubMed

    Furukawa, Keisuke; Shibuya, Masatoshi; Yamamoto, Yoshihiko

    2015-05-01

    Chemoselective catalytic oxidation from 1,2-diols to α-hydroxy acids in a cat. TEMPO/cat. NaOCl/NaClO2 system has been achieved. The use of a two-phase condition consisting of hydrophobic toluene and water suppresses the concomitant oxidative cleavage. A study of the mechanism suggests that the observed selectivity is derived from the precise solubility control of diols and hydroxy acids as well as the active species of TEMPO. Although the oxoammonium species TEMPO(+)Cl(-) is hydrophilic, the active species dissolves into the organic layer by the formation of the charge-transfer (CT) complex TEMPO-ClO2 under the reaction conditions.

  7. Chemoselective Catalytic Oxidation of 1,2-Diols to α-Hydroxy Acids Controlled by TEMPO-ClO2 Charge-Transfer Complex.

    PubMed

    Furukawa, Keisuke; Shibuya, Masatoshi; Yamamoto, Yoshihiko

    2015-05-01

    Chemoselective catalytic oxidation from 1,2-diols to α-hydroxy acids in a cat. TEMPO/cat. NaOCl/NaClO2 system has been achieved. The use of a two-phase condition consisting of hydrophobic toluene and water suppresses the concomitant oxidative cleavage. A study of the mechanism suggests that the observed selectivity is derived from the precise solubility control of diols and hydroxy acids as well as the active species of TEMPO. Although the oxoammonium species TEMPO(+)Cl(-) is hydrophilic, the active species dissolves into the organic layer by the formation of the charge-transfer (CT) complex TEMPO-ClO2 under the reaction conditions. PMID:25886211

  8. Highly stable and re-dispersible nano Cu hydrosols with sensitively size-dependent catalytic and antibacterial activities

    NASA Astrophysics Data System (ADS)

    Zhang, Yu; Zhu, Pengli; Li, Gang; Wang, Wenzhao; Chen, Liang; Lu, Daoqiang Daniel; Sun, Rong; Zhou, Feng; Wong, Chingping

    2015-08-01

    Highly stable monodispersed nano Cu hydrosols were facilely prepared by an aqueous chemical reduction method through selecting copper hydroxide (Cu(OH)2) as the copper precursor, poly(acrylic acid) (PAA) and ethanol amine (EA) as the complexing agents, and hydrazine hydrate as the reducing agent. The size of the obtained Cu colloidal nanoparticles was controlled from 0.96 to 26.26 nm by adjusting the dosage of the copper precursor. Moreover, the highly stable nano Cu hydrosols could be easily concentrated and re-dispersed in water meanwhile maintaining good dispersibility. A model catalytic reaction of reducing p-nitrophenol with NaBH4 in the presence of nano Cu hydrosols with different sizes was performed to set up the relationship between the apparent kinetic rate constant (kapp) and the particle size of Cu catalysts. The experimental results indicate that the corresponding kapp showed an obvious size-dependency. Calculations revealed that kapp was directly proportional to the surface area of Cu catalyst nanoparticles, and also proportional to the reciprocal of the particle size based on the same mass of Cu catalysts. This relationship might be a universal principle for predicting and assessing the catalytic efficiency of Cu nanoparticles. The activation energy (Ea) of this catalytic reaction when using 0.96 nm Cu hydrosol as a catalyst was calculated to be 9.37 kJ mol-1, which is considered an extremely low potential barrier. In addition, the synthesized nano Cu hydrosols showed size-dependent antibacterial activities against Pseudomonas aeruginosa (P. aeruginosa) and the minimal inhibitory concentration of the optimal sample was lower than 5.82 μg L-1.Highly stable monodispersed nano Cu hydrosols were facilely prepared by an aqueous chemical reduction method through selecting copper hydroxide (Cu(OH)2) as the copper precursor, poly(acrylic acid) (PAA) and ethanol amine (EA) as the complexing agents, and hydrazine hydrate as the reducing agent. The size of the

  9. Highly catalytic hollow palladium nanoparticles derived from silver@silver-palladium core-shell nanostructures for the oxidation of formic acid

    NASA Astrophysics Data System (ADS)

    Chen, Dong; Cui, Penglei; He, Hongyan; Liu, Hui; Yang, Jun

    2014-12-01

    Hollow Palladium (hPd) nanoparticles (NPs) are prepared via a simple and mild successive method. Firstly, core-shell NPs with silver (Ag) cores and silver-palladium (Ag-Pd) alloy shells are synthesized in aqueous phase by galvanic replacement reaction (GRR) between Ag NPs and Pd2+ ion precursors. Saturated aqueous sodium chloride (NaCl) solution was then employed to remove the Ag component from the core and shell regions of core-shell Ag@Ag-Pd NPs, resulting in the formation of hPd NPs with shrunk sizes in comparison with their core-shell parents. Specifically, the hPd NPs exhibit superior catalytic activity and durability for catalyzing the oxidation of formic acid, compared with the Pd NPs reduced by NaBH4 in aqueous solution and commercial Pd/C catalyst from Johnson Matthey, mainly due to the large electrochemically active surface areas of the hollow particles. In addition, The Ag component in core-shell Ag@Ag-Pd NPs has an unfavorable influence on catalytic activity of NPs for formic acid oxidation. However, the durability could be improved due to the electron donating effect from Ag to Pd atoms in the core-shell NPs.

  10. Catalytic conversion of furfural into a 2,5-furandicarboxylic acid-based polyester with total carbon utilization.

    PubMed

    Pan, Tao; Deng, Jin; Xu, Qing; Zuo, Yong; Guo, Qing-Xiang; Fu, Yao

    2013-01-01

    One divided into two combined into one: The catalytic conversion of furfural into a 2,5-furandicarboxylic acid-based polyester, linked by the disproportionation of furoate to furan and 2,5-furandicarboxylate, is reported. In this manner, all carbons are utilized, demonstrating the success of combining a platform molecule from C(5) sugars (furfural) to one from C(6) sugars (2,5-FDCA). PMID:23239596

  11. Probing Active Cocaine Vaccination Performance through Catalytic and Noncatalytic Hapten Design

    PubMed Central

    Cai, Xiaoqing; Whitfield, Timothy; Hixon, Mark S.; Grant, Yanabel; Koob, George F.; Janda, Kim D.

    2013-01-01

    Presently, there are no FDA-approved medications to treat cocaine addiction. Active vaccination has emerged as one approach to intervene through the rapid sequestering of the circulating drug, thus terminating both psychoactive effects and drug toxicity. Herein, we report our efforts examining two complimentary, but mechanistically distinct active vaccines, i.e., noncatalytic and catalytic, for cocaine treatment. A cocaine-like hapten GNE and a cocaine transition-state analogue GNT were used to generate the active vaccines, respectively. GNE-KLH was found to elicit persistent high-titer, cocaine-specific antibodies, and blunt cocaine induced locomotor behaviors. Catalytic antibodies induced by GNT-KLH were also shown to produce potent titers and suppress locomotor response in mice; however, upon repeated cocaine challenges the vaccine’s protecting effects waned. In depth kinetic analysis suggested that loss of catalytic activity was due to antibody modification by cocaine. The work provides new insights for the development of active vaccines for the treatment of cocaine abuse. PMID:23627877

  12. Catalytic activity of various Y-type zeolites on disproportionation of nitrogen monoxide

    SciTech Connect

    Yoshinori, K.; Hisao, I.

    1982-09-01

    Disproportionation of NO has been investigated on various Y-type zeolites by the pulse-reaction technique. Alkaline-earth Y-type zeolites showed high activity. The order of catalytic activity presently obtained is given. A volcano-type relationship was found between the catalytic activity and the radius of the exchanged cation in the case of alkaline-earth, zinc family and alkali-metal Y-type zeolites. CaY, CdY and NaY-type zeolites, each with a radius of exchanged cation 1A in size, showed maximum activity of their families. TPD profiles had three peaks corresponding to NO, NO and N/sub 2/O desorption with increasing temperature. The volcano-type relationship was also found between the peak area of each TPD profile and the radius of exchanged cation. The catalytic activity increases with increase of pretreatment temperature, reaches a broad maximum at 700/sup 0/C and decreases with the collapse of zeolite structure in further increase of the pretreatment temperature.

  13. Catalytic oxidation ofS(IV) on activated carbon in aqueous suspension: kinetics and mechanism

    SciTech Connect

    Brodzinsky, R.

    1981-02-01

    Activated carbon and combustion produced soot particles have been studied for their catalytic effect on the oxidation of aqueous sulfur(IV) species. Detailed kinetic studies of the reaction were performed on three different activated carbons and on a soot collected in a highway tunnel. Combustion produced soots were tested for their catalytic behavior and found to be similar to the activated carbons. The reaction rate was found to be linearly dependent on the concentration of carbon particles in the solution. The rate was found to follow a Langmuir adsorption isotherm for its dependence on oxygen and the product of two adsorption isotherms for S(IV). The reaction is independent of the pH of the solution when the pH is below 7.6. The reaction does not occur when the pH is above 7.6. The three aqueous S(IV) species are catalyzed in their oxidation by the carbon particles in a similar manner. Activation energies for the reactions on the different carbons are all about 8.5 kcal/mole. A possible four-step reaction mechanism is proposed. It consists of the adsorption of a dissolved oxygen molecule onto the carbon surface, followed by the adsorption of two S(IV) molecules or ions. These are oxidized on the surface to sulfate, which desorbs from the surface, regenerating the catalytically active site.

  14. Reversible Regulation of Catalytic Activity of Gold Nanoparticles with DNA Nanomachines.

    PubMed

    Zhou, Peipei; Jia, Sisi; Pan, Dun; Wang, Lihua; Gao, Jimin; Lu, Jianxin; Shi, Jiye; Tang, Zisheng; Liu, Huajie

    2015-09-23

    Reversible catalysis regulation has gained much attention and traditional strategies utilized reversible ligand coordination for switching catalyst's conformations. However, it remains challenging to regulate the catalytic activity of metal nanoparticle-based catalysts. Herein, we report a new DNA nanomachine-driven reversible nano-shield strategy for circumventing this problem. The basic idea is based on the fact that the conformational change of surface-attached DNA nanomachines will cause the variation of the exposed surface active area on metal nanoparticles. As a proof-of-concept study, we immobilized G-rich DNA strands on gold nanoparticles (AuNPs) which have glucose oxidase (GOx) like activity. Through the reversible conformational change of the G-rich DNA between a flexible single-stranded form and a compact G-quadruplex form, the catalytic activity of AuNPs has been regulated reversibly for several cycles. This strategy is reliable and robust, which demonstrated the possibility of reversibly adjusting catalytic activity with external surface coverage switching, rather than coordination interactions.

  15. Reversible Regulation of Catalytic Activity of Gold Nanoparticles with DNA Nanomachines

    PubMed Central

    Zhou, Peipei; Jia, Sisi; Pan, Dun; Wang, Lihua; Gao, Jimin; Lu, Jianxin; Shi, Jiye; Tang, Zisheng; Liu, Huajie

    2015-01-01

    Reversible catalysis regulation has gained much attention and traditional strategies utilized reversible ligand coordination for switching catalyst’s conformations. However, it remains challenging to regulate the catalytic activity of metal nanoparticle-based catalysts. Herein, we report a new DNA nanomachine-driven reversible nano-shield strategy for circumventing this problem. The basic idea is based on the fact that the conformational change of surface-attached DNA nanomachines will cause the variation of the exposed surface active area on metal nanoparticles. As a proof-of-concept study, we immobilized G-rich DNA strands on gold nanoparticles (AuNPs) which have glucose oxidase (GOx) like activity. Through the reversible conformational change of the G-rich DNA between a flexible single-stranded form and a compact G-quadruplex form, the catalytic activity of AuNPs has been regulated reversibly for several cycles. This strategy is reliable and robust, which demonstrated the possibility of reversibly adjusting catalytic activity with external surface coverage switching, rather than coordination interactions. PMID:26395968

  16. Comprehensive Characterization of AMP-Activated Protein Kinase Catalytic Domain by Top-Down Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Yu, Deyang; Peng, Ying; Ayaz-Guner, Serife; Gregorich, Zachery R.; Ge, Ying

    2016-02-01

    AMP-activated protein kinase (AMPK) is a serine/threonine protein kinase that is essential in regulating energy metabolism in all eukaryotic cells. It is a heterotrimeric protein complex composed of a catalytic subunit (α) and two regulatory subunits (β and γ). C-terminal truncation of AMPKα at residue 312 yielded a protein that is active upon phosphorylation of Thr172 in the absence of β and γ subunits, which is refered to as the AMPK catalytic domain and commonly used to substitute for the AMPK heterotrimeric complex in in vitro kinase assays. However, a comprehensive characterization of the AMPK catalytic domain is lacking. Herein, we expressed a His-tagged human AMPK catalytic domin (denoted as AMPKΔ) in E. coli, comprehensively characterized AMPKΔ in its basal state and after in vitro phosphorylation using top-down mass spectrometry (MS), and assessed how phosphorylation of AMPKΔ affects its activity. Unexpectedly, we found that bacterially-expressed AMPKΔ was basally phosphorylated and localized the phosphorylation site to the His-tag. We found that AMPKΔ had noticeable basal activity and was capable of phosphorylating itself and its substrates without activating phosphorylation at Thr172. Moreover, our data suggested that Thr172 is the only site phosphorylated by its upstream kinase, liver kinase B1, and that this phosphorylation dramatically increases the kinase activity of AMPKΔ. Importantly, we demonstrated that top-down MS in conjunction with in vitro phosphorylation assay is a powerful approach for monitoring phosphorylation reaction and determining sequential order of phosphorylation events in kinase-substrate systems.

  17. When ruthenia met titania: Achieving extraordinary catalytic activity at low temperature by nanostructuring of oxides

    SciTech Connect

    Graciani, J.; Stacchiola, D.; Yang, F.; Evans, J.; Vidal, A. B.; Rodriguez, J. A.; Sanz, J. F.

    2015-09-09

    Nanostructured RuOx/TiO2(110) catalysts have a remarkable catalytic activity for CO oxidation at temperatures in the range of 350–375 K. Furthermore, the RuO2(110) surface has no activity. The state-of-the-art DFT calculations indicate that the main reasons for such an impressive improvement in the catalytic activity are: (i) a decrease of the diffusion barrier of adsorbed O atoms by around 40%, from 1.07 eV in RuO2(110) to 0.66 eV in RuOx/TiO2(110), which explains the shift of the activity to lower temperatures and (ii) a lowering of the barrier by 20% for the association of adsorbed CO and O species to give CO2 (the main barrier for the CO oxidation reaction) passing from around 0.7 eV in RuO2(110) to 0.55 eV in RuOx/TiO2(110). We show that the catalytic properties of ruthenia are strongly modified when supported as nanostructures on titania, attaining higher activity at temperatures 100 K lower than that needed for pure ruthenia. As in other systems consisting of ceria nanostructures supported on titania, nanostructured ruthenia shows strongly modified properties compared to the pure oxide, consolidating the fact that the nanostructuring of oxides is a main way to attain higher catalytic activity at lower temperatures.

  18. When ruthenia met titania: Achieving extraordinary catalytic activity at low temperature by nanostructuring of oxides

    DOE PAGES

    Graciani, J.; Stacchiola, D.; Yang, F.; Evans, J.; Vidal, A. B.; Rodriguez, J. A.; Sanz, J. F.

    2015-09-09

    Nanostructured RuOx/TiO2(110) catalysts have a remarkable catalytic activity for CO oxidation at temperatures in the range of 350–375 K. Furthermore, the RuO2(110) surface has no activity. The state-of-the-art DFT calculations indicate that the main reasons for such an impressive improvement in the catalytic activity are: (i) a decrease of the diffusion barrier of adsorbed O atoms by around 40%, from 1.07 eV in RuO2(110) to 0.66 eV in RuOx/TiO2(110), which explains the shift of the activity to lower temperatures and (ii) a lowering of the barrier by 20% for the association of adsorbed CO and O species to give CO2more » (the main barrier for the CO oxidation reaction) passing from around 0.7 eV in RuO2(110) to 0.55 eV in RuOx/TiO2(110). We show that the catalytic properties of ruthenia are strongly modified when supported as nanostructures on titania, attaining higher activity at temperatures 100 K lower than that needed for pure ruthenia. As in other systems consisting of ceria nanostructures supported on titania, nanostructured ruthenia shows strongly modified properties compared to the pure oxide, consolidating the fact that the nanostructuring of oxides is a main way to attain higher catalytic activity at lower temperatures.« less

  19. Hydrodechlorination catalytic activity of gold nanoparticles supported on TiO 2 modified SBA-15 investigated by IR spectroscopy

    NASA Astrophysics Data System (ADS)

    Hannus, I.; Búza, M.; Beck, A.; Guczi, L.; Sáfrán, G.

    2009-04-01

    The hydrodechlorination catalytic activity of gold nanoparticles on SBA-15 silica modified by TiO 2 promoters has been investigated. Comparing the hydrodechlorination catalytic activity platinum nanoparticles supported on TiO 2 catalyst was used in the hydrodechlorination of CCl 4 as model compound. The IR spectroscopic experimental results showed that the gold nanoparticles have higher catalytic activity, than platinum ones. The two samples were tested also in CO oxidation, in which Au/TiO 2/SBA-15 possess also somewhat higher activity than Pt/TiO 2.

  20. Highly stable and re-dispersible nano Cu hydrosols with sensitively size-dependent catalytic and antibacterial activities.

    PubMed

    Zhang, Yu; Zhu, Pengli; Li, Gang; Wang, Wenzhao; Chen, Liang; Lu, Daoqiang Daniel; Sun, Rong; Zhou, Feng; Wong, Chingping

    2015-08-28

    Highly stable monodispersed nano Cu hydrosols were facilely prepared by an aqueous chemical reduction method through selecting copper hydroxide (Cu(OH)2) as the copper precursor, poly(acrylic acid) (PAA) and ethanol amine (EA) as the complexing agents, and hydrazine hydrate as the reducing agent. The size of the obtained Cu colloidal nanoparticles was controlled from 0.96 to 26.26 nm by adjusting the dosage of the copper precursor. Moreover, the highly stable nano Cu hydrosols could be easily concentrated and re-dispersed in water meanwhile maintaining good dispersibility. A model catalytic reaction of reducing p-nitrophenol with NaBH4 in the presence of nano Cu hydrosols with different sizes was performed to set up the relationship between the apparent kinetic rate constant (kapp) and the particle size of Cu catalysts. The experimental results indicate that the corresponding kapp showed an obvious size-dependency. Calculations revealed that kapp was directly proportional to the surface area of Cu catalyst nanoparticles, and also proportional to the reciprocal of the particle size based on the same mass of Cu catalysts. This relationship might be a universal principle for predicting and assessing the catalytic efficiency of Cu nanoparticles. The activation energy (Ea) of this catalytic reaction when using 0.96 nm Cu hydrosol as a catalyst was calculated to be 9.37 kJ mol(-1), which is considered an extremely low potential barrier. In addition, the synthesized nano Cu hydrosols showed size-dependent antibacterial activities against Pseudomonas aeruginosa (P. aeruginosa) and the minimal inhibitory concentration of the optimal sample was lower than 5.82 μg L(-1). PMID:26219381

  1. Highly stable and re-dispersible nano Cu hydrosols with sensitively size-dependent catalytic and antibacterial activities.

    PubMed

    Zhang, Yu; Zhu, Pengli; Li, Gang; Wang, Wenzhao; Chen, Liang; Lu, Daoqiang Daniel; Sun, Rong; Zhou, Feng; Wong, Chingping

    2015-08-28

    Highly stable monodispersed nano Cu hydrosols were facilely prepared by an aqueous chemical reduction method through selecting copper hydroxide (Cu(OH)2) as the copper precursor, poly(acrylic acid) (PAA) and ethanol amine (EA) as the complexing agents, and hydrazine hydrate as the reducing agent. The size of the obtained Cu colloidal nanoparticles was controlled from 0.96 to 26.26 nm by adjusting the dosage of the copper precursor. Moreover, the highly stable nano Cu hydrosols could be easily concentrated and re-dispersed in water meanwhile maintaining good dispersibility. A model catalytic reaction of reducing p-nitrophenol with NaBH4 in the presence of nano Cu hydrosols with different sizes was performed to set up the relationship between the apparent kinetic rate constant (kapp) and the particle size of Cu catalysts. The experimental results indicate that the corresponding kapp showed an obvious size-dependency. Calculations revealed that kapp was directly proportional to the surface area of Cu catalyst nanoparticles, and also proportional to the reciprocal of the particle size based on the same mass of Cu catalysts. This relationship might be a universal principle for predicting and assessing the catalytic efficiency of Cu nanoparticles. The activation energy (Ea) of this catalytic reaction when using 0.96 nm Cu hydrosol as a catalyst was calculated to be 9.37 kJ mol(-1), which is considered an extremely low potential barrier. In addition, the synthesized nano Cu hydrosols showed size-dependent antibacterial activities against Pseudomonas aeruginosa (P. aeruginosa) and the minimal inhibitory concentration of the optimal sample was lower than 5.82 μg L(-1).

  2. Molecular cloning and catalytic activity of a membrane-bound prenyl diphosphate phosphatase from Croton stellatopilosus Ohba.

    PubMed

    Nualkaew, Natsajee; Guennewich, Nils; Springob, Karin; Klamrak, Anuwatchakit; De-Eknamkul, Wanchai; Kutchan, Toni M

    2013-07-01

    Geranylgeraniol (GGOH), a bioactive acyclic diterpene with apoptotic induction activity, is the immediate precursor of the commercial anti-peptic, plaunotol (18-hydroxy geranylgeraniol), which is found in Croton stellatopilosus (Ohba). From this plant, a cDNA encoding a prenyl diphosphate phosphatase (CsPDP), which catalyses the dephosphorylation of geranylgeranyl diphosphate (GGPP) to GGOH, was isolated using a PCR approach. The full-length cDNA contained 888bp and encoded a 33.6 kDa protein (295 amino acids) that was phylogenetically grouped into the phosphatidic acid phosphatase (PAP) enzyme family. The deduced amino acid sequence showed 6 hydrophobic transmembrane regions with 57-85% homology to the sequences of other plant PAPs. The recombinant CsPDP and its 4 truncated constructs exhibited decreasing dephosphorylation activities relative to the lengths of the N-terminal deletions. While the full-length CsPDP successfully performed the two sequential monodephosphorylation steps on GGPP to form GGOH, the larger N-terminal deletion in the truncated enzymes appeared to specifically decrease the catalytic efficiency of the second monodephosphorylation step. The information presented here on the CsPDP cDNA and factors affecting the dephosphorylation activity of its recombinant protein may eventually lead to the discovery of the specific GGPP phosphatase gene and enzyme that are involved in the formation of GGOH in the biosynthetic pathway of plaunotol in C. stellatopilosus.

  3. Bicarbonate Modulates Photoreceptor Guanylate Cyclase (ROS-GC) Catalytic Activity.

    PubMed

    Duda, Teresa; Wen, Xiao-Hong; Isayama, Tomoki; Sharma, Rameshwar K; Makino, Clint L

    2015-04-24

    By generating the second messenger cGMP in retinal rods and cones, ROS-GC plays a central role in visual transduction. Guanylate cyclase-activating proteins (GCAPs) link cGMP synthesis to the light-induced fall in [Ca(2+)]i to help set absolute sensitivity and assure prompt recovery of the response to light. The present report discloses a surprising feature of this system: ROS-GC is a sensor of bicarbonate. Recombinant ROS-GCs synthesized cGMP from GTP at faster rates in the presence of bicarbonate with an ED50 of 27 mM for ROS-GC1 and 39 mM for ROS-GC2. The effect required neither Ca(2+) nor use of the GCAPs domains; however, stimulation of ROS-GC1 was more powerful in the presence of GCAP1 or GCAP2 at low [Ca(2+)]. When applied to retinal photoreceptors, bicarbonate enhanced the circulating current, decreased sensitivity to flashes, and accelerated flash response kinetics. Bicarbonate was effective when applied either to the outer or inner segment of red-sensitive cones. In contrast, bicarbonate exerted an effect when applied to the inner segment of rods but had little efficacy when applied to the outer segment. The findings define a new regulatory mechanism of the ROS-GC system that affects visual transduction and is likely to affect the course of retinal diseases caused by cGMP toxicity. PMID:25767116

  4. Catalytic Diamination of Olefins via N–N Bond Activation

    PubMed Central

    2015-01-01

    Conspectus Vicinal diamines are important structural motifs present in various biologically and chemically significant molecules. Direct diamination of olefins provides an effective approach to this class of compounds. Unlike well-established oxidation processes such as epoxidation, dihydroxylation, and aminohydroxylation, direct diamination of olefins had remained a long-standing challenge and had been less well developed. In this Account, we summarize our recent studies on Pd(0)- and Cu(I)-catalyzed diaminations of olefins using di-tert-butyldiaziridinone and its related analogues as nitrogen sources via N–N bond activation. A wide variety of imidazolidinones, cyclic sulfamides, indolines, imidazolinones, and cyclic guanidines can be obtained from conjugated dienes and terminal olefins. For conjugated dienes, the diamination proceeds regioselectively at the internal double bond with the Pd(0) catalyst. Mechanistic studies show that the diamination likely involves a four-membered Pd(II) species resulting from the insertion of Pd(0) into the N–N bond of di-tert-butyldiaziridinone. Interestingly, the Cu(I)-catalyzed process occurs regioselectively at either the terminal or internal double bond depending on the reaction conditions via two mechanistically distinct pathways. The Cu(I) catalyst cleaves the N–N bond of di-tert-butyldiaziridinone to form a Cu(II) nitrogen radical and a four-membered Cu(III) species, which are likely in rapid equilibrium. The Cu(II) nitrogen radical and the four-membered Cu(III) species lead to the terminal and internal diamination, respectively. Terminal olefins are effectively C–H diaminated at the allylic and homoallylic carbons with Pd(0) as catalyst and di-tert-butyldiaziridinone as nitrogen source, likely involving a diene intermediate generated in situ from the terminal olefin via formation of a π-allyl Pd complex and subsequent β-hydride elimination. When di-tert-butylthiadiaziridine 1,1-dioxide is used as nitrogen source

  5. Catalytic diamination of olefins via N-N bond activation.

    PubMed

    Zhu, Yingguang; Cornwall, Richard G; Du, Haifeng; Zhao, Baoguo; Shi, Yian

    2014-12-16

    CONSPECTUS: Vicinal diamines are important structural motifs present in various biologically and chemically significant molecules. Direct diamination of olefins provides an effective approach to this class of compounds. Unlike well-established oxidation processes such as epoxidation, dihydroxylation, and aminohydroxylation, direct diamination of olefins had remained a long-standing challenge and had been less well developed. In this Account, we summarize our recent studies on Pd(0)- and Cu(I)-catalyzed diaminations of olefins using di-tert-butyldiaziridinone and its related analogues as nitrogen sources via N-N bond activation. A wide variety of imidazolidinones, cyclic sulfamides, indolines, imidazolinones, and cyclic guanidines can be obtained from conjugated dienes and terminal olefins. For conjugated dienes, the diamination proceeds regioselectively at the internal double bond with the Pd(0) catalyst. Mechanistic studies show that the diamination likely involves a four-membered Pd(II) species resulting from the insertion of Pd(0) into the N-N bond of di-tert-butyldiaziridinone. Interestingly, the Cu(I)-catalyzed process occurs regioselectively at either the terminal or internal double bond depending on the reaction conditions via two mechanistically distinct pathways. The Cu(I) catalyst cleaves the N-N bond of di-tert-butyldiaziridinone to form a Cu(II) nitrogen radical and a four-membered Cu(III) species, which are likely in rapid equilibrium. The Cu(II) nitrogen radical and the four-membered Cu(III) species lead to the terminal and internal diamination, respectively. Terminal olefins are effectively C-H diaminated at the allylic and homoallylic carbons with Pd(0) as catalyst and di-tert-butyldiaziridinone as nitrogen source, likely involving a diene intermediate generated in situ from the terminal olefin via formation of a π-allyl Pd complex and subsequent β-hydride elimination. When di-tert-butylthiadiaziridine 1,1-dioxide is used as nitrogen source

  6. Positional effects of hydroxy groups on catalytic activity of proton-responsive half-sandwich Cp*Iridium(III) complexes

    SciTech Connect

    Suna, Yuki; Fujita, Etsuko; Ertem, Mehmed Z.; Wang, Wan-Hui; Kambayashi, Hide; Manaka, Yuichi; Muckerman, James T.; Himeda, Yuichiro

    2014-11-12

    Proton-responsive half-sandwich Cp*Ir(III) complexes possessing a bipyridine ligand with two hydroxy groups at the 3,3'-, 4,4'-, 5,5'- or 6,6'-positions (3DHBP, 4DHBP, 5DHBP, or 6DHBP) were systematically investigated. UV-vis titration data provided average pK a values of the hydroxy groups on the ligands. Both hydroxy groups were found to deprotonate in the pH 4.6–5.6 range for the 4–6DHBP complexes. One of the hydroxy groups of the 3DHBP complex exhibited the low pKa value of < 0.4 because the deprotonation is facilitated by the strong intramolecular hydrogen bond formed between the generated oxyanion and the remaining hydroxy group, which in turn leads to an elevated pKa value of ~13.6 for the second deprotonation step. The crystal structures of the 4– and 6DHBP complexes obtained from basic aqueous solutions revealed their deprotonated forms. The intramolecular hydrogen bond in the 3DHBP complex was also observed in the crystal structures. The catalytic activities of these complexes in aqueous phase reactions, at appropriate pH, for hydrogenation of carbon dioxide (pH 8.5), dehydrogenation of formic acid (pH 1.8), transfer hydrogenation reactions using formic acid/formate as a hydrogen source (pH 7.2 and 2.6) were investigated to compare the positional effects of the hydroxy groups. The 4– and 6DHBP complexes exhibited remarkably enhanced catalytic activities under basic conditions because of the resonance effect of the strong electrondonating oxyanions, whereas the 5DHBP complex exhibited negligible activity despite the presence of electron-donating groups. The 3DHBP complex exhibited relatively high catalytic activity at low pH owing to the one strong electron-donating oxyanion group stabilized by the intramolecular hydrogen bond. DFT calculations were employed to study the mechanism of CO₂ hydrogenation by the 4DHBP and 6DHBP complexes, and comparison of the activation free energies of the H₂ heterolysis and CO

  7. Positional effects of hydroxy groups on catalytic activity of proton-responsive half-sandwich Cp*Iridium(III) complexes

    DOE PAGES

    Suna, Yuki; Fujita, Etsuko; Ertem, Mehmed Z.; Wang, Wan-Hui; Kambayashi, Hide; Manaka, Yuichi; Muckerman, James T.; Himeda, Yuichiro

    2014-11-12

    Proton-responsive half-sandwich Cp*Ir(III) complexes possessing a bipyridine ligand with two hydroxy groups at the 3,3'-, 4,4'-, 5,5'- or 6,6'-positions (3DHBP, 4DHBP, 5DHBP, or 6DHBP) were systematically investigated. UV-vis titration data provided average pK a values of the hydroxy groups on the ligands. Both hydroxy groups were found to deprotonate in the pH 4.6–5.6 range for the 4–6DHBP complexes. One of the hydroxy groups of the 3DHBP complex exhibited the low pKa value of < 0.4 because the deprotonation is facilitated by the strong intramolecular hydrogen bond formed between the generated oxyanion and the remaining hydroxy group, which in turn leadsmore » to an elevated pKa value of ~13.6 for the second deprotonation step. The crystal structures of the 4– and 6DHBP complexes obtained from basic aqueous solutions revealed their deprotonated forms. The intramolecular hydrogen bond in the 3DHBP complex was also observed in the crystal structures. The catalytic activities of these complexes in aqueous phase reactions, at appropriate pH, for hydrogenation of carbon dioxide (pH 8.5), dehydrogenation of formic acid (pH 1.8), transfer hydrogenation reactions using formic acid/formate as a hydrogen source (pH 7.2 and 2.6) were investigated to compare the positional effects of the hydroxy groups. The 4– and 6DHBP complexes exhibited remarkably enhanced catalytic activities under basic conditions because of the resonance effect of the strong electrondonating oxyanions, whereas the 5DHBP complex exhibited negligible activity despite the presence of electron-donating groups. The 3DHBP complex exhibited relatively high catalytic activity at low pH owing to the one strong electron-donating oxyanion group stabilized by the intramolecular hydrogen bond. DFT calculations were employed to study the mechanism of CO₂ hydrogenation by the 4DHBP and 6DHBP complexes, and comparison of the activation free energies of the H₂ heterolysis and CO₂ insertion steps

  8. Engineering catalytic activity via ion beam bombardment of catalyst supports for vertically aligned carbon nanotube growth

    DOE PAGES

    Islam, A. E.; Zakharov, D.; Stach, E. A.; Nikoleav, P.; Amama, P. B.; Sargent, G.; Saber, S.; Huffman, D.; Erford, M.; Semiatin, S. L.; et al

    2015-09-16

    Carbon nanotube growth depends on the catalytic activity of metal nanoparticles on alumina or silica supports. The control on catalytic activity is generally achieved by variations in water concentration, carbon feed, and sample placement on a few types of alumina or silica catalyst supports obtained via thin film deposition. We have recently expanded the choice of catalyst supports by engineering inactive substrates like c-cut sapphire via ion beam bombardment. The deterministic control on the structure and chemistry of catalyst supports obtained by tuning the degree of beam-induced damage have enabled better regulation of the activity of Fe catalysts only inmore » the ion beam bombarded areas and hence enabled controllable super growth of carbon nanotubes. A wide range of surface characterization techniques were used to monitor the catalytically active surface engineered via ion beam bombardment. The proposed method offers a versatile way to control carbon nanotube growth in patterned areas and also enhances the current understanding of the growth process. As a result, with the right choice of water concentration, carbon feed and sample placement, engineered catalyst supports may extend the carbon nanotube growth yield to a level that is even higher than the ones reported here, and thus offers promising applications of carbon nanotubes in electronics, heat exchanger, and energy storage.« less

  9. Engineering catalytic activity via ion beam bombardment of catalyst supports for vertically aligned carbon nanotube growth

    SciTech Connect

    Islam, A. E.; Zakharov, D.; Stach, E. A.; Nikoleav, P.; Amama, P. B.; Sargent, G.; Saber, S.; Huffman, D.; Erford, M.; Semiatin, S. L.; Maruyama, B.

    2015-09-16

    Carbon nanotube growth depends on the catalytic activity of metal nanoparticles on alumina or silica supports. The control on catalytic activity is generally achieved by variations in water concentration, carbon feed, and sample placement on a few types of alumina or silica catalyst supports obtained via thin film deposition. We have recently expanded the choice of catalyst supports by engineering inactive substrates like c-cut sapphire via ion beam bombardment. The deterministic control on the structure and chemistry of catalyst supports obtained by tuning the degree of beam-induced damage have enabled better regulation of the activity of Fe catalysts only in the ion beam bombarded areas and hence enabled controllable super growth of carbon nanotubes. A wide range of surface characterization techniques were used to monitor the catalytically active surface engineered via ion beam bombardment. The proposed method offers a versatile way to control carbon nanotube growth in patterned areas and also enhances the current understanding of the growth process. As a result, with the right choice of water concentration, carbon feed and sample placement, engineered catalyst supports may extend the carbon nanotube growth yield to a level that is even higher than the ones reported here, and thus offers promising applications of carbon nanotubes in electronics, heat exchanger, and energy storage.

  10. Chemoselective Boron-Catalyzed Nucleophilic Activation of Carboxylic Acids for Mannich-Type Reactions.

    PubMed

    Morita, Yuya; Yamamoto, Tomohiro; Nagai, Hideoki; Shimizu, Yohei; Kanai, Motomu

    2015-06-10

    The carboxyl group (COOH) is an omnipresent functional group in organic molecules, and its direct catalytic activation represents an attractive synthetic method. Herein, we describe the first example of a direct catalytic nucleophilic activation of carboxylic acids with BH3·SMe2, after which the acids are able to act as carbon nucleophiles, i.e. enolates, in Mannich-type reactions. This reaction proceeds with a mild organic base (DBU) and exhibits high levels of functional group tolerance. The boron catalyst is highly chemoselective toward the COOH group, even in the presence of other carbonyl moieties, such as amides, esters, or ketones. Furthermore, this catalytic method can be extended to highly enantioselective Mannich-type reactions by using a (R)-3,3'-I2-BINOL-substituted boron catalyst.

  11. The Catalytic Scaffold fo the Haloalkanoic Acid Dehalogenase Enzyme Superfamily Acts as a Mold for the Trigonal Bipyramidal Transition State

    SciTech Connect

    Lu,Z.; Dunaway-Mariano, D.; Allen, K.

    2008-01-01

    The evolution of new catalytic activities and specificities within an enzyme superfamily requires the exploration of sequence space for adaptation to a new substrate with retention of those elements required to stabilize key intermediates/transition states. Here, we propose that core residues in the large enzyme family, the haloalkanoic acid dehalogenase enzyme superfamily (HADSF) form a 'mold' in which the trigonal bipyramidal transition states formed during phosphoryl transfer are stabilized by electrostatic forces. The vanadate complex of the hexose phosphate phosphatase BT4131 from Bacteroides thetaiotaomicron VPI-5482 (HPP) determined at 1.00 Angstroms resolution via X-ray crystallography assumes a trigonal bipyramidal coordination geometry with the nucleophilic Asp-8 and one oxygen ligand at the apical position. Remarkably, the tungstate in the complex determined to 1.03 Angstroms resolution assumes the same coordination geometry. The contribution of the general acid/base residue Asp-10 in the stabilization of the trigonal bipyramidal species via hydrogen-bond formation with the apical oxygen atom is evidenced by the 1.52 Angstroms structure of the D10A mutant bound to vanadate. This structure shows a collapse of the trigonal bipyramidal geometry with displacement of the water molecule formerly occupying the apical position. Furthermore, the 1.07 Angstroms resolution structure of the D10A mutant complexed with tungstate shows the tungstate to be in a typical 'phosphate-like' tetrahedral configuration. The analysis of 12 liganded HADSF structures deposited in the protein data bank (PDB) identified stringently conserved elements that stabilize the trigonal bipyramidal transition states by engaging in favorable electrostatic interactions with the axial and equatorial atoms of the transferring phosphoryl group.

  12. Esterification and Transesterification of greases to fatty acid methyl esters with highly active diphenylamine salts

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Diphenylamine sulfate (DPAS) and diphenylamine hydrochloride (DPACl) salts were found to be highly active catalysts for esterification and transesterification of inexpensive greases to fatty acid methyl esters (FAME). In the presence of catalytic amounts of DPAS or DPACl and excess methanol, the fr...

  13. Improving the catalytic activity of isopentenyl phosphate kinase through protein coevolution analysis

    PubMed Central

    Liu, Ying; Yan, Zhihui; Lu, Xiaoyun; Xiao, Dongguang; Jiang, Huifeng

    2016-01-01

    Protein rational design has become more and more popular for protein engineering with the advantage of biological big-data. In this study, we described a method of rational design that is able to identify desired mutants by analyzing the coevolution of protein sequence. We employed this approach to evolve an archaeal isopentenyl phosphate kinase that can convert dimethylallyl alcohol (DMA) into precursor of isoprenoids. By designing 9 point mutations, we improved the catalytic activities of IPK about 8-fold in vitro. After introducing the optimal mutant of IPK into engineered E. coli strain for β-carotenoids production, we found that β-carotenoids production exhibited 97% increase over the starting strain. The process of enzyme optimization presented here could be used to improve the catalytic activities of other enzymes. PMID:27052337

  14. Improving the catalytic activity of isopentenyl phosphate kinase through protein coevolution analysis.

    PubMed

    Liu, Ying; Yan, Zhihui; Lu, Xiaoyun; Xiao, Dongguang; Jiang, Huifeng

    2016-01-01

    Protein rational design has become more and more popular for protein engineering with the advantage of biological big-data. In this study, we described a method of rational design that is able to identify desired mutants by analyzing the coevolution of protein sequence. We employed this approach to evolve an archaeal isopentenyl phosphate kinase that can convert dimethylallyl alcohol (DMA) into precursor of isoprenoids. By designing 9 point mutations, we improved the catalytic activities of IPK about 8-fold in vitro. After introducing the optimal mutant of IPK into engineered E. coli strain for β-carotenoids production, we found that β-carotenoids production exhibited 97% increase over the starting strain. The process of enzyme optimization presented here could be used to improve the catalytic activities of other enzymes. PMID:27052337

  15. Crystal structure of the catalytic domain of human bile salt activated lipase.

    PubMed Central

    Terzyan, S.; Wang, C. S.; Downs, D.; Hunter, B.; Zhang, X. C.

    2000-01-01

    Bile-salt activated lipase (BAL) is a pancreatic enzyme that digests a variety of lipids in the small intestine. A distinct property of BAL is its dependency on bile salts in hydrolyzing substrates of long acyl chains or bulky alcoholic motifs. A crystal structure of the catalytic domain of human BAL (residues 1-538) with two surface mutations (N186D and A298D), which were introduced in attempting to facilitate crystallization, has been determined at 2.3 A resolution. The crystal form belongs to space group P2(1)2(1)2(1) with one monomer per asymmetric unit, and the protein shows an alpha/beta hydrolase fold. In the absence of bound bile salt molecules, the protein possesses a preformed catalytic triad and a functional oxyanion hole. Several surface loops around the active site are mobile, including two loops potentially involved in substrate binding (residues 115-125 and 270-285). PMID:11045623

  16. Twinning in fcc lattice creates low-coordinated catalytically active sites in porous gold.

    PubMed

    Krajčí, Marian; Kameoka, Satoshi; Tsai, An-Pang

    2016-08-28

    We describe a new mechanism for creation of catalytically active sites in porous gold. Samples of porous gold prepared by de-alloying Al2Au exhibit a clear correlation between the catalytic reactivity towards CO oxidation and structural defects in the fcc lattice of Au. We have found that on the stepped {211} surfaces quite common twin boundary defects in the bulk structure of porous gold can form long close-packed rows of atoms with the coordination number CN = 6. DFT calculations confirm that on these low-coordinated Au sites dioxygen chemisorbs and CO oxidation can proceed via the Langmuir-Hinshelwood mechanism with the activation energy of 37 kJ/mol or via the CO-OO intermediate with the energy barrier of 19 kJ/mol. The existence of the twins in porous gold is stabilized by the surface energy.

  17. Twinning in fcc lattice creates low-coordinated catalytically active sites in porous gold

    NASA Astrophysics Data System (ADS)

    Krajčí, Marian; Kameoka, Satoshi; Tsai, An-Pang

    2016-08-01

    We describe a new mechanism for creation of catalytically active sites in porous gold. Samples of porous gold prepared by de-alloying Al2Au exhibit a clear correlation between the catalytic reactivity towards CO oxidation and structural defects in the fcc lattice of Au. We have found that on the stepped {211} surfaces quite common twin boundary defects in the bulk structure of porous gold can form long close-packed rows of atoms with the coordination number CN = 6. DFT calculations confirm that on these low-coordinated Au sites dioxygen chemisorbs and CO oxidation can proceed via the Langmuir-Hinshelwood mechanism with the activation energy of 37 kJ/mol or via the CO-OO intermediate with the energy barrier of 19 kJ/mol. The existence of the twins in porous gold is stabilized by the surface energy.

  18. Gold Incorporated Mesoporous Silica Thin Film Model Surface as a Robust SERS and Catalytically Active Substrate.

    PubMed

    Sunil Sekhar, Anandakumari Chandrasekharan; Vinod, Chathakudath Prabhakaran

    2016-01-01

    Ultra-small gold nanoparticles incorporated in mesoporous silica thin films with accessible pore channels perpendicular to the substrate are prepared by a modified sol-gel method. The simple and easy spin coating technique is applied here to make homogeneous thin films. The surface characterization using FESEM shows crack-free films with a perpendicular pore arrangement. The applicability of these thin films as catalysts as well as a robust SERS active substrate for model catalysis study is tested. Compared to bare silica film our gold incorporated silica, GSM-23F gave an enhancement factor of 10³ for RhB with a laser source 633 nm. The reduction reaction of p-nitrophenol with sodium borohydride from our thin films shows a decrease in peak intensity corresponding to -NO₂ group as time proceeds, confirming the catalytic activity. Such model surfaces can potentially bridge the material gap between a real catalytic system and surface science studies. PMID:27213321

  19. Synthesis of Iron Nanoparticles Using Azadirachta indica Extract and Its Catalytic Activity Toward Nitrophenol Reduction.

    PubMed

    Karthikeyan, C; Ranjani, M; Kim, Ae Rhan; Yoo, Dong Jin; Kumar, G Gnana

    2016-03-01

    A simple, hasty and eco-friendly approach for the synthesis of iron nanoparticles has been developed using the medicinally important Azadirachta indica extract, which act as both reducing and stabilizing agent. The formation and morphological properties of iron nanoparticles as a function of metallic precursor and Azadirachta indica extract concentration have been investigated. The influence of solvent over the size and texture of iron nanoparticles has also been evaluated in detail. The thermal behavior of prepared nanoparticles was identified from thermogravimetric analysis. Furthermore, the catalytic activity of prepared iron nanoparticles toward the reduction of p-nitrophenol was analyzed and the reduction process was occurred within 30 sec. The cost and time efficient biosynthesis process and excellent catalytic activity of the prepared iron nanoparticles construct this protocol attractive.

  20. Characterization and catalytic activity of gold nanoparticles synthesized using ayurvedic arishtams

    NASA Astrophysics Data System (ADS)

    Aswathy Aromal, S.; Dinesh Babu, K. V.; Philip, Daizy

    2012-10-01

    The development of new synthesis methods for monodispersed nanocrystals using cheap and nontoxic chemicals, environmentally benign solvents and renewable materials remains a challenge to the scientific community. The present work reports a new green method for the synthesis of gold nanoparticles. Four different ayurvedic arishtams are used for the reduction of Au3+ to Au nanoparticles. This method is simple, efficient, economic and nontoxic. Gold nanoparticles having different sizes in the range from 15 to 23 nm could be obtained. The nanoparticles have been characterized by UV-Visible spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and FTIR analysis. The high crystallinity of nanoparticles is evident from bright circular spots in the SAED pattern and peaks in the XRD pattern. The synthesized gold nanoparticles show good catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol by excess NaBH4. The synthesized nanoparticles are found to exhibit size dependent catalytic property, the smaller nanoparticles showing faster activity.

  1. ALD Functionalized Nanoporous Gold: Thermal Stability, Mechanical Properties, and Catalytic Activity

    SciTech Connect

    Biener, M M; Biener, J; Wichmann, A; Wittstock, A; Baumann, T F; Baeumer, M; Hamza, A V

    2011-03-24

    Nanoporous metals have many technologically promising applications but their tendency to coarsen limits their long-term stability and excludes high temperature applications. Here, we demonstrate that atomic layer deposition (ALD) can be used to stabilize and functionalize nanoporous metals. Specifically, we studied the effect of nanometer-thick alumina and titania ALD films on thermal stability, mechanical properties, and catalytic activity of nanoporous gold (np-Au). Our results demonstrate that even only one-nm-thick oxide films can stabilize the nanoscale morphology of np-Au up to 1000 C, while simultaneously making the material stronger and stiffer. The catalytic activity of np-Au can be drastically increased by TiO{sub 2} ALD coatings. Our results open the door to high temperature sensor, actuator, and catalysis applications and functionalized electrodes for energy storage and harvesting applications.

  2. Catalytically Active and Spectator Ce(3+) in Ceria-Supported Metal Catalysts.

    PubMed

    Kopelent, René; van Bokhoven, Jeroen A; Szlachetko, Jakub; Edebeli, Jacinta; Paun, Cristina; Nachtegaal, Maarten; Safonova, Olga V

    2015-07-20

    Identification of active species and the rate-determining reaction steps are crucial for optimizing the performance of oxygen-storage materials, which play an important role in catalysts lowering automotive emissions, as electrode materials for fuel cells, and as antioxidants in biomedicine. We demonstrated that active Ce(3+) species in a ceria-supported platinum catalyst during CO oxidation are short-lived and therefore cannot be observed under steady-state conditions. Using time-resolved resonant X-ray emission spectroscopy, we quantitatively correlated the initial rate of Ce(3+) formation under transient conditions to the overall rate of CO oxidation under steady-state conditions and showed that ceria reduction is a kinetically relevant step in CO oxidation, whereas a fraction of Ce(3+) was present as spectators. This approach can be applied to various catalytic processes involving oxygen-storage materials and reducible oxides to distinguish between redox and nonredox catalytic mechanisms.

  3. ALD functionalized nanoporous gold: thermal stability, mechanical properties, and catalytic activity.

    PubMed

    Biener, Monika M; Biener, Juergen; Wichmann, Andre; Wittstock, Arne; Baumann, Theodore F; Bäumer, Marcus; Hamza, Alex V

    2011-08-10

    Nanoporous metals have many technologically promising applications, but their tendency to coarsen limits their long-term stability and excludes high temperature applications. Here, we demonstrate that atomic layer deposition (ALD) can be used to stabilize and functionalize nanoporous metals. Specifically, we studied the effect of nanometer-thick alumina and titania ALD films on thermal stability, mechanical properties, and catalytic activity of nanoporous gold (np-Au). Our results demonstrate that even only 1 nm thick oxide films can stabilize the nanoscale morphology of np-Au up to 1,000°C, while simultaneously making the material stronger and stiffer. The catalytic activity of np-Au can be drastically increased by TiO(2) ALD coatings. Our results open the door to high-temperature sensor, actuator, and catalysis applications and functionalized electrodes for energy storage and harvesting applications.

  4. Twinning in fcc lattice creates low-coordinated catalytically active sites in porous gold.

    PubMed

    Krajčí, Marian; Kameoka, Satoshi; Tsai, An-Pang

    2016-08-28

    We describe a new mechanism for creation of catalytically active sites in porous gold. Samples of porous gold prepared by de-alloying Al2Au exhibit a clear correlation between the catalytic reactivity towards CO oxidation and structural defects in the fcc lattice of Au. We have found that on the stepped {211} surfaces quite common twin boundary defects in the bulk structure of porous gold can form long close-packed rows of atoms with the coordination number CN = 6. DFT calculations confirm that on these low-coordinated Au sites dioxygen chemisorbs and CO oxidation can proceed via the Langmuir-Hinshelwood mechanism with the activation energy of 37 kJ/mol or via the CO-OO intermediate with the energy barrier of 19 kJ/mol. The existence of the twins in porous gold is stabilized by the surface energy. PMID:27586937

  5. Aqueous synthesis of hierarchical bismuth nanobundles with high catalytic activity to organic dyes

    NASA Astrophysics Data System (ADS)

    Ma, Dechong; Zhao, Yan; Zhao, Jingzhe; Li, Yawen; Lu, Yan; Zhao, Duijia

    2015-07-01

    Bundle-like bismuth (Bi) nanoarchitectures were successfully prepared on a large scale by an aqueous reducing strategy with polyethylene glycol (PEG) as directing agent at 90 °C for 55 min. The bundle-like Bi nanoarchitectures have a length of 4-5 μm and diameter of 0.5-1 μm with fairly uniform construction. Catalytic activities of the as-prepared hierarchical Bi nanobundles were investigated for degrading Rhodamine B (RhB) dye solution under visible-light irradiation. The Bi nanostructures extended excellent catalytic activity and good cycling performance toward photodegradation of RhB. Possible mechanism was proposed for Bi-assisted photocatalytic degradation of RhB under visible-light.

  6. Selective nitrogen doping in graphene: Enhanced catalytic activity for the oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Wang, Xianlong; Hou, Zhufeng; Ikeda, Takashi; Huang, Sheng-Feng; Terakura, Kiyoyuki; Boero, Mauro; Oshima, Masaharu; Kakimoto, Masa-Aki; Miyata, Seizo

    2011-12-01

    The structural and electronic properties of N-doped zigzag graphene ribbons with various ratios of dihydrogenated to monohydrogenated edge carbons are investigated within the density functional theory framework. We find that the stability of graphitic N next to the edge, which is claimed to play important roles in the catalytic activity in our previous work, will be enhanced with increasing the concentration of dihydrogenated carbons. Furthermore, the dihydrogenated edge carbons turn out to be easily converted into monohydrogenated ones in the presence of oxygen molecules at room temperature. Based on our results, we propose a possible way to enhance the oxygen reduction catalytic activity of N-doped graphene by controlling the degrees of hydrogenation of edge carbons. The characteristic features in the x-ray absorption and emission spectra for each specific N site considered here will also be given.

  7. Methods and apparatuses for preparing a surface to have catalytic activity

    DOEpatents

    Cooks, Robert G.; Peng, Wen-Ping; Ouyang, Zheng; Goodwin, Michael P.

    2011-03-22

    The invention provides methods and apparatuses that utilize mass spectrometry for preparation of a surface to have catalytic activity through molecular soft-landing of mass selected ions. Mass spectrometry is used to generate combinations of atoms in a particular geometrical arrangement, and ion soft-landing selects this molecular entity or combination of entities and gently deposits the entity or combination intact onto a surface.

  8. Synthesis of Pt-Mo-N Thin Film and Catalytic Activity for Fuel Cells

    SciTech Connect

    Miura, Akira; Tague, Michele E.; Gregoire, John M.; Wen, Xiao-Dong; van Dover, R. Bruce; Abruña, Héctor D.; DiSalvo, Francis J.

    2010-05-13

    Pt-Mo-N composition gradient film was synthesized by combining thin-film deposition techniques and subsequent thermal nitridation. A ternary platinum-based nitride, Pt2Mo3N, showed catalytic activities for fuel cell applications and higher electrochemical stability when it was compared with a PtMo alloy with the same Pt:Mo ratio.

  9. Effect of size of catalytically active phases in the dehydrogenation of alcohols and the challenging selective oxidation of hydrocarbons.

    PubMed

    Zhang, Qinghong; Deng, Weiping; Wang, Ye

    2011-09-01

    The size of the active phase is one of the most important factors in determining the catalytic behaviour of a heterogeneous catalyst. This Feature Article focuses on the size effects in two types of reactions, i.e., the metal nanoparticle-catalysed dehydrogenation of alcohols and the metal oxide nanocluster-catalysed selective oxidation of hydrocarbons (including the selective oxidation of methane and ethane and the epoxidation of propylene). For Pd or Au nanoparticle-catalysed oxidative or non-oxidative dehydrogenation of alcohols, the size of metal nanoparticles mainly controls the catalytic activity by affecting the activation of reactants (either alcohol or O(2)). The size of oxidic molybdenum species loaded on SBA-15 determines not only the activity but also the selectivity of oxygenates in the selective oxidation of ethane; highly dispersed molybdenum species are suitable for acetaldehyde formation, while molybdenum oxide nanoparticles exhibit higher formaldehyde selectivity. Cu(II) and Fe(III) isolated on mesoporous silica are highly efficient for the selective oxidation of methane to formaldehyde, while the corresponding oxide clusters mainly catalyse the complete oxidation of methane. The lattice oxygen in iron or copper oxide clusters is responsible for the complete oxidation, while the isolated Cu(I) or Fe(II) generated during the reaction can activate molecular oxygen forming active oxygen species for the selective oxidation of methane. Highly dispersed Cu(I) and Fe(II) species also function for the epoxidation of propylene by O(2) and N(2)O, respectively. Alkali metal ions work as promoters for the epoxidation of propylene by enhancing the dispersion of copper or iron species and weakening the acidity. PMID:21629889

  10. Isolated metal active site concentration and stability control catalytic CO2 reduction selectivity.

    PubMed

    Matsubu, John C; Yang, Vanessa N; Christopher, Phillip

    2015-03-01

    CO2 reduction by H2 on heterogeneous catalysts is an important class of reactions that has been studied for decades. However, atomic scale details of structure-function relationships are still poorly understood. Particularly, it has been suggested that metal particle size plays a unique role in controlling the stability of CO2 hydrogenation catalysts and the distribution of active sites, which dictates reactivity and selectivity. These studies often have not considered the possible role of isolated metal active sites in the observed dependences. Here, we utilize probe molecule diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) with known site-specific extinction coefficients to quantify the fraction of Rh sites residing as atomically dispersed isolated sites (Rhiso), as well as Rh sites on the surface of Rh nanoparticles (RhNP) for a series of TiO2 supported Rh catalysts. Strong correlations were observed between the catalytic reverse water gas shift turn over frequency (TOF) and the fraction of Rhiso sites and between catalytic methanation TOF and the fraction of RhNP sites. Furthermore, it was observed that reaction condition-induced disintegration of Rh nanoparticles, forming Rhiso active sites, controls the changing reactivity with time on stream. This work demonstrates that isolated atoms and nanoparticles of the same metal on the same support can exhibit uniquely different catalytic selectivity in competing parallel reaction pathways and that disintegration of nanoparticles under reaction conditions can play a significant role in controlling stability.

  11. Direct Visualization of Catalytically Active Sites at the FeO-Pt(111) Interface.

    PubMed

    Kudernatsch, Wilhelmine; Peng, Guowen; Zeuthen, Helene; Bai, Yunhai; Merte, Lindsay R; Lammich, Lutz; Besenbacher, Flemming; Mavrikakis, Manos; Wendt, Stefan

    2015-08-25

    Within the area of surface science, one of the "holy grails" is to directly visualize a chemical reaction at the atomic scale. Whereas this goal has been reached by high-resolution scanning tunneling microscopy (STM) in a number of cases for reactions occurring at flat surfaces, such a direct view is often inhibited for reaction occurring at steps and interfaces. Here we have studied the CO oxidation reaction at the interface between ultrathin FeO islands and a Pt(111) support by in situ STM and density functional theory (DFT) calculations. Time-lapsed STM imaging on this inverse model catalyst in O2 and CO environments revealed catalytic activity occurring at the FeO-Pt(111) interface and directly showed that the Fe-edges host the catalytically most active sites for the CO oxidation reaction. This is an important result since previous evidence for the catalytic activity of the FeO-Pt(111) interface is essentially based on averaging techniques in conjunction with DFT calculations. The presented STM results are in accord with DFT+U calculations, in which we compare possible CO oxidation pathways on oxidized Fe-edges and O-edges. We found that the CO oxidation reaction is more favorable on the oxidized Fe-edges, both thermodynamically and kinetically.

  12. A microreactor array for spatially resolved measurement of catalytic activity for high-throughput catalysis science

    SciTech Connect

    Kondratyuk, Petro; Gumuslu, Gamze; Shukla, Shantanu; Miller, James B; Morreale, Bryan D; Gellman, Andrew J

    2013-04-01

    We describe a 100 channel microreactor array capable of spatially resolved measurement of catalytic activity across the surface of a flat substrate. When used in conjunction with a composition spread alloy film (CSAF, e.g. Pd{sub x}Cu{sub y}Au{sub 1-x-y}) across which component concentrations vary smoothly, such measurements permit high-throughput analysis of catalytic activity and selectivity as a function of catalyst composition. In the reported implementation, the system achieves spatial resolution of 1 mm{sup 2} over a 10×10 mm{sup 2} area. During operation, the reactant gases are delivered at constant flow rate to 100 points of differing composition on the CSAF surface by means of a 100-channel microfluidic device. After coming into contact with the CSAF catalyst surface, the product gas mixture from each of the 100 points is withdrawn separately through a set of 100 isolated channels for analysis using a mass spectrometer. We demonstrate the operation of the device on a Pd{sub x}Cu{sub y}Au{sub 1-x-y} CSAF catalyzing the H{sub 2}-D{sub 2} exchange reaction at 333 K. In essentially a single experiment, we measured the catalytic activity over a broad swathe of concentrations from the ternary composition space of the Pd{sub x}Cu{sub y}Au{sub 1-x-y} alloy.

  13. Direct Visualization of Catalytically Active Sites at the FeO-Pt(111) Interface

    SciTech Connect

    Kudernatsch, Wilhelmine; Peng, Guowen; Zeuthen, Helene; Bai, Yunhai; Merte, L. R.; Lammich, Lutz; Besenbacher, Fleming; Mavrikakis, Manos; Wendt, Stefen

    2015-08-25

    Within the area of surface science, one of the “holy grails” is to directly visualize a chemical reaction at the atomic scale. Whereas this goal has been reached by high-resolution scanning tunneling microscopy (STM) in a number of cases for reactions occurring at flat surfaces, such a direct view is often inhibited for reaction occurring at steps and interfaces. Here we have studied the CO oxidation reaction at the interface between ultrathin FeO islands and a Pt(111) support by in situ STM and density functional theory (DFT) calculations. Time-lapsed STM imaging on this inverse model catalyst in O2 and CO environments revealed catalytic activity occurring at the FeO-Pt(111) interface and directly showed that the Fe-edges host the catalytically most active sites for the CO oxidation reaction. This is an important result since previous evidence for the catalytic activity of the FeO-Pt(111) interface is essentially based on averaging techniques in conjunction with DFT calculations. The presented STM results are in accord with DFTþU calculations, in which we compare possible CO oxidation pathways on oxidized Fe-edges and O-edges. We found that the CO oxidation reaction is more favorable on the oxidized Fe-edges, both thermodynamically and kinetically.

  14. Isolated metal active site concentration and stability control catalytic CO2 reduction selectivity.

    PubMed

    Matsubu, John C; Yang, Vanessa N; Christopher, Phillip

    2015-03-01

    CO2 reduction by H2 on heterogeneous catalysts is an important class of reactions that has been studied for decades. However, atomic scale details of structure-function relationships are still poorly understood. Particularly, it has been suggested that metal particle size plays a unique role in controlling the stability of CO2 hydrogenation catalysts and the distribution of active sites, which dictates reactivity and selectivity. These studies often have not considered the possible role of isolated metal active sites in the observed dependences. Here, we utilize probe molecule diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) with known site-specific extinction coefficients to quantify the fraction of Rh sites residing as atomically dispersed isolated sites (Rhiso), as well as Rh sites on the surface of Rh nanoparticles (RhNP) for a series of TiO2 supported Rh catalysts. Strong correlations were observed between the catalytic reverse water gas shift turn over frequency (TOF) and the fraction of Rhiso sites and between catalytic methanation TOF and the fraction of RhNP sites. Furthermore, it was observed that reaction condition-induced disintegration of Rh nanoparticles, forming Rhiso active sites, controls the changing reactivity with time on stream. This work demonstrates that isolated atoms and nanoparticles of the same metal on the same support can exhibit uniquely different catalytic selectivity in competing parallel reaction pathways and that disintegration of nanoparticles under reaction conditions can play a significant role in controlling stability. PMID:25671686

  15. Effect of the synthetic method on the catalytic activity of alumina: Epoxidation of cyclohexene

    SciTech Connect

    Valderruten, N.E.; Peña, W.F.; Ramírez, A.E.; Rodríguez-Páez, J.E.

    2015-02-15

    Graphical abstract: Temperature influence on percent conversion and selectivity in the epoxidation of cyclohexene using commercial alumina as a catalyst. - Highlights: • Aluminum oxide was synthesized using Pechini method. • The alumina obtained showed a mix of boehmite and γ-alumina phases. • We research an economically feasible method to obtain alumina for use as a catalyst. • Alumina obtained by Pechini showed high percent conversion and/or selectivity. • The best results were 78% conversion and 78% selectivity to epoxidation reactions. - Abstract: Al{sub 2}O{sub 3} was prepared from different inorganic precursors via the Pechini method and compared with Al{sub 2}O{sub 3} prepared by the sol–gel method. Structural characterization of these materials was carried out by FTIR, X-ray diffraction (XRD), N{sub 2} adsorption at −196 °C and transmission electron microscopy (TEM). The solids were tested in the epoxidation of cyclohexene and a difference in their catalytic activities was observed. The characterization results indicate that the samples prepared by Pechini have a mixture of γ-alumina and boehmite, a condition favoring catalytic activity, whereas the sol–gel sample is less crystalline due to higher boehmite content. These results indicate that both the nature of the precursor and the method of synthesis strongly affect the catalytic activity of Al{sub 2}O{sub 3}.

  16. Supercritical CO{sub 2} mediated synthesis and catalytic activity of graphene/Pd nanocomposites

    SciTech Connect

    Tang, Lulu; Nguyen, Van Hoa; Shim, Jae-Jin

    2015-11-15

    Highlights: • RGO/Pd composite was efficiently prepared via a facile method in supercritical CO{sub 2}. • Graphene sheets were coated uniformly with Pd nanoparticles with a size of ∼8 nm. • Composites exhibited excellent catalytic activity in the Suzuki reaction even after 10 cycles. - Abstract: Graphene sheets were decorated with palladium nanoparticles using a facile and efficient method in supercritical CO{sub 2}. The nanoparticles were formed on the graphene sheets by the simple hydrogen reduction of palladium(II) hexafluoroacetylacetonate precursor in supercritical CO{sub 2}. The product was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Highly dispersed nanoparticles with various sizes and shapes adhered well to the graphene sheets. The composites showed high catalytic activities for the Suzuki reaction under aqueous and aerobic conditions within 5 min. The effects of the different Pd precursor loadings on the catalytic activities of the composites were also examined.

  17. Hydrolysis of biomass using a reusable solid carbon acid catalyst and fermentation of the catalytic hydrolysate to ethanol.

    PubMed

    Goswami, Mandavi; Meena, S; Navatha, S; Prasanna Rani, K N; Pandey, Ashok; Sukumaran, Rajeev Kumar; Prasad, R B N; Prabhavathi Devi, B L A

    2015-01-01

    Solid acid catalysts can hydrolyze cellulose with lower reaction times and are easy to recover and reuse. A glycerol based carbon acid catalyst developed at CSIR-IICT performed well in acid catalysis reactions and hence this study was undertaken to evaluate the catalyst for hydrolysis of biomass (alkali pretreated or native rice straw). The catalyst could release 262 mg/g total reducing sugars (TRS) in 4h at 140 °C from alkali pretreated rice straw, and more importantly it released 147 mg/g TRS from native biomass. Reusability of the catalyst was also demonstrated. Catalytic hydrolysate was used as sugar source for fermentation to produce ethanol. Results indicate the solid acid catalyst as an interesting option for biomass hydrolysis.

  18. Catalytic actions of alkaline salts in reactions between 1,2,3,4-butanetetracarboxylic acid and cellulose: II. Esterification.

    PubMed

    Ji, Bolin; Tang, Peixin; Yan, Kelu; Sun, Gang

    2015-11-01

    1,2,3,4-Butanetetracarboxylic acid (BTCA) reacts with cellulose in two steps with catalysis of alkaline salts such as sodium hypophosphite: anhydride formation and esterification of anhydride with cellulose. The alkali metal ions were found effective in catalyzing formation of BTCA anhydride in a previous report. In this work, catalytic functions of the alkaline salts in the esterification reaction between BTCA anhydride and cellulose were investigated. Results revealed that acid anions play an important role in the esterification reaction by assisting removal of protons on intermediates and completion of the esterification between cellulose and BTCA. Besides, alkaline salts with lower pKa1 values of the corresponding acids are more effective ones for the reaction since addition of these salts could lead to lower pH values and higher acid anion concentrations in finishing baths. The mechanism explains the results of FTIR and wrinkle recovery angles of the fabrics cured under different temperatures and times.

  19. Effects of novel supports on the physical and catalytic properties of tungstophosphoric acid for alcohol dehydration reactions

    SciTech Connect

    Herrera, Jose E.; Kwak, Ja Hun; Hu, Jian Zhi; Wang, Yong; Peden, Charles HF

    2008-08-17

    The catalytic behavior of tungstophosphoric acid supported on modified mesoporous silica materials for the dehydration of 2-butanol and methanol was studied. Specifically, the supports evaluated here consisted of unmodified MCM-41 and SBA-15 mesoporous silicas, and these materials coated with sub-monolayer quantities of alumina, titania, and zirconia. UV-Vis DRS and 31P-NMR spectroscopy showed that the tungstophosphoric acid species retained their chemical identity in the synthesized supported form, although the spectra were influenced by the specific support material used. In addition, their acidic properties were evaluated using temperature programmed oxidation of isopropyl amine. The differences in reaction rates between the samples reflect both the diversity in the amount of Brønsted acidic sites available for catalysis and dissimilarities in coking resistance. These two characteristics depend, in turn, on the type of support modifier used to prepare the catalyst.

  20. Nanorods, nanospheres, nanocubes: Synthesis, characterization and catalytic activity of nanoferrites of Mn, Co, Ni, Part-89

    SciTech Connect

    Singh, Supriya; Srivastava, Pratibha; Singh, Gurdip

    2013-02-15

    Graphical abstract: Prepared nanoferrites were characterized by FE-SEM and bright field TEM micrographs. The catalytic effect of these nanoferrites was evaluated on the thermal decomposition of ammonium perchlorate using TG and TG–DSC techniques. The kinetics of thermal decomposition of AP was evaluated using isothermal TG data by model fitting as well as isoconversional method. Display Omitted Highlights: ► Synthesis of ferrite nanostructures (∼20.0 nm) by wet-chemical method under different synthetic conditions. ► Characterization using XRD, FE-SEM, EDS, TEM, HRTEM and SAED pattern. ► Catalytic activity of ferrite nanostructures on AP thermal decomposition by thermal techniques. ► Burning rate measurements of CSPs with ferrite nanostructures. ► Kinetics of thermal decomposition of AP + nanoferrites. -- Abstract: In this paper, the nanoferrites of Mn, Co and Ni were synthesized by wet chemical method and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive, X-ray spectra (EDS), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HR-TEM). It is catalytic activity were investigated on the thermal decomposition of ammonium perchlorate (AP) and composite solid propellants (CSPs) using thermogravimetry (TG), TG coupled with differential scanning calorimetry (TG–DSC) and ignition delay measurements. Kinetics of thermal decomposition of AP + nanoferrites have also been investigated using isoconversional and model fitting approaches which have been applied to data for isothermal TG decomposition. The burning rate of CSPs was considerably enhanced by these nanoferrites. Addition of nanoferrites to AP led to shifting of the high temperature decomposition peak toward lower temperature. All these studies reveal that ferrite nanorods show the best catalytic activity superior to that of nanospheres and nanocubes.

  1. The support effect on the size and catalytic activity of thiolated Au25 nanoclusters as precatalysts

    NASA Astrophysics Data System (ADS)

    Fang, Jun; Li, Jingguo; Zhang, Bin; Yuan, Xun; Asakura, Hiroyuki; Tanaka, Tsunehiro; Teramura, Kentaro; Xie, Jianping; Yan, Ning

    2015-03-01

    In this study, 6-mercaptohexanoic (MHA) protected Au25(MHA)18 nanoclusters (or thiolated Au NCs) deposited on various inorganic supports, including hydroxyapatite (HAP), TiO2 (Degussa P25), activated carbon (AC), pyrolyzed graphene oxide (PGO), and fumed SiO2 were prepared via a conventional impregnation method. Following that, calcination under a N2 stream was conducted to produce surface ligand free, highly dispersed Au NCs catalysts. The effects of supports on the size and catalytic activity of Au NCs were systematically investigated. No obvious size growth was observed for Au NCs on HAP and P25 after thermally induced ligand removal, due to the strong interaction between the metal and the supports. However, severe aggregations of Au NCs were seen after thermal treatment on three other supports, including AC, PGO, and SiO2. The removal of surface thiol ligands from the Au NCs is crucial to catalyze nitrobenzene hydrogenation, where only calcined Au/HAP and Au/P25 exhibited good catalytic activity. On the other hand, all the supported Au NCs were active for the styrene oxidation, where Au/HAP exhibited the best catalytic performance. Altogether, both the size effect and metal-support interaction are crucial for the design of supported Au NCs as efficient catalysts for targeted reactions.In this study, 6-mercaptohexanoic (MHA) protected Au25(MHA)18 nanoclusters (or thiolated Au NCs) deposited on various inorganic supports, including hydroxyapatite (HAP), TiO2 (Degussa P25), activated carbon (AC), pyrolyzed graphene oxide (PGO), and fumed SiO2 were prepared via a conventional impregnation method. Following that, calcination under a N2 stream was conducted to produce surface ligand free, highly dispersed Au NCs catalysts. The effects of supports on the size and catalytic activity of Au NCs were systematically investigated. No obvious size growth was observed for Au NCs on HAP and P25 after thermally induced ligand removal, due to the strong interaction between the

  2. Molecular Basis of Reduced Pyridoxine 5′-Phosphate Oxidase Catalytic Activity in Neonatal Epileptic Encephalopathy Disorder*

    PubMed Central

    Musayev, Faik N.; Di Salvo, Martino L.; Saavedra, Mario A.; Contestabile, Roberto; Ghatge, Mohini S.; Haynes, Alexina; Schirch, Verne; Safo, Martin K.

    2009-01-01

    Mutations in pyridoxine 5′-phosphate oxidase are known to cause neonatal epileptic encephalopathy. This disorder has no cure or effective treatment and is often fatal. Pyridoxine 5′-phosphate oxidase catalyzes the oxidation of pyridoxine 5′-phosphate to pyridoxal 5′-phosphate, the active cofactor form of vitamin B6 required by more than 140 different catalytic activities, including enzymes involved in amino acid metabolism and biosynthesis of neurotransmitters. Our aim is to elucidate the mechanism by which a homozygous missense mutation (R229W) in the oxidase, linked to neonatal epileptic encephalopathy, leads to reduced oxidase activity. The R229W variant is ∼850-fold less efficient than the wild-type enzyme due to an ∼192-fold decrease in pyridoxine 5′-phosphate affinity and an ∼4.5-fold decrease in catalytic activity. There is also an ∼50-fold reduction in the affinity of the R229W variant for the FMN cofactor. A 2.5 Å crystal structure of the R229W variant shows that the substitution of Arg-229 at the FMN binding site has led to a loss of hydrogen-bond and/or salt-bridge interactions between FMN and Arg-229 and Ser-175. Additionally, the mutation has led to an alteration of the configuration of a β-strand-loop-β-strand structure at the active site, resulting in loss of two critical hydrogen-bond interactions involving residues His-227 and Arg-225, which are important for substrate binding and orientation for catalysis. These results provide a molecular basis for the phenotype associated with the R229W mutation, as well as providing a foundation for understanding the pathophysiological consequences of pyridoxine 5′-phosphate oxidase mutations. PMID:19759001

  3. Liquid/Liquid interfacial fabrication of thermosensitive and catalytically active Ag nanoparticle-doped block copolymer composite foam films.

    PubMed

    Liu, Mei; Wang, Qian; Geng, Yuanyuan; Wang, Changwei; Lee, Yong-Ill; Hao, Jingcheng; Liu, Hong-Guo

    2014-09-01

    An aqueous solution of AgNO3 (upper phase) and a DMF/CHCl3 solution of polystyrene-b-poly(acryl acid)-b-polystyrene (PS-b-PAA-b-PS) or PS-b-PAA-b-PS/1,6-diaminohexane (DAH) (lower phase) constituted a planar liquid/liquid interface. The lower phase gradually transformed to a water-in-oil (W/O) emulsion via spontaneous emulsification due to the "ouzo effect". Polymer molecules, DAH molecules, and Ag(+) ions assembled into microcapsules around emulsion droplets that adsorbed at the planar liquid/liquid interface, resulting in formation of a foam film. DAH acted as a cross-linker during this process. Transmission electron microscopic observations indicated that Ag nanoclusters that were generated through reduction of Ag(+) ions by DMF were homogeneously dispersed in the walls of the foam structure. X-ray photoelectron spectroscopic investigations revealed that Ag(I) and Ag(0) coexisted in the film, and Ag(I) transformed to Ag(0) after further treatment. The film formed without DAH was not stable, while the film formed with DAH was very stable due to intermolecular attraction between PAA and DAH and formation of amides, as revealed by FTIR spectra. The film formed with DAH exhibited high and durable catalytic activity for hydrogenation of nitro compounds and, very interestingly, exhibited thermoresponsive catalytic behavior.

  4. Tough and catalytically active hybrid biofibers wet-spun from nanochitin hydrogels.

    PubMed

    Das, Paramita; Heuser, Thomas; Wolf, Andrea; Zhu, Baolei; Demco, Dan Eugen; Ifuku, Shinsuke; Walther, Andreas

    2012-12-10

    Sustainable alternatives for high-performance and functional materials based on renewable resources are intensely needed as future alternatives for present-day, fossil-based materials. Nanochitin represents an emerging class of highly crystalline bionanoparticles with high intrinsic mechanical properties and the ability for conjugation into functional materials owing to reactive amine and hydroxyl groups. Herein we demonstrate that hydrogels containing surface-deacetylated chitin nanofibrils of micrometer length and average diameters of 9 nm, as imaged by cryogenic transmission electron microscopy, can be wet-spun into macrofibers via extrusion in a coagulation bath, a simple low energy and large-scale processing route. The resulting biofibers display attractive mechanical properties with a large plastic region of about 12% in strain, in which frictional sliding of nanofibrils allows dissipation of fracture energy and enables a high work-of-fracture of near 10 MJ/m3. We further show how to add functionality to these macrofibers by exploiting the amine functions of the surface chitosan groups to host catalytically active noble metal nanoparticles, furnishing biobased, renewable catalytic hybrids. These inorganic/organic macrofibers can be used repeatedly for fast catalytic reductions of model compounds without loss of activity, rendering the concept of hybridized chitin materials interesting as novel bioderived supports for nanoparticle catalysts. PMID:23102411

  5. Reduced graphene oxide supported platinum nanocubes composites: one-pot hydrothermal synthesis and enhanced catalytic activity

    NASA Astrophysics Data System (ADS)

    Li, Fumin; Gao, Xueqing; Xue, Qi; Li, Shuni; Chen, Yu; Lee, Jong-Min

    2015-02-01

    Reduced graphene oxide (rGO) supported platinum nanocubes (Pt-NCs) composites (Pt-NCs/rGO) were synthesized successfully by a water-based co-chemical reduction method, in which polyallylamine hydrochloride acted as a multi-functional molecule for the functionalization of graphene oxide, anchorage of PtII precursor, and control of Pt crystal facets. The morphology, structure, composition, and catalytic property of Pt-NCs/rGO composites were characterized in detail by various spectroscopic techniques. Transmission electron microscopy images showed well-defined Pt-NCs with an average size of 9 nm uniformly distributed on the rGO surface. The as-prepared Pt-NCs/rGO composites had excellent colloidal stability in the aqueous solution, and exhibited superior catalytic activity towards the hydrogenation reduction of nitro groups compared to commercial Pt black. The improved catalytic activity originated from the abundant exposed Pt{100} facets of Pt-NCs, excellent dispersion of Pt-NCs on the rGO surface, and synergistic effect between Pt-NCs and rGO.

  6. Co-Cu Nanoparticles: Synthesis by Galvanic Replacement and Phase Rearrangement during Catalytic Activation.

    PubMed

    Nafria, Raquel; Genç, Aziz; Ibáñez, Maria; Arbiol, Jordi; de la Piscina, Pilar Ramírez; Homs, Narcís; Cabot, Andreu

    2016-03-01

    The control of the phase distribution in multicomponent nanomaterials is critical to optimize their catalytic performance. In this direction, while impressive advances have been achieved in the past decade in the synthesis of multicomponent nanoparticles and nanocomposites, element rearrangement during catalyst activation has been frequently overseen. Here, we present a facile galvanic replacement-based procedure to synthesize Co@Cu nanoparticles with narrow size and composition distributions. We further characterize their phase arrangement before and after catalytic activation. When oxidized at 350 °C in air to remove organics, Co@Cu core-shell nanostructures oxidize to polycrystalline CuO-Co3O4 nanoparticles with randomly distributed CuO and Co3O4 crystallites. During a posterior reduction treatment in H2 atmosphere, Cu precipitates in a metallic core and Co migrates to the nanoparticle surface to form Cu@Co core-shell nanostructures. The catalytic behavior of such Cu@Co nanoparticles supported on mesoporous silica was further analyzed toward CO2 hydrogenation in real working conditions. PMID:26878153

  7. Layered Double Hydroxide Nanoclusters: Aqueous, Concentrated, Stable, and Catalytically Active Colloids toward Green Chemistry.

    PubMed

    Tokudome, Yasuaki; Morimoto, Tsuyoshi; Tarutani, Naoki; Vaz, Pedro D; Nunes, Carla D; Prevot, Vanessa; Stenning, Gavin B G; Takahashi, Masahide

    2016-05-24

    Increasing attention has been dedicated to the development of nanomaterials rendering green and sustainable processes, which occur in benign aqueous reaction media. Herein, we demonstrate the synthesis of another family of green nanomaterials, layered double hydroxide (LDH) nanoclusters, which are concentrated (98.7 g/L in aqueous solvent), stably dispersed (transparent sol for >2 weeks), and catalytically active colloids of nano LDHs (isotropic shape with the size of 7.8 nm as determined by small-angle X-ray scattering). LDH nanoclusters are available as colloidal building blocks to give access to meso- and macroporous LDH materials. Proof-of-concept applications revealed that the LDH nanocluster works as a solid basic catalyst and is separable from solvents of catalytic reactions, confirming the nature of nanocatalysts. The present work closely investigates the unique physical and chemical features of this colloid, the formation mechanism, and the ability to act as basic nanocatalysts in benign aqueous reaction systems. PMID:27124717

  8. Layered Double Hydroxide Nanoclusters: Aqueous, Concentrated, Stable, and Catalytically Active Colloids toward Green Chemistry.

    PubMed

    Tokudome, Yasuaki; Morimoto, Tsuyoshi; Tarutani, Naoki; Vaz, Pedro D; Nunes, Carla D; Prevot, Vanessa; Stenning, Gavin B G; Takahashi, Masahide

    2016-05-24

    Increasing attention has been dedicated to the development of nanomaterials rendering green and sustainable processes, which occur in benign aqueous reaction media. Herein, we demonstrate the synthesis of another family of green nanomaterials, layered double hydroxide (LDH) nanoclusters, which are concentrated (98.7 g/L in aqueous solvent), stably dispersed (transparent sol for >2 weeks), and catalytically active colloids of nano LDHs (isotropic shape with the size of 7.8 nm as determined by small-angle X-ray scattering). LDH nanoclusters are available as colloidal building blocks to give access to meso- and macroporous LDH materials. Proof-of-concept applications revealed that the LDH nanocluster works as a solid basic catalyst and is separable from solvents of catalytic reactions, confirming the nature of nanocatalysts. The present work closely investigates the unique physical and chemical features of this colloid, the formation mechanism, and the ability to act as basic nanocatalysts in benign aqueous reaction systems.

  9. Green synthesis of silver nanoparticles, decorated on graphene oxide nanosheets and their catalytic activity

    NASA Astrophysics Data System (ADS)

    Sreekanth, T. V. M.; Jung, Min-Ji; Eom, In-Yong

    2016-01-01

    In this study, we develop an inexpensive and green route for the synthesis of silver nanoparticles (AgNPs) using Picrasma quassioides bark aqueous extract as reducing and capping agent and also eco-friendly decorate graphene oxide (GO) nanosheets with AgNPs (GO-AgNPs). Green synthesized AgNPs and GO-AgNPs composites were characterized by UV-Visible spectroscopy, SEM-EDX, and TEM-SAED techniques. The resulting GO-AgNPs contained about 41.35% of Ag and the AgNPs size ranges 17.5-66.5 nm, and GO-AgNPs size ranges 10-49.5 nm. Moreover, the GO-AgNPs exhibited excellent catalytic activity towards the methylene blue (MB) in the presence of sodium borohydride (NaBH4) at room temperature. This catalytic reaction completed within 15 min.

  10. Influence of support hydroxides on the catalytic activity of oxidized gold clusters

    SciTech Connect

    Veith, Gabriel M; Lupini, Andrew R; Pennycook, Stephen J; Dudney, Nancy J

    2010-01-01

    Gold oxide nanoparticles were prepared on the native surface and a hydroxylated surface of a non-porous TiO2 support (Degussa P25). Scanning transmission electron microscopy results show the formation of similarly sized clusters on both support materials (1.86 and 1.61 nm clusters on the native oxide and the hydroxylated oxide respectively). X-ray absorption near edge spectroscopy and X-ray photoelectron spectroscopy clearly indicate the formation of Au3+ rich oxide nanoparticles. Despite the similar cluster sizes and oxidation states the gold oxide clusters grown on the hydroxylated surface were at least 180 times more catalytically active for the oxidation of carbon monoxide then those grown on the native oxide surface. These hydroxides are conveniently introduced during the solution phase synthesis of gold catalysts and play a dominate, but previously unrecognized, role in the catalytic properties of both oxidized and metallic gold particles.

  11. Versatile DNAzyme-based amplified biosensing platforms for nucleic acid, protein, and enzyme activity detection.

    PubMed

    Zhao, Xu-Hua; Gong, Liang; Zhang, Xiao-Bing; Yang, Bin; Fu, Ting; Hu, Rong; Tan, Weihong; Yu, Ruqin

    2013-04-01

    DNAzymes have been widely applied as signal amplifiers for enzyme-free and highly sensitive detection of DNA. A few of them have also been employed for amplified detection of other biomolecules via a target-triggered assembly of split or mutated DNAzyme strategy. However, most of these designs adopt Mg(2+)-dependent DNAzyme as the catalytic unit, which suffered from low catalytic cleavage activity. Meanwhile, some DNAzymes with high catalytic activity are not suitable for these designs because the slight modification of the catalytic core might results in remarkably decreased or even no catalytic activity of these DNAzymes. On the basis of DNAzyme topological effect or the terminal protection of small-molecule-linked DNA, we developed two versatile sensing platforms for amplified detection of different biotargets. Since no modification is necessary for the catalytic core of the DNAzyme in these designs, they can employ any DNAzyme with high catalytic activity as amplified unit, which affords a high amplified efficiency for the sensing platform. A catalytic and molecular beacon design was further employed to realize the true enzymatic multiple turnover of DNAzyme. These designs together allow a high sensitivity for the biotargets, resulting in a detection limit of 20 pM, 0.2 U/mL, and 1 ng/mL for target DNA, DNA adenine methylation methyltransferase (Dam MTase), and streptavidin, respectively, much lower than previously reported biosensors. In addition, the proposed sensing strategy is versatile. By conjugating with various recognition units, it can be employed to detect a wide range of biotargets, varying from nucleic acids to proteins with high sensitivity.

  12. Acid Rain: Activities for Science Teachers.

    ERIC Educational Resources Information Center

    Johnson, Eric; And Others

    1983-01-01

    Seven complete secondary/college level acid rain activities are provided. Activities include overview; background information and societal implications; major concepts; student objectives; vocabulary/material lists; procedures; instructional strategies; and questions/discussion and extension suggestions. Activities consider effects of acid rain on…

  13. Optimizing anti-coking abilities of zeolites by ethylene diamine tetraacetie acid modification on catalytic fast pyrolysis of corn stalk

    NASA Astrophysics Data System (ADS)

    Zhang, Bo; Zhong, Zhaoping; Song, Zuwei; Ding, Kuan; Chen, Paul; Ruan, Roger

    2015-12-01

    In order to minimize coke yield during biomass catalytic fast pyrolysis (CFP) process, ethylene diamine tetraacetie acid (EDTA) chemical modification method is carried out to selectively remove the external framework aluminum of HZSM-5 catalyst. X-ray diffraction (XRD), nitrogen (N2)-adsorption and ammonia-temperature programmed desorption (NH3-TPD) techniques are employed to investigate the porosity and acidity characteristics of original and modified HZSM-5 samples. Py-GC/MS and thermo-gravimetric analyzer (TGA) experiments are further conducted to explore the catalytic effect of modified HZSM-5 samples on biomass CFP and to verify the positive effect on coke reduction. Results show that EDTA treatment does not damage the crystal structure of HZSM-5 zeolites, but leads to a slight increase of pore volume and pore size. Meanwhile, the elimination of the strong acid peak indicates the dealumination of outer surface of HZSM-5 zeolites. Treatment time of 2 h (labeled EDTA-2H) is optimal for acid removal and hydrocarbon formation. Among all modified catalysts, EDTA-2H performs the best for deacidification and can obviously increase the yields of positive chemical compositions in pyrolysis products. Besides, EDTA modification can improve the anti-coking properties of HZSM-5 zeolites, and EDTA-2H gives rise to the lowest coke yield.

  14. β-Amino acid catalyzed asymmetric Michael additions: design of organocatalysts with catalytic acid/base dyad inspired by serine proteases.

    PubMed

    Yang, Hui; Wong, Ming Wah

    2011-09-16

    A new type of chiral β-amino acid catalyst has been computationally designed, mimicking the enzyme catalysis of serine proteases. Our catalyst approach is based on the bioinspired catalytic acid/base dyad, namely, a carboxyl and imidazole pair. DFT calculations predict that this designed organocatalyst catalyzes Michael additions of aldehydes to nitroalkenes with excellent enantioselectivities and remarkably high anti diastereoselectivities. The unusual stacked geometry of the enamine intermediate, hydrogen bonding network, and the adoption of an exo transition state are the keys to understand the stereoselectivity.

  15. Catalytic Y-tailed amphiphilic homopolymers - aqueous nanoreactors for high activity, low loading SCS pincer catalysts.

    PubMed

    Patterson, Joseph P; Cotanda, Pepa; Kelley, Elizabeth G; Moughton, Adam O; Lu, Annhelen; Epps, Thomas H; O'Reilly, Rachel K

    2013-01-01

    A new amphiphilic homopolymer bearing an SCS pincer palladium complex has been synthesized by reversible addition fragmentation chain transfer polymerization. The amphiphile has been shown to form spherical and worm-like micelles in water by cryogenic transmission electron microscopy and small angle neutron scattering. Segregation of reactive components within the palladium containing core results in increased catalytic activity of the pincer compound compared to small molecule analogues. This allows carbon-carbon bond forming reactions to be performed in water with reduced catalyst loadings and enhanced activity.

  16. Detailed characterization of the cooperative mechanism of Ca(2+) binding and catalytic activation in the Ca(2+) transport (SERCA) ATPase.

    PubMed

    Zhang, Z; Lewis, D; Strock, C; Inesi, G; Nakasako, M; Nomura, H; Toyoshima, C

    2000-08-01

    Expression of heterologous SERCA1a ATPase in Cos-1 cells was optimized to yield levels that account for 10-15% of the microsomal protein, as revealed by protein staining on electrophoretic gels. This high level of expression significantly improved our characterization of mutants, including direct measurements of Ca(2+) binding by the ATPase in the absence of ATP, and measurements of various enzyme functions in the presence of ATP or P(i). Mutational analysis distinguished two groups of amino acids within the transmembrane domain: The first group includes Glu771 (M5), Thr799 (M6), Asp800 (M6), and Glu908 (M8), whose individual mutations totally inhibit binding of the two Ca(2+) required for activation of one ATPase molecule. The second group includes Glu309 (M4) and Asn796 (M6), whose individual or combined mutations inhibit binding of only one and the same Ca(2+). The effects of mutations of these amino acids were interpreted in the light of recent information on the ATPase high-resolution structure, explaining the mechanism of Ca(2+) binding and catalytic activation in terms of two cooperative sites. The Glu771, Thr799, and Asp800 side chains contribute prominently to site 1, together with less prominent contributions by Asn768 and Glu908. The Glu309, Asn796, and Asp800 side chains, as well as the Ala305 (and possibly Val304 and Ile307) carbonyl oxygen, contribute to site 2. Sequential binding begins with Ca(2+) occupancy of site 1, followed by transition to a conformation (E') sensitive to Ca(2+) inhibition of enzyme phosphorylation by P(i), but still unable to utilize ATP. The E' conformation accepts the second Ca(2+) on site 2, producing then a conformation (E' ') which is able to utilize ATP. Mutations of residues (Asp813 and Asp818) in the M6/M7 loop reduce Ca(2+) affinity and catalytic turnover, suggesting a strong influence of this loop on the correct positioning of the M6 helix. Mutation of Asp351 (at the catalytic site within the cytosolic domain

  17. The Contribution of Non-catalytic Carbohydrate Binding Modules to the Activity of Lytic Polysaccharide Monooxygenases*

    PubMed Central

    Crouch, Lucy I.; Labourel, Aurore; Walton, Paul H.; Davies, Gideon J.; Gilbert, Harry J.

    2016-01-01

    Lignocellulosic biomass is a sustainable industrial substrate. Copper-dependent lytic polysaccharide monooxygenases (LPMOs) contribute to the degradation of lignocellulose and increase the efficiency of biofuel production. LPMOs can contain non-catalytic carbohydrate binding modules (CBMs), but their role in the activity of these enzymes is poorly understood. Here we explored the importance of CBMs in LPMO function. The family 2a CBMs of two monooxygenases, CfLPMO10 and TbLPMO10 from Cellulomonas fimi and Thermobispora bispora, respectively, were deleted and/or replaced with CBMs from other proteins. The data showed that the CBMs could potentiate and, surprisingly, inhibit LPMO activity, and that these effects were both enzyme-specific and substrate-specific. Removing the natural CBM or introducing CtCBM3a, from the Clostridium thermocellum cellulosome scaffoldin CipA, almost abolished the catalytic activity of the LPMOs against the cellulosic substrates. The deleterious effect of CBM removal likely reflects the importance of prolonged presentation of the enzyme on the surface of the substrate for efficient catalytic activity, as only LPMOs appended to CBMs bound tightly to cellulose. The negative impact of CtCBM3a is in sharp contrast with the capacity of this binding module to potentiate the activity of a range of glycoside hydrolases including cellulases. The deletion of the endogenous CBM from CfLPMO10 or the introduction of a family 10 CBM from Cellvibrio japonicus LPMO10B into TbLPMO10 influenced the quantity of non-oxidized products generated, demonstrating that CBMs can modulate the mode of action of LPMOs. This study demonstrates that engineered LPMO-CBM hybrids can display enhanced industrially relevant oxygenations. PMID:26801613

  18. The Contribution of Non-catalytic Carbohydrate Binding Modules to the Activity of Lytic Polysaccharide Monooxygenases.

    PubMed

    Crouch, Lucy I; Labourel, Aurore; Walton, Paul H; Davies, Gideon J; Gilbert, Harry J

    2016-04-01

    Lignocellulosic biomass is a sustainable industrial substrate. Copper-dependent lytic polysaccharide monooxygenases (LPMOs) contribute to the degradation of lignocellulose and increase the efficiency of biofuel production. LPMOs can contain non-catalytic carbohydrate binding modules (CBMs), but their role in the activity of these enzymes is poorly understood. Here we explored the importance of CBMs in LPMO function. The family 2a CBMs of two monooxygenases,CfLPMO10 andTbLPMO10 fromCellulomonas fimiandThermobispora bispora, respectively, were deleted and/or replaced with CBMs from other proteins. The data showed that the CBMs could potentiate and, surprisingly, inhibit LPMO activity, and that these effects were both enzyme-specific and substrate-specific. Removing the natural CBM or introducingCtCBM3a, from theClostridium thermocellumcellulosome scaffoldin CipA, almost abolished the catalytic activity of the LPMOs against the cellulosic substrates. The deleterious effect of CBM removal likely reflects the importance of prolonged presentation of the enzyme on the surface of the substrate for efficient catalytic activity, as only LPMOs appended to CBMs bound tightly to cellulose. The negative impact ofCtCBM3a is in sharp contrast with the capacity of this binding module to potentiate the activity of a range of glycoside hydrolases including cellulases. The deletion of the endogenous CBM fromCfLPMO10 or the introduction of a family 10 CBM fromCellvibrio japonicusLPMO10B intoTbLPMO10 influenced the quantity of non-oxidized products generated, demonstrating that CBMs can modulate the mode of action of LPMOs. This study demonstrates that engineered LPMO-CBM hybrids can display enhanced industrially relevant oxygenations.

  19. Influence of hydrophobic mismatch on the catalytic activity of Escherichia coli GlpG rhomboid protease.

    PubMed

    Foo, Alexander C Y; Harvey, Brandon G R; Metz, Jeff J; Goto, Natalie K

    2015-04-01

    Rhomboids comprise a broad family of intramembrane serine proteases that are found in a wide range of organisms and participate in a diverse array of biological processes. High-resolution structures of the catalytic transmembrane domain of the Escherichia coli GlpG rhomboid have provided numerous insights that help explain how hydrolytic cleavage can be achieved below the membrane surface. Key to this are observations that GlpG hydrophobic domain dimensions may not be sufficient to completely span the native lipid bilayer. This formed the basis for a model where hydrophobic mismatch Induces thinning of the local membrane environment to promote access to transmembrane substrates. However, hydrophobic mismatch also has the potential to alter the functional properties of the rhomboid, a possibility we explore in the current work. For this purpose, we purified the catalytic transmembrane domain of GlpG into phosphocholine or maltoside detergent micelles of varying alkyl chain lengths, and assessed proteolytic function with a model water-soluble substrate. Catalytic turnover numbers were found to depend on detergent alkyl chain length, with saturated chains containing 10-12 carbon atoms supporting maximal activity. Similar results were obtained in phospholipid bicelles, with no proteolytic activity being detected in longer-chain lipids. Although differences in thermal stability and GlpG oligomerization could not explain these activity differences, circular dichroism spectra suggest that mismatch gives rise to a small change in structure. Overall, these results demonstrate that hydrophobic mismatch can exert an inhibitory effect on rhomboid activity, with the potential for changes in local membrane environment to regulate activity in vivo.

  20. Unraveling the hidden catalytic activity of vertebrate class IIa histone deacetylases

    PubMed Central

    Lahm, A.; Paolini, C.; Pallaoro, M.; Nardi, M. C.; Jones, P.; Neddermann, P.; Sambucini, S.; Bottomley, M. J.; Lo Surdo, P.; Carfí, A.; Koch, U.; De Francesco, R.; Steinkühler, C.; Gallinari, P.

    2007-01-01

    Previous findings have suggested that class IIa histone deacetylases (HDACs) (HDAC4, -5, -7, and -9) are inactive on acetylated substrates, thus differing from class I and IIb enzymes. Here, we present evidence supporting this view and demonstrate that class IIa HDACs are very inefficient enzymes on standard substrates. We identified HDAC inhibitors unable to bind recombinant human HDAC4 while showing inhibition in a typical HDAC4 enzymatic assay, suggesting that the observed activity rather reflects the involvement of endogenous copurified class I HDACs. Moreover, an HDAC4 catalytic domain purified from bacteria was 1,000-fold less active than class I HDACs on standard substrates. A catalytic Tyr is conserved in all HDACs except for vertebrate class IIa enzymes where it is replaced by His. Given the high structural conservation of HDAC active sites, we predicted the class IIa His-Nε2 to be too far away to functionally substitute the class I Tyr-OH in catalysis. Consistently, a Tyr-to-His mutation in class I HDACs severely reduced their activity. More importantly, a His-976-Tyr mutation in HDAC4 produced an enzyme with a catalytic efficiency 1,000-fold higher than WT, and this “gain of function phenotype” could be extended to HDAC5 and -7. We also identified trifluoroacetyl-lysine as a class IIa-specific substrate in vitro. Hence, vertebrate class IIa HDACs may have evolved to maintain low basal activities on acetyl-lysines and to efficiently process restricted sets of specific, still undiscovered natural substrates. PMID:17956988

  1. Phosphorylation by protein kinase C decreases catalytic activity of avian phospholipase C-beta.

    PubMed Central

    Filtz, T M; Cunningham, M L; Stanig, K J; Paterson, A; Harden, T K

    1999-01-01

    The potential role of protein kinase C (PKC)-promoted phosphorylation has been examined in the G-protein-regulated inositol lipid signalling pathway. Incubation of [32P]Pi-labelled turkey erythrocytes with either the P2Y1 receptor agonist 2-methylthioadenosine triphosphate (2MeSATP) or with PMA resulted in a marked increase in incorporation of 32P into the G-protein-activated phospholipase C PLC-betaT. Purified PLC-betaT also was phosphorylated by PKC in vitro to a stoichiometry (mean+/-S. E.M.) of 1.06+/-0.2 mol of phosphate/mol of PLC-betaT. Phosphorylation by PKC was isoenzyme-specific because, under identical conditions, mammalian PLC-beta2 also was phosphorylated to a stoichiometry near unity, whereas mammalian PLC-beta1 was not phosphorylated by PKC. The effects of PKC-promoted phosphorylation on enzyme activity were assessed by reconstituting purified PLC-betaT with turkey erythrocyte membranes devoid of endogenous PLC activity. Phosphorylation resulted in a decrease in basal activity, AlF4(-)-stimulated activity, and activity stimulated by 2MeSATP plus guanosine 5'-[gamma-thio]triphosphate in the reconstituted membranes. The decreases in enzyme activities were proportional to the extent of PKC-promoted phosphorylation. Catalytic activity assessed by using mixed detergent/phospholipid micelles also was decreased by up to 60% by phosphorylation. The effect of phosphorylation on Gqalpha-stimulated PLC-betaT in reconstitution experiments with purified proteins was not greater than that observed on basal activity alone. Taken together, these results illustrate that PKC phosphorylates PLC-betaT in vivo and to a physiologically relevant stoichiometry in vitro. Phosphorylation is accompanied by a concomitant loss of enzyme activity, reflected as a decrease in overall catalytic activity rather than as a specific modification of G-protein-regulated activity. PMID:10024500

  2. Probing Substrate Interactions in the Active Tunnel of a Catalytically Deficient Cellobiohydrolase (Cel7)*

    PubMed Central

    Colussi, Francieli; Sørensen, Trine H.; Alasepp, Kadri; Kari, Jeppe; Cruys-Bagger, Nicolaj; Windahl, Michael S.; Olsen, Johan P.; Borch, Kim; Westh, Peter

    2015-01-01

    Cellobiohydrolases break down cellulose sequentially by sliding along the crystal surface with a single cellulose strand threaded through the catalytic tunnel of the enzyme. This so-called processive mechanism relies on a complex pattern of enzyme-substrate interactions, which need to be addressed in molecular descriptions of processivity and its driving forces. Here, we have used titration calorimetry to study interactions of cellooligosaccharides (COS) and a catalytically deficient variant (E212Q) of the enzyme Cel7A from Trichoderma reesei. This enzyme has ∼10 glucopyranose subsites in the catalytic tunnel, and using COS ligands with a degree of polymerization (DP) from 2 to 8, different regions of the tunnel could be probed. For COS ligands with a DP of 2–3 the binding constants were around 105 m−1, and for longer ligands (DP 5–8) this value was ∼107 m−1. Within each of these groups we did not find increased affinity as the ligands got longer and potentially filled more subsites. On the contrary, we found a small but consistent affinity loss as DP rose from 6 to 8, particularly at the higher investigated temperatures. Other thermodynamic functions (ΔH, ΔS, and ΔCp) decreased monotonously with both temperature and DP. Combined interpretation of these thermodynamic results and previously published structural data allowed assessment of an affinity profile along the length axis of the active tunnel. PMID:25477511

  3. Dynamic formation of single-atom catalytic active sites on ceria-supported gold nanoparticles

    SciTech Connect

    Wang, Yanggang; Mei, Donghai; Glezakou, Vassiliki Alexandra; Li, Jun; Rousseau, Roger J.

    2015-03-04

    Ab initio Molecular Dynamics simulations and static Density Functional Theory calculations have been performed to investigate the reaction mechanism of CO oxidation on Au/CeO2 catalyst. It is found that under reaction condition CO adsorption significantly labializes the surface atoms of the Au cluster and leads to the formation of isolated Au+-CO species that resides on the support in the vicinity of the Au particle. In this context, we identified a dynamic single-atom catalytic mechanism at the interfacial area for CO oxidation on Au/CeO2 catalyst, which is a lower energy pathway than that of CO oxidation at the interface with the metal particle. This results from the ability of the single atom site to strongly couple with the redox properties of the support in a synergistic manner thereby lowering the barrier for redox reactions. We find that the single Au+ ion, which only exists under reaction conditions, breaks away from the Au cluster to catalyze CO oxidation and returns to the Au cluster after the catalytic cycle is completed. Generally, our study highlights the importance of the dynamic creation of active sites under reaction conditions and their essential role in a catalytic process.

  4. Probing substrate interactions in the active tunnel of a catalytically deficient cellobiohydrolase (Cel7).

    PubMed

    Colussi, Francieli; Sørensen, Trine H; Alasepp, Kadri; Kari, Jeppe; Cruys-Bagger, Nicolaj; Windahl, Michael S; Olsen, Johan P; Borch, Kim; Westh, Peter

    2015-01-23

    Cellobiohydrolases break down cellulose sequentially by sliding along the crystal surface with a single cellulose strand threaded through the catalytic tunnel of the enzyme. This so-called processive mechanism relies on a complex pattern of enzyme-substrate interactions, which need to be addressed in molecular descriptions of processivity and its driving forces. Here, we have used titration calorimetry to study interactions of cellooligosaccharides (COS) and a catalytically deficient variant (E212Q) of the enzyme Cel7A from Trichoderma reesei. This enzyme has ∼10 glucopyranose subsites in the catalytic tunnel, and using COS ligands with a degree of polymerization (DP) from 2 to 8, different regions of the tunnel could be probed. For COS ligands with a DP of 2-3 the binding constants were around 10(5) m(-1), and for longer ligands (DP 5-8) this value was ∼10(7) m(-1). Within each of these groups we did not find increased affinity as the ligands got longer and potentially filled more subsites. On the contrary, we found a small but consistent affinity loss as DP rose from 6 to 8, particularly at the higher investigated temperatures. Other thermodynamic functions (ΔH, ΔS, and ΔCp) decreased monotonously with both temperature and DP. Combined interpretation of these thermodynamic results and previously published structural data allowed assessment of an affinity profile along the length axis of the active tunnel. PMID:25477511

  5. Dynamic formation of single-atom catalytic active sites on ceria-supported gold nanoparticles

    DOE PAGES

    Wang, Yanggang; Mei, Donghai; Glezakou, Vassiliki Alexandra; Li, Jun; Rousseau, Roger J.

    2015-03-04

    Ab initio Molecular Dynamics simulations and static Density Functional Theory calculations have been performed to investigate the reaction mechanism of CO oxidation on Au/CeO2 catalyst. It is found that under reaction condition CO adsorption significantly labializes the surface atoms of the Au cluster and leads to the formation of isolated Au+-CO species that resides on the support in the vicinity of the Au particle. In this context, we identified a dynamic single-atom catalytic mechanism at the interfacial area for CO oxidation on Au/CeO2 catalyst, which is a lower energy pathway than that of CO oxidation at the interface with themore » metal particle. This results from the ability of the single atom site to strongly couple with the redox properties of the support in a synergistic manner thereby lowering the barrier for redox reactions. We find that the single Au+ ion, which only exists under reaction conditions, breaks away from the Au cluster to catalyze CO oxidation and returns to the Au cluster after the catalytic cycle is completed. Generally, our study highlights the importance of the dynamic creation of active sites under reaction conditions and their essential role in a catalytic process.« less

  6. The substrate specificity and the catalytic mechanism of N-carbamyl- D-amino acid amidohydrolase: A theoretical investigation

    NASA Astrophysics Data System (ADS)

    Han, Wei-Wei; Zhan, Dong Ling; Luo, Quan; Zhou, Yi-Han; Yao, Yuan; Li, Ze-Sheng; Feng, Yan

    2009-04-01

    N-carbamyl- D-amino acid amidohydrolasecatalyzes the hydrolysis of N-carbamyl- D-amino acids to D-amino acids, ammonia and the carbon dioxide. The docking studies validate that D-NCAase possesses of preference for D-enantiomers, predict that Gly194 and Arg174 may take part in the catalytic mechanism, and Glu136 is essential to maintain the stable conformation for catalysis. The initial step of the acylation reaction catalyzed by D-NCAase has been studied by density functional calculations. It was furthermore demonstrated that Lys126, His143, and Asn196 decrease the reaction barrier, while Asn172 raise the barrier. The structural and mechanistic insights obtained from computational study should be valuable for the mechanisms of cysteine proteases.

  7. Conformational Itinerary of Pseudomonas aeruginosa 1,6-Anhydro-N-acetylmuramic Acid Kinase during Its Catalytic Cycle*

    PubMed Central

    Bacik, John-Paul; Tavassoli, Marjan; Patel, Trushar R.; McKenna, Sean A.; Vocadlo, David J.; Khajehpour, Mazdak; Mark, Brian L.

    2014-01-01

    Anhydro-sugar kinases are unique from other sugar kinases in that they must cleave the 1,6-anhydro ring of their sugar substrate to phosphorylate it using ATP. Here we show that the peptidoglycan recycling enzyme 1,6-anhydro-N-acetylmuramic acid kinase (AnmK) from Pseudomonas aeruginosa undergoes large conformational changes during its catalytic cycle, with its two domains rotating apart by up to 32° around two hinge regions to expose an active site cleft into which the substrates 1,6-anhydroMurNAc and ATP can bind. X-ray structures of the open state bound to a nonhydrolyzable ATP analog (AMPPCP) and 1,6-anhydroMurNAc provide detailed insight into a ternary complex that forms preceding an operative Michaelis complex. Structural analysis of the hinge regions demonstrates a role for nucleotide binding and possible cross-talk between the bound ligands to modulate the opening and closing of AnmK. Although AnmK was found to exhibit similar binding affinities for ATP, ADP, and AMPPCP according to fluorescence spectroscopy, small angle x-ray scattering analyses revealed that AnmK adopts an open conformation in solution in the absence of ligand and that it remains in this open state after binding AMPPCP, as we had observed for our crystal structure of this complex. In contrast, the enzyme favored a closed conformation when bound to ADP in solution, consistent with a previous crystal structure of this complex. Together, our findings show that the open conformation of AnmK facilitates binding of both the sugar and nucleotide substrates and that large structural rearrangements must occur upon closure of the enzyme to correctly align the substrates and residues of the enzyme for catalysis. PMID:24362022

  8. Biosynthesised palladium nanoparticles using Eucommia ulmoides bark aqueous extract and their catalytic activity.

    PubMed

    Duan, Liansheng; Li, Ming; Liu, Huihong

    2015-12-01

    Palladium nanoparticles (PdNPs) are of great importance as catalytic materials. Their synthesis has been widely studied and interest in their properties is growing. Bio-based methods might be a greener option for designing the PdNPs with reduced environmental impacts. This study reports the synthesis of PdNPs by utilising the aqueous extract of medicinally important Eucommia ulmoides (E. Ulmoides) bark which functions as both reducing and capping agent in moderate reaction conditions. Reduction potential of E. Ulmoides bark aqueous extract was about -0.08 V vs. saturated calomel electrode by open-circuit voltage method and the rich polyphenolics was confirmed by cyclic voltammetry, which helps to reduce palladium ions to PdNPs. The characterisation through high-resolution transmission electron microscopic, energy dispersive X-ray spectroscopy and X-ray diffraction infer that the as-synthesised PdNPs were spherical in shape with a face cubic crystal structure. The results from dynamic light scattering suggest the PdNPs have the narrow size distribution with an average size of 12.6 nm. The lower zeta potential (-25.3 mV) and the Fourier transform infrared spectra indicate that the as-synthesised PdNPs keep remarkably stable for a long period due to the capped biomolecules on the nanoparticle surface. This method for synthesis of PdNPs is simple, economic, non-toxic and efficient. The PdNPs show excellent catalytic activity for the electro-catalytic oxidation of hydrazine and the catalytic reducing degradation of p-aminoazobenzene, a model compound of azo-dyes.

  9. Biosynthesised palladium nanoparticles using Eucommia ulmoides bark aqueous extract and their catalytic activity.

    PubMed

    Duan, Liansheng; Li, Ming; Liu, Huihong

    2015-12-01

    Palladium nanoparticles (PdNPs) are of great importance as catalytic materials. Their synthesis has been widely studied and interest in their properties is growing. Bio-based methods might be a greener option for designing the PdNPs with reduced environmental impacts. This study reports the synthesis of PdNPs by utilising the aqueous extract of medicinally important Eucommia ulmoides (E. Ulmoides) bark which functions as both reducing and capping agent in moderate reaction conditions. Reduction potential of E. Ulmoides bark aqueous extract was about -0.08 V vs. saturated calomel electrode by open-circuit voltage method and the rich polyphenolics was confirmed by cyclic voltammetry, which helps to reduce palladium ions to PdNPs. The characterisation through high-resolution transmission electron microscopic, energy dispersive X-ray spectroscopy and X-ray diffraction infer that the as-synthesised PdNPs were spherical in shape with a face cubic crystal structure. The results from dynamic light scattering suggest the PdNPs have the narrow size distribution with an average size of 12.6 nm. The lower zeta potential (-25.3 mV) and the Fourier transform infrared spectra indicate that the as-synthesised PdNPs keep remarkably stable for a long period due to the capped biomolecules on the nanoparticle surface. This method for synthesis of PdNPs is simple, economic, non-toxic and efficient. The PdNPs show excellent catalytic activity for the electro-catalytic oxidation of hydrazine and the catalytic reducing degradation of p-aminoazobenzene, a model compound of azo-dyes. PMID:26647810

  10. Physics-based enzyme design: predicting binding affinity and catalytic activity.

    PubMed

    Sirin, Sarah; Pearlman, David A; Sherman, Woody

    2014-12-01

    Computational enzyme design is an emerging field that has yielded promising success stories, but where numerous challenges remain. Accurate methods to rapidly evaluate possible enzyme design variants could provide significant value when combined with experimental efforts by reducing the number of variants needed to be synthesized and speeding the time to reach the desired endpoint of the design. To that end, extending our computational methods to model the fundamental physical-chemical principles that regulate activity in a protocol that is automated and accessible to a broad population of enzyme design researchers is essential. Here, we apply a physics-based implicit solvent MM-GBSA scoring approach to enzyme design and benchmark the computational predictions against experimentally determined activities. Specifically, we evaluate the ability of MM-GBSA to predict changes in affinity for a steroid binder protein, catalytic turnover for a Kemp eliminase, and catalytic activity for α-Gliadin peptidase variants. Using the enzyme design framework developed here, we accurately rank the most experimentally active enzyme variants, suggesting that this approach could provide enrichment of active variants in real-world enzyme design applications.

  11. Visible-Light-Induced Effects of Au Nanoparticle on Laccase Catalytic Activity.

    PubMed

    Guo, Sijie; Li, Hao; Liu, Juan; Yang, Yanmei; Kong, Weiqian; Qiao, Shi; Huang, Hui; Liu, Yang; Kang, Zhenhui

    2015-09-23

    A deep understanding of the interaction between the nanoparticle and enzyme is important for biocatalyst design. Here, we report the in situ synthesis of laccase-Au NP (laccase-Au) hybrids and its catalytic activity modulation by visible light. In the present hybrid system, the activity of laccase was significantly improved (increased by 91.2% vs free laccase) by Au NPs. With a short time visible light illumination (λ > 420 nm, within 3 min), the activity of laccase-Au hybrids decreased by 8.1% (vs laccase-Au hybrid without light), which can be restored to its initial one when the illumination is removed. However, after a long time illumination (λ > 420 nm, over 10 min), the catalytic activity of laccase-Au hybrids consecutively decreases and is not reversible even after removing the illumination. Our experiments also suggested that the local surface plasma resonance effect of Au NPs causes the structure change of laccase and local high temperature near the Au NPs. Those changes eventually affect the transportation of electrons in laccase, which further results in the declined activity of laccase.

  12. Catalytically Important Residues of E6AP Ubiquitin Ligase Identified Using Acid-Cleavable Photo-Cross-Linkers.

    PubMed

    Krist, David T; Statsyuk, Alexander V

    2015-07-28

    Inactivation of the E6AP E3 ubiquitin ligase (UBE3A gene) causes Angelman syndrome, while aberrant degradation of p53 by E6AP is implicated in cervical cancers. Herein, we describe the development of photo-cross-linkers to discover catalytic residues of E6AP. Using these cross-linkers, we identified covalent modifications of the E6AP catalytic cysteine and two lysines: Lys(847) and Lys(799). Lys(847) is required for the formation of Lys(48)-linked polyubiquitin chains, while the K799A E6AP mutant was more active at producing Lys(48)-linked polyubiquitin chains. Thus, opposing roles of Lys(799) and Lys(847) pave the path forward to pharmacological inhibitors or activators of E6AP for therapeutic purposes. PMID:26161728

  13. Reconciling Ligase Ribozyme Activity with Fatty Acid Vesicle Stability

    PubMed Central

    Anella, Fabrizio; Danelon, Christophe

    2014-01-01

    The “RNA world” and the “Lipid world” theories for the origin of cellular life are often considered incompatible due to the differences in the environmental conditions at which they can emerge. One obstacle resides in the conflicting requirements for divalent metal ions, in particular Mg2+, with respect to optimal ribozyme activity, fatty acid vesicle stability and protection against RNA strand cleavage. Here, we report on the activity of a short L1 ligase ribozyme in the presence of myristoleic acid (MA) vesicles at varying concentrations of Mg2+. The ligation rate is significantly lower at low-Mg2+ conditions. However, the loss of activity is overcompensated by the increased stability of RNA leading to a larger amount of intact ligated substrate after long reaction periods. Combining RNA ligation assays with fatty acid vesicles we found that MA vesicles made of 5 mM amphiphile are stable and do not impair ligase ribozyme activity in the presence of approximately 2 mM Mg2+. These results provide a scenario in which catalytic RNA and primordial membrane assembly can coexist in the same environment. PMID:25513761

  14. Structure of Human Acid Sphingomyelinase Reveals the Role of the Saposin Domain in Activating Substrate Hydrolysis.

    PubMed

    Xiong, Zi-Jian; Huang, Jingjing; Poda, Gennady; Pomès, Régis; Privé, Gilbert G

    2016-07-31

    Acid sphingomyelinase (ASM) is a lysosomal phosphodiesterase that catalyzes the hydrolysis of sphingomyelin to produce ceramide and phosphocholine. While other lysosomal sphingolipid hydrolases require a saposin activator protein for full activity, the ASM polypeptide incorporates a built-in N-terminal saposin domain and does not require an external activator protein. Here, we report the crystal structure of human ASM and describe the organization of the three main regions of the enzyme: the N-terminal saposin domain, the proline-rich connector, and the catalytic domain. The saposin domain is tightly associated along an edge of the large, bowl-shaped catalytic domain and adopts an open form that exposes a hydrophobic concave surface approximately 30Å from the catalytic center. The calculated electrostatic potential of the enzyme is electropositive at the acidic pH of the lysosome, consistent with the strict requirement for the presence of acidic lipids in target membranes. Docking studies indicate that sphingomyelin binds with the ceramide-phosphate group positioned at the binuclear zinc center and molecular dynamic simulations indicate that the intrinsic flexibility of the saposin domain is important for monomer-dimer exchange and for membrane interactions. Overall, ASM uses a combination of electrostatic and hydrophobic interactions to cause local disruptions of target bilayers in order to bring the lipid headgroup to the catalytic center in a membrane-bound reaction. PMID:27349982

  15. Structure of Human Acid Sphingomyelinase Reveals the Role of the Saposin Domain in Activating Substrate Hydrolysis.

    PubMed

    Xiong, Zi-Jian; Huang, Jingjing; Poda, Gennady; Pomès, Régis; Privé, Gilbert G

    2016-07-31

    Acid sphingomyelinase (ASM) is a lysosomal phosphodiesterase that catalyzes the hydrolysis of sphingomyelin to produce ceramide and phosphocholine. While other lysosomal sphingolipid hydrolases require a saposin activator protein for full activity, the ASM polypeptide incorporates a built-in N-terminal saposin domain and does not require an external activator protein. Here, we report the crystal structure of human ASM and describe the organization of the three main regions of the enzyme: the N-terminal saposin domain, the proline-rich connector, and the catalytic domain. The saposin domain is tightly associated along an edge of the large, bowl-shaped catalytic domain and adopts an open form that exposes a hydrophobic concave surface approximately 30Å from the catalytic center. The calculated electrostatic potential of the enzyme is electropositive at the acidic pH of the lysosome, consistent with the strict requirement for the presence of acidic lipids in target membranes. Docking studies indicate that sphingomyelin binds with the ceramide-phosphate group positioned at the binuclear zinc center and molecular dynamic simulations indicate that the intrinsic flexibility of the saposin domain is important for monomer-dimer exchange and for membrane interactions. Overall, ASM uses a combination of electrostatic and hydrophobic interactions to cause local disruptions of target bilayers in order to bring the lipid headgroup to the catalytic center in a membrane-bound reaction.

  16. Residues Distal to the Active Site Contribute to Enhanced Catalytic Activity of Variant and Hybrid β-Lactamases Derived from CTX-M-14 and CTX-M-15

    PubMed Central

    He, Dandan; Chiou, Jiachi; Zeng, Zhenling; Liu, Lanping; Chen, Xiaojie; Zeng, Li; Chan, Edward Wai Chi

    2015-01-01

    A variety of CTX-M-type extended-spectrum β-lactamases (ESBLs), including hybrid ones, have been reported in China that are uncommon elsewhere. To better characterize the substrate profiles and enzymatic mechanisms of these enzymes, we performed comparative kinetic analyses of both parental and hybrid CTX-M enzymes, including CTX-M-15, -132, -123, -64, -14 and -55, that are known to confer variable levels of β-lactam resistance in the host strains. All tested enzymes were susceptible to serine β-lactamase inhibitors, with sulbactam exhibiting the weakest inhibitory effects. CTX-M-55, which differs from CTX-M-15 by one substitution, A77V, displayed enhanced catalytic activity (kcat/Km) against expanded-spectrum cephalosporins (ESCs). CTX-M-55 exhibits higher structure stability, most likely by forming hydrophobic interactions between A77V and various key residues in different helices, thereby stabilizing the core architecture of the helix cluster, and indirectly contributes to a more stable active site conformation, which in turn shows higher catalytic efficiency and is more tolerant to temperature change. Analyses of the hybrids and their parental prototypes showed that evolution from CTX-M-15 to CTX-M-132, CTX-M-123, and CTX-M-64, characterized by gradual enhancement of catalytic activity to ESCs, was attributed to introduction of different substitutions to amino acids distal to the active site of CTX-M-15. Similarly, the increased hydrolytic activities against cephalosporins and sensitivity to β-lactamase inhibitors, clavulanic acid and sulbactam, of CTX-M-64 were partly due to the amino acids that were different from CTX-M-14 and located at both the C and N termini of CTX-M-64. These data indicate that residues distal to the active site of CTX-Ms contributed to their enhanced catalytic activities to ESCs. PMID:26169409

  17. The role of acidic sites and the catalytic reaction pathways on the Rh/ZrO2 catalysts for ethanol steam reforming.

    PubMed

    Zhong, Ziyi; Ang, Hanwee; Choong, Catherine; Chen, Luwei; Huang, Lin; Lin, Jianyi

    2009-02-01

    Rh catalysts supported on ZrO(2)-based oxides were studied for ethanol steam reforming (SR) reaction. Pure ZrO(2) as the support resulted in higher H(2) production yield compared to the ZrO(2) oxide decorated with CeO(2), Al(2)O(3), La(2)O(3) or Li(2)O at the reaction temperature of 300 degrees C. Above 450 degrees C, all the catalysts exhibited similar catalytic activity. However, at low reaction temperatures (below 400 degrees C), a significant enhancement in the catalytic activity, selectivity and stability was achieved by replacing the ZrO(2) support prepared by a precipitation method (ZrO(2)-CP) with that prepared by a hydrothermal method (ZrO(2)-HT). A deactivation was observed during the EtOH SR reaction at 300 degrees C on the two catalysts of Rh/ZrO(2)-CP and Rh/ZrO(2)-HT. NH(3)-TPD experiments confirmed that the ZrO(2)-HT support had two types of acidic sites while the ZrO(2)-CP support had only one type of weak acidic sites. DRIFTS studies showed that the absorption of EtOH molecules was strong on the Rh/ZrO(2)-HT catalyst and a number of C(2) oxygenates were accumulated on the catalyst surface. Meanwhile, the EtOH absorption on the Rh/ZrO(2)-CP catalyst was weak and the accumulation of CO, carbonate and CH(x) was observed. It is concluded that the relatively strong Lewis acidic sites in the Rh/ZrO(2)-HT catalyst is responsible for the strong absorption of EtOH molecules, and the subsequent C-H breakage step (formation of acetaldehyde or called as dehydrogenation reaction) is a fast reaction on it; on the Rh/ZrO(2)-CP catalyst, the EtOH adsorption was weak and the C-C breakage was the dominating reaction which led to the accumulation of surface CO, CH(x) and CO(2) species. Therefore, it is believed that, in order to promote the absorption of EtOH molecules and to reduce the formation of metastable carbonaceous species (C(2) oxygenates) during the reaction, the catalyst should be enhanced both with Lewis acidity and with C-C bond breakage function. Also

  18. Screening acidic zeolites for catalytic fast pyrolysis of biomass and its components

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Zeolites have been shown to effectively promote cracking reactions during pyrolysis resulting in highly deoxygenated and hydrocarbon-rich compounds and stable pyrolysis oil product. Py/GC-MS was employed to study the catalytic fast pyrolysis of lignocellulosic biomass samples comprising oak, corn...

  19. A Mesoporous Indium Metal-Organic Framework: Remarkable Advances in Catalytic Activity for Strecker Reaction of Ketones.

    PubMed

    Reinares-Fisac, Daniel; Aguirre-Díaz, Lina María; Iglesias, Marta; Snejko, Natalia; Gutiérrez-Puebla, Enrique; Monge, M Ángeles; Gándara, Felipe

    2016-07-27

    With the aim of developing new highly porous, heterogeneous Lewis acid catalysts for multicomponent reactions, a new mesoporous metal-organic framework, InPF-110 ([In3O(btb)2(HCOO)(L)], (H3btb = 1,3,5-tris(4-carboxyphenyl)benzene acid, L = methanol, water, or ethanol), has been prepared with indium as the metal center. It exhibits a Langmuir surface area of 1470 m(2) g(-1), and its structure consists of hexagonal pores with a 2.8 nm aperture, which allows the diffusion of multiple substrates. This material presents a large density of active metal sites resulting in outstanding catalytic activity in the formation of substituted α-aminonitriles through the one-pot Strecker reaction of ketones. In this respect, InPF-110 stands out compared to other catalysts for this reaction due to the small catalyst loadings required, and without the need for heat or solvents. Furthermore, X-ray single crystal diffraction studies clearly show the framework-substrate interaction through coordination to the accessible indium sites. PMID:27420904

  20. A Mesoporous Indium Metal-Organic Framework: Remarkable Advances in Catalytic Activity for Strecker Reaction of Ketones.

    PubMed

    Reinares-Fisac, Daniel; Aguirre-Díaz, Lina María; Iglesias, Marta; Snejko, Natalia; Gutiérrez-Puebla, Enrique; Monge, M Ángeles; Gándara, Felipe

    2016-07-27

    With the aim of developing new highly porous, heterogeneous Lewis acid catalysts for multicomponent reactions, a new mesoporous metal-organic framework, InPF-110 ([In3O(btb)2(HCOO)(L)], (H3btb = 1,3,5-tris(4-carboxyphenyl)benzene acid, L = methanol, water, or ethanol), has been prepared with indium as the metal center. It exhibits a Langmuir surface area of 1470 m(2) g(-1), and its structure consists of hexagonal pores with a 2.8 nm aperture, which allows the diffusion of multiple substrates. This material presents a large density of active metal sites resulting in outstanding catalytic activity in the formation of substituted α-aminonitriles through the one-pot Strecker reaction of ketones. In this respect, InPF-110 stands out compared to other catalysts for this reaction due to the small catalyst loadings required, and without the need for heat or solvents. Furthermore, X-ray single crystal diffraction studies clearly show the framework-substrate interaction through coordination to the accessible indium sites.

  1. An efficient Rh/O2 catalytic system for oxidative C-H activation/annulation: evidence for Rh(I) to Rh(III) oxidation by molecular oxygen.

    PubMed

    Zhang, Guoying; Yang, Lei; Wang, Yanyu; Xie, Yinjun; Huang, Hanmin

    2013-06-19

    A novel and efficient Rh/O2 catalytic system has been developed and shown to catalyze highly efficient oxidative C-H activation/annulation reactions, producing a broad range of isoquinolinium salts with high turnover numbers (up to 740). Mechanistic studies provided strong evidence of facile oxidation of Rh(I) to Rh(III) by molecular oxygen facilitated by acid.

  2. Site-dependent catalytic activity of graphene oxides towards oxidative dehydrogenation of propane.

    PubMed

    Tang, Shaobin; Cao, Zexing

    2012-12-28

    Graphene oxides (GOs) may offer extraordinary potential in the design of novel catalytic systems due to the presence of various oxygen functional groups and their unique electronic and structural properties. Using first-principles calculations, we explore the plausible mechanisms for the oxidative dehydrogenation (ODH) of propane to propene by GOs and the diffusion of the surface oxygen-containing groups under an external electric field. The present results show that GOs with modified oxygen-containing groups may afford high catalytic activity for the ODH of propane to propene. The presence of hydroxyl groups around the active sites provided by epoxides can remarkably enhance the C-H bond activation of propane and the activity enhancement exhibits strong site dependence. The sites of oxygen functional groups on the GO surface can be easily tuned by the diffusion of these groups under an external electric field, which increases the reactivity of GOs towards ODH of propane. The chemically modified GOs are thus quite promising in the design of metal-free catalysis. PMID:22801590

  3. Facile synthesis of pristine graphene-palladium nanocomposites with extraordinary catalytic activities using swollen liquid crystals

    PubMed Central

    Vats, T.; Dutt, S.; Kumar, R.; Siril, P. F.

    2016-01-01

    Amazing conductivity, perfect honeycomb sp2 arrangement and the high theoretical surface area make pristine graphene as one of the best materials suited for application as catalyst supports. Unfortunately, the low reactivity of the material makes the formation of nanocomposite with inorganic materials difficult. Here we report an easy approach to synthesize nanocomposites of pristine graphene with palladium (Pd-G) using swollen liquid crystals (SLCs) as a soft template. The SLC template gives the control to deposit very small Pd particles of uniform size on G as well as RGO. The synthesized nanocomposite (Pd-G) exhibited exceptionally better catalytic activity compared with Pd-RGO nanocomposite in the hydrogenation of nitrophenols and microwave assisted C-C coupling reactions. The catalytic activity of Pd-G nanocomposite during nitrophenol reduction reaction was sixteen times higher than Pd nanoparticles and more than double than Pd-RGO nanocomposite. The exceptionally high activity of pristine graphene supported catalysts in the organic reactions is explained on the basis of its better pi interacting property compared to partially reduced RGO. The Pd-G nanocomposite showed exceptional stability under the reaction conditions as it could be recycled upto a minimum of 15 cycles for the C-C coupling reactions without any loss in activity. PMID:27619321

  4. Facile synthesis of pristine graphene-palladium nanocomposites with extraordinary catalytic activities using swollen liquid crystals.

    PubMed

    Vats, T; Dutt, S; Kumar, R; Siril, P F

    2016-09-13

    Amazing conductivity, perfect honeycomb sp(2) arrangement and the high theoretical surface area make pristine graphene as one of the best materials suited for application as catalyst supports. Unfortunately, the low reactivity of the material makes the formation of nanocomposite with inorganic materials difficult. Here we report an easy approach to synthesize nanocomposites of pristine graphene with palladium (Pd-G) using swollen liquid crystals (SLCs) as a soft template. The SLC template gives the control to deposit very small Pd particles of uniform size on G as well as RGO. The synthesized nanocomposite (Pd-G) exhibited exceptionally better catalytic activity compared with Pd-RGO nanocomposite in the hydrogenation of nitrophenols and microwave assisted C-C coupling reactions. The catalytic activity of Pd-G nanocomposite during nitrophenol reduction reaction was sixteen times higher than Pd nanoparticles and more than double than Pd-RGO nanocomposite. The exceptionally high activity of pristine graphene supported catalysts in the organic reactions is explained on the basis of its better pi interacting property compared to partially reduced RGO. The Pd-G nanocomposite showed exceptional stability under the reaction conditions as it could be recycled upto a minimum of 15 cycles for the C-C coupling reactions without any loss in activity.

  5. Design of activated serine-containing catalytic triads with atomic level accuracy

    PubMed Central

    Rajagopalan, Sridharan; Wang, Chu; Yu, Kai; Kuzin, Alexandre P.; Richter, Florian; Lew, Scott; Miklos, Aleksandr E.; Matthews, Megan L.; Seetharaman, Jayaraman; Su, Min; Hunt, John. F.; Cravatt, Benjamin F.; Baker, David

    2014-01-01

    A challenge in the computational design of enzymes is that multiple properties must be simultaneously optimized -- substrate-binding, transition state stabilization, and product release -- and this has limited the absolute activity of successful designs. Here, we focus on a single critical property of many enzymes: the nucleophilicity of an active site residue that initiates catalysis. We design proteins with idealized serine-containing catalytic triads, and assess their nucleophilicity directly in native biological systems using activity-based organophosphate probes. Crystal structures of the most successful designs show unprecedented agreement with computational models, including extensive hydrogen bonding networks between the catalytic triad (or quartet) residues, and mutagenesis experiments demonstrate that these networks are critical for serine activation and organophosphate-reactivity. Following optimization by yeast-display, the designs react with organophosphate probes at rates comparable to natural serine hydrolases. Co-crystal structures with diisopropyl fluorophosphate bound to the serine nucleophile suggest the designs could provide the basis for a new class of organophosphate captures agents. PMID:24705591

  6. Facile synthesis of pristine graphene-palladium nanocomposites with extraordinary catalytic activities using swollen liquid crystals

    NASA Astrophysics Data System (ADS)

    Vats, T.; Dutt, S.; Kumar, R.; Siril, P. F.

    2016-09-01

    Amazing conductivity, perfect honeycomb sp2 arrangement and the high theoretical surface area make pristine graphene as one of the best materials suited for application as catalyst supports. Unfortunately, the low reactivity of the material makes the formation of nanocomposite with inorganic materials difficult. Here we report an easy approach to synthesize nanocomposites of pristine graphene with palladium (Pd-G) using swollen liquid crystals (SLCs) as a soft template. The SLC template gives the control to deposit very small Pd particles of uniform size on G as well as RGO. The synthesized nanocomposite (Pd-G) exhibited exceptionally better catalytic activity compared with Pd-RGO nanocomposite in the hydrogenation of nitrophenols and microwave assisted C-C coupling reactions. The catalytic activity of Pd-G nanocomposite during nitrophenol reduction reaction was sixteen times higher than Pd nanoparticles and more than double than Pd-RGO nanocomposite. The exceptionally high activity of pristine graphene supported catalysts in the organic reactions is explained on the basis of its better pi interacting property compared to partially reduced RGO. The Pd-G nanocomposite showed exceptional stability under the reaction conditions as it could be recycled upto a minimum of 15 cycles for the C-C coupling reactions without any loss in activity.

  7. A Redox 2-Cys Mechanism Regulates the Catalytic Activity of Divergent Cyclophilins1[W

    PubMed Central

    Campos, Bruna Medéia; Sforça, Mauricio Luis; Ambrosio, Andre Luis Berteli; Domingues, Mariane Noronha; Brasil de Souza, Tatiana de Arruda Campos; Barbosa, João Alexandre Ribeiro Gonçalvez; Leme, Adriana Franco Paes; Perez, Carlos Alberto; Whittaker, Sara Britt-Marie; Murakami, Mario Tyago; Zeri, Ana Carolina de Matos; Benedetti, Celso Eduardo

    2013-01-01

    The citrus (Citrus sinensis) cyclophilin CsCyp is a target of the Xanthomonas citri transcription activator-like effector PthA, required to elicit cankers on citrus. CsCyp binds the citrus thioredoxin CsTdx and the carboxyl-terminal domain of RNA polymerase II and is a divergent cyclophilin that carries the additional loop KSGKPLH, invariable cysteine (Cys) residues Cys-40 and Cys-168, and the conserved glutamate (Glu) Glu-83. Despite the suggested roles in ATP and metal binding, the functions of these unique structural elements remain unknown. Here, we show that the conserved Cys residues form a disulfide bond that inactivates the enzyme, whereas Glu-83, which belongs to the catalytic loop and is also critical for enzyme activity, is anchored to the divergent loop to maintain the active site open. In addition, we demonstrate that Cys-40 and Cys-168 are required for the interaction with CsTdx and that CsCyp binds the citrus carboxyl-terminal domain of RNA polymerase II YSPSAP repeat. Our data support a model where formation of the Cys-40-Cys-168 disulfide bond induces a conformational change that disrupts the interaction of the divergent and catalytic loops, via Glu-83, causing the active site to close. This suggests a new type of allosteric regulation in divergent cyclophilins, involving disulfide bond formation and a loop-displacement mechanism. PMID:23709667

  8. Nitrogen-Rich Manganese Oxynitrides with Enhanced Catalytic Activity in the Oxygen Reduction Reaction.

    PubMed

    Miura, Akira; Rosero-Navarro, Carolina; Masubuchi, Yuji; Higuchi, Mikio; Kikkawa, Shinichi; Tadanaga, Kiyoharu

    2016-07-01

    The catalytic activity of manganese oxynitrides in the oxygen reduction reaction (ORR) was investigated in alkaline solutions to clarify the effect of the incorporated nitrogen atoms on the ORR activity. These oxynitrides, with rock-salt-like structures with different nitrogen contents, were synthesized by reacting MnO, Mn2 O3 , or MnO2 with molten NaNH2 at 240-280 °C. The anion contents and the Mn valence states were determined by combustion analysis, powder X-ray diffraction, and X-ray absorption near-edge structure analysis. An increase in the nitrogen content of rock-salt-based manganese oxynitrides increases the valence of the manganese ions and reinforces the catalytic activity for the ORR in 1 m KOH solution. Nearly single-electron occupancy of the antibonding eg states and highly covalent Mn-N bonding thus enhance the ORR activity of nitrogen-rich manganese oxynitrides. PMID:27193352

  9. Facile synthesis of pristine graphene-palladium nanocomposites with extraordinary catalytic activities using swollen liquid crystals.

    PubMed

    Vats, T; Dutt, S; Kumar, R; Siril, P F

    2016-01-01

    Amazing conductivity, perfect honeycomb sp(2) arrangement and the high theoretical surface area make pristine graphene as one of the best materials suited for application as catalyst supports. Unfortunately, the low reactivity of the material makes the formation of nanocomposite with inorganic materials difficult. Here we report an easy approach to synthesize nanocomposites of pristine graphene with palladium (Pd-G) using swollen liquid crystals (SLCs) as a soft template. The SLC template gives the control to deposit very small Pd particles of uniform size on G as well as RGO. The synthesized nanocomposite (Pd-G) exhibited exceptionally better catalytic activity compared with Pd-RGO nanocomposite in the hydrogenation of nitrophenols and microwave assisted C-C coupling reactions. The catalytic activity of Pd-G nanocomposite during nitrophenol reduction reaction was sixteen times higher than Pd nanoparticles and more than double than Pd-RGO nanocomposite. The exceptionally high activity of pristine graphene supported catalysts in the organic reactions is explained on the basis of its better pi interacting property compared to partially reduced RGO. The Pd-G nanocomposite showed exceptional stability under the reaction conditions as it could be recycled upto a minimum of 15 cycles for the C-C coupling reactions without any loss in activity. PMID:27619321

  10. Effect of Manganese Additive on the Improvement of Low-Temperature Catalytic Activity of VO(x)-WO(x)/TiO2 Nanoparticles for Chlorobenzene Combustion.

    PubMed

    He, Fei; Chen, Chunxiao; Liu, Shantang

    2016-06-01

    In this study, V-W/TiO2, Mn-V-W/TiO2 and Mn-W/TiO2 nanoparticles were prepared by homogeneous precipitation method and investigated for the catalytic combustion of chlorobenzene (CB), which was used as a model compound of chlorinated volatile organic compounds (CVOCs). The samples were characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption, transmission electron microscope (TEM) and hydrogen temperature-programed reduction (H2-TPR). The average size of the nanoparticles was -20 nm. Manganese species were evenly distributed on the surface of the V-W/TiO2 catalyst, and a small amount of manganese addition did not affect the crystal form, crystallinity and morphology of the V-W/TiO2 catalyst. In addition, low-temperature catalytic activity of V-W/TiO2 catalysts could be effectively improved. When the molar ratio of Mn/(Mn + V) was 0.25 or 0.4, the catalyst displayed the highest low-temperature activity. This was possibly due to Mn (VO3)x formed by the reaction of manganese and vanadium species. Meanwhile, we also found that the addition of oxalic acid was benefit to the improvement of the catalytic activities. When manganese content was high, such as Mn (0.75) VW/Ti, the catalyst activity declined seriously, and the reason was also discussed.

  11. Effect of Manganese Additive on the Improvement of Low-Temperature Catalytic Activity of VO(x)-WO(x)/TiO2 Nanoparticles for Chlorobenzene Combustion.

    PubMed

    He, Fei; Chen, Chunxiao; Liu, Shantang

    2016-06-01

    In this study, V-W/TiO2, Mn-V-W/TiO2 and Mn-W/TiO2 nanoparticles were prepared by homogeneous precipitation method and investigated for the catalytic combustion of chlorobenzene (CB), which was used as a model compound of chlorinated volatile organic compounds (CVOCs). The samples were characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption, transmission electron microscope (TEM) and hydrogen temperature-programed reduction (H2-TPR). The average size of the nanoparticles was -20 nm. Manganese species were evenly distributed on the surface of the V-W/TiO2 catalyst, and a small amount of manganese addition did not affect the crystal form, crystallinity and morphology of the V-W/TiO2 catalyst. In addition, low-temperature catalytic activity of V-W/TiO2 catalysts could be effectively improved. When the molar ratio of Mn/(Mn + V) was 0.25 or 0.4, the catalyst displayed the highest low-temperature activity. This was possibly due to Mn (VO3)x formed by the reaction of manganese and vanadium species. Meanwhile, we also found that the addition of oxalic acid was benefit to the improvement of the catalytic activities. When manganese content was high, such as Mn (0.75) VW/Ti, the catalyst activity declined seriously, and the reason was also discussed. PMID:27427700

  12. Electro-catalytic activity of Ni–Co-based catalysts for oxygen evolution reaction

    SciTech Connect

    Ju, Hua; Li, Zhihu; Xu, Yanhui

    2015-04-15

    Graphical abstract: The electro-catalytic activity of different electro-catalysts with a porous electrode structure was compared considering the real electrode area that was evaluated by cyclic measurement. - Highlights: • Ni–Co-based electro-catalysts for OER have been studied and compared. • The real electrode area is calculated and used for assessing the electro-catalysts. • Exchange current and reaction rate constant are estimated. • Ni is more useful for OER reaction than Co. - Abstract: In the present work, Ni–Co-based electrocatalysts (Ni/Co = 0:6, 1:5, 2:4, 3:3, 4:2, 5:1 and 6:0) have been studied for oxygen evolution reaction. The phase structure has been analyzed by X-ray diffraction technique. Based on the XRD and SEM results, it is believed that the synthesized products are poorly crystallized. To exclude the disturbance of electrode preparation technology on the evaluation of electro-catalytic activity, the real electrode surface area is calculated based on the cyclic voltammetry data, assumed that the specific surface capacitance is 60 μF cm{sup −2} for metal oxide electrode. The real electrode area data are used to calculate the current density. The reaction rate constant of OER at different electrodes is also estimated based on basic reaction kinetic equations. It is found that the exchange current is 0.05–0.47 mA cm{sup −2} (the real surface area), and the reaction rate constant has an order of magnitude of 10{sup −7}–10{sup −6} cm s{sup −1}. The influence of the electrode potential on OER rate has been also studied by electrochemical impedance spectroscopy (EIS) technique. Our investigation has shown that the nickel element has more contribution than the cobalt; the nickel oxide has the best electro-catalytic activity toward OER.

  13. Dynamics of the active site architecture in plant-type ferredoxin-NADP(+) reductases catalytic complexes.

    PubMed

    Sánchez-Azqueta, Ana; Catalano-Dupuy, Daniela L; López-Rivero, Arleth; Tondo, María Laura; Orellano, Elena G; Ceccarelli, Eduardo A; Medina, Milagros

    2014-10-01

    Kinetic isotope effects in reactions involving hydride transfer and their temperature dependence are powerful tools to explore dynamics of enzyme catalytic sites. In plant-type ferredoxin-NADP(+) reductases the FAD cofactor exchanges a hydride with the NADP(H) coenzyme. Rates for these processes are considerably faster for the plastidic members (FNR) of the family than for those belonging to the bacterial class (FPR). Hydride transfer (HT) and deuteride transfer (DT) rates for the NADP(+) coenzyme reduction of four plant-type FNRs (two representatives of the plastidic type FNRs and the other two from the bacterial class), and their temperature dependences are here examined applying a full tunnelling model with coupled environmental fluctuations. Parameters for the two plastidic FNRs confirm a tunnelling reaction with active dynamics contributions, but isotope effects on Arrhenius factors indicate a larger contribution for donor-acceptor distance (DAD) dynamics in the Pisum sativum FNR reaction than in the Anabaena FNR reaction. On the other hand, parameters for bacterial FPRs are consistent with passive environmental reorganisation movements dominating the HT coordinate and no contribution of DAD sampling or gating fluctuations. This indicates that active sites of FPRs are more organised and rigid than those of FNRs. These differences must be due to adaptation of the active sites and catalytic mechanisms to fulfil their particular metabolic roles, establishing a compromise between protein flexibility and functional optimisation. Analysis of site-directed mutants in plastidic enzymes additionally indicates the requirement of a minimal optimal architecture in the catalytic complex to provide a favourable gating contribution. PMID:24953402

  14. Fe-Mn bi-metallic oxides loaded on granular activated carbon to enhance dye removal by catalytic ozonation.

    PubMed

    Tang, Shoufeng; Yuan, Deling; Zhang, Qi; Liu, Yameng; Zhang, Qi; Liu, Zhengquan; Huang, Haiming

    2016-09-01

    A Fe-Mn bi-metallic oxide supported on granular activated carbon (Fe-Mn GAC) has been fabricated by an impregnation-desiccation method and tested in the catalytic ozonation of methyl orange (MO) degradation and mineralization. X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy characterizations revealed that Fe-Mn oxides were successfully loaded and uniformly distributed on the GAC, and nitrogen adsorption isotherms showed that the supported GAC retained a large surface area and a high pore volume compared with the pristine GAC. The catalytic activity was systematically assessed by monitoring the MO removal efficiencies at different operational parameters, such as catalyst dosage, initial solution pH, and ozone flow rate. The Fe-Mn GAC exhibited better catalytic activity relative to ozone alone and GAC alone, improving the TOC removal by 24.5 and 11.5 % and COD removal by 13.6 and 7.3 %, respectively. The reusability of the hybrid was examined over five consecutive cyclic treatments. The Fe-Mn GAC catalytic activity was only a slight loss in the cycles, showing good stability. The addition of Na2CO3 as hydroxyl radicals (•OH) scavengers proved that the catalytic ozonation mechanism was the enhanced generation of •OH by the Fe-Mn GAC. The above results render the Fe-Mn GAC an industrially promising candidate for catalytic ozonation of dye contaminant removal.

  15. Fe-Mn bi-metallic oxides loaded on granular activated carbon to enhance dye removal by catalytic ozonation.

    PubMed

    Tang, Shoufeng; Yuan, Deling; Zhang, Qi; Liu, Yameng; Zhang, Qi; Liu, Zhengquan; Huang, Haiming

    2016-09-01

    A Fe-Mn bi-metallic oxide supported on granular activated carbon (Fe-Mn GAC) has been fabricated by an impregnation-desiccation method and tested in the catalytic ozonation of methyl orange (MO) degradation and mineralization. X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy characterizations revealed that Fe-Mn oxides were successfully loaded and uniformly distributed on the GAC, and nitrogen adsorption isotherms showed that the supported GAC retained a large surface area and a high pore volume compared with the pristine GAC. The catalytic activity was systematically assessed by monitoring the MO removal efficiencies at different operational parameters, such as catalyst dosage, initial solution pH, and ozone flow rate. The Fe-Mn GAC exhibited better catalytic activity relative to ozone alone and GAC alone, improving the TOC removal by 24.5 and 11.5 % and COD removal by 13.6 and 7.3 %, respectively. The reusability of the hybrid was examined over five consecutive cyclic treatments. The Fe-Mn GAC catalytic activity was only a slight loss in the cycles, showing good stability. The addition of Na2CO3 as hydroxyl radicals (•OH) scavengers proved that the catalytic ozonation mechanism was the enhanced generation of •OH by the Fe-Mn GAC. The above results render the Fe-Mn GAC an industrially promising candidate for catalytic ozonation of dye contaminant removal. PMID:27316651

  16. Synthesis, characterization and catalytic activity of novel large network polystyrene-immobilized organic bases

    DOE PAGES

    Tassi, Marco; Bartollini, Elena; Adriaensens, Peter; Bianchi, Luca; Barkakaty, Balaka; Carleer, Robert; Chen, Jihua; Hensley, Dale K.; Marrocchi, Assunta; Vaccaro, Luigi

    2015-12-07

    In view of searching for efficient polymeric supports for organic bases to be used in environmentally friendly reaction conditions, novel gel-type cross-linked polystyrenes functionalized with diethylamine and 1,5,7-triazabicyclo[4.4.0]dec-5-ene, have been prepared. Moreover, the structural properties and morphology of these catalysts have been determined by extensive solid state NMR experiments, FTIR spectroscopy and SEM/TEM microscopy. SPACeR-supported bases were found to exhibit high catalytic activity in the epoxide ring opening by phenols. Finally, a range of β-substituted alcohols have been readily and regioselectively synthesized.

  17. Catalytic Ester–Amide Exchange Using Group (IV) Metal Alkoxide–Activator Complexes

    PubMed Central

    Han, Chong; Lee, Jonathan P.; Lobkovsky, Emil; Porco, John A.

    2005-01-01

    A process for preparation of amides from unactivated esters and amines has been developed using a catalytic system comprised of group (IV) metal alkoxides in conjunction with additives including 1-hydroxy-7-azabenzotriazole (HOAt). In general, ester–amide exchange proceeds using a variety of structurally diverse esters and amines without azeotropic reflux to remove the alcohol byproduct. Initial mechanistic studies on the Zr(Ot-Bu)4–HOAt system revealed that the active catalyst is a novel, dimeric zirconium complex as determined by X-ray crystallography. PMID:16011366

  18. Synthesis of sulfonated porous carbon nanospheres solid acid by a facile chemical activation route

    SciTech Connect

    Chang, Binbin Guo, Yanzhen; Yin, Hang; Zhang, Shouren; Yang, Baocheng

    2015-01-15

    Generally, porous carbon nanospheres materials are usually prepared via a template method, which is a multi-steps and high-cost strategy. Here, we reported a porous carbon nanosphere solid acid with high surface area and superior porosity, as well as uniform nanospheical morphology, which prepared by a facile chemical activation with ZnCl{sub 2} using resorcinol-formaldehyde (RF) resins spheres as precursor. The activation of RF resins spheres by ZnCl{sub 2} at 400 °C brought high surface area and large volume, and simultaneously retained numerous oxygen-containing and hydrogen-containing groups due to the relatively low processing temperature. The presence of these functional groups is favorable for the modification of –SO{sub 3}H groups by a followed sulfonation treating with sulphuric acid and organic sulfonic acid. The results of N{sub 2} adsorption–desorption and electron microscopy clearly showed the preservation of porous structure and nanospherical morphology. Infrared spectra certified the variation of surface functional groups after activation and the successful modification of –SO{sub 3}H groups after sulfonation. The acidities of catalysts were estimated by an indirect titration method and the modified amount of –SO{sub 3}H groups were examined by energy dispersive spectra. The results suggested sulfonated porous carbon nanospheres catalysts possessed high acidities and –SO{sub 3}H densities, which endowed their significantly catalytic activities for biodiesel production. Furthermore, their excellent stability and recycling property were also demonstrated by five consecutive cycles. - Graphical abstract: Sulfonated porous carbon nanospheres with high surface area and superior catalytic performance were prepared by a facile chemical activation route. - Highlights: • Porous carbon spheres solid acid prepared by a facile chemical activation. • It owns high surface area, superior porosity and uniform spherical morphology. • It possesses

  19. Macroporous ZnO foams by high internal phase emulsion technique: synthesis and catalytic activity.

    PubMed

    Kovačič, Sebastijan; Anžlovar, Alojz; Erjavec, Boštjan; Kapun, Gregor; Matsko, Nadejda B; Žigon, Majda; Žagar, Ema; Pintar, Albin; Slugovc, Christian

    2014-11-12

    Zinc(II) oxide nanoparticles were used for the stabilization of dicyclopentadiene (DCPD)-water-based high internal phase emulsions (HIPEs), which were subsequently cured using ring-opening metathesis polymerization (ROMP). The morphology of the resulting ZnO-pDCPD nanocomposite foams was investigated in correlation to the nanoparticle loading and nanoparticle surface chemistry. While hydrophilic ZnO nanoparticles were found to be unsuitable for stabilizing the HIPE, oleic acid coated, yet hydrophobic ZnO nanoparticles were effective HIPE stabilizers, yielding polymer foams with ZnO nanoparticles located predominately at their surface. These inorganic/organic hybrid foam-materials were subsequently calcined at 550 °C for 15 min to obtain inorganic macroporous ZnO foams with a morphology reminiscent to the original hybrid foam, and a specific surface area of 1.5 m(2) g(-1). Longer calcination time (550 °C, 15 h) resulted in a sea urchin like morphology of the ZnO foams, characterized by higher specific surface area of 5.5 m(2) g(-1). The latter foam type showed an appealing catalytic performance in the catalytic wet air oxidation (CWAO) process for the destruction of bisphenol A.

  20. Enhanced catalytic activity over MIL-100(Fe) loaded ceria catalysts for the selective catalytic reduction of NOx with NH₃ at low temperature.

    PubMed

    Wang, Peng; Sun, Hong; Quan, Xie; Chen, Shuo

    2016-01-15

    The development of catalysts for selective catalytic reduction (SCR) reactions that are highly active at low temperatures and show good resistance to SO2 and H2O is still a challenge. In this study, we have designed and developed a high-performance SCR catalyst based on nano-sized ceria encapsulated inside the pores of MIL-100(Fe) that combines excellent catalytic power with a metal organic framework architecture synthesized by the impregnation method (IM). Transmission electron microscopy (TEM) revealed the encapsulation of ceria in the cavities of MIL-100(Fe). The prepared IM-CeO2/MIL-100(Fe) catalyst shows improved catalytic activity both at low temperatures and throughout a wide temperature window. The temperature window for 90% NOx conversion ranges from 196 to 300°C. X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) analysis indicated that the nano-sized ceria encapsulated inside MIL-100(Fe) promotes the production of chemisorbed oxygen on the catalyst surface, which greatly enhances the formation of the NO2 species responsible for fast SCR reactions.

  1. Nanocaged enzymes with enhanced catalytic activity and increased stability against protease digestion.

    PubMed

    Zhao, Zhao; Fu, Jinglin; Dhakal, Soma; Johnson-Buck, Alexander; Liu, Minghui; Zhang, Ting; Woodbury, Neal W; Liu, Yan; Walter, Nils G; Yan, Hao

    2016-02-10

    Cells routinely compartmentalize enzymes for enhanced efficiency of their metabolic pathways. Here we report a general approach to construct DNA nanocaged enzymes for enhancing catalytic activity and stability. Nanocaged enzymes are realized by self-assembly into DNA nanocages with well-controlled stoichiometry and architecture that enabled a systematic study of the impact of both encapsulation and proximal polyanionic surfaces on a set of common metabolic enzymes. Activity assays at both bulk and single-molecule levels demonstrate increased substrate turnover numbers for DNA nanocage-encapsulated enzymes. Unexpectedly, we observe a significant inverse correlation between the size of a protein and its activity enhancement. This effect is consistent with a model wherein distal polyanionic surfaces of the nanocage enhance the stability of active enzyme conformations through the action of a strongly bound hydration layer. We further show that DNA nanocages protect encapsulated enzymes against proteases, demonstrating their practical utility in functional biomaterials and biotechnology.

  2. Catalytic activity of bimetal-containing Co,Pd systems in the oxidation of carbon monoxide

    NASA Astrophysics Data System (ADS)

    Oleksenko, L. P.; Lutsenko, L. V.

    2013-02-01

    The catalytic activity of low-percentage Co,Pd systems on ZSM-5, ERI, SiO2, and Al2O3 supports in the oxidation of CO was studied. The activity of bimetal-containing catalysts was shown to depend on the nature of the catalyst and the amount and ratio of their active components. According to the results of thermoprogrammed reduction with H2 (H2 TPR) and X-ray photoelectron spectroscopy (XPS) data, the metals are distributed as isolated cations or Coδ+-O-Pdδ+ clusters with cobalt and palladium cations surrounded by off-lattice oxygen in Co,Pd systems. The 0.8% Co,0.5% Pd-ZSM-5 bimetal catalysts were found to be more active due to the presence of clusters.

  3. Outer-sphere residues influence the catalytic activity of a chalcone synthase from Polygonum cuspidatum.

    PubMed

    Shen, Yalin; Li, Xing; Chai, Tuanyao; Wang, Hong

    2016-06-01

    We have previously cloned a chalcone synthase (PcCHS1) from Polygonum cuspidatum and biochemically identified its enzymatic dynamic properties. Here, we found that the outer sphere residues, Q82 and R105, could affect the catalytic activity and product profile of PcCHS1. Both Q82P and R105Q mutations of PcCHS1 could also change the pH dependence activity as well as the product profile of PcCHS1. Moreover, the Q82P/C198F double mutant could rescue the complete loss of enzyme activity caused by the C198F single mutation. Our study demonstrated that these outer-sphere residues of PcCHS1 play important roles both in structural maintenance and enzyme activity. PMID:27419064

  4. Nanocaged enzymes with enhanced catalytic activity and increased stability against protease digestion

    PubMed Central

    Zhao, Zhao; Fu, Jinglin; Dhakal, Soma; Johnson-Buck, Alexander; Liu, Minghui; Zhang, Ting; Woodbury, Neal W.; Liu, Yan; Walter, Nils G.; Yan, Hao

    2016-01-01

    Cells routinely compartmentalize enzymes for enhanced efficiency of their metabolic pathways. Here we report a general approach to construct DNA nanocaged enzymes for enhancing catalytic activity and stability. Nanocaged enzymes are realized by self-assembly into DNA nanocages with well-controlled stoichiometry and architecture that enabled a systematic study of the impact of both encapsulation and proximal polyanionic surfaces on a set of common metabolic enzymes. Activity assays at both bulk and single-molecule levels demonstrate increased substrate turnover numbers for DNA nanocage-encapsulated enzymes. Unexpectedly, we observe a significant inverse correlation between the size of a protein and its activity enhancement. This effect is consistent with a model wherein distal polyanionic surfaces of the nanocage enhance the stability of active enzyme conformations through the action of a strongly bound hydration layer. We further show that DNA nanocages protect encapsulated enzymes against proteases, demonstrating their practical utility in functional biomaterials and biotechnology. PMID:26861509

  5. Nanocaged enzymes with enhanced catalytic activity and increased stability against protease digestion

    NASA Astrophysics Data System (ADS)

    Zhao, Zhao; Fu, Jinglin; Dhakal, Soma; Johnson-Buck, Alexander; Liu, Minghui; Zhang, Ting; Woodbury, Neal W.; Liu, Yan; Walter, Nils G.; Yan, Hao

    2016-02-01

    Cells routinely compartmentalize enzymes for enhanced efficiency of their metabolic pathways. Here we report a general approach to construct DNA nanocaged enzymes for enhancing catalytic activity and stability. Nanocaged enzymes are realized by self-assembly into DNA nanocages with well-controlled stoichiometry and architecture that enabled a systematic study of the impact of both encapsulation and proximal polyanionic surfaces on a set of common metabolic enzymes. Activity assays at both bulk and single-molecule levels demonstrate increased substrate turnover numbers for DNA nanocage-encapsulated enzymes. Unexpectedly, we observe a significant inverse correlation between the size of a protein and its activity enhancement. This effect is consistent with a model wherein distal polyanionic surfaces of the nanocage enhance the stability of active enzyme conformations through the action of a strongly bound hydration layer. We further show that DNA nanocages protect encapsulated enzymes against proteases, demonstrating their practical utility in functional biomaterials and biotechnology.

  6. Hot-electron-mediated surface chemistry: toward electronic control of catalytic activity.

    PubMed

    Park, Jeong Young; Kim, Sun Mi; Lee, Hyosun; Nedrygailov, Ievgen I

    2015-08-18

    nanoparticles on oxide supports and Pt-CdSe-Pt nanodumbbells. We show that the accumulation or depletion of hot electrons on metal nanoparticles, in turn, can also influence catalytic reactions. Mechanisms suggested for hot-electron-induced chemical reactions on a photoexcited plasmonic metal are discussed. We propose that the manipulation of the flow of hot electrons by changing the electrical characteristics of metal-oxide and metal-semiconductor interfaces can give rise to the intriguing capability of tuning the catalytic activity of hybrid nanocatalysts. PMID:26181684

  7. Hot-electron-mediated surface chemistry: toward electronic control of catalytic activity.

    PubMed

    Park, Jeong Young; Kim, Sun Mi; Lee, Hyosun; Nedrygailov, Ievgen I

    2015-08-18

    nanoparticles on oxide supports and Pt-CdSe-Pt nanodumbbells. We show that the accumulation or depletion of hot electrons on metal nanoparticles, in turn, can also influence catalytic reactions. Mechanisms suggested for hot-electron-induced chemical reactions on a photoexcited plasmonic metal are discussed. We propose that the manipulation of the flow of hot electrons by changing the electrical characteristics of metal-oxide and metal-semiconductor interfaces can give rise to the intriguing capability of tuning the catalytic activity of hybrid nanocatalysts.

  8. Structural and mechanistic analysis of engineered trichodiene synthase enzymes from Trichoderma harzianum: towards higher catalytic activities empowering sustainable agriculture.

    PubMed

    Kumari, Indu; Chaudhary, Nitika; Sandhu, Padmani; Ahmed, Mushtaq; Akhter, Yusuf

    2016-06-01

    Trichoderma spp. are well-known bioagents for the plant growth promotion and pathogen suppression. The beneficial activities of the fungus Trichoderma spp. are attributed to their ability to produce and secrete certain secondary metabolites such as trichodermin that belongs to trichothecene family of molecules. The initial steps of trichodermin biosynthetic pathway in Trichoderma are similar to the trichothecenes from Fusarium sporotrichioides. Trichodiene synthase (TS) encoded by tri5 gene in Trichoderma catalyses the conversion of farnesyl pyrophosphate to trichodiene as reported earlier. In this study, we have carried out a comprehensive comparative sequence and structural analysis of the TS, which revealed the conserved residues involved in catalytic activity of the protein. In silico, modelled tertiary structure of TS protein showed stable structural behaviour during simulations. Two single-substitution mutants, i.e. D109E, D248Y and one double-substitution mutant (D109E and D248Y) of TS with potentially higher activities are screened out. The mutant proteins showed more stability than the wild type, an increased number of electrostatic interactions and better binding energies with the ligand, which further elucidates the amino acid residues involved in the reaction mechanism. These results will lead to devise strategies for higher TS activity to ultimately enhance the trichodermin production by Trichoderma spp. for its better exploitation in the sustainable agricultural practices.

  9. Structural and mechanistic analysis of engineered trichodiene synthase enzymes from Trichoderma harzianum: towards higher catalytic activities empowering sustainable agriculture.

    PubMed

    Kumari, Indu; Chaudhary, Nitika; Sandhu, Padmani; Ahmed, Mushtaq; Akhter, Yusuf

    2016-06-01

    Trichoderma spp. are well-known bioagents for the plant growth promotion and pathogen suppression. The beneficial activities of the fungus Trichoderma spp. are attributed to their ability to produce and secrete certain secondary metabolites such as trichodermin that belongs to trichothecene family of molecules. The initial steps of trichodermin biosynthetic pathway in Trichoderma are similar to the trichothecenes from Fusarium sporotrichioides. Trichodiene synthase (TS) encoded by tri5 gene in Trichoderma catalyses the conversion of farnesyl pyrophosphate to trichodiene as reported earlier. In this study, we have carried out a comprehensive comparative sequence and structural analysis of the TS, which revealed the conserved residues involved in catalytic activity of the protein. In silico, modelled tertiary structure of TS protein showed stable structural behaviour during simulations. Two single-substitution mutants, i.e. D109E, D248Y and one double-substitution mutant (D109E and D248Y) of TS with potentially higher activities are screened out. The mutant proteins showed more stability than the wild type, an increased number of electrostatic interactions and better binding energies with the ligand, which further elucidates the amino acid residues involved in the reaction mechanism. These results will lead to devise strategies for higher TS activity to ultimately enhance the trichodermin production by Trichoderma spp. for its better exploitation in the sustainable agricultural practices. PMID:26207800

  10. Catalytic activity of catalase under strong magnetic fields of up to 8 T

    NASA Astrophysics Data System (ADS)

    Ueno, S.; Iwasaka, M.

    1996-04-01

    The question of whether or not magnetic fields affect enzymatic activity is of considerable interest in biomagnetics and biochemistry. This study focuses on whether magnetically related enzymatic activities can be affected by magnetic fields. We examined the effect of magnetic fields of up to 8 T on catalytic decomposition of hydrogen peroxide (H2O2). We observed changes in absorbance of reaction mixture of hydrogen peroxide and catalase at 240 nm, during and after magnetic field exposures. When the reaction mixture was not treated with nitrogen-gas bubbling, it was observed that the initial reaction rate of the reaction which was exposed to magnetic fields of up to 8 T was 50%-85% lower than the control data. This magnetic field effect was not observed, however, when the reaction mixture was bubbled with nitrogen gas to remove the dissolved oxygen molecules which were produced in the solution. We also measured concentration of dissolved oxygen which was produced by the decomposition of hydrogen peroxide. Dissolved oxygen concentration in the reaction mixture which was exposed to magnetic fields increased 20%-25% compared to the control solution. The results of the present study indicate that magnetic fields affect dynamic movement of oxygen bubbles which are produced in the reaction mixture by the decomposition of hydrogen peroxide, but not the catalytic activity of catalase itself.

  11. Enhanced Activity of Nanocrystalline Zeolites for Selective Catalytic Reduction of NOx

    SciTech Connect

    Sarah C. Larson; Vicki H. Grassian

    2006-12-31

    Nanocrystalline zeolites with discrete crystal sizes of less than 100 nm have different properties relative to zeolites with larger crystal sizes. Nanocrystalline zeolites have improved mass transfer properties and very large internal and external surface areas that can be exploited for many different applications. The additional external surface active sites and the improved mass transfer properties of nanocrystalline zeolites offer significant advantages for selective catalytic reduction (SCR) catalysis with ammonia as a reductant in coal-fired power plants relative to current zeolite based SCR catalysts. Nanocrystalline NaY was synthesized with a crystal size of 15-20 nm and was thoroughly characterized using x-ray diffraction, electron paramagnetic resonance spectroscopy, nitrogen adsorption isotherms and Fourier Transform Infrared (FT-IR) spectroscopy. Copper ions were exchanged into nanocrystalline NaY to increase the catalytic activity. The reactions of nitrogen dioxides (NO{sub x}) and ammonia (NH{sub 3}) on nanocrystalline NaY and CuY were investigated using FT-IR spectroscopy. Significant conversion of NO{sub 2} was observed at room temperature in the presence of NH{sub 3} as monitored by FT-IR spectroscopy. Copper-exchanged nanocrystalline NaY was more active for NO{sub 2} reduction with NH{sub 3} relative to nanocrystalline NaY.

  12. Efficient anchorage of Pt clusters on N-doped carbon nanotubes and their catalytic activity

    NASA Astrophysics Data System (ADS)

    Lepró, Xavier; Terrés, Eduardo; Vega-Cantú, Yadira; Rodríguez-Macías, Fernando J.; Muramatsu, Hiroyuki; Kim, Yoon Ahm; Hayahsi, Takuya; Endo, Morinobu; Torres R., Miguel; Terrones, Mauricio

    2008-09-01

    We report an efficient method for anchoring Pt clusters (e.g., 6 nm in size) on the surfaces of N-doped multi-walled carbon nanotubes (MWNTs-CN x) using a relatively simple method consisting of a hydrothermal treatment of Na 2[PtCl 6] · 6H 2O and N-doped nanotubes dispersed in acetic acid. The catalytic properties of this material were evaluated finding that the conversion of cinnamaldehyde using Pt-coated MWNTs-CN x could increase up to 6 times with respect to that obtained for uncoated MWNTs-CN x and pure carbon CNTs. Therefore, we envisage this material could be either used as an efficient catalyst or as a sensor.

  13. Nitrated graphene oxide and its catalytic activity in thermal decomposition of ammonium perchlorate

    SciTech Connect

    Zhang, Wenwen; Luo, Qingping; Duan, Xiaohui; Zhou, Yong; Pei, Chonghua

    2014-02-01

    Highlights: • The NGO was synthesized by nitrifying homemade GO. • The N content of resulted NGO is up to 1.45 wt.%. • The NGO can facilitate the decomposition of AP and release much heat. - Abstract: Nitrated graphene oxide (NGO) was synthesized by nitrifying homemade GO with nitro-sulfuric acid. Fourier transform infrared spectroscopy (FTIR), laser Raman spectroscopy, CP/MAS {sup 13}C NMR spectra and X-ray photoelectron spectroscopy (XPS) were used to characterize the structure of NGO. The thickness and the compositions of GO and NGO were analyzed by atomic force microscopy (AFM) and elemental analysis (EA), respectively. The catalytic effect of the NGO for the thermal decomposition of ammonium perchlorate (AP) was investigated by differential scanning calorimetry (DSC). Adding 10% of NGO to AP decreases the decomposition temperature by 106 °C and increases the apparent decomposition heat from 875 to 3236 J/g.

  14. Identification by mutagenesis of a conserved glutamate (Glu487) residue important for catalytic activity in rat liver carnitine palmitoyltransferase II.

    PubMed

    Zheng, Guolu; Dai, Jia; Woldegiorgis, Gebre

    2002-11-01

    Mammalian mitochondrial membranes express two active but distinct carnitine palmitoyltransferases: carnitine palmitoyltransferase I (CPTI), which is malonyl coA-sensitive and detergent-labile; and carnitine palmitoyltransferase II (CPTII), which is malonyl coA-insensitive and detergent-stable. To determine the role of the highly conserved C-terminal acidic residues glutamate 487 (Glu(487)) and glutamate 500 (Glu(500)) on catalytic activity in rat liver CPTII, we separately mutated these residues to alanine, aspartate, or lysine, and the effect of the mutations on CPTII activity was determined in the Escherichia coli-expressed mutants. Substitution of Glu(487) with alanine, aspartate, or lysine resulted in almost complete loss in CPTII activity. Because a conservative substitution mutation of this residue, Glu(487) with aspartate (E487D), resulted in a 97% loss in activity, we predicted that Glu(487) would be at the active-site pocket of CPTII. The substantial loss in CPTII activity observed with the E487K mutant, along with the previously reported loss in activity observed in a child with a CPTII deficiency disease, establishes that Glu(487) is crucial for maintaining the configuration of the liver isoform of the CPTII active site. Substitution of the conserved Glu(500) in CPTII with alanine or aspartate reduced the V(max) for both substrates, suggesting that Glu(500) may be important in stabilization of the enzyme-substrate complex. A conservative substitution of Glu(500) to aspartate resulted in a significant decrease in the V(max) for the substrates. Thus, Glu(500) may play a role in substrate binding and catalysis. Our site-directed mutagenesis studies demonstrate that Glu(487) in the liver isoform of CPTII is essential for catalysis. PMID:12200419

  15. Reduction of nitrogen oxides with catalytic acid resistant aluminosilicate molecular sieves and ammonia

    DOEpatents

    Pence, Dallas T.; Thomas, Thomas R.

    1980-01-01

    Noxious nitrogen oxides in a waste gas stream such as the stack gas from a fossil-fuel-fired power generation plant or other industrial plant off-gas stream is catalytically reduced to elemental nitrogen and/or innocuous nitrogen oxides employing ammonia as reductant in the presence of a zeolite catalyst in the hydrogen or sodium form having pore openings of about 3 to 10 A.

  16. α-Lytic protease can exist in two separately stable conformations with different His57 mobilities and catalytic activities

    PubMed Central

    Haddad, Kristin Coffman; Sudmeier, James L.; Bachovchin, Daniel A.; Bachovchin, William W.

    2005-01-01

    α-Lytic protease is a bacterial serine protease widely studied as a model system of enzyme catalysis. Here we report that lyophilization induces a structural change in the enzyme that is not reversed by redissolution in water. The structural change reduces the mobility of the active-site histidine residue and the catalytic activity of the enzyme. The application of mild pressure to solutions of the altered enzyme reverses the lyophilization-induced structural change and restores the mobility of the histidine residue and the enzyme's catalytic activity. This effect of lyophilization permits a unique opportunity for investigating the relationship between histidine ring dynamics and catalytic activity. The results demonstrate that His57 in resting enzymes is more mobile than previously thought, especially when protonated. The histidine motion and its correlation to enzyme activity lend support to the reaction-driven ring flip hypothesis. PMID:15657134

  17. Catalytic activity of metal oxides in hydrogen sulfide oxidation by oxygen and sulfur dioxide

    SciTech Connect

    Marshneva, V.I.; Mokrinskii, V.V.

    1989-02-01

    Separate investigations have been made of the catalytic activities of a wide range of oxides by groups I-VIII metals in the Claus reaction and oxidation of H/sub 2/S by oxygen. Only 9 of 21 oxides used in the Claus reaction exhibit stable activity. The remaining oxides are deactivated, mainly by absorbing H/sub 2/S and being converted into sulfides. There are similar tendencies in the changes of sulfur formation specific velocities in both processes in the series of stable oxides V/sub 2/O/sub 5/, TiO/sub 2/, Mn/sub 2/O/sub 3/, Al/sub 2/O/sub 3/, MgO, Cr/sub 2/O/sub 3/. Vanadium pentoxide is the most active catalyst in the total and partial oxidations of H/sub 2/S and the Claus reaction.

  18. Preparation of gold nanoparticles using Salicornia brachiata plant extract and evaluation of catalytic and antibacterial activity.

    PubMed

    Ayaz Ahmed, Khan Behlol; Subramanian, Swetha; Sivasubramanian, Aravind; Veerappan, Ganapathy; Veerappan, Anbazhagan

    2014-09-15

    The current study deals with the synthesis of gold nanoparticles (AuNPs) using Salicornia brachiata (Sb) and evaluation of their antibacterial and catalytic activity. The SbAuNPs showed purple color with a characteristic surface plasmon resonance peak at 532 nm. Scanning electron microscopy and transmission electron microscopy revealed polydispersed AuNPs with the size range from 22 to 35 nm. Energy dispersive X-ray and thin layer X-ray diffraction analysis clearly shows that SbAuNPs was pure and crystalline in nature. As prepared gold nanoparticles was used as a catalyst for the sodium borohydride reduction of 4-nitro phenol to 4-amino phenol and methylene blue to leucomethylene blue. The green synthesized nanoparticles exhibited potent antibacterial activity against the pathogenic bacteria, as evidenced by their zone of inhibition. In addition, we showed that the SbAuNPs in combination with the regular antibiotic, ofloxacin, exhibit superior antibacterial activity than the individual.

  19. Preparation of gold nanoparticles using Salicornia brachiata plant extract and evaluation of catalytic and antibacterial activity

    NASA Astrophysics Data System (ADS)

    Ayaz Ahmed, Khan Behlol; Subramanian, Swetha; Sivasubramanian, Aravind; Veerappan, Ganapathy; Veerappan, Anbazhagan

    2014-09-01

    The current study deals with the synthesis of gold nanoparticles (AuNPs) using Salicornia brachiata (Sb) and evaluation of their antibacterial and catalytic activity. The SbAuNPs showed purple color with a characteristic surface plasmon resonance peak at 532 nm. Scanning electron microscopy and transmission electron microscopy revealed polydispersed AuNPs with the size range from 22 to 35 nm. Energy dispersive X-ray and thin layer X-ray diffraction analysis clearly shows that SbAuNPs was pure and crystalline in nature. As prepared gold nanoparticles was used as a catalyst for the sodium borohydride reduction of 4-nitro phenol to 4-amino phenol and methylene blue to leucomethylene blue. The green synthesized nanoparticles exhibited potent antibacterial activity against the pathogenic bacteria, as evidenced by their zone of inhibition. In addition, we showed that the SbAuNPs in combination with the regular antibiotic, ofloxacin, exhibit superior antibacterial activity than the individual.

  20. Promoting effect of vanadium on catalytic activity of Pt/Ce-Zr-O diesel oxidation catalysts.

    PubMed

    Huang, Haifeng; Jiang, Bo; Gu, Lei; Qi, Zhonghua; Lu, Hanfeng

    2015-07-01

    A series of Pt-V/Ce-Zr-O diesel oxidation catalysts was prepared using the impregnation method. The catalytic activity and sulfur resistance of Pt-V/Ce-Zr-O were investigated in the presence of simulated diesel exhaust. The effect of vanadium on the structure and redox properties of the catalysts was also investigated using the Brunauer-Emmett-Teller method, X-ray diffraction, H2 temperature-programmed reduction, CO temperature-programmed desorption, X-ray photoelectron spectroscopy, and Energy Dispersive Spectroscopy. Results showed that the Pt particles were well dispersed on the Ce-Zr-O carrier through the vanadium isolation effect, which significantly improved the oxidation activity toward CO and hydrocarbons. An electron-withdrawing phenomenon occurred from V to Pt, resulting in an increase in the metallic nature of platinum, which was beneficial to hydrocarbon molecular activation.

  1. Catalytic activity of unsaturated coordinated Cu-MOF to the hydroxylation of phenol

    NASA Astrophysics Data System (ADS)

    Jian, Lijuan; Chen, Chao; Lan, Fan; Deng, Shengjun; Xiao, Weiming; Zhang, Ning

    2011-05-01

    A 2D metal-organic framework [Cu 2 (BPTC) (Im) 4(H 2O) (DMF)] n ( 1) with unsaturated coordinated Cu(II) sites has been prepared under solvothermal condition, and applied to the hydroxylation of phenol after activating. The catalytic results indicate that 1a (the activated 1) exhibits an obvious activity for phenol hydroxylation at 40 °C for 4 h. Compared to the control experiments where the free Cu(II) (from Cu(OAc) 2 salt) has been utilized as the catalysts, 1a shows the higher selectivity to diphenols. This suggests that the coordinated environment of unsaturated coordinated Cu(II) sites in the 2D layer play the key role in the phenol hydroxylation.

  2. Tuning laccase catalytic activity with phosphate functionalized carbon dots by visible light.

    PubMed

    Li, Hao; Guo, Sijie; Li, Chuanxi; Huang, Hui; Liu, Yang; Kang, Zhenhui

    2015-05-13

    The phosphate functionalized carbon dots (PCDs) with high biocompatibility and low toxicity can be used as efficient additives for the construction of laccase/PCDs hybrids catalyst. A series of experiments indicated that the activity of laccase/PCDs was higher than that of free laccase (increased by 47.7%). When laccase/PCDs hybrids catalyst was irradiated with visible light (laccase/PCDs-Light), its activity was higher than that of laccase/PCDs hybrids without light irradiation (increased by 92.1%). In the present system, the T1 Cu in laccase was combined with the phosphate group on PCDs, which can increase binding capacity of laccase/PCDs hybrids and substrate. Further, the visible light irradiation increased the donating and accepting electronic capability of the laccase/PCDs hybrids, improving their catalytic activity.

  3. Green synthesis of gold nanoparticles using a glucan of an edible mushroom and study of catalytic activity.

    PubMed

    Sen, Ipsita K; Maity, Kousik; Islam, Syed S

    2013-01-16

    Gold nanoparticles were synthesized by reducing chloroauric acid with a glucan, isolated from an edible mushroom Pleurotus florida, cultivar Assam Florida. Here, glucan acts as reducing as well as stabilizing agent. The synthesized gold nanoparticles were characterized by UV-visible spectroscopy, HR-TEM, XRD, SEM, and FT-IR analysis. The results indicated that the size distribution of gold nanoparticles (Au NPs) changed with the change in concentration of chloroauric acid (HAuCl(4)). The resulting Au NPs-glucan bioconjugates function as an efficient heterogeneous catalyst in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP), in the presence of sodium borohydride. The reduction of 4-nitrophenol with Au NPs-glucan bioconjugates followed pseudo-first-order kinetics. The effect of particle size and gold loading on reduction rate of 4-NP was studied with Au NPs-glucan bioconjugates prepared with different concentrations of HAuCl(4). The synthesis of catalytically active Au NPs using a pure mushroom polysaccharide of known structure is reported for the first time.

  4. Photo-catalytic Activities of Plant Hormones on Semiconductor Nanoparticles by Laser-Activated Electron Tunneling and Emitting

    NASA Astrophysics Data System (ADS)

    Tang, Xuemei; Huang, Lulu; Zhang, Wenyang; Jiang, Ruowei; Zhong, Hongying

    2015-03-01

    Understanding of the dynamic process of laser-induced ultrafast electron tunneling is still very limited. It has been thought that the photo-catalytic reaction of adsorbents on the surface is either dependent on the number of resultant electron-hole pairs where excess energy is lost to the lattice through coupling with phonon modes, or dependent on irradiation photon wavelength. We used UV (355 nm) laser pulses to excite electrons from the valence band to the conduction band of titanium dioxide (TiO2), zinc oxide (ZnO) and bismuth cobalt zinc oxide (Bi2O3)0.07(CoO)0.03(ZnO)0.9 semiconductor nanoparticles with different photo catalytic properties. Photoelectrons are extracted, accelerated in a static electric field and eventually captured by charge deficient atoms of adsorbed organic molecules. A time-of-flight mass spectrometer was used to detect negative molecules and fragment ions generated by un-paired electron directed bond cleavages. We show that the probability of electron tunneling is determined by the strength of the static electric field and intrinsic electron mobility of semiconductors. Photo-catalytic dissociation or polymerization reactions of adsorbents are highly dependent on the kinetic energy of tunneling electrons as well as the strength of laser influx. By using this approach, photo-activities of phytohormones have been investigated.

  5. Photo-catalytic Activities of Plant Hormones on Semiconductor Nanoparticles by Laser-Activated Electron Tunneling and Emitting

    PubMed Central

    Tang, Xuemei; Huang, Lulu; Zhang, Wenyang; Jiang, Ruowei; Zhong, Hongying

    2015-01-01

    Understanding of the dynamic process of laser-induced ultrafast electron tunneling is still very limited. It has been thought that the photo-catalytic reaction of adsorbents on the surface is either dependent on the number of resultant electron-hole pairs where excess energy is lost to the lattice through coupling with phonon modes, or dependent on irradiation photon wavelength. We used UV (355 nm) laser pulses to excite electrons from the valence band to the conduction band of titanium dioxide (TiO2), zinc oxide (ZnO) and bismuth cobalt zinc oxide (Bi2O3)0.07(CoO)0.03(ZnO)0.9 semiconductor nanoparticles with different photo catalytic properties. Photoelectrons are extracted, accelerated in a static electric field and eventually captured by charge deficient atoms of adsorbed organic molecules. A time-of-flight mass spectrometer was used to detect negative molecules and fragment ions generated by un-paired electron directed bond cleavages. We show that the probability of electron tunneling is determined by the strength of the static electric field and intrinsic electron mobility of semiconductors. Photo-catalytic dissociation or polymerization reactions of adsorbents are highly dependent on the kinetic energy of tunneling electrons as well as the strength of laser influx. By using this approach, photo-activities of phytohormones have been investigated. PMID:25749635

  6. Photo-catalytic activities of plant hormones on semiconductor nanoparticles by laser-activated electron tunneling and emitting.

    PubMed

    Tang, Xuemei; Huang, Lulu; Zhang, Wenyang; Jiang, Ruowei; Zhong, Hongying

    2015-01-01

    Understanding of the dynamic process of laser-induced ultrafast electron tunneling is still very limited. It has been thought that the photo-catalytic reaction of adsorbents on the surface is either dependent on the number of resultant electron-hole pairs where excess energy is lost to the lattice through coupling with phonon modes, or dependent on irradiation photon wavelength. We used UV (355 nm) laser pulses to excite electrons from the valence band to the conduction band of titanium dioxide (TiO₂), zinc oxide (ZnO) and bismuth cobalt zinc oxide (Bi₂O₃)₀.₀₇(CoO)₀.₀₃(ZnO)₀.₉ semiconductor nanoparticles with different photo catalytic properties. Photoelectrons are extracted, accelerated in a static electric field and eventually captured by charge deficient atoms of adsorbed organic molecules. A time-of-flight mass spectrometer was used to detect negative molecules and fragment ions generated by un-paired electron directed bond cleavages. We show that the probability of electron tunneling is determined by the strength of the static electric field and intrinsic electron mobility of semiconductors. Photo-catalytic dissociation or polymerization reactions of adsorbents are highly dependent on the kinetic energy of tunneling electrons as well as the strength of laser influx. By using this approach, photo-activities of phytohormones have been investigated.

  7. Activities of human RRP6 and structure of the human RRP6 catalytic domain

    SciTech Connect

    Januszyk, Kurt; Liu, Quansheng; Lima, Christopher D.

    2011-08-29

    The eukaryotic RNA exosome is a highly conserved multi-subunit complex that catalyzes degradation and processing of coding and noncoding RNA. A noncatalytic nine-subunit exosome core interacts with Rrp44 and Rrp6, two subunits that possess processive and distributive 3'-to-5' exoribonuclease activity, respectively. While both Rrp6 and Rrp44 are responsible for RNA processing in budding yeast, Rrp6 may play a more prominent role in processing, as it has been demonstrated to be inhibited by stable RNA secondary structure in vitro and because the null allele in budding yeast leads to the buildup of specific structured RNA substrates. Human RRP6, otherwise known as PM/SCL-100 or EXOSC10, shares sequence similarity to budding yeast Rrp6 and is proposed to catalyze 3'-to-5' exoribonuclease activity on a variety of nuclear transcripts including ribosomal RNA subunits, RNA that has been poly-adenylated by TRAMP, as well as other nuclear RNA transcripts destined for processing and/or destruction. To characterize human RRP6, we expressed the full-length enzyme as well as truncation mutants that retain catalytic activity, compared their activities to analogous constructs for Saccharomyces cerevisiae Rrp6, and determined the X-ray structure of a human construct containing the exoribonuclease and HRDC domains that retains catalytic activity. Structural data show that the human active site is more exposed when compared to the yeast structure, and biochemical data suggest that this feature may play a role in the ability of human RRP6 to productively engage and degrade structured RNA substrates more effectively than the analogous budding yeast enzyme.

  8. Structural basis for catalytic activation by the human ZNF451 SUMO E3 ligase

    PubMed Central

    Cappadocia, Laurent; Pichler, Andrea; Lima, Christopher D.

    2015-01-01

    E3 protein ligases enhance transfer of ubiquitin-like (Ubl) proteins from E2 conjugating enzymes to substrates by stabilizing the thioester-charged E2~Ubl in a closed configuration optimally aligned for nucleophilic attack. Here, we report biochemical and structural data that define the N-terminal domain of the Homo sapiens ZNF451 as the catalytic module for SUMO E3 ligase activity. ZNF451 catalytic module contains tandem SUMO interaction motifs (SIMs) bridged by a Proline-Leucine-Arginine-Proline (PLRP) motif. The first SIM and PLRP motif engage thioester charged E2~SUMO while the next SIM binds a second molecule of SUMO bound to the backside of E2. We show that ZNF451 is SUMO2 specific and that SUMO-modification of ZNF451 may contribute to activity by providing a second molecule of SUMO that interacts with E2. Our results are consistent with ZNF451 functioning as a bona fide SUMO E3 ligase. PMID:26524494

  9. Activity, expression and function of a second Drosophila protein kinase a catalytic subunit gene

    SciTech Connect

    Melendez, A.; Li, W.; Kalderon, D.

    1995-12-01

    The DC2 was isolated previously on the basis of sequence similarity to DC0, the major Drosophila protein kinase A (PKA) catalytic subunit gene. We show here that the 67-kD Drosophila DC2 protein behaves as a PKA catalytic subunit in vitro. DC2 is transcribed in mesodermal anlagen of early embryos. This expression depends on dorsal but on neither twist nor snail activity. DC2 transcriptional fusions mimic this embryonic expression and are also expressed in subsets of cells in the optic lamina, wing disc and leg discs of third instar larvae. A saturation screen of a small deficiency interval containing DC2 for recessive lethal mutations yielded no DC2 alleles. We therefore isolated new deficiencies to generate deficiency trans-heterozygotes that lacked DC2 activity. These animals were viable and fertile. The absence of DC2 promoter did not efficiently rescue a variety of DC0 mutant phenotypes. These observations indicate that DC2 is not an essential gene and is unlikely to be functionally redundant with DC0, which has multiple unique functions during development. 62 refs., 10 figs., 2 tabs.

  10. Process for forming a homogeneous oxide solid phase of catalytically active material

    DOEpatents

    Perry, Dale L.; Russo, Richard E.; Mao, Xianglei

    1995-01-01

    A process is disclosed for forming a homogeneous oxide solid phase reaction product of catalytically active material comprising one or more alkali metals, one or more alkaline earth metals, and one or more Group VIII transition metals. The process comprises reacting together one or more alkali metal oxides and/or salts, one or more alkaline earth metal oxides and/or salts, one or more Group VIII transition metal oxides and/or salts, capable of forming a catalytically active reaction product, in the optional presence of an additional source of oxygen, using a laser beam to ablate from a target such metal compound reactants in the form of a vapor in a deposition chamber, resulting in the deposition, on a heated substrate in the chamber, of the desired oxide phase reaction product. The resulting product may be formed in variable, but reproducible, stoichiometric ratios. The homogeneous oxide solid phase product is useful as a catalyst, and can be produced in many physical forms, including thin films, particulate forms, coatings on catalyst support structures, and coatings on structures used in reaction apparatus in which the reaction product of the invention will serve as a catalyst.

  11. Characterization and catalytic activity of gold nanoparticles synthesized using ayurvedic arishtams.

    PubMed

    Aromal, S Aswathy; Babu, K V Dinesh; Philip, Daizy

    2012-10-01

    The development of new synthesis methods for monodispersed nanocrystals using cheap and nontoxic chemicals, environmentally benign solvents and renewable materials remains a challenge to the scientific community. The present work reports a new green method for the synthesis of gold nanoparticles. Four different ayurvedic arishtams are used for the reduction of Au(3+) to Au nanoparticles. This method is simple, efficient, economic and nontoxic. Gold nanoparticles having different sizes in the range from 15 to 23 nm could be obtained. The nanoparticles have been characterized by UV-Visible spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and FTIR analysis. The high crystallinity of nanoparticles is evident from bright circular spots in the SAED pattern and peaks in the XRD pattern. The synthesized gold nanoparticles show good catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol by excess NaBH(4). The synthesized nanoparticles are found to exhibit size dependent catalytic property, the smaller nanoparticles showing faster activity. PMID:22954810

  12. Electrochemical, catalytic and antimicrobial activity of N-functionalized tetraazamacrocyclic binuclear nickel(II) complexes

    NASA Astrophysics Data System (ADS)

    Prabu, R.; Vijayaraj, A.; Suresh, R.; Shenbhagaraman, R.; Kaviyarasan, V.; Narayanan, V.

    2011-02-01

    The five binuclear nickel(II) complexes have been synthesized by the Schiff base condensation of 1,8-[bis(3-formyl-2-hydroxy-5-methyl)benzyl]-l,4,8,11-tetraazacyclo-tetradecane (PC) with appropriate aliphatic diamines and nickel(II) perchlorate. All the five complexes were characterized by elemental and spectral analysis. The electronic spectra of the complexes show three d-d transition in the range of 550-1055 nm due to 3A 2g → 3T 2g(F), 3A 2g → 3T 1g(F) and 3A 2g → 3T 1g(P). These spin allowed electronic transitions are characteristic of an octahedral Ni 2+ center. Electrochemical studies of the complexes show two irreversible one electron reduction waves at cathodic region. The reduction potential of the complexes shifts towards anodically upon increasing the chain length of the macrocyclic ring. All the nickel(II) complexes show two irreversible one electron oxidation waves at anodic region. The oxidation potential of the complexes shift towards anodically upon increasing the chain length of the macrocyclic ring. The catalytic activities of the complexes were observed to be increase with increase the macrocyclic ring size. The observed rate constant values for the catalytic hydrolysis of 4-nitrophenyl phosphate are in the range of 5.85 × 10 -3 to 9.14 × 10 -3 min -1. All the complexes were screened for antimicrobial activity.

  13. Catalytic activity of non-cross-linked microcrystals of aspartate aminotransferase in poly(ethylene glycol).

    PubMed Central

    Kirsten, H; Christen, P

    1983-01-01

    The molar activity of crystalline mitochondrial aspartate aminotransferase is decreased to 10% of that of the enzyme in solution. The activity was measured in suspensions of non-cross-linked microcrystals (average dimensions 22 microns X 5 microns X 0.8 microns) in 30% (w/v) poly(ethylene glycol). Kinetic tests ruled out the possibility that diffusion of the substrate in the crystals is rate-limiting. The observed decrease in catalytic efficiency can be attributed exclusively to crystal-packing effects. A direct inhibition by poly(ethylene glycol) is excluded because poly(ethylene glycol), with average Mr 6000, cannot penetrate the liquid channels of the crystals, owing to its large Stokes radius. The crystals examined were triclinic and of the same habit as those used for high-resolution X-ray-crystallographic analysis [Ford, Eichele & Jansonius (1980) Proc. Natl. Acad. Sci. U.S.A. 77, 2559-2563]. The catalytic competence of crystalline aspartate aminotransferase confirms the relevance of the spatial model of this protein for the elucidation of its mechanism of action. Images Fig. 1. PMID:6870840

  14. Preparation of platinum nanoparticle and its catalytic activity for toluene oxidation.

    PubMed

    Kim, Sang Chai; Shim, Wang Geun; Lee, Man Seung; Jung, Sang Chul; Park, Young-Kwon

    2011-08-01

    Colloidal Pt nanoparticles are prepared using H2PtCl6 as a precursor, polyvinylpyrrolidone (PVP: molecular weight = 10,000 and 40,000) and hydrogen as a stabilizing agent and a reducing agent, respectively. The amounts of the precursor and the stabilizing agent and the molecular weight of PVP have an effect on the formation of Pt nanoparticles. Supported Pt catalyst (CSPt) is prepared from colloidal Pt nanoparticles and y-Al2O3. Another supported Pt catalyst (ISPt) is prepared by using the conventional incipient wetness impregnation method with an aqueous H2PtCl6 solution and gamma-Al2O3. The catalytic activities of CSPt and ISPt catalysts are compared for VOC (toluene) oxidation. Transmission Electron Microscopy (TEM), UV-vis, X-ray diffraction (XRD) and temperature programmed reduction (TPR) are used to characterize CSPt and ISPt catalysts. The experimental results reveal that the catalytic activity of CSPt is superior to that of ISPT. PMID:22103193

  15. [Effects and mechanism of catalytic decomposition of ozone by activated carbon].

    PubMed

    Liu, Hai-Long; Zhang, Zhi-Ye; Zhang, Zhong-Ming; Jiao, Ru-Yuan; Wang, Rui-Jun

    2012-10-01

    Effects and mechanism of catalytic decomposition of ozone by activated carbon (AC) were studied by detection of residual components in released gas and temperature of reactor pole, and heat analysis through the ozone decomposition pole (ODP). Results showed that ozone could be thoroughly decomposed (removal rate was maintaining 100% all along the process studied) for 5 h under the condition of O3 12.89 mg x min(-1), 18 mm diameter glass tube was stuffed by activated carbon (made from coal, 2.0-2.5 mm diameter). The temperature of ODP was found rise during the treatment. The temperature became stable after quickly rise to 65-69 degrees C; and the CO2 output reduced with the stable temperature. The mechanisms of ozone decomposition were found including three parts. The first is catalytic decomposition by AC. AC enriches O3 and enhances O3 decomposition to form O2. The second is AC reaction with O3, which leads to destruction of the surface structure or group and output of CO2 and NOx are released with offgas. The third is temperature rising caused by heat production of CO2 and NOx formation according to the above two mechanisms, which enhances O3 thermal decomposition. Meanwhile, some basic design principles of ozone decomposition device were discussed.

  16. Phase- and morphology-controlled synthesis of cobalt sulfide nanocrystals and comparison of their catalytic activities for hydrogen evolution

    NASA Astrophysics Data System (ADS)

    Pan, Yuan; Liu, Yunqi; Liu, Chenguang

    2015-12-01

    Colalt sulfide nanocrystals (NCs), including dandelion-like Co9S8 and sphere-like Co3S4, have been synthesized via a thermal decomposition approach using cobalt acetylacetonate as the cobalt source, 1-dodecanethiol as the sulfur source and oleic acid or oleylamine as the high boiling organic solvent. It is found that the molar ratio of the Co:S precursor and the species of solvent play an important role in the control of phase and morphology of cobalt sulfide nanostructures. The phase structure and morphology of the as-synthesized nickel sulfide NCs are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscope (SEM), energy dispersive spectrum (EDS) mapping, X-ray photoelectron spectroscopy (XPS) and N2 adsorption-desorption. Then we further compare the electrocatalytic activity and stability of as-synthesized cobalt sulfide NCs for hydrogen evolution reaction (HER). The results show that sphere-like Co3S4 exhibits better electrocatalytic activity than the dandelion-like Co9S8 NCs for HER, which can be attributed to the difference of phase structure and morphology. The sphere-like Co3S4 NCs have large surface area and high electrical conductivity, both are beneficial to enhance the catalytic activity. This study indicates that the crystalline phase structure and morphology of cobalt sulfide NCs are important for designing HER electrocatalysts with high efficiency and good stability.

  17. Direct observation of enhanced plasmon-driven catalytic reaction activity of Au nanoparticles supported on reduced graphene oxides by SERS.

    PubMed

    Liang, Xiu; You, Tingting; Liu, Dapeng; Lang, Xiufeng; Tan, Enzhong; Shi, Jihua; Yin, Penggang; Guo, Lin

    2015-04-21

    Graphene-based nanocomposites have recently attracted tremendous research interest in the field of catalysis due to their unique optical and electronic properties. However, direct observation of enhanced plasmon-driven catalytic activity of Au nanoparticles (NPs) supported on reduced graphene oxides (Au/rGO) has rarely been reported. Herein, based on the reduction from 4-nitrobenzenethiol (4-NBT) to p,p'-dimercaptoazobenzene (DMAB), the catalytic property of Au/rGO nanocomposites was investigated and compared with corresponding Au NP samples with similar size distribution. Our results show that Au/rGO nanocomposites could serve as a good catalytic and analytic platform for plasmon-driven chemical reactions. In addition, systematic comparisons were conducted during power- and time-dependent surface-enhanced Raman scattering (SERS) experiments, which exhibited a lower power threshold and higher catalytic efficiency for Au/rGO as compared to Au NPs toward the reaction. PMID:25793752

  18. Catalytic therapy of cancer by ascorbic acid involves redox cycling of exogenous/endogenous copper ions and generation of reactive oxygen species.

    PubMed

    Hadi, S M; Ullah, M F; Shamim, U; Bhatt, S H; Azmi, A S

    2010-01-01

    Catalytic therapy is a cancer treatment modality based on the generation of reactive oxygen species (ROS) through administration of ascorbate/medicinal herbal extracts and copper. It is known that antioxidants such as ascorbate also exhibit prooxidant activity in the presence of transition metals such as copper. Based on our work and that in the literature, in this review we propose a mechanism for the cytotoxic action of ascorbate against cancer cells. It involves redox cycling of exogenous/endogenous copper ions and the consequent generation of ROS leading to oxidative DNA breakage. Using human peripheral lymphocytes and the Comet assay, we have shown that ascorbic acid is able to cause oxidative breakage in cellular DNA. Such DNA degradation is inhibited by neocuproine (a Cu(I) sequestering agent) and scavengers of ROS indicating that the cellular DNA breakage involves the generation of Cu(I) and formation of ROS. Similar results are also obtained with plant polyphenol antioxidants that are important constituents of medicinal herbal extracts. Copper is an essential component of chromatin and can take part in redox reactions. It is well established that tissue, cellular and serum copper levels are considerably elevated in various malignancies. Therefore, cancer cells may be more subject to electron transfer between copper ions and ascorbate/plant polyphenols to generate ROS. In this review we cite evidence to indicate that in catalytic therapy cytotoxic action against cancer cells involves redox cycling of exogenous/endogenous copper ions.

  19. Deletion of a non-catalytic region increases the enzymatic activity of a β-agarase from Flammeovirga sp. MY04

    NASA Astrophysics Data System (ADS)

    Han, Wenjun; Gu, Jingyan; Liu, Huihui; Li, Fuchuan; Wu, Zhihong; Li, Yuezhong

    2015-10-01

    A Glycoside hydrolase (GH) typically contains one catalytic module and varied non-catalytic regions (NCRs). However, effects of the NCRs to the catalytic modules remain mostly unclear except the carbohydrate-binding modules (CBMs). AgaG4 is a GH16 endo- β-agarase of the agarolytic marine bacterium Flammeovirga sp. MY04. The enzyme consists of an extra sugar-binding peptide within the catalytic module, with no predictable CBMs but function-unknown sequences in the NCR, which is a new characteristic of agarase sequences. In this study, we deleted the NCR sequence, a 140-amino acid peptide at the C-terminus and expressed the truncated gene, agaG4-T140, in Escherichia coli. After purification and refolding, the truncated agarase rAgaG4-T140 retained the same catalytic temperature and pH value as rAgaG4. Using combined fluorescent labeling, HPLC and MS/MS techniques, we identified the end-products of agarose degradation by rAgaG4-T140 as neoagarotetraose and neoagarohexaose, with a final molar ratio of 1.53:1 and a conversion ratio of approximately 70%, which were similar to those of rAgaG4. However, the truncated agarase rAgaG4-T140 markedly decreased in protein solubility by 15 times and increased in enzymatic activities by 35 times. The oligosaccharide production of rAgaG4-T140 was approximately 25 times the weight of that produced by equimolar rAgaG4. This study provides some insights into the influences of NCR on the biochemical characteristics of agarase AgaG4 and implies some new strategies to improve the properties of a GH enzyme.

  20. Control of product selectivity using solid acids for the catalytic addition of phenol to hydroxy fatty acids

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The acid catalyzed reactions of hydroxy fatty acids, such as ricinoleic and lesquerolic, in the presence of phenolics can lead to four products or product groups. These include simple dehydration to dienoic acids, cyclization to epoxides, Friedel-Crafts alkylations of the double bonds, or ether for...